GB1452696A - Thermoforming thermoplastics receptacles - Google Patents

Abstract

1452696 Sheet forming plunger M P GOURNELLE 31 Jan 1974 [31 Jan 1973] 04633/74 Heading B5A At least a portion of the lateral surface of a sheet forming plunger is provided with a multi. plicity of raised formations in order to minimize the area of contact between the portion and the sheet and thus reduce non-uniform stretching due to non-uniform heat transfer between the plunger portion and sheet. The formations, which preferably cover the whole of the lateral surface and the leading face of the plunger, may be formed by knurling, milling, shot peening, grooving, chemically or electrically pitting or by a coating. The plunger body has a peripherally extending recess 31 which defines a peripheral part of triangular cross-section. The part has an edge 16 which may be rounded (Fig. 3), or sharp (Fig. 5) and may be milled (Fig. 6). The part may be provided with holes 27 for reducing heat transfer to the body of the plunger. The recess 31 may communicate with vent/blow holes (20, Fig. 2). The plunger may be provided with a prestretching element (7, Figs. 2, 7, 8) which may be provided with a cylindrical (34, Fig. 7) or milled frusto-conical tip (35, Fig. 8). The plunger may have a circular or rectangular cross-section. Graphic design or inscription may be preprinted in a contracted form on thermoplastics sheet, film or strip so that the final form is obtained after stretching of the material.