Device for splicing strips of thermoplastic material

Abstract: A device (7) for splicing strips of thermoplastic material to splice a first strip (5a) extending along a first path (Pa) and a second strip (5b) extending along a second path (Pb); the device having first guides (18) for guiding the first strip (5a), and second guides (14) for guiding the second strip (5b), the first and second guides (18,14) being movable with respect to each other to bring together a portion (61) of the first strip (5a) and a portion (60) of the second strip (5b); a heat-seal block (48) movable between a rest position and a work position to grip and heat seal the portions (61,60) of the first and second strips (5a,5b) between the heat-seal block and the second guides (14); and a heatable element (55) which is movable to intercept a portion of at least one of the first and second strips (5a,5b) and cut the strip (5a,5b) by melting the portion of the strip (5a,5b) contacting the element (55).

Description: The present invention relates to a device for splicing strips of thermoplastic material. More specifically, the present invention relates to a device for splicing strips of thermoplastic material on a machine for conditioning packets of cigarettes, to which the following description refers purely by way of example. On machines for conditioning packets of cigarettes, the finished packets of cigarettes are wrapped in an overwrapping, normally comprising a sheet of polypropylene, to protect the cigarettes from the atmosphere. The sheets are formed from a strip of polypropylene, which is unwound from a reel and guided to a cutting station upstream from a folding station, and are cut off the strip, which is held taut by supporting and guide elements, as the strip is fed forward. Given the extremely high output rate, and hence high strip consumption, of modern cigarette conditioning machines, these are equipped with automatic reel-change and strip splicing devices. The reel-change device provides for replacing the running-out reel with a new one, and the splicing device for joining the strip on the new reel to that of the running-out reel and so ensuring continuity between the strips on the two reels without interrupting the wrapping work on the machine, which, pending splicing of the strips, is supplied by a strip store downstream from the splicing device. Splicing the strips involves cutting the strip on the running-out reel and a surplus strip portion on the new reel by means of respective cutters, the respective blades of which are brought into contact with the respective strips and with respective counterblades. US2724426 discloses a web splicing apparatus for a wrapping machine of the aforementioned type. Though satisfactory, splicing devices of the above type are structurally complex on account of the blades and respective counterblades. In addition to which, the blades require frequent sharpening and, consequently, frequent adjustment of the position of the blades with respect to the counterblades. DE19607495 discloses a method and an apparatus for automatically exchanging foil rolls, particularly in the manufacture of folding boxes with foil windows, wherein the end of one foil web is automatically connected to the beginning of the next following foil web. The method includes the steps of temporarily holding the end portion of the foil web which is about to run out, simultaneously connecting the end portion to the beginning of the next foil web, releasing the end portion after the connection has been effected, subsequently severing the end of the first foil web and, during these steps, further conveying without interruptions the foil web from a loop; the end of the first foil web is severed by using a heated wire movable to and from an active position, in which the heated wire is brought in contact with the first foil. It is an object of the present invention to provide a device for splicing strips of thermoplastic material, designed to eliminate the aforementioned drawbacks, and which, in particular, is simple, compact, inexpensive and involves less maintenance. According to the present invention, there is provided a device for splicing strips of thermoplastic material as recited by claim 1. A number of non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a schematic side view of a machine for cellophaning packets of cigarettes and comprising two preferred embodiments of a device for splicing strips of thermoplastic material in accordance with the present invention; Figures 2 to 6 show schematic side views of the Figure 1 device in different operating positions; Figures 2a, 3a, 4a, 5a, 6a show schematic side views of details of the Figure 1 device in the respective Figure 2 to 6 operating positions; Figure 7 shows a plan view, with parts removed for clarity, of a detail of the device according to the invention; Figure 8 shows a schematic side view of a variation of the device according to the invention. Number 1 in Figure 1 indicates a machine for cellophaning known packets of cigarettes (not shown). Machine 1 comprises a frame 2 to which are fitted successively from left to right in Figure 1 : a reel-change device 3, which acts on reels 4a, 4b defined by respective strips 5a, 5b of thermoplastic material wound about respective cores 6; a splicing device 7 for splicing strips 5a, 5b; and a compensating store 8 for at least one of strips 5a, 5b. Device 3 comprises a platform 9, which rotates, anticlockwise in Figure 1, about an axis 10 perpendicular to the Figure 1 plane, and supports a pin 11 and a pin 12 parallel to and on either side of axis 10. Pin 11 supports a running-out reel 4a, and pin 12 a new reel 4b located below reel 4a in Figure 1. Splicing device 7 comprises a circular plate 13 fitted to frame 2 and supporting a lever 14, which comprises a pin 15a rotating about an axis 15 perpendicular to the Figure 1 plane, and provides for supporting and guiding strip 5b of new reel 4b. Device 7 also comprises a cutting tool 16 fitted to plate 13, alongside lever 14, and rotating about an axis 17 parallel to axis 15; and a cutting and heat-seal tool 18 fitted to plate 13, over lever 14, and which comprises a pin 19a rotating about a respective axis 19 parallel to axis 15. Device 7 also comprises a pin 20, which is fitted to plate 13, below lever 14, extends parallel to axis 15, and in turn comprises suction holes 21 for retaining one end of strip 5b, as shown more clearly in Figures 3, 6 and 8. Store 8 comprises an elongated chamber 22 extending in a vertical direction and comprising two lateral walls 23 and 24, an end wall 25, a rear wall 26, and a transparent front wall 27. At the respective bottom ends, lateral walls 23 and 24 have respective beveled edges 29 and 28 for guiding strip 5a. Suction holes 30 are formed in end wall 25 and along rear wall 26 to produce a vacuum inside chamber 22; and strip 5a is sucked by the vacuum in chamber 22 onto lateral walls 23 and 24, between which, strip 5a forms a bend, the position of which varies according to the difference in the strip supply speeds up- and downstream from store 8. Store 8 is substantially used during the splicing of strips 5a and 5b, when supply of strip 5a is arrested temporarily, and the wrapping operations on machine 1 are continued using strip 5a in store 8. During operation of machine 1, strip 5a is unwound off reel 4a and fed through splicing device 7 7 and chamber 22 to cutting and folding devices (not shown) on machine 1. That is, strip 5a extends, in a traveling direction Da from left to right in Figure 1, along an unwinding path Pa defined partly by reel 4a, partly by cutting and heat-seal tool 18, and partly by chamber 22. Reel 4a, tool 18 and chamber 22 also provide for guiding strip 5a along path Pa. Strip 5b extends along a path Pb between reel 4b and splicing device 7, with strip 5b resting on lever 14, and with the end of the strip contacting pin 15a. That is, the operator takes the end of strip 5b from reel 4b, and places strip 5b on lever 14 and the end of the strip on pin 15a along path Pb pending splicing to strip 5a. In actual use, as it is about to run out, reel 4a is arrested by a known control device (not shown) to arrest supply of strip 5a at splicing device 7, which provides for splicing strip 5b to strip 5a, and for cutting strip 5a between reel 4a and the splice. Supply of strip 5b is then activated; platform 9 rotates anticlockwise to set reel 4b to the position previously occupied by reel 4a; and the runout reel 4a is removed off pin 11 and replaced by a new reel (not shown). With reference to Figures 2 and 2a, lever 14 is set to a standby position and comprises a curved arm 31, which in turn comprises an arm portion 32 extending radially with respect to axis 15 and connected to pin 15a coaxial with axis 15, and an arm portion 33 sloping anticlockwise with respect to, and forming a given angle B with, arm portion 32. Arm 31 defines a lateral supporting surface 34 having suction holes (not shown) for retaining strip 5b; and an end surface 35 having suction holes 36 connected to a suction conduit 37 extending inside arm 31 and connected to a known suction device (not shown). A groove 38 (Figure 3a) is formed inside arm portion 33 and along end surface 35, and extends in a direction perpendicular to the Figure 3a plane. Surface 34 comprises a flat portion 34a extending along portion 32; and a flat portion 34b, which extends along portion 33, is connected to portion 34a by a curved portion 34c, and forms a substantially right angle with end surface 35. As shown in Figures 2 and 2a, cutting tool 16 comprises two arms 39 (only one shown in Figure 2), which extend radially with respect to respective axis 17, are fitted to a pin 17a coaxial with axis 17, and have respective free ends between which is placed a wire 40 of conducting material, which is supplied with electric current to heat wire 40 to a temperature ranging between 100°C and 150°C. The ends of wire 40 are gripped by respective insulating blocks 41 located at the ends of respective arms 39 and tightened by screws 42. Tool 16 also comprises a fume hood 43 fitted to pin 17a and located over arms 39. Arms 39 rotate about axis 17 between a rest position, as shown in Figures 3 and 3a, and a work position, as shown in Figures 2 and 2a. When passing from the rest to the work position, wire 40 is positioned at end surface 35 of lever 14, with lever 14 in the standby position, and engages groove 38 with arms 39 on either side of lever 14. Electric current is supplied to wire 40 by known components (not shown), and each block 41 insulates wire 40 electrically and thermally from the other components of tool 16. In Figures 3 and 3a, lever 14 is set to the work position with strip 5b positioned for heat sealing to strip 5a, and with cutting tool 16 and cutting and heat-seal tool 18 set to the rest position. As shown more clearly in Figure 7, tool 18 comprises a substantially U-shaped, flexible blade 44 having a base 45 projecting with respect to pin 19a coaxial with axis 19, and two appendixes 46 and 47, to the ends of which is fitted a heat-seal block 48 having a curved heat-seal surface 49 (Figures 3 and 3a), the generating lines of which are perpendicular to the Figure 3a plane and parallel to axis 19. The face of heat-seal block 48 facing axis 19 comprises a groove 50 parallel to axis 19 and extending along the whole of block 48. As shown in Figures 4a, 5a and 7, tool 18 also comprises two blades 51 and 52, which project with respect to pin 19a, extend in the same direction as blade 44, and are coplanar with blade 44. Blades 51 and 52 are fitted to pin 19a and have respective free ends supporting respective fastening assemblies 53 and 54, between which extends a wire 55 of conducting material which is heated by electric current to a temperature ranging between 100°C and 150°C. With respect to axis 19, blades 51 and 52 are shorter in length than appendixes 46 and 47, so that wire 55 engages groove 50 when tool 18 is in the rest position. That is, with tool 18 in the rest position, wire 55 is located between axis 19 and heat-seal block 48, and is substantially adjacent to block 48. Each fastening assembly 53, 54 comprises an insulating body 56 fitted to respective blade 51, 52; and an insulating block 57 fastened to respective body 56 by a screw 58 to retain the ends of wire 55. As shown in Figures 3, 3a, 5 and 5a, tool 18 also comprises a fume hood 59 fitted to pin 19a and extending over heat-seal block 48 and blade 44. In actual use, device 7 splices strips 5a and 5b in the steps shown in Figures 2 to 6 and 2a to 6a. In Figures 2 and 2a, strip 5a is fed through device 7 to store 8 along path Pa, and strip 5b extends along path Pb between reel 4b and device 7, and rests on surfaces 34 and 35 of lever 14, and on pin 20 which retains the end of strip 5b by means of suction holes 21. At this step, cutting tool 16 is moved into the work position shown in Figure 2, in which wire 40, fed along a trajectory G, intercepts strip 5b extending along path Pb. Along trajectory G, wire 40 is brought into contact with, and burns and melts, the portion of strip 5b at groove 38 to detach from strip 5b a portion 60 of strip 5b extending between groove 38 and pin 20, and which is then removed by the operator. Wire 40 is housed inside groove 38 and does not come into contact with arm 31. As shown more clearly in Figures 3 and 3a, strip 5b therefore now has a new end located precisely and directly at groove 38 and along end surface 35. That is, portion 60 extends between groove 38 and the edge between portion 34b and surface 35, and directly contacts surface 35. The small amount of fumes generated by wire 40 burning strip 5b is retained and fed by fume hood 43 to a fume exhaust conduit (not shown). With reference to Figures 3 and 3a, cutting tool 16 is rotated clockwise, in Figure 3, about axis 17 back into the rest position; and lever 14 is rotated anticlockwise, in Figure 3, about axis 15 into a work position wherein surface 35 is substantially parallel to and separated by a fairly small distance from strip 5a, so that portion 60 of strip 5b contacting surface 35 is also positioned parallel to and separated by the same small distance from strip 5a. Supply of strip 5a between reel 4a and store 8 is then arrested, so that a portion 61 of strip 5a is located directly over portion 60. As shown in Figure 4, tool 18 is rotated clockwise, in Figure 4, about axis 19 into a work position, so that surface 49 of heat-seal block 48 is brought into contact with strip 5a, and portion 61 of strip 5a is brought into contact with portion 60 of strip 5b resting on supporting surface 35 of arm 31. That is, portions 60 and 61 are sandwiched between arm 31 and heat-seal block 48, which is heated to a temperature ranging between 100°C and 120°C to transmit a given amount of heat to and so seal portions 60 and 61 to each other. Given the curved shape of surface 49 of block 48 and the substantially flat shape of surface 35 of arm 31, block 48 is brought to rest on arm 31 along only one generating line of surface 49, and with no direct contact, on account of portions 61 and 60 of respective strips 5a and 5b being interposed between surface 35 and surface 49. As shown in Figures 5 and 6, pin 19a is rotated further clockwise, in Figure 5, about respective axis 19, so that, seeing as any movement of block 48 clockwise, in Figure 5, is prevented by arm 31, appendixes 46 and 47 of blade 44 are flexed into an upwardly-concave position; the further rotation of pin 19a and the deformation of appendixes 46 and 47 cause block 48 to roll surface 49 with respect to surface 35 of arm 31 to bring successive generating lines into contact with surface 35; and the further rotation of pin 19a causes wire 55 to rotate clockwise, in Figures 5 and 6, about axis 19 and along a circular trajectory A (Figure 5) with respect to block 48. Along trajectory A, wire 55 is extracted from groove 50 and is fed towards and intercepts strip 5a to detach portion 61 of strip 5a from strip 5a attached to reel 4a. Strip 5b on the other hand is retained along surface 34 of arm 31 and relatively far from wire 55 by known suction holes (not shown), and is also maintained at a safe distance from wire 55 by the shape of surface 34. Once portions 60 and 61 are heat-sealed and strip 5a cut, tool 18 is rotated anticlockwise, in Figure 6, about axis 19 back into the Figure 2 rest position; in the meantime, the known suction holes (not shown) along surface 34, and suction holes 36 along surface 35 are disabled to free strip 5b, which extends between reel 4b and store 8 and is fed to store 8; and, with reference to Figure 1, platform 9 is rotated 180° anticlockwise to invert the positions of reels 4b and 4a so that strip 5b extends along path Pa. In the Figure 8 variation, arm 31 is omitted, and lever 14 comprises an arm 62, which is fitted to pin 15a, extends substantially radially with respect to axis 15, and comprises a substantially flat lateral surface 63 and an end surface 64. A number of known suction holes (not shown) are distributed along surface 63; a number of suction holes 65 are distributed along surface 64, which forms a given angle with surface 63 and comprises a groove 66 perpendicular to the Figure 8 plane; and arm 62 comprises a conduit 67 connecting holes 65 to a known suction device (not shown). Arm 62 in the Figure 8 variation is simplified with respect to curved arm 31, and may be used when working with a strip 5b made of material which is not damaged by temporary proximity to wire 55 at a temperature ranging between 100°C and 150°C. Besides involving none of the complications posed by a blade and counterblade, the present invention is particularly advantageous by enabling precise cuts directly at splicing portions 60 and 61, and so preventing the various stations of cellophaning machine 1 from being supplied with portions of strip 5a, 5b attached to respective portions 60 and 61 but not heat sealed to each other, and which may therefore possibly result in stoppage of machine 1.

Claims: A device for splicing strips of thermoplastic material to splice at least a first strip (5a) extending along a first path (Pa), and a second strip (5b) extending along a second path (Pb); the device (7) comprising first supporting and guide means (18) for the first strip (5a), and second supporting and guide means (14) for the second strip (5b), the first and second supporting and guide means (18, 14) being movable with respect to each other to bring together a portion (61) of the first strip (5a) and a portion (60) of the second strip (5b); a heat-seal block (48) movable between a rest position and a work position to grip and heat seal said portions (61;60) of the first and second strips (5a,5b) between said heat-seal block (48) and said second supporting and guide means (14); and movable cutting means (55) for intercepting and cutting at least one of said first and second strips (5a,5b); said device (7) being characterized in that said cutting means (55) comprise a heatable element (55) which is brought into contact with said strip (5a,5b) to melt a portion of the strip (5a,5b); said element (55) comprising a first wire (55), which is made of conducting material and is movable along a given first trajectory (A) intercepting said first path (Pa) to cut said first strip (5a); said first supporting and guide means (18) comprising a heat-seal and cutting tool (18) rotating about the first axis (19) and comprising said first wire (55) and said heat-seal block (48) parallel to said first wire (55); and said first wire (55) being located at a relatively small distance with respect to said heat-seal block (48). A device as claimed in Claim 1, wherein said first wire (55) is located between a pair of first arms (51,52); said first arms (51,52) rotating about a first axis (19) parallel to said first wire (55) to feed said first wire (55), parallel to itself, along the given said first trajectory (A). A device as claimed in Claim 1 or 2, wherein said heat-seal block (48) is carried by a flexible second arm (44); said second arm (44) rotating with respect to the first axis (19). A device as claimed in Claim 3, wherein said second arm (44) is fitted to a first pin (19a) rotating with respect to the first axis (19); said first arms (51,52) being fitted to said first pin (19a), on opposite sides of said second arm (44). A device as claimed in any one of Claims 1 to 4, further comprising a cutting tool (16) for removing a surplus portion of the second strip (5b); said surplus portion extending between said second supporting and guide means (14) and a pin (20) for retaining an end of said second strip (5b). A device as claimed in any one of Claims 1 to 5, wherein the second supporting and guide means (14) comprise a lever (14) rotating about a second axis (15) parallel to said first axis (19), and movable between a rest position and a work position; said second strip (5b) contacting said first strip (5a) in said work position. A device as claimed in Claim 5 or 6, wherein said lever (14) comprises a third arm (31;62) having an end surface (35;64) which cooperates with said cutting tool (16) when said lever (14) is in the rest position. A device as claimed in Claim 5, wherein said cutting tool (16) comprises a second wire (40) made of heatable conducting material and movable along a second trajectory (G); said second wire intercepting said second strip (5b) extending along the second path (Pb) to detach said surplus portion of the second strip (5b). A device as claimed in Claim 5 or 7, wherein said third arm (31;62) comprises a groove (38;66) formed along said end surface (35;64) and parallel to said second axis (15); said second wire (40) occupying said groove (38;66). A cellophaning machine comprising a device (7) as claimed in any one of Claims 1 to 9, wherein said device (7) is located between a reel-change device (3) and a store (8) for storing at least one of said first and second strips (5a;5b).

Inventors: DRAGHETTI FIORENZO, DRAGHETTI, FIORENZO
Applicants: GD SPA, G.D SOCIETA' PER AZIONI
Application year: 1999
Main classification: B65H19
IPC codes: B65H19, B65B19