| 摘要 |
<p>970,753. Seaming non-metallic sheet material. HAMAC-HANSELLA A.G. July 9, 1962 [Oct. 11, 1961 (2)], No. 26235/62. Heading B5K. [Also in Division B8] Transverse weld seams are produced on a tube 11 of thermoplastic film by first pressing the tube flat at two positions spaced on opposite sides of the desired position of the seam; freeing the tube 11 in this region from any external tensile stress in the longitudinal direction thereof so that it is free to shrink in that direction when softened by heat; and welding the seam in such a manner that the welding tools, after the fusion of the material of the tube in the region of the seam, are moved away from the seam before the seam has cooled down and solidified. In one embodiment, Figs. 1 and 2, a thermoplastic tube 11 in a packaging machine passes between channel section clamping bars 1, 2 which close so that resilient strips 5 thereon flatten and clamp the tube 11 therebetween. Welding bars 6, 7 are moved towards each other by rods 13 and a knife 12 secured to the bar 7 reaches the tube 11 first to sever it to relieve longitudinal stresses therein generated by downward movement thereof and the weight of a filled bag at the lower end thereof. The bars 6, 7 then close and transversely seal the tube 11, the bar 6 carrying an electrically heated element 10 and the bar 7 a counter element 10 which may also be heated. The bars 1, 2 remain closed for a short time after the bars 6, 7 have opened, the fused region of the unstressed thermoplastic film shrinking during cooling. In a modification in which the bags are not severed the external longitudinal stresses in the film are relieved by moving flanges 3 of each of the bars 1, 2 towards one another after the closing of these bars. In an alternative embodiment, Fig. 8, bars 26, 27 cut and weld. The bar 26 carries an intermittently or continuously heated electrical resistance element 28 preferably thermostatically controlled and having a triangular cross-section and the bar 27 carries a counter-bar 29 which may also be heated. Heat of radiation from the two adjacent faces of the element 28 assists in forming the seals 32. Alternatively, the element 28 may have a rectangular profile with a cutting-sealing rib thereon.</p> |
