METHOD AND APPARATUS FOR BONDING THERMOPLASTIC SHEET MATERIALS

1,196,769. Sealing bags. UNION SPECIAL MACHINE CO. 15 Sept., 1967 [19 Sept., 1966], No. 42064/67. Heading B8C. [Also in Division B5] Pieces 15, 16 of sheet material are ultrasonically bonded by advancing the pieces 15, 16 along a feed path 20 in contiguous facing relationship with each other, locating the pieces 15, 16 between a pair of movable dielectric members 68, 69, leading the members 68, 69 along the path 20 at a rate which is less than the rate of movement of the pieces 15, 16 therebetween to a vibratory tool 80, and vibrating the tool 80 at a predetermined frequency to transmit vibratory energy through the members 68, 69 to form a bulge-type seal between the pieces 15, 16. As shown, the pieces 15, 16 comprise the open upper ends of a filled polyethylene bag 17 supported on a conveyer 18. The pieces 15, 16 pass between adjacent runs 36, 37 of driven endless belts 22, 23 urged together by springs 28, 35 acting on guide pulleys 25, 26 and 30, 31 therefor. The belts 22, 23 may be inclined at a slight angle to each other, Fig. 10 (not shown). Plates 58, 59 biased towards each other by springs 60 act on the runs 36, 37 to squeeze the pieces 15, 16. Whilst moving between the plates 58, 59, cleaning fluid is applied to the inner faces of the pieces 15, 16 at a station 65. The members 68, 69 comprise tapes of polytetrafluoroethylene, polyethylene terephthalate or fibre glass impregnated with polytetrafluoroethylene provided with smooth inner surfaces and supported by supply reels 70, 72 and storage reels 71, 73 at a short distance above the runs 36, 37. The reels 71, 73 continuously drive the tapes 68, 69 in the same direction as that of the movement of the pieces 15, 16 but at a considerably slower speed. The tool 80 comprises a horn 81 vibrated ultrasonically by a transducer 82 supplied with A.C. from a controller 84 and an amplifier 87 on an anvil 90 urged towards the horn 81 by a spring 92. During sealing the tapes 68, 69 prevent heat loss so that the outer surfaces of the pieces become soft and form continuous bulges (100) (101), Fig. 4 (not shown), along the seal. The tapes also prevent adhesion of the pieces 15, 16 to the tool 80. The anvil 90 may be inclined at a slight angle with respect to the horn 81 Fig. 8 (not shown). After sealing, plates 95, 96 engages the pieces 15, 16 immediately above the seal and then plates 97, 98 urged together by springs 99 hold the pieces 15, 16 together immediately beneath the seal as it cools. The sealed bag is dis