Patent GB-1281206-A (GB)
Title: Continuous seam-welding of thermoplastic webs
IPC: B31B155/00
Filed: 1969-09-02
Abstract: 1281206 Seaming non-metallic sheet material WINDMOLLER & HOLSCHER 2 Sept 1969 [18 Sept 1968] 43419/69 Heading B5K Apparatus for continuously longitudinally heat-sealing a thermoplastic web F comprises a guide roll 2 about which the web can be passed, the roll 1 being associated at least at one end thereof with a strip-like circumferential heating surface about which the web can also be passed, and a pressure roll 4 which is effective to press the web F to the heating surface and which is disposed substantially in that region of the heated roll periphery where the web F leaves the guide roll. As shown in Figs. 1 and 2, a heating roll 1 and the guide roll or drum 2 are mounted on a shaft 3 and the roll 4 is mounted on an arm 5 pivotally mounted on the shaft 3 and connected to an arm 5<SP>1</SP> by a cross-bar 6 carrying a rotatable guide roller 7 for the web. By tilting the arms 5, 5<SP>1</SP> and thus the rolls 4, 7 about the shaft 3 through an angle # the arc of contact of the web F with the roll 1 may be increased upon an increase in the speed of the web F through the apparatus and vice versa, the web F being fed by rollers 21. The arms 5, 5<SP>1</SP> may be swung manually to a position which will result in the optimum welding period and then locked in position by a set screw (not shown). Alternatively, the arms 5, 5<SP>1</SP> are linked by a bar 8 and a lever 9 to a setting element 10 of a centrifugal regulator 11 driven at a rotary speed dependent upon the speed of the web F. When the web speed increases the displacement of flyweights 12 increases to increase the angle # and vice versa. The roll 1 is made of heat-conductive material and contains a heating element 14 supplied with current through sliprings 15 and brushes 16. The periphery of the roll 1 is tapered to the desired seam width b. The roll 4 may be made of, or covered with, elastic material. Alternatively, the roll 4 is of hard material and is carried by a spring arm pivoted at 17 to the arm 5. A spring 18 urges the roll 4 into contact with the roll 1. The rolls 1, 4 may be coupled through gears 19, 20. The web F may comprise a longitudinallyfolded thermoplastic film or two superposed film layers. In an alternative embodiment, Figs. 5 and 6, the heated roll 22 is secured to a drum 23 by screws 30 and is made in two parts of heatresistant electrical insulating material, e.g. asbestos cement. The roll 22 carries a high electrical-resistance metal strip 31 in a peripheral groove. The ends of the strip 31 extend into a radial recess 32 where they are connected to terminals 33, 34. A thrust member 35 acted on by a spring 36 holds the strip 31 to the roll 22 under tension. The strip 31 may be coated or covered with polytetrafluoroethylene. The terminals 33, 34 are carried by an insulating disc 37. Contacts 38 are spring biased into contact with the terminals 33, 34 and each is connected to a slipring 40, 401 by a conductor 39, 39<SP>1</SP>, current being supplied by brushes 41, 41<SP>1</SP>. The strip 31 forms an open ring which leaves gaps in the seam weld. These gaps may be closed by passing the web (F), through a second seam-welding apparatus (22<SP>1</SP>), Fig. 3 (not shown).