GB891519A - Improvements in or relating to apparatus for sealing overlapping layers of material - Google Patents

Abstract

891,519. Seaming non-metallic sheet material. SPERRY RAND CORPORATION. Nov. 10, 1960, No. 38684/60. Class 42 (1). [Also in Group XVII] Apparatus for sealing an overlap seam comprises a paramagnetic back-up bar 30 positioned against the seam on one side of the material to be seamed, a magnetic sealing head 40 engageable with the other side of the seam to magnetically attract the bar 30 to apply pressure to the seam, an edge portion 44, 50 on the head 40 comprising spaced paramagnetic elements 44 defining adjacent polefaces and means for magnetizing the elements. The apparatus forms part of a packaging machine (see Group XVII) and is used to form the longitudinal seam of a tube formed from a heat-sealable web 4. The tube has overlapping edges 18, Fig. 3. The machine includes mechanism to periodically grip the tube to form a transverse seal thereacross and also to draw the tube downwardly through the former a distance corresponding to the length of each package formed thereby and severed from the tube. The soft steel bar 30 having a weakened upper portion is secured to a bracket 24, is covered with a layer 36 of polytetrafluoroethylene or fibreglass impregnated therewith and extends downwardly within the former a distance at least equal to a bag length. The head 40 comprises plates 42, Fig. 3, of soft steel, iron or other paramagnetic material. A body 46 of non-magnetic, heat conducting material, such as aluminium or brass, is secured between the forward converging ends of the plates 42. The edge portion of the head 40 is formed by the forward edge portion 50 of the body 46 and end faces 44 of the plates 42. A heating element 52 and a thermostatic control element 54 are provided in the body 46. Wire coils 56 are arranged about magnetic cores 58 clamped between the plates 42. When D.C. is supplied to the coils 56 the faces 44 attract the bar 30 to form a heat seal, the bar returning to its original position upon de-energization of the coils or upon a current of reversed polarity flowing therethrough. The sealing assembly is mounted on the machine frame for adjustment towards and away from the centre of the tube 14. Brackets 62 are mounted on one plate 42 and have a link 64 pivoted thereto and which is pivoted to a bracket 74. To adjust for different size tubes the bracket 74 is shifted along slots 107, Fig. 2 (not shown). The head 40 is swung about an axis 66 by a screw 70 to align the head with the bar 30. When the machine is switched on a solenoid 90 is energized and remains so until the machine is switched off. The solenoid 90 draws its armature 92 inwardly to cause a lever 80 to pivot about screws 76 to swing the head 40 into its operative position shown. After switching off the machine a spring 98 moves the lever 80 and the link 64, as limited by an arm 101, clockwise to retract the head 40. To gain access to the bar 30 whilst the solenoid 90 is energized a clamp screw 82 may be loosened to swing the head rearwardly without altering the position of the lever 80. In a modification of the head 40 for forming narrow seams, Fig. 9, plates 120 have spaced fingers 122 formed at their forward ends, those on one plate being alternate with those on the other plate so that the pole faces 124 are in the same vertical plane. A body 126 of non-magnetic material is cast about the fingers. In a further modification, Fig. 10, core bars 142 extend rearwardly beyond a heat-conducting, non-magnetic body 144 and succeeding pairs are bridged by elements 148 each surrounded by a coil 150 to energize the pole faces 140.