Patent GB-1350224-A (GB)
Title: Machines for the manufacture of plastic bags
IPC: B31B23/00
Filed: 1971-11-25
Abstract: 1350224 Making and accumulating bags; seaming non-metallic sheet material LES ATELIERS DE CONSTRUCTIONS MECANIQUES C & A HOLWEG SA 25 Nov 1971 [30 Nov 1970 16 July 1971 28 Oct 1971] 54692/71 Headings B5D and B5K [Also in Division B8] A machine for making bags from a flattened tubular web of plastics material comprises an arrangement 6-8 for transversely perforating the web, a pair of snatch rollers 13, 14 which separate bag lengths from the remainder of the web along the perforations, a welding drum 21 which grips and transversely welds the trailing edges of the bag lengths, and a transfer drum 35 which grips the leading edges of the bags and transfers them to a collecting drum 38 on which a predetermined number of bags are accumulated one on top of the other before being discharged as a stack on to an endless belt 51. In a further embodiment (Figs. 4, 5, 6) a vacuum gripping drum (66) is used to deliver the bag lengths from the snatch rollers 13, 14 to the welding drum 21, and a device, Fig. 8, which retards the speed of the accumulated bags before they are deposited on the belt 51, is positioned between the collecting drum and the belt 51. Tubular web may be delivered to the machine from reels, or the machine may include an arrangement for producing a tubular web from sheet material. The welding drum includes a plurality of welding stations, each of which, Fig. 15, comprises a pivotable flap 29 having a piece of glass fibre fabric 115 or insulating foil secured thereto, a fixed welding element 32 and a welding gripper 33. In operation, a bag length 116 is gripped by vacuum on to the flap 29 which in conjunction with the gripper 33 pivots inwardly to clamp the bag length, as shown, adjacent the element 32. In the event of machine malfunction, air may be blown, instead of drawn, through the flaps 29 to urge the bag lengths away from welding elements 32. The speed of the machine as a whole may be controlled automatically so as to be dependent upon the temperature of the welding elements. Various lengths of bags may be produced on the machine by changing the angular position of the drum so that the trailing edge of the bag section is always engageable by the flap 29. The transfer drum. The bags are removed from the welding drum by engagement with pivotable grippers, extensible and retractable spikes or a vacuum source associated with the transfer drum. The collecting drum 38 in the embodiment shown in Fig. 2 includes sets of grippers 40, 41, grippers 40, 41 of each set being independently and alternatively pivotable. During one revolution of the collecting drum gripper 40 is closed and grasps the leading edges, via the open mouths, of the bags and the gripper 41 is opened ready to grasp a bag from the transfer drum 35 and pin it to the collecting drum and during the following revolution of the collecting drum the gripper 40 opens and grasps the next bag whilst the gripper 41 pins the bags already collected to the drum 38. In an alternative embodiment the bags are accumulated in the same manner by extensible and retractable spikes. The discharge of the bags from the collecting drum, in the embodiment shown in Fig. 2, is effected by grippers 47 fixed on a pair of chains 48 for grasping the accumulated bags. The grippers 47 draw the bags to the right, as in Fig. 2, and release them when the whole length of the bags is supported on the belt 51. A fixed blower 54 associated with the collecting drum assists in the detachment of the bags from the collecting drum. The chains 48 are driven at a variable speed by eliptical pinions so that the speed of the grippers 47 is equal to the peripheral speed of the collecting drum at the moment when the grippers 47 grasp the bags and is at a minimum when the bags are deposited on the belt 51. In an alternative arrangement the accumulated bags are delivered to the grippers 47 by a retarding device, Fig. 8. This retarding device includes rotatable arms 84 carrying grippers 83 which have the same peripheral speed as the collecting drum, and two discs 76 which are slowly rotated in the same direction as the arm and at the same peripheral speed as a brake roller 96. In operation the brake roller 96, which is mounted in levers pivoted at 99, is lowered on to the rear of the accumulated bags by a cam 101 in timed relation with the release of the bags by the grippers 83 and the grasping of the bags by grippers 47.