Lubrication Fundamentals 2011 Part 3 pdf

Tests for oxidation stability and bearing corrosion protection 2.. Someadditional new engine tests or extensions of existing engine tests are used to evaluate theability of oils to provi

Table 3.4 Gasoline and Diesel Engine Oil Tests

Sequence IID Rust and corrosionSequence IIIE Oxidation, varnish, cam wear

Mack T-6 Oil consumption, oxidation, piston cleanliness

Mack T-8 (T-8E) Oxidation, soot, filterabilityMack T-9 Ring-liner wear, bearing wear, extended drain capabilityCat 1-K Piston cleanliness, oil consumption, ring and liner scuffingCat 1M-PC Piston cleanliness, varnish, ring and liner wear

Cat 1-N Piston cleanliness, ring and liner wear, oil consumptionCat 1-P Deposit control, oil consumption

DD 6V-92TA Wrist pin bushing wear, liner scuffing, port depositsCummins M-11 Bearing corrosion, sliding wear, filterability, sludge

GM 6.2, 6.5 liter Roller cam follower wear, ring sticking

for their specific engines Examples are the Mack EO-L, EO-L Plus, and EO-M using theMack T-6, T-8, and T-9 engine tests Cummins Diesel uses the NTC 400 and the M-11tests All these engine tests are very expensive to develop and run, significantly increasingthe cost of engine oil development and testing All these tests can be grouped into eightcategories of performance measurement:

1 Tests for oxidation stability and bearing corrosion protection

2 Single-cylinder high temperature tests

3 Multicylinder high temperature tests

4 Multicylinder low temperature tests

5 Rust and corrosion protection

6 Oil consumption rates and volatility

7 Emissions and protection of emission control systems

8 Fuel economy

A summary of the common engine oil tests used in the U.S is shown in Table 3.4 Someadditional new engine tests or extensions of existing engine tests are used to evaluate theability of oils to provide extended drain capability The ability to extend drain intervals

is important to builders because of the pressure from users to reduce costs associated withmaintenance and also to conserve nonrenewable resources Extended drain capability isperceived by users to mean higher quality engines and oils

A Oxidation Stability and Bearing Corrosion Protection

Several engine tests are used to evaluate the ability of an oil to resist oxidation and oilthickening under high temperature conditions as well as to protect sensitive bearing materi-

als from corrosion The tests are operated under conditions that promote oil oxidation andthe formation of oxyacids that cause bearing corrosion Copper-lead inserts are used forconnecting rod and main bearings in many gasoline and diesel engines Even the fewengines that use aluminum rod and main bearings will use a lead-tin flashing for break-

in purposes Although the aluminum bearings are more resistant to oxyacid corrosion, theycan still experience some effects of acids in the oil After the tests have been completed, thebearing inserts are examined for surface condition and weight loss to determine the protec-tion afforded by the oil The engine is also rated for varnish and sludge deposits Themost commonly used bearing corrosion test is the CRC L-38 (CEC L-02-A-78), but theMack T-9 engine test also evaluates bearing protection capabilities of the oil

B Single-Cylinder High Temperature Tests

Single-cylinder engines are designed and operated to duplicate longer term operating ditions in a laboratory They are specifically designed for oil test purposes The tests areused primarily for the evaluation of detergency and dispersancy: that is, the ability of theoil to control piston deposits and ring sticking under operating conditions or with fuelsthat tend to promote the formation of piston deposits These tests also evaluate oil consump-tion rates All the current single-cylinder tests are of the diesel engine design After comple-tion of the test, the engine is disassembled and rated for piston deposits, top ring groovefilling, and wear The operating conditions for several of these tests are shown in Table3.5

con-C Multicylinder High Temperature Engine Tests

While the single-cylinder engine tests just discussed provide useful information and areextremely valuable in the development of improved oil formulations, there is a trendtoward use of full-scale commercial engines for oil testing and development This trendhas been precipitated by the different needs of the various engine designs as well by therequirement to satisfy demands for reduced emissions and improved fuel economy Thefull-scale engine tests are used to evaluate several of the oil’s performance characteristicsunder the different conditions subjected by the various designs Oxidation stability, depositcontrol, wear and scuffing, and valve train wear are a few of the oil characteristics evaluated

Table 3.5 Single-Cylinder Engine Oil Test Conditions

Table 3.6 Multicylinder Test Conditions

II 2500III 750

by these tests Some of the full-scale engine tests used to evaluate the oil’s performancecharacteristics are the ASTM sequence IIIE, Mack T-6 and T-7, the XUD 11ATE (CECL-56-T-95), the OM 602A (CEC L-51-T-95), and the Toyota 1G-FE (JASO M 333-93).Several of the multicylinder test conditions are shown in Table 3.6

D Multicylinder Low Temperature Tests

Since many engines can idle for long periods of time, particularly in diesel engines incolder weather or in driving conditions characterized by frequent starting and stopping,

it is important that the oil have enough detergency and dispersancy to satisfactorily controlsoot (unburnt fuel) and sludge in engines Both sludges and soot will increase an oil’sviscosity in addition to reducing antiwear protection, filterability, and fuel economy (higherviscosity reduces fuel economy) The oil’s detergency and dispersancy characteristics must

be balanced with the other performance requirements to handle the negative effects ofsoot and reduce the buildup of sludge in the engines that can often occur in low temperatureoperations Several multicylinder tests are designed to predict the oil’s ability to handlethe soot and sludging The Mack T-8, the M111 (CEC L-53-T-95), and the Sequence VEtests are used to evaluate low temperature sludge and soot handling capabilities of oils

E Rust and Corrosion Protection Tests

The ability to protect metal parts from rust and corrosion has received more attention inthe United States than in many other countries, probably because of the high proportion

of stop-and-go driving in combination with severe winter weather These conditions tend

to promote condensation and accumulation of partially burnt fuel in the crankcase oil,both of which promote rust and corrosion in addition to the soot and sludge problemsalready discussed Two engine tests are currently used to evaluate rust and corrosionprotection properties of oils These are the Mack T-9 and the sequence IID At the end

of the tests, valve train components, oil pump relief valves, and bearings are rated for rustand any sticking of lifters and relief valves is noted The Sequence IID test will be gradually

replaced by the ball rust test (BRT).

F Oil Consumption Rates and Volatility

There is a direct association with an oil’s volatility characteristics and oil consumptionrates Although volatility is not the sole reason for oil consumption in any given engine, itprovides a measure of the oil’s ability to resist vaporization at high temperatures Typically,distillations were run to determine volatility characteristics of base stocks used to formulateengine oils This is still true today The objective of further defining an oil’s volatility led

to the introduction of several new nonengine bench tests The most common of these tests

is the NOACK Volatility, Simulated Distillation, or ‘‘sim-dis’’ (ASTM D 2887), and theGCD Volatility (ASTM D 5480) All these tests measure the amount of oil in percent that

is lost upon exposure to high temperatures and therefore, serve as a measure of the oil’srelative potential for increased or decreased oil consumption during severe service Re-duced volatility limits are placing more restraints on base stock processing and selectionand the additive levels to achieve the required volatility levels As discussed inChapter

2(Refining Processes and Lubricant Base Stocks), more and more of the base stocks used

to formulate engine oils will be from API groups II, III and IV, group IV being PAOs

In addition to the bench tests already discussed, many of the actual engine tests monitorand report oil consumption rates as part of the test criteria Caterpillar, Cummins, andMack are all concerned about controlling oil consumption for extended service conditions

G Emissions and Protection of Emission Control Systems

Control of engine emissions is becoming increasingly important because of health aspects

as well as the long-term effects in the earth’s atmosphere (greenhouse effects) As a result,pressure is being placed on engine builders and users to reduce engine emissions Theseemissions include sulfur dioxide, oxides of nitrogen, carbon monoxide, hydrocarbons, andparticulates An oil can contribute to an engine’s emissions in several ways The mostcommon is by providing a seal between the pressure in the combustion chamber at therings and pistons Wear or deposits in this area will reduce combustion efficiency andlead to greater emissions Control of piston land and groove deposits is crucial to maintain-ing low oil consumption rates and long-term engine performance Oil can also contribute

to increased emissions by blocking or poisoning catalysts on the engines equipped withcatalytic converters Blocking of catalyst reactions can occur through excessive oil con-sumption, and the poisoning effects result from chemical components either in the fuel

or the oil’s additive package A common additive used in engine oil formulations is phorus, an element known to poison catalysts; yet phosphorus is a key element for protect-ing the long-term performance of engines Since phosphorus cannot currently be effectivelyeliminated from engine oil formulations, the oils are formulated to keep oil consumptionrates low, which minimizes the effects of phosphorus that gets into the exhaust gases

phos-H Fuel Economy

Related to emissions, the trend is to increase the fuel efficiency of both gasoline and dieselengines The first engine test developed to measure fuel economy was the Sequence VI,which was developed in the mid-1980s with a Buick V-6 This test was well correlated

to the now obsolete ASTM five-car test method The Sequence VIA replaced the Sequence

VI in the mid-1990s, substituting a 1993 Ford 4.6-liter V-8 A new test, the SequenceVIB, is replacing Sequence VIA in 2001 All the fuel economy tests indicate the importance

of oil viscosity in achieving mandated CAFE (corporate average fuel economy) ments The lower viscosity oils such as the 10W-30s and 5W-30s, and now 0W-20s which

require-are the principal recommendations of the automobile manufacturers, provide measurableeconomy benefits relative to heavier viscosity grades Although the foregoing tests areused to measure an oil’s contribution to fuel economy, the official federal test uses a carbonbalance of the tailpipe emissions, and it is this test that is used to establish compliance toCAFE requirements.

The automotive vehicles manufactured today and in the past have all required gearing ofsome sort to allow transfer of the engine’s power to the driving wheels This gearing iscomposed of a range of gear design encompassing spur, helical, herringbone, and/or hypoidgears All these gears require lubrication Just as there is a wide range of gearing andapplication requirements, so is there a range of performance levels to meet mild to severeoperating and application conditions

Finished gear lubricants typically are composed of high quality base stocks (mineraland/or synthetics) and between 5 and 20% additive, depending on desired performancecharacteristics Up to as many as 10 different additive materials could be used to formulatethese oils and, based on the increasing requirements of extended service intervals andenvironmental concerns, more may be needed These additives include antiwear com-pounds, extreme pressure agents, oxidation stabilizers, metal deactivators, foam suppres-sors, corrosion inhibitors, pour point depressants, dispersants, and viscosity index improv-ers As with the other high performance lubricants, these additives compete with eachother to perform their functions and must be balanced to provide the required performancerequirements

Three primary technical societies composed of and working in conjunction withequipment builders, lubricant formulators, additive suppliers, and the users of the equip-ment have combined efforts to define automotive gear lubricant requirements These threetechnical societies are SAE, ASTM, and API SAE has established the viscosity classifica-tion system (SAE J306) for automotive gear lubricants shown earlier (Table 3.2).ASTMestablishes test methods and criteria for judging performance levels and defining test limits.API defines performance category language In addition to SAE, ASTM, and API, theU.S military has established a widely used specification for automotive gear lubricants:MIL-PRF-2105E

Unlike automotive engine oils, there are no current licensing requirements for gearoils by API Some major OEMs, however, offer licenses to use their designations fortransmission and axle lubricants

The API performance categories are as follows:

API GL-1 Lubricants for manual transmissions operating under mild service ditions These oils do not contain antiwear, extreme pressure, or friction modifieradditives They do contain corrosion inhibitors, oxidation inhibitors, pour pointdepressants, and antifoam agents

con-API GL-4 Lubricants for differentials containing spiral bevel or hypoid gearingoperating under moderate to severe conditions These oils may be used in somemanual transmissions and transaxles where EP oils are acceptable

API GL-5 Lubricants for differentials containing hypoid gears operating undersevere conditions of torque and occasional shock loading These oils generallycontain high levels of antiwear and extreme pressure additives

Table 3.7 Gear Lubricant Testing

API MT-1 Lubricants for manual transmissions that do not contain synchronizers.These oils are formulated to provide higher levels of oxidation and thermal stabil-ity when compared to API GL-1, GL-4 and GL-5 products

The military specification MIL-PRF-2105E combines the performance levels of both theAPI GL-5 and MT-1 (Table 3.7)

In addition to the automotive gear lubricant tests, various car and other automotiveaxle and transmission manufacturers have gear tests, many of which are conducted in cars

or over-the-road vehicles, either on dynamometers or in actual road tests These testsgenerally represent special requirements such as the ability of lubricants to provide satisfac-tory performance in limited slip axles Generally, most laboratory and bench testing hasshown good correlation to field performance

VI AUTOMATIC TRANSMISSION FLUIDS

Automatic transmission fluids are among the most complex lubricants now available Inthe converter section, these fluids are the power transmission and heat transfer medium;the gearbox, they lubricate the gears and bearings and control the frictional characteristics

of the clutches and bands; and in control circuits, the act as hydraulic fluids All thesefunctions must be performed satisfactorily over temperatures ranging from the lowestexpected ambient temperatures to operating temperatures on the order of 300⬚F (149⬚C)

or higher, and for extended periods of service Obviously, very careful evaluation is quired before a fluid can be considered acceptable for such service

re-The major U.S automotive companies (General Motors, Ford, and DaimlerChrysler)continue to strive for improved automatic transmission fluids (ATF’s) These improvementsare aimed at fill-for-life applications (100,000–150,000 miles), which means that improve-ments are needed in oxidation stability, antiwear retention, shear stability, low temperaturefluidity, material compatibility, and fluid friction stability Ford Motor Company is looking

at additional improvements to their Mercon V; GM will update Dexron III to Dexron IV;and DaimlerChrysler has improved its MS 7176D specification to MS 9602

BIBLIOGRAPHY

Mobil Technical Bulletins

Engine Oils Specifications and Tests—Significance and LimitationsAdditives for Petroleum Oils

Extreme Pressure Lubricant Test Machines

Lubricating Greases

The American Society for Testing and Materials defines a lubricating grease as follows:

‘‘A solid to semifluid product of dispersion of a thickening agent in liquid lubricant.Other ingredients imparting special properties may be included’’ (ASTM D 288, StandardDefinitions of Terms Relating to Petroleum) This definition indicates that a grease is aliquid lubricant thickened to some extent in order to provide properties not available inthe liquid lubricant alone

I WHY GREASES ARE USED

The reasons for the use of greases in preference to fluid lubricants are well stated by theSociety of Automotive Engineers in SAE Information Report J310, Automotive Lubricat-ing Grease This report states:

Greases are most often used instead of fluids where a lubricant is required to maintain itsoriginal position in a mechanism, especially where opportunities for frequent relubricationmay be limited or economically unjustifiable This requirement may be due to the physicalconfiguration of the mechanism, the type of motion, the type of sealing, or to the need forthe lubricant to perform all or part of any sealing function in the prevention of lubricant loss

or the entrance of contaminants Because of their essentially solid nature, greases do notperform the cooling and cleaning functions associated with the use of a fluid lubricant Withthese exceptions, greases are expected to accomplish all other functions of fluid lubricants

A satisfactory grease for a given application is expected to:

1 Provide adequate lubrication to reduce friction and to prevent harmful wear ofcomponents

2 Protect against rust and corrosion

3 Act as a seal to prevent entry of dirt and water

4 Resist leakage, dripping, or undesirable throw-off from the lubricated surfaces

5 Retain apparent viscosity or relationship between viscosity, shear, and ture over useful life of the grease in a mechanical component that subjects thegrease to shear forces

tempera-6 Not stiffen excessively to cause undue resistance to motion in cold environments

7 Have suitable physical characteristics for the method of application

8 Be compatible with elastomer seals and other materials of construction in thelubricated portion of the mechanism

9 Tolerate some degree of contamination, such as moisture, without loss of cant characteristics

signifi-While the SAE statement is concerned primarily with the use of lubricating greases

in automotive equipment, the same considerations and performance requirements apply

to the use of greases in other applications

II COMPOSITION OF GREASE

In the definition of a lubricating grease given here, the liquid portion of the grease may

be a mineral or synthetic oil or any fluid that has lubricating properties The thickenermay be any material that, in combination with the selected fluid, will produce the solid

to semifluid structure The other ingredients are additives or modifiers that are used toimpart special properties or modify existing ones As shown in Figure 4.1, greases aremade by combining three components: oil, thickener, and additives

Figure 4.1 Grease components

A Fluid Components

Most of the greases produced today have mineral oils as their fluid components Theseoils may range in viscosity from as light as mineral seal oil up to the heaviest cylinderstocks In the case of some specialty greases, products such as waxes, petrolatums, orasphalts may be used Although perhaps these latter materials are not precisely describable

as ‘‘liquid lubricants,’’ they perform the same function as the fluid components in tional greases

conven-Greases made with mineral oils generally provide satisfactory performance in mostautomotive and industrial applications In very low or high temperature applications or inapplications where temperature may vary over a wide range, greases made with syntheticfluids generally are now used For a detailed discussion on synthetics, seeChapter 5

B Thickeners

The principal thickeners used in greases are metallic soaps The earliest greases were madewith calcium soaps, then greases made with sodium soaps were introduced Later, soapssuch as aluminum, lithium, clay, and polyurea came into use Some greases made with

mixtures of soaps, such as sodium and calcium, are usually referred to as mixed-base

greases Soaps made with other metals have been used but have not received commercialacceptance, either because of cost, health, and safety issues, environmental concerns, orperformance problems

The earlier forms of greases were hydrated metallic soaps, which were made by

combining steric acid with a soap These low cost greases provided good water resistance,fair low temperature properties, and fair shear stability, but limited temperature perfor-mance Improvements to hydrated greases were necessary to provide higher temperature

capability These improvements were made by use of 12-hydroxysteric acid with the metallic soaps to produce the next class of greases, anhydrous metallic soaps This change

increased dropping points above 290⬚F but the products were also more costly to makethe earlier than hydrated metallic soap greases

Modifications of metallic soap greases, called complex greases, are continuing to

gain popularity These complex greases are made by using a combination of a conventionalmetallic soap forming material with a complexing agent The complexing agent may beeither organic or inorganic and may or may not involve another metallic constituent.Among the most successful of the complex greases are the lithium complex greases Theseare made with a combination of conventional lithium soap forming materials and a lowmolecular weight organic acid as the complexing agent Greases of this type are character-ized by very high dropping points, usually above 500⬚F (250⬚C), and may also haveexcellent load-carrying properties Other complex greases—aluminum and calcium—arealso manufactured for certain applications

A number of nonsoap thickeners are in use, primarily for special applications fied bentonite (clay) and silica aerogel are used to manufacture nonmelting greases forhigh temperature applications Since oxidation can still cause the oil component of thesegreases to deteriorate, regular relubrication is required Thickeners such as polyurea, pig-ments, dyes, and various other synthetic materials are used to some extent However, sincethey are generally more costly, their use is somewhat restricted to applications wherespecific performance requirements are desired Lithium and lithium complex greases are

Modi-Table 4.1 Typical Lubricating Grease Characteristics by Thickener Type

excellent

Trenda

Principal usesb Thread Rolling contact General uses for Military

a Lithium grease over 50% of production and all others below 10%.

b Multiservice includes rolling contact bearings, plain bearings, and others.

Source: Courtesy of NLGI.

the most widely used greases today Table 4.1 outlines lubricating grease characteristics

as determined by thickener type for various major grease soaps

C Additives and Modifiers

Additives and modifiers commonly used in lubricating greases are oxidation or rust tors, pour point depressants, extreme pressure additives, antiwear agents, lubricity- orfriction-reducing agents, and dyes or pigments Most of these materials have much thesame function as similar materials added to lubricating oils

inhibi-Aluminum Calcium Lithium

reversible reversible inherent

Multiservice Multiservice Multiservice Multiservice Multiservice High

industrial industrial industrial relube)

In addition to these additives or modifiers, boundary lubricants such as molybdenumdisulfide or graphite may be added to greases to enhance specific performance characteris-tics such as load-carrying ability An EP agent reacts with the lubricated surface to form

a chemical film Molybdenum disulfide is used in many greases for applications in whichloads are heavy, surface speeds are low, and restricted or oscillating motion is involved

In these applications, the use of ‘‘molysulfide,’’ (or ‘‘moly’’ as it is sometimes called)reduces friction and wear without adverse chemical reactions with the metal surfaces.Polyethylene and modified tetrafluoroethane (Teflon) may also be used for applications

of this type

III MANUFACTURE OF GREASE

The manufacture of a grease, whether by a batch or continuous process, involves thedispersion of the thickener in the fluid and the incorporation of additives or modifiers.This is accomplished in a number of ways In some cases, the thickener is purchased bythe grease manufacturer in a finished state and then mixed with oil until the desired greasestructure is obtained In most cases with metallic soap thickeners, the thickener is produced,through reaction, during the manufacture of the grease

In the manufacture of a lithium soap grease, for example, hydrogenated castor oil,fatty acids, and/or glycerides are dissolved in a portion of the oil and then saponified with

an aqueous solution of lithium hydroxide This produces a wet lithium soap that is partiallydispersed in the mineral oil and is then dehydrated by heating After drying, the mixture

is cut back with additional oil and additives to produce the desired consistency and tion characteristics intended of the finished grease In this case, the dehydrated soap–oilmixture would be a plastic mass with a grainy structure During or following the cutbackoperation, the grease might be further processed by kettle milling or homogenization tomodify this structure Once the proper structure and consistency have been obtained, thegrease is ready for finishing and packaging

formula-As noted in the preceding discussion, manufacture of one of the basic greases volves all or some of the following five steps:

of the mixing kettle carries out heating and cooling of the grease Adding oil to thegrease also cools the grease to a temperature appropriate for both including additives andpackaging A typical batch manufacturing process is illustrated inFigure 4.2

As mentioned earlier, the structure may be modified by milling This milling may

be continuous in the kettle during the cooling period or it may be accomplished in aseparate operation If milling is done in a separate operation, a high shear rate pump,homogenizer, or colloid mill may be used Usually, the purpose of milling is to break afibrous structure or to improve the dispersion of the soap in the lubricating fluid Kettlemilling will break a fibrous structure, but milling in a homogenizer or other milling equip-ment is required to improve dispersion

During processing, grease may become aerated Generally, aeration does not detractfrom the performance of a grease as a lubricant, but it does affect the appearance and the

grease Most of the other tests that are used to describe greases come under the category

of evaluation and performance tests

A Consistency

Consistency is defined as the degree to which a plastic material resists deformation underthe application of a force In the case of lubricating greases, it is a measure of the relativehardness or softness and may indicate something of flow and dispensing properties Consis-tency is reported in terms of ASTM D 217, Cone Penetration of Lubricating Grease, orNational Lubricating Grease Institute (NLGI) grade Consistency is measured at a specifictemperature, 77⬚F (25⬚C) and degree of shear (working)

1 Cone Penetration

The cone penetration of greases is determined with the ASTM penetrometer, see Figure4.3 After a sample has been prepared in accordance with ASTM D 217, the cone isreleased and allowed to sink into the grease, under its own weight, for 5 s The depth the

Figure 4.3 Grease consistency by penetrometer: in the drawing the cone is in its initial position,just touching the surface of the grease in the cup; in the photograph, the cone has penetrated intogrease, and the amount of penetration is recorded on the dial