Abstract:
Devices for cross-welding or cross-separating welding plastic films ( 2 ) are used in a manner known per se in machines for producing bags, said devices comprising a welding roller ( 3 ) and a heated welder terminal ( 4 ) which can be moved reciprocally and between which the plastic films ( 2 ) are guided for welding. According to the invention, the welding roller ( 3 ) is covered by a continuous belt ( 5 ).

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to a device for the cross-welding or the cross-separation welding in the production of bags, pouches and the like from plastic film on a bag-making machine according to the preamble of claim  1 .  
         STATE OF THE ART  
         [0002]    It is known in practice to provide machines of the transverse welding or cross-welding or for the transverse separation welding or cross-separation welding of plastic films. In these cases at least two superposed horizontal films are welded together. While this can apply as well to a single film which is folded in a longitudinal direction and thus lies doubled up, in the following description, at least two plastic films will always be referred to.  
           [0003]    Note further that additional film layers can be welded during the welding operation so that three film layers or more can lie one above another during a welding process.  
           [0004]    When the weld seam is to extend transversely to the travel direction of the plastic film, one can speak of transverse welding or cross-welding. When the cross-welding occurs simultaneously with separation of bag or a pouch from the remainder of the film, in this weld process, one is dealing with a transverse separation welding or cross-separation welding.  
           [0005]    In the publication DE 19 10 598 A1, a cross-welding, especially a cross-separation welding is described. The welding device is comprised basically of a heated welding beam and a welding roll or drum. The films to be welded are disposed between the welding drum or roll and the welding beam. For welding, the welding beam is pressed against the welding roll. The welding roll is preferably rubber jacketed.  
           [0006]    Since in the welding of plastic film the heated plastic can adhere to the welding roll and the welded bag and/or the welded plastic film can remain hanging on the welding roll, the fabrication process can be disturbed. For that reason, the welding roll is coated on its surface with PTFE (teflon) [polytetrafluoroethylene]. The PTFE has not only good slidability properties but also a limited adhesion. For that reason only no plastics remain adherent to the PTFE even if they are heated by welding.  
           [0007]    As the heated welding beam is lowered onto the plastic foils during the welding process, its welding edge presses somewhat into the PTFE backing and into the rubber jacket lying therebelow and which, for example, is composed of a silicone. When the welding beam is withdrawn after the welding process again from the welding rolls, the rubber jacket and the PTFE backing spring back. It has however been found that with the passage of time the PTFE backing can develop folds. The result is a reduction in the quality of the weld seams and a reduction in the life of the welding beam. Because of the fold formation in the PTFE, the PTFE backing which is adhesively bonded to the jacket becomes loose and must be replaced by a new one. This gives rise to production interruptions which are associated with cost.  
         DESCRIPTION OF THE INVENTION  
         [0008]    It is therefore an object of the invention to provide a device for cross-welding or for cross-separation welding which avoids the drawbacks of the state of the art or reduces them.  
           [0009]    This object is achieved with the characterizing features of claim  1 . Advantageous refinements are given in the dependent claims and the description of the Figures.  
           [0010]    According to the invention no backing which ensheathes the welding roll is required on the welding roll but a continuously traveling belt rests upon the welding roll. It has been found that in this way the fold formation can be reduced and the quality of the weld seams improved.  
           [0011]    Additionally it is advantageous that the belt according to the invention does not have to be replaced as often as with the ensheathing backing or jacket with the state of the art.  
           [0012]    It is advantageous when the belt is composed at least on its outer surface of PTFE (teflon). In this manner the heated plastic is readily released or does not adhere to the belt initially.  
           [0013]    Since the welding roll on its outer diameter has a rubber/silicone jacket and exactly this outer surface contributes to stiffness, the welding roll may have insufficient bending strength especially when it is required to span large working widths. The inner metallic core of the weld roll is then not able to provide support with sufficient bend stiffness. The welding pressure of the welding beam upon the welding roll can then produce a nonparallel welding gap. In an advantageous configuration of the invention, the welding roll is supported by a bracing roll along its side opposite the press gap. In this manner a possible bending of the welding roll is counteracted.  
           [0014]    The welding roll and the bracing roll are journaled at their ends in bearing plates and guided therein so that these bearing plates will always maintain a defined parallel position with respect to one another by means of a traverse. The traverse is disposed in the loop of the belt which is advantageous since it utilizes the space available in the loop.  
           [0015]    An a advantageous refinement of the invention is also the arrangement of a bracing or backup roll in the loop of the belt whereby the bracing roll is arranged substantially parallel to the welding roll [parallel axes]. This bracing roll holds the belt taut so that no folds or irregularities can be formed in the belt. In addition, the belt is reliably guided by the bracing roll. In order to hold the belt taut, even with an increase in its length in the peripheral direction, it is advantageous for the bracing roll to be spring-loaded. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0016]    The invention is described in the following in greater detail based upon FIG. 1. It shows:  
         [0017]    [0017]FIG. 1 a cross section through a welding tool. 
     
    
     MODE OF CARRYING OUT THE INVENTION  
       [0018]    In FIG. 1 a welding tool  1  can be seen for the cross welding or cross separation welding. A welding beam  4  and a welding roll  3  are the significant components of the welding device  1 . During the welding, plastic foils are enclosed between them. In the embodiment shown the welding beam has a movement  12  from top to bottom and the reverse. In another configuration of the invention, the welding roll  3  can also be moved against the welding beam  4 .  
         [0019]    According to the invention, the welding roll  3  is looped by a belt  5 . The belt  5  lies upon a silicone jacket  11  of the welding roll  3 .  
         [0020]    The belt  5  is endless and is formed without abutting edges and constitutes therefore an endless loop. For guiding and tensioning the belt  5 , within the loop a pair of tensioning rollers  6  are provided in parallel-axis relationship in the loop. Preferably a belt of PTFE (teflon) which has been reinforced with fibers or with a fabric of glass or aramid, is used.  
         [0021]    To brace the welding roll  3 , a packing roll  7  is disposed along its side opposite that provided with the welding beam  4  and which rolls in the opposite rotational sense against the welding roll  3 . The backup or bracing roll  7  is journaled in bearing plates, not shown here, like the welding roll  3  and the belt-tension rolls  6 . With a predetermined pressing of the backup or  
         [0022]    bracing roll  7  against the welding roll  3 , it can be ensured that the welding gap will remain parallel during the pressing of the welding beam against the welding roll  3 .  
         [0023]    Within the loop of the belt  5  a traverse  8  is also disposed. This traverse  8  interconnects the bearing plates which have here not been shown. To enable the traverse  8  to provide as much stiffness as possible, the right upper corner and the left upper corner of the traverse  8  are extended upwardly. To increase the stiffness of the traverse  8  it is also conceivable to extend the left lower and the right lower corners downwardly.  
         [0024]    In the welding of plastic film, plastic residues can remain suspended from the belt  5 . For this reason a beltper is provided in the form of a beltping blade  15  forming part of a wiper arrangement  9  juxtaposed with the belt  5 . The wiper blade  15  contacts the belt  5  in an unsupported region so that the belt  5  can yield under the pressing force of the wiper blade  15 .  
         [0025]    Since the belt  5  can yield in the peripheral direction under the mechanical and/or thermal stresses, the belt  5  is tensioned by means of a tension roller  5 . It is advantageous to spring-load the bearings of the tension roller  6 , for example by a coil spring or a pneumatic cylinder. In that case a manual adjustment of the tension roller  6  by service personnel is rendered superfluous.  
         [0026]    In FIG. 1 the belt  5  has a brush device  10  juxtaposed therewith. This brush device  10  is formed as a brush roller. By rotation of the brush roller possibly adhering plastic residues can be better removed from the surface of the belt  5  than when the brush arrangement  10  is only a stationary brush element.  
       Reference Character Listing  
       [0027]    [0027] 1  Welding apparatus  
         [0028]    [0028] 2  Plastic film  
         [0029]    [0029] 3  Welding roller  
         [0030]    [0030] 4  Welding beam  
         [0031]    [0031] 5  Belt  
         [0032]    [0032] 6  Tension roller  
         [0033]    [0033] 7  Backing roller  
         [0034]    [0034] 8  Traverse  
         [0035]    [0035] 9  Stripping wiper  
         [0036]    [0036] 10  Brush device  
         [0037]    [0037] 11  Silicone jacket  
         [0038]    [0038] 12  Movement of the weld beam  
         [0039]    [0039] 13  Travel direction of the belt  
         [0040]    [0040] 14  Tensioning path of the belt  
         [0041]    [0041] 15  Wiper blade  
         [0042]    [0042] 16  Direction of movement of the plastic film  
         [0043]    [0043] 17  Drawing break line