GB812844A - Improvements in and a mould for the production from thermoplastic synthetic materials of cellular articles having closed cells - Google Patents

Abstract

812,844. Moulding cellular materials. CHEMISCHE WERKE HœLS A.G. April 16, 1957 [Dec. 12, 1956], No. 12360/57. Class 87(2). In a process for manufacturing cellular articles having closed cells wherein a mass of thermoplastic synthetic material containing a blowing agent is heated in a closed mould to plasticise it and to activate the blowing agent, the mass being then cooled, removed from the mould, and then subsequently heated to expand it, the cavity of the mould is completely filled with the mass and thermal expansion of the latter is permitted by providing an elastic cushion within the mould. The elastic cushion may consist of a body of air such as that contained in an annular groove 1 in the wall of a mould 5, 6, Fig. 1, for forming circular slabs, the body of air communicating through restricted passages 2 with the mould cavity 4. The passages 2 may be formed by flattening circumferentially spaced portions of the upper surface, of a packing ring 3, Fig. 3. During the heating of the mass some of the material passes from the cavity 4 through the passages 2 into the groove 1, the volume of which may be 5 to 30 per cent. of that of the cavity 4. The surplus material in the groove 1 may subsequently be utilized in form of small pieces. Alternatively the elastic cushion may consist of a body of air separated from the mould cavity by a resilient metal membrane, e.g. of copper, and preferably in the upper part of the mould. In examples are described the manufacture of slabs of cellular polyvinyl chloride material in a mould of the construction illustrated.