Patent FR-1529235-A (FR)
IPC: B29C65/30
Filed: 1967-06-27
Granted: 1968-06-14
Abstract: 1,195,557. Seaming non-metallic sheet material; heated cutting dies. WILLCOX & GIBBS Inc. 22 Sept., 1967 [8 Dec., 1966], No. 43133/67. Headings B5A and B5K. [Also in Divisions B3 and H5] A device for sealing and/or severing thermoplastic film comprises a die member 15 of electrically conducting material having a rigid portion 16 forming a narrow film-engaging edge 17 of the desired configuration and adapted to be moved into contact with the film to seal and/or sever the same and means for heating the edge 17 comprising a circuit including a source of high frequency electrical energy having two terminals 19, 23, the terminal 19 being connected at 20 to one region of the portion 16 adjacent the edge 17 and another region of the portion 16 adjacent the edge 17 and spaced from the one region being electrically connected to the terminal 23 to cause the current to flow along the edge 17 between the regions to quickly heat the edge 17 when the circuit is energized. In one embodiment, Fig. 1, the die member 15 is mounted on a block 14 carried by a reciprocable plunger 18 in a press (not shown) to be moved into and out of engagement with film layers 11, 12 positioned on a base 10. Preferably, the base 10 and the member 15 are made of magnetic steel but they may also be made of copper, aluminium or bronze. The terminals 19, 23 of a RF generator are connected respectively at 20, 24 to one end of the portion 16 and to the base 10. The other end of the portion 16 is connected at 21 by a strap 22 to the base 10. Since the portion 16 has a thin cross-section the edge 17 cools quickly upon de-energization of the circuit. Additionally, cooling tubes (not shown) may be connected to the portion 16 or passages (25), Fig. 2 (not shown), through which a cooling fluid circulates may be provided in the block 14. A "non-stick" buffer layer 30, Fig. 4, of polytetrafluoroethylene or silicone rubber, may be positioned between the portion 16 and the layers 11, 12 and a buffer layer 31, of polytetrafluoroethylene, silicone rubber or a hard material, e.g. phenolic laminated paper, is positioned between the layers 11, 12 and the base 10. The invention is applicable to forming thermoplastic gloves, Fig. 3 (not shown). In another embodiment, Figs. 5 and 6 (both not shown), the base (10b) comprises a rigid hollow cylinder having an end surface to support a flange (11b) of a hemispherically-shaped film (A) and the die member (15b) comprises a rigid hollow cylinder (16b) having the edge (17b) thereof shaped to engage a flange (12b) of a hemispherically-shaped film (B). The cylinder (16b) is connected at diametrically opposite positions (20b), (21b) to one terminal (19b) of the generator and to the base (10b), the current dividing at the position (20b) and travelling in opposite directions along the edge (17b) to the position (21b). The other terminal (23b) of the generator is connected to the base at (24b). In a further embodiment, Figs. 7-9 (all not shown), to seal a thermoplastic cover (38) on to the open end of a thermoplastic tube (39), the die member (15c) comprises a plate having a hole (40) therein. The portion (16c) of the plate around the hole being shaped to provide a sealing edge (17c) and the plate is provided with a narrow slit (41). The terminals (19c), (23c) of the generator are connected to the plate at opposite sides of the slit. In a modification, Fig. 10 (not shown), the plate (15c) of Fig. 8 is formed in two sections (15d), (15e) hinged together at (45). Specified thermoplastic films are polyethylene, polystyrene, polypropylene and FEP fluorocarbon. The term "film" also includes woven, knitted or non-woven fabrics of natural or synthetic fibres, a suitable heat sealing adhesive being used, e.g. applied as a coating, if necessary. Metal foil, e.g. aluminium or magnesium, is also specified.