Improvements in or relating to devices for and methods of joining thermoplastic sheets

摘要

1,001,793. Seaming non-metallic sheet material. COMMUNICATIONS PATENTS Ltd. May 24, 1962 [June 2, 1961], No. 19927/61. Heading B5K. A device for welding thermoplastic sheets 1, 2 comprises a central shoe-like live electrode 6, a pair of shoe-like earthed electrodes 7, 8 arranged one on each side of the electrode 6, all mounted for alignment of the soles thereof on one side of a planar surface of the sheets 1, 2 and co-operating with a metal surface 5 on the opposite side of the sheets 1, 2. The sheets 1, 2, e.g. of polyvinyl chloride, having respectively undercut and bevelled edges are placed on a table 3 with these edges abutting to overly an aluminium foil strip 5. The electrode 6 is positioned over the join 4 and the electrodes 7, 8 lie above the strip 5 near the edges thereof. The field passes from the electrode 6 through the sheets 1, 2 in the region of the join to the strip 5 and returns through the sheets near the edges of the strip to the electrodes 7, 8. The underneath surface area of electrodes 7, 8 is at least twice that of the electrode 6 which is radiused at 61. In one embodiment, Fig. 3, the electrode 6 slides along the join 4 and comprises a copper shoe having a spigot 17 engaging in a block 18 with springs 19 bearing on the upper face of the shoe. A polytetrafluoroethylene band 10 passes around rollers 11, 12 mounted on a carriage 15 to prevent adhesion of the thermoplastic material to the electrode 6. A double hookshaped tension spring 16 urges a shaft 13 carrying the roller 11 forwardly to tension the band 10. In a modification, Fig. 4, the electrode 6 is provided with polytetrafluoroethylene side cheeks and the band 10 of fibreglass impregnated with polytetrafluoroethylene is tensioned by a jockey pulley (not shown) bearing thereagainst. The electrodes 7, 8 are covered by a plate 20 and each has forward and rear spigots 21 or 22 carried by insulated guides 23 or 24. In a further modification, Fig. 11, the electrode 6 has a circular or square section core 61 and an outer polytetrafluoroethylene sheath 62. Each electrode 7, 8 has spigots 26, Fig. 6, extending into recesses 42 in a member 25 on a chassis 34, coil springs 27 spring-loading the electrodes. A wheel 39 applies pressure to the cooling seam. The plate 20 is carried by a fork member 28 pivoted to an arm 29 pivoted to the chassis 34. A spring 37 urges the arm 29 clockwise and, therefore, the electrode 6 downwardly. An adjustment screw 38 is provided. The chassis 34 is mounted in a housing 45, Fig. 7, on a trolley 42 having an oscillator unit 46, a power unit 47, a drive unit 48 with a driven wheel 49, a control unit 51 and a manual control 52. The device may also be used for bonding veneer, paper or cardboard to panels.