TLT SYSTEMS, STRATEGIES & RESEARCH FOR LUBRICATION PROFESSIONALS AN PUBLICATION | AUGUST 2019

TRIBOLOGY & LUBRICATION TECHNOLOGY Unstoppable 15 YEARS Wind Turbines of publishing excellence STLE 75 Why they 1944-2019 keep growing in numbers, capacity and physical size.

President’s Report The New Generation Gap

Battery Electric Vehicles Now with multi-speed transmissions

Virtual Bearing Testing Q&A with Dr. Xiaolan Ai

Grease Incompatibility Uncharted challenges

Tribology Education A global perspective

Articular Cartilage New research on recovery process

Digital TLT: Sponsored this month by Acme-Hardesty at www.stle.org. QUALITY DRIVES.

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TLT / AUGUST 2019 / VOLUME 75 / NO. 8

FEATURES

20 MINUTES WITH… 18 Xiaolan Ai 24 This Timken scientist discusses bearing fatigue life and the advantages of virtual bearing testing. By Rachel Fowler

LUBRICATION FUNDAMENTALS 24 Solid lubricants These materials are well suited for extreme conditions where liquid lubricants are impractical. By Jane Marie Andrew

WEBINARS 32 Fundamentals of wind turbines Global capacity has grown continuously since 2001, including a 9% increase in 2018. By Jane Marie Andrew 18

32

Front Cover photo © Can Stock Photo / sonnydaez

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 1 Contents

DEPARTMENTS

12 Tech Beat by Dr. Neil Canter • Developing a hybrid heavy-duty truck • New thermoelectric material based on cobalt • Redox flow batteries: New approach may boost performance.

42 Newsmakers • ExxonMobil • BASF 12 • Pilot Chemical • LANXESS and more.

50 New Products • OLOA® 55600 • ST100 gas flow meter 72 • Automated solution for endotoxin detection.

56 Sounding Board What is the status of tribology education in your country?

64 Advertisers Index

66 Resources • Technical Books – Nanomaterials in Advanced Medicine COLUMNS – Biomaterials Science and Technology: Fundamentals and Developments 6 President’s Report 68 Automotive Tribology • STLE Local Sections Calendar The New Generation Gap Gearboxes and battery electric & Certification Exams vehicles • Industry Conferences 8 From the Editor – COMADEM 2019 Grease (in)compatibility 70 Cutting Edge – Tribochemistry Hakodate 2019 Sliding your way to rehydration 10 Headquarters Report – ITC Sendai 2019 Charting our future 72 Machinery – ESMATS 2019 The challenge of metal-removal – ROTRIB’19 fluid specifications

Copyright © 2019 Society of Tribologists and Lubrication Engineers. All Rights Reserved. TLT magazine is owned and published in print and electronically by the Society of Tribologists and Lubrication Engineers (STLE). The views set forth in this magazine are those of the authors and not necessarily the views of STLE. Material from TLT magazine may be reproduced only with written permission from STLE. TLT magazine assumes no liability or responsibility for any inaccurate, delayed or incomplete information. For more information, contact us at [email protected]. Subscription and Single Copies: Current volume single copies are $25 (not including shipping and handling). Annual subscription rate is $248/U.S., $320/international. Prepayment is required before subscription is started. Remittances from foreign countries must be by international money order or bank draft drawn on U.S. bank. Tribology & Lubrication Technology (USPS 865740) Vol. 75, Number 8, (ISSN-1545-858), is published monthly by the Society of Tribologists and Lubrication Engineers, 840 Busse Hwy, Park Ridge, IL 60068-2376. Periodicals Postage is Paid at Park Ridge, IL and at additional mailing offices. POSTMASTER: Send address changes to Tribology and Lubrication Technology, 840 Busse Hwy, Park Ridge, IL 60068-2376.

2 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Now in its 75th year, STLE invites you to join Drive 75

A growing group of companies helping STLE celebrate its Diamond Anniversary.

STLE is observing its 75th Anniversary with a year of • A Welcome to Drive 75 message with your logo events and activities, culminating in a festive celebration in TLT. at the 2020 Annual Meeting & Exhibition in Chicago • Listing in a Drive 75 monthly, evolving ad in TLT (where the society was formed in March 1944). through the June 2020 Convention Issue. (The sooner To honor the industry’s premier technical association you join, the longer your recognition lasts!) and support this momentous event, your company can • Listings in Drive 75 ads in STLE’s Website, become a Drive 75 Sponsor and reap a series of e-newsletter and 365 Mobile App. benefits throughout the year! • A Drive 75 badge ribbon for your company’s person- Your Drive 75 sponsorship includes: nel at STLE’s 2020 Annual Meeting in Chicago. • Listing in a large Drive 75 banner at STLE’s 2020 • A $100 donation in your company’s name to a Annual Meeting. high school STEM program of your choosing with matching funds from STLE. (If you don’t have a For details about the Drive 75 program and benefits, preferred program, the donations will be made pricing and eligibility, contact Tracy VanEe at to a Chicago-area program chosen by STLE.) 630-922-3459 or at [email protected].

Drive 75

Sponsor

Society of Tribologists and Lubrication Engineers, 840 Busse Highway, Park Ridge, IL 60068, [email protected], www.stle.org. TRIBOLOGY & LUBRICATION TECHNOLOGY

PUBLISHED BY Society of Tribologists and Lubrication Engineers “Educating lubrication engineers & tribology researchers since 1944”

STLE International Headquarters 840 Busse Highway, Park Ridge, Illinois 60068-2376 Phone: 847-825-5536 • Fax: 847-825-1456 • www.stle.org • [email protected]

EDITOR Evan Zabawski, CLS TestOil [email protected]

PUBLISHER/EDITORINCHIEF Thomas T. Astrene [email protected]

MANAGING EDITOR Rachel Fowler [email protected]

SENIOR FEATURE WRITER Jeanna Van Rensselar

CONTRIBUTING EDITORS Jane Marie Andrew, Mary Beckman, Dr. Neil Canter, Dr. Robert M. Gresham, Dr. Nancy McGuire

COLUMNISTS Dr. Edward P. Becker, Michael P. Duncan, Ken Pelczarski, Edward P. Salek, Dr. Nicholas D. Spencer, Dr. Don Smolenski, Dr. Wilfred T. Tysoe, R. David Whitby

CIRCULATION COORDINATORS Myrna Scott, Nadine Sanchez (847) 825-5536

ADVERTISING SALES Tracy Nicholas VanEe Phone: (630) 922-3459 Fax: (630) 904-4563 [email protected]

DESIGN/PRODUCTION Joe Ruck

TECHNICAL EDITORS

Dr. William Anderson Afton Chemical Corp. [email protected] Robert Austin QualiChem, Inc. [email protected] Dr. Salil Bapat University of Arkansas [email protected] Michelle Brakke Lubrication Technologies Inc. [email protected] Jerry Byers Industry Consultant [email protected] Dr. Ashok Cholli Polnox Corp. [email protected] Peter Deegan LOC Group [email protected] Bridget Dubbert Engineered Lubricants Co. [email protected] Dr. Rovelyn Dytioco Boeing [email protected] Dr. T. Reg Forbus Santolubes [email protected] Dr. Monica A. Ford Ingevity [email protected] Dr. Mohammad Motaher Hossain Texas A&M University-Kingsville [email protected] Tyler Housel Zschimmer & Schwarz, Inc. [email protected] Dr. Anoop Kumar Chevron Corp. [email protected] New research Lawrence Ludwig Schaeffer Manufacturing Co. [email protected] sheds light on how Jory Maccan Imperial Oil [email protected] Dr. Filippo Mangolini The University of Texas at Austin [email protected] articular joints Mandi McElwain Univar [email protected] recover after Dr. Hamidreza Mohseni CARBO Ceramics Inc. [email protected] compression. Rob Morien Rexnord [email protected] Dr. Anup Pandkar Sentient Science [email protected] Dr. Ning Ren Valvoline Inc. [email protected] See Dr. Eugene Scanlon BASF [email protected] Cutting Edge Dr. Shuangwen Sheng National Renewable Energy Laboratory [email protected] on Page 70. Edward Sunghing Chem-Ecol, Ontario, Canada [email protected] Dr. Rohit Voothaluru The Timken Co. [email protected] Dr. Dehua Yang Ebatco [email protected] Dr. Jack Zakarian JAZTech Consulting [email protected] Dr. Wenyang Zhang NanoMech, Inc. [email protected]

© Can Stock Photo / Eraxion

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4 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG

PRESIDENT’S REPORT

The New Generation Gap We must continue educating young people about the role our products play in making the world a better place.

By Michael P. Duncan

One of our strategic goals for the STLE board of directors is to communicate with the general population (people not familiar with tribology and lubrication engineers) in order to inform and advocate the merits of our organization for the betterment of society. With that in mind, I would like to share a conversa- tion that my son and I had a few years ago. My son came home af- ter a day at school during his freshman year of high school and said to me, “Dad, you’re a chemist, right?” I said, “Yes,” and he continued, “You make stuff that is bad for the envi- ronment?” I thought for just a second because I knew he was taking a course in school on the environment. I responded with, “My company wouldn’t stay in Whether you’re in industry or academia, encourage your younger employees or students to get involved in STLE. business if I didn’t consider the effect of our products on the environment. Yes, we produce need for additional energy. If My advice to you—connect dent Maureen Hunter is heading chemicals, but we are a respon- we didn’t manufacture chemi- with our younger generation in up a poster contest for children sible producer. We minimize cals for this purpose, we would some fashion, and the earlier as part of our year-long 75th be irresponsible to the environ- the better. Perhaps just talk Anniversary celebration that ment. We are always trying to with your children or grand- culminates at the 2020 Annual We need to be better find better ways to manufacture children in the car on a family Meeting & Exhibition in Chica- advocates for our our current products. We also vacation or a young relative at go. There are four age divisions profession. work with our customers to a family get together. Consider ranging from four to 18, and you develop cleaner, greener and getting involved in a local STEM can learn more details, includ- longer-lasting products.” activity in your community. Vol- ing how to enter, on Page 55. waste and follow all laws and He looked at me and said, unteer to be a science fair judge Keep your eyes open for further regulations regarding air and “Well, that is good then,” and in your local town or city. En- information of this activity. water emissions and possess walked away. courage a younger employee to Have a great summer. the necessary licenses and per- Obviously we need to re- become more active in an STLE mits to operate. member that learning happens local section. Our younger STLE Mike Duncan is vice presi- “Also, our products extend everywhere, not just in the members seem to be able to dent of technology of Daubert the life of cars, trucks, planes, classroom. And, obviously, we better understand and connect Chemical Co. in Chicago. trains and heavy machinery ex- need to be better advocates for to the younger generation. You can reach him at ponentially, thus reducing the our profession. In addition, STLE Past Presi- [email protected].

6 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG We create chemistry that makes lubricant formulators love ester and PAG base stocks.

Ester and PAG base stocks are used as co-solvents or main fl uids in lubricant formulations. Top performance criteria as energy effi ciency, longer drain intervals and improved equip- ment protection will be achieved. When formulators meet these performance criteria and take advantage of BASF’s best-in-class technology and manufacturing strengths, it’s because at BASF we create chemistry. If you are interested in our products please contact us: [email protected] www.basf.com/lubes FROM THE EDITOR

Grease (in)compatibility Just say, ‘No!’

By Evan Zabawski

“Are these two greases compatible?” is a question that is not answered simply by referring to a grease-compatibility chart. Such charts vary in both terminology and data but also do not represent a conclusion determined by comprehensive testing. Even so, existing standards may not completely fill that void. Some of the variations in terminology for the thickeners are minor and not likely to cause confusion, such as clay versus ben- tonite clay. Others, like stearate, 12-hydroxy and 12-hydroxy stearate, are not clear that they refer to the same lithium- or calcium-

based thickener. These differences can make of Evan Zabawski. Photo courtesy it difficult to match the terminology from the packaging or product data sheet to the com- Compatibility charts do not contain enough data to properly determine compatibility between two patibility chart. products but may provide a quick reference for known incompatibilities. The data is often presented as a matrix, with trinary recommendations (compatible, ibilities. Compatibility charts simply do not prescribes performing a series of tests on incompatible and moderate/borderline contain enough data to properly determine three different mix ratios: 50:50, 10:90 and compatibility). The variances between two compatibility between two products but may 90:10. The standard describes evaluating the charts are easily explained with an example: provide a quick reference for known incom- mixture to confirm there is no significant de- suppose the current grease is a clay-based patibilities. crease in dropping point, the mechanical sta- grease from Company A, and the new grease Even if two different greases of the same bility remains in range and the consistency under consideration is a lithium-based thickener type were being compared, the remains in range after heating. grease from Company B. base oil itself must be taken into consider- While this provides a standardized ap- Company A’s chart may list clay/lithium ation. The base oils could have different vis- proach, the greases are not really put into as incompatible, while Company B’s chart cosities that might lead to increased friction completely realistic working conditions. As may say it is compatible. Neither chart is or wear, but they also could be different oil such, certain additive properties like rust wrong, though neither may be right. The types. Some of the API Group V synthetics, and corrosion protection or wear preven- problem lies in the proprietary nature of the in particular, are not compatible with other tion cannot be evaluated without requesting data. Company A’s chart is comparing Com- mineral and synthetic base oils. extra testing not required by the standard. pany A’s clay-based grease with Company However, even if the thickener, base Still, this is far better at unveiling potential A’s lithium-based grease, and Company B’s oil type and viscosity are identical, there incompatibilities that would not be seen by chart is comparing Company B’s clay-based is still a potential issue for the additives to visual inspection alone. grease with Company B’s lithium-based be incompatible with each other or some Evidently, compatibility charts cannot be grease. But neither chart shows Company metallurgies. A common example would relied upon as the sole source to confirm A’s clay-based grease with Company B’s be using a non-EP grease and switching to compatibility, but even standardized testing lithium-based grease. an EP grease; there is a possibility that the could be expanded to uncover more poten- These charts are generally not based on EP additive could interfere with the perfor- tial issues between two greases. an exhaustive regimen of testing but, rather, mance of other surface-active additives like only the structural stability of mixtures of rust inhibitors or that the EP additive could different thickeners. They also do not ad- be reactive toward yellow metals (brass or Evan Zabawski, CLS, is the senior techni- dress any performance characteristics of bronze) in contact with the grease. cal advisor for TestOil in Calgary, Alberta, the grease mixtures, nor do they identify any One method used to determine com- Canada. You can reach him at base oil or additive differences or incompat- patibility is ASTM D6185; this standard [email protected].

8 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Polymeric Phosphite Ester DOVERPHOS for Metalworking Applications EP-425

DOVERPHOS EP-425, developed by Dover Chemical Corporation, is a revolutionary patented polymeric phosphite ester that excels in all metalworking applications.. Not only can it be incorporated in neat oils, but due to its strong resistance to hydrolysis, it can be used in various water-soluble coolants and semi-synthetic fluids.

ADVANTAGES AND BENEFITS

Light color and very low odor Stable in a wide variety of mineral oils, synthetic oils, and esters Extremely low acidity, thus reducing the possibility of staining to nonferrous alloys High Viscosity Index (VI) providing excellent boundary film at elevated temperatures Globally registered and REACh registered

PERFORMANCE ASPECTS

Provides 30% reduced 4-Ball scar diameter compared to sulphurised esters Provides 30-40% reduced 4-Ball scar diameter compared to other phosphite and phosphate esters Higher efficiency over chlorinated, sulphurised, and other phosphorus-containing additives in drawing of carbon steel and stainless steel Can be used as an alternative to chlorinated additives in tapping carbon steel operations Can be used as an ashless alternative to ZDDP (Zinc Dialkyldithiophosphate)

For more information, visit us at www.doverchem.com

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Charting our future

Work is under way. Please help STLE collect data for the 2020 edition of our Emerging Trends Report.

By Edward P. Salek, CAE Part two of the 2020 report examines Executive Director 80 trends in five field discipline areas, a section that includes three holdover top- ics (workforce issues, government regu- STLE’s Report on Emerging Issues and lations and safety, the environment and Trends in Tribology and Lubrication Engi- basic human needs) and two new topics neering, informally known as the Trends (research funding and materials cost and Report, has gained a reputation for identify- availability). ing current and future developments in the That last topic was added to incorporate field since it was first published in 2014. A new challenges that have emerged since the second edition, released in 2017, continued Trends Report series began in 2014. For ex- to capture the interest of individuals and ample, “A potential lithium shortage for the companies in the tribology and lubricants grease market has an indirect impact on business sector, as well as other stakehold- lithium batteries in electric vehicles. How ers in academia, government and the gen- much will that restrict the growth of electric eral public. vehicles?” wondered one expert. STLE and others have used the report The research funding discussion has re- to facilitate a conversation on a global scale volved around the fact that tribology is not through conference presentations in North a “buzz word” to get research money from America, Europe and Asia and at individual public or private sources, especially in the meetings with corporate members. The re- U.S. “We have to sell tribology differently, port has helped to identify and predict the © Can Stock Photo / tobkatrina incorporate it into different topics. What we impact of important technologies and areas would need is success in a field that doesn’t of concern as they relate to the field, industry Work to date has identified more than 140 trends have a solution yet, like osteoarthritis. That and even society and the world economy. in the report’s four target sectors: manufacturing, would bring us back on the map,” is how one transportation, energy and medical and health. Work is underway on a third edition of individual framed the issue. the Trends Report with a target release The next phase for the 2020 Trends Re- date of early 2020. The research is being port is collecting data through a general directed by a blue-ribbon Advance Innova- 140 trends for consideration in these four survey of STLE members this month and tions team of STLE members chaired by sectors. The Advance Innovations team has September. The Advance Innovations team Thomas W. Scharf, professor in the depart- been supported in this analysis by 20 in- invites STLE members to support the project ment of materials science and engineering vited experts from industry, academia and and take the opportunity to contribute their at the University of North Texas. McKinley government labs. Transportation yielded expertise to this important research project. Advisors (Washington, D.C.) is again serv- the highest number (57) with considerable They survey questionnaire asks members to ing as research and data analytics consul- interest surrounding the implications and rate the significance of trends and to com- tant as well as providing overall project opportunities presented by electric and self- ment on their future impact. management. driving vehicles but also developments in Data analysis and editorial work on the The third edition builds on the previous internal combustion engines. 2020 Report will occur in the fourth quarter trends and conclusions but also has been re- “Improving lubricants and additives in of this year in advance of the target release focused and reorganized to reflect the rapid response to unique torque performance of date early next year. In the meantime, all TLT pace of change affecting all areas of relevant electric motors. They have a much higher readers have the opportunity to download a technology. As a result, the 2020 report has torque and lower RPM than internal com- free copy of both the 2017 and 2014 reports consolidated application sectors into four bustion motors, and the lubricants we have from www.stle.org. high-interest topics: transportation, medi- today weren’t designed to deal with that,” is cal and health, energy and manufacturing. how one expert characterized the impact of You can reach Certified Association Work to date has identified more than EV technology. Executive Ed Salek at [email protected].

10 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG For Innovative Additive Solutions

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Developing a hybrid heavy-duty truck

By Dr. Neil Canter Contributing Editor

Current battery technology does not enable an all-electric heavy-duty truck option to be viable.

The movement to commercial- Dr. Leslie Bromberg, principal given to finding an alterna- izing alternatives to the internal research engineer in the Plas- tive to trucks using an internal combustion engine has focused ma Science and Fusion Center combustion engine, because on light-duty vehicles. This at the Massachusetts Institute such vehicles contribute two column has shared different of Technology in Cambridge, gigatons of carbon dioxide research approaches such as Mass., says, “Efforts are under- emissions globally of the seven KEY CONCEPTS batteries and fuel cells. way to produce an all-electric gigaton emissions attributed to An approach developed for a With the growth of hybrid heavy-duty truck. We believe all vehicles. Bromberg believes hybrid heavy-duty truck uses a electric vehicles, attention the only logical alternative is to spark ignition engine with a again is being paid to improving develop a concept for a hybrid battery. efficiency. In a previous TLT ar- ‘We are looking for the heavy-duty truck that relies on ticle,1 a real-time energy-man- both batteries and an internal The spark ignition engine was SI engine to operate agement system was devised to combustion engine. preferred over a diesel engine in the sweet spot that optimize the use of the battery A new approach to produce because it can produce lower is optimized by use of pack and the internal combus- a hybrid heavy-duty truck con- emissions when used with a tion engine. A reinforcement- high-octane fuel.’ cept has now been developed flexible fuel such as a learning energy management by Bromberg and his co-author combination of gasoline and an system was used to maximize and research scientist Dr. Dan- alcohol. efficiency. This system also this approach will be extremely iel Cohn. Researchers proposed several was given the ability to learn challenging because the truck options to boost performance through a reward-by-action fac- would require between 10 and Spark ignition engine and reduce emissions, tor. In a commuter study done 15 tons of batteries that would Bromberg and Cohn outlined an including running the truck at a in Southern California, this re- add excessive weight and be approach for the development high compression ratio, using inforcement model reduced fuel costly. Both size and weight of a hybrid heavy-duty truck that pre-chamber jet ignition and consumption by 12%. would limit the payload the uses a spark ignition (SI) engine alcohol-enabled high- In contrast, there has been truck could carry and limit its in combination with a battery. performance exhaust recovery. limited development of a hybrid driving range.” They provided options that can

heavy-duty truck (see Figure 1). Consideration should be be used to further enhance the © Can Stock Photo / welcomia

12 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG performance of this heavy-duty truck. One interesting strategy used by the researchers was to not use a diesel engine but, rath- er, to propose that a flexible fuel gasoline-alcohol spark ignition engine be the preferred choice. Bromberg says, “We believe the SI engine has advantages over a diesel engine in running cleaner with lower levels of emissions, particularly when combined with a flexible fuel that can be a combination of gasoline and an alcohol (either methanol or ethanol).” Diesel engines typically run at higher fuel efficiencies than gasoline engines. The research- ers believe that this disadvan- tage can be overcome by opti- Figure 1. A concept for a hybrid heavy-duty truck that contained a spark ignition engine and a battery was devised mizing the operating conditions that has the potential for excellent performance while minimizing emissions. (Figure courtesy of the Massachusetts of the hybrid heavy-duty truck. Institute of Technology.) Bromberg says, “In our ap- proach, we are looking for the SI engine to operate in the sweet the researchers determined hol enabled high performance size. He says, “We developed spot that is optimized by use of that the SI engine delivers the exhaust recovery. Bromberg our approach with the feeling high-octane fuel.” Two strate- same power (380 kilowatts) as says, “Alcohols have the prop- that a 200-kilowatt sized battery gies to optimize the SI engine a diesel engine. erty when exposed to tempera- will be required.” include running at a compres- The high compression ratio tures between 200-300 C and The researchers are con- sion ratio of 14 that is higher increases the likelihood of en- in the presence of a catalyst to ducting further modeling to op- than the typical ratio of 10 and gine knocking. Bromberg says, decompose into hydrogen and timize the engine size and the using a smaller gasoline engine. “We proposed in our modeling carbon monoxide. The process battery. Bromberg says, “We The latter case will reduce the to include two fuel tanks in the is endothermic and can readily hope to propose this idea to amount of fuel required which hybrid heavy-duty truck. One be conducted under the high the automotive industry as an will save weight.” fuel tank would be gasoline temperature engine operating approach for introducing elec- Bromberg says, “To achieve while the second fuel is an al- conditions. The hydrogen-rich trification to heavy-duty trucks.” this objective, the SI engine will cohol that exhibits a high-octane gas can be reintroduced into the Additional information can need to operate under higher value. The two fuels can be engine leading to potentially a be found in a recent presenta- temperature conditions than blended to the desired ratio to 10%-15% increase in efficiency.” tion2 or by contacting Bromberg the diesel engine. This will lead minimize knocking without add- The inefficiencies of the gen- at [email protected]. to an exhaust emanating from ing too much weight.” erator/motor can be compen- the gasoline engine at a higher Pre-chamber jet ignition sated by the increased energy REFERENCES temperature (700-800 C) than also is proposed by the re- recovery using the endothermic 1. Canter, N. (2016), “Improving for a conventional diesel engine searchers to maintain high ef- reforming of the alcohols. the Efficiency of Plug In-Hybrid (400-500 C).” ficiency. Bromberg says, “This In contrast, the engine gas Electric Vehicles,” TLT, 72 (5), In Bromberg’s opinion, the approach can increase the com- recirculation (EGR) system pp. 16-17. higher operating temperature bustion rate while minimizing present in a diesel engine will 2. Cohn, D. and Bromberg, L. will represent a challenge to engine variability from cycle to not be necessary with the SI (2019), “Flex Fuel Gasoline- the lubricant industry to de- cycle.” engine and its absence also im- Alcohol Engine for Near Zero velop an engine oil that will be An intriguing option offered proves efficiency. Emissions Plug-In Hybrid Long-Haul Trucks,” Presented by the researchers is to use the From the battery perspec- able to handle severer condi- at the SAE World Congress & tions than what are currently flexible fuel option built into tive, Bromberg is not as con- Exhibition in Detroit, Mich., on experienced. In their modeling, their modeling to propose alco- cerned about the type as the April 11, 2019.

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 13 TECH BEAT

New thermoelectric material based on cobalt

A theoretical study is underway to use spin caloritronics to identify an oxide based on cobalt, nickel and zinc.

The inefficiency of machinery researchers developed a new the magnetic properties be- KEY CONCEPTS such as automobiles is continu- approach for producing a ther- tween the ferromagnetic mate- A theoretical study is being ing to lead researchers to iden- moelectric material than taking rial, nickel and a normal metal, conducted to identify tify materials that can convert advantage of a temperature platinum. superior thermoelectric waste heat into electricity. Au- gradient. A new thermoelectric Dr. Anveeksh Koneru, se- materials based on cobalt, tomobiles are a prime example nior lecturer in mechanical nickel and zinc oxides. because 60% of fuel efficiency engineering at the Univer- is lost due to waste heat (see 'Cobalt oxide is an sity of Texas Permian Basin in The objective is to find a Figure 2). appealing material Odessa, Texas, is focused on transition metal oxide that Thermoelectric materials to work with because trying to determine how to in- combines the benefits of are known to convert heat into crease the figure of merit (ZT) the conventional other transition metals electricity by using a tempera- for a thermoelectric material. thermoelectric effect with such as nickel can be ture difference such as observed He says, “ZT is a unitless, non- a contribution from the substituted without at the tailpipe of an automobile dimensional parameter that is spin thermoelectric effect. where there is a significant dif- an issue.' directly related to the efficiency Initial work found that a ference in the temperature of of a thermoelectric material. A combination of 25% zinc the automotive exhaust and material containing randomly higher ZT directly correlates to and 75% nickel in the the ambient temperature. The dispersed platinum nanopar- a better performing thermo- tetrahedral configuration of challenge is to improve the ef- ticles in a nickel matrix utilized electric material.” the transition metal oxide ficiency of thermoelectric mate- the inverse spin Hall effect to ZT is directly proportional to produced superior rials to enable the process to be create an electric voltage. Elec- the Seebeck coefficient and the performance. commercially viable. tricity was generated by taking electrical conductivity of the 1

In a previous TLT article, advantage of the difference in material while inversely propor- © Can Stock Photo / docer

14 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG theoretically for band gap, lat- tice parameter, the effective mass of conduction electrons and spin polarization. The chal- lenge is to find a material that maximizes the difference in the population densities of elec- trons in the upward spin state compared to the lower spin state. Koneru says, “A perfectly symmetric system with equal number of electrons in both states is not desired. The more asymmetry between the two electron spin states will lead to a better spin thermoelectric effect.” The researchers are substi- tuting nickel and zinc atoms for one of the three cobalt atoms in the transition metal oxide. Koneru says, “We found that a combination of 25% zinc and Figure 2. Theoretical studies are underway to develop a superior thermoelectric material that could potentially convert waste heat produced during internal combustion into useful electricity. (Figure courtesy of The University 75% nickel in the tetrahedral of Texas Permian Basin.) configuration of the transition metal oxide produced optimum performance in our initial calcu- tional to the thermal conductivi- key factor is that any change in and zinc that displays supe- lations.” ty. Koneru says, “Most materials the Seebeck coefficient leads to rior thermoelectric properties. Koneru considers this to be encountered exhibit both strong a four-fold improvement in ZT.” Koneru says, “Cobalt oxide is a sweet spot but is looking at electrical and thermal conduc- The spin Seebeck effect is an appealing material to work other configurations in the fu- tivity. Finding a material with derived from the difference in with because other transition ture, including those based on strong electrical conductivity the number of electrons with metals such as nickel can be manganese and iron. He says, but weak thermal conductivity their spins in the upward direc- substituted without an issue. “We also are going to take a is very challenging. One other tion compared to the number Our objective is to work with close look at how the thermal factor is that the temperature with their spins in the down- different percentages of cobalt, conductivity parameters can be of the system can impact the ward direction. Koneru envi- nickel and zinc in order to opti- minimized to also increase ZT.” efficiency of the thermoelectric sions a model for a thermo- mize the characteristics of the Additional information can material. In moving from a tem- electric material that combines thermoelectric material.” be found in the recent presen- perature of 300 K to 700 K, the the conventional thermoelectric The three metals have dif- tation and by contacting Koneru efficiency of the thermoelectric effect with a contribution from ferent properties with respect to at [email protected]. device can exhibit a five-fold im- the spin thermoelectric effect. magnetism and electrical con- provement in efficiency.” Koneru is in the process of ductivity. Cobalt and nickel are REFERENCES Koneru believes that ZT can conducting theoretical studies both magnetic and conductive be increased further by incor- using supercomputers to iden- while zinc is neither magnetic 1. Canter, N. (2017), “Transverse Thermoelectric Device,” TLT, porating the spin of electrons tify a superior thermoelectric nor conductive. Differences in 73 (3), pp. 12-13. in polarized materials through material. the magnetic properties may 2. Hines, N., Resende, G., Girondi, the use of the inverse spin Hall enable the band gap between F., Boadi, S., Musho, T. and effect. This is known as spin Oxides of cobalt, nickel and zinc electron states to increase Koneru, A. (2019), “Substitu- caloritronics. He says, “The In a recent presentation2 leading to better thermoelectric tional Effects of Bivalent Zn spin Seebeck effect should al- where their initial results were properties. and Ni Cations on Spin low the harnessing of extra shared, Koneru and his col- The researchers are devis- Thermoelectric Properties of Co O ,” Presented at the ing between 1,000 and 1,500 3 4 voltage in addition to the con- leagues discussed the use of Materials Research Society ventional voltage generated by spin caloritronics to develop configurations of cobalt, nickel Meeting in Phoenix, Ariz., on the thermoelectric material. A an oxide based on cobalt, nickel zinc oxides that are evaluated April 22, 2019.

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 15 TECH BEAT

Redox flow batteries: New approach may boost performance

A newly developed electrolyte known as CVBH shows promise in redox flow batteries.

A good deal of attention has oxometalates with a hexavana- CVBH does not been paid to the development date core. In evaluation testing, become unstable in of batteries for use as a power the researchers found that this comparison to other source in machinery such as electrolyte enabled the redox automobiles. This column has flow battery to exhibit superior vanadium-based focused on providing updates stability without a reduction in species. on efforts to commercialize lith- charge carrier performance. ium-ion and other battery types. In contrast to a lithium-ion tation on the voltage potential The steady development of battery, the charge-carrying for aqueous electrolytes. Cap- renewable and carbon-neutral species in a redox flow battery pillino says, “Water has a ther- energy sources such as wind are in solution. Patrick Cap- modynamic limit of 1.23 volts KEY CONCEPTS and solar power has been on- pillino, assistant professor of because at that point oxidation A close analogue to a going at the same time. One chemistry and biochemistry will generate oxygen creating natural material known challenge in working with at University of Massachu- operational problems. A simi- as Amavadin holds these technologies is to figure setts Dartmouth in Dartmouth, lar scenario occurs below 0 promise as a non- out how to continue to supply Mass., says, “The potential of a volts where hydrogen is gen- aqueous electrolyte for energy when the wind is not redox flow battery to act as a erated and occasionally needs redox flow batteries. blowing and the sun is obscured storage device is based on the to be bled off. Moving to a by clouds. Storing energy when ability to increase the size of non-aqueous solvent provides The analogue known as excess electricity is generated battery’s storage tank to boost much more flexibility as there CVBH displayed for use during downtimes is a energy storage. This compen- are a wide variety of options to excellent stability in feasible option. sates for redox flow batteries choose from including gamma cyclic voltammetry and Redox flow batteries have having only 20% of the charge valerolactone which has an static cell testing. been identified as a potential en- density of a lithium-ion battery electrochemical window of 8 Better solubility was ergy-storage device. In a previ- but shows there is a need for volts, which is more than six 1 achieved in polar ous TLT article, a new type that improvement.” times higher than the thermo- solvents by reacting uses a non-aqueous electrolyte As mentioned in the previ- dynamic limit of water.” 1 CVBH with other was discussed. The electrolyte ous TLT article, non-aqueous Another important factor in cations. is based on a series of multime- redox flow batteries (NFRB) working with a NFRB is the use

tallic clusters known as poly- are desired because of a limi- of vanadium. Cappillino says, © Can Stock Photo / chungking

16 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG was retained after hundreds of cycles. Further analysis by UV-Vis spectroscopy indicated that the concentration of CVBH remained stable. Cappillino says, “CVBH ap- pears to be more stable than other vanadium-based electro- lytes but its solubility is limited to only a few non-aqueous sol- vents such as dimethyl sulfox- ide (DMSO) which was used in this study.” ‡ (QJLQHHULQJ6WDELOLW\ To improve solubility, Cap- ‡ (QJLQHHULQJ6ROXELOLW\ pillino’s group has reacted ‡ (QJLQHHULQJ2SHQ&LUFXLW9ROWDJH CVBH with other cations. He says, “We found that these new species display better solubility in polar solvents such as tetra- Figure 3. A new non-aqueous electrolyte that has a high affinity for vanadium was developed based on a natural hydrofuran and acetonitrile.” material found in a mushroom and displays potential for use in redox flow batteries. (Figure courtesy of the University Additional information can of Massachusetts Dartmouth.) be found in an article2 pub- lished in 2017, a recent article3 “This element is used because been implemented as a NFRB Cappillino noted that other that was just published or by of its many stable oxidation active material but has experi- vanadium-based species such contacting Cappillino at pcap- states. In the operation of a re- enced challenges with instabil- as vanadyl (acac)2 exhibit rapid [email protected]. dox flow battery, during charg- ity. In evaluating Amavadin, we hydrolysis in the presence of ing, vanadium (3+) is converted modified a synthetic process water. He says, “These species Neil Canter heads his own to vanadium (2+) in one half-cell for making a close analogue form vanadyl (V=O) moieties consulting company, Chemical and vanadium (4+) is converted known as calcium (II) vanadium that are readily detected by ana- Solutions, in Willow Grove, Pa. to vanadium (5+) in the second (IV) bis-hydroxyliminodiacetate lytical spectroscopy techniques. Ideas for Tech Beat can half cell.” (CVBH). The process is straight- Due to their high stability, this be submitted to him at A new vanadium-based spe- forward, uses inexpensive start- decomposition mechanism is [email protected]. cies inspired by a natural prod- ing materials and can readily be shut down in the mushroom- uct has now been synthesized scaled up.” inspired compounds.” and shows superior stability for Figure 3 shows the steps In static cell testing, no de- REFERENCES use in a NFRB. taken by the researchers in composition was seen over 100 developing the idea from the cycles and 95% conversions 1. Canter, N. (2018), “Non-aque- ous Redox Flow Batteries,” CVBH Amanita mushroom, synthesiz- were achieved with bulk oxida- TLT, 74 (5), pp. 20-21. Cappillino and his colleagues ing CVBH and then evaluating tion and bulk reduction. Flow 2. Huang, H., Howland, R., Agar, have developed a new vanadium it as an electrolyte in a NFRB. cell cycling was conducted in E., Nourani, M., Golen, J. and based non-aqueous electrolyte The researchers evaluated collaboration with Ertan Agar, Cappillino, P. (2017), that is inspired from a natural CVBH’s electrochemical prop- assistant professor of mechani- “Bioinspired, High-stability, material found in the poisonous erties by using cyclic voltam- cal engineering at the Univer- Nonaqueous Redox Flow Amanita mushrooms. The mate- metry and in static cell cycling sity of Massachusetts Lowell in Battery Electrolytes,” Journal of Materials Chemistry A, 5 rial is known as Amavadin and and flow cell cycling. Cappillino Lowell, Mass. Cappillino says, (23), pp. 11586-11591. exhibits an extremely strong says, “CVBH demonstrated ex- “In this process, a 1:1 mixture of 3. Gokoglan, T., Pahari, S., Hamel, affinity to chelate vanadium for cellent stability in cyclic voltam- vanadium (IV/V) was prepared. A, Howland R., Cappillino, P. an unknown biological function. metry over 800 cycles as there During discharging, vanadium and Agar, E. (2019), “Operando Cappillino says, “Our inter- was no sign of a decrease in (IV) was oxidized at the nega- Spectroelectrochemical est in Amavadin originated be- peak current and no changes tive electrode while vanadium Characterization of a Highly cause one of the precursors of in reversibility. Even the addi- (V) was reduced at the positive Stable Bioinspired Redox Flow Battery Active Material,” this material is vanadyl (acac) tion of 20% water (by volume) electrode.” 2 Journal of the Electrochemical which exhibits interesting elec- to the system did not lead to a The researchers observed Society, 166 (10), pp. trochemical properties and has decrease in performance.” that almost all of the capacity A1745-A1751.

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 17 20 MINUTES WITH...

Xiaolan Ai This Timken scientist discusses bearing fatigue life and the advantages of virtual bearing testing.

By Rachel Fowler Managing Editor

Xiaolan Ai at the patent wall of the research lab.

Xiaolan Ai The Quick File:

Dr. Xiaolan Ai received his bachelor’s of science and master’s of led the development of a comprehensive virtual bearing life test science degrees in mechanical engineering from Tsinghua model which, among other unique and desirable features, University, Beijing, China, in 1984 and 1986. He earned his established for the first time the ability to quantify the impact of doctorate in mechanical engineering from Northwestern University steel cleanliness on bearing performance. in Evanston, Ill., in 1993. Ai joined The Timken Co. in 1995 as a Ai has authored 61 peer-reviewed journal papers and book principal engineer and later became a research specialist and then chapters. He holds 60 patents (38 U.S. and 22 foreign) and has a a senior product development specialist. He is now in the lead dozen pending patent applications. Ai’s invention covers areas of scientist role. bearings, sensors, cutting tools, traction drives, gear drives and Ai is a prolific inventor and one of the go-to experts of The motor drives. Timken Co. He has wide research interests in bearing Ai is a Fellow of the American Society of Mechanical Engineers fundamentals, tribology, electromechanical systems, transmissions (ASME). He served as section editor of rolling element bearings for and powertrains. He is instrumental in broadening and advancing Encyclopedia of Tribology and associate editor for ASME Journal of the company’s engineering analysis capabilities. He initiated and Tribology from 2012 to 2018.

18 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG TLT: Why is modeling such bearings are selected based load, speed and lubrication rig are modeled numerically an important tool in bear- on their load ratings, which conditions. The test may last for through a layered structure to ing useful life prediction, are closely associated with fa- several weeks or even months. ensure the required resolution and how does it work? tigue life performance. Thus, As bearing size increases, the and computational efficiency. the ability to predict bearing cost of physical testing quickly The model contains more than Ai: The damage mode of roll- fatigue life is of paramount skyrockets. For large and ultra- a dozen individual modules ing element bearings varies importance. Physic testing large bearings, such as those to describe various aspects of widely. It depends on bearing played a very important role used for the main shafts of wind bearing performance attributes. design, manufacturing, han- in establishing bearing ratings turbines, physical bearing life VBLT starts with finite el- dling, installation, maintenance and an equally important role testing is often cost prohibitive. ement (FE) modeling of the and operating conditions. The in product quality assurance. This creates a pressing need to test rig from which the loads ultimate damage mode, howev- Due to its statistical nature, develop a means to conduct vir- acting on each of bearings are er, in a well-designed, quality- bearing fatigue testing is a very tual bearing life testing (VBLT). obtained (step a in Figure 1). built, carefully maintained roll- time-consuming and costly ex- An example of a VBLT model Detailed FE models of the test ing element bearing is fatigue ercise. It requires multiple bear- is shown in Figure 1. It can be bearings are built with a finer damage. ings (usually 24 or more) with viewed as a digital representa- mesh grid where load distribu- For the great majority of essentially identical attributes tion of an actual physical test tion at the contacts between applications, rolling element to be tested under the same where the test bearings and the rollers and raceways is esti-

Virtual test rig model (a) Roller load (a) Contact stress & stressed volume (c) Inclusion distribution (e)

Residual stress and hardness (b) Fatigue risk (d & e) Stress alteration (e)

Bearing life reduction due to inclusions (f)

Figure 1. VBLT model structure and computational work flow. (Copyright by ASME: A Comprehensive Model for Assessing the Impact of Steel Cleanliness on Bearing Performance,” by Xiaolan Ai, Journal of Tribol. 2014; 137(1).)

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 19 Q 20 MINUTES WITH... © Can Stock Photo / scanrail

mated (also step a). Roller loads tion is derived based on Miner’s Through careful calibration not yet fully understood or well are then passed on to a contact Rule of damage accumulation with test data, VBLT, as a first controlled. module where detailed contact using the resulting stress fluc- principle-based model, can be One of the challenges in analysis is performed for sur- tuations and is subsequently extended to cover different bearing fatigue modeling is ma- face and subsurface stress dis- applied to the contact stresses bearing size and types, and terial microstructure response tributions at each of the contact of smooth surfaces subjected to to model different test condi- to stress cycles. To a certain locations (step c). the same load level. tions quickly with high fidelity. extent, our current knowledge The model includes a heat Additional modules have It not only provides an alter- is still primarily experimental treatment module to model the been developed for calculating native to large and ultra-large and phenomenon based. A material’s response to different the stress alterations resulting bearing tests but also is a cost- unified damage mechanism heat treatment processes. This from inclusions within the ma- effective means for conducting across different material types module provides the resultant terial or surface indentations life tests on conventional sized and microstructures needs to residual stress distributions on the bearing raceways. The bearings. be further explored. A com- and hardness profiles within inclusion module reads in inclu- putationally effective material the bearing components (step sion information—including in- TLT: What are the main response model applicable to b). A fatigue risk assessment clusion size, location, material advantages and challenges all bearing steel material is yet module then combines the property and orientation for in virtual bearing testing? to be established and validated. contact stresses and residual every inclusion found within stresses to generate a critical the bearing components—and Ai: As mentioned, one of the TLT: What’s your view on stress, which is compared to calculates stress alterations main advantages is cost effec- the emerging powertrain the material strength to estab- within a super cell surrounding tiveness. It allows application technologies and their lish the risk of fatigue damage the inclusion. engineers anywhere to conduct impacts in the next 10-15 at the given point. The fatigue The super cell is usually set bearing tests under various ap- years? risk assessment module further at approximately 10 times larg- plication scenarios quickly with integrates fatigue risk over the er in volume than the inclusion minimum cost. In addition, Ai: We are in an era of rapid entire stressed volume of the it encapsulates. The original it allows research and design change. We are currently at material for all bearing compo- stress field is then modified by engineers to conduct what-if a converging point of several nents to derive an estimate of substituting the super cells at studies to gain better insight mega trends. Cyber-physical bearing life based on a three- their respective locations (step into various factors that affect systems are a common theme parameter Weibull statistical e). The fatigue life of the bear- bearing life performance. This, across many industries. They distribution (step d). ing is re-evaluated using the in turn, could lead to improved call for product digitization, con- To consider the impact of modified stress field. A relative bearing designs to achieve ap- nectivity, intelligence and flex- surface roughness on bearing life with respect to nominal life plication objectives. ible automations. Concurrently, fatigue life, a rough contact can thus be obtained (step f). Bearing fatigue life model- the automotive industry is expe- module calculates contact A similar methodology can ing is by no means an easy task. riencing a major transformation stress fluctuations for a given be applied to the surface inden- The statistical nature of bear- of electrification. This technical load level using the measured tation module from which a life ing fatigue indicates there are trend was originally driven by 3D surface topography of the reduction factor due to the sur- a host of influential variables energy conservation and envi- bearing raceway surfaces. An face indentations is estimated that affect bearing life perfor- ronmental concerns and more effective stress correction func- for the dented bearings. mance; some of them are still recently has been fueled

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by the rapid advancements in port powertrain electrification. currently looking at expending autonomous and artificial in- Cyber-physical Design options for creating such the horizon of virtual bearing telligence technologies. It is systems are a products include bearing mate- life testing beyond fatigue— expected that the process of common theme rial cleanness, bearing macro- building a full virtual labora- transformation will last for the and micro-geometries, surface tory to include virtual tests of next few decades. This transfor- across all industries. finishing and manufacturing all performance attributes such mation is also occurring in other process control. Bearing design as dynamics, noise and vibra- mobile industries. engineers may need to push tion, surface wear, scuffing, As we are embracing the tions to reduce friction and drag boundaries and establish new torque and heat generation new powertrain technologies losses. Housing material, lubri- design practices to provide cost- for all types of rolling element and enjoy the many benefits cation method and operating effective solutions and competi- bearings. they bring to society and end- temperature also are expected tive products. I am currently working us ers, we must also be prepared to change. System noise, vibra- closely with a group of talented for the impact they bring upon tion and harshness (NVH) and TLT: What’s your current colleagues toward this ambi- manufacturing processes and thermal management become focus and interests? tious goal. Creating something component suppliers. For the critically important. new and useful has always bearings industry, this imposes To meet these challenges, Ai: Virtual bearing life testing, been my passion, whether it’s challenges but also creates new rolling element bearings may from a higher perspective, is a piece of software, a product opportunities. Bearings in elec- need to be specifically engi- a part of a digital engineering or a process. trified powertrains are required neered to attain the performance ecosystem. To support and be to operate at higher speeds and attributes of precision, quietness well prepared for the industry- You can reach Xiaolan Ai at under thin lubricant film condi- and higher fuel efficiency to sup- wide digital revolution, we are [email protected].

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Solid lubricants

These materials are well suited for extreme conditions where liquid lubricants are impractical. © Can Stock Photo / Eraxion

KEY CONCEPTS By Jane Marie Andrew Contributing Editor Solid lubricants are ideal for but not limited to extreme conditions. They are usually applied Although liquid lubricants are the typical solution for reducing as coatings by a variety of friction, sometimes they are impractical or inadequate, for instance, where methods. there is extreme contact pressure, elevated temperature or a vacuum. Such atypical conditions call for atypical solutions. Fortunately lubrication tech- Advances are focused on nology now includes a range of solid lubricants (also called dry or dry-film coatings whose properties lubricants) that are well suited for extremes. can change with operating Solid lubricants take the form of either a coating applied to a surface conditions. or solids added to a composite. Unlike liquids or gases, solid lubricants do

24 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG not volatilize or decompose in extreme operating conditions. However, they often have spe- cific operation criteria and thus require careful selection or cus- tomization to the application. Most solid lubricants fall into one of four classes:

1. Carbon-based solid lubri- cants such as graphite, dia- mondlike carbon (DLC) and nanocrystalline diamond 2. Transition-metal dichalco- genides such as molybde-

num disulfide (MoS2) and

tungsten disulfide (WS2) 3. Polymers and polymer com- posites, including polytet- rafluoroethylenes (PTFEs, e.g., Teflon) and polyimides © Can Stock Photo / Leaf 4. Soft metals, such as gold, Solid lubricants are a good choice for diagnostic imaging machines because the bearings in these tubes operate at silver, lead and copper. high rotational speeds, at high temperature and in a hard vacuum.

First developed for applica- tions in the 1980s, these coating be replaced periodically. For can sometimes react with the Once a candidate material is have become more structurally coatings used in environments contacting material during op- identified, larger-scale bench sophisticated as research has where replacement is not pos- eration to form a thin film of testing, such as engine tests, advanced. In a review chapter sible, physical and chemical va- solid lubricant, often called a are conducted. for an ASM handbook,1 Sandia por deposition processes may tribofilm. Such a film can func- Laboratories scientist and STLE be required. In these processes, tion like a solid lubricant as long Lubrication mechanisms Past President Michael T. Dug- atoms or molecules of the solid as the film remains in the mov- The fundamental lubrication ger classified solid lubricants lubricant are vaporized from a ing contact. For example, tribo- mechanism for a solid lubricant according to their chronologi- films can form on DLC in the is interfacial sliding between cal development, moving from presence of liquid lubricants the wear track that forms on the single-component structures Solid lubricants are as a result of friction-induced solid lubricant and the transfer to multicomponent or multi- at the forefront of chemical reactions between the film or tribofilm that adheres to layer structures, then later to adaptive or smart DLC and additives in the lubri- the sliding counter face mate- nanostructured, superlattice or structure. cant. Thus, DLC can be used to rial. When low interfacial shear functional gradient structures. mitigate friction and wear in au- can be achieved, friction be- At the forefront today are adap- tomotive piston rings and cam tween the contacting surfaces tive or smart structures. piece of the solid and depos- followers, for example. is often very low, extending ited on a substrate material. wear life. Application or fabrication For polymer-based solid lu- Characterization and The wear life can be further Solid lubricants can be either bricants and their composites evaluation increased by using a hard, load- monolithic or applied as a (e.g., PTFE containing nickel), The composition and structure bearing underlayer to minimize coating or thin film. Most sol- electrochemical processes are of solid lubricants are studied the contact area. This soft-on- id lubricants are applied as a used. with a range of spectroscopic hard combination is often re- powder that is burnished, ther- Although solid lubrication and structural microscopy ferred to as the Bowden-Tabor mal sprayed or cold sprayed usually requires an applica- techniques. Their performance concept.2 The four classes of on a part to form a coating tion or fabrication step, under is evaluated initially with stan- solid lubricants mentioned or film. Such methods can be some conditions a similar ef- dard tribological lab tests such previously all provide low in- inexpensive and are appropri- fect is created during opera- as pin-on-disk sliding and high- terfacial shear at the moving ate for coatings that need to tion. Liquid or gas lubricants frequency reciprocating wear. contact.

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 25 Q LUBRICATION FUNDAMENTALS

Properties and operating Table 1. Advantages and Disadvantages of Solid Lubricants parameters In general, the parameters that Advantages Disadvantages control friction and wear with • Very stable in high-temperature, cryogenic, • Higher coefficients of friction and wear than liquid solid lubricants are low inter- vacuum and high-pressure environments lubricants facial shear in the direction of • High heat dissipation (with high thermally • Poor heat dissipation with low thermally conductive sliding; strong adhesion to the conductive lubricants) lubricants such as polymer-based films surface; adequate lubricant co- • High resistance to deterioration in the presence • Poor self-healing properties (a broken solid film may hesion; and physical, chemical of radiation shorten the lubricant life) and mechanical compatibility • High resistance to abrasion in the presence of dust • Possibly undesirable color (i.e., graphite). with the contacting surface. • High resistance to deterioration in corrosive These parameters must be environments satisfied for the intended op- • High resistance to deterioration in storage erating contact pressure, tem- • More effective than fluids at high load and high speeds perature and chemical envi- • Lighter and less complex operation—lubrication ronment. Other parameters to distribution systems and seals are not required be considered include thermal • Reliable—suitable for applications where servicing stability, oxidation stability, vol- is difficult or impossible. atility, chemical reactivity and melting point. Table adapted from Van Rensselar, J. (2009), “Aerospace Lubricants: Solid is essential in every sense,” TLT, 65 (6), p. 44. Sliding friction coefficients for solid lubricants are usually <0.1-0.2, and wear rates range characteristics and operating ble (see Figure 1). For example, about 100 C). Such applica- -6 -7 3 between 10 and 10 mm / conditions of the main classes coatings on satellite compo- tions usually use an MoS2- Nm, thus somewhat higher of solid lubricants are summa- nents must function in an ul- based coating. Increasingly, than those of liquid lubricants. rized in Table 2 on Page 28. trahigh vacuum atmosphere in however, designers are choos- (See Scharf and Prasad3 for Typically, solid lubricants low Earth orbit, resist exposure ing solid lubricants even within a summary of friction coeffi- are used at extremes of tem- to radiation and atomic oxygen the traditional liquid lubricant cients for many common solid perature and pressure at which and cycle between extreme regime. For some cases, solid lubricants.) The latter wear rate liquid lubricants are not feasi- temperatures (cryogenic to lubricants are cheaper and eas- equates to an average removal ier to implement than liquid or rate of less than 1 atomic layer gas-phase lubricants. per 1 cm pass of a counter body These operating ranges 108 loaded at 5 N. A maximum can be tailored to a degree, but hardness of 5 on the Mohs scale no single solid lubricant mate- 4 is the practical limit for solid lu- 10 rial can function over the entire bricants. Liquid Lubricants range of extremes. Attention As to operating parameters, 100 and Greases has thus turned to composite in general, solid lubricants do solid lubricants in which each not volatize or evaporate; they 10-4 phase in the composite can tar- are less sensitive to picking up get given operational range(s). Pressure (Pa) dust or other contaminants, 10-8 For example, a composite coat- and they can be stored or dor- ing consisting of CaF2/BaF2 (for mant for long periods of times high temperatures), silver (for 10-12 without lubricant escaping low temperatures) and CrOx from the contact. Their general 0 100 200 300 400 500 600 700 800 (for wear resistance) has been advantages and disadvantages Temperature (K) developed for use to ~900 C. are summarized in Table 1. Sol- Other composites that have id lubricants are available for a Figure 1. Typical operational and temperature range of liquid lubricants and been qualified for applications grease. Traditionally solid lubricants have been used in the region outside wide range of temperatures include MoS2/Sb2O3/C for (cryogenic to approximately the box, but increasingly they are used throughout the entire pressure/ space coatings and WC-doped 700 C), environments (humid temperature space. (Adapted from Doll, G.L., (2017), “Lubricant strategies DLC for rolling elements. for challenging environments,” ASM Handbook, Vol. 18: Friction, Lubrication, to dry air, ultrahigh vacuum), and Wear Technology, edited by G.E. Totten. Materials Park, Ohio: ASM Inter- In addition to the main cat- and contact pressures (mega- national, pp. 213-219. Reprinted with permission of ASM International. All egories listed in Table 2, a va- pascals to gigapascals). General rights reserved. www.asminternational.org.) riety of other materials

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can function as solid lubricants Table 2. Operating Parameters of Solid Lubricants under certain conditions. Fluo- Lubricant Mechanism Operating conditions ride coatings (e.g., CaF2 and

BaF2) and oxide coatings (e.g., B O ) are lubricating at high Carbon-based materials • Graphite: Interlamellar shear • Thermal range: –200 C to 350 C 2 3 • graphite between covalently bonded hex- temperatures (i.e., over 500 C) • Require oxygen and/or moisture • diamondlike carbon (DLC) agonal basal planes. (Hexagonal (except highly hydrogenated where their shear strengths are crystal structure has the intrinsic DLC) small. PbO has good lubricat- property of easy shear.) ing properties from about 450 • DLC: Both high hardness and low C-700 C but is limited by its friction through an amorphous structure that combines diamond shear strength at low tempera- and graphitic phases. Can be tures and by phase change, doped with hydrogen, nitrogen reactivity and melting at high and other elements for tailored temperatures. Other materials properties. that are sometimes desirable for their high-temperature lu- Transition-metal dichalcogenides • Interlamellar shear between co- • Thermal range: –150 C to 350 C • crystalline MoS valently bonded hexagonal basal bricating properties include ox- 2 • Best performance in vacuum or • crystalline WS planes. 2 dry environments ygen-deficient TiO materials (2-x) • Coating density and oxidative with mechanically weak shear • Performance in humidity stability improve when produced improves with modified planes, oxides and double ox- as a composite with a soft metal composition or a binder material (e.g., Sb O ) ides, and Cs-based compounds. 2 3

Applications Polymers (e.g., polytetrafluoroethyl- • Highly linear molecules provide • Thermal range: –70 C to 200 C An application that illustrates ene [PTFE]) low-friction surfaces. • Vacuum and air • PTFE: the value of solid lubricants is - Long-chain fluorocarbon • Performs best at low contact coatings for rolling bearings - Low chemical reactivity loads/pressures in rotating anode X-ray tubes - Does not rely on adsorbed • Fails at higher contact loads/ vapors or moisture pressures; additives required to used in diagnostic imaging. - Low surface energy support higher loads Bearings in these tubes oper- ate at high rotational speeds, Soft metals (e.g., lead, tin, indium, • Shear accommodation (solid • Rapid thermal degradation at high temperature and in silver, copper, gold) state) typically occurs above ~600 C to a hard vacuum. In addition, • Liquid film (molten state) 700 C electrical current must pass • Improved thermal behavior from the bearing housing to above 400 C may be possible the shaft, which is connected with layered binary oxides to the anodic material. Some of the important criteria for solid lubricants used in this appli- cation include high electrical and thermal conductivities, ating in space.4 They also are but experience periods of inter- tribofilm. In contrast, where the low wear rates and high lubric- used to mitigate fretting-type rupted oil flow.6 During these goal is to minimize frictional ity at operating temperatures. wear in mechanical components interruptions, the DLC coatings heating from intermittent con- These criteria limit the solid that experience low-amplitude, function as solid lubricants. tact, a low friction coefficient is lubricants to materials such as oscillating motion. Rolling bear- more critical than good wear re- lead, gold and silver. Additional ings used in high-speed turbine Customization sistance. It is sometimes possi- application requirements limit engines employ silver coatings For some applications it is advis- ble to meet conflicting tribologi- the thickness and deposition on steel cages to lubricate the able to customize solid lubricant cal demands with a composite. processes that can be used to ball/cage and cage/land con- coatings to meet the demands Some composites are self-lu- deposit these materials. tacts. Foil bearings used in gas of the contact environment. For bricating—that is, the contact In general, solid lubricants turbines now employ a spe- example, when the operational surface material incorporates a are highly valued for mechani- cially developed solid lubricant lifetime of the component de- solid lubricant (such as graphite 5 cal devices that operate in coating. Diamondlike carbon pends entirely upon the dura- or MoS2). In other composites, vacuum, high temperatures or lubricants are now being used bility of the coating, the solid different components provide inert atmospheres, and they are on rolling bearings and gears lubricant must have adequate the necessary properties at dif- essential for components oper- that are normally oil-lubricated wear resistance and/or a stable ferent conditions.

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Future approaches • Nanocomposites with and STLE-member Gary Doll, Jane Marie Andrew is a The next step beyond compos- diffusion barriers Timken professor of surface en- free-lance science writer and edi- ites, in terms of broadening the • Dichalcogenide compos- gineering, chemical and biomo- tor based in the Chicago operating range of solid lubri- ites with phosphates and lecular engineering department, area. You can contact her at [email protected] cants, appears to be adaptive soft metals University of Akron (gdoll@ . lubricants. Adaptive lubricants uakron.edu). are materials that react with the • Fullerene-like nanoclusters environment to form new lubri- of transition-metal dichal- cious phases as temperature cogenides in metal nitride increases. Adaptive lubricants matrices. have a low-friction surface at Adaptive solid lubricants Further reading room temperature, and as tem- may enable machine elements • In addition to a general review, Tribology and Applica- perature increases, the com- to operate more effectively in tions of Self-Lubricating Materials7 (CRC Press, 2017) ponents react with each other changing and/or demanding focuses on composites and self-lubricating materials. and with oxygen to form a high- application environments. temperature lubricious phase. • ASM Handbook, Vol. 18: Friction, Lubrication, and Examples of adaptive lubricants About the experts Wear Technology (2017) includes an overview of the include This article is based in large part history, characteristics, processing methods and qualifi- 1 on contributions by STLE-mem- cation of solid lubricants and a discussion of lubrica- 8 • Transition-metal dichalco- ber Thomas Scharf, professor, tion in challenging conditions. genides strengthened with department of materials science • Scharf and Prasad3 provide an overview of research on oxides and doped with soft and engineering, University of lubrication mechanisms in solid lubricants as well as a metals North Texas ([email protected]), detailed listing of 20 solid lubricants with their charac- teristics and applications. • A classic resource on the mechanisms of solid lubrica- tion is the 1942 Nature article Mechanism of Metallic Friction by Bowden and Tabor.2 Ask Us About Specialty Kettle REFERENCES Bodied and Blown Oils 1. Dugger, M.T. (2017), “Solid lubricants,” in ASM Handbook, Vol. 18: Friction, Lubrication, and Wear Technology, edited by G.E. Totten. Materials Park, Ohio: ASM International, pp. 191-206. 2. Bowden, F.P. and Tabor, D. (1942), “Mechanism of Metallic Friction,” Nature, August 15, pp. 197-199. 3. Scharf, T.W. and Prasad, S.V. (2013), “Solid Lubricants: A Review,” Journal of Materials Science, 48, pp. 511-531. 4. Van Rensselar, J. (2009), “Aerospace Lubricants: Solid is Essential in Every Sense,” TLT, 65 (6), p. 44. 5. DellaCorte, C. (2000), “The Evaluation of a Modified Chrome Oxide Based High Temperature Solid Lubricant Coating for Foil Gas Bearings,” Tribology Transactions, 43 (2), pp. 257-262. 6. Mutyala, K.C., Singh, H., Evans, R.D. and Doll, G.L. (2016), “Effect of Diamond-Like Carbon Coatings on Ball Bearing Performance in Normal, Oil-Starved, and Debris-Damaged Conditions,” Tribology Transactions, 59 (6), pp. 1039-1047. Bio-sustainable — Bio-renewable — Biodegradable 7. Omrani, E., Rohatgi, P.K. and Menezes, P.L. (2017), Tribology and Applications of Self-Lubricating Materials, 1st ed., Boca Raton, Fla.: wernergsmithinc.com CRC Press. [email protected] / 1.800.535.8343 8. Doll, G.L. (2017), “Lubricant Strategies for Challenging Environ- ments,” ASM Handbook, Vol. 18: Friction, Lubrication, and Wear Technology, edited by G.E. Totten. Materials Park, Ohio: ASM International, pp. 213-219.

30 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG <:4HU\MHJ[\YLYVM3\IYPJH[PUN6PS .YLHZLHUK;YPIVSVN`,X\PWTLU[

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Fundamentals of wind turbines Global capacity has grown continuously since 2001, including a 9% increase in 2018. © Can Stock Photo / ssuaphoto

KEY CONCEPTS By Jane Marie Andrew Contributing Editor As an industry, wind energy is growing fast; both total capacity and individual turbine output have increased steadily The rising concerns over climate change, environmental pollution and energy security have in- over the last decade. creased interest in developing renewable energy. We are seeing unparalleled enthusiasm, demand and growth in renewable energy production, with wind energy being at the forefront. Wind energy is expand- The wind characteristics ing both onshore and offshore with bigger, more powerful turbines, creating new demands and markets. change with geographical location, terrain, season, height, Market direction and time of day. The global capacity for generating power from wind energy has grown continuously since 2001, reach- 1 The power output of a turbine ing 591 GW in 2018 (9% growth compared to 2017), according to the Global Wind Energy Council. 2 depends primarily on the blade In the U.S., capacity figures are reported by the American Wind Energy Association. According to length and the wind speed. this trade association, the total wind power capacity in the U.S. was 96,488 MW at the end of 2018, an 8% increase from the 88,964 MW installed at the end of 2017 (see Figure 1). (Generation capacity means the

32 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG MEET THE PRESENTER This article is based on a Webinar originally presented by STLE Education on Feb. 27. Fundamentals of Wind Turbines is available at www.stle.org: $39 to STLE members, $59 for all others. Dr. Harpal Singh is a senior scientist at Sentient Science where he is engaged in wind turbine and aerospace-related mechanical and materials science research involving tribology, materials characterization and failure analysis. Singh has more than six years of experience in the field of tribology and metallic materials. He holds a patent, several peer-reviewed publications and two best paper awards from STLE in the field of solid lubricants. He earned his doctorate in mechanical engineering from the University of Akron, Ohio. His research was focused on the mechanical, material and tribological properties of materials and coatings used in wind, automotive and aerospace applications. His expertise includes materials Dr. Harpal Singh characterization, tribological testing, coatings and failure analysis. You can reach Singh at [email protected].

output of a wind turbine when running at rated power.) New installed capacity grew steadily from 2000 to 2012. After a spike and a trough in 2012 and 2013, new installations recovered in 2014 and have leveled out at about 7,000-8,500 MW annu- ally since 2015. Capacity growth in the U.S. in 2018 was concentrated in the central states (the “wind belt”), the West Coast states and, to a lesser extent, the tier of states along the northern border. Tex- as leads in overall installed ca- pacity, followed by Oklahoma and Iowa. Similar trends are ob- served in new capacity instal- lations, with Texas far outstrip- ping any other state, followed Figure 1. Trends in U.S. wind energy growth. (Figure courtesy of the American Wind Energy Association’s U.S. Wind at a distant second by Iowa (see Industry Fourth Quarter 2018 Market Report.) Figure 2 on Page 34). Five cen- tral states were in the next tier in 2018: Colorado, Oklahoma, states with 3,000-10,000 jobs 4% of the global 2018 capac- of wind energy dropped 69% Nebraska, Kansas and Illinois. by the end of 2018. ity of 591 GW, according to the from 2009 to 2018, and the This growth has resulted in In addition to exploiting in- Global Wind Energy Council.1 mean levelized cost of energy strong employment growth. In terior wind belt regions, many The cost of onshore wind for wind power is now $29 to the decade from 2008 to 2018, countries with ocean coastlines energy has become competitive $56 per megawatt-hour.3 Coal is the number of full-time equiva- are developing offshore wind with utility-scale solar photovol- the only other technology that lent jobs in the wind industry power generation. The trends taics and gas combined-cycle approaches the same range. grew from about 50,000 to in offshore capacity mirror generation joining them as the In a growing trend, large more than 110,000. Texas has those for land-based capacity, three least expensive sources corporations are including the most wind-related employ- showing steady growth. The of energy. According to Lazard, wind power in their power pur- ment, with 25,000-26,000 jobs, global offshore capacity as of a financial advisory and as- chase strategy, either through distantly followed by 10 other 2018 was 23,140 MW or about set management firm, the cost direct ownership of wind proj-

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 33 Q WEBINARS

ects or purchase agreements. Among commercial and indus- trial (C&I) purchasers, Walmart made an early mark in this area with a purchase announced in 2008. Google Energy has an- nounced purchases each year since 2010 and is currently the largest C&I wind customer, with total contracted capacity of 1,096 MW. AT&T contract- ed the most new wind power in 2018, a total of 820 MW.2 Other major purchasers include not only large technology com- panies and manufacturers but also a municipality, a regional transit system and a govern- ment agency. Figure 2. New U.S. capacity installed in 2018 and (inset) cumulative installed capacity by state. (Figure courtesy of As the market has grown, the American Wind Energy Association’s U.S. Wind Industry Fourth Quarter 2018 Market Report.) turbine models have prolifer- ated; in 2018 there were more than 30. According to the American Wind Energy As- sociation, three manufactur- ers hold over 85% of the U.S. market: GE Renewable Energy (41.4%), Vestas (24.2%) and Siemens Gamesa Renewable Energy (19.7%). Smaller play- ers are Mitsubishi, Suzlon, Clipper and Senvion. In terms of capacity, GE Renewable En- ergy and Vestas are the clear leaders at 39,912 and 23,318 MW, respectively.2 The products created by these companies are growing ever larger in both generating capacity and physical size. For turbines installed in the U.S. Figure 3. Turbine models installed in 2018. (Figure courtesy of the American Wind Energy Association’s U.S. Wind from 2000 to 2018, average Industry Fourth Quarter 2018 Market Report.) generating capacity roughly quadrupled from 660 kW to 2.43 MW. For a sense of scale, Liberty—and rotor diameter Wind physics Wind is shaped by both the average U.S. household uses has more than doubled from fundamentals global and local forces. Global 2 kW of electricity annually. A 160 feet (49 m) to 380 feet (116 Wind arises from processes patterns are in part the result of 2.5-MW turbine running at peak m), about the length of a soccer driven by solar energy. The the Coriolis force, which arises capacity all year round would field. The majority of turbines sun’s energy creates tempera- from the Earth’s rotation. As power about 1,250 homes. installed in the U.S. in 2018 had ture differences that drive air cool air flows from higher to In the same period, the av- capacity ratings in the range of circulation. Hot air rises, re- lower pressure areas, it is de- erage height of the turbine hub 2-3 MW, followed by units rated ducing the local atmospheric flected by the Coriolis force; the increased from 190 feet (58 m) for 3-3.5 MW. Sixteen models pressure; nearby cooler air direction of deflection depends to 288 feet (88 m)—approach- dominated the 2018 installa- flows into this region of lower on latitude. As a result, differ- ing the height of the Statue of tions, as shown in Figure 3. pressure; this air flow is wind. ent regions of Earth

34 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG

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captive wings.) The lift generat- ed as wind passes over the blade causes it to move, thereby rotat- ing the main shaft. The rotation is transmitted through a gearbox to a generator, which converts it into electricity. The magnitudes of the lift and drag on the tur- bine blade are dependent on the angle of attack between the apparent wind direction and the chord line of the blade. Several different factors influence the power output of a wind turbine. Among other factors, wind speed and rotor diameter are the two primary parameters (see Technical Note: Equations for Wind Turbines). Figure 4. Plot of the frequency of occurrence of different wind speeds over a period of a year. (Figure courtesy of

Sentient Science Corp.) • Turbine power increases with the square of blade have different prevailing wind A stable flow with a consis- Wind power fundamentals length. For example, in- directions. tent speed is very important for Energy is captured from wind creasing the rotor diameter At the other end of the both generating efficiency and through the lift phenomenon— from 262 feet (80 m) to 394 spectrum, local geographical structural integrity. Variability the same phenomenon that al- feet (120 m) allows power features can have very specific leads to wind shear and wake lows birds and airplanes to fly. to increase from 2 MW to 5 effects. One such effect, famil- forces. Wind shear is a function (Turbine blades are, in essence, MW (a factor of 2.5). iar to anyone living near the of wind speed, which increases ocean, is the land breeze. At with height above the surface. night, the water is warm relative Thus, the shear forces on the to the land, so air is warmed rotor blade are greater when it Technical Note: Equations for wind turbines over the water and rises; the is in the top position (see Tech- Wind Shear resulting low pressure draws nical Note: Equations for Wind cool air from land out to sea: Turbines). An important consideration for turbine siting and operation is the land breeze. Wake forces are created be- wind shear when the blade is at the top position. Wind shear is Although there may be a pre- cause the wind slows down and calculated as ܪ ܪ௥௘௙ vailing wind direction, it is not becomes turbulent as it passes ܸൌܸ Ž ൬ ൰ȀŽሺ ሻ ௥௘௙ ܪ ܪ the only wind direction. Both the wind turbine rotor blades. ଴ ଴ direction and speed are highly This is why turbines are widely variable with geographical loca- spaced, usually five to nine ro- V = wind speed at height H above ground level tion, season, height above the tor diameters in the direction of Vref = reference speed surface and time of day. Under- the prevailing wind and three Href = reference height standing this variability is key to to five rotor diameters in the H = height above ground level for the desired velocity, V siting wind power generation, perpendicular direction. H0 = roughness length in the current wind direction. because higher wind speeds Wind speed also changes mean higher duty cycles (i.e., as a result of turbulence, which For instance, assume we know that the wind is blowing at 8 longer periods of active power can be caused by nearby rough m/s at a height of 20 m. We want to calculate the wind speed at generation). It is necessary to terrain, including trees and 70 m. If the roughness length is 0.1 m, then measure the characteristics of buildings; these can cause Vref = 8 the wind in great detail, includ- wind speed to vary greatly even H = 70 ing how often winds of certain within several hundred yards or H0 = 0.1 and speeds occur (see Figure 4) and meters. This effect, called tur- Href = 20, hence, how the surrounding terrain af- bulence, decreases efficiency V = 8 ln(70/0.1) / ln(20/0.1) = 9.8915 m/s. fects the stability of wind flow. and causes fatigue loading.

36 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Turbine power increases with the cube of wind velocity.

• Turbine power increases not transmit enough energy with the cube of wind ve- to overcome the friction in the locity. For example, a tur- drivetrain. At the rated out- bine at a site with an aver- put wind speed, the turbine age wind speed of 16 mph produces its peak power (its would produce 50% more rated power). Below the cut- electricity than the same out wind speed, the turbine turbine at a site with aver- must be stopped to prevent age wind speeds of 14 mph. damage. A typical power pro- file for wind speed is shown in These two fundamental Figure 5. physical relationships are be- In addition to an operating hind the drive to scale up the range, an installed turbine has physical size of turbines. A a capacity factor that reflects larger rotor diameter allows its actual power generation. a single turbine to generate The capacity factor is the an- more electricity, providing bet- nual average of power gener- ter return on installation cost. ated divided by the rated peak And because wind speed and power. For example, if a turbine consistency both increase with rated at 5 MW produces power height, taller turbines produce at an average of 2 MW, then its Figure 5. Profile of power output from a wind turbine over a year. (Figure a higher and more consistent capacity factor is 40%. In gen- courtesy of Sentient Science Corp.) supply of electricity. eral, a higher capacity factor is A given design operates preferred, although it may not with a range of wind speeds. be advantageous economically. with the same rotor diameter. transmitted from the rotors to Below the cut-in wind speed, For instance, in a windy loca- This would tend to lower the the generator. In a direct-drive the turbine cannot produce tion, it will be advantageous capacity factor, but it will lead design, the speed is transmitted power because the wind does to use a large-size generator to substantially larger annual directly to an annular genera- production. tor. Aside from the gearbox, the components are generally simi- Wind turbine technology lar; however, in a direct-drive Turbines come in several gen- turbine the generator diam- eral categories based on orien- eter is much bigger to increase Turbine Power tation and drivetrain type. generator torque as it rotates at The energy contained in a mass m of moving air with velocity The turbine blades can be the same speed as the turbine v is oriented around either a verti- blades. ଵ -ൌ ݉ݒଶ . cal or horizontal axis. An ad- The wind turbine compoܧ ଶ vantage of the vertical axis is nents that experience friction The mass flow rate of moving air with a density l through a that blades do not have to be and wear and require lubrica- cross-section area A is mechanically reoriented when tion are the following: .the wind direction changes . ܣൌUݒ݉ The power contained in a flowing mass of air through area A is Horizontal-axis turbines come • Pitch bearing (grease) in two general designs. In a • Main shaft bearing (grease) ௗா ଵ ଵ (downwind design, the blades • Gearbox if any (oil . ܣൌ ൌ ݉ݒଶ ൌ Uݒଷܲ ௗ௧ ଶ ଶ face away from the incoming • Yaw drive (grease) The power extracted by blades of diameter d is wind; in an upwind design, the • Generator bearing (grease). blades face into the wind (see S ൌ ܿ Uݒଷ݀ଶ Figure 6 on Page 38). More than The pitch drive is used toܲ ଼ ௣ , 90% of currently installed tur- adjust the angle of the blades. bines are of the upwind type, This adjustment is made for where the power coefficient cp has a theoretical limit of ~0.6; this is referred to as the Betz limit, which defines the maxi- as this design does not create two reasons: 1.) to capture max- mum amount of wind kinetic energy that can be converted to wind shade behind the tower. imum power from winds below kinetic energy. For the drivetrain, in a gear- the rated output wind speed or box-drive design, a gearbox is 2.) to slow the blades for safe used to increase the speed operation at winds above the

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 37 Q WEBINARS

rated speed. The yaw drive moves the blade and housing assembly (the nacelle) to the optimum wind direction in re- lation to the wind. An anima- tion prepared by the Union of Concerned Scientists is helpful in visualizing the action of these drives.4 Figure 7 shows a typical three-stage wind turbine gear- box. A planetary stage (bottom left) transfers the torque first to a low-speed intermediate stage (bottom right) and then to a high-speed intermediate stage (middle), which drives a high- speed stage (top) that feeds the generator. Such a design might, for example, convert 14 RPM input from the rotors into 1,500 Figure 6. Simplified view of components of an upwind-facing, horizontal-axis wind turbine with a gearbox drive. An 4 RPM to the generator; the exact animation is available. (Figure courtesy of Union of Concerned Scientists, www.ucsusa.org.) conversion of course depends on the gear ratio. Different bearing types are used in these various components, as shown in Table 1 on Page 40. Some technical differences should be noted between land- based and offshore turbines. Offshore installations account for more than 3% of global ca- pacity. Offshore construction presents different challenges, the most obvious being how the structure is anchored. The strategy differs depending on the water depth. For depths less than about 100 ft (30 m), monopile construction is used. For transitional waters (100- 200 ft or 30-60 m), a cross- braced “jacket” foundation is Figure 7. Power flow diagram of a typical three-stage wind turbine gearbox. The low-speed input from the rotors used. For deeper waters, pro- (far left) is converted into high speed at the output shaft (HSS) to feed the generator (top right). (Figure courtesy of totype floating platforms are Sentient Science Corp.) being tested. The transformer design also is different for dif- turbulence, designers can the surface area of the blade stalling one 12-MW turbine ferent water depths, and in pursue truly giant scales. GE sweep is equivalent to seven is cheaper than installing six general offshore installations has built an offshore design American football fields. This 2-MW ones; thus the final cost are moving from gearbox to rated at 12 MW, significantly is a direct drive design where per megawatt is lower. For direct-drive designs. higher than the 2017 average speed is transmitted directly to these reasons, and because Another very significant of about 2.3 MW. It is indeed the generator. Why build such of the abundance of offshore difference is size. Without a giant: the rotor diameter is giants? In addition to raising wind resources, the industry the need to limit noise or ac- on the scale of the towers of power output, large turbines is moving to an emphasis on commodate terrain-induced the Golden Gate Bridge, and reduce installation cost. In- offshore wind power.

38 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG

Q WEBINARS Offshore construction presents different challenges.

Summary Table 1. Application of Different stallations are becoming more number of basic designs are Wind turbines are the fastest- Bearing Types in Wind Turbine attractive and viable. in use, but most commercial Drivetrains growing renewable energy In terms of technology, installations use a horizontal source, and wind energy is turbine design focuses on op- axis, upwind-facing design. Wind Turbine now cost-competitive with Bearing Type timizing power output by fo- Turbines are becoming ever nonrenewable resources. System cusing on two key parameters: larger, in both physical size Growth in generating capac- • Yaw system blade length and average wind and generating capacity, in ity is concentrated in five to Ball • Pitch system speed. The latter is affected order to capture more stable 10 states, notably Texas. The • Generator by surface terrain and varies winds and to maximize return field of turbine manufacturers Cylindrical spatially, directionally and on installation costs. • Gearbox is crowded, but GE Renewable roller seasonally. The effectiveness Energy and Vestas are lead- • Gearbox of a particular installation is Jane Marie Andrew is a free- ers in the U.S. wind market. Tapered roller • Main shaft quantified by a capacity fac- lance science writer and editor Increasingly, capacity is being • Pitch system tor: the ratio of actual annual based in the Chicago area. You • Main shaft jane@jane- purchased by entities other Spherical roller energy output to the theo- can contact her at • Gearbox than utilities, and offshore in- retical maximum output. A marieandrew.com.

REFERENCES 1. Global Wind Report 2018, by Global Wind Energy Council. Available at https://gwec.net/global-wind-report-2018/. 2. U.S. Wind Industry Fourth Quarter 2018 Market Report by American Wind Energy Association, January 30, 2019; public version available at www.awea. org/resources/publications-and-reports/market-reports/2018-u-s-wind-industry-market-reports/4q2018_public. 3. Lazard’s Levelized Cost of Energy Analysis – Version 12 by Lazard, 2018, pp. 4 and 8. Available at www.lazard.com/media/450784/lazards-levelized- cost-of-energy-version-120-vfinal.pdf. 4. “How Wind Energy Works,” by the Union of Concerned Scientists. Available at www.ucsusa.org/clean-energy/renewable-energy/how-wind-energy-works. LEADING EDGE BASE OIL PERFORMANCE AND SERVICE YOUR PREMIER PARTNER FOR HIGH PERFORMANCE BASESTOCKS

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40 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG

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42 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG GRAPHITE

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of Quadra Chemicals Ltd. “We are excited oritize and carefully craft a healthy workplace package Additin RC 9200 N, as well as other about this new partnership and look forward culture that supports employee engagement.” fluids. These high-performance additives are to working in collaboration with BASF.” “This is truly a great recognition and a used to formulate hydraulic fluids that are tribute to all the employees who work hard utilized in large commercial vehicles such Pilot Chemical every day to make Pilot a successful and as excavators, combine harvesters or con- receives top workplace award enjoyable place to work,” says Pam Butch- struction vehicles. er, CEO of Pilot Chemical. “For the past 67 As the market requires test runs to be West Chester, Ohio-based, Pilot Chemical years, Pilot has consistently encouraged a performed using various grades of oil and Co. has been awarded a Top Workplaces commitment to the interests and welfare of the test capacity at hydraulic unit manu- 2019 honor by The Cincinnati Enquirer. its employees and their families, as well as facturer Bosch Rexroth is only available The list is based solely on employee feed- the communities where it operates.” on a limited basis, the LANXESS additives back gathered through a third-party survey “Becoming a Top Workplace isn’t some- business unit decided to build its own test administered by research partner Energage, thing organizations can buy,” Claffey says. bench to conduct these tests. Additin RC LLC, a leading provider of technology-based “It’s an achievement organizations have 9200 N had already been approved by the employee engagement tools. The anonymous worked for and a distinction that gives them mechanical engineering company in March survey measures several aspects of work- a competitive advantage. It’s a big deal.” 2018. All end products that pass the test are place culture, including alignment, execution published in a list of recommended products and connection, just to name a few. LANXESS expands test capacity for for high operational safety. “Top Workplaces is more than just recog- high-performance additives nition,” says Doug Claffey, CEO of Energage. Richard Baker launches TriboTonic “Our research shows organizations that earn Specialty chemicals company LANXESS the award attract better talent, experience has taken a new test bench for additivated STLE-member Dr. Richard Baker, formerly lower turnover and are better equipped to hydraulic fluids into operation at its Mann- of PCS Instruments, has set up a company deliver bottom-line results. Their leaders pri- heim site. It is being used to test the additive to distribute tribology equipment

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across Europe. Having graduated from Imperial College in London with a bachelor’s of science degree in mathematics and attained a doc- torate from the same school, Bak- er worked for PCS for more than 16 years in a variety of positions includ- ing international Dr. Richard Baker sales and market- ing and business development manager. Baker’s company, TriboTonic (www. tribotonic.com), distributes tribology products within Europe. Based in Lon- STLE LOCAL SECTIONS don, TriboTonic will be the exclusive dis- tributor for both PCS Instruments and The STLE Louisiana Section held its quarterly meeting on May 9. Louisiana Tech University in Falex equipment, supplying sales, sup- Ruston, La., hosted the event, and many engineering students were in attendance. A technical port and service for these instruments topic was presented by Amanda Nicholas Hall of International Paper and STLE-member Wade in Europe. Stephens of Lard Oil Co.

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46 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Call for Presentations

75th STLE Annual Meeting & Exhibition May 3-7, 2020 Hyatt Regency Chicago Chicago, Illinois (USA)

STLE’s Annual Meeting & Exhibition is the industry’s most respected venue for technical information, professional development and international networking opportunities. Each year STLE’s conference showcases some 500 technical presentations, applications-based case studies, best practice reports and discussion panels on technical or market trends.

Education courses support professional development and prepare qualified individuals for STLE’s three certification programs: Certified Lubrication Specialist™, Oil Monitoring Analyst™ (I&II) and Certified Metalworking Fluids Specialist™. Our annual trade show and Commercial Marketing Forum spotlight the latest products and services of interest to lubrication professionals. STLE’s conference is a truly international event with some 1,600 professionals from around the world attending.

2020 presentations are being sought in the following areas:

• Biotribology • Nanotribology • Condition Monitoring • Nonferrous Metals • Engine & Drivetrain • Power Generation • Environmentally Friendly Fluids • Rolling Element Bearings • Fluid Film Bearings • Seals • Gears • Surface Engineering • Grease • Synthetic and Hydraulic • Lubrication Fundamentals Lubricants • Materials Tribology (includes • Tribotesting Ceramics and Composites) • Wear • Metalworking Fluids • Wind Turbine Tribology

Abstract Submission If you are interested in presenting at STLE’s 2020 Annual Meeting & Exhibition, submit a 100-150-word abstract at www.stle.org. Abstracts are due Oct. 1, 2019. Notification of acceptance will be sent in December 2019. While you do not need to prepare a full manuscript to be included on the meeting technical program, you are invited and encouraged to submit a manuscript for review and possible publication in STLE’s peer-reviewed journal, Tribology Transactions.

For more information, please contact: Merle Hedland • [email protected] • 630-428-2133

Follow us on #STLE2020

Society of Tribologists and Lubrication Engineers, 840 Busse Highway, Park Ridge, IL 60068, [email protected], www.stle.org. Q NEWSMAKERS

NLGI honors Wayne Mackwood try. He has served on the NLGI board of field include authoring more than a doz- for meritorious service directors for eight consecutive years and en technical papers, holding two patents contributed mightily in several committee and giving more than 20 technical presen- LANXESS global head of detergent and and technical roles. Wayne’s acumen and tations at leading grease technology and STLE-member leadership capabilities also were recently industry confer- Wayne Mackwood was recently honored validated by his elevation to the position ences and semi- by the National Lubricating Grease Insti- of treasurer and appointment to the NLGI nars around the tute (NLGI) with the esteemed John A. Bel- executive committee in 2018.” world. lanti Sr. Memorial Award during the 2019 Mackwood is recognized as an expert In addition to Annual Meeting in Las Vegas. in the design, manufacture and use of his NLGI service, The award acknowledges meritorious calcium sulfonate complex grease. He Mackwood also service on the NLGI Board, on technical has developed more than 150 grease for- has served on committee projects or to the industry in mulations and continues to be active in the STLE board general. the development and introduction of new of directors and Wayne Mackwood NLGI president and STLE-member Joe detergent formulations and technology. remains active Kaperick states: “Wayne is richly deserv- Although he has spent the majority of his at the local level. He holds a master’s de- ing of this tremendous recognition for 25-year career as a scientist, Mackwood gree in materials engineering science with his tireless work on behalf of the NLGI has held roles in marketing and asset a focus on tribology from the University of and within the lubricating grease indus- management. His contributions to the Western Ontario.

Want to be recognized in TLT? If you have news about a new employee or if someone in your company has been recognized with an award or any other interesting items, let us know. Please send us your news releases and photos for publication in Newsmakers to TLT Magazine, Attn: Rachel Fowler, 840 Busse Highway, Park Ridge, IL 60068, [email protected].

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Chevron Oronite San Ramon, Calif. (713) 954-6060 www.oronite.com Photo courtesy of Chevron Oronite.

50 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Mark Your Calendar!

And learn about the technical, environmental and social issues 2019 STLE that will most impact tribology Tribology research in the 21st Century.

For the fifth year STLE is convening an international Frontiers community to share tribology’s most cutting-edge research. Come join us for four information-packed Conference days with tribology’s top minds—you’ll leave with a better understanding of how your company’s products will fit into an ever-evolving technical future. The Drake Hotel Visit www.stle.org for program updates, online Chicago registration and hotel reservations. TFC registration Oct. 20-23, 2019 opens following the 74th STLE Annual Meeting & Exhibition, May 19-23, 2019, in Nashville. See you in Chicago! • Cutting-edge tribology research • Networking • Industry recognition • Leadership opportunities • Invited speakers • International community • Idea sharing

Co-sponsored by ASME Tribology Division. © Can Stock Photo / anderm Photo Stock © Can

To learn about Sponsorship opportunities, contact Tracy Nicholas VanEe at [email protected], 630-922-3459.

Places of Interest • The Art Institute of Chicago • Museum of Science and Industry • Follow us on: Field Museum • Shedd Aquarium • Willis Tower • Lincoln Park Zoo • John Hancock Building • Navy Pier • Millennium Park • Michigan Avenue shopping

Society of Tribologists and Lubrication Engineers, 840 Busse Highway, Park Ridge, IL 60068 • [email protected] • www.stle.org • 847-825-5536 Q NEW PRODUCTS

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52 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG The 4th North American Industrial Lubricants Congress

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Lonza introduces the PyroTec™ PRO, the first-ever fully automated, plate-based robotic solution for endotoxin detection. Integrated with the latest version of Lonza’s proprietary dynamic control WinKQCL™ 6.0 software platform, the new system has been designed to meet the needs of rapidly changing requirements of QC testing laboratories for fully automated processing of simple to complex sample matrices. As a pow- erful combination of robotic liquid-handling technology with an automation software module, the system improves data integrity organically with the capture of new metadata from the automated preparation, adding traceability into tracking, trending and audit controls. It enhances assay robustness and reproducibility for increased confidence in the accu- racy and precision of results and significantly reduces manual intervention, simplifying QC testing workflows and eliminating the human error potential. It also re- duces re-test rates as well as out-of-specification and out-of-trend deviations, thereby improving the labora- tory’s performance. It offers considerable cost savings compared with conventional cartridge-based systems, which require the use of expensive reagents.

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Tribology Encompassed An education event hosted by the STLE Chicago Section b When: Oct. 16 and 17 Where: River Forest Country Club, 15W468 Grand Ave., Elmhurst, Ill. Price: Both days: $295 STLE member, $375 nonmember Day 1: $149 STLE member, $189 nonmember Day 2: $149 STLE member, $189 nonmember TBD discounted student rates

Schedule: Day 1: Lubrication Basics The event begins with tech talks based on the fundamentals of lubrication. Topics include base oils, lubrication fundamentals, lubrication additives, lubrication testing and synthetic lubricants. This is followed by a session of STLE expert speed dating! It’s exactly what you think. Maybe this is the technical H[SHUW\RXōYHEHHQORRNLQJIRUPD\EHQRW(LWKHUZD\\RXōOOKDYHƓYHPLQXWHVZLWKHDFKLQGXVWU\H[SHUWDQGDIWHU ƓYHPLQXWHVř6:,7&+,I\RXFDQōWLPDJLQH\RXUVHOIVSHHGGDWLQJWKHQWKLQNRILWDVQHWZRUNLQJLQKLJKVSHHG

Day 2: Tribology in Life 7KHVHFRQGGD\IRFXVHVRQDYDULHW\RIWRSLFVWKDWJHWDZD\IURPWKHEDVLFVRIOXEULFDWLRQ,WōVDGD\ƓOOHGZLWK presentations casting a wide net on the world of tribology. Topics include medical tribology, engine lubrication, ELREDVHGOXEULFDQWVPDULQHOXEULFDWLRQJUHDVHIRRGJUDGHOXEULFDQWVDQGGU\ƓOPOXEULFDQWV

*All leading into the October STLE Chicago Section dinner.* For more information and to register, visit www.chicagostle.org.

54 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Worldwide Student Poster Contest

Help Spread the News: Celebrating STLE’s #STLEPOSTER75 75th Anniversary Four Age Categories 4-8 9-11 12-14 15-18 Winners in Each Category Receive Cash Prizes! Contestants Should Submit a Poster Showing How Tribology* Can Affect the Future World. *The science and engineering of interacting surfaces in relative motion.

Poster submission period July 1-Dec. 31, 2019 Contest information and entry form available at www.stle.org.

Questions? Contact Dr. Maureen Hunter: [email protected] © Can Stock Photo / yupiramos

Society of Tribologists and Lubrication Engineers, 840 Busse Highway, Park Ridge, IL 60068, [email protected], www.stle.org. SOUNDING BOARD

A global view of tribology education © Can Stock Photo / photography33

Executive Summary

If the world is looking for a cause to bring all nations together, the lack of quality tribology education globally might be a good place to start. That was the message delivered by TLT readers responding to this month’s Sounding Board survey. TLT heard from tribologists from Canada to Ecuador, from Germany to Nigeria, and the story was universal—little or no tribology education or training at virtually all levels of education. Despite claiming Auburn University, the only school nationwide to offer a tribology minor, the U.S. fared no better than other countries and received more than its share of criticism. “99% of people in the U.S. think tribology is the study of dinosaurs; they are clueless,” opined one STLE member. The survey’s numbers supported the anecdotal reports—only 18% of TLT readers, regardless of nationality, have taken a formal course in tribology.

56 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG What is the current state of tribology education in your country Q.1 and how could it be improved?

Low. Almost any type of Canada. Very little except in In India the tribology education In the U.S. it is growing educational programs would the workforce. Universities varies from mediocre to very as many companies are help. have too much to cram good. It is mostly driven by understanding that correct into four years already, but the grease/oil manufacturing lubrication is an asset to their In Germany the tribology perhaps a five-year specialist’s companies. So any tribology bottom lines. education of engineers differs program. education/seminar is mixed from university to university. with product promotion and Some online courses, but they Sometimes tribology is just U.S. Deficient. In chemical paper presentation. Pure are not helping me to improve. a side issue of machine curriculums there is not much research is limited. components. attention paid to friction and U.S. Good. wear or their molecular basis. Turkey. Actually nothing—no Likewise, I’m not sure how Specialized training for networking for between common screening techniques graduate students. related academics and no correlate with real world. During your university tribology-specific departments. For most students this is not studies, did you take a U.S. Subject matter is mostly that relevant, so an online specific course focusing on overlooked in most standard Trinidad & Tobago. Almost approach would magnify the tribology? mechanical engineering non-existent. benefit. programs. Yes 18% These are very interesting U.S. Many in sales have U.S. Lubrication education times for young tribologists. minimal training. No 82% needs to be a course at the We need to train and pay the undergraduate level in college. Based on responses sent to 15,000 TLT next generation appropriately. There are not enough courses readers. STLE needs to take more or programs concentrating action in getting lubrication U.S. We are not too bad, but on tribology topics. The education available at colleges there is definitely room for increasing demands of as well as other venues more education at the college precision machining and other (outside of STLE activities). level and even trade schools. technological requirements Restore tribology courses call for the education of more even if they are embedded in U.S. It is moderately promoted. It is 25% in Nigeria. tribology specialists. subjects such as safety and reliability. Australia. Canada. Very little. Some In the Netherlands we South Africa. It does not courses at the Universities of have three universities of get enough focus at tertiary Is the U.S. tops? Waterloo and Toronto. technology where some level. Should be made a tribology is present, but compulsory module for In our country, tribology Not high. We don’t tend to currently there is only one bachelor’s of science chemical studies related to automotive focus on things of practical very active one: Twente and mechanical engineering components, bio-tribology of value in education. University. This is the only degrees. implants, surface coatings, university with a full-time etc., can be improved In my country (Ecuador, South chair in tribology and surface In Lithuania, tribology by surface-modification America) tribology education is modifications. In addition, education is available only techniques. really poor. I think it is highly there is a full-time chair in for graduate students or important that we improve fluid mechanics who also is researchers. Setting up the tribology it. Influence of industries and teaching advanced tribology department in the college companies could be important stuff, and there are three part- South Africa. Outside of the or university level as to obtain progress. time professors from industry universities, there are a few the chemistry, chemical and some associate and organizations that provide engineering and mechanical U.S. Needs to be more broadly assistant professors. general courses on tribology. engineering departments. spread across all industries.

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 57 Q SOUNDING BOARD

U.S. The company I work for In the Netherlands only OK. Not a lot of people know There’s a small number of includes ongoing training. We one university is providing what it is and how it directly universities that specialize also attend training outside the a master track dedicated affects their lives. Not readily in some aspects of tribology company for such things as to surface engineering and seen as an option for a career (e.g., automotive engine wear, refrigeration and refining. tribology. Student interest path. Start earlier. It is not bearings, aerospace, medical, is generally low. Somehow really discussed at entry-level knee/hip replacements); U.S. Poor. I know only Auburn the perception is that chemistry classes. I have a however, very little is done University offers a tribology tribology is complex and not bachelor’s of science degree regarding metal machining, undergraduate degree. so interesting or relevant. It in professional geology. In my metal forming, etc., regarding should start with changing undergrad classes, I wasn’t the tooling required to make U.S. Minimal. the perception. Second, time exposed to tribology. those parts in the first place. is mostly spent on theoretical UK. Generally good. Needs parts. I would opt for a better It’s beginning to happen. Very 99% of people in the U.S. more interdisciplinary balance between theory focused on engineering, not think tribology is the study of teaching, e.g., lubricant and experiment by adding chemistry. dinosaurs; they are clueless. chemistry for mechanical more practical exercises to Very few understand what it is. engineers and vice versa. the curriculum. This should Latin America. Either regular Those that do seem to take it already start in the bachelor or bad. STLE needs to turn to extremes. Sweden. Tribology courses phase to also increase the toward Latin America and are given at several major interest of the students. focus in the region, invest time In Western Canada tribology universities. There also is and funds to develop short training is hard to get unless a joint national research in Re-establish STLE. The courses, seminars, congress, you are affiliated with a major tribology for doctoral students. organization is not credible. etc. I live in Bolivia. oil marketer. Automate Your Viscosity Testing EmailEmail [email protected]@csales@c or go to www.cannoninstrument.com for more information about viscosity testing automation today! 10 Reasons to Automate Now Ensure objective viscosity measurement 2 Reduce operator to operator variability 3 Improve lab safety 4 Lesson operational inefficiency 5 Save calibration costs 6 Save time 7 Improve traceability and reporting 8 Enjoy happier operators 9 Lower consumable usage and cost 10 Decrease mathematical errors

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www.crcpress.com Q SOUNDING BOARD

Tribology education in the is a wide diversity and Very labor intensive. Look at Canada. Not many courses that U.S. is fragmented, but some unevenness in the type and A.I. for better, more accurate I have seen or found. Most of areas are making progress depth of available courses. analysis. my learning has been through by doing such things as Students will be presented STLE avenues. offering new graduate majors with potentially incomplete Does not exist (Ecuador). in tribology. The range of or biased views of the subject U.S. I believe it is and has been tribology educational content depending on the duration of U.S. and the state of tribology informative in the professional varies widely in short courses the courses and the specific is marginally acceptable. world; however, I am not sure (days to 1-2 weeks), college experience of the speakers. I’m from the U.S., and I believe of its application in academia term-length courses and This is true especially in that most universities do not or if there is a formal way courses given by consultants team-taught courses in which offer tribology as a course to introduce it to the world to private companies. The instructors may change from of study. All of my training of chemical engineers at the shorter the course, the more year to year. came from on the job or from college level. Admittedly, it is likely it will have a bias either organizations like STLE, ILMA, not clear if higher education toward lubrication, materials, Formal curriculum-based NLGI, etc. is incorporating lubrication coatings, mechanical designs, education within the U.S. is technology. contact mechanics or trouble limited and focuses on select UK. Introduce tribology to shooting. Therefore, there areas of study. undergraduates.

Machine learning is defined as the ability of artificial intelligence Q.2 to learn from data without additional programming. How could that concept be applied to tribology?

Machine learning could be It would be good to examine The vast array of data By using data acquisition, we used to evaluate measurement results of laboratory and available from past and can predict the current state of data from tribological tests. bench simulations, e.g., engine present tribology studies is object. For example, wearable oil approvals. well-suited for AI applications. parts can be monitored Actually, bearing by ML techniques, and we manufacturers are into it. It can be applied through In tribology we have to ensure can optimize or predict the But surface hardness and the parameters observed for that the optimum life of the outcomes. stress online monitoring may various used oil analysis tests lubricant is obtained to keep contribute into power drives to regarding limits for copper, costs and environmental Micro analysis inline and react set the thresholds for real-life silicon, etc., but based on effects low. By closely to real-time data. conditions. OEM requirements for various monitoring the operating machines and components. temperature, we can develop Sensors for lubricant quality, Directly tying AI to real-time models that ensure more torque, temperature, etc., lube analysis and operational AI could be used to determine accurate quantity of refill would feed their recordings to data will perfect predictive the remaining useful life of a and re-lube intervals for the AI processing, hoping that AI programs. mechanical system based on grease/lubricating oils. can predict onset of wear or wear profiles and historical other failures. It can be applied in the area data on specific makes and Collating data from trends in of monitoring the wear rate, models of machines and also lubricant analysis from various Condition monitoring; lubrication efficiency and to auto-diagnose condition applications would make it formulation improvement; non- frictional process in any monitoring data like oil possible to predict possible lubricant solutions in design to mechanical machines. analysis and vibration data. failures. reduce friction and wear.

60 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Ever wish you could remember that TLT article you read…when was that again?

Search thousands of articles at TLT Archives: www.stle.org.

TLT is the lubricant industry’s premier technical magazine and STLE’s No. 1-rated member service. Many readers say they rely on TLT as their only source for reliable, accurate and industry-specific technical information on lubricants.

TLT is offering its library of technical articles in a searchable new format. Just go to www.stle.org and click the Technical Library tab.

TLT provides best-in-the-industry technical information on:

• Aeronautics • Automobiles • Bearings • Ceramics/Composites • Energy • Gears • Grease • Hydraulic Equipment • MWFs • Mobile Equipment • Nanotribology • Nonferrous Metals • Power Generation • Seals • Solid Lubricants • Synthetics • Tribotesting & more.

If you are an engineer, chemist, tribology researcher or student, you can depend on TLT Archives to deliver the industry-specific technical information you need.

TLT Archives Log on to www.stle.org and get the TLT article you need now.

© Can Stock Photo / dragon_fang

Society of Tribologists and Lubrication Engineers, 840 Busse Highway, Park Ridge, IL 60068 • www.stle.org. Q SOUNDING BOARD

I am not sure we can utilize The concept of mass loss in a It seems that the How much potential do you AI in tribology in the near material can be monitored. understanding of lubrication think online courses can future with tons of data. The concepts within a process have have on exposing people development of a computer Several ways from formulating diminished as technological to the fundamentals, that powerful is the immediate to independent testing advancements have been challenges and impact of problem. of all raw materials and made with the process. When finished products to surface tribology? something goes wrong, but the Data from equipment in real technology. data shows everything is OK, Great potential 57% time will have users be able no one understands how to to correct any problems with Precisely controlling where Some potential 40% correct the situation. vibration, incorrect lubrication and when oil or friction and others. reduction treatment fluid can Little potential 3% Courses online. be applied. Determine acceptable Based on responses sent to 15,000 TLT AI would be able to define readers. operation and maintenance Predictive maintenance, the fluid’s type and condition, ranges, monitor machine predicting complex tribo- the application, the time in operation parameters and system behavior by deriving operation, the susceptibility trigger alert or corrective black box friction and/or wear Onboard analysis to change factors, real-time vibration action when operation is out of models from data, finding telemetry on the move. analysis, real-time particle acceptable range. proper interaction potentials analysis to provide for molecular dynamics with AI-designed systems. recommended service Used oil analysis would be a the aim of modeling sliding intervals and to what extent. good start. interfaces, understand how With proper programming, extensive the tribo-system oil analysis and the First, industry needs to better Tribology is not a key area for is by being able to correlate recommendations and trends understand AI’s value to this technology. It is overkill. seemingly unimportant that follow could be performed their world and appreciate influences. by artificial intelligence. it potential. I am not sure if Artificial intelligence should it is widely understood. In include tribology training. Oil analysis would be a good More data needs to be my world of consultancy, it start. captured. has not come up with great Ongoing reading by machines regularity. Looking at other of temps, viscosity, pressures, Lubrication analysis in real This sounds good in principle, liquid technologies to see how etc. time. Oil analysis and condition but I think it works better in AI is being used might help. monitoring seems a scam to some fields (manufacturing/ Having universities promote Yes, it could but would put suck money. When I take oil machining/production its use in tribology would people out of jobs in tribology. samples and there is water engineering) than in others foster downstream greater use and drilling fluid in them, it where the content is very or testing in lubrication and Depends on what we are would be good to know now broad and interdisciplinary. metalworking fluids. looking to find. This will likely and not in 45 days when the What works in one tribo- require additional hardware results are sent to corporate. system may not necessarily One would need a huge amount and might not be economically work in the general case or of data for machine learning. viable. Used oil diagnosis. for other tribo-systems that If there are instances where might superficially seem to be large amounts of good data can In industries with a high This is predominantly used in similar. be obtained to predict friction focus on uptime, reliability oil analysis already and will be and wear, that might work. and energy consumption, the continued in other aspects of Determine origin of wear ability to analyze, interpret and tribology. material/metal, i.e., what I am not sure. I learned the apply data from many systems component might be fundamentals of tribology in a complex production Evaluating big data from generating it, more specific by running friction and wear environment. tribology tests in literature. metallurgy. testers.

Editor’s Note: Sounding Board is based on an informal poll of 15,000 TLT readers. Views expressed are those of the respondents and do not reflect the opinions of the Society of Tribologists and Lubrication Engineers. STLE does not vouch for the technical accuracy of opinions expressed in Sounding Board, nor does inclusion of a comment represent an endorsement of the technology by STLE.

62 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG You work in a technical world. Should you belong to a technical society?

Keeping current with technical changes in the lubricants field is a daunting task. More than 3,000 of your peers have solved this problem by joining the Society of Tribologists and Lubrication Engineers. STLE is the premier technical organization representing lubrication professionals and tribology researchers. Professionals from industry, academia and government join STLE because they know no organization offers a more in-depth and complete look at the field of tribology. STLE provides the lubricant industry’s highest level of technical training and professional development. But the benefits of membership don’t stop there. STLE membership is a mark of distinction. It confers the seal of authority on you and your organization and affiliates you with the world’s leading experts in lubrication. You work in a technical world. You belong in a technical society. You belong in STLE. Learn more about the benefits of STLE membership and how to join at www.stle.org. © Can Stock Photo Inc. / sjenner13 Photo Stock © Can

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AUGUST 2019 • VOL. 75, NO. 8 Next in TLT:

Company Page September Ad close: July 25 Acme-Hardesty Co. 22 Materials: Aug. 1 BASF 7 (Bonus Distribution: ILMA Calumet Specialty Products Partners, L.P. 35 Annual Meeting, Sept. 21-24, Colorado Springs, Colo.) Cannon Instrument Co. 58 • Additives Chevron Oronite Co., LLC 11 • Seals CRC Press - Taylor & Francis Group 59 • Oil Analysis Dover Chemical Corp. 9 • Surface Engineering • Wind Turbine Special Series: Ducom Instruments 39 © Can Stock Photo / miraclemoments Part II Eastman Chemical Co. 52 Emery Oleochemicals 21 Evonik Oil Additives 5 Fluid Line Products 67 October Ad close: Aug. 23 Italmatch Chemicals Group 44 Materials: Aug. 30 J.A.M. Distributing Co. 40 • Synthetic Lubricant Base King Industries, Inc. OBC Stocks • Marine Tribology Koehler Instrument Co., Inc. 31 • Computer-aided Tribology LANXESS Corp. IFC • Automotive Tribology

MJ Tribology 50 © Can Stock Photo / Elnur • Wind Turbine Special Series: Part III Napoleon Engineering Services 42 Pelichem Associates 49 Pilot Chemical 46 Sea-Land Chemical Company 48 November Ad close: Sept. 24 Soltex, Inc. 43 Materials: Oct. 1 SONGWON Industrial Group 23 • Metalworking Fluids STLE 2019 Tribology Frontiers Conference 51 • Oil Analysis STLE 2020 Annual Meeting Call for Papers 47 • Lube Fundamentals • Wear STLE 365 App 71 • Market Trends © Can Stock Photo / SafakOguz STLE 75th Anniversary Poster Contest 55 STLE Chicago Section Education Event 54 STLE Drive 75 3 STLE Learning Pathways 65 December Ad close: Oct. 25 STLE Membership 63 Materials: Nov. 1 The 4th North American Industrial Lubricants 53 • Additives Congress • Oil Analysis TH Hilson, A Ravago Chemicals Co. 41 • Metalworking Fluids • Automotive Tribology TLT Archives 61 • Lube Fundamentals Troy Corp. 45

UL Prospector 69 © Can Stock Photo / kadmy United Color Manufacturing 27 Vanderbilt Chemicals, LLC IBC For information on how to customize a multi-media marketing program that reaches 15,000 lubricant-industry decision-makers, contact: Werner G. Smith, Inc. 30 National Sales Manager, Tracy Nicholas VanEe Zschimmer & Schwarz, Inc. 29 (630) 922-3459 • [email protected]

64 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Education inDIVIDUALIZED APPROACH TO PROFESSIONAL DEVELOPMENT

ABOUT THE LEARNING PATHWAYS STLE has a well-known tradition of providing continuing education to industry professionals ready to take their career to the next level and create value to their employers, customers & peers. Now we’ve expanded our online offerings with the launch of STLE’s Learning Pathways - a reorganization of all STLE content that is more focused, easier to search & accessible in a variety of formats that is right for you. This content is organized to allow individuals to continue developing skills in two major vocational segments: Lubrication Specialists & Oil Analyst.

STLE is a trusted provider of education and a workforce development partner, and the Learning Pathways is just one more valuable information-sharing service STLE offers to benefit industry professionals in their career development.

More products & services to come from STLE Education. Please visit www.stle.org.

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Nanomaterials in Advanced Medicine Events listed here are local section programs. For further details and a full listing of other Author: Hossein Hosseinkhani upcoming section events in your area, visit Publisher: Wiley www.stle.org. Meeting announcements can be sent to TLT Magazine, Attn: Rachel Fowler, A comprehensive and multidisciplinary review of the [email protected]. fundamental concepts and medical applications of nanomaterials development technology, nanomed- August icine offers a range of multi-interdisciplinary ap- STLE Cleveland Section Golf Outing, proaches and brings together the field of chemistry, Aug. 12, 10 a.m. (check in), 10 a.m. (put- pharmaceutical science, biology and clinical medi- ting contest), 11 a.m. (modified shotgun cines by focusing on design and preparation of bio- start), 4 p.m. (dinner), Shale Creek Golf degradable or non-biodegradable biomaterials for Club, 5420 Wolff Rd., Medina, Ohio. Con- their biological, medical and pharmaceutical applica- tact: Buck Evans, buck.evans@sealand- tions. Nanomaterials in Advanced Medicine reviews chem.com. the concepts and applications of the combination of the technology of biology and engineering that are emerging as an integral aspect of today’s advanced medicine. Nanomedicine provides the technology for imaging, cancer treatment, medical tools, bone treatment, drug delivery, diag- nostic tests, drug development and angiogenesis and aims to exploit the improved and often novel physical, chemical and biological properties of materials at the nanometer scale. Available at www.wiley.com. List Price: $124 (USD), hardcover. STLE Certification Exams

Biomaterials Science and Technology: STLE is offering certification exams in the Fundamentals and Developments coming months. Here is the information on each exam: Author: Yaser Dahman Publisher: CRC Press • Aug. 16 from 8-11 a.m. at the Hampton Inn & Suites Cleveland-Airport/Middle- Biomaterials Science and Technology: Fundamen- burg Heights, 7074 Engle Rd., Middle- tals and Developments presents a broad scope of burg Heights, Ohio. the field of biomaterials science and technology, • Sept. 27 from 8:30-11:30 a.m. at Lubri- focusing on theory, advances and applications. It cation Engineers Inc., 1919 Tulsa St. E, reviews the fabrication and properties of different Wichita, Kansas. classes of biomaterials such as bioinert, bioactive and bioresorbable, in addition to biocompatibility. It further details traditional and recent techniques For the online registration form, go to www. and methods that are utilized to characterize major stle.org; click on the professional develop- properties of biomaterials. The book also discuss- ment tab at the top. Then go to certifica- es modifications of biomaterials in order to tailor tion, then registration. Online registration properties and, thus, accommodate different ap- closes two weeks prior to the exam date. plications in the biomedical engineering fields and Onsite registration may be available on a summarizes nanotechnology approaches to bio- first come, first serve basis. For more infor- materials. This book targets students in advanced undergraduate and graduate mation and for other methods of register- levels in majors related to fields of chemical engineering, materials engineering ing, you may contact STLE headquarters by and science, biomedical engineering, bioengineering and life sciences. Available emailing certifi[email protected] or calling at www.crcpress.com. List Price: $159.95 (USD), hardcover. (847) 825-5536.

66 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG Industry Conferences

COMADEM 2019 face analysis, additive tribochemistry and OHB. The Space Tribology Course and more. For more information, visit www. Advanced Mechanism Design courses The 32nd International Congress and tribology.jp/Tribochemistry_Hako- will be held on the Monday and Tuesday Exhibition on Condition Monitoring and date_2019/index.html. prior to ESMATS 2019. Full details will be Diagnostic Engineering Management released soon. Delegates will have the op- (COMADEM 2019) is Sept. 3-5 in Hud- ITC Sendai 2019 portunity to tour the OHB Centre for Op- dersfield, UK. The University of Hudder- tics and Science in Oberpfaffenhofen. For sfield is working in close collaboration and The International Tribology Conference more information, visit www.esmats. partnership with COMADEM Internation- (ITC Sendai 2019) is Sept. 17-21 at the Sen- eu/esmats2017/home/esmats-2019. al and aims to be the premier internation- dai International Center. The conference al event for industrialists, scientists and was founded by JAST. The ITC was first ROTRIB ’19 exhibitors worldwide. The congress will held in Tokyo (1985) following the JSLE- give you a unique opportunity to compare ASLE International Lubrication Confer- ROTRIB’19 is Sept. 19-21 at the Technical scientific and technical achievements with ence (1975). Following successful confer- University of Cluj-Napoca in Romania. It is each other to determine how good they ences in Nagoya (1990), Yokohama (1995), the 14th conference organized in a series are internationally. For more information, Nagasaki (2000), Kobe (2005), Hiroshima of international scientific events on tribol- visit www.comadem2019.com. (2011) and Tokyo (2015), ITC 2019 is held ogy. The general objective of this confer- in Sendai, Japan. Tribology is the inter- ence is to bring scientific contributions to Tribochemistry Hakodate 2019 disciplinary study encompassing surface fundamental and applied tribology. The physics and chemistry, material science event will provide an interdisciplinary The 8th International Forum on Tribo- and fluid dynamics. For this reason, an in- forum for discussions and networking chemistry (Tribochemistry Hakodate tegrative approach is imperative to clarify and will also aim to initiate collaborations 2019) is Sept. 12-14 at the Hotel Takubo- issues related to tribology. Interdisciplinary among specialists. These collaborations kutei in Hakodate, Hokkaido, Japan. The studies and discussion on the future direc- will be focused on materials in tribology forum is organized by the Tribochemistry, tion of various fields is heavily promoted. and their real-life applications in product Technical Committee, Japanese Society of Active participation of young researchers, design and reliability. Another key goal of Tribologists (JAST). The forum will dis- specifically students, is strongly encour- this conference is the exchange of ideas cuss the basic mechanisms, applications aged. For more information, visit www2. and theories on new research methods and future prospects of tribochemistry convention.co.jp/itc2019. and future trends. This will be achieved based on the most recent results of re- by bringing together specialists from vari- search. All fields concerned with tribo- ESMATS 2019 ous industries and academic backgrounds chemistry are welcome. Presentations and leading researchers from diverse en- will be on mechanism of tribochemical The 18th ESMATS is Sept. 18-20 at the vironments and scientific fields. For more reactions, tribophysics related to tribo- Gasteig Cultural and Conference Centre information, visit https://minas.utcluj. chemistry, static and dynamic in situ sur- in Munich, Germany, and is hosted by ro/rotrib2019.html.

WWW.STLE.ORG TRIBOLOGY & LUBRICATION TECHNOLOGY AUGUST 2019 • 67 AUTOMOTIVE TRIBOLOGY

Gearboxes and battery electric vehicles +SJRG QNCCBˢRP?LQKGQQGMLQˢMˏCPˢ substantial advantages—plus a few drawbacks.

By Dr. Edward P. Becker electric motors for vehicles typ- chanical complexity. Transmis- complicates the issue. Now the ically have top speeds around sion suppliers point to increases gears must be able to mesh and 20,000 rpm, while the wheels of in efficiency, as much as 15%, as unmesh smoothly and without I’ve taken some heat for re- a typical passenger car rotate offsetting these considerations. excessive wear under high-load, ferring to the reduction gear at less than 1,000 rpm at 100 One remaining problem, howev- low-speed conditions as well as assembly in battery electric kph (62 mph). Since electric er, is primarily tribological. low load, high speed. vehicles (BEV) as a gearbox. motors have poor efficiency The reduction gears in cur- The automotive industry While it is true that all produc- at low speed, the reduction rent BEVs are usually lubricat- should recognize the need for in- tion BEVs to date have used a gear allows the engine to turn tensive research into new ATFs single-speed reduction gear much faster than the wheels for electric vehicles, perhaps contained in a structure (i.e., (typically 7-10 times faster) so Downsides include modeled after the way engine a box with gears), the popular the motor is running near peak additional cost, weight oils are currently developed. definition of gearbox generally efficiency while cruising, thus Working on a common solution seems to require gears of vari- increasing range. and mechanical would greatly benefit automak- ous ratios, able to be connected Since electric motors pro- complexity. ers worldwide, and customers and disconnected by a shifting vide little torque at high speed, and service technicians would mechanism. A flurry of activity little power is available for ac- be able to avoid the confusion of by transmission suppliers, how- celeration or hill climbing. One ed with conventional automatic possibly dozens of fluids, each ever, suggests the single-speed way to remedy this situation is transmission fluid (ATF), which specific to a particular manufac- gearbox may be about to go the a multi-speed gearbox, which is optimized to manage friction turer or model. way of the carburetor, inner would allow the engine to turn and wear on gears that operate tube and mechanical brake. slower when the vehicle is at at high load only at high engine Ed Becker is an STLE Fellow Multi-speed transmissions high speed, thus increasing the speeds. The electric motor, as and past president. He is for BEVs are now available, power available. previously noted, generates president of Friction & Wear and they offer substantial ad- There are downsides to a maximum torque at zero speed. Solutions, LLC, in Brighton, vantages. multi-speed transmission for a While research into an ideal Mich., and can be reached A reduction gear is required BEV, however. Most obvious are BEV gear fluid is ongoing, add- through his website at www. in the first place as modern additional cost, weight and me- ing additional speeds further frictionandwearsolutions.com. © Can Stock Photo / Trimitrius

Multi-speed gearboxes allow electric vehicle engines to turn slower at higher vehicle speeds, increasing available power.

68 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG PROSPECTOR® YOUR SOURCE FOR RAW MATERIAL INFORMATION

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Sliding your way to rehydration Articular cartilage loses fluid when compressed, but how does it recover so quickly?

By Drs. Wilfred T. Tysoe & boundary lubricant. The HA also Nicholas D. Spencer led to a reduction in the speed at which both deformation and friction began to drop. In other As soon as we put any load on words, the HA, surprisingly, ap- our articular joints (e.g., knees peared to facilitate the rehydra- and hips when we stand), fluid tion process. While the increase is squeezed out of the cartilage, in viscosity due to HA addition which comprises the sliding might be expected to reduce the surfaces in our joints and con- rate of cartilage rehydration by sists of about 80% water. This hindering flow into the tissue, process, which can cause as the increased hydrodynamic much as a 50% compression, is pressure caused by the pres- one of the mechanisms by which ence of HA appeared to more cartilage sustains load and than compensate for this effect. protects itself from damage. It This work moves us a little is less clear how the cartilage Figure 1. Cartilage samples were extracted from the central region of closer to understanding the recovers after loading, which it bovine femoral condyles (a), machined to size (b) and tested in a bath of buffer mechanism by which cartilage solution, with or without added hyaluronic acid on a rotary pin-on-disk does at a rate of a few percent functions so effectively and over tribometer (c). (Figure courtesy of Ref. 1.) per hour, total recovery taking such a long time in our joints place overnight. and hopefully toward approach- STLE-member David Burris direction reversal in the recip- had been eliminated here)—and es to both repairing and imitat- and colleagues Brian Graham, rocating test rig. The induced also showed that increased slid- ing this extraordinary tissue at Chris Price and Lucas Ramsey squeeze-film effect from this ing speed above 10 mm/s led some point in the future. from the University of Delaware, wedge compression also could to a dramatic reduction in both in collaboration with Axel Moore be a potential rehydration deformation and friction. Eddy Tysoe is a distinguished from Imperial College, UK, re- mechanism. As expected, higher loads professor of physical cently reported results that In order to settle the issue, led to greater compression, chemistry at the University of offer a convincing explanation Burris et al. changed their mea- but higher loads also required Wisconsin-Milwaukee. You can as to how this recovery may be suring setup to a unidirectional higher speeds for fluid recov- reach him at [email protected]. occurring.1 Previously they had sliding configuration (see Figure ery, reflecting the competition carried out experiments on real 1), thereby eliminating any pos- between the hydrodynamic Nic Spencer is professor of cartilage in a reciprocating tri- sibility of reciprocal wedging. pressure induced by sliding and surface science and technolo- bometer and observed that the The experiment involved mea- the interstitial pressure in the gy at the ETH Zurich, Switzer- sliding itself appeared to induce suring the steady-state values cartilage resulting from loading. land, and editor-in-chief of rehydration. They suggested a of both friction coefficient and Increasing the pin diameter ap- STLE-affiliated Tribology possible mechanism for the “tri- vertical deformation (once the peared to facilitate the recov- Letters journal. You can reach bological rehydration” that was initial elastic effects at a giv- ery of both deformation and him at [email protected]. based on the idea that hydrody- en load had been subtracted) the drop in friction coefficient, namic forces generated in the as a function of sliding speed, consistent with a hydrodynamic sliding contact pushed the fluid load, fluid composition and car- mechanism. FOR FURTHER READING back into the cartilage. tilage-pin size. The deforma- The addition of a large poly- Burris, D. L., Ramsey, L., Gra- However, an alternative ex- tion-versus-speed and μ-ver- saccharide, hyaluronic acid ham, B. T., Price, C. and Moore, planation could be the influence sus-speed graphs reproduced (HA), to the tribometer bath, led A. C. (2019), “How Sliding and of “reciprocal wedging,” which the results from the reciprocat- to a reduction in friction, espe- Hydrodynamics Contribute to involves the fluid “wedge” that ing study—a clear indication that cially at low speeds, suggesting Articular Cartilage Fluid and is produced during sliding hydrodynamic effects dominate that it also may interact with the Lubrication Recovery, Tribology becoming compressed upon over any wedge effect (which cartilage surface and act as a Letters, 67: 46.

70 • AUGUST 2019 TRIBOLOGY & LUBRICATION TECHNOLOGY WWW.STLE.ORG The Society of Tribologists and Lubrication Engineers (STLE) introduces the STLE 365 App, available for free in iOS, Android STLE and HTML5 formats.

Stay up to date with hot topics circling 365 STLE and the lubricants industry View the STLE events calendar to know what’s happening app throughout the year Quickly access members-only content such as the Learning Pathways, Tribology Transactions and Tribology Letters Access to TLT magazine and other publications Access the STLE Events app for the Annual Meeting and Tribology Frontiers Conference

Start discussions with other members with the in-app activity feed

Test your knowledge with STLE Challenge and win prizes.

Download the app from The App Store (Apple products) or The Play Store (Android products). Log in using your STLE member ID and password.

For additional questions about the app, please contact Bruce Murgueitio at [email protected]. © Can Stock Photo / stevanovicigor Photo Stock © Can

Society of Tribologists and Lubrication Engineers • 840 Busse Highway, Park Ridge, IL 60068 Phone: 847-825-5536 • Fax: 847-825-1456 • [email protected] • www.stle.org MACHINERY

3GDˣBG@KKDMFDˣNEˣLDS@K QDLNU@KˣȀTHCˣRODBHǾB@SHNMR If you’re thoroughly confused, that probably means you understand.

By Don Smolenski uble oils were loosely defined (by many but not everyone) as emulsions (with water), semi-synthetics as micro- In a previous TLT article, I emulsions and synthetic fluids discussed the GM LS2 plant as true solutions. Each of the lubricant standards and how three categories was further we used them to put more subdivided based on whether rigor into how GM specified or not they had extreme pres- and procured plant lubricants. sure additives. These MRFs are In this article, I examine how diluted with water prior to use, much more challenging it is to and the characteristics of the specify metal-removal fluids diluent water (e.g., hard or soft, (MRFs) than “ordinary” plant chloride concentration, etc.) lubricants such as hydraulic have very significant effects fluids. on fluid performance. Some of Whereas GM LS2 basically the performance tests were to had one specification for an be run on the neat concentrate antiwear mineral hydraulic and others on the concentrate fluid (with different viscosi- diluted to the recommended © Can Stock Photo / sergeidvornikov ty grades), MRFs include the concentration with either a broad categories of straight “standard” diluent water or the and aqueous fluids, each with are a multitude of A multitude of as to what a reason- specific plant water, if agreed markedly different composi- different machining different machining able passing limit upon between the supplier and tions and performance char- processes (milling, processes each might be. the plant. acteristics. I won’t claim that drilling, grinding, needs its own fluid. So what the Did these tests alone speci- what we developed at GM is the broaching, etc.), heck good are fy a fluid that would enable pro- best way to define MRFs, so if each with their own fluid needs. they? We included them in the ductive machining? Absolutely you are thoroughly confused It would probably be easier to specification as report only, the no, not even close! But they did when you finish reading this ar- train a Labrador not to chase thought being that we could, in exclude fluids that failed these ticle, you grasp the complexity squirrels than to write a com- the future, review in-use per- basic tests, so at least we were of what we were trying to do! prehensive specification. formance in any given proper- starting to narrow the field. Straight oil MRFs, like min- So how on earth do you ty area and see if—at least in a Machining trials would still be eral hydraulic fluids, are used write specifications for MRFs? qualitative sense—we observed required. Even with all this, in neat form. Several key prop- In the LS2 standard we first a correlation between the we still haven’t begun to ad- erties can be specified using specified tests for certain prop- bench test results and perfor- dress the in-use maintenance available standard tests. Un- erties (such as rust, corrosion, mance in actual machining pro- of MRFs, which is very compli- fortunately some of the most foaming tendency), where we cesses. If so, we could use this cated and extremely critical to important fluid properties, such believed there was a relevant as a basis for setting a pass/ their machining performance. as machining performance or existing standard test that fail limit (very much easier said Thoroughly confused yet? misting tendency, are general- could be applied and reason- than done!). ly lacking for standard tests— able pass/fail limits chosen. Specifying aqueous fluids Don Smolenski is president much less for passing limits. Then we considered addition- provides an even greater chal- of his own consultancy, To further complicate matters, al tests that we considered at lenge. We considered three Strategic Management of Oil, the workpiece (and its relative least reasonably relevant (OK, different broad categories of LLC, in St. Clair Shores, Mich. machinability) and tool materi- maybe a little bit of a reach) to fluids: soluble oils, semi-syn- You can reach him at als can vary greatly, and there machining, but we had no clue thetics and synthetic oils. Sol- [email protected].

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