Patent GB-1115686-A (GB)
Title: Method and apparatus for continuous welding of plastics sheets, in particular for use in the manufacture of exploratory balloons
IPC: B29C65/08
Filed: 1967-03-09
Abstract: 1,115,686. Seaming non-metallic sheet material. CENTRE NATIONAL D'ETUDES SPATIALES. 9 March, 1967 [8 April, 1966], No. 11205/67. Heading B5K. Thin sheets of plastics material, e.g. polyethylene terephthalate, are continuously welded to produce an exploratory balloon by placing two sheets 4, 11 edge-to-edge with a small degree of overlap, continuously ultrasonically welding the overlapped edges together in the longitudinal sense, shifting the assembly thus produced sideways to enable another continuous ultrasonically welded joint to be produced between this assembly and a further sheet overlapping the free edge of the assembly, repeat this process and finally welding together the free edges of the first and last sheets. As shown in Fig. 1, the sheet 4 is fed across a table 3 level with an anvil 2 above which an ultrasonic welding tool 1 is located. A hemispherical support 5 for the already welded sheets is rotatable about a horizontal shaft 9 and comprises a vertical disc 6 from which extend semi-circular arcuate pieces 7 equipped with magnets 8. The disc 6 may be inclined at an angle of 3-4 degrees to the vertical. At the polar level, the pieces 7 are linked to a solid cap portion 10 which is carried on the end of the shaft 9. Metal elements 13 situated opposite the magnets 8 hold the already welded sheets or gores in position. When the sheets 4,11 have been overlapped the tool 1 is operated and the sheets are fed by rotation of the support 5 by frictional engagement thereof with a motor-driven roller 12. After each welding operation the already welded sheets 11 are shifted sideways on the support 5. From the eighth welded sheet onwards, in a balloon having eighteen gores, the welded sheets are folded as shown at 11a. To carry out the welding of the last gore to the first gore, the assembly is folded into concertina-form along the weld lines and welding is effected, Fig. 2 (not shown). To weld the first polar cap 16 to the balloon, Fig. 3, a circular rotating anvil 14 is used and the tool 1 operates through an aperture 15 into which the second cap is to be subsequently fitted. Welding of the second cap. (17), Fig. 4 (not shown), is effected using a metal part of a valve (18) on the cap (16) as an anvil. The welding head comprises a magnetostrictive transducer 20, Fig. 5, mounted on a support 19 and which ultrasonically vibrates the aluminium tool 1. A pneumatic ram 21 controlled by a solenoid valve 22 acts on the support 19 so that vertical movement of the tool 1 may be effected. The tool 1 and the transducer 20 are cooled by an air circuit 23. The sheets 4, 11 are guided to the welding head by a block 24, Fig. 7, having, at two levels, grooves 25, 26 which partially overlap each other. Rollers (27), (28), Fig. 6 (not shown), arranged in converging planes feed the sheets 4, 11 to the block (24). Alternatively, before being introduced into the block (24), the sheet (4) is lifted over a rotating shaft (34), Fig. 9 (not shown), so as to enter the block from above. Infra-red heaters (not shown) may be positioned in front of the block 24 to prevent stiffening of the plastics material in cold weather. In a modification, instead of being fed by the roller 12, the sheets 4, 11 are fed by a rubber roller 29, Fig. 8, driven through a flexible drive 30 and bearing against the anvil 2. The roller 29 is mounted on a lever 31 pivoted at 32 and is acted on by a spring 33 secured to the support 19.