Patent GB-1517211-A (GB)
Title: Device for heat sealing seams of thermoplastic overwraps on packets
IPC: B65B51/10
Filed: 1975-07-04
Abstract: 1517211 Seaming non-metallic sheet material GD SpA 4 July 1975 [10 July 1974] 28377/75 Heading B5K A heat sealing device to be associated with an intermittently-rotatable wrapping wheel having at least two sealing stations II, III comprises a heat sealing member 20, 29 movable by a support 19, 28 into and out of contact with the seam to be sealed at each station II, III, each support 19, 28 being reciprocable during each periodic dwell of the wheel 7 by a cam 13, 14 and linkage system, the cam 13 having a profile for providing the required total time of contact of the member 20 at the lowermost operating speed level of the wheel 7 and during a periodic dwell thereof, a tripping means being provided to trip the linkage system of the cam 14 in response to changes of the speed level from the lowermost up to the normal operating speed level of the wheel 7, to maintain the required total time of contact of the mebers 20, 29 with the seam regardless of the changes of the speed levels. As shown in Fig. 1, a machine for providing an outer wrap, e.g. of polypropylene, on a cigarette packet P, comprises a wrapping wheel 7 intermittently driven through 60 degrees steps by a six compartment Geneva mechanism 5 driven from a main shaft 1. The wheel 7 has six radial compartments 8 which define stations at station I of which a packet P is inserted on edge into the adjacent compartment 8 together with a transparent wrapping sheet the two radially protruding ends of which are folded on to the external side of the packet by stationary and movable folders. At stations II, III defined by apertures in an arcuate guide 9, the electrically heated sealing members 20, 29 are carried by the supports 19, 28 on bars 18, 27 carried by shafts 17, 26 having pivoted thereto levers 16, 25 carrying rollers 15, 24 running on the cams 13, 14, respectively, on an oscillatable shaft 12. The levers 16, 25 are connected to vertical rods 21, 30, respectively, integral with the keepers of electromagnets 23, 32 and restrained by springs 22, 31. Bars 33, 34 fixed to the plates 19, 20 are connected by a tension spring 35 which offsets the action of the electromagnets 23, 32. With the machine running at its normal operating speed, both electromagnets 23, 32 are energized so that the rollers 15, 24 run on the cams 13, 14 and, each time the wheel 7 is stationary, the members 20, 29 approach the sides F of the two packets P at the stations II, III and move away thereform after sealing. If the machine is running at a slower speed, to prevent undue heating of the wrapper, the electromagnet 32 is de-energized so that the member 29 is lifted by rotation about the shaft 26 under the action of the springs 31, 35. If the machine stops, both electromagnets 23, 32 are de-energized to lift both members 20, 29 away from their sealing positions. The packets are transferred from the wheel 7 to an exit channel in which the ends F<SP>1</SP>, F<SP>11</SP> are sealed. A shaft 37 is driven from the shaft 1 through meshing gears 2, 36 and carries a cam 38 having two concentric tracks 39, 39<SP>1</SP>. With the wrapping machine running at its normal speed, the track 39 is engaged by a roller 40 on a shaft 41 connected, by a rod 42, to the keeper of an excited electromagnet 43. Movement of the shaft 41 is transmitted to a lever 45 pivotable about a fixed shaft, the shaft 41 being slidable in a hollow end of the lever 45 with a tension spring 44 located therebetween. The lever 45 is connected to a block 47 carrying an electrically heated member 48 for sealing the packet end F<SP>1</SP>. The block 47 is connected through a lever 49 to a shaft 50 having an integral lever 51 one end of which has a pin 52 engaging in a slot in a lever 53 and the other end being connected by a spring 54 to a fixed plate 55. The lever 53 is pivoted to a shaft 56 connected to the keeper of an electromagnet 58 restrained by a spring 57 when it is excited. The lever 53 is connected to a block 60 carrying an electrically heated member 61 for sealing the end F<SP>11</SP>. At the normal operating speed of the machine, with the roller 40 running on the track 39, the members 48, 61 approach and seal the ends F<SP>1</SP>, F<SP>11</SP> during each of the halts of the exit channel and move away at the time the channel moves forward. If the machine runs at a slower speed, the electromagnet 43 is de-energized and the spring 44 pulls the shaft 41 so that the roller 40 is moved on to the track 39<SP>1</SP> the profile of which is such that the members 48, 61 are held away from the packet for a greater number of degrees than is the case with the track 39. Thus, the members 48, 61 are held in contact with the packet for the required sealing time. If the machine stops, the electromagnet 58 is deenergized to allow, under the pull of the spring 57, the members 48, 61 to move simultaneously away from the ends F<SP>1</SP>, F<SP>11</SP> and to be rotated about the shafts 50, 59 to non-operative positions. An electrical control circuit is described, Fig. 2 (not shown).