GB1311422A - Production of multi-part mouldings by injection-moulding - Google Patents

Abstract

1311422 Injection moulding machines DESMA-WERKE GmbH 6 May 1970 11342/71 Heading B5A Multi-part articles are made by successive injections of materials of different kinds and/or colours into mould cavities in each case larger than the relevant part and subsequent reduction of the size of the cavity to the size of the part, the materials being injected through different passages 18, 19, and the sprue being removed from the first injection passage 18 before the mould cavity is reduced to the desired final size of the second part of the moulding. The sprue removal allows the passage 18 to serve as a vent, and is preferably effected before the injection of the material for the second moulding part. The invention is applied to the injection moulding of two-layer shoe soles 10, 11 of polyurethane on to uppers 15. The first injection is effected with a bottom plunger 14 in a position 17, and the plunger is then raised to a position 20, thereby shearing the sprue in passage 18. When the material has set, the plunger 14 is lowered to a position 21, the sprue in 18 removed and a second material injected at 19. Finally the plunger is raised to a position 22. Fig. 3 shows apparatus for controlling the position of plunger 14, comprising two pistons 28, 29 in separate cylinders 26, 27 connected through slide valves 34, 35 to different pressure sources. The lower piston 29 is under higher pressure and acts to limit the stroke of piston 28, stop portions being provided by parts 38, 40, 41 and 42. The plunger 14 has a peripheral channel 23 in which moulding material can collect and set so as to form a sealing ring.