IMPROVEMENTS IN AND RELATING TO WELDING

摘要

971,431. Seaming non-metallic sheet material. UNION CARBIDE CORPORATION. May 8, 1963 [May 28, 1962], No. 18133/63. Heading B5K. A number of superimposed plies of thermoplastic film are welded together by positioning the plies 36, 38 on a support 34, compressing the area of the plies surrounding the weld area between the support 34 and a clamp 30, bringing a heat sealing element 12 into contact with the weld area and into the combined thickness of the plies to a predetermined depth, welding the plies whilst simultaneously cooling the clamp 30, first withdrawing the element 12 from the weld and then withdrawing the clamp 30 from the plies 34, 36. The element 12 of aluminium or brass comprises a shaped bar heated by an element 18 and having sealing surfaces 26, 261. The clamping platen 30 of aluminium or brass has grooves 42 therein to retain tubing 44 through which cooling water is circulated. The machine base 32 has a resilient member 34 of rubber mounted thereon. In operation, the platen 30 is first lowered to compress the plies 36, 38 against the member 34. The sealing bar 12 is then lowered so that the surfaces 26, 261 pass through slots 40, 401, respectively, in the platen 30 until shoulders 28 on the bar 12 abut adjustable screws 48 on the platen 30 to limit the advance of the surfaces 26, 261. After welding, the bar 12 is retracted from the welds 50 whilst the platen 30 continues to clamp and cool the plies 36, 38 to permit a clean stripping of the surfaces 26, 261 from the welds 50. The screws 48 are adjusted so that the surfaces 26, 261 penetrate into the plies to a depth of from onethird to two-thirds of the combined thickness of the plies to be welded. In a modification, Fig. 4, for simultaneously forming a weld 501 through two plies and a weld 50 through three plies, the sealing surface 26 of the weld 50 is machined an amount " D " equal to one-third to two-thirds the difference in thickness between the greater and lesser number of plies. Alternatively, Fig. 5 (not shown), the zone 501 is deviated by underlaying it with a ply 39 of a thickness " D." In another modification, Fig. 8, the sealing element comprises separately mounted sections 12, 13, each of which welds a different number of plies. When the sections 12, 13 are advanced adjustable stoppins 80, 82, 84, 86 thereon engage the top surface of the platen 30 to independently regulate the penetration of each section into the plies. The method may be used for welding oriented or bioriented films of polyethylene, polyethylene copolymers, polypropylene, copolymers of ethylene and propylene and mixtures of polyethylene and polypropylene.