螺纹紧固件

Lesson4ThreadedFastenersThreadedfastenersperformthefunctionoflocating,clamping,adjustingandtransmittingforcefromonemachinemembertoanother.Theyarethoroughlystandardizedandgenerallydesignedforuseinmassproductionofmachines.Theuseofthethreadedfastenersremainsthebasicassemblymethodinthedesignandconstructionofmachinesdespiteadvancesinothermethodsofjoining.Thusthedesignersmustselectstandardfastenersofthetypeandsizethatwillmostadequatelysuittheapplicationathand.threadedfastener螺纹紧固件locating定位clamping夹紧massproduction大批量生产Athreadedfastenerisadevicethatcaneffectivelyexertandmaintainalargeforceinonedirection(axially)throughtheapplicationofasmallforceinanotherdirection(tangentially).Allarebasedonthesinglethreadedscrew,asimplemachinethatyieldsalargemechanicaladvantageinminimalspaceandtheoreticallyisselflocking.Effectiveusehowever,requirestheaidoftwoothersimplemachines:theleverandthewheel-and-axelmachine.Thewrenchisbasicallyalever,thescrewdriverisawheel-and-axlemachine.Threadedfastenersarebasicallysmall,highlystressedtensilecomponents.exert施加axially轴向的tangentially切向的mechanicaladvantage机械增益self-locking自锁的lever手柄wrench扳手adjustablewrench活扳手Threadsarehelicalridgesformedbycuttingorcoldformingagrooveontothesurfaceofacylindricalbar,thusproducingwhatisknownasascrew,bolt,orstud.Threadsarealsoformedinternallyincylindricalholesandconstitutewhatisknownasanut.Matchingexternalandinternalthreadssothattheymaybeassembledisthekeytoallthreadedfasteners.Therotarymotionofanutagainstastationaryscrewfirstimpartsanaxialmovementalongthescrew.Whenresistanceisencountered,thethreadsgenerateanaxialforceasdictatedbytheprincipleofthewedge.Furtherrotationdemandsincreasedefforts(torque),witharesultingincreaseinaxialforce.Thustheconnectionremainstightunlesssomeexternalinfluencesuchasvibrationortemperaturechangeoverridestheinitialcondition.helical螺旋状的ridge凸起coldforming冷加工groove凹槽bolt螺栓stud双头螺栓nut螺母principleofthewedge斜楔原理Unifiedstandardthreadisavailableinthreebasicseriesofdiameter-pitchcombinations.Thecoarse-threadseries(UNC)ismostcommonandisrecommendedforgeneralassemblyusewherevibrationisnotaproblemandwherefrequentdisassemblyisrequired.Thefine-threadseries(UNF)issomewhatstrongerintensionandismoresuitablewherefineadjustmentmayberequired.Thisseriesisoftenusedinaircraftassemblies.Theextra-fine-threadseries(UNEF)isemployedwherethematingexternalthreadisinathin-walledmember.Thisseriesisalsomoreresistancetovibrationandprovidesforveryfineadjustment.diameter-pitch直径螺距coarse-thread粗牙螺纹fine-thread细牙螺纹tension抗拉强度mating配合的thin-walled薄壁的Unifiedstandardthreadsareidentifiedondrawings,partslists,andsoforth,withashorthandnotationthatincludessize,threadseries,classoffit,externalorinternalthreadsymbol(Aisforexternalthreads,Bisforinternalthreads),andthehandofthread.Forexample,thedesignation1/4-20UNC-2A-RHidentifiesanexternallythreadedparthavingabasicmajordiameterof1/4in.,unifiedcoarsethreadwith20threadsperinch,toleranceclass2,andright-handthreads.Usuallythehanddesignationisomittedforright-hand,sincethesearestandard.Anotherexampleis3/4-16UNF-2B-LHwhichdesignatesaninternal,left-handthreadhavingabasicmajordiameterof3/4in.,and16unifiedfinethreadsperinchoflength.partslist零件清单shorthandnotation简单标注法classoffit配合等级externalthread外螺纹internalthread内螺纹handofthread螺纹旋向basicmajordiameter公称直径tolerance公差ISOstandardsincludemanydiameter-pitchcombinations,butproposedUSstandardsspecifyasinglediameterpitchseries.MetricthreadsaredesignatedbytheletterMfollowedbybasicmajordiameterinmillimeters,whichisthenfollowedbythepitchinmillimetersseparatedbythesymbol“x”.Forexample,M4x0.7specifiesametricthreadwithbasicmajordiameterof4mmandpitchof0.7mm.pitch螺距metricthread公制螺纹Washersareoftenusedwiththreadedfastenerstoprovideabetterbearingsurfacefornutsandboltheads,toprovideabearingsurfaceoverlargeclearanceholesorslots,todistributetheloadoveralargerarea,topreventmarringofpartsduringassembly,toimprovetorque-tensionratio(byreducingfriction),andtoprovidelocking,insomecasesthroughspringaction.washer垫片bearingsurface支撑面clearancehole光孔Flatwashersarethin,annular-shapeddisksusedprimarilyforbearingsurfaceandloaddistributionandhavenolockingcapacity.Helicalspringlock-washersareessentiallysinglecoilhelicalspringsthatflattenunderload.Springactionassistsinmaintainingtheboltload,whilesplitedgesprovidesomelockingactionbybitingintothebearingsurfaces.Lockwashersgenerallymadeofhardenedsteel.flatwasher平垫annular-shaped圆环状的lockwasher自锁垫圈flatten变平splitedge开口边缘biteinto咬入hardenedsteel淬火钢Carbonsteelandsteelalloysaremostcommonlyusedfastenersmaterials.Manystainlesssteelalloysareusedforthreadedfastenerswhereimprovedcorrosionresistanceisrequired.Nickel-basedsuper-alloyssuchasMonelandInconelareusedforfastenerswherestrengthathightemperaturesaswellascorrosionresistanceisrequired.Aluminum,bronzeandbrassarealsousedforthreadedfasteners.Incorrosiveenvironmentswheregreatstrengthisnotrequired,fastenersmadeofnylonandotherplasticsarebothsuitableandeconomical.superalloy高温合金Monel一种铜镍合