Patent GB-1050347-A (GB)
IPC: B29C65/00
Abstract: 1,050,347. Seaming non-metallic sheet material. KALLE A.G. July 25, 1963 [July 28, 1962], No. 29578/63. Heading B5K. Thermoplastic films or webs coated with thermoplastic material are welded together by applying a plurality of spaced resiliently yieldable welding elements heated to a welding temperature to the films to form a discontinuous weld comprising relatively short component welds spaced apart by unwelded areas and, after solidfication of the weld, applying to the films a plurality of spaced resiliently yieldable welding elements arranged to correspond with the unwelded areas to form further relatively short component welds intercalating with the first component welds. The component welds of the welded area may merge to form a continuous welded area or may have unwelded spaces therebetween. In one embodiment of apparatus for use in the above method, Fig. 2, component welding elements 1a, 1b 1c are slidably mounted in a block 2 containing electrical heating means 3 and are preferably arranged in staggered rows. The elements are arranged to be reciprocated so that the elements 1b of the middle row move downwardly as the elements 1a, 1c move upwardly and vice versa. Alternatively, all component welding elements exert a welding pressure simultaneously. The elements may be spaced, as shown, or may slide against each other, graphite or molybdenum sulphide being used as a lubricant in the latter case. Each component element 1 is resiliently mounted in the block 2 by a spring 4, Fig. 3, which prevents the welding pressure exceeding a certain value. A plunger 8 actuated by a cam (not shown) acts as a control member and inserted in a bore 5a, 5b in the element 1. After welding, the element 1 is retracted by a spring 6. Each element 1 may have a coating 7 of polytetrafluoro-ethylene, vaporized silica or a sintered metal to prevent adhesion of the film thereto. The coating 7 may be a moulding pressed by a plug 16 into the element 1. To effect differential heating of the component elements the heating elements 3 may be disposed at different distances therefrom or the component elements may be made from materials having different thermal conductivities. To produce a continuous welded surface using a block having spaced elements 1 the films to be welded and the welding block are moved relatively to each other and welding pressure is repeatedly applied. The relative movement may be effected by crank discs having links connected to the block 2 to cause oscillation thereof, Fig. 6 (not shown), or by conveying the films to be welded past the block 2, Fig. 7 (also not shown). The elements 1 may be reciprocated by the apparatus shown in Figs. 4 and 5. The elements are arranged in two groups of three, each consisting of outer rows of elements la, 1c and an inner row 1b. The plungers 8 of the elements 1b are depressed directly by cam-shafts 10, each forming part of a rotatable shaft 9 and the elements 1a, 1c are depressed by rockers 11. The cams on the shaft 10 may be selected so that the rows are depressed consecutively or so that the component elements of a single row are depressed consecutively. In apparatus in which the work to be welded is conveyed along a circular or arcuate track the block 2 may be of a corresponding curved shape. In an alternative embodiment (not shown), the welding elements are formed as contiguous or spaced discs movable against radial spring-loading about their axes to form a rotatable roller-like welding element. In a further embodiment the welding elements are constituted by the resilient coils of a heated spring which is rotatably mounted.