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

Description:
FIELD OF THE INVENTION 
     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. 
     BACKGROUND OF THE INVENTION 
     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 of 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. 
     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. 
     SUMMARY OF THE INVENTION 
     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, involves less maintenance. 
     According to the present invention, there is provided a device for splicing strips of thermoplastic material to splice at least a first strip extending along a first path, and a second strip extending along a second path; the device comprising first supporting and guide means for the first strip, and second supporting and guide means for the second strip, the first and second supporting and guide means being movable with respect to each other to bring together a portion of the first strip and a portion of the second strip; a heatseal block movable between a rest position and a work position to grip and heat seal said portions of the first and second strips between said heat-seal block and said second supporting and guide means; and movable cutting means for intercepting and cutting at least one of said first and second strips; said device being characterized in that said cutting means comprise a heatable element which is brought into contact with said strip to melt a portion of the strip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 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; 
     FIGS. 2,  3 ,  4 ,  5 , and  6  show schematic side views of the FIG. 1 device in different operating positions; 
     FIGS. 2 a ,  3   a ,  4   a ,  5   a ,  6   a  show schematic side views of details of the FIG. 1 device in the respective FIG. 2 to  6  operating positions; 
     FIG. 7 shows a plan view, with parts removed for clarity, of a detail of the device according to the invention; 
     FIG. 8 shows a schematic side view of a variation of the device according to the invention. 
     FIG. 8 a  is an enlarged version of a detail from FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in FIG. 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 FIG. 1 : a reel-change device  3 , which acts on reels  4   a ,  4   b  defined by respective strips  5   a ,  5   b  of thermoplastic material wound about respective cores  6 ; a splicing device  7  for splicing strips  5   a ,  5   b ; and a compensating store  8  for at least one of strips  5   a ,  5   b.    
     Device  3  comprises a platform  9 , which rotates, anticlockwise in FIG. 1, about an axis  10  perpendicular to the FIG. 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  4   a , and pin  12  a new reel  4   b  located below reel  4   a  in FIG.  1 . 
     Splicing device  7  comprises a circular plate  13  fitted to frame  2  and supporting a lever  14 , which comprises a pin  15   a  rotating about an axis  15  perpendicular to the FIG. 1 plane, and provides for supporting and guiding strip  5   b  of new reel  4   b.    
     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 , above lever  14 , and which comprises a pin  19   a  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  5   b , as shown more clearly in FIGS. 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  5   a.    
     Suction holes  30  are formed in end wall  25  and along rear wall  26  to produce a vacuum inside chamber  22 ; and strip  5   a  is sucked by the vacuum in chamber  22  onto lateral walls  23  and  24 , between which, strip  5   a  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  5   a  and  5   b , when supply of strip  5   a  is arrested temporarily, and the wrapping operations on machine  1  are continued using strip  5   a  in store  8 . 
     During operation of machine  1 , strip  5   a  is unwound off reel  4   a  and fed through splicing device  7  and chamber  22  to cutting and folding devices (not shown) on machine  1 . That is, strip  5   a  extends, in a traveling direction Da from left to right in FIG. 1, along an unwinding path Pa defined partly by reel  4   a , partly by cutting and heat-seal tool  18 , and partly by chamber  22 . Reel  4   a , tool  18  and chamber  22  also provide for guiding strip  5   a  along path Pa. 
     Strip  5   b  extends along a path Pb between reel  4   b  and splicing device  7 , with strip  5   b  resting on lever  14 , and with the end of the strip contacting pin  15   a . That is, the operator takes the end of strip  5   b  from reel  4   b , and places strip  5   b  on lever  14  and the end of the strip on pin  15   a  along path Pb pending splicing to strip  5   a.    
     In actual use, as it is about to run out, reel  4   a  is arrested by a known control device (not shown) to arrest supply of strip  5   a  at splicing device  7 , which provides for splicing strip  5   b  to strip  5   a , and for cutting strip  5   a  between reel  4   a  and the splice. 
     Supply of strip  5   b  is then activated; platform  9  rotates anticlockwise to set reel  4   b  to the position previously occupied by reel  4   a ; and the runout reel  4   a  is removed off pin  11  and replaced by a new reel (not shown). 
     With reference to FIGS. 2 and 2 a , 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  15   a  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  5   b ; 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  (FIG. 3 a ) is formed inside arm portion  33  and along end surface  35 , and extends in a direction perpendicular to the FIG. 3 a  plane. 
     Surface  34  comprises a flat portion  34   a  extending along portion  32 ; and a flat portion  34   b , which extends along portion  33 , is connected to portion  34   a  by a curved portion  34   c , and forms a substantially right angle with end surface  35 . 
     As shown in FIGS. 2 and 2 a , cutting tool  16  comprises two arms  39  (only one shown in FIG.  2 ), which extend radially with respect to respective axis  17 , are fitted to a pin  17   a  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  17   a  and located over arms  39 . 
     Arms  39  rotate about axis  17  between a rest position, as shown in FIGS. 3 and 3 a , and a work position, as shown in FIGS. 2 and 2 a.    
     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 FIGS. 3 and 3 a , lever  14  is set to the work position with strip  5   b  positioned for heat sealing to strip  5   a , and with cutting tool  16  and cutting and heat-seal tool  18  set to the rest position. 
     As shown more clearly in FIG. 7, tool  18  comprises a substantially U-shaped, flexible blade  44  having a base  45  projecting with respect to pin  19   a  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  (FIGS. 3 and 3 a ), the generating lines of which are perpendicular to the FIG. 3 a  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 FIGS. 4 a ,  5   a  and  7 , tool  18  also comprises two blades  51  and  52 , which project with respect to pin  19   a , extend in the same direction as blade  44 , and are coplanar with blade  44 . Blades  51  and  52  are fitted to pin  19   a  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 FIGS. 3,  3   a ,  5  and  5   a , tool  18  also comprises a fume hood  59  fitted to pin  19   a  and extending over heat-seal block  48  and blade  44 . 
     In actual use, device  7  splices strips  5   a  and  5   b  in the steps shown in FIGS. 2 to  6  and  2   a  to  6   a . In FIGS. 2 and 2 a , strip  5   a  is fed through device  7  to store  8  along path Pa, and strip  5   b  extends along path Pb between reel  4   b  and device  7 , and rests on surfaces  34  and  35  of lever  14 , and on pin  20  which retains the end of strip  5   b  by means of suction holes  21 . At this step, cutting tool  16  is moved into the work position shown in FIG. 2, in which wire  40 , fed along a trajectory G, intercepts strip  5   b  extending along path Pb. Along trajectory G, wire  40  is brought into contact with, and burns and melts, the portion of strip  5   b  at groove  38  to detach from strip  5   b  a portion  60  of strip  5   b  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 FIGS. 3 and 3 a , strip  5   b  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  34   b  and surface  35 , and directly contacts surface  35 . The small amount of fumes generated by wire  40  burning strip  5   b  is retained and fed by fume hood  43  to a fume exhaust conduit (not shown). 
     With reference to FIGS. 3 and 3 a , cutting tool  16  is rotated clockwise, in FIG. 3, about axis  17  back into the rest position; and lever  14  is rotated anticlockwise, in FIG. 3, about axis  15  into a work position wherein surface  35  is substantially parallel to and separated by a fairly small distance from strip  5   a , so that portion  60  of strip  5   b  contacting surface  35  is also positioned parallel to and separated by the same small distance from strip  5   a.    
     Supply of strip  5   a  between reel  4   a  and store  8  is then arrested, so that a portion  61  of strip  5   a  is located directly over portion  60 . 
     As shown in FIG. 4, tool  18  is rotated clockwise, in FIG. 4, about axis  19  into a work position, so that surface  49  of heat-seal block  48  is brought into contact with strip  5   a , and portion  61  of strip  5   a  is brought into contact with portion  60  of strip  5   b  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  5   a  and  5   b  being interposed between surface  35  and surface  49 . As shown in FIGS. 5 and 6, pin  19   a  is rotated further clockwise, in FIG. 5, about respective axis  19 , so that, seeing as any movement of block  48  clockwise, in FIG. 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  19   a  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  19   a  causes wire  55  to rotate clockwise, in FIGS. 5 and 6, about axis  19  and along a circular trajectory A (FIG. 5) with respect to block  48 . Along trajectory A, wire  55  is extracted from groove  50  and is fed towards and intercepts strip  5   a  to detach portion  61  of strip  5   a  from strip  5   a  attached to reel  4   a . Strip  5   b  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  5   a  cut, tool  18  is rotated anticlockwise, in FIG. 6, about axis  19  back into the FIG. 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  5   b , which extends between reel  4   b  and store  8  and is fed to store  8 ; and, with reference to FIG. 1, platform  9  is rotated 180° anticlockwise to invert the positions of reels  4   b  and  4   a  so that strip  5   b  extends along path Pa. 
     In the FIG. 8 variation, arm  31  is omitted, and lever  14  comprises an arm  62 , which is fitted to pin  15   a , 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 FIG. 8 plane; and arm  62  comprises a conduit  67  connecting holes  65  to a known suction device (not shown). 
     Arm  62  in the FIG. 8 variation is simplified with respect to curved arm  31 , and may be used when working with a strip  5   b  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  5   a ,  5   b  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 .