机械专业英语省公共课一等奖全国赛课获奖课件.pptx

Part 2:Machine Elements and Mechanisms第1页2.1 Introduction Machine elementsMachineelementsrefertoanelementarycomponentofamachine.Theyinclude:structural components suchasbearings,axles,keys,fasteners,seals,andlubricants.Mechanismssuchasgeartrains,beltorchaindrives,linkages,camandfollowersystems,includingbrakesandclutches第2页Control components suchasbuttons,switches,indicators,sensors,actuatorsandcomputercontrollers.Machine elements are basic mechanicalparts and features used as the buildingblocksofmostmachines.第3页Figure2.1Machineelementsarethebuildingblocksofmostmachines第4页2.2 Fastenings2.2.1 IntroductionAfastenerisadeviceusedtoconnectorjointwoormorecomponents.Traditionalformsoffasteningincludenuts,bolts,screwsandrivets.Theyarefrequentlyusedandmostofthemhavebeenstandardizedwiththeirshapesandsizes.The importance of fasteners in a machine第5页2.2.2 Thread TerminologyFigure2.2Screwthreads(b)Left-handthread.(a)Right-handthread.第6页Figure2.3Specialistterminologyusedfordescribingthreads.第7页2.2.3 Thread Forms3.Squarethread1.Metricthreads2.Acmethreads第8页4.ButtressthreadsBasicpipethreadwith55angle.5.Pipethread第9页2.2.4 Power ScrewFigure.2.9Aworm-gearscrewjack.Apowerscrew,alsoknown as a leadscrew(orlead screw)or translationscrew,is a device used inmachinerytochangeangularmotion into linear motion,and,usually,totransmitpower.第10页Theadvantagesofaleadscreware：LargeloadcarryingcapabilityCompactSimpletodesignEasytomanufacture;nospecializedmachineryisrequiredLargemechanicaladvantagePreciseandaccuratelinearmotionSmooth,quiet,andlowmaintenanceMinimalnumberofpartsMostareself-lockingThedisadvantagesarethatmostarenotveryefficient.Leadscrewefficiencyistypicallybetween25and70%第11页Ahigherperformingbutmoreexpensivealternativeistheball screw.Figure2.10Ballscrews.第12页2.2.4 Bolts,Studs,Nuts and Plain WasherFigure2.11Boltsandscrews.1.Bolts2.StudsFigure2.12Studs.第13页Figure2.13Standardnuts.3.Nuts4.WashersFigure2.14Washers.第14页2.2.5 Alternative Screw Heads and End PointsFigure2.15Alternativescrewheads.90。SlottedcountersunkSlottedroundheadSlottedcheeseheadSquareheadSlottedfillisterheadSlottedinstrumentheadSlottedheadHexagonsocketheadPhillipshead第15页Figure2.16Alternativescrewpoints.FlatDogConicalRoundCup2.2.6 Selection of Screwed FastenersSelectioncriteriaforthescrewmaterials：temperature；requiredstrength；resistancetocorrosion；jointmaterialandcost；assemblyconsiderations.第16页2.2.7 Systems for Specifying the Dimensions of Screws1.ISOmetricscrewthread第17页2.BritishStandardWhitworth第18页3.BritishAssociationscrewthread第19页4.UnifiedThreadStandard第20页2.2.8 Applications of Screwed FastenersFigure2.17Applicationsofscrewedfasteners.Nameallpartsandfastenersinthedrawing第21页 2.3 Keys and Pins(a)Parallelkeys 2.3.1 Keys (b)SemicircularkeysFigure2.19Parallelkeyjoints.（1-Shaft.2-Hub,3-Key,4-Nut,5-Washer）(c)TaperedkeysFigure2.18Keys.第22页Figure2.20Semicircularkeys.Figure2.21Taperedkeys.2.3.2 Pins (a)Taperpins(b)Parallelpins(C)splitpinsFigure2.22Pinjoints.第23页 2.4 Riveted JointsFigure2.23Conventionalrivetbeforeandaftersetting 2.5 Welded JointsWeldingcanbedescribedastheprocessofjoiningmaterialtogetherbyraisingthetemperatureofthesurfacestobejoinedsothattheybecomeplasticormolten.第24页 Types of Welding:ungsteninertgaswelding(TIG)submergedarcwelding(SAW)metalinertgaswelding(MIG)manualmetalarcwelding(MMA)resistanceweldinggaswelding第25页 2.6 SpringlClamplStoreelasticenergylReduceshock.Functions of springs:(a)Helicalcompressionsprings.(b)Helicalextensionsprings.(c)Torsionsprings.(d)Spiraltorsionsprings.(f)Leafsprings.第26页2.7 Bearings2.7.1 Bearing classificationJournalbearingDeepgrooveballbearings第27页Types:Figure2.26Bearingclassification.第28页Factors for consideration when selecting bearings：(1)Load(2)speed(3)location(4)size(5)cost(6)startingtorque(7)noise(8)lubricationsupply 2.7.2 Bearing type selection第29页2.27Bearingtypeselectionbyloadcapacityandspeed.第30页Table 2.9Comparisonofbearingperformanceforcontinuousrotation第31页Table2.10 Merits of different rolling contact bearings 第32页2.8 Clutches and BrakesClutches and brakes provide frictional,magnetic,hydraulic or mechanical connectionbetweentwomachineelements,usuallyshafts.Inreality,thesamedevicecanfunctionasabrakeorclutchbyfixingitsoutputelementtoashaftthatcanrotateortoground,respectively.第33页The similarities between clutches and brakes?Figure2.28Idealizedfrictiondiscclutchorbrake.DrivingdiscActuatorPusher discstogetherDrivendiscFrictionmaterialOutputInputFigure2.29Typicalapplicationsofclutchesandbrakes.第34页Method ofengagementMagneticPneumaticand hydraulicMechanicalElectricalOverrunningPositivecontactFrictionMagneticFluidcouplingSquare jawSpiral jawToothedDiscDrumConeRollerSpragSpring woundMagnetic particleHysteresisEddy currentDry fluidHydraulicClutch classification:第35页2.9 Shafts and CouplingsCommonly used shafts：(b)Steppedshafts.（a）Plainshafts.(c)Crankshafts.第36页Shaft design considerations include:1.sizeandspacingofcomponents(asonageneralassemblydrawing),tolerances;2.materialselection,materialtreatments;3.deflectionandrigidity:bendingdeflection;torsionaldeflection;slopeatbearings;sheardeflection;4.stressandstrength：staticstrength；fatigue；reliability;5.frequencyresponse;6.manufacturingconstraints.第37页Figure2.32AtypicalshaftarrangementNamepartsinthedrawing 2.9.2 ShaftHub ConnectionFigure2.30Alternativemethodsofshaft-hubconnection.第38页（a）PinjointsPinShaftHub（b）Keyjoints（c)Setscrewjoints第39页Functions of couplings 2.9.3 ShaftShaft Connection Couplingstransmit power from one shaft to another.Two general types of coupling:RigidcouplingsUniversaljointsFlexiblecouplings第40页2.10.1 Introduction 2.10 Belts and Chains（a）BeltdriveBeltandchaindrivesconsistofflexibleelementsrunningoneitherpulleysorsprockets.(b)Chaindrive第41页The advantages and disadvantages of a belt over gears and chains:1.ConsequenceofFailure.2.VersatilityinShaftConnection.3.EffectonShaftBearingLife.4.SpeedRatio.5.Cost.6.NoiseandVibration.7.SpeedandPower.8.Maintenance.第42页Types:2.10.2 Belt Drives（a）Flatbeltdrives.(b)Roundbeltdrives.(c)Vbeltdrives(d)Synchronousbeltdrives.第43页Types:Figure2.39Variousbeltcross-sections.Figure2.40Pulleyconfiguration.第44页Achainisapowertransmissiondeviceconsistingofaseriesofpin-connectedlinks2.10.3 Chain Drives(a)SimplechainFigure2.41Rollerchain.(b)Duplexchain（c）TriplexchainFigure2.42Simplechaindrive.第45页 Chain types:Figure2.43Chaintypes.ChainsSilentConveyorLeafRollerBritish standardrangeStandardseriesDoublepitchBushchainANSIrangeStandardseriesHeavyseries第46页Figure2.44Rollerchaincomponents.第47页Figure2.45ConveyorchainFigure2.47SilentchainFigure2.46Leafchain第48页Figure2.48Sperbergearbox,silentchains第49页2.11.1 Introduction 2.11 GearsFigure2.49Spurgearschematicshowingprincipleterminology.Gearsaretoothedcylindricalwheelsusedfortransmittingmechanicalpowerfromonerotatingshafttoanother.第50页Figure2.50Basicgeargeometryandnomenclature第51页 2.11.2 Gear Classification1.Parallel axis gearsFigure2.51StraighttoothspurgearsFigure2.52Helicalgears(Single-helicaltooth).2.Non-parallel,coplanar gears(nonintersecting axes):第52页Figure2.53Straighttoothbevelgears.3.Non-parallel,noncoplanar gears(nonintersecting axes)Figure2.54Crossaxishelicalgears.Figure2.55Wormandwormwheel.第53页Figure2.56EpicyclicgearsMore complicated gear chains:第54页 2.11.3 Gear Chains ApplicationFigure2.57Ashiftgearbox.Atypicalmanuallyshifted gearbox forapassengercar第55页 2.11.3 Gear Chains ApplicationFigure2.57Ashiftgearbox.第56页Great works are performed not by strength,but by perseverance第57页