m —.

. .

TECHNICALNOTE4211

FRICTION STUDIES OF VARIOUS MATERIALS IN LIQUIDNITROGEN

By D. W. Wisander,W. F.Hady,andR. L.Johnson

LewisFlightPropulsionLaboratoryCleveland,Ohio

Washington

February1958

❑

TECHLIBRARYKAFB,NM

I!l!llllll[lll[llll!llllNATIONALADVISCIRYCOMMITTEEFORAeronautic OObb/i3h

TEKHNICALNOTE4211

FRICTIONSTUDIESOFVARIOUSMATERIALSINLIQUD NITROGEN

I&D.W.Wisander,W.F.Eady,andR. L.Johnson

F!ciction,wear,andsmface-failurepropertiesofvariousmaterialsweredeterminedinliquidnitrogen.Datawereobtainedata slidingvelocityof 2300feetTerminuteanda loadof 1000gramswitha hemi-

q sphere(3/18-in.radius) slidingontheflatsurfaceofa rotatingdisk.~

Variousmetalsandnonmetalsincludingcarbon,phenoliclaminates,andfilledTeflonwererunagainstmetals.Hlled Teflongavelowerfrictioncoefficients(0.15)andwearthananyoftheothermaterialsstudied,andshouldbe usefulas a sealandbearingmaterialin somecryogenicapplications.A carbonsealmaterialwitha phenolicimpreg-nantworerapidly.A metal-haloiclimpregnantgavethebestwearproper-

. tiestomoldedcarbon.Phenoliclaminates,formedthinsmearfilmsonmatingmetalsurfacesandgaverelativelyhighfrictioncoefficients(>0.5]. A cermetthathasbeenusedsuccessfullyasa high-temp”ffature$ sealringfailedbecauseof subsurfacebrittlefractureduringsliding.Decreasingtheloadto800gramsreducedthetendencytowardbrittlefracture.

INTRODUCTION

Friction,wear,andsurface-failurepropertiesofmaterialsslidingtogetherin cryogenicliquidarevitallyimportanttothedevelopmentofefficientpumpsforadvancedpowerplantsystems.Bearingsandshaftsealsinparticularhavecriticalslidingsurfacesandsreusedinalltypesof pumps.Positive-displacementpumpshaveadditionalpsrtssuchasvanes,pistons,org-s withsurfacesinslidingcontact.

Thephysicalandchemicalpropertiesofmostcryogenicliquidsofinterestaresuchthattheymipjhtbe expectedtohaveverypoorlubri-catingproperties.me dataofreference1,however,indicatethatconventionalbearingsandsealsmayoperatewithoutdifficultyinliquidhitrogenandhydrogen.Ibreference2 failuresw=e reportedforsomeminiatureballbearingso~eratingingaseoushydrogenat temp~atures

2 NACATN4211

approachingthoseof liquidnitrogenandhydrogen.*

Inthesameinvesti-gation,bearingsoftype440stainlesssteelweremadeto operatewithoutdifficultyby usingthickMicartaretainers. o

Temperaturemightbe expectedtoplaya vitalroleintheslidingpropertiesofmetals.Completesurfacefailureandhighwearofbear-ingmetalsareusuallycharacterizedbysurfacewelding.Reference3advancesthetheorythatthereisa “transitiontemperature”forsliding

—

metalliccouplesinanygivenfluidabovewhichweldingis observedandbelowwhich“slidingby shear”withoutweldingoccurs.Thetransition .%.-temperaturewasfoundtodependontheliquid,themetalliccouples,and .Etheslidingvelocity.Thisconcepttoomightsuggestthatitwouldnotbe difficulttoobtainsatisfactorymaterialsforslidingcontactincryogenicliquids. —

—

Thegenerallyacceptedadhesionconceptof slidingfriction(refs.4 and5) considersthatcoldweldingoccursbetweenslidfngmetalsinclosecontactandthatfrictionalforceistheproductofthecross-sectionalareaoftheweldedjunctionandtheshearstrengthofthemetalintheplaneof shear.E%aticfriction.aperimentsreportedinreference6 supporttheadhesiontheoryoffrictionat-temperaturesrangingfromthatofliquidhelium(4.2°K)up to6000K. Withmostmqterials, ufrictiondidnotchangesignificantlywiththevarioustemperatures.

.—

Surfacefilmsofoxideshavea primaryinfluenceonthefriction, hwear,andsurface-failurepropertieso?metalsin.slidingcontact(ref.7). Theliteraturecontainsnumerousinstanceswhereformationofoxidefilmsduringslidingpreventedsurfaceweldingofmutuallysolublemetalcouples.Manycryogenicliquids,includingnitrogenandhydrogen,preventthereformationorrepairof surfaceoxides,oncetheseoxidefilmsaxebrokenordisrupted.Theprobabilityofmetallicweldingcouldthereforebe greaterwhentheoriginal.oxide~Yer iswornaw’aYduringsliding.These~ectionof slidez.materialsincryogenicengineer-ing,therefore,mightbe morecriticalthanforapplicationsinroomatmosphere.Nonsolublemetalcouplesandcouplesincludinga nonmetallicmaterialmightbe ofparticularinterestforcryogenicslidingsurfaces.”

Thepresentinvestigationwasan exploratorystudyto determinethefriction,wear,andsurface-failurepropertiesofvarious.tyPesof slid~materialsoperatinginliquidnitrogen.Thedatawereobtainedwithasliding-frictionapparatusconsistingofa hemisphere-.tipped.(3/l6-in.radius)riderspecimenslidingin-a.circgmferentialyathontheflat —surfaceofa rotatingdisk(2.&+n.diameter]submergedinliquidnitrogen.A smfacespeedof 2300feetperminutewasc~osenasrefiesentativeofconditionsinsomepositive-displacementpumpsforcryogenicliquids.Thetestloadof 10CX3gramsgavean initialHWtz s~facestressof x.approximately150,000poundspersquareinchwithsteelspecimens.

—-

NACATN4211 3

●

●

Experimentalsamplesof someoftheslidermaterialsusedinthisinvestigationwereprovidedby TheIbrmicaCompany,PlasticsDivisionof The&rlockPackingCompany,PureCarbonCompany,MtcartaDivisionofWestinghouseElectricCorporation,andKoppersGmpany,Inc.

mPARAm ANDmmumTheapparatususedinthisinvestigationisshowninfigure1.

!lhebasicelementsconsistofa rotating-diskspecimen{~in. diameter,

l/2-in.thick)anda hemisphere-tipped(3/16-in.radius)riderspecimen.Theriderspecimenslidesina circumferentialpathonthelowerflatsurfaceoftherotatingdisk. Unlessotherwisespecified,thespecimenswererunsubmergedinliquidnitrogen.

Thediskspecimenwasdrivenbya 5-horsepowerhydraulicrotor.!d assemblythrougha 6:1speedincreasercapableof shaftspeedsashigh8@ as 29,000rpm. Surfacespeedwasusually2300feetperminute(5000y rpm)forthedatareportedherein;somedatasrereported,however,with

~ surfacespeedsup to 6400feetperminute.Twosetsofhelium-purgedshaftsealspreventedleakagefromthetestchmiber.Thelowerseal●

wasa double-bellowsfacesealwithcarbonsealringsslidingonbothfacesofa shoulderthatwasan imte~alpartoftheshaft.Theshaft

●wasmadeof type304stainlesssteel,asweremosttiternalpartsoftheapparatus.Theuppersealwasa doublecontrolled-gapsealthathadtwocloselyfittedcarbonringsslidingontherotatingshaft.

Theriderspecimenwassupportedbyanarmassemblythatallowedbothapplicationof loadandmeasurementoffrictionforceoutsidethetestchaniber.Theverticalshaftofthisasseniblywaspivotedthroughgitialbearingsmountedinthetophousing.Theshaftwassealedatthetopandbottomofthegifialmountingby flexiblemetallicbellowsand,inoperation,theenclosedvolumewaspressurized[7lb/sqin.gage)withhelium.Fkictionforcewasmeasuredlya strain-gagedynamom-eterringasseniblyconnectedtothetopoftheshaft.me deflectionnecesssryforfrictionmeasurementwasso snW_l(<0.CM33in.)thattherestrainingspringactionofthebellowswasnegligible.Thespringpropertiesof thebellowswereimportant,however,whereextremewearofriderspecimensnecessitatedconsiderable(>0.040in.)displacementofthearmtowardthecenteroftherotatingspecimen.Thisdeflectionofthebellowsreducedthetrueloadonthewearingsurface.Deflectionofthetopofthearminthedirectionof loadingwasmeasuredwithafixedmicrometer.Therunswe.yeterminatedifexcessivewearcaused20-percentunloadingofthespecimens.Previouscalibrationmadeitpossibleto determinetrueloadwithanyamountof deflection.Load

r wasappliedby a pulleyanddead-weightsystem.

4

4 NACATN4211

Thetophousingoftheapparatuswas-fi-sulatedby foamed-in-place ●

urethane.Thelowerhousingandthetransferlinewereinsulatedbyvacuumjackets.Thestaticheatleakintheapparatusresultedinvapor-izationof lessthan1/2literofliquidnitrogenperhour.

~Inopera-

tion,however,thevaporizationwasprimarilya resultoffrictionheatfromthetestspecimensandtheshaftseals.b mostcases,a 25-literDewarofnitrogenwassufficienttoprecooltheapparatusandmakeal-hourrun;a 100-literDeWarwassufficientfora 5-hourrun.

Theliquidnitrogenwastransferredtotheapparatus,as showninfigure2,by pressurizingthestorageDew” withgaseousheliumat”2to6 poundspersquareinchgage.Nitrogenwasforcedthroughthevacuum-jacketedl/4-inch-diameterstainless-steeltubingabout20feettothetestchamber.&@eousnitrogenwasventedthrougha 3]4-inch-diametertubewitha pressurereliefvalvesetat l+poundspersquareinchgage.

Theventlinewasinsulatedbyblocktiethanefoamfor3 feetbeyondthetestchamber.About2 litersof liquidinthetestchamberwasrequiredforproperoperation.Theliquidlevelwasdeterminedby carbonresist-ors atdifferentlevelsinthetestchamber.Althoughtheremotelyoperatedvalvesinthetransferlinewereeitherfullyopenor closed,itwaspossibletomaintainthedesiredflowratefortheproperliquidlevel(about3 in.abovethetestspecimens]by controllingtheDewarpressure.A safetycircuitmadeitimpossibleto closebothvalvesinthetransferlineat thesametime.

Stainless-steelo-ringswereoriginallyincludedintheapparatus_design.Wherepossible,thinsectionswereusedintheapparatustominimizeheatleak. Thistypeofdesignmadetheapparatustooflexibleto allowthehighclampingpressuresthatarenecessarywithstainless-steelO-rings.Hence,allthestaticsealsweremadeof eitherTeflonorKel-F.NotroubleexceptcoldflowhasbeenexperiencedwithTeflonandKel-Fstaticseals.TwoconcentricKel-F&ringswereusedasasealbetweenthelowerandupperhousingswhentheywereboltedtogetherbeforeeachexperiment.Theseringswerereused45timesormorebeforereplacementwasnecessary.

Theexperimentalmaterialsusedinthesestudiesarelistedintable1;theyincludeseveralmetalcouplesandseveralseriesofnon-metallicriderspecimensusuallyinconibinationwithtype304stainlesssteel.Thereasonsforselectingthevariousrideranddiskmaterialsarediscussedastheresultsarepresented.

Tbemethodsof specimenfinishingwerenecessarilyvariedbecauseofthegreatdifferenceinmaterials.Themetaldiskswereallfinish-groundonthetestsurfacesandhada surfaceroughnessof 4 to8 rmsasmeasuredwitha profilometer.Theriderspecimenswereusuallyfinishedona lathe,thetoolsandproceduresdependingonthematerial.

%wCn

Y

u

NACATN4211

.Extremelyhsrdmaterialswerefinishedby grinding.Theradius(3/16in.) of eachriderspecimenwascheckedwitha radiusgageand

= a stronglightsourcepriortotheexperiment.

Themetalspecimenswerecleanedby thefollowingprocedure:

5

mm (1)Washingina solutionof50percentacetoneand50 percent~ benzene

(2)

(3)

(4)

{5}

(6)

Repeatedscrubbingwithmoistlevigatedalumina

Washingintapwater

Washingindistilledwater

Washingin95percentethylalcoholor c.p.acetone

Dryingina streamofwarmajrandstoringina desiccator

Nonmetallicspecimenswerecleanedwithsuitablesolventsandstoredina desiccator.

dAftertheexperimentalspecimenswereinstalled,thelowerhousing

wassecurelyboltedinplace.Thesealswerepressurizedwithhelium,* andthetransfertube,thetestchanib~,andtheventwerepurgedfor

15minuteswithgaseousheliumornitrogen.ThestorageDeWarwaspres-surizedat 6 pounds persquareinchgagewithgaseousheliumornitrogen.Itrequiredat least20minutesto coolthetransferlinesandapparatusandobtainabout2 litersof liquidto submergethespecimensinthetestchaniber.me gaseousnitrogenwasventedoutsidethebuildingthrougha pressurereliefvalvesetat l+poundspersquareinchgage.

Withtheliquidlevelstabilized,thedriverotorwasturnedonanda predeterminedrotativespeed(5000rpm)obtained.The1000-gramloadwasthenappliedandtheexperimentbegun.Frictionalforcewasmeasuredby a recordingpotentiometerusedas a strainindicator.Dewarpressurewasadjustedtomaintainthedesiredliquidlevelinthetestchaniber.

Displacementof theverticalarmwascheckedwitha verniermicrom-eter,andtherunwasterminatedi.fwearwassufficientto causepartial(morethan20percent)unloadingofthespecimens.Specimensthatgaveacceptablewearwereusuallyrunfor1 to5 hours.Theoccurrenceofweldingandsurfacefailurewasindicatedby highandunstablefriction;suchrunswereterminatedaftera fewminutesofoperation.

w“ Aftercompletionoftherun,thelowerhousingwasrenmvedandthespecimenswereheatedwithan electricairheatertopreventcondensation

d

,.

6

ofatmosphericmoisture.mensquicklytominimize

NACATN4211

Itwasnecessarytoremovesomeofthespeci-.

corrosion.

Thewearofthespecimenswasdeterminedby: (1)measuringthe ●

diameterofthewearareaandcalculatingwearvolume,and(2)measuringweightlosswithananalyticalbalance.Wearwasalsocheckedduringtherunby themicrometer-displacementmethod.Thespecimenswerecare-fullystudiedandphotographedat lowmagnificationaftereachrun.Unlessnoted,allphotographsweremadeunderobliqueillumination. *

;C.rRESULTS

MetalsandMetal(bmpounds

Austeniticstainlesssteelisperhapsthemostthoroughlystudied(e.g.,ref.8)andmostgenerallyusedstructuralmaterialforcryo-genicequipment.Itisalsowidelyknownasan extremelypooralloyasfaras slidingfriction,wear,andsurface-failurepropertiesarecon-cerned.Thecatastrophictypeof surfacefailurethatoccurswithausteniticstainlesssteelin slidingcontactwithmetalsisexplained(ref.5,p. 81)by thefactthatthecon@etelyhomogeneousaustenitedoesnotprovideanycontaminatingphaseto inhibitsurfaceweldingand

v

adhesion.H, however,the“transition-temperature”criterionofrefer-ence3 wereapplicable(andthusresultinnowelding),theproblemofselectingslidermaterialsforcryogenicapplicationsmightbe more

b

easilysolved.

Resultsobtainedfromslidingausteniticstainlesssteel(t~e 304)on itselfinliquidnitrogenaregiveninfignre3. Theappearanceofthespecimensindicatedthatsurfaceweldingwascharacteristicof thisslidercouple.Hi@friction(p= 0.78),rapidwear[6.2x10-3cu in./hr],andcatastrophicmetaltransferoccurred.Itwasappmentthatthe“transition-temperature”criteriondidnotapplyinthiscase. Otherrunsatroomtemperaturein dry air and indrygaseousnitrogenproducedsimilarfrictionresults,butsurfacefailurewasmoreseverethaninliquidnitrogen.

Manycommercialballbearingshavecagesofpressedmildsteelandballsandracesof SAE52100or similarchromesteel.Theresultsofreference1 undernonsevereoperatingconditionsindicatethatbearingsof thistypewillrunin cryogenicfluidswithoutdifficultyforshortperiods.Ingeneralservice,mostball-bearingfailuresresultfromwearorgallingof cagesurfacesthatoperateinpuresliding.

Theresultsof slidingmildsteel(SAE1020)againstchromesteel(ME 52100)aregiveninfigure4(a). IYictioncoefficient(0.59)andwear(1.18x10-3cu in./hr}weresignificantlylowerthanthoseobtained

.,

NAC4TN42U 7

.withtheausteniticstainless-steelcouple.Thedisksurfaceshowedevidenceofmetaltransferfromtheriderspecimen.Thefeatheredmetal

& onthetrailingedgeoftheriderwearareaindicatedthatplasticflowoccurredatthecontactinginterface.AlthoughtheinitialHertzsurfacestresswasveryhigh(=150,000lb/sqin.),thefinalunitpressurebasedonprojectedwearareawaslow{e120lb/sqin.). It isinterestingthatplasticflowcontinuedto occurunderlownominalloadandat extremelylowtemperatures.“Atroomtemperatures,similarslidingexperimentsinairdidnotproduceplasticflowsosevereas thatshowninfigure4.

TWOspecimensofhardenedchromesteel(SAH521co)~=e ~n to-getherfora veryshorttimeinliquidnitrogento obtainthedataoffigure4(b). Thefrictioncoefficientwas0.52,whichisaboutthesameas thatobtainedatroomtemperature.Itmightbe expectedthat,inarunof suchshortduration(0.2rein},thenormaloxidefilminitiallypresenton themetalspecimenswouldbe capableofpreventingsurfacewelding.Thedisksurface,however,showedmetaltransfer;alsotheslightfeatheron thetrailingedgeoftheriderspecimenwasindicativeofplasticflowattheinterface.

Wrfaceweldingandmetaltransferwiththesemetalcouplesindicatew thatthelowtemperatureandanyboundarylubricatinginfluenceof the

liquidnitrogenwerenotsufficienttomaketheuseofthesecombinationspracticableundertheconditionsreportedherein.As previouslymentioned,

. witha surfaceoxidefilmwornaway,themutualvolubilityofmetalcouplesshouldbe of increasedimportanceintheoccurrenceof surfacewelding.Silverhaslittleorno volubilityintheprimaryalloyconstituentsoft~e 304stainlesssteel(refs.9 and10). Therefore,runsweremadewithcastelectrolyticsilverridersslidingon type 304stainlesssteel;theresultsareshowninfigure5(a). Severeplasticflowofthesilverwasindicatedby theextensivefeatheredge. !Ihisdetrituswasseparatedhorntheriderspecimenas a resultofhandlingaftertherun. Theinitialfrictioncoefficientwas0.80andthewearwas0.63x10-3cubicinchperhour.

Surfaceweldingintheusualsensedidnotoccur,buta thinplasti-callysmearedfilmofmetallicsilvexwasformedon thesteeldisk. Thereisnodoubt,however,thatthetrueslidingsurfacesduringmuchof therunweresolidsilveragainsta transferredsilverfilm. Chemicalspottestswereusedtoverifythatthefilmwassilverandto etchitawayfromthebasemetal.Theunderlyingmetalsufferedlittleor noweldingdeformation.Themetaltransferexperienc~inthiscasemightbe partlyexplainedby thetheory(ref.11)thatmetaltransfercanbe duetome-chanicalinterlockingofmetalsurfaceasperitiesorroughness.

As discussedindetailinreferenceE (p.548),tangentialforcesd betweenbodiesin contactproduceplasticyieldingandcontributeto thegrowthof thecontactarea.R&lucingtheeffectiveshearstrength(based

b onthefrictionprocess)attheinterfacecanthusinhibitplastic

8

flow,contactareagrowth,smearfilm.A hot-pressed

NACATN4211

.andpssiblytheformationofa transferredsilvkr,copper,andMS2 composition,reported

inreference13as a self-lubricatingbearingmaterial,shouldhaveless *plasticdeformationthansolidsilverbecausetheh% shouldreducetheeffectiveshearstrengthat theinterface. —

Datafora co~sitloncontaining85percentsilver,5 percentcop~r,and10percentM82 giveninfigure5(b)canbe comparedwiththedataof figure5(a]forsolidsilver.mere wasa markedreductionintheamountof silversmearedonthematingsurface,andno evidence ;ofweldingdeformationofthebasemetalcouldbe detected.Thefriction ulcoefficient(0.34)wasmoreconstantandsignificantlylowerthanwithsolidsilver.Weer(0.66x10-3cuin./hr)wasessentiallythesameas forthesolidsilver.ItappesrsthattheimprovedlubricationbytheM~-containingmaterialwassufficientonlyto compensateforthepoorerphysicalstrength.Thecastsilverwouldhavegreaterstrengththanthehot-pressedbodyweakenedbytheinclusionofa solidlubricant.

Observationoftheplasticbehavior[ductility)ofthevariousmetalcotiinationsduringslidinginliquidterialsnormallyconsideredbrittleatroomtobe usefulin cryogenicapplications.Ina titaniumcarbide-basecermetwasfoundtosurfacefailurewhenrunagainsttoolsteel

nitroge~indicatesthatma-temperaturemightcontinueunreportedNICAexperimentshavelowwearandto resistattemperaturesfrom800to

7000F. Experimentswereperformedinliquidnitrogenwiththecermet

[K162B)slidingagainsthardened440-Cstainlesssteel.HighhardnessRockwellC-54)ofthematingdiskwasutilizedinorderto obtaintheminimumrealareaof contactandsustainthehighcontactstressesthatshouldprovidea continuingseveretestofa brittlematerial.Thedatashowninfigure6{a)indicatethatthetestwastooseverewiththe1~0-gramnormalload.

Subsurfacebrittlefractureappearedtohaveoccurredinthecermetrider.Bothhighfriction(W= 0.63)andhighHertzsurfacestress(>150,000lb/sqin.}probablycontributedto thesurfacedeterioration.Thenominalwearrate,basedonvolumecalculatedfromtheprojecteddiameteroftheweararea,indicatesthatwearwasrelativelylow(0.05x10-3cuin./hr).Thesurfaceoftheridershowedseveralfurrowswherelocalfractureoccurred.Theconsiderabledepthofthefurrows,however,makesthewearrateof questionablesignificance.Theriderirregularitiescutgroovesintheweartrackon thedisk. ‘Il=emS noevidenceof surfacewelding;however,thiscouldhavebeenmaskedby thesurfacefracture.

Figure6(b)showstheresultofreducingtheinitialloadto800gramsforthecombinationofKl_62Bcermeton44CLCsteel.Friction

NAGATN4211 9

.remainedhigh,wearwaslow(0.014x10-3cuin./hr),buttheseverityofsurfacefracturewasreduced.‘lhediskshowedsomeevidenceoftrans-

b ferredparticles,whichmayhavebeenenibeddedfragmentsfromtherider.

Nonmetals

Theuseofnonmetalsincryogenicbearingsandsealswouldseempracticablebecause,asa group,theyareconsideredinherentlynon-weldingtometalsurfaces.Mlded carbonproductsshouldbe ofparti-cularinterestbecausetheyareusedforslidingcontactsealsonro-tatingshaftsmoreoftenthananyothertypeofmaterial.~lded carbonsimpregnatedwithphenolresinsarefrequentlyusedinalltypesof seals,includingsomeforcryogenicapplications.~ese andothercarbonsandtheirhigh-temperaturew-r propertiessredescribedinreference14.

Duringthepreliminaryoperationoftheapparatus,anobservationworthyof commentwasmadewitha carbonmaterial.-me experimentswererunwithan openDewarinsteadoftheclosedtestchamber.TheopenDewarwasraisedintoplaceto submergethetestspecimens,thusquenching

y themrapidlyfromroomtemperature.Runsmadewitha phenol-impregnatedM carbon(Purebon~] slidingontype304stainlesssteelgaveverylowu wear(0.009xl&3cuin.~hr]as indicatedinfigure7(a}. Therewasno

surfacedisturbanceonthediskandonlyslightevidenceof solidcontact., Whenthesamecotiinationwasrunintheclosedtestchaniber,entirely

differentresultswereobserved[fig.7(b)}.Sevenduplicaterunsgaveextremelyhighanderraticwesrvaluesfkom34x10-3to 91K10-3cubicinchperhour. ComparingthesedatawiththoseobtainedwtththeopenDeWar{O.009x10-3cuin./hr) showsthattheclosedsystemresultedinup to10,000timesgreaterwearrate. Theapparentexplanationforthisdif-ferenceisthatwiththeopenDeWaradsorbedmoisturefilmson boththecarbonandthemetalsurfacesandwithinthecarbonbodywerefrozeninsituwhenthespecimenswffeplungedintoliquidnitrogen.me stand-=d=sed system,however,providedforpre~gm ofthetransferl~es~thetestchamber,andventlineswithhelium@s. ~iw thePrecool@periodbeforeliquidc?ntactedthespecimens,gaseousnitrogenof’de-creasingtemperatureflowedthroughthesystem.Theflowofgasthroughthesystemwasbelievedtohaveremovedthemoistmefilmsadsorbedbythetestspecimensduringthebriefexposuretoroomatmospherethatwasnecessaryforinstallationintheapparatus.

Thesamebasicgradeof carbonwasalsorunwithno impregnant(PurebonP5),witha doublephenolic~PreWnt (-ebon 652),and~than organic-metalliccompleximpregnant(W=rebonP5HT).W addition,datawereobtainedwithanotherphenolic-impre~tedcarbonmterial(Graphitar39)thatis comparablewithPurebonP5J. Thesurfacesof thesecarbon

$ materialsaftertestwereverysimilartothatshowninfi~e 7(b);thewearrateswereallhigh(from10xl.0-3to 30K10-3cuin./hr);andthe

10

initialfriction0.53to 0.62fororganic-metallic

NACATN4211

coefficientswere0.84forthenonimpregnatedcarbon,thephenolic-ingpegnatedcarbon,and1.C$3forthecompleximpregnatedmaterial.

Serviceexperiencewithcarbonbrushesofaircraft-enginegeneratorshasshownthatrapidwearcanoccurathighaltitudes.Laboratoryexperi-ence(ref.15)indicatedthatthiswearphenomenon,called“dusting”?oc-curredintheabsenceofmoistureandoxygen.Insomeinstancesdustingwaseliminatedby theuseofa metal-haloidimpregnantthatwascapableofforminga protectivesurfacefilm.A carbonmaterialhavingsuchametal-haloidimpregnant(PurebonF5N)wasrunagainsttype304stainlesssteel.Itgavemch lowerwear(1.04x10-3ctiin./hr)thanthephenolic-impregnatedcarbon,butthefriction(~= 0.59)wasaboutthesame.Themetal-haloidimpregnatedmaterialwasthebestcarbonruninliquidnitrogen,butwasnotsogoodas othernonmetalstobe discussedlater.

Fabric-1aminatedphenolicresins(forexample,MicartaandFormica)havefoundnumerousapplicationsas slidingsurfaces.Rolli~-contact-bearingretainersmadeofphenolicshavegivenexcellentserviceinhigh-speed,normal-temperature

[.c2750F)applicationsandmayhavepromise

at cryogenictemperaturesref.2).

Severallaminatedphenolics(seetableI(b))wererunagainsttype304stainlesssteel.Itwasfeltthatvariedfinenessofthefabricandadditionsof solidlubricantstothematerialsmightinfluencewearandfrictionproperties.Thelowest.initialfrictioncoefficientobtainedwitha cotton-fabric-laminatedphenolicslidingagainsttype304stain-lesssteelinliquidnitrogenwas0.49.Theadditionofgraphiteandmolybdenumdisulfideneitherreducedwearnorlowere”d“friction.Forexample,FormicaINgavea wearrateof 0.11x10-3cubicinchperhour,andtheadditionofgraphiteorM& resultedinwearratesfrom0.28x10-3to 0.42x10-3cubicinchperhour. me additivesalsohadanadverseeffectonfriction,resultingininitialfrictioncoefficientsfrom0.81to 1.40.

A fiberglass-filledmelamineresin(ForxiicaFF-55)wasreportedbythemanufacturertohavegoodstrengthproperties.atcryogenictempera-turesandwasthereforeconsidered-asa slider-terial. me resultsindicatedextremelyhighwear(10.6x10-3ggig./hr),highfriction(p=l.04),andabrasionofthemetalsurfacebytheglassparticle~..:

‘Ibesurfacesofallthephenolicmaterialsweregoodafterslidingcontact.(Seefig.8,forexample.) Thematingmetalsurfaceusuallyhada slightlyburnishedtransferfilm.ASmentioned,highfrictionwasnotedforthephenolicmat~.ials....I@mrnlsheda~y~ance.qndhigh ,

.. ...

NACATN4211 11

.frictionsuggestthat heatdissipationmom theinterfacemaybe a prob-leminspiteofthelowtemperatureof liquidnitrogen.

bTeflon(Polytetrafluoroethylene)andKel-F(polytrifluorochloro-

ethylene)havefoundconsiderableapplicationincryogenicstaticseals.Thesematerialsalsohaveexcellentfrictionpropertiesunderlow-speedslidingconditions(ref.16). Thelimitingfactorsintheuseof Teflonforhigh-speedslidingapplicationsappeartobe itspoorabilityto con-ductheatfromtheslidinginterfaceanditstendencyto cold-flowunderload.Kel-Fhassomewhatlesstendencyto cold-flowthanTeflon.Fillers,suchas graphiteormetals,canbe addedto Teflontodecreasecold-flowtendenciesandshouldalsoincreasethermalconductivity.Reference17reportsthefrictionandwearpropertiesofa varietyoffilledTefloncompositions. Someofthemosteffectiveusesof Tefloninlubricationhavedevelopedfromitsapplicationsinthinfilmsonmetals,suchasthosedescribedinreference18.

Figures9(a)and(b)showsurfacesthatweretypicalof TkflonandAl filledTefloncompositionsslidingontype304stainlesssteelinliquid3.-Q nitrogen.Theriderspecimenswerealwaysverysmooth,usuallyhighly

reflectiveto light,andshowedno evidenceofanyadverseslidingcondi-‘1 tions.Thehighlyreflectivecharacterofthewesrsurfacesmadeitpos-a sibleto detectelasticrecoverythatwasata maximuminthecenterof

thecontactarea.A quantitativeevaluationofthiselasticbehavioris● beyondthescopeofthisinvestigation.Thediskspecimenshadvery

snoothhighlypolishedsurfacesinnmstcases.However,thinuniformtransferfilmsoftheTefloncompositionswerevisibleonthedisksafteroperation.EtchingofthedisksurfacesthathadkeenrunwithunfilledTeflonshowedthatthetransferfilmonthediskwashighlyprotectivetothebasemetal.

Figure10 summarizeswearandfrictiondataformostofthematerialsstudied.As figure10shows,thewearandfrictionfortheseTefloncowpositionswas,ingeneral,lowerthanforanyothertypeofmaterialcon-sidered.Thebehaviorwassomewhaterraticindifferentexperimentswithoneofthebestcompositions,as indicatedby thehatchedareainthebargraphs.Wearofthegraphite-filledmaterialinonerun(0.011x10-3cu in./hr)wasnearlytentimesgreaterthaninanotheressentiallyiden-ticalexperiment(0.0013~0-3cuin./hr).Frictionforcealsohadperiodicfluctuationsduringtheindividualruns. Closeexaminationofthespeci-mensshoweda lackofhomogeneity,whichistheprobableexplanationofthesevaryingresults.BImanycasesitwaseasyto identifyverylargeaggregates(approxiutelyl/16-in.diameter)of Teflonparticles.

Glass-filledTeflonhadrelativelygoodcharacteristicsbutdidnotgiveas lowwearorfrictionas a graphite-filledTeflon(fig.10). The

-’ glass-filledTeflondidnotabradethematingmetalsurfaceincontrastto theresultswiththeglass-filledmelamineresin.

12 NACATN4211

MLscellaneousObservations

Thelubricatingabilityof liquidnitrogenwasnotevaluated,perse. Significantdifferenceswereobserved,however,whenseveralmateri-alswererunindryairatroomtemperature,indrygaseousnitrogenatroomtemperature,or indrygaseousnitrogenattemperaturesapproachingthatoftheliquid.Inparticular,wearwassignificantlyhigherforthenonmetalsrunninginthegases.Therelativeeffectofthegasesandtheliquidon tiictionwasnotsowelldefinedastheeffectonwearintheselimitedexperiments.

IsolatedexperimentswithbothEWE52100andtype440-Csteeldiskswererunwitha fewoftheridermaterials.Withthevarioustypesofnonmetalsstudi~,theriderspecimensinliquidnitrogenalwaysshowedlesswearslidingagainstSAE52100andtype440-Cthanagainsttype304steel.

Theeffectof slidingvelocityonwearwasdeterminedfortheTefloncompositioncontaining10percentgraphite.Figurel.1showsthewearperunitdistanceof sliding.Below30(X)feetperminute,thecurveindicatesthatwearincreasedlinearlywiththeslidingvelocity,aswouldbeex- —

pettedwithadhesivewear. Thecurveshowsthat,at slidingvelocitiesabove30W feetperminute,wearincreasesexponentiallywithsliding

t

velocity.w

EVALUATIONOFRESULTS

Liquidnitrogendoesnothavetheabilityto formthestronglyad-sorbedinterfacefilmthatisbasicto effectiveboundarylubrication,butitdoesprovidean excellentheatsinkforfrictionalenergy.ThischaracteristicprobablyaccountsforthegoodperformanceoffilledTefloncompositionsintheseexperiments.Someresultsindicatethatthewearof oneofthesecompositionsincreasedata greater-than-line=rateas slidingvelocitiesincreased.A similarincreaseinweexwithgreaterloadsmightbe expected.Athigherratesofheatrejectionfromthespecimen,heattransferfromtheinterfacemaynotbe adequatetopreventthermaldegradationoftheTeflon.

TheTefloncompositionreportedweresamplesof commercialproductsanddidnotgiveconsistentresults.Therewasa markedlackofhomo-geneityinthesematerials,whichwasalsotrueforsimilarcommercialmaterialsfromothersources.Homogeneousmaterialscanbe obtainedbymorecarefulprocessingandshouldgiveconsistentresults.TbeworstresultsforthefilledTefloncompositionswerebetterthanthemostfavorabledataobtainedwiththeothertypesofmaterialsstudied. —

aMetalcouplesslidingtogetherinliquzdnitrogengavefrictionco-

efficientsthatweresimilarinmostcasestothoseobtainedat-.

.

NACATN4211 13

mWYr-&-

.atmospherictemperatures.Adhesionofmetalsby weldingoccurredinspiteofthelowanibienttemperature.Frictionalheatingat theinter-

. faceundoubtedlycausedsurfaceasperitiestoexperiencehighflashtemperatures.Reference5 (p.57)indicatesthat,duringslidingatlightloadsandlowspeedsandinthepresenceofa liquid,surfacetem-peraturesofmetalsmaybe severalhundreddegreesCentigradeabovetheambienttemperature.!Ihissuggeststhatthethermalaspectsof surfacewelding(ref.19]maybe importantduringslidingcontact,evenat thetemperatureof liquidnitrogen.

Solidvolubility,alloyingcharacteristics,andsimilarcriteriaarenotsufficientguidesforselectingmetalcouplesto slideinliquidnitrogen.Transferofridermaterialstothemetaldisksoccurredbothwithnonsolublemetalsandwithnonmetals.b suchcasessmearfilmswereformedonthedisksbuttherewasnodetectabledistortionofthebasemetal.

Smearingandtheplasticgrowthof slidingJunctionsmayhavepro-gressedasa resultofthermalsoftening.Themetalslidingsurfacesexhibitedsurprisingductility.Theliteraturesuggests,however,thatthisductilityneednotbe associatedwiththermalsofteninginanyway.

● Forexample,itwasdemonstrated(ref.20,p. 26)thatsomeausteniticstainlesssteelshadbetterductilityat subzerotemperaturesthanatroomtemperature.Reference20 suggeststhatthecohesivestrengthofthe

. metalincreasesrapidlyat subzerotemperatures,withtheresultthatthemetalresistsfractweuntiltheplasticdeformationisconsiderablygreaterthanwould.be possibleatroomtemperature.Thisobservationshouldnotbe confusedwiththepropertyof impactstrengthat lowtemperature.

CONCLUDINGREMARKS

An exploratorystudywasmadeof thefriction,wear,andsurface-failurepropertiesofvariousmetallicandnonmetallicmaterialsslidingtogetherinliquidnitrogen.Datawereobtainedat a slidingvelocityof2300feetperminutewithan initialloadof 1000gramsona hemisphere-tipped(3~16-in.radius)riderspecimenslidingontheflatsurfaceofarotatingdisk(usuallytype304stainlesssteel).

FilledTefloncompositions,suchas onecontatiiu10Percentgraph-ite,gavelowfriction{v= 0.12to 0.15)andwe=. Theymaybe usefulas sliderandbearingsurfacesin cryogenicliquids.Fatlureof !l?efloninsliderapplicationsatrmm temperaturehaspreviouslybeenassociatedwiththermalde~adationaccentuatedby poorthermalconductivity.cool-ingby theliquidnitrogenprobablyplayeda vitalroleinthegoodre-

S sul.tsobtainedwithTefloncompositions.

.

14 NACATN4211

I&ictionandsurface-failurepropertiesofmetalcombinationsinliquidnitrogenwerebasicallythesameasatroomtemperature.Metaltransfereitherby weldingorby mechanicaladhesionoccurredwithbothsoluble(304on304)andnonsoluble(silveron304)metalcombinations.Considerableplasticdeformationwasobserved,andinterfaceductilitywasgreaterthanatroomtemperature.Exceptfora silvercompositioncontainingl+bS2(~= 0.34),aIlmetalcombinations,includingSAE1020on S&E52100,gavefrictioncoefficientsgreaterthan0.52.A cermetsufferedsubsurfacebrittlefracture;thedepthoffracturewascon-siderablyreducedby decreasingtheloadto8(XIgrams.

Mlded-carbonmaterialsthatarecomnmnlyusedinslidingsealsworeveryrapidlyinliquidnitrogen.Wearofthecarbonswasdecreasedsignificantlyby a metal-haloid@pregnantofthetypeusedto inhibit“dusting”ofaticraftgeneratorbrushesathighaltitude.

Iaminatedphenoliccompositionshadhighfriction,developedaburnishedtransferfilmon thematingsurface,andworeconsiderablymorethanTefloncompositions.Additivessuchasgraphiteand~~ didnotimprovetheperformanceofthephenolic.materials.

LewisFlightPropulsionLaboratoryNationalAdvisoryCommitteeforAeronautics

Cleveland,Ohio,November14,1957

REFERENCES

.

Jacob,R. B.,Martin,K.B.,Van’WYlen,G.J.,andBirmingham,1.

z?.

3.

4.

5.

B. W.:PumpingCryogenicLiquids:Tech.lle~o.N0.-36,Rep.3569,CryogenicEng.Lab.,NBS,Feb.24,1956.

Tanza,G.F.: DevelopmentProgramfora Non-Lubricated10,000RPMBearingOperatingOvera TemperatureRangefrom40°R to 56@ R.Froc.1956CryogenicEng.Conf.,Boulder(Colo.),Sept.5-7,1956,pp.145-155.

Coffin,L. F.,Jr.: TransitionTemperatureforSurfaceDamageinSlidingMetallicContact.LubricationEng.,vol.13,no.7,July1957,pp.399-405.

Merchant,M.E.: TheMechanismof StaticFriction.Jour.APP1.Phys.,vol.11,no.3,Mar.1940,P. 230.

Bowden,F. P.,and~bor?D“: TheFrictionandLubricationof Solids.ChrendonPress(Oxford),1950. t

.

NACATN4211 15

.6. Simon,I.,Mcliahon,E. O.,andBowen,R.J.: DryMetallicI&iction

asa Ibctionof TemperatureBetween4.20K and6000K. Jour.Appl.k ~S., VO1.22,no.2;Feb.1951,pp.177.184.

7.Bisson,EdmondE.,Johnson,RobertL.,~kert, ~ A.,and&@&-,Douglas:Friction,Wesr,and~face DamageofMetalsasAffectedby SolidSurfaceFilms.NACARep.1254,1956. (SupersedesNACAm 3444.)

8.fiivobok,V.N.:Temperatures-Cir.520,NBS,

9.Ernst,Hans,and

10.

. 11.

. I-2.

M.

14.

15.

16.

17.

Metals.Proc.

PropertiesofAusteniticStainlessSteelsat LowMechanicalPropertiesof I&talsatLowTemperatures.Wy 7,1952,pp.112-134;discussion,pp.134-136.

Merchant,M.Eugene:SurfaceFrictionofCleanSpecialSummerConf.onF&ictionandSurfacelRLnish,

M.Z.T.,June1940,~. 76-101.

Roach,ArvidE.,Goodzeit,CarlL.,and!Ibtta,PaulA.: ScoreRe-sistanceofBearingMetals.Nature,vol.172,no. 4372,Au. 15,1953,p.301.

Feng,I.M@: MetalTYansferandWear.Jour.ApplephyS.,VO1.23,no.9, Sept.1952,pp.1011-1019.

Courtney-Pratt,J.W.,andEisner,E.: TheEffectof TangentialForceontheContactofMetallicBodies.=OC. Roy.Sot.(London),SSI’.A,VO1.238,1957,Pp.259-550.

Johnson,RobertL.,Swikert,MEWA.,andBisson,Edmmd E.: lYric-tionandWearofHot-FYessedBesringMaterialsContainingWlyb-denumDisulfide.NACATN2027,1950.

Johnson,RobertL.,Swikert,MaxA.,andBailey,JohnM.: Wearof&picalCarbon-BaseSlidingSealtiterialsat Temperaturesto7000F. NACATN3595,1956.

~, C.,andElsey,H. M.: Effectsof ComutatorSurfaceFilmCon-ditionson Ccmmmtation.&aIIS.A=, VO1.68,pt.1, 1949,pp.106-112.

Allan,A.J. G.: Plasticsas %lid LubricantsandB-rings. PaperpresentedatASLEmeeting,Detroit(Mich.),Apr.1957.

Twiss,S.B.,Willson,R.J.,andSydor,E.J.: TetrafluoroethyleneCompositionsforDryLubricantBearings.PaperpresentedatASLJZmeeting,Detroit(Mich.),Apr.1957.

16 NACATN4211

18.l?itzSinmons,V. G.,andZis~n,W.A.:.

ThinFilmsof Pol.ytetrafluoro-ethylene’-Resin(Teflon)asLubricantsandPreservativeCoatingsforMetals.Rep.4753,NavalRes.Lab.,June15,1956. u

19.Ling,F.F.,andSaibel,E.: T!hermalAspectsof &31ingofIlcyMetal-licSurfacesinSliding(hntact.%p= NO.55-Lub-4,A8ME-ASIJI,1955.

20.KYivobok,V.N.,andWlbot,A. M.: Effectof TemperatureontheMechanicalProperties,Characteristics,andProcessingofAustenitic :Stainless8teels.fiOC.~TM, VO1.50,1950,pp.895-928;diSCUS- ulsion,pp.929-930.

NAC!ATN 4211 17

“

u

.

TABLEI. - EXPERIMENTALMATERIALS

(a)Metalsandmetalliccompounds

Type lkmufacturer Typicalanalysis, Averageorsource percentbyweight hsrdness

304StainlessNAC!Astock c 0.07 Rockwellsteel Cr 18.40 B-63

Si 0.29Ni 8.41Fe Remainder

440-C Allegheny c 0.95to 1.20 RockwellStainlesssteelLudlumSteelMnmax)

[1.00 c-54

Corp. Siuwc) 1.00

[P max) 0.04B max) 0.03

16.00to 18.00&naX] 0.75Fe Remainder

SAE52100 NACAstock c 0.95to1.10 Rockwellchromiumsteel w 0.25to0.45 C-60

[1Pmax 0.025s= 0.025Si 0.20to0.35Cr 1.30to 1.60Fe Remainder

w 1020 NACAstock c 0.18to0.23 Rockwellmildsteel Mn 0.30to0.60 A-50

P(~1

0.04s(mx 0.05Fe Remainder

Silver,cast NACAstock & 99.9+ --------electrolytic

Hot-pressed Formedby Ag 85 --------silvercomposi-NACA Cu 5tionwithMoS2 MoS2 10

Kentanium~62BKennametal,Ni 25 --------(titanium Inc. Mo 5carbidecermet} (Cb,Ta,Ti)C 8

TiC Remainder

18 NACATN 4211

TABLEI.- Concluded. EXPERIMENTALMATERIKE3 .

(b)Nonmetals

Typeof Manufacturerhknufac- Descriptionofmaterial. Averagematerialorsource turertB hardness

designa-tIon

MoldedPureCarbonPurebonAmorphou6carbonpluBsmallamountof Scleroscope90c=bon Co.,Inc. P5J gr@itej phenolicimpregnant

P5 Hoiqpregnant --------------

652 Doublephenolicimpregnant -------------

P5ET Organic-metalliccoqplexiqpregnant-------------

PEN Metal-haloidiurpregnant --------------

Us. GraphitarAmorphouscarbonplusSUE1lamountof Scleroscope95GraphiteCo. 36 graphite;phenolichpregnant

MoldedTheFormica CN Coarse-weavecotton-fabriclaminate;--------------plasticco. phenolicresin

m Fine-weavecotton-fabriclami~tej -------------phenolicresin

IL-84 Fine-weavecotton-fabriclaminate; --------------phenolicresin;umlybdenum-dl.sulfideadditive

OH-9 Medium-weavecotton-fabriclaminate;------.-------phenolicresin;graphtteadditive

CH-93 SameasCH-9exceptforhighergraphite--------------content

FF-55 Continuous-filamentfiberglass --------------laminate;melamineresin

Mi.carta 221 Fine-weavecotton-fabricl~i~tej RockwellM-113Division, phenolicresinWestinghouseElectric 273 Fine-weavecptton-fabriclaminate; RockwellM-115Corp. phenolicre8in(bearing-retainer

material)286 Medium-weavecotton-fabriclaminate;RockwellM-108

phenolicresinTeflonPlasticB 9507 Teflonfilledwithapprox.3percent --------------and Division, graphitefilledTheGarlockTeflonPackingCo. 9281 Kel-Funplasticized(nofiller) --------------

8764 Teflonplain(nofiller) Durometer50to65

9412 Teflonfilledwithapprox.10percent--------------graphite

9429 Teflonfilledwithcopper --------------

9453 TeflonftlledwithMoS2 ----------.---

Kow”ersCO., ---- Teflonfilledwithfiberglass(cut --------------Inc. fromumldedpistonrings]

ii

.

.

.

NACATN 4211 19

,.,

. .

.-d --- .-

.,.-. . . . ,. ..-..,

- .,.

55XctXon”””f”&ce””1

Eydraullcdriverotor,5 hp

6peedincreaser(6:1)‘

iE!-i RotatLng-disk

Figure1. - Cryogenicfriction-and-wear

specimen‘”.-

~

apparatus.

Helium Supply

seals ad valve B!l A ttraufm presmme Opnation Furge I

Q Ble.triosafetyvalve@ Preseure regulator

Q mow Coatrol

‘@ Presmme gageIf

LLi

-—. — .

1

1

:

------ j__________~,

D~-I-im!!!! I

----------E2mtziiVacuumputpsystem

* J

Fi@ue2.- Systemfortransferof~genic fluidtotestchaml.sroffriction-emd-vearappsmatus.

* 4 S!LLV. .

2!

. 4733, ,

l.1--o.w—q

RlaerWeaxarea Iliakweartrack

Figure3. - Surfacesof audmnitictypeXM staiflesB-steelriderontype304stainless-steeldiskafterslidingin liquidnitrogen.xJ.5.Wration, 4.75minu~ea;riderweaxratej6.2%10-3cubictichperhour;initialfrictioncoefficient,0.78;slidingvelocity,2300feetperminute;initialload,1000gmm.

N1-

NN

RiderW- area

11-c.,cv-l

Diskweartrack

(a) SAX 1020rideronSAE52UI0 disk. -ti~, 10.1’8mfnutes;ri&r wear rate,1.l&xlo-3cubicinchPer hour;imitialfrictioncoefficient,0.59. :

Figure4.*

- Surfacesof conventionalbearingrmtarial.aafterslidingin liquidmi.trogen.X15.Slidingvelocity,2200feetper minute;bitial l~a,1~0 grams. s

1%PP

,

, ,

Riderweararea

“47’35( ,

ULiL...

[

C-45589

t’-”.’””+

Diskwear track

(b)SAE52100rlcleron W 52100 disk. Duration,0.2minute;riderweerratenot significantbecauseofshortduration;initialfrlctioncoefficieti,0052.

Figure4.- concluded.surfacesofconvemkionslbeerimgmaterialsafternitrogen.x15. Slidingvelocity,2300feetperminute;Initialload,

sliaq inliquid1000~sms.

Riderweararea

(a)Castelectrolyticsilverriderwearrate,O.S3CL0-3,:!

Rklu=e5. - Surfacesof solld

,,J,:

}0.10”-4

Diskweextrack

rideron type 304 Etaitiess-tieeldi~. ~atio% @ ~~tes;cubicinchp= hour;initialfrictioncoefficient,O.@O.

silverand a silvercompositionand the metingmetalafterslidlng% liquttlnitrogen.x15. Slidingvelocity,2300feetpar minute;initial~~a, 10~ grama.

,“,..,

,’,“, # !7i2L%’* L,.

, C&i 4735 ‘,

(b)Hot-pressedGilver(85percent),copper(5percent),andl@2 (10percent)ccmqxmitlonrldarontype304stainless-steeldisk.Duration,46.5minutes;riderwearrate,0.6&10-3cubichch perhour;initialfrictioncofllcient,0.34.

Mgllre5.- Conoluded.Surfacesofsolidsilveranda EilvarccmpositionandL& matingmetal@ter slidinginliquidnitrogen.x15. Slidingvelocity,2300feetPer minute;ititialload,1000grams.

Riderweararea

+0.’0”+Mak wear track

-.

Nm

+0”10”+Riderweararea Diskweartrack

(a)TitaDIuIocarbidecermet(KI.6ZB)rideron type4443-Cstainless-steeldisk. Durathn, 22.4minutes;riderwe.sn’rate (O.051.xl.0-3cu in./hr)is not significa?xtbecauseof subsurfacebrittlefracture;tit id frictioncoefficient,O.63; Wtial load,10m @rams.

Figure6. - SUIYWXIGOf titaniumcarbide-basecarmetandmtingmetal&er slidinginliquidnitrogen.X15. Slidingvelocity,2300feetperdmute.

I ,

C17-4baok 4735 p ‘

=!

+“.’””+Riderweararea DiOkwear track

(b)Reduce&loadexperimentwithtitaniumcerbidececrmet(KL62B)ridaron type440-Cstainles6-tieeldisk. Duration,31..44titeE; riderwearrate (0.014xUY+cu in./hr)is not sQnlfi-cantbecauseof Efubsm’facebrittlefracture;initialfrictioncoefficient,O.69; idtial load,MO gmms .

Figure 6. - Concluded.Surfacesof tit+mlumcarbide-basecermetaridmatingmetalafterslidlngh liquidllftiO@?l. M5. SWling velocity,2500feetpm *e.

Nm

t--”.’””+Riderweexarea Diskweartrack

(a)Phenol-impregnatedmohledcwbon (weknp5J) rid~ on tYPe~ Bta~esB-*el disk. ~-tion,60 minutes;riderweerrate,0.009XL0-3cubicInchper hour;initialfrictioncoeffichrt,0.35. Surfacesbelievedcontaminatedwfthfrozenadsorbedmoisturefilmwhen specimenswere Fphmged intoliquidnitzw$minopenDemmm. ~

Figure7.- Surfacesormoldedcarbanandmat~ metalafterslia~ IIIliquidnitrogen.X15. !3

Slidingvelocity,2500feetperminute;initialload,1000~ams. RPP

9 , * 4

4735u . # 1.

Riderweararea

(b)Phenol-impregnatedmoldedcarbon

585

t-”.’””+Diskweax track

(FurebonP5J)_ridemon type?04 stainless-steeldisk.

E

lMrati.on,1.4minutes;rid= wearrate (91.3x10-3cu in./hr)not quantitativelysignificantbecauseof shortduration;initialfrictioncoefficient,0.40.Standerdexperimentalprocedure.

Figure7. - Concluded.Surface8of moldedcerbonandmwklngmetaleftarslidingin liguidnitrogen.X15. Slidingvelocity,2300feetperminute;initialload,1000warns.

.-

—

;: ,:: ;,; l , , .:

h. :

,-A. .&&l. . . .

.--d...,... &..” .d...&.a-.-.;...-. ~ .,.:C-45592

t-”.’””+Rids W~ area Diskweartrack

Figure8. - Surfacesof lemlutedplmnolicresin(lbrmlcaLW)rideron type304 stainless-steeldiskafterslidingin liquidnitrogen.x15. Duration,60.25mlmutes;riderwearrate,O.llXLO-3cubicinchper ham; initialfrictioncoefficient,O.~; slidingvelocity,2XQ feetper minute;initialload,UXIOgrams.

, , , .SsLv ‘ ‘

4735 ●u , ,

Riderweararea

+“.’””+Dick wew track

(a)MoldedTeflon(Garlock8764)rideron typeXM stainleas+teeldisk. Duration,15.2Sminuteg;riderwearrate,0.31x10-5cubicinchP hour;initialfrictioncoefficient,0.27.

Ftgure9, - StnYacesof Teflonand filledTeflonafterslidhg In liquidnttrogen.XL5.Slid@ ~lo~ity, 2300feetpm MS; hitid lCXKI,10@ WQRIS.

.-

RiderW6EX area

(b)Mddadgaphite-fil@lTeflon (GarlockIRzration,61.0-es; ridermar rate,tioncoefficiemb,0.14.

Figure9. - C~luded. Surf=es of

X15. Slidingvelocity,23OOfeet

, 3

+0-10”+Diskweartrack

9412)rideron type334 stainless-steeldisk.0.011XIO-3cubicinchperhour;initialfric-

TeflonandfilledTeflonafterslidingin liquidnitrogen.perti~tej initialload,1030gramEI.

Wearrate,cuin./hr

4735

o304Steelon304steel 1

L

F 102oSteelon 52100steeli! 1

I~ Silveron304steel

!Silver+ copper+MoS~on304steel

Csrbon+phenolichnpregnants

Carbon+ haloidimpregnant

IaminatedphenolicsLaminatedphenolics+additives

Iss

wo*m t 1~ Kel-F J. [~ Teflon Imm Teflon+ copperm

(DP Teflon+MOS2

Teflon+ ~aphite

)

34 NACATN4211

1

i

1.

1.

1.

1.

.

.

.,.

.

.

.

.

Ez!Dataspreadin identicalruns

—

..7

+

—Metals

Fimre10.- Concluded.Wearandfrictionpropert.iea

Nonmetalsonthe 304stainlesssteel

&Fvarioustypesofmaterialsslidinginliquidnitrogen.Slidingvelocity,2300feetperminute;Imd, 1000grams;durationlfrom5 minutesto5 hoursdependingonwearrate.

* . * , * #

160x10-~

120

<

im~

$#

40

H-ao Km 2000 3003 4000 5000 6000 7000

Sliding velocity,ft/min

Figure11. - Effectof slidingvelocityon wearper unitdistanceof slidingformoldedgraphite-filledTefloprideron type304 stainless-steeldisksulmergedin lfquidnitrogen.Initialload,1000grama;radiusof ridertip,3/16 inch.