液压系统和气压系统外文文献翻译中英文翻译.docx

液压系统和气压系统外文文献翻译中英文翻译.docx

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液压系统和气压系统外文文献翻译中英文翻译

HydraulicsystemandPeumaticSystem

Hui-xiongwan

JunFan

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,verylittleinputtorqueisrequiredtoproducethecontrolneededfort