Patent GB-1533127-A (GB)
Title: Sealing and severing method and mechanism for thermosealable materials
IPC: B31B23/00
Filed: 1976-07-29
Abstract: 1533127 Seaming non-metallic sheet material FMC CORP 29 July 1976 [10 Sept 1975] 31563/76 Headings B5K and B5D Apparatus for sealing a thermosealable web fed along a path in a predetermined direction comprises two pairs of sealing bars 330, 156, and 332, 154, one pair of each pair being disposed on the opposite side of the web path to the other, and heating means 342, 168, 342a, 166 for selectively heating each bar 330, 156, 332, 154, respectively, to a sealing temperature. As shown in Fig. 1, the apparatus 20 forms part of a thermoplastic bag making machine 22 in which the web W is fed from a roll R around drive rolls 26, 28 and dancer rolls 30 and is intermittently fed into the apparatus 20 by draw roll 32, 34. The bars 330, 332 are mounted on an upper sealing head 36, Figs. 3 and 5, reciprocable by cams 37, 38 on a driven crank shaft 50 and each engaged by a spring-urged follower 88 on the end of a push rod 92 having a trunnion mount 102 of the upper end thereof with an annular bushing 108 in which a stub shaft 112 of the head 36 is journalled. Each mount 102 is adjustable on its rod 92 by a screw 114 and is maintained with this vertical adjustment during sealing and severing by air directed into the rod end of an air cylinder 118. The cams 37, 38 are adjustable to alter the dwell time of the bars 330, 332 on the web. If web feed is interrupted, to prevent damage thereto, the head 36 is raised by directing air into the closed end of each cylinder 118. A manually-operated latch device (126), Fig. 4 (not shown), is provided to allow the head 36 to be moved from its vertical position to a horizontal inoperative position. The bars 154, 156 are bolted to beams 140, 142 on a lower sealing head 35 and comprise knurled or grooved web-gripping portions 154a, 156a, Fig. 5B, and seal pads 158, 160 of electrically and heat insulating material and each having a notch therein for receiving a flat electrical resistance wire 166, 168. One end of each wire 166, 168 is held by a rigid terminal clamp (170), (172), Figs. 6 and 7 (both not shown), and the other end by a pivotal terminal clamp (174), (176), Figs. 6 and 8 (both not shown), to compensate for expansion and contraction. Polytetrafluoroethylene cloth aprons 201, 202, Fig. 5, pass over the wires 166, 168 and are wound between spools 206, 208 and 220, 222, respectively, liftable from supports so that they can be turned through 90 degrees to present a fresh apron surface to the respective wire. Severing means 230 comprises a toothed blade cutter reciprocated by a cam 40, Figs. 3 and 5B (the latter not shown), on the shaft 50 and engaged by a follower 232 on a spring- biased crank arm 234 pivoted to an adjustable link 254 pivoted to a bell crank 256 pivoted between the beams 140, 142. A beam 264 on which the cutter 230 is mounted by easily removable spring clamps 268 is pivotally supported by the bell crank 256 and a lever 262 pivoted between the beams 140, 142. The link 254 is adjustable to alter the position of the cutter so that it completely cuts through or merely perforates the web. Clamps 304, 306 comprise two rows of segments 304a-304f, 306a-306f, Fig. 10A, mounted one row on each side of a tongue 298 of a T-section beam 292 bolted to a beam 290, Figs. 3 and 5, carrying the stub shafts 112 and each urged downwardly by springs 300. Resilient rubber strips 324 are bonded to the lower edges of the segments to grip the web against the portions 154a, 156a. The bar 330, Figs. 5 and 9, is rigidly mounted on the beam 290 and carries an electrical sealing wire 342 received in an electrically and heat insulating pad 338. The bar 332 carries a similar wire 342a in a pad 338a and is mounted on a bracket 380 urged downwardly by a spring 386, an abutment block 390 limiting the downward movement of the bracket 380. The wires 342, 342a are held by resilient spring-loaded clamps (344), Figs. 10 and 11 (both not shown). Polytetrafluorethylene cloth aprons 366, 366a are trained around the pads 338, 338a and are wound on spools 368, 370 and 368a, 370a rotatable to present a fresh apron area over the wires 342, 342a. Both bars 330, 332 have a slight convex crown. In use, the apparatus is adapted to produce (a) side weld bags, Fig. 14 (not shown), from a longitudinally folded web by heating all four wires 166, 168, 342, 342a, (b) bottom weld, closed end bags, Fig. 15 (not shown), by heating the wires 168, 342, (c) bottom weld, open end bags, Fig. 16 (not shown), by heating the wires 166, 342a, or (d) flat sheets, Fig. 17 (not shown), by cutting single or multiple webs without any of the wires being heated. An electrical control circuit, Fig. 13 (not shown), for the heating wires is described. In each operation of the apparatus, the speed of the draw rolls 32, 34 gradually increases from zero through a maximum and has back to zero to minimize excessive acceleration forces on the web. Prior to each bag length advancement, the rolls 32, 34 are rotated momentarily in the reverse direction to positively strip the web from the seal bars. A timing diagram illustrating the sequence of operation is provided, Fig. 18 (not shown).