塑料注射成型外文文献翻译@中英文翻译@外文翻译

外文翻译 原文： Injection Molding Many different processes are used to transform plastic granules, powders, and liquids into product. The plastic material is in moldable form, and is adaptable to various forming methods. In most cases thermosetting materials require other methods of forming. This is recognized by the fact that thermoplastics are usually heated to a soft state and then reshaped before cooling. Theromosets, on the other hand have not yet been polymerized before processing, and the chemical reaction takes place during the process, usually through heat, a catalyst, or pressure. It is important to remember this concept while studying the plastics manufacturing processes and polymers used. Injection molding is by far the most widely used process of forming thermoplastic materials. It is also one of the oldest. Currently injection molding accounts for 30% of all plastics resin consumption. Since raw material can be converted by a single procedure, injection molding is suitable for mass production of plastics articles and automated one-step production of complex geometries. In most cases, finishing is not necessary. Typical products include toys, automotive parts, household articles, and consumer electronics goods. Since injection molding has a number of interdependent variables, it is a process of considerable complexity. The success of the injection molding operation is dependent not only in the proper setup of the machine hydraulics, barrel temperature variations, and changes in material viscosity. Increasing shot-to-shot repeatability of machine variables helps produce parts with tighter tolerance, lowers the level of rejects, and increases product quality (i.e., appearance and serviceability). The principal objective of any molding operation is the manufacture of products: to a specific quality level, in the shortest time, and using repeatable and fully automatic cycle. Molders strive to reduce or eliminate rejected parts in molding production. For injection molding of high precision optical parts, or parts with a high added value such as appliance cases, the payoff of reduced rejects is high. A typical injection molding cycle or sequence consists of five phases； 1. Injection or mold filling 2. Packing or compression 3. Holding 4. Cooling 5. Part ejection Plastic granules are fed into the hopper and through an in the injection cylinder where they are carried forward by the rotating screw. The rotation of the screw forces the granules under high pressure against the heated walls of the cylinder causing them to melt. As the pressure building up, the rotating screw is forced backward until enough plastic has accumulated to make the shot. The injection ram (or screw) forces molten plastic from the barrel, through the nozzle, sprue and runner system, and finally into the mold cavities. During injection, the mold cavity is filled volumetrically. When the plastic contacts the cold mold surfaces, it solidifies (freezes) rapidly to produce the skin layer. Since the core remains in the molten state, plastic follows through the core to complete mold filling. Typically, the cavity is filled to 95%98% during injection. Then the molding process is switched over to the packing phase. Even as the cavity is filled, the molten plastic begins to cool. Since the cooling plastic contracts or shrinks, it gives rise to defects such as sink marks, voids, and dimensional instabilities. To compensate for shrinkage, addition plastic is forced into the cavity. Once the cavity is packed, pressure applied to the melt prevents molten plastic inside the cavity from back flowing out through the gate. The pressure must be applied until the gate solidifies. The process can be divided into two steps (packing and holding) or may be encompassed in one step(holding or second stage). During packing, melt forced into the cavity by the packing pressure compensates for shrinkage. With holding, the pressure merely prevents back flow of the polymer malt. After the holding stage is completed, the cooling phase starts. During, the part is held in the mold for specified period. The duration of the cooling phase depends primarily on the material properties and the part thickness. Typically, the part temperature must cool below the materials ejection temperature. While cooling the part, the machine plasticates melt for the next cycle. The polymer is subjected to shearing action as well as the condition of the energy from the heater bands. Once the short is made, plastication ceases. This should occur immediately before the end of the cooling phase. Then the mold opens and the part is ejected. When polymers are fabricated into useful articles they are referred to as plastics, rubbers, and fibers. Some polymers, for example, cotton and wool, occur naturally, but the great majority of commercial products are synthetic in origin. A list of the names of the better known materials would include Bakelite, Dacron, Nylon, Celanese, Orlon, and Styron. Previous to 1930 the use of synthetic polymers was not widespread. However, they should not be classified as new materials for many of them were known in the latter half of the nineteenth century. The failure to develop them during this period was due, in part, to a lack of understanding of their properties, in particular, the problem of the structure of polymers was the subject of much fruitless controversy. Two events of the twentieth century catapulted polymers into a position of worldwide importance. The first of these was the successful commercial production of the plastic now known as Bakelite. Its industrial usefulness was demonstrated in1912 and in the next succeeding years. Today Bakelite is high on the list of important synthetic products. Before 1912 materials made from cellulose were available, but their manufacture never provided the incentive for new work in the polymer field such as occurred after the advent of Bakelite. The second event was concerned with fundamental studies of the nature polymers by Staudinger in Europe and by Carohers, who worked with the Du Pont company in Delaware. A greater part of the studies were made during the 1920s. Staudingers work was primarily fundamental. Carothers achievements led to the development of our present huge plastics industry by causing an awakening of interest in polymer chemistry, an interest which is still strongly apparent today. The Nature of Thermodynamics Thermodynamics is one of the most important areas of engineering science used to explain how most things work, why some things do not the way that they were intended, and why others things just cannot possibly work at all. It is a key part of the science engineers use to design automotive engines, heat pumps, rocket motors, power stations, gas turbines, air conditioners, super-conducting transmission lines, solar heating systems, etc. Thermodynamics centers about the notions of energy, the idea that energy is conserved is the first low of thermodynamics. It is starting point for the science of thermodynamics is entropy； entropy provides a means for determining if a process is possible. This idea is the basis for the second low of thermodynamics. It also provides the basis for an engineering analysis in which one calculates the maximum amount of useful that can be obtained from a given energy source, or the minimum amount of power input required to do a certain task. A clear understanding of the ideas of entropy is essential for one who needs to use thermodynamics in engineering analysis. Scientists are interested in using thermodynamics to predict and relate the properties of matter； engineers are interested in using this data, together with the basic ideas of energy conservation and entropy production, to analyze the behavior of complex technological systems. There is an example of the sort of system of interest to engineers, a large central power stations. In this particular plant the energy source is petroleum in one of several forms, or sometimes natural gas, and the plant is to convert as much of this energy as possible to electric energy and to send this energy down the transmission line. Simply expressed, the plant does this by boiling water and using the steam to turn a turbine which turns an electric generator. The simplest such power plants are able to convert only about 25 percent of the fuel energy to electric energy. But this particular plant converts approximately 40 percent； it has been ingeniously designed through careful application of the basic principles of thermodynamics to the hundreds of components in the system. The design engineers who made these calculations used data on the properties of steam developed by physical chemists who in turn used experimental measurements in concert with thermodynamics theory to develop the property data. Plants presently being studied could convert as much as 55 percent of the fuel energy to electric energy, if they indeed perform as predicted by thermodynamics analysis. The rule that the spontaneous flow of heat is always from hotter to cooler objects is a new physical idea. There is noting in the energy conservation principle or in any other law of nature that specifies for us the direction of heat flow. If energy were to flow spontaneously from a block of ice to a surrounding volume of water, this could occur in complete accord with energy conservation. But such a process never happens. This idea is the substance of the second law of thermodynamics. Clear, a refrigerator, which is a physical system used in kitchen refrigerators, freezers, and air-conditioning units must obey not only the first law (energy conservation) but the second law as well. To see why the second law is not violated by a refrigerator, we must be careful in our statement of law. The second law of thermodynamics says, in effect, that heat never flows spontaneously from a cooler to a hotter object. Or, alternatively, heat can flow from a cooler to a hotter object only as a result of work done by an external agency. We now see the distinction between an everyday spontaneous process, such as the flow of heat from the inside to the outside of a refrigerator. In the water-ice system, the exchange of energy takes place spontaneously and the flow of heat always proceeds from the water to the ice. The water gives up energy and becomes cooler while the ice receives energy and melts. In a refrigerator, on the other hand, the exchange of energy is not spontaneous. Work provided by an external agency is necessary to reverse the natural flow of heat and cool the interior at the expense of further heating the warmer surroundings. 译文： 塑料注射成型 许多不同的加工过程习惯于把塑料颗粒、粉末和液 体转化成最终产品。塑料材料用模具成型，并且适合用多种方式成型。在大多数情况下，热塑性材料可以用许多方法成型，但热固性塑料需要用其他方法成型。对于热塑性材料有这种事实的认识，它常常被加热成为另一种柔软状态，然后在冷却以前成型。对于热固性塑料，换句话说，在它加工以前还没有形成聚合物，在化学反应加工过程中发生变化，如通过加热、催化剂或压力处理。记住这个概念在学习塑料加工过程和聚合物的形成是很重要的。 塑料注射成型越来越广泛地运用于热塑性材料的成型工艺。它也是最古老的一种方式。突然间，塑料注射成型材料占所有成型材料 消费的 30%。塑料注射成型适合于大批量生产，当原材料被成单一的步骤转换成为塑料物品和单步自动化的复杂几何形状制品。在大多数情况下，对于这样的制品，精加工是不需要的。所生产的各种各样的产品包括：玩具、汽车配件、家用物品和电子消费物品。 因为塑料注射模具有很多易变的相互影响，那是一种复杂的虚慎重考虑的加工过程。塑料注射模具设备的成功是不依赖于机器变化到恰当的步骤，只有淘汰了需要注射变化的机器，才会导致适应液压变化、料筒温度变化和材料黏度变化的机器的产生。增加机器重复注射的能力的变化可以帮助减少公差，降低次品等级 和增加产品质量。 对于任何模具注射设备的操作人员目的是制造产品，成为特等品、用最短的时间、用重复精度和全自动化生产作为周期。模塑人员在生产过程中总是想尽办法降低或消除不合格产品。对于塑料注射模具有高要求的光学制品，或者有高附加值的制品如：家用电器制品，它的利润大大降低。 一种塑料注射模具的生产周期或顺序由五个阶段组成： 注射或填充模具 补料或压缩 保压 冷却 局部注射 塑料颗粒被投入料斗并且打开塑料注射料筒，在那里颗粒被旋转螺杆带动进入料筒。螺杆的旋转强迫塑料颗粒在高压下挤压料筒筒壁导致它变成熔体。随着压力的增加，旋转螺杆被迫后退直到有足够的塑料被注射成为储料。塑料螺杆强迫熔融的塑料从料筒流到喷嘴、主流道经浇注系统，最终进入模具型腔。当注射模具型腔容积被充满。当塑料接触冷的模具表面，它被固化以减少表层。当模具保持熔融状态，塑料沿着模芯充满整个模具。，利用率特别高，在注射时型腔被充满95%98%。接着成型过程进入补料阶段。 当型腔被充满，熔融塑料便开始冷却。冷却塑料的收缩，就增加了诸如凹痕、孔洞和尺寸不稳定等制品缺陷的发生。为了补偿收缩，增加塑料压入型腔。当型腔被封裹，为防止的熔融状态塑料从型腔内流向出口，把 压力应用于熔体。这种压力必须应用直到出口为固态。这种加工可分为两步（补料和保压）或可能包含成为一步（保压或第二阶段）。在补料时，熔体被补料压力收缩补偿压入型腔。在保压时，压力仅仅防止聚合物回流。 在保压阶段完成以后，冷却阶段开始。在冷却时，是制品在型腔内保持需具体说明的一个阶段。在冷却持久的阶段主要依靠材料的特性和制品的收缩率。典型的，制品温度必须冷却到材料的注射温度。在冷却制品时，这种机器塑料熔体被冷却到下一个周期。聚合物是以剪切作用为主题的，如同加热圈获得能量一样。当注射开始，到塑料注射终止。聚合物会立 刻出现在冷却阶段以前，直到模具打开和制品被注射。 当聚合物被编制成有用的文章，它们被称为：塑料、橡胶和纤维。许多聚合物，例如棉花和羊毛来自自然，但是绝大多数商业的产品都是人造的，都来源于此。一系列众所周知的材料包括酚醛塑料，涤纶，尼龙，聚硅氧烷，有机玻璃，纤维素，聚丙乙烯和特氟隆。 在 1930 年以前，商业用的聚合物没有广泛应用。然而它们本应该作为新材料在19 世纪下半叶出名，却没有成功。在该期间，它们所以未能发展，部分原因是不了解它们的性质，特别是，聚合物结构曾是许多无结果争论的主题。 二十世纪的两次事件使聚 合物声名雀起，并且在世界范围内占据了很重要的地 位。第一次是成功的商业塑料产品叫做酚醛塑料。它有用的工业价值在 1912 年表现得近乎疯狂，并且在以后许多年发挥着巨大的价值。今天，酚醛塑料仍然在一系列的人造的产品中占有一席之地。在 1912 年以前，由塑料制造的材料是有用的，但是那种材料的制造从未提供像发明了酚醛塑料以后，形成新聚合物的动力那样有价值