GB1433136A - Moulding articles - Google Patents

Abstract

1433136 Injection moulding IMPERIAL METAL INDUSTRIES (KYNOCH) Ltd 11 May 1973 [25 May 1972] 24615/72 Heading B5A In a method of moulding an article having a thin wall portion from synthetic plastics material, e.g. a cartridge case, the material is injected in the molten state at a temperature of up to 30‹ C. above the crystalline melting temperature of the material into a mould which is at a temperature lower than the crystalline melting temperature so that the injected material is chilled and molecular orientation is induced adjacent at least some of the mould surfaces to increase the tensile strength of the plastics material in the direction of molecular orientation by at least 80%. The plastics material may be a crystalline polyolefinic polymer, e.g. high density polyethylene. In an example, a cartridge case is produced in a mould 1 comprising a cylindrical cavity 3 having a tubular extension 7 into which can slide a boss 20 mounted on a platen 16. The mould also includes a tubular core 11 surrounding an ejector rod 10. The boss 20 may carry a heat insulating tube 22. The extension 7 may be thermally insulated from the body 2 of the mould by an annulus 9. The mould body 2 has channels (not shown) for continuous water cooling. In operation, the mould parts are partly closed (Fig. 2) and injection effected through a nozzle 19 into the extension 7. After a few seconds delay to permit partial solidifying in a passage 21, the nozzle 19 is retracted and the mould fully closed (Fig. 3). An extension 13 on the ejector rod 10 thus enters and seals the passage 21 so that higher pressure is applied to the material in the mould. The solidified plug in the passage 21 is ejected by the extension 13.