Patent GB-1086641-A (GB)
Title: Device for welding thermoplastic sheets
Inventor: SWARTZ HENRY DAVID
IPC: B29C65/22
Filed: 1965-01-08
Abstract: 1,086,641. Seaming non-metallic sheet material. THERMOPLASTIC INDUSTRIES Inc. Jan. 8, 1965, No. 1056/65. Heading B5K. A device for welding thermoplastic sheets comprises a pair of elastomeric pressure faces 63, 68 directed toward each other and the face 63 of which is included as one of a succession of increments in an endless belt; a pair of rigid backing platens 64, 66 of which the platen 66 is movable relative to the platen 64 to compress and release the pressure faces 63, 68; and a heat sealing element 70 movable with the platen 66 to weld the sheets. In the embodiment shown, Fig. 4, to produce transverse welds in a longitudinally folded web of thermoplastic film, the web 50 is fed into a welding station 60 by the belt 63 which is backed by the platen 64. A number of heat sealing wires 70 are rigidly stretched across the face 68. The platen 66 is reciprocated by a cylinder 82 connected to a central shaft 80 thereof and is guided by shafts 72, 74 sliding in guides 76, 78. In operation, the web 50 is threaded from a supply roll 56 around idler rollers 94, 96, 98, between rolls 92, 126 into contact with the belt 63 and to a take-up roll 58. The rolls 94, 98 are mounted on a cross-piece 100 which is rotated in a clockwise direction by the advance of the web 50 to actuate a micro-switch 108 to cause the roll 56 to be rotated. A manual switch 120 is depressed to drive the belt 63 from the roll 126 from a motor 84 and to apply pressure to the roll 92. A predetermined length of the web 50 is advanced into the station 60, the length being determined by the relative positions of discs 134, 136 of a variable speed transmission. The take-up roll 58 is driven by a belt transmission from the belt 63. The platen 66 is pushed downwardly against the platen 64 by the cylinder 82 and a pulse of current is applied through the wires 70 by a power supply 156, the configuration of the pulse being determined by a timer 158. After a predetermined time, a cam 140 operates a clutch brake 122 to cause the roll 126 to be driven by the motor 84 through transmission 86. In a modification, Fig. 2 (not shown), the movable platen 26 has a silicone rubber face 28 to which a curved current conductor 30 is secured by thin metallic threads at points 32, 34, 36. Alternatively, the conductor is attached to the face 28 by a pressure sensitive adhesive tape, e.g. a polytetrafluoroethylene or glass cloth web backed by a heat curing partially polymerized synthetic plastic. In a further modification, Fig. 3 (not shown), a number of wires 42 are tensioned at spaced intervals over a silicone rubber facing 40 between connectors 44, 46 positioned on the rigid movable platen 38. The electrical conductor may be any high resistance metallic or metalloidal material, e.g. a nickel-chrome alloy. The resilient face against which the conductor abuts may be a silicone elastomer containing high molecular weight linear silicon polymer, finely divided silicon dioxide as a filler and a peroxidic curing agent. The belt may be natural rubber such as cis-1,4-polyisoprene or a synthetic rubber such as butadiene-styrene, neoprene, butylrubber, nitrile rubber, polysulphide rubber, chlorosulphonated polyethylene, polyurethane, cis-1,4-polybutadiene and adduct rubber. Examples relate to sealing polyethylene sheets. A release stratum either of heat resistance polytetrafluorethylene or of wax paper, e.g. felted cellulose fibres impregnated with paraffin) may be interposed between the electrical conductor and the sheets and a release stratum either of fibreglass impregnated with polytetrafluoroethylene or of a wax paper may be interposed between the sheets and the other resilient face.