液压系统和气压系统外文文献翻译中英文翻译Word下载.docx
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Abstract:
Hydraulicsystemiswidelyusedinindustry,suchasstamping,grindingofsteeltypeworkandgeneralprocessingindustries,agriculture,mining,spacetechnology,deepseaexploration,transportation,marinetechnology,offshoregasandoilexplorationindustries,inshort,Fewpeopleintheirdailylivesdonotgetcertainbenefitsfromthehydraulictechnology.Successfulandwidelyusedinthehydraulicsystem'
ssecretliesinitsversatilityandeaseofmaneuverability.Hydraulicpowertransmissionmechanicalsystemsasbeingnotlikethemachinegeometryconstraints,Inaddition,thehydraulicsystemdoesnotliketheelectricalsystem,asconstrainedbythephysicalpropertiesofmaterials,itpassedalmostnoamountofpowerconstraints.
Keywords:
Hydraulicsystem,Pressuresystem,Fluid
Thehistoryofhydraulicpowerisalongone,datingfromman’sprehistoriceffortstoharnesstheenergyintheworldaroundhim.Theonlysourcereadilyavailablewerethewaterandthewind—twofreeandmovingstreams.
Thewatermill,thefirsthydraulicmotor,wasanearlyinvention.OneispicturedonamosaticattheGreatPalaceinByzantium,datingfromtheearlyfifthcentury.ThemillhadbeenbuiltbytheRomans.Butthefirstrecordofawatermillgoesbackevenfurther,toaround100BC,andtheoriginsmayindeedhavebeenmuchearlier.Thedomesticationofgrainbegansome5000yearsbeforeandsomeenterprisingfarmerisboundtohavebecometiredofpoundingorgrindingthegrainbyhand.Perhaps,infact,theinventorweresomefarmer’swives.Sincetheoftendrewtheheavyjobs.
Fluidisasubstancewhichmayflow。
thatis,itsconstituentparticlesmaycontinuouslychangetheirpositionsrelativetooneanother.Moreover,itoffersnolastingresistancetothedisplacement,howevergreat,ofonelayeroveranother.Thismeansthat,ifthefluidisatrest,noshearforce(thatisaforcetangentialtothesurfaceonwhichitacts)canexistinit.
FluidmaybeclassifiedasNewtonianornon--Newtonian.InNewtonianfluidthereisalinearrelationbetweenthemagnitudeofappliedshearstressesandtheresultingrateofangulardeformation.Innon—Newtonianfluidthereisanonlinearrelationbetweenthemagnitudeofappliedshearstressandtherateofangulardeformation.
Theflowoffluidsmaybeclassifiedinmanyways,suchassteadyornonsteady,rotationalorirrotational,compressibleorincompressible,andviscousornoviscous.
AllhydraulicsystemsdependonPascal’slaw,suchassteadyorpipeexertsequalforceonallofthesurfacesofthecontainer.
Inactualhydraulicsystems,Pascal’slawdefinesthebasisofresultswhichareobtainedfromthesystem.Thus,apumpmovestheliquidinthesystem.Theintakeofthepumpisconnectedtoaliquidsource,usuallycalledthetankorreservoir.Atmosphericpressure,pressingontheliquidinthereservoir,forcestheliquidintothepump.Whenthepumpoperates,itforcesliquidfromthetankintothedischargepipeatasuitablepressure.
Theflowofthepressurizedliquiddischargedbythepumpiscontrolledbyvalves.Threecontrolfunctionsareusedinmosthydraulicsystems:
(1)controloftheliquidpressure,
(2)controloftheliquidflowrate,and(3)controlofthedirectionofflowoftheliquid.
Hydraulicdrivesareusedinpreferencetomechanicalsystemswhen
(1)powersistobetransmittedbetweenpointtoofarapartforchainsorbelts。
(2)hightorqueatlowspeedinrequired。
(3)averycompactunitisneeded。
(4)asmoothtransmission,freeofvibration,isrequired。
(5)easycontrolofspeedanddirectionisnecessary。
and(6)outputspeedisvariedsteplessly.
Fig.1givesadiagrammaticpresentationofthecomponentsofahydraulicinstallation.Electricallydrivenoilpressurepumpsestablishanoilflowforenergytransmission,whichisfedtohydraulicmotorsorhydrauliccylinders,convertingitintomechanicalenergy.Thecontroloftheoilflowisbymeansofvalves.Thepressurizedoilflowproduceslinearorrotarymechanicalmotion.Thekineticenergyoftheoilflowiscomparativelylow,andthereforethetermhydrostaticdriverissometimesused.Thereislittleconstructionaldifferencebetweenhydraulicmotorsandpumps.Anypumpmaybeusedasamotor.Thequantityofoilflowingatanygiventimemaybevariedbymeansofregulatingvalves(asshowninFig.7.1)ortheuseofvariable-deliverypumps.
Theapplicationofhydraulicpowertotheoperationofmachinetoolsisbynomeansnew,thoughitsadoptiononsuchawidescaleasexistsatpresentiscomparativelyrecent.Itwasinfactindevelopmentofthemodernself-containedpumpunitthatstimulatedthegrowthofthisformofmachinetooloperation.
Hydraulicmachinetooldriveoffersagreatmanyadvantages.Oneofthemisthatitcangiveinfinitely-variablespeedcontroloverwideranges.Inaddition,theycanchangethedirectionofdriveaseasilyastheycanvarythespeed.Asinmanyothertypesofmachine,manycomplexmechanicallinkagescanbesimplifiedorevenwhollyeliminatedbytheuseofhydraulics.
Theflexibilityandresilienceofhydraulicpowerisanothergreatvirtueofthisformofdrive.Apartfromthesmoothnessofoperationthusobtained,agreatimprovementisusuallyfoundinthesurfacefinishontheworkandthetoolcanmakeheaviercutswithoutdetrimentandwilllastconsiderablylongerwithoutregrinding.
Hydraulicandpneumaticsystem
Thereareonlythreebasicmethodsoftransmittingpower:
electrical,mechanical,andfluidpower.Mostapplicationsactuallyuseacombinationofthethreemethodstoobtainthemostefficientoverallsystem.Toproperlydeterminewhichprinciplemethodtouse,itisimportanttoknowthesalientfeaturesofeachtype.Forexample,fluidsystemscantransmitpowermoreeconomicallyovergreaterdistancesthancanmechanicaltypes.However,fluidsystemsarerestrictedtoshorterdistancesthanareelectricalsystems.
Hydraulicpowertransmissionsystemareconcernedwiththegeneration,modelation,andcontrolofpressureandflow,andingeneralsuchsystemsinclude:
1.Pumpswhichconvertavailablepowerfromtheprimemovertohydraulicpowerattheactuator.
2.Valveswhichcontrolthedirectionofpump-flow,thelevelofpowerproduced,andtheamountoffluid-flowtotheactuators.Thepowerlevelisdeterminedbycontrollingboththeflowandpressurelevel.
3.Actcatorswhichconverthydtaulicpowertousablemechanicalpoweroutputatthepointrequired.
4.Themedium,whichisaliquid,providesrigidtransmissionandcontrolaswellaslubricationofcomponts,sealinginvalves,andcoolingofthesystem.
5.Conncetotswhichlinkthevarioussystemcomponents,providepowerconductorsforthefluidunderpressure,andfluidflowreturntotank(reservoir).
6.Fluidstorageandconditioningequipmentwhichensuresufficientqualityandquantityaswellascoolingofthefluid.
Hydraulicsystemsareusedinindustrialapplicationssuchasstampingpresses,steelmills,andgeneralmanufacturing,agriculturalmachines,miningindustry,aviation,spacetechnology,deep-seaexploration,transportion,marinetechnology,andoffshoregasandpetroleumexploration.Inshort,veryfewpeoplegetthroughadayoftheirliveswithoutsomehowbenefitingfromthetechnologyofhydraulicks.
Thesecretofhydraulicsystem’ssuccessandwidespreaduseisitsversatilityandmanageability.Fluidpowerisnothinderedbythegeometryofthemachineasisthecaseinmechanicalsystems.Also,powercanbetransmittedinalmostlimitlessquantitiesbecausefluidsystemsarenotsolimitedbythephysicallimitationsofmaterialsasaretheelectricalsystems.Forexample,theperformanceofanelectromangnetislimitedbythesaturationlimitofsteel.Ontheotherhand,thepowerlimitoffluidsystemsislimitedonlybythestrengthcapacityofthematerial.
Industryisgoingtodependmoreandmoreonautomationinordertoincreaseproductivity.Thisincludesremoteanddirectcontrolofproductionoperations,manufacturingprocesses,andmaterialshandling.Fluidpoweristhemuscleofautomationbecauseofadvantagesinthefollowingfourmajorcategories.
1.Easeandaccuracyofcontrol.Bytheuseofsimpleleversandpushbuttons,theoperatorofafluidpowersystemcanreadilystart,stop,speeduporslowdown,andpositionforceswhichprovideanydesiredhorsepowerwithtolerancesaspreciseasoneten-thousandthofaninch.
2.Multiplicationofforce.Afluidpowersystem(withoutusingcumbersomegears,pulleys,andlevers)canmultiplyforcessimplyandefficientlyfromafractionofanouncetoseveralhundredtonsofoutput.
3.Constantforceortorque.Onlyfluidpowersystemsarecapableofprovidingcontantforceortorqueregardlessofspeedchanges.Thisisaccomplishedwhethertheworkoutputmovesafewinchesperhour,severalhundredinchesperminute,afewrevolutionsperhour,orthousandsofrevolutionsperminute.
4.Simplicity,safely,economy.Ingeneral,fluidpowersystemsusefewermovingpartsthancomparablemechanicalorelectricalsystems.Thus,theyaresimplertomaintainandoperate.This,inturn,maximizessafety,companctness,andreliability.Forexample,anewpowersteeringcontroldesignedhasmadeallotherkindsofpowersystemsobsoleteonmanyoff-highwayvehicles.Thesteeringunitconsistsofamanuallyoperateddirectionalcontrolvalveandmeterinasinglebody.Becausethesteeringunitisfullyfluid-linked,mechanicallinkages,universaljoints,bearings,reductiongears,etc,areeliminated.Thisprovidesasimple,compactsystem.Inaddition,verylittleinputtorqueisrequiredtoproducethecontrolneededforthetoughestapplica