GB1166381A - Method of Forming a Thermoplastic Article. - Google Patents

Abstract

1,166,381. Moulding thermoplastic compositions. SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ N.V. 1 Feb., 1967 [3 Feb., 1966; 4 March, 1966; 25 Aug., 1966], No. 4820/67. Heading B5A. A method of forming a thermoplastic article comprises placing a predetermined amount of a molten thermoplastic polymer into a mould cavity defined by a rigid surface and another surface which deforms under moulding pressure applied by forcing down a second rigid surface into contact with the polymer to close the mould; at least one of the rigid surfaces is heatconducting whereby the polymer is cooled while under pressure and solidified. The composition treated may be polypropylene, high density polyethylene, a polyamide or a polyacetal &c., and particularly a composition which shrinks on cooling; it may contain additives such as pigments, stabilizers and powdered or fibrous fillers such as glass fibres, asbestos &c. In one embodiment a stream of molten polymer is extruded on to a plate and then transferred to preform mould 21, Fig. 2, where it is compressed to slab form by a plunger 22 and cooled. An elastomeric liner insert 23 surrounds the polymer, and during the compression causes the edges of the slab to become concave. The resultant slab 25, which is smooth surfaced and void-free is then held on a base 31 by a ring 33 and cut into annular billets by a downwardly forced cutting die 37. Each billet 39 is compressively shaped into a wheel by opposed dies 51, 52 acting within a cylinder 53; a mandrel 55 is forced through the central opening of the billet. The wheel may then be further trimmed. Scrap material from the cutting and trimming operations is returned to re-grinding apparatus for further use. The preform may be formed by placing the molten material on a flat ram and within a liner also placed on the ram, and compressing the material by an opposed ram. The liner may comprise an inflated rubber tube.