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注塑
設計
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切刀注塑設計,注塑,設計
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大連交通大學 2017 屆本科生畢業(yè)設計調(diào)研報告6大連交通大學 畢業(yè)設計調(diào)研報告 學 院_機械工程學院_ 專 業(yè)_機械工程_ 班 級_機械133_ 姓 名_吳 東_ 學 號_1304010731_ 指導教師_朱建寧_調(diào)研報告一、 課題的來源及意義放眼望去，在目前的經(jīng)濟發(fā)展背景下，世界上大多數(shù)國家都把注塑模具成型放在國民工業(yè)發(fā)展的優(yōu)先地位。查閱相關資料可知當前工業(yè)零件的粗加工和的精加工產(chǎn)品都是通過注塑模具成型來完成的。很顯然，我們平常生活中所用的洗衣機、冰箱、手機、筆記本、電扇等各種家庭常用電器和日常工具中大約有的零件都是屬于注塑模具成型工藝產(chǎn)品。注塑模具成型是通過將多種多樣的原材料在高溫下融化后，在一定壓力的作用下按原件的要求去設計制造出滿足不同要求的模型，。注塑模具有良品率高、產(chǎn)品品質(zhì)穩(wěn)定、現(xiàn)代化程度高、成本相對較低等優(yōu)點，在塑料生產(chǎn)中的地位居于前列，其大都可以進行重復使用且適應于大批量生產(chǎn)，是現(xiàn)代工業(yè)生產(chǎn)的必備裝備，其在注塑成型中處于核心地位1。零件模型的設計水平、加工質(zhì)量、模具材料、技術含量等都大大影響著眾多相關行業(yè)生產(chǎn)的發(fā)展，對眾多企業(yè)研究新產(chǎn)品、保障高質(zhì)量、拉動經(jīng)濟的快速發(fā)展、進行技術的改革創(chuàng)新都有相當重要的作用。因此，注塑模具成型設計制造的應用無論是對普通百姓生活還是對國家經(jīng)濟的發(fā)展，都有著巨大意義。近些年塑料應用范圍越來越廣泛，無論是生活用品還是軍事裝備，到處可見塑料制品。一個國家制造業(yè)發(fā)展水平的重要標志之一就是模具行業(yè)的發(fā)展，在工業(yè)發(fā)達國家，注塑模具制造業(yè)的基本特征就是標準化、網(wǎng)絡化、智能化2。 本設計以社會實際產(chǎn)品（蛋糕切刀）為課題，通過使用 Pro/E、AutoCAD 等繪圖軟件設計一合理的注塑模具。在設計過程中，使我們在塑件結構設計、塑料成型工藝分析、塑料模具數(shù)字化設計、塑料模具零件的選材、熱處理、塑料模具零件的制造，以及資料檢索查詢、論文格式方法、英文翻譯等方面得到了綜合訓練。培養(yǎng)了我們設計創(chuàng)新的能力，提高了我們對模具設計基本原理及過程的理解和認識。二、 國內(nèi)外發(fā)展狀況以及發(fā)展趨勢2.1 國內(nèi)外發(fā)展狀況就目前來說，我國的模具工業(yè)體系相對來說比較現(xiàn)代化，包括模具設計研發(fā)體系；模具材料研發(fā)、生產(chǎn)和供應體系；模具標準件生產(chǎn)、供應體系；專業(yè)模具制造廠商。從行業(yè)結構上來看，民營企業(yè)發(fā)展相對來說較快，國有企業(yè)對比以前更有活力，模具廠家的數(shù)量和能力都有較大提升，其產(chǎn)品明顯有了符合市場需求的專業(yè)性。模具行業(yè)方向的工業(yè)園發(fā)展很快，相關產(chǎn)業(yè)彼此匯聚一起，彼此促進發(fā)展3。在技術方面，近年來，我國模具行業(yè)產(chǎn)品結構調(diào)整加快，以大型、精密、復雜、長壽命模具為代表的技術含量較高模具的發(fā)展速度高于行業(yè)總體發(fā)展速度，占模具總量的35%左右。但從總體來說高技術含量模具自給率還比較低，有很大一部分依靠進口。近年來，我國模具行業(yè)結構調(diào)整取得不小成績，無論是企業(yè)組織結構、產(chǎn)品結構、技術結構和進出口結構，都在向著合理化的方向發(fā)展。目前全世界模具總產(chǎn)值約為680 億美元，中國只占8%左右，為更新和提高裝備水平，模具企業(yè)每年都需進口幾十億元的設備。在創(chuàng)新開發(fā)方面的投入仍顯不足，模具行業(yè)內(nèi)綜合開發(fā)能力的提升已嚴重滯后于生產(chǎn)能力的提高3。從地區(qū)分布來看, 以珠江三角洲和長江三角洲為中心的東南沿海地區(qū)發(fā)展快于中西部地區(qū), 南方的發(fā)展快于北方。目前來說廣東和浙江是模具發(fā)展最快、模具生產(chǎn)最集中、模具水平高的省份, 其模具方面的產(chǎn)值約占到全國模具總產(chǎn)值的60 %以上。雖然我國模具總量很大，甚至居于世界前列, 但無論是設計水平還是制造水平，與工業(yè)發(fā)達國家還差很遠，尤其是德、美、日、英、意等工業(yè)國家, 無論是模具產(chǎn)品的商品化還是制造的智能化以及模具的標準化程度，也都遠低于國際水平4。在國外，模具行業(yè)是應用CAD技術比例比較高的行業(yè)之一。模具制造業(yè)正以一個高自動化、高生產(chǎn)效率、高經(jīng)濟性、高靈活性、高速計算、高速繪圖和人工智能的全新面貌展現(xiàn)在人們面前，并迅速發(fā)展，以適應當今社會激烈的產(chǎn)品和市場競爭5。澳大利亞Moldflow公司的Moldflow系統(tǒng),該系統(tǒng)具有很強大的注塑模分析模擬功能,包括繪制型腔圖形的線框造型軟件SMOD,有限元網(wǎng)格生成軟件FMESH,流動分析軟件FLOW,冷卻分析軟件COOLING,流動、冷卻分析結果和模架應力場分布的可視化顯示軟件FRES以及翹曲分析模擬軟件5。美國GRATEK公司的注塑模CAD/CAM/CAE 系統(tǒng)。該系統(tǒng)包括三維幾何形狀描述軟件OPTIMOLD，二維有限元流動分析軟件SIMUUFLOW，冷卻分析軟件SIMUCOOL，標準模架（美國DME標準）選擇軟件OPTMOLD等部分5。2.2發(fā)展趨勢隨著國際交往的日益增多和外資在中國模具行業(yè)的投入日漸增加，中國模具已經(jīng)與世界模具密不可分，中國模具在世模具中的地位和影響越來越重要。查閱相關資料分析，未來十年，中國模具工業(yè)和技術的主要發(fā)展方向?qū)⒅饕性谝韵聨讉€方面。2.2.1 CAD/CAE/CAM 技術是模具技術發(fā)展史上的一個重要里程碑, 實踐證明,CAD/CAM/CAE 技術是模具設計制造的發(fā)展方向?，F(xiàn)在, 全面普CAD/CAM/CAE技術的條件已基本成熟。除了可用于建模、為數(shù)控加工提供NC 程序，也可針對不同類型的模具，通過數(shù)值模擬方法達到預測產(chǎn)品成型（形）過程的目的，改善模具結構、功能。從CAD/CAE/CAM 一體化上來說，其發(fā)展趨勢是集成化、系統(tǒng)化、智能化和網(wǎng)絡化，以便充分發(fā)揮各單元的優(yōu)勢和功效6。2.2.2要想改善模具制造周期，同時提高模具的總體質(zhì)量和降低模具制造各項成本，應推廣模具標準化及標準件的應用。模具標準件應進一步規(guī)劃、完善，以滿足不同行業(yè)需求，在降低成本的前提下能保證相應的質(zhì)量。2.2.3 采用新型熱流道技術是塑料模設計制造中的一大變革，可顯著提高模具制造的生產(chǎn)效率和質(zhì)量，并能大幅度節(jié)省制作的原材料和節(jié)約能源，國外模具企業(yè)已有一半用上了該項技術，甚至已達80%以上；氣體輔助注射成型也是塑料成型的一種新工藝，它具有注射壓力低、制品翹曲變形少、表面好、易于成型、壁厚差異較大等優(yōu)點，可在保證產(chǎn)品質(zhì)量的前提下，大幅度降低成本7。 2.2.4 氣體輔助注射成形是一種塑料成形的新工藝, 它具有注射壓力低、制品翹曲變形小、表面質(zhì)量好以及易于成形壁厚差異較大的制品等優(yōu)點, 可在保證產(chǎn)品質(zhì)量的前提下, 大幅度降低成本。氣體輔助注射成形包括塑料熔體注射和氣體(一般均采用氮氣)注射成形兩部分, 比傳統(tǒng)的普通注射工藝有多的工藝參數(shù)需要確定和控制, 而且氣體輔助注射常用于較復雜的大型制品, 模具設計和控制的難度較大, 因此, 開發(fā)氣體輔助成形流動分析軟件顯得十分重要7。 2.2.5 模具表面的光整加工是模具加工中未能很好解決的難題之一。模具表面的質(zhì)量對模具使用壽命、制件外觀質(zhì)量等方面均有較大的影響, 手工研磨是傳統(tǒng)模具精加工手段，也是目前普遍采用的方法。手工研磨不需要特殊的設備，操作簡便，適應性較強，這種加工模式更多的是依賴有經(jīng)驗的技師，依靠他們的精湛技術解決技術難題，但是此種手段對于技師的體能要求較高，另外依靠經(jīng)驗并不是最可靠的，也會出現(xiàn)質(zhì)量問題，大大影響了磨具加工的高水平發(fā)展?，F(xiàn)在隨著科技發(fā)展，新型加工機器不斷產(chǎn)生應用，結合數(shù)字化的拋光機器，利用自動化控制，電子顯示技術參數(shù)設置，可以根據(jù)環(huán)境情況變化，調(diào)整研磨參數(shù)和工藝參數(shù)，可以實現(xiàn)全自動和半自動拋光。對工人技術經(jīng)驗要求并不是很高，所以操作簡便，另外還有其他的特點：可以實現(xiàn)平整功能，平整的波紋長度可達75毫米，數(shù)字化拋光機和手工拋光相比，工作效率提高一倍，其拋光質(zhì)量穩(wěn)定且精度高，還有對材料的適應性高，可以適合各種材料如鑄鋼、鍛鋼、鋁合金及鋅基合金，適合加工的磨具尺寸范圍寬泛8。 三、本課題的研究內(nèi)容 充分利用所學知識，完成要求設計產(chǎn)品（蛋糕切刀）的結構與工藝分析，并進行相應塑料注射模的設計，形成比較完善的技術材料。 a 塑件成型工藝性分析b 擬定模具的結構形式c 分型面的設計d 澆注系統(tǒng)的設計e 成型零件的結構設計及計算f 模架的確定g 排氣槽的設計h 脫模推出機構的設計i 冷卻系統(tǒng)的設計j 導向與定位機構的設計k 總裝圖和零件圖的繪制l 編寫設計說明書四、課題的研究目標及方法分析蛋糕切刀外形尺寸及其原料成型工藝性，運用PRO/E軟件生成產(chǎn)品根據(jù)粗略設計的產(chǎn)品，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，并對原產(chǎn)品參數(shù)作出適當?shù)男薷摹Ｍㄟ^查閱相關資料，確定加工所需工序。按照課本實例對模具進行設計及計算，并用Pro/E、AutoCAD 軟件軟件繪制總裝圖和零件圖。五、進度安排第 1 周：寫調(diào)研報告。第 2 周：翻譯外文資料。第 3 周：確定該塑件零件尺寸，進行工藝分析，制作零件模型；設計分型面、型腔。第 4-6 周：設計模體、澆注系統(tǒng)、冷卻系統(tǒng)，導向與定位機構，并進行相關計算。第 7-9 周：用 Pro/E、AutoCAD 繪制模具零件三維圖、零件二維圖及實體裝配圖。第 10-11 周：繪制模具裝配圖，標注尺寸。第 12 周：編寫計算說明書。第 13 周：修改圖紙，整理資料。第 14 周：準備答辯。參考文獻1 肖微. 淺析塑料注塑成型及其模具的應用J. 科技創(chuàng)新與應用, 2017(2):31-31.2 徐世虎. 淺析注塑模具成型設計制造的應用J. 現(xiàn)代制造, 2014(15):116-117.3 夏琴香. 模具行業(yè)發(fā)展現(xiàn)狀分析J. 機電工程技術, 2014(7):1-4.4 劉少達. 我國塑料模具工業(yè)的現(xiàn)狀及發(fā)展趨勢J. 仲愷農(nóng)業(yè)工程學院學報, 2004, 17(3):66-715 陶秀, 李鋒, 管鋒. 注塑模具計算機輔助設計的發(fā)展與應用J. 機械工程師, 2005(7):42-45.6 洪麗華, 陳永祿. 中國模具工業(yè)現(xiàn)狀和模具技術發(fā)展趨勢J. 機電技術, 2007, 30(2):96-99.7 周永泰. 我國塑料模具現(xiàn)狀與發(fā)展趨勢J. 塑料, 2000, 29(6):23-27.8 陳明耀. 模具制造中模具表面精加工技術分析J. 中國新技術新產(chǎn)品, 2015(10):63-63.9 洪麗華, 陳永祿. 中國模具工業(yè)現(xiàn)狀和模具技術發(fā)展趨勢J. 機電技術, 2007, 30(2):96-99. 10 陶秀, 李鋒, 管鋒. 注塑模具計算機輔助設計的發(fā)展與應用J. 機械工程師, 2005(7):42-45.11 Nardin B, agar B, Glojek A, et al. Adaptive system for electrically driven thermoregulation of moulds for injection mouldingJ. International Journal of Microstructure & Materials Properties, 2007, 187(2/3):690-693. Ta b le o f Co n t e n t s A Gu id e t o Po lyo le fin In je ct io n Mo ld in g In t ro d u ct io n Packaging Mo le cu la r st ru ct u re a n d co m p o sit io n a ffe ct p ro p e rt ie s a n d p ro ce ssa b ilit y Sporting goods Toys and novelties 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. 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. Four basic molecular properties affect most of the resin characteris- tics essential to injection molding high quality polyolefin parts. These molecular properties are: Polyolefins that can be injection molded include: Chain branching Low density polyethylene (LDPE) Po lyo le fin s a re d e rive d fro m p e t ro ch e m ica ls Crystallinity or density Average molecular weight Molecular weight distribution Linear low density polyethylene (LLDPE) High density polyethylene (HDPE) Ethylene copolymers, such as ethylene vinyl acetate (EVA) The materials and processes used to produce the polyolefins determine these molecular properties. 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 and propylene copolymers (PP) 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, C2H4. Thermoplastic olefins (TPO) In general, the advantages of injection molded polyolefins com- pared with other plastics are: polypropylene (PP) and propylene copolymer resins. Lightweight H | H | Outstanding chemical resistance 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. C = C Good toughness at lower temperatures | H | H Excellent dielectric properties Non hygroscopic 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. 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. 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. H H H H H H H H H H | | | | | | | | | | C C C C C C C C C C Major application areas for poly- olefin injection molding are: | H H H H H H H H H H | | | | | | | | | Appliances The resulting product is polyethyl- ene resin. Automotive products Consumer products Furniture Housewares Industrial containers Materials handling equipment 2 For polypropylene, the hydrogen and carbon atoms are combined to form the propylene monomer, CH CH:CH . occur which may adversely affect the polymers properties. This oxida- tion or degradation may cause cross-linking in polyethylenes and chain scission in polypropylenes. Figure 3. Linear polyethylene chain w ith short side branches C 3 2 C C C C C C C C C C C C C C C C C C H H | C C | 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. H C C = C | H | H | H nominal specific gravity range of 0.895 to 0.905 g/cm3, which is the lowest for a commodity thermo- plastic and does not vary appreciably from manufacturer to manufacturer. The third carbon atom forms a side branch which causes the backbone chain to take on a spiral shape. 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. H | H | H | H | H | H | C C C C C C | H HCH H HCH H HCH | | | | | De n sit y | H | H | H 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. 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). Ch a in b ra n ch in g LDPE resins have densities rang- ing from 0.910 to 0.930 grams 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- per cubic centimeter (g/cm LLDPE resins range from 0.915 to 0.940 g/cm 3) 3 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 HDPE resins range from 0.940 to 0.960 g/cm3 As can be seen, all natural poly- olefin resins, i.e, those without any fillers or reinforcements, have densities less than 1.00 g/cm3. 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. 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 Figure 2. Crystalline (A) and amor- phous (B) regions in polyolefin Mo le cu la r w e ig h t 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. Figure 1. Polyethylene chain w ith 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 3 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. 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 resins average molecular weight: as the average molecular weight increases, MFR decreases and vice versa. 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 190C (374F) using a static load of 2,160 g. MFR values for polypropy- lenes are determined at the same load but at a higher temperature 230C (446F). 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. 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. 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. Mo le cu la r w e ig h t d ist rib u t io n 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. 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, Melt flow rate (MFR) is a simple measure of a polymers melt vis- cosity under standard conditions of temperature and static load (pressure). For polyethylenes, it is often referred to as melt index (MI). 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 Table 1. General guide to the effects of polyethylene physical properties on properties and processing weight distribution.” Polyolefins with “broad molecular weight distribution” are resins with a wider variety of chain lengths. In general, resins with narrow molecular AS MELT INDEX INCREASES AS DENSITY INCREASES Durometer hardness (surface) Gloss remains the same improves increases improves 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). Heat resistance (softening point) Stress crack resistance Mechanical flex life remains the same decreases improves decreases decreases remains the same increases decreases Processability (less pressure to mold) Mold shrinkage improves decreases The type of catalyst and the Molding speed (faster solidification) remains the same increases 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 Permeability resistance Stiffness remains the same remains the same decreases improves increases Toughness decreases decreases increases Transparency Warpage remains the same decreases 4 chains. This results in a narrower molecular weight distribution and a higher melt flow rate. Mo d ifie rs a n d a d d it ive s 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. 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: Co p o lym e rs 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. Antioxidants Acid scavengers Process stabilizers Anti-static agents Mold release additives Ultraviolet (UV) light stabilizers Nucleators 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. 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). Clarifiers Lubricants Wo rkin g clo se ly w it h m o ld e rs Ho w p o lyo le fin s a re m a d e Equistar offers a wide range of polyolefin resins for injection mold- 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 Ethylene is used as a comonomer with propylene to produce ing, including Alathon Alathon LDPE, Petrothene and LLDPE, Equistar PP, Ultrathene EVA copolymers and Flexathene TPOs. These resins are tailored to HDPE, 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. LDPE Figure 5. Olefin manufacturing process ETHYLENE CRACKER PURIFIED PROPYLENE TO PIPELINE OR POLYMERIZATION Figure 4. Schematic representation of molecular w eight distribution LPG, HYDROCARBONS, AND FUEL COMPONENTS SEPARATION COLUMN PROPYLENE Narrow Molecular Weight Distribution 6 5 4 6 5 4 Broad Molecular Weight Distribution PURIFICATION COLUMNS 3 2 1 3 2 1 PURIFIED ETHYLENE TO PIPELINE OR POLYMERIZATION FRACTIONATION COLUMN ETHYLENE AND PROPYLENE MIXED FEEDSTOCK ETHYLENE ETHANE AND PROPANE FEED TO CRACKER MOLECULAR WEIGHT 5 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. Figure 6. Left, polypropylene unit at Morris, Illinois plant. Right, HDPE unit at Matagorda, Texas plant Equistar can produce polyolefins by more polymerization technologies and with a greater range of catalysts than any other supplier can. Two of Equistars plants are pictured in Figure 6. Lo w d e n sit y p o lye t h yle n e (LDPE) Figure 7. LDPE high temperature tubular process diagram T o 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. FIRST STAGE SECOND STAGE COMPRESSOR COMPRESSOR HIGH PRESSURE TUBULAR REACTOR ETHYLENE UNREACTED MONOMER TO RECOVERY POLYETHYLENE MELT SECOND STAGE SEPARATOR FIRST STAGE SEPARATOR ADDITIVES Additives, if required for specific applications, are incorporated at this point. POLYETHYLENE MELT Hig h d e n sit y p o lye t h yle n e (HDPE) HOT MELT EXTRUDER 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 Figure 8. LDPE high temperature autoclave process diagram FIRST STAGE COMPRESSOR SECOND STAGE COMPRESSOR HIGH PRESSURE AUTOCLAVE REACTOR ETHYLENE UNREACTED MONOMER TO RECOVERY POLYETHYLENE MELT SECOND STAGE SEPARATOR FIRST STAGE SEPARATOR ADDITIVES POLYETHYLENE MELT where additives are incorporated prior to pelletizing. Equistar also utilizes a multi-reactor solution process for the production HOT MELT EXTRUDER 6 of HDPE (Figure 10). In this process, the HDPE formed is dissolved in the solvent carrier and then precipitated in a downstream process. An addi- tional adsorption step results in a very clean product with virtually no catalyst residues. Sh ip p in g a n d h a n d lin g p o lyo le fin re sin s out resin manufacture and subse- quent handling, right through delivery to the molder, ensures the cleanliness of the products. When bulk containers are delivered, the molder must use appropriate procedures for unloading the resin. Maintenance of the in-plant materi- al handling system also is essential. When bags and boxes are used, It is of utmost importance to keep polyolefin resins clean. Equistar ships polyolefin resins to molders in hopper cars, hopper trucks, corru- gated boxes, and 50-pound plastic bags. Strict quality control through- Because both of these processes utilize multiple reactors, Equistar has the capability of tailoring and optimizing the molecular weight distribution of the various product grades to provide a unique range of processability and physical properties. Figure 9. HDPE parallel reactors slurry process UNREACTED MONOMERS TO RECOVERY STIRRED SEPARATION VESSEL REACTOR VESSEL STIRRED REACTOR VESSEL Lin e a r lo w d e n sit y p o lye t h yle n e (LLDPE) ETHYLENE BUTENE ETHYLENE BUTENE Equistar uses a gas phase process for making LLDPE (Figure 11). This process is quite different from the LDPE process, but somewhat similar to the HDPE process. The major differences from the LDPE process are that relatively low pressure and low temperature polymerization reactors are used. Another differ- ence is that the ethylene is copoly- merized with butene or hexene comonomers in the reactor. Unlike HDPE, the polymer exits the reactor in a dry granular form, which is subsequently compounded with additives in an extruder. CATALYST CATALYST POWDER DRYER HOLD VESSELS POWDER SLURRY POWDER FEED ADDITIVES ADDITIVE BLENDER EXTRUDER Figure 10. HDPE solution process With changes in catalysts and operating conditions, HDPE resins also can be produced in some of these LLDPE reactors. FIRST STAGE PARALLEL REACTORS ADSORPTION UNIT (CATALYST REMOVAL) ETHYLENE OCTENE Po lyp ro p yle n e UNREACTED CATALYST SOLVENT T o make PP, Equistar uses both a vertical, stirred liquid-slurry process (Figure 12) and a vertical, stirred, fluidized-bed, gas-phase process (Figure 13). Equistar was the first polypropylene supplier in the United States to use gas-phase technology to produce PP. Impact copolymers are produced using two, fluidized bed, gas phase reactors operating in series. MONOMERS AND SOLVENT TO RECOVERY ADDITIVES SECOND STAGE REACTOR ETHYLENE SOLVENT THREE STAGE SEPARATOR SYSTEM Equistars polyolefin production facilities are described in Table 2. TUBULAR REACTOR HOT MELT EXTRUDER 7 special care is necessary in opening the containers, as well as covering them, as they are unloaded. When cartons of resin are moved from a cold warehouse environment to a warm molding area or when transferring cold pellets from a silo to an indoor storage system, the temperature of the material should be allowed to equilibrate, for up to eight hours to drive off any conden- sation before molding. The best way to improve resin uti- lization is to eliminate contaminants from transfer systems. If bulk han- dling systems are not dedicated to one material or are not adequately purged, there is always the possibili- ty of contamination resulting from remnants of materials previously transferred. Reground resin, whether used as a blend or as is, should also be strin- gently protected to keep it free of contamination. Whenever possible, the regrind material should be used as it is generated. When this is not possible, the scrap should be col- lected in a closed system and recy- cled with the same precautions taken for virgin resin. In all cases, the proportion of regrind used should be carefully controlled to assure consistency of processing and part performance. Figure 11. LLDPE fluidized bed process UNREACTED MONOMERS TO RECOVERY FLUIDIZED BED REACTOR Ma t e ria l h a n d lin g Equistar utilizes material handling systems and inspection procedures that are designed to prevent exter- nal contamination and product cross-contamination during produc- tion, storage, loading and shipment. CATALYST REACTOR POWDER ADDITIVES BUTENE OR HEXENE Since polyolefin resins are non- hygroscopic (do not absorb water) they do not require drying prior to being molded. However, under certain conditions, condensation may form on the pellet surfaces. POWDER FEED ADDITIVE BLENDER ETHYLENE EXTRUDER Table 2. Equistar polyolefin production facilities Figure 12. PP slurry process BAYPORT, TX Polypropylene Low Density Polyethylene DILUENT AND UNREACTED MONOMER TO RECOVERY CHOCOLATE BAYOU, TX High Density Polyethylene PROPYLENE CATALYST DILUENT CLINTON, IA WET REACTOR POWDER Low Density Polyethylene High Density Polyethylene SEPARATION VESSEL LAPORTE, TX Low Density Polyethylene Linear Low Density Polyethylene POWDER DRYER ADDITIVES STIRRED REACTOR VESSEL MATAGORDA, TX High Density Polyethylene POWDER FEED MORRIS, IL Low Density Polyethylene Linear Low Density Polyethylene Polypropylene ADDITIVE BLENDER VICTORIA, TX High Density Polyethylene EXTRUDER 8 Occasionally, clumps of “angel hair” or “streamers” may accumulate in a silo and plug the exit port. Contaminants of this type can also cause plugging of transfer system filters and/or problems that affect the molding machine. All of these problems can result in molding machine downtime, excessive scrap and the time and costs of cleaning silos, transfer lines and filters. Figure 13. PP dual reactors gas-phase process UNREACTED MONOMERS TO RECOVERY ETHYLENE REACTOR POWDER ADDITIVES SEPARATION VESSEL STIRRED SECONDARY REACTOR VESSEL Polyolefin dust, fines, streamers and angel-hair contamination may be generated during the transfer of polymer through smoothbore ADDITIVE BLENDER piping. These transfer systems also may contain long radius bends to convey the resin from a hopper car to the silo or holding bin. A poly- olefin pellet conveyed through a transfer line travels at a very high velocity. As the pellet contacts the smooth pipe wall, it slides and friction is generated. The friction, in turn, creates sufficient heat to raise the temperature of the pellet surface to the resins softening point. As this happens, a small amount of molten polyolefin is deposited on the pipe wall and freezes almost instantly. Over time, this results in deposits described as angel hair or streamers. PROPYLENE CATALYST POWDER FEED STIRRED PRIMARY REACTOR VESSEL EXTRUDER Ho w t o so lve m a t e ria l h a n d lin g p ro b le m s hardness, which in turn leads to longer surface life. The rounded edges obtained minimize the initial problems encountered with dust and fines. They also reduce metal contamina- tion possibly associated with the sandblasted finish. Since smooth piping is a leading contributor to angel hair and streamers, one solution is to rough- en the interior wall of the piping. This causes the pellets to tumble instead of sliding along the pipe, minimizing streamer formation. However, as the rapidly moving polyolefin pellets contact an Whenever a new transfer system is installed or when a portion of an existing system is replaced, the interior surfaces should be treated by either sand or shot blasting. The initial cost of having this done is far outweighed by the prevention of future problems. As the pellets meet the pipe wall, along the interior surface of a long radius bend, the deposits become almost continuous and streamers are formed. Eventually, the angel hair and streamers are dislodged from the pipe wall and find their way into the molding process, the storage silo or the transfer filters. The amount of streamers formed increases with increased transfer air temperature and velocity. extremely rough surface, small particles may be broken off the pellets creating fines or dust. Two pipe finishes, in particular, have proven to be effective in minimizing buildup and giving the longest life in transfer systems. One is a sand- blasted finish of 600 to 700 RMS roughness. This finish is probably the easiest to obtain. However, due to its sharp edges, it will initially create dust and fines until the Elimination of long-radius bends where possible is also important as they are probably the leading contrib- utor to streamer formation. When this type of bend is used, it is critical that the interior surface should be either sand- or shot-blasted. Other good practices of material handling include control (cooling) of the transfer air temperature to minimize softening and melting of the pellets. Proper design of the transfer lines is also critical in terms of utilizing the optimum bend radii, blind tees, and proper angles. Consult your Equistar technical service engineer for guidance in this area. edges become rounded. The use of self-cleaning, stainless steel “tees” in place of long bends prevents the formation of streamers along the curvature of the bend, causing the resin to tumble instead of slide (Figure 14). However, there is a loss of efficiency within the transfer system when this method is used. Precautions should be taken The other finish is achieved with shot blasting using a #55 shot with 55-60 Rockwell hardness to produce a 900 RMS roughness. Variations of this finish are com- monly known as “hammer-finished” surfaces. The shot blasting allows deeper penetration and increases 9 Figure 14. Eliminate long-radius bends w here possible. The use of stainless steel “tees” prevents the formation of streamers along the curvature of the bend. Allow blowers to run for several minutes after unloading to clear the lines and reduce the chance of cross-contamination of product. transfers the finished blend to the individual molding machines. Th e in je ct io n m o ld in g p ro ce ss Information regarding transfer sys- tems and types of interior finishes available can be obtained from most suppliers of materials handling equipment or by consulting your Equistar technical service engineer. Complete systems can be supplied which, when properly maintained, efficiently convey contamination- free product. The injection molding process begins with the gravity feeding of polyolefin pellets from a hopper into the plasticating/injection unit of the molding machine. Heat and pressure are applied to the polyolefin resin, causing it to melt and flow. The melt is injected under high pressure into the mold. Pressure is mai
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