Patent GB-1381635-A (GB)
Title: Machines suitable for use in performing hf operations on work- pieces
Inventor: BRADLEY R W
IPC: B23K13/00
Filed: 1972-05-25
Abstract: 1381635 Seaming non-metallic sheet material; laminating apparatus BRITISH UNITED SHOE MACHINERY CO Ltd 25 May 1972 [26 May 1971] 24564/72 Headings B5K and B5N [Also in Divisions B6 and H5] A machine for performing a HF operation on a workpiece 14 of material having a high dielectric loss factor comprises two platen portions 16, 20 between which a workpiece 14 can be supported and one of which is movable relative to the other to apply pressure to a workpiece 14 so positioned, and means for creating a HF electric field between the platens 16, 20 and including a resonant cavity 10 within which the HF operation is performed. The HF operation is a welding operation, i.e. the securing together by heat and pressure of two parts of weldable material or two parts of non-weldable material with a heat-activatable adhesive layer therebetween, or an embossing operation, i.e. providing the surface of a workpiece with a desired pattern by heat and pressure. As shown, the cavity 10 is formed between two relatively movable portions 22, 23. The electric field is applied to the cavity 10 through an input 24, the platen portions 16, 20 electrically communicating with the cavity 10 to apply the field to the workpiece 14. If the workpiece 14 is to be embossed, a die 25 is secured to the portion 20. The portion 23 has copper walls 40, 42 and internal walls 44 shielding a central shaft 46, on which the portion 16 is supported, from the electric field. Wall parts 48 electrically connect the walls 44 to the periphery of the platen 16. Members 50 of electrically non- conducting material, e.g. ceramic material, support the portion 16 to prevent deflection thereof. The steel portion 16 supports a silicone glass insulating panel 60 extending to the walls 40. A resilient workpiece-supporting panel 62, e.g. of silicone rubber, is coextensive with the portion 16. The portion 20 is movable vertically by a piston and cylinder 63 connected to a steel cover plate 72 and a heat-insulating asbestos plate 70. Electrical heating elements 64 to heat the portion 20 are embedded therein. An aluminium angled strip 74 is secured to the underside of the plate 72 and, by means of four profiled strips 78, is electrically connected to the portion 20. The inner edges of the strips 78 also connect with flanges 69 of the die 25. An aluminium contact member 84 is electrically connected to the periphery of the strip 74 by copper spring fingers 86. An outflanged portion 90 of the member 84 is arranged to contact an outflanged portion 92 of an aluminium contact member 94 secured to the walls 40. Copper spring fingers 96 ensure an electrical "seal" between the portions 90, 92. Springs 100 urge the member 84 towards the member 94. Thus, in use, the cavity 10 is completely enclosed and the contained electric field does not radiate into the space adjacent the machine. The machine comprises a HF power supply including an oscillator triode valve the anode of which is directly coupled to a wall part 48 (or to a wall 44), by the input 24 through a blocking capacitor 102. A coupling coil 106, e.g. a loop coil, is accommodated with the cavity 10 and is connected to the grid of the triode valve to provide a feed back for the HF power supply. The outside of the cavity 10 is earthed by a plate 104.