模具毕业设计外文翻译

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 recog ni zed by the fact that therm opl astics are usually heated to a soft state and then reshaped before cooling. Theromosets, on the other hand have not yet bee n poly merized before p rocess ing, and the chemical reacti on takes place during the process, usually through heat, a catalyst, or pressure. It is important to remember this concept while studying the plastics manufacturing p rocesses and poly mers used.

Injectio n moldi ng is by far the most widely used p rocess of formi ng therm op lastic materials.

It is also one of the oldest. Curre ntly injectio n moldi ng acco unts for 30% of all p lastics res in consump ti on. Since raw material can be conv erted by a sin gle procedure, injection molding is

suitable for mass production of plastics articles and automated on e-ste p p roduct ion of complex geometries. In most cases, finishing is not n ecessary.T yp ical p roducts in clude toys, automotive p arts, household articles, and con sumer electr onics goods.

Since in jecti on mold ing has a nu mber of in terde pendent variables, it is a p rocess of con siderable comp lexity. The success of the injectio n moldi ng op erati on is dependent not only in the proper set up of the machi ne hydraulics, barrel temp erature variati ons, and cha nges in material viscosity. In creas ing shot-to-shot rep eatability of machi ne variables helps produce parts with tighter toleranee, lowers the level of rejects, and in creases p roduct quality (i.e., app eara nee and serviceability).

The principal objective of any moldi ng op erati on is the manu facture of p roducts: to a sp ecific quality level, in the shortest time, and using rep eatable and fully automatic cycle. Molders strive to reduce or elimi nate rejected p arts in moldi ng p roducti on.

For injection molding of high precision optical parts, or parts with a high added value such as app lia nee cases, the p ayoff of reduced rejects is high.

A typ ical injectio n moldi ng cycle or seque nee con sists of five p hases;

1.Injectio n or mold filling

2.P ack ing or comp ressi on

3.Holdi ng

4.Cooli ng

5.Part ejection

P lastic granu les are fed into the hopper and through an in the injectio n cyli nder where they are carried forward by the rotat ing screw. The rotati on of the screw forces the granu les un der high p ressure aga inst the heated walls of the cyli nder caus ing them to melt. As the p ressure buildi ng up, the rotati ng screw is forced backward un til eno ugh p lastic has accumulated to make the shot. The injectio n ram (or screw) forces molte n p lastic from the barrel, through the no zzle, sprue and runner system, and fin ally into the mold cavities. During injectio n, the mold cavity is filled volumetrically. When the p lastic con tacts the cold mold surfaces, it solidifies (freezes) ra pidly to p roduce the sk in layer. Since the core remai ns in the molte n state, p lastic follows through the core to compiete mold filling. Typically, the cavity is filled to 95%~98% during inject ion. Then the mold ing p rocess is switched over to the p ack ing p hase.

Eve n as the cavity is filled, the molte n p lastic beg ins to cool. Si nee the cooli ng p lastic con tracts or shri nks, it gives rise to defects such as sink marks, voids, and dime nsional in

stabilities. To compen satefor shri nkage, additi on pl astic is forced into the cavity. Once the

cavity is p acked, p ressure app lied to the melt p reve nts molte n p lastic in side the cavity from back flow ing out through the gate. The p ressure must be app lied un til the gate solidifies. The p rocess can be divided into two ste ps (p ack ing and hold ing) or may be encompassedin one step(holding or second stage). During packing, melt forced into the cavity by the packing pressure compensates for shrinkage. With holdi ng, the p ressure merely p reve nts back flow of the poly mer malt.

After the hold ing stage is compi eted, the cooli ng p hase starts. During, the part is held in the mold for sp ecified p eriod. The durati on of the cooli ng p hase depends p rimarily on the material prop erties and the part thick ness. Typ ically, the part temp erature must cool below the material ' s ejection temperature. While cooling the part, the machine pl asticates melt for the next cycle.

The polymer is subjected to shearing action as well as the condition of the energy from the heater ban

ds. Once the short is made, p lasticati on ceases. This should occur immediately before the end of the cooli ng p hase. The n the mold opens and the part is ejected.

When poly mers are fabricated into useful articles they are referred to as p lastics, rubbers, and fibers. Some p olymers, for exa mp le, cott on and wool, occur n aturally, but the great majority of commercial products are synthetic in origin. A list of the n ames of the better known materials would

in clude Bakelite, Dacro n, Nylon, Cela nese, Orlon, and Styr on.

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 nin etee nth cen tury. The failure to devel op them duri ng this p eriod was due, in p art, to a lack of un dersta nding of their prop erties, in p articular, the p roblem of the structure of poly mers was the subject of much fruitless con troversy.

Two eve nts of the twen tieth cen tury cata pulted poly mers into a po siti on of worldwide imp orta nee. The first of these was the successful commercial p roducti on of the pl astic now known as Bakelite. Its in dustrial usef uln ess was dem on strated in 1912 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 manu facture n ever pro vided the incen tive for new work in the poly mer field such as occurred after the adve nt of Bakelite. The sec ond eve nt was concerned with

fun dame ntal studies of the n ature poly mers by Staud in ger in Europe and by Carohers, who worked with the Du Pont company in Delaware. A greater part of the studies were made duri ng the 1920' sStaudi nger ‘work was p rimarily fun dame ntal. Carother ' s achievements led to the development of our present huge plastics industry by caus ing an awake ning of in terest in poly mer chemistry, an in terest which is still stron gly apparent today.

The Nature of Thermodynamics

Thermodynamics is one of the most important areas of engineering scienee used to explain how most

things work, why some things do not the way that they were inten ded, and why others things just cannot p ossibly work at all. It is a key part of the scienee engineers use to design automotive engines, heat pumps, rocket motors, po wer stati ons, gas turb in es, air con diti on ers, super-con duct ing tran smissi on lin es, solar heati ng systems, etc.

Thermodynamics centers about the notions of energy, the idea that energy is con served is the first low of thermod yn amics. It is start ing point for the scie nee of thermod yn amics is entropy; entropy p rovides a means for determ ining if a p rocess is po ssible.

This idea is the basis for the sec ond low of thermod yn amics. It also pro vides the basis for an engin eeri ng an alysis in which one calculates the maximum amount of useful that can be obta ined from a give n en ergy source, or the minimum amount of po wer input required to do a certa in 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 thermod yn amics to p redict and relate the prop erties of matter; engin eers are in terested in using this data, together with the basic ideas of en ergy con servati on and entropy p roduct ion, to an alyze the behavior of comp lex tech no logical systems.

There is an example of the sort of system of interest to engineers, a large central po wer stati ons. In this p articular plant the en ergy source is p etroleum in one of several forms, or sometimes n atural gas, and the plant is to convert as much of this en ergy as po ssible to electric en ergy and to send this en ergy dow n the tran smissi on line.

Simply exp ressed, the plant does this by boili ng water and using the steam to turn a turb ine which turns an electric gen erator.

The simp lest such po wer plants are able to con vert only about 25 p erce nt of the fuel en ergy to electric en ergy. But this p articular plant con verts app roximately 40 p erce nt; it has bee n ingenio usiy desig ned through careful app licati on of the basic principles of thermod yn amics to the hun dreds of components in the system.

The design engineers who made these calculations used data on the properties of steam devel oped by p hysical chemists who in turn used exp erime ntal measureme nts in con cert with thermod yn amics theory to devel op the prop erty data.

Plants p rese ntly being studied could con vert as much as 55 p erce nt of the fuel en ergy to electric en ergy, if they in deed p erform as p redicted by thermod yn amics an alysis.

The rule that the spontan eous 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 n ature that sp ecifies for us the directi on of heat flow. If en ergy were to flow spontan eously from a block of ice to a surr ounding volume of water, this could occur in compi ete accord with en ergy con servatio n. But such a p rocess n ever happens. This idea is the substa nee of the sec ond law of thermod yn amics.

Clear, a refrigerator, which is a p hysical system used in kitche n refrigerators, freezers, and air-c

on diti oning un its must obey not on ly the first law (en ergy con servati on) but the sec ond law as well.

To see why the sec ond law is not violated by a refrigerator, we must be careful in our stateme nt of law. The sec ond law of thermod yn amics says, in effect, that heat n ever flows spontan eously 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 exter nal age ncy. We now see the disti nction betwee n an everyday spontan eous process, such as the flow of heat from the in side to the outside of a refrigerator.

In the water-ice system, the exchange of energy takes place spontaneously and the flow of heat always p roceeds from the water to the ice. The water gives up en ergy and becomes cooler while the ice receives en ergy and melts.

In a refrigerator, on the other hand, the excha nge of en ergy is not spontan eous. Work pro vided by an exter nal age ncy is n ecessary to reverse the n atural flow of heat and cool the in terior at the expense of further heati ng the warmer surr oundin gs.

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、 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。 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。

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， 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。

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， 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

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。第二次事件与孔 当型腔 这种压

直到模具打开和 许多聚合物, 都来源于

1912年表现

基础学科的自然聚合物有关，被欧洲的史涛丁格和美国的卡罗瑟夫发现，他们在特达华州的杜邦公司工作。一些重要的研究在20世纪20

年代被开展，史涛丁格主要从事基础工作。卡罗瑟夫的成功导致了我们目前巨大塑料工业的发展，引起了对化学聚合物的关注，并且在今天仍然引起了强烈而明显的关注。

热力学的性质

热力学是工程科学最重要的领域之一。这门科学是用来解释大多数东西是如何做功的，有些东西为什么不按所预期的那样做功，另外一些东西又为什么根本不做功。热力学是工程师在设计汽车发动机、热泵、火箭发动机、发电站燃汽轮机、空气调节器、超导电输电线，太阳能加热系统等所用的科学知识的关键部分。

热力学以能的各种概念为中心，能量守恒这一概念是热力学的第一定律。这是热力学以及工程分析的起点，热力学的第二个要领是熵；熵提供一种用以确定某一过程是否可行的手段。产生熵的过程是可行的，消灭熵的过程是不可行的，这个要领是热力学第二定律的基础。

他还为一种工程分析奠定了基础，在这种工程分析中，人们可以算出从给定的能源中所能获得的有用功率的最大值，或算出做某种工作所能获得的有用功率的最小值。

若要在工程分析中应用热力学，就必须对能和熵这些概念有一个清楚的了解。科学家关心的是利用这些数据，结合能量守恒及熵的产生这些基本概念来分析复杂系统性能。

举一个工程师感兴趣的例子------ 一个大型中心发电站。在该发电站，能源是某

种形式的石油，有时是天然气；该发电站的作用是把燃料能尽可能地转化成电能，并把电能沿输电线输送出去。

简单的说，该发电站的发电方式是：使水沸腾，利用蒸汽转动汽轮机，汽轮机再转动发电机。

这类发电站中最简单的只能把大约25%勺燃料转化成电能。但该发电站却能把大约40%勺燃料转化成电能，这是因为该发电站是经过精心设计的结果，把热力学的基本原理仔细的用于该系统内的数百个零部件。

进行这些计算的设计工程师，利用了由物理学家研究出来的有关蒸汽特性的数据；而物理学家则是利用实验测得的数据，结合热力学理论，研究出这种特性的数据的。

目前在研究中的一些发电站，如果说的确按热力学分析所预测的那样工作，可以将多达55%勺燃料能转化成电能。

热始终是自发的从较热的物体流向较冷的物体，这一规律是一种新的物理概念。在能量守恒原理中或其他任何一种自然规律中，没有给我们规定热的方向。如果

能量能自发的从冰块流向周围的水中，这可能和能量的守恒完全一致，但这一过程决不发生。这一概念是热力学第二定律的实质。很明显，冷冻机是一种物理系统，用于厨房的电冰箱、冷场库和空调装置，它不仅必须遵从第一定律（能量守恒）也必须遵从第二定律。

为了弄清冷冻机为什么没有违背第二定律，必须对这一定律加以说明，热力学第二定律实质上是说：热不会自发地从较冷的物体流向较热的物体。

换句话说，热之所以能从较冷的物体流向较热的物体，是外界力量做功的结果，现在我们弄清了某一日常的自然过程。如水和冰之间的热流动和冷冻机热从里面向外面流动之间的区别。

在水、冰系统中，能量的交换是自发产生的，因而热的流动是水流向冰。水放出了能量从而变冷，而冰吸收热量从而融化。

另一方面，在冷冻机中，能量交换不是自发产生的，而需要改变热的流动方向, 并通过进一步加热较暖的周围环境而使冷冻机内部变冷，就必须依靠外力做功。