1、Lesson 11 EjectionA 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 f
2、orms it . 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 moulds ejector system will be most effectively operated if placed in the m
3、oving 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 th
4、ree headings, namely: (i) the ejector grid; (ii) the ejector plate assembly; and (iii) the method of ejection.EJECTOR GRIDThe 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 .Figure 11-1 Ejector grid
