Patent GB-1472702-A (GB)
Title: Method and apparatus for continuous production of bags from thermoplastics film
IPC: B31B23/00
Filed: 1975-01-17
Abstract: 1472702 Seaming non-metallic sheet material; making bags L VAN DER MEULEN 17 Jan 1975 [19 Jan 1974] 2053/75 Headings B5K and B5D In a process for continuously producing bags from a longitudinally advanced two-layer thermoplastics web W which is fed substantially tangentially on to the outer surface 10c of a rotating welding drum 10 on which transverse welding and severing of the web W is carried out, the web W is drawn taut as each length portion thereof corresponding to a bag to be produced is drawn on to the drum and, before welding is effected, the tension in the web portion about to be welded is slackened. The web W may be flattened tubular thermoplastic film which may be slit longitudinally, a strip of sheet stock folded along the longitudinal centre line thereof, or a flattened film tube longitudinally slit along its centre line to form two parallel coplanar double layered webs to produce two side seam bags at a time. As shown in Fig. 1, the drum D is driven by belts or chains 21, engaging reduced diameter end portions 10d thereof, from an electric motor 12 via a cog or sprocket wheel 13, a belt or chain 14, a wheel 15 keyed to the centre of a shaft 16, wheels 17 on the ends of the shaft 16 and belts or chains 22. A web loop forming and web tensioning device L comprises two rolls 30, 31, rotatably supported in a vertically adjustable frame 32, and a vertically reciprocable roll 37 the ends of which are guided by vertical elements 38 and which is pivotally connected to rods 36 pivoted to aligned crank pins 23 one on each wheel 17. Rubber or rubber-faced rolls 28, 29 at least one of which is driven feed the web W into the mechanism L. A welding bar mechanism B, Figs. 1 and 2, comprises a shaft 39 suitably driven from the shaft 16 and which carries end plates 39a between which are mounted metal welding bars 40 heated by an electrical resistance element 40r. Each bar 40 is provided with an integral triangular welding and severing rib 40w shaped to produce a seam on each side of the severance line, as shown, or to form a seam on one side only of this line. The mechanism B may be rotated continuously, driven in an oscillatory manner in timed relation to the rotation of the drum 10, or intermittently driven. In a modification, the mechanism B comprises a bar radially shiftable towards and away from the drum axis at appropriate times. Six anvil assemblies A are evenly spaced about the drum periphery and each comprises, between elements 41, a silicone rubber bar 42 urged outwardly to project slightly above the drum surface 10c by a spring 47. The surface 10c is formed by curved perforated plates. Chord-like metal plates 52 and partition plates 52p form chambers 48, 49 between adjacent assemblies A. Each chamber 48, 49 communicates with a conduit 50, 51 connected to suction or pressurized air as the mouths of the conduits pass successively a suction manifold chest 53 and a pressurized air manifold chest 54. A bag discharge assembly C comprises a driven perforated hollow suction roll 57 and a set of endless pick-off tapes 59. A conveyer belt 60 or a plurality of tapes is mounted beneath a horizontal run of the tapes 59. In operation, in the position of Figs. 1 and 2, a weld and severance has just been performed by the mechanism B. The roll 37 is out of contact with the web W. When the just-used bar 40 recedes from the web and additional web is drawn under a roll 33 on to the surface 10c, the suction gripped new leading end of the web passes the station B. The roller 37 is raised and pushes the web upwardly between the rolls 30, 31 to produce a loop and to tension the web. As the anvil 42 to be used for the next welding operation approaches the mechanism B, the roller 37 descends to slacken the loop and the tension before completion of the welding operation. The severed bag is lifted from the surface 10c by pressurized air from the manifold 54 and is engaged by the tapes 59 and discharged. If it is desired to produce bags longer than the arc length between two successive anvils, the extent of slip between the web and the drum, i.e. the excess of the drum peripheral speed over the web linear speed, is adjusted. In a modification, Fig. 5, the mechanism B comprises a rotating cage having end discs 65 between which are rotatably mounted bars 67 each carrying a bar 40. Each bar 67 has an extension (68), Fig. 6 (not shown), projecting through a disc 65. A radial guide rod 70, to ensure that each bar 40 approaches an anvil 42 in a plane through the drum axis, is secured to each extension (68) and extends into a slideway 71 pivoted to the drum shaft 10s. Each disc 65 is rotated by a pinion 80 engaging teeth thereon and rests on support rollers 78, 79.