機械類畢業(yè)設計外文翻譯范文

機械類畢業(yè)設計外文翻譯、畢業(yè)設計（論文）外譯文題目：軸承的摩擦與潤滑10月15日外文文獻原文：Friction,LubricationofBearingInmanyoftheproblemthusfar,thestudenthasbeenaskedtodisregardorneglectfriction.Actually,frictionispresenttosomedegreewhenevertwopartsareincontactandmoveoneachother.Thetermfrictionreferstotheresistanceoftwoormorepartstomovement.Frictionisharmfulorvaluabledependinguponwhereitoccurs.frictionisnecessaryforfasteningdevicessuchasscrewsandrivetswhichdependuponfrictiontoholdthefastenerandthepartstogether.Beltdrivers,brakes,andtiresareadditionalapplicationswherefrictionisnecessary.Thefrictionofmovingpartsinamachineisharmfulbecauseitreducesthemechanicaladvantageofthedevice.Theheatproducedbyfrictionislostenergybecausenoworktakesplace.Also,greaterpowerisrequiredtoovercometheincreasedfriction.Heatisdestructiveinthatitcausesexpansion.Expansionmaycauseabearingorslidingsurfacetofittighter.Ifagreatenoughpressurebuildsupbecausemadefromlowtemperaturematerialsmaymelt.Therearethreetypesoffrictionwhichmustbeovercomeinmovingparts:(1)starting,(2)sliding,and(3)rolling.Startingfrictionisthefrictionbetweentwosolidsthattendtoresistmovement.Whentwopartsareatastateofrest,thesurfaceirregularitiesofbothpartstendtointerlockandformawedgingaction.Toproducemotionintheseparts,thewedge-shapedpeaksandvalleysofthestationarysurfacesmustbemadetoslideoutandovereachother.Therougherthetwosurfaces,thegreaterisstartingfrictionresultingfromtheirmovement.Sincethereisusuallynofixedpatternbetweenthepeaksandvalleysoftwomatingparts,theirregularitiesdonotinterlockoncethepartsareinmotionbutslideovereachother.Thefrictionofthetwosurfacesisknownasslidingfriction.Asshowninfigure,startingfrictionisalwaysgreaterthanslidingfriction.Rollingfrictionoccurswhenrollerdevcesaresubjectedtotremendousstresswhichcausethepartstochangeshapeordeform.Undertheseconditions,thematerialinfrontofarollertendstopileupandforcestheobjecttorollslightlyuphill.Thischangingofshape,knownasdeformation,causesamovementofmolecules.Asaresult,heatisproducedfromtheaddedenergyrequiredtokeepthepartsturningandovercomefriction.Thefrictioncausedbythewedgingactionofsurfaceirregularitiescanbeovercomepartlybytheprecisionmachiningofthesurfaces.However,eventhesesmoothsurfacesmayrequiretheuseofasubstancebetweenthemtoreducethefrictionstillmore.Thissubstanceisusuallyalubricantwhichprovidesafine,thinoilfilm.Thefilmkeepsthesurfacesapartandpreventsthecohesiveforcesofthesurfacesfromcominginclosecontactandproducingheat.Anotherwaytoreducefrictionistousedifferentmaterialsforthebearingsurfacesandrotatingparts.Thisexplainswhybronzebearings,softalloys,andcopperandtiniolitebearingsareusedwithbothsoftandhardenedsteelshaft.Theiolitebearingisporous.Thus,whenthebearingisdippedinoil,capillaryactioncarriestheoilthroughthespacesofthebearing.Thistypeofbearingcarriesitsownlubricanttothepointswherethepressuresarethegreatest.Movingpartsarelubricatedtoreducefriction,wear,andheat.Themostcommonlyusedlubricantsareoils,greases,andgraphitecompounds.Eachlubricantservesadifferentpurpose.Theconditionsunderwhichtwomovingsurfacesaretoworkdeterminethetypeoflubricanttobeusedandthesystemselectedfordistributingthelubricant.Onslowmovingpartswithaminimumofpressure,anoilgrooveisusuallysufficienttodistributetherequiredquantityoflubricanttothesurfacesmovingoneachother.Asecondcommonmethodoflubricationisthesplashsysteminwhichpartsmovinginareservoiroflubricantpickupsufficientoilwhichisthendistributedtoallmovingpartsduringeachcycle.Thissystemisusedinthecrankcaseoflawn-mowerenginestolubricatethecrankshaft,connectingrod,andpartsofthepiston.Alubricationsystemcommonlyusedinindustrialplantsisthepressuresystem.Inthissystem,apumponamachinecarriesthelubricanttoallofthebearingsurfacesataconstantrateandquantity.Therearenumerousothersystemsoflubricationandaconsiderablenumberoflubricantsavailableforanygivensetofoperatingconditions.Modernindustrypaysgreaterattentiontotheuseoftheproperlubricantsthanatprevioustimebecauseoftheincreasedspeeds,pressures,andoperatingdemandsplacedonequipmentanddevices.Althoughoneofthemainpurposesoflubricationisreducefriction,anysubstance-liquid,solid,orgaseous-capableofcontrollingfrictionandwearbetweenslidingsurfacescanbeclassedasalubricant.VarietiesoflubricationUnlubricatedsliding.Metalsthathavebeencarefullytreatedtoremoveallforeignmaterialsseizeandweldtooneanotherwhenslidtogether.Intheabsenceofsuchahighdegreeofcleanliness,adsorbedgases,watervapor,oxides,andcontaminantsreducefrictio9nandthetendencytoseizebutusuallyresultinseverewear;thisiscalled“unlubricated”ordrysliding.Fluid-filmlubrication.Interposingafluidfilmthatcompletelyseparatestheslidingsurfacesresultsinfluid-filmlubrication.Thefluidmaybeintroducedintentionallyastheoilinthemainbearingofanautomobile,orunintentionally,asinthecaseofwaterbetweenasmoothtubertireandawetpavement.Althoughthefluidisusuallyaliquidsuchasoil,water,andawiderangeofothermaterials,itmayalsobeagas.Thegasmostcommonlyemployedisair.Boundarylubrication.Aconditionthatliesbetweenunlubricatedslidingandfluid-filmlubricationisreferredtoasboundarylubrication,alsodefinedasthatconditionoflubricationinwhichthefrictionbetweensurfacesisdeterminedbythepropertiesofthesurfacesandpropertiesofthelubricantotherthanviscosity.Boundarylubricationencompassesasignificantportionoflubricationphenomenaandcommonlyoccursduringthestartingandstoppingoffmachines.Solidlubrication.Solidsuchasgraphiteandmolybdenumdisulfidearewidelyusedwhennormallubricantsdonotpossesssufficientresistancetoloadortemperatureextremes.Butlubricantsneednottakeonlysuchfamiliarformsasfats,powders,andgases;evensomemetalscommonlyserveasslidingsurfacesinsomesophisticatedmachines.FunctionoflubricantsAlthoughalubricantprimarilycontrolsfrictionandordinarilydoesperformnumerousotherfunctions,whichvarywiththeapplicationandusuallyareinterrelated.Frictioncontrol.Theamountandcharacterofthelubricantmadeavailabletoslidingsurfaceshaveaprofoundeffectuponthefrictionthatisencountered.Forexample,disregardingsuchrelatedfactorsasheatandwearbutconsideringfrictionalonebetweenthesamesurfaceswithonlubricant.Underfluid-filmconditions,frictionisencountered.Inagreatrangeofviscositiesandthuscansatisfyabroadspectrumoffunctionalrequirements.Underboundarylubricationconditions,theeffectofviscosityonfrictionbecomeslesssignificantthanthechemicalnatureofthelubricant.Wearcontrol.wearoccursonlubricatedsurfacesbyabrasion,corrosion,andsolid-to-solidcontactwearbyprovidingafilmthatincreasesthedistancebetweentheslidingsurfaces,therebylesseningthedamagebyabrasivecontaminantsandsurfaceasperities.Temperaturecontrol.Lubricantsassistincontrollingcorrosionofthesurfacesthemselvesistwofold.Whenmachineryisidle,thelubricantactsasapreservative.Whenmachineryisinuse,thelubricantcontrolscorrosionbycoatinglubricatedpartswithaprotectivefilmthatmaycontainadditivestoneutralizecorrosivematerials.Theabilityofalubricanttocontrolcorrosionisdirectlyrelatlytothethicknessofthelubricantfilmremainingonthemetalsurfacesandthechermicalcompositionofthelubricant.OtherfunctionsLubricationarefrequentlyusedforpurposesotherthanthereductionoffriction.Someoftheseapplicationsaredescribedbelow.Powertransmission.Lubricantsarewidelyemployedashydraulicfluidsinfluidtransmissiondevices.Insulation.Inspecializedapplicationssuchastransformersandswitchgear,lubricantswithhighdielectricconstantsactsaselectricalinsulators.Formaximuminsulatingproperties,alubricantmustbekeptfreeofcontaminantsandwater.Shockdampening.Lubricantsactasshock-dampeningfluidsinenergytransferringdevicessuchasshockabsorbersandaroundmachinepartssuchasgearsthataresubjectedtohighintermittentloads.Sealing.Lubricatinggreasefrequentlyperformsthespecialfunctionofformingasealtoretainlubricantsortoexcludecontaminants.Theobjectoflubricationistoreducefriction,wear,andheatingofmachineparswhichmoverelativetoeachother.Alubricantisanysubstancewhich,wheninsertedbetweenthemovingsurfaces,accomplishesthesepurposes.Mostlubricantsareliquids(suchasmineraloil,siliconefluids,andwater),buttheymaybesolidforuseindrybearings,greasesforuseinrollingelementbearing,orgases(suchasair)foruseingasbearings.Thephysicalandchemicalinteractionbetweenthelubricantandlubricatingsurfacesmustbeunderstoodinordertoprovidethemachineelementswithsatisfactorylife.Theunderstandingofboundarylubricationisnormallyattributedtohardyanddoubleday,whofoundtheextrememlythinfilmsadheringtosurfaceswereoftensufficienttoassistrelativesliding.Theyconcludedthatundersuchcircumstancesthechemicalcompositionoffluidisimportant,andtheyintroducedtheterm“boundarylubrication”.Boundarylubricationisattheoppositeendofthespectrumfromhydrodynamiclubrication.Fivedistinctofformsoflubricationthatmaybedefined:(a)hydrodynamic;(b)hydrostatic;(c)elastohydrodynamic(d)boundary;(e)solidfilm.Hydrodynamiclubricationmeansthattheload-carryingsurfacesofthebearingareseparatedbyarelativelythickfilmoflubricant,soastopreventmetalcontact,andthatthestabilitythusobtainedcanbeexplainedbythelawsofthelubricantunderpressure,thoughitmaybe;butitdoesrequiretheexistenceofanadequatesupplyatalltimes.Thefilmpressureiscreatedbythemovingsurfacesitselfpullingthelubricantunderpressure,thoughitmaybe.Thefilmpressureiscreatedbythemovingsurfacetocreatthepressurenecessarytoseparatethesurfacesagainsttheloadonthebearing.hydrodynamiclubricationisalsocalledfullfilm,orfluidlubrication.Hydrostaticlubricationisobtainedbyintroducingthelubricant,whichissometimeairorwater,intotheload-bearingareaatapressurehighenoughtoseparatethesurfacewitharelativelythickfilmoflubricant.So,unlikehydrodynanmiclubrication,motionofonesurfacerelativetoanotherisnotrequired.Elasohydrodynamiclubricationisthephenomenonthatoccurswhenalubricantisintroducedbetweensurfaceswhichareinrollingcontact,suchasmatinggearsorrollingbearings.Themathematicalexplanationrequiresthehertziantheoryofcontactstressandfluidmechanics.Whenbearingmustbeoperatedatexetremetemperatures,asolidfilmlubricantsuchasgraphiteormolybdenumdisulfidemustbeuseusedbecausetheordinarymineraloilsarenotsatisfactory.Mustresearchiscurrentlybeingcarriedoutinaneffort,too,tofindcompositebearingmaterialswithlowwearratesaswellassmallfrictionalcoefficients.Inajournalbearing,ashaftrotatesoroscillateswithinthebearing,andtherelativemotionissliding.inanantifrictionbearing,themainrelativemotionisrolling.afollowermayeitherrollorslideonthecam.Gearteethmatewitheachotherbyacombinationofrollingandsliding.pistionsslidewithintheircylinders.Alltheseapplicationsrequirelubricationtoreducefriction,wear,andheating.Thefieldofapplicationforjournalbearingsisimmense.Thecrankshaftandconnectingrodbearingsofanautomotiveenginemustpoerateforthousandsofmilesathightemperaturesandundervaryingloadconditions.thejournalbearingsusedinthesteamturbinesofpowergeneratingstationissaidtohavereliabilitiesapproaching100percent.Attheotherextremetherearethousandsofapplicationsinwhichtheloadsarelightandtheservicerelativelyunimportant.asimple,easilyinstalledbearingisrequired,suinglittleornolubrication.Insuchcasesanantifrictionbearingmightbeapooranswerbecausebecauseofthecost,theclose,theradialspacerequired,ortheincreasedinertialeffects.Recentmetallurgydevelopmentsinbearingmaterials,combinedwithincreasedknowledgeofthelubricationprocess,nowmakeitpossibletodesignjournalbearingswithsatisfactorylivesandverygoodreliabilities.參考文獻：1.ChambersT.L.,ParkinsonA.R.,1998,“KnowledgeRepresentationandConversionofHybridExpertSystems.”TransactionsoftheASME,v120,pp468-4742.Koelsch,JamesR.,1999,“Softwareboostsmolddesignefficiency“MoldingSystems,v57,n3,p16-23.3.Lee,Rong-Shean,Chen,Yuh-Min,Lee,Chang-Zou,1997“Developmentofaconcurrentmolddesignsystem:Aknowledge-basedapproach”,ComputerIntegratedManufacturingSystems,v10,n4,p287-3074.SteadmanSally,PellKynricM,1995,“Expertsystemsinengineeringdesign:Anapplicationforinjectionmoldingofplasticparts“JournalofIntelligentManufacturing,v6,p347-353.5.FernandezA.,CastanyJ.,SerrallerF.,JavierreC.,1997,“CAD/CAEassistantforthedesignofmoldsandprototypesforinjectionofthermoplastics“InformationTechnological,v8,p117-124.6.DouglasMBryce,1997,“Plasticinjectionmolding-Materialselectionandproductdesign”,v2,pp1-48.7.DouglasMBryce,1997,“Plasticinjectionmolding-Molddesignfundamentals”,v2,pp1-120中文譯文：軸承的摩擦與潤滑現(xiàn)在看來，有很多這種情況，許多學生在被問到關于摩擦的問題時，往往都沒引起足夠的重視，甚至是忽視它。實際上，摩擦從某種程度上說，存在于任何兩個相接觸并有相對運動趨勢的部件之間。而摩擦這個詞，本身就意味著，兩個或兩個以上部件的阻止相對運動趨勢。在一個機器中，運動部件的摩擦是有害的，因為它降低了機械對能量的充分利用。由它引起的熱能是一種浪費的能量。因為不能用它做任何事情。還有，它還需要更大的動力來克服這種不斷增大的摩擦。熱能是有破壞性的。因為它產(chǎn)生了膨脹。而膨脹能夠使得軸承或滑動表面之間的配合更緊密。如果因為膨脹導致了一個足夠大的積壓力，那么，這個軸承就可能會卡死或密封死。另外，隨著溫度的升高，如果不是耐高溫材料制造的軸承，就可能會損壞甚至融化。在運動部件之間會發(fā)生很多摩擦，如1.啟動摩擦2.滑動摩擦3.轉(zhuǎn)動摩擦。啟動摩擦是兩個固體之間產(chǎn)生的傾向于組織其相對運動趨勢的摩擦。當兩個固體處于靜止狀態(tài)時，這兩個零件表面的不平度傾向于相互嵌入，形成楔入作用，為了使這些部件“動”起來。這些靜止部件的凹谷和尖峰必須整理光滑，而且能相互抵消。這兩個表面之間越不光滑，由運動造成的啟動摩擦（最大靜摩擦力）就會越大。因為，一般來說，在兩個相互配合的部件之間，其表面不平度沒有固定的圖形。一旦運動部件運動起來，便有了規(guī)律可循，滑動就能夠?qū)崿F(xiàn)這一點。兩個運動部件之間的摩擦就叫做滑動摩擦。啟動摩擦一般都稍大于滑動摩擦。轉(zhuǎn)動摩擦一般發(fā)生在轉(zhuǎn)動部件和設備上，這些設備“抵觸”極大的外作用力，當然這種外力會導致部件的變形和性能的改變。在這種情況下，轉(zhuǎn)動件的材料趨向于堆積而且強迫運動部件緩慢運動，這種改變就是一般所說的形變。能夠使分子運動。當然，最終的結(jié)果是，這種額外的能量產(chǎn)生了熱能，這是必須的。因為它能夠保證運動部件的運動和克服摩擦力。由運動部件的表面不平度的楔入作用引起的摩擦能夠被部分的克服，那就需要靠兩表面之間的潤滑?？墒牵词故欠浅９饣膬蓚€表面之間也可能需要一種物質(zhì)，這種物質(zhì)就是一般所說的潤滑劑，它能夠提供一個比較好的、比較薄的油膜。這個油膜使兩個表面分離，而且組織運動部件的兩個表面的相互潛入，以免產(chǎn)生熱量使兩表面膨脹，又引起更近的接觸。減小摩擦的另一種方式是用不同的材料制造軸承和轉(zhuǎn)動零件。能夠拿黃銅軸承、鋁合金和含油軸承合金做例子進行解釋。也就是說用軟的或硬的金屬組成表面。含油軸承合金是軟的。這樣當軸承在油中浸泡過以后，因為毛細管的作用，將由帶到軸承的各個表面。這種類型的軸承把它的潤滑劑帶到應力最大的部位。對運動部件潤滑以減小摩擦，應力和熱量，最常見的是油、脂、還有合成劑。每一種潤滑劑都有其各自不同的功能和用途。兩個運動部件之間的運動情況決定了潤滑劑的類型的選擇。潤滑劑的分布也決定了系統(tǒng)的選擇。在低速度運動的部件，一個油溝足以將所需要的數(shù)量的潤滑劑送到相互運動的表面。第二種通用的潤滑方法是飛濺潤滑系統(tǒng)，在每個周期內(nèi)這個系統(tǒng)內(nèi)一些零件經(jīng)過潤滑劑存儲的位置，帶起足夠的潤滑油，然后將其散布到所有的運動零件上。這種系統(tǒng)用于草坪修剪機中發(fā)動機的曲軸箱，對曲軸、連桿和活塞等零件進行潤滑。在工業(yè)裝置中，常見的有一種潤滑系統(tǒng)是壓力系統(tǒng)。這種系統(tǒng)中，一個機器上的一個泵，能夠?qū)櫥瑒У剿械妮S承表面。而且以一種連續(xù)的固定的速度和數(shù)量。關于潤滑，還有許多其它的系統(tǒng)，針對各種類型的潤滑劑，對不同類型的運動零件是有效的。由于設備或裝置的速度、壓力和工作要求的提高，現(xiàn)代工業(yè)比以前任何時候都更注重選用適當?shù)臐櫥瑒?。盡管潤滑的主要目的之一是為了減小摩擦力，任何能夠控制兩個滑動表面之間摩擦和磨損的物質(zhì)，不論是液體還是固體或氣體，都能夠歸類于潤滑劑。潤滑的種類無潤滑滑動。經(jīng)過精心處理的、去除了所有外來物質(zhì)的金屬在相互滑動時會粘附或熔接到一起。當達不到這么高的純凈度時，吸附在表面的氣體、水蒸氣、氧化物和污染物就會降低摩擦力并減小粘附的趨勢，但一般會產(chǎn)生嚴重的磨損，這種現(xiàn)象被稱為“無潤滑”摩擦或者叫做干摩擦。流體膜潤滑。在滑動面之間引入一層流體膜，把滑動表面完全隔離開，就產(chǎn)生了流體膜潤滑。這種流體可能是有意引入的。例如汽車主軸承中的潤滑油；也可能是無意中引入的，例如在光滑的橡膠輪胎和潮濕的路面之間的水。盡管流體一般是油、水和其它很多種類的液體，它能夠是氣體。最常見的氣體是空氣。為了把零件隔離開，潤滑膜中的壓力必須和作用在滑動面上的負荷保持平衡。如果潤滑膜中的壓力是由外源提供的，這種系統(tǒng)稱為流體靜壓潤滑。如果滑動表面之間的壓力是由于滑動面本身的形狀和運動所共同產(chǎn)生的，這種系統(tǒng)就稱為流體動壓力潤滑。邊界潤滑。處于無潤滑滑動和流體膜潤滑之間的潤滑被稱為邊界潤滑。它能夠被定為這樣一種潤滑狀態(tài)，在這種狀態(tài)中，表面之間的摩擦力取決于表面的性質(zhì)和潤滑劑中的其它性質(zhì)。邊界潤滑包括大部分潤滑現(xiàn)象，一般在機器的啟動和停止時出現(xiàn)。固體潤滑。當普通潤滑劑沒有足夠的承受能力或者不能在溫度極限下工作時，石墨和二硫化鉬這一類固體潤滑劑得到廣泛應用。但潤滑劑不但僅以脂肪、粉末和油脂這樣一些為人們所熟悉的形態(tài)出現(xiàn)，在一些精密的機器中，金屬也一般作為滑動面。潤滑劑的作用盡管潤滑劑主要是用來控制摩擦和磨損的，它們能夠而且一般也確實起到許多其它的作用，這些作用隨其用途不同而不同，但一般相互之間是有關系的。控制摩擦力。滑動面之間潤滑劑的數(shù)量和性質(zhì)對所產(chǎn)生的摩擦力有很大的影響。例如，不考慮熱和磨損這些相關因素，只考慮兩個油膜潤滑表面見的摩擦力，它能比兩個同樣表面，但沒有潤滑時小200倍。在流體潤滑狀況時，摩擦力與流體黏度成正比。一些諸如石油衍生物這類潤滑劑，能夠有很多黏度，因此能夠滿足范圍寬廣的功能要求。在邊界潤滑狀態(tài)，潤滑劑黏度對摩擦力的影響不象其化學性質(zhì)的影響那么顯著。磨損控制。磨蝕、腐蝕與固體和固體之間的接觸就會造成磨損。適當?shù)臐櫥瑒⒛軒椭朔鲜鎏岬降囊恍┠p現(xiàn)象。潤滑劑經(jīng)過潤滑膜來增加滑動面之間的距離，從而減輕磨料污染物和表面不平度造成的損傷，因此，減輕了磨損和由固體與固體之間接觸造成的磨損。控制溫度。潤滑劑經(jīng)過減小摩擦和將產(chǎn)生的熱量帶走來降低溫度。其效果取決于潤滑劑的用量和外部冷卻措施。冷卻劑的種類也會在較小的程度上影響表面的溫度?？刂聘g。潤滑劑在控制表面腐蝕方面有雙重作用。當機器閑置不工作時，潤滑劑起到防腐劑的作用。當機器工作時，潤滑劑經(jīng)過給被潤滑零件涂上一層可能含有添加劑，能使腐蝕性材料中和的保護膜來控制腐蝕。潤滑劑控制腐蝕的能力與潤滑劑保留在金屬表面的潤滑膜的厚度和潤滑劑的化學成分有直接的關系。其它作用