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1、英文原文ExperimentalinvestigationoflasersurfacetexturedparallelthrustbearingsPerformanceenhancementsbylasersurfacetexturing(LST)ofparallel-thrustbearingsisexperimentallyinvestigated.Testresultsarecomparedwithatheoreticalmodelandgoodcorrelationisfoundovertherelevantoperatingconditions.Acompari-sonofthepe

2、rformanceofunidirectionalandbi-directionalpartial-LSTbearingswiththatofabaseline,untexturedbearingispresentedshowingthebenetsofLSTintermsofincreasedclearanceandreducedfriction.KEYWORDS:uidlmbearings,sliderbearings,surfacetexturing1.IntroductionTheclassicaltheoryofhydrodynamiclubricationyieldslinear(

3、Couette)velocitydistributionwithzeropressuregradientsbetweensmoothparallelsurfacesundersteady-statesliding.Thisresultsinanunstablehydrodynamiclmthatwouldcollapseunderanyexternalforceactingnormaltothesurfaces.However,experienceshowsthatstablelubricatinglmscandevelopbetweenparallelslidingsurfaces,gene

4、rallybecauseofsomemechanismthatrelaxesoneormoreoftheassumptionsoftheclassicaltheory.Astableuidlmwithsucientload-carryingcapacityinparallelslidingsurfacescanbeobtained,forexample,withmacroormicrosurfacestructureofdierenttypes.Theseincludewaviness1andprotrudingmicroasperities24.Agoodliteraturereviewon

5、thesubjectcanbefoundinRef.5.Morerecently,lasersurfacetexturing(LST)68,aswellasinletrougheningbylongitudinalortransversegrooves9weresuggestedtoprovideloadcapacityinparallelsliding.TheinletroughnessconceptofTonder9isbasedoneectiveclearancereductionintheslidingdirectionandinthisrespectitisidenticaltoth

6、epar-tial-LSTconceptdescribedinref.10forgeneratinghydrostaticeectinhigh-pressuremechanicalseals.VeryrecentlyWangetal.11demonstratedexperimentallyadoublingoftheload-carryingcapacityforthesurface-texturedesignbyreactiveionetchingofSiCparallel-thrustbearingsslidinginwater.Thesesimpleparallelthrustbeari

7、ngsareusuallyfoundinseal-lesspumpswherethepumpeduidisusedasthelubricantforthebearings.Duetotheparallelslidingtheirperformanceispoorerthanmoresophisticatedtaperedorsteppedbearings.Brizmeretal.12demon-stratedthepotentialoflasersurfacetexturingintheformofregularmicro-dimplesforprovidingload-carryingcap

8、acitywithparallel-thrustbearings.Amodelofatexturedparallelsliderwasdevelopedandtheeectofsurfacetexturingonload-carryingcapacitywasanalyzed.Theoptimumparametersofthedimpleswerefoundinordertoobtainmaximumload-carryingcapacity.Amicro-dimplecollectiveeectwasidenti-edthatiscapableofgeneratingsubstantiall

9、oad-carryingcapacity,approachingthatofoptimumconventionalthrustbearings.ThepurposeofthepresentpaperistoinvestigateexperimentallythevalidityofthemodeldescribedinRef.12bytestingpracticalthrustbearingsandcomparingtheperformanceofLSTbearingswiththatofthetheoreticalpredictionsandwiththeperformanceofstand

10、ardnon-texturedbearings2.BackgroundAcrosssectionofthebasicmodelthatwasanalyzedinRef.12isshowninfigure1.AsliderhavingawidthBispartiallytexturedoveraportionBp=Bofitswidth.Thetexturedsurfaceconsistsofmultipledimpleswithadiameter，depthandareadensitySp.Asaresultofthehydrodynamicpressuregeneratedbythedimp

11、lestheslidingsurfaceswillbeseparatedbyaclearancedependingontheslidingvelocityU,theuidviscositylandtheexternalloadItwasfoundinRef.12thatanoptimumratioexistsfortheparameterthatprovidesmaximumdimensionlessload-carryingcapacitywhereListhebearinglength,andthisoptimumvalueishp=1.25.ItwasfurtherfoundinRef.

12、12thatanoptimumvalueexistsforthetexturedportionadependingonthebearingaspectratioL/B.Thisbehaviorisshowningure2forabearingwithL/B=0.75atvariousvaluesoftheareadensitySp.AscanbeseenintherangeofSpvaluesfrom0.18to0.72theoptimumavaluevariesfrom0.7to0.55,respectively.Itcanalsobeseenfromgure2thatfora0.85noo

13、ptimumvalueexistsforSpandthemaximumloadWincreaseswithincreasingSp.Hence,thelargestareadensitythatcanbepracticallyobtainedwiththelasertexturingisdesired.Itisalsointerestingtonotefromgure2theadvantageofpartial-LST(a1)overthefullLST(a=1)forbearingapplications.AtSp=0.5,forexample,theloadWata=0.6isaboutt

14、hreetimeshigherthanitsvalueata=1.AfullaccountofthisbehaviorisgiveninRef.12.3.ExperimentalThetestedbearingsconsistofsinteredSiCdisks10mmthick,having85mmouterdiameterand40mminnerdiameter.Eachbearing(seegure3)comprisesaatrotor(a)andasix-padstator(b).Thebearingswereprovidedwithanoriginalsurfacenishbylap

15、pingtoaroughnessaverageRa=0.03lm.Eachpadhasanaspectratioof0.75whenitswidthismeasuredalongthemeandiameterofthestator.Thephotographsoftwopartial-LSTstatorsareshowningure4wherethetexturedareasappearasbrightermattsurfaces.Therststatorindicated(a)isaunidirectionalbearingwiththepartial-LSTadjacenttothelea

16、dingedgeofeachpad,similartothemodelshowningure1.Thesecondstator(b)isabi-directionalversionofapartial-LSTbearinghavingtwoequaltexturedportions,a/2,oneachofthepadends.Thelasertexturingparameterswerethefollowing；dimpledepth,dimplediameteranddimpleareadensitySp=0.60.03.Thesedimpledimensionswereobtainedw

17、ith4pulsesof30nsdurationand4mJeachusinga5kHzpulsatingNd:YAGlaser.Thetexturedportionoftheunidirectionalbearingwasa=0.73andthatofthebi-directionalbearingwasa=0.63.Ascanbeseenfromgure2boththeseavaluesshouldproduceload-carryingcapacityvaryclosetothemaximumtheoreticalvalue.Thetestrigisshownschematicallyi

18、ngure5.Anelectricalmotorturnsaspindletowhichanupperholderoftherotorisattached.Asecondlowerholderofthestatorisxedtoahousing,whichrestsonajournalbearingandanaxialloadingmechanismthatcanfreelymoveintheaxialdirection.Anarmthatpressesagainstaloadcellandtherebypermitsfrictiontorquemeasurementspreventsthef

19、reerotationofthishousing.Axialloadingisprovidedbymeansofdeadweightsonaleverandismeasuredwithasecondloadcell.Aproximityprobethatisattachedtothelowerholderofthestatorallowson-linemeasurementsoftheclearancechangebetweenrotorandstatorasthehydrodynamiceectscauseaxialmovementofthehousingtowhichthestatorho

20、lderisxed.Tapwaterissuppliedbygravityfromalargetanktothecenterofthebearingandtheleakagefromthebearingiscollectedandre-circulated.Athermocoupleadjacenttotheouterdiameterofthebearingallowsmonitoringofthewatertemperatureasthewaterexitthebearing.APCisusedtocollectandprocessdataon-line.Hence,theinstantan

21、eousclearance,frictioncoecient,bearingspeedandexitwatertemperaturecanbemonitoredconstantly.Thetestprotocolincludesidentifyingareference“zero”pointfortheclearancemeasurementsbyrstloadingandthenunloadingastationarybearingoverthefullloadrange.Thenthelowestaxialloadisapplied,thewatersupplyvalveisopeneda

22、ndthemotorturnedon.Axialloadingisincreasedbystepsof40Nandeachloadstepismaintainedfor5minfollowingthestabilizationofthefrictioncoecientatasteady-statevalue.Thebearingspeedandwatertemperaturearemonitoredthroughoutthetestforanyirregularities.Thetestendswhenamaximumaxialloadof460Nisreachedorifthefrictio

23、ncoecientexceedsavalueof0.35.Attheendofthelastloadstepthemotorandwatersupplyareturnedoandthereferencefortheclearancemeasurementsisrechecked.Testsareperformedattwospeedsof1500and3000rpmcorrespondingtoaverageslidingvelocitiesof4.9and9.8m/s,respectivelyandeachtestisrepeatedatleastthreetimes.4.Resultsan

24、ddiscussionAsarststepthevalidityofthetheoreticalmodelinRef.12wasexaminedbycomparingthetheoreticalandexperimentalresultsofbearingclearanceversusbearingloadforaunidirectionalpartial-LSTbearing.Theresultsareshowningure6forthetwospeedsof1500and3000rpmwherethesolidanddashedlinescorrespondtothemodelandexp

25、eriment,respectively.Ascanbeseen,theagreementbetweenthemodelandtheexperimentisgood,withdierencesoflessthan10%,aslongastheloadisabove150N.Atlowerloadsthemeasuredexperimentalclearancesaremuchlargerthanthemodelpredictions,particularlyatthehigherspeedof3000rpmwhereat120Nthemeasuredclearanceis20lm,whichi

26、sabout60%higherthanthepredictedvalue.Itturnsoutthatthecombinationofsuchlargeclearancesandrelativelylowviscosityofthewatermayresultinturbulentuidlm.Hence,theassumptionoflaminarowonwhichthesolutionoftheReynoldsequationinRef.12isbasedmaybeviolatedmakingthemodelinvalidespeciallyatthehigherspeedandlowestload.InordertobeconsistentwiththemodelofRef.12itwasdecidedtolimitfurthercomparisonstoloadsabove150N.