ZM122-蛋糕切刀注塑模具设计【1.1万字+18张CAD图+PROE三维图】
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大连交通大学 2017 届本科生毕业设计调研报告6大连交通大学 毕业设计调研报告 学 院_机械工程学院_ 专 业_机械工程_ 班 级_机械133_ 姓 名_吴 东_ 学 号_1304010731_ 指导教师_朱建宁_调研报告一、 课题的来源及意义放眼望去，在目前的经济发展背景下，世界上大多数国家都把注塑模具成型放在国民工业发展的优先地位。查阅相关资料可知当前工业零件的粗加工和的精加工产品都是通过注塑模具成型来完成的。很显然，我们平常生活中所用的洗衣机、冰箱、手机、笔记本、电扇等各种家庭常用电器和日常工具中大约有的零件都是属于注塑模具成型工艺产品。注塑模具成型是通过将多种多样的原材料在高温下融化后，在一定压力的作用下按原件的要求去设计制造出满足不同要求的模型，。注塑模具有良品率高、产品品质稳定、现代化程度高、成本相对较低等优点，在塑料生产中的地位居于前列，其大都可以进行重复使用且适应于大批量生产，是现代工业生产的必备装备，其在注塑成型中处于核心地位1。零件模型的设计水平、加工质量、模具材料、技术含量等都大大影响着众多相关行业生产的发展，对众多企业研究新产品、保障高质量、拉动经济的快速发展、进行技术的改革创新都有相当重要的作用。因此，注塑模具成型设计制造的应用无论是对普通百姓生活还是对国家经济的发展，都有着巨大意义。近些年塑料应用范围越来越广泛，无论是生活用品还是军事装备，到处可见塑料制品。一个国家制造业发展水平的重要标志之一就是模具行业的发展，在工业发达国家，注塑模具制造业的基本特征就是标准化、网络化、智能化2。 本设计以社会实际产品（蛋糕切刀）为课题，通过使用 Pro/E、AutoCAD 等绘图软件设计一合理的注塑模具。在设计过程中，使我们在塑件结构设计、塑料成型工艺分析、塑料模具数字化设计、塑料模具零件的选材、热处理、塑料模具零件的制造，以及资料检索查询、论文格式方法、英文翻译等方面得到了综合训练。培养了我们设计创新的能力，提高了我们对模具设计基本原理及过程的理解和认识。二、 国内外发展状况以及发展趋势2.1 国内外发展状况就目前来说，我国的模具工业体系相对来说比较现代化，包括模具设计研发体系；模具材料研发、生产和供应体系；模具标准件生产、供应体系；专业模具制造厂商。从行业结构上来看，民营企业发展相对来说较快，国有企业对比以前更有活力，模具厂家的数量和能力都有较大提升，其产品明显有了符合市场需求的专业性。模具行业方向的工业园发展很快，相关产业彼此汇聚一起，彼此促进发展3。在技术方面，近年来，我国模具行业产品结构调整加快，以大型、精密、复杂、长寿命模具为代表的技术含量较高模具的发展速度高于行业总体发展速度，占模具总量的35%左右。但从总体来说高技术含量模具自给率还比较低，有很大一部分依靠进口。近年来，我国模具行业结构调整取得不小成绩，无论是企业组织结构、产品结构、技术结构和进出口结构，都在向着合理化的方向发展。目前全世界模具总产值约为680 亿美元，中国只占8%左右，为更新和提高装备水平，模具企业每年都需进口几十亿元的设备。在创新开发方面的投入仍显不足，模具行业内综合开发能力的提升已严重滞后于生产能力的提高3。从地区分布来看, 以珠江三角洲和长江三角洲为中心的东南沿海地区发展快于中西部地区, 南方的发展快于北方。目前来说广东和浙江是模具发展最快、模具生产最集中、模具水平高的省份, 其模具方面的产值约占到全国模具总产值的60 %以上。虽然我国模具总量很大，甚至居于世界前列, 但无论是设计水平还是制造水平，与工业发达国家还差很远，尤其是德、美、日、英、意等工业国家, 无论是模具产品的商品化还是制造的智能化以及模具的标准化程度，也都远低于国际水平4。在国外，模具行业是应用CAD技术比例比较高的行业之一。模具制造业正以一个高自动化、高生产效率、高经济性、高灵活性、高速计算、高速绘图和人工智能的全新面貌展现在人们面前，并迅速发展，以适应当今社会激烈的产品和市场竞争5。澳大利亚Moldflow公司的Moldflow系统,该系统具有很强大的注塑模分析模拟功能,包括绘制型腔图形的线框造型软件SMOD,有限元网格生成软件FMESH,流动分析软件FLOW,冷却分析软件COOLING,流动、冷却分析结果和模架应力场分布的可视化显示软件FRES以及翘曲分析模拟软件5。美国GRATEK公司的注塑模CAD/CAM/CAE 系统。该系统包括三维几何形状描述软件OPTIMOLD，二维有限元流动分析软件SIMUUFLOW，冷却分析软件SIMUCOOL，标准模架（美国DME标准）选择软件OPTMOLD等部分5。2.2发展趋势随着国际交往的日益增多和外资在中国模具行业的投入日渐增加，中国模具已经与世界模具密不可分，中国模具在世模具中的地位和影响越来越重要。查阅相关资料分析，未来十年，中国模具工业和技术的主要发展方向将主要集中在以下几个方面。2.2.1 CAD/CAE/CAM 技术是模具技术发展史上的一个重要里程碑, 实践证明,CAD/CAM/CAE 技术是模具设计制造的发展方向。现在, 全面普CAD/CAM/CAE技术的条件已基本成熟。除了可用于建模、为数控加工提供NC 程序，也可针对不同类型的模具，通过数值模拟方法达到预测产品成型（形）过程的目的，改善模具结构、功能。从CAD/CAE/CAM 一体化上来说，其发展趋势是集成化、系统化、智能化和网络化，以便充分发挥各单元的优势和功效6。2.2.2要想改善模具制造周期，同时提高模具的总体质量和降低模具制造各项成本，应推广模具标准化及标准件的应用。模具标准件应进一步规划、完善，以满足不同行业需求，在降低成本的前提下能保证相应的质量。2.2.3 采用新型热流道技术是塑料模设计制造中的一大变革，可显著提高模具制造的生产效率和质量，并能大幅度节省制作的原材料和节约能源，国外模具企业已有一半用上了该项技术，甚至已达80%以上；气体辅助注射成型也是塑料成型的一种新工艺，它具有注射压力低、制品翘曲变形少、表面好、易于成型、壁厚差异较大等优点，可在保证产品质量的前提下，大幅度降低成本7。 2.2.4 气体辅助注射成形是一种塑料成形的新工艺, 它具有注射压力低、制品翘曲变形小、表面质量好以及易于成形壁厚差异较大的制品等优点, 可在保证产品质量的前提下, 大幅度降低成本。气体辅助注射成形包括塑料熔体注射和气体(一般均采用氮气)注射成形两部分, 比传统的普通注射工艺有多的工艺参数需要确定和控制, 而且气体辅助注射常用于较复杂的大型制品, 模具设计和控制的难度较大, 因此, 开发气体辅助成形流动分析软件显得十分重要7。 2.2.5 模具表面的光整加工是模具加工中未能很好解决的难题之一。模具表面的质量对模具使用寿命、制件外观质量等方面均有较大的影响, 手工研磨是传统模具精加工手段，也是目前普遍采用的方法。手工研磨不需要特殊的设备，操作简便，适应性较强，这种加工模式更多的是依赖有经验的技师，依靠他们的精湛技术解决技术难题，但是此种手段对于技师的体能要求较高，另外依靠经验并不是最可靠的，也会出现质量问题，大大影响了磨具加工的高水平发展。现在随着科技发展，新型加工机器不断产生应用，结合数字化的抛光机器，利用自动化控制，电子显示技术参数设置，可以根据环境情况变化，调整研磨参数和工艺参数，可以实现全自动和半自动抛光。对工人技术经验要求并不是很高，所以操作简便，另外还有其他的特点：可以实现平整功能，平整的波纹长度可达75毫米，数字化抛光机和手工抛光相比，工作效率提高一倍，其抛光质量稳定且精度高，还有对材料的适应性高，可以适合各种材料如铸钢、锻钢、铝合金及锌基合金，适合加工的磨具尺寸范围宽泛8。 三、本课题的研究内容 充分利用所学知识，完成要求设计产品（蛋糕切刀）的结构与工艺分析，并进行相应塑料注射模的设计，形成比较完善的技术材料。 a 塑件成型工艺性分析b 拟定模具的结构形式c 分型面的设计d 浇注系统的设计e 成型零件的结构设计及计算f 模架的确定g 排气槽的设计h 脱模推出机构的设计i 冷却系统的设计j 导向与定位机构的设计k 总装图和零件图的绘制l 编写设计说明书四、课题的研究目标及方法分析蛋糕切刀外形尺寸及其原料成型工艺性，运用PRO/E软件生成产品根据粗略设计的产品，从外形尺寸、精度等级、脱模斜度、材料性能、材料的注射成型过程及工艺参数等方面做出合理的工艺分析，并对原产品参数作出适当的修改。通过查阅相关资料，确定加工所需工序。按照课本实例对模具进行设计及计算，并用Pro/E、AutoCAD 软件软件绘制总装图和零件图。五、进度安排第 1 周：写调研报告。第 2 周：翻译外文资料。第 3 周：确定该塑件零件尺寸，进行工艺分析，制作零件模型；设计分型面、型腔。第 4-6 周：设计模体、浇注系统、冷却系统，导向与定位机构，并进行相关计算。第 7-9 周：用 Pro/E、AutoCAD 绘制模具零件三维图、零件二维图及实体装配图。第 10-11 周：绘制模具装配图，标注尺寸。第 12 周：编写计算说明书。第 13 周：修改图纸，整理资料。第 14 周：准备答辩。参考文献1 肖微. 浅析塑料注塑成型及其模具的应用J. 科技创新与应用, 2017(2):31-31.2 徐世虎. 浅析注塑模具成型设计制造的应用J. 现代制造, 2014(15):116-117.3 夏琴香. 模具行业发展现状分析J. 机电工程技术, 2014(7):1-4.4 刘少达. 我国塑料模具工业的现状及发展趋势J. 仲恺农业工程学院学报, 2004, 17(3):66-715 陶秀, 李锋, 管锋. 注塑模具计算机辅助设计的发展与应用J. 机械工程师, 2005(7):42-45.6 洪丽华, 陈永禄. 中国模具工业现状和模具技术发展趋势J. 机电技术, 2007, 30(2):96-99.7 周永泰. 我国塑料模具现状与发展趋势J. 塑料, 2000, 29(6):23-27.8 陈明耀. 模具制造中模具表面精加工技术分析J. 中国新技术新产品, 2015(10):63-63.9 洪丽华, 陈永禄. 中国模具工业现状和模具技术发展趋势J. 机电技术, 2007, 30(2):96-99. 10 陶秀, 李锋, 管锋. 注塑模具计算机辅助设计的发展与应用J. 机械工程师, 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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