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Though, once plastic has been heated, it degrades a bit and some molding processes will not allow for "regrind" to be mixed back in with virgin material as it can cause problems with the final part. In cases like this the regrind is used elsewhere or it is discarded completely. Shrinkage plays a crucial role in molding and most plastic shrinks 20% as it cools. In order to combat this phenomenon in critical plastic pieces (not really toys) it is up the mold designer to build this factor into his design so that the finished parts will meet the original product design specifications. "Ejector pins" are part of the mold itself and are used to push the molded parts from the cavity once the mold is opened. This ejecting process is controlled by the molding machine. The molding cycle is basically "close - shoot - open - eject". The mold is clamped into the machine with the front half remaining stationary (on the barrel side of the machine) and the back half being the movable half. Also on this movable half are the ejector pins that push the molded parts from the cavity. The parting surfaces of a mould are those portion of both mould plates, adjacent to the impressions, which butt together to form a seal and prevent the loss of plastic material from the impression.When all molds open up, the parts are stuck to the back half of the mold so that they can be ejected with the built-in pins.
These are related to the introduction of the injection mold.
1.模具基本知识
1.1引言
我们日常生产、生活中所使用到的各种工具和产品，大到机床的底座、机身外壳，小到一个胚头螺丝、纽扣以及各种家用电器的外壳，无不与模具有着密切的关系。模具的形状决定着这些产品的外形，模具的加工质量与精度也就决定着这些产品的质量。因为各种产品的材质、外观、规格及用途的不同，模具分为了铸造模、锻造模、压铸模、冲压模等非射胶模具，以及射胶模具。近年来，随着射料工业的飞速发展和通用与工程射料在强度和精度等方面的不断提高，射料制品的应用范围也在不断扩大，论文网如：家用电器、仪器仪表，建筑器材，汽车工业、日用五金等众多领域，射料制品所占的比例正迅猛增加。一个设计合理的射料件往往能代替多个传统金属件。工业产品和日用产品射料化的趋势不断上升。