| 摘要 |
1490194 Sheet forming PLASTONA (JOHN WADDINGTON) Ltd 4 Oct 1974 [12 Oct 1973] 47848/73 Heading B5A [Also in Division B8] A bead 24 is formed on a component of thermoformable synthetic plastics material, e.g. a lid, by heating a sheet of material and clamping it between one-piece male and female dies 48 and 28 respectively, moving the dies together to perform a shearing opeation on the material and forcing it into the bead cavity, the clearance between the dies in the region of the cavity being less than the initial thickness of the material. The operation of forming the component can be assisted by gas under pressure, and forced cooling can be used. The dies have air vent passages (46) and (62), Figs. 4 and 5, not shown. The male die in Figs. 9 to 11, not shown, has a frusto-conical face (52A) without a step. The bead can be in the form of a screw-thread. The plastics material can be polypropylene, polystyrene, PVC or polyethylene. |
