Bulk August 2019 by Promech Publishing

BULK

HANDLING Endorsed by: CMA l LEEASA l SAIMechE l SAIMH

T O D A Y

Aug 2019

ZERO BEARING FAILURE CONVEYOR MONITORING

ELB Promise Right Job

Right Time

Right Way

Scan Me Download any QR reader/scanner from the Google Play or Apple App Store

Premiertrak 600 Distribution and Product Support

elb@elbquip.co.za

Branches and Dealers throughout Southern Africa

+27 (0)11 306 0700

www.elbequipment.co.za

BULK

HANDLING Endorsed by: CMA l LEEASA l SAIMechE l SAIMH

T O D A Y

Aug 2019

BULK D

ZERO BEARING FAILURE CONVEYOR MONITORING

Aug 2019

T O D A Y

Contents On the cover: Demag Tel: (011) 898-3500 Email: Richard.roughly@ demagcranes.co.za. www.demagcranes.com

CMA News 4 5

Effective Tool

Company Profile From the Desk

22 Discrete Element Modelling: Overcoming the Challenges

Cover Story 6

Kbk Light Crane Systems Flexible and Affordable

Market Forum

Conveying

Endorsing Bodies

•

CMA (Conveyor Manufacturers Association)

Bearings

•

LEEASA (Lifting Equipment Engineering Association of South Africa)

•

SAIMechE (SA Institution of Mechanical Engineering)

16 Considerations When Making a Purchase

•

SAIMH (SA Institute of Materials Handling)

Lifting

•

also mailed to members of the RFA (Road Freight Association)

Maximum Uptime Thanks to Technology 10 Optimising Belt Cleaning

12 Zero Failure

Mineral Sampling

15 The Key to Success

Cranes

19 Two South Africans on International Crane Support Team

All rights reserved. No editorial matter published in “Bulk Handling Today” may be reproduced in any form or language without written permission of the publishers. While every effort is made to ensure accurate reproduction, the editor, authors, publishers and their employees or agents shall not be responsible or in any way liable for any errors, omissions or inaccuracies in the publication, whether arising from negligence or otherwise or for any consequences arising therefrom. The inclusion or exclusion of any product does not mean that the publisher or editorial board advocates or rejects its use either generally or in any particular field or fields.

Our e-mail address is bulkhandling@promech.co.za Visit our website on www.bulkhandlingtoday.co.za

The monthly circulation is 3 673

Proprietor and Publisher: PROMECH PUBLISHING Tel: (011) 781-1401 E-mail: bulkhandling@promech.co.za www.promech.co.za Managing Editor: Susan Custers Advertising Sales: Louise Cresswell DTP: Sanette Badenhorst Administration: Netta Janse van Rensburg Subscriptions: Please email us at accounts@promech.co.za if you wish to subscribe to “Bulk Handling Today” at R550,00 (excl postage and VAT) per year; R1 380,00 per year for Africa/Overseas. Printed by: Typo Colour Printing, Tel: (011) 402-3468 FSC (Forestry Stewardship Accreditation)

BULK HANDLING TODAY

August 2019

COMPANY PROFILE

REMA TIP TOP Rema Tip Top is a market leader, offering high quality products and services, within the rubber industry.

tate-of-the-art technology and pioneering innovations deliver a product that is customer centric, ensuring sustainability of our customers’ operation and in turn our organisation. Our international sales and service network offers a wide range of effcient services and maximum customer proximity. Our products and service systems are tailored especially to the customers' needs providing economically effcient and technically proven solutions. The customer profits from a differentiated product range and optimum all-round customer care by our qualified specialists. With a history dating back to the 1900s, in South Africa, we are fortunate to have obtained several industry-leading blue-chip customers who take advantage of the company's expanding product offering. Gone are the days of simply supplying a core product. Due to the quality of product, the saving for the customer is far greater in the long term and this is what gives us a competitive edge. In support of this vision to ultimately become an integrated solution provider, and with the understanding that our products are a lifeline to our customers operations, we continue to be active in our R&D division creating innovative solutions. We

SERVICE

MATERIAL PROCESSING

SURFACE PROTECTION

SOUTH AFRICA Benoni Plant 22 - 24 Lincoln Road, Industrial Site, Benoni +27 11 741 2500 ZIMBABWE 145 Kwame Nkrumah Avenue, Harare, Zimbabwe Tel: +263 4 707038 / 706458 Email: info@rematiptop.co.zw

BULK HANDLING TODAY

Conveyor belting

Our Conveyor Belting Portfolio of products and service systems are tailored to the customers’ needs providing economically efficient and technically proven solutions.

Material processing

The use of specific Rema Tip Top products lengthens the service life of conveying and processing plant and reduces downtime. Special products optimize operational readiness, increase production capacities and thus maximize profit for the plant operator.

Surface protection

Where chemicals and abrasive materials cause damage to containers, pipes, valves etc, we offer a “onestop shop” corrosion and wear protection solution.

Automotive

As the worldwide market leader in the tyre repair systems sector, we offer specialist operators everything they require for tyres and wheels, while our cooperation with famous tyre manufacturers and suppliers of retreads always ensures innovative high-quality solutions.

AUTOMOTIVE

Howick Plant 1 Induna Mills Road, Howick, Kwazulu Natal +27 33 239 7200

MOZAMBIQUE Unit 4 Bairo Bagamoyo, EN7 Zona Industrial Moatize, Mozambique Tel: +258 25 242230 /242241 Email: info@rematiptop.co.mz

August 2019

now provide a more integrated customer centric solution. One of our breakthrough innovations, focusing on our customer needs to reduce downtime in their operations, has been the use of technology to create monitoring solutions, increasing transparency and efficiency of our maintenance offering.

MADAGASCAR 76 Rue De Lattre De Tasigny, Toamasina Bp 97 501 Toamasina Tel: +2613 481 55858 Email: info@rematiptop.co.mg

info@rematiptop.co.za www.rema-tiptop.co.za ZAMBIA Plot 3709, Mansa Road, Light Industrial Area, Kitwe Tel (ofﬁce): +260 967 688 233 Tel (sales): +260 963 474 777 Email: admin@rematiptop.co.zm

MAURITIUS Villa Intemporelles Chemin Vingt Piends, Grand Baie Tel: +261 34 815 5858 Email: Anthony@rematiptop.mg

CONVEYOR MANUFACTURERS ASSOCIATION

From The Chairman’s Desk

eltcon 20 was the highlight of last month, with 18 papers of exceptional quality and very topical to the 160 people who attended. Of special interest were the local research papers. One was on assessing the braking performance of uni-directional idlers, and the other was on induced belt stress local to the idler junction due to the effect of idler support configuration. A third research paper on idlers came from the University of Newcastle research team and this assessed the influence of skewed idler rolls. There were six papers on six different types of conveyors: Ropecon, Flying belt, Pipe conveyors, Adder Snake, Long overlands and rail-based systems. The rest of the programme highlighted belt feeder hoppers, belt flexure resistance, gearless drives, pulley design, lessons learnt on 17 years of in-pit crushing projects, as well as the role of health and safety standards and finally, advances in technology.

Jay Pillay

The exhibition was well supported with exhibitors reporting useful contacts made and good exposure to their customers and potential customers. All in all it was a great Beltcon and we look forward with anticipation to another conference in 2021. The CMA Annual General Meeting was held on 20 August and a warm welcome is extended to the incoming Board: Henk Brink (CedoTech), Nealon Burger (DRA), Simon Curry (Flexco), Trevor du Toit (Ringspann), Jay Pillay (Brelko), Dave Pitcher (Dunlop), Graeme Skeen (Dymot), Jacques Swart (Worley) and Mpho Tshidzumba (Hatch). Welcome to our new members: Magnet Service Binder SA cc, represented by Mathew Visser and Marco Paschkewitz; Leoka Engineering represented by Themba Xhamfu and Tumelo Malefahlo; and Electromote (Pty) Ltd, represented by Geoffrey Ruis and Brian Campbell. Looking forward to a mutually beneficial relationship between each and the CMA. Jay Pillay Chairman

Membership at August 2019 All members subscribe to the CMA Code of Ethics Acrow Limited Actom Afripp Projects Altra Industrial Motion South Africa (Pty) Ltd Bauer Bearings International Belt Brokers Belting Supply Services BMG Bonfiglioli Power Transmissions Bosworth Brelko Conveyor Products CedoTech cc Closeal Manufacturing Collisen Engineering ContiTech South Africa (Pty) Ltd Conveyor Watch (Pty) Ltd Conveyor & Engineering Equipment CT Systems David Brown Gear Industries DRA Projects SA (Pty) Ltd Dunlop Belting Products Dymot Engineering Company

ELB Engineering Services Electromote (Pty) Ltd Fenner Conveyor Belting (South Africa) Flexco SA (Pty) Ltd FLSmidth Roymec Giza Technologies (Pty) Ltd Habasit South Africa (Pty) Ltd Hägglunds Drives South Africa Hatch Africa (Pty) Ltd HMA South Africa (Pty) Ltd Hosch - Fördertechnik (SA) International Belting & Marketing (Pty) Ltd Iptron Technology cc KevConBelt (Pty) Ltd Leoka Engineering Lesa Mining Equipment and Conveyor Belt Lorbrand Magnet Service Binder CC Martin Engineering Megaroller Melco Conveyor Equipment Merlin consulting (Pty) Ltd Moret Mining Nautilus Projects (Pty) Ltd

Nepean Conveyors OE Bearings Oriental Rubber Industries SA Osborn Engineered Products Pegasus Industrial Services cc Regal Beloit South Africa Rema Tip Top South Africa Ringspann South Africa Rossi Gearmotors (Pty) Ltd Rula Bulk Materials Handling SENET SEW Eurodrive Shaft Engineering (Pty) Ltd SKF South Africa Tenova Takraf ThyssenKrupp Industrial Solutions South Africa (Pty) Ltd Timken South Africa (Pty) Ltd Transvaal Rubber Company Voith Turbo Weba South Africa (Pty) Ltd WorleyParsons RSA Zest Electric Motors

BULK HANDLING TODAY

August 2019

COVER STORY

Kbk Light Crane Systems – Flexible and Affordable Super light, highly flexible and affordable, Demag’s KBK Light Crane Systems are easily adaptable to customers’ individual lifting requirements.

aunched 50 years ago, they have been perfected over time and with their modular system can be combined to create individual suspension monorail, suspension crane, pillar and wall-mounted slewing jib crane solutions. They can also be modified at any time and be integrated easily into any production line.

Design almost any overhead suspension crane or monorail system with outstandingly smooth operation One of the most popular in South Africa is the KBK Aluline Light Crane system. The extremely low weight aluminium overhead crane system enables the design of almost any overhead suspension crane or monorail system with outstandingly smooth operation.

Right solution

KBK Aluline is the light-weight element of our KBK light crane system – and the right solution wherever a track and crane installation has to provide high performance for a low weight. It is used in a very wide range of applications. The aluminium overhead crane system enables you to design almost any overhead suspension crane or monorail system with outstandingly smooth operation.

BULK HANDLING TODAY

August 2019

Single or double-girder suspension cranes from our KBK light crane system enable you to achieve fast and reliable area-serving overhead handling and exact positioning of a wide variety of goods. Larger loads can also be moved beyond the crane runway using overhang and extending cranes from our KBK light crane system. These cranes are fitted with crane girders that extend beyond the width of the crane runway, up to 2 500mm beyond the runway span.

Versatility

Our KBK manipulator cranes are an outstanding example for the versatility of our KBK light crane system. They can be designed to meet the exact needs of a wide variety of loads, processes and production conditions. They reliably accommodate kick-up forces with great positioning accuracy and at high operating speeds. Another option is the KBK suspension monorail from our KBK light crane. This system is specifically designed for linear, overhead handling for complex installations.

Quick and easy

Manually handling and combining or moving relatively light loads is often not only time-consuming, but also time consuming for employees. Together with a wide selection of hoist units, our pillar mounted slewing jibs and cranes installed direct at the workplace enable all types of work pieces to be lifted and transported quickly and easily and

deposited gently and precisely. Our KBK stacker cranes make it possible to complete all storage and handling tasks in one operating cycle without the need for ladders, orderpicking trolleys or similar equipment. Unit loads, containers or pallets weighing up to 500kg can be safely and reliably transported, sorted and stored.

Work pieces to be lifted and transported quickly and easily and deposited gently and precisely Ideal

And lastly, KBK portal cranes are the ideal solution wherever a permanent crane would be too complicated or cannot be installed. They run on solid, even floors and can be easily manoeuvred in any direction. This makes them ideal for a wide variety of loading and unloading operations in your factory as well as for maintenance and repair work. All Demag’s Light System Cranes come with the significant benefit of being adjustable to any requirements.

Demag Richard Roughly Tel: (011) 898-3500 Richard.roughly@demagcranes.co.za. www.demagcranes.com

BULK HANDLING TODAY

August 2019

Transport Evolution presents

15 - 16 October 2019 | Durban International Convention Centre, South Africa

THE MEETING PLACE FOR AFRICA’S PORT AND RAIL PROFESSIONALS 30+

countries represented

30+

70+

expert speakers

leading companies exhibiting

co-located events

3 000+

transport professionals

technical workshops

BOOK NOW TO SHOWCASE YOUR BRAND TO THE TRANSPORT SECTOR This is the most important event in the transport calendar on the African continent. Should you wish to promote your brand, product or solutions to industry leaders, please contact: Kemantha Naidoo KemanthaNaidoo@dmgevents.com +27 11 783 7250

www.transportevolution.com 8

BULK HANDLING TODAY

August 2019

CONVEYING

Maximum Uptime Thanks to Technology Future Fibre Technologies (FFT), the technology division of AVA Risk Group, has released the Aura IQ solution. It aims to change conveyor health monitoring by using real-time data to optimise production and onsite performance, enhance occupational health, hygiene and safety management and introduce new predictive maintenance and support capabilities.

ura IQ harnesses the power of FFT’s fibre optic detection and sensing technology platform, and is combined with development partner, Mining3's advanced signal processing algorithms and predictive analytics, to acoustically monitor and assess conveyor health via cloud-based analysis, reporting and alerts.

Aura IQ Cloud and the Internet of Things The Aura IQ Cloud and Internet of Things (IoT) Network solution provides a means to wirelessly connect one or more Aura IQ Edge servers to a central cloud reporting and analytics platform. This enables alerts and reports from conveyor assets to be accessible on any internet-enabled device in near real-time, with no specialist software or equipment.

length of a conveyor. Acoustic disturbances from the conveyor system cause microscopic changes in the backscattered laser light that is then categorised into known parameters. Data is simultaneously gathered from every metre of the conveyor and processed by Aura IQ to pre-emptively alert operators, either on or off-site (in operational hubs or control rooms), to potential failures before they happen.

Early warning system

Aura IQ is a low cost, highly reliable solution for monitoring, measuring and detecting conveyor roller health, with no power required at the point of measurement

How it works

Aura IQ is a low cost, highly reliable solution for monitoring, measuring and detecting conveyor roller health, with no power required at the point of measurement. The solution transmits a series of short, laser pulses through a single fibre optic cable retrofitted along the

Alerts that can be set include the detection of a broken ball or a cracked cage in a ball race, the observation and tracking of idler bearings as they progressively wear, and the prediction of potential bearing seizures.

Commenting at the launch, Aura IQ's, Andrew Hames, says that distributed fibre optic acoustic monitoring is the way of the future for conveyor health monitoring. "This is a game changing solution which will optimise conveyor performance and create substantial cost savings for operators.” Andrew concludes by mentioning that a typical conveyor can have up to 7 000 bearings per kilometre, which means 7 000 potential points of failure. Aura IQ can monitor the condition of every conveyor roller, eliminating the need to ‘walk the belt’ and allowing for a controlled and scheduled plan of roller maintenance and replacement to be put in place. Future Fibre Technologies sales@fftsecurity.com www.fftsecurity.com

BULK HANDLING TODAY

August 2019

CONVEYING

Optimising Belt Cleaning Given the number of conveyor-related accidents that occur during routine maintenance and cleanup, every bulk material handler has a vested interest in technologies to help reduce hazards and prevent injuries.

eemingly mundane tasks such as adjusting belt cleaners and removing spillage often require employees to work in close proximity to the moving conveyor, where even incidental contact can result in serious injury in a split second. Further, spillage can contribute to the risk of fire by interfering with pulleys and idlers and by providing potential fuel. Even worse, in confined spaces, airborne particles can create the right ingredients for an explosion.

If the spillage amounts to just one shovelful per hour (not an uncommon occurrence in some operations), personnel can expect to have to deal with more than 225kg of fugitive material every day. The buildup of fugitive material can occur with surprising speed. As the table below illustrates, spillage in an amount equal to just one sugar packet (about 4 grams) per hour will result in an accumulation of about 700 grams at the end of a week. If the rate of escape is 4 grams per minute, the accumulation will be more than 45kg per week, or more than two tons per year. If the spillage amounts to just

Table 1: Material loss from conveyors

one shovelful per hour (not an uncommon occurrence in some operations), personnel can expect to have to deal with more than 225kg of fugitive material every day.

Belt cleaning to reduce carryback

Although there are a number of belt cleaning technologies available to conveyor operators, most designs in use today are blade-type units of some kind, using a urethane or metal-tipped scraper to remove material from the belt’s surface. These devices typically require an energy source such as a spring, a compressed air reservoir or a twisted elastomeric element to hold the cleaning edge against the belt. Because the blade directly contacts the belt, it is subject to abrasive wear and must be regularly adjusted and periodically replaced to maintain effective cleaning performance.

Tensioning

The ability to maintain the proper force required to keep the blade edge against the belt is a key factor in the performance of any cleaning system. Blade-to-belt pressure must be controlled to achieve optimal cleaning with a minimal rate of blade wear. There is a popular misconception that the harder the cleaner is pressing against the belt, the better it will clean. But research has shown that there is actually an optimum range of blade pressure, which will most effectively remove carryback material. Increasing tension beyond this range raises blade-to-belt friction, thus shortening blade life, increasing belt wear and increasing power consumption without improving cleaning performance. Operating a belt cleaner below the optimum pressure range also delivers less effective cleaning and can actually accelerate blade wear. A belt cleaner lightly touching the belt may appear to be in working order from a distance, whereas in reality, excessive amounts of carryback are being forced between the blade and the belt at high velocity. This passage of material between the belt and the blade creates channels of uneven wear on the face of the cleaner. As material continues to pass between the blade and the belt, these channels increase in size, rapidly wearing the blade to a jagged edge.

Empty

Constant Cleaning angle and Pressure

BULK HANDLING TODAY

August 2019

A common source of blade wear that often goes unnoticed, even with a properly installed and adjusted cleaner, is running the belt empty for long periods of time. Small particles embedded in the empty belt’s surface can create an effect like sand-paper, increasing the wear rate of both the blade and the belt. Even though the cargo may

be abrasive, it often has moisture in it that serves as a lubricant and coolant. Another potential source of wear is when the cleaner blade is wider than the material flow, causing the outside portion of the cleaning blade to hold the centre section of the blade away from the belt. As a result, carryback can flow between the belt and the worn area of the blade, accelerating wear on this centre section. Eventually, the process creates a curved wear pattern sometimes referred to as a ‘smiley face’ or ‘mooning.’ As urethane cleaner blades wear, the surface area of the blade touching the belt increases. This causes a reduction in blade-to-belt pressure and a corresponding decline in cleaner efficiency. Therefore, most mechanically-tensioned systems require periodic adjustment (re-tensioning) to deliver the consistent pressure needed for effective carryback removal. To overcome the problem of the blade angle changing as the blade wears, a radial-adjusted belt cleaner can be designed with a specially-engineered curved blade, known as 'CARP' for Constant Angle Radial Pressure. With this design, the changes in contact angle and surface area are minimised as the blade wears, helping to maintain its effectiveness throughout the cleaner’s service life.

Ease of service should be a key element in any belt cleaner tensioning system

Air tensioning

New air-powered tensioning systems are automated for precise monitoring and tensioning throughout all stages of blade life, reducing the labour typically required to maintain optimum blade pressure and extending the service life of both the belt and the cleaner. Equipped with sensors to confirm that the belt is loaded and running, the devices automatically back the blade away during stoppages or when the conveyor is running empty, minimising unnecessary wear to both the belt and cleaner. The result is consistently correct blade tension, with reduced power demand on start-up, all managed without operator intervention. For locations lacking convenient power access, one self-contained design uses the moving conveyor to generate its own electricity, which powers a small air compressor to maintain optimum blade pressure at all times.

Sensors can be used to back the blade away during stoppages or when running empty.

Maintenance

Even the best-designed and most efficient of mechanical belt cleaning systems require periodic maintenance and/or adjustment, or performance will deteriorate over time. Proper tensioning of belt-cleaning systems minimises wear on the belt and cleaner blades, helping to prevent damage and ensure efficient cleaning action. Belt cleaners must be engineered for durability and simple maintenance, and conveyors should be designed to enable easy service, including required clearances for access. Service chores that are straightforward and ‘worker-friendly’ are more likely to be performed on a consistent basis. Martin Engineering, Rick Felde Tel: (013) 656-5135 Email: rickf@martin-eng.com Email: feedback@martin-eng.com www.martin-eng.com.za

As the centre of the blade wears unevenly, the outer edges create a 'smiley face' or 'mooning.'

BULK HANDLING TODAY

August 2019

BEARINGS

Zero Failure Bearing Services Bethal, supported by SKF, has been supplying a key customer in Mpumalanga’s coal mining industry with over 400 bearings which have delivered zero failure whilst operating in a highly aggressive application.

he coal mining industry is a notoriously highly corrosive environment. Continuous water and coal dust contamination as a result of the coal mining and conveying processes play havoc with machine reliability giving rise to frequent downtime and subsequent costly production losses. “Our customer was facing Mean Time between Failures (MTBF) on their tail end pulley bearings every two weeks and on their sizer crusher bearings every three months,” explains Marchant Taylor, SKF Regional Sales Manager - North East Region. Lubrication difficulties further compound the situation affecting equipment and component reliability.

Triple the protection

Working in close cooperation with SKF, the team from Bearing Services Bethal stepped in and presented the SKF triple-barrier solution for the conveyor tail end pulleys and the

BULK HANDLING TODAY

August 2019

two scroll sizer crushers, which were replaced with Sealed Spherical Roller Bearings (SSRBs). Marchant explains that the triple-barrier solution which comprises a SSRB and labyrinth seal combination is the ultimate sealing arrangement to protect bearings from contamination in highly contaminated areas. The SSRB and the Labyrinth seal offer three barriers through which contamination must penetrate before it will reach and subsequently affect the bearing.

The triple-barrier solution comprises a SSRB and labyrinth seal combination which is the ultimate sealing arrangement to protect bearings from contamination in harsh areas The solution presents inner seal protection from the sealed spherical roller bearing itself which is installed in a housing with a 70 to 90% grease fill that completely isolates it from the sealed bearing, forming the second barrier. The third barrier is formed by the Labyrinth multi-stage labyrinth cartridge seal that is used to seal the housing from outside contamination which has its own greasefilled sealing configuration. A sealed-for-life bearing is also included.

Increased uptime and production

“Our supply of a total of 254 tail end pulley bearings and 156 crusher bearings to date has delivered seamless bearing performance with our customer reporting zero failures. This solution has reduced costs for our customer in terms of replacement components and maintenance, subsequently resulting in increased uptime, productivity and production, and ultimately a more profitable mine,” notes Marchant.

Our supply of a total of 254 tail end pulley bearings and 156 crusher bearings to date has delivered seamless bearing performance with our customer reporting zero failures From an after-sales service perspective, Bearing Services Bethal, continues to deliver ongoing service and support to ensure reliability of critical machinery and subsequently constant uptime for the customer through technical knowledge, drive and dedication. SKF samantha.joubert@skf.com Tel: (011) 821-3602 www.skf.com

BULK HANDLING TODAY

August 2019

WORLD-CLASS performance requires speed, agility and endurance

STRATEGY

INFRASTRUCTURE

OPERATIONS

Planning strategic direction benchmarked to world-class standards

Development of world-class infrastructure from concept to realisation

Development of operations to best practice and world-class standards

Supply Chain Strategy

Facility Design & Development

Process & Operations Design

• Supply Chain network analysis & design • National & Regional DC strategy development • Facility Sizing and OPEX estimates • On-line fullllment • Slow vs. Fast movers network set-up • A Supply Chain that supports business strategy • Site development strategies • Technology, IOT and digitilisation strategy

• Greennelds site development

• Operations assessment and benchmarking • WMS / WCS review • WMS / WCS functional requirements • Process and operations optimisation • Long term operational development strategies • Process audit • Labour standards and incentive programs

planning • Brownnelds site development planning • Functional building requirements speciication • Technical liaison to professional / development team • Facility sizing requirements (short to long term) • Design to execution • Procurement, program and vendor management

In today’s competitive business world you need to focus on every opportunity to advance your company mission

BULK HANDLING TODAY

August 2019

Cape Town: (021) 816 2000 | ils-ct@ils.co.za Johannesburg: (011) 656 1100 | ils-jhb@ils.co.za www.ils.co.za

MINERAL SAMPLING

The Key to Success The growth and diversification of West Africa’s mining sector is making the precision of mineral sampling a vital priority.

“

West Africa is a growing market for Multotec samplers and services, with the increased output of commodities adding a new dimension to the importance of our equipment,” says Willem Slabbert, process manager at Multotec Process Equipment.

Any imperfection in the sampling process can lead to unnecessary contractual disputes and potential financial losses for the mine or client For over two decades, Multotec has been active in the West African market, with its proven samplers at over 30 sites in countries including Ghana, Liberia, Burkina Faso, Guinea, Sierra Leone, Mali and Guinea-Bissau. A range of commodity sectors use the equipment for both slurry and dry sampling applications, among them gold, bauxite, iron ore and heavy minerals.

Ensuring bottomline success Willem Slabbert, applications and process manager at Multotec Process Equipment.

“In bulk minerals like bauxite, where our sampling plants have been in

operation with a major West African producer for 17 years, the sampling protocol and ‘correctness’ of equipment design is key to ensuring bottom-line success,” says Willem. He highlights the importance of reproducible and accurate sampling, cumulatively termed representative, at the interface between the mine and port, and on the ship-loading conveyor to the client. The sampling, which must comply with ISO standards and best practice as prescribed by the Theory of Sampling (TOS), confirms the mine is supplying product to the end-customer’s contractual specification. “Any imperfection in the sampling process can lead to unnecessary contractual disputes and potential financial losses for the mine or client,” he says.

Good accounting and reconciliation

Multotec supplies wet slurry samplers to many gold mines in West Africa, who rely on good gold accounting and reconciliation at their processing plants. The equipment is popular among large gold producers as well as the smaller entrants. “With a comprehensive range of Two-In-One, primary and ancillary samplers, we are able to tailor each installation to the customer’s specific application. This means accommodating variables like throughput rates and slurry densities, including accounting for grade variability from various mine sources feeding a single processing plant, in many of the West African deposits,” Willem concludes. Multotec, Willem Slabbert Tel: (011) 923-6000 Email: marketing@multotec.com www.multotec.com

Bias-free sampling is a non-negotiable for any mining operation, and Multotec has a comprehensive range of samplers, wet or dry, to suit various applications.

BULK HANDLING TODAY

August 2019

CRANES

Considerations When Making a Purchase Overhead travelling cranes are big machines with price tags to match. A purchase dents even the most generous capital expenditure budget. For this reason, price often heads the list of factors holding sway over the buying decision.

ut is price the right focus? Could a pricebased decision be flawed not only because it ignores maintenance costs, but also because it overlooks production losses should the crane be forced to stop work for any reason?

Condra believes that the buying focus should be different. First, it should be on the total cost South to company over the life of Africa’s big the crane instead of on initial capital cost alone, four crane companies and second, it should have strong reputations examine the projected for technical capability productive uptime of the and long product life if crane based on back-up their cranes are operated service and the lead time under the right on spare parts manufacconditions tured abroad.

Strong reputations

Marc Kleiner, Condra’s managing director, is the first to point out that South Africa’s Big Four crane companies have strong reputations for technical capabilities and

BULK HANDLING TODAY

August 2019

Condra’s managing director, Marc Kleiner

long product lives if their cranes are operated under the right conditions. But he points out that African operating environments are often less forgiving than those in Europe.

Completed double-girder overhead crane leaving Condra’s Johannesburg factory for delivery by road by sister company, Transcon Haulers

And, he adds, European players manufacture only the steel structures of their overhead cranes in Africa. All key components such as hoists and end-carriages are imported. So what does this mean in practical, useful terms?

Questions raised Marc lists a few questions that any overhead crane buyer should ask before deciding on a supplier, and explains the potential impact of each of them on running costs and production.

taken for them to arrive and be installed can take up to two months, resulting in a long downtime,” he says. In addition, after sales service is a must. A company that does not have a local office could be problematic in terms of response time.

If the tendered price of a crane with imported components is low, how has that price been achieved with a weak rand? In other words, the low price is made possible by a sub-par crane

If the tendered price of a crane with imported components is low, how has that price been achieved with a weak rand? In other words, the low price is made possible by a sub-par crane. Secondly, is the proposed crane the best machine for the operational environment? What is the reputation of the proposed brand in terms of product reliability under these conditions? Marc believes that it is the durability of the crane that determines the customer’s productivity and the ideal crane is one that continues working without the breakdowns that cause production stoppages. “Thirdly, customers need to think of spare parts and their delivery time. Ordering from Europe is expensive because of exchange rates and the time

Marc goes on to mention standards. Is the crane the most suitable for the job at hand? Is the machine fast enough, durable enough and reliable enough? Lifting capabilities also need to be considered. “International standards state the lifting height of more than 25 metres as very high, but perhaps the job requires lifting higher than that,” he adds.

Case in point

Marc uses the Condra K-Series of cranes that use motor-starting silumin rotor cores to enhance torque in the high-lift role, and has developed variable speed control levels on the drives to enable precise load positioning even on lifts of 100 metres or more. Hoist speeds of between zero and 60 metres per minute, and travel speeds of between zero and 200 metres per minute are possible. Condra, Marc Kleiner Tel: (011) 776-6000 Email: sales@condra.co.za www.condra.co.za

BULK HANDLING TODAY

August 2019

Tough demands have met their match.

With a hydraulic drive system from Hägglunds, you get compact, durable power - without foundations or gearbox. A full range of rugged motor types and complete solutions for monitoring and control give you total assurance, even in the most demanding applications. Let us know your demands. Hägglunds Drives South Africa (Pty) Ltd P.O.Box 2851, 1610 Edenvale, Johannesburg Phone: + 27 (0)11 454 4933, Fax: +27 (0)11 454 5088 E-mail: info@za.hagglunds.com, www.hagglunds.com

18 drive BULKisHANDLING TODAY August Our your performance.

2019

LIFTING

Two South Africans on International Crane Support Team Konecranes South Africa now has two members on an elite team, Marius Naude (Global Technical Support Specialist) and Niekie Erasmus (Senior Service Technician).

“

Being part of the Global Technical Support group is an honour and an achievement, but also comes with huge responsibility and dedication to Konecranes,” says John MacDonald, Service, Sales, and Marketing Director for Konecranes South Africa. “We are very proud of our two home grown experts playing such a vital role in supporting crane projects across the globe.” Konecranes’ Global Technical Support is responsible for providing 24/7 international support for Konecranes technicians and regional specialists all over the world as well as troubleshooting and special crane commissioning services. Customers often call directly for support when serious problems are encountered that could cause costly delays in the production process.

Marius Naude

To become part of the Konecranes Global Specialist Team, the person is nominated either by someone from Global

Technical Support, Technical Training Group or the Country/Regional Support Specialist. An assessment by the Specialist Trainer will follow to ensure that the candidate has the necessary skills level to participate in this elite group. Only ten candidates are accepted per year and the current group brings the total candidates trained since the start of this program to 110. Unfortunately quite a few are lost with promotions, job role changes, resignations and retirements.

Second nomination

“After successful completion of this training, I was tasked with Regional Specialist Support which covered Southern Africa and sub-Saharan Africa”, said Marius. “Over time, some countries were added when other members were not available or were restricted to travel there. These countries include Panama, Turkey and Iraq. Due to the expanding Konecranes footprint on the African continent, the workload also increased. “We therefore decided to nominate a second Country Specialist. Niekie Erasmus from our Amanzimtoti Branch was nominated and assessed by the current Global Technical Support Team at the end of 2018. He was successful with the assessment and started his Specialist Training in March 2019. This should be completed by the end of October 2019”, Marius concludes. “With Niekie and I covering sub-Saharan Africa, we can keep our technicians as well as the customers happy with quick, accurate and productive support.” Conecranes, Marius Naudé, Tel: 072-604-2766 Email: marius.naude@konecranes.com

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EFFECTIVE TOOL

Discrete Element Modelling: Overcoming the Challenges The behaviour of bulk granular material is different from that of solids and fluids, making it difficult to predict the dynamic and even static behaviour. Until fairly recently, the design of bulk materials handling equipment relied on empirical-analytical approaches.

he Discrete Element Method (DEM) was introduced in the 1970’s as a numerical method for the modelling of granular materials as discrete particles. Over the years, advances in computer technologies have made it possible to use DEM as a design tool, either to solve existing problems in bulk handling systems or as a predictive tool to model and investigate the performance of new concepts and developments. However, there are still challenges that need to be overcome for DEM to be an effective tool in analysing large scale industrial applications.

Introduction

DEM models granular material as an assembly of individual or are discrete particles. The interaction between the particles

and between the particles and walls (used to define containing structures, equipment, etc) is described by a contact model as shown in Figure 1. The particles are considered rigid and allowed to overlap at the contact instead of deforming, as the physical particles would do. The contact model defines the relation between the forces and the overlap as defined by the stiffness, damping and friction at the point of contact. A single DEM time step consists of three phases: contact detection, calculation of contact forces and the integration of the equations of motion which includes updating the position and orientation of the particles. The most commonly used contact models include the linear and Hertz-Mindlin models. In the case of the linear model, the contact force is a linear function of the overlap while in the Hertz-Mindlin model the force is a function of the overlap to the power 1.5, resulting in a non-linear response or stiffness. In both models, the contact stiffness can be related to a combination of the elastic properties of the individual elements (particle and/or wall) in contact, namely Young’s modulus, the shear modulus and Poisson’s ratio. The force in the tangential direction is limited by a Coulomb type friction coefficient which allows for relative sliding between the elements at the contact. The friction is responsible for the dissipation of energy from the system which can be increased by introducing a damper (dashpot) at each contact.

Figure 1 – Schematic representation of the typical normal, tangential and rolling contact models for cohesionless materials

Rolling resistance in the form of a moment acting at the point of contact can also be introduced. Similar to sliding

Figure 2 – The large scale laboratory conveyor transfer facility at Stellenbosch University for testing chute designs and validating DEM models

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friction, the magnitude of this moment is limited by a rolling coefficient of friction.

Application of DEM in bulk materials handling

DEM can easily model the discrete behaviour of granular materials which includes large displacements, gravity driven flow, forced flow, mixing and segregation. Typical industrial applications that can be analysed include belt conveying and transfer chutes where the flow of material can be modelled from the feeding belt, through the whole transfer chute and onto the receiving belt. Typical results include the particle trajectories and complete flow path, impact velocities and forces on the chute liners and the receiving belt (which can be used to predict rates of wear and dust liberation), the prediction of any blockage, build-up, spillage and off-centre loading. The Granular Materials Research Group (GMRG) at Stellenbosch University is currently undertaking studies to develop DEM procedures for accurate and efficient modelling of transfer chutes. The models are validated using a large scale laboratory conveyor transfer facility with transparent chutes and instrumented with flow sensors and high speed cameras as shown in Figure 2. The filling, static behaviour and dynamic discharge from bins, silo’s and hoppers can be analysed and used to predict the rate of flow, the flow patterns (mass flow and funnel flow) and the pressures exerted on the walls which can be used in structural design and analysis. Equipment can be analysed and improved or fully optimised. For example: ship unloading grabs, excavator and dragline buckets and bucket elevators. Other applications include feeders, mixers (blending), screens, crushers and tumbling mills.

Viable for analysing industrial scale applications

Although most bulk handling systems and equipment can be analysed with DEM, models are only of practical value if the results are accurate enough to be of use as an effective design and predictive tool. This can be applied to industrial

scale applications only if an appropriate set of model/material parameter values can be determined and the results obtained within a reasonable time frame. The behaviour of the particles in the model is governed by the parameter values which in general include particle shape, particle size, particle density, contact stiffness, friction (sliding and rolling) and damping characteristics. Determining the correct parameter values is referred to as DEM calibration. Most DEM codes make use of an explicit time integration scheme which requires the use of small time steps or increments which is inversely proportional to the square root of the contact stiffness. The typical size of a time step ranges from 10-4 to 10-6 seconds. Thus, to model minutes or hours of real time, a large number of time steps is required which, depending on the model complexity, can take up to hours, days or even weeks to complete. Methods to decrease the computational effort exist, but should be implemented with care. These include particle coarse graining where the particles are scaled up in size to reduce the total number of particles in the model and reducing the contact stiffness to increase the size of the time step. These measures should already be accounted for during the calibration phase and cannot be adjusted afterwards unless the calibration process is repeated or the model results compared with a benchmark.

Calibration of DEM parameters Although most of the model parameters have a direct physical interpretation, research has shown that measuring the material properties at particle or contact level does not necessarily provide accurate results at bulk level. DEM models rely on simplifications and assumptions to ensure a solution can be obtained in a timely manner. For example, the particle shape can never be exactly modelled in terms of shape and texture, especially if natural materials are modelled as typically found in the mining and agricultural sectors,

Table 1 – Relation between DEM parameters and bulk material properties (adopted from [14])

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since including all these details would be computationally too demanding. Even if the shape could be exactly modelled, each individual particle in a bulk mixture will have a unique shape which is impossible to include in the model. Thus, some simplifications must be made regarding the modelled shape and surface texture.

process, laboratory or field tests are conducted to measure a number of bulk properties. The tests are then repeated in DEM, using the same geometry and constraints as in the physical tests while the parameter values are adjusted until the bulk behaviour in each of the tests is modelled with acceptable accuracy.

The shape influences the amount of interlocking between the particles, and this phenomenon in combination with the coefficient of friction, governs the flow properties at bulk level. Measuring the coefficient of friction is very difficult due to the size and shape of typical particles. Therefore if simplifications are made to the modelled shape, the coefficient of friction should be adjusted (from the physical value) to compensate for the lack of accurate shape modelling, ensuring that the bulk behaviour is accurately modelled. The same reasoning applies to the other parameters and it is important to understand the influence that each parameter might have on the predicted bulk behaviour.

Although this approach seems simple enough, the inter-relations between the parameters and the bulk behaviour adds additional complexity. For example, the particle-particle coefficient of friction influences not only the bulk friction but also the bulk density. Table 1 provides the qualitative relations between the parameters and the bulk properties for dry cohesionless materials under relatively low consolidation pressures.

Due to the reasons highlighted above, the parameter values are usually obtained through a calibration process. During this

Since a number of parameters need to be calibrated simultaneously, a single test or experiment would not be sufficient because more than one combination of parameter values might provide the same bulk behaviour. A unique set of parameter values can only be obtained if the number of tests performed (bulk measures) is at least equal to the number of parameters to calibrate. However, research has identified tests that are either sensitive or insensitive to certain parameters which can then be used to calibrate and pin down the value of one specific parameter. The GMRG has worked on the development of calibration procedures and equipment for the last decade and is currently collaborating with international partners on a white paper to establish a standardised calibration process. The steps in this process are shown in Figure 3 and further discussed in this article. Note that the calibration sequence is important since it minimises the need for iterations. For now, the calibration is limited to cohesionless (dry) materials under relatively low consolidation pressures (less than 100kPa). However, ongoing research is undertaken to develop similar methods for cohesive (wet and sticky) materials. Such materials can be modelled by introducing cohesive forces to the contact model but is not the focus of this article

Particle Shape

Computationally, spherical particles are the most efficient due to easy contact detection and overlap calculations. More complex shapes can be modelled by ‘gluing’ spheres together with any amount of overlap to form what is called multi-sphere particles, clumped particles or simply clumps. Other less efficient shape models include mathematical descriptions such as super-quadrics, polyhedrons and faceted particles. Although spherical particles remain the most efficient, they cannot account for the shape and rolling behaviour of real particles unless rolling resistance is incorporated in the contact model. Non-spherical particle models usually do not require the use of rolling resistance, unless the particle has a symmetry axis (for example an ellipsoidal shape) around which it can easily roll or if the material has a very high resistance to flow. Spherical particles can be used if the bulk material is relatively homogeneous in terms of particle size and shape. If non-spherical particles are used for large systems, it is proposed to use simple clumps comprising only three or four spheres in a triangular or pyramid shape, see Figure 4. The clumps can be created manually or the particles can be 3D scanned

Figure 3 –Calibration steps

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and software used to fill the geometry with spheres in an optimised manner. If segregation, mixing, and complex flow patterns in screening processes should be analysed, more complex and realistic particle shapes should be considered.

scaling’ (coarse graining) or ‘scalping’. In coarse graining, the whole PSD is scaled up, however, scalping is usually preferred where the finer particles are simply ignored and not included in the model.

The chosen shape will influence all the other parameter values which should be re-calibrated even if a small change is made to the particle shape. The particle shape will influence the packing porosity and hence the modelled bulk density under static conditions, but also changes to the bulk density when the material is flowing where dilation or compaction could be observed.

Modifying the PSD should be done with care since it can have significant effects on the results. The ratio between the size of the equipment and the particles should be kept to a maximum and as close as possible to that of the real system, while ensuring results can be obtained in an acceptable time frame.

The bulk friction is also influenced by the particle shape in combination with the sliding coefficient of friction. Particle interlocking is higher for non-spherical shapes which will result in higher bulk friction values, for example the angle of repose. However, spherical particles with sliding and rolling friction can also produce accurate levels of bulk friction.

Particle size distribution

In large scale industrial applications, the number of particles can be in the order of billions to trillions. The computation time increases exponentially with an increase in the number of particles and for practical purposes using a high-end computer, the total number of particles should be kept well below one million. DEM software making use of graphics processing units (GPUs) can compute faster, but appropriate GPUs can be expensive and not readily available. The number of particles in the model can be reduced by modifying the particle size distribution (PSD) through ‘exact

Care should be taken when modelling bin and hopper openings and transfer chutes for example. For small scale calibration tests, it is recommended that the geometry controlling the volume flow be a minimum of 10 to 20 times larger than the maximum particle size.

Contact damping

The contact damping is often expressed in terms of the coefficient of restitution (COR) which relates the velocity of a particle before and after impact. The bulk behaviour of the material is usually insensitive to the damping and values of COR = 0.2 to 0.4 are appropriate in most cases. COR can be measured via drop tests which will require the use of high speed cameras to obtain the velocity just before and after impact or the rebound height. This should be repeated for each possible contact interface and material type. However, this procedure shows high variability if the particles are not close to spherical and more sophisticated instrumentation might be needed to measure the 3D rebound path of the particles including particle rotation. Drop tests are also not suitable for particle-particle contact, but double pendulum impact testing can be considered. Values of COR determined from drop or pendulum tests can be directly used in the DEM model.

Particle-wall friction

The easiest method for measuring the particle-wall coefficient of sliding friction is the inclined wall test. In this test, a single particle is placed on a wall or plane manufactured from the material in question. The wall is then slowly inclined from the original horizontal position until the particle starts to slide.

Figure 4 – (a) Classification of gravel particle shapes and (b) the corresponding models

The particle-wall friction angle would be equal to the inclination angle q from which the coefficient of friction is easily calculated as mpw = tan(q). This test needs to be repeated for each of the interface material types. If the particle is close to spherical, it might roll and not slide down the incline. In this case it is recommended to glue a number of particles to a base plate, which is then

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placed on the inclining wall. The inclining wall test will provide the friction values only for low contact forces. It is known that under higher pressures, the friction might be different and needs to be measured under similar conditions in a direct shear tester. However, this would require access to such an apparatus or laboratory to perform the testing. Values for the particle-wall coefficient of friction obtained in any of these two tests can be directly used in the DEM model without the need for further calibration.

Contact stiffness

The values specified for the stiffness will depend on the specific contact model used. If the linear model is used, the stiffness is specified in the normal and tangential directions in units of N/m. These two stiffness values are independent of each other, although the tangential stiffness is usually taken between 0.5 and 1.0 times the normal stiffness. The value of the normal stiffness can be estimated using kn = 4.E.R where E is the effective Young’s modulus at the contact and R the radius of curvature (usually taken as the radius of the particle or that of a volume equivalent sphere). If the Hertz-Mindlin contact model is used, the user needs to specify the contact effective elastic properties namely Young’s modulus E, or the shear modulus G, and Poisson’s ratio (usually assumed as n = 0.3). Equipment is usually manufactured from hard materials such as steel or ceramics and it is sufficient to specify the particle-wall stiffness twice that of the particle-particle contacts. The contact stiffness and elastic properties are difficult to measure at contact or particle level and are best calibrated using a confined uniaxial compression test. A container (usually cylindrical) is filled with the material, closed with a lid and compressed, Figure 5.

The load-displacement response is measured while the sample is compressed to a maximum pressure which should be of the same order as expected in the final application to be modelled. The slope of the load-displacement curve is defined as the bulk stiffness. The experiment is repeated in DEM under similar boundary conditions and the contact stiffness adjusted iteratively until the bulk stiffness is accurately modelled. The relation between contact stiffness and bulk stiffness is close to linear. The container should be large enough to minimise any wall effects and should be at least equal to 10 particles in diameter. The integration time step is inversely proportional to the square root of the contact stiffness and it is usually impractical to model large industrial scale applications without reducing the modelled stiffness. Research has shown that the stiffness can be scaled down by a factor of 10 when modelling bulk material flow under relatively low pressures. In some cases, the stiffness can even be reduced by a factor 100 without any significant loss in accuracy. Using the linear contact model, a minimum value of kn = 1.103 N/m is recommended for free flowing conditions under low pressures for materials with low bulk densities (less than 1 000kg/m3). However, a value between kn = 1.104 N/m and 1.105 N/m is appropriate in most cases. Using the Hertz-Mindlin model, the proposed minimum value for the shear modulus is G = 1.107 N/m2.

Particle and bulk density

The bulk density should be accurately modelled if both the volume flow rate and mass flow rate are to be modelled accurately. For example, if a transfer chute is analysed and the throughput is specified in ton per hour, the DEM model can be setup to ensure the correct mass flow. However, to accurately predict any blockage and build-up, the volume flow rate should also be accurately modelled. Modelling the bulk density accurately ensures that both the mass flow and volume flow rates are accurately modelled. The bulk density can be measured by filling a container with known volume and weighing it to get the mass (weight). This process is then repeated in DEM and the particle density adjusted until the measured bulk density is achieved. Note that, depending on the accuracy of the particle shape, the particle density used in DEM will not necessarily be equal to that of the real particles.

Figure 5 – Confined uniaxial compression test of corn grains

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In modelling bulk materials handling, the aim is always to accurately model the bulk density rather than the particle density. Also note that at this stage in the calibration process, guesstimated values of the coefficients of friction are used which might influence the bulk density. For that reason, the density at the end of the calibration process should be re-checked and the

particle density adjusted until an acceptable level of accuracy is achieved (step 8 in Figure 3).

Particle-particle friction

The coefficients of friction at contact level should be calibrated in such a way that the bulk flow or frictional behaviour is accurately modelled. If spherical particles are used in the model, sliding friction alone will not be sufficient and rolling friction should be included. If non-spherical particles are used, sliding friction alone will suffice in most cases. In general any test or experiment which is sensitive to the particle-particle friction can be used to calibrate both the sliding and rolling friction. The tests that are commonly used include a number of angle of repose tests, direct shear tests and the draw down test as described below.

Angle of repose

The easiest test to perform is the bucket or cylinder lift test where an open ended cylinder placed on the ground is filled with material. The cylinder is then slowly lifted which allows the material to form a natural heap. One advantage of

this method is that it is scale invariant and the ratio of the cylinder to particle diameter has no significant effect on the results. This is advantageous when up-scaled particles are calibrated, but care should be taken since the lifting velocity can influence the results in this case. Another approach is shown in Figure 6 where a large cylinder is filled with material. A smaller disk at the bottom of this container is then slowly pushed upwards through the material bed, allowing the material to form a heap. Note that the flow behaviour and kinetic energy involved in each of these tests are different and will not result in the same angle of repose. Therefore it is extremely important that when the test is repeated in DEM, the geometry and velocities used should be the same as those in the experiment. The angle of repose is also sensitive to the friction between the particles and the horizontal plane/wall on which the heap is formed. Any uncertainty can be eliminated by adding a ring to the wall so that a layer of particles is trapped inside. The two methods described here provide a static angle of

Figure 6 – Push-up angle of repose test of coal showing the DEM model at the top (not to scale) and the experiment at the bottom

Figure 7 – The dynamic angle of repose of corn grains as measured in a large rotating drum

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repose while a rotating drum can be used to measure the dynamic angle of repose, Figure 7. This test should be performed in the so-called rolling regime with the Froude number in the range 10-4 < Fr < 10-2 where Fr=w2 R/g with w the rotation speed, R the drum radius and g the gravitational acceleration. Furthermore, the ratio of the drum diameter to the particle diameter should be 25 or more for reliable results. Independent of the method used, the angle of repose is usually determined by taking pictures of the heap from various directions and image processing tools used to fit a straight line to a part of the slope, ignoring the most upper and lower extremities.

Direct shear tests

The direct shear test can be performed in a translational shear cell/box or an annular ring (rotating) shear cell, Figure 8. Geometrical constraints in the translational test limit the maximum shear strain which is unlimited in the rotating cell. In both cases, commercially available equipment is designed for geotechnical applications for particles not larger than approximately 15mm. Larger shear cells are available at research institutions for particles up to 50mm in size. Tests on cohesionless material can be performed by applying a normal load to the lid and translating/ rotating the bottom half of the box/cell to induce shear failure in the sample while measuring the shear stress.

Figure 9 – Draw down testing of corn grains showing the experiment on the left and the DEM model on the right with the four bulk properties used for calibration

Repeating this procedure for at least three increasing normal loads, the Mohr-Coulomb failure envelope can be constructed from which the bulk friction and apparent cohesion can be derived. Direct shear tests are suitable for the calibration of materials which would be subjected to high pressures or levels of consolidation (> 100kPa) in the final application.

Draw down tests

The draw down test (DDT) is a combination of a bin discharge test and an angle of repose test. The apparatus has an upper compartment which is filled with material and a trapdoor in

the floor which is opened to allow the material to flow into the bottom compartment while the mass flow rate (kg/s) is measured, Figure 9. At the end of the test, the material in the upper compartment forms what is referred to as the shear angle and the material in the lower compartment forms an angle of repose. Depending on the material tested, these two angles can be significantly different. The two angles, the mass flow rate and the mass of the discharged material provide four bulk measures which can be used to calibrate the friction parameters. The draw down apparatus is easy to manufacture and should be large enough to eliminate any significant wall effects. The dimensions of the compartments and door opening should be at least 10 to 20 particle diameters.

A unique set of friction parameter values

Individually modelling the above tests, the bulk properties are sensitive to both the sliding and the rolling coefficients of friction. Furthermore, an infinite number of Figure 8 – Top row: direct shear testing of coal in a large translational shear cell (diameter 590mm); Bottom parameter combinations might provide the row: an annular ring shear test with a steel and acrylic cell – all performed at Stellenbosch University

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same bulk response, which raises the question: “Which parameter set is the correct one?” Finding a final set of parameter values relies on combining the different test results to identity a unique, or close to unique, parameter set which provides accurate results for all measures. Calibrating two parameter values in this way requires at least two independent bulk measures, but using more measures will help to refine the results. The draw down test provides four bulk measures in one single test: the shear angle, the angle of repose, the mass flow rate and the discharged mass. Varying the sliding and rolling coefficients of friction from 0.1 to 0.7 in a sensitivity study, the response surface for each of the four bulk measures can be obtained as shown in Figure 10 as contour plots. In each case, the region between the isolines representing the experimentally measured values (mean ± std) is highlighted to indicate the feasible Figure 11 – Overlaying the isolines from each of the four bulk measures region for this measure. Thus, any combination in the draw down test to find the final set of parameter values of the two parameters falling within this region would result in that bulk measure being accurately modelled. Isolating the feasible regions from each measure and direct shear test can also be used, or any combination and overlaying them on a single graph, a final parameter set of these. This approach provides transparency and the user can be selected with the sliding friction between 0.20 and can identify how sensitive the model is to each parameter. 0.30 and the rolling friction between 0.10 and 0.15 as shown However, completing a full sensitivity study to obtain the in Figure 11. Parameter combinations within this range will response surface for each combination of parameter values can be time consuming. simultaneously satisfy all four measures. Although the DDT alone provides enough information to calibrate the two friction parameters, the angle of repose

Optimisation and design of experiment techniques can be used to get to an optimal parameter set more efficiently. Also note that the particle-wall rolling friction is usually taken equal to that of the particle-particle contacts which eliminates one parameter from the calibration process.

Conclusion

DEM can be used as a design tool only if accurate results can be obtained within a reasonable time frame. The accuracy of any DEM model depends on the input parameter values which should be carefully calibrated, while speed-up can be achieved by scaling the particles size and reducing the contact stiffness in the model. This article presents a tried and tested calibration procedure for cohesionless (dry) granular materials which will result in a set of parameter values suitable for modelling most bulk materials handling systems and equipment.

Figure 10 – Draw down model results showing the contour plots for each of the four bulk measures, from the top left: shear angle, mass flow rate, mass discharged and the angle of repose

Stellenbosch University Corné Coetzee Tel: (021) 808-9111 Email: info@sun.ac.za www.sun.ac.za

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August 2019

MARKET FORUM

Digitalisation Strategy Since early 2019 an artificial intelligence solution (AI), supported by Microsoft’s cloud platform Azure, has been integrated into the processes of the largest materials distribution and service provider in the Western world. "alfred" supports his colleagues at Materials Services in dynamically managing the global logistics network with 271 warehouse sites and more than 150 000 products and services. As with his namesake, Alfred Krupp, all information comes together at alfred. As a first step, alfred will help to optimise transport routes and thus save on the transport cost of thousands of tons of material per year. In addition, materials will be available more quickly at the right locations in the future. In the medium term, materials services will be able to make all processes along the supply chain more flexible, for example, in order to better take into account specific customer requirements for delivery speed, pricing or material quality. Klaus Keysberg, CEO of thyssenkrupp Materials Services, summarises alfred’s strengths: "Artificial intelligence is one of the technologies that will make a decisive contribution to competitiveness in materials distribution in the future. With alfred we are taking an important step towards making our processes even more efficient and optimising our value chain.

At the same time, he gives us better insight into our customers' needs so that we can align our offerings accordingly. In the medium term, this holistic approach will also open up new business opportunities for us." "From procurement through warehousing and logistics to sales, we rely on integrated digitalisation concepts. While we simplify cooperation with our suppliers in the area of procurement by means of a cloud-supported platform, for example, we create possibilities for networking internal machinery with our self-developed IIoT platform toii. toii allows us to flexibly coordinate and optimise the processes of warehousing and logistics. In sales, we offer our customers access to 150 000 products and services at 271 warehouse sites sites in the world's largest virtual materials warehouse," Klaus says. As a link between all these areas, alfred fits into the ecosystem and ensures continuous optimisation of speed and service quality through intelligent data processing with corresponding recommendations. thyssenkrupp Materials Services www.thyssenkrupp-materials-services.com

Putting a Shine on Cullinan Osborn, a mining and quarrying equipment specialist has secured an order from Petra Diamonds for an apron feeder that will be employed at the diamond mining group’s Cullinan diamond mine in Gauteng. Eight Osborn apron feeders of the same size were installed underground at the Cullinan Mine as part of a previous order. These are successfully servicing the operation’s underground silos and crushing stations. A further five Osborn apron feeders have since been supplied to the operation’s process plant.

Petra Diamonds’ Cullinan Mine also employs Osborn screens and crushers. Seven new screens were ordered from Osborn when the mine set up a new tailings reclamation plant. “These heavy duty crushers are currently operating underground at Cullinan, while two jaw crushers have been supplied to Cullinan’s process plant,” concludes Chris. Osborn Engineered Products Chris Slade, Tel: (011) 820-7600, www.osborn.co.za

“With their heavy-duty construction, Osborn apron feeders are designed to handle feed sizes of up to 1 500mm where no fines removal is required or where fines are removed by a separate dribble conveyor,” says Osborn East Africa area manager, Chris Slade. He explains that the Osborn apron feeder can be installed in a horizontal or inclined position (up to 15°), depending on space limitations and provides a reliable means of controlling the feed rate to prevent surge loads to primary crushers, belt conveyors and other plant and equipment. BULK HANDLING TODAY

August 2019

MARKET FORUM

Stablilising South Africa’s Power Supply South Africa could go a long way to cut the risk of future load-shedding by adopting a minimum efficiency performance standard (MEPS) for electric motors.

low voltage motors from 0,75kW to 375kW capacity. The MEPS is applied at import stage, so the process would be handled in the conventional manner by customs agencies.

According to Fanie Steyn, manager for rotating machines at Zest WEG Group, a MEPS would significantly reduce the peak power demand on the national grid. Importantly, the step could be made at no cost to government and would also bring substantial savings to the industry’s electrical energy costs.

Zest WEG Group Tel: (011) 723-6000 Email: info@zestweg.com www.zestweg.com

“The MEPS would phase out the least-efficient electric motor classes by setting a minimum standard for the efficiency of motors imported and sold in South Africa,” he says. “The essential challenge now is that about 280 000 electric motors are imported each year, many of which are low efficiency motors rated at IE1 level as standard.” Fanie highlights the great strides recently achieved in the efficiency of electric motors. Energy savings of between 2,1% and 12,4%, depending on the individual power rating can be made by converting from a standard efficiency IE1 motor to a premium efficiency IE3 motor. The capital cost differential is slight and is quickly recouped by lower operating costs. “It is estimated that as much as 30% of all energy produced globally is consumed by electric motors,” he says. “It is therefore easy to see why improving motor efficiencies has a huge impact on national energy consumption.” It is significant that more than 42 countries already have MEPS in place. These standards apply mostly to three-phase

Implementing MEPS will have significant benefits for South Africa

ABSOLUTE MATERIAL FLOW CONTROL

CHUTE SYSTEMS & SOLUTIONS • Optimum material flow • Up to 80% decrease in material degradation

• Reduced dust and noise levels • Virtually maintenance free

Tel: +27 (0) 11 827-9372 email: info@webachutes.com

www.webachutes.com

BULK HANDLING TODAY

August 2019

• Greatly reduced spillage • Significant reduction in belt damage

High security welded mesh

Pallisade

Gates

Gate Automation

Razor wire and more ....

What is High Security Weld Mesh HIGH Security Weld Mesh is wire fused and welded at a Horizontal distance of 76.2mm and a vertical distance of 12.7mm also known as 35B/3510 where 3 denotes 3”(distance between vertical wires), 5 denotes 0.5” (distance between horizontal wires), and B or 10 denotes gauge of wire

Salient Features • Difficult to Climb: The spaces between the Horizontal wires are too narrow for fingers to have grip • Impregnable: Extremely difficult to cut with a hand cutter as the beak of a wire cutter will not be able to penetrate the horizontal wires • Excellent Replacement option to Solid Wall as: 1. More economical than a solid wall 2. Faster to install than a solid wall 3. CCTV Camera has a clear view • Further upgrade possible with electric security system • Anti-corrosive & low maintenance

Standards

• Manufactured according to BS EN 10016-2 • Wire Sizes in accordance with BS EN 10218-2 • Tolerance on Mesh Size in accordance wiht EN 10223-7 • Tolerance on Panel Size in accordance with EN 10223-4 • Welding Strength in accordance with BS EN 1461 • Zinc Coating in accordance with EN 10245-1 • Anti Corrosion in accordance with BS En 3900 E4/F4

Tensile Strength • Wire has a tensile strenght of min 550 MPA

MARK: 083 454 6488

Email: mark@palifence.co.za

www.palifence.co.za

BULK HANDLING TODAY

August 2019

BULK HANDLING TODAY

August 2019

Bulk August 2019

Articles inside

Discrete Element Modelling Overcoming the Challenges

The Key to Success

Zero Failure

Considerations When Making a Purchase

Two South Africans on International Crane Support Team

Kbk Light Crane Systems Flexible and Affordable

Maximum Uptime Thanks to Technology 10 Optimising Belt Cleaning

Company Profile

From the Desk