DE1950406

• Main Authors: SIMMONDS JUN., ROBERT CHARLES, TOPSFIELD, MASS., US, KYRITSIS, WILLIAM THOMAS, BEVERLY FARMS, US
• Format: Patent
• Language: English
• Published: 03.12.1981
• Subjects: AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING; PERFORMING OPERATIONS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDEDFOR; SHAPING OR JOINING OF PLASTICS; TRANSPORTING; WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL

1292318 Injection moulding cellular articles BRITISH UNITED SHOE MACHINERY CO Ltd 14 Oct 1969 [15 Oct 1968] 50363/69 Heading B5A [Also in Division C3] A method of moulding cellular articles comprises (a) melting a thermoplastic material containing a heat decomposable blowing agent at a temperature below that at which the blowing agent decomposes; (b) increasing the temperature of the molten material to above that at which the blowing agent decomposes and injecting the mixture into a mould cavity to fill it to a pressure sufficient to prevent foaming; and (c) expanding the mould cavity to allow expansion of the material into cellular form, wherein the lapse of time between the increasing of the temperature and the filling of the cavity is sufficiently short that no foaming takes place before expansion of the cavity. The method may be carried out in the apparatus shown, the temperature increase being effected by forcing the material through a restriction formed by a nozzle 18 and sprue passageway 60. The injection cylinder 6 contains an axially reciprocable screw 10 and comprises a temperature control fluid passage 22. Means are provided for moving a piston 57 in a cylinder 58 and therefore a mould member 54 away from a mould member 50 at a substantially constant speed. The moulding material may be polypropylene, polystyrene or polyethylene copolymer and the blowing agent may be azobisformamide.