机械制造专业外文翻译锤片式粉碎机.docx

机械制造专业外文翻译锤片式粉碎机.docx

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机械制造专业外文翻译锤片式粉碎机

外文原文：

Hammermills:

hammer-mills

Inthefeedprocessingprocesstheremaybeanumberofingredientsthatrequiresomeformofprocessing.Thesefeedingredientsincludecoarsecerealgrains,cornswhichrequireparticlesizereductionwhichwillimprovetheperformanceoftheingredientandincreasethenutritivevalue.Thereareamanywaystoachievethisparticlesizereduction,herewearelookingatusinghammer-mills,forinformationonrollermills,seetherelatedlinksatthebottomofthispage.

Bothhammeringandrollingcanachievethedesiredresultofachievingadequatelygroundingredients,butotherfactorsalsoneedtobelookedatbeforechoosingthesuitablemethodtogrind.Excessivesizereductioncanleadtowastedelectricalenergy,unnecessarywearonmechanicalequipmentandpossibledigestiveproblemsinlivestockandpoultry.Formoreindepthinformationregardingwhatactuallyoccurstotheingredientsduringsizereductionpleaserefertothislink:

particlesizereduction.

Hammer-mills

Advantages:

-areabletoproduceawiderangeofparticlesizes

-Workwithanyfriablematerialandfiber

-easeofuse

-Lowerinitialinvestmentwhencomparedwitharollermill

-Minimalmaintenanceneeded

-Particlesproducedusingahammer-millwillgenerallybespherical,withasurfacethatappearspolished.

Disadvantages:

-Lessenergyefficientwhencomparedtoarollermill

-maygenerateheat（sourceofenergyloss）

-producegreaterparticlesizevariability（lessuniform）

-Hammer-millsarenoisyandcangeneratedustpollution

GeneralDesign

Themajorcomponentsofthesehammer-mills,showninthepicture,include:

-adeliverydeviceisusedtointroducethematerialtobegroundintothepathofthehammers.Arotorcomprisedofaseriesofmachineddisksmountedonthehorizontalshaftperformsthistask.-Free-swinginghammersthataresuspendedfromrodsrunningparalleltotheshaftandthroughtherotordisks.Thehammerscarryoutthefunctionofsmashingtheingredientsinordertoreducetheirparticlesize.-aperforatedscreenandeithergravity-orair-assistedremovalofgroundproduct.Actstoscreentheparticlesizeofthehammermilltoensureparticlesmeetaspecifiedmaximummeshsize.

Feederdesign

Materialsareintroducedintothepathsofthehammersbyavariablespeedveinfeeder.Thistypeoffeedercanhaveitsmotorslavedbyaprogrammablecontrollertothemaindrivemotorofthehammermill.Theoperationalspeedofthefeederiscontrolledtomaintainoptimumamperageloadingofthemainmotor.

Hammerdesignandconfiguration

Thedesignandplacementofhammersisdeterminedbyoperatingparameterssuchasrotorspeed,motorhorsepower,andopenareainthescreen.Optimalhammerdesignandplacementwillprovidemaximumcontactwiththefeedingredient.Hammermillsinwhichtherotorspeedisapproximately1,800rpm,shouldbeusinghammerswhicharearound25cm（~10inches）long,6.35cm（~2.5inches）wide,and6.4mm（0.25inches）thick.Forarotorspeedofabout3,600rpm,hammersshouldbe15to20cm（~6-8incheslong,5cm（~2inches）wide,and6.4mm（0.25inches）thick.

Thenumberofhammersusedforahammermillof1,800rpm,shouldbe1forevery2.5to3.5horsepower,andfor3,600rpm,oneforevery1to2horsepower.Hammersshouldbebalancedandarrangedontherodssothattheydonottrailoneanother.Thedistancebetweenhammerandscreenshouldbe12to14mm（~1/2inch）forsizereductionofcerealgrains.

Thevelocityortipspeedofthehammersiscriticalforpropersizereduction.Tipspeedisthespeedofthehammeratitstiporedgefurthestawayfromtherotor,andiscalculatedbymultiplyingtherotationalspeedofthedrivesource（shaftrpm）bythecircumferenceofthehammertiparc.Seethefollowingformula:

Acommonrangeoftipspeedsseeninhammer-millsiscommonlyintherangebetween5,000and7,000m/min（~16,000and23,000feetperminute）.Whenthetipspeedsexceed23,000feetperminute,carefulconsiderationmustbegiventothedesignofthehammermill,thematerialsusedinitsconstruction,andthefabricationofallthecomponents.Simplychangingtherotationalspeedofthedrivesourceisnotarecommendedmethodofincreasinghammerspeedinexcessof23,000feetperminute.

Impactistheprimaryforceusedinahammer-mill.Anythingwhichincreasesthechanceofacollisionbetweenahammerandatarget;increasesthemagnitudeofthecollision;orimprovesmaterialtake-awayprovidesanadvantageinparticlesizereduction.Themagnitudeofthecollisionscanbeescalatedbyincreasingthespeedofthehammers.

ScreenDesign

Theamountofopenareainahammermillscreendeterminestheparticlesizeandgrindingefficiency.Thescreenmustbedesignedtomaintainitsintegrityandprovidethegreatestamountofopenarea.Screenopenings（holes）thatarealignedina60-degreestaggeredpatternoptimizeopenareawhilemaintainingscreenstrength.Thismethodwillresultina40percentopenareausing3.2mm（1/8inch）holesalignedon4.8mm（3/16inch）centers.

Feedproducersneedtopayparticularattentiontotheratioofopenscreenareatohorsepower.Recommendedratioforgrainswouldbe55cm2（~8-9inchessquare）perhorsepower（Bliss,1990）.Notenoughopenareaperhorsepowerresultsinthegenerationofheat.Whentheheatgeneratedexceeds44Cto46C（120-125F）,capacitymaybedecreasedasmuchas50percent.

Theremovalofsizedmaterialfromahammer-millisacriticaldesignfeature.Properoutputofmaterialaffectsnotonlytheefficiencyofoperation,butalsoparticlesize.Whenthecorrectratioofscreenareatohorsepowerisusedandproperdistancebetweenhammersandscreenfaceismaintained,mostofthecorrectlysizedparticleswillexitthescreeninatimelymanner.Anderson（1994）statedtheparticlesthatdonotpassthroughthescreenholesbecomepartofafluidizedbedofmaterialsweptalongthefaceofthescreenbythehigh-speedrotationofthehammers.Astheseparticlesrubagainstthescreenandeachothertheirsizeiscontinuallyreducedbyattrition.Thisexcessivesizereductioniscounterproductive.Energyiswastedintheproductionofheat,throughputisrestricted,andparticlesbecometoosmall.

Mostnewhammermillsareequippedwithanair-assistsystemthatdrawsairintothehammermillwiththeproducttobeground.Systemsaredesignedtoprovidereducedpressureontheexitsideofthescreentodisruptthefluidizedbedofmaterialonthefaceofthescreen,thusallowingparticlestoexitthroughscreenholes.Somefullcirclehammermillsaredesignedsothescreenisintwopieces.Itispossibletousealargerwholesizeontheupwardarcofthehammerstofurtherreducetheamountofmaterialonthefaceofthescreen.

HammerMillsHammers

Hammersareusedinsidethehammer-milltoimpactsmashingredientsupintosmallerparticles,makingitmoresuitableforuniformmixingandusageinfeed.Hammersareavailableinahugerangeofconfigurations,shapes,facingsandmaterials.Hammersareavailableassingleholedorwithtwoholes,withtwoholesallowingthehammerstobeusedtwiceasthewearisdonetooneendofthehammer;thehammercanberotatedandusedasecondtime.Theholefitsontoarodinsidethehammermillandswingstohitthematerial.

Dimensionsofahammer

 A:

Thickness

 B:

Width

 C:

Diametertofitrodsize

 D:

SwingLength

 E:

TotalLength

HammerMillPerforatedScreens

Hammermillsscreensareusedinsideahammermilltoseparateparticlesizes.Particleofsmallenoughdiameterthathasbeensuccessfullygrindedbythehammermillpassesthroughthescreenandleavesthehammermillwiththeaidofthepneumaticsystem.

ParticleSizeReduction

SizeReduction:

Theinitialreductionofcerealgrainsbeginsbydisruptingtheouterprotectivelayeroftheseed（hull）,exposingtheinterior,seethepicture.Continuedsizereductionincreasesboththenumberofparticlesandtheamountofsurfaceareaperunitofvolume.Itisthisincreasedsurfaceareathatisofprimaryimportance.Agreaterportionofthegrain'sinteriorisexposedtodigestiveenzymes,allowingincreasedaccesstonutritionalcomponentssuchasstarchandprotein.Theenhancedbreakdownofthesenutritionalcomponentsimprovesabsorptioninthedigestivetract.Theoveralleffectisincreasedanimalperformance.Sizereductionisalsousedtomodifythephysicalcharacteristicsofingredientsresultinginimprovedmixing,pelleting,and,insomeinstances,handlingortransport.

Hammermills:

Reducetheparticlesizeofmaterialsbyimpactingaslowmovingtarget,suchasacerealgrain,witharapidlymovinghammer.Thetargethaslittleornomomentum（lowkineticenergy）,whereasthehammertipistravelingataminimumof4,880m/min（~16,000feetpermin）andperhapsinexcessof7,015m/min（~23,000feetpermin）（highkineticenergy）.Thetransferofenergythatresultsfromthiscollisionfracturesthegrainintomanypieces.Sizingisafunctionofhammer-tipspeed;hammerdesignandplacement;screendesignandholesize;andwhetherornotairassistanceisutilized.

BecauseimpactistheprimaryforceusedinaHammermilltoreducethesizeoftheparticles,anythingthat;increasesthechanceofacollisionbetweenahammerandatarget,increasesthemagnitudeofthecollision,orimprovesmaterialtake-away,wouldbeadvantageoustoparticlesizereduction.Themagnitudeofthecollisionscanbeescalatedbyincreasingthespeedofthehammers.Anderson（1994）statedthatwhendrivespeedandscreensizewerekeptconstant,theincreasedhammer-tipspeedobtainedfromincreasedrotordiameterproducedparti