模具专业英语 作者 王浩钢 14456第11章.pptVIP

Lesson 11 Ejection 　　A molding is formed in mould by injecting a plastic melt, under pressure, into an impression via a feed system. It must therefore be removed manually. 　　Furthermore, all thermoplastic materials contract as they solidify, which means that the molding will shrink on to the core which forms it①. This shrinkage makes the molding difficult to remove. 　　Facilities are provided on the injection machine for automatic actuation of an ejector system, and this is situated behind the moving platen. 　　Because of this, the mould’s ejector system will be most effectively operated if placed in the moving half of the mould, i.e. the half attached to the moving platen. 　　We have stated previously that we need to eject the molding from the core and it therefore follows that the core, too, will most satisfactorily be located in the moving half. 　　The ejector system in a mould will be discussed under three headings, namely: (i) the ejector grid; (ii) the ejector plate assembly; and (iii) the method of ejection. EJECTOR GRID 　　The ejector grid (Figure 11-1) is that part of the mould which supports the mould plate and provides a space into which the ejector plate assembly can be fitted and operated. 　　The grid normally consists of a back plate on to which is mounted a number of conveniently shaped ‘support blocks ’. EJECTOR PLATE ASSEMBLY 　　The ejector plate assembly is that part of the mould to which the ejector element is attached. The assembly is contained in a pocket, 　　formed by the ejector grid, directly behind the mould plate .The assembly (Figure 11-2) consists of an ejector plate, a retaining plate and an ejector rod. 　　One end of this latter member is threaded and it is screwed into the ejector plate. 　　In this particular design the ejector rod functions not only as an actuating member but also as a method of guiding the assembly. 　　Note that the parallel portion of the ejector rod passes through an ejector rod bush fitted in t