Abstract:
For the continuous formation of bags for containing bulk materials--in the form of granules, powders and the like--the end of the web (EN), from a new bobbin (BA) in readiness, is laid, with the surface to be welded on the outside, around a welding bar (18) carried by a movable element (12), and the bar (18) is positioned opposite a counterbar (20), along which the web (N) being exhausted from the previous bobbin (B) runs; bar and counterbar are brought close to one another to carry out transverse welding and cutting, in such a manner that a superimposed and welded edge (BS) emerges transversely from the continuous web thus joined, from the surface opposite that of welding. (FIG. 2)

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to a method and an apparatus for making a joint between ends of webs made of weldable material, intended for the formation of bags for containing bulk material in general, and in particular (but not exclusively) food products in grains or small pieces or in the form of powder. The webs in such cases are expediently to be welded by means of corresponding surfaces, that is to say the two surfaces intended generally to be internal or the two surfaces intended to be external in the finished bag. In the two bobbins--that being exhausted and the new one--such surfaces are oriented in the same direction. 
     SUMMARY AND OBJECTS OF THE INVENTION 
     The invention makes it possible to carry out rapidly cutting and welding of the ends to be joined, in the correct mutual position. These and other aims and advantages will become clear from the following text. 
     A first subject of the invention is a method for joining ends of webs of material made of weldable film, as indicated above. According to this method, the end of the web, from a new bobbin in readiness, is laid around one of the two components of a transverse welding group, with the surface to be welded on the outside. The other of the two components is brought close to the surface opposite that to be welded of the web being exhausted from the previous bobbin, and the two components of the welding group are brought close to one another in order to carry out transverse welding and cutting, in such a manner that a superimposed and welded edge emerges transversely from the continuous web thus joined, from the surface opposite that of welding. 
     A further subject of the invention is an apparatus for making a joint between ends of webs made of film of weldable material, which essentially comprises a combination of: 
     a work position for a first, unwinding bobbin, and a position of readiness for a second bobbin arranged for replacement; 
     guide means for the web unwinding with a trajectory not far from the second bobbin; 
     a movable element with a bar for transverse welding, constituting a first of the two components of a welding group, capable of being displaced adjacently to the second bobbin and of receiving from it, laid around the bar itself, the end with the weldable surface on the outside and turned towards the weldable surface of the web unwinding along the trajectory; 
     an opposing bar or counterbar, constituting a second transverse bar component, arranged on the side opposite the bar, in relation to the trajectory of the unwinding web; 
     and means for bringing close the bar and the counterbar in order to weld and to cut transversely the double thickness of web material situated between them. 
     The movable element can be developed in the form of a portal with arms articulated about an axis parallel to the axes of the bobbins and connected by said the bar. The bar, in a position removed from that of welding, positions itself to receive the end of the second bobbin in the position of readiness with the weldable surface on the outside. 
     The counterbar also can be movable towards and away from the trajectory of the web, synchronously with the bar. 
     The apparatus can comprise guide means between the two positions of readiness and of work, for the transfer of a bobbin to the work position, after lowering of the bar element in the space between said guide means. 
     The invention will be understood more clearly by following the description and the attached drawing, which shows a non-limiting exemplary embodiment of the invention itself and in which: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1, 2, 3 and 4 show diagrammatically a vertical longitudinal cross-section of the machine in four successive stages of a cycle of operation for replacement of the bobbin and joining the webs, and 
     FIG. 5 shows a detail of the bar and the counterbar for welding. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to what is illustrated in the attached drawings, a structure 1 forms a seat 3 for a position of readiness and a seat 5 for a work position. The latter at least being defined by rotary rollers 5A, on which the hub M of a bobbin in the work position can rotate for the distribution of the web N towards the utilization, and in particular towards a packaging machine for the formation of bags which--immediately after formation--are filled with bulk material (such as food products), then to be closed, in particular welded. Between the position 3 and the position 5, the structure 1 forms guide means 7 which can be sliding means--with chain drive--for maning the projecting ends of the hub M of the bobbin B. Elements 9A, 9B, 9C indicate some of the guide means for the web N which is fed from the bobbin B and made to run along a trajectory T towards the packaging machine or other utilization. 
     A second bobbin BA, which is to replace the first bobbin B after the latter has been exhausted, can be positioned in a position of readiness 3. The final end of the web of the first bobbin B and the beginning of the web of the second bobbin BA, which is in the position of readiness, are to be welded to one another. 
     Webs of film, which are especially intended for the packaging of food products or the like, generally have an internal surface which is weldable and an external surface which generally is not, or is not easily, weldable. The apparatus forming the subject of the invention makes possible welding between the weldable surfaces of the web which are generally the internal surfaces of a bag and which in any case are the surfaces of the web which are turned towards the bobbin and for example, therefore, the lower surfaces of the web N unwinding from the bobbin B in FIG. 1 and, correspondingly, the surface which faces the bobbin of the end EN of the web of the second bobbin BA in the position of readiness (see FIG. 2). 
     In order to carry out welding with rapid operation between the end of the web of the bobbin B being exhausted (see FIG. 2) in the position 5 and the front end EN of the web of the second bobbin BA in the position of readiness 3, the apparatus described below is provided. 
     This apparatus comprises an element 12 which is movable angularly about an articulation 14 with an axis parallel to the axis of the bobbins B and BA. The movable element 12 is developed in the form of a portal with arms 16 articulated at 14 and a bar 18 which connects the movable ends of the portal structure of the element 12 and which constitutes one of the two components of the welding group. The element 12 is capable of being displaced from a lowered position 18X below the guides 7 to a raised welding position, passing between the two guides 7 which support the hub M of the bobbin during the transfer between the two positions. The element 12 can be considered a movement means of the first component of the welding group. 
     The other component of the welding group comprises a counterbar 20 which is carried by arms 22 articulated at 24 about an axis which is also parallel to the axes of the bobbins installed in the positions. The entire counter bar 20 and arms 22 assembly is controllable by means of an actuator, for example 25. In relation to the trajectory T of the unwinding web, which is defined by the guide means 9A, 9B, 9C or equivalents, the two components of the welding group (12, 16, 18 and 20, 22, 24 respectively) are situated on opposite sides and can be displaced into the active position of approach of the bar 18 to the counterbar 20 as shown in FIG. 3, reaching beforehand the almost contraposed position shown in FIG. 2. 
     In the state indicated in FIG. 1, the first bobbin B in the work position 5 unwinds the web which is drawn expediently along the trajectory T. The positions of readiness 3 is available to receive a second bobbin BA to be arranged to continue the distribution essentially continuously. The front end EN of the web on the bobbin BA, located in the position of readiness 3, is wound around the bar 18 which is situated in the lowered position 18X of readiness as shown by way of indication in FIG. 2 in FIG. 1. The arrangement of the end EN on the bar 18 can also be carried out after raising from the position 18X to the position shown. When the first bobbin B is being exhausted as shown in FIG. 2, the element 12 is raised from the position in FIG. 1 to the position in FIG. 2 so as to bring the welding bar 18 from the position 18X to the position shown in FIG. 2 which is essentially contraposed to the counterbar 20. The end EN wound on the bar 18 has its welding surface facing the welding surface of the web N coming from the bobbin B. By bringing the counterbar 20 close to the bar 18, and possibly with a corresponding displacement of the guide means 9A and 9B, the welding and the cutting is brought about of the double thickness of material which remains between bar and counterbar. As can be seen in particular in FIG. 5, the active welding portion of the bar 18 is that indicated by 18S, while 20S indicates the corresponding active welding part of the counterbar 20. The latter also comprises a cutting blade 20L which at the right time brings about the cutting of the two thicknesses upstream of the weld carried out by the portions 20S, 18S, in relation to the direction of displacement of the web. As a result, the double thickness of the edges welded to one another, which are adjacent to the cut effected by the blade 20L, is capable of ensuring the continuity of the final end of the web coming from the bobbin B and the beginning of the web coming from the bobbin BA. From the welding condition indicated by FIG. 3, distribution is brought about from the bobbin BA. The front end EN of the web on bobbin BA is welded by means of the double welding edge BS to the end of the web previously unwound from the bobbin B, the residue of the weld id discarded. 
     From the state in FIG. 4, the state in FIG. 1 is reached, having brought about the disposal of the empty bobbin from the work position 5 and the displacement of the bobbin BA from the position 3 of readiness to the work position 5 by sliding or rolling along the guide means 7. The state in FIG. 1 is thus reached once again with a replaced bobbin. 
     It is clear that it is possible by means of this arrangement to bring about essential continuity in the distribution of the web upon replacement of an exhausted bobbin by a new bobbin. This apparatus is particularly suitable for the uses mentioned above. 
     It is intended that the drawing only show an exemplary embodiment which is given only by way of practical demonstration of the invention, it being possible for the invention to vary in form and arrangement without moreover leaving the scope of the idea which forms the invention itself. Any presence of reference numbers in the enclosed claims has the purpose of facilitating reading of the claims with reference to the description and to the drawing, and does not limit the scope of protection represented by the claims.