已阅读5页,还剩4页未读, 继续免费阅读
版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
南通职业大学(论文)外文翻译外文翻译原文:InjectionMoldingManydifferentprocessesareusedtotransformplasticgranules,powders,andliquidsintoproduct.Theplasticmaterialisinmoldableform,andisadaptabletovariousformingmethods.Inmostcasesthermosettingmaterialsrequireothermethodsofforming.Thisisrecognizedbythefactthatthermoplasticsareusuallyheatedtoasoftstateandthenreshapedbeforecooling.Theromosets,ontheotherhandhavenotyetbeenpolymerizedbeforeprocessing,andthechemicalreactiontakesplaceduringtheprocess,usuallythroughheat,acatalyst,orpressure.Itisimportanttorememberthisconceptwhilestudyingtheplasticsmanufacturingprocessesandpolymersused.Injectionmoldingisbyfarthemostwidelyusedprocessofformingthermoplasticmaterials.Itisalsooneoftheoldest.Currentlyinjectionmoldingaccountsfor30%ofallplasticsresinconsumption.Sincerawmaterialcanbeconvertedbyasingleprocedure,injectionmoldingissuitableformassproductionofplasticsarticlesandautomatedone-stepproductionofcomplexgeometries.Inmostcases,finishingisnotnecessary.Typicalproductsincludetoys,automotiveparts,householdarticles,andconsumerelectronicsgoods.Sinceinjectionmoldinghasanumberofinterdependentvariables,itisaprocessofconsiderablecomplexity.Thesuccessoftheinjectionmoldingoperationisdependentnotonlyinthepropersetupofthemachinehydraulics,barreltemperaturevariations,andchangesinmaterialviscosity.Increasingshot-to-shotrepeatabilityofmachinevariableshelpsproducepartswithtightertolerance,lowersthelevelofrejects,andincreasesproductquality(i.e.,appearanceandserviceability).Theprincipalobjectiveofanymoldingoperationisthemanufactureofproducts:toaspecificqualitylevel,intheshortesttime,andusingrepeatableandfullyautomatic南通职业大学(论文)外文翻译cycle.Moldersstrivetoreduceoreliminaterejectedpartsinmoldingproduction.Forinjectionmoldingofhighprecisionopticalparts,orpartswithahighaddedvaluesuchasappliancecases,thepayoffofreducedrejectsishigh.Atypicalinjectionmoldingcycleorsequenceconsistsoffivephases;1.Injectionormoldfilling2.Packingorcompression3.Holding4.Cooling5.PartejectionPlasticgranulesarefedintothehopperandthroughanintheinjectioncylinderwheretheyarecarriedforwardbytherotatingscrew.Therotationofthescrewforcesthegranulesunderhighpressureagainsttheheatedwallsofthecylindercausingthemtomelt.Asthepressurebuildingup,therotatingscrewisforcedbackwarduntilenoughplastichasaccumulatedtomaketheshot.Theinjectionram(orscrew)forcesmoltenplasticfromthebarrel,throughthenozzle,sprueandrunnersystem,andfinallyintothemoldcavities.Duringinjection,themoldcavityisfilledvolumetrically.Whentheplasticcontactsthecoldmoldsurfaces,itsolidifies(freezes)rapidlytoproducetheskinlayer.Sincethecoreremainsinthemoltenstate,plasticfollowsthroughthecoretocompletemoldfilling.Typically,thecavityisfilledto95%98%duringinjection.Thenthemoldingprocessisswitchedovertothepackingphase.Evenasthecavityisfilled,themoltenplasticbeginstocool.Sincethecoolingplasticcontractsorshrinks,itgivesrisetodefectssuchassinkmarks,voids,anddimensionalinstabilities.Tocompensateforshrinkage,additionplasticisforcedintothecavity.Oncethecavityispacked,pressureappliedtothemeltpreventsmoltenplasticinsidethecavityfrombackflowingoutthroughthegate.Thepressuremustbeapplieduntilthegatesolidifies.Theprocesscanbedividedintotwosteps(packingandholding)ormaybeencompassedinonestep(holdingorsecondstage).Duringpacking,meltforcedintothecavitybythepackingpressurecompensatesforshrinkage.Withholding,thepressuremerelypreventsbackflowofthepolymermalt.南通职业大学(论文)外文翻译Aftertheholdingstageiscompleted,thecoolingphasestarts.During,thepartisheldinthemoldforspecifiedperiod.Thedurationofthecoolingphasedependsprimarilyonthematerialpropertiesandthepartthickness.Typically,theparttemperaturemustcoolbelowthematerialsejectiontemperature.Whilecoolingthepart,themachineplasticatesmeltforthenextcycle.Thepolymerissubjectedtoshearingactionaswellastheconditionoftheenergyfromtheheaterbands.Oncetheshortismade,plasticationceases.Thisshouldoccurimmediatelybeforetheendofthecoolingphase.Thenthemoldopensandthepartisejected.Whenpolymersarefabricatedintousefularticlestheyarereferredtoasplastics,rubbers,andfibers.Somepolymers,forexample,cottonandwool,occurnaturally,butthegreatmajorityofcommercialproductsaresyntheticinorigin.AlistofthenamesofthebetterknownmaterialswouldincludeBakelite,Dacron,Nylon,Celanese,Orlon,andStyron.Previousto1930theuseofsyntheticpolymerswasnotwidespread.However,theyshouldnotbeclassifiedasnewmaterialsformanyofthemwereknowninthelatterhalfofthenineteenthcentury.Thefailuretodevelopthemduringthisperiodwasdue,inpart,toalackofunderstandingoftheirproperties,inparticular,theproblemofthestructureofpolymerswasthesubjectofmuchfruitlesscontroversy.Twoeventsofthetwentiethcenturycatapultedpolymersintoapositionofworldwideimportance.ThefirstofthesewasthesuccessfulcommercialproductionoftheplasticnowknownasBakelite.Itsindustrialusefulnesswasdemonstratedin1912andinthenextsucceedingyears.TodayBakeliteishighonthelistofimportantsyntheticproducts.Before1912materialsmadefromcellulosewereavailable,buttheirmanufactureneverprovidedtheincentivefornewworkinthepolymerfieldsuchasoccurredaftertheadventofBakelite.ThesecondeventwasconcernedwithfundamentalstudiesofthenaturepolymersbyStaudingerinEuropeandbyCarohers,whoworkedwiththeDuPontcompanyinDelaware.Agreaterpartofthestudiesweremadeduringthe1920s.Staudingersworkwasprimarilyfundamental.Carothersachievementsledtothedevelopmentofourpresenthugeplasticsindustrybycausinganawakeningofinterestinpolymerchemistry,aninterestwhichisstillstronglyapparenttoday.南通职业大学(论文)外文翻译TheNatureofThermodynamicsThermodynamicsisoneofthemostimportantareasofengineeringscienceusedtoexplainhowmostthingswork,whysomethingsdonotthewaythattheywereintended,andwhyothersthingsjustcannotpossiblyworkatall.Itisakeypartofthescienceengineersusetodesignautomotiveengines,heatpumps,rocketmotors,powerstations,gasturbines,airconditioners,super-conductingtransmissionlines,solarheatingsystems,etc.Thermodynamicscentersaboutthenotionsofenergy,theideathatenergyisconservedisthefirstlowofthermodynamics.Itisstartingpointforthescienceofthermodynamicsisentropy;entropyprovidesameansfordeterminingifaprocessispossible.Thisideaisthebasisforthesecondlowofthermodynamics.Italsoprovidesthebasisforanengineeringanalysisinwhichonecalculatesthemaximumamountofusefulthatcanbeobtainedfromagivenenergysource,ortheminimumamountofpowerinputrequiredtodoacertaintask.Aclearunderstandingoftheideasofentropyisessentialforonewhoneedstousethermodynamicsinengineeringanalysis.Scientistsareinterestedinusingthermodynamicstopredic
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. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,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。
最新文档
- 2024年大学试题(财经商贸)-国际物流笔试参考题库含答案
- 2024年大学试题(计算机科学)-信息组织学笔试参考题库含答案
- 2024年大学试题(教育学)-综合实践活动课标笔试参考题库含答案
- 内分泌学(医学高级):血脂代谢及其他代谢异常
- 木工技能考试:手工木工高级工考试题库考点(题库版)
- 全球生物活性玻璃市场现状及未来趋势分析(简报)
- 中国PS装饰板行业市场发展分析及前景趋势与投资风险研究报告2024-2034版
- 2023-2024学年云南省普洱市墨江第二中学高三第三次测评英语试卷含解析
- 2023-2024学年中山市重点中学高三下学期联合考试英语试题含解析
- 投影机设备租赁协议书
- 直线与平面垂直的判定的评课记录
- 销售心理学读后感_读后感读书心得
- powerbuilder技术讲座(摘自计算机的世界报)
- 校园诗词大会活动方案
- 桥牌队式赛记分表
- 小学教师说课比赛评分表及评分细则
- 银行贷款合同样本银行贷款合同样本
- 田径运动会各种用表、检录表、统计表(朱)
- 储罐施工技术交底
- 注塑车间绩效考核方案_
- IEC61215:2021-2地面光伏组件-测试内容,,中文
评论
0/150
提交评论