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外文翻译---振动筛的选择.doc

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外文翻译---振动筛的选择.doc

辽宁科技大学本科生毕业设计第1页ScreeningVibratingscreensPrinciplesVibratingscreenssavespaceandweightandoperateonlittlepowerbecausethescreeningsurfacemaybeactuatedbyvibrating,gyratingorpulsatingmovementofsmallamplitude,butatfrequenciesthatnormallyexceed3,000/min.SelectionofProperVibrationSereenBesurethescreensupplierknowsalldetailsoftheapplication.Thecentrifugalforcefactor,orcombinationoffrequencyofvibrationspeedandamplitudethrow,mayaffectperformanceofanyvibratingscreen.Also,acorrectcombinationofslopeanddirectionofmechanismrotationisvitalforinclinedscreens.Usually,thelargertheopening,thegreatertheamplitudeneededforascreen.Ifthethrowistoosmall,thematerialmayclogorwedgeintheopenings.Increasingthethrowbeyondwhatisrequiredtopreventblindingorpluggingdoesnotnecessarilyincreasethelifeofthebearingsandreducescreeningefficiency.Increasedrateoftravelpermitsmoretonnagetobepassedoverthescreenperunitoftime.Foragiventonnage,afasterrateoftravelresultsinathinnerbedofmaterialandhighscreeningefficiency.Maximumslopeisreachedwhenthematerialtravelstoofastforthefinestopenetratetheribbonofmaterialandreachtheaperturesinthescreencloth.Atthispointanexcessiveamountoffinematerialpassesoverthescreenwiththeoversize,resultinginpoorefficiency.Whenanexistingscreenistobeusedforanapplicationotherthanthatforwhichitwasoriginallyintended,checkwiththeSuppliertoseeifanyoftheoperatingcharacteristicsneedmodificationandifthethescreenisstructurallysuitableforthenewapplication.TheoperatorcangetthecorrectvibratingscreenbyprovidingthesupplierwiththefollowinginformationMaximumtonsperhourtobescreened,includinganycirculatingloadoranysurgesinthefeedrate.Acompletesizeconsistorsieveanalysisofthematerialor,ifavailable,anestimatedanalysis.Typeofmaterialandweightpercubicfootinbrokenstate.Separationsdesiredoneachdeck.Surfacemoisturecarriedbythematerialifscreeningistobedryoramountofwaterwithfeedifwet.Specialoperatingrequirementsorconditionssuchastemperature,abrasiveness,corrosivenessorotherphysicalcharacteristicsofthefeed,辽宁科技大学本科生毕业设计第2页efficiencyorproductrequirementswhichdetermineselectionofscreeningsurface,orinstallationproblemswhichaffectscreensizeselectionorcapacity.GeneralTypesVibratingscreensmaybedividedintotwomainclassesmechanicallyvibratedandelectriallyvibrated.Theformercanbesubdividedintoclassesbasedonhowthevibrationisproducedbyeccentricsbyunbalancedweightbycamsorbumpers.Theycanalsobesubdividedasinclinedandhorizontal.SizesVibratingscreensaremadeinstandardsizesoffrom12in.to10ftwideandfrom21/2ftto28ftlong.Commonpracticedictatesthatthelengthofthescreenshouldbe2.5timesthewidthfordryscreening.Forwetscreening,widerandshorterscreenisbest.Screensforscalpingaheadofprimarycrushers,operateataslopeoffrom12degreesto18degreesandhaveopeningsaslargeas11in.square.Theeccentricthrowforopeningsfrom5to11in.isusually1/2in.foropeningsfrom3to5in.about3/8in.andforsmalleropenings1/4in.Thescreeningsurfaceconsistsofaheavycastdesk,perforatedsteelwithorwithoutskidbarsweldedbetweentheholes,roddeck,etc.Themechanicalshakingscreencomprisesarectangularframe,withperforatedsteelorwireclothscreeningmedium.Itisusuallyinclinedandsuspendedonlooserodsorcables.Thesescreensnowareusedmainlyforspecialtasksofcoarsescreening,havinggivenwaytovibratingscreens.ElectricallyHeatedScreensElectricallyheatedscreenclothdeckshaveaffordedbetterscreeningandlessdust.Modernorupdatedscreeningoperations,nowhandlingclays,limestone,potash,salts,phosphatesandvarioushydroscopicmaterials,reportminimumdustlosswhenequippedwithheatedscreens.Thecontrollingfactorinthisimprovementistheelectricallyheatedscreendothdeck.Anyvibratoryscreenwithfineopeninglessthan1/2in.canbeequippedwithlowvoltagehighamperageresistanceheating.Theprincipleofelectricheatingisbasedonthefactthatsmalldiameterwireofscreenclothespeciallystainlesssteelservesasaconductor,butoffersresistancetoahighamperagecurrent.Thisresistancecausesheatingofthewirewhenpowerfultransformerandspeciallydesignedbusbarsconnectedtoscreendothdeckspushupto6,000ampscurrentintoacircuit.Thecurrentissafeandshockproofbecausevoltageislow,rangingfromapproximately11/2to16volts.Workerscandotheirjobsaroundelectricallyheatedscreenswithoutspecialprecautions.Heatedscreensareeffectiveinpreventingmoisturecontentofmaterialfromcausingbuildupandblinding.Thescreenwireiskeptat100degreesto130degreesFdependingoncharacterandtonnageofthematerialprocessed.Thistemperatureisnothighenoughtoweakenthewireclothorscreenstructure,nordoesitsufficetodriveoffmoistureheldinmaterial.Thewarmwirestaysdry,breakingthesurfacetensionthatotherwisewouldbinddampmaterialtocold,dampmetal.Thisdifferentialor辽宁科技大学本科生毕业设计第3页warm,dryscreenwireversuscold,dampmaterialcanbemaintainedeconomicallythroughtransformercontrolsettings.Witheveryopeningintheheatedscreenmeshprotectedagainstblinding,thereisnoguessworkaboutwhatsizeparticlewillbedelivered.Auniform,unvaryingqualitytomeettoughspecificationscomesthroughdayafterday,nomatterwhattheweather.Highhumiditymakestroublewithunheatedscreens.Plantsoperatingheatedscreenswillhavenotroublewithexcessiveamountsoffine,dustymaterialthatformerlysiftedthroughreducedmeshesoncloggedscreens.Servicelifeofscreenclothisgreatlyincreasedwhenelectricheatingendsthepunishmentofoldfashionedcleaningmethods,suchasroughpoundingorbrushing.Blowtorchflamesputtoomuchheatinonespotandbouncingchainsaddedtowearandtear.But,screenskeptcleanandopenwithelectricheatingreportedlyareseldommistreatedandlastuptoeighttimesaslong.Heateddecksendthethreatofpileupsandstrainsthatcanbreakthemesh.Economicaloperationofelectricheatingforscreensrequiresonetransformerforinstallationsofuptothreepanelsofscreenclothmaximumarea4x12ft.Twotransformersareusedonlongerdecks.Anydecktop,centerorbottomcanbeheated.Electricheatingismostdesirableofallwhereascreensurfaceishardtogetat.Changingheatedscreensdoesnotinvolvemoreunboltingthanneededforordinaryscreens.Inspecifyingscreenstodeliverauniformparticlethroughheatedmesh,thefirstthingtoconsiderisweightpersquarefootofthewireclothneededtosetupappropriateresistance.Mostcalculationsarebasedonsquareopenings.Slottedopeningsmustbeidentifiedastowidthofclearopening,diameterofwireandnumberofwiresperinchbeforeweightpersquarefootcanbefoundinanyscreenclothmanufacturerscatalog.Havingdeterminedtheusableweightpersquarefootofscreencloth,thenextstepistoselectthesizeofclearopeningneeded,makingnoallowanceforreductioninthissizeasformerlywasthecasewhenmaterialstucktothewires.Heatedwireswillmaintaintheclearopeningatalltimes,makingitpossibletoscreenfinerwithoutblinding.Fromawirecatalog,selectameshweighingnomorepersquarefootcanweighlessthandeterminedusingthemethodabovewiththeclearopeningcharacteristicsdesired.Thisoftenturnsouttobeamoreefficientscreenbecausethewirediameterwillbesmallerandthepercentageoftheopenareawillbegreater.Forexample,wherea1/8in.clearopeningwasdesiredbutoftenblindedonunheatedscreens,thewirediameterwas0.63andtheopenareawas44percent.Theclothweighed1.43lb/ft.2.Foraheated3x12ftscreen,theweightmustnotexceed辽宁科技大学本科生毕业设计第5页1.1lb/ft2.Twooptionswerefoundinclothwith1/8in.clearopeningwirediameter.054weighing1.09lb/ft2providing48.8percentopenareaandwirediameter.047weighing0.85lb/ft2witha52.8percentopenarea.Loadconditionsmaymakefinediametersofcarbonsteelwireinadequate.Insuchcases,stainlesssteelwireoflargerdiameterwithgreaterloadcarryingcapacitywillhavethenecessaryresistanceforgoodheating.Lighterwirewithmoreopenareayieldshighertonnageandheatedmeshstaysopen100percent.Twoscreenclothsconnectedinaseriesmaybeofdifferentmeshsizesorclearopenings,aslongastheybothweighthesameperft2anddonotexceedtheweightallowedforthatparticularsizeofscreen.Withheatedscreens,majorsavingsinpollutioncontrolarepossible.Alsomoisturecontentofmaterialisreportedlyincreasedinarangeof5to8percent.Thismoistureisaddedduringoraftercrushinggrindingoperationsandholdsdowndustduringtransferofmaterialandpassageoverheatedscreens.Warmwirehandles5to8percentmoistureinstride.Thecostofheatingequipmentandmistsprayingreportedlyislessthanthecostofhavingbagtowersandprecipitators.振动筛的选择振动筛的选择原则选择振动筛的原则是所选择的振动筛要节省空间、重量并且驱动的功率要小,因为筛选表面可以驱动并且发生振动。同时还要保证旋转或脉动运动振幅要小,但振动筛的振动频率在通常情况下是要超过三千次每分钟的。选择合适的振动显示屏要确定显示屏供应商知道所有有关方面的使用细节。离心力或组合频率振动(速度)以及振幅(投掷)等因素都可能影响到任何振动筛的正常工作。此外,需要有一个正确的组合坡度和方向的轮换机制,这对于显示屏来说是至关重要的。通常情况下,振动筛需要大开放、大振幅的显示屏。如果投入太少的话,则这些材料可能出现木屐或楔形开口等情况。增加投入以后,需要知道如何防止堵塞因为堵塞是不必要的,而且会增加日常轴承的磨损以及和降低筛选的效率。

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