16磨损和润滑

Wearcanbedefinedastheprogressivelossofmaterialfromtheoperatingsurfaceofabodyoccurringasaresultofrelativemotionatthesurface.Theproblemofwearariseswhereverthereareloadandmotionbetweensurface,andisthereforeimportantinengineeringpractice,oftenbeingthemajortypesofweararedescribenext:磨损可以被定义为材料的发生于表面的相对运动的结果，一个主体的操作表面上的逐渐丧失。磨损的问题出现了任何存在负荷和运动表面之间，并因此在工程实践中重要的是，往往是磨损的主要类型是描述下：AdhesiveWear.Whentwosurfacesareloadedagainsteachother,thewholeofthecontactloadiscarriedonverysmallareaoftheasperitycontacts.Therealcontactpressureattheseasperitiesisveryhigh,andadhesiontakesplacebetweenthem.IfatangentialforceisappliedtothemodelshowninFig.16.1,shearingcantakeplaceeither(a)attheinterfaceor(b)beloworabovetheinterface,causingadhesivewear.Becauseoffactorssuchasstrainhardeningattheasperitycontact,theadhesivebondsoftenarestrongerthanthebasemetals.Thus,duringsliding,fractureusuallyoccursintheweakerorsoftercomponent,andawearfragmentisgenerated.Althoughthisfragmentisattachedtothehardercomponent(uppersurfaceinFig.16.1c),iteventuallybecomesdetachedduringfurtherrubbingattheinterfaceanddevelopsintoloosewearparticle.粘着磨损。当两个表面加载针锋相对，整个接触载荷进行上的粗糙的接触面积非常小。在这些凹凸的实际接触压力是非常高的，和粘附以在它们之间的地方。如果切向力施加到在Fig.16.1所示的模型，剪切可以发生或者（a）在界面处或（b）下面或上面的界面，引起粘着磨损。由于因素如应变硬化的凹凸接触时，粘合剂粘合往往比贱金属更强。因此，滑动过程中，骨折通常发生在较弱或较软的成分，并产生磨损碎片。虽然此片段被连接到较硬部件（在图上表面。16.1c）中，它最终变得期间进一步摩擦界面处分离，并发展成松散磨粒。AbrasiveWear.Thistypeofweariscausedbyahard,roughsurface(orasurfacecontaininghard,protrudingparticles)slidingacrossanothersurface.Asaresult,microchipsareproduced,therebyleavinggroovesorscratchedonthesoftersurface(Fig.16.2).Infact,processessuchasfilingandgrindingactinthismanner.Thedifferenceisthat,intheseoperations,theprocessparametersarecontrolledtoproducethedesiredshapesandsurfacesthroughwear;whereas,abrasiveweargenerallyisunintendedandunwanted.磨料磨损。这种类型的磨损是由坚硬，粗糙的表面（或含有硬质，突出颗粒表面）穿过另一面滑动造成的。其结果是，微芯片的生产，从而留下凹槽或划痕对较软的表面（Fig.16.2）。事实上，过程如锉磨的行为以这种方式。所不同的是，在这些操作中，工艺参数控制，以产生通过磨损所需要的形状和表面;然而，磨损一般是无意的和不必要的。CorrosiveWear.Alsoknownasoxidationorchemicalwear,thistypeofweariscausedbychemicalorelectrochemicalreactionsbetweenthesurfacesandtheenvironment.Thefinecorrosionproductsonthesurfaceconstitutethewearparticlesinthistypeofwear.Whenthecorrosivelayerisdestroyedorremovedthroughsliding,anotherlayerbeginstoform,andtheprocessofremovalandcorrosivelayerformationisrepeated.腐蚀磨损。也被称为氧化或化学磨损，这种类型的磨损被表面与环境之间的化学或电化学反应引起的。表面上的精细的腐蚀产物构成在这种类型的磨损的磨损颗粒。当腐蚀层是通过滑动破坏或除去，另一层开始形成，并去除和腐蚀层形成的过程被重复。FatigueWear.Fatigueweariscausedwhenthesurfaceofamaterialissubjectedtocyclicloading;oneexampleofthisistherollingcontactinbearings.Thewearparticlesusuallyareformedthroughspallingorpitting.Anothertypeoffatiguewearisbythermalfatigue.Cracksonthesurfacearegeneratedbythermalstressesfromthermalcycling,suchaswhenacoolforgingdierepeatedlycontactshotworkpieces.Thesecracksthenjoin,andthesurfacebeginstospall,producingfatiguewear.疲劳磨损。疲劳磨损是造成当一种材料的表面进行循环加载；这样的一个例子是在轴承的滚动接触。磨损颗粒通常是通过剥落、点蚀的形成。另一种类型的疲劳磨损是由热疲劳。表面上的裂纹是由热应力产生的热循环，如当一个冷锻模具反复接触热的工件。这些裂缝然后加入，和表面开始剥落，产生疲劳磨损。Althoughweargeneralaltersapart’ssurfacetopographyandmayresultinseveresurfacedamage,italsocanhaveabeneficialeffect.Therunning-inperiodforvariousmachinesandenginesproducesthistypeofwearbyremovingthepeaksfromasperities(Fig.16.3).Thus,undercontrolledconditions,wearmayberegardedasatypeofsmoothingorpolishingprocess.虽然磨损一般改变一个部件的表面形貌，并可能导致严重的表面损伤，它也可以具有有益效果。在磨合期关于各种机器和发动机通过从凹凸（Fig.16.3）除去峰产生这种类型的磨损。因此，在受控条件下，磨损可被视为一种类型的平滑或抛光过程的。Lubricationisaprocessbywhichthefrictionandwearbetweentwosolidsurfacesinrelativemotionisreducedsignificantlybytheinterposingalubricantbetweenthem.Thesearefourtypesoffluidlubricationthataregenerallyofinterestinengineeringpractice(Fig.16.4):润滑是一个过程，它相对运动之间的摩擦表面两个固体磨损是由插入它们之间的润滑剂明显减少。有四类流体润滑通常在实际工程利息（fig.16.4）：后面翻译是作业1.Inthick-filmlubrication,thetwosurfacesarecompletelyseparatedfromeachotherbyacontinuousfluidfilm.Thefluidfilmcanbedevelopedeitherhydrostaticallyor,moreoftenbythewedgeeffectoftheslidingsurfacesinthepresenceofaviscousfluidattheinterface.1.厚膜润滑，两个表面彼此完全由连续流体膜分离。流体薄膜既产生静压力，或更通常由滑动面的粘性流体的界面处的存在的楔效应。2.Astheloadbetweenthetwosurfacesincreasesorastheslidingspeedandviscosityofthefluiddecrease,thelubricantfilmbecomesthinner(thin-filmlubrication).Thisconditionraisesthefrictionattheslidinginterfacesandresultsinslightwear.2.由于两个表面之间的负载增加或作为滑动速度和流体的粘度降低，润滑膜的厚度变薄（薄膜润滑）。这种情况引起了摩擦的滑动界面，并导致轻微磨损。3.Inmixedlubrication,althoughthecontactingsurfacesareseparatedbyathinlubricantfilm,asperitycontactalsomaytakeplace.Thetotalappliedloadisthoughttobecarriedbyasperitycontactsandpartlybyhydrodynamicaction.3。在混合润滑，虽然接触表面被一层薄的润滑油膜隔开，接触也可能发生。总载荷是由粗糙的接触部分由水动力作用。4.Inboundarylubrication,theloadissupportedbycontactingsurfacescoveredwithaboundaryfilmoflubricant(Fig.16.4d).Thisisathin(molecular)lubricantlayerthatisattractedphysicallytothemetalsurfaces,thuspreventingdirectmetal-to-metalcontactofthetwobodiesandreducingwear.4。在边界润滑条件下在边界润滑，负载由接触覆盖有润滑剂（Fig.16.4d）边界膜表面支撑。这是一个薄（分子）润滑层，引起身体上的金属表面，从而防止金属直接对两体金属接触和减少磨损。