A device for the proper and free stacking of welded bags in a welding machine

Abstract: A device for the proper and free stacking of welded bags in a welding machine (11), wherein the welding machine comprises at least a pair of opposed rolls (13) which feed a plastic tubular material (12), an upper welding device (15) and a lower welding device (16) which cooperate to execute the transverse welding of the plastic tubular material (12), a support (20) for stacking the welded bags (21) as they come out from the two welding devices (15, 16), said support (20) is positioned downstream of the welding devices and it carries needles (22) on which the bags (21, 21') are steadily positioned by means of a small upper press (23), said device comprises a driven transverse displacement element (25) which acts on the single bag (21') to be welded, and causes the backing of one of the free front end (27) of the bag, said displacement element (25) is positioned between the two welding devices (15, 16) and the support (20) and it acts every second bag, in order to displace one bag from the next one (21, 21').

Description: The present invention refers to a device for the proper and free stacking of welded bags in a welding machine, in particular said device avoids sticking between the welded portions of the surfaces. In the manufacturing process of bags, obtained from plastic tubular material or the like, welded either at one end, the so called "open mouth" bags, or at both ends, it has been more and more frequently used the operation of stacking said bags, coming directly from the welding transverse bars, on a support provided with needles. In fact, instead of providing transportation means to carry away the single bags, there are provided suitable stacking supports having needles sufficiently thin to firmly position the just welded bags. Currently, because of the high working speeds of the modern welding machines for thermoplastic materials, the weld lines, or more simply the weldings, along the transverse direction (which have been executed on the bags or on the bag tubular material) are still hot when the bags are stacked together. During said stacking phase on said needles, said weldings, still hot, get in contact with each other during the stacking phase and there is, easily, a gluing activity among the bags. This fact causes several problems to the bag users since it is necessary to separate one bag from the other along such glued areas. The separation, besides causing an effective loss of time to the final user, might cause the partial breaking of the welding. As a consequence, the bag or the bags involved in such gluing, even though just locally, might not be utilised any more. Further, a broken bag may not appear as such, but, when carrying a certain weight, the welding breaks and the bag content falls down. The conclusion is that a welding machine, without a suitable and proper solution to the problem of accidental gluing of the bags along the transverse weld lines, will not be sufficiently competitive. In fact, such a machine should work at a lower rate of production in order to allow the cooling of the bags while they are stacked together so that they do not stick to each other. Such a solution is proposed in US-A-5 312 317. An alternative solution to the low production rate has been obtained by realising a support for the stacking of the welded bags which is movable back and forth along the transport direction of the bags, i.e. back and forth horizontally in relation to the bags which are progressively welded. This fact leads to a stacking on the needle support with a displacement of the end edges of the bags, i.e. a phase displacement thereof. This alternate positioning of the edges and therefore of the displaced transverse weld lines of one bag in respect to the preceding one as well as the next one, avoids the gluing between consecutive bags. The preamble of claim 1 is based on this prior art. However, such a solution requests the realisation of a special support swinging back and forth in respect of each bag and of a special driving device able to act whenever a bag is welded. Therefore, the support has to follow this quick succession of operations, even in presence of significant inertial masses. Further, the alternate motion run has to be adjusted according to the changes in length of the bag which is being manufactured. Therefore, the welding machine has to have a certain construction complexity downstream of the welding system, i.e. in the stacking support area. A purpose of the present invention is to find a solution that, besides solving the previously shown and outlined technical problem will realise a welding machine as simple as possible. Another purpose is to realise a device that avoids a complicate construction, by minimizing the masses and the elements in motion, and nonetheless able to fully reach its required working features. Another purpose is to reduce to the minimum all the necessary adjustments, even in presence of a very simple assembly, therefore achieving a low construction and assembly costs. These and other purposes, according to the present invention, are attained by a device for the proper and free stacking of welded bags in a welding machine, wherein the welding machine comprises at least a pair of opposed rolls which feed a plastic tubular material, an upper welding device and a lower welding device which cooperate to execute the transverse welding of the plastic tubular material, a support for stacking the welded bags as they come out from the two welding devices, said support is positioned downstream of the welding devices and it carries needles on which the bags are steadily positioned by means of a small upper press, characterised in that said device comprises a driven transverse displacement element which acts on a bag to be welded, and causes the backing of the free front end of this bag, said displacement element is positioned between the two welding devices and the support and it acts on every second bag, in order to displace one bag from the next one, such that there is alternate positioning of the welded edges. By means of a device according to the present invention, an embodiment is very easily obtainable since it is made of elements suitable for a simple construction and assembly, such elements are even commercially available. Further, such a device is quickly adaptable to any kind of application. Such a device has construction and drive advantages since it works every two bags. Such a device will be easier to drive and it will work at lower speeds than the previous devices. Such a device will not require very sophisticated materials. The functional and structural features and the advantages of a device according to the invention will be better understood by way of a non limiting example, making reference to the accompanying schematic drawing. In fact, the drawing shows a schematic front elevation view of a device according to the invention which is applied to a welding machine for the production of welded bags, shown in its welding arrangement. In the drawing, a full line indicates an extended bag, without the intervention of the device of the present invention; meanwhile a chain (dash and dot) line indicates a bag on which an intervention is performed by the device of the present invention. With reference to the drawing, a possible embodiment of a portion of the welding machine is shown (indicated by reference numeral 11), wherein a tubular material 12 is fed, having a flattened shape and being devoted to the bag production. The type of the welding machine is of no relevance for the application of this invention, since this new device is built so that it can be applied to any welding machine, even to existing and already working machines. The welding machine 11 generally comprises a pair of opposed rolls 13 which feed the material 12, nozzles 14 associated to such rolls to feed air in order to maintain the material fed through the rolls 13 in a flat position. An upper welding device 15 and a lower welding device 16 cooperate to execute the transverse welding of the tubular material and said devices have a cutting blade 17 which works between two weld lines realised by the welding devices when they engage. A swivel 18 is positioned downstream of the two welding devices 15 and 16 , said swivel, by means of transverse bars 19, moves downward the welded bag ends. Further downstream, a support 20 is positioned in order to stack the welded bags 21, 21' coming out from the welding devices 15 and 16. The support 20 carries needles 22 (just one is shown) whereon the bags 21, 21' are steadily positioned by means of a small upper press 23. The bags 21 are indicated by a full line and the bags 21' are indicated by a chain line. Some of the bags 21, 21' lay on a table or on a similar element 24 and some of the bags are hanged to and dangle from the needles 22 of the support 20, moved downward thanks also to the action of the bars 19 of the swivel 18. According to the present invention, a specific device is positioned between the two welding devices 15 and 16 and the support 20 for the stacking of the welded bags 21, 21' in order to realise the proper and free stacking of welded bags in a welding machine. In fact, this device avoids the gluing of consecutive bags along the still hot weld lines. In particular, a pushing element 25 will be provided and it will be driven downward or upward, being positioned above or below a bag 21', by means of an actuator 26, as a cylinder or the like. In fact, the pushing element 25 pushes only the bags 21', indicated by a chain line, which have to be displaced in respect to the bags 21 which are stacked without any displacement. The pushing element 25, shaped as a plate or as a roll, works as a transverse displacement element of the single bag 21' to be welded, and said element 25 pushes an intermediate area of the bag and causes the backing of the free front end 27 of the bag positioned on the table 24. The needles 22 of the support 20 penetrate into the bag 21' in a displaced position, towards the center of the bag, in respect to the penetration area of the preceding bag 21. In this way, when the bag 21' welded also in its back free end 28, is released by the two welding devices 15 and 16, this end falls downward below the corresponding end of the preceding bag 21. It is understood that the device according to the present invention will have to work every two bags in order to displace two consecutive bags. According to this simple arrangement, the problem, due to the accidental gluing along the weld lines of two consecutive bags welded at high speed, is solved. It is therefore evident that, according to the present invention, a new and innovative technical solution to the problem of the gluing between the weld lines of consecutive bags has been found in a simple and easy way.

Claims: A device for the proper and free stacking of welded bags in a welding machine (11), wherein said welding machine comprises at least a pair of opposed rolls (13) which feed a plastic tubular material (12), an upper welding device (15) and a lower welding device (16) which cooperate to execute the transverse welding of the plastic tubular material (12), a support (20) for stacking the welded bags (21, 21') as they come out from the two welding devices (15, 16), such support (20) is positioned downstream of the welding devices and it carries needles (22) on which the bags (21, 21') are steadily positioned by means of a small upper press (23), characterised in that said device comprises a driven transverse displacement element (25) which acts on a bag (21') to be welded, and causes the backing of the free front end (27) of this bag, said displacement element (25) is positioned between the two welding devices (15, 16) and the support (20) and it acts on every second bag, in order to displace one bag from the next one (21, 21'), such that there is alternate positioning of the welded edges. A device according to claim 1, characterised in that said displacement element is a pushing element (25), driven by a corresponding actuator (26). A device according to claim 1, characterised in that close to said displacement element (25) there is a swivel device (18) which, by means of transverse bars (19) moves downward the welded back ends (28) of said bags (21, 21'). A device according to claim 1, characterised in that said transverse displacement element (25) is movable upward. A device according to claim 1, characterised in that said transverse displacement element (25) is movable downward.

Inventors: DRAGONI FRANCESCO, LUONI AGOSTINO, DRAGONI, FRANCESCO, LUONI, AGOSTINO
Applicants: ELBA SPA, ELBA S.P.A.
Application year: 1998
Main classification: B31B19
IPC codes: B31B19