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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

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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ExperimentalinvestigationoflasersurfacetexturedparallelthrustbearingsPerformanceenhancementsbylasersurfacetexturingLSTofparallelthrustbearingsisexperimentallyinvestigated.Testresultsarecomparedwithatheoreticalmodelandgoodcorrelationisfoundovertherelevantoperatingconditions.AcomparisonoftheperformanceofunidirectionalandbidirectionalpartialLSTbearingswiththatofabaseline,untexturedbearingispresentedshowingthebenefitsofLSTintermsofincreasedclearanceandreducedfriction.KEYWORDSfluidfilmbearings,sliderbearings,surfacetexturing1.IntroductionTheclassicaltheoryofhydrodynamiclubricationyieldslinearCouettevelocitydistributionwithzeropressuregradientsbetweensmoothparallelsurfacesundersteadystatesliding.Thisresultsinanunstablehydrodynamicfilmthatwouldcollapseunderanyexternalforceactingnormaltothesurfaces.However,experienceshowsthatstablelubricatingfilmscandevelopbetweenparallelslidingsurfaces,generallybecauseofsomemechanismthatrelaxesoneormoreoftheassumptionsoftheclassicaltheory.Astablefluidfilmwithsufficientloadcarryingcapacityinparallelslidingsurfacescanbeobtained,forexample,withmacroormicrosurfacestructureofdifferenttypes.Theseincludewaviness1andprotrudingmicroasperities2–4.AgoodliteraturereviewonthesubjectcanbefoundinRef.5.Morerecently,lasersurfacetexturingLST6–8,aswellasinletrougheningbylongitudinalortransversegrooves9weresuggestedtoprovideloadcapacityinparallelsliding.TheinletroughnessconceptofTonder9isbasedoneffectiveclearancereductionintheslidingdirectionandinthisrespectitisidenticaltothepartialLSTconceptdescribedinref.10forgeneratinghydrostaticeffectinhighpressuremechanicalseals.VeryrecentlyWangetal.11demonstratedexperimentallyadoublingoftheloadcarryingcapacityforthesurfacetexturedesignbyreactiveionetchingofSiCparallelthrustbearingsslidinginwater.Thesesimpleparallelthrustbearingsareusuallyfoundinseallesspumpswherethepumpedfluidisusedasthelubricantforthebearings.Duetotheparallelslidingtheirperformanceispoorerthanmoresophisticatedtaperedorsteppedbearings.Brizmeretal.12demonstratedthepotentialoflasersurfacetexturingintheformofregularmicrodimplesforprovidingloadcarryingcapacitywithparallelthrustbearings.Amodelofatexturedparallelsliderwasdevelopedandtheeffectofsurfacetexturingonloadcarryingcapacitywasanalyzed.Theoptimumparametersofthedimpleswerefoundinordertoobtainmaximumloadcarryingcapacity.Amicrodimplecollectiveeffectwasidentifiedthatiscapableofgeneratingsubstantialloadcarryingcapacity,approachingthatofoptimumconventionalthrustbearings.ThepurposeofthepresentpaperistoinvestigateexperimentallythevalidityofthemodeldescribedinRef.12bytestingpracticalthrustbearingsandcomparingtheperformanceofLSTbearingswiththatofthetheoreticalpredictionsandwiththeperformanceofstandardnontexturedbearings2.BackgroundAcrosssectionofthebasicmodelthatwasanalyzedinRef.12isshowninfigure1.AsliderhavingawidthBispartiallytexturedoveraportionBpαBofitswidth.Thetexturedsurfaceconsistsofmultipledimpleswithadiameter,depthandareadensitySp.AsaresultofthehydrodynamicpressuregeneratedbythedimplestheslidingsurfaceswillbeseparatedbyaclearancedependingontheslidingvelocityU,thefluidviscositylandtheexternalloadItwasfoundinRef.12thatanoptimumratioexistsfortheparameterthatprovidesmaximumdimensionlessloadcarryingcapacitywhereListhebearinglength,andthisoptimumvalueishp1.25.ItwasfurtherfoundinRef.12thatanoptimumvalueexistsforthetexturedportionadependingonthebearingaspectratioL/B.Thisbehaviorisshowninfigure2forabearingwithL/B0.75atvariousvaluesoftheareadensitySp.AscanbeseenintherangeofSpvaluesfrom0.18to0.72theoptimumavaluevariesfrom0.7to0.55,respectively.Itcanalsobeseenfromfigure2thatfora0.85nooptimumvalueexistsforSpandthemaximumloadWincreaseswithincreasingSp.Hence,thelargestareadensitythatcanbepracticallyobtainedwiththelasertexturingisdesired.Itisalsointerestingtonotefromfigure2theadvantageofpartialLSTa1overthefullLSTa1forbearingapplications.AtSp0.5,forexample,theloadWata0.6isaboutthreetimeshigherthanitsvalueata1.AfullaccountofthisbehaviorisgiveninRef.12.3.ExperimentalThetestedbearingsconsistofsinteredSiCdisks10mmthick,having85mmouterdiameterand40mminnerdiameter.Eachbearingseefigure3comprisesaflatrotoraandasixpadstatorb.ThebearingswereprovidedwithanoriginalsurfacefinishbylappingtoaroughnessaverageRa0.03lm.Eachpadhasanaspectratioof0.75whenitswidthismeasuredalongthemeandiameterofthestator.ThephotographsoftwopartialLSTstatorsareshowninfigure4wherethetexturedareasappearasbrightermattsurfaces.ThefirststatorindicatedaisaunidirectionalbearingwiththepartialLSTadjacenttotheleadingedgeofeachpad,similartothemodelshowninfigure1.ThesecondstatorbisabidirectionalversionofapartialLSTbearinghavingtwoequaltexturedportions,a/2,oneachofthepadends.Thelasertexturingparameterswerethefollowingdimpledepth,dimplediameteranddimpleareadensitySp0.60.03.Thesedimpledimensionswereobtainedwith4pulsesof30nsdurationand4mJeachusinga5kHzpulsatingNdYAGlaser.Thetexturedportionoftheunidirectionalbearingwasa0.73andthatofthebidirectionalbearingwasa0.63.Ascanbeseenfromfigure2boththeseavaluesshouldproduceloadcarryingcapacityvaryclosetothemaximumtheoreticalvalue.Thetestrigisshownschematicallyinfigure5.Anelectricalmotorturnsaspindletowhichanupperholderoftherotorisattached.Asecondlowerholderofthestatorisfixedtoahousing,whichrestsonajournalbearingandanaxialloadingmechanismthatcanfreelymoveintheaxialdirection.Anarmthatpressesagainstaloadcellandtherebypermitsfrictiontorquemeasurementspreventsthefreerotationofthishousing.Axialloadingisprovidedbymeansofdeadweightsonaleverandismeasuredwithasecondloadcell.Aproximityprobethatisattachedtothelowerholderofthestatorallowsonlinemeasurementsoftheclearancechangebetweenrotorandstatorasthehydrodynamiceffectscauseaxialmovementofthehousingtowhichthestatorholderisfixed.Tapwaterissuppliedbygravityfromalargetanktothecenterofthebearingandtheleakagefromthebearingiscollectedandrecirculated.Athermocoupleadjacenttotheouterdiameterofthebearingallowsmonitoringofthewatertemperatureasthewaterexitthebearing.APCisusedtocollectandprocessdataonline.Hence,theinstantaneousclearance,frictioncoefficient,bearingspeedandexitwatertemperaturecanbemonitoredconstantly.Thetestprotocolincludesidentifyingareferencezeropointfortheclearancemeasurementsbyfirstloadingandthenunloadingastationarybearingoverthefullloadrange.Thenthelowestaxialloadisapplied,thewatersupplyvalveisopenedandthemotorturnedon.Axialloadingisincreasedbystepsof40Nandeachloadstepismaintainedfor5minfollowingthestabilizationofthefrictioncoefficientatasteadystatevalue.Thebearingspeedandwatertemperaturearemonitoredthroughoutthetestforanyirregularities.Thetestendswhenamaximumaxialloadof460Nisreachedorifthefrictioncoefficientexceedsavalueof0.35.Attheendofthelastloadstepthemotorandwatersupplyareturnedoffandthereferencefortheclearancemeasurementsisrechecked.Testsareperformedattwospeedsof1500and3000rpmcorrespondingtoaverageslidingvelocitiesof4.9and9.8m/s,respectivelyandeachtestisrepeatedatleastthreetimes.4.ResultsanddiscussionAsafirststepthevalidityofthetheoreticalmodelinRef.12wasexaminedbycomparingthetheoreticalandexperimentalresultsofbearingclearanceversusbearingloadforaunidirectionalpartialLSTbearing.Theresultsareshowninfigure6forthetwospeedsof1500and3000rpmwherethesolidanddashedlinescorrespondtothemodelandexperiment,respectively.Ascanbeseen,theagreementbetweenthemodelandtheexperimentisgood,withdifferencesoflessthan10,aslongastheloadisabove150N.Atlowerloadsthemeasuredexperimentalclearancesaremuchlargerthanthemodelpredictions,particularlyatthehigherspeedof3000rpmwhereat120Nthemeasuredclearanceis20lm,whichisabout60higherthanthepredictedvalue.Itturnsoutthatthecombinationofsuchlargeclearancesandrelativelylowviscosityofthewatermayresultinturbulentfluidfilm.Hence,theassumptionoflaminarflowonwhichthesolutionoftheReynoldsequationinRef.12isbasedmaybeviolatedmakingthemodelinvalidespeciallyatthehigherspeedandlowestload.InordertobeconsistentwiththemodelofRef.12itwasdecidedtolimitfurthercomparisonstoloadsabove150N.

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