注塑模具外文翻译原文

注塑模具外文翻译原文内容摘要：

l, although highgrade materials are often used, as a rule standard materials are used in mold making. New, stateofthe art (highperformance) materials, such as ceramics, for instance, are almost pletely absent. This may be related to the fact that their desirable characteristics, such as constant properties up to very high temperatures, are not required on molds, whereas their negative characteristics, e. g. 桂林电子科技大学毕业设计（论文）报告用纸 6 lo w tensile strength and poor thermal conductivity, have a clearly related to ceramics, such as sintered material, is found in mild making only to a limited degree. This refers less to the modern materials and ponents produced by powder metallurgy, and possibly by hot isocratic pressing, than to sintered metals in the sense of porous, airpermeable materials. Removal of air from the cavity of a mold is necessary with many different processing methods, and it has been proposed many times that this can be acplished using porous metallic materials. The advantages over specially fabricated venting devices, particularly in areas where melt flow fronts meet, I, e, at weld lines, are as obvious as the potential problem areas: on one hand, preventing the texture of such surfaces from being visible on the finished product, and on the other hand, preventing the microspores from quickly being clogged with residues (broken off flash, deposits from the molding material, socalled plate out, etc.). It is also interesting in this case that pletely new possibilities with regard to mold design and processing technique result from the use of such materials. . The basic mold . Mold cavity space The mold cavity space is a shape inside the mold, ―excavated‖ in such a manner that when the molding material is forced into this space it will take on the shape of the cavity space and, therefore, the desired product. The principle of a mold is almost as old as human civilization. Molds have metals into sand forms. Such molds, which are still used today in foundries, can be used only once because the mold is destroyed to release the product after it has solidified. Today, we are looking for permanent molds that can be used over and over. Now molds are made from strong, durable materials, such as steel, or from softer aluminum or metal alloys and even from certain plastics where a long mold life is not required because the planned production is small. In injection molding the plastic is injected into the cavity space with high pressure, so the mold must be strong enough to resist the injection pressure without deforming. . Number of cavities Many molds, particularly molds for larger products, are built for only cavity space, but many molds, especially large production molds, are built with 2 or more cavities. The reason for this is purely economical. It takes only little more time to inject several cavities than to inject one. For example, a 4cavity mold requires only onefourth of the machine time of a singlecavity mold. Conversely, the production 桂林电子科技大学毕业设计（论文）报告用纸 7 increases in proportion to the number of cavities. A mold with more cavities is more expensive to build than a singlecavity mold, but not necessarily 4 times as much as a singlecavity mold. But it may also require a larger machine with larger platen area and more clamping capacity, and because it will use 4 times the amount of plastic, it may need a large injection unit, so the machine hour cost will be higher than for a machine large enough for the smaller mold. . Cavity shape and shrinkage The shape of the cavity is essentially the ―negative‖ of the shape of the desired product, with dimensional allowance added to allow for shrinking of the plastic. The shape of the cavity is usually created with chipremoving machine tools, or with electric discharge machining, with chemical etching, or by any new method that may be available to remove metal or build it up, such as galvanic processes. It may also be created by casting certain metals in plaster molds created from models of the product to be made, or by casting some suitable hard plastics. The cavity shape can be either cut directly into the mold plates or formed by putting inserts into the plates. . Cavity and core By convention, the hollow portion of the cavity space is called the cavity. The matching, often raised portion of the cavity space is called the core. Most plastic products are cupshaped. This does not mean that they look like a cup, but they do have an inside and an outside. The outside of the product is formed by the cavity, the inside by the core. The alternative to the cup shape is the flat shape. In this case, there is no specific convex portion, and sometimes, the core looks like a mirror image of the cavity. Typical examples for this are plastic knives, game chips, or round disks such as records. While these items are simple in appearance, they often present serious molding problems for ejection of the product. The reason for this is that all injection molding machines provide an ejection mechanism on the moving platen and the products tend to shrink onto and cling to the core, from where they are then ejected. Most injection molding machines do not provide ejection mechanisms on the injection side. . Polymer Processing Polymer processing, in its most general context, involves the transformation of a solid (sometimes liquid) polymeric resin, which is in a random form (., powder, pellets, beads), to a solid plastics product of specified shape, dimensions, and properties. This is achieved by means of a transformation process: extrusion, molding, 桂林电子科技大学毕业设计（论文）报告用纸 8 calendaring, coating, thermoforming, etc. The process, in order to achieve the above objective, usually involves the following operations: solid transport, pression, heating, melting, mixing, shaping, coo。