会员注册 | 登录 | 微信快捷登录 QQ登录 微博登录 | 帮助中心 人人文库renrendoc.com美如初恋!
站内搜索 百度文库

热门搜索: 直缝焊接机 矿井提升机 循环球式转向器图纸 机器人手爪发展史 管道机器人dwg 动平衡试验台设计

外文翻译--简单的双螺杆挤压设备的设计制造和测试.doc外文翻译--简单的双螺杆挤压设备的设计制造和测试.doc -- 5 元

收藏

编号:201311171658247556    大小:361.08KB    格式:DOC    上传时间:2013-11-17
  【编辑】
5
关 键 词:
教育专区 外文翻译 精品文档 外文翻译
资源描述:
Asimplifiedtwinscrewco-rotatingfoodextruder:design,fabricationandtestingAbstractAsimplifiedco-rotatingtwinscrewfoodextruderwasdesigned,fabricatedandtestedinEngland,followedbyextensivetestinginSriLanka.Itwasbuiltasamodeltomeetthespeci®cproductand®nancialconstraintsoflessdevelopedcountriesandwasexpectedtobeusedinthosecountriestowidentheproductioncapabilitiesofextrudedfoods.Themachinehadanestimateddeliveryof10kg/handwasmademainlywithmildsteel.Twotypesofscrewweremade,onewithaconstantpitchof14mmandtheotherwithvaryingpitchinsegmentsof14,12and10mm.Themachinewaspoweredbya2.2kWelectricmotorwithelectronicspeedcontrols.Themachinealsohadelectricalheatingwithatemperaturecontrollerandapressuresensingdevice.Thecostoffabricationofthemachinewasestimatedat£2000withmostofthepartsbuiltinafairlysimpleworkshop.Amixtureofriceanddriedbananawassuccessfullyextrudedasapotentialsnackfoodandonthebasisofmaximumexpansionthebestresultswasobtainedfromabarreltemperatureof120°C,screwspeed125rpm,feedmoisture15%andwithadieori®cesizeof3mm.Whenthealternativecompressionscrewwastestedverysimilarresultswereachievedwithnosigni®cantimprovementinproductexpansion.Ó1999ElsevierScienceLtd.Allrightsreserved.Keywords:Twinscrewextruder;Design;Lowcost;Snackfood;Continuouscooker;Localconstruction;CerealmixturesNomenclatureADiediameter(mm)BChannelwidth(mm)CScrewcircumference(mm)dScrewcorediameterDOuterdiameterofscrews(mm)HFlightdepth(mm)MMoisturecontent(%wetbasis)nNumberoffightturnsNSpeedangular(rev/min)pPitch(mm)QDeliveryrate(mm3/min)STotalhelicallengthofscrews(mm)tTemperature(C)TResidencetime(min)Overlapangleofscrewfights(degrees)Calendergap(mm)Sideclearance(mm)Productdensity(g/mm3)Helixangle(degrees)1.IntroductionExtrusioncookingisfindingeverincreasingapplicationsinthefoodprocessindustry.Apartfromprovidingameansofmanufacturingnewproducts,ithassuccessfullyrevolutionisedmanyconventionalmanufacturingprocesses(Harlow,1985,Frame,1994).Today,extruderscomeinawidevarietyofsizes,shapesandmethodofoperation.Therearethreetypesoffoodextruderfoundinindustry:hydraulicram,rollerandscrewtypeextruders(Frame,1994).Thescrewextrudersareverydifferenttotheothertwohavingspecialfeaturessuchascontinuousprocessingandmixingability.Singleandtwinscrewtypesarebothwidelyusedinthefoodprocessindustry.Unfortunately,mostofthefoodextrudersavailableinthemarketareeithersocostlythatlessdevelopedcountriescannota.ordtobuythemexceptbysomeformofassistanceoroutsideinvestmentorelsearenotappropriateforthewidevarietyofmaterialsthatneedtobeprocessed.Asaresultthegrowthofextrusiontechnologyoffoodintothesecountrieshasbeenhindereddespiteitsmanyadvantages.Inparticularthereappearsnottobeasuitabletwinscrewextruderavailableatsuffcientlylowcostforuseindevelopingcountries.Thehighcostofthesemachinesislargelyduetothesophisticatedconstructionalfeatureswithmanycontrolsthatarenotessentialformanyapplications.Theinitialpurchasecostisthereforeamajorbarriertothewiderintroductionofextrusiontodevelopingcountrieswheremanyrawmaterialsareavailabletobeprocessedintonutritiousandpalatablefooditems.AttemptshavebeenmadetoutiliselowpressureandsimpleextrudersforbabyweaningfoodssomeofwhichhavebeenverysuccessfulwithprogramsthroughorganizationssuchasFeedtheMillions(SantaMonica,California,90406,USA)andThriposha(USDA/USAID).Theneedhaslongbeenrecognisedforsimple,yetversatilemachinesataffordablepriceswhicharecapableofexploitingthenaturalfoodresources(Sahagun,1977),JansenandHarper(1980),HarperandJansen(1985).Thesecouldincorporatealltheusualcerealssuchasrice,millet,maizeandsorghumwitharichvarietyofnutritionalandtastyadditivessuchasfruits,vegetablesandspices.Theobjectiveofthisstudythereforewastoeliminateorsimplifymanyoftheunnecessaryfeaturesofthecurrentlyavailablemachinessothatfabricationcouldbedoneinanunsophisticatedworkshop,whileensuringtheversatilitytopermittheproductionofacceptableextrudedfoodsespeciallyusingblendsoffruitsandcereals.ThislattertechniquewasdevelopedbyGamlath(1995)usingasinglescrewextrudertoproducearangeofextrudatesthatsheadjudgedtoshowgreatpromiseasasnackfoodorbreakfastcerealinSriLankainparticularbutalsoinmanydevelopingcountriesandalsoasahighvalueexport.Theseproductswerelargelybasedonmixturesoffruitandcerealssuchasmango,bananaandtomatowithmaize,riceandwheat.Attractivelytexturedandflavoureditemswereproducedwhichcouldeasilybefurtherflavouredwithspices,sugarandsalt.Manydevelopingcountriesusehomebasedbusinessestoproducesnacksandready-to-eatmealsandtheseproductwellintothiswellestablishedculture.Machinesmadeinthedevelopingcountry,however,needtobelowcostandrelativelysimple,easytomaintainandoperate.Inthisstudytheparticularfeaturesrequiredweregoodtransportcharacteristicsforstickymaterialsandgoodmixingabilitywhichareneededfortheblendedcropsselected.Shortresidencetimesandlowtomediumpressureswereacceptable.2.DesignapproachThedesignoftheextruderinthisstudywasmostlybasedontheresultsofextrusionstudiesdoneusingasinglescrewlaboratoryscaleextruders(Brabender,Warrington,Cheshire,UK)aspartofthesameprogramme,andsupportedbyengineeringprinciplesandconstraintsapplicabletoadevelopingcountry.Inthedesignprocess,thelevelofpressurelikelytobedevelopedwithintheextruderbarrelbecomesthemostimportantfactorasitdeterminesthesizesofalltheimportantcomponentsoftheextrudersuchasbearings,shaftdiametersandbarreldimensions.Asthesemachinesoftenoperateunderelevatedtemperatures,pressuretendstovaryunpredictablybecauseofcomplexrheologicalpropertiesoffooddoughasrelatedtovaryingtemperaturealongthebarrel.Therefore,actualmeasurementsofextruderprocessvariables,weremadeonthechosenrangeoffoodmaterialsonthelaboratorysinglescrewextruder.Thisapproachwasreckonedtobemoreappropriateratherthanatheoreticalone,thatcannotbegeneralisedespeciallyformaterialsofunknownrheology.Hence,approximatevaluesforsomeofthemostimportantparameterssuchasdiesizes,pressures,temperaturesetc.werequantified.Thesevalueswerethentestedagainintheexperimentsdescribedlaterforthetwinscrewsystem.2.1.SinglevstwinscrewsManycomparisonsbetweentwinandsinglescrewextrudershavebeenmade(Harper,1992)(Hauck,1985)(Hauck&BenGera,1987)(VanZuilichem,Stolp&Janssen,1984)andmanyofthefeaturesdiscussedarerelevanttothecurrentapplication.Singlescrewmachinesmeetmostofthecriteriafordevelopingcountriesbutunfortunatelycertainofthetechnicalrequirementscanonlybemetbytwinscrewssuchasversatility,adequate¯owoffeedintothescrewsand,particularlyinthiscase,¯owofthematerialdownthebarrelwithoutspinningwithinit.ThisisacommonproblemwiththeratherstickyorhighmoisturematerialsthatwereenvisagedwiththeincorporationoffruitsandvegetablesandothertropicalcropsandflavoursandexperiencedbyGamlath(1995).Theforwardmotionofthefooddoughreliesentirelyonthefrictionbetweenthematerialandtheinteriorsurfacesofbothscrewandbarrel.Thisisparticularlysoinasinglescrewbutlesssoinatwinscrew.Singlescrewextrudersaregenerallycheaperthanthetwinscrewtypeowingtotheirsimplerconstruction,buttheyaremorelikelytoblockthantwinscrewextruders.Thedilemmafacingthedesigner,therefore,isthatalthoughtheoperationalproblemscanbeavoidedbyusingtwinscrewstheirsophisticatedconstructionalfeatureswouldhavetobesimplifiedsignificantlytoachievethelowcostobjective.Intwinscrewextrudersthescrewscanbemadeaseitherco-rotatingorcounterrotating,withdifferingamountsofintermesh,pitchandclearances,allofwhichaffecttheprocessingcharacteristicsofthemachine(Martelli,1983).Sincetheflightofonescrewengagesthechanneloftheotherthetwinscrewspreventmaterialfromstickingtothescrewsandrotatingwiththescrew,henceencouragingforwardmotionofdoughwithreducedslip(Jansen,1978).Thisalsoenhancesthemixingofmaterialsinthechannelsofthescrews.Thecounterrotatingtypeoftwinscrewextrudercangivebettermaterial¯owcharacteristicspushingthematerialpositivelyforwardtowardsthediebutreducingthedegreeofmixingofmaterialswithintheextruder.Anotherunfortunatefeatureisthatseparatingforcesbetweenthescrewscancauseseverewearofthesidewalls.Ontheotherhand,co-rotating,twinscrewextrudersgiveadditionaladvantagessuchaspressurebalanceintransverseplanesofthescrewsandawipingactionofthefightsduetotheopposinglinearvelocitiesatthefightsofintermeshingregion.Therefore,itwasdecidedthatatwinscrewco-rotatingextruderwouldprovidealltheversatilityandcharacteristicsrequiredforprocessingthefoodmaterialsenvisagedinadevelopingcountry.Theonlyproblemthenwastodesignasatisfactorymachinethatwouldalsomeetthecostcriteria.2.2.ScrewsThecentralpartofanextruderisthescrew.Thescrewsrotateinatightlyfittingbarrelandconveythematerialfromfeedendtodieend,mixingandcom-pressingtheingredients.Thecapacityoftheextruderismainlydeterminedbythescrewouterandrootdiameters,pitchandfightwidth(Fig.1).Therefore,thescrewoveralldimensionshavetobefirstdeterminedaccordingtothedesiredoutputtoinitiatethedesignprocess.Oneotherimportantfactoristheresidencetime,asitdeterminesthedegreeofcookingtakingplaceintheextruder.ExploratorytrialsandtheworkofGamlath(1995)indicatedthataresidencetimeofabout16swouldbeadequateatthemeanspeed.Itis,however,influencedbymanyofthedesignparametersincludingthelength,diameterandpitchofthescrewsalthoughitcanbecontrolledlargelybytheoperationalscrewspeedoftheextruderandtheselecteddiesize.Therheologyofthematerialalsohasamajorinfluenceonthethroughputsoresidencetimecannotbeaccuratelypredicted.Inthisstudyseveraldimensionsofthescrewsweredeterminedinordertosuittheexpectedoutputandresidencetime.ThegeometryandequationsrelatingmanyofthesefactorsaregiveninFig.1andEqs.(1)±(3)below.Themaximumoutputwasnotthe®rstprioritybutsimilarsizedextrudersandsinglescrewtrialsindicatedatypicaldeliveryrateofupto10kg/h.Theresidencetimewasdesignedtobeshortasthenovelproductsplannedwerenotexpectedtorelyonlongprocessingtimes.TheshortresidencetimewasparticularlysoughtinordertomaintainthevitaminCcontentofperishableproductswhichcouldbeeasilydestroyedifcookedtoolong(Seiler,1984).Theinfluenceofscrewpitchissuchthatlowvalueswithsmallhelixanglesleadtolongerresidencetimesbecauseoftheincreasednumberofcyclesthatthematerialhastogothrough.Ontheotherhand,largepitcheswouldreducethedegreeofmixinganduniformityofheatdistributionduetotheincreaseinvolumeofmaterialcontainedinthescrewchannels.
温馨提示:
1: 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
2: 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
3.本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
5. 人人文库网仅提供交流平台,并不能对任何下载内容负责。
6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
  人人文库网所有资源均是用户自行上传分享,仅供网友学习交流,未经上传用户书面授权,请勿作他用。
0条评论

还可以输入200字符

暂无评论,赶快抢占沙发吧。

当前资源信息

4.0
 
(2人评价)
浏览:10次
英文资料库上传于2013-11-17

官方联系方式

客服手机:17625900360   
2:不支持迅雷下载,请使用浏览器下载   
3:不支持QQ浏览器下载,请用其他浏览器   
4:下载后的文档和图纸-无水印   
5:文档经过压缩,下载后原文更清晰   

相关资源

相关资源

相关搜索

教育专区   外文翻译   精品文档   外文翻译  
关于我们 - 网站声明 - 网站地图 - 友情链接 - 网站客服客服 - 联系我们
[email protected] 2015-2017 人人文库网网站版权所有
苏ICP备12009002号-5