外文翻译--实验研究激光加工表面微观造型平行的推力轴承.doc

英文原文ExperimentalinvestigationoflasersurfacetexturedparallelthrustbearingsPerformanceenhancementsbylasersurfacetexturing(LST)ofparallel-thrustbearingsisexperimentallyinvestigated.Testresultsarecomparedwithatheoreticalmodelandgoodcorrelationisfoundovertherelevantoperatingconditions.Acompari-sonoftheperformanceofunidirectionalandbi-directionalpartial-LSTbearingswiththatofabaseline,untexturedbearingispresentedshowingthebenetsofLSTintermsofincreasedclearanceandreducedfriction.KEYWORDS:uidlmbearings,sliderbearings,surfacetexturing1.IntroductionTheclassicaltheoryofhydrodynamiclubricationyieldslinear(Couette)velocitydistributionwithzeropressuregradientsbetweensmoothparallelsurfacesundersteady-statesliding.Thisresultsinanunstablehydrodynamiclmthatwouldcollapseunderanyexternalforceactingnormaltothesurfaces.However,experienceshowsthatstablelubricatinglmscandevelopbetweenparallelslidingsurfaces,generallybecauseofsomemechanismthatrelaxesoneormoreoftheassumptionsoftheclassicaltheory.Astableuidlmwithsucientload-carryingcapacityinparallelslidingsurfacescanbeobtained,forexample,withmacroormicrosurfacestructureofdierenttypes.Theseincludewaviness1andprotrudingmicroasperities24.AgoodliteraturereviewonthesubjectcanbefoundinRef.5.Morerecently,lasersurfacetexturing(LST)68,aswellasinletrougheningbylongitudinalortransversegrooves9weresuggestedtoprovideloadcapacityinparallelsliding.TheinletroughnessconceptofTonder9isbasedoneectiveclearancereductionintheslidingdirectionandinthisrespectitisidenticaltothepar-tial-LSTconceptdescribedinref.10forgeneratinghydrostaticeectinhigh-pressuremechanicalseals.VeryrecentlyWangetal.11demonstratedexperimentallyadoublingoftheload-carryingcapacityforthesurface-texturedesignbyreactiveionetchingofSiCparallel-thrustbearingsslidinginwater.Thesesimpleparallelthrustbearingsareusuallyfoundinseal-lesspumpswherethepumpeduidisusedasthelubricantforthebearings.Duetotheparallelslidingtheirperformanceispoorerthanmoresophisticatedtaperedorsteppedbearings.Brizmeretal.12demon-stratedthepotentialoflasersurfacetexturingintheformofregularmicro-dimplesforprovidingload-carryingcapacitywithparallel-thrustbearings.Amodelofatexturedparallelsliderwasdevelopedandtheeectofsurfacetexturingonload-carryingcapacitywasanalyzed.Theoptimumparametersofthedimpleswerefoundinordertoobtainmaximumload-carryingcapacity.Amicro-dimplecollectiveeectwasidenti-edthatiscapableofgeneratingsubstantialload-carryingcapacity,approachingthatofoptimumconventionalthrustbearings.ThepurposeofthepresentpaperistoinvestigateexperimentallythevalidityofthemodeldescribedinRef.12bytestingpracticalthrustbearingsandcomparingtheperformanceofLSTbearingswiththatofthetheoreticalpredictionsandwiththeperformanceofstandardnon-texturedbearings2.BackgroundAcrosssectionofthebasicmodelthatwasanalyzedinRef.12isshowninfigure1.AsliderhavingawidthBispartiallytexturedoveraportionBp=Bofitswidth.Thetexturedsurfaceconsistsofmultipledimpleswithadiameter，depthandareadensitySp.AsaresultofthehydrodynamicpressuregeneratedbythedimplestheslidingsurfaceswillbeseparatedbyaclearancedependingontheslidingvelocityU,theuidviscositylandtheexternalloadItwasfoundinRef.12thatanoptimumratioexistsfortheparameterthatprovidesmaximumdimensionlessload-carryingcapacitywhereListhebearinglength,andthisoptimumvalueishp=1.25.ItwasfurtherfoundinRef.12thatanoptimumvalueexistsforthetexturedportionadependingonthebearingaspectratioL/B.Thisbehaviorisshowningure2forabearingwithL/B=0.75atvariousvaluesoftheareadensitySp.AscanbeseenintherangeofSpvaluesfrom0.18to0.72theoptimumavaluevariesfrom0.7to0.55,respectively.Itcanalsobeseenfromgure2thatfora0.85nooptimumvalueexistsforSpandthemaximumloadWincreaseswithincreasingSp.Hence,thelargestareadensitythatcanbepracticallyobtainedwiththelasertexturingisdesired.Itisalsointerestingtonotefromgure2theadvantageofpartial-LST(a1)overthefullLST(a=1)forbearingapplications.AtSp=0.5,forexample,theloadWata=0.6isaboutthreetimeshigherthanitsvalueata=1.AfullaccountofthisbehaviorisgiveninRef.12.3.ExperimentalThetestedbearingsconsistofsinteredSiCdisks10mmthick,having85mmouterdiameterand40mminnerdiameter.Eachbearing(seegure3)comprisesaatrotor(a)andasix-padstator(b).ThebearingswereprovidedwithanoriginalsurfacenishbylappingtoaroughnessaverageRa=0.03lm.Eachpadhasanaspectratioof0.75whenitswidthismeasuredalongthemeandiameterofthestator.Thephotographsoftwopartial-LSTstatorsareshowningure4wherethetexturedareasappearasbrightermattsurfaces.Therststatorindicated(a)isaunidirectionalbearingwiththepartial-LSTadjacenttotheleadingedgeofeachpad,similartothemodelshowningure1.Thesecondstator(b)isabi-directionalversionofapartial-LSTbearinghavingtwoequaltexturedportions,a/2,oneachofthepadends.Thelasertexturingparameterswerethefollowing；dimpledepth,dimplediameteranddimpleareadensitySp=0.60.03.Thesedimpledimensionswereobtainedwith4pulsesof30nsdurationand4mJeachusinga5kHzpulsatingNd:YAGlaser.Thetexturedportionoftheunidirectionalbearingwasa=0.73andthatofthebi-directionalbearingwasa=0.63.Ascanbeseenfromgure2boththeseavaluesshouldproduceload-carryingcapacityvaryclosetothemaximumtheoreticalvalue.Thetestrigisshownschematicallyingure5.Anelectricalmotorturnsaspindletowhichanupperholderoftherotorisattached.Asecondlowerholderofthestatorisxedtoahousing,whichrestsonajournalbearingandanaxialloadingmechanismthatcanfreelymoveintheaxialdirection.Anarmthatpressesagainstaloadcellandtherebypermitsfrictiontorquemeasurementspreventsthefreerotationofthishousing.Axialloadingisprovidedbymeansofdeadweightsonaleverandismeasuredwithasecondloadcell.Aproximityprobethatisattachedtothelowerholderofthestatorallowson-linemeasurementsoftheclearancechangebetweenrotorandstatorasthehydrodynamiceectscauseaxialmovementofthehousingtowhichthestatorholderisxed.Tapwaterissuppliedbygravityfromalargetanktothecenterofthebearingandtheleakagefromthebearingiscollectedandre-circulated.Athermocoupleadjacenttotheouterdiameterofthebearingallowsmonitoringofthewatertemperatureasthewaterexitthebearing.APCisusedtocollectandprocessdataon-line.Hence,theinstantaneousclearance,frictioncoecient,bearingspeedandexitwatertemperaturecanbemonitoredconstantly.Thetestprotocolincludesidentifyingareference“zero”pointfortheclearancemeasurementsbyrstloadingandthenunloadingastationarybearingoverthefullloadrange.Thenthelowestaxialloadisapplied,thewatersupplyvalveisopenedandthemotorturnedon.Axialloadingisincreasedbystepsof40Nandeachloadstepismaintainedfor5minfollowingthestabilizationofthefrictioncoecientatasteady-statevalue.Thebearingspeedandwatertemperaturearemonitoredthroughoutthetestforanyirregularities.Thetestendswhenamaximumaxialloadof460Nisreachedorifthefrictioncoecientexceedsavalueof0.35.Attheendofthelastloadstepthemotorandwatersupplyareturnedoandthereferencefortheclearancemeasurementsisrechecked.Testsareperformedattwospeedsof1500and3000rpmcorrespondingtoaverageslidingvelocitiesof4.9and9.8m/s,respectivelyandeachtestisrepeatedatleastthreetimes.4.ResultsanddiscussionAsarststepthevalidityofthetheoreticalmodelinRef.12wasexaminedbycomparingthetheoreticalandexperimentalresultsofbearingclearanceversusbearingloadforaunidirectionalpartial-LSTbearing.Theresultsareshowni