January / February 2015 NLGI Spokesman

NLGI

SPOKESMAN

Serving the Grease Industry Since 1933 – VOL. 78, NO. 6, JAN/FEB 2015

In this issue . . .

8 Study of Wear Properties of Environmentally Friendly Lubricants for Gearing Applications 30 An Advanced Technique for Grease Oxidation Measurement 42 U se of Lincoln Ventmeter on Gauging the Impact of Various Contributing Factors on Grease Pumpability

MOLYVAN 3000 ®

Friction Reducer

PRESIDENT:

VICE-PRESIDENT:

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

David Como Dow Corning Corp.

P.O. Box 0994 Midland, MI 48686

SECRETARY:

TREASURER:

Kim Smallwood Citgo Petroleum Corp.

1293 Eldridge Pkwy.

Houston, TX 77077

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

PAST-PRES./ADVISORY:

EXECUTIVE DIRECTOR:

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

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

DIRECTORS Richard Burkhalter Covenant Engineering Services 140 Corporate Place Branson, MO 65616

Thomas J. Pane King Industries, Inc. Science Road Norwalk, CT 06852

Curt Ellison Chemtool/Metalcote P.O. Box 538 Crystal Lake, IL 60039-0538

Dennis Parks Texas Refinery Corp.

One Refinery Place Ft. Worth, TX 76101

Dave Facchiano The Lubrizol ­Corpo­ration 29400 ­Lakeland Blvd.

Wickliffe, OH 44092

Tom Schroeder Axel Americas, LLC P.O. Box 12337 Kansas City, MO 64116

Gian L. Fagan Chevron Lubricants 100 Chevron Way Room 71-7338 Richmond, CA 94802-0627

Raj Shah Koehler Instrument Co. 1595 Sycamore Ave. Bohemia, NY 11716 Dr. Huafeng “Bill” Shen Bel-Ray Co. P.O. Box 526 Farmingdale, NJ 07727

Paul Grives Exxon Mobil Corporation 3225 Gallows Road Room 7C1906 Fairfax, VA 22037

Terry Smith Lubrication Engineers, Inc. P.O. Box 16447 Wichita, KS 67216

Jim Hunt Tiarco Chemical 1300 Tiarco Drive Dalton, GA 30720

Thomas W. Steib The Elco Corporation 1000 Belt Line Street Cleveland, OH 44109

Tyler Jark Lubricating Specialties Co. 8015 Paramount Blvd.

Pico Rivera, CA 90660

MOLYVAN® 3000 Friction Reducer is an exceptional oil soluble MoDTC friction modifier containing 10% molybdenum with anti-wear and antioxidant properties.

Ed Oravec Shell Canada Products 400-4th Avenue S.W. Calgary, Alberta Canada T2L 1Y8

LLC

Van de

, ls

CO-CHAIRS:

CHAIR, SESSION PLANNING:

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

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

David Turner Shell Global Solutions (US) Inc. 3333 Hwy. 6 South Houston, TX 77082

SERVICE INDUSTRY ASSISTANCE COMMITTEE

46

J im Hunt Tiarco Chemical 1300 Tiarco Drive Dalton, GA 30720

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008 100

30 Winfield Street, PO Box 5150, Norwalk, CT 06856-5150 (203) 853-1400 • F: (203) 853-1452 petro@vanderbiltchemicals.com • www.vanderbiltchemicals.com

02

Serving the Grease Industry Since 1933 – VOL. 78, NO. 6, JAN/FEB 2015

5 NLGI President’s Podium 7 8

NLGI Announcement!

tudy of Wear Properties of Environmentally S Friendly Lubricants for Gearing Applications Jason T. Galary, Nye Lubricants, Inc., Fairhaven, MA

30 An Advanced Technique for Grease Oxidation Measurement - S amina Azad & Jonathan C. Evans, Savant Group, Midland, MI

42 Use of Lincoln Ventmeter on Gauging the

Impact of Various Contributing Factors on Grease Pumpability - Paul Conley, Dr. Raj Shah, Canlong He, Jesse Kelly, SKF/Lincoln, St. Louis, MO

49 A dvertiser’s Index ON THE COVER

Ideal greases are the ones that can stay put in the bearing and yet have sufficient base oil viscosity to prevent metal to metal contact. Read more beginning on page 42.

CHAIR:

®

90

SPOKESMAN

TECHNICAL COMMITTEE

hemic ilt C a rb

O

Ruiming “Ray” Zhang R.T. Vanderbilt Company, Inc. 30 Winfield St. Norwalk, CT 06855

Wayne Mackwood Chemtura 199 Benson Rd. Middlebury, CT 06749

Its unique molecular branching provides superior fluid compatibility/stability at low temperature and enhanced robustness for improved retention of friction reduction in aged oil.

UL

Lisa Tocci Lubes ’n’ Greases 6105 Arlington Blvd., Suite G Falls Church, VA 22044

Dr. Anoop Kumar Royal Manufacturing Co., LP 516 S, 25th West Ave. Tulsa, Oklahoma 74127

NLGI

Branching Makes It Better with

OFFICERS

Registered and pending trademarks appearing in these materials are those of R.T. Vanderbilt Holding Company, Inc. or its respective wholly owned subsidiaries. For complete listings, please visit this location for trademarks, www.rtvanderbiltholding.com.

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

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

PRESIDENT’S PODIUM

President’s Podium Bruce Urban

Good News.

Thought provoking and thorough reporting is at your fingertips.

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GET YOUR SUBSCRIPTIONS TODAY -4www.LubesnGreases.com VOLUME 78, NUMBER 6

President Bruce Urban welcomes the Sponsorship (SIA) Committee to this month’s Podium The Sponsorship (SIA) Committee wishes our NLGI members, Annual Meeting sponsors and participants a happy and prosperous 2015!

We’re very excited about our upcoming meeting at the Coeur d’Alene Resort, Coeur d’Alene, Idaho, June 6 – 9, 2015. The beautiful scenery, premiere resort and temperate climate combine to make this one of our best venues ever.

Due to popular demand and survey responses, we’re changing up our meeting schedule a bit, to include the Awards Presentation Sunday evening prior to the Keynote Address and a much more casual Tuesday night closing celebration with an international “dinearound”, tranquil networking/mingling area, magic & more. Therefore, new sponsorship opportunities have been created due to these meeting agenda changes.

We appreciate the high demand for these sponsorship opportunities, and we encourage you to commit early to obtain your preferred sponsor category.

Look for our new 2015 Sponsorship Benefits and Opportunities information coming to you via email and in the next issue of the Spokesman. Please contact myself, Kim Hartley or Marilyn Brohm for more details.

Again, NLGI will be offering several levels of sponsorships for 2015, ranging from Bronze to Platinum.

Our program has been designed to provide our sponsors with one of the most value-added benefit packages in the grease and lubricant industry with recognition on our website (all year!), in print (and on-line) in the Spokesman magazine, preliminary meeting advertisement (commitment by March 2, 2015), final meeting program, and on signage & monitors during the meeting.

We would like to offer our sincere gratitude for everyone’s tremendous past support and commitment to the NLGI sponsorship program. 2014 was another banner year with more than 475 attendees in Palm Beach Gardens, Florida. Your generosity to the NLGI Annual Meeting made this success possible!

At this year’s 2015 Annual NLGI meeting, we are once again anticipating exceptional attendance, dynamic speakers, industry focus groups, and one of a kind networking opportunities.

Thank you for your continued support and all of us at the NLGI look forward to seeing all of you in Coeur d’Alene in June!

Warm regards,

Jim Hunt Marilyn Brohm Chair – NLGI SIA Committee Manager ~ Marketing/Membership (Tiarco Chemical) NLGI -5NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

NLGI

INTRODUCING

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NLGI SPOKESMAN

GOING DIGITAL! GREASE

IN THE UNCOMPROMISING WORLD OF INDUSTRIAL, WHERE METAL MEETS METAL - HIGH LOADS, CORROSION AND CONTAMINATION RARELY RELENT.

The NLGI Spokesman will be offered in print, as well as, digital for the 2015 calendar year. During this year, we will be ensuring that we have correct email addresses for all of our subscribers, to ensure a seamless transition in 2016 to all digital.

THAT’S WHERE AFTON’S GREASE MICROBOTZ™ SMOOTH THE WAY. PROTECTING EQUIPMENT, PREVENTING WEAR, AND PROLONGING THE LIFE OF INDISPENSABLE MACHINERY WHERE CONDITIONS ARE AT THEIR HARSHEST.

If you would like to see the magazine digitally, click below:

AFTON’S BROAD RANGE OF MULTIFUNCTIONAL GREASE ADDITIVE PACKAGES AND COMPONENTS KEEP GREASE FORMULATION SIMPLE; MAKING COMPLEX, MULTI-INVENTORY MANUFACTURING A THING OF THE PAST, AND GRANTING MAXIMUM FLEXIBILITY FOR PRODUCERS OF SPECIALIZED GREASES.

https://issuu.com/kim0824/docs/janfeb2015

THE GREASE MICROBOTZ™ WORK HARD SO YOU DON’T HAVE TO. CUSHIONING THE GRIND OF HEAVY LOADS. KEEPING WEAR, CORROSION AND CONTAMINATION AT BAY. BEARING DOWN ON BEARING DAMAGE, AND GIVING BOTH GREASE MANUFACTURERS AND CONSUMERS PEACE OF MIND. UNRIVALLED ALLIES. ALWAYS PROTECTING. ALWAYS FIGHTING. ALWAYS THERE.

www.aftonmicrobotz.com

-6-

NUMBER 6 Corporation (NYSE:NEU). © 2013. Afton Chemical Corporation VOLUME is a wholly owned78, subsidiary of NewMarket AFTON®, HiTEC®, MicrobotzTM and Passion for Solutions® are trademarks owned by Afton Chemical Corporation. Passion for Solutions® is a registered trademark in the United States.

Oh, our apologies, you can’t click!

One of the many advantages of having a digital version of the NLGI Spokesman. If you would like to begin receiving the magazine in digital form only, please let us know at nlgi@nlgi.org -7NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

Study of Wear Properties of Environmentally Friendly Lubricants for Gearing Applications by: Jason T. Galary Nye Lubricants, Inc., Fairhaven, MA

ABSTRACT

The purpose of this study is to examine the tribofilm formation and the associated degrees of wear for environmentally friendly synthetic lubricants and their conventional counterparts. Wear was studied using an SRV4 Rotational Tribometer to simulate the FZG scuffing wear test (ASTM D-5182) giving wear, friction, and load coefficients. To simulate gear wear a semispherical upper specimen and a lower disc both made of 20MnCr5 case hardened steel were used as they represent the same contact geometry as meshing gear teeth. The Gear Wear Simulation was run with a maximum Hertzian Contact Pressure of 2,600 N/mm2, speeds of 50Hz, and

INTRODUCTION

With the world moving towards more environmentally friendly and renewable lubricants, there are some very challenging engineering issues that have been created for lubrication in gearing applications. Over the last decade gears have been pushed to design limits as they are now required to run at higher speeds, heavier loads, and for longer periods of time. Along with new materials and improved manufacturing processes, Synthetic Lubrication Technology has helped to achieve these higher industry expectations. Synthetic lubricants have found a home in the gearing industry based on several important advantages they have over conventional petroleum lubricants. Although both mineral oils and polyalphaolefin (PAO) are derived from hydrocarbon feedstocks, PAO is synthesized from highly refined linear alpha olefins (LAO) which results in a highly purified hydrocarbon oil with a more controlled molecular weight and structure. This additional processing imparts several intrinsic properties into the PAO like reduced volatility and a lower pour point. These two properties improve both the high and low temperature capabilities as they lower the evaporation and increase the lubricant’s functionality in colder environments (key to automotive

temperatures ranging from 20°C to 150°C. Formulated fluids utilizing a conventional anti-wear/extreme pressure additive package will be examined as well as neat fluid.

The wear surfaces will be analyzed through the use of an Optical 3D Profiler. This will show the effect of the surface film regime on the wear and friction properties of environmentally friendly biodegradable/renewable synthetic lubricants versus conventional lubricants.

KEY WORDS: Wear, Biodegradability, PAO, Ester, β-Farnesene, Gear Wear Simulation, Gearing, Complex Ester

gearing applications). In the power tool industry great advances have been made by using synthetic lubricants as they have been able to optimize the motor efficiency because of the reduced internal drag. This allows for lower wear on the gear and an extended operating life for the tool.

Synthetic lubricants also have several tribological advantages over petroleum fluids with the most important being the reduction of wear and increased endurance which extends the re-lubrication cycle and will improve economics. The term Tribology refers to the study of Friction, Wear, and Lubrication Film. Friction (μ) is typically characterized as the ratio of Frictional Force to Normal Load between two moving bodies.

μ = Ff N Wear can be defined simply as the reduction of material from a solid surface via mechanical (abrasive/adhesive) or chemical actions. It is characterized by the volume of material (V) removed from a surface over a sliding distance (s) modeled below by Archards Wear Equation [1].

-8VOLUME 78, NUMBER 6

V = k.N s

NLGI Lubrication film is also very important to the amount of friction and wear that occur on a surface. There are three distinct types of film: Boundary, Mixed, and Hydrodynamic which are determined by the amount of contact between the surfaces. By knowing the roughness of the two surfaces (RqA and RqB ) as well as the lubricant film thickness (h0) you can predict which film regime you will be in.

A=

h0

2 + R2 √ RqA qB

During Boundary, lubrication film thickness is very small due to high loads and rubbing of the two surfaces.

When in this regime it is important to have a polar fluid (stronger metal affinity and bonding) and to use anti-wear and extreme pressure additives. It is in these conditions that gearing applications typically fall. As shown in the Stribeck Curve (Figure 1) shown below as we move from Boundary lubrication to Hydrodynamic, the coefficient of friction drops as the surfaces separate and a full fluid lubrication film is formed. At this point there is a continuous lubricating film that adheres to the moving part and is drawn in-between the two moving surfaces forming a pressure wedge.

Figure 1: Stribeck Curve

Complex esters are comprised of alcohol end-capped complex fluids that typically contain a monofunctional acid and alcohol. These complex polymers can then be polymerized to meet the desired viscosity and polarity Advantages include good load carrying capability, excellent viscosity indexes, and low pour points. Because complex esters are shorter chained molecules, even for high viscosities, they tend not to shear into smaller molecules, which means they will provide a consistent lubricant film strength.

The second group of environmentally friendly fluids tested are a hydrocarbon lubricant that contains β-Farnecene in the backbone (referred to as β-Farnecene fluid). Β-Farnecene is a pure linear olefin similar to the linear alpha olefins (LAO) used to prepare PAO. The structures of the olefins are very similar in that they are both linear pure hydrocarbons except that the β-Farnecene has more branching. β-Farnecene is a terpene molecule that is made by a biological process that provides this branching structure. Because β-Farnecene is an organic molecule made through this biological process it is found in nature and this branching structure allows it to biodegrade more inherently than purely synthetic molecules created through refining processes like LAO. There were two sets of viscosities tested for each fluid with the lower viscosity grade being approximately ISO32 and the higher viscosity grade being ISO-100.

Figure 2: Mineral Oil

In this study three main groups of lubricants were tested, Conventional Mineral Oils, Polyalphaolephins (PAO), and Synthetic Esters. Two groups of environmentally friendly fluids were also tested which comprised of a highly biodegradable Complex Ester and a fluid based on a renewable olefin called β-Farnesene.

Figure 2a: PAO

-9NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

NLGI OBJECTIVE FOR TESTING:

The primary purpose of this study was to compare conventional fluids used for gearing applications which includes Mineral Oil, PAO, and Esters (Polyol) with a Complex Ester and β-Farnesene fluid which are more environmentally friendly and renewable.

The key factors to this study will be in two parts.

1. Performance in the Gear Wear Simulation which will illustrate the ability for the fluid to perform in a high performance gearing application.

2. Benchmark the wear characteristics using a 3D Optical Profilometer to compare the wear volume and profile.

Figure 2b: Polyol Ester (Pentaerithritol)

Experiments:

To compare these five fluids, four main physiochemical tests were performed as well as five tribological tests.

Kinematic Viscosity and Viscosity Index Kinematic viscosities at 40°C and 100°C were measured on a Stabinger viscometer using ASTM D-7042. Viscosity index was calculated using ASTM D-2270.

Figure 2c: Complex Ester

Figure 2d: Linear Alpha Olefin (LAO) from Refined Petroleum Feedstock

Figure 2e: β-Farnesene from Natural Sources

stage is 11 minutes long with a 2mm stroke length and 50hz frequency. The load stages were created using the same hertzian contact stresses as in ASTM D-5182.

Additionally, using the contact stress progression in D 5182 (156 MPa increase per load stage) five more theoretical Load stages were added to the profile. The failure criteria is either a seizure (loss of stroke) or a COF spike. The Profilometery and wear analysis were performed using a Taylor Hobson Talysurf CCI Optical Profilometer. Figures 3 & 4 show the SRV setup in the Gear Wear Simulation Configuration and the test pieces.

Biodegradability The Biodegradability at 23°C was measured for 28 days using OECD 301B. The test method establishes threshold criteria for the classification of materials under the terms of readily or ultimately biodegradable.

A material is considered readily biodegradable if 60% of the organic carbon in the material is converted

to CO2 within a 10 day window as well as a full 28 day test period. A material is considered ultimately biodegradable (under the sub classification of Inherent Biodegradability) if 60% of the organic carbon in the material is converted to CO2 over the duration of the test.

Figure 3: SRV Setup for Gear Wear Simulation & test Specimens

GEAR WEAR SIMULATION VALIDATION: Table 1 – Comparison Chart of Contact Pressures for FZG and the GearWear Simulation

Coefficient of Friction The coefficient of Friction at 50°C and the Ball Scar were measured on a SRV Tribometer using ASTM D-5707.

The Profilometery, wear volume, and wear analysis were calculated using a Taylor Hobson Talysurf CCI Optical Profilometer.

Extreme Pressure Properties of a Lubricant using an SRV (OK Load) The OK Load at 50°C was measured on a SRV Tribometer using ASTM D- 5706.

Gear Wear Simulation () The Gear Wear Simulation was performed at 50°C, 90°C, and 150°C on a SRV Tribometer using an experimental test method which was co-developed by Optimol Instruments and Nye Lubricants. This method uses 20MnCr5 steel specimens (equivalent to AISI 5120) with a ground disc and polished ball stub. Each load

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- 11 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

Table 2 – Comparative Data between samples tested to ASTM D-5182 and the Gear Wear Simulation test.

Tables 1 & 2 show the previous work done to correlate the ASTM D-5182 (FZG) test and the Gear Wear Simulation we have used for this study. Table 1 outlines the contact pressures for the FZG and the Gear Wear Simulation we performed. Each stage for the Gear Wear Simulation is within 1-2 MPa of the pressure using in the FZG test. In the traditional ASTM D-5182 test, there are only 12 stages due to limitations on the equipment.

In our simulation using the SRV, we have been able to add 5 additional stages. Table 2 shows results for four commercial gear oils from different manufacturers tested to the conventional FZG test and the Gear Wear Simulation. Overall this data gives us good confidence in the Gear Wear Simulation as there is very good correlation in the data between the two tests which was run on four different oils in duplicate.

Results and Discussion:

Table 3 summarizes the physiochemical properties of the low viscosity fluids used in this study. The Mineral Oil, PAO, and β-Farnesene are all ISO-32 classified fluids while both of the Ester fluids are ISO-22 grade. The Viscosity Indexes range from 100 to 150 and the volatility of the fluids are all low (below 0.2%) except for the Mineral Oil which is 0.56% which was expected as it is the only non-synthetic fluid. The biodegradability of these fluids reveals that the complex ester fluid and the β-Farnesene are ultimately biodegradable while the other fluids are considered not inherently biodegradable.

Table 4 – Tribological Properties of Low Viscosity Gear Fluids In figure 4 & 5, the load failure stages for the Gear Wear Simulation for all three temperatures is plotted. The fluids that were formulated performed better and achieved a higher load before failing at 150°C in all fluids but the Esters.

With the esters, their inherent surface energy and polarity appears to be in competition with the additive package.

Table 3 – Physiochemical Properties of Low Viscosity Gear Fluids In Table 4, there is a summary of the tribological properties of the low viscosity fluids both NEAT and formulated. At a first look, the additive package does not appear to have any benefit in the Gear Wear Simulation as no improvement was seen in the failure stage for the Gear Wear Simulation although there were some notable improvement in the SRV OK Load for the Mineral Oil, PAO, and β-Farnesene fluids where improvements of 25-60% were seen in the EP characteristics. The ball scar from the SRV Coefficient of Friction test also showed a reduction in wear scar from 28-50%.

- 12 VOLUME 78, NUMBER 6

Figure 4 – Gear Wear Simulation of Low Viscosity Fluids - 13 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

Table 5 – Wear Volumes after Gear Wear Simulation of Low Viscosity Fluids

In Table 6, the wear volumes are shown for the Low Viscosity Fluids both NEAT and formulated at 150°C. At higher temperatures, the additive package performs better in all fluids except the Mineral Oil allowing them to reach a higher failure load than at 50°C. The PAO and β-Farnesene were the only fluids that showed improved performance over the NEAT fluid with the β-Farnesene

fluid showing a strong performance increase of 2 load levels with the additive. Looking at the wear volumes, the additive package helped the PAO reduce wear by 44% and in the β-Farnesene fluid it was reduced by over 54% and also helped it to achieve a level 15 failure stage which was 2 stages better than the NEAT fluid at higher temperatures and 3 better than the low temperature test.

Figure 5 – Gear Wear Simulation of Low Viscosity Formulated Fluids In Table 5, the wear volumes at 50°C are shown for the Low Viscosity Fluids both NEAT and formulated. In all of the fluids except for the β- Farnesene, the additive package showed a negative effect on the failure stage of the Gear Wear Simulation. The polyol ester fluid failed at a significantly lower level once an additive package was applied. The formulated ester and PAO can be compared with the NEAT mineral oil as they all failed at the same level. The ester fluid had considerably more wear with the additive package compared to the comparable mineral oil fluid and formulated PAO. With this ester fluid there is a

negative competition with the additive which is possibly causing neither the ester or the additive to properly bond with the substrate. The selected additive package shows a 93% reduction in wear volume with the β-Farnesene fluid compared to the NEAT version and while this does not show a benefit in the failure load, the benefit in an application is tremendous when considering endurance and life. When the NEAT fluid is compared to the PAO, a significant reduction in wear volume, depth, and peaks is found.

- 14 VOLUME 78, NUMBER 6

Table 6 – Wear Volumes after Gear Wear Simulation of Low Viscosity Formulated Fluids

- 15 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

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Figure 6 through 15 are the 3D profiles of the wear surface on the disc from the Gear Wear Simulation.

Figure 8: Low Viscosity PAO Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 6: Low Viscosity Mineral Oil Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 9: Low Viscosity PAO Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 7: Low Viscosity Mineral Oil Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

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Figure 10: Low Viscosity Ester oil Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

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Figure 13: Low Viscosity Complex Ester oil Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 11: Low Viscosity Ester Oil Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 14: Low Viscosity β-Farnesene oil Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 12: Low Viscosity Complex Ester oil Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

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Figure 15: Low Viscosity β-Farnesene oil Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

NLGI Table 7 summarizes the physiochemical properties of the high viscosity fluids used in this study. All of the fluids were ISO-100 classified. The Viscosity Indexes range from 100 to 150 and the volatility of these fluids were are all low (below 0.2%). The biodegradability of these fluids shows that for the high viscosity fluids only the Complex Ester fluid is inherently biodegradable while the other fluids are not readily biodegradable.

In figure 16 & 17, the load failure stage for all three temperatures in the Gear Wear Simulation is plotted. The formulated samples in the high viscosity fluids did not see the same benefits as the lower viscosity fluids. The additive package performed well at 50°C in all samples except the esters helping the fluids to survive longer in the Gear Wear Simulation. In this high viscosity testing, there was no performance benefit for the Esters with this additive package.

Table 7 – Physiochemical Properties of High Viscosity Gear Fluids

Table 8 – Tribological Properties of High Viscosity Gear Fluids

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In Table 8 there is a summary of the tribological properties of the high viscosity fluids both NEAT and formulated. At this first look, the additive package does not seem to have any benefit to the Gear Wear Simulation as it did not show any improvement in the failure stage. There were some notable improvements in the SRV OK Load of the PAO and β-Farnesene fluids where a 71-79% improvement was seen in the EP characteristics. The ball scar from the SRV Coefficient of Friction test showed a reduction in wear scar in all fluids from 5-47%.

Figure 16 – Gear Wear Simulation of High Viscosity Fluids

Figure 17 – Gear Wear Simulation of High Viscosity Formulated Fluids

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In Table 9, the wear volumes at 50°C are shown for the High Viscosity Fluids both NEAT and formulated. In all of the fluids except for the Esters, the additive package showed a positive effect on the Gear Wear Simulation failure stage. The ester fluids also failed at a significantly lower level once an additive package was applied. The Mineral Oil and PAO can be compared as they all failed at the same level as can the two ester fluids. The esters performed almost identically although the complex ester had a slightly less amount of wear. The Mineral Oil had 40% less wear than the PAO at the same failure stage. The

ester fluids showed that there is a negative competition with the additive which is possibly causing neither the ester or the additive to properly bond with the substrate and fail at a significantly lower stage than the NEAT fluid.

In Table 10, the wear volumes are shown for the High Viscosity Fluids both NEAT and formulated at 150°C. At higher temperatures, the additive package performs worse in all fluids except the Ester fluids where there was no effect.

The selected additive package shows an 80% reduction in wear volume with the β-Farnesene fluid compared to the NEAT version and a 2 stage increase in the failure load.

Table 10 – Wear Volumes after Gear Wear Simulation of High Viscosity Formulated Fluids Figure 18 through 27 are the 3D profiles of the wear surface on the disc from the Gear Wear Simulation.

Table 9 – Wear Volumes after Gear Wear Simulation of High Viscosity Fluids - 22 VOLUME 78, NUMBER 6

Figure 18: High Viscosity Mineral Oil Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

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Figure 19: High Viscosity Mineral Oil Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 20: High Viscosity PAO Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

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Figure 21: High Viscosity PAO Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 22: High Viscosity Ester Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

- 25 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

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Figure 23: High Viscosity Ester Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 24: High Viscosity Complex Ester Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

- 26 VOLUME 78, NUMBER 6

Figure 25: High Viscosity Complex Ester Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Figure 26: High Viscosity β-Farnesene oil Disc after 50°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

- 27 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

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This becomes very apparent in the higher viscosity testing where the β-Farnesene has a strong enough film strength to transition and stay in Hydrodynamic lubrication but in the lower viscosity study the materials stay towards the Mixed Film Regime.

Figure 27: High Viscosity β-Farnesene oil Disc after 150°C Gear Wear Simulation. NEAT fluid on left and formulated fluid on right.

Table 9: Pressure Viscosity Coefficients (2) Most of these Gear Wear Simulation for both viscosity fluids took place in a Mixed Film regime where there is a lubrication fluid film present but still some contact between surfaces. When the testing started, the contacts would be temporarily in a Boundary Condition until the fluid film forms and it moves into hydrodynamic lubrication.

Looking at the Mineral Oil, PAO, and β-Farnesene fluids, as the load stages increased these materials moved towards the Boundary side of the Mixed Film Regime.

The Pressure Viscosity (PV) coefficient for the Mineral Oil and PAO are very similar as can be seen by the similar failure stages for these two fluids. The Ester fluids which have a very consistent PV coefficient across the

temperature range as well as a stronger film thickness have stayed in Hydrodynamic lubrication for the majority of the test with greatly reduced levels of friction and wear compared to the Mineral Oil and PAO. Also these Esters unlike long chain hydrocarbon fluids, do not exhibit a temporary loss of viscosity when high contact stresses are exerted. This would cause the Mineral Oil, PAO, and β-Farnesene fluids to have a temporary boundary condition at the start of each load stage where the Esters will have a smoother transition.

The β-Farnesene has an unknown PV coefficient but from the data generated we can conclude that it is very similar to PAO at Temperatures less than 90°C but at temperatures over 90°C the fluid film thickness is greater.

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Looking at the wear profiles, the PAO, Mineral Oil and β-Farnesene when tested at temperatures lower than 90°C show typical wear patterns of materials in the Boundary side of the Mixed Film Regime with more adhesive wear from asperity/surface contact. This agrees with the failure mode for these materials which was loss of stroke from the upper and lower specimens welding together.

Once these fluids are tested at the higher temperatures, specifically 150°C the fluid film becomes smaller and provides less viscous drag between the surfaces which helps create a more uniform wear profile as well helping the fluids survive longer in the test. The PAO and Mineral Oil which failed the test at temperatures lower than 90°C now passed at higher temperatures. The wear profiles for the Ester based fluids were very consistent across the temperature range and reflect surfaces that were in Hydrodynamic lubrication for the majority of the test.

Conclusions

Both the ultimately biodegradable and renewable Complex Ester and β- Farnesene (Low Viscosity version only) were found to be comparable or exceed the performance standards of traditional Esters, PAO, and Mineral Oils in the Gear Wear Simulation Testing. With their higher

level of biodegradability and the fact that they are a renewable resource, these materials can used as drop in replacements in formulations for Industrial Gear Oil, Hydraulic Fluids, and lubricating greases where PAO, Ester, and Mineral Oils are currently used.

Looking deeper at the β-Farnesene fluid which is presented as a material with all the properties as a similar grade PAO, we have found that there are comparable failure stages using the Gear Wear Simulation as well as a significant reduction in wear volume. When an additive was applied to the β-Farnesene fluid we saw an 80-93% reduction in wear on top of the improvement already over PAO. This improvement in tribological performance is due to the branching structure that is attached to the β- Farnesene molecule and also provides the inherent biodegradability. With these performance aspects of this fluid combined with its ultimate biodegradability and renewability, the benefits in applications is significant.

The β-Farnesene and Complex Ester fluids studied here could help extend the endurance and life of a fluid and allow the most strenuous gearing applications to now use an environmentally conscious fluid.

With the wear, load, and endurance improvements seen in these two fluids, they could be substituted in any gear oil formulation where Mineral Oil, PAO, and Esters are used or blended together and extend the life and usability of the gear oil.

Future Work

Perform further comparative testing with polyalkylene glycol (PAG) as well as Vegetable Oils.

Take a deeper look at formulated gear oils using the β- Farnesene and Complex Ester fluids substituted for Mineral Oils, PAO, and conventional Esters. Additional blending studies with the high viscosity β- Farnesene will be looked at to try and improve its biodegradability while taking advantage of its other strengths. We will also look at further additive and thickener compatibility with the Complex Ester and β-Farnesene to see if they can be used efficiently in blending processes and greases.

Acknowledgements

I would like to thank my colleagues in the R&D Lab at Nye Lubricants Inc who conducted the Physical property and Tribological testing, specifically John Doherty, Craig Deschenes, and Robert Mulkern . I would also like to thank Johannes Ebrecht and Ronald Maier of Optimol Instruments Prüftechnik GmbH for the development and support of the Gear Wear Simulation test routine for the SRV and Jamie Ross from Taylor Hobson for his support of with Profilometry analysis.

References

[1] Archard JF: Contact and rubbing of flat surfaces. Journal of Applied Physics 1953; 24:981-988 [2] Roelands, D.J.A.: Correctional aspects of the viscosity- temperature- pressure relationship of lubricating oils. 1966

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An Advanced Technique for Grease Oxidation Measurement

by Samina Azad & Jonathan C. Evans Savant Group, Midland, MI

°C in a liquid bath. The published ASTM Test Method has always been limited to determine batch-to-batch uniformity of grease in the manufacturing process, although, in fact, the Test Method has been applied in screening new grease formulations in development work. The test length may be anywhere between 100 to 500 hours. Thus, application of the method is timeconsuming and encourages development of ways of increasing the information from such tests.

The opportunity to limit the test configuration of the equipment to a relatively small footprint, to eliminate the need for a liquid bath (and its associated care and safety demands), led the authors to considerably modify and expand application of ASTM D942 Test Method.

Test Techniques

Abstract

Oxidation stability is a very important property of lubricating greases. Any bench test capable of measuring this property is thus important to the degree that it is capable of predicting either or both the shelf and service life of greases. A well-known test method used to assess oxidation stability of grease is ASTM D942, which was introduced by the ASTM in 1947 and has become a standard. The method is routinely used to measure batch-to-batch grease oxidation stability.

However, the Test Method states that it is not suitable for comparing the relative oxidation stability of different greases. Moreover, Test Method D942 is a very time consuming and labor intensive test requiring a comparatively large sample size thus making it nonapplicable to measuring small sample sizes taken from operating bearings or other applications to determine remaining oxidation resistance.

On the other hand, because ASTM D942 is relatively simple to set up and operate, it was desirable to improve this Test Method by elimination of its liquid bath, reduction of sample size and application of Fourier Transform Infrared (FTIR) analysis to extend the

application of the method to comparative oxidation response of greases. Beyond this, it seemed reasonable that simultaneous analysis of several small grease sample sizes could extend the productivity of the bench test in determining grease oxidation resistance.

In this paper, the authors present a modified ASTM D942 Test Method as well as further extension of the method in gaining greater efficiency with reduced sample size and simultaneous evaluation of multiple grease samples.

Introduction

Resistance to oxidation and degradation of lubricating greases under the stresses imposed by high temperatures and thousands of hours of operation has always been an important feature of its performance. Of the bench tests designed to assess oxidation stability of greases, ASTM D942 is one of the most common. The test became an ASTM Test Method in 1947 as a quality-control tool in grease manufacturing.

Presently, this ASTM bench test is conducted on a 20 g grease sample in a small oxygen-containing chamber pressurized to 110 PSI at a temperature of 99

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Use of FTIR – One of the main techniques employed for the studies reported in this paper, is the use of modern FTIR equipped with Attenuated Total Reflectance (ATR). It is evident that a technique for oxidation measurement that combines the D942 test with Fourier Transform Infrared (FTIR) analysis would overcome the limitations of the original D942 test. The combination of FTIR with D942, referred to hereafter as the Advanced Technique, would provide much more in-depth information on grease oxidation which would consequently allow comparison of the oxidation stability of various types of grease.

It was found at the initial stages of this study that sufficient information could be obtained from IR of the surface of the grease samples. This led to the consideration of using much smaller grease samples in the pans and, thus the ability of applying the principles of D942 and FTIR to samples having the same surface area in the test, but much less grease mass. This approach would not produce the same oxygen pressure decrease, but the FTIR oxidation information would be the same.

The foregoing study led to an additional test concept in which it was considered that rapid screening of grease or additive formulations based on oxidation resistance should be possible. The Screening Technique uses the

D942 test conditions to oxidize grease, however, infrared analysis is used primarily to measure oxidation resistance of the sample. This method can be used to significantly increase the speed of acquiring information on oxidative stability of greases in the development process.

GREASE OXIDATION MEASUREMENT TECHNIQUES Background

This paper builds upon a previous study from 2013.

That study compared the oxidation resistance of several greases of varying oxidation resistance.

The study was performed in a specially modified iso-thermal reactor normally used in determining oxidation resistance of liquid lubricants per ASTM D2272. Figures 1 and 2 show the instrument before and after a modification that permits the instrument to be used alternatively in either test configuration.

The advantage of modifying the iso-thermal reactor to conduct the D942 test was that it did not require the care and concerns of a liquid bath as the sample chamber is heated by electrical resistance. A stainless steel insert was used to obtain the appropriate chamber volume for D942. Accessories, including a sample rack and sample pans were designed to comply with the method and are shown in Figure 3. The same test setup was utilized in the current work.

Application of the modified iso-thermal reactor for the D942 method was validated in the previous work by testing multiple grease samples for 100 and 200 hours.

Consistent results were obtained from repeat tests and show good agreement with D942 tests run at an external laboratory with standard test equipment. All results were within the method’s repeatability and reproducibility.

According to the ASTM D942 Test Method, 20 g of a grease sample is tested in five glass dishes with an exposed surface area of approximately 25 cm2 per dish and a total surface area of 125 cm2 per test. The dishes are stacked with a gap of approximately 5 mm between them. The combined stack of grease-filled dishes are

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then inserted into a cylindrical pressure chamber and exposed to oxygen of not less than 99.5% purity at an initial pressure of 100 pounds per square inch (PSI) and room temperature which is then increased to 99 ± 0.5 °C. Under the increased temperature, the oxygen pressure is maintained at 110 ± 2 PSI. The test is continued for a chosen period of time and decrease in oxygen pressure resulting from grease oxidation is reported in PSI as the test result.

Five lithium based greases of varying oxidation resistance were chosen for the current work. Greases 1, 2 and 3 are developmental greases provided by Loadmaster Lubricants LLC, interested in extending the information gained from ASTM D942. Respectively, Greases 1, 2 and 3 are said to be high load-carrying lithium grease, fully synthetic lithium complex grease and high load carrying lithium complex grease. Greases 4 and 5 are commercial lithium-complex greases and the compositions are proprietary.

Advanced Technique for Oxidation Measurement

For this study the authors used a PerkinElmer Spectrum 100 FTIR Spectrometer equipped with a universal Attenuated Total Reflectance (ATR) sampling accessory. The latter was indispensable in applying IR to opaque materials by using the reflection from the sample surface. Infrared analysis was conducted using about 2-4 mg sample. Multiple IR taken from the same sample showed no measurable difference in the resulting spectra indicating effects of the small variation in sample size is negligible. Sample was skimmed from the surface of the grease.

Screening Technique

Attempts have been made in the past to design a simple and rapid screening test based on grease oxidation stability that correlates well with in-service oxidation conditions7. In this work, a test concept has been developed for rapid screening of grease samples based on oxidation resistance. The concept is similar to the High Throughput Screening (HTS) technique used in drug discovery.

Infrared spectroscopy has been used for over half a century in the study of grease oxidation2,3,4,5,6. The level of oxidation in petroleum-based lubricants in general is measured in the carbonyl region (1670 to 1800 cm-1).

Infrared energy is absorbed in this region as a result of the carbonyl group (C=O) stretch from various carbonyl compounds including, ketones, esters, carboxylic acids, carbonates, aldehydes, anhydrides and amides. The FTIR peak around 1715 cm-1, is generally known as the “oxidation peak” results from C=O stretch and indicates breakdown of the lubricant and formation of oxidation by-products.

In the Drug Discovery process, biological targets are identified and potential compounds are screened against the target. This was originally an expensive, tedious, and time-consuming manual process termed Low Throughput Screening (LTS), which usually took months. Over the last two decades, innovations in technology transformed the LTS into an automated microprocessor controlled robotic process called High Throughput Screening (HTS). This quantitative step makes it possible to screen 10,000-100,000 compounds within 24 hours.

Combining the ASTM D942 method with infrared analysis seemed to be a solid approach to grease oxidation measurement. The following steps were used in the technique: 1) Response of a grease to ASTM D942 is determined by measuring change in oxygen pressure in 100 hours 2) The grease is sampled from the pans after the test 3) Oxidation resistance of the grease is analyzed using ATR-FTIR spectroscopy

A Screening Technique similar to HTS may be useful to speed up the grease development process. As the D942 Method requires five sample pans, the authors considered the possibility of evaluating five different greases in the same test. The Screening Technique does not need to be limited to five grease samples. In the initial work, five greases were chosen mainly because the current D942 Test setup is equipped with five sample pans. The setup can be easily modified to test any reasonable number of greases at the same time.

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The screening test concept was evaluated in the following two steps.

Step 1: Reduced Sample D942 Test

A modified D942 test with smaller sample amounts was evaluated using Grease 2. Four and five g of Grease 2 was tested in the following two configurations: 1) 5g, 5-Pan Test: five pans, each containing 1g of Grease 2, was tested in the iso-thermal reactor for 100 hours following the D942 test conditions (99 ºC and initial pressure of 110 PSI).

2) 4g, 1-Pan Test: one sample pan, containing 4g of Grease 2, was tested in the same way.

Grease 2 was spread out in each pan and the surface was leveled using a clean spatula to minimize the impact of any differences in surface area between pans.

Following the 4g, 1-Pan and 5g, 5-Pan Tests, 2-4 mg of Grease 2 was sampled for infrared analysis.

Step 2: High Throughput Screening Test

Next, a Screening Test concept was developed where 5 different greases were oxidized simultaneously under D942 test conditions and then oxidation resistance of the greases was measured by infrared analysis. The Screening Technique uses the D942 test equipment to oxidize the grease samples however oxidation is measured primarily by infrared analysis. The following two configurations were evaluated: 1) 5 grease-5 pan @1g: 1g each of the 5 grease samples was tested in the iso-thermal reactor for 100 hours at the D942 test conditions (99 ºC and initial pressure of 110 PSI).

2) 5 grease-5 pan @4g: 4g each of the 5 greases was tested in the same way.

of the individual grease samples. The 5 grease Screening Test disregards the change in pressure generated by the oxidation process and utilizes infrared analysis to assess the extent of oxidation of the grease samples.

RESULTS Standard ASTM D942 Test

Utilizing the iso-thermal reactor shown in Figure 2, each of the five greases was subjected to 100 hours of the standard D942 Test.

Figure 4A shows overlay of pressure vs. time plots for Greases 1, 2 and 3. Greases 1 and 3 show relatively small changes in pressure in 100 hours compared to Grease 2.

The results indicate that Greases 1 and 3 are relatively resistant to oxidation. In contrast, Grease 2 appears to be highly susceptible to oxidation as the chamber pressure reduced to an atmospheric level of about 15 PSI as a result of complete oxygen uptake during the 100-hour D942 test.

Figure 4B shows the responses of Greases 4 and 5 to 100-hour ASTM D942 tests. Very small change in pressure was observed for both of the greases indicating that these greases are highly resistant to oxidation. Table 1 below, compares the changes in oxygen pressure for all five grease samples during the ASTM D942 tests.

Advanced Technique

The grease samples were spread out in the pans and the surfaces were leveled using a clean spatula to minimize the impact of any differences in surface area between the pans.

In the advanced technique, the grease samples oxidized by 100-hour D942 test were analyzed by FTIR-ATR. Initially, each of the five dishes of grease from the D942 test was sampled for infrared analysis. No significant differences were observed between the dishes from the five-dish rack. In subsequent tests, only the top dish was sampled for IR analysis.

As would be expected, oxygen uptake during the 5 grease tests does not correlate with the oxidation stability

The infrared peak around 1715 cm-1, known as the “oxidation peak”, was evaluated to measure the extent of

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oxidation in the five greases following individual 100hour D942 tests. Figure 5A compares the ATR-FTIR spectra from Greases 1, 2 and 3 following oxidation by 100-hour D942 tests. Intensity of the oxidation peak is higher for all three greases after the D942 tests compared to the fresh grease samples. The infrared analysis clearly indicates oxidation of the grease samples, however, the level of oxidation is substantial for Grease 2 compared to the other two greases. As observed previously in Figure 4A, the change in oxygen pressure for Grease 2 during the 100-hour D942 test was also much higher compared to Greases 1 and 3.

Figure 5B compares infrared spectra of fresh and oxidized Greases 4 and 5. No oxidation peak is observed in either grease before or after 100-hour D942 test. As discussed previously, both of these greases produced very little change in pressure during the 100-hour D942 tests.

Infrared analysis, therefore, agrees well with D942 test results confirming that Grease 2 is highly susceptible to oxidation, Greases 1 and 3 are moderately stable and Greases 4 and 5 are extremely resistant to oxidation under similar oxidative conditions.

The results also support the approach of using infrared analysis as an alternate way to measure grease oxidation stability. The combination of ASTM D942 method and the subsequent FTIR analysis evidently enhances the relatively simplistic information provided by ASTM D942 alone. Moreover, the limitations of ASTM D942 when used alone are overcome with the more in-depth information provided by infrared analysis.

Reduced Sample-D942 Tests

Figure 6A shows a comparison of the responses of Grease 2 to the standard D942, 4g, 1-Pan and 5g, 5-Pan Tests, where each test was conducted for 100 hours.

Five g of Grease 2 distributed in five sample pans were evaluated in the 5g, 5-Pan Test whereas only one sample pan containing 4g of Grease 2 was evaluated in the 4g, 1-Pan Test. As observed in Figure 6A, the standard D942 produces a pressure loss of 95 PSI for this grease, which is significantly higher compared to 56.9 and 32.7 PSI obtained during the 4g, 1-Pan and 5g, 5-Pan Tests

respectively.

The results clearly indicate a correlation between the change in pressure during these tests with the volume of oxygen available per mass of sample grease. Table 2 compares the results of the standard D942 test with 4g, 1-Pan and 5g, 5-Pan Tests on Grease 2.

FTIR spectra taken from Grease 2 following the standard D942 and the 4g, 1-Pan and 5g, 5-Pan tests are compared in Figure 6B. The modified tests with reduced sample mass caused a higher level of oxidation in Grease 2 compared to the standard D942 test. Infrared analysis clearly shows that the standard D942 does not completely oxidize Grease 2 during the 100 hours.

It is apparent in these results that the standard D942 test leaves Grease 2 partially oxidized, because of complete exhaustion of oxygen in the reaction chamber before the test ends, whereas the reduced sample tests allow further oxidation of the grease. The ratio of oxygen volume in the chamber to the sample mass is higher in case of the latter.

Incomplete information is likely obtained from the standard D942 test for greases that are highly susceptible to oxidation. The results demonstrate another limitation of the ASTM D942 method, as well as, the significance of coupling the test with infrared analysis.

Screening Test

As discussed previously, there was considerable agreement between the test results obtained by the standard D942 test and the Advanced Technique.

In an effort to develop a Screening Test concept, the five greases were tested simultaneously in the following two configurations: 5 grease, 5-pan Test (@1g) and a 5 grease, 5-pan Test (@4g).

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Figure 7A compares the effect of oxidation on Grease 2 for the standard D942 test, 5 grease, 5-pan (@1g) and 5 grease, 5-pan (@4g) Screening Tests where each test was conducted for 100 hours. The Screening Tests clearly obtained a higher level of oxidation of this sample compared to the standard ASTM D942, as measured by infrared analysis. Both the standard D942 test and the Screening Tests found Grease 2 to be highly susceptible to oxidation compared to the other four greases.

As observed in Figure 7B, infrared analysis detected no oxidation of Grease 4 after the standard D942 test, however, a minimal level of oxidation was measured in the same grease after the Screening Tests. Both tests indicated that Grease 4 is highly resistant to oxidation.

The results imply that the 5-Grease Test creates a relatively harsh oxidative environment compared to the standard test, which is designed to measure oxidation of a single grease sample.

The preliminary results obtained in this work demonstrate that the Screening Test concept may be useful in rapid selection of grease or additive formulations. This approach could significantly reduce the time needed for grease research and development.

Conclusion

ASTM D942 is severely limited in its applications to any other use than quality control in grease manufacturing processes. The goal of this work was to improve the ASTM D942 Test Method, by combining precise control of test temperature and measurement of oxygen pressure with infrared analysis. The in-depth information provided by FTIR analysis expands the applications of the original method. The extended test is capable of comparing oxidation stability of various types of grease. Based on this analysis, we believe that the ASTM D942 should be extended to include the use of infrared analysis.

of multiple grease samples under ASTM D942 conditions and measurement of oxidation resistance by infrared analysis. The results indicated that the Screening Test and the standard ASTM D942 Test Method measure comparable oxidation tendency of the grease samples.

The Screening Test can be useful in selecting preliminary formulations in the grease development process by significantly shortening the analysis time.

References

1. T. Selby, et. al.: A Comparative Study of Grease Oxidation Using an Advanced Bench Test, Proceedings of the 19th International Colloquium Tribology Technische Akademie Esslinegen, Ostfildern, Germany (January 2014) 2. G. Rappoport, Lubrication Engineering, vol. 8 (1952) 3. O. Z. Pencheva et. al.: Use of IR Spectroscopy in Research of Grease Oxidation, Khimiya Teckhnollogiya Topliv í Masel, 7 (July, 1973) 4. Z. M. Zhang, et. al.: Infrared Refractive Index and Extinction Coefficient of Polyimide Films, International Journal of Thermophysics 19 (1998) 5. P. M. Cann, et. al.: Grease Degradation in ROF Bearing Tests, Tribology Transactions, 50 (2007) 6. S. Hurley et. al.: Infrared Spectroscopic Characterization of Grease Lubricant Films on Metal Surfaces, NLGI Spokesman 64 (October, 2000) 7. W. W. Bailey et. al.: Dynamic Oxidation Stability of Lubricating Greases, NLGI Spokesman 15 (April, 1982)

Acknowledgement

The authors would like to thank Loadmaster Lubricants LLC for supporting this research work by providing three Lithium based grease samples. Similar support and encouragement was provided by Ted Selby of Savant Laboratories. Again, the authors would like these colleagues to know that their support and encouragement are sincerely appreciated.

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Figure 1. Iso-thermal reactor before modification

Figure 4A. Responses of Greases 1, 2 and 3 to 100 hours D942 Test Figure 2. Iso-thermal reactor after modification

Figure 3. Accessories for the iso-thermal reactor specially designed for D942 test

Figure 4B. Responses of Greases 4 and 5 to 100 hours D942 Test - 36 VOLUME 78, NUMBER 6

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Figure 5A. Effect of Oxidation on Greases 1, 2 and 3 to For 100 hours 942 test

Figure 5B. Effect of oxidation on Greases 4 and 5 for 100-hour D942 test

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Figure 6A. Response of Grease 2 to 100 hours of ASTM D942 and 4g, 1-pan and 5g, 5-pans

Figure 6B. Effect of oxidation on Grease 2 for 100 hours of standard D942, 4g, 1-Pan and 5g, 5-Pan tests - 39 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

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ANNUAL MEETING EXHIBITS Again this year the Institute is planning to have space for a limited number of “Table-Top” displays for display materials at the 82nd Annual Meeting, Coeur d’Alene, ID, June 6-9, 2015.

For additional information and exhibit forms please visit our website, https://www.nlgi.org/annual_meeting/ or call Marilyn at 816-524-2500.

Figure 7A. Effect of oxidation on Grease 2 for 100 hours of ASTM D942 and 5 Grease tests

CLGS (Certified Lubricating Grease Specialist) NLGI CLGS Professional Certification NLGI will offer the certification exam on Tuesday, June 9, 2015 at 2:00 p.m. at the 82nd Annual Meeting, located at the Coeur d’Alene Resort, Coeur d’Alene, Idaho. The fee for taking the exam is $225 for members, and $275 for non-members. You do not have to attend the meeting to sit for the examination.

Certification is an indicator that the individual possesses a high level of expertise in the field of grease. NLGI recognizes CLGS certified individuals as grease industry experts. CLGS certification will serve as a useful tool for employers to screen potential employees and for OEMs and end users to ensure that consultants and suppliers are qualified to make grease related recommendations.

Exam participation is available for any individual who has worked in the grease industry and has attained a high level of expertise in this field.

Figure 7B. Effect of oxidation on Grease 4 for 100 hours of ASTM D942 and Five-Grease tests - 40 VOLUME 78, NUMBER 6

For more information including recommended study tools, please visit our website, https://www.nlgi.org/professional_certification/info.php - 41 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

Use of Lincoln Ventmeter

on Gauging the Impact of Various Contributing Factors on Grease Pumpability (Using statistical factorial experiments to show the impact that grease thickener content interaction and base oil viscosity have on grease pumpability) by: Paul Conley, Dr. Raj Shah, Canlong He, Jesse Kelly SKF/Lincoln, St. Louis, MO

Abstract:

Lincoln ventmeter testing can be extended to quantify how two levels of NLGI grades of grease with different levels of base oil viscosity impact the grease yield stress and pumpability over the temperature range of 30 °F (-1°C) and 77 °F (25 °C). By using statistical factorial experiments, the study shows the impact that thickener contents and base oil viscosity have on grease pumpability.

It is important for grease manufactures, when developing grease for use in automatic lubrication systems, to know application requirements and the pumpability limits. Ideal greases are the ones that can stay put in the bearing and yet have sufficient base oil viscosity to prevent metal to metal contact.

Thus the stiffest grease possible, but still within pumpability limits of an automatic system is best.

This paper serves as a guide to quantify how different types of grease chemistry, two NLGI grades (NLGI 1 and NLGI 2) and two levels of base oil viscosity (460 cSt at high temperature and 220 cSt at low temperature), affect grease pumpability. For example, it would be useful to know the extended temperature range one can expect by using an NLGI 1 with a 220 cSt base oil ((30 °F, -1 °C). Similarly, how would the temperature range be restricted by using an NLGI 2 grade with a 460 cSt (77°F, 25 °C) base oil?

As a baseline, it can be considered that a grease yield stress value of 800 Pascal or below with a maximum apparent viscosity of 50,000 cSt the upper limit for grease pumpability in a normal system at ambient temperature. Depending on system design, larger diameter pipes or shorter pumping distances, the maximum yield stress or apparent viscosity can be extended.

In this paper the Lincoln ventmeter was used as a tool to study grease pumpability. The Lincoln ventmeter has been a useful tool in determining grease suitability for use in automatic lubrication systems since its introduction in 1965. The Lincoln ventmeter effectively determines the grease yield stress/stiffness and shear thinning index at various temperatures which can be used to estimate a grease apparent viscosity, and ultimately, pumpability. The Lincoln ventmeter is a valuable tool to gauge the impact of various factors affecting grease pumpability such as thickener content, base oil viscosity, temperatures, etc. The Lincoln ventmeter was used to quantify how two levels of NLGI grades of grease with different levels of base oil viscosity impact the grease yield stress and pumpability over the temperature range of 30 °F (-1°C) and 77 °F (25 °C). By using statistical factorial experiments, the study shows the impact that thickener content interaction and base oil viscosity have on grease pumpability. The data and trends that are developed from the Lincoln ventmeter testing are relevant in all types of lubrications system.

Background

Since the introduction of the Lincoln ventmeter to the industry at the 1965 NLGI conference, the device has been extensively used for testing of grease. In particular, the instrument has been used to determine yield stress, shear thinning index, and low temperature flow limits of grease. Rotter1 discussed one way to calculate grease yield stress and shear thinning values which allows for a method of determining a grease’s apparent viscosity.

A paper by Buehler2 shows how grease stiffness affects bearing start up torque.

In a follow up paper, He and Conley3, showed how lubrication system design can be more reliable by using data provided by the Lincoln ventmeter. Another paper4 introduced an improved method to estimate a grease’s apparent viscosity. In Conley, Lugt, and He5, the authors describe a more precise method of calculating a grease yield stress and shear thinning index for determining a grease’s apparent viscosity for use in designing lubrication systems.

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Looking at the relationship between grease yield stress, shear stress and shear rates, the graph below shows that as grease begins to flow, the shear stress increases from the yield stress value (shear rate =0) but the overall apparent viscosity is reduced as shear rate increases.

Figure 1

In figure 1, the slope of the tangent line to any of the curves is the value of the apparent viscosity at the respective test temperatures.

As seen in this figure, the lower the grease thinning index or power law index, the lower the apparent viscosity and the more pumpable the product. With any grease, the value of the yield stress is the starting point of shearing that shows how stiff the grease will be and is the basis of the response used in this paper.

Samples Used in Testing

A three-factor, two-level design of experiments was performed on 4 different type thickeners. The three factors were temperature, NLGI consistency grade, and - 43 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

base oil viscosity. Base oil viscosity is mineral type. The two levels for each factor are described below. a. Temperature High (70°F, 21 °C) b. Temperature Low (30 °F, -1 °C) c. NLGI High – (NLGI 2) d. NLGI Low – (NLGI 1) e. Base Oil Viscosity High (460 cSt(70 °F, 21 °C)) f. Base Oil Viscosity Low (220 cSt(30 °F, -1 °C)) Four types of greases are listed below with 28 total samples.

1. Lithium Complex – 8 samples 2. Lithium – 8 samples 3. Calcium Sulfonate – 8 samples 4. Aluminum Complex – 4 samples Instrument Used: Lincoln Ventmeter

Test Procedure Lincoln ventmeter as pictured in Figure 1 and diagramed in Figure 3 was used to perform standard Ventmeter test 30 °F (-1°C) and 77 °F (25 °C).Grease was pumped up to 1,800 psi via. a grease gun and then the vent valve (valve one, figure 3) opened. Pressure reading was taken and recorded at the gauge, 30 seconds after the vent valve opened. The test was repeated 4 times for each sample, and averages were recorded.

(4 replicating tests done on all 28 grease samples)

For each grease category and level, the average ventmeter value was recorded and plotted. The corresponding grease yield stress (in Pascal) was tabulated using equation 1 and 2 and plotted.

Yield stress calculation Y = P*r / 2L Eq. 1 Y = yield stress [reyns (lb*s/in2)] (1 reyn = 6.890 kPa × s) P = pressure in psi (6.890 kPa) of gauge reading after 30 seconds. r= radius of tubing (0.125 inches (0.3175 cm) for Ventmeter) L = l ength of tubing (300inches (762 cm)) for Ventmeter) Having Y = P * .125/2*300 = P*.00021. Using conversion of 6,890 kPa, the Lincoln ventmeter parameters for radius and length of tubing, the equation is simplified below.

Figure 2

Yield Point Y (in Pascal) = ventmeter pressure P (psi) x 1.45 Eq. 2.

Results

70 °F (21 °C) and 30 °F (-1 °C) grease relates to NLGILow, Oil-Low level response in yield stress to the rest of the levels. In all figures 4 through 8, NLGI Low, Oil low is set a unity of 1.

Figure 3

- 44 VOLUME 78, NUMBER 6

Figure 4

Discussion of results for lithium complex group in Figure 4.

As seen from the graph, the most distinct jump in yield stress happens between NLGI 1 to NLGI 2.The oil viscosity change is less dominant. In the NLGI 2 greases, the base oil viscosity shows an effect of additional yield stress. The black dotted line with synthetic base oil (high VI index) is flat with a small slope of 1.88. This suggests that mineral base oil has moderate level effects on pumpability. For the NLGI 2, and high viscosity base oil grease, the yield stress is greater than 1300 Pascal at 30 °F (-1 °C). A temperature of 65 °F (18 °C) is needed to achieve a good pumpability (yield stress < 800 Pascal.)

With NLGI 2 and low viscosity base oil grease, the temperature needed to achieve good pumpability is 50 °F (10 °C). This is a 15 °F (8.34 °C) improvement. The effect is minimal with NLGI 1 between oil high and oil low.

As indicated by the steeper slope of the lines for NLGI 2 grade for base oil low, suggest that the oil has a significant but not dominate impact on pumpability with decrease in temperature.

Figure 5

Discussion of results with lithium group in Figure 5.

As with the lithium complex group, the lithium group shows the most distinct jump in yield stress happens between NLGI 1 to NLGI 2 grades. The oil viscosity change is less dominant. With the NLGI 2, and high base oil grease, the greatest stiffening occurs as evident by the slope of 16.68. The temperate needed for good pumpability is near 65 °F (18 °C). For NLGI 2, base oil low, a temperature of 55°F (13 °C) is also required for good pumpability. This is a 10 °F (6.56 °C) improvement.

Although not as dramatic as with the lithium complex group data, the oil viscosity still impacts the yield stress as the temperature drops. For NLGI 1 greases, good pumpability is achieved at or below 30 °F (-1 °C).

- 45 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

NLGI

NLGI shows that NLGI grade is more significant than the base oil viscosity by a factor of approximately 2.7.

ffect ( NLGI Grade + Base Oil Viscosity)= E 337+131=468 Effect of NLGI Grade 337/468 = 72 % Effect of Base Oil Viscosity 131/468 = 28 %

Table 1 Summary and Conclusion

Figure 8

Figure 6

Figure 7

Discussion on results of calcium sulfonate group in Figure 6. As with lithium complex and lithium, the most dramatic increase in yield stress was between NLGI 1 and NLGI 2. We can start to see a trend develop with the first few types of grease. The base oil has an effect but as shown earlier is less dominant. With this set of data, there is less dramatic stiffening between 70 °F (21 °C) and 30 °F (-1 °C) as evident by the relatively lower slope index. The change in base oil contributes little to the yield stress value. When looking at the NLGI 2 high viscosity base oil grease, the temperature to achieve good pumpability is 65 °F (18 °C). For NLGI 2 grease with low viscosity base oil, the temperature is near 55 °F (13°C), a ten degree difference. With NLGI 1 base oil high and low, good pumpability is achieved below 30 °F (-1°C).

Discussion on results of aluminum complex group in Figure 7. With this thickener type, there is less of an increase in yield stress between NLGI 1 and NLGI2 as with the previous grease thickener types. The NLGI 2 grease values of yield stress are very close between NLGI 1 with a high viscosity oil to that of a NLGI 2 with a low viscosity oil. This suggests that the base oil for this type of thickener plays a more important role in pump ability.

With aluminum complex, there is a more pronounced change due to base oil viscosity than in the previous three thickener types. For NLGI 2, base on high, the temperature to achieve good pumpability is near 70 °F (21°C).For NLGI 1, base oil low, the temperature to achieve good pumpability is near 60 °F (15°C). Here a 10 °F (6.56 °C) improvement is recorded. With this thickener, NLGI 1 with base oil high or low, 55 °F (13 °C) is required for good pumpability. This 55 °F (13°C) temperature is 20°F (11.11 °C) higher than the other three grease thickeners, thus the grease is limited to fewer applications due to its lower pumpability.

- 46 VOLUME 78, NUMBER 6

Discussions on Composite Group. This graph represents the combined data from all 4 grease thickener types. The composite group shows the most distinct jump in yield stress happens between NLGI 1 to NLGI 2 grade. The oil viscosity change is less dominant. With the NLGI high Oil high, the greatest stiffening occurs as evident by the slope of 10.38. The temperate for NLGI 2, base oil high, to achieve a good pumpability of 800 Pascal is approximately 62 °F (17 °C). For NLGI 2, base oil low, the temperature to achieve good pumpability is 50 °F (10°C). Here a 12 °F (6.67 °C) improvement.

Below in Table 1 is the Anova table for the composite group. The df column is the degrees of freedom, the MS column is the mean square of the error, the F column represents the statistical impact for each factor, and the Effect column represents the relative impact for each factor. Table 1 shows that the values for temperature have the highest impact, but in this paper, the effects of interest are between base oil viscosity and NLGI grade.

The higher the number in the Effect column, the higher the impact that factor has on the response. The table

Testing shows, what would be self-evident with grease makers and chemists, that lighter grade grease and lighter grade base oil will result in improved pumpability of a grease. But the value of this paper and results provide some level of magnitude on the effect of pumpability between NLGI Grade 1 and 2 and low and high viscosity base oil. For an automatic lube system, yield stress of 800 Pascal or below is ideal and can be achieved with most NLGI 1 grease with either a high or low level base oil viscosity. The exception in this test is with aluminum complex grease where NLGI 1 and 460 cSt showed yield stress values over 800 Pascal near 55 °F (13°C).

Testing that was performed between 30 °F (-1°C) and 70 °F (21°C)and it was shown that improvement in temperature of 10°F can typically be realized between a NLGI 2, 220 cSt base oil viscosity base oil to that of a NLGI 2, 460 cSt base oil viscosity. Between a NLGI 2 and NLGI 1, as seen by the graphs an improvement to achieve good pumpability at 20 to 25 °F (-7 to -4 °C) can be realized. As seen from the lithium complex group test, when using a synthetic base oil with a high

- 47 NLGI SPOKESMAN, JANUARY/FEBRUARY 2015

NLGI (VI index >120), a significant improvement can be made in pumpability. It will be the focus of further test to do more experiments with grease containing synthetic base oils and compare to the data obtained in this paper with mineral oil.

Finally from the Anova table1, the relative magnitudes of the effects are show as indicated in the effect column.

Ignoring temperature effects as we are mostly concerned with the NLGI grade thickener level and base oil viscosity level, the thickener has 72 percent effect on the pumpability were base oil viscosity has 28 percent effect on pumpability.

References

1. LC Rotter, J Wegmann; (1965)”The Lincoln Ventmeter and its Possibilities”, NLGI Spokesman,pp268-273.

2. F.A. Buehler and H Raich; (1967) “Low Temperature Flow Limits for Greases”, NLGI Spokesman,pp 49-54.

3. P Conley and C He; (2007 vol 71 Number 9) “Lincoln Ventmeter Provides Invaluable Information in Addition to Aiding Lubrication System Design, NLGI Spokesman pp17-21.

4. P Conley and C He, (2009, vol 73, Number 6) “Lincoln Ventmeter Reading could be used to Estimate Apparent Viscosity”, NLGI Spokesman pp 18-22.

5. P Conley, C He, P Lugt, (Nov 2013),“Effective Viscosity Determination for Lubrication Systems using the Lincoln Ventmeter”. Tribology Transactions, pp 771-780.

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