Patent GB-1438299-A (GB)
Title: Welding apparatus
IPC: B29C65/02
Filed: 1973-09-06
Abstract: 1438299 Seaming non-metallic sheet material; making bags HOECHST AG 6 Sept 1973 [8 Sept 1972 22 Feb 1973] 41966/73 Headings B5K and BSD Apparatus for welding an end of a flattened tube of a thermoplastic material to form a bag or sack comprises clamping means 5a, 5b movable between an open position and closed a position, means 12 for cooling at least a part of the means 5a, 5b, means for cyclically introducing a predetermined length of the tube between the means 5a, 5b when the latter is in its open position such that a short length of one end of the tube projects from the means 5a, 5b, and infra-red radiation means 8 located at a distance from the means 5a, 5b for heating the projecting length when the means 5a, 5b is in its closed position. In one embodiment, Fig. 1, gripper tongs 9 intermittently feed flattened tubular film from a roll 1 through one bag length, the tension being kept constant by a dancer roller 2. Static electricity is discharged by a corona discharge device 4 and the lateral edges of the film are guided by optical or pneumatic control means 13, e.g. a selenium cell system. Upper and lower clamping plates 5a, 5b are opened and closed by pneumatic, hydraulic, magnetic or mechanical devices 6a, 6b or a combination thereof, and are made of steel, aluminium, copper or brass. After closing of the plates 5a, 5b, a cutting device 7 is moved along the edge thereof to leave a predetermined film projection which is fused by an elongate infrared radiator 8 lowered by a pneumatic, hydraulic, magnetic or mechanical device 16 or a combination thereof. After opening of the plates 5a, 5b, resilient plates 15 hold the fused film until the tongs 9 grasp the film to feed it through a bag length. Static electricity is again discharged by a corona discharge device 10. The finished bag is deposited on a stack ST by the co-operation of the tongs 9 with a swinging arm 14. At least one plate 5a, 5b is cooled either by the circulation of a cooling medium, e.g. cold water, through channels therein or by blowing cold air thereagainst. The region of the plates from which the tube projects may be straight or curved to produce a correspondingly-shaped weld. The shape of the radiator 8 may also correspond to the shape of the projecting tube end. The ends of the radiator 8 may be angled or curved towards the plates 5a, 5b and/or a movably-mounted reflector, e.g. 17b, may be mounted at each end thereof. The output of the radiator 8 may be regulable and the distance between the radiator 8 and the plates 5a, 5b may be adjustable. In another embodiment, Fig. 3, the plate 5a is fixed and the plate 5b is movable. In further embodiments, Figs. 4-6 (all not shown), two or more flattened tubular films are fed simultaneously between the plates 5a, 5b and adjacent tubes are separated by plates (18), e.g. of aluminium, steel, an alloy, polytetrafluoroethylene or a polyester. Separate cutting devices, infra-red radiators and transporting means may be provided for each tube. Preferably, the thermoplastic film is polyester, polyamide or polypropylene, is biaxially oriented, has a wall thickness of 6-100 Á, preferably 20-50 Á, and is heat shrinkable.