VOLUME 116
NO. 4
APRIL 2016
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The Southern African Institute of Mining and Metallurgy ) ) ) ) ) ) ! ! Mike Teke President, Chamber of Mines of South Africa ! ! ! Mosebenzi Zwane Minister of Mineral Resources, South Africa Rob Davies Minister of Trade and Industry, South Africa Naledi Pandor Minister of Science and Technology, South Africa ! ! R.T. Jones ! ! ! C. Musingwini ! ! ! S. Ndlovu A.S. Macfarlane ! ! ! ! J.L. Porter ! ! C. Musingwini ! ! Z. Botha V.G. Duke I.J. Geldenhuys M.F. Handley W.C. Joughin M. Motuku D.D. Munro
G. Njowa A.G. Smith M.H. Solomon J.D. Steenkamp M.R. Tlala D. Tudor D.J. van Niekerk
! ! ! N.A. Barcza R.D. Beck J.R. Dixon M. Dworzanowski F.M.G. Egerton H.E. James
G.V.R. Landman J.C. Ngoma S.J. Ramokgopa M.H. Rogers G.L. Smith W.H. van Niekerk
! Botswana
L.E. Dimbungu
DRC
S. Maleba
Johannesburg
I. Ashmole
Namibia
N.M. Namate
Northern Cape
C.A. van Wyk
Pretoria
P. Bredell
Western Cape
A. Mainza
Zambia
D. Muma
Zimbabwe
S. Ndiyamba
Zululand
C.W. Mienie
) *Deceased * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
W. Bettel (1894–1895) A.F. Crosse (1895–1896) W.R. Feldtmann (1896–1897) C. Butters (1897–1898) J. Loevy (1898–1899) J.R. Williams (1899–1903) S.H. Pearce (1903–1904) W.A. Caldecott (1904–1905) W. Cullen (1905–1906) E.H. Johnson (1906–1907) J. Yates (1907–1908) R.G. Bevington (1908–1909) A. McA. Johnston (1909–1910) J. Moir (1910–1911) C.B. Saner (1911–1912) W.R. Dowling (1912–1913) A. Richardson (1913–1914) G.H. Stanley (1914–1915) J.E. Thomas (1915–1916) J.A. Wilkinson (1916–1917) G. Hildick-Smith (1917–1918) H.S. Meyer (1918–1919) J. Gray (1919–1920) J. Chilton (1920–1921) F. Wartenweiler (1921–1922) G.A. Watermeyer (1922–1923) F.W. Watson (1923–1924) C.J. Gray (1924–1925) H.A. White (1925–1926) H.R. Adam (1926–1927) Sir Robert Kotze (1927–1928) J.A. Woodburn (1928–1929) H. Pirow (1929–1930) J. Henderson (1930–1931) A. King (1931–1932) V. Nimmo-Dewar (1932–1933) P.N. Lategan (1933–1934) E.C. Ranson (1934–1935) R.A. Flugge-De-Smidt (1935–1936) T.K. Prentice (1936–1937) R.S.G. Stokes (1937–1938) P.E. Hall (1938–1939) E.H.A. Joseph (1939–1940) J.H. Dobson (1940–1941) Theo Meyer (1941–1942) John V. Muller (1942–1943) C. Biccard Jeppe (1943–1944) P.J. Louis Bok (1944–1945) J.T. McIntyre (1945–1946) M. Falcon (1946–1947) A. Clemens (1947–1948) F.G. Hill (1948–1949) O.A.E. Jackson (1949–1950) W.E. Gooday (1950–1951) C.J. Irving (1951–1952) D.D. Stitt (1952–1953) M.C.G. Meyer (1953–1954) L.A. Bushell (1954–1955) H. Britten (1955–1956) Wm. Bleloch (1956–1957)
* * * * * * * * * * * * * * * * * * * * * *
*
*
*
*
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H. Simon (1957–1958) M. Barcza (1958–1959) R.J. Adamson (1959–1960) W.S. Findlay (1960–1961) D.G. Maxwell (1961–1962) J. de V. Lambrechts (1962–1963) J.F. Reid (1963–1964) D.M. Jamieson (1964–1965) H.E. Cross (1965–1966) D. Gordon Jones (1966–1967) P. Lambooy (1967–1968) R.C.J. Goode (1968–1969) J.K.E. Douglas (1969–1970) V.C. Robinson (1970–1971) D.D. Howat (1971–1972) J.P. Hugo (1972–1973) P.W.J. van Rensburg (1973–1974) R.P. Plewman (1974–1975) R.E. Robinson (1975–1976) M.D.G. Salamon (1976–1977) P.A. Von Wielligh (1977–1978) M.G. Atmore (1978–1979) D.A. Viljoen (1979–1980) P.R. Jochens (1980–1981) G.Y. Nisbet (1981–1982) A.N. Brown (1982–1983) R.P. King (1983–1984) J.D. Austin (1984–1985) H.E. James (1985–1986) H. Wagner (1986–1987) B.C. Alberts (1987–1988) C.E. Fivaz (1988–1989) O.K.H. Steffen (1989–1990) H.G. Mosenthal (1990–1991) R.D. Beck (1991–1992) J.P. Hoffman (1992–1993) H. Scott-Russell (1993–1994) J.A. Cruise (1994–1995) D.A.J. Ross-Watt (1995–1996) N.A. Barcza (1996–1997) R.P. Mohring (1997–1998) J.R. Dixon (1998–1999) M.H. Rogers (1999–2000) L.A. Cramer (2000–2001) A.A.B. Douglas (2001–2002) S.J. Ramokgopa (2002-2003) T.R. Stacey (2003–2004) F.M.G. Egerton (2004–2005) W.H. van Niekerk (2005–2006) R.P.H. Willis (2006–2007) R.G.B. Pickering (2007–2008) A.M. Garbers-Craig (2008–2009) J.C. Ngoma (2009–2010) G.V.R. Landman (2010–2011) J.N. van der Merwe (2011–2012) G.L. Smith (2012–2013) M. Dworzanowski (2013–2014) J.L. Porter (2014–2015)
! !($( ) ' $ ) # &"'(" Van Hulsteyns Attorneys
! ! ! Australia: I.J. Corrans, R.J. Dippenaar, A. Croll, C. Workman-Davies Austria: H. Wagner Botswana: S.D. Williams United Kingdom: J.J.L. Cilliers, N.A. Barcza USA: J-M.M. Rendu, P.C. Pistorius
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# '(%&"& ) ' ('"' %$%& ' Barbara Spence Avenue Advertising Telephone (011) 463-7940 E-mail: barbara@avenue.co.za The Secretariat The Southern African Institute of Mining and Metallurgy ISSN 2225-6253 (print) ISSN 2411-9717 (online)
VOLUME 116 NO. 4 APRIL 2016
Contents Journal Comment—A Council for our Youth by V. Duke. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
iv–v
Obituary—Richard Peter Mohring by J.A. Cruise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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President’s Corner %THICS by R.T. Jones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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STUDENT EDITION — MINING Improving the ventilation system at Rosh Pinah zinc mine by E. Develo, M. Pillalamarry, and E. Garab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
301
Sub-standard practices: effects on safety performance in South African gold mines by G. Kleyn and J.J.L. du Plessis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
307
A critical investigation into tyre life on an iron ore haulage system by G.C. Lindeque . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
317
Review of support systems used in poor ground conditions in platinum room and pillar mining: a Zimbabwean case study by T. Chikande and T. Zvarivadza . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
323
STUDENT EDITION — METALLURGY
CopyrightŠ 1978 by The Southern African Institute of Mining and Metallurgy. All rights reserved. Multiple copying of the contents of this publication or parts thereof without permission is in breach of copyright, but permission is hereby given for the copying of titles and abstracts of papers and names of authors. Permission to copy illustrations and short extracts from the text of individual contributions is usually given upon written application to the Institute, provided that the source (and where appropriate, the copyright) is acknowledged. Apart from any fair dealing for the purposes of review or criticism under The Copyright Act no. 98, 1978, Section 12, of the Republic of South Africa, a single copy of an article may be supplied by a library for the purposes of research or private study. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means without the prior permission of the publishers. Multiple copying of the contents of the publication without permission is always illegal. U.S. Copyright Law applicable to users In the U.S.A. The appearance of the statement of copyright at the bottom of the first page of an article appearing in this journal indicates that the copyright holder consents to the making of copies of the article for personal or internal use. This consent is given on condition that the copier pays the stated fee for each copy of a paper beyond that permitted by Section 107 or 108 of the U.S. Copyright Law. The fee is to be paid through the Copyright Clearance Center, Inc., Operations Center, P.O. Box 765, Schenectady, New York 12301, U.S.A. This consent does not extend to other kinds of copying, such as copying for general distribution, for advertising or promotional purposes, for creating new collective works, or for resale.
Slurry abrasion of WC-4wt%Ni cold-sprayed coatings in synthetic minewater by N.B.S. Magagula, N. Sacks, and I. Botef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
333
Matte – tap-hole clay – refractory brick interaction in a PGM smelter by J. Du Toit, R.D. Cromarty, and A.M. Garbers-Craig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
339
Separation of kimberlite from waste rocks using sensor-based sorting at Cullinan Diamond Mine by T. Mahlangu, N. Moemise, M.M. Ramakokovhu, P.A. Olubambi, and M.B. Shongwe. . . . . . . . .
343
An evaluation of the thermal fatigue performance of three alloys for casting mould applications by V. van der Merwe and C.W. Siyasiya. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
349
The effect of particle size on the rate and depth of moisture evaporation from coal stockpiles by * DE 'OEDE " -ULLER Q.P. Campbell, M. le Roux, AND C.B. Espag de Klerk . . . . . . . . . . . . . . . .
353
%'( $%&! $ ) # &"!( ) !$(# VOLU ME 11 6
NO. 4
APRIL 2016
R. Dimitrakopoulos, McGill University, Canada D. Dreisinger, University of British Columbia, Canada E. Esterhuizen, NIOSH Research Organization, USA H. Mitri, McGill University, Canada M.J. Nicol, Murdoch University, Australia E. Topal, Curtin University, Australia
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THE INSTITUTE, AS A BODY, IS NOT RESPONSIBLE FOR THE STATEMENTS AND OPINIONS ADVANCED IN ANY OF ITS PUBLICATIONS.
Journal Comment A Council for our Youth
M
embership of the Southern African Institute of Mining and Metallurgy (SAIMM) includes mining and metallurgical students and new graduates from various universities and colleges in the southern African region. Among these young people are those who have either authored or co-authored papers similar to the ones in this edition of the Journal, and the quality of these submissions leads me to believe that we are on the right track in terms of the academic part of the training that we provide in developing our future mining and metallurgical engineers. However, these undergraduates also require vocational training, and after graduation, need an opportunity to develop their knowledge and experience sufficiently to be allowed to register as a professional engineer with ECSA. In this regard, we are failing to teach our youngsters properly. Responsibilities around safety, health, and a duty of care for the environment while also regularly engaging with communities, demand much of the time and attention of our managers, who need to meet transformation and sustainable development targets as well as production targets. Yes, some mining companies are still sponsoring individual students or employing certain graduates as they enter the workplace, but the dearth of opportunities for our young people to develop themselves under the mentorship of experienced professionals and practitioners is huge. After recently checking, I found that 42 years is now the average age of a SAIMM member who is also registered as a professional engineer. Should this number not be far lower if we are to effectively compete in a fast-changing mineral resource industry where much of the endowment of Southern Africa sits? For me, this situation was somewhat expected. While working on the mines during the early 1990s I heard the comment, ‘why train when it is probably more cost-effective to simply buy in the skills as and when needed?’ This mindset coincided with a period when South Africa’s large mining houses started unbundling, with the consequence that opportunities for young people to find pre- and postgraduate employment started to dwindle.
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In August 2013, our students used a ‘Career Development in the Minerals Industry’ event to remind us of their plight. Ironically, the main objective of the event was on ‘mapping a career path’, advising students on what to expect in their first five years of employment, and reassuring them that they would receive the necessary training in their chosen careers. The students complained about uncertainty regarding career prospects in the mining industry, the need for on-the-job training for undergraduates with effective mentoring by suitable mentors, and the lack of experiential training opportunities on a mine for new graduates. This forced Council to go back and question whether the Institute, as a technical society, actually meets the needs of all members, even those recently graduated or still at university. It was acknowledged that our younger members represent a different demographic – one on which the long-term success or failure of the Institute will eventually depend. This resulted in agreement on a need for a renewed focus on the ‘youth’ amongst our current and potential future mining and metallurgical engineers, and that by developing them from within the SAIMM, all of our youth within the industry would benefit. A Career Guidance and Education Committee was formed some time ago by the SAIMM. It successfully encouraged new students to enter the mining industry by focusing on the building of a mining and metallurgy exhibition at the Sci-Bono Exhibition Centre and by attendance at various school science festivals in South Africa. It seemed logical to widen the focus of this committee to include the needs of our undergraduates. This plan did not succeed. There was very little support from industry, and it also became clear that our youth have a very different viewpoint to that of the majority of the members of the committee, and even Council, when it comes to debating the opportunities or threats to their future careers. We were trying to make decisions for younger people without knowing what their ‘real’ requirements were. At a meeting in July 2014 the question was raised whether we should rather be looking at how to enable our youth to help themselves. Subsequent engagements with undergraduates and young postgraduates at various academic institutions
Journal Comment resulted in overwhelming agreement on the merits of such an approach. So at the same time, volunteers were nominated from each of the institutions and on 12 September 2014 the SAIMM held a ‘Workshop on Youth Development’ at Sci-Bono to map out a way forward. The outcome exceeded all expectations, with the formation of a Young Professionals Council (YPC), under the umbrella of the SAIMM Council, to effectively replace the long-serving but outdated Career Guidance and Education Committee. The YPC’s main focus is to engage with the mining industry across the SADEC region to assist in finding support for younger members of the Institute. Some members of the previous committee have stayed on as observers to advise, guide, and assist wherever possible in this regard. The YPC is also well positioned to provide students with a better understanding of:
The various career paths that a mining and metallurgy qualification affords them
The training and registrations that they will require early on in their careers
(continued)
Tshepo Mmola, Chairman of the YPC, talks of six focus areas covered with the help of three Working Groups (WGs):
One WG for education to represent the interests of
primarily pre-graduates in basic and higher education on matters of career guidance, academic development, and life skills The second WG for career guidance to represent the interests of primarily postgraduates in mining and metallurgy on matters of training, professional development, and life skills The third, or Enterprise, WG to concentrate on various industry initiatives to serve the interests of our young professionals It is my hope that senior executives, mine managers, retired professionals, and entrepreneurs in the mining industry will support this initiative. I know that these young people can and, if they are helped, will positively impact the future of our industry. For more information contact the YPC Secretary, Vulani Maseko at vulanimasek@yahoo.com
The personal development plans or initiatives that graduates can undertake to differentiate themselves in the marketplace.
The newly elected members of the YPC know that they can contribute significantly towards appropriate transformation, meaningful succession planning, and a solid portfolio of skills from the next generation.
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V. Duke
Richard Peter Mohring It is with great sadness that we announce the passing of Richard Peter Mohring, fondly known by us all as ‘Rick’. Rick was born in Johannesburg in 1947 and died in Johannesburg in March 2016 after a two-year struggle with cancer. He received his formative education at King Edward VII School, also in Johannesburg. Therefore, Rick was surrounded by mine dumps from an early age and it must have been during these years that mining crept into his blood, because on leaving school he enrolled at the University of the Witwatersrand to read for a Bachelor’s degree in Mining Engineering. On graduation as a mining engineer in 1972, Rick started his career with Rand Mines on Durban Roodepoort Deep gold mine, where he progressed through the ranks to that of Underground Manager. In 1975, Rick was transferred to the Rand Mines coal division, where he began his illustrious career in coal mining. He underwenr a meteoric rise in the coal division – in 1981 at the age of 34, Rick was appointed General Manager of Welgedacht Exploration Company and in 1984 he was appointed Managing Director of Rand Coal. Rick was involved with many achievements in the South African coal mining industry, inter alia the design and running of Middelburg Mine, a 10 million ton per annum coal mine the development of the Khutala and Majuba collieries utilizing high-capacity continuous miners conducting coal-bed methane drainage tests (the precursor of ‘fracking’), and combining a large export colliery (Middelburg) with an Eskom supply colliery (Duhva). During this time he rose to be the Senior Operations ManAger of Ingwe Coal Corporation and then the Chief Executive Officer of NewCoal, an initiative set up by Anglo Coal and Ingwe to create a Black Economic Empowerment entity in the coal mining industry. After an 18-month process the largest BEE coal company, Eysizwe Coal, was formed with Rick as the Deputy Chief Executive Officer to oversee a smooth transformation. Thus, Rick has played a major role in the transformation of the South African coal mining industry to the inclusion of Black entrepreneurs having a major stake in the industry. Apart from his direct work as a professional mining engineer, Rick was associated with the Engineering Council of South Africa for many years. He served as a Council Member from 1992 to 2008 and as Chairman of various ECSA committees. He represented ECSA internationally in the negotiation for ECSA’s acceptance in the Washington Accord and the Engineers Mobility Forum, which gave rise to the recognition of registered engineers throughout the world. Rick was also involved with tertiary education. He was not only a member of many of ECSA university accreditation teams over the years, but also a member of the Industry Advisory Councils for mining engineering at both the University of Pretoria and the University of the Witwatersrand. Rick served with many industry associations, including the Chamber of Mines of South Africa, the Fossil Fuel Foundation, the International Committee for Coal Research, and the International Energy Agency, where he represented South Africa on the IEA Coal Industry Advisory Board from 2000 to 2003. With the Southern African Institute of Mining and Metallurgy, Rick’s involvement has been prolific. He was a Member from 1971 and a Council Member since 1988. He served on many committees – TPC Mining, Publications, Membership, Banquet, and Scrutineers among others, and was a trustee of the SAIMM Scholarship Fund. Rick was the President of the SAIMM for the 1997/1998 term and was an Honorary Life Fellow of the Institute. The Institute’s highest honour, the Brigadier Stokes Memorial Award, was presented to Rick at the 115th AGM in August 2012. Rick, we in the Institute will miss you and remember you fondly.
J.A. Cruise
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t’s iden s e r P er Corn
Ethics ‘Never let your sense of morals get in the way of doing what's right’ – Isaac Asimov
O
ne of the characteristic features of a professional society is that its members are governed by a code of professional ethics. The term ‘ethics’ is derived from the Greek word ethos, meaning ‘character’. Ethics and morals both relate to ‘right’ and ‘wrong’ conduct. ‘Morals’ often refers to an individual’s own principles or habits that provide a personal compass regarding right and wrong conduct. ‘Ethics’ refers to the rules of conduct that are provided by an external source within a particular context, and can be considered a social system or a framework for acceptable behaviour. An often-quoted example in the field of law illustrates how professional ethics might apparently conflict with personal morals. A lawyer’s morals may tell him/her that murder is reprehensible and that murderers should be punished, but professional ethics require a lawyer to defend a client to the best of his/her abilities, even if the client is guilty. There are good reasons for this ethical requirement, as it helps to build a fair society. Ethics is intended to be practical, and is conceived as shared principles promoting fairness in social and business interactions. However, ethical decisions should recognize the context within which they are set, and must recognize that duties can be ranked in a hierarchy (for example, to stop at an accident to render assistance takes precedence over the promise of meeting for lunch). ‘The word “good� has many meanings. For example, if a man were to shoot his grandmother at a range of five hundred yards, I should call him a good shot, but not necessarily a good man.’ – G.K. Chesterton ‘Right is right, and wrong is wrong, and a body ain’t got no business doing wrong when he ain’t ignorant and knows better.’ – Mark Twain, The Adventures of Huckleberry Finn In South African society in 2016, we are acutely aware of the prevalence of dishonesty and corrupt business dealings around us. The need for integrity in business and politics has never been greater. I would like to live in a world where we all work towards the welfare, safety, and health of all people, and care for our environment. ‘Educating the mind without educating the heart is no education at all.’ – Aristotle ‘Ethics are more important than laws.’ – Wynton Marsalis When people sign up for membership of a professional society such as the SAIMM, it is expected that they will always conduct themselves in a professional manner, and act with integrity and sincerity in all of their work. The SAIMM’s Code of Professional Conduct appears as By-law H in the ‘Constitution and By-Laws’ document in the ‘About SAIMM’ section of our website, and is worth reading as a reminder about our professional obligations. In essence, the code of professional conduct requires Members to eschew fraudulent or dishonest practices, not to conceal unethical acts, and to avoid working with others who behave unprofessionally. A professional should work to the highest possible standards, stay up-to-date with their field, and should undertake only work that he or she is trained for. Conflicts of interest should be avoided, and financial dealings should be open and fair, with no bribery. Honesty and confidentiality are expected. Professional behaviour involves no misrepresentation in advertising or unfair criticism of the work of others. Any transgressions of this code are dealt with in terms of our ‘Complaints and Disciplinary Procedure’ (also on the website) by the Complaints Committee, which gathers facts, and screens complaints to ensure that they are neither frivolous nor malicious, before assessment by the Ethics Committee. The assessment is handled in a firm, fair, and confidential way, and can result in a warning, a reprimand, a requirement for further training, or even suspension, expulsion, or referral to statutory bodies. ‘Live so that when your children think of fairness and integrity, they think of you.’ – H. Jackson Brown, Jr.
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L
R.T. Jones President, SAIMM
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PAPERS IN THIS EDITION
Papers — Student Edition–Mining Improving the ventilation system at Rosh Pinah zinc mine by E. Develo, M. Pillalamarry, and E. Garab . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 A number of options were considered In order to improve the ventilation conditions and these were simulated using an appropriate software package. A workable solution was proposed that could improve the overall ventilation in the mine and lead to significant savings in the cost of providing the ventilation. Sub-standard practices: effects on safety performance in South African gold mines by G. Kleyn and J.J.L. du Plessis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 The purpose of this investigation was to establish the root causes of sub-standard practises and the consequent effect on safety performance at an underground production operation of a gold mine in the Free State. The established methods of addressing sub-standard practices and improving safety performance were found to discourage employees from performing work safely and according to procedure. A critical investigation into tyre life on an iron ore haulage system by G.C. Lindeque. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 This investigation compared ‘Best PractiCe’ to the current tyre management strategy at the mine to determine the elements that could be improved. A new Tyre Management Strategy was formulated as a Step-by-Step guide on how to implement the proposed changes. Review of support systems used in poor ground conditions in platinum room and pillar mining: a Zimbabwean case study by T. Chikande and T. Zvarivadza . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323 The results from this study showed that the current support system and mining practices in bad ground areas need to be adjusted to improve safety and productivity. A number of recommendations were made to change the explosive, pillar design, and roof bolting practice.
These papers will be available on the SAIMM website
http://www.saimm.co.za
Papers — Student Edition–Metallurgy Slurry abrasion of WC-4wt%Ni cold-sprayed coatings in synthetic minewater by N.B.S. Magagula, N. Sacks, and I. Botef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 A number of tests were conducted to assess the wear behaviour of mild steel that had been subjected to a low pressure cold gas dynamic spraying to produce a coating deposit of tungsten carbide containing a known amount of nickel. Matte – tap-hole clay – refractory brick interaction in a PGM smelter by J. Du Toit, R.D. Cromarty, and A.M. Garbers-Craig. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339 This laboratory scale investigation examined the ability of the tap-hole clay to form a protective layer on the brick which could limit the matte penetration into the tap-hole brick. Separation of kimberlite from waste rocks using sensor-based sorting at Cullinan Diamond Mine by T. Mahlangu, N. Moemise, M.M. Ramakokovhu, P.A. Olubambi, and M.B. Shongwe . . . . . . . . . . . . . . . . . . . 343 This paper describes the initial test work that led to the decision to conduct a pilot scale study. The mineralogical characterization of the feed and product streams, to validate the sorting criteria and the operational data obtained during the pilot plant campaign is shown. An evaluation of the thermal fatigue performance of three alloys for casting mould applications by V. van der Merwe and C.W. Siyasiya . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 The aim of the project was to find an alternative alloy that would outperform the current low alloy cast steel that was experiencing premature thermal fatigue failure of the casting moulds that are used in catalyst production. The effect of particle size on the rate and depth of moisture evaporation from coal stockpiles by * DE 'OEDE " -ULLER Q.P. Campbell, M. le Roux, AND C.B. Espag de Klerk . . . . . . . . . . . . . . . . . . . . . . . . . . . 353 The objective of this project was to determine the effect of coal bed particle size on the rate of evaporation as well as the depth to which evaporation extends in a coal stockpile.
http://dx.doi.org/10.17159/2411-9717/2016/v116n4a1
Improving the ventilation system at Rosh Pinah zinc mine by E. Develo*, M. Pillalamarry*, and E. Garab†Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)
Recent geological exploration at Rosh Pinah mine revealed that the mine’s major production is shifting towards the western orefield, which will increase the demand for air flow to be supplied to this area. A snapshot of the ventilation survey carried out in December 2014 at the western orefield drill drive B (WOF-DDRB) showed that the air flow was well below the required standards. In order to improve the existing conditions, possible options were considered and simulated using Ventsim™ software. The best option found was to replace the existing western orefield fans with the larger fans from the inactive southern orefield workings, to increase the air flow in the DDRB district. Simulation showed that as much as 20 m3/s of air can be received at the working faces of WOF 30, compared to the previously received amount of 1.37 m3/s. The economic analysis indicated that the above option can reduce the ventilation cost by N$1.9 million annually. It was also noticed that after implementing this option together with other projects, the ventilation conditions in the mine were greatly improved and currently give no cause for concern. 2. )*!& mine ventilation, simulation.
1(+*)!' +-)( A good mine ventilation system should be capable of providing adequate quantity and quality of air to all working faces, and is critical to the occupational health, safety, and comfort of underground employees (Luxbacher and Ramani, 1977; Exikis and Kapageridis, 2006). No ventilation system can remain adequate indefinitely; as the mine workings are extended, the ventilation characteristics such as system pressures, air volumes, leakages, and airway resistances change considerably. Continuous improvement of the ventilation system is needed to ensure compliance with health and safety regulations (Lovejoy, 2010). It also ensures that the right quality and quantity of air is delivered to all the necessary areas at the lowest possible cost. This can be achieved by identifying inefficient airways and poorly ventilated areas in the mine and planning how best to upgrade them. The latest geological exploration shows that the focus of production at Rosh Pinah mine is shifting towards the western orefield (WOF). As mining progressed, the working areas have advanced away from the main fans, which increased the resistance to air flow
0, #*)'(! Rosh Pinah is an underground mine that produces primarily zinc and lead. The mine is owned by Glencore and is located approximately 360 km southwest of Keetmanshoop in Namibia. This underground operation is 420 m deep and uses sill-and-bench open stoping methods. The mine workings are divided into
Department of Mining and Process Engineering, University of Science and Technology, Namibia, Windhoek. †Rosh Pinah Zinc CORporation, Rosh Pinah, Namibia. Š The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received Mar. 2016. *
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drastically and resulted in increasing demands being imposed on the main fan in order to supply an adequate air flow. This process also created more leakage paths between the fan and the working areas, which has caused the air to short-circuit before it can reach the faces. Consequently, a much larger quantity of air has to be circulated by the fan so that the stipulated quantity reaches the face, which increases operating costs (Singh et al., 2004). An investigation was carried out to optimize the existing ventilation system along the WOF at Rosh Pinah, in order to accommodate the growing ventilation demand. This entailed an evaluation of all the feasible alternatives available to improve air flow to the working faces (Mukherjee et al., 1982). The current distributions of air flow, pressure, leakages, and air quality throughout the main flow paths of the WOF were quantified by conducting a pressure-quantity survey. Survey data was used to identify ventilation inefficiencies along the WOF drives and also to simulate the current ventilation network. Finally, the ventilation network and regulators were modified in order to distribute sufficient fresh air at the working faces in the WOF with minimum cost. Ventsim™ software was used to simulate the ventilation network.
Improving the ventilation system at Rosh Pinah zinc mine different sections according to the location of the orebodies, which are termed the western, eastern, southern, and northern orefields. Figure 1 shows the layout of the mine sections at Rosh Pinah. Rosh Pinah practices very high safety and health standards and the ventilation officers are required to conduct daily ventilation surveys before the underground employees enter a working area. If these areas do not meet the ventilation standards, no personnel are allowed to enter that particular area until the conditions are improved by the Rosh Pinah technical team.
Access, C-mine entrance, and C5 tunnel. This simulation was simply used to redirect the airflow through the WOF decline by placing a curtain at the entrance to the northern orefield intake tunnel, since no mining is taking place at this location. A permanent stopping was also placed close to the Quick Access portals where the air moves towards the workshop and is returned to the Quick Access through a stope. The workshops are dormant and therefore ventilation is not needed. After the simulation, the airflow distribution was analysed. The location of the stopping along the WOF decline is indicated in Figure 3.
3.(+-",+-)(/(.+ )* / The WOF has three major ventilation intakes, namely the C-mine adit, Quick Access, and the 390 BME adit. The eastern orefield has one major intake, the eastern orefield adit. The intake to the southern orefield is the C5 access tunnel. Figure 2 illustrates the layout of the five main intakes at Rosh Pinah, including the eastern orefield adit. The intake air is passed through the decline while the exhaust air is returned to the atmosphere by an exhaust fan connected to a raise. Rosh Pinah has a complex ventilation network requiring efficient use and management of air control within the mine. The deeper sections of the mine are hot and humid, which necessitates the use of auxiliary ventilation. Rosh Pinah currently has five main exhaust fans installed at the top of the worked-out stopes, which are responsible for extracting the return air out of the stopes and to the atmosphere. Maintenance on the main fans is carried out once every three months by the mine mechanics, and once yearly on contract maintenance. The specifications and locations of these fans are detailed in Table I.
Since production is shifting towards the WOF, more air flow will be required in this area. Two J67 Airtec Davidson fans are installed at the southern orefield stope, which will be mined-out soon (Figure 4). The fan upgrade at WOF includes removing the existing Howden D7 fans, which supply 125 m3/s when operating in parallel, and replacing them with the two J67 Airtec Davidson fans from the SOF (Figure 4).
- '",+-)(/ )!."& The air flow requirement at the working faces was calculated according to the mine ventilation standards of Namibia (Ministry of Mines and Energy, 1992). The figure includes the requirements for machinery as well as personnel working at the face. Prior to the simulation, the current ventilation model of Rosh Pinah was updated with the new working areas by importing extended level plans (survey plans) as DXF files. The extended branches were drawn and edited in Ventsim. The ventilation network was then simulated with the new ventilation data, using various possible options and different control methods. The changes that could be made to the network were identified from the ventilation survey data. The following two options were considered for simulation.
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Table I
Specifications of main fans used at Rosh Pinah Fan type
Connection
2 Ă— centrifugal Donkin fans 2 Ă— axial flow Howden D7 fans 1 Ă— axial flow J67 Airtec Davidson fan
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Capacity 2 Ă— 160 kW at180 m3/s 2 Ă— 110 kW at 125 m3/s 185 kW at 100 m3/s
Location EOF 310 level WOF 190 level Surface, SOF
Improving the ventilation system at Rosh Pinah zinc mine newly developed workings, the adequacy of the ventilation under the existing system was surveyed to improve the conditions in this area. However, no production was taking place at this area during the survey, and production will be started only after the ventilation conditions are improved.
The oxygen concentration at all five working faces (no. 1, 5, 6, 8, and 9) in the WOF met the required minimum of 20%. The methane concentration at the working faces was found to be negligible. The nitrogen oxide levels were minimal, and did not cause any major concern.
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High temperatures and humidity in an underground workplace may result in reduced performance and impair the attention of workers (Rostami, 2011). Therefore, it is important to study the humidity levels at the working face to ensure comfortable conditions. The humidity measured at all the working faces of WOF 30L was slightly above the maximum allowable level of 85% (Figure 6). A maximum humidity of 90% was measured at working face 8. The humidity at all the other working faces at WOF level 30 was found to be satisfactory.
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Prior to the fan installation, a bulkhead with a width of 8 m and a height of 4 m was drawn at WOF level 30 to locate the fan. The purpose of this bulkhead is to reduce the shock losses that may occur if the fan was to be located perpendicular to the direction of the air flow. Three raises were planned from WOF 30 to WOF 90 to link the new fan location with the return raise at WOF 90. This is shown in Figure 5. The length of the raises from 30 level to 190 level is 163 m. The diameter of the raise that was inserted is 4.0 m. The new airflow distribution along WOF was then simulated. The new location of the fans at WOF is shown in Figure 5
The air flow required at the working faces of the mine was determined using the mining ventilation standards of Namibia (Ministry of Mines and Energy, 1992). Rosh Pinah mine makes use of Cat AD 30 trucks in combination with scoops. Usually, there are a maximum of six personnel at a working face. The cross-sectional areas of the working faces are 22.7 m2, therefore, the calculated minimum required airflow at the working face is 18.2 m3/s. The measured air flow at the working faces of the WOF is shown in Figure 7.
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The objective of the survey was to assign resistances to all the branches in the ventilation network by quantifying the air flows and pressure drops (Nixon, 1983). Moreover, accurate quantity and pressure measurements are an absolute necessity since the validation of the computer-generated output is heavily dependent on the accuracy of the input data (Gelhn et al., 2008; Rostami, 2011). The characteristics of the existing mine ventilation system were determined by conducting an underground survey. The direction of the airflow and the location of intakes, returns, stoppings, etc. were determined by inspection of the mine plan. The ventilation results below are a snapshot from December 2014. No personnel were allowed to enter the area due to the mine’s safety and health policy. Since these are
Improving the ventilation system at Rosh Pinah zinc mine Costs of drilling a raise per metre Ă— number of holes Ă— length of raise = N$710 Ă— 21Ă— 160 m = N$2 385 600 Total capital costs to install the fans = costs of drilling and blasting (160 m) raise + installation costs from contractor = N$2 385 600 + N$288 216 = N$2 673 816 Equivalent annual costs are therefore, 320 549Ă—0.1 $-#'*./ .,&'*.!/,-*/%") /,+/+ ./ )* -(#/%, .&/
The air flow entering the working faces was 41.0 m3/s compared to the total air flow of 11.41 m3/s. reaching the working faces. The volumetric efficiency was therefore 27.83 %. In addition, the efficiency of the existing Howden fans during the ventilation survey was found to be only 67.1%.
Sealing the entrance to the workshop near the Quick Access at level 370 and placing a curtain at the northern orefield fan tunnel entrance resulted in the air flow at the WOF increasing from 60 m3/s to 83 m3/s. However, air flow at the working faces was still inadequate; this increase in air flow was rather supplied to other areas in the mine. The maximum air flow that was achieved was 11.2 m3/s, and this was at working face 8. The air flow entering the working faces increased slightly to 44 m3/s. The air flow at the working faces after redirecting is shown in Figure 8.
(EAC) =
= N$501 190.81 -1 ) (1 (1.1)8 The annual operating costs for the two fans are (McPherson, 1993): Operating costs (N$) = Pft × Q × e ×24 ×365 ̀ where Pft = Fan total pressure (kPa), Q = Air flow (m3/s), e = Cost of electricity in kWh (N$) 2×185 Operating costs (N$) = ×0.85×24×365 0.671 =N$4 105842.027 per year The total yearly cost is obtained by adding the cost of developing the airways/raises and the annual operating cost of ventilation. Total cost to implement option 2 = N$501 190.81 + N$4 105 842.027 = N$4 607 032.84
4)( "'&-)(& Ventilation survey results revealed that gas concentration and humidity levels at the western orefield decline met the Namibian ventilation standards and did not cause any major concern (Ministry of Mines and Energy, 1992). Since the
By replacing the existing WOF fans with the southern orefield fans, the air flow increased significantly, meeting the regulatory requirements at all the working faces. The air flow entering the WOF was 122 m3/s, and the air flow at working face 8 increased to 25.2 m3/s. The total air flow reaching the working faces was 103.2 m3/s; the volumetric efficiency therefore is 68.8%, and the rest of the air was leaking through the stopping to the return raise. The air flow at all five working faces is given in Figure 9. Working faces 1, 5, 6, 8 at WOF 30 are parallel with working face 9 at WOF 90.
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The costs of making changes to the ventilation network at Rosh Pinah were evaluated for option 2. The costs to replace the two main fans at WOF level 90 with the two fans at southern orefield level 262 (J67 Airtec Davidson fans) were determined. Since the main fans are not new, the capital costs of alteration include the fan installation costs and the costs for drilling the three 160 m raises from 30 level to 90 level of WOF. According to the project planner at Rosh Pinah, the costs of drilling and blasting a raise is N$710 per metre, including labour costs. Hence: Total costs of drilling and blasting the 160 m raise =
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Improving the ventilation system at Rosh Pinah zinc mine
() ".!#. .(+& The authors thank Rosh Pinah Zinc Corporation for the provision of data and the use of its facilities and ventilation measuring instruments during the investigation.
.%.*.( .& DUCKWORTH, I.J. and LOWNDES, I.S. 2003. Modelling of auxiliary ventilation systems. Transactions of the Institution of Mining and Metallurgy, vol. 12, no. 2. pp. 2–9 EXIKIS, A. and KAPAGERIDIS, I.K. 2006. Simulation of air and contaminant flow in underground mine ventilation networks. Proceedings of the 2nd International Conference on Advances in Mineral Resources Management
and Environmental Geotechnology (AMREG 2006), Technical University Crete, Chania. pp. 89–93. GLEHN, F.H., MARX, W.M., and BLUHM, S.J. 2008. Verification and calibration of ventilation network models. Proceedings of the 12th U.S./North American Mine Ventilation Symposium 2008, University of Nevada, Reno, NV. Wallace, K.G. (ed.). Society of Mining Engineers of AIME. pp. 275–279. HARTMAN, H.L., MUTMANSKY, J.M., RAMANI, R.V., and WANG. Y.J. 1997. Mine Ventilation and Air Conditioning. Wiley, Hoboken, NJ. LOVEJOY, C. 2010. A breath of fresh air. Mining Magazine, July/August 2010. pp.16-21. LUXBACHER, G.W. 2008. Developing input data for computer simulation of mine ventilation. Kentucky: Pennsylvania State University. LUXBACHER, G.W. and RAMANI, R.V. 1979. Optimization of coal mine ventilation systems. AIME Transactions, vol. 286. pp. 1801–1809. MCPHERSON, M. 1993. Subsurface Ventilation Systems. Chapmann & Hall, New York. pp.25-120. MINISTRY OF MINES AND ENERGY. 1992. Mine Health and Safety Regulations, 10th draft. Windhoek. NIXON, T.R., DEAKIN, J.J., and RALPH, A.M. 1983. Ventilation analysis for mine planning and operation. Computers in Mining Symposium, Southern Queensland Branch, Australasian Institute of Mining and Metallurgy. pp 231–240. ROSTAMI, P., DANKO, G., and BAHRAMI, D. 2011. Ventilation and climate simulation of development ends in metal mines. Proceedings of the SME Annual Meeting, Denver, CO. Preprint no. 11–135. pp. 732–735. SINGH, A.K., AHMAD, I., SAHAY, N., VERMA, N.K., and SINGH, V.K. 2004. Air leakage through underground ventilation stoppings and in situ assessment of air leakage characteristics of remote filled cement concrete plug by tracer gas technique. Journal of the South African Institute of Mining and Metallurgy, vol. 104, no. 2. pp 101–106. TIEN, J. 2008. Determining the optimal mine regulator location using computer simulation. Peabody Coal Company, Kentucky. pp.2-6 WALLACE, K. and MCPHERSON, M.J. 1983. The efficiency and economics of mine ventilation systems. TMS/AIME Meeting, Atlanta, GA, 6 March 1983. pp. 2-7. N
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workings are still at the developing stage, the air flow measured at the western orefield decline was below the minimum required. The volumetric efficiency of the western orefield decline was found to be 27.3%. The most feasible solution to increase the air flow at the working faces would be to replace the western orefield main fans with the southern orefield main fans. Along the western orefield decline, 25.23 m3/s of the air is flowing out of the western orefield into the northern orefield fan tunnels. No mining activity is currently taking place in this area; therefore it is recommended that the flow of air can be controlled by placing a brattice cloth at the entrance of the fan tunnel. Real-time air quantity and air quality control would reduce the effort of ventilation surveys. The real-time monitoring ventilation system, together with Ventsim™, could improve the accuracy of the simulation and provide the most accurate results.
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http://dx.doi.org/10.17159/2411-9717/2016/v116n4a2
Sub-standard practices: effects on safety performance in South African gold mines by G. Kleyn* and J.J.L. du Plessis* Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)
(Figure 1). These include meeting the Mine Health and Safety Milestones (Department of Mineral Resources, 2011). Most South African mining companies have adopted a ‘zero harm’ policy in an effort to improve the health and safety of employees at their operations. After the 2003 Mine Health and Safety Summit, the following milestone was set with regard to the gold mining industry (Department of Mineral Resources, 2011): ‘Achieve safety performance levels equivalent to current international benchmarks for underground metalliferous mines, at the least, by 2013.’ These milestones were revised in 2014 and new targets for 2024 were set for the South African mining industry (Association of Mine Managers of South Africa, 2014). The new milestones that were set in terms of occupational safety are listed below (Association of Mine Managers of South Africa, 2014):
Sub-standard practices and their adverse impact on safety performance remain a challenge in the South African gold mining industry. The purpose of this study was to investigate the root causes of sub-standard practices and the effect on safety performance in South African gold mines. The focus of the study was on the underground production operations at a gold mine in the Free State. The study consisted of three parts: a personal investigation into the causes of sub-standard practices at the mine, a comparison with the results of a cultural study performed at the West Wits mines, and a behavioural survey. The studies described in this article yielded similar results in terms of the key drivers behind sub-standard practices. It was found that substandard practices had a number of causes, and the origin lies within the habits, attitude, and behaviour of employees. Current methods of addressing sub-standard practices and improving safety performance were found to discourage employees from performing work safely and according to procedure. It was concluded that the lack of critical behavioural habits for the given work environment and job title could possibly be the primary reason for the occurrence of sub-standard practices. 40! *-(& sub-standard practices, safety, behaviour, habits.
3+.-*(,'./*+ Since the implementation of the Mine Health and Safety Act, 1996 (Act 29 of 1996) and the Mine Health and Safety Regulations, the South African mining industry has been striving to improve health and safety performance and has placed great emphasis on adherence to mine standards. The Act requires employers in the mining industry to report accidents, incidents, and dangerous situations to the Regional Principal Inspector of Mines in their area. The data provided by employers is captured and analysed by the South African Mines Reportable Accident Statistical System (SAMRASS) and made available for public viewing (Department of Mineral Resources, 2011). A review of the national mine-related accident statistics shows clearly that the South African gold mining industry has improved its safety performance markedly over the past decade, but is still facing major challenges
Ž ‘Every mining company must have a target of ZERO FATALITIES Ž Every Fatality is one too many, we will eliminate fatalities by December 2020 Ž Up to December 2016, 20% reduction in Serious Injuries per year Ž From January 2017, 20% reduction in Lost Time Injuries (LTI) per year.’ The 2024 targets include new milestones for the implementation of the approved culture transformation framework (CTF). These milestones included the following (Association of Mine Managers of South Africa, 2014): Ž ‘By December 2020 there will be 100% implementation of:
* Department of Mining Engineering, University of Pretoria, South Africa. Š The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received Dec. 2015.
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– The Leadership Pillar of the CTF – The Risk Management Pillar of the CTF – The Bonus and Performance Incentive Pillar of the CTF – The Data Management Pillar of the CTF – The Diversity Management of the CTF – The Leading Practice pillar of the CTF Ž After December 2020 the remaining pillars will be implemented: – The Integrated Mining Activity Pillar of the CTF – The Technology Pillar of the CTF – The Inspectorate Pillar of the CTF – Tripartism Pillar of the CTF – Regulatory Framework Pillar of the CTF’ Sub-standard practices compromise the effectiveness of any safety measures, devices, or procedures that have been put in place. They create a weak spot in the system that is bound to fail with the slightest amount of interference. Standards and safety are very closely related and standards are necessary not only to maintain the safety of underground employees, but also to improve current safety practices. The information below represents some of the safety performance statistics at the study mine and was compiled from data obtained from the mine’s safety department. From 17 February 2009 to 22 December 2014 a total of 2042 accidents occurred on the study mine. A total of 26 of these accidents led to fatalities. Upon analysis, it was found that the mine experienced approximately 0.94 accidents per day. The accident distribution by shift is shown in Figure 2. Figure 2 shows that the majority of accidents at the mine occurred during the morning shift. The average time of occurrence of morning shift accidents was 11:58:17 am. Figure 3 shows that the largest number of accidents at the study mine occurred in the stopes. The second highest number occurred in development, and the third highest in tramming. Not surprisingly, these are also the departments underground that have shown the greatest amount of substandard practices. It is estimated that approximately 40–50% of all accidents underground occur as the inevitable result of sub-standard acts. From Figure 1 it is clear that safety performance in gold mining has lagged that in other sectors of the mining industry for the past 10 consecutive years, and despite the recorded improvements, further efforts are required.
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Figure 4 shows the relative distribution of accidents at the study mine between the surface and underground environments. These statistics show that the underground work environment is more hazardous. The question remains: why do employees at the mine still engage in sub-standard acts and how does this affect safety? It is this question that gave rise to this investigation into the root causes of sub-standard practices at the mine. The hypothesis is that sub-standard practices usually have multiple causes on different organizational levels and have an adverse effect on the safety performance of South African gold mines in general. To understand the current culture and the need to change, an investigation into what causes employees to engage in sub-standard acts and how to change the behaviour at all levels of the organization was required.
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conducted on shift bosses in order to determine benchmark attitudes and behaviour for this group of employees. The rest of the participants’ habits were then compared to the benchmark and analysed. The results of a cultural survey performed by Dupont were analysed in order to determine previously known causes of sub-standard practices and their relation to employee behaviour. The Society for Mining, Metallurgy and Exploration (SME) Mining Engineering Handbook, (1973) states that all mining operations are required to adhere to local, provincial, and governmental regulations that among other things specify mine safety regulations and standards, environmental protection, and labour relations. The nature, scope, and stringency of these regulations ultimately govern the mining operation. Over the past three decades, the number and extent of mining regulations and governing authorities have dramatically increased on an annual basis. The major reason behind this is a continuous effort of governments to promote health and safety standards in the global mining industry (Hansen, 1973). According to Hansen, (1973), a statistical study that was performed over a period of 50 years showed that awareness of the effects of sub-standard practices resulted in a decreased frequency of accidents. The majority of mine health and safety authorities around the world agree that the major causes of mine accidents and fatalities are unsafe conditions, poor management, and especially unsafe practices, which according to the SME, is often cited as the primary cause (Society for Mining, Metallurgy and Exploration, 2011). Due to a combination of sub-standard practices and hazardous conditions, one must consider not only the physical causes of sub-standard practices, but also elements such as training of employees, the mental state of employees, and employee behaviour (American Institute of Mining, Metallurgical and Petroleum Engineers, 1973) The major shortcoming of most of the approaches used to identify the causes of sub-standard practices is that the studies were usually based on hasty investigations, obvious physical factors, and common causes of sub-standard acts while neglecting the psychological, cultural, and behavioural drivers. Poor human behaviour, however, is a known detrimental factor in mine safety. This is evident from the cyclical recurrence of repeat accidents. The key shortcoming of considering only incident and accident frequency rates as the focus of safety performance is that it neglects the root causes of the incidents (American Institute of Mining, Metallurgical and Petroleum Engineers Inc., 1973). The Mine Health and Safety Act (MHSA) aims to enforce health and safety measures and legislation in the South African mining industry (Department of Mineral Resources, 2011). The open question remains whether the implementation of the MHSA was sufficient to create a safety-wise culture in the mining industry. Published fatality and injury rates often reveal a false picture of what is actually occurring in the mining industry. Deep-level mining unfortunately has associated hazards and risks and requires commitment and adherence to health and safety standards (This is Gold, 2015). VOLUME 116
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In order to ensure compliance with regulations, the mine has implemented a full compliance policy. However, the sharp increase in sub-standard practices indicated that the policies implemented by the company have not led to the desired result. Furthermore, a major concern is that the new generation of mine employees is adopting a culture where sub-standard practices are the norm. The language barriers that exist among the majority of the workforce raise a number of questions with regards to mine standards in terms of comprehension. Figure 5 shows the number of accidents and fatalities recorded at the mining operation over the past 5 years. Although there was a steady decline in the number of accidents from 2009 to 2014, this is not reflected in the number of fatalities. Thus although the number of accidents has decreased, their severity has not. Ideally, the accident statistics should show a steady decline, indicating that the ‘zero harm’ policy of the company is becoming a reality. Unfortunately, the fluctuations in the injury and fatality rates indicate a high probability of recurrence of accidents and fatalities. It is believed that proactive standards have a far greater impact than reactive standards. Firstly, it was necessary to carry out research on accidents related to sub-standard work at the mine. This was done in order to identify the root causes of sub-standard practices in the underground working environment and the effects on safety performance. The findings of the study at the mine were compared to those of a cultural study that was completed at mines in a different mining region. The last part of the study involved conducting Shadowmatch surveys on first line supervisors (shift bosses) and making recommendations for further studies. A literature study was completed to determine what investigations have been completed in South African gold mines, and the safety performance and factors that influence it. This included a previous cultural study that was performed at mines in the West Wits region. Personal interviews were conducted to try to determine the factors that influence sub-standard practices. Production supervisors were also interviewed in order to compare how their opinions on sub-standard practices differed from those of the underground employees. Questions were posed in such a way as to determine how the work culture (attitudes and behaviour) influences the implementation of mine standards. Towards the end of the study, a Shadowmatch survey was
Sub-standard practices: effects on safety performance in South Africa The published data on mine-related incidents and fatalities (Department of Mineral Resources, 2011) shows that conditions in the underground gold mining environment can be extremely challenging. Since most gold mines in South Africa still use conventional methods (drilling and blasting in narrow-reef stopes) it remains a highly labour-intensive industry. The CSIR (2013) conducted a study to develop an accident investigation tool that can be used to determine the root causes of incidents and which provides better insight into the systematic factors that eventually led to the occurrence of the incident. The CSIR was of the opinion that the injured person is not the sole cause of the accident, but that a series of events leads to such occurrences, and that supervisory and managerial aspects also contribute either directly or indirectly to such events (CSIR, 2013). It is important to determine the human error aspect of an accident as well as the path that led to its occurrence (Society for Mining, Metallurgy and Exploration, 2011). It must be realized that the majority of incidents generally result from at least one act and one condition. However, the majority of mine-related accidents are caused by more than one condition or act. If this is not taken into account, the opportunity to determine the real root cause(s) of the incident is lost. An integrated diagnostic review of cultural transformation was performed at the West Wits gold mines in 2012. The purpose of the study was to determine employee attitudes and behaviour within the company and the factors that resulted in a certain attitude or behaviour (Gold Fields, 2012). The study employed a number of different analysis tools in order to identify all the cultural issues and to ensure that all the levels of employment within the organization were covered. An accident or fatality is usually the outcome of a number of sub-standard practices that ultimately led to the event. The probability of occurrence of the unwanted event (accident or injury) and its severity are increased by sub-standard practices. As the number of sub-standard practices increases, the probability of accidents, as well as their severity, also increases. It is therefore important to look at accident causation theories in order to link the current situation in the South African gold mining industry to sub-standard practices and their causes. A review of the available literature shows clearly that all accident causation theories have a number of common goals, namely: ÂŽ ÂŽ ÂŽ ÂŽ ÂŽ
Identifying risks Identifying influencing factors Attempting to explain why the accident occurred Identifying the root causes of the accident Using the above knowledge to predict and prevent accidents.
The majority of authors, (e.g. Guttierez, 2010; Mol, 2002; Raouf, 2011; Saari, n.d.) agree that there are several theories of accident causation, and that a single theory is often not enough to establish the true cause of the incident.
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The different accident causation models often show conflicting perspectives when it comes to establishing the cause of the incident. It is important to understand that there is no single accident causation theory that is applicable to the mining industry, universally speaking. Some models, however, enjoy preference due to their simplicity and perspective on what ultimately led to the accident. (Raouf, 2011) The theories that were investigated included: ÂŽ ÂŽ ÂŽ ÂŽ ÂŽ
The Domino Theory Multiple Causation Theory The Swiss Cheese Model The Risk Homeostasis Theory Bird and Germain’s Loss Causation Theory.
Research has found (De Villiers, 2009) that many individuals occupy job positions in which they are extremely unhappy. This was also the case with regard to the working environment. The associated problem lies in this: it results in negative implications not only for the individual, but also for the working environment and fellow workers. The Shadowmatch system was developed to prevent the above-mentioned scenario by allocating individuals to environments that best suit them in order to preserve harmony between the individual and the environment. The Shadowmatch system can also be used to identify employees that best suit a specific working environment and specific job. The system possesses the capability to provide personal development programmes for individuals that require specific habits in order to be successful in their occupation (De Villiers, 2009). This process is completed by comparing the habits of the individual concerned to the habits of employees who are deemed successful, based on the performance management system of the company, in performing a specific task within the organization The Shadowmatch research team identified a number of aspects that ultimately define the work environment (a detailed description of each can be found in the Shadowmatch e-book available at www.shadowmatch.com): ÂŽ ÂŽ ÂŽ ÂŽ
Physical environment Social environment Emotional environment Operational environment.
Behaviour, being a complex field of study, can be motivated by more than one motivator, and a number of motivators may be present within a single one. Most people are uncertain of why they behave the way they do (De Villiers, 2009).
60&, .& It was found that when employees were interviewed in their specific working environment, their opinions differed greatly from when interviewed on surface. It was therefore decided to conduct all interviews in the appropriate underground working environment. Based on the personal interviews with employees at the mine and the results of the 2012 cultural survey executed by
Sub-standard practices: effects on safety performance in South Africa
Ž The mine currently has a large number of young employees who do not have many years’ experience in the mining industry Ž Older people have been appointed in certain occupations without a great amount of previous mining experience.
Both of these situations could have influenced the findings. After discussion with a psychologist specializing in public health, it was established that in the mining industry, the following behaviour patterns are expected with regard to age and years’ experience in the mining environment (van Zyl, 2015): Ž Younger employees are more likely to exhibit risktaking behaviour such as engaging in sub-standard practices, due to the nature of younger persons’ thought patterns Ž Older employees are the least likely to exhibit risktaking behaviour due to thought patterns commonly associated with age, such as being more careful in the work environment Ž The less experience an employee has, the more likely they would be to engage in sub-standard practices, since they have no recollection of previously encountered dangerous situations or loss of life Ž Conversely, older employees are seen as the more responsible in terms of implementing standards as opposed to risk-taking behaviour. They are more likely to be focused on issues such as health, job security, and avoiding danger.
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Table I
Number of employees by years' experience in the mining industry Years of experience Less than 3 3-5 6-10 11-15 16-20 21-25 26-30 31-35 More than 35 Overall total
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Number of employees 13 17 38 31 18 13 4 1 0 135
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Mandala Consulting, (2012), it came to light that accidents and fatalities are in the majority of cases not caused by a single event. A total of 135 employees were interviewed during the investigation. The focus of the study was mainly on underground production personnel. The majority of the duration of the study was spent in the stopes, thus the greatest pool of information was obtained from rock-drill operators, winch drivers, team leaders, miners, and shift bosses. The previous general manager at the mine stressed that the area of concern with regard to sub-standard practices and unsafe acts was the production personnel at the mine. Figure 6 shows the distribution of employees interviewed by occupation. The mode of the age categories was 46–55 years. The greater amount of employees interviewed were from the higher age categories, and the majority were from the morning shift. Only six employees interviewed were working the night shift. The final parameter was the number of years’ experience of employees. This is one of the most important parameters, since it is generally believed that the more experience an employee has, the less likely they are to perform an unsafe act or be involved in an accident. Table I shows that the largest category of employees that were interviewed had between 6 and 15 years’ experience in the mining industry. The behaviour of employees during interviews raised concerns in terms of the findings: if employees were too scared to disclose their occupation, how accurate and honest is the information that they have provided in the questionnaires and during personal interviews? Honesty and fear of losing employment seemed to be a major problem at the mine. Employees were found to be extremely anxious to voice their opinions while in the presence of their colleagues. On other occasions, some of the ’new ones’ (as new employees are referred to underground) were often silenced by the elder employees when an interview was conducted. The interviewees’ behaviour during interviews also opens a window for speculation that employees are hiding certain things from management as well as their supervisors. It raises the question of complete honesty – some interviewees might have lied and others were maybe too scared to answer the questions honestly. One can thus not conclude that the results of this study are absolutely complete and accurate, due to the external influencing factors in the working environment and observed differential behaviour. Despite the occasional behavioural patterns and trust issues, it was possible to determine trends. From the data-set of interviewees it is clear that a greater number of older employees were interviewed (Table I). The data showed no correlation between age, years of experience, and the execution of sub-standard acts, which could indicate one of two possible situations:
Sub-standard practices: effects on safety performance in South Africa There are, however, a great number of factors that could influence any employee, irrespective of age category and level of experience. These factors include mental health, job satisfaction, remuneration, stress, and education, to mention just a few. In order to establish and analyse certain trends in employee behaviour with regard to sub-standard practices, some of the questions in the questionnaire were grouped together in order to analyse them for similarities and conflicting answers.
One group of questions dealt with whether employees had encountered sub-standard practices, and the other group dealt with whether employees understood what standards were and the necessity for them. More than 80% of the interviewees indicated that they were aware of sub-standard practices in the workplace. This might show that employees were very aware of what substandard practices meant in terms of their occupations. More than 91% of employees that were interviewed felt that they were trained to understand why standards were required and needed to be upheld. The result is somewhat contradictory, since personal experience and discussions with management indicated that employees often do not understand the implementation of standards. It was found that 89% of the interviewees had a good understanding of standards and their importance. The correlation between understanding standards and implementation is that if employees understand what standards are and why they are important in the working environment, they should also be able to identify sub-standard practices without difficulty. The 22% of employees that said they were not aware of any sub-standard practices could have felt this way due to: Ž Fear of losing their job Ž Not understanding the questions Ž Not understanding what the standards at the mine are A fairly high percentage (11%) of the interviewees were of the opinion that they were not adequately trained in understanding the standards. This shows a strong feeling among employees that a lack of training and education on standards is a root cause of sub-standard practices. It is clear that an employee who does not understand a standard would be highly likely to implement the standard incorrectly, not be able to identify sub-standard practices due to a lack of understanding of the standard itself. 14% of the interviewees claimed that they did not understand the consequences of sub-standard practices. During the interviews, a number of employees often apportioned blame on the ’new ones’ for performing substandard acts. The problem here might lie in lack of underground experience. The majority of interviewees were concerned about the consequences of sub-standard acts since they had experienced consequences themselves, witnessed them, or heard accounts of serious injuries from colleagues. Although 86% of employees claimed to understand the consequences of sub-standard practices, a shocking 46% of them were still prepared to perform sub-standard acts if the opportunity was presented.
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These results prompt the question as to why would employees be willing to take the risk of incurring a loss, if they understood the probability and severity of the loss? The answer lies in the behaviour and mind-set of underground production personnel. Supervisory skills seemed to be lacking in the majority of workplaces that were visited. Due to a lack of respect and no fixed structure of authority, there was no control over employees’ behaviour. It was also found that teamwork skills were not favoured underground. Every employee had the mind-set of ’I’m here only to do my job’. Sub-standard practices were therefore closely related with communication gaps, lack of teamwork, and apportioning blame to younger employees, instead of accepting fault. It was found that approximately 56% of employees, at some point in their careers, had performed sub-standard work and approximately 33% of employees also instructed other employees to do so. Most of the employees who were interviewed encountered some form of sub-standard practice on a weekly basis. Surprisingly, some employees felt that they encountered substandard practices only on a yearly basis, which is hard to believe based on the author’s personal experience at the mine. Figure 7 shows that 39% of employees said that their work was always up to standard, while only 5% said that their work was completely sub-standard. This is, however, a misleading result according to personal investigation. If the majority of employees feel that their work is always up to standard, then why is there a problem with sub-standard practices? According to the results, the sub-standard acts that were encountered varied widely, with some types of sub-standard practices mentioned more frequently than others. The general types of sub-standard work that were encountered included, but were not limited to, the following: Ž Incorrect procedures when entering and exiting man carriages Ž Incorrect tramming procedures (speeding, leaving locos running without an operator inside, attaching too many hoppers etc.) Ž T-sprags almost never in place and ventilation doors always open, since it interferes with tramming according to loco guards Ž Unequipped travelling ways (no steps, footwall not cleaned, no handrails or rope guides, sometimes not sufficient support)
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Sub-standard practices: effects on safety performance in South Africa
The abovementioned examples of sub-standard acts, procedures, and installation are but a few compared to the great number of sub-standard practices that were encountered during the investigation. Employees’ reasons for performing sub-standard work or instructing someone else to do so indicated clearly that engagement in sub-standard practices is a behaviour-based issue. The majority of employees showed an inclination towards taking matters into their own hands when events did not go according to their personal plan. It was observed that everyone wanted to be leaders, and seldom followers, even when it was necessary. Many experienced employees were extremely set on respect. If they felt that they were not respected, they would not assist in the task or deliberately work slowly in order to annoy the person who had assumed seniority in the situation. A lack of ‘soft’ skills is definitely a major cause of sub-standard practices. Teamwork is essential in the mining industry and interpersonal skills are vital; this is an area that employees at the mine need to be trained in. Ignorance was found to be a major driving force behind sub-standard acts. Employees believed that because they have never been involved in an accident, it will never happen to them. They have been involved in sub-standard acts for so long that they are now accepting them as the norm. It was clear that revenge also played a major role in sub-standard procedures and acts. The belief amongst interviewees was that if a colleague has done them wrong, he must pay for it. Sub-standard acts are often the result of payback to try and regain status by being rebellious. The results confirmed that production supervisors were often seen as lead agents by not adhering to safe practices as they have instructed to their gangs to do. This behaviour results in a shared anger by production personnel, which engenders a less motivated work culture. Employees feel that they can do as they please, since production supervisors do not care. Although one might not have expected the physical location and working conditions of stopes to be a leading factor driving sub-standard practices, the results clearly showed the opposite. Many employees complained about the travel distances on foot in order to reach the workplace early enough so that there was still adequate time available for completing mining activities. Associated fatigue resulted in employees performing work that was of poor quality, as they claimed a lack of energy to perform the tasks correctly. Other employees were of the opinion that they did not have the correct tools to perform the given tasks to standard. A combination of fatigue, incorrect tools, and limited time resulted in sub-standard acts. The responses to a question on what employees felt had to be done to remedy the problem showed a number of general ideas to remedy sub-standard practices. The suggested actions to take control of the situation can be summarized as follows:
ÂŽ ÂŽ ÂŽ ÂŽ ÂŽ
Improve training Reward implementation of standards Address mental wellbeing of employees Address attitude-related issues Provide education on standards and their importance
A factor that stood out was that employees at the mine seemed to lack motivation in performing their jobs. They want to feel part of something larger than themselves and be rewarded for performing a good job. The level of education of employees influences the training methods to a great extent. Interviewees felt that onthe-job training in the underground environment would be more suited to their level of education than theoretical training in a training centre. The general feeling was that there is a major difference between executing tasks in the training centre and executing the same task a few hundred metres underground. Great variation in the origin of sub-standard practices was observed. Some employees believe that this is more of a psychological and behavioural problem, while others tend to blame management and direct supervisors for the issue. The investigation at the mine indicated a number of potential issues that can be further investigated to determine the root causes of sub-standard acts and their effects on safety. Perhaps the most interesting question yet to be answered is if sub-standard acts are largely a result of human behaviour and individual mentality. This question will be addressed in the analysis of the results from the Shadowmatch survey.
*# )-/&*+1 0. 00+150&.15/.&1', .,-) .-)+&$*-#)./*+1)+(1. /&1&.,(! A number of responses to questions in the gold mine study revealed that employees were often just there to get the job done, not willing to go the extra mile with regard to their job descriptions, lacked a feeling of corporate ownership, and often did not take control of conflict situations. The cultural transformation study at the West Wits gold mines yielded the same results. About a quarter of the employees that took part in the study were not interested in doing more than what was expected of them. About 70% of employees did not want to take control of situations that resulted in conflict. This showed that conflict resolution skills were lacking with most employees. It was found that employees that took part in the cultural study at West Wits also did not feel competent to perform all work tasks all of the time. The results also showed that adaptability, tenacity, and resilience were often a problem for employees. These findings strongly agree with the results obtained at the study mine. The results indicated a strong similarity in the safety culture at the study mine and in the West Wits mines. Employees did not understand the safety vision clearly and did not always follow standard procedures. It can therefore be postulated that employees in the gold sector show a general disregard for safety and standards in the underground working environment. Acceptance of teamwork as an inevitable factor in mining and safety showed exactly the same trend at the West Wits gold mines and the study mine. Almost half of the employees VOLUME 116
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ÂŽ Incorrect explosive storage, transport, and handling procedures ÂŽ Incorrect rigging practices ÂŽ No supervision
Sub-standard practices: effects on safety performance in South Africa believed that interdependence during teamwork played no role in the quality of work and relationships. Employees preferred working individually, although this is almost impossible in the production environment. When performing teamwork, employees had great difficulty in trusting each other. This was the case at both the study mine and in the West Wits study. However, trust was not the only underlying issue. Many employees also felt that they were not fully equipped for performing teamwork and that they were often not informed on their specific role within the team. From the results obtained in the West Wits study, it was evident that the study mine was not the only operation that indicated quality of supervision as a major problem. It was shown that employees did not possess proper supervisory skills, nor did the supervisors themselves. A lack of on-thejob coaching, lack of motivation and acknowledgement, and relationships with supervisors again came up as causes of sub-standard practices. The studies performed at the study mine and the West Wits study showed that there were almost no differences in the cultures with regard to safety and sub-standard practices. In fact, most of the influencing factors that were investigated were similar, and it can be concluded that the findings may be applicable to the entire gold mining industry of South Africa.
60&, .&1*$1. 01 )(* #).' 1&,- 0! A total of 88 shift bosses were selected by senior management of the company to participate in the Shadowmatch survey. Included in this number was a benchmark study group of 10 shift bosses, who were selected based on their performance in terms of safety and production. The purpose of the benchmark group was to determine the habits exhibited by successful shift bosses and enable the profiles of the other shift bosses to be compared with those of the benchmark group. This was done to determine poor habits that may result in sub-standard practices and a poor safety record. The majority of participants were day-shift stoping shift bosses. The day-shift vamping shift bosses were the smallest group within the data-set.
The Shadowmatch results that were obtained from the benchmark group showing the most embedded or critical habits exhibited by successful shift bosses. were identified and are listed below: 1. 2. 3. 4. 5.
Team inclination Conflict handling Discipline Resilience Altruism
These critical habits correlate well with the problematic areas identified at the mine, indicating that the study delivered accurate results with regard to the identification of the root causes of sub-standard practices. The benchmark group showed relatively low scores in the following habits:
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1. 2. 3. 4.
Individual inclination Innovation Propensity to delegate Propensity to change
Successful shift bosses definitely preferred to work in teams, as indicated by the low score for individual inclination. Based on the results obtained from the behavioural study performed at the mine, it was anticipated that employees would obtain a low score for innovation in a Shadowmatch survey. The reason behind this is that employees showed a strong inclination towards performing tasks the way they were used to, and not to embrace new technology or innovative solutions to problems. The group showed a thinking style opposite to an out-of-the-box thinking style. As mentioned previously, this type of behaviour could hamper safety performance due to the fact that new ways of performing tasks were often deemed as additional work or unnecessary change. The score for propensity to delegate is lower than that for propensity to own. The benchmark group of shift bosses showed that they preferred to take ownership of problems and handle challenges themselves as opposed to getting another individual to deal with the problem. This habit, in the opinion of the author, should actually be much more prevalent, since it reflects the shift bosses’ ability to take control of a situation. The Shadowmatch results with regard to propensity to change confirmed the findings from the study mine as well as the West Wits study. In both of the studies, shift bosses found it difficult to adapt to change in their working environment. They were not comfortable with new methods of performing work, new environments, and new technologies.
The Shadowmatch attitude analysis delivered results that strongly correspond to the critical habits that were identified within the benchmark group. The majority of participants in the benchmark group formed part of categories 1 and 2, while equal numbers of participants formed part of category 3 and 4. The significance of the attitude distribution is as follows: ÂŽ Categories 1 and 2 exhibit a shared habit of involvement. ÂŽ Categories 2 and 3 share habits of assertiveness and, sometimes, unaggressive behaviour. ÂŽ Categories 3 and 4 exhibit a habit of less involvement or complete uninvolved attitude. ÂŽ Categories 1 and 4 represent a shared attitude of unaggressive behaviour Figure 8 shows the attitude distribution of the benchmark group. As shown in Figure 8, the benchmark group displays a strong attitude of involved, unaggressive behaviour. This group showed positive involvement in their work environment. They found it easy to get involved and this formed part of their natural behaviour. The group thus showed positivity when working with people and exhibited optimism.
Sub-standard practices: effects on safety performance in South Africa
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The attitude is associated with altruism since the group proved to be unconditional in their actions and willing to make the necessary sacrifices to achieve a greater goal. Importantly, the benchmark group may be seen as materialistic, but emphasizing the value of all life. The way they perform work is not to serve others, but to drive a certain principle. With regards to conflict handling, the benchmark group resolved conflict in a mature way without feeling compelled to become aggressive. This type of attitude does not seek revenge or personal gain.
The attitude scores in the results of the best performer are of particular interest. Although there is a strong correlation with the benchmark group in category 1 and 2 attitudes, the individual showed a significantly stronger category 4 attitude than the benchmark group. As opposed to the best performer, the worst performer showed strong category 2 and 3 attitudes and a low category 1 attitude. The recommended personal development programme (PDP) for the worst performer was problem-solving. As described earlier, the fact that this individual has none of the critical habits of the benchmark group indicates that he/she would be likely to see all aspects of the job as a major challenge. A number of different PDPs were recommended for the study group, based on the habits that were determined as critical habits of the benchmark group. The recommended PDP addresses the habit that needs development. Based on the results of the benchmark group, the Shadowmatch system recommended the following PDPs for shift bosses that were not part of the benchmark group (ranked in terms of number of recommendations from high to low): 1. 2. 3. 4. 5. 6.
Handling frustration Routine Problem solving Propensity to delegate Individual inclination Team inclination
Table II
Comparison between critical habit scores of benchmark group and the best and worst performing individuals Habit Team inclination Conflict handling Discipline Resilience Altruism
Benchmark
Best performer
Worst performer
63 59 58 57 57
61 67 65 57 64
46 38 39 32 43
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The purpose of the comparison was to establish any differences and correlations between the habits and behaviours exhibited by the two groups. It was decided to compare the ‘worst’ and ‘best’ performers in terms of the Shadowmatch study to the data obtained from the benchmark group in order to determine any similarities or differences. First, the results of the best and worst performers were compared to the results of the benchmark group. The best performer’s scores with regards to the critical habits showed a high correlation with the scores of the benchmark group. The comparison of the scores is shown in Table II. The worst performer scored significantly lower in all the critical habits of the benchmark group. This individual had a high likelihood of being extremely problematic in the working environment due to his/her habits. The best performer showed significantly stronger habits than the benchmark group in conflict handling, discipline, and altruism. For this specific individual, it could be said that these three habits are ultimately the drivers behind success. The worst performer scored higher than the benchmark group in only two habits, namely propensity to delegate and individual inclination. However, it is necessary to discuss the possible reasons for these two higher scores. Propensity to delegate is almost self-explanatory. This individual’s critical habits showed very low scores. It may be speculated that he/she would be the type of person who is not involved at all, has no confidence in what he does, showed no altruism, and prefers to give the task at hand to someone else to complete.
Sub-standard practices: effects on safety performance in South Africa Again, the set of PDPs that were recommended by the system fits the results obtained from the study mine and the cultural study extremely well. It further emphasizes the habits and behavioural patterns that were identified that could lead to sub-standard practices in the working environment with adverse effects on safety. Figure 9 shows the different PDPs that were recommended for the study group as well as the number of each recommended PDP. It is clear from the figure that the habit of being able to simplify problems is a major concern. This habit is closely related to the habit of problem-solving which was recommended for eight individuals. Frustration handling is the third habit that requires intervention. The underground working environment is full of challenges and definitely requires a radical habit of frustration handling.
to improve on the current situation if the necessary habits such as propensity to change, simplification of problems, selfmotivation, and team inclination are not addressed.
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DEPARTMENT OF MINERAL RESOURCES. 2011. Mine Health & Safety.
Sub-standard practices and their adverse effects on safety remains a challenge in the South African gold mining industry. Although a number of previous efforts have been made to determine the root causes of sub-standard practices, the results were inconclusive or addressed the same technical issues that have long been present in the mining industry. The origin of sub-standard practices in the underground working environment was found to be in the habits, attitudes, and behaviour of employees. However, it is important to realize that habits and attitude are not fixed characteristics like personality. Habits and attitude can be changed and developed with the correct instruments. The research described in this paper (the study performed at a gold mine in the Free State, the cultural survey conducted at West Wits, and the Shadowmatch survey) all highlighted correlating causes of sub-standard practices which had their roots in the habits and behaviour of employees. The absence of certain radical habits (such as team inclination, conflict handling, leadership, altruism, discipline, and resilience) for a specific working environment and a specific job title (in this case underground production employees with the focus on shift bosses) could be the primary reason behind substandard practices. Aspects such as a lack of education, inappropriate onthe-job training, and shortcomings in managerial style were found to increase the occurrence of sub-standard practices, which in turn had adverse effects on the safety culture at the gold mine. The problem extends beyond a specific section at one mine or a specific shaft, and is most likely an industry-wide issue that needs to be addressed. The best solution would be to determine whether the habits and attitude of an individual are suited for a specific job position and working environment before employing that person. This would avoid the need for subsequent remedial action on sub-standard practices. However, there is no single solution that would alleviate the current problem. In order to address the different aspects of the problem, a number of solutions such as a Shadowmatch survey, improved training, basic education, revision of risk control programs, are suggested. Finally, the gold mining environment in South Africa poses some of the most extreme challenges with regards to working conditions. Looking forward, it would be impossible
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60$0-0+'0& AMERICAN INSTITUTE OF MINING, METALLURGICAL AND PETROLEUM ENGINEERS. 1973. SME Mining Engineering Handbook. 1st edn. New York. ASSOCIATION OF MINE MANAGERS OF SOUTH AFRICA. 2014. AMMSA Safety Summit. CSIR. 2013. Accident investigation practices in the South African mining industry. Pretoria. DE VILLIERS, P. 2009. Shadowmatch: The Full Story. 1st edn. DBA, Johannesburg.
http://www.dmr.gov.za/ [Accessed 16 February 2015]. FURNESS, J. 2003. Beatrix Gold Mine, South Africa. Mining Weekly, 12 December. GOLD FIELDS LTD. 2012. SA Culture Transformation: Integrated Diagnostic View-KDC. GUTTIEREZ, A. 2010. Slideshare: Theories of Accident Causation. http://www.slideshare.net/yorkypab/theories-of-accident-causation [Accessed 27 June 2015]. HANSEN, L. 1973. Health and Safety. SME Mining Engineering Handbook. Given, I. (ed.). American Institute of Mining, Metallurgical and Petroleum Engineers Inc., New York. pp. 3-2-3-10. MASEKHOA, N.O. 2012. Mine Health and Safety Council. www.mhsc.org.za/ sites/default/files/CTF%20and%20CoE.pdf [Accessed 2 May 2015]. MINE HEALTH AND SAFETY COUNCIL. 2014. Facts and Figures. http://www.thisisgold.co.za/downloads/finish/6-presentations/44-mhsc2014-zero-harm-presentation [Accessed 21 April 2015]. MOL, T. 2002. EHSToday: An Accident Theory that Ties Safety and Productivity Together. http://ehstoday.com/mag/ehs_imp_35910 [Accessed 25 June 2015]. RAOUF, A. 2011. ILO Encyclopaedia of Occupational Health & Safety. http://www.ilo.org/iloenc/part-viii/accident-prevention/item/894-theoryof-accident-causes [Accessed 29 June 2015]. SAARI, J. Not dated. Encyclopaedia of Occupational Health and Safety: Part VIIAccidents and Safety Management. http://www.ilocis.org/documents/ chpt56e.htm [Accessed 25 June 2015]. SOCIETY FOR MINING, METALLURGY AND EXPLORATION. 2011. SME Mining Engineering Handbook. 3rd edn. Littleton, Co. THIS IS GOLD. 2015. Facts and Figures: Safety Performance February 2015. http://www.thisisgold.co.za/downloads/finish/4-fact-sheets/3-fact-sheetjuly-2014-safety-performance/0 [Accessed 23 April 2015]. VAN ZYL, A. 2015. Clinical psychology of behaviour. [Interview]. 21 March 2015.
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http://dx.doi.org/10.17159/2411-9717/2016/v116n4a3
A critical investigation into tyre life on an iron ore haulage system by G.C. Lindeque* Paper written on project work carried out in partial fulfilment of B. Eng. (Mining Engineering)
+$ Two main methods of increasing tyre life were identified:
( " A downward trend in tyre life on haul trucks at an open pit iron ore mine prompted an investigation into the current tyre management strategy in order to improve tyre life. ‘Best practice’ was compared to the current tyre management strategy at the mine to determine aspects that could be improved. Aspects that showed significant room for improvement included employee tyre awareness, tyre pressure maintenance, and road conditions. For each of these aspects a plausible alternative was suggested. A new tyre management strategy was formulated as a step-by-step guide on how to implement the proposed changes. Each step introduces new initiatives but at the same time builds on the previous step’s success. A sensitivity analyses was performed to determine the impact of the proposed changes, with the variables being the reduction in the percentage of premature tyre failure, and the reduction of the site wear rate. The ‘most likely’ scenario showed an increase in tyre life of 41% for the Komatsu 730 trucks and 105% for the CAT 777 trucks if the entire tyre management model is implemented. This would result in a possible annual saving related to tyre usage of R9.2 million.
ÂŽ Method A: reducing the site wear rate of tyres, as measured in millimetres per 1000 hours ÂŽ Method B: reducing the percentage of tyres that fail prematurely.
! ! ! The most common reason to scrap a tyre is simply because it is worn out. In 2014 it was determined that 59% of all tyres scrapped were classified as worn out. A tyre that is worn out has reached its maximum life achievable due to a specific wear rate. The wear rate at the mine in terms of each tyre classification is shown in Table II. The data shows that the achievable tyre life for each truck is significantly higher than the recorded tyre life. This is due to abnormal wear of tyres or tyres that fail prematurely.
*$ # tyre life, tyre management, wear rate, premature tyre failure, tyre awareness.
! ! ! ! ) $# "$ The study focused on the tyre life on the main haul fleet at an open pit iron ore mine. The haul fleet consisted of 17 Komatsu 730 (180 t) haul trucks and 12 CAT 777 (90 t) haul trucks. The haulage operation consists entirely of tyre-based haul trucks. Five per cent of the total mining budget is related to tyre costs. Since 2012 there has been a steady decrease in tyre life as measured in operating hours (Figure 1) due to the high percentage of tyres that fail prematurely. In 2014 a total of 41% of all tyres failed prematurely and 61% were classified as ‘worn out’.
In 2014 it was determined that 41% of all tyres failed prematurely. This is an increase of 8% from the previous year. The increasing number of tyres that fail prematurely is the biggest contributor to the decreasing trend in tyre life over the last two years. If fewer tyres fail prematurely, more tyres will be worn out and therefore the overall tyre life will be increased. Figure 2 shows the monthly costs associated with each premature failure mode for a period from 2012 to 2014. In November 2014 the year-to-date premature failure cost totalled R2.5 million (Jordaan, 2014), an increase of 92% from November 2013 (R1.3 million). The cost associated with tyre failure is based on the value of remaining tread on a
$ %! % '$ " $
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The purpose of this study was to evaluate the current tyre management strategy at the mine and to identify possible aspects that can be altered in order to increase tyre life. A detailed breakdown of the objectives and methodologies followed during the project is shown in Table I.
A critical investigation into tyre life on an iron ore haulage system Table I
Objectives and methodologies Objective
Methodology
Quantify the problem
The tyre performance history was thoroughly investigated to: • Determine the tyre life trend and outlook • Determine the current tyre-associated targets • Determine the cost of premature tyre failure • Determine the main causes of premature tyre failure through analysing component failure reports and general monthly tyre management reports
Identify all the parameters that can influence tyre life
A literature survey was conducted to: • Determine the different factors that influence tyre life • Identify the main element of a proper tyre management strategy (best practice)
Determine the impact of each parameter on tyre life
Each factor that was identified through the literature survey was investigated to determine the extent of the impact if not managed properly
Investigate the operational practises.
The current tyre management strategy was investigated and analysed through: • On-site observations • Historical tyre failure data • Historical road and pit conditions data
Determine which aspects of the current tyre management strategy can be altered to comply with best practice in order to increase the tyre life of both the waste and ore haul trucks
After the evaluation of each aspect of the current tyre management strategy a plausible alteration was suggested, if found unsatisfactory
Determine the impact of the proposed changes.
The qualitative impact of the proposed alterations was estimated and the financial impact thereof was calculated.
Table II
Tyre wear rate Truck
Komatsu 730 CAT 777
Tyre size
40.00Ă—R57 27.00Ă—49
Target tyre life
Tread available
Wear rate (mm per 1000 hours
(hours)
(mm)
To achieve target tyre life
Actual
7200 5600
87.0 79.0
12.1 14.1
9.0 8.0
Tyre life at actual wear rate (hours)
9667 9875
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scrapped tyre, which is referred to as lost tread. The lost tread value of scrapped tyres for 2014 was in the range of R5.5–6.0 million. This is the total value of tread left on all the tyres that were scrapped in the year. Lost tread is caused not only by the various premature failure modes, but also abnormal wear of tyres.
tyre management strategy has to be aligned with ‘best practice’ in order to significantly improve tyre life. The results from the literature survey suggested that a ‘best practice’ tyre management strategy should consist of the key elements that are summarized in Table III.
! ! !
! !
From the literature survey it was determined that a single tyre failure mode cannot be associated with a certain aspect of tyre management. This led to the conclusion that the entire
The operational practices at the mine were then evaluated to determine whether the following elements were adequately addressed.
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A critical investigation into tyre life on an iron ore haulage system Table III
Key elements of ‘best practice’ tyre management Maintenance
• • • •
Tyre pressure maintenance Haul road maintenance Tyre maintenance Vehicle maintenance
Haul road design
• • • • • • •
Horizontal and vertical alignment Cross fall Drainage Super elevation Curve radius Road construction Road width
Loading practice
The payload policy of the haul truck manufacturer should be strictly adhered to and monitored
Vehicle speed
Specific attention to maximum speed, acceleration, and braking
Tons-kilometres per hour (TKPH)
The TKPH rating of the tyre should never be exceeded due to the site work load (speed and payload)
Matching of tyres
In order to ensure even wear, tyre assemblies operating as dual pairs must: • Have the same outside diameter • Be from the same manufacturer • Be of the same type (industry code).
The tyre pairs on the rear axle of a truck need to match in order to ensure even wear of both tyres. The mine does this well, as matching spare tyre pairs are kept in a tyre bank. The tyre bank is kept well stocked by replacing tyres on the front axle after 30% tread wear with new tyres (Jordaan, 2014). Pairs of equally worn tyres are made up from the replaced tyres and stored in the tyre bank. The mine keeps a well-stocked tyre bank, with 99 Komatsu 730 tyres and 69 CAT 777 tyres recorded during November 2014.
TKPH is a measure of the heat buildup in a tyre due to the load it has to carry and the speed at which it is travelling. The TKPH is currently not being monitored. A TKPH study was done to determine the suitability of the current tyres for the working conditions. The results are summarized in Table IV. The table shows the average TKPH of the tyres on the axle with the heaviest load, thus showing the average maximum TKPH of each cycle. From Table IV it is clear that the actual TKPH for tyre types is well below the TKPH rating of the manufacturer. This suggests that the correct tyres for each truck type in terms of TKPH are being used, and that the tyres are not failing prematurely due to the work load.
differ if the actual amount of incorrect inflation was known. According to the tyre management contractor (Woodman, 2002), 10% underinflation in very demanding conditions such as an iron ore mine can lead to a reduction in tyre life of 27%. Another concern is that an individual tyre is only checked seven times per month, and not the minimum required frequency of once a day.
It was found that the mine adheres strictly to the payload policy of Komatsu (2014) in the case of the Komatsu 730 trucks, due to the built-in system on those trucks. This is, however, not the case for the CAT 777 truck. The payload study revealed that only 44% of all loads were less than the optimum load of 90.5 t. Of the 56% of the loads that exceeded the optimum, 13% were overloaded more than 20%. This data is summarized in Figure 3.
Table IV
TKPH study results Truck Komatsu 730E - 7 Komatsu 730E - 8 CAT 777
Tyre type
TKPH rating
Actual site TKPH
40.00Ă—R57 40.00Ă—R57 27.00Ă—49
960 960 480
523.9 785.7 386.4
The average vehicle speed is well within the limits prescribed by the mine. There is, however, no means of live monitoring of acceleration and braking. This is where the real danger to tyres lies. Some elements of the mine’s current tyre management strategy showed room for improvement.
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Only 90% of tyres are correctly inflated at any given time – thus 20 tyres in the haul fleet are at an incorrect tyre pressure. To what extent these tyres are incorrectly inflated is unknown. A sensitivity analyses was done and the results were based on the assumption that the 10% of tyres that are at an incorrect tyre pressure are 90% inflated. Results would
A critical investigation into tyre life on an iron ore haulage system Road conditions can be assessed according to two categories of road – permanent and in-pit. Currently, the permanent roads are monitored and assessed using an assessment and reporting system. This system has a number of drawbacks, the main one being the lack of communication between assessor and operator who can correct the error. A new system is proposed (Dust-a-Side, 2013) that will fill the communication gap. This new system will make continuous road evaluation possible, because road defects can be identified and logged by using a handheld device. This information is immediately shared with the operators of road maintenance equipment by using wireless technology.
The main challenge at the mine is not the tyre management strategy, but the level of tyre awareness amongst employees. Figure 4 show the results of a questionnaire completed by employees of various levels. The employees would have known the correct answers to the questions if their level of tyre awareness was adequate. The most concerning fact is that the operators, who have the largest impact on tyre life, showed the lowest level of tyre awareness. If tyre awareness increases amongst employees, common operator errors would decrease. These include: ÂŽ ÂŽ ÂŽ ÂŽ ÂŽ
Reversing onto the muck pile while loading Speeding around corners while loaded Spillage in the loading area Driving through spillage and water Incorrect loading practices.
! " % %#$ The results were reworked into a physical and realistic implementable tyre management model. The model consists of a step-by-step strategy, with different aspect of tyre management to be implemented or changed at specific stages. The model focuses on the three main elements of the current tyre management strategy that showed room for improvement. These are: ÂŽ Tyre awareness ÂŽ Tyre pressure maintenance ÂŽ Road conditions. The tyre management model consists of three phases. Each phase uses different tools to improve tyre management, but at the same time builds on the previous phase. Table V describes the initiatives in each phase. It also indicates which tyre life improvement method (A or B) each initiative will have the most significant positive effect on.
certain aspects of tyre- and road-related elements. This step involves some capital cost and the associated increased operating costs. Phase 2 builds on Phase 1. The initiatives implemented in Phase 1 continue to be practised, with the additional changes described in Table V.
! ! ! Phase 3 is the culmination of the tyre management model. This phase involved the majority of the capital spend and has the highest additional operating cost. This step can be implemented only if Phase 1 and 2 were successful.
! By thoroughly analysing all the results, informed estimations of the cumulative effect of the various initiatives under each phase could be made. A sensitivity analysis was done to determine the impact of different scenarios for each step. These scenarios were classified as ‘worst case’, ‘most likely’, and ‘best case’. Each of these scenarios is characterized by a different impact of each step on: Ž Reducing premature tyre failure (improvement method B) Ž Reducing the site wear rate (improvement method A) This is demonstrated by Table VI. The results of the sensitivity analysis are shown in Figure 5 by displaying the calculated savings associated with each phase. Phase 1 has the largest positive impact on tyre life and results in the largest possible annual saving. Phases 2 and 3 have a smaller positive impact on tyre life, resulting in less annual saving. This is due to the fact that phases 2 and 3 involve fewer changes to the tyre management system. The better the tyre life on a mine becomes, the harder it is to improve it.
" %! %#$ $ ! " A tyre forum needs to be established at the mine. This forum should include representatives from various divisions of the mine. It is recommended that the tyre forum implement Phase 1 of the tyre management model. The most significant positive impact on tyre life is associated with Phase 1, with an increase in tyre life of 20% for the Komatsu 730 tyres and 75% for the CAT 777 tyres according to the ‘most likely’ scenario. Such an increase in tyre life will reduce the annual tyre usage and result in an annual saving of approximately R6 million.
! ! ! The employee mind-set and tyre awareness have to change before large sums of capital are spent on technology in an effort to increase tyre life. Phase 1 consisted of most of the changes to the current tyre management strategy, and thus it was estimated to have the most significant positive impact on tyre life.
! ! Phase 2 is associated with automated information regarding
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A critical investigation into tyre life on an iron ore haulage system Table V
Tyre management model description Phase 1
Initiatives
Method B A
Tyre awareness campaign
Based on similar tyre awareness campaign results at another mine. Cost based on one full-time employee salary to drive the programme
Tyre life monitoring and feedback Operator education
Work with people, give information but also hold them accountable. Information is distributed using the current systems and discussed in the daily 09:00 production meeting and during the daily Operator Caucus sessions √
In house (no extra cost)
Incentives
Payload control
Description
Exact incentive strategy will be designed by a tyre forum but will be based on individual truck tyre performance. This will single out and reward hard-working employees and will serve as extra motivation to take good care of tyres √
√
Only CAT 777 trucks. Payloads will be manually monitored by operators with much more care
√
Vehicle speed will be manually monitored by all truck operators with much more care
√
Increase the number of pressure checks to two per truck per shift. This will require two new employees.
Site severity survey
√
Reinstate the site severity survey as discussed previously. No extra cost
Specialist grader operator training
√
This requires the training of current grader operators by outside specialist to become specialist graders. R100 000 annual fee converted to a rand per month value. New training and refresher courses would be needed
Supervisor application engineering training
√
This entails the supervisors of grader operators to be trained by outside specialist in order to become experts in the field of grading (know what to look at in terms of grader performance, advice to give to operators, and how to apply the equipment to achieve the best result). R100 000 annual fee converted to a rands per month value. New training and refresher courses would be needed
Vehicle speed Pressure monitoring Manual pressure checks (4 per day)
√
Road conditions
Total impact 2
15%
0.1
Road conditions Permanent roads
√
Implementation of the new monitoring system for main haul roads. Capital cost for units and operating cost for information processing
Grader operator made higher level status
√
Four specialist grader operators are appointed and a new career path is created with the total salary increased to match that of a haul truck operator. This will ensure that graders are operated only by grader specialists
Pressure monitoring iTrack for CAT 777 fleet
√
Vehicle speed
3
√ √
TKPH monitoring
√
Total impact
2.5%
0.3
iTrack for entire fleet
√
√
Vehicle speed
√
√
TKPH monitoring
√
iTrack TPMS installed for CAT 777 fleet. Operating cost includes two dedicated employees to monitor the system.
Pressure Monitoring iTrack System for entire fleet. Free trial period is available. Operating cost includes three dedicated employees to monitored and drive the system. Capital cost includes the installation of system on the remaining 17 Komatsu 730 trucks
Road conditions Grader operator made increased
√
√
Total impact
2.5%
0.1
Six specialist graders operators are appointed and a new career path is created with the total salary higher level status to match that of a haul truck operator. This will ensure that graders are operated only by grader specialists
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A critical investigation into tyre life on an iron ore haulage system Table VI
Sensitivity analysis estimations Phase
Tyre life improvement method
Scenario Worst case
Most likely
1
B A
2
B A
2.5% 0.3
5.0% 0.6
6.5% 0.8
3
B A
2.5% 0.1
5.0% 0.2
6.5% 0.35
The main component of Phase 1 is the tyre awareness campaign. The exact details and specifications of this programme need to be designed and driven by the tyre forum to specifically suit the mine. Tyre life improvement needs to be a dynamic and ever-improving process. Due to the capital sensitivity of the current mining environment, implementation of phases 2 and 3 is optional. The sensitivity analysis showed that the largest opportunity for savings lies with phase 1, which has virtually no extra cost associated with it. It is the role of the tyre forum to conduct monthly meetings where the newly formulated tyre management model is discussed and evaluated, focusing on four major areas: ÂŽ ÂŽ ÂŽ ÂŽ
Conditions Operations Maintenance Tyre performance.
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15% 0.1
20% 0.2
Best case 25% 0.35
& $ $ $ This paper is based on project work carried out in partial fulfilment of the degree B Eng (Mining Engineering)
+$ $#$ $ DUST-A-SIDE. 2013. Dasmetrics introduction and overview. http://www.dustaside.com/services/quality-management-systems/dasmetrics JORDAAN, A. 2014. General Monthly Report-November, Mine X: OTRACO International, Redcliffe, Western Australia. JORDAAN, T. 2015. Mining Manager. Personal communication. KOMATSU. 2014. About Komatsu. http://www.komatsu.com.au/AboutKomatsu [Accessed 10 December 2014]. MICHELIN. 2015. Technical Data- Earthmover Tyres. WOODMAN, C.A. 2002. Tyre selection, use and operational issues to maximise tyre life. OTRACO International, Redcliffe, Western Australia. N
http://dx.doi.org/10.17159/2411-9717/2016/v116n4a4
Review of support systems used in poor ground conditions in platinum room and pillar mining: a Zimbabwean case study by T. Chikande* and T. Zvarivadza* Paper written on project work carried out in partial fulfilment of BSc. (Mining Engineering)
Dyke is almost like a trumpet, comprising layers that dip towards the centre. The reef exploited at the mine, the Mineralised Sulphide Zone (MSZ), is located in the pyroxenite layer, which is hosted in the ultramafic sequence. The MSZ is a uniform layer about 2– 3.5 m thick, dipping at around 10–14° from surface outcrop towards the axis of the basin, and located between bronzite and websterite horizons. The visible disseminated sulphide mineralization shows a typical and consistent vertical distribution of platinum group metal (PGM) and base metal values. The research was undertaken to review the current support systems used in geotechnically poor ground conditions in a bid to improve both safety and productivity.
*;:06=6 Falls of ground pose costly hazards to personnel and equipment and thus measures should be taken to prevent them. This study endeavours to improve the support systems used in geotechnically poor ground at a Zimbabwean platinum mine by analysing the status quo and recommending an effective support system. Various techniques were used to determine the quality of ground conditions, predict the rock mass behaviour, and to identify the appropriate rockbolt type. An analysis of the current ground control methods and their limitations was also undertaken. The results showed that the current support system and mining practices in poor ground need to be modified to improve safety and productivity. Stoping overbreak is influenced by poor ground conditions and the explosives currently used. The use of emulsion is recommended to replace ANFO. Redesigning of pillars is also recommended in poor ground conditions. An evaluation of the current roofbolt system indicated an opportunity for improvement. With new insight on the performance of the shorter length roofbolts currently in use, a new support system was recommended taking into consideration cost-benefit analysis. Barring down using pinch bars in poor ground was seen as a risky and time-consuming exercise, hence the use of mechanical scalers is recommended to achieve zero harm and to meet production targets. Smoothwall blasting is recommended in poor ground to minimize excavation damage. Other recommendations include the use of hydrological surveys to determine groundwater levels and implement corrective measures. Both empirical and numerical modelling approaches need to be utilized in determining the optimum support.
($($ ) %# " ) The mine is fully mechanized and uses the bord and pillar mining method. Access is via two declines, one for access of men and materials and the other for hoisting ore. The mining layout used in poor ground conditions is shown in Figure 1.
($($ )%$ (!"$ %$#)
?;<7:.43<=:; The presence of geological discontinuities such as faults and joints weakens the rock mass. Adequate support is critical in achieving zero harm in underground mines. This paper reviews the current support systems used in poor ground conditions at a Zimbabwean platinum mine. The area of research is located on the Great Dyke of Zimbabwe. The mine exploits platinum group elements (PGEs) and base metals. It is shallow, having a maximum depth of less than 300 m. The Great Dyke is the second largest reserve of PGEs, following the South African Bushveld Complex (OberthĂźr et al., 2012). It is a linear layered intrusion that extends for about 550 km with a maximum width of 11 km (Prendergast, 1989). The generalized section of the Great
The area investigated is characterized by upthrows usually related to sympathetic faults and increased joint frequency. This imposes challenging mining conditions and increases the risk of rockfalls. The reef-subparallel planes in the hangingwall can give rise to unstable hangingwall environments, resulting in block and wedge failures when the planes of weakness are intersected by the J1 and J2 joint (discontinuity) sets. As the number of joint sets increases, the strength of the rock mass deteriorates. There are three prominent joint sets at the mine:
* School of Mining Engineering, University of the Witwatersrand, Johannesburg, South Africa. Š The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received Dec. 2015.
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@8* :7.6 bord and pillar mining, support systems, pillar design, explosives, roofbolts.
Review of support systems used in poor ground conditions excavated. Virgin stresses exist in rocks prior to any excavations (Brady, 1985). The magnitude of the vertical component of virgin stress is given (Brady, 1985) by: virgin = g h
[1]
where is the density of the rock mass, g is acceleration due to gravity, and h is the depth below the surface in metres.
& '%')" )($'#& ( (# +=5478> %-=;=;5>29*:4<>=;>0::7>57:4;.
Ž J1, which trends east-west with an average dip of 70° and a strike of close to 90° Ž J2, which trends north-south and has an average strike of 008° Ž J3, which comprises a shallow-dipping plane parallel to sub-parallel to the orebody.
Wood (1987) pointed out that instability can be caused by the following: ÂŽ A decrease in strength to stress ratios, which results in failure of material around the excavation ÂŽ Geological structures that result in collapse ÂŽ A combination of the above two points ÂŽ Seismic events.
Talc and serpentine are the common types of joint infill material.
The authors investigated the strength to stress ratios in a bid to determine the factor of safety. There is no history of seismic events in the area of the investigation, hence seismic forces were ignored: however, the authors recommended that the mine install seismic monitoring devices.
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The company uses a mechanized room and pillar mining method. As mining progresses, the intensity of faulting and jointing increases. This has led to general support failure and a challenge in maintaining a stoping width of 2 m. Associated problems and consequences of this include stoping overbreak, grade dilution, unpredictable unravelling of rocks, a decreased factor of safety, increased support costs, and failure to meet production targets. The problems and consequences of poor ground conditions led to the need to review the current support system at the mine. Figure 2 shows the mine layout and the area where the research was conducted. The need to conduct the research is justified by the following:
Brady (1985) noted that when there is no core available but there are traces of geological discontinuities, Equation [2] can be used to determine Rock Quality Designation (RQD).
ÂŽ The obligation to improve safety by ensuring that there is adequate regional and local support ÂŽ The need to improve productivity by meeting production targets in the required time ÂŽ The need to minimize PGE grade dilution ÂŽ The need to minimize cost of re-supporting ÂŽ The opportunity to add value to the company.
!" % #)" % #( %' The main objectives were to analyse and improve the current support systems used in poor ground. This was done by: ÂŽ Reviewing the current support system and identifying its limitations ÂŽ Designing an effective support system to be used in poor ground ÂŽ Making recommendations that can be used to improve the support systems.
RQD = 115 - 3.3 Jv
[2]
where Jv is the sum of the number of joints per unit length for all discontinuity sets, and is known as the volumetric joint count. RQD is a directionally dependent factor when determined using drill core. The use of volumetric joint count is of paramount importance in reducing this directional dependence (Brady, 1985). RQD is envisioned to indicate the quality of the in situ rock mass. The calculated RQD will then be used to determine the Q rating and Rock Mass Rating (RMR).
%" % &$( ') &''( ( &#("$) ) " ) &'') &#($ The RMR system incorporates the sum of six parameters (Bieniawski, 1989): 1. Uniaxial compressive strength of rock material 2. Rock Quality Designation (RQD) 3. Spacing of discontinuities 4. Condition of discontinuities 5. Groundwater condition. 6. Orientation of discontinuities.
=<879<478>78 =8 To effectively pin down the research problem and come up with effective solutions, a critical review of relevant literature was undertaken. Rock masses experience primitive stress before mining and induced stresses after openings are
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7.00 6.50 6.00 6.00 6.00 5.00 6.00 6.00 6.00 6.00 6.00 5.00 6.20 6.00 5.40 6.00 5.00 6.50 6.20 6.00 5.40 6.00 5.00 6.50 6.20 6.00
2.6 2.2 2.5 3.0 2.2 3.6 2.8 3.0 2.3 2.8 3.3 3.6 2.7 2.7 2.8 2.8 3.2 2.9 2.9 3.0 3.1 2.5 3.4 2.8 3.4 2.7
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2.3 2.2 2.3 2.0 2.0 2.1 2.3 2.1 2.1 2.2 2.1 2.2 2.0 2.0 2.2 2.2 2.2 2.2 2.1 2.1 2.2 2.2 2.2 2.2 2.1 2.1
3.9 3.6 3.5 4.5 7.0 6.7 6.5 5.7 5.2 5.9 5.2 6.4 6.5 7.0 5.9 5.5 5.0 5.9 5.2 6.2 6.4 5.9 5.5 6.8 6.7 7.1
100 52 48 98 79 100 100 89 200 87 203 200 96 200 202 97 93 89 55 100 200 102 100 100 58 55
8.3 7.9 7.3 9.2 11.5 12.5 11.6 11.3 10.1 10.7 10.9 11.8 11.3 11.9 10.4 10.1 10.5 11.0 10.2 12.2 11.6 10.6 10.4 12.2 12.9 13.0
88 89 91 85 77 74 77 78 82 80 79 76 78 76 81 82 80 79 81 75 77 80 81 75 72 72
nbg: north bottom gully, ntb: north top gully)
RMR = 9ln Q + 44
)' '#% Barton et al. (1974) noted that the Q system classification is based on the following three aspects: ÂŽ Block size (RQD/Jn) ÂŽ Inter-block shear strength (Jr /Ja) ÂŽ Active stress (Jw/SRF)
RQD J Jw Q = J x J r x SRF n a
[3]
The authors used the Q system to estimate the required support based on charts, which are discussed under results.
"!#)' '#% ' A sound strategy for overall mine stability is critical to avoid accidents or conditions that may give rise to incidents. The major hazards addressed by a sound mining method design and layout include uncontrolled collapses, surface subsidence, and major fall of ground incidents.
( &!) %'( $ The pillar support system is the chief basis of support in underground mines using the room and pillar mining method. In order to design pillars for supporting mine
openings, pillar strengths and pillar stresses need to be determined (Wilson, 1972). After determining pillar strengths and stresses, separate pillars and pillar layouts will be designed depending on the degree of stability needed.
The strength of pillars depends on: ÂŽ The strength of the intact rock that makes up the pillar material, suitably downrated to take into account the scale effect ÂŽ The geometry of the pillar, taking into account the shape and width to height (W:H) ratio. For W:H ratios less than 4.5, the strength of hard rock pillars is given by:
Ps = K.Weff0.5/H0.75
[4]
where Ps is the pillar strength K is the design rock mass strength (DRMS) in MPa Weff is the effective pillar width. Weff = 4 Ă&#x2014; pillar area / pillar perimeter.
In situ stress conditions, together with local and regional extents of mining, will determine the stresses acting on a pillar (Wilson, 1972). For a horizontal mining layout, pillar stress (Pstress) is given by VOLUME 116
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The relationship between RMR and Q is given by (Brown and Hoek, 1980):
Review of support systems used in poor ground conditions Pstress = , v 1-e
[5]
where: v is the vertical field stress and e is the extraction ratio
( &!) %'( $) !" % !% After determining the pillar strength and pillar stress, the factor of safety (FoS) of the pillar can be calculated as follows:
Pillar FoS = Pstrength/Pstress
[6]
For primary extraction, the minimum design FoS of pillars is 1.6. Due to the effect of the explosives used and poor ground conditions, the authors reviewed the current practices by measuring the actual pillar dimensions in a bid to calculate the actual factor of safety. Redesigning of pillars was considered where current pillar system is not adequate. The conclusion will be drawn after analysis of the results.
"'( %) !" %!#(%' Ammonium nitrate-fuel oil (ANFO) is a supreme explosive used in the mining industry. Its advantages include simple production, low cost, and lack of sensitivity to mechanical impact during mechanical loading into drill-holes (Mather, 1997). ANFO has also some disadvantages, which include lack of water resistance and low detonation parameters, which reduce its use to dry blast-holes in truncated compact rock masses (Maranda, 2011). Since the type of explosive used has an effect on support systems, the authors reviewed the literature on ANFO as well as the other bulk explosives, which include emulsion and watergel. The merits of bulk emulsion explosives over ANFO and packaged products include easy transportation and handling, increased safety, string charging, low gas emissions, water resistance, full coupling, increased velocity of detonation, detonator sensitivity, and improved work environment (Maranda, 2011). ANFO generates a lot of gases upon detonation, thereby widening pre-existing cracks. ANFO usage will therefore result in the formation of keyblocks, which will lead to an unstable hangingwall. In addition, the cut slice will increase due to overbreak and more poor hangings will be formed that require intense barring-down. Barring down becomes a risky operation due to frequent keyblocks and is also time-consuming, leading to failure to meet production targets.
/868973,>9007:93, A comprehensive revision of the background literature was conducted as per the requirements of the project objectives. The background literature was then combined with contributions from the relevant experts in the field of study, such as rock mechanics engineers on a practical level. A field study of the areas of concern was supplemented by the contribution of experts in order to assemble a system of results that would be used for analysis.
%'%&! ) !(#%!("$ The research started with the literature review on geological and geotechnical factors, underground support systems, mining methods, and types of explosive used. In order to obtain a clear understanding of the existing mining and
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support system, a study was carried out in all sections of the mine with poor ground conditions, which included Levels 14 to 24. Underground observations, recordings, and data collection were done in these sections. Observations and analysis were carried out on the geological structure of the orebody to identify the nature and magnitude of the jointing and faulting system. The effects of current mining practices and explosives used were assessed. Interviews were also conducted as part of the study approach. Observations were made in each level and the following parameters were measured and noted: ÂŽ Structural data â&#x20AC;&#x201C; number of joints, separation of joints etc. ÂŽ Pillar dimensions ÂŽ Stope widths of each gully ÂŽ Time taken to support one gully ÂŽ Fallout heights ÂŽ Type of support used. The results of these observations were analysed using rock engineering principles.
This exercise comprised the methodical collection of all fracture statistics of the underground rock face. The data collected included joint roughness, joint sets, joint alteration, joint water, stress reduction factor, and RQD. These parameters were used in the calculation of the Q rating of the pillars.
" ) &'') &''( ( &#("$ The determination of the rock mass state was critical to the investigation. Various techniques were applied to determine the ground classes in the research area. A comparative analysis of these techniques was then conducted to select the most effective method. Substantiated recommendations of the suitable support to be installed were based on the chosen method. The methods that were used include: ÂŽ The Q system ÂŽ RMR ÂŽ MRMR.
%! "! &$ %)" )($'#& % )' "!#)% % %$#' Installed support elements used at the mine include rockbolts, shotcrete, and straps. These were analysed for their performance and effectiveness with regard to the fallout heights and the ground characteristics by means of log data and previous reports to ascertain whether failures could be attributed to the support, the conditions, or both. The analyses included examining situations of failure and of likely failure.
$ %'#( &#("$)" )# %)% % #( %$%'')" ) ( &!' The pillar strength calculations were carried out through measurement of pillar heights and widths. The stress acting on a selected pillar was determined by calculation. Pillars are usually less than the designed size due to poor blasting and can undergo spalling attributed to poor ground. The frequency of such occurrences was investigated with the view to highlight the short-term and long-term problems associated with these practices.
Review of support systems used in poor ground conditions three methods were compared to identify the most suitable method of ground classification.
&'#) %'( $)&$ ) ($($ ) !& #( %' The current blast design and explosives used were analysed to: ÂŽ Attain the planned face advance through efficient blasting ÂŽ Mitigate overbreak for grade control and mine design purposes ÂŽ Reduce damage to rock ÂŽ Identify the explosives suitable for use in poor ground conditions.
Table II shows the data used to calculate Q in each bord.
Jx = number of joints per unit distance
[7]
where Jx represents Js, Jd, and Jh.
Jv = Js + Jd + Jh
[8]
Using Equation [2], RQD = 115-3.3Jv
!" % #) "$'#!&($#'
Table III shows the RMR calculated from Bieniawskiâ&#x20AC;&#x2122;s six parameters for each gully.
Constrains encountered during the research included the following: ÂŽ Measuring of pillars was rather dangerous as rockfalls are mostly from the shoulders of pillars ÂŽ Difficulties in logging of some ends due to waterlogging or delays in pumping out water.
The calculated RMR was adjusted to calculate the MRMR. A blasting effect adjustment of 97% was used, together with a weathering adjustment of 96%, and 80% for joint orientation. Table IV shows the adjusted RMR to give the MRMR.
/8642<6>
RMR = 9lnQ + 44
The results are based mainly on geotechnical data collected from the area of research. This includes results from rock mass classification methods, numerical modelling, reefsubparallel planes, FoS approach, stoping dimensions, and pillar strength. The current support system data was also included.
The average RMR is below 50, which shows that the rock mass is poor. RMR values from Bieniawski are comparable with calculated values from Q ratings. Rock-related risks due to the three joint sets are reduced by cutting larger pillars and through the use of cable bolts. In Ground Control District-D (GCD-D), the bord is reduced to 6 m and the in situ pillars are designed to be 3 Ă&#x2014; 3 m for shallower areas (up to 160 m depth) and 3.5 Ă&#x2014; 3.5 m for depths greater than 160 m. The main pillars measure 3 Ă&#x2014;
& &#("$)" )!" ) &'') &''( ( &#("$ The rock mass was classified according to each of the three systems, which are the RMR, MRMR, and the Q system. The
Table II
/:3$>-966> 2966=1=39<=:;> >">6*6<8) :39<=:; 66nbg 65nbg 64ntb 64nbg 63ntg 63nbg 62nbg 62ntg 61nbg 67nbg 68nbg 68ntg 82ntg 83nbg 83ntg 84nbg 84ntg 85ntg 81nbg 81ntg 86nbg 86nbg 87nbg 87ntg 88nbg 88ntg
/"#
Jn
Jr
Ja
Jw
88 89 91 85 77 74 77 78 82 80 79 76 78 76 81 82 80 79 81 75 77 80 81 75 72 72
3 6 6 6 6 12 3 6 4 9 3 6 3 3 4 9 9 9 9 9 4 9 9 9 9 9
1.5 1.5 1.5 1.5 1.5 3.0 1.5 1.5 3.0 1.5 1.5 2.0 3.0 1.5 3.0 1.5 1.5 2.0 1.5 1.5 3.0 1.5 1.5 2.0 1.5 1.5
6.0 6.0 6.0 6.0 3.0 5.0 6.0 3.0 6.0 3.0 3.0 2.0 6.0 3.0 6.0 3.0 3.0 2.0 3.0 3.0 6.0 3.0 3.0 2.0 3.0 3.0
1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00
/+ 7.5 4.0 6.0 8.0 6.0 6.0 10.0 4.0 4.0 10.0 6.0 6.0 8.0 6.0 4.0 10.0 6.0 6.0 8.0 6.0 4.0 10.0 6.0 6.0 8.0 6.0
"
/-/
0.97 0.93 0.63 0.44 1.07 0.61 0.64 1.62 2.55 0.44 2.19 2.11 1.62 2.10 2.52 0.45 0.74 1.46 0.56 0.69 2.39 0.44 0.75 1.38 0.50 0.67
44 43 40 37 45 40 40 48 52 37 51 51 48 51 52 37 41 47 39 41 52 37 41 47 38 40
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nbg: north bottom gully, ntg: north top gully
Review of support systems used in poor ground conditions Table III
/:3$>-966>/9<=;5 :39<=:;>
> - 9 > 79<=;5
/"#> 79<=;5
093=;5>:1> .=63:;<=;4=<* 79<=;5
:;.=<=:;6>:1> .=63:;<=;4=<* 79<=;5
7:4;. 9<87> 79<=;5
.(46<)8;<> 1:7>:7=8;<9<=:; 79<=;5
/-/
923429<8.> /-/ 17:)>"
66nbg
53 7
88 17
100 mm 8
1â&#x20AC;&#x201C;5 mm 10
Completely dry 15
Unfavourable -10
47
44
65nbg
53
89
52 mm
1â&#x20AC;&#x201C;5 mm
Completely dry
Unfavourable
44
43
7
17
5
10
15
-10
64nbg
53 7
91 17
48 mm 5
1â&#x20AC;&#x201C;5 mm 10
Completely dry 15
Unfavourable -10
44
40
64ntg
53 7
85 17
98 8
15 mm 10
Completely dry 15
Unfavourable -10
47
37
63nbg
53
77
79 mm
1â&#x20AC;&#x201C;5 mm
Completely dry
Unfavourable
47
45
7
17
8
-10
15
-10
63ntg
53 7
74 13
100 mm 8
1â&#x20AC;&#x201C;5 mm 10
Completely dry 15
Unfavourable -10
43
40
62nbg
53 7
71 11
100 mm 8
1â&#x20AC;&#x201C;5 mm 10
Completely dry 15
Unfavourable -10
41
40
62ntg
53 7
78 17
89 mm 8
1â&#x20AC;&#x201C;5 mm 10
Completely dry 15
Unfavourable -10
47
48
61nbg
53 7
82 17
200 mm 10
1â&#x20AC;&#x201C;5 mm 10
Completely dry 15
Unfavourable -10
49
52
nbg: north bottom gully, ntg: north top gully
Table IV
-=;=;5>/:3$>-966>/9<=;5 :39<=:;>
/-/
89<,87=;5>9.(46<)8;<
296<6>81183<6>9.(46<)8;<
:=;<>:7=8;<9<=:;>9.(46<)8;<
-/-/>
66nbg 65nbg 64ntb 64nbg 63ntg 63nbg 62nbg 62ntg 61nbg 67nbg 68nbg 68ntg 82ntg 83nbg 83ntg 84nbg 84ntg 85ntg 81nbg 81ntg 86nbg 86nbg 87nbg 87ntg 88nbg 88ntg Average
44 43 40 37 45 40 40 48 52 37 51 51 48 51 52 37 41 47 39 41 52 37 41 47 38 40
0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96 0.96
0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97
0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8
33 32 30 27 33 30 30 36 39 27 38 38 36 38 39 27 31 35 29 30 39 27 31 35 28 30 33
nbg: north bottom gully, ntg: north top gully
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Review of support systems used in poor ground conditions 10 m and 10 Ă&#x2014; 3.5 m in most sections. The authors also measured the main pillar dimensions and calculated the infringements. The actual pillar dimensions of in situ pillars were measured and the FoS in the gullies calculated. J3 structures are found in the hangingwall and ground penetrating radar (GPR) is used to identify these structures. The authors, with the assistance of geotechnicians, took GPR data and assessed the orientations and the average depth into the hangingwall. Analysis was conducted to ascertain whether the 1.8 m resin bolts and cable bolts currently used are sufficient. Figure 3 shows a typical slice obtained. A clino-rule was used to determine the dip of J1 and J2 structures. The authors deduced that J1 joint set is the dominant joint set, with an average strike direction of 088° and an average dip of 70°. The J2 joint set has an average strike of 005° and dips at an average of 65°. The J1, J2, and J3 joint set data from GPR was used in numerical modelling.
;92*6=6>:1>78642<6
#! # !& ) &#&)&$& '(' The Q values obtained indicated that the rock is extremely weak. The values of the measured RMR were comparable with the calculated values from the Q values. From this, it can be deduced that the ground conditions in the area of research pose a risk due to high probability of potential unstable blocks. The authors recommend that the mine uses more systems for rock mass classification, since a single system cannot give a clear indication of the quality of the rock due to its inherent limitations. For GCD D, 1.8 m bolts are currently used and are spaced at 1 m by 1 m. Bartonâ&#x20AC;&#x2122;s Q chart was used to determine the appropriate support system for GCD D as shown in Figure 4. Based on this chart, the current support system used seems to be adequate, although other systems need to be considered also in the design of the required parameters. The fallout height was found to be 1.8 m in the research area. Roofbolts with a length of 1.8 m are therefore considered inadequate to clamp the overlying layers, since there will be no bond length. The use of shorter roofbolts has resulted in support failure, hence new systems of tendons need to be designed. The issue of reef-subparallel planes and numerical modelling will be discussed later in this paper. All joints in the area of research are currently assumed to be dry; however, the authors recommend the use of hydrological surveys to obtain a clear picture of the
groundwater. Groundwater reduces the stabilizing normal stress acting on discontinuity planes, hence weakening the rock. From the results of rock mass classification, it can be concluded that adequate support is required for safe mining practices. A new roofbolt system envisaged to improve safety and productivity is discussed later in this paper.
!" $ ) %$%#!&#($ )!& &!) )&$& '(' A slice showing reef-subparallel planes is shown in Figure 3. It can be noted that shallow-dipping planes occur at a depth greater than 1.8 m into the hangingwall. The current support system of 1.8 m length is not adequate to clamp these layers, hence a new system that uses longer roofbolts needs to be implemented to reduce the risk of support failure and possible injuries, fatalities, and equipment damage. All these factors lead to heavy cost to the mine, hence it is of paramount importance to improve safety and productivity through the implementation of the new support system. The authors therefore recommend the use of longer roofbolts in addition to the cable bolts used.
%!( & ) " % ($ )&$& '(' JBlock was used to deduce the probability of failure of keyblocks in the gully. The structural data for the three joint sets, together with tendon data, was used to simulate unstable keyblocks. The authors started by simulating unstable keyblocks using the current support system of 1.8 m roofbolts spaced at 1 m by 1 m. The area simulated is a 6 m gully in order to check the effectiveness of the current support. Figure 5 shows the probability at which various blocks fail using the current support system consisting of grouted tendons 1.8 m in length spaced at 1 m by 1 m in poor ground conditions. From the histograms, it can be seen that the probability of block failure for 1 m3 blocks is 30% and the probability of maximum support failure is 16%. The probability of both block falls and support failure is thus too high. The current support system is inadequate. Integrating the results from all the techniques used, longer roofbolts are required to give improved safety. The new support system designed and simulated by the authors consists of grouted tendons with a capacity of 160 kN, 2.1 m length, and spaced at 1.2 Ă&#x2014; 1.2 m. The new system yields the results shown in Figure 6. The probability of block failure for 1 m3 blocks decreases to 11%, and the maximum support failure to 4%.
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+=5478> % >6<743<4786>=;> >28 82>;:7<,
Review of support systems used in poor ground conditions
+=5478> % 97<:; 6>">3,97<>6400:7<>6093=;5>1:7> #>#
+=5478> % 7:'9'=2=<*>:1>'2:3$>19=2478>46=;5><,8>34778;<>6400:7<>6*6<8)
+=5478> % 7:'9'=2=<*>:1>'2:3$>19=2478>46=;5><,8>;8 >6400:7<>6*6<8)
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Review of support systems used in poor ground conditions Taking into account a cost-benefit analysis, a comparison was made between the current support system and the new support system Although the 2.1 m tendons are more expensive than the current 1.8 m tendons, taking into consideration the cost-benefit analysis it can be concluded that the recommended system gives more benefits than the current support system. As well as improved safety, the new system leads to a decrease in support density since the tendons will be spaced at 1.2 Ă&#x2014; 1.2 m as opposed to the current roofbolts spaced at 1 Ă&#x2014; 1 m.
& &#("$)" ) ( &!) %'( $)&$ ) ##($ ) !& #( %') The authors evaluated the pillar design and cutting practices in poor ground conditions. Actual pillar dimensions in various bords were measured and the resulting factors of safety were calculated (Figure 7). The results show that most teams have failed to maintain the required safety factor of 1.6 due to stoping overbreak. Figure 8 shows how overbreak reduces the FoS. Stoping overbreak is caused by poor ground which unravels unpredictably, and also by ANFO explosive being used. It is thus critical to redesign pillars so that they are less influenced by a small change in overbreak. Pillar robbing also affects the FoS. Zvarivadza (2012) illustrated the relationship of probability of failure and FoS as shown in Figure 9. From Figure 9 it can be seen that for a FoS of 1.6, the probability of pillar failure is 0.5%, and at the lowest FoS of 1.33 obtained for Bord 66 (Figure 7), the probability of failure increases to 5%. A decrease in FoS therefore increases the probability of failure, hence it is critical to implement a pillar design that is less influenced by overbreak since the ground conditions are poor. Moreover, an alternative to ANFO needs to be considered to reduce stoping overbreak and unravelling of the rocks. Ore dilution occurs as a result of overbreak, as seen in Figure 10, since the grade of PGMs decreases above and below the required slice.
subparallel planes at depths greater than 1.8 m into the hangingwall implies that the current tendons used will fail to support keyblocks. The current type of explosives used also results in stoping overbreak, which decreases the factor of safety and increases PGE dilution. The ground conditions thus require redesigning of the pillars and tendon system to improve productivity and safety. The current design assumes that all joints at the mine are dry, but the effect of groundwater weakens the cohesion of some joints, which increases the frequency of unstable keyblocks. Barring down using pinch bars is time-consuming and is regarded as a risky exercise, since the barring team is exposed to unstable blocks with a higher probability of failure. Because of frequent unstable blocks, barring down using pinch bars wastes more cycle time, which has led to most sections failing to meet their production targets since fewer faces are prepared.
/83:))8;.9<=:;6> ÂŽ A study of the new support system designed by the authors is recommended. Longer roofbolts of 2.1 m length spaced at 1.2 Ă&#x2014; 1.2 m are proposed, as opposed to the current bolts of 1.8 m length spaced at 1 Ă&#x2014; 1 m. The 2.1 m roofbolts are more expensive than the current roofbolts; however, there is improved safety and less support density with the 2.1 m roofbolts. The extra cost of the roofbolts will be offset by the increased spacing, since fewer roofbolts will be used
:;3246=:;6 Safe mining practices and installation of adequate support lead to stable excavations. This review of the current support systems used in poor ground at a Zimbabwean platinum mine shows that the current support systems are not adequate in poor ground conditions. The presence of reef+=5478> % 1183<>:1>: 87'789$>:;>+: >9<> >)>.80<,
+=5478> %/829<=:;6,=0>'8< 88;>07:'9'=2=<*>:1>19=2478>9;.>+: 97= 9. 9 > VOLUME 116
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+=5478> %+93<:7>:1>6918<*>:1>in situ 0=22976
Review of support systems used in poor ground conditions
+=5478> %-=;8>579.8>07:1=28>937:66><,8>-
ÂŽ A study of alternative explosives is recommended to minimize rockfalls. ANFO explosives generate a lot of gases, which widen the joints. The authors recommend that the mine uses bulk emulsion, which is a lowenergy explosive, in poor ground conditions ÂŽ Additional support is required where there is pillar robbing. The use of timbers and pillar bolting is recommended to improve strength ÂŽ The mine should use both empirical and numerical modelling to design the optimum support, since relying on one system has limitations ÂŽ The use of hydrological surveys is recommended to determine joint water. Hydrological surveys will give an indication of the exact groundwater conditions within joints, thereby increasing safety by designing for the actual groundwater conditions ÂŽ The use of mechanical scalers is recommended in poor ground conditions to improve both worker safety and productivity. Fewer faces being prepared result in failure to meet production targets, hence the use of mechanical scalers will improve productivity ÂŽ The authors recommend redesigning of pillars to improve safety and production ÂŽ Smoothwall blasting is recommended in poor ground conditions to minimize excavation damage ÂŽ Adequate training of workers and close monitoring is required when drilling.
BIENIAWSKI, Z.T. 1989. Engineering Rock Mass Classification. 1st edn. Wiley, New York.
BRADY, B.H. 1985. Rock Mechanics for Underground Mining. 2nd edn. Allen and Unwin, London.
MARANDA, A. 2011. ANFO detonation parameters. Central European Journal of Energetic Materials, vol 8, no. 4. pp. 280â&#x20AC;&#x201C;291.
MATHER, W. 1997. Bulk Explosives. https://miningandblasting.files. wordpress.com [Accessed 13 December 2014].
OBERTHĂ&#x153;R, T., MELCHER, F., BUCHHOLZ, P., and LOCMELIS, M. 2012. The oxidized ores of the main sulphide zone, Great Dyke, Zimbabwe: turning resources into minable reserves â&#x20AC;&#x201C; mineralogy is the key. Platinum 2012. Proceedings of the Fifth International Platinum Conference. 'A Catalyst for Change', Sun City, South Africa, 17â&#x20AC;&#x201C;21 September 2012. Southern Afican Institute of Mining and Metallurgy, Johannesburg. pp. 647â&#x20AC;&#x201C;671.
PRENDERGAST, M.D. 1989. The platinum deposits of the, Great Dyke, Zimbabwe. Magmatic Sulphides â&#x20AC;&#x201C; The Zimbabwe Volume. Proceedings of the 5th Magmatic Sulphide Field Conference, 3â&#x20AC;&#x201C;13 August 1987. Prendergast M.D. and Jones, M.J. (eds). 1st edn. Institution of Mining and Metallurgy, London. pp. 43â&#x20AC;&#x201C;69.
WILSON, A.H. 1972. A hypothesis concerning pillar stability. The Mining
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BROWN, E.T. and HOEK, E. 1980. Rock mass classification. Underground Excavations in Rock. Institution of Mining and Metallurgy, London.
WOOD, D. 1987. Support in underground hard rock mines. https://rocscience.com [Accessed 10 December 2014].
pp. 40â&#x20AC;&#x201C;60.
BARTON, N., LIEN, R., and LUNDE, J. 1974. Engineering classification of rock
ZVARIVADZA, T. 2012. Evaluation of pillar design systems for low reef platinum
masses for the design of tunnel support. International Journal of Rock
mining. MSc thesis, University of Witwatersrand, Johannesburg, South
Mechanics, vol. 6, no. 4. pp. 190â&#x20AC;&#x201C;235.
Africa.
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http://dx.doi.org/10.17159/2411-9717/2016/v116n4a5
Slurry abrasion of WC-4wt%Ni coldsprayed coatings in synthetic minewater by N.B.S. Magagula*â&#x20AC; , N. Sacks*â&#x20AC; , and I. Botefâ&#x20AC;Ą Paper written on project work carried out in partial fulfilment of BSc. Eng. (Metallurgical and Materials Engineering)
51 &-/(+ tungsten carbide, nickel, cold spray, coatings, abrasion, minewater.
4.,/-(%),0-. Slurry abrasion is a common phenomenon in mining operations, particularly in pipelines transporting, for example, sand-water slurries. This type of wear can cause pipeline fracture, shortened operational lifetimes, and impede pipeline efficiency. To reduce or limit abrasion, thermally sprayed tungsten-carbide-based coatings are often used as pipe linings (Kanchan et al., 2010). This is due to their attractive mechanical properties, which include high wear resistance, stiffness, hardness, compressive strength, and tensile strength. These properties are provided by the coating microstructure and composition, which is a blend of hard, wear-resistant tungsten carbide (WC) particles embedded in a fracture-tough metallic binder phase (Brookes, 1997). Cobalt (Co) is the most commonly used binder due to its excellent wetting of the WC phase and moderate mechanical properties; however, its application is limited to non-corrosive environments as it has a low corrosion and oxidation resistance (Andren, 2001). Nickel (Ni) may also be used as a binder, and has been shown to have superior oxidation and corrosion resistance, but in some applications
School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa. â&#x20AC; DST-NRF Centre of Excellence in Strong Materials, South Africa. â&#x20AC;Ą School of Mechanical, Aeronautical and Industrial Engineering, University of the Witwatersrand, Johannesburg, South Africa. Š The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received Feb. 2016. *
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Low-pressure cold gas dynamic spraying was used to deposit WC-4wt%Ni and WC-4wt%Ni-1wt%Mo coatings onto mild steel. Dense coatings with very low porosities were produced. No decarburization occurred during deposition and no deleterious phases were formed. The coatings were subjected to standardized material characterization tests, as well as slurry abrasion testing to assess their wear behaviour. The wear tests were conducted in synthetic minewater-silica slurries, while distilled watersilica slurries were used as a control. The hardness of the coatings, 512HV0.3 and 458HV0.3 for WC-4wt%Ni and WC-4wt%Ni-1wt%Mo respectively, are comparable to those achieved using high-temperature coating processes. The abrasion wear rates for both coatings were less than 5 mg/min and 10 mg/min in the distilled water-silica and synthetic mine water-silica slurries respectively. The approximately 50% increase in wear rate in the synthetic minewater slurry is attributed to a synergistic corrosive wear mechanism. The predominant wear mechanisms were identified as binder smearing and delamination, with carbide grain fracture and pull-out.
may not have the required mechanical properties (Kim et al., 2006). The WC-based coatings are generally deposited by flame, arc, plasma, or highvelocity oxy-fuel (HVOF) spraying, all of which require melting or partial melting of the feedstock powder constituents (Jacobs et al., 1998; Kear et al., 2000; Zikin et al., 2012). These high-temperature deposition processes may adversely affect the properties of the coating, as oxidation, decarburization, unwanted phase transformations, and tensile residual stresses may occur. An alternative deposition method that claims to reduce and/or eliminate these undesirable effects is the coldgas dynamic spray process (CGDS) (Champagne, 2007). In this technique, the feedstock powders are heated only to low temperatures which are below the melting points of the constituent materials. This process has been shown to produce coatings with low porosity and good wear and corrosion resistance, comparable to HVOF coatings, and may have compressive residual stresses which could improve the coatingâ&#x20AC;&#x2122;s mechanical properties (Lima et al., 2002). Due to the low temperatures employed, this cold spray technique also has significantly lower energy requirements compared to the hightemperature deposition processes, which make it attractive in an energy-conscious society (Papyrin et al., 2006). In the current study, the use of a lowpressure cold gas dynamic spray system to produce WC-4wt%Ni coatings was investigated. The aim of the research was to
Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater produce coatings that have a good resistance to slurry abrasion, and which may find application in a mining environment. Nickel was selected as the binder due to its superior corrosion properties compared to Co, which would make it more suitable for mining applications. In addition, a small amount of molybdenum (Mo) was added to investigate its effect on the coating properties. A brief review of the cold spray process will be given first, followed by the methodology and results of the research.
-"(3*2+3( .2$0)3+#/2 0.* Cold gas dynamic spraying (CGDS) is a process whereby metal powder particles are utilized to form a coating by means of ballistic impingement upon a suitable substrate (Champagne, 2007). The fine powder particles, usually 5â&#x20AC;&#x201C;45 m, may be accelerated at supersonic speeds of 300â&#x20AC;&#x201C; 1200 m.s-1 towards the substrate, using air or a suitable carrier gas (Figure 1). The process was first developed in the mid-1980s at the Institute for Theoretical and Applied Mechanics of the Siberian Division of the Russian Academy of Science in Novosibirsk (Stoltenhoff et al., 2002). The discovery began as a study of the erosive behaviour of particle-laden flow on an object in a wind tunnel. Above a certain minimum particle velocity, the particles adhered to the target rather than abrading it, leading to the formation of coatings; a trend found to be characteristic for each of the metal powders tested. Further depositions were then made of a wide range of pure metals, metallic alloys, polymers, and composites onto a variety of substrate materials. Since its initial discovery, CGDS has developed into two fundamental deposition methods, namely high-pressure cold gas spraying and low-pressure cold gas spraying, in which the operational parameters such as pressure, temperature, and the carrier gases differ (Villafuerte, 2010). High-pressure systems typically use nitrogen or helium gas with pressures reaching approximately 7 MPa to accelerate the gas flow to the supersonic regime. Low-pressure systems typically use air (sometimes nitrogen) with pressures between 0.550â&#x20AC;&#x201C; 0.695 MPa. Due to the low temperatures used, limited or no melting occurs during deposition, so that the chemical composition of the coatings typically remains identical to the feedstock powders (Papyrin et al., 2006). In order to achieve sufficient adhesion and coating buildup, the powder particles must undergo severe plastic deformation on impact; hence the successful deposition of ductile metals such as nickel, copper, and aluminium. According to Hussain et al. (2009), during impact the pressure that is generated causes material interlocking and
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mechanical bonding. The deposition of ceramic materials such as WC is difficult. Due to their hard and brittle nature, such materials tend to shatter on impact, often leading to erosion of the substrate and previously deposited layers (Karthikeyan, 2007; Ang et al., 2011). For successful deposition, hard materials must be co-deposited with ductile binders (Wang and Villafuerte, 2009; Lioma et al., 2015). An additional advantage of the CGDS process over many high-temperature processes is that it may be applied by means of a portable system, which enables on-site repairs to be done. This is more cost-effective than having components disassembled and shipped off-site for repairs.
2,1/02"+32.(3$1,'-(-"-* 3 In this study two different coatings were investigated, namely a WC-4wt%Ni coating and a WC-4wt%Ni-1wt%Mo coating. The coatings were deposited onto mild steel substrates, 20 Ă&#x2014; 20 mm in size, which were grit-blasted with -300+100 Îźm alumina grit prior to the deposition process in order to facilitate adhesion of the coatings. A low-pressure cold spray machine (Centreline Series P SST) was used to deposit the powder blends onto the mild steel using air as the carrier gas. Following deposition, the coatings were polished to a 1 m surface finish for material characterization tests. The microstructure was studied using a Carl Zeiss Sigma field emission scanning electron microscope (FESEM) coupled with an energy dispersive X-ray spectrometer (EDS), which was used for elemental composition analysis and mapping. The coating thickness, porosity, WC grain size, and Ni binder mean free path were measured using lineal analysis on the FESEM images. Phase identification was done using a BRUKER D2 X-ray diffraction (XRD) instrument with Co-K radiation and PANalytical X'Pert High Score software. Vickers micro-hardness tests were done according to ASTM E384 (2011). Slurry abrasion testing of the coatings were conducted using a modified ASTM G105 (2002) machine. A schematic diagram of the machine is shown in Figure 2. Three samples were tested simultaneously using an applied load of 22 N per sample, with the abrasion wheel rotating at 0.66 m.s-1. Silica sand with an angular morphology and an average hardness of 1084 Âą 156HV was used as the abrasive medium. The silica was mixed with two different liquid media, namely distilled water and synthetic minewater. The composition of the synthetic minewater was 37 ppm Ca2+, 1500 ppm Cl , 40 ppm Mg2+, 980 ppm SO2-, and 943 ppm Na+ (Machio et al., 2005). The distilled water slurry was used as a control to assess the aggressiveness of the synthetic minewater slurry. The test duration was 60 minutes, with the mass loss of each
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Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater coating being measured at 5-minute test intervals for the first 20 minutes, and thereafter in 10-minute intervals. The abrasion wear rate was calculated as mass loss as a function of time. The abraded surfaces were examined using electron microscopy (FEI SEM Quanta 200) in order to identify the wear mechanisms.
1+%",+32.(3(0+)%++0-.3
Figure 3 shows the FESEM images of the two coating microstructures adjacent to their respective XRD patterns. An inhomogeneous distribution of the WC carbide phase within the Ni matrix was observed for both coatings. The smaller WC particles are due to fracturing of the carbide phase during deposition as the particles impact the substrate. Similar observations have been made by other authors (Bhaumik et al., 1991). The XRD patterns show the main phases of WC, Ni, and Mo, and it is noted that no decarburization occurred. A summary of the coating properties is listed in Table I. The WC-4wt%Ni coating has a higher average hardness than the WC-4wt%Ni-1wt%Mo coating. This is due to the smaller average WC grain size measured for the WC-4wt.%Ni coating. It is well known that cemented tungsten carbide materials with finer WC grain sizes have higher hardness values (Brookes, 1997). It was noted that the addition of 1wt %Mo to the WC-4wt%Ni coating reduced the hardness by 10.5%, which is quite significant given the small amount of Mo added. The reason for this effect is as yet unclear. Despite the differences in the carbide grain sizes, the Ni binder mean free path and wt% retained WC of both coatings were similar. The
average amount of WC retained in the coatings was 41wt%, which is low given the original feedstock powder composition of 95â&#x20AC;&#x201C;96wt%. This is a common phenomenon in cold-spray coatings when hard ceramic particles are deposited as mentioned earlier. Due to their hard and brittle nature, a certain percentage of the particles will bounce off the substrate during deposition, while some particles fracture on impact. The porosity of both coatings is very low and acceptable, suggesting that fairly dense coatings were produced.
The slurry abrasion wear rates of the two coatings are shown in Figure 4. The average wear rate of the WC-4wt%Ni coating is slightly lower than that of the WC-4wt%Ni-1wt%Mo coating in both slurries tested. This concurs with the higher average hardness of the WC-4wt%Ni coating, which aligns
0*%/13 1/2*13&12/3/2,1+3- 3 -,'3)-2,0.*+30.3,'13,&-3+"%//01+
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Table I
Coating composition WC-4wt.%Ni WC-4wt.%Ni-1wt.%Mo
Hardness (HV30)
WC retained (wt%)
DWC ( m)
Ni (Îźm)
Porosity (%)
512 Âą 42 458 Âą 36
41 Âą 1.0 41 Âą 4.2
0.71 Âą 0.08 0.78 Âą 0.09
0.10 Âą 0.01 0.11 Âą 0.02
0.01 0.02
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Summary of the coating properties
Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater with well-established theory that a higher hardness should provide better resistance against wear (Hutchings, 1992). The wear rates of the coatings in the synthetic minewater slurries are approximately 50% higher than those in the distilled water slurries. This large increase was unexpected given that the pH of the distilled water was 7, while that of the synthetic minewater was only 6.2. However, these wear rates indicate the extent to which synergistic action between wear and corrosion can lead to high material removal rates. While abrasion may be the dominant degradation mechanism based on the direct contact between the silica abrasive particles and the coating, the breakdown of the coating surface provides access for the liquid medium to attack the subsurface material. Thus while abrasion proceeds on the coating surface in contact with the silica, corrosion of the coating occurs simultaneously at subsurface level. This corrosive process facilitates material removal by preferentially attacking the binder phase, thereby weakening the bonding between binder and carbide, and subsequently making it easier for larger volumes of material to be removed as abrasion continues. Figure 5 is an elemental mapping of one of the WC-4wt%Ni-1wt%Mo coating surfaces exposed to synthetic minewater. Apart from the expected coating elements, traces of sulphur were found on the surface, which are remnants of the chemical salts used to produce the synthetic minewater solution. According to Hutchings (1992), when the ratio of the hardness of the abrasive to the hardness of a surface is greater than 1.2 (Ha/Hs >1.2) then hard abrasion associated with plastic indentation is expected to occur on the surface. In this research, the Ha/Hs ratios for both coatings were 2.1 and 2.4 for WC-4wt%Ni and WC-4wt%Ni-1wt%Mo respectively. Thus both coatings experienced hard abrasion, with the silica particles indenting the coating surface. The precise mechanisms of material removal were identified using SEM, and examples of the worn surfaces are shown in Figures 6 and 7. The predominant mechanisms observed were carbide grain cracking, chipping, and removal, with extensive binder smearing and delamination. Grooving of the surfaces was also observed, which indicates the path followed by the silica particles and wear debris. These wear mechanisms are similar to those typically observed for cemented WC materials subjected to abrasion (Larsen-Basse, 1985). The angularity of the hard silica particles facilitated the preferential removal of the softer nickel binder phase from between the carbide
grains. This leaves the carbide grains unsupported, making their removal easier as abrasion proceeds. The removed material tends to form hard micro-abrasives which then
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Slurry abrasion of WC-4wt%NI cold-sprayed coatings in synthetic minewater
-.)"%+0-. This research showed that a low-pressure cold gas dynamic spray system could be used to deposit WC-4wt%Ni and WC4wt%Ni-1wt%Mo coatings onto mild steel. Dense coatings exhibiting very low porosities, an average of 41wt% retained WC, and hardnesses comparable to high-temperature deposited coatings, were produced. No decarburization or deleterious phases were formed in the coatings. The addition of 1wt% Mo to the WC-4wt%Ni coating did not improve the hardness or abrasion resistance. Both coatings showed an approximate 50% increase in abrasion wear rate when subjected to a synthetic minewater-silica slurry. This was attributed to a synergistic corrosive-wear mechanism. The predominant wear mechanisms for both coatings are those typically experienced by cemented tungsten carbide coatings when subjected to abrasion.
%,%/13&-/6 Although the coatings have shown good abrasion resistance under laboratory conditions, further detailed research needs to be undertaken to determine their suitability for industrial application. This should include field testing on carefully monitored slurry transportation pipelines to observe the performance of the coatings. As slurries may also have a corrosive nature, corrosion testing should be done on the coatings, with exposure to varying media found in mining operations. Pipelines have elbows which experience eccelerated erosion, often leading to pipe failure, and therefore the coatings should be subjected to erosion testing at various impact angles and using different slurry media. Finally, an in-depth financial analysis should be done to assess the viability of substituting the cold spray process for some of the high-temperature processes currently being used to produce wear-resistant pipe linings.
)6.-&"1(*1$1.,+ The authors wish to acknowledge the financial support received from the Department of Science and Technology and the National Research Foundation in South Africa. The assistance of Ms D. Lioma, Mr N. Nelwalani, Mr S. Maqobelane, Professor A. Ziegler, and the workshop staff of the School of Chemical and Metallurgical Engineering, University of the Witwatersrand, is greatly appreciated.
1 1/1.)1+ ANDREN, H-O. 2001. Microstructures of cemented carbides. Materials and Design, vol. 22, no. 6. pp. 491â&#x20AC;&#x201C;498. ANG, A.S.M., BERNDT, C.C., and CHEANG, P. 2011. Deposition effects of WC particle size on cold sprayed WC-Co coatings. Surface and Coatings Technology, vol. 205, no. 10. pp. 3260â&#x20AC;&#x201C;3267. ASTM E384. 2011. Standard Test Method for Knoop and Vickers Hardness of Materials. ASTM International, West Conshohocken, NJ. ASTM G105-02. 2002. Standard Test for Conducting Wet Sand/Rubber Wheel
Abrasion Tests. ASTM International, West Conshohocken, NJ. BHAUMIK, S.K., UPADHYAYA, G.S., and VAIDYA, M.L. 1991. Properties and microstructure of WC-TiC-Co and WC-TiC-Mo2-Co(Ni) cemented carbides. Materials Science and Technology, vol. 7. pp. 723â&#x20AC;&#x201C;727. BROOKES, K.J.A. 1997. Hardmetals and other Hard Materials. 6th edn. International Carbide Data, UK. CHAMPAGNE, V.K. 2007. The Cold Spray Materials Deposition Process: Fundamentals and Applications. Woodhead Publishing, Cambridge. HUSSAIN, T., MCCARTNEY, D.G., SHIPWAY, P., and ZHANG, D. 2009. Bonding mechanisms in cold spraying: the contributions of metallurgical and mechanical components. Journal of Thermal Spray Technology, vol. 18, no. 3. pp. 364â&#x20AC;&#x201C;379. HUTCHINGS, I.M. 1992. Tribology: Friction and Wear of Engineering Materials. Edward Arnold, London. JACOBS, L., HYLAND, M.M., and DE BONTE, M. 1998. Comparative study of WCcermet coatings sprayed via the HVOF and the HVAF process. Journal of Thermal Spray Technology, vol. 7, no. 2. pp. 213â&#x20AC;&#x201C;218. KANCHAN, K., ANAND, K., BELLACCI, M., and GIANNOZZI, M. 2010. Effect of microstructure on abrasive wear behaviour of thermally sprayed WC10Co-4Cr coatings. Wear, vol. 268, no. 11-12. pp. 1309â&#x20AC;&#x201C;1319. KARTHIKEYAN, J. 2007. The advantages and disadvantages of the cold spray coating process. The Cold Spray Materials Deposition Process. Champagne V.K. (ed.). Woodhead Publishing Series in Metals and Surface Engineering, Woodhead Publishing, Cambridge. pp. 62â&#x20AC;&#x201C;71. KEAR, B.H., SADANGI, R.K., JAIN, M., YAO, R., KALMAN, Z., SKANDAN, G., and MAYO, W.E. 2000. Thermal sprayed nanostructured WC/Co hardcoatings. Journal of Thermal Spray Technology, vol. 9, no. 3. pp. 399â&#x20AC;&#x201C;406. KIM, H-J., LEE, C-H., and HWANG, S-Y. 2005. Superhard nano WC-12%Co coating by cold spray deposition. Materials Science and Engineering A, vol. 391, no. 1â&#x20AC;&#x201C;2. pp. 243â&#x20AC;&#x201C;248. KIM, H-C., SHON, I-J., YOON, J-K., and DOH, J-M. 2006. Comparison of sintering behaviour and mechanical properties between WC-8Co and WC-8Ni hard materials produced by high-frequency induction heating sintering. Metals and Materials International, vol. 12, no. 2. pp. 141â&#x20AC;&#x201C;146. LARSEN-BASSE, J. 1985. Binder extrusion in sliding wear of WC-Co alloys. Wear, vol. 105. pp. 247â&#x20AC;&#x201C;256. LIMA, R.S., KARTHIKEYAN, J., KAY, C.M., LINDEMANN, J., and BERNDT, C.C. 2002. Microstructural characteristics of cold-sprayed nanostructured WC-Co coatings. Thin Solid Films, vol. 416, no. 1â&#x20AC;&#x201C;2. pp. 129â&#x20AC;&#x201C;135. LIOMA, D., SACKS, N., and BOTEF, I. 2015. Cold gas dynamic spraying of WC-Ni cemented carbide coatings. International Journal of Refractory Metals and Hard Materials, vol. 49. pp. 365â&#x20AC;&#x201C;373. MACHIO, C.N., AKDOGAN, G., WITCOMB, M.J., and LUCKYX, S. 2005. Performance of WC-VC-Co thermal spray coatings in abrasion and slurry erosion tests. Wear, vol. 258. pp. 434â&#x20AC;&#x201C;442. PAPYRIN, A., KOSAREV, V., KLINKOV, S., ALKHIMOV, A., and FOMIN, V. 2006. Cold Spray Technology. 1st edn. Elsevier Science. STOLTENHOFF, T., KREYE, H., and RICHTER, H.J. 2002. An analysis of the cold spray process and its coatings. Journal of Thermal Spray Technology, vol. 11, no. 4. pp. 542â&#x20AC;&#x201C;550. VILLAFUERTE, J. 2010. Recent trends in cold spray technology: looking at the future. Surface Engineering, vol. 26, no. 6. pp.393â&#x20AC;&#x201C;394. WANG, J., and VILLAFUERTE, J. 2009. Low pressure cold spraying of tungsten carbide composite coatings. Advanced Materials and Processes, vol. 167, no. 2. pp. 54. ZIKIN, A., ILO, S., KULU, P., HUSSAINOVA, I., KATSICH, C., and BADISCH, E. 2012. Plasma transferred arc (PTA) hardfacing of recycled hardmetal reinforced nickel-matrix surface composites. Materials Science (Medziagotyra), vol. 18, no. 1. pp. 12â&#x20AC;&#x201C;17. N VOLUME 116
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subject the coating to additional wear, causing fracture of the embedded carbide grains. The wear mechanisms were similar for both slurry types, although larger volumes of material were removed from the coatings subjected to the synthetic minewater.
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Matte â&#x20AC;&#x201D; tap-hole clay â&#x20AC;&#x201D; refractory brick interaction in a PGM smelter by J. Du Toit*, R.D. Cromarty*, and A.M. Garbers-Craig* Paper written on project work carried out in partial fulfilment of BEng (Metallurgical Engineering)
Penetration of matte into tap-hole bricks causes detrimental refractory wear, which can lead to furnace breakouts. The ability of the tap-hole clay to form a protective layer on the brick, thereby limiting matte penetration was investigated by examining the interaction between platinum group metal (PGM) matte, tap-hole clay, and alumina-chrome refractory bricks on a laboratory scale. Samples containing clay and brick as well as samples containing clay, brick, and matte were heated to different temperatures to establish the clay-brick interaction and the extent of matte penetration. The greatest degree of physical contact between the brick and clay was achieved at curing temperatures of 600°C. Poor clay-brick contact was observed in the sample that was heated to 900°C. Matte displaced the clay in the clay-brick-matte sample that was heated to 1350°C, with significant matte penetration into the brick. Less matte penetration was observed when the clay-brick-matte sample was heated to 1500°C. Less matte penetration was also observed in the claybrick-matte sample in which the clay and brick were pre-baked at 800°C, and the sample then reacted with matte at 1350°C. 30 6),%& tap-hole clay, alumina-chrome refractory bricks, PGM matte, reaction interface, penetration.
(.,)% +./)(11 Floatation concentrate from ore from the eastern Bushveld Complex of South Africa, specifically the Platreef, Merensky, and UG2 reefs, forms the feed to the Polokwane platinum smelter (Hundermark, De Villiers, and Ndlovu, 2006). The ore from the UG2 Reef has A high chromite content, which requires high operating temperatures (1500â&#x20AC;&#x201C;1700°C) to avoid chromium spinel build-up in the furnace hearth. These high operating temperatures lead to matte superheats in the vicinity of 500â&#x20AC;&#x201C; 600°C, which put increased demands on the refractory materials (Nelson et al., 2005). Upon tapping, the matte moves through the tap-hole, which consists of an aluminachrome refractory brick-lined tapping channel (Hundermark, De Villiers, and Ndlovu, 2006). The flow of molten matte is stopped by the injection of tap-hole clay to form a plug in the tap-hole. The tap-hole clay hardens and strengthens during curing to obtain the required hardness and refractoriness against penetration, corrosion and erosion (Nelson and Hundermark, 2014).
* Department of Materials Science and Metallurgical Engineering, University of Pretoria. Š The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received Feb. 2016.
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5 () &/&
The amount and positioning of tap-hole clay in the tap-hole and tapping channel affect the shape and length of the tapping channel, which in turn affect the consistency that can be achieved in the tapping process (Nelson and Hundermark, 2014). Wear of the tap-hole and tapping channel results in less control being possible on the tapping process and less safe operating conditions due to the possibility of burn-through and unintentional reopening of the tap-hole. Worn refractories have to be replaced, requiring significant expenses and downtime (Nelson and Hundermark, 2014). It is generally accepted that refractory wear by matte occurs in three steps. Penetration of the matte into the bricks occurs first. Penetration is followed by corrosion and erosion, during which the worn refractory bricks are corroded and pieces of brick are removed from the tapping channel along with molten material (Nelson and Hundermark, 2014). The extent of refractory wear depends on the amount of matte that penetrates into the brick and the temperature and viscosity of the matte. An increase in matte temperature leads to a decrease in matte viscosity and an associated increase in matte fluidity and ability to penetrate into the refractory brick (Nelson et al., 2005). Brick wear may be minimized through protection provided by the tap-hole clay. Ideally, upon injection of the tap-hole clay into the tapping channel and tap hole, interaction between the tap-hole clay and brick would make matte penetration into the brick more difficult since matte would be required to move through the clay before penetration into the brick is possible. This interaction between taphole clay and brick and the associated extent of matte penetration formed the focus of this study.
Matte â&#x20AC;&#x201D; tap-hole clay â&#x20AC;&#x201D; refractory brick interaction in a PGM smelter -.0,/-*& Primary PGM matte was obtained from the Anglo Platinum Polokwane smelter, while alumina-chrome bricks and taphole clay were obtained from the refractory suppliers to the Polokwane smelter1. These materials were characterized using X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), and scanning electron microscopy using energy-dispersive X-ray spectroscopy (SEM-EDS).
Quantitative XRD analysis indicated that the nickel-copperrich PGM matte consisted of 61.9% (Fe, Ni)9S8, 13.3% FeS, 6.6% Cu5FeS4, 6.8% SiO2, 6% CaAl2Si2O8, and 3.9% FeCr2O4.
XRF analysis confirmed that the brick contained 75% Al2O3, 20.7% Cr2O3, 2.2% P2O5, and 1% SiO2. XRD analysis revealed that Al2O3 and the (Al,Cr)2O3 solid solution phase were the major phases present in the brick (56.0% and 40.3% respectively), while trace amounts aluminium phosphate (AlPO4) and cristobalite (SiO2) could also be detected. Microstructurally, the brick consisted of large alumina grains embedded in an alumina-chrome-based matrix, bonded through the formation of the (Al,Cr)2O3 solid solution phase (Figure 1).
The tap-hole clay is an organically bound material. XRD analyses were conducted on the raw clay, and on clay samples that were heated to 950°C and subsequently cooled to room temperature in an oxidizing as well as an inert atmosphere. The raw clay was found to consist largely of the crystalline phases corundum and andalusite (55 wt% and 11 wt% respectively) with some silicon carbide, silicon, quartz, mullite, and a small amount of graphite. The carbon binder present in the clay is an amorphous phase which was not quantified by XRD analysis. Upon heating, graphite is retained in the sample in an inert atmosphere but is oxidized from the system when heated in air. In order to allow comparison between types and amounts of phases under oxidizing and inert atmospheric conditions, the analysis of the sample heated under inert atmosphere was normalized to exclude graphite. It was found that andalusite decomposes into mullite (3Al2O3.2SiO2) and SiO2 or a glassy phase when heated in both the inert and oxidizing atmospheres. According to Schneider and Komarneni (2006), andalusite is stable up to temperatures in the vicinity of 780°C, at which decomposition of andalusite into mullite and silica initiates (Schneider and Komarneni, 2006). The decrease in the amount of andalusite in the oxidizing and inert atmospheres is therefore expected with an associated increase in mullite and silica. This agrees with the findings of the XRD analysis, where mullite increased from 5.3% to almost 10% and silica from 6.9% to close to 10% in both samples.
1Names of suppliers omitted for confidentiality reasons
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Thermogravimetric analysis (TGA) was conducted on the tap-hole clay to establish the temperatures at which decomposition of the binder takes place (Figure 2). A 4% decrease in mass was observed between 100 and 200°C when the sample was heated in both air and nitrogen. An additional 10% mass loss was observed at temperatures between 450 and 600°C in air. The mass loss between 100 and 200°C can be ascribed to volatiles being driven from the sample. PĂŠrez et al. (2004), obtained similar results through thermogravimetric analysis of pitch binders. The 450â&#x20AC;&#x201C;600°C temperature range correlates to the temperature range at which oxidation of graphite occurs (Xiaowei, Jean-Charles, and Suyuan, 2004). The sample heated in air underwent a large mass loss in the 450â&#x20AC;&#x201C;600°C range due to graphite oxidation. The mass of the sample heated in nitrogen over this temperature range remained unchanged, indicating the completion of the pyrolysis of the binder.
24 0,/"0(.-* Laboratory-scale experiments were performed to simulate the clay-brick (CB) and the clay-brick-matte (CBM) interactions. In both sets of experiments argon gas was used for purging to avoid the oxidation of sulphur in the matte. For the clay-brick interaction a Phasecon tube furnace was used. The furnace was heated to temperatures of 600°C and 900°C and kept at temperature for one hour. A heating ramp rate of 15°C/min was used upon heating and 50°C/min upon cooling. Technical-grade argon (99.9% argon) was used to purge the furnace for the heating, dwell, and cooling periods. In the clay-brick experiment an alumina crucible assembly, containing a brick core surrounded by clay, was used (Figure 3). The clay-brick-matte experiments were done using an induction furnace with a graphite susceptor in an insulated gas-tight chamber. An Ambrell Ekoheat power supply was used and temperature was controlled using a Eurotherm temperature controller and a type B thermocouple.
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The induction furnace was purged with technical-grade argon for 30 minutes prior to heating to temperatures of 1350°C and 1500°C. Purging continued for the duration of the experiment. A heating rate of 20°C/min was used, followed by dwelling at temperature for 60 minutes and then cooling at a rate of 50°C/min. The crucible assembly consisted of an alumina crucible with a section of the brick placed at the bottom and clay added to the top and around the sides of the brick. Matte was then added on top of the clay (Figure 3). An additional experiment was performed in which the CBM set-up was modified by first baking the clay and brick in an alumina crucible in the Phasecon retort furnace at 800°C for one hour. After cooling, the matte was added and the CBM experiment was performed in the induction furnace as described previously. The purpose of this experiment was to establish whether pre-baking would increase the physical contact and extent of interaction between the clay and brick, thereby improving the resistance against matte penetration. The samples were sectioned, and polished samples prepared for analysis on completion of the CB and CBM experiments. Reflected light microscopy and SEM-EDS analysis were used to determine the amount of clay-brick interaction as well as the extent of matte penetration.
phase) could be distinguished in the solidified matte (Figure 7B), while an Fe-Ni-Cu-based alloy could also be observed. The brick (Figure 7C) was also penetrated by the matte. This was expected, since the matte displaced the clay and no protective layer was present to resist matte penetration into the brick. The sample heated to 1500°C also showed significant matte penetration; although complete displacement of the clay section with matte was not evident. There is a clear distinction between the initial matte section (light grey) and the initial clay section (dark grey), although droplets of matte seem to have penetrated into the clay region (Figure 8A). The bright phases in the clay are alloy droplets and not matte. Alloy droplets, however, were not observed in the brick, but only matte droplets. Greater interaction between the clay and the brick was observed in the 1350°C CBM sample that contained prebaked clay. There was, however, still matte penetration into the clay and the brick sections (Figure 9).
!)(+* &/)(& Decomposition of the binder occurs at temperatures up to 600°C with volatiles being driven off in the 100â&#x20AC;&#x201C;200°C temperature range. Oxidation of graphite occurs at 450â&#x20AC;&#x201C;600°C.
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The clay-brick interaction was limited, as areas at the claybrick interface could be distinguished where no direct contact occurred. Areas of poorer and better physical contact were observed, with overall better contact being achieved in the sample heated to 600°C (Figure 4), compared to the sample that was heated to 900°C (Figure 5). The gap between the clay and brick implies that chemical interaction did not occur. /' ,01 0#*0+.0%1*/'$.1"/+,)',- $1)#1+*- ,/+ 1/(.0,-+./)(1-.1 !
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The reflected light microscopy images of the samples containing clay, brick, and matte indicate that matte (brightly coloured) penetrated into both the clay (Figure 6A) and the brick (Figure 6B). In the CBM sample heated to 1350°C, the matte seemed to have displaced the clay. The top layer, which initially consisted of matte, contained clay (dark grey, Figure 7A), while the section above the brick, which was initially clay, contained matte only (light grey, Figure 7B). Copper sulphide (light sulphide phase) and an iron sulphide (dark sulphide
Matte â&#x20AC;&#x201D; tap-hole clay â&#x20AC;&#x201D; refractory brick interaction in a PGM smelter
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Without physical contact, chemical interaction could also not occur. Without clay-brick interaction, the clay provides little protection against matte penetration into the brick. The physical contact between the clay and the brick proved to be better when the clay and brick were reacted at a lower temperature (600°C), rather than a higher temperature (900°C). Matte penetrated through the clay and into the brick in samples heated to 1350°C as well as to 1500°C. Less matte penetration occurred in the 1500°C sample and the 1350°C sample that contained pre-baked tap-hole clay. In the CBM sample that was reacted at 1500°C, matte reacted with the tap-hole clay to form a Cu-Fe-Ni alloy. /' ,01 -+ &+-..0,0%10*0+.,)(1/"-'0&1)#1.$01! 1&-" *01$0-.0%1.) ! 1 1 (/./-*1"-..01,0'/)( 1 1/(/./-*1+*- 1,0'/)( 1 ! 1/(/./-*1 ,/+ ,0'/)(
+ ()6*0%'0"0(.& The authors would like to thank Anglo American (Dr Lloyd Nelson, Rodney Hundermark, and Keith Hines) for supplying the raw materials as well as for technical assistance. A word of thanks also goes to colleagues and analytical staff in the Department of Material Science and Metallurgical Engineering at the University of Pretoria.
0#0,0(+0& HUNDERMARK, R., DE VILLIERS, B., and NDLOVU, J. 2006. Process description and short history of Polokwane Smelter. Southern African Pyrometallurgy 2006. Jones, R.T. (ed.). Southern African Institute of Mining and Metallurgy, Johannesburg. pp. 35â&#x20AC;&#x201C;41. NELSON, L.R. and HUNDERMARK, R.J. 2014. â&#x20AC;&#x2DC;The tap-hole'â&#x20AC;&#x201D; key to furnace performance. Furnace Tapping Conference 2014. Southern African Institute of Mining and Metallurgy, Johannesburg. pp. 1â&#x20AC;&#x201C;32. NELSON, L.R., STOBER, F., NDLOVU, J., DE VILLIERS, L.P., and WANBLAD, D. 2005. Role of technical innovation delivery at the Polokwane Smelter. Nickel and Cobalt 2005. Challenges in Extraction and Production, Calgary. Donald, J. and Schonewille, R. (eds.). CIM, Montreal. pp. 91â&#x20AC;&#x201C;116. PEREZ, M., GRANDA, M.S., MORGAN, T., and MENENDEZ, R. 2004. A thermoanalytical study of the co-pyrolysis of coal-tar pitch and petroleum pitch. Fuel,
/' ,01 -+ &+-..0,0%10*0+.,)(1/"-'01)#1.$01! 1&-" *01$0-.0%1.) ! 1 1 (/./-*1"-..01-(%1+*- 1,0'/)(& 1 1/(/./-*1 ,/+ 1,0'/)(
vol. 83, no. 9. pp. 1257â&#x20AC;&#x201C;1265. SCHNEIDER, H. and KOMARNENI, S. 2006. Mullite. Wiley, Weinham.
Interaction between tap-hole clay and brick does not occur extensively at either 600°C or 900°C. Regions of poor physical contact between the clay and brick were observed.
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XIAOWEI, L., JEAN-CHARLES, R., and SUYUAN, Y. 2004. Effect of temperature on graphite oxidation behaviour. Nuclear Engineering and Design, pp. 273â&#x20AC;&#x201C;280.
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Separation of kimberlite from waste rocks using sensor-based sorting at Cullinan Diamond Mine by T. Mahlangu*â&#x20AC; , N. Moemiseâ&#x20AC; , M.M. Ramakokovhu*, P.A. Olubambiâ&#x20AC;Ą, and M.B. Shongwe* Paper written on project work carried out in partial fulfilment of BTech. Eng. (Metallurgical Engineering)
Near-infrared (NIR) spectroscopy sorting technology is incorporated in an automated optical mineral sorter that can discriminate between materials using the differences in characteristics when exposed to near-infrared radiation. During September 2014 to April 2015, a pilot plant that utilized NIR technology to discriminate between kimberlite and waste materials was commissioned to determine the viability of including this technology in the diamond winning process flow sheet at Cullinan Diamond Mine. The plant was used to minimize the waste content in the size fraction -70+35 mm that reports to the crushing section and then to the dense media separation process. This paper describes the initial test work, conducted at Mintek, that led to the decision to conduct a pilot-scale study. The mineralogical characterization of the feed and product streams to establish the sorting criteria and the operational data obtained during the pilot plant campaign are described. The results indicated a good possibility of discriminating between the kimberlite and waste material using NIR technology. However, the consistency of discrimination was not good enough to avoid the risk of potential diamond loss. Furthermore, a lower than expected availability of the machine reduced the throughput capabilities. !7 24#3 sensor-based sorting, NIR spetroscopy, kimberlite, preconcentration.
.642#*)652. Using near-infrared spectroscopy (NIRS) technology for ore sorting is a new concept for the mineral processing and mining industry. NIRS has been used for decades in the laboratory for the identification of pure minerals, and has its roots in the recycling, food, and pharmaceutical industries (Salter and Wyatt, 1991; Robben et al., 2009). Ore sorting in itself is not a new concept; it was introduced during the Stone Age with handsorting being the first method to separate valuable materials from gangue (Wills and Napier-Munn, 2006; Sassos, 1985). However, over the years the scale of mining has increased and hand-sorting has become challenging to implement (Joensson, 2014). Sensor-based sorting is an advanced technology that can help overcome problems such as ore dilution experienced in mineral processing operations. The benefits are lower energy and water costs, reduced ore dilution, lower environmental impact, and improved profit margin (Mathew, 1974; Jonsson, 2014;
Institute for NanoEngineering Research, Department of Chemical, Metallurgical and Materials Engineering, Tshwane University of Technology, Pretoria, South Africa. â&#x20AC; Cullinan Diamond Mine, Petra Diamonds Southern Africa (Pty) Ltd. â&#x20AC;Ą Department of Chemical Engineering Technology, University of Johannesburg, Johannesburg, South Africa. Š The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received Feb. 2016. *
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Salter and Wyatt, 2009; Death et al., 2009). In sensor-based sorting, materials are mechanically sorted based on certain physical properties that are detected by a sensor (Dalm, 2013). Research has found that with NIR scanners it is possible to obtain a â&#x20AC;&#x2DC;fingerprintâ&#x20AC;&#x2122; of a sample that is directly related to its mineralogical composition. According to Woutruba et al. (2009), molecules absorb NIR radiation by means of electronic and vibrational transitions. Nowadays, there are many sensors available in the market that utilize different material properties; the choice of a sensor is dependent on the mineralogy of the ore. Traditional metallurgical techniques for diamond winning from kimberlitic ore involve size reduction, dense medium separation (DMS), and final recovery by X-ray technology (Ketelhodt et al., 2013). These techniques have no ability to remove waste rocks that are often associated with the kimberlite. The kimberlite orebody at Cullinan Diamond Mine (CDM) is intruded by sills and dykes of waste rock, and the current mining method cannot separate the waste material (Bartlett, 1994). Waste hoisted from underground is mostly from development areas. This paper evaluates the viability of the new COLOR/NIR sorting technology to remove the waste rocks from the kimberlite ore stream, thus reducing the amount of waste going into the DMS process.
Separation of kimberlite from waste rocks using sensor-based sorting :; 745+7.61/8 42)7#*473 In order to provide background information for sensor-based sorting, mineralogical characterization of a run of mine (ROM) sample from CDM was performed by X-ray diffraction (XRD). The primary use of XRD is for the identification and characterization of compounds based on their diffraction patterns.The sample, which had a top size of -70 mm, was reduced using a single toggle jaw crusher followed by ball milling. The XRD results are shown in Figure 1 and Figure 2. Both the kimberlite (Figure 1) and the waste (Figure 2) were found to contain NIR-active minerals, and there is thus the possibility of using NIR technology to discriminate between the two streams. Images (Figure 3) extracted from the classifier also showed a very good possibility of separating kimberlite from the associated waste materials. Classifiers are part of the NIR technology programme and are used to classify materials (Korsten, 2014).
(a)
(b)
Tests work was conducted with the Pro Secondary COLOR/NIR sorter illustrated in Figure 4. The sorter uses a combination of a high-resolution line camera and NIR scanner to provide accurate detection of the mineral fingerprint of each rock (Ketelhodt et al., 2013). The working width of the COLOR/NIR sorter is 1200 mm. The technical set-up of the sorter is shown in Figure 5. The sorter used was a chute-type sorter, with the material fed by a vibratory feeder and accelerated down a chute under gravity. Scanning is done by means of an NIR and a colour sensor on the free-falling stream of particles. Prior to the sorter, a washing/sizing screen with a 10 mm aperture size was installed for the purpose of particle preparation. Sizing was done to obtained a size ratio of 1:3, because research on
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Separation of kimberlite from waste rocks using sensor-based sorting sensor based technology has shown that the sorting results can deteriorate at a particle size ratio greater than three (Woutruba and Riedel, 2005). The material that was supplied for the test work was a 12 t sample of Cullinan ROM material. The waste rocks at CDM comprise of gabbro, norite, felsite, and quartzite. The sample, which was collected by means of a belt cut, was within the size range of -70+35 mm. The sorter needs to be programmed with information obtained from a pre-classified sample. Thus, a 10 kg sample of the kimberlites and waste material was collected from underground at Cullinan. Groups were formed by statistical means and applied into the sorting algorithm, called the classifier, for bulk sorting. The process flow diagram configuration shown in Figure 6 was tested with the aim of maximizing overall kimberlite recovery with a target of 5% kimberlite loss to the waste stream.
sensitivity reduces the aggressiveness of the machine with respect to its ejecting potential. In both the rougher and scavenger stage the kimberlite recovery was calculated to be above 95%, which clearly indicates that the COLOR/NIR sorter is able to discriminate between the CDM kimberlitic and waste rocks.
The overall results of the tests that were carried out only in the rougher stage are shown in Table I and Figure 7. The average kimberlite recovery was calculated to be 97.8%, while the average waste removal was calculated to be 90.2%
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The scavenger stage was used to recover the kimberlite misclassified into the waste stream from the rougher stage. Approximately 4.1% of the kimberlite is calculated to be lost at the rougher stage. Table II and Figure 8 show the results for the scavenger stage. The average kimberlite recovery was calculated to be 99.8% and the average waste removal was calculated to be 93.1%. The results clearly indicate that the introduction of a scavenger stage improves the separation efficiency and minimizes the potential for diamond loss. It is also seen that the kimberlite recovery decreases at a low classifier sensitivity. This is due to the fact that low classifier
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Figure 9 compares the kimberlite loss in the rougher and scavenger stages against the target kimberlite loss of 5%. The kimberlite lost to the waste stream was monitored to prevent the risk of diamond loss. There is a relatively high loss of the kimberlite ore when using only a rougher stage. However, introducing the scavenger stage minimized the risk of kimberlite loss to an average of 0.3%. The kimberlite lost was above target for tests 2, 3, and 8 because the agressiveness of the machine was kept low.
Figure 11 shows the average tons treated through the pilot plant for a period of 6 months (November 2014 to -April 2015) when the plant was running at full production. The total tonnage fed to the pilot plant was lower than the design tonnage of 50 000 t/ month, due to the fact that the availability and utilization of the pilot plant was lower than expected. The availability of the pilot plant was critical for successful assessment of the sensor-based sorter and economic evaluation. Throughout the duration of the project the tailings stream was sampled to monitor the average kimberlite loss. Kimberlite loss is an indication of potential diamond loss, and should be kept at a minimum. The acceptable kimberlite loss was set at a target of below 5%. Figure 12 shows the kimberlite loss during the pilot plant campaign. It was possible to keep the kimberlite loss below 5% for several months, but in January 2015 a high loss of ore occurred. It was decided to stop the sorter until the problem was found and rectified. The sorter was found to have lost programming and had to be re-programmed with preclassified samples. It was also realized that the kimberlite loss was above target when the screen sprays were blocked and the feed coated with mud. After the problem was rectified
5/268 /1.68 42#*)652. The feed to the pilot plant was the discharge from the scrubber, screened to -70+35 mm size. The main goal of the sorting in this case was to preconcentrate the -70+35 mm material prior to the DMS process. A lower waste content in the DMS feed would reduce the impact of near-density waste material on the cyclone dynamics; with the benefit of the reduction of waste material reporting to the DMS concentrate, which could have a detrimental impact on the subsequent Xray sorting processes. The pilot plant was run from September 2014 to April 2015. The commissioning process was complete within a month. Figure 10 illustrates the pilot plant flow sheet, where only the single pass configuration was implemented.
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Separation of kimberlite from waste rocks using sensor-based sorting BARLETT, P.J. 1998. Premier Mine. Proceedings of the 7th International Kimberlite Conference, Cape Town. pp. 39â&#x20AC;&#x201C;49. BERRY, L.G. and MASON, B. 1959. Mineralogy: Concepts, Description and Determinants. Springer, San Franciso. pp. 296â&#x20AC;&#x201C;298. CHADWICK, J. 2008. Process progress. International Mining, May 2008. pp. 24â&#x20AC;&#x201C;40. CHRISTON, J. 2014. Sensor based sorting technology implementation in the mining and mineral processing. Lund University, Sweden.
%50*478 2..10738647167#86(42*0(86(78 5/268 /1.6
COMMODASTULTRASORT. 2009. Sorters reduce mining costs and increase profits. pp. 34â&#x20AC;&#x201C;36. DALM, M. 2012. TA3690 â&#x20AC;&#x201C; Project on sensor based sorting of coppermolybdenum ore. pp. 1â&#x20AC;&#x201C;4. DEATH, D.L., CUNNINGHAM, A.P., and POLLARD, L.J. 2009. Multi-element and mineralogical analysis of mineral ores using laser breakdown spectroscopy. Spectrochimica Acta Part B. Atomic Spectroscopy, vol. 64, no. 10. pp. 1048â&#x20AC;&#x201C;1058. HARMON, R.S., DELUCIA, F.C., MCMANUS, C.E., MCMILLAN, N.J., JENKINS, T.F., WALSH, M.E., and MIZIOLEK, A. 2006. Laser-induced breakdown spectroscopy â&#x20AC;&#x201C; an emerging chemical sensor technology for real-time field-
%50*478 !5+&74/5678/2337386286(78615/5.038 6140768$5+&74/5678/233
portable, geochemical, mineralogical, and environmental applications. Applied Geochemistry, vol. 21, no. 5. pp. 730â&#x20AC;&#x201C;747.
the kimberlite loss was acceptable, as can be seen in Figure 12.
HOLLAS, J.M. 2004. Modern Spectroscopy. 5th edn. Wiley. Chapters 1â&#x20AC;&#x201C;3. ROBBEN, M., WOTRUBA, H., BALTHASA, D., and REHIMANN, V. 2009, NIR spectral imaging in the mineral processing industry. RWTH Aachen University,
2.)/*352. Based on the test work, the COLOR/NIR sorter is generally a good tool to separate Cullinan kimberlite from waste rocks. The introduction of a scavenger stage will improve the kimberlite recovery and also minimize diamond loss. The pilot plant test work results were not consistent since the sensing technology is based on the surface properties of the material, hence the feed needs to be clean and free of dust or mud prior to sorting. However, this is not always the case in a production environment, particularly for kimberlite ores, which have a high content of clay material. Due to the risk of diamond loss as a function of kimberlite lost, it is recommended that a scavenger stage be implemented in further kimberlite preconcentration processes using the same sorting system.
Germany. pp. 2â&#x20AC;&#x201C;5. ROBBINSON, D.N. 1973. Magnetite-serpentine-calcite dykes at Premier Mine and aspects of their relationship to kimberlite and to carbonatite of alkali carbonatite complexes. Physics and Chemistry of the Earth, vol. 9. pp. 61â&#x20AC;&#x201C;70. SALTER, J.D. and WYATT, N.P.G. 1991. Sorting in the mineral industry: past, present and future. Minerals Engineering, vol. 4, no. 7. p. 779â&#x20AC;&#x201C;796. Sassos, M.P. 1985. Mineral sorters. Engineering and Mining Journal, vol. 186, no. 6. pp 68â&#x20AC;&#x201C;72. SMITH, C.B. 1983. Pb, Sr, and Nd isotopic evidence for sources of southern African Cretaceous kimberlites. Nature, vol. 304, no. 5921. pp. 51â&#x20AC;&#x201C;54 TONG, Y, 2009. Technical amenability study of laboratory scale sensor-based
9)$.2 /7#07+7.63 The author wishes to express her gratitude to Cullinan Diamond Mine (Pty) Ltd for the opportunity and funding for the project. The deepest thanks are extended to my mentor and supervisor for their guidance and technical input, and to the CDM laboratory personnel for their assistance during the test work and analysis. The inputs from Mintek and Tomra Sorting (Pty) Ltd, South Africa, are also acknowledged.
ore sorting on a Mississippi Valley type lead-zinc ore, MASc thesis, Department of Mining Engineering, University of British Columbia. pp. 19â&#x20AC;&#x201C;20. WAGNER, P.A. 1914. The Diamond Fields of South Africa. Transvaal Leader, Johannesburg. 347 pp. WESTHYZEN, P., BOUWER, W., and JAKINS, A. 2013. Current trends in the development of new or optimization of existing diamond processing plants, with the focus on beneficiation. Journal of the Southern African
ASD Inc. 2010. Fieldspec3 User Manual,
Institute of Mining and Metallurgy, vol. 114. pp. 539â&#x20AC;&#x201C;545. WILLS, B.A. and NAPIER-MUNN, T. 2006. Mineral Processing Technology.
http://support.asdi.com/document/documents.aspx [Accessed 28 May
7th edn. Elsevier Science & Technology, Brisbane. Chapter 14,
2015].
pp. 372â&#x20AC;&#x201C;377.
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http://dx.doi.org/10.17159/2411-9717/2016/v116n4a8
An evaluation of the thermal fatigue performance of three alloys for casting mould applications by V. van der Merwe* and C.W. Siyasiya* Paper written on project work carried out in partial fulfilment of B. Eng. (Metallurgical Engineering)
A petrochemical company experiences premature thermal fatigue failure of the casting moulds used in catalyst production. The aim of the project was to find an alternative alloy that would outperform the current low-alloy cast steel used for the moulds. Based on their thermo-fatigue properties, 3CR12 ferritic stainless steel and H11 tool steel were chosen for testing and comparison with the currently used BS3100 B7 cast steel. Samples of each material were subjected to temperature cycling in a Gleeble 1500TM thermo-mechanical processing simulator, followed by surface analyses. The main parameters derived from the test work were the total true strain, the hot strength of the materials, and the number of cycles to failure. Additionally, the coefficient of thermal expansion for each material was measured using a Bähr dilatometer. H11 tool steel yielded the best performance by way of having the fewest surface cracks, the lowest total true strain per cycle, the most cycles to failure, the highest hot strength, and the lowest coefficient of thermal expansion. =) 7;+8 thermal fatigue, fatigue failure, casting moulds, thermal expansion.
?6<;7+35<976 The Catalyst Manufacturing Plant (CMP) is a dusty environment with temperatures higher than ambient. Molten mill scale (magnetite, Fe3O4) is tapped from the electric arc furnace into the casting moulds at temperatures close to 1600°C. After 10 seconds the magnetite is quenched with a water spray for 50 seconds to a minimum temperature of 400°C. Sometimes there is residual water in the pans from the cooling fog process (water sprays) in the empty mould. In a typical plant, the factory produces 40â&#x20AC;&#x201C;44 batches a day containing between 150â&#x20AC;&#x201C;300 moulds, depending on the time required for the specific batch (Buchholz, 2014). The typical batch in the CMP usually weighs about 6 t. The thickness of the tap, speed of the casting belt, and tilting angle all affect the number of moulds per batch. One of the main problems faced during the molten mill scale casting is the premature failure of the casting moulds. Cracks initiate on the surface of the mould, which is in contact with the hot catalyst, and propagate into the interior of the mould. Cracks are generally concentrated in the middle area of the mould where the catalyst makes first contact with the mould, and which experiences
,=;1:4>.:<9/3=>.:943;= All materials of construction are affected by thermal fatigue. This is a result of cyclic stresses caused by variations in temperature. The damage occurs under repeated thermal cycling in the form of cracking in the metal, specifically where relative movement (differential expansion) is constrained (American Petroleum Institute, 2011). The failure of the moulds in the current investigation can be classified as a low-cycle high-strain fatigue problem, typically with N < 104 cycles. The number of cycles to failure is
* University of Pretoria, Department of Materials Science and Metallurgical Engineering, Pretoria, South Africa. Š The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received Apr. 2016. VOLUME 116
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')67-898
the highest temperature fluctuations. This suggests that the cracks are caused by thermal fatigue during the casting process. In order to prolong the life of the mould and improve the operational efficiency, a recommendation for a new alloy or an improvement of the existing casting mould had to be made. In many instances, there are no service life records for specific moulds to track their life span, as well as no records regarding the surface temperatures of the mould during the heating and cooling cycle. The operating conditions and safety concerns make it impossible to measure the surface temperatures. Therefore, the temperature fluctuations can only be estimated. On average, the casting moulds last about 6 months in this operating environment. One of the primary indications that the mould has reached the end of its life is the sticking of the catalyst to the mould due to the enlarged surface area caused by the surface cracks, as seen in Figure 1. This type of surface is called the â&#x20AC;&#x2DC;elephant skinâ&#x20AC;&#x2122; and is caused by thermal fatigue.
An evaluation of the thermal fatigue performance of three alloys [2] where p is the plastic strain range, Nf is the number of cycles to failure (fatigue life), C2 is a constant and is the fatigue ductility exponent (generally -0.5 > < -0.7) (Coffin Jr., L.F., 1954; Manson, S.S., 1954)
-=;91=6<:4>-;75=+3;= The physical properties of the three steels that were investigated are given in Table I. The selection of 3CR12 and H11 steels was based on their melting points, coefficients of thermal expansion, and thermal conductivities. The chemical compositions of the steels are given in Tables II. The thermal fatigue simulation was carried out in a Gleeble 1500TM thermo-mechanical processing simulator. This apparatus enables the specimen to be subjected to either isothermal compression or tensile tests at elevated temperature. However, in this investigation, the specimens were subjected to temperature cycling without constraint. Three samples, 10 mm in diameter and 116.5 mm in length, were prepared of each material (Figure 2). The test zone at the centre of each sample was milled to a thickness of 7 mm for entire gauge length of 50 mm so as to create sharp corners simulating the edges of the mould. Two K-type
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fewer that in typical high-frequency low-cycle fatigue. In these casting moulds, the thermal fatigue failure is controlled by a cyclic plastic strain rather than a cyclic stress. The cyclic plastic strain results from the thermal stresses, which are a consequence of the temperature fluctuations during the casting process. The number of cycles to failure, Nf , for this type of fatigue failure can be predicted by the Coffin-Manson equation. This approach is similar to what is known as the Paris equation for the stable crack growth regime. The Paris equation for high-frequency low-cycle fatigue is [1] where C2 = Constant = Cyclic strain amplitude. Low-cycle fatigue test data are often represented as a plot of the plastic strain range versus cycles to failure. When plotted on log-log coordinates, a straight line is obtained, which is represented by the Coffin-Manson relation:
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Table I
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1427 1430â&#x20AC;&#x201C;1510
11.9 13.3 12.8
42 28.6 40
BS 3100 B7 H11 tool steel 3CR12 ferritic stainless steel
Table II
447)>571-789<9768 !> *
*;
6
7
9
*3
*7
'9
9
4
0.025
-
BS 3100 B74
0.17
2.25
0.75
1.00
0.4
-
-
0.35
-
-
-
3CR12b
0.019
11.01
0.81
0.03
-
0.1
0.02
0.72
0.13
0.017
0.08
0.022 0.012
H11c
0.37
4.95
0.36
1.26
0.22
0.13
0.01
1.08
-
0.019
0.95
0.023
-
$
*:
'
2
3
0.02
-
-
0.001
-
-
-
0.001
0.04
-
-
0.0014 0.003
(
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Fe 2014 bASTM A240 and EN 10088-2 (Columbus Stainless, 2015) cDu Toit, 2015 aBuchholz,
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An evaluation of the thermal fatigue performance of three alloys thermocouples were spot-welded onto each specimen: one in the middle and one further away from the centre of the specimen, to measure the temperature. Each test was run for 100 cycles over approximately 3 hours. In a case where the cracks appeared before 100 cycles were completed, the experiment was stopped prematurely. The temperature was fluctuated between 400 and 1200°C. In the first 50 seconds, the specimen was heated to 1200°C at a heating rate of 20°C/s, followed by another 10 seconds of soaking at the elevated temperature. The specimen was then cooled to 400°C at a cooling rate of 20°C/s. This cycle was repeated 100 times. After completion of the test, the surface of each specimen was examined for cracks or other irregularities. Photographs of the surface were taken, before and after cleaning with Hibatex solution to remove oxides, using a stereo microscope at magnifications of 12Ă&#x2014; and 15Ă&#x2014;. The data generated was used to calculate the total plastic strain in 100 cycles. Three tests were conducted for each steel, and an average value for the total plastic strain after 100 cycles was obtained. Equation 3 was used to calculate the total plastic strain, , after 100 cycles.
As expected, the surface of BS3100 B7 was heavily oxidized. After removing the oxides, cracks were exposed and were visible in the centre area in both longitudinal and transverse directions (Figure 3). 3CR12, in contrast, exhibited less oxidation than BS3100 B7. However, cracks were visible in the transverse direction in Figure 4. Strain marks (material flow lines) in the lengthwise direction were also present. No visible cracks or irregularities like strain markings or necking were observed in H11 (Figure 5). The specimen was still in sound condition after 100 cycles. Figure 6 shows a summary of the total plastic strain for each steel after 100 thermal fatigue cycles. The total true plastic strain per 100 cycles for BS3100 B7, 3CR12, and H11 was 0.148, 0.182, and 0.058 respectively. The total plastic strain represents the measure of resistance to thermal fatigue.
[3] where L is the change in length (m) and Lo is the gauge length of the specimen (m). The hot strength of the steels was determined at 1100°C through an isothermal hot compression test, see Figure 7. The strain was limited to 0.8 to avoid barrelling effects. The coefficient of thermal expansion was determined using the Bahr dilatometer. This test was done in accordance with ASTM E831-14 specifications. The thermal expansion coefficient is a material constant. It is the amount of expansion or contraction a material undergoes per kelvin during heating or cooling and is given by the following equation:
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[4] where dL = Change in length ( m) dT = Change in temperature respectively (°K) L = Total length of the specimen (m) = Thermal expansion coefficient ( m/m.°K) The thermal expansion coefficient should be as low as possible when the material is used to make moulds used in the casting process. The specimens were 5 mm in diameter and 10 mm long. Three of these specimens were machined for each alloy. The sample was heated to 1220°C (above AC3) at a heating rate of 0.25°C/s. The specimen was then soaked for 60 seconds and afterwards cooled to room temperature at a cooling rate equivalent to that of the heating rate. Lastly, Ac3 is the temperature at which ferrite completes its transformation to austenite during the heating up cycle.
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Figures 3, 4, and 5 show stereo micrographs for BS3100 B7, 3CR12, and H11 after 100 thermal cycles between 400 and 1200°C.
An evaluation of the thermal fatigue performance of three alloys Table III
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3CR12 H11
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1:1.3 1:3.1
13 931 35 478
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Table IV
The average number of cycles to failure for BS3100 B7, based on the industrial data, is 11 340 i.e. Nf (BS3100 B7) =11 340 cycles. The cycles to failure for 3CR12 and H11 are unknown. However, the ratios of the cycles to failure for BS3100 B7:3CR12 and BS3100 B7:H11 can be determined based on the total true strain per 100 cycles. The number of cycles to failure for 3CR12 and H11 can then be calculated by multiplying the respective ratios by Nf (BS3100 B7). The results are shown in Table III. Although H11 tool steel looks promising, it is more expensive than BS3100 B7. Therefore, before H11 can be recommended as an alternative material, a comprehensive cost benefit analysis would be required. Based on a rough calculation regarding the raw material cost, the cost of H11 is 3.5 times higher than that of BS3100 B7 (Table IV).
Figure 7 shows the Von Mises true stress versus true strain for the three steels. H11 exhibited the highest hot strength of 31 MPa. The hot strengths of 3CR12 and BS3100 B7 were lower than H11, and similar i.e. 16 and 18 MPa respectively.
": >1:<=;9:4>578<8>.7;>('&200>( > :6> :;+=! 02 >:6+> 22><774>8<==4> 49$:$:> ;73-!> 02 '<==4><)-= BS3100 B7 H11
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Figure 8 shows a typical dilatometer-generated plot of change in length versus temperature. The values for BS3100 B7, 3CR12, and H11 were found to be 15.8, 13.1, and 12.8 m/m°.C respectively.
*7654389768 The thermal fatigue behaviours of BS3100 B7, 3CR12, and H11 were compared under similar conditions. H11 had the lowest total true strain of 0.058 per 100 cycles, indicating that it had the highest resistance to thermal fatigue compared with 3CR12 and BS3100 B7. The mould life would be longer than for the other two steels, and was estimated to be about 35 478 cycles. However, before H11 tool steel can be recommended as an alternative material, a comprehensive cost analysis is required. Based on a rough calculation regarding the raw material cost, the cost of H11 is 3.5 times higher than that of BS3100 B7.
"=.=;=65=8 ALIBABA GROUP. 2015. Minerals & Metallurgy. http://www.alibaba.com/showroom/alloy-raw-material-price-h11-toolsteel.html [Accesed 18 October 2015]. AMERICAN PETROLEUM INSTITUTE. 2011. API recommended practice 571: Damage mechanisms affecting fixed equipment in the refining industry. 2nd edn. API Publishing Services, Washington. ASTM INTERNATIONAL. 1978. Metals Handbook: Properties and selection on irons steels. Benjamin, D. (ed.). Materials Park, OH. pp. 114â&#x20AC;&#x201C;116.
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ASTM International. 1980. Metals Handbook: Properties and selection on tool steels. Benjamin, D. (ed.). Materials Park, OH. ASTM INTERNATIONAL. 2015. ASTM E831. Standard test method for linear thermal expansion of solid materials by thermomechanical analysis. Materials Park, OH. AZO MATERIALS. 2014. Investigation of fatigue crack propagation in polymers. http://www.azom.com/article.aspx?ArticleID=11114 [Accessed 17 March 2016]. BUCHHOLZ, H. 2014. Catalyst Manufacturing Unit, Secunda. Personal communication and unpublished results. COFFIN JR., L.F. (1954), A study of the effects of cyclic thermal stresses on a ductile metal, Trans. ASME, vol. 76, pp. 931â&#x20AC;&#x201C;950. COLUMBUS STAINLESS. 2015. Unpublished results. Middelburg, South Africa. DU TOIT, W. 2015. Orion Engineering, Pretoria. Unpublished results. HERTZBERG, J.L. 2013. Deformation and Fracture Mechanics of Engineering Materials. 5th edn. Courier Westford, North Chelmsford, MA. MANSON, S.S. (1954), Behaviour of materials under conditions of thermal stress, NACA TN-2933, National Advisory Committee for Aeronautics STUMPF, W. 2014. Department of Materials Science and Metallurgical Engineering, University of Pretoria. Unpublished results. VAN AARDE, B. 2015. Steloy, Johannesburg. Personal communication.
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http://dx.doi.org/10.17159/2411-9717/2016/v116n4a9
The effect of particle size on the rate and depth of moisture evaporation from coal stockpiles by J. de Goede*, B. Muller*, Q.P. Campbell*, M. le Roux*, and C.B. Espag de Klerk*, Paper written on project work carried out in partial fulfilment of B.Eng. (Chemical Engineering with specialisation in mineral processing)
J.F. and Szladow, A.J. 1973) â&#x20AC;&#x201C; as well as by the porosity, heat conductivity, and chemical nature of the coal particles (Karthikeyan, M., Zhonghua, W., and Mujumdar, A.S. 2009). Moisture from a coal stockpile surface will evaporate until equilibrium is reached between the ambient atmosphere and the coal particles. When the relative humidity increases as the temperature decreases, the coal particles can reabsorb moisture to re-establish equilibrium (de Korte, G.J. and Mangena, S.J. 2004; Karthikeyan, M., Zhonghua, W., and Mujumdar, A.S. 2009). This process of desorption and reabsorption can be repeated on a daily cycle(de Korte, G.J. and Mangena, S.J. 2004).
1 "' #(# Excessive amounts of moisture in product coal can influence the efficiency of downstream utilization processes due to a decreased calorific value and handling problems. Stockpiles can be used to decrease the moisture content of coal by means of gravity drainage and evaporation. This paper is focused on the evaporation of moisture from a coal stockpile surface with the aim of investigating the effect of particle size on the rate of evaporation as well as the depth to which evaporation extends. It was observed that moisture initially evaporates at a higher rate from a stockpile consisting of fine particles (-6.7 mm) than from coarser particles (-13.2 mm +6.7 mm). This high rate of evaporation is restricted to the outer shell of the fine coal stockpile. However, for coarse coal, the porous nature increases the depth at which evaporation occurs. Evaporation of moisture was observed up to the fourth day of each experimental run, after which steady state was obtained. It was shown the water can evaporate from the surface into the body of the stockpile, depending on the coal particle size and void spacing. An experimental reclaim depth of 0.4 m was achieved after 4 days.
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-"%$' %('" Coal stockpiles serve as surge capacity for downstream utilization processes and can also be used for moisture reduction by means of gravity drainage and evaporation. Excessive amounts of moisture in coal can cause handling problems and, most importantly, will decrease the calorific value, leading to inefficient combustion. Research has shown that evaporation by means of wind and solar action is considerably more effective than gravity drainage(Williams, D.J. 2006), but the effect is limited to a restricted depth from the exterior of the stockpile (Boyapati, E. and Oates, A. 1994; CSEM-UAE, 2010). The effectiveness of wind and solar action can be improved by orienting the stockpile perpendicular to the predominant wind direction, maximizing the surface area of the pile, and reclaiming the coal from the pile gradually in shallow cuts over a large area (Williams, D.J. 2006). The extent of evaporation is mainly influenced by the weather â&#x20AC;&#x201C; in particular solar radiation, temperature, wind strength, and relative humidity (Deodhar, M.J. 2008; Fryer,
Washed South African bituminous coal from the Witbank No. 2 seam was used for the experiments. The proximate analysis of the coal can be seen in Table I. The coal was used as received and was sieved into three size ranges: fine (-6.7 mm), total range (-13.2 mm), and coarse (-13.2 mm + 6.7 mm).
, )$( )"%&!* )% ' The objective of this investigation was to establish the effect of coal bed particle size on
Table I
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Inherent moisture content Ash content Volatile matter Fixed carbon
2.6 15.9 25.2 56.4
* School of Chemical and Minerals Engineering, North-West University, Potchefstroom, South Africa. Š The Southern African Institute of Mining and Metallurgy, 2016. ISSN 2225-6253. Paper received Feb 2016.
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.) '$ # coal, stockpile, dewatering, depth of evaporation, rate of evaporation.
The effect of particle size on the rate and depth of moisture evaporation from coal the rate and depth of moisture evaporation. The investigation was divided into two parts. In both cases saturated samples of the three different size ranges were prepared. The first experiment was designed to determine the depth to which evaporation extends. The samples were loaded into sectioned PVC pipes, using 12 pipes for each size range, and placed outside for 10 to 12 days and exposed to ambient conditions to facilitate the process of evaporation. In the second experiment, coal samples were placed in three shallow containers to investigate the rate at which moisture evaporates from a coal stockpile surface. These samples were exposed to ambient conditions while the masses of the containers were continuously measured. The experimental set-up included a weather station that continuously measured temperature, relative humidity, and wind speed and direction.
oven at a constant pressure of 101.3 kPa and temperature of 105â&#x20AC;&#x201C;110°C. for 6 hours. The inherent moisture content of the coal was determined by difference. The evaporation rate (experiment 2) was determined by analysing the data from the data logger of the load cells and the weather station.
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The PVC pipes for the first experiment were cut into seven 0.1 m sections and connected with duct tape as seen in Figure 1. The shallow containers for the second experiment, with dimensions of 34 cm Ă&#x2014; 25 cm Ă&#x2014; 20 cm, were placed on load cells that continuously recorded the weight of the containers. This set-up can be seen in Figure 2. Both structures were covered with Perspex roofs.
From Figure 3, a sharp decrease in total moisture content is noted from start-up to day two. This is due to drainage of moisture under gravity . From day two to day four, evaporation occurred from the top 0.2 m below the surface. From Figure 3 it can be seen that the coal samples reached steady state at day four, after which the total moisture content remained relatively constant until day twelve. This is an indication that no surface moisture is available to evaporate into the atmosphere. The void spacing of the coal bed had a major influence on the depth to which evaporation occurs. The coarse (-10 mm +6.7 mm) coal bed was more porous than the fine (-6.7 mm) coal bed. It was found that evaporation took place up to 0.4 m below the surface of the coarse coal bed, and that only the surface of the fine coal bed showed signs of evaporation.
To determine the depth to which evaporation occurs, one PVC pipe containing each particle size of coal was removed on a daily basis for moisture analysis. The coal samples from each section of the three pipes were removed and weighed, then dried for 72 hours in a climate-controlled room at a constant temperature of 22°C and a constant relative humidity of 40%, and re-weighed. The samples were then placed in a vacuum
Figure 4 illustrates the cyclic behaviour in the mass loss profile of each size range. Evaporation generally occurred from 09:00 to 17:00 when the temperatures were high and the relative humidity low. As evening fell, the temperature decreased and the relative humidity increased, resulting in the reabsorption of moisture into the porous coal particles as the particles tried to stay in equilibrium with the atmosphere.
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It can be seen that all coal samples reached the same moisture content by the end of the experimental run. The coarse coal sample reached the final moisture content first. To compare the effect of particle size on the rate of evaporation, the daily rates of evaporation were calculated for each size range as shown in Figure 5. It can be seen that moisture initially evaporates faster from the fine coal sample (-6.7 mm) than from the other coal samples. After two days, the surface of the fine coal sample was dry and the rate of evaporation decreased. The same phenomenon was seen in the experiments that investigated the depth to which evaporation occurs. This is attributed to the porous structure of the coarse sample. During the investigation, it was found that the initial moisture content had an influence on the rate of evaporation. A lower initial moisture content resulted in a lower maximum rate of evaporation.
University (NWU). The research was supported by the South African Research Chairâ&#x20AC;&#x2122;s Initiative of the Department of Science and Technology and the National Research Foundation of South Africa (NRF). Any opinion, finding, or conclusion or recommendation expressed in is that of the authors and the NRF does not accept any liability in this regard.
0) )$)" )#** BOYAPATI, E. and OATES, A. 1994. A mathematical model for stockpile management. 6th International Working Conference on Stored-product Protection, Canberra, Australia, 17â&#x20AC;&#x201C;23 April 1994. pp. 684â&#x20AC;&#x201C;688.
CSEM-UAE INNOVATION CENTER. 2010. Water evaporation rate at Ras-AlKhaimah, UAE. http://www.csem-uae.com/pdfs/Water%20Evaporation% 20rate%20%20in%20Ras-Al-Khaimah,%20UAE [Accessed 18 June 2014].
'" ! #('"# This study showed that bed particle size affects the extent of moisture evaporation, and that the porous structure of a coarse coal stockpile aids the process. Experimental results indicate that moisture drainage takes place within the first two days of exposure to environmental conditions. Evaporation of moisture can be seen up to the fourth day, but this is a function of the initial moisture content of the coal. Coal with a higher initial moisture content will take a longer time to lose all surface moisture. It was shown that water can evaporate from underneath the surface of coal stockpiles. Increased void spacing has a positive influence on the effectiveness of evaporation for coal stockpile drying. The results obtained in this study can be used to manage stockpiles efficiently. Up to 0.4 m of coal can be reclaimed from the stockpile surface and the remaining coal can be left to dry for another four days â&#x20AC;&#x201C; if no rain occurs.
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KORTE, G.J. and MANGENA, S.J. 2004. Thermal Drying of Fine and Ultra-fine Coal. CSIR.Fryer, J.F. and Szladow, A.J. 1973. Storage of coal samples. Alberta Geological Survey, Edmonton.
DEODHAR, M.J. 2008. Elementary Engineering Hydrology. Pearson Education, India. Dorling Kindersley.
KARTHIKEYAN, M., ZHONGHUA, W., and MUJUMDAR, A.S. 2009. Low-rank coal drying technologies-current status and new developments. Drying Technology, vol. 27. pp. 403â&#x20AC;&#x201C;145.
PRIYAL, D. and TOERIEN, A. 2010. The effect of salinity on evaporation rates of brines resulting from the treatment of mine water.http://www.google.co.za/url?sa=t&rct=j&q=&esrc=s&source= web&cd=1&cad=rja&uact=8&ved=0CCcQFjAA&url=http%3A%2F%2Fww
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The authors would like to thank the following institutions for their contributions towards this project:
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WILLIAMS, D.J. 2006. Application of Unsaturated Soil Mechanics to Product Coal Dewatering. Australian Mining Technology Conference, Hunter Valley, NSW, 26â&#x20AC;&#x201C;27 September 2006. VOLUME 116
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For more information contact 011-620 1500 or your nearest BMG branch.
INTERNATIONAL ACTIVITIES 2016
18â&#x20AC;&#x201C;19 May 2016 â&#x20AC;&#x201D; Aachen International Mining Symposia (AIMS 2016) First International Conference Mining in Europe Aachen, Germany Contact: Conference Organisation of AIMS Tel: +49-(0)241-80 95673, Fax: +49-(0)241-80 92272 E-mail: aims@mre.rwth-aachen.de Website: http://www.aims.rwth-aachen.de 21â&#x20AC;&#x201C;28 May 2016 â&#x20AC;&#x201D; ALTA 2016 Perth, Western Australia Contact: Allison Taylor Tel: +61 (0) 411 692 442, E-mail: allisontaylor@altamet.com.au Website: http://www.altamet.com.au 9â&#x20AC;&#x201C;10 June 2016 â&#x20AC;&#x201D; New technology and innovation in the Minerals Industry Colloquium Emperors Palace, Johannesburg Contact: Camielah Jardine Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: camielah@saimm.co.za, Website: http://www.saimm.co.za 27â&#x20AC;&#x201C;28 June 2016 â&#x20AC;&#x201D; The 2nd School on Manganese Ferroalloy Production Johannesburg Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za 19â&#x20AC;&#x201C;20 July 2016 â&#x20AC;&#x201D; Innovations in Mining Conference 2016 â&#x20AC;&#x2DC;Redesigning the Mining and Mineral Processing Cost Structureâ&#x20AC;&#x2122; Holiday Inn Bulawayo Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za 25â&#x20AC;&#x201C;26 July 2016 â&#x20AC;&#x201D;Production of Clean Steel Mintek, Randburg Contact: Camielah Jardine Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: camielah@saimm.co.za, Website: http://www.saimm.co.za 31 Julyâ&#x20AC;&#x201C;3 August 2016 â&#x20AC;&#x201D; Hydrometallurgy Conference 2016 â&#x20AC;&#x2DC;Sustainability and the Environmentâ&#x20AC;&#x2122; in collaboration with MinProc and the Western Cape Branch Belmont Mount Nelson Hotel, Cape Town Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za 16â&#x20AC;&#x201C;18 August 2016 â&#x20AC;&#x201D; The Tenth International Heavy Minerals Conference â&#x20AC;&#x2DC;Expanding the horizonâ&#x20AC;&#x2122; Sun City, South Africa Contact: Camielah Jardine
Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: camielah@saimm.co.za, Website: http://www.saimm.co.za 31 Augustâ&#x20AC;&#x201C;2 September 2016 â&#x20AC;&#x201D; MINESafe Conference Striving for Zero Harm Emperors Palace, Hotel Casino Convention Resort Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za 12â&#x20AC;&#x201C;13 September 2016 â&#x20AC;&#x201D; Mining for the Future 2016 â&#x20AC;&#x2DC;The Future for Mining starts Nowâ&#x20AC;&#x2122; Electra Mining, Nasrec, Johanannesburg Contact: Camielah Jardine Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: camielah@saimm.co.za, Website: http://www.saimm.co.za 12â&#x20AC;&#x201C;14 September 2016 â&#x20AC;&#x201D; 8th International Symposium on Ground Support in Mining and Underground Construction Kulturens Hus â&#x20AC;&#x201C; Conference & Congress, LuleĂĽ, Sweden Contact: Erling Nordlund Tel: +46-920493535, Fax: +46-920491935 E-mail: erling.nordlund@ltu.se, Website: http://groundsupport2016.com 19â&#x20AC;&#x201C;21 October 2016 â&#x20AC;&#x201D; AMI Ferrous and Base Metals Development Network Conference 2016 Southern Sun Elangeni Maharani, KwaZulu-Natal, South Africa Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za 25 October 2016 â&#x20AC;&#x201D; The Young Professionals Week, 14th Annual Student Colloquium Mintek, Randburg Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za
2017 25â&#x20AC;&#x201C;28 June 2017 â&#x20AC;&#x201D; Emc 2017: European Metallurgical Conference Leipzig, Germany Contact: Paul-Ernst-StraĂ&#x;e Tel: +49 5323 9379-0, Fax: +49 5323 9379-37 E-mail: EMC@gdmg.de, Website: http://emc.gdmb.de 27â&#x20AC;&#x201C;29 June 2017 â&#x20AC;&#x201D;4th Mineral Project Valuation Mine Design Lab, Chamber of Mines Building, The University of the Witwatersrand, Johannesburg Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za 2â&#x20AC;&#x201C;7 October 2017 â&#x20AC;&#x201D;AfriRock 2017: ISRM International Symposium â&#x20AC;&#x2DC; Rock Mechanics for Africaâ&#x20AC;&#x2122; Cape Town Convention Centre, Cape Town Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za
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17â&#x20AC;&#x201C;18 May 2016 â&#x20AC;&#x201D; The SAMREC/SAMVAL Companion Volume Conference Emperors Palace, Johannesburg Contact: Raymond van der Berg Tel: +27 11 834-1273/7, Fax: +27 11 838-5923/833-8156 E-mail: raymond@saimm.co.za, Website: http://www.saimm.co.za
Company Affiliates The following organizations have been admitted to the Institute as Company Affiliates 3 M South Africa
Engineering and Project Company Ltd
Namakwa Sands (Pty) Ltd
AECOM SA (Pty) Ltd
eThekwini Municipality
New Concept Mining (Pty) Limited
AEL Mining Services Limited
Exxaro Coal (Pty) Ltd
Northam Platinum Ltd - Zondereinde
Air Liquide (PTY) Ltd
Exxaro Resources Limited
Outotec (RSA) (Proprietary) Limited
AMEC Mining and Metals
Fasken Martineau
PANalytical (Pty) Ltd
AMIRA International Africa (Pty) Ltd
FLSmidth Minerals (Pty) Ltd
ANDRITZ Delkor(Pty) Ltd
Fluor Daniel SA (Pty) Ltd
Paterson and Cooke Consulting Engineers (Pty) Ltd
Anglo Operations Ltd
Franki Africa (Pty) Ltd Johannesburg
Anglo Platinum Management Services (Pty) Ltd
Fraser Alexander Group
Precious Metals Refiners
Geobrugg Southern Africa
Anglogold Ashanti Ltd
Polysius A Division Of Thyssenkrupp Industrial Solutions (Pty) Ltd
Rand Refinery Limited
Glencore
Atlas Copco Holdings South Africa (Pty) Limited
Goba (Pty) Ltd
Aurecon South Africa (Pty) Ltd
Hall Core Drilling (Pty) Ltd
Aveng Moolmans (Pty) Ltd
Hatch (Pty) Ltd
Axis House (Pty) Ltd
Herrenknecht AG
Bafokeng Rasimone Platinum Mine
HPE Hydro Power Equipment (Pty) Ltd
Barloworld Equipment -Mining
Impala Platinum Limited
BASF Holdings SA (Pty) Ltd
IMS Engineering (Pty) Ltd
Bateman Minerals and Metals (Pty) Ltd
Ivanhoe Mines SA
Salene Mining (Pty) Ltd
BCL Limited
JENNMAR South Africa
Becker Mining (Pty) Ltd
Joy Global Inc. (Africa)
Sandvik Mining and Construction Delmas (Pty) Ltd
BedRock Mining Support (Pty) Ltd
Kadumane Manganese Resources
Sandvik Mining and Construction RSA(Pty) Ltd
Bell Equipment Company (Pty) Ltd
Leco Africa (Pty) Limited
SANIRE
Blue Cube Systems (Pty) Ltd
Longyear South Africa (Pty) Ltd
Sasol Mining(Pty) Ltd
Bluhm Burton Engineering (Pty) Ltd
Lonmin Plc
Blyvooruitzicht Gold Mining Company Ltd
Lull Storm Trading (PTY)Ltd T/A Wekaba Engineering
BSC Resources
Redpath Mining (South Africa) (Pty) Ltd Rosond (Pty) Ltd Royal Bafokeng Platinum Roymec Tecvhnologies (Pty) Ltd
Rustenburg Platinum Mines Limited SAIEG
Sebilo Resources (Pty) Ltd
Shaft Sinkers (Pty) Limited
Magotteaux(PTY) LTD
Caledonia Mining Corporation
Sibanye Gold (Pty) Ltd
MBE Minerals SA Pty Ltd
CDM Group
Smec SA
MCC Contracts (Pty) Ltd
CGG Services SA
SMS Siemag South Africa (Pty) Ltd
MDM Technical Africa (Pty) Ltd
Chamber of Mines
Metalock Industrial Services Africa (Pty)Ltd
Concor Mining
SENET Senmin International (Pty) Ltd
Magnetech (Pty) Ltd
CAE Mining (Pty) Limited
Runge Pincock Minarco Limited
Sound Mining Solutions (Pty) Ltd
Metorex Limited
South 32
Metso Minerals (South Africa) (Pty) Ltd
SRK Consulting SA (Pty) Ltd
Minerals Operations Executive (Pty) Ltd
Technology Innovation Agency
MineRP Holding (Pty) Ltd
Time Mining and Processing (Pty) Ltd
Department of Water Affairs and Forestry
Mintek
Tomra Sorting Solutions Mining (Pty) Ltd
Digby Wells and Associates
MIP Process Technologies
Ukwazi Mining Solutions (Pty) Ltd
Downer EDI Mining
Modular Mining Systems Africa (Pty) Ltd
Umgeni Water
DRA Mineral Projects (Pty) Ltd
MSA Group (Pty) Ltd
VBKOM Consulting Engineers
DTP Mining
Multotec (Pty) Ltd
Webber Wentzel
Duraset
Murray and Roberts Cementation
Weir Minerals Africa
Elbroc Mining Products (Pty) Ltd
Nalco Africa (Pty) Ltd
WorleyParsons (Pty) Ltd
Concor Technicrete Council for Geoscience Library CSIR-Natural Resources and the Environment
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Educating and leading mining engineers to become Imagineers The broad-based curriculum of the Department of Mining Engineering at the University of Pretoria, emphasises the international engineering education model of conceptualising, designing, implementing and operating mines. :H RÎ?HU D UDQJH RI SURJUDPPHV Č? 8QGHUJUDGXDWH 3URJUDPPHV >$FFUHGLWHG E\ WKH (QJLQHHULQJ &RXQFLO RI 6RXWK $IULFD (&6$ @ Č? 3RVWJUDGXDWH 3URJUDPPHV Č? 5HVHDUFK 3URJUDPPHV Č? &RQWLQXHG 3URIHVVLRQDO 'HYHORSPHQW &3' &RXUVHV $ GHJUHH IURP WKLV 'HSDUWPHQW FRYHUV DOO DVSHFWV RI PLQLQJ HQJLQHHULQJ Č&#x192; IURP SUH IHDVLELOLW\ DVVHVVPHQWV WR FORVXUH RI PLQHV ZKHWKHU LW EH KDUG URFN RU FRDO GHSRVLWV VXUIDFH RU XQGHUJURXQG RSHUDWLRQV 7KH GHYHORSPHQW RI PDQDJHPHQW DQG SHRSOH VNLOOV DUH LQFRUSR UDWHG LQ VRPH RI WKH Č´QDO \HDU PRGXOHV LQ WKH XQGHU JUDGXDWH SURJUDPPH
7KH 'HSDUWPHQW KRVWV WKH Č´UVW LQ $IULFD .XPED 9LUWXDO 5HDOLW\ &HQWUH IRU 0LQH 'HVLJQ DV ZHOO DV WKH 0LQLQJ 5HVLOLHQFH 5HVHDUFK Î&#x2013;QVWLWXWH DW LWV VWDWH RI WKH DUW IDFLOLWLHV 7KH SRUWIROLR RI XQGHUJUDGXDWH SRVWJUDGXDWH DQG UHVHDUFK GHJUHH SURJUDPPHV SURYLGH DQ H[FHOOHQW EDVLV IRU D UHZDUGLQJ FDUHHU LQ PLQLQJ For more information contact the Head of Department: 3URI 5RQQ\ :HEEHU <RXQJPDQ 7HO (PDLO GDOHHQ JXGPDQ]#XS DF ]D