| 摘要 |
988,975. Moulding hollow articles. IMPERIAL CHEMICAL INDUSTRIES Ltd. March 25, 1964 [June 20, 1963], No. 24582/63. Heading B5A. In a blow moulding process, in which part of the mould cavity wall is formed by at least two intersecting planes, the sheet material is urged towards said part of the mould by a plunger which contacts only the small area of the sheet which will be formed by said mould part. In this way undue thinning of the sheet in this region is avoided. In the embodiment shown in the Figures, a cover, for use with a light fitting, having a re-entrant portion (see Fig. 4, not shown) is formed by clamping a heat softened sheet of thermoplastic material 15 against a base 5 by a female mould, comprising a box-like member 1 clamped by clips 4 to a two-piece base frame 2, and blowing the sheet into the mould. The base 5 carries four piston and cylinder mechanisms 7, each of which carries a wedge 9 of e.g. rubber, the wedges being biased to a retracted position by e.g. springs 13. In operation, air is introduced at a relatively low pressure through aperture 6 to blow the sheet partly into the mould, the pistons 7 then being actuated to push the appropriate portions of the sheet material into the corners of the mould. Increased air pressure is then applied to the sheet to completely shape it against the mould wall, the mould being disassembled and then withdrawn and the formed article removed when the sheet has sufficiently cooled.
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