GB796821A - Method of and apparatus for moulding containers, such as bottles, cans, boxes, and the like from thermoplastic material - Google Patents

Abstract

796,821. Moulding thermoplastic containers. AMERICAN PLASTON CORPORATION. July 19, 1955, No. 20815/55. Class 87(2). Bottles and other containers are moulded from a sheet of thermoplastic material by a method which comprises applying a die to the sheet so as to draw the plastic into a mould cavity which is larger than the die and to form an airtight seal at the mouth of the mould and diffusing air under pressure into the drawn plastic so as to expand it against the walls of the mould, to form the container. A sheet of thermoplastic material 62, e.g., polystyrene, is supplied from an extruder 60 of known construction and is intermittently advanced past an electric radiant heater 78 which heats the material uniformly to the desired moulding temperature. To advance the sheet it is gripped along its edges by grippers 64, 66, the operation of which, as well as other elements of the apparatus, is governed in known manner by timing devices and control valves operated from a control panel 58. The grippers slide on guides 80, 82, Fig. 3, actuated by hydraulic cylinders 68, 70, and hold the sheet stationary while a platen 42, carrying dies 40, descends for the moulding operation. Corresponding to the dies 40 are moulds 30. Tension in the extruded sheet is maintained by a roller 76. Each die 40 comprises a block 106, Fig. 6, and a plunger 108 secured by a bolt 110. The plunger is smaller than the mould cavity 100 formed in a body 96 and in a hard steel die ring 98, comprising a mould assembly 30. On the descent of the platen 42, by the movement of a piston 46 in a cylinder 48, plastic material is drawn into the moulds and the containers partially formed. A partially formed container is expanded against the wall of its mould cavity by compressed air introduced into the plunger 108, which is hollow, through ports 134 to which it is directed by a passageway in the platen 42, which is supplied from a compressed air source through a flexible conduit 126. The air leaves through passages 136 in the wall of the plunger and is diffused by the action of a covering 138 of cotton, nylon yarn or other fabric, this diffusion obviating lumps in the moulded article. A rounded flange 112, Fig. 8, is formed on the die ring 98 and has a shoulder 116. The plastic sheet 62 is gripped between the flange 112 and a flange 120 on the die block 106 and seals the upper ends of the partially formed containers against escape of air. As soon as the plastic material has been forced against the mould wall the compressed air, which is sufficient to cool it, is shut off and the platen 41 is raised slightly and allowed to fall again, at which the sheet is severed between the edges of the flange 120 and the shoulder 116. The platen 42 is then raised to withdraw the plungers 108, and a hydraulic cylinder 32 is operated and moves the platen 28, carrying the moulds and moulded containers, along-rails 24, 26 to a position above a platen 84. A hydraulic cylinder 88 then raises the platen 84, carrying ejector pins, and these pass through holes 104 and eject the moulded containers. Compressed air is forced through holes 80 in a pipe 92 to blow the ejected containers across the platen 28 to a shoot or conveyer. The waste parts of the sheet may be re-processed. Strengthening criss-cross ribs may be embossed inside the container by fitting metallic fabric over the woven fabric covering the moulding plungers, or embossing may be done during initial preforming by the plunger. When moulding containers with restricted mouths, e.g., bottles, split moulds are necessary for removal of the moulded article, Figs. 12, 13. The mould body is in two halves 176, 178 and the die ring in two halves 180,182. The halves 176, 178 are slidable on rods 184, 186 carried by brackets 188, 190 on the platen 28. Springs 192, 194 tend to separate the mould halves, which are held together, during the moulding, by the pressure of cam fingers 200, 202, depending from the platen 42, against rollers 196, 198 mounted on the mould halves.