January / February 2016 NLGI Spokesman

NLGI

SPOKESMAN

Serving the Grease Industry Since 1933 – VOL. 79, NO. 6, JAN/FEB 2016

In this issue . . .

8 “Rust Never Sleeps” An Investigation of Corrosion in Grease Lubrication 20 Investigation into the Dynamic Particle Generation of Lubricating Greases 46 Development of Next Generation Electrical Motor Greases Offering Improved Frictional Characteristics

“RUST NEVER SLEEPS” An Investigation of Corrosion in Grease Lubrication

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NLGI

OFFICERS PRESIDENT:

VICE-PRESIDENT:

Bruce M. Urban FMC-Lithium Division 2801 Yorkmont Rd., Ste. 300 Charlotte, NC 28208

David Como Dow Corning Corp.

P.O. Box 0994 Midland, MI 48686

SECRETARY:

TREASURER:

Kim Smallwood Citgo Petroleum Corp.

1293 Eldridge Pkwy.

Houston, TX 77077

Joe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

PAST-PRES./ADVISORY:

EXECUTIVE DIRECTOR:

Chuck Coe Grease Technology Solutions LLC 7010 Bruin Ct. Manassas, VA 20111

Kimberly Hartley NLGI Inter­national Headquarters 249 SW Noel, Suite 249 Lee’s Summit, MO 64063

DIRECTORS Barbara Bellanti Battenfeld Grease & Oil Corp. of NY P.O. Box 728 • 1174 Erie Ave. N. Tonawanda, NY 14120-0728 Richard Burkhalter Covenant Engineering Services 140 Corporate Place Branson, MO 65616 Faith Corbo King Industries, Inc. Science Road Norwalk, CT 06852 Gary Dudley Exxon Mobil Corporation 3225 Gallows Road Room 7C1906 Fairfax, VA 22037 Gian L. Fagan Chevron Lubricants 100 Chevron Way Room 71-7338 Richmond, CA 94802-0627 Jim Hunt Tiarco Chemical 1300 Tiarco Drive Dalton, GA 30720 Tyler Jark Lubricating Specialties Co. 8015 Paramount Blvd.

Pico Rivera, CA 90660 Dr. Anoop Kumar Royal Manufacturing Co., LP 516 S, 25th West Ave. Tulsa, Oklahoma 74127 Wayne Mackwood Chemtura 199 Benson Rd. Middlebury, CT 06749

Dennis Parks Texas Refinery Corp.

One Refinery Place Ft. Worth, TX 76101 Tom Schroeder Axel Americas, LLC P.O. Box 12337 Kansas City, MO 64116 Raj Shah Koehler Instrument Co. 85 Corporate Dr. Holtsville, NY 11716-1796 Dr. Huafeng “Bill” Shen Bel-Ray Co. P.O. Box 526 Farmingdale, NJ 07727 Terry Smith Lubrication Engineers, Inc. P.O. Box 16447 Wichita, KS 67216 Thomas W. Steib The Elco Corporation 1000 Belt Line Street Cleveland, OH 44109 Lisa Tocci Lubes ’n’ Greases 6105 Arlington Blvd., Suite G Falls Church, VA 22044 Mike Washington The Lubrizol ­Corpo­ration 29400 ­Lakeland Blvd.

Mail Drop 051E Wickliffe, OH 44092 Ruiming “Ray” Zhang R.T. Vanderbilt Company, Inc. 30 Winfield St. Norwalk, CT 06855

Dwaine (Greg) Morris Shell Lubricants 526 S. Johnson Drive Odessa, MO 64076

TECHNICAL COMMITTEE CO-CHAIRS:

CHAIR, SESSION PLANNING:

Chad Chichester Dow Corning Corporation 2200 W. Salzburg Rd., C40C00 Midland, MI 48686

Wayne Mackwood Chemtura 199 Benson Rd. Middlebury, CT 06749

David Turner 22110 Stone Cross Court Katy, TX 77450

SERVICE INDUSTRY ASSISTANCE COMMITTEE CHAIR: J im Hunt Tiarco Chemical 1300 Tiarco Drive Dalton, GA 30720

EDITORIAL REVIEW COMMITTEE CHAIR: Joe Kaperick Afton Chemical Corporation 500 Spring St. Richmond, VA 23218-2158

SPOKESMAN

Serving the Grease Industry Since 1933 – VOL. 79, NO. 6, JAN/FEB 2016

6 President’s Podium 8 “Rust Never Sleeps” An Investigation of Corrosion in Grease Lubrication

Joseph P. Kaperick, Gaston Aguilar, Michael Lennon Afton Chemical Corporation • Richmond, VA

16 NLGI Member Spotlight 18 Ask the Expert 20 Investigation into the Dynamic Particle Generation

of Lubricating Greases

Jason T. Galary, Gus Flaherty Nye Lubricants, Inc.

38 NLGI Industry News 42 NLGI 2015 New Members 46 Development of Next Generation Electrical Motor

Greases Offering Improved Frictional Characteristics John J. Lorimor1, Mihir Patel2, Brian Stunkel2, Rob Heverly2 1 Axel Americas LLC • Kansas City, MO 2Vanderbilt Chemicals LLC • Norwalk, CT

59 Advertiser’s Index

ON THE COVER “Rust Never Sleeps” An Investigation of Corrosion in Grease Lubrication. pg 8

Published bi-monthly by NLGI. (ISSN 0027-6782) KIMBERLY HARTLEY, Editor NLGI International Headquarters 249 SW Noel, Suite 249, Lee’s Summit, MO 64063 USA Phone (816) 524-2500, FAX: (816) 524-2504 Web site: http://www.nlgi.org — E-mail: nlgi@nlgi.org One-year subscriptions: U.S.A. $65.00; Canada $80.00; International $109.00; Airmail $147.00. Claims for missing issues must be made within six months for foreign subscribers and three months for domestic. Periodicals postage paid at Kansas City, MO. The NLGI Spokesman is indexed by INIST for the PASCAL database, plus by Engineering Index and Chemical Abstracts Service. Microfilm copies are available through University Microfilms, Ann Arbor, MI. The NLGI assumes no responsibility for the statements and opinions advanced by contributors to its publications. Views expressed in the editorials are those of the editors and do not n­ ecessarily represent the official position of NLGI. Copyright 2015, NLGI. Postmaster: Send address corrections to the above address.

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PRESIDENT’S PODIUM Interim President David Como welcomes Dennis Parks, Awards Committee Chair, to the Podium.

To quote Thomas Wolfe:

“ If a man has talent and cannot use it, he has failed. If he has a talent and uses only half of it, he has partly failed. If he has a talent and learns somehow to use the whole of it, he has gloriously succeeded, and won a satisfaction and a triumph few men ever know.”

Each year, during the NLGI Annual Meeting, distinguished individuals are recognized for their efforts in advancing knowledge and understanding in the grease industry. We strive to recognize and honor those who have furthered themselves, their company and this industry.

Most likely you know an individual who is deemed successful by the above quote and therefore deserving of such special recognition. Now is the time to take the first step toward honoring that individual by nominating them for one of the NLGI Awards.

The following prestigious awards are now open for nominations from NLGI members:

• N LGI Award for Achievement – The Institute’s highest award honors the achievement of those who have made exceptional contributions to the growth and development of the Institute.

• N LGI Fellows Award – Acknowledges valuable work within the Institute, in the technical development of greases, grease tests, or the promotion of grease usage.

• J ohn A. Bellanti Sr. Memorial Award – Acknowledges meritorious service on the NLGI Board, or on Technical Committee projects or to the industry.

• N LGI Honorary Membership – Entitles lifetime honorary membership to those who, over a period of years, have served the Institute in some outstanding capacity and are not now with a member company.

• A ward for Educational Excellence – For outstanding instruction as exemplified by subject knowledge and presentation skills in NLGI educational courses.

• N LGI Author Award (Development) - For the best paper presented at our Annual Meeting that focuses on formulation, development, and manufacture of finished greases.

• N LGI Author Award (Application) - For the best paper presented at our Annual Meeting that focuses on testing, selection, application or use of greases.

• C larence E. Earle Memorial Award - For an outstanding contribution to the technical literature relating to lubricating greases during the year.

-6VOLUME 79, NUMBER 6

If you have thought about nominating someone in the past, please don’t wait any longer - now is the time to spring into action. The next NLGI Annual Meeting is being held this coming June at the wonderful Homestead Resort. Imagine the pride you will feel should your nominee be honored with one of these significant NLGI Awards.

Please fax, mail, or e-mail your nominations for the 2015 awards to NLGI Headquarters, nlgi@nlgi.org Dennis Parks, Chair Chuck Coe, Joe Kaperick, David Turner

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“Rust Never Sleeps”

An Investigation of Corrosion in Grease Lubrication Joseph P. Kaperick, Gaston Aguilar, Michael Lennon Afton Chemical Corporation • Richmond, VA Abstract

Corrosion of steel or iron doesn’t just happen “out of the blue”. Rust causes damage to untold numbers of machine components not only through direct electrochemical erosion of the metal but through incidental increase in pitting and wear caused by the iron oxide particles. This can be of special significance in mining operations where the potential for exposure to wet or humid environments is extremely high. While grease itself can inhibit some corrosion by reducing ingress of moisture, the addition of rust or corrosion inhibitors is often needed to give additional protection. There is a wide variety of additive solutions as well as a number of different corrosion tests to screen their effectiveness. An overview of some common corrosion tests along with studies comparing the severity of the tests with various aqueous solutions and under different test conditions will be presented.

Introduction

A study on the cost of corrosion in the United States was conducted between 1999 and 2001 with support from the Federal Highway Administration (FHWA) and National Association of Corrosion Engineers (NACE). Their definition of corrosion was that it is a natural phenomenon which results in deterioration of a substance (usually metal) or its properties because of a reaction with its environment. This phenomenon affects everything from cars and appliances, to drinking water systems, to pipeline, bridges and public buildings.

According to their statistics, over the past 22 years the U.S. has incurred total normalized losses of more than $380 billion (averaging $17 billion annually) from natural disasters such as tornadoes, hurricanes and earthquakes. In comparison, the direct cost of metallic corrosion is $276 billion on an annual basis which

represents 3.1% of U.S. Gross Domestic Product (GDP).

[1] Mining uses a huge amount of water in its daily operations. According to the United States Geological Survey (USGS), roughly 4 billion gallons a day are used in the United States alone. “Mining water use is water used for the extraction of minerals that may be in the form of solids, such as coal, iron, sand, and gravel; liquids, such as crude petroleum; and gases, such as natural gas. The category includes quarrying, milling (crushing, screening, washing, and flotation of mined materials), re-injecting extracted water for secondary oil recovery, and other operations associated with mining activities.”[2] According to its 2005 study, 43% of the water used is saline. The use of saltwater or seawater is increasing in some areas as mines look to take advantage of convenient water sources for their needs. Just one example is BHP Billiton, an Australian-British mining company, whose chemical process needs large amounts of water pumped via pipeline from the nearby Indian Ocean. “Some of the seawater is used in its raw state to cool the bearings in all 152 pumps around the plant, while some is desalinated on site for the metallurgical process. Steam and acid are used to prepare the ore for the refining process.“[3] The focus for the grease formulator, with respect to corrosion, is obviously on providing protection from the rust which often occurs in the presence of water and several studies have been documented by NLGI over the last couple of decades. Hunter and Baker [4, 5] evaluated different rust inhibitors and greases using the two versions of the traditional static rust test (ASTM D1743 and D5969) and the dynamic EMCOR corrosion test

-8VOLUME 79, NUMBER 6

(ASTM D6138). They mainly focused on the use of 5% synthetic seawater solution and showed good correlation between the tapered bearing static test and the EMCOR dynamic test. Hunter et al. also focused on ashless rust inhibitors in different grease thickeners in a study using the same tests in 2000. [6]

Experiment

The focus of this study was to examine in more detail three standard industry bench tests for testing grease with respect to steel corrosion – the dynamic EMCOR bearing corrosion test (ASTM D6138) and two “standard” bearing corrosion tests (ASTM D1743, D5969). There are several other types of corrosion tests for lubricants including salt spray corrosion (ASTM B117), humidity cabinet (ASTM D1748) as well as test to measure corrosion of copper and other metals, however, they are not included in this study.

Test Methods

ASTM D1743 “Standard Test Method for Determining Corrosion Preventive Properties of Lubricating Greases” [7] This is often referred to as the “standard bearing” or “static corrosion” test. It utilizes a tapered roller bearing with a Timken bearing cone/roller assembly and cup which is packed, run in, exposed to water and let sit for 48 + 0.5 hours at 52 + 1˚C in 100% humidity. The water used in this method is restricted to distilled water.

ASTM D5969 “Standard Test Method for CorrosionPreventive Properties of Lubricating Greases in Presence of Dilute Synthetic Sea Water Environments” [8]

Determination of Corrosion-Preventive Properties of Lubricating Greases Under Dynamic Wet Conditions (Emcor Test)” [9] This test is often referred to as a “dynamic corrosion” test. It employs a ball bearing (double row self-aligning bearing [30 by 72 by 19 mm], which conforms to 1306 K of ISO 15, with a steel cage. The referee bearing is SKF 1306 K/236 725 bearings but other bearings meeting this description can also be used. The bearing is packed and run in, then cycled for one week under specific conditions (8 hours on and 16 hours off for first 3 days, then sitting at rest for 4 days). The test rotating speed is 83 + 5 rpm and the rig is held at room temperature for the duration of the test. Distilled water, in addition to dilutions of synthetic seawater and sodium chloride, are allowed by the method.

Ratings for the D1743 rust test changed in 1987 to a pass/fail system under which a bearing with no spots larger than 1.0 mm in diameter is considered a pass and two out of three bearings must pass for the test to be considered acceptable. The old system attempted to show the extent of rust using a numbering system as shown in Figure 1. The EMCOR corrosion test still uses a numerical rating system with “0” indicating no visible rust while a “5” indicates more than 10% surface coverage and is the highest rating for the test. Typically, the EMCOR test is run in duplicate and numbers reported as “x/x”. Some specifications set limits that allow for some rust and therefore it is possible to see a performance target of “2/2” or even “3/3”. Alternatively, some older specifications will show a specification value of “1,1,1” for the D1743 test which is likely a holdover

This test is identical to ASTM D1743 with two exceptions: it is only run for 24 hours and the water used is detailed as various dilutions of synthetic seawater (as specified in ASTM D665B).

ASTM D6138 “Standard Test Method for -9NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

from the pre-1987 rating indicating three bearings with no visible rust.

Grease Samples

The base grease used for the majority of the work done in this study (Base Grease #1) is a commercially-sourced straight lithium NLGI Grade #2 base containing Group I mineral oil. It was chosen for its moderate severity and response to additives so that better or worse results could be seen under the different conditions studied.

A second base grease (Base Grease #2) was also employed for part of this study. This base was made in the author’s facility using a lab scale kettle. It is a lithium 12-hydroxy stearate grease cut to an NLGI #2 grade and containing an ISO 150 Group I mineral oil blend. This grease was used to better understand the role of the thickener in protecting against corrosion.

The additive systems used were of two types. The first set was a group of packages that were formulated specifically for use in grease and contain combinations of rust inhibitors optimized for use in grease applications (Pack A, B, C). The second set was a group of packages that were optimized for gear oil applications (Pack D, E, F). These types of additive packages are often used in grease formulations because of desirable performance aspects that can be achieved.

Synthetic Seawater Solution

The formulation for synthetic seawater (SSW) is shown in ASTM D665B, and is referred to in both D6138 and D5969 (see Figure 2). All dilutions used in rust testing are shown as some percentage of the “100%” formulation described in D665B.

Results

Initial testing was completed on Base Grease #1 alone and with 1.5 wt% of an EP additive blend. As can be seen from the results (Figure 3), the base grease by itself does a good job of protecting the EMCOR bearing in the presence of distilled water only but when a small amount of ionic character is added with a 5% mixture of SSW that ability disappears completely. Even the small amount of ionic material that was introduced with the EP additive system introduces some rust which hints at a tendency to break down that limited protection.

Following this initial testing, Base Grease #1 was treated with Packs A thru F at various treat rates (Figure 4). Treat rates were chosen based on typical dosages and, for Packs D and E, two treat rates were used for each pack to be able to compare the effect of increased rust inhibitor on corrosion protection. The use of 5% SSW was decided on to give moderate rust results so that good comparison across different packages and rust inhibitor levels could be achieved. To

- 10 VOLUME 79, NUMBER 6

give a good comparison with a solution of pure sodium chloride (NaCl), it was decided to use the equivalent amount of salt on a weight percent basis. Using the SSW recipe, this was determined to be 0.212 wt% of NaCl in aqueous solution.

Examining the results in Figure 4, rough correlation can be seen between the severity of test results and the amount of rust inhibitor present. This is especially noticeable in comparing Packs A, B and C, as well as in looking at the different treat rates of both Pack D and E. The same trend is seen, generally, with both the 5% SSW and 0.212 wt% NaCl

solutions although the NaCl solution appears to have a significantly milder effect on corrosion when compared head-to-head with the SSW solution.

This milder effect also appears to reduce the level of differentiation in corrosion results seen with treat rate in the SSW solution. Based on the results seen in this general screening of different packages and rust inhibitor levels, it was decided to use Packs C and D-2 for further study.

The next stage of the study was an investigation of the effect of increasing salt water concentration using the SSW solution, as well as similar dilutions of NaCl (Figure 5).

The effect of different salts was also studied by including magnesium chloride (MgCl2.6H2O) and calcium chloride (CaCl2). The practical reason to use these salts is that they often are used in de-icing solutions and therefore, automobiles, trucks and heavy equipment can all be exposed in colder climates. The dilution level of these additional salts was determined based on molar equivalents to the 0.212 wt% NaCl solution. It was obvious from these different ways of comparing salt solutions (weight percent versus molar equivalents) that a more universal way of comparing the solutions was needed. The ionic

activity should have some effect on the amount of corrosion seen in a particular test, so these activities were calculated for each solution and are shown in Figure 5 as well.

As expected, the severity of the corrosion seen increases with the increase in concentration of the salt water solutions both in the case of SSW and NaCl solutions.

As discussed earlier, there is a slightly milder effect seen when using 0.212 wt% NaCl versus the 5% SSW solution. However, as the concentration of the solutions was increase, a larger disparity between the two solutions was seen with the NaCl being more severe than the equivalent SSW solutions (2.12 wt% NaCl vs 50% SSW, and 4.24 wt% NaCl vs 100% SSW).

When looking at the additional salt solutions, the MgCl2 appeared to be more severe than either the CaCl2, the NaCl (0.212 wt%) or the SSW (5%) solutions with 4 bearings giving ratings of “2” while the other salts gave slightly milder ratings between “0” and “2”.

It is recognized that the concentrations of the different salt solutions may not allow an easy comparison due to different weight percents and molar equivalents being used. For this reason, a comparison was made with respect to the calculated ionic activity for each of the solutions (see Figure 6).

From the graph, a rough correlation is seen between corrosion and the ionic activity of the salt solution to which it is exposed. The effect seems to plateau at higher activities but this may well be due to the non-linearity of the EMCOR rating system which gives its highest rating of “5” to any bearing with

corrosion on more than 10% of its surface. Another observation is that there appears to be better protection provided by Pack C at lower ionic activities (in the range of 0 to 0.2) but that same advantage is not seen at the higher levels of activity.

To compare the severity of the EMCOR “dynamic” corrosion test to the “static” corrosion test (ASTM D1743 and D5969), testing was carried out under similar conditions with a minor modification in the rating methodology. The tapered roller bearings of D1743 and D5969 are typically judged as “pass” or “fail” with two out of three “passes” needed for a successful test.

For comparison purposes and to better judge the effect of different conditions and salt solutions, the EMCOR rating system was applied to the bearings in this portion of the testing yielding ratings from “0” to “5” for each bearing. Following the methodology of D1743 and D5969, three bearings were run in almost all cases.

Additives used in the testing in this section were limited to Packs C and D-2 with the focus being comparison to the work done with the EMCOR bearings discussed above. Base Grease #1 was also used in this section for the same reason.

The results for Base Grease #1 with both distilled water and 5% SSW were very similar to those seen with the EMCOR testing (Figure 7). Again, a small increase in ionic activity showed a large increase in corrosion with ratings going from “2/0/0” to “5/5/5”. The same was seen with the additized greases with both Pack C and D-2 giving adequate protection of the bearings in distilled water while the presence of the 5% SSW solution caused significantly more corrosion in each grease (although less than the unadditized base grease).

- 12 VOLUME 79, NUMBER 6

Comparison with the other salt solutions used in the EMCOR study, showed very little differences when using Pack C as the additive. However, Pack D-2 appeared to give better protection against corrosion in the presence of NaCl solution as compared to the other solutions. In general, Pack C provided better protection in all the salt solutions except for NaCl in which case there appeared to be no difference between the additive packages.

Interestingly, when compared to the results from the EMCOR testing (shown in red in Figure 7), the ASTM D5969 results appear to be more severe in each of the salt solutions regardless of the rust inhibitor system employed. This is in spite of conditions which would seem to make the EMCOR test more severe – longer time (1 week vs 24 hours) and environmental setting (dynamic rotation through water vs static exposure to humid atmosphere).

To further explore these differences, the ASTM D5969 test was modified to use the EMCOR bearing under the D5969 conditions. Sufficient water was used to raise the level, relative to the bearing, to the same height as the standard test and 30 ml was left in the container to provide the humid atmosphere necessary for the test.

Several run-in conditions were used to judge the effect of this parameter (Figure 8). The standard EMCOR run-in procedure provides a total of about 2490 revolutions over a 30 minutes period whereas the D5969 procedure uses a much higher speed process which gives about 1750 revolutions in a minute. As can be seen from the results neither the amount of break in time or total number of revolutions seemed to have a significant impact on the results. Based on the data generated, it appears that the bearing itself is the main factor in the severity of the test. The first possible reason for this is that the tapered bearing configuration gives significantly more areas for rust to form with the linear geometry of the contact points with the outer race. The EMCOR ball bearing design only allows point contact with the outer race and therefore fewer overall opportunities for rust to occur.

Another possibility is that the design of the EMCOR bearing somehow allows better distribution of the grease and less ingress of water.

The effect of time and temperature on extent of corrosion was also studied using the ASTM D5969 test method with 5% SSW solution. The standard test method calls for exposure to a humid atmosphere at 52 ËšC for 24 hours. The method was modified (as

- 13 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

shown in Figure 9) to look at lower (room temperature – RT) and higher (70 ˚C) temperatures as well as an extended period of time (48 hours). The modified temperatures gave surprising results in that the lower temperature appears to give more severe results. Both additive packages gave better corrosion protection at the higher temperature than at the lower temperature even though at the standard test temperature Pack C was more effective. One possible explanation that is suggested in the literature [x] is that raising the surface temperature of the part may reduce the relative humidity at the surface and therefore reduce corrosion. Other possible explanations are that the softer grease gives better surface coverage at the higher temperature leading to better overall protection, or that the additives are more effective at higher temperature which might also explain the differences between the two packages at the standard temperature.

The longer time resulted, unsurprisingly, in more severe corrosion but this result does lead to the question of correlation of results of a 24 hour test to actual field conditions. How long does a grease that protects against moisture for 24 hours in the D5969 test actually protect against moisture in the field? The increase in severity seen with doubling the length of the test may indicate some need for additional study in this area.

A final aspect of corrosion was addressed by looking at the role that the grease itself plays in preventing corrosion. As was seen earlier in this study, base grease by itself supplies sufficient protection against rust in the presence of distilled water, but an increase in ionic activity quickly overcomes that basic protection. It is not clear whether the grease thickener system is protecting against rust, in part or in whole, by preventing water from getting to the surface, or if the additives in the grease are sufficiently surface active to protect the bearing from corrosion by themselves.

For this study, a lithium 12-hydroxy stearate grease made with an ISO 150 cSt Group I mineral oil blend (Base Grease #2) in the author’s lab was used. This allowed the separate study of the grease thickener/oil combination and the oil by itself. Both were additized with the same amount of Pack C and therefore the only difference between sample #2 and #3 was the presence of the grease thickener in sample #2. The samples were then tested in the standard EMCOR test using a 50% SSW solution (Figure 10). This had resulted in a medium rating of “3/2” with Base Grease #1 and the same conditions were used in order to see if there were any changes for better or worse.

As can be seen, there were no significant differences in the results for samples #2 and #3. While obviously based on a small sample set, this seems to indicate that the additive system itself is responsible for the corrosion protection under these circumstances and no additional benefit is seen from the presence of the grease thickener.

It is in fact possible that the thickener has resulted in more corrosion although further study would be needed to confirm that with any statistical significance.

Summary and Conclusions

Under the conditions of the study, there does appear to be a rough correlation between ionic activity of various salt water solutions and the amount of corrosion seen in bearings. However, the type of molecule present in the salt solution does appear to have some effect separate from the overall ionic activity of the solution. This could indicate that the type of salt in the environmental water to which greases are exposed in the field could be important in formulating a grease for use in that application.

Higher concentrations of salt solutions as well as increased amounts of time exposed to them under test conditions increases the amount of corrosion seen. In addition, an increase in temperature of the test showed a

decrease in the amount of rust seen. These observations seem to indicate that reliance strictly on bench tests under limited conditions may not be sufficient to guarantee corrosion protection in environments that do not mimic these standardized conditions. Time and temperature seem to be especially critical and further study into the correlation of these two parameters in both bench and field testing would appear to be warranted.

The type of bearing was also shown to be critical with the tapered roller bearing giving more severe results than the EMCOR in almost all side-by-side testing. This was likely due to the larger number of contact points (and potential areas for rust to begin) seen with the tapered bearing. This indicates the importance of using the right bench testing to formulate for different bearing applications.

Finally, the importance of additive chemistry was seen with the severity of corrosion varying depending on the type of additive system and the treat rate of a specific additive system. The additive system can be optimized depending on the amount of corrosion protection needed and the environment to which the grease will be exposed.

It was also seen, in limited testing, that the additive system by itself may be sufficient to provide the corrosion protection needed.

Additional study is indicated in a number of areas including the role of thickener in corrosion protection, the effect of temperature on rust formation and activity of corrosion inhibitors, and reason for differences in severity of different types of salt solutions. It is hoped that the information provided here will stimulate further investigation into these areas.

References

1. Koch, G.H., Brongers, M.P.H., Thompson, N.G., Virmani, Y.P., Payer, J.H. “Corrosion Costs and Preventive Strategies in the United States” Publication No. FHWA-RD-01-156.

2. Kenny, J.F., Barber, N. L., Hutson, S.S., Linsey, K.S., Lovelace, J.K. and Maupin, M.A., “Estimated Use of Waater in the United States in 2005”, United States Geological Survey, http://water.usgs.gov/edu/wumi. html.

3. Neil, M. “Overcoming Saltwater Corrosion”, Water and Waste Digest, Oct 2, 2009. http://www.wwdmag. com/pipe/overcoming-saltwater-corrosion.

4. Hunter, M. E. and Baker, R. F., “Corrosion-Rust and Beyond”, NLGI Spokesman, Vol. 63, No. 1, March 1999.

5. Hunter, M. E. and Baker, R. F., “The Effects of Rust Inhibitors on Grease Properties”, NLGI Spokesman, Vol. 63, No. 12, 2000.

6. Hunter, M. E., Rizvi, S.Q.A., and Baker, R. F., “Ashless Rust Inhibitors for Greases”, Presented at 67th NLGI Annual Meeting, Asheville, NC, October 2000.

7. ASTM D1743-13 “Standard Test Method for Determining Corrosion-Preventive Properties of Lubricating Greases”, (2013) ASTM International, West Conshohocken, PA. 8. ASTM D5969-11e1 “Standard Test Method for Corrosion-Preventive Properties of Lubricating Greases in Presence of Dilute Synthetic Sea Water Environments”, (2011) ASTM International, West Conshohocken, PA. 9. ASTM D6138-13 “Standard Test Method for Determination of Corrosion-Preventive Properties of Lubricating Greases Under Dynamic Wet Conditions (Emcor Test)”, (2013) ASTM International, West Conshohocken, PA.

- 15 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

NLGI MEMBER

SPOTLIGHT

We hope you’ll enjoy learning more about our first Member Spotlight company, ILCO Industriale srl from Premenugo di Settala, Italy. ILCO has

been a valuable member of NLGI since 1956 – exactly 60 years! Their long-time NLGI

membership has been due, in part, to their vast and invaluable NLGI Spokesman technical library.

Company: ILCO Industriale srl Member Category: Manufacturer Contact Name: Mario Cagliani Region: Province of Milan Country: Italy Address: V ia F.lli Rosselli 2, Settala (MI), Italy 20090 Telephone: +39 02.9577901 Email: sarah.pirronello@ilco.it

ILCO began as an oil and lubricating grease manufacturer in 1945, founded by Francesco Cagliani, and later assisted by his brother Emilio. At the present time, most of the business is still owned by the Cagliani family and management is entrusted to the General Manager, Mario Cagliani.

The factory is nearly 5,000 square meters with a total area of nearly 14,000 square meters with storage tank capacity of nearly 1,000 tons. The output of our company in 2014 was nearly 15 million Euros. IlCO has a highly trained staff of twenty-seven employees.

and which allows us to study new kinds of products and to control the raw materials.

As a manufacturer, ILCO specializes in the production of lubricating greases as a third-party provider for many oil companies and can list among its customers nearly all the biggest international oil companies.

ILCO’s current production includes nearly 500 different kinds of lubricating greases, managed and studied in it’s laboratory, with the most updated technologies available including: New generation viscometers, rheometers, IR, ASTM tests and a pilotplant which exactly reproduces the production’s reactors

Currently, ILCO has a modern grease production department, always up-to-date with its own innovative technologies with a production capacity of nearly 12,000 tons per year. This guarantees speediness and a capability to satisfy the needs and requirements of our customers for the approximate 6,000 tons per year produced and sold.

ILCO gives its customers complete service for lubricating greases, starting from formulation to final packaging. ILCO is able to manufacture 50-gram tubes, to a whole tanker both of oils and bulk greases.

- 16 VOLUME 79, NUMBER 6

We have modern facilities for production, filling, screenprinting, and for molding of our new grease cartridge model, with its own registered mark “Speedy Grease”.

To round out our business, ILCO also owns another company for the production of professional equipment for the use in greases, in particular pumping; also this equipment is studied and personalized according to our customer’s needs.

The customization of the equipment is possible because we work with a graphic agency that analyzes and carries out the dedicated customization.

The synergy of internal grease production, packaging, printing, equipment and graphic capability makes ILCO a unique leader in this field. (All work is naturally managed according to ISO 9001:2008 procedures.)

NLGI is proud to announce the introduction of the ‘NLGI Member Spotlight’, a new feature of the 2016 all-digital Spokesman magazine.

All NLGI members may take advantage of this opportunity to highlight your company’s history, global reach, vision, employees or whatever you’d like our readership to know about your company. You may talk about products & services, however, no competitor trade names may be used, nor mention of product pricing.

There is no limit on words and we welcome many photos

of your headquarters, offices, plant & employee photos. We will accept articles for publication on a first received, first published basis. Contact Marilyn Brohm Marilyn@nlgi.org at NLGI if you would like to submit an article for possible publication in an upcoming issue.

There is absolutely no charge to have your article appear in the NLGI Member Spotlight

the Expert Q:

Is there a recent pie chart showing the breakup of the world grease usage, by sector, by soap type?

A:

Please consult the NLGI Grease Production Survey - available for purchase on the NLGI website - to get a break-down by thickener type. Here’s the link: https:// www.nlgi.org/products-page/2014-nlgi-greaseproduction-survey/ As far as usage by sector, it’s a fairly even split between industrial and transport. Beyond that, they would need to contact a market research firm for more detailed information.

Q:

I have a 1.5 fluid ounce tube of Permatex WL-9 White Lithium Grease. Is it safe to use this grease on the gear that is exposed when the ice storage bin is removed from the freezer? The grease is used to keep the gear from sticking when the bin is removed. If this grease is not safe what do you recommend?

A: NLGI does not endorse any commercial products. Permatex WL-9 White Lithium Grease appears to be an industrial grease and would likely not perform satisfactorily at the operating temperature of an icemaker. We suggest you contact the manufacturer of the refrigerator/freezer/icemaker to get their product recommendation for the application described.

Q:

I’ve been running some grease corrosion tests in accordance with ASTM D4048 and getting quite varying results on the same test sample. The main variable I can see is the amount of cleaning at the end of the test should this just be a simple wipe? The grease leaves an oxidised coating behind and it is difficult to determine if I’m removing the grease coating or tarnish. Mainly I get some black streaking / spotting with a coppery undertone. There is no red / green / or brassy discolouration. Would this be a 1b or a 4? Any advice with this test method would be greatly appreciated.

A:

“ASTM International, formerly known as the American Society for Testing and Materials (ASTM), is a globally recognized leader in the development and delivery of international voluntary consensus standards. ASTM D 4048 method is the responsibility of the ASTM D.02.

G0 Lubricating Grease sub-committee which is split into 7 sections. Section G.01 is directly responsible for Chemical and General Laboratory Tests which includes ASTM D4048-10 “Standard Test Method for Detection of Copper Corrosion from Lubricating Grease”. Inquiries about this test can be directed to Joe Kaperick, the chair of Section G.01, at joe.kaperick@aftonchemical.com.”

Q:

Please help with finding conversions from civilian greases to military greases. The approved grease list that I have from Dexter Axles lists greases such as: Conoco Phillips Multiplex RED #2, Kendall L427 Super Blu, Citgo Lithoplex MP #2, Lithoplex CM #2, Mystik JT-6

- 18 VOLUME 79, NUMBER 6

High Temp Grease #2, Exxon Mobil Ronex MP, Mobilith AW2, Mobil 1 Synthetic Grease. There are many more listed. Where can I find what those greases cross to in military numbers such as MIL-G-24508?

A:

The greases that you have listed are all commercial or industrial products. Those products typically do not carry military approvals. To find a list of products that are approved against a specific military specification, we suggest you consult the Assist database at http:// quicksearch.dla.mil/. That application contains a database of approved products, and is maintained by the US military.

Q:

I run a tree stump grinding service using diesel powered stump grinding machinery. The pillar block bearings supporting the machines spinning cutter wheel at a max speed of 1500 rpm are subjected to a constant bombardment of soil grit, stones, etc. It is as though a grit-blasting nozzle is permanently aimed at the bearings whenever the machine grinds out a tree stump. This cutter wheel is also subjected to extreme intermittent shock loads throughout an eight-hour workday. I have been on a quest in search of the most appropriate grease to lengthen bearing life and hope you can assist in that regard.

A:

Q2:

Thank you so much for your fast response. I have contacted the manufacturer (J.P. Carlton Co. “sales@ stumpcutters.com”)awaiting a reply.

Heat build up over an eight hour period is an issue. What ASTM D2266/D2596 results should I be looking for with your suggested grease characteristics.

Would CS thickener with 5% moly be excessive and what is the next upward base oil viscosity.

A2:

If the bearings tend to run hot, a product containing a lithium complex thickener is recommended over the simple lithium thickener. The lithium complex thickener has higher temperature capability. With regard to D2596 (Four-ball EP), we recommend a minimum weld point of 250 kgf (kilograms force). A weld point of 315 kgf (the next higher load stage) would be even better. For D2266 (Four-ball Wear), we recommend the product have a value no higher than 0.6 mm. A product containing a calcium sulfonate thickener could also be considered for this application, but molybdenum disulfide (“moly”) is not recommended in this case. Although moly can be beneficial in shock load situations, for rolling element bearings turning at 1500 rpm, moly is not typically recommended. It can congregate at roller ends, cage pockets, etc. in the bearings and take out clearances, causing the bearings to run hot. It can also lead to sliding rather than rolling of the bearing elements.

First and foremost, always follow the lubrication Other things to consider: What product is currently recommendations of the manufacturer of the being used? Based on the properties of that product and equipment. That being said, and without clear guidance the level of service it is providing, we may be able to give from the equipment manufacturer, we recommend a better generic product recommendation than done a heavy-duty grease with the following general previously. If the bearings are running hot, a lower base characteristics: oil viscosity of 220 cSt @ 40°C may be a better choice for NLGI Grade 2 this application. Finally, a product based on a synthetic Base Oil Viscosity 460 cSt @ 40°C base fluid (such as polyalphaolefin (PAO)) may provide Thickener Type Lithium or Lithium Complex lower bearing temperatures than a mineral oil based Additive Package Extreme Pressure additive product of similar viscosity at 40°C. A grease with the above characteristics should provide satisfactory protection to the bearings in the equipment.

- 19 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

In this study, various PAO lubricating greases made from different thickener chemistries were tested to evaluate their particle generation properties. This particle generation phenomenon was studied using a custom test rig utilizing a high precision cleanroom ball-screw to simulate true application conditions. The ball-screw was tested at speeds from 200 RPM to 2,400 RPM to illustrate the effect of speed on the particle generation across different applications. This paper will show the tendencies of certain base oils and thickener chemistries to generate particles and which ones present advantages of improved durability and environmental cleanliness for critical processes and applications.

KEY WORDS: Particle Generation, DOE Introduction

The thought of Particle Generation is one that haunts many Engineers’ minds especially if they are working on applications in the Aerospace, Semiconductor, or Clean Room industries. The idea of foreign particles of unknown or dubious nature flying through the air (or travelling through vacuum) only to deposit on a critical area like a semiconductor fab, optical sensor, or even into the human body as the case may be with medical robots for surgery can certainly bring nightmares. This has been such a critical area and movement in the last thirty years and given rise to Clean Rooms manufacturing and the characterization of air cleanliness.

Jason T. Galary, Gus Flaherty Nye Lubricants, Inc.

INVESTIGATION INTO THE DYNAMIC PARTICLE GENERATION OF LUBRICATING GREASES

The purpose of this study is to examine the phenomenon of Dynamic Particle Generation in Lubricating Greases that are used in a variety of applications in critical Industries which include Aerospace, Semiconductor Manufacturing, Medical, and Cleanrooms. This Particle Generation occurs in bearings, ball screws, and other mechanical devices when dynamic conditions are present and should not be confused with Outgassing which is related to the pressure effects on a system. This is a critical factor in many systems as particle generation can contaminate critical systems or processes causing them to fail. These failures can lead to excessive costs, production lines going down, and equipment damage.

The focus for so long has been on the quality of the air in the room and the perception has long been that lubricants are a source of contamination in cleanroom and vacuum environments. In order to alleviate the worries of many customers across various applications and industries, the solution over the last twenty years has been to Ultrafilter1 the lubricant to reduce the number of particles and the size of them.

There are three levels for cleanliness in a grease:

• Unfiltered grease – Can contain particles larger than 75 µm.

• Filtered or so-called “Clean” grease – For example MIL-G81322 Aircraft grease cannot have any particles greater than - 20 VOLUME 79, NUMBER 6

75µm and there must be fewer than 1,000 particles/cm3 between 24µm and 74µm.

• Ultrafiltered or “Ultraclean” grease – Such as MIL-G-81937 must not contain any particles greater than 35µm. In addition to this it cannot have more than 1,000 particles/cm3 between 10µm and 34µm in size.

This process will certainly help remove bulk and “hard” contaminants which will lead to smoother operation and lower noise in applications like bearings and ball screws but it may have little effect in regards to the amount of particles “shed” or generated from a lubricant in a dynamic condition.

This question has long stuck in our minds, wondering what the lubricant was truly doing and how the base fluid, thickener, additive, and manufacturing processes effected this property and ultimately the application environment around it. The first step to investigate this new area of lubricant properties required the construction of a new test apparatus and creation of an accurate and repeatable test method.

newly created test method and fixture, a DOE project was also put together to investigate repeatability, functionality, and statistical significance.

The core of the test apparatus is a high precision cleanroom ball screw assembly meant for low outgassing applications. This ball screw design was used due to the fact that when lubricated correctly and under light load, a ball screw assembly experiences virtually zero wear on its components. Since a ball screw assembly utilizes a system of rolling elements, the amount of frictional wear on any components especially under no load is greatly reduced. With the addition of a lubricant that provides a protective layer between all surfaces, the main component of wear on the system is the lubricating grease, which then generates the particles being examined in this study.

This ensures that the particles generated in the dynamic system are purely generated from the lubricating grease.

The primary purpose of this study was to develop a new test method and apparatus that could be used to accurately and repeatedly measure the Dynamic Particle Generation of a lubricating grease.

To supply clean, filtered air to the system, a laminar flow clean air handler supplies clean ISO 2 Class air to the system. The air handler can deliver filtered air at a range of velocities, depending on operator input, but for the sake of repeatability and comparison, a velocity of 1m/s +/- .25 m/s was used for all testing. This value was decided on after investigating the average volume of clean air turned over in a clean air environment. This filtered air passes over the test system as the ball screw assembly operates for the length of the test.

The Key Factors of this study will be:

1. The repeatability and statistical significance of Dynamic Particle Generation results.

2. To study the effects of different lubricating thickeners that all utilize the same PAO base fluid.

3. To examine the effect that speed plays on the particle generation of a particular system

4. To examine the profile of the particle generation results plot; that is how the system behaves with respect to time and number of particles generated.

Particles are collected via an inlet tube mounted at the end of the ball screw assembly. The location of the pickup tube is key, as it captures only particles generated by the grease on the ball screw, and none generated by the servo motor, bearings, linear guides, or flex coupling. The pickup tube leads to a Light-scattering Airborne Particle Counter. The particle counter features simultaneous 5-stage particle measurement of .3µm and above, .5µm and above, 1µm and above, 2µm and above, and 5µm and above via the use of a transverse light-scattering system which provides the most accurate and repeatable measurements available.

Objective for Testing:

Experimental Test Method:

To compare the dynamic particle generation characteristics of various lubricating greases, a custom test apparatus was designed and built to detect, analyze, and classify the products being examined. As this is a

During the test a particle count profile is then constructed, plotting the count of each category vs test duration. This profile chart is an important asset to have in order to understand the behavior of the grease being run as two greases may share the same ISO cleanliness

- 21 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

value, but may have completely different particle distribution profiles over the duration of the test.

The dynamic particle generation test apparatus has the ability to run at 3 rpm’s, 200, 1,200, and 2,400 RPM. This translates to .02, 0.1, and 0.21 m/s of linear velocity, respectively. Comparison between greases should only be conducted at like rotational speeds, as particle generation typically increases as RPM increases. For this study we will only be looking at 1,200 and 2,400 RPM. Grease is applied to the ball screw assembly at 200RPM with a sample volume of 2cc being applied via syringe and a 10 cycle run-in to evenly distribute the grease. The test begins with the motor stationary while the particle counter takes a series of background readings. The number of readings taken is user defined.

The average of these background readings are subtracted from the particle count under dynamic conditions before ISO, JIS, or Federal Classes are calculated. This ensures that the particles being counted are only those produced by the grease and not the filtered air passing over the system.

compared against the ISO classification table and the ISO, Federal, and JIS classification are determined. All run parameters, a plot of the data collected over time, and the class are reported out to a prefabricated report template to be sent to the customer.

The ISO cleanliness levels are determined by the following formula and table.

Cn= 10N x [ 0.1/D ]2.08 (2) Where Cn = represents the maximum permitted concentration (in particle/m3of air) of airborne particles that are equal to or larger than the considered particle size; Cn is rounded to the nearest whole number N = ISO class number, which must be a multiple of 0.1 and be 9 or less D = the particle size in microns

At the conclusion of the test, the collected data is

- 22 VOLUME 79, NUMBER 6

The JIS cleanliness levels are determined by the following formula and table.

Cn= 10N x [ 0.1/D ]2.08 (3) Where Cn = represents the maximum permitted concentration (in particle/m3of air) of airborne particles that are equal to or larger than the considered particle size; Cn is rounded to the nearest whole number N = JIS class number, which must be a multiple of 0.1 and be 9 or less D = the particle size in microns

Repeatability and Statistical Significance:

To validate this new experimental test method, materials were tested with a minimum of three replications. Afterwards, statistical analysis was performed on the sample sets to look for any statistically significant differences. Different lots of the same material and different sections of a specific batch were also tested.

Repeatability between Tests (Same Material, Same Operator).

- 24 VOLUME 79, NUMBER 6

The results of statistically testing the same material multiple time with the same operator and using a Standardized t-test on the data shows that the means of the data are equivalent. A 95% confidence interval was constructed and the means of both sample distributions fall within these intervals. Based on this we can conclude with 95% confidence that the two samples have the same mean and this test equipment produces reproducible results.

- 25 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

Testing the same material from different lots with the same Operator.

- 26 VOLUME 79, NUMBER 6

The results of statistically testing the same material from different lots with the same operator and using a Standardized t-test on the data shows that the means of the data are significantly different. A 95% confidence interval was constructed and the mean of the 0.3Âľm sample distributions did not include all values from both sets. Based on this we can conclude with 95% confidence that the two samples do not have the same mean and there were significant differences between the different lots tested.

- 27 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

Results and Discussion:

Tables 4 and 5 Summarize the ISO classifications for the six different greases that were studied in this experiment, at 1,200RPM and 2,400 RPM, respectively.

- 28 VOLUME 79, NUMBER 6

Figures 5-8 highlight the comparison between lubricants in relation to motor speed and particle size. (Note: For simplicity of comparison, only the smallest (.3Âľm) and largest (5Âľm+) particle size categories were examined.

- 29 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

- 30 VOLUME 79, NUMBER 6

The Urea based thickeners have performed the best in this study with PAO as a base fluid. The tetraurea version did outperform the diurea. The size, complexity, and shear stability of the urea structures are helping to keep the lubricant anchored to the surface and lowering the probability of particles from escaping the thickener matrix and becoming particle generation.

One curious result from the study is that the diurea based material generated almost double the amount of 0.3µm particle at the lower speed/shear than all of the other samples. The first thought might be that this amount of particle generation is from initial startup and wear in but as seen in Figure 13 this trend continues for the life of the test. At the same time the clay thickened material produced one of the lowest results. But once the samples were tested at a higher speed/sheer then we saw results that align better with expectations of these chemistries with the diurea generating a much smaller amount of particle and the clay generating the highest as there is very little more than a mechanical bond holding that system together. In low speed/shear conditions the clay grease and its distribution of smaller thickener particles are free to move around and stay bound together. Once the speed/sheer is increased then these materials have a higher tendency to agglomerate and create internal friction forces which will then allow some of the particles to be freed from the thickener system and out of the ball-screw.

Additional testing on different grades of diurea thickener as well as various speed/shear rates, manufacturing process, filtration, etc will be looked at in the future to determine why this PAO diurea grease generated almost double the amount of 0.35µm or smaller particles compared to all the other thickeners.

While the ISO classification system is very useful for classifying air cleanliness levels, it is lacking when used as a comparative tool for lubricants as all of the samples at both 1,200 and 2,400 RPM received either an ISO Class 5 or 6 rating. This is mainly driven by the 5µm particle requirement in the ISO/JIS/Fed Spec. Without any other way to compare materials, this would leave profile analysis as one of the only simple tools to differentiate between classes beyond a more complicate statistical analysis. To help differentiate materials, we broke each particle size sample set into ISO class sub-classes, which yields more differentiation between materials tested.

Tables 4 and 5 break out the ISO sub-classes into a .1 increment scale (using previously mentioned formula2).

The highest classification per chemistry is highlighted in bold.

- 31 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

From this data we can see that the majority of classifications were driven by the particle result in the 5µm+ range. As Table 1 shows, in order for any grease to be rated at anything less than an ISO Class 5 there must be zero particles present at 5µm+ category even if the remaining categories consistently rate lower. Due to this requirement all of the greases run in this study were classified as an ISO Class 5 or higher.

Examining the run profile of the greases, it can be noted that all runs displayed an upward trending profile at 2,400 RPM. Figures 9-12 illustrate the run data profile associated with motor speed and a .3µm particle size.

- 32 VOLUME 79, NUMBER 6

The steady increase in particle generation over the duration of the test can be attributed to many factors which will need to be investigated in future work. This increase as a factor of speed could be a result of the nature of the PAO chmistry to shed particles, not fully maximized thickener, Manufacturing process, etc.

Figures 15 & 16 graphically illustrate the particle generation response of the various lubricating greases with speed of the ball screw as a factor.

- 34 VOLUME 79, NUMBER 6

Conclusions

The classification of particle generation of lubricating greases in dynamic conditions is a new area that we are just starting to explore. As presented in our study, many factors play into the behavior of a grease in respect to particle generation characteristics. Variables such as run speed, base oil chemistry, and thickening agent properties all play into how a grease will perform in a clean room environment.

We have developed a new test method that has proven to be repeatable and reproducible. This method can differentiate between materials, lots, and chemistries. Looking ahead this new testing method for Dynamic Particle Generation could be used not only for comparing products but also for Quality Certifications or R&D investigation into particle distribution in a lubricating grease or effects of processing equipment.

We now have a small set of data that is giving us a glimpse into the effects of thickening agents on particle generation. With more complex and in-situ thickeners providing a better matrix for the oil to hold onto as well as helping bond with the surface, they are at the top performers in this new performance measurement. The innate shear stability of these thickeners also helps them perform in this measurement as the thickener is less likely to be broken down which would allow particles to be freed from the thickener matrix and into the environment as particle generation.

The ability to plot particle generation over time and see differences in the distributions of various materials/lots, this will help us to form hypothesis about particle generation over time using normalized probability. Utilizing this type of analysis can also be used to predict lubricant service life. From these estimations, maintenance schedules could be determined which would help to keep units performing optimally.

The future goal is to develop a lubricating grease which will produce no more particles than its environment is rated for. Ideally a lubricant can be developed that will generate less particles than the clean air system that is being used

in an applications environment. When this is accomplished, it will give end users the confidence that the lubricant they are using will not contaminate their clean environment or possibly effect their application

Future Work

We would like to expand testing to include additional lubricant chemistries and thickener combinations including Esters, Mineral Oils, Phenyl Ethers, PFPE’s, and Multiply-Alkylated Cyclopentanes. We also plan to investigate the effects of different types of manufacturing processes and their effect on the particle size of thickeners and the resultant Particle Generation.

Finally we will also add additional tests to run the samples investigated in this study for longer periods of time to look at the trend of particle generation.

Acknowledgements

We would like to thank our colleagues in the Application Development and Validation Testing (ADVT) Lab at Nye Lubricants Inc. who conducted the Dynamic Particle Generation testing, specifically Mason Wood. We would also like to Akira Nogami from THK Inc., for his collaboration on this project development and his help on the optimal ball-screw design. Finally we would like to William Galary for all of his support and consultation about the Clean Room Industry and its technologies.

References

[1] Galary, William: Ultraclean Grease. Journal of Advancing Applications in Contamination Control 1999; Volume 2, No. 7:23-27 [2] Cleanrooms and associated controlled environments Part 1 : Classification of air cleanliness. ISO 14644-1 1999; [3] Classification of air cleanliness for cleanrooms. JIS B 9920 2002; [4] Cleanroom and Work Station Requirements, Controlled Environments. Federal Standard 209 1963;

- 36 VOLUME 79, NUMBER 6

SAVE THE DATE!

NLGI 83rd Annual Meeting

The Omni Homestead • Hot Springs, VA, USA

June 11th -14th 2016 On-line registration will open in early March 2016

NLGI Industry News Please send all industry news, events, employment news and press releases to Marilyn Brohm (Your company does not have to be an NLGI member to post items.)

Phillips 66 Lubricants Names Best Line Oil Co., Inc. TOP TIER Marketer Tampa, Florida-Based Distributor Receives Distinguished Status for Excellence in Best Practices

TAMPA (Jan. 19, 2016) - Phillips 66 Lubricants, one of the largest finished lubricants suppliers in North America, today announced that Best Line Oil Company, Inc. has achieved TOP TIER Marketer status for exceeding quality, safety and environmental operations standards. The elite recognition is awarded to a select number of Phillips 66 Lubricants distributors that have exceeded the company’s rigorous Marketer Operations Standards practices. These standards were created to help protect the product quality of the Phillips 66 Lubricants brands and improve the efficiency of safety and environmental programs, according to Bryan Faria, Manager, Finished Lubricants. Best Line Oil Co., Inc. is a third generation family owned wholesale lubricants distributor servicing the central Florida region since 1935. “We are very proud of Best Line Oil Co., Inc. and the exceptional work they have done,” said Faria. “They have proven to be extremely successful in achieving the high operation and quality standards of Phillips 66 Lubricants and will be joining an elite group of Marketers from across North America that share this distinguished recognition.”

To read the complete Press Release visit: https://www.nlgi.org/news-and-events/industry-news/

Partner Collaborations Advance Second-Generation Elevance Biorefinery Technology

Woodridge, Illinois, USA (Jan. 19, 2016) – In collaboration with several partners, including the special contribution of Versalis under a strategic partnership started in early 2014, Elevance Renewable Sciences, Inc. — a high-growth company that creates novel specialty chemicals from natural oils — has successfully completed scale-up of a secondgeneration biorefinery technology of the company’s olefin metathesis technology, utilizing ethylene and natural oil feedstocks. To read the complete Press Release visit: https://www.nlgi.org/news-and-events/industry-news/

January 6, 2016: World Demand for Lubricants to Exceed 45 Million Metric Tons in 2019

World demand for lubricants is projected to rise 2.0 percent annually to 45.4 million metric tons in 2019. The fastest gains are expected in the Asia/Pacific region, where an expanding number of motor vehicles in use and continued industrialization in large countries such as China and India will support rising demand. Developing regions such as Central and South America and the Africa/Mideast region will also exhibit healthy gains in response to economic growth, rising manufacturing output, and increasing motor vehicle production and ownership rates. These and other trends are presented in World Lubricants, a new study from The Freedonia Group, Inc., a Cleveland-based industry research firm. To read the complete Press Release visit: https://www.nlgi.org/news-and-events/industry-news/ - 38 VOLUME 79, NUMBER 6

BECHEM Lubrication Technology, LLC Continues To Expand Their Sales & Application Engineering Team BECHEM announces that Jillian Jurvelin has joined the BECHEM Sales & Application Engineering team. After graduating from University of Detroit with a Bachelors of Arts and Masters Degree in Industrial Organizational Psychology, Jillian comes to BECHEM with consulting and sales experience in both Automotive and General Industry market areas. Jill will be joining the Specialty Lubricants Team for BECHEM that continues to further expand in North America. “We look forward to having Jill join our team of professional sales & application engineers. She brings another dimension to our group that will blend well with the rest of team as we continue to expand our market penetration in the Specialty Lubricants market sector”, says John Steigerwald, President of BECHEM Lubrication Technology, LLC. BECHEM Lubrication Technology, LLC. • 5601 Chagrin Road, Chagrin Falls, OH Phone: (440) 263-4773 • Toll Free: (844) 883-4420 • Internet: www.bechem.com

York, PA January 4, 2016 – At the recent American Society of Testing and Materials (ASTM) meeting held in Austin, Texas, the society presented an Award of Appreciation to Lisa Williams of MRG Labs. This reflected on her contributions as a member of the ASTM D02 Grease Subcommittee and In-Service Lubricant Testing and Condition Monitoring Subcommittee, where she serves as the vice-Chairman. The citation for her award reads, “Lisa Williams worked tirelessly to the benefit of industry with the introduction of a new technology to perform comprehensive testing of inservice grease samples. The culmination of her efforts recently led to the new standard, D7918, Standard Test Method for Measurement of Flow Properties and Evaluation of Wear, Contaminants and Oxidative Properties of Lubricating Grease by Die Extrusion Method and Preparation.”

To read the complete Press Release visit: https://www.nlgi.org/news-and-events/industry-news/

Molykote® brand lubrication scientist Manfred Jungk of Dow Corning elected to board of German tribology group

Wiesbaden, Germany: At the recent conference of GfT – Gesellschaft für Tribologie e.V. (the German Tribological Society), a globally recognized Dow Corning lubrication expert was elected to the group’s Board of Directors. To read the complete Press Release visit: https://www.nlgi.org/news-and-events/industry-news/ - 39 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

NLGI Industry News

TEKNOR APEX APPOINTS VANDERBILT CHEMICALS AS EXCLUSIVE GLOBAL DISTRIBUTOR OF ITS TRUVISTM ESTER PRODUCT LINE

PAWTUCKET, RI, U.S.A., December 21, 2015: Teknor Apex Company has appointed Vanderbilt Chemicals, LLC as the exclusive global distributor of its TruVis™ line of ester products. To read the complete Press Release visit: https:// www.nlgi.org/news-and-events/industry-news/

More than 5,000 Attendees to the 2015 Chem Show Underscore Event’s Long-Standing and ForwardLooking Value

WESTPORT, Conn., December 17, 2015 – The 2015 Chem Show, held November 17 to 19 at the Javits Center in New York, welcomed 5,170 registered attendees at the chemical process industries’ (CPI) leading event for processing technology. To read the complete Press Release visit: https://www.nlgi.org/news-and-events/industry-news/

Phillips 66 Lubricants Expands Commercial Line with Two New Heavy-Duty Synthetic Transmission Lubricants

Both Triton® Synthetic MTF and Kendall SHP® Synthetic MTF Meet Eaton PS-386 Specification for Service Fill HOUSTON (December 10, 2015)—Phillips 66 Lubricants, one of the largest finished lubricants suppliers in North America, today announced the addition of two new heavy-duty synthetic transmission lubricants to its Commercial product line—Triton® Synthetic MTF and Kendall SHP® Synthetic MTF. The new manual transmission fluids are fullsynthetic, fuel-efficient transmission lubricants designed for use in heavy-duty commercial manual transmissions operating in extreme temperatures and extended service intervals. Both products are approved for service fill under the new Eaton PS-386 specification (supersedes Eaton PS-164 Rev 7). To read the complete Press Release visit: https:// www.nlgi.org/news-and-events/industry-news/

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DuPont Announces 2020 Sustainability Goals

Centerpiece Innovation Goal to Embed Sustainability into DuPont Innovation Process WILMINGTON, Del., Nov. 18, 2015 – DuPont today announced its 2020 Sustainability Goals as the next step in its more than 25-year commitment to sustainability. The centerpiece of the new DuPont 2020 Sustainability Goals is a companywide commitment to embed sustainability into its innovation process and R&D pipeline. To read the complete Press Release visit: https://www.nlgi.org/news-and-events/industry-news/

Elevance to Present Trends in High-Performance Synthetic Industrial Lubricants at 2015 ICIS and ELGI Industrial Lubricants Conference

At the 2015 ICIS and ELGI Industrial Lubricants Conference, Elevance Renewable Sciences, Inc. will present market, performance and technology trends in high-performance synthetic industrial lubricants.

As part of the presentation, Elevance will discuss new tools and derivatives for the lubricants market as well as comparing properties and performance of alphaolefin/alphaolefin ester synthetic base stock technology. To read the complete Press Release visit: https://www.nlgi.org/news-and-events/industry-news/

- 41 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

Welcome our new 2015 NLGI members!

(Note: If your company is an NLGI member, you may login to our website’s ‘Members Area’ and obtain direct contact names and email addresses for all NLGI members.)

AkzoNobel Surface Chemistry – Manufacturer 525 W Van Buren St Chicago, IL 60607-3835 USA 717-808-2076 http://www.akzonobel.com

E-360 - Marketing 601 108th Ave NE, Suite 2250 Bellevue, WA 98004 USA 206-920-4134 http://www.e-360.com

BASF Corporation - Supplier 4900 Este Ave., Bldg 53 Cincinnati, OH 45232 USA 513-482-2138 http://www.basf.com

Ferreyros S.A – Technical Calle la Huaca, 306 Pueblo Libre Lima, Peru 51-1 51-1-647-1821 Fluid-Bag Ltd - Supplier

Cartier Watchmaking – Consumer Manufacture CARTIER Rue des Alisters La Chaux-De-Fonds. France 2300 41-32-927-7391

Bottenviksvagen 54-56 Jakobstad, Finland 68600 358-20-779-0444 http://www.fluid-bag.com

Chevron Phillips Chemical Company – Supplier 8231 Cove Timbers Lane Tomball, TX 77375 USA 832-559-3120 http://www.cpchem.com/

Frigmaires Engineers – Manufacturer Unit No. 8, Janata Industrial Estate, S.B. Marg Opp.High Street Phoenix, Lower Parle(W) Mumbai, Maharashtra. India 400 013 91-222-494-5624 http://www.lubeoil.co.in

Ducom Instruments (USA) Inc. – Technical 1907 N Mendell St., Ste 115B Chicago, IL 60657 USA 847-737-1590 http://www.ducom.com

GreenTime – Marketing Mozhaiskoe shosse 2, Office 2 Moscow, Russia 121 374 7-916-900-0342 http://greentime.ru/

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Italmatch Chemicals – Supplier Via Vismara 114, Arese Milan, Italy 20020 00-393-351-464-003 http://www.italmatch.it/

Masac Interoil S.A. de C.V. – Manufacturer 5 de Mayo, 1439 Pte, Centro Monterrey Monterrey, Nuevo Leon, Mexico 64000 52-81-8882-(2828 - 2831) http://www.masac.com.mx/

Jaykamal Petroleum Services – Technical PO Box 30154 Dubai, United Arab Emirates (UAE) 4444 97-150-640-2887

MRG Labs – Technical 410 Kings Mill Rd York, PA 17401 717-843-8884 http://www.mrgcorp.com

Jinduicheng Molybdenum Co., Ltd – Supplier No. 88, Jinye 1st Road, Hi-Tech Development Zone Xi’an, Shaanxi Province, P.R. China 710 077 +86-298-837-8612 http://www.jdemoly.com JV Yukoil Ltd.- Manufacturer 3A Bazovaya Str Zaporozhye, Ukraine 69014 38-050-341-9088 yuko.eu/en

Nasyn Group Inc. – Supplier 206-887 Bay St. Toronto, Ontario, Canada M5S 3K4 +1(416) 800 4496 http://en.nasyn.com/ Oil Analysis Lab – Technical 2121 E Riverside Spokane, WA 99202 800-366-8596 https://oillab.com/

Laugfs Lubricants Ltd – Marketing No 760/A Dr. Danister De Silva Mawatha Plot No 10 Malwatte Epp Malwattee Nittambuwa Colombo, Western Province, Sri Lanka 009 94-11-533-7658 https://www.laugfs.lk/ M RAAB Consulting LLC – Marketing 932 Berkeley Ave Trenton, NJ 08618 USA 609-571-5026 http://www.mraabconsulting.com

Pavlo Rudenko – Student 1008 S East St Colfax, WA 28251 USA 509-339-3737 Petro-Lubricant Test Labs – Technical PO Box 300 Lafayette, NJ 07848 USA 973-579-3448 http://www.petrolube.com

- 43 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

Pressure Chemical Co. – Supplier 3419 Smallman St Pittsburgh, PA 15201 USA 412-682-5882 x 104 http://www.presschem.com

Stanhope-Seta – Technical London St Chertsey, Surrey, KT16 8AP UK 44-01-93-256-4391 http://www.stanhope-seta.co.uk

Resource Innovations, Inc. - Supplier 8 Riverside Dr Cartersville, GA 30120 USA 770-606-6901 http://www.riichemicals.com/

Trans Ocean Bulk Logistics – Supplier 3027 Marina Bay Drive, Suite 301 League City, TX 77573 USA 281-334-6585 http://www.transoceanbulk.com

Rizol Petro Products Pvt. Ltd. – Manufacturer Plot No-69, Sector - 16, HSIIDC Bahadurgarh, Haryana, India 124 507 91-989-111-3709 http://www.rizolpetro.com

istony Compania Industrial del Peru SAC – V Manufacturer MZ B LT 1, Parque Industrial de Ancon Lima, Peru +51 1-552-1325 http://www.vistony.com

RSC Bio Solutions – Manufacturer 9609 Jackson St Mentor, OH 44060 440-639-8633 X 102 http://www.rscbio.com Schaeffler Holding (China) Co., Ltd – Technical No. 1 Antuo Rd, Anting, Jiading District Shanghai, China 201 804 86-213-957-6921 http://www.schaeffler.com/content.schaeffler.cn/en/ company/company.jsp The Shepherd Chemical Company – Supplier 4900 Beech Street Norwood, OH 45212-2398 USA 513-731-1110 http://www.shepherdchemical.com

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NLGI 83rd Annual Meeting June 11-14, 2016 The Homestead Hot Springs, VA

Development of Next Generation Electrical Motor Greases Offering Improved Frictional Characteristics

John J. Lorimor1, Mihir Patel2, Brian Stunkel2, Rob Heverly2 Axel Americas LLC • Kansas City, MO Vanderbilt Chemicals LLC • Norwalk, CT

1 2

ABSTRACT

The global recession and resulting decline in commodity prices have caused the mining industry to increasingly focus on energy efficiency measures.

Electric motors are used extensively in every facet of mining including excavation, mineral preparation and material transfer, but energy efficiency gains in these motors through specific selection of lubricating grease have not been widely promoted.

Bearing grease exhibiting low friction performance may reduce energy consumption in electrical motors compared to grease offering the standard frictional performance. Novel grease thickeners based upon polymers have shown improvements in many functional areas over conventional grease thickener types, including low-friction performance.

The objective of this project is to characterize and improve upon the frictional performance of common commercially available electric motor greases. Once benchmarked, the work will focus upon the evaluation and use of friction reducing additive chemistries to develop novel polymer based grease formulations offering improved frictional performance. Experimental greases will be evaluated in both conventional bench testing and actual field trial versus their commercial

counterparts as a potential new low-friction option for electric motor service. The results of experimentation and field trial will be discussed in detail.

INTRODUCTION

According to the International Energy Agency [1], electrical motors account for 45% of global electricity consumption. The efficiency of an electric motor can only be improved through a reduction in motor losses.

Motor designs have improved resulting in energy efficiency gains, but grease selection specifically for energy savings potential has not been widely promoted.

Grease components can be broken down into three major groups; base fluid, thickener, and additives. Energy efficient greases must have a designed approach to their formulation. In this designed approach, each component of the grease must be selected specifically for its ability to provide improvements in one of the three lubrication related conditions which influence energy efficiency.

These three lubrication related conditions are churn, traction and friction.

Churn

The first lubrication related condition influencing energy efficiency in a mechanical system is churn under hydrodynamic lubrication. Under full-film lubrication, the surfaces are completely separated by lubricant film.

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Energy is required to move mechanical parts (gears, bearing elements, etc.) through the lubricant medium.

Churn is energy loss caused by the movement of these mechanical parts through the grease, and this energy loss is a function of the grease’s overall consistency and base oil viscosity.

Heavy grease consistency is a function of high thickener content, and is usually described as a beneficial characteristic in bearing lubrication. An example of this benefit is improved stay-in-place performance, providing a better seal to prevent contaminant ingress.

Additionally, heavy grease consistency provides for a reserve of grease thickener that is gradually degraded during service, improving long term mechanical stability. In the formulation of energy efficient greases, the thickener type and amount needs to be carefully controlled to reduce churning losses in the formulation of energy efficient greases.

Polymer thickened grease compositions have been well described in the literature [2, 3, 4]. Leckner describes the polymer thickener as fundamentally different in its lubrication mechanism compared to regular soap based greases. Polymer thickeners have allowed the use of significantly different base oil viscosities compared to what is possible with soap based grease. Reducing viscosity can reduce churning losses. In his paper presented at ELGI, the energy savings obtained through the use of polymer thickened greases and reduced oil viscosity were described in detail through actual end user case studies.

During operation, churning losses can also be attributed to oxidative thickening of the grease components. In most cases, thickening and polymerization of conventional grease components exposed to high-temperatures results in an increased overall grease consistency. However, Polymer thickened greases have exhibited softening under these same

circumstances. The theory of this mechanism is explained by Leckner to be the result of two opposing effects: As base fluid components oxidize and polymerize, the polymer thickener components slowly degrade into the lubricating fluid under high temperature exposure. This reduction in overall thickener content and consistency offsets the grease thickening effect of oxidation. This explanation was confirmed in testing

by Westbroek, where aged conventional soap based grease became harder, while the consistency of polymer grease became softer. This influences the duration of the churning reducing effect, and improves the longevity of energy savings benefits.

A recent trend in the automotive segment for improving mechanical system efficiency has been to reduce the viscosity of the lubricant. Lower viscosity fluids seem to be more appropriate for energy efficiency because of the reduced churning losses. Unfortunately by reducing the viscosity, this also results in a thinner film and a move toward boundary lubrication and a potential increase in component wear. Under these conditions, grease will experience a high degree of shear and the thickener can be degraded. The degradation products of soap based greases do not actually participate in improving the fluid viscosity. However, polymer based greases have demonstrated the unique characteristic in that these degradation products can be absorbed into the lubricating fluid where they do contribute to improved fluid film thickness.

In general, the goal of bearing lubrication is to provide the minimum viscosity required at the expected operating temperature. At operating temperature, this minimum viscosity for proper lubrication of ball bearings has been determined by one manufacturer to be 13 mm2/s [5]. For most electric motors, the typical bearing operating temperature falls somewhere within the range of 60 °C to 80 °C [6]. Within this range, the typical electric motor grease provides a base oil viscosity

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that is significantly higher than what is required for proper lubrication. The table below compares the base fluid viscosity of commercial electric motor greases, and calculates their actual viscosity under various operating temperature conditions.

When comparing two greases formulated with different base oil viscosity, the churning losses would be expected to be higher for the higher viscosity fluid. These increased churning energy losses would then manifest as heat. In this comparison the result should indicate that, all other properties being identical, the bearing lubricated with grease of higher base fluid viscosity will run at a higher temperature than a grease with a lower base fluid viscosity. Higher temperature exposure leads to faster grease degradation and a shorter grease life, in which case the lower base fluid viscosity can promote a longer grease life.

Traction

The second source of energy losses is traction under elastohydrodynamic lubrication (EHL) conditions. In this case, shearing in the EHL contact causes energy losses associated with the internal resistance of the lubricant to shearing. Under conditions of EHL contact, energy is required to shear the lubricant film between the sliding surfaces. Traction coefficient is a measure of this energy. The lower the traction coefficient, the less energy it takes to shear the lubricant film. Traction coefficient depends upon the molecular type and shape of each

lubricant component. Traction is primarily a property of the lubricant’s base oil. It is generally not affected by additives; nor is it related to metal-metal contact. Since energy losses in lubrication are typically manifested as heat, traction behavior may be one indicator of operating temperatures in certain applications.

In the search for reduced energy loss potential, the type of base oil used in a grease formulation is therefore an important consideration. PAO’s have long been known for their reduced traction. Vinci [7] demonstrates that comparative traction profiles offer guidance in energy efficient base fluid selection, illustrating that at the same viscosity PAO offers a much lower traction profile compared to Group I and II base oils.

Traction coefficient can also be measured and used to differentiate the energy loss potential between greases.

In recent work [8], polymer thickened greases have demonstrated the ability to achieve very low traction coefficients compared to lithium and lithium complex grease thickeners.

Friction

The final condition influencing energy efficiency in a mechanical system is friction under boundary or mixed lubrication conditions. In this condition, the lubricant film is not thick enough to fully separate surfaces. Under boundary and mixed lubrication conditions, metalto-metal contact occurs as surfaces slide by each other leading to friction and energy loss. Friction is a significant source of energy loss in mechanical systems, and all lubricants offer some degree of friction reduction. Energy efficient lubricants are differentiated from conventional lubricants in the degree of friction reduction observed.

When energy in a mechanical system is lost to friction, it typically is characterized by its conversion to heat. As a result, systems operating with increased friction are typically operating at an increased temperature, when compared to energy efficient lubricants. An increase in bearing temperatures means that the lubricant viscosity is lowered and film formation is made more difficult, leading to even higher friction and compounding further temperature increases [5]. High temperature exposure can also lead to

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evaporation and oxidative thickening of the grease’s base oil component, and a resulting reduction in the amount of oil bleed that provides lubrication. As lubrication starvation occurs, the lubrication film thickness will decrease, resulting in increased friction. The increased friction creates more heat. [6] Low friction grease can Influence the operating temperature of a bearing by reducing frictional heat generation. By lowering the operating temperature several additional benefits also occur. Grease degradation is commonly a major cause of premature bearing failure. As grease life is shortened by exposure to high temperatures, the grease can last significantly longer at reduced operating temperatures, promoting longer component life.

Experimental formulation

In designing energy efficient greases, the key to lubricant performance is a balanced formulation in which the energy loss reducing potential of each component is the selection criteria. We believe that by targeting the three lubrication conditions influencing energy losses, we can positively influence the energy consumption in an electric motor bearing application.

Thickener:

Polymer thickened greases are based upon four major components; base oil, polypropylene, elastomer/rubber and additives. The benefits of polymer thickened greases have been well documented [2] and include:

• Non-ionic thickener system

• Very good oxidation resistance

• Excellent water resistance

• Excellent resistance against process water, acidic and alkali solutions

• Controlled oil bleeding

• Long life

• Mechanically stable

• Good compatibility property with almost all greases

• Recommended application temperature up to 120 °C In a recent presentation at the ELGI [4] , Westbroek explained how polymer thickened greases have many qualities which make them very suitable for bearing lubrication, especially controlled oil release properties.

In a rheometer equipped with rolling bearing assembly,

Westbroek subjected commercially available test greases to a series of high temperature tests, including oil separation from a greased bearing. In his experiments, Westbroek identified oil loss having a significant role in the process causing bearing failure. Through this work he discovered that polymer thickened greases have a very controlled oil release, and are superior to the other thickener types tested.

Greases for electric motor bearing lubrication must be capable of maintaining their consistency even when subjected to the continuous rolling action of bearing elements. The polymer thickener provides a very shear stable structure, excellent grease life, controlled oil release properties, and outstanding low friction properties.

Base oil:

Based upon the known improved traction performance of the PAO fluids, and the operating viscosity requirements published by the major bearing manufacturers, an 8 mm2/s @ 100 °C viscosity PAO base fluid was selected for use in the experimental low friction grease formulation.

Additives:

In his paper at ELGI [9], Fish indicates that of the three major grease components, base oil, thickener and additives, each have different effects on grease performance, and that the additives were primarily responsible for friction reduction. Accordingly, we identified SRV® coefficient of friction within the operating temperature range as a key screening mechanism for these additive formulations. A discussion of the friction reducing additive chemistry is found in the results of experimentation. Greases emerging favorably from our screening program would then be considered for electric motor temperature and efficiency testing.

Reference Greases

The current state of the art grease technology has many differences when compared with novel blends based upon a unique polymer thickener. In order to demonstrate differences in energy efficiency between the author’s experimental grease formulation and the current products in service, reference greases were selected that were most representative of the electric motor grease technology in use today. The most common types of greases employed in electric motor bearing lubrication

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are based upon the lithium complex and polyurea thickener types. These two grease thickeners are mechanically stable, and capable of resisting softening even upon exposure to elevated temperatures. In addition, they are typically formulated with antiwear, oxidation and corrosion inhibiting additives, to address the major performance requirements of the application.

As references in our testing program, we selected the following (Table 2) widely used commercial electric motor greases, each unique in their base fluid and additive systems. The mineral-based polyurea formulation is widely used for electric motor applications. The synthetic lithium complex grease is a formula recognized for reducing operating temperatures by utilizing a low friction additive system.

EXPERIMENTAL TECHNIQUE

In this work, the three different base greases were studied in rolling/sliding contacts. A standard mini traction machine (MTM) was used to measure rolling/ sliding friction. MTM uses two different motors to independently control different speed of upper and lower specimen thereby apply any slide/roll ratio for the experiments. The machine is computer controlled so that any required test routine can easily be programmed.

Before the experiments both specimens (ball and disc) were cleaned thoroughly using n-heptane. A new ball and disc were used for each test, both of AISI 52100 steel. The root mean square (r.m.s.) roughness of the balls was 10 nm and their hardness 750 VPN. Smooth discs of 5 nm r.m.s. were employed with a hardness of 780 VPN. Rig was assembled and lubricant pot is filled with sufficient amount of grease. The applied load was 35N, corresponding to a Hertzian pressure of 1 GPa. Temperature was raised to 40 °C. Tests begin at entrainment speed of 3000 mm/s and end at 10 mm/s at specified intervals. The slide/roll ratio (SRR) was 50 percent. Slide-roll ratio is defined as the ratio of sliding speed to ub-ud mean speed, where ub and ud are speed

of ball and disc respectively.

A comparison of the performance of each grease sample can be made by integrating the area under each Stribeck curve. The value of this integral, Traction CoF.log (u), is known as the Stribeck Friction Coefficient (SFC). Lower values of SFC indicate that less energy will be absorbed by the lubricant under mixed and boundary regimes.

Lower values would therefore be expected to correlate with better performance in reducing frictional losses.

RESULTS AND DISCUSSION Rolling and sliding friction of base grease at 40 °C

The frictional property of polymer thickened grease was compared with two greases; LiCx-PAO and PU-Min using Mini Traction Machine (MTM) as shown in Figure 2. Typical Stribeck curves were generated at 50% slide-roll ratio where friction is measured over a range of entrainment speeds at a temperature of 40 °C. As the test time progresses friction increases when entrainment speed decreases for all three grease samples at 40 °C. The polymer thickened grease had the lowest coefficient of friction at all entrainment speeds compared to both greases LiCx-PAO and PU-Min. At a lower speed and a higher temperature, the Stribeck curve operates under boundary lubrication regime where an increased number of asperity to asperity contact occurs which leads to higher possibilities of wear and friction. However, a reduction in friction in the boundary lubrication regime indicates the formation of a friction reducing film by polymer thickened grease.

Rolling and sliding friction of base grease at 120 °C To understand the frictional performance at higher temperatures, Stribeck curves were also acquired at 120 °C for all three greases using similar test conditions mentioned above. As shown in figure 3, the Stribeck curve demonstrates noticeably different frictional behavior at 120 °C. Grease PU-Min exhibited higher

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friction at 120 °C than at 40°C. Grease LiCx- PAO exhibited lower friction coefficient than grease PU-Min. On the other hand, polymer thickened grease exhibits lower friction coefficient at higher temperature of 120 °C than at 40 °C. All grease systems show different friction coefficients at different entrainment speeds; they also show downward trends or reduction in friction at lower speed.

Influence of Temperature on Frictional Energy Consumption

Stribeck friction coefficient (SFC) was calculated by computing the area under the Stribeck curve. Lower values of SFC indicate that less energy will be absorbed by the lubricant under mixed and boundary regimes. Lower values would therefore be expected to correlate with better performance in reducing frictional losses. SFC values were calculated for the curves acquired at 40 °C, 60 °C, 80 °C, 100 °C, 120 °C and plotted as shown in figure 4.

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Figure 4 shows area under the Stribeck curve as a function of temperature. SFC values of grease PU-Min reduces as temperature increases from 40 °C to 60 °C. SFC value increases at 80°C and then stabilizes with higher temperature. Grease LiCx-PAO shows reduction in SFC values, followed by continuous increased in the SFC values. Polymer thickened grease exhibits reduction in SFC values at 60 °C, followed by increase at 80 °C. With further increases in the temperature, SFC values generated using polymer thickened grease exhibits continuous reduction in the SFC values.

Results indicate that greases LiCx-PAO and PU-Min consume different frictional energy with increasing temperature. Grease PU-Min seems to consume higher frictional energy during the test compared to grease LiCx-PAO. The polymer thickened grease shows lowest frictional energy consumption at all the temperatures.

While after 80 °C, grease PU-Min maintained higher energy consumption while the polymer thickened grease exhibited reduction in the frictional energy consumption.

SRV® Testing

For some applications, particularly when studying the behavior of a lubricant under dynamic conditions, an oscillating motion is more representative than a continuously rotating disc. An SRV®3 test system from

Optimal Instruments was used to measure friction and wear under pure sliding, boundary lubrication conditions. In this test, a 10.0 mm diameter steel ball is loaded downwards on the flat face of cylindrical disc. The disc is held stationary and ball reciprocates at given test frequency. The ball and disc are both of AISI 52100 steel. The ball is 10 mm diameter with a Rockwell hardness number of 60±2 on Rockwell C scale (HRC), 0.025±0.005-µm Ra surface finish. The lower disc (24-mmx7.85mm thick) is of the same hardness as the ball but with a surface finish between 0.5µm˂Rz˂0.650µm. The applied load was 50 N for 30 seconds as a break-in period followed by 200N for the duration of 2 hours. Ball was oscillating at 50 Hz for 1000µm stroke. Tests were conducted at 40 °C or 80 °C. Final coefficient of friction values were reported. Wear volume was measured using optical profilometer.

In this study, efforts were made to improve friction reduction and wear resistance properties of polymer thickened grease. A combinatorial approach using molybdenum friction modifier, sulfur chemistry and phosphorus chemistry were used to improve friction reduction and wear resistance.

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Grease formulations were prepared as shown in table above. All the tests were conducted at 80 째C. The base grease by itself shows very high friction and poor wear resistance in the pure sliding and reciprocating motion compared to polyurea based grease PU-Min. Formulation 5 shows the influence of the molybdenum friction modifier alone at 3.0 wt. %. Formulations 8 and 15 show the influence of sulfur chemistry maintaining 3.0 wt. % treat rate. Comparison of formulation 5, 8 and 15 indicates that addition of antiwear and friction modification improves both the friction and wear resistance performance of polymer thickened base grease over the base grease. Addition of molybdenum friction modifier at 3 wt. % (formulation 5) improved the friction reduction performance of polymer thickened base grease compared to poly urea based grease PU-Min but further improvement is needed to reduce wear compared to poly urea grease. Addition of sulfur chemistry at 1 wt. % while maintaining total treat rate of 3 wt. % (formulation 8) further improved the friction reduction properties compared to formulation 5 and polyurea base grease but antiwear properties deteriorate. Adjusting the treat rate of the combination of molybdenum friction modifier and sulfur chemistry does not exhibit significant improvement.

Phosphorus chemistry was added to improve the antiwear properties of the two additive combination of molybdenum friction modifier and sulfur chemistry as shown in the table below.

As exhibited by formulation 24, addition of phosphorus chemistry maintains friction reduction properties of two way combination of molybdenum friction modifier and sulfur chemistry but further deteriorates the wear resistance properties. This phenomenon probably can be explained in terms of competition of additive for surface adsorption and hence formulations were further optimized by reducing treat rate of molybdenum friction modifier, i.e. formulation 27 and 28. Reduction in the molybdenum friction modifier treat rate and addition of phosphorus chemistry as antiwear shows significant improvement in the friction reduction compared to polymer thickened and polyurea base grease. This phenomenon probably can be explained in terms of competition of - 53 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

additive for surface adsorption or the balance between the friction modifier additive and antiwear additive surface coverage. The higher the friction modifier surface coverage, the better the friction reduction. Since both friction modifier and antiwear additives are competing for the same metal surfaces in relative motion, higher friction modifier additive surface coverage also means the lower the antiwear additive surface coverage. So when better friction modifier performance is achieved, wear often suffers. However, with the right balance of additives, desired performance can be achieved.

Similar formations were also evaluated conducted at 40 °C as shown in the table below. Interesting results were obtained. Formulation 27 was formulated at 1 wt. % of molybdenum friction modifier failed after 6 minutes due to extremely high friction that exceeded the set limit of the SRV® tester. Increasing the treat rate of molybdenum friction modifier to 2 wt. % passed the 2 hour test duration and maintained both the friction reduction

and wear resistance properties as demonstrated at 80 °C. Further increasing the treat rate of the molybdenum friction modifier to 3 wt. % improves wear resistance but adversely affected the friction reduction at 80 °C. These phenomena may be explained by the activation energy each additive chemistry requires. In pure sliding and oscillating condition, molybdenum friction modifier typically activates at 60-80 °C temperature range to reduce friction by formation of lattice layer type MoS2 based tribofilm. On the other hand antiwear chemistries tend to activate faster than friction modifiers at lower temperatures. Hence an improvement in wear resistance at lower temperatures might be due to the more active role of antiwear additives compared to the molybdenum friction modifier. An improvement in the friction reduction and wear resistance at higher temperatures is due to activation of friction modifiers as well as due to optimization of additives.

Motor trial results

To test the influence of lubricating grease selection on electric motor bearing operating temperatures and total energy consumption, a test rig was fabricated to perform a controlled comparison of author’s experimental grease with industry benchmark greases. The laboratory testing rig was fabricated utilizing a single phase AC powered 1/3 HP electric motor operating at a 1075 rpm shaft speed. To the shaft was mounted an 18-inch, four blade fan with 30-degree pitch. The fan blade provided a fully loaded state for the motor, allowing it to draw the maximum 3.3 Amp current from the 120V source.

In each test, the test motor was disassembled and two identical bearings, each containing the same test grease, were installed. A fixed 2.4 gram quantity of each test grease was applied to new 6203 size - 54 VOLUME 79, NUMBER 6

deep groove ball bearings using a manual bearing packer. The quantity of grease required was calculated from published formulas [10] based upon the bearing dimensions. As per instruction by the bearing manufacturer [5] new bearings were not washed prior to grease application. The test bearings were then press mounted to the motor shaft using a hydraulic press. The test motor was reassembled, and each test run was conducted over a 48 hour interval to allow for break-in or running in wear and temperature stabilization.

The electric motor was modified to allow for direct contact temperature measurement of each individual bearing race by thermocouple probe. The temperature readings were captured by a 4-channel ONSET thermocouple data logger. The power supply to the electric motor was run through a data logging recorder for measuring and recording of power and energy consumption of 120V plug loads. The ONSET plug load data logger was used for determination of electrical current requirement during the course of operation, and has a measurement accuracy of 1-Watt (W). The results of the comparative evaluation are shown below.

- 55 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

In the examination of the logged data, the commercial polyurea (PU – Min) electric motor grease had the highest resulting energy consumption measurement. The lithium complex (LiCx – PAO) energy consumption measurement was 2.17% lower than the baseline polyurea, which was expected due to its use of PAO base fluid and friction reducing additives. However, the lowest energy consumption was measured for the authors experimental polymer thickened grease (Polymer – PAO). In this final measurement, the resulting energy consumption was over 3.12% lower than the benchmark polyurea reference grease.

Unexpectedly, bearing temperatures remained fairly consistent over the duration of the test, and within a similar range for each of the three tested greases. Based upon this observation, we believe the bearings require more time than the 48 hours allowed to reach a steady state temperature. Once a steady state temperature is achieved, we believe the expected differentiation in operating temperatures among the test greases will be evident. This explanation is consistent with others findings, where bearing temperatures were found to be inconsistent for up to 20 days from the initial start-up [11].

SUMMARY AND CONCLUSIONS

Energy savings for electric motors can only be achieved through a reduction in energy losses. Three lubrication related conditions influence these energy losses, and they are churn, traction and friction. Greases can be specifically designed to influence these lubrication related conditions through the selection of formulating components with specific characteristics, including low traction, reduced viscosity, and low friction.

Differences can be observed between current technology commercial greases utilizing conventional thickener types and experimental polymer based greases in laboratory bench testing. These polymer thickened greases have unique characteristics which contribute toward friction and traction reduction, especially at higher temperatures. MTM and SRV® are versatile tools for measurement of a lubricant’s friction and traction reducing potential, and are therefore valuable for analyzing and optimizing grease formulations for this purpose. Greases for electric motor application based upon novel polymer thickeners have demonstrated in these tests that they can provide a very low coefficient of friction and low traction, resulting in low Stribeck friction coefficients. The Stribeck friction coefficient can be a valuable tool in screening greases for energy savings potential.

A laboratory rig based upon full-scale electric motor was successfully used to evaluate the energy consumption differences provided by the use of different greases. In this motor test rig, greases based upon novel polymer thickeners with low Stribeck friction coefficients have demonstrated they can positively influence the energy consumption of an electric motor. The energy and cost savings impact through use of this next generation technology is evident, and simple to apply today.

- 56 VOLUME 79, NUMBER 6

ACKNOWLEDGEMENTS

The authors would like to acknowledge the contribution of Doug Majors and Nathan Claycamp of Axel Americas LLC for their assistance in conducting the electric motor energy evaluation. Authors would also like to acknowledge Axel Americas LLC and Vanderbilt Chemicals LLC for their gracious support in conducting this research.

REFERENCES 1. P . Walde, “Energy efficiency policy opportunities for electric motor driven systems”, International Energy Agency publication, 2011 2. B. Jacobson, “Polymer thickened lubricant”, (Lubrisense White Paper 2007/07) Axel Christiernsson 3. J. Leckner, “Energy efficiency and lubrication mechanisms of polymer thickened greases – Apples and oranges”, in ELGI 27th AGM, Barcelona Spain, 2015 4. R. Westbroek, “Upper Operating Temperature of Grease: Too Hot to Handle?,” in ELGI 26th AGM, Dubrovnik Croatia, 2014 5. Anonymous, “SKF Bearing Handbook for Electric Motors,” SKF publication 140-­ ‐430, Version 11/2005 6. W.H. Detweiler, “Common causes and cures for roller bearing overheating” SKF USA Inc., King of Prussia, PA 7. J. Vinci, “Developing Next Generation Axle Fluids: Part II – Systematic Formulating Approach”, SAE publication 02SFL-­‐ 154 8. Axel Christiernsson internal report 9. G. Fish, “”Grease additives for high temperature bearing applications”, in ELGI 26th AGM, Dubrovnik Croatia, 2014 10. Anonymous, “Mobil technical topic: Guide to electric motor lubrication”, Exxon Mobil publication, 2009 11. G. Fish, “The development of energy efficient greases”, in ELGI 27th AGM, Barcelona Spain, 2015

- 57 NLGI SPOKESMAN, JANUARY/FEBRUARY 2016

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