Abstract:
A method and a device for producing and filling sacks with at least four longitudinal seams provide a more cost-effective approach to producing and filling sacks. The material that forms the sacks is supplied from an unwinding device in the form of a tubular material to a sack forming device. The tubular material is provided with longitudinal seams in the sack forming device, with the seams extending over a major part of the sacks.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a nationalization of PCT/EP2005/007157 filed 30 Jun. 2005 and published in German. 
   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The invention relates to a method and device for producing and filling sacks. The material that forms the sacks is supplied in the form of a tubular material from an unwinding device to a sack-forming device. The tubular material is separated into individual tube pieces in the sack-forming device and the tube pieces are transported by grippers during at least one part of their path in the sack-forming device. 
   2. Description of the Prior Art 
   Sacks are produced inter alia by so-called “Form, Fill and Seal” machines (referred to as FFS machines in the following). 
   These machines, which are shown inter alia in the patent specifications DE 199 33 486, EP 534 062, DE 44 23 964, DE 199 20 478 and DE 199 36 660, have unwinding devices, on which tubes are stored. The tube is unwound by these unwinding devices and separated into tube pieces. Usually, tube bottoms are formed, filling material is filled in the resulting sack and the sack is sealed in the additional work steps. The type of sack formation and filling shown in the afore-mentioned documents forms a part of the contents disclosed in this document. The same applies to the definitions of the term “Form, Fill and Seal” machines (FFS) provided in these documents and also to the transport of the film tubes, film sections and sacks into these machines. Usually bulk materials are filled using these machines. 
   As a rule, for the purpose of processing on the FFS machines, film tubes are formed by blown film extrusion, the format of the film tubes (here their circumference) corresponding to that of the formed sack. However, as a result of this approach, it is necessary to carry out expensive format changes at the extrusion systems with relative frequency in order to be able to realize different sack formats. Furthermore, the formats required for the sack formation, are relatively small and can be produced in a relatively uneconomic manner. Blown film extrusion systems of a larger format produce the same film at lower costs per unit of area. 
   Therefore, many a time attempts are made to produce initially very broad film webs by flat film extrusion or by blown film extrusion on systems of a large format, wherein usually blown film extrusion systems were preferred likewise primarily for reasons of economy. The resulting film tubes or film webs of large format were then processed further into flat film webs by cutting them in accordance with the format. 
   Subsequently, one of these laid flat film webs was folded together into a tube and joined by a longitudinal weld seam to form a tube. However, the use of the machines described is primarily limited to industrial applications, such as the bagging of dyes, plastic granulate, fertilizers and other bulk materials. 
   Consumer goods sold by retail are usually transported and distributed in sacks of a higher quality. It is thus known, for example, to produce side-gusseted bags or side-gusseted sacks from tube pieces, which are formed from several film sections. The edges of the respective film sections are usually heat-sealed to one another for this purpose. This procedure is carried out between welding jaws, which arrest the material to be heat-sealed during the welding process. 
   Tube pieces are usually produced in this way, the length of which corresponds to that of the sacks formed subsequently. In other cases, directly after production, the tube pieces formed are provided with the length of the sack formed subsequently and supplied individually to the sack-forming and filling devices. This type of forming high-quality sacks is well known, for example, in the field of pet foods. Here, emphasis is laid on side-gusseted sacks, which have edge seams on each of their outer folds. These sacks are rumored to have greater stability and a better appearance, in particular. These sacks are usually produced by initially producing a tube by the longitudinal welding of a flat film. This tube is separated into individual tube pieces and is provided with additional longitudinal weld seams. 
   However, both the transport of the individual tube pieces and the subsequent introduction of the latter into a sack-forming and filling process are complex. This usually takes place using rotary feeders or other suction devices, which grasp the tube pieces individually and supply them to the sack-forming device. Such suction devices are expensive and prone to faults. 
   SUMMARY OF THE INVENTION 
   It is therefore the object of the present invention to provide a more cost-effective method for producing and filling sacks as described herein. 
   This object is achieved
         by supplying the material that forms the sacks in the form of a tubular material from an unwinding device to a sack-forming device, and   by providing the tubular material in the sack-forming device with longitudinal seams, which extend at least over a large part of the sacks.       

   The term “seams” or “longitudinal seams” in this context is meant to connote a generic term for joining seams and all other seams, which also include the edge seams. It is not the function of the edge seams, in particular, to hold together the joining points of flat films like joining seams. The function of the edge seams consists in the described stabilization of the sack, which supports particularly the formation of an approximately cuboid shape in its filled state and thus facilitates the stacking of such sacks. 
   In order to now process the tubular material into sacks, it is advantageous to initially form sack bottoms using transverse welds. Transverse welds can be formed with particular ease on the material that is still tubular since this material can be grasped at different points by grippers or pliers or similar holding means. 
   For the same reason, it is recommended to also form longitudinal seams before the material is separated into individual tube pieces. The formation of the longitudinal seams can precede the formation of the transverse weld seams. In addition, the tubular material can be provided before or after the formation of the longitudinal seams, with diagonal welds, which form so-called corner welds on the sacks formed subsequently. Said corner welds further increase the stability of the sacks. 
   In an advantageous improved development of the invention, the sacks are also filled in the sack-forming device. A tube piece, which is held using holding means for the purpose of forming longitudinal seams or transverse seams, can be supplied by the same or additional holding means to a filling device. The time-consuming processes of depositing, storing and again gathering the tube pieces are thus omitted. Holding means designed advantageously as grippers carry out the transportation through the sack-forming device. The grippers can be present in pairs in each case, wherein they engage around the tube pieces laterally in the region of the upper edge. It may be necessary to deliver the tube piece from one pair of grippers to another. For this purpose, transfer positions are provided at which both the pairs of grippers hold the tube piece temporarily. The transport of the tube pieces or the sacks takes place in the horizontal direction at least for the first half of their path, i.e. in every movement of the tube pieces or the sacks the horizontal distance exceeds the vertical distance. 
   In the sack-forming device, the tubular material can be provided with longitudinal seams during the stop phases of the intermittent transport. Basically, longitudinal seams can also be applied during the transport of the tubular material. However, in the previous case, the longitudinal seams can be formed over different periods of time, which are indeed limited upwards by the reciprocal cycle speed, but are variable in other respects. If the longitudinal seams are formed, for example, using welds, then the weld time can be selected, for example, as a function of the material thickness. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional exemplary embodiments of the invention are specified in the present description and the claims. The figures underlying the present description show: 
       FIG. 1 : a device for producing and filling sacks, with which device the method according to the invention can be performed. 
       FIG. 2 : a cross-section of a tubular material, which was provided with longitudinal seams according to the inventive method. 
       FIG. 3 : a cross-section of another tubular material, which was provided with longitudinal seams according to the inventive method. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
   This device  1  comprises a supporting arm  2 , on which lies a roll  3  of tubular film  4 . The tubular film  4  has side gussets that are not illustrated. The transport rollers  5 , which can also be driven partially, ensure a usually continuous unwinding of the tubular film  4 . The lever  9 , which is provided with a load by a piston-cylinder unit  10  and which carries a deflecting roller  6  and is frequently referred to as dancer device when taken as a whole, and the transport roller  7 ,  8  and the pair of feed rollers  15  altogether ensure in a manner known per se that the tubular film  4  is moved further on its route of transport in a cyclically intermittent manner. In its further course, the tubular film  4  passes through a station  28  for applying longitudinal seams. Longitudinal seams are applied to the outer edges of the side gussets of the tubular film  4  in a manner that is not illustrated in detail, the working length of the station  28  being at least of the length of the sacks formed subsequently. The longitudinal seams are usually produced by applying the welds during the stop phases of the intermittent transport. The tubular film  4  provided with longitudinal seams is conveyed using additional transport rollers  8  to a corner weld station  11  and a cooling station  12 . 
   Using the pair of feed rollers  15 , the tubular film  4  is pushed through the welding jaws of a cross welding station  13  and through a cross cutting station  16 . The tools of the cross welding station  13  and the cross cutting station  16  can be moved toward and away from the tubular film  4  in a manner that is not described in detail here, for example, using a parallelogram arrangement  14 , in planes that are orthogonal to the feed direction of the tubular film  4 . After the grippers  17  have grasped the tubular film  4 , a tube piece  18  is cut off in the cross cutting station  16  from the tubular film  4  above the grippers  17 . Simultaneously, in the cross welding station  13 , a cross weld is added to the tubular film above its cut edge. This cross weld represents the bottom of the tube piece  18  to be formed in the next work cycle of the device  1 . The cross-weld is the preferred, though not the only option for creating the bottoms. Additional joining techniques, such as for example, gluing are also feasible. 
   The grippers  17  convey the tube piece  18  to a transfer point at which additional grippers  19  grasp the tube piece  18  and transport it to a filling station  20 . There the tube piece  18  is transferred to stationary grippers  21  and opened by the suction devices  22  so as to enable the filling material which is led by the filling pipe  23  to enter into the tube piece  18 . In doing so, the tube piece  18  lies with its lower end on a conveyor belt  24  so as to prevent it  18  from being loaded excessively along its longitudinal edges during the filling process. Additional grippers  25  convey the filled tube piece to the head seam welding station  26  in which the tube piece  18  is sealed with a head weld seam and it thus forms a finished sack  27 . It is also possible to use other joining techniques to seal the head region of the tube piece  18 . The finished sack is guided out of the device  1  by the conveyor belt  24 . 
     FIGS. 2 and 3  show cross-sections of tubular materials  4 , which were provided with longitudinal seams according to the inventive method. The material  4  shown in  FIG. 2  is usually produced as a tubular film and is wound up into a roll  3  after being provided with side gussets  30 . The tubular material  4  is provided with edge seams  29  on its outer edges  31  in the station  28  for the application of longitudinal seams. The tubular material  4  shown in  FIG. 3  differs from that  4  shown in  FIG. 2  in terms of a longitudinal seam  32 , with which both the edge regions of a flat film are joined to one another for the purpose of forming a tube. As a rule, this joining process is carried out by heat-sealing. However, other joining techniques such as sealing or the application of adhesives or hot melt adhesives are also used in practice. After such a formation of a tubular material  4 , which can likewise be provided with side gussets  30 , the tubular material  4  is wound up into a roll. 
   The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims. 
   LIST OF REFERENCE SYMBOLS 
   
       
         1  Device for producing and filling sacks 
         2  Supporting arm 
         3  Roll 
         4  Film 
         5  Transport roller 
         6  Deflecting roller 
         7  Transport roller 
         8  Transport roller 
         9  Lever 
         10  Piston-cylinder unit 
         11  Corner weld station 
         12  Cooling station 
         13  Cross-welding station 
         14  Parallelogram arrangement 
         15  Pair of feed rollers 
         16  Cross-cutting station 
         17  Gripper 
         18  Tube piece 
         19  Gripper 
         20  Filling station 
         21  Stationary gripper 
         22  Suction device 
         23  Filling pipe 
         24  Conveyor belt 
         25  Gripper 
         26  Head seam welding station 
         27  Sack 
         28  Station for applying longitudinal seams 
         29  Edge seams 
         30  Side gussets 
         31  Outer edges 
         32  Longitudinal seam