28 M A R C H 2 0 0 8 T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y

ubricant selection is a pivotal starting point in thepursuit of precision lubrication practices. All theeffort applied to clean delivery and handling, fil-

tration, dehydration, alignment, balancing, etc., is lostif the lubricant cannot support the demands placedupon the lubricant film when the machine is running.

Quality-conscious lubricant manufacturers providefield support to ensure products are properly selectedfor their customers’ machines. In the end, though, thelubricant supplier doesn’t face production losses andsevere organizational stress when the machine fails.Regardless of the amount of effort provided by thesupplier, the machine owner must be aware of whichproducts were selected and whether the selectionsmeet the demands imposed by the production processand environment.

It is to the equipment owner’s benefit to have theentire mechanical staff (millwrights, mechanics, lubri-cation technicians, maintenance planners, mainte-

Article highlights:

■ The six functions of a

lubricant.

■ Hydrodynamic vs. elastohy-

drodynamic film regimes.

■ Overview of basestocks

and key additives.

■ Three types of common

finished lubricants.

BEST PRACTICES NOTEBOOK

Selecting the correct lubricant

By Mike Johnson, CMRP, CLS

Contributing Editor

L

Before making your decision, evaluate the

component function, lubricant film requirement

and lubricant capability.

T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y M A R C H 2 0 0 8 2 9

nance engineers) understand these general ideas.In addition, a few of them need to master lubricantselection and management criteria in order todevelop reliability-centered lubrication practices.

This article addresses the nature of oil film for-mation and properties of fluid oil lubricants thatare important to the selection process. Greases,solid film lubricants and additives will be ad-dressed in a later article. Gases will not be ad-dressed in this series since gases are not com-monly used as lubricants for machines operatingin industrial service.

Lubricant functionsIt’s been said that the industrial world floats on a10-micron film of oil. If only that were true! Thereality is much less assuring: components that rolltogether ride on an oil film in the 0.5 to 1.5 micronrange, and components that slide together experi-ence a relatively fat 3- to 5-micron thick film. Thatthe lubricant is capable of sustaining itself at thesedimensions is remarkable.

The lubricant has six clear responsibilities:1. Reduce friction. Friction occurs when surface

high spots, called asperities, collide. The small sur-face area of the asperity, combined with the fullload of the machine components and productionmaterials, causes extremely high unit loads.Machine surfaces resist movement under these cir-cumstances. This resistance to movement is calledfriction.

2. Reduce wear. Wear occurs between machinesurfaces when the asperities and/or surroundingsurfaces cut, tear, fatigue and weld. These surface-to-surface wear modes occur at a microscopiclevel, well below the sensitivity of our humanssenses and are consequently overlooked until thecomponents require repair. There are other com-mon wear modes for industrial machines that arefluid to surface in nature, including cavitation, cor-rosion and erosion (which are all fluid-to-surfacewear modes).

3. Remove heat. The microscopic oil filmabsorbs heat from the machine’s surfaces andtransfers that heat into the sump, the machine cas-ing and eventually the local atmosphere or a heat-removal device. The key work of heat removaloccurs at the point where the machine surfacesinteract with the microscopic film.

4. Remove contaminants. Fluid lubricants col-lect any wear debris or atmospheric debris or fluidcontaminants from the working contact area andtransfer the contaminants away from the workingzone. Semisolid and solid-type lubricants areunable to perform this role as efficiently as a liquid

lubricant, but the responsibility still exists. 5. Control corrosion. Some production environ-

ments contain large concentrations of either mois-ture or corrosive chemicals. These environmentsseep into the production machines through thenormal heating and cooling process. The lubricantis equipped to resist the corrosive action of mois-ture and mild production environments. The needfor corrosion control is pronounced in combustion(spark and compression ignited) engines. In addi-tion, as the lubricant ages it becomes more corro-sive itself and must be fortified to prevent corro-sion attack of the surfaces that it is assigned toprotect.

6. Provide a means for power transfer. Thisfunction may be debated on semantic terms. In ahydraulic system, the lubricant (hydraulic oil) pro-vides a dual function: fulfilling these previouslynoted obligations and providing the meansthrough which electrical energy is converted tofluid energy (increased pressure) and transferredthrough the hydraulic system piping to mechanicalcomponents where work can be accomplished.Power transfer also occurs through fluid clutchapplications in many industrial systems.1

The lubricant performs these functions by creat-ing a fluid cushion between the interactingmachine components and by continuously flush-ing the interacting surfaces. As was previously stat-ed, the fluid cushion is not very thick, but it onlyneeds to be thick enough to separate the surfacesand clear the high spots (asperities) between thetwo surfaces. Table 1 shows the typical roughnessof surfaces based on common machine surface fin-ishing techniques.

CONTINUED ON PAGE 30

The six responsibilities of a lubricant

Table 1. Common surface roughness dimensions

30 M A R C H 2 0 0 8 T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y30 M A R C H 2 0 0 8 T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y

The most common interacting surfaces includevarious types and sizes of bearings (plain journalbearings; element bearings [roller, ball, sphericalroller, needle, tapered thrust]; gears (spur, helical,hypoid, worm); pump surfaces (gear, sliding vane,piston); and other incidental components (linearscrew, ball joint, spline, pivot, bushing, etc.). All ofthese components interact in a sliding action, arolling action or a combination of the two.

Film formationFour factors influence the type of oil films thatdevelop and the speed with which they develop:

■ The size of the lubricated machine surface (area).

■ The type of surface interaction (sliding orrolling).

■ The speed with which the machine surfacesinteract.

■ The viscosity of the lubricant supplied to themachine.

The machine designer controls the componentsurface area, the nature of the interaction of thesurfaces (rolling or sliding) and the speed at whichthe surfaces interact (at least initially). It is worthnoting that the machine load and lubricant viscos-ity dimensions don’t determine the type of oil filmbut do greatly influence the lowest speed require-ment for film formation and whether the film canbe maintained at normal running speed.

The type of oil film created within the machine isdependent on the nature of the machine componentinteractions. When machine components experi-ence sliding interaction (such as a journal and plainbearing), the resulting lubricant film is called ahydrodynamic (HD) oil film, as shown in Figure 1. Awater skier floats on a hydrodynamic film when theskier achieves enough speed to rise on top of thewater on a pressure wedge formed between the skiand the water. If the skis are enlarged, the requiredspeed to lift the skier declines and vice versa.

Machine hydrodynamic films occur in a similarfashion with the moment of lift being dictated bythe combined influences of component surfacearea, machine speed, machine load and lubricantviscosity. HD oils films are, relatively speaking, fair-ly fat at 3 to 10 micrometers thick.

The type of oil film created by components thatexperience rolling interaction is called elastohydrody-namic (EHD) oil film, as shown in Figure 2. Thedynamics surrounding this type of oil film are sim-ilar to that of a tire hydroplaning on a wet pave-ment surface. This type of lifting action begins withthe tire creating a flat spot where it contacts theroad. Without the flat spot the tire would not haveenough surface area in contact with the pavementto hold onto the road surface. The tire must be softenough to deflect at the point of contact with thepavement but firm enough to withstand long-termrubbing against the dry pavement.

On a wet surface, though, the flat spot providesenough surface area that, at a given speed, thevehicle can float on a very thin film of water restingon the pavement. The thicker the film of water, thelower the speed required to make the vehicle float.

EHD oil films are relatively thin, ranging from 0.5to 1.5 micrometers thick. These films occur wherev-er machine surfaces interact with a rolling motion.One or both of these surfaces experience a momen-tary deformation, just like a tire. The resulting flatspot provides enough surface area that at somespeed of interaction the rolling surface floats. Thewider the surface and the thicker the oil, the lowerthe speed at which the machine surface floats.

Regardless of the nature of the oil film (HD orEHD), films form after reaching an equilibriumstate where the oil (lubricant) is being suppliedinto the gap at a high enough rate that the squeez-ing force applied by the machine cannot push itout of the way. When that balance is reached the

CONTINUED FROM PAGE 29

Figure 1. Hydrodynamic oil film

Figure 2. Elastohydrodynamic film formation

(Courtesy of LubCon Turmo Lubrication, Inc.)

pressure that builds at the point of machine sur-face interaction overcomes the machine dynamicload and the surfaces separate.

There are several factors that influence the long-term stability of the HD or EHD films:

■ The type of materials used to create themachine surfaces (both surfaces).

■ The way the lubricant is applied to themachine (static-bath or dynamic-forced flow).

■ The total (static) load that is applied to themachine surface.

■ The degree of “shock loads” or dynamic loadpeaks that occur during operation.

■ The lubricant itself (viscosity, additive types,ongoing maintenance of lubricant health).

These factors influence the extent to which theoil film is adequate for the machine’s routine oper-ating state, and/or whether specialized additivesare required to provide an additional protectivephysi-chemical surface protection film.

The performance properties required from alubricant are based on a combination of the type offilm that forms when the machine is running, themachine’s ability to sustain the full fluid film duringnormal operation and the machine’s operatingenvironment. These factors may change somewhatduring operation but mostly are set by the machinedesigner and the production process itself.

Now let’s examine lubricant composition andfunction.

BasestocksA lubricant is a complex organic chemical blend ofcomplimentary and competing ingredients. Creat-ing a successful lubricant is a balance of chemical

engineering and trial and error and requires atremendous amount of testing during development.

The largest component of the lubricant, and thepart of the lubricant that does most of the work, isthe basestock. The basestock can be any one of awide variety of man-made (synthetic) or nature-made (refined petroleum) materials.

In 1993 the American Petroleum Institute (API)began categorizing base oils by their productionmethods in order to differentiate between conven-tional and higher performance materials that thelubricants industry was starting to produce. Asshown in Table 2, there are five categoriesi of mate-rials with varying degrees of quality and perform-ance characteristics. Mineral oil-based productsare identified as either Group I, II or III, and theremaining two groups are reserved for man-madesynthetic base oil types.ii

Footnotesi American Petroleum Institute Publi-

cation 1509. API Base Stock Cate-

gories.

ii Kramer, D.C., Lok, B.K. and Krug, R.

R., “The Evolution of Base Oil Tech-

nology,” Turbine Lubrication in the 21st

Century, ASTM STP #1407, Herguth,

W.R. and Warne, T.M., Eds., American

Society of Testing and Materials,

West Conshohocken, Pa.

CONTINUED ON PAGE 32

Table 2. The API base stock categories

T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y M A R C H 2 0 0 8 3 1

32 M A R C H 2 0 0 8 T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y

API Group I (G-I) base oils are manufactured bythe solvent-extraction refining technique. Thistechnique, pioneered in the 1930s, separates oilmolecules by size and uses solvents to wash outsome of the harmful constituents (some wax, somearomatic species) found in raw crude petroleum.

G-I base oils are comprised of three primarymolecule types (paraffinic, naphthenic and aro-matic) as well as a variety of sulfur- and nitrogen-based compounds. G-I oils, as shown in Table 3,contain a large amount of unsaturated molecules,aromatics and polar compounds and may containappreciable sulfur. These polar constituents areresponsible for accelerating aging and degradationof finished lubricants.

Some aromatic compounds and sulfur-contain-ing materials behave as natural antioxidants in theabsence of specific oxidation-inhibiting agents(additives).2 However, these species of moleculesalso can interfere with the function of the primaryantioxidants (amines and phenols) added to inter-rupt the oxidation-reaction processes. It is alsowell known that the sulfur compounds and aro-matic molecule structures themselves are unstableand tend to react rapidly with oxygen to form vari-ous soluble and insoluble oxidation degradationbyproducts.

A hydrotreating process was added to solventrefining techniques in the 1950s. Hydrotreating is aprocess where hydrogen is added to the basestockat high temperatures and in the presence of a cat-alyst in order to stabilize the reactive components,improve the color and extend the useful life of thefinished lubricant product. This step helpedimprove product quality but was not severeenough to fully neutralize the aromatic compo-nents in the finished products. Roughly two-thirdsof lubricant base oil in North America is producedusing the solvent-refining technique.4

Group II (G-II) base oils follow a processing pathsimilar to the G-I products except that instead ofusing solvents to extract the problematic com-

pounds, G-II oils are “hydrocracked.” Hydrocrackingtechniques, borrowed from fuel-refining processes,are a more severe hydrogen processing methodwherein hydrogen is added to the base oil feed atmuch higher temperatures and pressures than withconventional hydrotreating. The hydrogen catalyti-cally reacts with the basestock, restructures thenaphthenic and aromatic molecules and eliminatessulfur and nitrogen components. This is accom-plished through a series of molecular rearrange-ments (formation of paraffin isomers, breaking oflong chain molecules and ring structures).

Group III (G-III) base oils follow the same hydro-gen processing path as the G-IIs except they aremore severely treated (higher pressure, highertemperature, longer process times). G-III oils per-form on par with, and in some cases superior to,some synthetic Group IV (polyalphaolefin) types.

Group IV (G-IV) and Group V (G-V) base oilstocks are man-made. The G-IV base oil category isreserved for a single type of basestock calledpolyalphaolefin (also known as PAO and synthetichydrocarbon). PAOs are made from ethylene(derived from petroleum) but are not hydrocarbonsin the naturally occurring sense. G-V base oils aremade using a wide variety of hydrocarbon and non-hydrocarbon raw materials and are also strictlyman-made.

The performance properties of the G-III, G-IVand G-V basestocks are fairly predictable, both thepros and cons. Given their production methods,their cost of raw materials and their relatively lowdemand levels, the prices are higher than Group Iand Group II products. The resulting finished lubri-cants purchase prices range from three to 10 timesthat of Group I and Group II products.

Basestock characteristics are considered,according to the type of machine, to be lubricatedand how the basestock supports the needs of themachine’s components. Several key properties areconsidered:

1. Compatibility. Degree to which the basestockmixes with other hydrocarbons.

2. Additive response. Characteristics determin-ing how the base oil and additives worktogether.

3. Viscometrics. Measures of viscosity, viscosityindex and pour point.

4. Safety. Flash point and toxicity.5. Consistency. Repeatability from batch to batch.6. Oxidation stability. Influenced by raw materi-

al properties and response to antioxidants.7. Volatility. Flash point and NOACK volatility

(engine oils in particular).8. Appearance. Color, cleanliness and clarity.

Table 3. Properties of light neutral base oils3

Solvent Refined Hydrocracked

100N Base Oil 100N Base Oil

Clay Gel Analysis (ASTM D2007)Saturates, wt. % 85 – 90 >99Aromatics, wt. % 9-15 <1Polar compounds, wt. % 0-1 0

Sulfur, wt. % .05 - .11 <.001

Nitrogen, PPM 20 – 50 <2

Color (ASTM D1500) 0.5 – 1.0 <0.5

CONTINUED FROM PAGE 31

Additive types and functions

Individual additives impart chemical or physicalreactions that create three different types ofresponses. An individual lubricant additive may:

1. Enhance existing favorable base oil proper-ties (viscosity, pour point, water release).

2. Suppress existing unfavorable base oil prop-erties (oxidation and corrosion control).

3. Impart properties to the lubricant that thebase oil cannot provide (EP, AW performance).

Lubricant manufacturers use a variety of addi-tives to support the basestock or add new proper-ties. There are a few standardized recipes that lu-bricant manufacturers might use to create the com-mon lubricant types: AW (antiwear), EP (extremepressure), R&O (rust and oxidation inhibited).

For this reason, it is always best to avoid mixingdifferent brands of lubricants, even within a partic-ular viscosity grade and additive type. In addition,practitioner should know about the following spe-cific additive properties:

1. Viscosity modifiers (VI improvers for hightemperatures; pour point depressants for lowtemperatures).

2. Wear resistance additives (EP and AW).3. Oxidation inhibitors.4. Demulsifiers.5. Foam inhibitors.

Viscosity modifiers help change the viscositybehavior of the lubricant across a temperaturerange. All base oils thin as the temperature rises.Viscosity modifiers help to slow the thinningprocess such that it is possible to use a lightergrade of oil for a cold-start requirement and stillhave sufficient oil thickness at normal operatingtemperature to protect the machine surfaces.

The tell-tale indicator for the use of a viscositymodifier is the ‘W’ designation in the label. A80W90 gear oil is one designed to behave like 80-weight gear oil during cold start-up and performlike 90-weight oil once the machine has reached itsnormal operating temperature.

Pour point depressants help a lubricant stayfluid to lower temperatures than would otherwisebe possible. Some lubricant base oils, particularlysynthetics, remain fluid to extremely low tempera-tures (-40 F) and do not require any help in thisarea. Most petroleum base lubricants are eitherparaffinic or contain sufficient paraffin stocks andhave a waxy component that causes the lubricantto solidify at low temperatures. The higher the vis-cosity grade, the higher the temperature at whichthe lubricant will solidify.

Pour point depressants prevent the waxy compo-nent (paraffin wax) from crystallizing, which, in turn,

lowers the point at which the lubricant solidifies. Wear resistance (EP and AW). There are two

classes of surface-protecting additives that arecommonly used in industrial machines. AW (anti-wear) additives work by forming resilient films onmetal surfaces that are somewhat like the layer oftarnish that forms on silver eating utensils. AWadditives often include zinc phosphorous chemi-cals that adsorb onto the metal surface to createan organo-metallic oxide layer. This tarnish-likelayer is easily rubbed off when the opposing metal-lic surfaces interact. The malleable oxide layerreforms and rubs away continuously, and at lowoperating component temperatures, leaving themachine component’s metal surface intact.

EP (extreme pressure) additives function simi-larly but have quite a different end result. EPagents are intended to prevent seizure of surfacesdue to severe metal contact where AW additivesare intended to prevent ongoing wear due to light-to-moderate metal contact. EP additives operateby chemically reacting with a metallic surface fol-lowing a destructive scoring or adhesive contactevent. The event produces spike temperatures andthe EP additives go to work at the localized hot sur-face. The EP agent, typically a sulphur-phospho-rous compound, chemically reacts with the hotarea forming an organo-metallic oxide layer that issofter and more forgiving than the underlyingmetal layer. Once the additives have bonded theyare removed only after another adhesive or abra-sive event scours away the organo-metallic filmand underlying metal surface.

The difference between the two is the way theadditives function and the amount of protectioneach offers. AW additives afford only mild wear

T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y M A R C H 2 0 0 8 3 3

CONTINUED ON PAGE 35

The type of oil filmcreated within themachine is dependenton the nature of themachine componentinteractions.

What’s in your bargainhydraulic fluid?

Fire-Resistant Hydraulic Fluids

The Answer Shouldn’t be a Costly SurpriseYou can spend less for a fire-resistant hydraulic fluid. But that

doesn’t mean you’ll save. In fact, a fluid that cuts corners to cut

cost is no bargain at all.

Bargain water glycol hydraulic fluids (WGHFs) are often made

with low-cost glycol bottoms instead of virgin glycol. Because

the content of glycol bottoms can be inconsistent and include

unexpected substances, fluid wear performance and corrosion

protection are unreliable. And that can mean expensive prob-

lems: Equipment damage. Downtime. Shortened service life.

Possibly even hidden health risks.

Choose UCON Hydrolubes for Proven ReliabilityIn contrast, UCON™ Hydrolubes are always made with virgin

glycols—not glycol bottoms. That means you get the performance

you expect and no hidden surprises. UCON Hydrolubes are FM

Approved† products, engineered for more than 50 years to

deliver consistent, reliable lubrication and corrosion protection.

Call to Receive Our Special ReportU.S., Canada, Mexico (toll-free): 1-800-447-4369

Latin America: (+55) 11-5188-9222Europe (toll-free): +800-3-694-6367

Europe: (+32) 3-450-2240Asia-Pacific (toll-free): +800 7776-7776

Asia-Pacific: (+60) 3-7958-3392www.ucon.com

With so much at stake, why settle for a cut-rate hydraulic fluid.

UCON Hydrolubes deliver performance you can count on. Not

less than you bargained for.

®™ Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow

† UCON Hydrolubes are tested to Standard 6930 Flammability Classification of Industrial

Fluids and approved by FM Approvals as “FM Approved” products.

UCON™ Hydrolubes

protection. In severe wear environments, they pro-vide little protection. When selecting oils for wearprotection, it is necessary to gauge how much wearthe normal operating environment will generate.

Oxidation inhibitors are provided to extendlubricant life cycles and reduce the formation ofoxidation reaction byproducts in the sump. How-ever, the primary driver for determining the typeand amount of oxidation inhibitors is the base oilquality and type.

High operating temperatures, high moistureand air concentrations and the catalytic effects ofwear metals all increase the need for oxidationinhibitors. The greater the additive treatment, themore complex the additive balance and the greaterneed for oxidation inhibitors.

Demulsifiers help the lubricant release mois-ture. This is important when the equipment isoperating in very humid climates or in a plantatmosphere that is wet or humid. Paper mills, steelmills and food-processing operations have signifi-cant exposure to water-based process fluids.

Although oil is hydrophobic it still retains a cer-tain amount of water from the atmosphere. Even atlow levels moisture is particularly harmful to lubri-cated components and increases wear from cavita-tion, adhesion and abrasion. In addition, whenmixed with heat and wear metals, moisture rapidlyaccelerates the rate of oxidation. Moisture controlis one of several critical contamination controlparameters.

Foam inhibitors help prevent accumulation ofair (formation of a foam layer) in the oil sump. Aircontains oxygen, which is a primary cause of oxi-dation. Foaming increases the extent of air-to-oilsurface contact and increases oxidation. Low vis-cosities do not require foam-release agents. Medi-um to heavy grade oils (ISO 150 and higher) tendto retain air and benefit from foam inhibitors. Thistype of additive is one of the few additives that canbe replaced if/when it is stripped from the lubri-cant through filtration or normal use.

Lubricant selectionFinished lubricants represent a carefully engi-neered balancing act between the strengths andweaknesses of the many types of additive agentsand basestocks. Practitioners should be well awareof the performance properties of the three com-mon types of finished lubricants.

■ R&O (rust and oxidation inhibited) lubricantsare selected for machines that operate with-out any expected metallic component interac-tion (a constantly turning journal bearing, forexample), where machines with interacting

components run with continuous moderate tohigh speeds and/or relatively low loads(pumps, compressors, bearing circulation sys-tems) and where the lubricant is needed pri-marily to keep surfaces wetted and protect thesurfaces from moisture-induced corrosion.

■ Antiwear lubricants are selected for machinesthat operate with expected metallic compo-nent interaction but where the interactionsare moderate to low loads and generally mod-erate to high speeds. These conditions arefound almost universally in hydraulic applica-tions where a significant amount of the AWproduct type is found. Other machines withlight and continuous machine interactionsalso may be served with AW products, such asplain and element bearing circulation sys-tems, crankcase applications (compressorcrankcases) and some instances of chain bathlubrication.

T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y M A R C H 2 0 0 8 3 5

Table 4. Lubricant types, additive concentrations and typical applications

CONTINUED FROM PAGE 33

CONTINUED ON PAGE 36

Finished lubricants area carefully engineeredbalancing act betweenthe strengths andweaknesses of themany types of additiveagents and basestocks.

36 M A R C H 2 0 0 8 T R I B O L O G Y & L U B R I C A T I O N T E C H N O L O G Y

■ EP lubricants are selected for machine appli-cations that operate routinely (by design)with continuous component interaction orwith high continuous loads and intermittentshock loading. EP lubricants are typically rec-ommended for geared machines (excludingthose with internal backstops and yellow-metal gears).

ConclusionMachine surface interactions dictate the type of oilfilms that form during normal machine use. Lubri-cant chemists work to define the types of condi-tions that exist and match the best blend of lubri-cant basestocks and additives to meet lubricantfilm requirements. There are many individual addi-tive functions, and three common types of finishedlubricant: EP, AW and R&O product types. Each ofthese product types can be achieved by blending awide variety of petro-chemical compounds, andsome of these compounds conflict with one anoth-er. Therefore, it is generally best not to mix finishedlubricants.

Once the lubricant types and grades are under-stood, it is possible to apply a systematic processfor identifying the best options from the wide vari-

ety of combinations of base oils, additives andlubricant weight grades.

In ensuing articles we will look more closely atthe oil films and the physi-chemical barrier films.We’ll also go through a systematic process forselecting specific product types and grades forfive common types of industrial machine compo-nents.

Mike Johnson, CMRP, CLS, MLT, is the principal consultantfor Advanced Machine Reliability Resources, headquarteredin Franklin, Tenn. You can reach him at mjohnson@amrri.com.

References

1. Heale, M.J. (1985), The Tribology Handbook, SecondEdition, Elsevier, p. A7 (Table 7.2)

2. Dension, D.H., Jr. (1944), “Oxidation of Lubricat-ing Oils: Effect of Natural Sulfur Compounds andPeroxides,” Industrial and Engineering Chemistry, 36 (5).

3. Gaw, W.J., Black, E.D., Hardy, B.J., “FinishedLubricant Benefits from Higher Quality BaseOils,” Hart’s World Conference on Refining Tech-nology and Reformulated Fuels, March 1997.

4. IBID, ref. II.

TLT

Services

We have detailed and specific experience in the following fields -

Tribology and Lubricant-Metal TribochemistryLubrication Technology : Lubricant Additives Interactions

Lubricant Development

Pitting Fatigue

Failure Investigation

Ultra-high Vacuum Tribology

Surface Analysis : Surface Corrosion Reactions

Trace Chemicals Analysis

Thickness and Composition of Surface Layers

Applied Radioactivity : Selection and Uses of Isotopes

Nuclear Methods of Analysis

6, Charney Ave., Abingdon, Oxon. OX14 2NY. England.

www.adtechconsultancy.com

Advance Tribology Consultancy

CONTINUED FROM PAGE 35