lnjection moulding is principally used for the production of thermopared with parts made by compression moulding.plastic parts, although some progress has been made in developing a method for injectionmoulding some thermosetting materials, The principle of injection moulding is quite similarto that of die-casting, Plastic powder is loaded into the feed hopper and a certain amountfeeds into the heating chamber when the plunger draws back, This plastic powder under heatand pressure in the heating chamber becomes a fluid, Heating temperatures range from 265to 500'F. After the mould is closed, the plunger moves forward, forcing some of the plasticmelt into the mould cavity under pressures range from 12000 to 30000 psi. Since the mould iscooled by circulating cold water, the plastic hardens and the part may be ejected when theplunger draws back and the mould opens, Injection-moulding machines can be arranged formanual operation, automatic single-cycle operation, and full automatic operation, Typicalmachines produce moulded parts weighing up to 22 ounces at the rate of four shots per mi-nute, and it is possible on some machines to obtain a rate of six shots per minute. Themoulds used are similar to the dies of a die-casting machine with the exception that the sur.faces are chromium plated, The advantages of injection moulding are :

① A high moulding speed adapted for mass production is possible.

② There is a wide choice of thermoplastic materials providing a variety of useful proper.

③ It is possible to mould threads, groove, side holes, and large thin sections.