机械外文翻译中英文Word下载.docx
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机械外文翻译中英文Word下载.docx
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英文原文
BeltConveyingSystemsDevelopmentofdrivingsystem
Amongthemethodsofmaterialconveyingemployed,beltconveyorsplayaveryimportantpartinthereliablecarryingofmaterialoverlongdistancesatcompetitivecost.Conveyorsystemshavebecomelargerandmorecomplexanddrivesystemshavealsobeengoingthroughaprocessofevolutionandwillcontinuetodoso.Nowadays,biggerbeltsrequiremorepowerandhavebroughttheneedforlargerindividualdrivesaswellasmultipledrivessuchas3drivesof750kWforonebelt(thisisthecasefortheconveyordrivesinChengzhuangMine).Theabilitytocontroldriveaccelerationtorqueiscriticaltobeltconveyors’performance.Anefficientdrivesystemshouldbeabletoprovidesmooth,softstartswhilemaintainingbelttensionswithinthespecifiedsafelimits.Forloadsharingonmultipledrives.torqueandspeedcontrolarealsoimportantconsiderationsinthedrivesystem’sdesign.Duetotheadvancesinconveyordrivecontroltechnology,atpresentmanymorereliable.Cost-effectiveandperformance-drivenconveyordrivesystemscoveringawiderangeofpowerareavailableforcustomers’choices[1].
1Analysisonconveyordrivetechnologies
1.1Directdrives
Full-voltagestarters.Withafull-voltagestarterdesign,theconveyorheadshaftisdirect-coupledtothemotorthroughthegeardrive.Directfull-voltagestartersareadequateforrelativelylow-power,simple-profileconveyors.Withdirectfu11-voltagestarters.nocontrolisprovidedforvariousconveyorloadsand.dependingontheratiobetweenfu11-andno-1oadpowerrequirements,emptystartingtimescanbethreeorfourtimesfasterthanfullload.Themaintenance-freestartingsystemissimple,low-costandveryreliable.However,theycannotcontrolstartingtorqueandmaximumstalltorque;
therefore.theyarelimitedtothelow-power,simple-profileconveyorbeltdrives.
Reduced-voltagestarters.Asconveyorpowerrequirementsincrease,controllingtheappliedmotortorqueduringtheaccelerationperiodbecomesincreasinglyimportant.Becausemotortorque1safunctionofvoltage,motorvoltagemustbecontrolled.Thiscanbeachievedthroughreduced-voltagestartersbyemployingasiliconcontrolledrectifier(SCR).AcommonstartingmethodwithSCRreduced-voltagestartersistoapplylowvoltageinitiallytotakeupconveyorbeltslack.andthentoapplyatimedlinearrampuptofullvoltageandbeltspeed.However,thisstartingmethodwillnotproduceconstantconveyorbeltacceleration.Whenaccelerationiscomplete.theSCRs,whichcontroltheappliedvoltagetotheelectricmotor.arelockedinfullconduction,providingfu11-linevoltagetothemotor.Motorswithhighertorqueandpull—uptorque,canprovidebetterstartingtorquewhencombinedwiththeSCRstarters,whichareavailableinsizesupto750KW.
Woundrotorinductionmotors.WoundrotorinductionmotorsareconnecteddirectlytothedrivesystemreducerandareamodifiedconfigurationofastandardACinductionmotor.Byinsertingresistanceinserieswiththemotor’srotorwindings.themodifiedmotorcontrolsystemcontrolsmotortorque.Forconveyorstarting,resistanceisplacedinserieswiththerotorforlowinitialtorque.Astheconveyoraccelerates,theresistanceisreducedslowlytomaintainaconstantaccelerationtorque.Onmultiple-drivesystems.anexternalslipresistormaybeleftinserieswiththerotorwindingstoaidinloadsharing.Themotorsystemshavearelativelysimpledesign.However,thecontrolsystemsforthesecanbehighlycomplex,becausetheyarebasedoncomputercontroloftheresistanceswitching.Today,themajorityofcontrolsystemsarecustomdesignedtomeetaconveyorsystem’sparticularspecifications.Woundrotormotorsareappropriateforsystemsrequiringmorethan400kW.
DCmotor.DCmotors.availablefromafractionofthousandsofkW,aredesignedtodeliverconstanttorquebelowbasespeedandconstantkWabovebasespeedtothemaximumallowablerevolutionsperminute(r/min).withthemajorityofconveyordrives,aDCshuntwoundmotorisused.Whereinthemotor’srotatingarmatureisconnectedexternally.ThemostcommontechnologyforcontrollingDCdrivesisaSCRdevice.whichallowsforcontinualvariable-speedoperation.TheDCdrivesystemismechanicallysimple,butcanincludecomplexcustom-designedelectronicstomonitorandcontrolthecompletesystem.Thissystemoptionisexpensiveincomparisontoothersoft-startsystems.butitisareliable,cost-effectivedriveinapplicationsinwhichtorque,1oadsharingandvariablespeedareprimaryconsiderations.DCmotorsgenerallyareusedwithhigher-powerconveyors,includingcomplexprofileconveyorswithmultiple-drivesystems,boostertrippersystemsneedingbelttensioncontrolandconveyorsrequiringawidevariable-speedrange.
1.2Hydrokineticcoupling
Hydrokineticcouplings,commonlyreferredtoasfluidcouplings.arecomposedofthreebasicelements;
thedrivenimpeller,whichactsasacentrifugalpump;
thedrivinghydraulicturbineknownastherunnerandacasingthatenclosesthetwopowercomponents.Hydraulicfluidispumpedfromthedrivenimpellertothedrivingrunner,producingtorqueatthedrivenshaft.Becausecirculatinghydraulicfluidproducesthetorqueandspeed,nomechanicalconnectionisrequiredbetweenthedrivinganddrivenshafts.Thepowerproducedbythiscouplingisbasedonthecirculatedfluid’samountanddensityandthetorqueinproportiontoinputspeed.Becausethepumpingactionwithinthefluidcouplingdependsoncentrifugalforces.theoutputspeedislessthantheinputspeed.Referredtoasslip.thisnormallyisbetweenl%and3%.BasichydrokineticcouplingsareavailableinconfigurationsfromfractionaltoseveralthousandkW.
Fixed-fillfluidcouplings.Fixed-fillfluidcouplingsarethemostcommonlyusedsoft-startdevicesforconveyorswithsimplerbeltprofilesandlimitedconvex/concavesections.Theyarerelativelysimple,1ow-cost,reliable,maintenancefreedevicesthatprovideexcellentsoftstartingresultstothemajorityofbeltconveyorsinusetoday.
Variable-filldraincouplings.Drainable-fluidcouplingsworkonthesameprincipleasfixed-fillcouplings.Thecoupling’simpellersaremountedontheACmotorandtherunnersonthedrivenreducerhigh-speedshaft.Housingmountedtothedrivebaseenclosestheworkingcircuit.Thecoupling’srotatingcasingcontainsbleed-offorificesthatcontinuallyallowfluidtoexittheworkingcircuitintoaseparatehydraulicreservoir.Oilfromthereservoirispumpedthroughaheatexchangertoasolenoid-operatedhydraulicvalvethatcontrolsthefillingofthefluidcoupling.Tocontrolthestartingtorqueofasingle-driveconveyorsystem,theACmotorcurrentmustbemonitoredtoprovidefeedbacktothesolenoidcontrolvalve.Variablefilldraincouplingsareusedinmediumtohigh-kWconveyorsystemsandareavailableinsizesuptothousandsofkW.Thedrivescanbemechanicallycomplexanddependingonthecontrolparameters.thesystemcanbeelectronicallyintricate.Thedrivesystemcostismediumtohigh,dependinguponsizespecified.
Hydrokineticscoopcontroldrive.Thescoopcontrolfluidcouplingconsistsofthethreestandardfluidcouplingcomponents:
adrivenimpeller,adrivingrunnerandacasingthatenclosestheworkingcircuit.Thecasingisfittedwithfixedorificesthatbleedapredeterminedamountoffluidintoareservoir.Whenthescooptubeisfullyextendedintothereservoir,thecouplingisl00percentfilled.Thescooptube,extendingoutsidethefluidcoupling,ispositionedusinganelectricactuatortoengagethetubefromthefullyretractedtothefullyengagedposition.Thiscontrolprovidesreasonablysmoothaccelerationrates.tobutthecomputer-basedcontrolsystemisverycomplex.Scoopcontrolcouplingsareappliedonconveyorsrequiringsingleormultipledrivesfroml50kWto750kW.
1.3Variable-frequencycontrol(VFC)
Variablefrequencycontrolisalsooneofthedirectdrivemethods.Theemphasizingdiscussionaboutithereisbecausethatithassouniquecharacteristicandsogoodperformancecomparedwithotherdrivingmethodsforbeltconveyor.VFCdevicesProvidevariablefrequencyandvoltagetotheinductionmotor,resultinginanexcellentstartingtorqueandaccelerationrateforbeltconveyordrives.VFCdrives.availablefromfractionaltoseveralthousand(kW),areelectroniccontrollersthatrectifyAClinepowertoDCand,throughaninverter,convertDCbacktoACwithfrequencyandvoltagecontro1.VFCdrivesadoptvectorcontrolordirecttorquecontrol(DTC)technology,andcanadoptdifferentoperatingspeedsaccordingtodifferentloads.VFCdrivescanmakestartingorstallingaccordingtoanygivenS-curves.realizingtheautomatictrackforstartingorstallingcurves.VFCdrivesprovideexcellentspeedandtorquecontrolforstartingconveyorbelts.andcanalsobedesignedtoprovideloadsharingformultipledrives.easilyVFCcontrollersarefrequentlyinstalledonlower-poweredconveyordrives,butwhenusedattherangeofmedium-highvoltageinthepast.thestructureofVFCcontrollersbecomesverycomplicatedduetothelimitationofvoltageratingofpowersemiconductordevices,thecombinationofmedium-highvoltagedrivesandvariablespeedisoftensolvedwithlow-voltageinvertersusingstep-uptransformerattheoutput,orwithmultiplelow-voltageinvertersconnectedinseries.Three-levelvoltage-fedPWMconvertersystemsarerecentlyshowingincreasingpopularityformulti-megawattindustrialdriveapplicationsbecauseofeasyvoltagesharingbetweentheseriesdevicesandimprovedharmonicqualityattheoutputcomparedtotwo-levelconvertersystemsWithsimpleseriesconnectionofdevices.ThiskindofVFCsystemwiththree750kW/2.3kVinvertershasbeensucc
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