Patent GB-645687-A (GB)
Title: Improvements in the manufacture of containers and covers therefor
IPC: B29C51/04
Filed: 1946-06-18
Abstract: 645,687. Moulding hollow articles from thermoplastic sheet material. BRITISH CELANESE, Ltd. June 18, 1946, No. 18308. Convention date, June 19, 1945. [Class 87 (ii)] [Also in Group XVI] Apparatus for making containers or covers therefor from a heated blank 47, Fig. 2, of thermoplastic sheet material, e.g. cellulose acetate, comprises a force or male die 13 cooperating with an apertured die-plate 38, and a hold-down plate 33 adapted to be held firmly adjacent to the die-plate with the opposing faces of the plates separated by a distance slightly greater than the thickness of the blank to be shaped. As shown, the plates are held separated by a spacer ring 43 which is fixed in a groove in the die-plate 38. The hold-down plate slides on rods 45 fixed to the die-plate and is carried by rods 32 passing loosely through holes in a plate 26 secured to the ram 9. Compression springs 35 surround the rods and carry collars 36 slidable on the rods. The ram carries the force 13, which is hollow and has an external recess 18 in which is fixed a cylindrical sleeve 19 of resilient material such as rubber secured upon a packing band 21 of fabric, the fabric being coated with coarse abrasive and backed by shims 22 of paper. The outer surface of the sleeve may be lubricated with talc &c. The force 13 tapers slightly inwardly from its extremity 17, this ascending taper reducing the effect of the contractive pressure of the heated plastic on the sleeve 19, so that the risk of forming surface blemishes on the plastic is reduced. The working surfaces of the plate 33 and the die-plate 38, which plates are machined flat and then ground, whilst rotating, by a high-speed abrasive wheel traversed across the surfaces so that minute roughening grooves are formed. Chromium-plating may then be applied. The die-plate 38 is heated by medium in a channel 48 and is heat-insulated from its support 53 by a gasket 54. The support is vented at 56. A concave surface is imparted to the base of the container by a pad 59 mounted in a cooling chamber 64; alternatively, the concave surface may be obtained by removing the pad and forcing in air under pressure through duct 67. Fig. 3 shows part of a modified apparatus having an annular rubber pad 71 with which the force co-operates. A concave container base 72 is formed by suction through ducts 23, Fig. 1, in the force, the material of the base being set in the concave shape by cold air blown through pipe 74. Alternatively, a convex base 76 may be formed by air pressure through ducts 24, Fig. 1. Figs. 4, 5 and 6 (not shown) illustrate apparatus, similar to that of Fig. 3, having an electricallyheated embossing element which acts on the base of the container. Specifications 600,046 and 645,688 are referred to. The Specification as open to inspection under Sect. 91 states that the preheating (before the blank is placed in the apparatus) may be such that the centre of the blank is cooler (150‹ F.) than the margin (280‹ F.); or three or more areas may be heated to differing temperatures. This subject-matter does not appear in the Specification as accepted.