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1、外文翻译原文 Plastics forming processes There is a wide range of processing methods that may be used for plastics. Nevertheless, they all involve three or four basic stages: softening, shaping, solidifying and cooling of the moulds (for thermoplastics only). Common materials for moulding processes are the
2、rmoplastics and thermoset polymers. Principal methods of processing thermoplastics include extols ion, blow moulding, rotational moulding, thermoforming and injection moulding; but as for thermosets, compression, transfer and reaction injection moulding are frequently used.1 ExtrusionExtrusion is on
3、e of the most important forming processes for the reason that pellets, which are used for many other moulding processes, are normally produced by this process. In fact, some moulding processes are post-extrusion operations, such as blow moulding and thermoform moulding. Extnlsion is basically a proc
4、ess of continuously shaping a fluid polymer through the orifice of a die, and subsequently solidifying it into a product of a uniform cross-section. An extruding machine may have one or two screws, or no screw (screwless). Single-screw extruders, as seen in Figure 1, are the most commonly used machi
5、nes. Screwless (ram) extruders allow a precise control of the melt flow rate and are gaining popularity. They are particularly suited for high viscosity. In recent years, there has been a steady increase in the use of twin screw extruders. These machines permit a wider ranger of possibilities in ter
6、ms of output rates, mixing efficiency and heat generation. They are, however, considerably more expensive.Common extrusion products include filaments of circular cross-section, profiles of irregular cross-section, axisymmetric tubes and pipes, and flat products such as films or sheets. Almost all ty
7、pes of intricate cross-sectional shapes with large lengths are made by extrusion moulding, which many other discrete forming processes, such as compression, transfer and injection moulding, are incapable of producing. FIGURE 1.Single-screw extruder.2 Blow mouldingThis process begins with the prepara
8、tion of a soft, extruded and preformed thermoplastic tube over a core pin.As the mould halves close, air pressure inflates the thinwalled preform and forces it outwards against the mould sides. Figure 2 shows the process at two stages. The preform can be made by either extras ion or injection. Blow
9、moulds are subjected to moderate pressures and clamping forces, compared to injection moulds. Thus, they can be made of a light material such as aluminmm, which has advantages of light weight and high heat conductivity.Blown-ware containers are commonly used for packaging beverage and other fluid fo
10、od, e.g. narrow neck plastic bottles for mineral water, milk, alcoholic beverage and carbonated beverages. Other non-food products packed in the blown-ware containers include cosmetics, pharmaceuticals, paint and powder products. Blow moulding is also used to produce some huge products in size, such
11、 as shipping drums and stationary storage tanks whose volumes may reach as high as 10 000 litres 5. These tanks are used for underground fuel storage and septic tanks. Stage 1: Preform extrusion Stage 2: Blowing FIGURE 2.Extrusion blow moulding3 Rotational mouldingLike blow moulding, rotational moul
12、ding is also used to produce hollow plastic articles, though the principles in each method differ a lot. During the process, a carefully weighed charge of plastic powder is placed in one half of a metal mould. The mould halves are then clamped together and heated on an oven. When heated, the mould r
13、otates about two axes at right angles to each other. After a time the plastics will be sufficiently softened to form a homogeneous layer on the surface of the mould. The process is attractive for a number of reasons. Firstly, as it is a low-pressure process, the moulds are relatively simple and inex
14、pensive. Secondly, the product is virtually strata-free. Thirdly, a uniform thickness can be easily achieved. Finally, it is possible to introduce reinforcement into the products, and their surface can be textured as desired. However, the cycle times are longer compared to blow or injection moulding
15、. The mould-handling device, capable of imparting double rotations, is the central element of rotational moulding equipment. There are two major types of equipment: shuttle cart system, as shown Figure 3, and swing/rotary arm system. Rotational moulding is good at producing very large, thick-walled
16、articles which could not be produced economically by any other processes. The largest capacity of a rotational-moulding made tank is recorded at about 75 000 litres 4.FIGURE 3.Shuttle cart rotational moulding. The Institution of Professional Engineers New Zealand4 Compression mouldingCompression mou
17、lding is often used to produce articles from thermoset materials, though it can also be used for thermoplastics. The moulding operation used for thermosets is illustrated in Figure 4. A large number of compression moulded thermoset products can be found in electrical and electronic applications. Gla
18、ss-fibre reinforcement can be easily added to meet the heat resistance requirement. However, the limitation with this process is that the product has to be simple in shape and without thin walls or fragile inserts. Numerous rubber products are compression moulded. A useful feature of it is its abili
19、ty to have metal inserts that form strong bonds with the product and are often used to attach the product to structures. Tyres are the most common products made by compression moulding.FIGURE 4.Compression moulding.5 Transfer mouldingTransfer moulding is similar to compression moulding except that,
20、instead of the moulding material being pressurised in the cavity, it is pressurised in a separate chamber and then forced through an opening and into a closed mould cavity. The advantage of transfer moulding is that the preheating of the material injected through a narrow orifice improves the temper
21、ature distribution in the material and hence accelerates the cross-linking reaction in thermosets. As a result the cycle time is reduced and there is less distortion in the product. The improved flow of material also means that more intricate shapes can be produced. Parts with fragile inserts like e
22、lectric appliance parts, electronic components and connectors that may enclose coils, integrated circuits, and plugs can also be easily made.6 ThermoformingSheet thermoforming was developed in the 1950s. The limitations such as poor wall thickness distribution and large peripheral waste restricted i
23、ts use to simple packaging applications. In recent years, however, there have been major advances in machine design and materials, which have resulted in a wide range of products being made by thermoforming. There are three types of thermoforming processes (Figure 5): vacuum moulding, air pressure m
24、oulding, and mechanical moulding.The moulds, which are not subjected to high pressure, are often made from cast or machined alumininm for small and medium sizes, and they do not require a good surface finish. The product surface quality is largely dependent upon that of the sheet material.Products m
25、ade by thermoforming can be small as well as large. Smaller products are made in high output machines, using multi-cavity moulds. Such products are often found in the food industry and medical applications, for example, jelly or cream containers, cups, robs and trays. These small items can have rela
26、tively complex shapes with reasonably even thickness. Large products are generally made from cut sheets at a lower though-put rate, and they are usually of simple shapes. Fisher & Paykels vacuum form moulding machines produce the majority of pre-forms for refrigerators and freezers. Many other inter
27、ior parts are also made by the same or similar processes. FIGURE 5.Three basic methods of thermoforming.7 Injection mouldingInjection moulding has always been one of the most common processing methods for plastics. Nowadays countless parts in many electrical appliances, automobiles and office equipm
28、ent are injection moulded. The most common injection moulding machinery is the reciprocating screw machine, whose process can be divided into several stages as seen in Figure 6. At the plastication stage, the feed unit operates as an extntder, melting and homogenising the material in the screw/barre
29、l system. The screw, however, is allowed to retract in order to make room for the molten material in a space at the cylinder head, called material reservoir, between the screw tip and a closed valve or an obstntction of solidified material from the previous shot. At the injection stage, the screw is
30、 used as a ram (piston) for rapid transfer of the molten material from the reservoir to the cavity between the two halves of the closed mould. Since the mould is kept at a temperature below the solidification temperature of the material, it is essential to inject the molten material rapidly enough t
31、o ensure complete filling of the cavity. A high holding or packing pressure is normally exerted, to partially compensate for the thermal contraction of the material upon cooling. The cooling of the material in the mould often limits the production time because of the low thermal conductivity of poly
32、mers. The mould, after being cooled, can be opened and the solid product ejected.Although the screw machine is by far the most popular, plunger injection machines are also used to give products some unique features. There is no shearing or mixing action, as a plunger does not rotate. The resulting m
33、oulded part can take on a marbled appearance with swirls of two or more colours. This may be the desired finish for certain products. Regardless of different machines, injection moulding yields a high productivity and allows the products to have many fine details such as bosses, location pins, mount
34、ing holes, bushings, ribs, flanges, etc. All these features can eliminate many subs equent assembly and finishing operations.A large variety of products can be injection moulded. These include (a) micro-products, moulded in multiple cavity moulds on small precision machines, such as components for w
35、atches and microelectronics; (b) medium size products, moulded continuously in very large numbers in dedicated machines or in relatively small runs; and (c) large products, moulded by large machines, such as car dashboard frames, TV cabinets, garden furniture, and small boat hulls. Many of these lar
36、ge plastic parts have a solid skin and a cellular inner structure, hence the process is also known as structural foam moulding. FIGURE 6. Sequence of operations in injection moulding.8 Reaction injection mouldingReaction injection moulding is a relatively new process, which involves the rapid mixing
37、, in precise proportions, of two or more highly reactive liquid components and the immediate injection of the mixture in a closed mould Polymerisation takes place in the mould in a very short period of time, yielding a solid product. The process is particularly suited to the production of large and
38、relatively thin parts, with less capital investment and operating costs than in thermoplastic injection moulding. The process is also energy efficient, but requires good control of complex reactions.9 ConclusionsBy and large, each moulding process mentioned above has its pros and cons in terms of th
39、e materials, products and cost. The plastics industry plays an important role in todays manufacturing industry. Plastics moulding is the most popular process. Whereas injection moulding continues to dominate the sector, other moulding processes make some important contributions toward manufacture of
40、 many specific products. Faced by numerous challenges, new processes are making their way into the market. Conscious of energy consumption, moulding machine manufacturers are contemplating innovative designs to economise on the process. There is also a demand for these manufacturers to develop eithe
41、r smaller or larger moulding machines to meet customer demands. The fact that more and more newly developed materials use moulding processes for a manufacturing method provides an extra dimension for the development of the moulding industry.外文翻译译文 塑料成型过程有很多关于塑料成型的方法。尽管如此，它们都包跨三个或者四个基本环节：软化、修整、凝固、模具冷
42、却（仅适用于热塑性模具）。一般的对于模具成型过程的材料是热塑性和热固性的聚合体。主要的处理热塑性塑料的方法包括等离子法、吹铸法、旋转铸法、加热成形法、注塑模法，但是关于热固性塑料，压缩法、转移法和反推注塑法常常被使用。1 挤压法挤压法是最重要的成形方法之一因为用作许多其它的模制过程的小球很普遍地在这个过程中被引长。事实上，一些模制方法是一些加速挤压的操作，如吹模法和加热成形模制法。挤压法是一个通过模具孔和后来把它固化为的一个统一的横截面的不断修正流动聚合体的基本过程。一个挤压机拥有一个或者两个螺杆，或者没有螺杆（无螺杆型）。单一螺杆挤压机，正如图形1所示，是最通常使用的机器。无螺杆型（撞锤型）
43、挤压机通常流行为开槽型并且允许对熔体流动率的精确控制。他们特别适合高粘度的场合。近些年，对双螺杆挤压机的应用已经有了稳定的增长。这些机器根据产出率、混合效率、生热性允许一个宽的可能性范围。尽管如此他们相比较而言更加的贵。普通的挤压产品包括圆形横截面的细丝、不规则横截面的侧面、轴对称的管子、和诸如薄片或者薄膜之类的扁平轧材。几乎所有有很大尺寸的复杂的代表性形状都是用挤压模制做成的，许多是其它单独的成型过程，诸如压制、移动和注塑成形难以生产的。 图片1.单丝杠挤压机2 吹铸成型这个过程从准备一个软的被挤压了并且预成型的压在中心梢上的热塑料性软管开始。当模具关拢时，空气压力会使得薄壁的成型腔膨胀并使
44、它向外地扩张模具面。图片2展现了这两个时期的过程。这个预先变形可以由增加元素和注塑形成。相比较注塑模而言，吹塑模需要适中的压力和夹紧力。所以，他们可以由一种比较轻的材料组成，比如铝，它有重量轻和高热传导性等优点。吹塑容器一般被用来包装饮料和其它液体食物。窄瓶颈塑料瓶子则被用来装矿物质水、牛奶、酒精饮料、碳酸饮料。其它的非食用产品被包装在吹铸容器中包括化妆品、医药品、油漆和粉末产品。吹铸品也被用在生产一些大型的产品上，如船仓和固定的储油罐，它们的容积也许会达到10000毫升之高。这些容器被用来作为地下燃料储藏库和化粪池。 时期一 预先成型挤压 时期二 吹铸 图片2.挤压吹铸模具3 旋转铸模如吹铸
45、模具，旋转铸模也被用来生产空洞的塑料商品，尽管每种方法的原理有很大的不同。在这个过程中，一个经过仔细称重得到的塑料粉末置于一半的金属模中。然后这一半模具被夹在一起并在一个炉里面进行加热。当加热好以后，模具关于两个轴进行每次90的旋转。在一段时期之后，塑料将均匀地软化在模具表面上形成一个相似层。这个过程是很有魅力的，这里有很多原因存在。首先，它是一个低压力过程，模具相应就比较简单和便宜。第二，产品事实上是免费的。第三，均匀厚度可以很简单地被实现。最后，就可以进行产品加固，他们的表面可以按照要求达到。尽管如此，周期相比于吹铸或者注塑要长。模具操作装置，可以安装双旋转，是旋转模具设备的中心元件。有两
46、个主要的设备类型：穿梭车系统，如图像3所示，和摇摆臂系统。旋转模具非常适于生产那些非常大的有厚墙的用其它过程难于很经济地生产的产品。最大的旋转模容积被记载大约有75000升左右。 图片3.穿梭车转动模 新西兰职业工程师协会 4 压缩模制 压缩模型通常被用来生产热固性材料商品，尽管它也可以被用于生产热塑性塑料。用作热固塑料的铸模操作插图于图4。一个很大的数目的模制热固塑料产品能够在电力和电子应用中得到发现。玻璃纤维增加层能够轻松地增加材料的热抵抗要求。尽管如此，这个过程的局限性是产品必须形状简单而且没有薄壁或者易碎内嵌物。很多的橡胶产品都是压缩模制的。它的有用的外表是它有可以形成强大的产品镣铐的
47、金属内嵌物经常被用来联系产品与框架。轮胎是压力铸模的最普通的产品。 图片4. 压缩模制5 移动模制移动模制与压缩模制很像，除了那个，取代将材料压缩在容器里，它被压缩在一个分模镗里然后压缩在一个开阔空间中然后被压缩在一个封闭的模具容器中。移动模具的好处是材料的预热通过一个窄的空洞注入增加了温度在材料中的分配所以促进了热固塑料的横向连接反作用力。结果是周期减少了并且产品的扭曲也减少了。物资流程的改进也意味着更多的复杂情况能够被生产。有易碎内嵌的零件如电力内嵌零件、电子元件和放入封套的连接器、集成电路和插栓也能够轻松地被生产出来。6 热力塑形薄片热力塑形是在1950年被发展起来的。限制诸如弱薄墙分部
48、和大的外围浪费把它的用途限制在简单的包装应用上面了。尽管如此，在近年来，在机器设计和材料方面已经有了很大的进步，已经有了一个很广的热力塑形的产品系列。有三种热力塑形过程的形式(图5)：真空成型、空气压力成型、和机械成型。这些不受高压的模具，通常来自铸造的或者车出来的小型或者中型的铝材，它们不需要一个好的表面成型。零件表面质量很大程度上取决于薄材。热力塑形产品可小可大。小的产品在高输出机械里运用多槽模具制造。这些产品通常能在食品和医药行业中看到，举个例子，剩果子冻或者奶油的容器、杯子、弯管和碟子。这些小的项目能够相应地有一些带有适度厚度的复杂的形状。大型的产品通常由切片在很低的输入速率下制成，而且它们通常都是简单的形状。费舍尔和佩凯尔的真空铸
