毕业设计外文翻译英文加中文传送带.docx

毕业设计外文翻译英文加中文传送带.docx

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毕业设计外文翻译英文加中文传送带

AComparisonofSoftStartMechanismsforMiningBeltConveyors

1800WashingtonRoadPittsburgh,PA15241BeltConveyorsareanimportantmethodfortransportationofbulkmaterialsintheminingindustry.Thecontroloftheapplicationofthestartingtorquefromthebeltdrivesystemtothebeltfabricaffectstheperformance,lifecost,andreliabilityoftheconveyor.Thispaperexaminesapplicationsofeachstartingmethodwithinthecoalminingindustry.

INTRODUCTION

Theforcerequiredtomoveabeltconveyormustbetransmittedbythedrivepulleyviafrictionbetweenthedrivepulleyandthebeltfabric.Inordertotransmitpowertheremustbeadifferenceinthebelttensionasitapproachesandleavesthedrivepulley.Theseconditionsaretrueforsteadystaterunning,starting,andstopping.Traditionally,beltdesignsarebasedonstaticcalculationsofrunningforces.Sincestartingandstoppingarenotexaminedindetail,safetyfactorsareappliedtostaticloadings（Harrison,1987）.Thispaperwillprimarilyaddressthestartingoraccelerationdutyoftheconveyor.Thebeltdesignermustcontrolstartingaccelerationtopreventexcessivetensioninthebeltfabricandforcesinthebeltdrivesystem（Suttees,1986）.Highaccelerationforcescanadverselyaffectthebeltfabric,beltsplices,drivepulleys,idlerpulleys,shafts,bearings,speedreducers,andcouplings.Uncontrolledaccelerationforcescancausebeltconveyorsystemperformanceproblemswithverticalcurves,excessivebelttake-upmovement,lossofdrivepulleyfriction,spillageofmaterials,andfestooningofthebeltfabric.Thebeltdesignerisconfrontedwithtwoproblems,Thebeltdrivesystemmustproduceaminimumtorquepowerfulenoughtostarttheconveyor,andcontrolledsuchthattheaccelerationforcesarewithinsafelimits.Smoothstartingoftheconveyorcanbeaccomplishedbytheuseofdrivetorquecontrolequipment,eithermechanicalorelectrical,oracombinationofthetwo（CEM,1979）.

SOFTSTARTMECHANISMEVALUATIONCRITERION

Whatisthebestbeltconveyordrivesystem?

Theanswerdependsonmanyvariables.Thebestsystemisonethatprovidesacceptablecontrolforstarting,running,andstoppingatareasonablecostandwithhighreliability（LewdlyandSugarcane,1978）.BeltDriveSystemForthepurposesofthispaperwewillassumethatbeltconveyorsarealmostalwaysdrivenbyelectricalprimemovers（GoodyearTireandRubber,1982）.Thebelt"drivesystem"shallconsistofmultiplecomponentsincludingtheelectricalprimemover,theelectricalmotorstarterwithcontrolsystem,themotorcoupling,thespeedreducer,thelowspeedcoupling,thebeltdrivepulley,andthepulleybrakeorholdback（Cur,1986）.Itisimportantthatthebeltdesignerexaminetheapplicabilityofeachsystemcomponenttotheparticularapplication.Forthepurposeofthispaper,wewillassumethatalldrivesystemcomponentsarelocatedinthefreshair,non-permissible,areasofthemine,orinnon-hazardous,NationalElectricalCode,Article500explosion-proof,areasofthesurfaceofthemine.

BeltDriveComponentAttributesSize

Certaindrivecomponentsareavailableandpracticalindifferentsizeranges.Forthisdiscussion,wewillassumethatbeltdrivesystemsrangefromfractionalhorsepowertomultiplesofthousandsofhorsepower.Smalldrivesystemsareoftenbelow50horsepower.Mediumsystemsrangefrom50to1000horsepower.Largesystemscanbeconsideredabove1000horsepower.Divisionofsizesintothesegroupsisentirelyarbitrary.Caremustbetakentoresistthetemptationtoovermotororundermotorabeltflighttoenhancestandardization.Anovermotoreddriveresultsinpoorefficiencyandthepotentialforhightorques,whileanundermotoreddrivecouldresultindestructiveoverspendingonregeneration,oroverheatingwithshortenedmotorlife（Lords,etal.,1978）.

TorqueControl

Beltdesignerstrytolimitthestartingtorquetonomorethan150%oftherunningtorque（CEMA,1979;Goodyear,1982）.Thelimitontheappliedstartingtorqueisoftenthelimitofratingofthebeltcarcass,beltsplice,pulleylagging,orshaftdeflections.Onlargerbeltsandbeltswithoptimizedsizedcomponents,torquelimitsof110%through125%arecommon（Elberton,1986）.Inadditiontoatorquelimit,thebeltstartermayberequiredtolimittorqueincrementsthatwouldstretchbeltingandcausetravelingwaves.Anidealstartingcontrolsystemwouldapplyapretensiontorquetothebeltatrestuptothepointofbreakaway,ormovementoftheentirebelt,thenatorqueequaltothemovementrequirementsofthebeltwithloadplusaconstanttorquetoacceleratetheinertiaofthesystemcomponentsfromresttofinalrunningspeed.Thiswouldminimizesystemtransientforcesandbeltstretch（Shultz,1992）.Differentdrivesystemsexhibitvaryingabilitytocontroltheapplicationoftorquestothebeltatrestandatdifferentspeeds.Also,theconveyoritselfexhibitstwoextremesofloading.Anemptybeltnormallypresentsthesmallestrequiredtorqueforbreakawayandacceleration,whileafullyloadedbeltpresentsthehighestrequiredtorque.Aminingdrivesystemmustbecapableofscalingtheappliedtorquefroma2/1ratioforahorizontalsimplebeltarrangement,toa10/1rangesforaninclinedorcomplexbeltprofile.

ThermalRating

Duringstartingandrunning,eachdrivesystemmaydissipatewasteheat.Thewasteheatmaybeliberatedintheelectricalmotor,theelectricalcontrols,,thecouplings,thespeedreducer,orthebeltbrakingsystem.ThethermalloadofeachstartIsdependentontheamountofbeltloadandthedurationofthestart.Thedesignermustfulfilltheapplicationrequirementsforrepeatedstartsafterrunningtheconveyoratfullload.Typicalminingbeltstartingdutiesvaryfrom3to10startsperhourequallyspaced,or2to4startsinsuccession.Repeatedstartingmayrequirethedreadingoroversizingofsystemcomponents.Thereisadirectrelationshipbetweenthermalratingforrepeatedstartsandcosts.VariableSpeed.Somebeltdrivesystemsaresuitableforcontrollingthestartingtorqueandspeed,butonlyrunatconstantspeed.Somebeltapplicationswouldrequireadrivesystemcapableofrunningforextendedperiodsatlessthanfullspeed.Thisisusefulwhenthedriveloadmustbesharedwithotherdrives,thebeltisusedasaprocessfeederforratecontroloftheconveyedmaterial,thebeltspeedisoptimizedforthehaulagerate,thebeltisusedatslowerspeedstotransportmenormaterials,orthebeltisrunaslowinspectionorinchingspeedformaintenancepurposes（Hager,1991）.Thevariablespeedbeltdrivewillrequireacontrolsystembasedonsomealgorithmtoregulateoperatingspeed.RegenerationorOverhaulingLoad.Somebeltprofilespresentthepotentialforoverhaulingloadswherethebeltsystemsuppliesenergytothedrivesystem.Notalldrivesystemshavetheabilitytoacceptregeneratedenergyfromtheload.Somedrivescanacceptenergyfromtheloadandreturnittothepowerlineforusebyotherloads.Otherdrivesacceptenergyfromtheloadanddissipateitintodesignateddynamicormechanicalbrakingelements.Somebeltprofilesswitchfrommotoringtoregenerationduringoperation.Canthedrivesystemacceptregeneratedenergyofacertainmagnitudefortheapplication?

Doesthedrivesystemhavetocontrolormodulatetheamountofretardingforceduringoverhauling?

Doestheoverhaulingoccurwhenrunningandstarting?

MaintenanceandSupportingSystems.Eachdrivesystemwillrequireperiodicpreventativemaintenance.Replaceableitemswouldincludemotorbrushes,bearings,brakepads,dissipationresistors,oils,andcoolingwater.Ifthedrivesystemisconservativelyengineeredandoperated,thelowerstressonconsumableswillresultinlowermaintenancecosts.Somedrivesrequiresupportingsystemssuchascirculatingoilforlubrication,coolingairorwater,environmentaldustfiltering,orcomputerinstrumentation.Themaintenanceofthesupportingsystemscanaffectthereliabilityofthedrivesystem.

Cost

Thedrivedesignerwillexaminethecostofeachdrivesystem.Thetotalcostisthesumofthefirstcapitalcosttoacquirethedrive,thecosttoinstallandcommissionthedrive,thecosttooperatethedrive,andthecosttomaintainthedrive.Thecostforpowertooperatethedrivemayvarywidelywithdifferentlocations.Thedesignerstrivestomeetallsystemperformancerequirementsatlowesttotalcost.Oftenmorethanonedrivesystemmaysatisfyallsystemperformancecriterionsatcompetitivecosts.

Complexity

Thepreferreddrivearrangementisthesimplest,suchasasinglemotordrivingthroughasingleheadpulley.However,mechanical,economic,andfunctionalrequirementsoftennecessitatetheuseofcomplexdrives.Thebeltdesignermustbalancetheneedforsophisticationagainsttheproblemsthataccompanycomplexsystems.Complexsystemsrequireadditionaldesignengineeringforsuccessfuldeployment.Anoften-overlookedcostinacomplexsystemisthecostoftrainingonsitepersonnel,orthecostofdowntimeasaresultofinsufficienttraining.

SOFTSTARTDRIVECONTROLLOGIC

Eachdrivesystemwillrequireacontrolsystemtoregulatethestartingmechanism.Themostcommontypeofcontrolusedonsmallertomediumsizeddriveswithsimpleprofilesistermed"OpenLoopAccelerationControl".Inopenloop,thecontrolsystemispreviouslyconfiguredtosequencethestartingmechanisminaprescribedmanner,usuallybasedontime.Inopenloopcontrol,drive-operatingparameterssuchascurrent,torque,orspeeddonotinfluencesequenceoperation.Thismethodpresumesthatthecontroldesignerhasadequatelymodeleddrivesystemperf