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1、Part2:MachineElementsandMechanisms2.1IntroductionMachineelementsMachineelementsrefertoanelementarycomponentofamachine.Theyinclude:structuralcomponentssuchasbearings,axles,keys,fasteners,seals,andlubricants.Mechanismssuchasgeartrains,beltorchaindrives,linkages,camandfoll
2、owersystems,includingbrakesandclutchesControlcomponentssuchasbuttons,switches,indicators,sensors,actuatorsandcomputercontrollers.Machineelementsarebasicmechanicalpartsandfeaturesusedasthebuildingblocksofmostmachines.Figure2.1Machineelementsarethebuildingblocksofmostmach
3、ines2.2Fastenings2.2.1IntroductionAfastenerisadeviceusedtoconnectorjointwoormorecomponents.Traditionalformsoffasteningincludenuts,bolts,screwsandrivets.Theyarefrequentlyusedandmostofthemhavebeenstandardizedwiththeirshapesandsizes.Theimportanceoffastenersinamachine2.2.2T
4、hreadTerminologyFigure2.2Screwthreads(b)Left-handthread.(a)Right-handthread.Figure2.3Specialistterminologyusedfordescribingthreads.2.2.3ThreadForms3.Squarethread1.Metricthreads2.Acmethreads4.ButtressthreadsBasicpipethreadwith55○angle.5.Pipethread2.2.4PowerScrewFigure.2.
5、9Aworm-gearscrewjack.Apowerscrew,alsoknownasaleadscrew(orleadscrew)ortranslationscrew,isadeviceusedinmachinerytochangeangularmotionintolinearmotion,and,usually,totransmitpower.Theadvantagesofaleadscreware：LargeloadcarryingcapabilityCompactSimpletodesignEasytomanufacture
6、;nospecializedmachineryisrequiredLargemechanicaladvantagePreciseandaccuratelinearmotionSmooth,quiet,andlowmaintenanceMinimalnumberofpartsMostareself-lockingThedisadvantagesarethatmostarenotveryefficient.Leadscrewefficiencyistypicallybetween25and70%Ahigherperformingbutmo
7、reexpensivealternativeistheballscrew.Figure2.10Ballscrews.2.2.4Bolts,Studs,NutsandPlainWasherFigure2.11Boltsandscrews.1.Bolts2.StudsFigure2.12Studs.Figure2.13Standardnuts.3.Nuts4.WashersFigure2.14Washers.2.2.5AlternativeScrewHeadsandEndPointsFigure2.15Alternativescrewhe
8、ads.90。SlottedcountersunkSlottedroundheadSlottedcheeseheadSquareheadSlottedfillisterheadSlottedinstrumentheadS
