Patent GB-1257693-A (GB)
IPC: B31B160/10
Filed: 1969-07-29
Abstract: 1,257,693. Seaming non-metallic sheet material. WINDMOLLER & HOLSCHER. 29 July. 1969 [8 Aug., 1968], No. 38013/69. Heading B5K. Apparatus for welding a web S of plastics film comprises means 6 for feeding the web S step-by-step to a welding tool 7 and means for reciprocating the tool 7 from an inoperative position spaced from the web S to an operative position adjacent the web, the web-feeding means 6 and the tool reciprocating means being operated by rotary drives 12 and 35, 35<SP>1</SP>, respectively, which are adapted to run at independently adjustable rotary speeds, wherein (a) the drive 35, 35<SP>1</SP> is adapted to be started with the tool 7 in the inoperative position by switching means 46 which are actuated by the drive 12 when the web S is near the end of a feeding step, (b) the drive 35, 35<SP>1</SP> is adapted to be halted temporarily by a self-actuated time switch 42 when the tool 7 has reached the operative position, the period during which the drive 35, 35<SP>1</SP> is thus temporarily halted being set on the switch 42, and (c) the drive 35, 35<SP>1</SP> is adapted to be switched off again by selfactuated switching means 44 when the tool 7 is back in the inoperative position. In a bag-making machine, a longitudinallyfolded web S is welded and severed transversely, the weld lines forming the bag sides. The web S is uniformly withdrawn from a roll 2 by rollers 1 and is fed to a compensating rocker 3 having rollers 4, 5, the rollers 5 being stationary, and which permits the web to be withdrawn continuously but to be fed step-bystep by rollers 6. After each bag is welded and severed by the tool 7 it is engaged by rollers 10 and fed by belts 10a to a stacking table 11. The rollers 6 are driven by the rotary drive 12 of a thrust and crank mechanism of which the connecting rod 13 is formed as a rack and passes through a pivoted slide 14 to engage a pinion 15 fixed to the rotatable pivotal axis of the slide 14. The drive 12 is rotated by a variable speed motor 17 or through transmission gearing from the main motor. The crank-pin is adjustable in a groove 18 of the drive disc to alter the stroke executed by the rack 13 according to the desired bag-width. The pinion 15 is turned in opposite direction during each half revolution of the drive 12, this movement being transmitted by gears 19, 20, 21, 22, 23 and a shaft 24 to a clutch 25 coupled to the rollers 6 through gears 26, 27. The clutch 25 transmits to the rollers 6 only that swing of the pinion 15 which is effective to advance the web S and freewheels when the pinion 15 swings in the opposite direction to advance the web S step-by-step. The tool 7 comprises an electrically-heated welding and severing bar 29 located above counter-pressure rollers 30, displaceable along rods 31, 31<SP>1</SP> and suspended from shoulders thereof by springs 32. The rods 31, 31<SP>1</SP> are mounted in fixed bearings 33, 33<SP>1</SP>. The tool 7 is rotated by a rotary crank drive 35, 35<SP>1</SP> driven by a variable-speed motor 36. The speed of the drive 35, 35<SP>1</SP> is greater than the speed of the drive 12. An electromagnetic clutch 38 is associated with an electromagnetic brake 39 and is seated on a shaft 37 of the drive 35, 35<SP>1</SP>. The clutch 38 and the brake 39 are synchronized so that the brake comes effective as soon as the clutch is open, and vice versa. A magnetic impulse generator or switch 40 is mounted on the shaft 37 and generates an impulse when the bar 29 has been applied to the web 5. After amplification in an amplifier 41, this impulse switches the clutch 38 off by acting through a time switch 42 and through a mixed amplifier 43, the brake 39 halting the drive 35, 35<SP>1</SP>. After the time delay has expired, the switch 42 switches the clutch 38 on and the brake 39 off so that the drive 35, 35<SP>1</SP> rotates to assume the upper dead-centre position at which the drive 35, 35<SP>1</SP> is stopped again by a switch 44 which generates an impulse which passes through amplifiers 45, 43 to disengage the clutch 38. To start a new operating cycle, the drive 35, 35<SP>1</SP> is switched on by a switch 46 mounted on a shaft 47 of the drive 12. The switch 46 is arranged so that it generates an impulse near the end of each feeding step of the web S and transmits this impulse through amplifiers 48, 43 to the clutch 38 which starts the drive 35, 351. A safety switch 49 connected to an amplifier 50 is provided on the shaft 47 and overrides the switch 42. The switch 49 operates to disengage the clutch 38 in good time before termination of the standstill period of the web S to ensure that the tool 7 will definitely have lifted off the web S when the latter commences its next feeding step.