GB618885A - Improvements relating to the moulding of articles made of or comprising synthetic resin - Google Patents

Abstract

618,885. Moulding pipes and other hollow articles. MIESZKIS, K. W. July 13, 1946, Nos. 20997 and 21064. [Class 87 (ii)] The inside of a moulded hollow plastic article 11, Fig. 2, is formed by one or more solid preformed cores 10 of a metal alloy fusible at a temperature below the moulding temperature and, after melting, the core takes an active part as a medium transmitting pressure to the interior of the moulded article from an external source. The core, which may be an assembly of several parts to give it the required shape, is covered with the material to be moulded, e.g., cloth impregnated with resin, and placed in a two-part mould 14, 15, which is subjected to hydraulic pressure and is maintained at the required temperature. Molten alloy is contained in a vessel 16 which, with the pipework &c., is kept at a temperature above the melting point of the alloy. The valves 18 and 19 are closed and the alloy is forced up the pipe 21 through the open valve 20 and into the bottom of the mould by compressed gas admitted through the valve 25. The alloy reaches the top of the mould through the ducts 22 and 23, air escaping through the valve 24. When all the spaces are full of the alloy the valves 20 and 24 are closed and the valves 19 and 26 are opened, so connecting the pipes leading to the mould with a hydraulic pump (not shown) through the vessel 17 which is partly filled with alloy and partly with a hydraulic liquid. Pressure (shown on the manometer 27) can thus be applied to the molten core. After a time the valve 19 is closed and the valve 24 opened to allow gases from the resin to escape. When moulding is complete the valve 19 is closed and the pressure is released by opening the valves 20 and 24, and the alloy returns to the vessel 16. To guard against spoiling the shape of the article by the core 10 melting, when put in the hot mould, before the mould is closed, an intermediate mould may be used of a suitable metal, e.g., stainless steel, as shown in Fig. 4, in which the plastic material 30 and fusible core 31 in the intermediate mould 32, 33, 34 are placed in a moulding chamber 38 and the intermediate mould is supported by blocks 40, 42 leaving a free space 41 for the flow of the molten alloy. The alloy 31 melts and connects with the molten alloy 41 through holes 35 in the intermediate mould, so equalising the pressure inside and outside the intermediate mould and preventing it from bursting. In a simpler arrangement, the walls of the intermediate mould are supported by the wall of the main mould, which has the same internal dimensions as the external dimensions of the intermediate mould. Specification 605,820 is referred to.