Abstract:
A method and machine for wrapping a product in a sheet of heat-seal wrapping material, whereby the product is wrapped in the sheet of wrapping material to form a product having an outer wrapping in turn having three distinct overlap portions, i.e. portions having at least two superimposed layers of the sheet of wrapping material; and the outer wrapping is stabilized, as the product is conveyed continuously inside a respective same pocket, by a seal formed at each of the three overlap portions.

Description:
The present invention relates to a method of wrapping a product in a sheet of heat-seal wrapping material. 
     The present invention is particularly advantageous for use on machines for cellophaning packets of cigarettes, to which the following description refers purely by way of example. 
     BACKGROUND OF THE INVENTION 
     Known machines for cellophaning packets of cigarettes normally comprise a step-operated first wrapping wheel on which a sheet of heat-seal wrapping material is wound about a packet of cigarettes to form a tubular wrapping, which is stabilized by means of a longitudinal seal, and which comprises two tubular end portions, each projecting from a respective end wall of the packet. The longitudinal seal is made by a sealing device mounted at a fixed sealing station, and which, at each stop of the first wrapping wheel, is brought into contact with a longitudinal overlap portion of two opposite portions of the sheet of wrapping material. 
     At the output of the first wrapping wheel, the packet and respective tubular wrapping are normally fed through a folding station where the projecting tubular portions of the tubular wrapping are folded onto respective end walls to form two further overlap portions closing the ends of an outer overwrapping. The two overlap portions are then stabilized by two end seals as the packet is conveyed on a continuously operated second wrapping wheel. 
     Finally, the overwrapped packet is normally fed to an output station where it is normally heat treated to shrink the outer wrapping about the packet. 
     Known cellophaning machines of the type described above have several drawbacks, mainly due to the fact that, over and above a given operating speed, the stops of the first wrapping wheel are not long enough to enable correct execution of the longitudinal seal. 
     Moreover, a further drawback of known cellophaning machines of the type described above lies in the longitudinal seal being made separately from the end seals, which means the tubular wrapping, at the output of the first wrapping wheel, may undergo localized heat shrinking at the longitudinal overlap portion only, thus impairing correct formation of the outer wrapping by shortening and tightening the overlap portion with respect to the rest of the tubular wrapping. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method of wrapping a product in a sheet of heat-seal wrapping material, designed to eliminate the aforementioned drawbacks. 
     According to the present invention, there is provided a method of wrapping a product in a sheet of heat-seal wrapping material, the method comprising the steps of wrapping the product in said sheet of wrapping material to form a tubular wrapping comprising a longitudinal first overlap portion, defined by superimposed portions of said sheet of wrapping material, and two projecting tubular end portions; folding each of said tubular end portions onto the product to form an outer wrapping having two further end overlap portions; and feeding said product along a sealing path, along which, said three overlap portions are stabilized by three sealing operations; and being characterized in that said product is fed along said sealing path by a respective same pocket, which is fed continuously along the sealing path. 
     The present invention also relates to a machine for wrapping a product in a sheet of heat-seal wrapping material. 
     According to the present invention, there is provided a machine for wrapping a product in a sheet of heat-seal wrapping material, the machine comprising first wrapping means for wrapping the product in said sheet of wrapping material and forming a tubular wrapping comprising a longitudinal first overlap portion, defined by superimposed portions of the sheet of wrapping material, and two projecting tubular end portions; second wrapping means for folding each said tubular end portion to form an outer wrapping having two further end overlap portions; sealing means located along a sealing path, and each for performing a respective sealing operation on a respective said overlap portion; and conveying means for feeding said product along said sealing path; and being characterized in that said conveying means comprise a single conveying pocket for said product; first actuating means being provided to feed said pocket continuously along said sealing path. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A non-limiting embodiment 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, with parts enlarged and parts removed for clarity, of a preferred embodiment of the machine according to the present invention; 
     FIG. 2 shows an enlarged view in perspective of a detail in FIG. 1; 
     FIG. 3 shows an axial section of the FIG. 2 detail. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Number  1  in FIG. 1 indicates as a whole a cellophaning machine for wrapping packets  2  of cigarettes in respective sheets  3  of transparent heat-seal wrapping material. 
     Machine  1  comprises a wrapping wheel  5  fitted to a powered shaft  6 , which is mounted to rotate in steps and in a given direction (clockwise in FIG. 1) about an axis  7  perpendicular to the FIG. 1 plane. 
     Wheel  5 , of known type, comprises a number of pockets  8 , which are equally spaced along the periphery of wheel  5 , are substantially U-shaped, and are open both radially and axially outwards. 
     When stopped at a loading station  9 , each pocket  8  receives a respective sheet  3  of wrapping material fed to station  9  by a known supply device  10 , and a respective packet  2 , which is inserted inside respective pocket  8  to fold sheet  3  into a U about packet  2 . 
     In connection with the above, it should be pointed out that, on machine  1 , packet  2  is fed by wheel  5 , and by successive conveying devices described later on, along a wrapping path P with the longitudinal axis  2   a  of the packet oriented crosswise at all times to path P and to the FIG. 1 plane. 
     As packet  2  and respective sheet  3  are fed by wheel  5  between loading station  9  and an unloading station  11 , sheet  3  is wrapped about packet  2  (as of said U-shaped configuration) by two known folding devices  12   a  and  12   b  to form a tubular wrapping  13 , which comprises a longitudinal overlap portion  13   a , defined by two superimposed portions of sheet  3 , and two tubular end portions  14 , each of which projects from a respective end wall  15  of packet  2 . 
     When wheel  5  is stopped, longitudinal overlap portion  13   a  is pre-stabilized by means of a spot seal made by a sealing device  16 , which is substantially fork-shaped, is mounted at a fixed sealing station, and is activated in known manner to move back and forth linearly to and from wheel  5  in a substantially radial direction to effect said spot seal. 
     Wheel  5  comprises, in known manner, two coaxial, parallel disks  17  (only one shown in FIG. 1) fitted to shaft  6  and each comprising a number of peripheral seats  18 , each of which defines a respective pocket  8  together with a corresponding seat  18  on the other disk  17 . 
     Machine  1  also comprises an endless conveyor  19  in turn comprising a belt  20  looped about two pulleys  21 —one of which is powered continuously—having respective axes  22  parallel to axis  7  of wheel  5 . Belt  20  comprises a number of push members  23  equally spaced along belt  20  and defining a succession of pockets  24 , the length of each of which is at least equal to the width of a packet  2  measured parallel to path P. 
     At said unloading station  11 , conveyor  19  extends between disks  17  of wheel  5  to enable one of push members  23  to extract a respective packet  2  and respective tubular wrapping  13  from respective pocket  8 , and feed packet  2  and tubular wrapping  13  through an input portion of a folding station  25 , which is defined partly by conveyor  19  and partly by a channel  26  located in series with conveyor  19  and defined at the bottom by a horizontal plate  27 , and at the top by a bottom conveying branch of an endless conveyor  28 . 
     Conveyor  28  comprises a belt  29  looped about two pulleys  30 —one of which is powered continuously having respective axes  31  parallel to axes  22 . Belt  29  comprises a number of push members  32  equally spaced along belt  29  and defining a succession of pockets  33 , each of which is fed forwards in time with a pocket  24  of conveyor  19  to receive packet  2  and tubular wrapping  13  housed inside pocket  24 , and feed packet  2  and tubular wrapping  13  through an output portion of folding station  25 . 
     For each of the two tubular portions  14 , station  25  comprises a series of known folding devices  34  for folding the relative tubular portion  14  in known manner onto the respective end wall  15  of respective packet  2 , so that, along station  25 , an overwrapped packet  35  is formed comprising a closed outer wrapping  36  having two end overlap portions  36   a , each defined by a number of superimposed portions of sheet  3  of wrapping material. 
     At the output of station  25 , overwrapped packet  35  is transferred, as described later on, from respective pocket  33  to a pocket  37  of a sealing wheel  38 . Sealing wheel  38  comprises, in known manner, two coaxial, parallel drums  39  fitted, a given distance apart, to a powered shaft  40  rotated continuously and in a given direction  41  (clockwise in FIG. 1) about an axis  42  parallel to axis  7  of wheel  5 . 
     Pockets  37  are equally spaced along the periphery of wheel  38 , are fed forwards in time with pockets  33 , and each comprise, for each of the two drums  39 , a respective substantially flat supporting surface  44  formed on the outer surface of relative drum  39 , and a respective push member  45 , which projects radially from the outer surface of relative drum  39  to engage the rear of respective overwrapped packet  35 . Each pocket  37  also comprises a respective gripping and sealing device  46  for retaining respective overwrapped packet  35  inside pocket  37  and in contact with both respective push member  45  and respective supporting surface  44 . 
     In connection with the above, it should be pointed out that overwrapped packet  35  is fed into respective pocket  37  “flat”, i.e. with two major lateral surfaces of the packet positioned horizontally, with axis  2   a  oriented crosswise to path P, and with longitudinal overlap portion  13   a  located frontwards in direction  41 . 
     With reference to FIG. 2, each gripping and sealing device  46  comprises two lateral jaws  47  located on opposite sides of path P; and a transverse jaw  48  located crosswise to path P and to the front of lateral jaws  47  in direction  41 . Jaws  47  and  48  are supported by a shaft  49 , which is mounted for rotation through the two drums  39 , and is oscillated—with respect to drums  39  and by a known cam device  50  housed inside one of drums  39 —about an axis  51  parallel to axis  42 . 
     With reference to FIG. 3, the two lateral jaws  47  are positioned facing each other, and each comprise a respective tubular body  52  fitted to shaft  49  and having a cylindrical outer surface  53 , the axis  54  of which forms a given angle  55  with axis  51 . Each jaw  47  also comprises a ball bearing  56  having an inner ring fitted to surface  53  of tubular body  52 ; and a bar  57  in turn comprising a central hub  58  fitted to an outer ring of bearing  56 , and two opposite arms  59  extending radially outwards from hub  58 . The two arms  59  are fitted respectively, on the free ends, with a known sealing device  60 , and a tappet roller  61  fitted in rotary manner to respective arm  59  and engaging a track  62 , which is formed on relative drum  39  and is parallel to axis  51  of shaft  49  and crosswise to path P. 
     When shaft  49  oscillates about axis  51 , bar  57  would therefore also oscillate about axis  51  if it were not forced, by track  62  and by angle  55  formed between axes  51  and  54 , to oscillate about an axis  63  extending perpendicular to the FIG. 3 plane at the intersection of axes  51  and  54 . 
     Transverse jaw  48  comprises a crank  64  fitted to shaft  49 , between tubular bodies  52  of the two lateral jaws  47 , and connected to a rocker arm  65  fitted to a shaft  66 , the opposite ends of which are mounted for rotation through the two drums  39  to enable shaft  66  to rotate, with respect to the two drums  39  and by virtue of said cam device  50 , about an axis  67  parallel to axis  51 . Rocker arm  65  comprises a first arm  68  connected in rotary manner, via the interposition of a connecting rod  68   a , to the free end of crank  64 ; and a second arm  69  supporting a known sealing device  70  extending crosswise to direction  41  and to path P. 
     In actual use, overwrapped packet  35  is fed to the output of folding station  25  inside respective pocket  33  and in time with a respective pocket  37 . At the output of station  25 , when shaft  49  is oscillated about axis  51  and portions of folding devices  34  are still positioned engaging outer wrapping  36 , the two lateral jaws  47  and transverse jaw  48  are all moved simultaneously from a detached position to a gripping position (FIG. 2) in which sealing devices  60  and sealing device  70  are respectively positioned contacting overlap portions  36   a  and overlap portion  13   a , so as to clamp overwrapped packet  35  inside respective pocket  37  and stabilize outer wrapping  36  by means of two end seals at overlap portions  36   a  and a longitudinal edge seal at overlap portion  13   a.    
     Jaws  47  and  48  are maintained in the gripping position along the whole of sealing path P 1 , which forms part of wrapping path P and extends along a curved plate  71  extending, from the output of folding station  25 , along an arc of about 180° about the periphery of sealing wheel  38 . 
     At the output of wheel  38 , jaws  47  and  48  are moved into the detached position to unload overwrapped packet  35  onto the top conveying branch of an output conveyor  72  forming part of a heat-shrink device  73  for heat treating overwrapped packet  35  to shrink sheet  3  of wrapping material about packet  2 .