Abstract:
A method of gumming articles includes feeding a succession of articles along a feed path by means of a gumming unit having a conveyor for conveying the articles, and two gumming assemblies located on opposite sides of the conveyor to apply respective given quantities of adhesive to each article; supplying adhesive to an outlet of a nozzle of each gumming assembly by means of a respective pump and along an adhesive supply path extending between the pump and the outlet; applying a given quantity of adhesive to each article by means of each nozzle; and metering the quantity of adhesive by means of the pump.

Description:
[0001]    The present invention relates to a method of gumming articles.  
           [0002]    More specifically, the present invention relates to a method of gumming packets of cigarettes on a packing machine, to which the following description refers purely by way of example.  
         BACKGROUND OF THE INVENTION  
         [0003]    On known packing machines, a cardboard blank is folded about a group of cigarettes to form a packet of cigarettes. As it is being folded, various portions of the blank are bonded using adhesive applied beforehand to one of the portions for bonding.  
           [0004]    Applying adhesive to a solid support such as a blank is normally referred to as gumming, and cigarette packing machines comprise gumming assemblies for applying adhesive to the flat or, if necessary, partly folded blank. Of the gumming assemblies normally used on cigarette packing machines, a roller gumming assembly is known, which comprises a tank from which a roller draws and transfers adhesive to a blank fed along a path tangent to the roller. Gumming assemblies of this sort call for frequent cleaning and tend to apply a jagged strip of adhesive of uneven thickness.  
           [0005]    Other commonly used gumming assemblies on cigarette packing machines are spray guns, which emit small quantities of adhesive at high pressure through nozzles and in time with the blanks as they are fed past. Though successful in certain applications, spray guns have the drawback of failing to keep up with the increasingly fast traveling speed of the blanks on modern packing machines. In particular, the high pressure at which the adhesive is emitted means minute quantities must be transferred in a sequence determined by a valve, which, in turn, means a large number of small, closely spaced quantities of adhesive must be deposited to cover a given area of the blank. In other words, using spray guns, the faster the traveling speed of the blanks, the faster the metering valves must be activated. Moreover, using spray guns, the adhesive tends to drip and set into lumps at the nozzle outlet, thus possibly affecting the direction of the adhesive issuing from the nozzle, and even clogging the outlet.  
           [0006]    EP292299 discloses a gluing apparatus for use with a form collator for collating continuous sheets of paper. The collator has a framework  1 , a plurality of rollers extending transversely of the framework, each roller being driven by a main motor and having a pin wheel for advancing a continuous sheet of paper hung over the roller. The gluing apparatus is positioned opposite each sheet of paper and comprises a gear pump having an inlet connected to a glue reservoir through a hose and an outlet provided with a nozzle for applying glue to the paper. The gear pump is driven by a motor to skippingly or linearly apply glue according to input data of a programmable computer responsive to pulse signals received from an encoder arranged to sense advancing movement of the paper. In another embodiment, mechanical means such as a cam is provided to swing the gear pump towards and away from the paper.  
           [0007]    U.S. Pat. No. 4,787,332 discloses an improved adhesive dispensing pump control system for automatically changing the flow rate of adhesive materials being dispensed onto a workpiece in conformance with changes in movement of an automatically controlled adhesive dispensing nozzle used to apply adhesive materials automatically onto the surface of a workpiece in accordance with a predetermined pattern. In operation, the adhesive or other mastic dispensing pump control system operates to maintain substantially constant inlet and outlet pressure difference across the dispensing pump thereby making the system relatively insensitive to changes in viscosity of the adhesive being dispensed and allowing adhesives to be dispensed at relatively high pressures.  
           [0008]    EP709539 discloses an apparatus for double-sided coating of spacer frames for insulating glass panes with an adhesive sealant. The device coats the frame on both sides with sealing and adhesive material. Two nozzles facing each other are mounted close above a horizontal conveyor, and are supplied via a metering device. Each nozzle has its own gear pump, the two being driven in synchronism and drawing from a common tank. The latter can be connected to an adjustable pressure-generator, and between each pump and respective nozzle mouth there can be merely a short passage containing no valves. The pumps can have a reversible drive mechanism, this being electronically synchronised with the drive to the conveyor.  
           [0009]    U.S. Pat. No. 4,333,420 discloses a glue applicator for applying glue to a moving web is in the form of a gear pump having its housing in close proximity to the web and having a discharge nozzle adapted to discharge glue directly onto the web. The drive and the mount for the housing permit adjustable movement transversely of and normal to the web.  
         SUMMARY OF THE INVENTION  
         [0010]    It is an object of the present invention to provide a method of applying adhesive, designed to eliminate the drawbacks of the known state of the art, and which, at the same time, provides for fast, precise application of the adhesive and reduced maintenance.  
           [0011]    According to the present invention, there is provided a method of gumming articles, and which comprises feeding said articles along a feed path; supplying adhesive to an outlet of an adhesive application nozzle by means of a pump and along a supply path extending between the pump and the outlet; and applying a given quantity of adhesive to said article by means of said nozzle; the method being characterized by metering said given quantity of adhesive by means of said pump.  
           [0012]    The pump can be controlled rapidly and with very little inertia, and permits a greater adjustment range than a metering valve, which simply provides for permitting or preventing adhesive flow.  
           [0013]    The present invention also relates to a gumming assembly for applying a given quantity of adhesive to an article.  
           [0014]    According to the present invention, there is provided a gumming assembly for applying a given quantity of adhesive to an article fed along a feed path; the gumming assembly comprising an adhesive supply pump, and an adhesive application nozzle having an outlet; said adhesive being supplied to said outlet along a supply path extending between said pump and said outlet; and the gumming assembly being characterized by comprising no metering valves for metering said quantity of adhesive; said pump metering each given quantity of adhesive.  
           [0015]    The present invention also relates to a unit for gumming articles.  
           [0016]    According to the present invention, there is provided a gumming unit for gumming articles, comprising a conveyor for feeding a succession of articles, equally spaced with a given spacing, along a feed path; and at least one gumming assembly, as claimed in any one of claims 15 to 23, for gumming each article in said succession. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    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:  
         [0018]    [0018]FIG. 1 shows a plan view, with parts in section and parts removed for clarity, of a gumming unit for implementing the method according to the present invention;  
         [0019]    [0019]FIG. 2 shows a partly sectioned front view of the FIG. 1 unit;  
         [0020]    [0020]FIG. 3 shows a view in perspective of a packet formed using the method according to the present invention;  
         [0021]    [0021]FIG. 4 shows a view in perspective of a partly formed packet gummed in accordance with the method of the present invention;  
         [0022]    [0022]FIG. 5 shows a larger-scale section of a detail of the FIG. 1 unit. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Number  1  in FIGS. 1 and 2 indicates as a whole a gumming unit for applying adhesive to blanks  2 , each folded partly about a group  3  of cigarettes (FIG. 2), to form a packet  4  of cigarettes (FIG. 3). Blank  2  folded partly about group  3  of cigarettes forms, in fact, a packet  4   a  as shown in FIG. 4, and which differs from packet  4  in FIG. 3 by having two tabs  5  to be folded onto respective sides  6  of substantially the same size as respective tabs  5 . Packet  4   a  comprises a panel  7  defining the front wall of packet  4  and which is coplanar with and hinged to tabs  5  along two crease lines  8 ; and a panel  9  defining the rear wall of packet  4  and forming two right-angles and two edges  10  with sides  6 . As shown in FIG. 4, unit  1  provides for depositing two strips  11  of even thickness and a given shape onto sides  6  and at edges  10  of each packet  4   a.    
         [0024]    With reference to FIGS. 1 and 2, gumming unit  1  is substantially symmetrical with respect to a plane A of symmetry perpendicular to the FIG. 1 and  2  planes, and comprises a frame T; a conveyor  12  extending in a direction Dl to feed packets  4   a  along a path P; an adhesive supply circuit  13 ; and two gumming devices  14  located on either side of plane A of symmetry.  
         [0025]    With reference to FIG. 1, conveyor  12  comprises a belt  15  extending perpendicularly to plane A of symmetry and having pockets  16  equally spaced with a spacing PS along path P. Each pocket  16  houses a respective packet  4   a  so as to keep packet  4   a  in a given position with respect to conveyor  12  in direction D 1 , with sides  6  parallel to path P and freely accessible. Frame T extends beneath belt  15 , supports the two gumming devices  14  in rotary manner, and comprises a plate  17  located directly beneath belt  15  along a portion of path P at gumming devices  14  to prevent belt  15  from flexing at gumming devices  14 .  
         [0026]    Each gumming device  14  comprises a supporting member  18  and a gumming assembly  19 . Supporting member  18  is fixed, at one end, to a shaft  20  rotating with respect to frame T about an axis  21  parallel to plane A, and comprises, at the opposite end, an adjustable stop  22  cooperating with plate  17 . Each supporting member  18  is also connected to frame T by a spring  23 , which pushes stop  22  against plate  17  to define a given position of respective gumming device  14  with respect to conveyor  12 . Supporting member  18  also comprises a guide  24  for adjusting the position of each packet  4   a  inside respective pocket  16  in a direction D 2  perpendicular to direction Dl. Each gumming assembly  19  comprises a cylindrical body  25  having an axis  26  parallel to axis  21 , and which is fixed to a respective supporting member  18 ; electric resistors  27  and a gear pump  28  housed inside body  25 ; a reversible brushless servomotor  29  for powering pump  28 ; and an adhesive application nozzle  30  having an outlet  30   a . Each body  25  comprises an annular groove  31 ; a channel  32  parallel to axis  26 ; a radial channel  33  connecting annular groove  31  and channel  32 ; and a further L-shaped channel  34  between pump : 28  and nozzle  30 .  
         [0027]    Pump  28  comprises two gears  35  and  36  meshing with each other between channel  32  and channel  34 .  
         [0028]    Gear  35  is integral with a shaft  37  having an axis coincident with axis  26  and connected to servomotor  29 ; and gear  36  rotates about an axis  38  parallel to axis  26 .  
         [0029]    Supply circuit  13  is the only asymmetrical part of unit  1  with respect to plane A of symmetry, and comprises a ring  39  fitted hermetically to body  25  of one gumming assembly  19 , and a ring  40  fitted to body  25  of the other gumming assembly  19 . Rings  39  and  40  are located at annular grooves  31  of respective gumming assemblies  19 , and rotate about respective gumming assemblies  19  and respective axes  26 . Ring  39  has, on one side, a fitting  41  connectable to a supply conduit  42 , and, on the opposite side, a fitting  43  fitted in sliding manner to a straight pipe  44 . Ring  40  differs from ring  39  by having only one fitting  45  similar to fitting  43  and fitted in sliding manner to pipe  44  as shown in FIG. 2.  
         [0030]    Gumming unit  1  is controlled by a control unit C shown schematically in FIG. 2 and which receives a signal V related to the traveling speed of conveyor  12 , and a signal S related to the presence of packets  4   a  in pockets  16  of conveyor  12 . Both signals V and S are received from respective known sensors not shown, and control unit C also controls activation of servomotors  29  on the basis of the incoming signals V and S.  
         [0031]    In actual use, gumming unit  1  provides for applying both hot and cold adhesive. If hot adhesive is used, electric resistors  27  heat body  25 , in which channels  32 ,  33 ,  34  are formed and which houses pump  28 , and heat is transmitted from body  25  to nozzle  30 . Adhesive is supplied by supply conduit  42 , which feeds the adhesive along fitting  41  of ring  39  to groove  31  of the first gumming assembly  19 , and along fitting  45  of ring  40  to annular groove  31  of the second gumming assembly  19 . Pipe  44  and fittings  43  and  45  of respective rings  39  and  40  connect the annular grooves  31  of first and second gumming assemblies  19 .  
         [0032]    The position of each gumming assembly  19  is adjustable, as a function of the position and width of packets  4   a , by means of adjustable stops  22 , which define a given position of supporting members  18  and, hence, of nozzles  30  with respect to conveyor  12 . Rings  39  and  40  rotate about respective bodies  25 , and are connected telescopically to each other by pipe  44  to adjust bodies  25  and adapt the shape of circuit  13  to the position of bodies  25 . The purpose of the adjustment is to achieve the best distance between outlets  30   a  of the two nozzles  30  as a function of the width of packets  4   a , so that each packet  4   a  can be fed between the two nozzles  30  with sides  6  at such a distance as to receive a thin, even layer of adhesive.  
         [0033]    The distance between outlets  30   a  of nozzles  30  is also determined as a function of the clearance between sides  6  and respective outlets  30   a , which clearance in turn depends on the viscosity of the adhesive used and the pressure at which it is applied.  
         [0034]    Once the distance between outlets  30   a  of nozzles  30  is adjusted, packets  4   a  are fed along path P in direction D 1 , and are positioned by guides  24  in direction D 2  so that sides  6  of each packet  4   a  are the same distance from plane A of symmetry.  
         [0035]    Packets  4   a  are fed continuously by conveyor  12  along path P in an orderly succession and equally spaced with spacing PS, and each nozzle  30  applies, synchronously with the passage of each packet  4   a , a respective continuous strip  11  of adhesive of length L onto side  6  and at edge  10  of each packet  4   a . That is, each nozzle  30  alternates between a work period in which a given quantity of adhesive is emitted and applied, and a rest period in which no adhesive is emitted by the nozzle. The duration of the work and rest periods depends on the traveling speed of conveyor  12 , on spacing PS, and on the length L of the strip  11  of adhesive to be applied. Each pump  28  is powered by respective servomotor  29 , which is controlled by control unit C as a function of signals V and S, length L of the strip  11  of adhesive to be applied, and spacing PS.  
         [0036]    Servomotor  29  is reversible, so that pump  28  can be operated in two opposite directions. When servomotor  29  is operated in a first direction, pump  28  delivers adhesive through nozzle  30  and creates a slightly higher than atmospheric pressure at outlet  30   a  of nozzle  30  to expel the adhesive from nozzle  30 . Conversely, to cut off adhesive flow through outlet  30   a , servomotor  29  is operated in a second direction opposite the first, to create a slight vacuum at outlet  30   a  of nozzle  30  and suck the adhesive projecting from outlet  30   a  of nozzle  30  back into nozzle  30 , as shown clearly in FIG. 5, in which the continuous line shows the free edge of the adhesive projecting from outlet  30   a  of nozzle  30 , and the dash-and-dot line shows the edge of the adhesive sucked back into nozzle  30  as a result of the vacuum formed by pump  28 .  
         [0037]    In other words, pump  28  meters the amount of adhesive to be applied to packet  4   a , with no need for a valve between pump  28  and nozzle  30 , and provides for sucking the adhesive projecting from nozzle  30  back into nozzle  30 .  
         [0038]    The adhesive is applied by spreading the portion of adhesive projecting from the nozzle towards the packet  4   b  traveling past nozzle  30 .  
         [0039]    Pump  28  is oversized with respect to the amount of adhesive expelled to form strip  11 , so that, to expel strip  11 , pump  28  need only be rotated at relatively low speed. For example, rotated at a few tens of revolutions per minute in the first direction, pump  28  produces a pressure of a few tens of bars at gears  35  and  36 , and a slightly higher than atmospheric pressure at outlet  30   a  of nozzle  30 . Similarly, rotated at the same speed in the second direction, pump  28  creates a slight vacuum at outlet  30   a  of nozzle  30 . The low rotation speed of pump  28  therefore enables the rotation direction of pump  28  to be inverted, on account of the relatively low forces of inertia involved, and the adhesive pressure to be varied between values above and below atmospheric pressure.  
         [0040]    Pump  28  and outlet  30   a  of nozzle  30  are located close to each other. That is, since the pressure and vacuum generated at outlet  30   a  depend on the length L 1  of the path P 1  of the adhesive between pump  28  and outlet  30   a , the smaller the length L 1  of path P 1  is, the more efficient pump  28  is in varying the pressure at outlet  30   a . Consequently, length L 1  of path P 1  of the adhesive between pump  28  and outlet  30   a  is the minimum compatible with the construction requirements of gumming assembly  19 . The rotation direction of each brushless servomotor  29  can therefore be inverted extremely rapidly to suck back the part of the adhesive already issuing from nozzle  30  but not yet applied to side  6  of packet  4   a , thus preventing smears and the formation of lumps of dried adhesive integral with the end of nozzle  30 .