Patent GB-1333450-A (GB)
Title: Device for welding together sheets or strips of a material capable of absorbing ultra high-frequency waves
IPC: B29C65/78
Filed: 1971-11-04
Abstract: 1333450 Seaming non-metallic sheet material COMPAGNIE FRANCAISE DE RAFFINACE 4 Nov 1971 [6 Nov 1970] 51270/71. Heading B5K A device for welding together two sheets 2, 2 1  of material capable of absorbing UHF waves, i.e. electromagnetic waves having a frequency of at least 900 MHz, comprises a resonant cavity 41 connected to a UHF electromagnetic wave generator 68, pressure rollers 44, 45 disposed in line with and at one end of the cavity 41, means for supplying and driving two sheets 2, 2 1  to cause the sheets to partly overlap in a region in line with the cavity 41, and means for simultaneously moving the cavity 41 and the rollers 44, 45 with respect to the sheets 2, 2 1  so that the overlapping parts of the sheets are conveyed first into the cavity 41 and then between the rollers 44, 45. The cavity 41, Fig. 5, is formed between two U-section elements 40, 40a disposed one on each side of the sheets 2, 2 1  and each having two projecting side flanges 69, 70 and 69a, 70a, respectively. The width of each flange is at least a quarter of the wave length corresponding to the excitation frequency to trap the waves. The device is disposed in a trench 1 in which an angle member 3 to support the sheet 2 is mounted and is supported on front wheels (12), (13), Fig. 3 (not shown), and rear wheels 17, 18, Fig. 4. A bracket 25 extends transversely across the device and mounts a fitting 27 for a shaft 28 on which a sheet 2 1 , to be welded to the sheet 2, is wound. A roller 32 guides the sheet 2 1  into the same plane as that bounded by conveyer rollers 29. Preferably, upper rollers 34 are also provided. The rollers 29, 34 extend over only part of the width of the sheet 2 1  and leave a space for jacks 37, 37a, 38 held by brackets 35, 35a, 36. The piston rods of the jacks 37, 37a are connected to spigots 39, 39a holding the movable element 40 defining the cavity 41. The piston rod of the jack 38 carries a cradle 43 the interior of which carries the pressure rollers 44 disposed above the rollers 45. Rollers 47 similar to the rollers 29 are provided to hold the sheet 2 1  as it leaves the device until its weld with the sheet 2 has cooled. A motor 50 drives the wheels 17, 18 in the forward stroke of the device and the rollers 44, 45 and, if desired, at least some of the rollers 34. In the return stroke of the device, a motor 60 drives the wheels 17, 18 at a higher speed than the forward speed. A lifting roller 63 is disposed at the leading edge of the device to travel below the edge of the sheet 2 and bring it to a locating mechanism 64, comprising photocells 65 or a sensing device and which actuates a jack 16 to pivot the front wheels (12), (13). The mechanism 64 is operative during the return stroke of the device and rollers (66), Fig. 3 (not shown), co-operate with the sides of the trench 1. A wave guide 67, Fig. 2, terminates in the cavity 41 and is connected to the UHF electromagnetic wave generator 68. Preferably, the sheets 2, 2 1  are made of butyl rubber and are heated to 180-220 C. in the cavity 41.