快餐勺子注塑模具設(shè)計(jì)【一模四腔含17張CAD圖紙及proe三維】

快餐勺子注塑模具設(shè)計(jì)【一模四腔含17張CAD圖紙及proe三維】,一模四腔含17張CAD圖紙及proe三維,快餐,勺子,注塑,模具設(shè)計(jì),一模四腔含,17,cad,圖紙,proe,三維 調(diào)研報(bào)告 畢業(yè)設(shè)計(jì)（論文）題目： 快餐勺子注塑模具設(shè)計(jì) 學(xué) 院： 專業(yè)班級： 姓 名： 學(xué) 號： 指導(dǎo)教師： 年 月 2 一、課題的來源及意義 注塑模具是生產(chǎn)各種工業(yè)產(chǎn)品的重要工藝裝備【1】，隨著塑料工業(yè)的迅速發(fā)展，以及塑料制品在航空、航天、電子、機(jī)械、船舶和汽車等工業(yè)部門的推廣應(yīng)用，產(chǎn)品對模具的要求也越來越高，傳統(tǒng)的模具設(shè)計(jì)方法已無法適應(yīng)當(dāng)今的要求. 與傳統(tǒng)的模具設(shè)計(jì)相比，計(jì)算機(jī)輔助工程（CAE）技術(shù)無論是在提高生產(chǎn)率、保證產(chǎn)品質(zhì)量方面，還是在降低成本、減輕勞動(dòng)強(qiáng)度方面，都具有極大的優(yōu)越性。 模具應(yīng)用廣泛，現(xiàn)代制造業(yè)中的產(chǎn)品構(gòu)件成形加工，幾乎都需要使用模具來完成【2】。所以，模具產(chǎn)業(yè)是國家高新技術(shù)產(chǎn)業(yè)的重要組成部分，是重要的、寶貴的技術(shù)資源。優(yōu)化模具系統(tǒng)結(jié)構(gòu)設(shè)計(jì)和型件的CAD/CAE/CAM，并使之趨于智能化，提高型件成形加工工藝和模具標(biāo)準(zhǔn)化水平，提高模具制造精度與質(zhì)量，降低型件表面研磨、拋光作業(yè)量和制造周期；研究、應(yīng)用針對各種類模具型件所采用的高性能、易切削的專用材料，以提高模具使用性能；為適應(yīng)市場多樣化和新產(chǎn)品試制，應(yīng)用快速原型制造技術(shù)和快速制模技術(shù)，以快速制造成型沖模、塑料注射?；驂鸿T模等，應(yīng)當(dāng)是未來5~20年的模具生產(chǎn)技術(shù)的發(fā)展趨勢.這也是我們進(jìn)行本次設(shè)計(jì)的目的【3】。 本次設(shè)計(jì)以快餐勺子為設(shè)計(jì)課題，并應(yīng)熟練地使用ProE、AutoCAD等軟件來完成課題。在設(shè)計(jì)過程中，應(yīng)對我們設(shè)計(jì)方法、軟件繪圖、資料查詢、論文寫作、外文翻譯等方面進(jìn)行全方位的訓(xùn)練，培養(yǎng)我們初步的設(shè)計(jì)能力，并加強(qiáng)我們對模具行業(yè)的理解和認(rèn)知。 二、國內(nèi)外發(fā)展?fàn)顩r 2.1國內(nèi)發(fā)展?fàn)顩r 歷經(jīng)半個(gè)多世紀(jì),我國的模具工業(yè)水平有了飛躍的發(fā)展,高效、復(fù)雜、大型、精密、長壽命的模具在整個(gè)模具產(chǎn)量中所占的比重越來越大,模具水平有了較大提高【4】。雖然中國模具工業(yè)發(fā)展迅速,但與需求相比,顯然供不應(yīng)求,其主要缺口集中于精密、大型、復(fù)雜、長壽命模具領(lǐng)域。由于在模具精度、壽命、制造周期及生產(chǎn)能力等方面。中國與國際平均水平和發(fā)達(dá)國家仍有較大差距，因此每年需要大量進(jìn)口模具。 近年來，我國塑料模具水平已有較大提高【5】。大型塑料模具已能生產(chǎn)單套重量達(dá)50t以上的注塑模，精密塑料模的精度已可達(dá)到3μm，制件精度為0.5μm的小模數(shù)齒輪模具及達(dá)到高光學(xué)要求的車燈模具等也已能生產(chǎn)，多腔塑料模已能生產(chǎn)一模7800腔的塑封模，高速模具方面已能生產(chǎn)4m/min以上擠出速度的高速塑料異型材擠出模及主型材雙腔共擠、雙色共擠、軟硬共擠、后共擠、再生料共擠出和低發(fā)泡鋼塑共擠等各種模具。在生產(chǎn)手段上，模具企業(yè)設(shè)備數(shù)控化率已有較大提高，CAD/CAE/CAM技術(shù)的應(yīng)用面已大為擴(kuò)大，高速加工及RP/RT等先進(jìn)技術(shù)的采用已越來越多【6】。模具標(biāo)準(zhǔn)件使用覆蓋率及模具商品化率都已有較大幅度的提高，熱流道模具的比例也有較大提高。三資企業(yè)蓬勃發(fā)展進(jìn)一步促進(jìn)了塑料模具設(shè)計(jì)制造水平及企業(yè)管理水平的提高。 但相比于不足，國內(nèi)生產(chǎn)的小模數(shù)塑料齒輪等精密塑料模具已達(dá)到國外同類產(chǎn)品水平。在齒輪模具設(shè)計(jì)中采用最新的齒輪設(shè)計(jì)軟件，糾正了由于成型壓縮造成的齒形誤差，達(dá)到了標(biāo)準(zhǔn)漸開線造型要求【7】。顯示管隔離器注塑模、高效多色注射塑料模、純平彩電塑殼注塑模等精密、復(fù)雜、大型模具的設(shè)計(jì)制造水平也已達(dá)到或接近國際水平。使用CAD三維設(shè)計(jì)、計(jì)算機(jī)模擬注塑成形、抽芯脫模機(jī)構(gòu)設(shè)計(jì)新穎等對精密、復(fù)雜模具的制造水平提高起到了很大作用。20噸以上的大型塑料模具的設(shè)計(jì)制造也已達(dá)到相當(dāng)高的水平。34英寸彩電塑殼和48英寸背投電視機(jī)殼模具，汽車保險(xiǎn)杠和儀表盤的注塑模等大型模具，國內(nèi)都已可生產(chǎn)。 2.2國外發(fā)展?fàn)顩r 國外注塑模具制造行業(yè)的最基本特征是高度集成化、智能化、柔性化和網(wǎng)絡(luò)化。追求的目標(biāo)是提高產(chǎn)品質(zhì)量及生產(chǎn)效率【8】。國外發(fā)達(dá)國家模具標(biāo)準(zhǔn)化程度達(dá)到70%～80%，實(shí)現(xiàn)部分資源共享，大大縮短設(shè)計(jì)周期及制造周期，降低生產(chǎn)成本.最大限度地提高模具制造業(yè)的應(yīng)變能力 滿足用戶需求。模具企業(yè)在技術(shù)上實(shí)現(xiàn)了專業(yè)化，在模具企業(yè)的生產(chǎn)管理方面，也有越來越多的采用以設(shè)計(jì)為龍頭、按工藝流程安排加工的專業(yè)化生產(chǎn)方式，降低了對模具工人技術(shù)全面性的要求，強(qiáng)調(diào)專業(yè)化。? 　　國外注塑成型技術(shù)在也向多工位、高效率、自動(dòng)化、連續(xù)化、低成本方向發(fā)展。因此，模具向高精度復(fù)雜、多功能的方向發(fā)展【9】。例如：組合模、即鈑金和注塑一體注塑鉸鏈一體注塑、活動(dòng)周轉(zhuǎn)箱一體注塑；多色注塑等；向高效率、高自動(dòng)化和節(jié)約能源，降低成本的方向發(fā)展。例如：疊模的大量制造和應(yīng)用，水路設(shè)計(jì)的復(fù)雜化、裝夾的自動(dòng)化、取件全部自動(dòng)化。? 目前在歐美，CAD/CAE/CAM已成為模具企業(yè)普遍應(yīng)用的技術(shù)。在CAD的應(yīng)用方面，已經(jīng)超越了甩掉圖板、二維繪圖的初級階段，目前3D設(shè)計(jì)已達(dá)到了70%～89%。PRO/E、UG、CIMATRON等軟件的應(yīng)用很普遍。應(yīng)用這些軟件不僅可完成2D設(shè)計(jì)，同時(shí)可獲得3D模型，為NC編程和CAD/CAM的集成提供了保證。應(yīng)用3D設(shè)計(jì)，還可以在設(shè)計(jì)時(shí)進(jìn)行裝配干涉的檢查，保證設(shè)計(jì)和工藝的合理性。數(shù)控機(jī)床的普遍應(yīng)用，保證了模具零件的加工精度和質(zhì)量。30～50人的模具企業(yè)，一般擁有數(shù)控機(jī)床十多臺。經(jīng)過數(shù)控機(jī)床加工的零件可直接進(jìn)行裝配，使裝配鉗工的人數(shù)大大減少【10】。CAE技術(shù)在歐美已經(jīng)逐漸成熟。在注射模設(shè)計(jì)中應(yīng)用CAE分析軟件，模擬塑料的沖模過程，分析冷卻過程，預(yù)測成型過程中可能發(fā)生的缺陷。在沖模設(shè)計(jì)中應(yīng)用CAE軟件，模擬金屬變形過程，分析應(yīng)力應(yīng)變的分布，預(yù)測破裂、起皺和回彈等缺陷。CAE技術(shù)在模具設(shè)計(jì)中的作用越來越大，意大利COMAU公司應(yīng)用CAE技術(shù)后，試模時(shí)間減少了50%以上。 三、主要研究內(nèi)容 1.塑件建模 2.塑料成型工藝分析 3.擬定模具結(jié)構(gòu)成型零件設(shè)計(jì)計(jì)算 4.澆注系統(tǒng)設(shè)計(jì) 5.成型零件設(shè)計(jì)計(jì)算 6.模架選型 7.排氣槽設(shè)計(jì) 8.脫模推出機(jī)構(gòu)設(shè)計(jì) 9.冷卻系統(tǒng)設(shè)計(jì) 10.導(dǎo)向和定位結(jié)構(gòu)設(shè)計(jì) 11.總裝圖和零件圖的繪制 12.編寫設(shè)計(jì)說明書 四、本課題的研究目標(biāo)及方法 1.首先從產(chǎn)品出發(fā)，首先對塑件建模，然后對塑件的尺寸，形狀，材料等方面通過查閱手冊進(jìn)行分析，從而得出產(chǎn)品的可行性。 2.塑件成型工藝性分析：從外形尺寸、精度等級、脫模斜度、材料性能、材料的注射成型過程及工藝參數(shù)等方面做出合理的工藝分析。 3.模具結(jié)構(gòu)分析：根據(jù)要求，通過計(jì)算確定模具的分型面，型腔數(shù)量和排列方式，并選出合適的注射機(jī)。 4.澆注系統(tǒng)的設(shè)計(jì)：根據(jù)塑件，通過Proe軟件輸出的數(shù)據(jù)，設(shè)計(jì)出主流道，并確定出主流道的具體尺寸、凝料體積、當(dāng)量半徑、澆口套等數(shù)據(jù)，同時(shí)計(jì)算出分流道和澆口的各個(gè)參數(shù)，如有冷料穴，需設(shè)計(jì)出其尺寸。 5.成型零件設(shè)計(jì)計(jì)算：選取鋼材并通過計(jì)算設(shè)計(jì)出凹凸模的尺寸。 6.脫模推出機(jī)構(gòu)：通過查手冊，確定推出方式，計(jì)算脫模力并且進(jìn)行校核。 7.圖紙的繪制和說明書的編寫：用 Pro/E、AutoCAD 軟件繪制總裝圖和零件圖；將設(shè)計(jì)過程中相應(yīng)的數(shù)據(jù)整理后完成計(jì)算說明書的編寫。 預(yù)期達(dá)到的目標(biāo)：在老師指導(dǎo)下，獨(dú)立完成適用于產(chǎn)品的注射模的設(shè)計(jì)，并完成英文文獻(xiàn)翻譯，繪制好圖紙及編寫好計(jì)算說明書。 五、進(jìn)度安排 第1 周：寫調(diào)研報(bào)告。 第2 周：翻譯外文資料。 第3 周：確定該塑件零件尺寸，進(jìn)行工藝分析，制作零件模型；設(shè)計(jì)分型面、型腔。 第4-6 周：設(shè)計(jì)模體、澆注系統(tǒng)、冷卻系統(tǒng)，導(dǎo)向與定位機(jī)構(gòu)，并進(jìn)行相關(guān)計(jì)算。 第7-9 周：用 Pro/E、AutoCAD 繪制模具零件三維圖、零件二維圖及實(shí)體裝配圖。 第10-11 周：繪制模具裝配圖，標(biāo)注尺寸。 第12 周：編寫計(jì)算說明書。 第13 周：修改圖紙，整理資料。 第14 周：準(zhǔn)備答辯。 六、實(shí)驗(yàn)方案的可行性分析 經(jīng)過深入的調(diào)研和各方面的查閱資料，本課題的研究十分迎合當(dāng)代的需求，注塑模具在現(xiàn)代工業(yè)中占有很重要的地位，需求量也很大。本課題在制定詳細(xì)進(jìn)度表的前提下，再加上老師的悉心指導(dǎo)，我覺得本課題具有較強(qiáng)的可行性。 七、參考文獻(xiàn) 【1】葉久新, 王群. 塑料成型工藝及模具設(shè)計(jì)[M]. 機(jī)械工業(yè)出版社, 2008. 【2】孫錫紅. 我國塑料模具發(fā)展現(xiàn)狀及發(fā)展建議[J]. 電加工與模具, 2010(S1):31-33. 【3】李良福. 國內(nèi)外模具加工現(xiàn)狀和今后發(fā)展[J]. 裝備機(jī)械, 1994(2):6-8. 【4】董金獅. 我國可降解塑料快餐餐具的研究現(xiàn)狀與發(fā)展方向[J]. 鐵路節(jié)能環(huán)保與安全衛(wèi)生, 1995(3):218-219. 【5】工程塑料網(wǎng)→標(biāo)準(zhǔn)頻道. 聚苯乙烯(PS)的應(yīng)用范圍和注塑特性[J]. 【6】吳清文, 王莉, 馬建旭. 塑料注塑模具CAD概略[J]. 光學(xué)精密工程, 1995, 3(6):11-17. 【7】汪佑思. 透明塑料勺注射模優(yōu)化設(shè)計(jì)[J]. 模具制造, 2013, 13(1):55-59. 【8】賈長明, 張廣興. 基于Pro/E的快餐碗熱流道模具設(shè)計(jì)[J]. 天津理工大學(xué)學(xué)報(bào), 2010, 26(2):79-81. 【9】王樹勛. 注塑模具設(shè)計(jì)[M]. 華南理工大學(xué)出版社, 2005. 【10】Guo H Y. Plastic Mould Design Optimization Method Research Based on the Reverse Engineering Technology[J]. Applied Mechanics & Materials, 2013, 278-280:2261-2264. 7 One Source More Resourceful A Guide to Polyolefin Injection Molding Equistar is one of the largest producers of ethylene propylene and polyethylene in the world today One of the largest yet we pay atten tion to even the smallest needs of our customers We re a leading producer of polypropylene oxygenated chemicals performance polymers and resins and compounds for wire and cable We re an industry leader with an unwavering commitment to being the premier petrochemicals and polymers company Our commitment starts with each of our more than 5 000 employees It stretches out from our headquarters in Houston across 16 manufac turing facilities along the U S Gulf Coast and in the Midwest It continues through our 1 400 mile ethylene propylene distribution system that spans the Gulf Coast We are the product of many minds coming together with the single focus of providing the right product for every customer That s what drives us to maintain an extended product line enhanced operating efficiencies greater geographic diversity and strong research and development capabilities That s what drives us to provide the resources that help us lead today and rise to the challenges of a changing industry tomorrow One Source More Resourceful 1 A Guide to Polyolefin Injection Molding Table of Contents Introduction 2 Polyolefins are derived from petrochemicals 2 Molecular structure and composition affect properties and processability 2 Chain branching 3 Density 3 Molecular weight 3 Molecular weight distribution 4 Copolymers 5 Modifiers and additives 5 Working closely with molders 5 How polyolefins are made 5 Low density polyethylene LDPE 6 High density polyethylene HDPE 6 Linear low density polyethylene LLDPE 7 Polypropylene 7 Shipping and handling polyolefin resins 7 Material handling 8 How to solve material handling problems 9 Other material handling practices 10 The injection molding process 10 Injection units 10 Plasticator specifications 13 Screw designs 13 Nozzles 14 Clamp mechanisms 14 Clamp specifications 15 Injection molds 16 Types of mold 16 Sprues and runners 17 Mold venting 18 Gating 19 Mold cooling 20 Ejection devices 20 Spiral flow measurement 20 General injection molding operating procedures 21 General safety 21 Heat 22 Electricity 22 Machinery motion 22 The injection molding process and its effect on part performance 22 The molding cycle 22 Shrinkage 27 Warpage 28 Color dispersion and air entrapment 29 Part ejection and mold release 29 Clarity 30 Gloss 30 Polypropylene integral hinges 30 Appendices 1 Injection Molding Terms 31 2 Metric Conversion Guide 35 3 Abbreviations 37 4 ASTM test methods applicable to polyolefins 38 5 Injection molding problems causes and solutions 39 6 ASTM and ISO sample preparation and test procedures 43 7 Compression and injection molded sample preparation for HDPE 44 Introduction Polyolefins are the most widely used plastics for injection molding This manual A Guide to Polyolefin Injection Molding contains general information concerning materials methods and equipment for producing high quality injection molded polyolefin products at optimum production rates Polyolefins that can be injection molded include Low density polyethylene LDPE Linear low density polyethylene LLDPE High density polyethylene HDPE Ethylene copolymers such as ethylene vinyl acetate EVA Polypropylene and propylene copolymers PP Thermoplastic olefins TPO In general the advantages of injection molded polyolefins com pared with other plastics are Lightweight Outstanding chemical resistance Good toughness at lower temperatures Excellent dielectric properties Non hygroscopic The basic properties of polyolefins can be modified with a broad range of fillers reinforcements and chemical modifiers Furthermore polyolefins are considered to be relatively easy to injection mold Major application areas for poly olefin injection molding are Appliances Automotive products Consumer products Furniture Housewares Industrial containers Materials handling equipment Packaging Sporting goods Toys and novelties This manual contains extensive information on the injection mold ing of polyolefins however it makes no specific recommendations for the processing of Equistar resins for specific applications For more detailed information please contact your Equistar polyolefins sales or technical service representative Polyolefins are derived from petrochemicals Polyolefins are plastic resins poly merized from petroleum based gases The two principal gases are ethylene and propylene Ethylene is the principal raw material for mak ing polyethylene PE and ethylene copolymer resins propylene is the main ingredient for making polypropylene PP and propylene copolymer resins Polyolefin resins are classified as thermoplastics which means that they can be melted solidified and melted again This contrasts with thermoset resins such as phenolics which once solidified can not be reprocessed Most polyolefin resins for injection molding are used in pellet form The pellets are about 1 8 inch long and 1 8 inch in diameter and usual ly somewhat translucent to white in color Many polyolefin resins con tain additives such as thermal stabi lizers They also can be compound ed with colorants flame retardants blowing agents fillers reinforce ments and other functional addi tives such as antistatic agents and lubricants Molecular structure and composition affect properties and processability Four basic molecular properties affect most of the resin characteris tics essential to injection molding high quality polyolefin parts These molecular properties are Chain branching Crystallinity or density Average molecular weight Molecular weight distribution The materials and processes used to produce the polyolefins determine these molecular properties The basic building blocks for the gases from which polyolefins are derived are hydrogen and carbon atoms For polyethylene these atoms are combined to form the ethylene monomer C 2 H 4 HH C C HH In the polymerization process the double bond connecting the carbon atoms is broken Under the right conditions these bonds reform with other ethylene molecules to form long molecular chains H H H H H H H H H H C C C C C C C C C C H H H H H H H H H H The resulting product is polyethyl ene resin 2 A Guide to Polyolefin Injection Molding For polypropylene the hydrogen and carbon atoms are combined to form the propylene monomer CH 3 CH CH 2 HH H C C C HHH The third carbon atom forms a side branch which causes the backbone chain to take on a spiral shape HHHHHH C C C C C C H H C H H H C H H H C H HHH Ethylene copolymers such as ethyl ene vinyl acetate EVA are made by the polymerization of ethylene units with randomly distributed comonomer groups such as vinyl acetate VA Chain branching Polymer chains may be fairly linear as in high density polyethylene or highly branched as in low density polyethylene For every 100 ethylene units in the polyethylene molecular chain there can be one to ten short or long branches that radiate three dimensionally Figure 1 The degree and type of branching are con trolled by the process reactor cat alyst and or any comonomers used Chain branching affects many of the properties of polyethylenes including density hardness flexibili ty and transparency to name a few Chain branches also become points in the molecular structure where oxidation may occur If excessively high temperatures are reached during processing oxidation can occur which may adversely affect the polymer s properties This oxida tion or degradation may cause cross linking in polyethylenes and chain scission in polypropylenes Polypropylene on the other hand can be described as being linear no branching or very highly branched Although the suspended carbon forms a short branch on every repeat unit it is also responsi ble for the unique spiral and linear configuration of the polypropylene molecule Density Polyolefins are semi crystalline poly mers which means they are com posed of molecules which are arranged in a very orderly crystalline structure and molecules which are randomly oriented amorphous This mixture of crystalline and amorphous regions Figure 2 is essential in providing the desired properties to injection molded parts A totally amorphous polyolefin would be grease like and have poor physical properties A totally crystalline poly olefin would be very hard and brittle HDPE resins have linear molecular chains with comparatively few side chain branches Therefore the chains are packed more closely together Figure 3 The result is crystallinity up to 95 percent LDPE resins generally have crystallinity from 60 percent to 75 percent LLDPE resins have crystallinity from 60 percent to 85 percent PP resins are highly crystalline but they are not very dense PP resins have a nominal specific gravity range of 0 895 to 0 905 g cm 3 which is the lowest for a commodity thermo plastic and does not vary appreciably from manufacturer to manufacturer For polyethylene the density and crystallinity are directly related the higher the degree of crystallinity the higher the resin density Higher density in turn influences numer ous properties As density increases heat softening point resistance to gas and moisture vapor permeation and stiffness increase However increased density generally results in a reduction of stress cracking resistance and low temperature toughness LDPE resins have densities rang ing from 0 910 to 0 930 grams per cubic centimeter g cm 3 LLDPE resins range from 0 915 to 0 940 g cm 3 HDPE resins range from 0 940 to 0 960 g cm 3 As can be seen all natural poly olefin resins i e those without any fillers or reinforcements have densities less than 1 00 g cm 3 This light weight is one of the key advantages for parts injection mold ed from polyolefins A general guide to the effects of density on the properties for various types of polyethylene resins is shown in Table 1 Molecular weight Atoms of different elements such as carbon hydrogen etc have differ ent atomic weights For carbon the atomic weight is 12 and for hydro gen it is one Thus the molecular weight of the ethylene unit is the sum of the weight of its six atoms two carbon atoms x 12 four hydrogen x 1 or 28 3 Figure 1 Polyethylene chain with long side branches C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C C Figure 2 Crystalline A and amor phous B regions in polyolefin Figure 3 Linear polyethylene chain with short side branches C C C C C C C C C C C C C C C C C C C C C Unlike simple compounds like ethylene or propylene every poly olefin resin consists of a mixture of large and small chains i e chains of high and low molecular weights The molecular weight of the polymer chain generally is in the thousands and may go up to over one million The average of these is called quite appropriately the average molecular weight As average molecular weight increases resin toughness increases The same holds true for tensile strength and environmental stress crack resistance ESCR cracking brought on when molded parts are subjected to stresses in the pres ence of materials such as solvents oils detergents etc However high er molecular weight results in an increase in melt viscosity and greater resistance to flow making injection molding more difficult as the average molecular weight increases Melt flow rate MFR is a simple measure of a polymer s melt vis cosity under standard conditions of temperature and static load pressure For polyethylenes it is often referred to as melt index MI MFR is the weight in grams of a melted resin that flows through a standard sized orifice in 10 minutes g 10 min Melt flow rate is inversely related to the resin s average molecular weight as the average molecular weight increases MFR decreases and vice versa Melt viscosity or the resistance of a resin to flow is an extremely important property since it affects the flow of the molten polymer filling a mold cavity Polyolefins with higher melt flow rates require lower injection molding processing pressures temperatures and shorter molding cycles less time needed for part cooling prior to ejection from the mold Resins with high viscosities and therefore lower melt indices require the opposite conditions for injection molding It should be remembered that pressure influences flow properties Two resins may have the same melt index but different high pressure flow properties Therefore MFR or MI must be used in conjunction with other characteristics such as molecular weight distribution to measure the flow and other properties of resins Generally injection molding resins are char acterized as having medium high or very high flow For injection molding grades the MFR MI values for polyethylenes are generally determined at 190 C 374 F using a static load of 2 160 g MFR values for polypropy lenes are determined at the same load but at a higher temperature 230 C 446 F The MFR of other thermoplastics may be determined using different combinations of temperatures and static load For this reason the accurate prediction of the relative processability of different materials using MFR data is not possible Molecular weight distribution During polymerization a mixture of molecular chains of widely varying lengths is produced Some may be short others may be extremely long containing several thousand monomer units The relative distribution of large medium and small molecular chains in the polyolefin resin is important to its properties When the distribu tion is made up of chains close to the average length the resin is said to have a narrow molecular weight distribution Polyolefins with broad molecular weight distribution are resins with a wider variety of chain lengths In general resins with narrow molecular weight distributions have good low temperature impact strength and low warpage Resins with broad molecular weight distributions generally have greater stress crack ing resistance and greater ease of processing Figure 4 The type of catalyst and the polymerization process used to produce a polyolefin determines its molecular weight distribution The molecular weight distribution MWD of PP resins can also be altered during production by con trolled rheology additives that selec tively fracture long PP molecular 4 AS MELT INDEX AS DENSITY INCREASES INCREASES Durometer hardness surface remains the same increases Gloss improves improves Heat resistance softening point remains the same improves Stress crack resistance decreases decreases Mechanical flex life decreases decreases Processability less pressure to mold improves remains the same Mold shrinkage decreases increases Molding speed faster solidification remains the same increases Permeability resistance remains the same improves Stiffness remains the same increases Toughness decreases decreases Transparency remains the same decreases Warpage decreases increases Table 1 General guide to the effects of polyethylene physical properties on properties and processing chains This results in a narrower molecular weight distribution and a higher melt flow rate Copolymers Polyolefins made with one basic type of monomer are called homopolymers There are however many polyolefins called copoly mers that are made of two or more monomers Many injection molding grades of LLDPE LDPE HDPE and PP are made with comonomers that are used to provide specific property improvements The comonomers most often used with LLDPE and HDPE are called alpha olefins They include butene hexene and octene Other comonomers used with ethylene to make injection molding grades are ethyl acrylate to make the copoly mer ethylene ethyl acrylate EEA and vinyl acetate to produce ethyl ene vinyl acetate EVA Ethylene is used as a comonomer with propylene to produce polypropylene random copolymers Polypropylene can be made more impact resistant by producing a high ethylene propylene copolymer in a second reactor forming a finely dispersed secondary phase of ethyl ene propylene rubber Products made in this manner are commonly referred to as impact copolymers Modifiers and additives Numerous chemical modifiers and additives may be compounded with polyolefin injection molding resins In some grades the chemical modi fiers are added during resin manu facture Some of these additives include Antioxidants Acid scavengers Process stabilizers Anti static agents Mold release additives Ultraviolet UV light stabilizers Nucleators Clarifiers Lubricants Working closely with molders Equistar offers a wide range of polyolefin resins for injection mold ing including Alathon HDPE Alathon LDPE Petrothene LDPE and LLDPE Equistar PP Ultrathene EVA copolymers and Flexathene TPOs These resins are tailored to meet the requirements of many areas of application Polyolefin resins with distinctly dif ferent properties can be made by controlling the four basic molecular properties during resin production and by the use of modifiers and additives Injection molders can work closely with their Equistar polyolefins sales or technical service representative to determine the resin which best meets their needs Equistar polyolefins technical service representatives are also available to assist injection molders and end users by providing guidance for tool and part design and the develop ment of specialty products to fulfill the requirements of new demand ing applications How polyolefins are made High purity ethylene and propylene gases are the basic feedstocks for making polyolefins Figure 5 These gases can be petroleum refinery by products or they can be extracted from an ethane propane liquified gas mix coming through pipelines 5 Figure 4 Schematic representation of molecular weight distribution MOLECULAR WEIGHT Narrow Molecular Weight Distribution Broad Molecular Weight Distribution PERCENT AGE OF EACH MOLECULAR WEIGHT MIXED FEEDSTOCK LPG HYDROCARBONS AND FUEL COMPONENTS FRACTIONATION COLUMN ETHANE AND PROPANE FEED TO CRACKER ETHYLENE AND PROPYLENE ETHYLENE CRACKER SEPARATION COLUMN PROPYLENE ETHYLENE PURIFIED ETHYLENE TO PIPELINE OR POLYMERIZATION PURIFICATION COLUMNS PURIFIED PROPYLENE TO PIPELINE OR POLYMERIZATION 6 5 4 3 2 1 6 5 4 3 2 1 Figure 5 Olefin manufacturing process from a gas field High efficiency in the ethane propane cracking and purification results in very pure ethylene and propylene which are critical in the production of high quality polyolefins Equistar can produce polyolefins by more polymerization technologies and with a greater range of catalysts than any other supplier can Two of Equistar s plants are pictured in Figure 6 Low density polyethylene LDPE To make LDPE resins Equistar uses high pressure high temperature tubular and autoclave polymeriza tion reactors Figures 7 and 8 Ethylene is pumped into the reac tors and combined with a catalyst or initiator to make LDPE The LDPE melt formed flows to a separator where unused gas is removed recovered and recycled back into the process The LDPE is then fed to an extruder for pelletization Additives if required for specific applications are incorporated at this point High density polyethylene HDPE There are a number of basic processes used by Equistar for mak ing HDPE for injection molding applications including the solution process and the slurry process In the multi reactor slurry process used by Equistar Figure 9 ethylene and a comonomer if used together with an inert hydrocarbon carrier are pumped into reactors where they are combined with a catalyst However in contrast to LDPE pro duction relatively low pressures and temperatures are used to produce HDPE The granular polymer leaves the reactor system in a liquid slurry and is separated and dried It is then conveyed to an extruder where additives are incorporated prior to pelletizing Equistar also utilizes a multi reactor solution process for the production 6 Figure 6 Left polypropylene unit at Morris Illinois plant Right HDPE unit at Matagorda Texas plant Figure 8 LDPE high temperature autoclave p