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Cutting Fluid Selection and ProcessControls for the Gear Manufacturing Industry

IntroductionThe last decade has been a period of

far-reaching change for the metal work-ing industry. The effect of higher lubri-cant costs, technical advances in machinedesign and increasing competition aremaking it essential that manufacturers ofgears pay more attention to testing,selecting and controlling cutting fluidsystems. lubricant costs are not a largepercentage of the process cost relative toitems such as raw materials, equipmentand labor, and this small relative cost hastended to reduce the economic incentiveto evaluate and to change cutting fluids.Nevertheless, one of the largest factorsin lost production during gear manufac-turing is excess tool wear, tool failure andsubsequent product rejection. In this dayand age of economic war of survival, ithas become essential to consider and toevaluate new cutting fluids with an eyetowards increasing tool life. improvingoverall productivity and product qualityand lowering costs.

Gear Cutting and FinishingA wide variety of manufacturing

techniques are used to manufacturegears. Specifically, this article addressesthe selection and process controls for thefluids used for gear hobbing, gear shap-ing and hard gear finishing.

AUTHOR:

MR. lKE TRIPP, JR. IS vice presiden: andgfflerai manager of £fnIl Products. Inc He hasbeen with the company since 1974. and is theauihor of over 30 techmcal papers on industrialmetalworking compounds He IS a member ofASLE. ASM. the Wire Association and SME.

Ike Tripp, Jr.Etna Products, Inc.Chagrin Falls, Ohio

Fig. 1- Gear hcbbing

The cutting tool used in gear hobbingis called the "hob". (See Fig. 1.) The ma-jority of hobs are cylindrical in form andgreater in length than in diameter. Thecutting teeth on the hob are arranged in

a helical thread corresponding to thethread of a worm. As the hob rotates intimed relationship with the gear blank,each row of teeth successively cuts thenext portion of the gear tooth-space. Thecutting action is continuous in one direc-tion until the gear is completed.

Conversely, the gear shaping methodoperates on the principle of two gearsrolling in mesh. In molding generatingprocesses, a gear-like cutter called ashaper tool is rotated and reciprocatedin the correct ratio with a gear blank.(See Fig. 2.) The gear blank rotates whilethe cutter rotates and reciprocates to pro-vide the cutting action. The shaper onlycuts in one direction so relief is providedfor the return stroke.

Fig. 2.-Gear Shaping

.July/August 1987 37

Hard gear finishing is a process whichuses either generative grindmg or fannedwheel grinding to finish the flanks ofparallel axis spur or helical gear~ afterthey have been hardened by heat treat-ment, The hard gear finishing techniqueusua1ly removes ,.0021 .0025" from eachside of the gear teeth,

In the form grinding process, thegrinding wheel has a profile mirroring thetooth space between two adjacent gearteeth. As the formed wheel moves be-tween the teeth of the gear, it removesexcess stock.

There are several types of machinesand tool configurations used in thegenerative grinding process. These pro-cesses either use a cutting tool designedas at. spur or helical gear, which grinds thegear using the shaving or gear shapingprinciple, ora. shaper cutter tool that usesa skiving principle or a worm type.finishing tool similar to a worm type geargrinding wheel.

Recently, grinding wheels plated withcubic boron nitride (CBN) have beenused in place of dressable, conventionalabrasive grinding wheels. CBN is a syn-thetic crystalline material that is verywear resistant, and it has pronouncedcutting edges because of its cubic shape.CBN applied by the electroplating pro-cess is considered the best for form geargrinding. CBN is very expensive, and itsuse dictates the need for improvedcoolants delivered at higher flow ratesthan used with conventional wheels.

Th.eory of LubricationThe aim of fluids used in cutting and

grinding operations is to provide coolingand lubrication.

Gear hobbing and gear shaping aremetal. cutting operations that generatechips. More than 97% of the cuttingwork appears as heat. Fig. 3 illustrates

a two dimensional view of meta] cutting.Of the heat generated, about two-thirdsis expended in sticking friction in theshearing zone, and one-third is expendedin sliding friction at. the tool/chip andtool/flank interfaces. The action of thefluid is ito [ower the heat generated inthese two zones, and the lubricant por-tion of the fluid reduces friction at the'tool/chip andtool/flank interface.

A fluid used in hard gear grindingoperation functions very much like a cut-ting fluid, but there are very pronounceddifferenoes between the dynamics of theprocesses, Gear grinding involvesnegative rake tool angles and randomorientation of cutting surfaces. Thetemperatures and surface feeds are alsohigher. Most of the heat of deformationis carried into the workpiece soa geargrinding fluid must act to reduce grindingforces, which reduces heat generation.The cooling function of the fluid is con-sidered secondary, but it is still impor-tant to the success of a hard gearfinishing operation,

Fluids used for gear cutting and grind-ing must exhibit a number of other pro-perties. They must not be adverselyaf-fected by metallic contaminants or trampoils that can enter a lubrication system.They must not leave excessive resldue onthe surface of a gear to be subsequentlyheat treated, and they should aid in theproduction of a gear that has, the desiredproperties - surface finish,runout, etc.

The study of the subject of wear be-tween two materials in motion relativeto ·oneanother is very complex, Anumber 'of parameters influence wear.Some of these include the shape of thecontacting bodies, applied load, relativevelocity between the surfaces, surfaceroughness, the elastic and plastic proper-ties of the contacting materials (par-ticularly those of the surface layers), and

fig. 3- Two-dimensional metal cutting diagram

SHEARANGLE

WORKPIECE

38 Gear Tecl1nology

the environment of deformation.

Types of Cutting FluidsA number of gear cutting and grinding

fluids meet the requirement of providingadequate lubrication. This range ,ofavailability was not always present, aslubricant research and development wasoncea black art with few practitioners,Now, through scientific research and thecooperative efforts of vendors andbuyers, lubricant development, applica-tion and behavior is becoming a 'science.

For the purposes of this article,lubricating fluids have been classified aseither oil-based or water emulsifiable.

Oil-Based Fluids.Oil-based fluids areused for gear cutting and hard gearfinishing where water emulsifiable com-pounds do not have the film strength orwetabili.ty to produce acceptable tool lifeor surface finish. Oil-based fluids aregen rally compounded with the follow-ing items:

1, Mineral oils, either napthenic gradethat have a saturated ring typestructure, or paraffinic grade,which have a straight or branchedchain structure.

.2. Mineral oils blended with polar ad-ditives, as the oils themselves ..arenonpolar. The function of the polaradditive is to affect the wetting ofthe metal surface at thetool/workpiece interface by reduc-ing the interfacial tension betweenthe mineral oi1 carrier and the gearblank. A polar additive has a sortof magnetism for the metal due toits molecular structure.

Polar active additives come fromseveral. sources. Animal. fats and oils arederived by rendering the f.atty tissues ofanimals such as cattle, pigs and sheep.Vegetable fats and oils are derived by

Table 1 - Coolants Grades by Contents

FAT

2 SlVHURANDIOR

HEAVY DUTY 10.1 CHL.ORINEWITH~FAT

FERROUS NON-FERROUS

SlMSYNTHETIC SEE MEDIUM DUTY SEE MEDIUM DUTY

SYNTHETIC NEW E P ADDITIVES NEW E P ADDITIVES

crushing and rendering the fruits ofplants such as palm or coconut trees.Marine fats and oils are derived fromcrushing and rendering the fatty tissuesof fish.

The mineral oils and polaradditivesare then often compounded with sup-plemental polar additives, which act asextreme pressure agents. The primary ex-treme pressure agents utilized are sulfur.chlorine or phosphorous. When sub-jected to the elevated temper.atUf'esat thetool/workpiece interface, these 'extremepressure additives react to form anorgano-metallic film which minimizesfriction and lowers heat generation.

Water Emulsifiable Fluids. Wateremulsifiable fluids are defined as thosewhere wate:r is the continuous phase ..Basically. water emulsifiable fluids com-bine the cooling properties of water withthe lubricating properties of anand/orvarious chemicals.

Over the years, a good deal of jargonhas evolved in the industry to describewater emulsifiable fluids for the gearmanubcturing industry, Water miscibleer ,emulsifiable lubricants are available in.many fonns. They can be classed basedon their components, performances andappearance.

Water soluble oils, sometimes called.emulsiens or walter miscible fluids, aremade by blending oil, either paraffinic Drnapthenic, with emulsifying agents. 5.0

the oil forms small droplets calledmicells, which range in size from .0002"to 0.00008" in diameter when mixed withwater. The emulsion appears milky asthe particles of oil reflect almost all ind~dent light, making them .opaque. Solu-ble oils are subdivided into light, mediumand heavy grades, dependmg on thecomponents used in their formulation.(See Table 1.)

Semi-synthetic fluids are mixtures .ofemulsifiers and surface-active chemicalsand have a low eil content of 10 % to25%. A typical soluble ell contains 45%to 70% oil, Because a semi-synthetic con-tainsless on than a water soluble lubri-cant, it can vary from being translucentto completely dear. as the micells rangein size between .000000n and .000001" indiameter. They can only be seen underan electron microscope.

Synthetic solutions are almost alwaysdear. as the particle size of the surface-

active agents and chemicals used in theformulation of the product are smallenough to transmit almost all incidentlight. True synthetics contain no mineraloil, and each component used in thefonnulation is soluble in water on itsown. The particles are smaller than.00000000H in diameter and cannot beviewed under any microscope.

GeneraUy most .of th wateremulsifiable fluids available contain anapthenic oil made soluble through theuse of emulsifiers or surface-activeagents.

The formulation of a comme:rcially ac-ceptable product depends on in-vestigating hu_ndredS ofemul ifiers whichcan be classed as:

1. Anionic- These are emulsifierswhose electrolytic properties arebased on the formation of anionicions. Examples include sulfonatedpolyester or sulfonated castor oils.

2. Cationic - These are emulsi ierswhose electrolytiC properttes arebased on the Iormation of cationicions. Examples .indude organic sal,t5

Hanslord Manufactunng Corp.31111 Winton Road SouthRochester, New York 14623,(71!6) 427-0660

CIRCLE A-15 ON READER REPLYCARD

..lllyIAugust 1987 3'9

or polyethoxylaredamines.

3. Non-ionic- These emulsifiers donot. behave as electrolytes and donot ionize in water. Examples in-clude ethoxylated vegetable oils.

Sllrtac,e-active or polar extremepressure additives are also added to theIorrnulauon of a water emulsifiable fluidto wet out and to penetrate thetool Iworkpiece interlace. These agen ts,reduce the interfacial tension between thewater, lubricant and the metal. The polaradditives have an affinity for the metalsubstrate and form an organa-metallicfilm which provides lubrication byreducing friction at the tool/workpieceinterface. There are a variety of oils, fats,waxes and synthetic polar additives suchas esters or complex. alcohols used assurface-active agents ..

Fluid Selection. A number of factors af-fect the type of fluid used in a gear hob-bing, gear shaping or hard gear finishingoperation. The primary criteria for selec-tion of material, which determinesmachinability, speed and severity ofoperation and the acceptability of a fluid,are alJ interrelated. Table 2 illustrates theadditives utilized when severity is corn-pared to difficulty of machinability.

The primary fluids used on CBNgrinding of hard gears are oil-basedbecause grinding wheel wear has beenfound to be related to the temperature ofthe wheel matrix ..As the temperature ofthe wheel matrix increases, the weal' ofthe wheel increases. Testing with bothoil-based and water-based Ilcids hasshown that oil-based fluids provided bet-ter lubricity and lower temperatures ofthe wheel matrix.

Another factor that influences grindingwheel. life is the cleanliness of the oil-based lubricant. The hard gear finishingprocess generates very fine swart whichmust be removed so as to' maximizewheel lif,e and improve surface finish.The most effective method of filtering agrinding oil-based Huid is a horizontalplate pre-coat Filter. The filteringcapability of a typical pre-coat filter isbetween one and three microns,

Testing and Process ControlsSelecting the appropriate lubricant for

gear hob bing, gear shaping or hard gearfinishing is very difficult. Effective tests

for screening the wi.de variety of 'can-didate Fluids must be developed. Thesecompounds vary greatly in theirchemical and physical properties, andbecause of the critical need for optimumtool life, any variation in the physicaland chemical properties of a given fluidbecomes important. To assure thereliability of a given fluid, many lubri-cant manufacturers perform a number oftests to assess its physical. chemical,metallurgical and humancompatibiUty.These tests yield data that ean be usedto, screen fluids prior to in-plant testing.

Physical L.abo~atory Tests. These labtests are designed to simulate as closelyas possible actual production conditionsand to generate data as to' the reliabilityof a fluid under actual conditions of use.

1. Stability of a neat oil. The productshould be stable under normal andadverse conditions. The followingtests can point out stability prob-lems: Place an ,eight ounce samplein a dosed sample bottle and allowi't to stand 21 to 30 days at ambienttemperature. Monitor for anychanges; i.e., separation, gelling. Totest the eHects of freezing and thaw-ing, put an eight ounce sample ofthe neat oil in a dosed containerand place the sample in a freezer for24 hours. Thaw, then refreeze for24 hours and thaw again. Examinethe neat oil for changes; i.e.,separation, sedimentation.

2. Nonferrous corrosion, One test fornonferrous corrosion is to place a30 ml sample of the neat fluid in a100 ml beaker and then to put aproperly abraded and cleaned cop-per strip in the beaker, heat to 220.F for three hours and check forstaining on the strip.

The eff,ect of a rutting and grind-ing fluid compound on the gearbeing manufactured must be as-sessed for two reasons.

a. Some of the 'extreme pressureagents, such as sulfur, used inthese compounds might corrodethe gear 'or the nonferrous partslike valve pipes and bearings inthe actual manufacturingmachine, as well as possiblyadversely affecting the finishedgear.

Table 2

IRIIIOIIII 4IC'IWE a M:INl$lOW 8WUII ....Ifllil

I...Ml'fIIII

SMIITY1IfWTAI.WIIIIIII80PfIIA1l0II

IMC1M ~ IIIC1M

MGt.,otI

_SPHD MJ .~.......-CI/Jl1IIII

--- 0fRIIWY1If11&- -..rt

b. Tests have indicated tha't it ispossible for sulfur used in ruttingfluids to, react with titaniumnitride coatings or CBNcoatings, causing erosion of thecoating and thus lowering tool.life.

3. Load carrying properties. The FourBall Test and the Falex Test weredeveloped to determine the loadcarryLng properties of euttlngandgrinding fluids.

a. Shell Four Ball EP J:est ASTM0-2596 and D-2783 .. The She[JFour Ball Test consists of four112" diameter balls arranged inthe form of an equilateraltetrahedron. The lower threehalls are held immovably in adamping pot to form a cradle inwhich the fourth ball is causedto, rotate about a vertical axis.The fluid under test is held in thedamping pot and covers the areaof contact of the four balls. Dur-ing the test, scars are formed onthe surface of the stationaryballs, and the diameter of thescars depends upon the load,duration, speed of rotation andtype of fluid. The scars ailemeasured by a microscope hav-ing a calibrated grid at the com-pletion of the test.

b. An alternative to, the Four Ball'test, the Falex test machine pro-vides a rapid means of measur-ing the load 'carrying capacities

and wear properties of a givenfluid. The test consists ofrotating a. test pin between twoloaded journal V-blocks im-mersed in the fluid sample. Thetest pin is driven by a 113 hpmotor at .290 rpm, and 'the [our-nalsare loaded against the testpin by means ofa spring gaugemicrometer. The Falex machineis also an extreme pressure tester,and can be used to conduct awear test, ASTM D-2670, toassess the effectiveness of a givenfluid.

4. Cast iron corrosion. This test is im-portant as the fluid must be testedto assess its effect on the interiorferrous parts of 'the gear cutting orgrinding machine. A chip test or aQ-Panel test conducted with aCleveland Condensing HumidityCabinet can assess the effect of agiven compound.

Chemica/.and Metallurgical Compatibil-ity. A candidate fluid must also be con-sidered from a chemical andmetallurgical standpoint. The gear hob-bing and gear shaping process and subse-quent hard gear finishing process involvethe exposure of unprotected, unoxidizedmetal surfaces to the chemical com-ponents of a lubricating fluid at elevatedtemperatures and pressures, Due to theelev-ated temperature and pressure, it isimportant to assess the effects of thosereactions prior to in-plant testing.

1. Turbine oil oxidation test ASTMD-943. This test predicts theoxidation life of hydraulic oil, tur-bine oil, and metalworking oils ..The test depends upon the catalyticeffect of metals at elevated'temperatures in the presence' ofwater to accelerate the rate of ox-.idation. The degree of oxidation isdetermined by an increase in theacid number of the oil

2. Rotary bomb oxidation test ASTMD-2272. The rotary bomb oxidation'test is a more' rapid method of com-paring the oxidation life of fluids insimilar formulations.

3. Turbine oil rust test ASTM 0-665.Contamination of gear manufactur-ing fluids with water can produce

rapid rusting of ferrous parts unlessthe oils are adequately treated withinhibitor compounds. The ASTMD-665 rust test is designed tomeasure the ability of industria'! oilsto prevent rust.

Process Controls forOil.-Based Compounds

There are many variables, such asfeeds, speeds and operator expertise, in-volved in the gear hob bing, gear shap-ing and hard gear finishing process;therefore, it follows that any variationin the effectiveness of a given lubricatingfluid will become important to overall.productivity and profitability. To assurethe long term reliability of each com-pound, i.tis important to monitor and tomaintain certain controls for straight oilcompounds.

1. Handling and storage - Oilsshould be stored at ambienttemperature. If the oil is frozen, itshould be thawed and mixed priorto use.

2. Temperature - It is important tomaintain the temperature of an 011-based fluid at ambient temperature;i.e., approximately 65° - 75°F, orat least to. maintain the temperaturebelow USaF if it is not possible tokeep it lower.

Excessive heat causes oxidationreactions which show up as sludgeformation, varnish formation andthe formation of acidic by-productswhich also cause corrosion. Theseby-products minimize lubricity. Ex-cessive oxidation can be controlledby maintaining correct operatingtemperatures.

3. Viscosity - The viscosity of astraight oil can change with timebecause of a number of factors,such as tramp oil leaking into thesystem or chemical reactions in theoil due to heat and oxidation.Viscosity is an important indicationof the condition of the oil.

4. Water and solids content - Properfiltration is necessary for good toollife and product quality, as excessmetal fines can plug supply lines orcatalyze chemical reactions to form.sludge or varnish ..

Wa't,er at quantities greater than

0.01 % by volume can cause a prob-lem because it turns to steam at thetool/workpiece interface, and thissteam blanket minimizes lubricity.

The level. of solids can be controlledthrough filtration, and the level ofsolids and water should be checkedperiodically to monitor the condi-tion of the oil.

s. Acid number - In oil-based fluidsthe acid number denotes the levelof acid-type components that in-fluence the behavior of the fluid.When oil. is oxidized, the acidnumber increases and adversechemical reactions, such as the for-mation of insoluble metallic soaps,'can occur. Therefore, it is impor-tant to monitor the acid number.

6. Additive content - Th additivesused to blend gear cutrlng andgrinding fluids are depleted throughuse; therefore, additive levels mustbe carefully monitored. The loadbearing capacity of a fluid is relatedto 'the concentration of theadditives.

7. Record keeping - A logbookshould be maintained to record 'thetest data. This logbook can be usedto track the performance of the oilin a system.

Quality Control of th« OperatingEmulsified Fluid. To effectively maintainan operating emulsifiable Iluid, theoperator is advised to observe severalbasic points.

1. Handling and storage - A goodemulsion starts with good storageconditions for 'the neat oil. Thecomplex chemical make up of mostemulsifiable fluids requires thestorage of neat oil al ambienttemperatures. If the neat oil isfrozen, it should be allowed toreturn to ambient temperature priorto. mixing the emulsion.

2. Mixing - As a general rule, mostemulsifiable fluidsal'e added towater in the reservoir whileagitating to form the emulsion, butthe supplier should always be con-sulted forcorr,ec't mixinginstructions.

3. Wat,er source and composition -Because water is a major compo-

Ju'lyj August 1981 41

nent of an operating emulsifiablefluid, its quality plays a large partin operating effectiveness, The lifeof the emulsion in the reservoir,foam characteristics, tool life andproduct quality are all influencedby the quality of the water. Make-up water should he as pure as possi-ble, Distilled or deionized water isidea" as hard water, which is con-taminated with minerals and dis-solved salts, adversely affects theemulsion. Basically, the mineralsand salts can cause corrosion prob-lems inthe equipment, and they canreact with the emulsifiers in thefluid to produce hard water soapswhich adversely affect emulsionstability and lubricity.

A reservoir supplying a gear cuttingor grinding machine is hot andaerated, which causes the water toevaporate. As this occurs, dissolvedsalts and minerals increase in con-centration, and, thus, evaporationaccelerates the formation of hardwater soaps. To counteract thisproblem, one should consider theuse of deionized water, boiler watercondensate or softened water tomake up water lost to evaporation,

4, Bacteria - In many systems,bacteria can become a problembecause bacteria degrade the emul-sion by digesting the emulsifiers andfats. This problem becomes moresevere as the bacteria secrete acidicwastes which adversely aff·ect thepH of the system, Changes in pHaffect emulsion stability and lubri-ciIy. There are a number ofbactericides available 'to control. theproblem.

S. Temperature - The tsmperature ofemulsions used to cut or grind gearsmust be kept between 1000 and1300 F. This is important for severalreasons.

a. If the emulsion is too cold, itmay not be fluid enough to bepumped to. the tool/work-piece interface, This could"starve" the tool and ad-versely affect tool life and pro-duct quality.

b. U the emulsion overheats, thehigh temperature degr.ades the

42 Gear Technology

emulsifier package, which af-fects stability. The highertemperature also does notallow for efficient heattransfer at the tool/workpieceinterface. This lack of coolingcan result in poor tool life andproduct quality, and oxida-tion of the oil phase of theemulsion. As a corollary toproblems caused by heat, therate of chemical reaction is in-creased and the formation ofinsoluble metallic soaps isaccelerated.

6. pH - pH is a measure of theacidity-alkalinity of a fluid .. pH iscontrolled by the content of thepolar additives, such as fatty acids.As detailed earlier, these polar ad-ditives 3Je responsible fora fluid'slubricity. If the pH falls because ofexhaustion of polar additives,lubricity will be diminished;whereas, if the pH rises too high,the emulsion will become unstable.Since the fatty acids affect pfl, it isimportant to measure them andmaintain pH at recommendedoperation levels. H is best to main-tain pH with regular additions ofneat oil.

7. Concentration - Maintaining thecorrect concentration of neat oil inthe reservoir is important becausetool. life and product quality willsuffer if the Iubrici.tyof thefluid is excessively diluted. Concen-tration can be monitored by theBabcock Method or by a hand-heldrefractometer.

8. Filtration - A dean fluid is essen-tial. to maintaining the emulsion,tool life and product quality. Gearmanufacturing fluid compoundscan be contaminated rapidly withthings such as oxide, chips, trampoil from lubricating or hydraulicsystems and even items such asfood, rags and mi.ll dirt. If thesecontaminants are not removedfrom the system,. the effective life ofthe fluid is shortened and productquaHty and productivity tails.

To overcome the inherent problemsassociated with disposal andreplacement of lubricants, it is im-

portant 'to filter the emulsion andextend its useful life.

9. Foaming - Care must be taken tomaintain pump seals so as tominimize pump cavitation andreduce foam. Excessive Ioamminimizes effective cooling andlubrication at the tool/workpieceinterface.

10. Record keeping - A log bookwhich can be used to record addi-tions of neat oil, temperature, con-centration, pH, etc. is important.The log book is a handy reference,providing a record of the operatingsystems.

Testi;ng in the PlantSeveral steps are required to insure 3.

successful in-plant testing program.

1. Obtain management commitmentfor a testing program.

2. Select a person to coordinatetesting. This person will serve as an.in-plant consultant and also pro-mote education of employees as tofluids.

3. Identify problem areas and initiatea program to evaluate lubricatingfluids.

4. Select vendors who are up to daterelative to the OSHA Hazard Com-munications Program.

S. Moni tor direct costs such as costper gallon, cost per pound and costof additions.

6. Monitor indir,ectcosts, such asmaintenance additives, cost ofdisposal and dumping frequency.

7. Find out if oil-based compoundscan be reclaimed to avoid problemswith disposal.

8. Monitor tool life by consideringoriginal cost and .reconditi.oningcost.

9. Consider finished product. qualityversus raw material utiliz-ed.

10. Monitor the condition of the fluidand of the gear manufactunngequipment relative to the fluidbeing used.

11 .. Evaluate the test program andreport results to management.

12. Implement changes wher,etheevaluation justifies the need.

13. Expand and maintain the testingprogram so as to be prepared Iorunexpected problems.

14. Be receptive to change as newtechnology supercedes the old.

After the testing program has beenestablished, it is important to have somemeans of measuring the effectiveness 'ofa given fluid when it is used on gear hob-bing, gear shaping or hard gear finishingoperations. Several test techniques areavailable that go beyond the simple toollife test.

"On~Une" Monitoring - Today'sstate-of-the-art CNC controls allow "on-line" optimizing and monitoring of cut-tin~ conditions during machine opera-tion. The information C3_nbe conect~d ona. peripheral microcomputer and ana-lyzed relative to changes in.cutting fluids.At the same time, new electronic gearchecking equipment can be used tomonitor such things as changes in pitch,involute and lead given changes, in cut-ting fluids or grinding fluids.

Statistical Quality Control - With theadvent 'of statistical quality control, it isnow possible to monitor product qual-ity relative to changes in the Huids usedon a g:iven gear hobber, gearshaper orhard gear .finishing machine. The qual-ity of the finished gear can varysignificantly based on the type of fluidbeing tested within the equipment.

Transducers for Fame and TorgueMeasurement - A muJti-componenttransducer can be used for analysis ofgrinding, This instrument provides ameasure of two Forces, the vertical forceand the vertical torque. In a typical ap-plication, this instrument would hemounted on the work table of the grinderand the test piece attached ina fixture onthe top of the instrument. The ratio ofthe vertical forc'f and the feed force isessentially a measure of the grindingfluid's effectiveness. -

New DevelopmentsThereare several new developments in

the field of lubricating fluids for tl'l? gearmanufacturing industry.

Microemulsions are generally clear IL~esynthetic solutions. Really an offshoot ofsemi-synthetics, microemulsions 'containa small amount of mineral oil in addi-tion to the other components which aresoluble in water. The difference is that

microemulsions are formulated to havesmaller micells than semi-synthetic emul-sions; hence, they have more dispersedparticles, The small micells aUow almostall incident light. to be transmitted. Thesmall miceUs mean microemulsions aregenerally marie stable than soluble oils orsemi-synthetics, Microemulsions have anumber of other advantages includinglow tendency to foam, non-corrosiveproperties, high detergency and wet out,reduced tendency to form insolublesoaps,easy rnixability and longer life ..

Synthetic hydrocarbons compoundedwith suitable diester fluids are yieldingnew high-molecular-weight syntheticfluids with superior viscosity index andshear stability compared to convendalpolymer-based viscosity improvers inhydrocarbon base stock. Synthetichydrocarbons exhibitexcellent oxidationand hydrolitic stability and have a veryhigh HIm strength. These synthetics aremore resistant to breakdown under hightemperature, and they are now beingblended intoa number of different gearcutting and grinding oils. Synthetichydrocarbons will probably not comeinto more widespread use until their costdecreases.

ConclusionThis article has reviewed lubrication

theory, fluid formulation, testmg andprocess controls. Particular emphasiswas placed on factors affecting fluidselection, classification and testing, toshed light on the chemical backgroundand maintenance of gear cutting andgrinding fluids. Rapid advances in gearmanufacturing technology, combinedwith customer demands for improvedproduct quality at lower cost, are mak-ing it essential that manufacturers ofgears obtain maximum utilization fromevery fluid used in a plant. Careful a't-tention to the techniques outlined in thisarticle can improve Auid maintenancethrough systematic checks. The attentionpaid to lubrication should yield im-proved product quality, higher produc-tivity and lower overall costs.

Refer'ences:1. SPRINGBORN, R.K., etal. Cutting and

Grinding RuidS: Selection and Applica-tion. ASTME, Dearborn, M[ 1967,

2. SCHEY, T ..A. Metal Deformation Pro-cesses: Friction and lubrication. MarcelDekker, lnc., New 'tork, NY, 1970.

3. HIXSON, D.R. "Countervailing CoolantForces,"Manufacturing Engineering, Oc-tober, 1980. p. 96.

4. REDGARD, M.P. ·Cutting Fluid Emul-sions," 1l1dustrial Lubrication andTribology, July/August, 1979. pp.149-152.

S. KIPP, E.M. 'Tribology Notes," Industriall.ubrication (;Ind Tr.ibology,September/October, 1980. PI'. 168-171.

6. JENTGEN, a.t, The Key Role ofLubrication. in Metal Defo.rmaJion Pro-~. SME, Detroit, Ml. 1972.

7, SCHEY, JOHN A. Tribol,ogy inMetalworking: Friction, Lubrication andWear. American Sodety of Metals,Metals Park, OH, 1983.

8. Federal Register, "CFR 1910:1200 HazardCommunication," Vol. 48, No. 228, Fri-day, November .25, 1983.

9, FELLOWS CORP,"Generating andChecking Involute Gear Teeth," GearTechnology, Ma.y/lune. 1986. pp, 38-48.

10. AINOURA, M., SAKURAGl. I..YONEKURA, M., NAGANO K. "AResearch on High-Speed Hobbins withthe Carbide Hob," Journal of MechanicalDesign, June, 1977. pp. 1-10.

n. MONCRIEFF. A.D. "Hard GearFinishing,' Proceedings of AGMAManufacturing Symposium, April, 1985.PI'. 1-23.

12. MAHAR, R.."Progress in CBN Produc-tion Grinding." Proc. Super Abrasives'85. Chicago, IL, 1985.

13. lANGE. J. "Gear Grinding Techniquesfor Parallel Axes Gears." GearTechnology. March/April, 1985. pp..34-48.

14. BOOTHROYD, G. Fundamentals ofMetal Machining and Machine Tools.McGraw-Hill.

Appendix A

Human Compatibility. Cutting fluidsmust be assessed not only from aphysical, chemical and metallurgicalstandpoint, but also from the point ofview of operator acceptability andsafety. Health and safety considerationsare discussed in Appendix A.

After the physical, chemical andmetallurgical studies have been com-pleted, it is important to assess the fluid'sacceptability from a operator's stand-point. The oil-based or water-based fluidof choice should not cause physiologicalproblems. It is important to recognizethat no material is competely hazard-

(continued on page 48)

July/August 198743

CUTTING FLUID SELECTION ...(continued from page 43)

free, but most fluids can be handledsafely given adequate safeguards.

One cannot simply pay lip service tothe acceptability of a given lubricatingfluid. Both labor and the general publicare now demanding that industry operatein a responsible manner that protects thehealth of workers, the general public andthe environment. increasing publicpressure prompted by major chemical ac-cidents in Bhopal. india, and severalsimilar, but less serious, accidents thatoccurred in West Virginia, has promptedthe federal and state governments toenact a number of new laws aimed ateliminating or reducing risk of exposureto hazardous chemicals.

One such law is the new federal stan-dard on Hazard Communication (29CFR 1910: 1200) thai was established bythe Department of Labor, OccupationalSafety and Health Administration(OSHA). As of November 25, 1985,chemical manufacturers, importers anddistributors are required to:

a. Label containers of hazardousmaterials and to provide MaterialSafety Data Sheets (MSDS) toanyone purchasing these chemicals,

b. Notify their employees of the haz-ardous materials in the workplace,

c. Demand appropriate training as tothe safe handling and use of thesematerials,

d. Properly label all hazardous mate-rials at the workplace,

e. Properly label all products shippedfrom suppliers,

f. File Material Safety Data Sheets(MSDS) that provide additionalhealth and safety information on allhazardous materials in theworkplace,

g. Post employee rights under the act,

h. Be in compliance with all require-ments of the Standard as of May2:5, 1986, as an employer in S[CCodes 20-39.

The new federal Standard on HazardCommunication has had a significant im-pact on all compounds containingpetroleum derived base stocks because

48 Gear Technology

OSHA has adopted the reports of severalmajor research groups into the Standard.

The International Agency for Researchon Cancer (lARC) has determined thatsome base oils are carcinogenic. An oilproduct which contains more than 0.1 %of such a base oil will be required byOSHA to have a statement On theMaterial Safety Data Sheet that it con-tains a carcinogenic component, and thatcomponent must be identified. The pro-duct container must also be labeled withsuch information. The oils in questionare primarily napthenic oils that have notundergone severe hydrogenation or sol-vent extraction.

At the same time. OSHA also requiresthat any product that contains a compo-nent having a polynuclear aromatic(PNA) content greater than 0.1 % to con-tain a statement to that eHect on theMSDS, as substances that contain .PNAare considered carcinogenic. Again, theproduct container must be labeled withsuch information.

Chlorine in the form of chlorinatedparaffin is a. widely used extreme pressureagent. Chlorinated paraffins have beentested, and OSHA requires that twotypes of these materials must indicate thepresence of a carcinogen on both thedrum label and the MSDS.

The concern over the carcinogenicnature of some base oils is justifiablefrom a health standpoint, as well as fromthe viewpoint of potential for adverseemployee reaction and litigation. Usersof all types of lubricating Huids are ad-vised to be familiar with the Standardand come into compliance.

Most manufacturers of gears use awide variety of lubricating fluids andvarious chemicals. but do not actuallymanufacture or import them for sale toothers. Therefore, the May 25, 1986, datewas the important cutoff for employersin SIC Codes 20-39, in that their HazardCommunications training program hadto be in place by that date.

There is a good deal of confusionrelating to the labeling of non-chemicalproducts. The OSHA standard does notrequire manufacturers of non-chemicalproducts to label or to supply MaterialSafety Data Sheets to customers. TheStandard provides complete exclusion forfour categories of items including articles.GeMS are an example of an article. While

customers of those items may requestMaterial Safety Data Sheets from theirsuppliers, it is not a legal requirement forthe supplier to provide one. Ultimately,many suppliers of articles are providingMaterial Safety Data Sheets, but it reallyis not necessary.

The OSHA Hazard Communicationrequirement is a good one. and manage-ment should support the law to the fullestextent possible ..There has to be a genuinecommitment to increasing the health andsafety of both labor and management.The compliance program must start froma base of respect for every individualemployed by a company. No companyhas ever gotten into financial difficultyor in trouble with OSHA because itadhered to a strict set of ethicalprinciples.

Acknowledgement: Presented Qt the SME Gem Pro-cesslllg Q1Id MIllluiuctwing Clinic. Novembi'r 11·13.

SdLQu.mburg. IL.