Device for sealing bags or packages of heatsealable plastics material provided with parts for regulating the welding pressure

Abstract: A device for sealing bags or packages in a heat-sealable plastic material containing a predefined portion of product, wherein a tubular strip is longitudinally fed and filled while said sealing device, by welding the opposite edges of said tubular strip, defines a plurality of packages individually containing said predetermined portion of product, said sealing device comprising two welding plates or elements (18) transverse to said strip and opposite one to the other and which are carried by a respective mobile support element (20). Between each of said welding elements and the respective mobile support at least a first and a second cylinder (24,26) are provided, which can be actuated by means of a pressurised fluid, said fluid-operable cylinders comprising a respective piston or plunger (25,28) and a compression chamber (30,32) integral respectively with the corresponding welding element (18) and with the corresponding support (20) of the respective welding element (18), each of said pressure chambers (30,32) having a connection (40) for the pressurised fluid with a plenum element (42), so as to discharge therein the increase in pressure which is generated inside the chambers (30,32) of the support cylinders (24,26) when said welding elements (18) come into contact one with the other.

Description: The present invention relates to a device for sealing bags or packages in a heat-sealable plastic material. It is preferably used in a machine for packaging a loose product in bags or the like in a heat-sealable material containing a predefined portion of said product. In packaging machines of the type referred above a tubular strip, generally in a heat-sealable material, is longitudinally fed and filled gradually with predetermined portions of product, while said sealing device, by welding the opposite edges of said tubular strip, defines a plurality of packages each containing a predetermined portion of product, which packages are subsequently separated one from the other by cutting the strip in the welding zone in order to provide individual packages of product intended for consumption. Known sealing devices comprise two opposite welding plates, transverse to said tubular strip, which have heated surfaces for contact and welding of the strip whereby the edges of the tubular strip are welded one to the other at the welding zone. Said welding plates are held by respective support elements which are driven to move cyclically, so that said two welding plates are moved one close to the other with the welding surfaces which compress one against the other the edges of said tubular strip, forcing them to weld one to the other, and are moved one away from the other to allow the passage between said welding elements of said strip containing a portion of product. In said known sealing devices, the welding plates, after having come into contact and having pressed between them the tubular packaging strip in plastic material, maintain the contact therewith for a certain length of time, following it for a certain longitudinal section for the time required for forming the weld. Moreover some of said known devices comprise between each of said welding elements and the respective mobile supports elastic springs which serve to damp the contact counterblow between said welding elements. In known sealing devices, the supports and the relevant sealing plates are made to move synchronously and in opposite directions on substantially circular paths, which in the case of use of springs allows the contact between the plates to be maintained for a certain section, wherein the paths cross. This elastic system of supporting the welding plates, although allowing the counterblow between the plates to be deadened and the risks of damage to the same to be reduced, has the disadvantage of not being able to vary the pressure of contact between the plates. This represents a problem for example when tubular strips having different technical features are welded, for example having a different thickness, which accordingly would require a greater or smaller contact pressure between the plates during welding. In fact, if they do not adequately compress the two edges of the strip, the risk of imperfect sealing of the package is incurred and said weld could later break, with the disadvantage that part of the product could leak or pollutants could penetrate the packaging, with serious damage particularly if the packaged product is one for nutritional use. On the other hand excessive pressure could ruin the external appearance of the package which would in this case be unattractive which would in turn make it unsaleable. Moreover said springs, after having been subjected to a certain number of work cycles, break due to fatigue. Another disadvantage noted in the use of traditional sealing devices concerns the fact that, if the material wherefrom it is formed or the thickness of the packaging strip requires a longer contact time, in order to provide a sufficient weld the strip feed rate has to be slowed down, i.e. reducing the packaging speed and hence reducing the quantity of units produced. EP-A-0 192 605 discloses a welding device for sealing bags or packages in heat sealable plastic material in which the regulation of the contact pressure between the welding elements occurs. EP-A-0 192 605 welding device comprising two welding elements in between of which the tubular film to be sealed is fed, wherein at least one of said welding elements is moved against the other welding element for sealing the film by means of a support rod driven along a rectilinear path. A compressor cushion being present between said support rod and said welding element and regulating means being provided for varying the pressure of a pressure fluid, such as oil or air, inside such cushion in order to obtain a desired variation of the pressing force between the welding elements. In EP-A-0 192 605 the welding elements performs a back and forth movement with stopping of the film fed in occasion of the sealing operation and the fluid-operable cushion (7) is only taught for providing a regulation of the contact pressure between the welding element. EP-A-0 469 819 discloses an apparatus in accordance with the preamble of claim 1 for horizontal sealing comprising a pair of elongated heater assemblies or elements on opposite sides of a film path along which a bag-forming film material is transported, rotating means for causing said pair of heater assemblies or the supports thereof to rotate in mutually opposite directions and each around one of said pair of mutually parallel horizontal axes while keeping both of said heater assemblies extended parallel to said axes, and axes-moving means for controllably varying the separation between said mutually parallel axes such that said heater assemblies press each other over a portion of said film path with a finite length while rotating around said axis. In EP-A-0 469 819 for allowing that said welding elements or assemblies are pressed one against the other for a certain longitudinal section when the circular paths of the welding elements cross, it is taught to move the axis of rotation of said welding elements. The rotation and axis-movement is achieved by means of complicated driving mechanism which comprises a Schmidt coupling having a set of rotary disks and corresponding links therebetween. The object of the present invention is that of providing a device for sealing bags or packages in heat-sealable plastic, suitable preferably for use in a machine for packaging a loose product in bags or the like, which overcomes the disadvantages shown by previous sealing devices. More particularly it allows a contact pressure to be obtained between the welding elements which can be varied and controlled as required in accordance with the type and thickness of the packaging strip used, as well as such as to achieve the possibility of varying the length of time of contact without causing variations in the packaging speed of the machine. Another object of the present invention is that of providing a sealing device which is suitable for being controlled fully automatically, by means of suitable computerised control means, in order to form part of a fully automated welding machine. The previous objects are achieved by providing a device for sealing bags or packages in a heat-sealable plastic material containing a predefined portion of product as defined in claim 1. In this way it is possible, by varying the pressure of the fluid in the cylinders-plenum circuit as required, to obtain a different contact pressure which allows the sealing device of the present invention to be adapted easily to the different types of plastic strip used for packaging the product. Moreover with the device of the present invention it is possible, with the availability of computerised means for varying the pressure of the fluid in said circuit, to avoid intervention by any operator and provide a fully automated packaging machine wherein any type of strip for packaging can be used. The present invention will be made clearer on reading the following description, relating to a preferred embodiment of the invention, to be read with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of a machine for packaging a product, with the sealing device of the present invention assembled thereon; Figure 2 is a schematic side view of the device for sealing bags according to a preferred embodiment of the present invention; Figure 3 is a plan view from above of the preferred embodiment of the device of the present invention. A packaging machine 8, with the device 10 of the present invention mounted thereon, is shown in Figure 1. In said machine a loose product is adequately weighed and divided into portions by means of the upper unit 9 and is then fed into a tubular strip 12, which is longitudinally fed and filled gradually with said predetermined portions of product before being sealed to define individual packages of product 13 by means of the sealing device 10 of the present invention. As is shown more clearly in Figure 2, the tubular strip 12, which is fed longitudinally and filled gradually with predetermined portions of product 14, is welded in 16, by means of the sealing device 10 which, by pressing and heating the opposite edges of said tubular strip 12, provides the packages 13 containing individually said predetermined portion of product. With reference also to the subsequent Figure 3, it can be seen that the sealing device comprises two opposite and transverse welding plates or elements 18, 18 wherein said strip 12 is made to pass and which are carried by a respective support element, denoted by reference numerals 20, 20 respectively in the Figures. Said supports 20, 20 of said two welding plates or elements 18, 18 are driven by suitable means, not described in detail here, to move synchronously along substantially circular paths in opposite angular directions, as shown by the dotted positions in Figure 2, so that said welding elements are brought close one to the other and, by pressing the edges of said tubular strip one against the other for a certain longitudinal section, force them to weld one to the other, and are moved away to allow the passage between the same welding elements of said strip containing a portion of product. Reference numeral 22 in Figure 2 denotes electric wires for supplying electric current for heating the welding surfaces of said welding elements 18. According to the embodiment of the present invention shown, at least a respective first and second cylinder 24 and 26 respectively, transversely distanced one from the other and which can be actuated by means of a pressurised fluid, are provided, as shown more clearly in Figure 3, for each of said two welding elements 18. Said fluid-operable cylinders 24, 26 comprise a relative piston or plunger 25, 28 integral by means of stems 27 and 29 with the respective welding element 18 and a respective compression chamber 30, 32 each containing the respective piston, integral with the support 20 of the welding element. The stems 27, 29 are guided and supported by means of respective bushes 31 and 33 on the support elements 20. Each of said pressure chambers 30, 32 is connected, by means of a respective conduit 34, 36, to a respective element 38 for distributing the pressurised fluid, in turn connected, via a respective conduit 40, to a plenum element 42 capable of containing a certain quantity of compressed fluid. Said plenum 42 for the pressurised fluid allows discharge therein of the pressure increase which is generated in the support cylinders chambers when said welding elements come into contact one with the other, so as to maintain substantially a predefined contact pressure between said welding elements. The pressurised fluid, fed by a network 44 or another source, is fed into the plenum 42 by means of a suitable pressure regulator 46 and the pressure inside the plenum is measured by means of a pressure gauge 48. 50 in Figure 3 denotes schematically means for setting the pressure which said regulator admits in the plenum 42. Said means 50 can be operated manually by the operator according to the production needs of that time, obtaining the necessary information from the pressure gauge 48, or could be actuated automatically by suitable computerised control means. According to a preferred mode of operation, provision could also be made, in order to make the impact between the welding elements extremely soft, but at the same time obtain a considerable contact pressure, during welding, for causing a certain and not excessive pressure to flow first of all into the cylinders and, after the impact between the welding elements has taken place, to bring said pressure in the cylinders to a higher level, according to the particular material being processed. According to the invention said cylinders are preferably pneumatic cylinders and the pressurised fluid is preferably compressed air. In this case the volume of the plenum element could indicatively be approximately 10 times the volume of the chamber of each cylinder. It is naturally understood that what has been written and shown in reference to the preferred embodiments of the present invention has been given purely by way of a non- limiting example of the principle claimed.

Claims: A device for sealing bags or packages in a heat- sealable plastic material containing a predefined portion of product, wherein a tubular strip is longitudinally fed and filled gradually with predetermined portions of product, while said sealing device, by welding the opposite edges of said tubular strip, defines a plurality of packages individually containing said predetermined portion of product, said sealing device comprising two welding elements (18, 18) transverse to said strip and opposite one to the other and which are carried by a respective support element (20, 20), and means for driving the supports (20, 20) of said two welding elements (18, 18) synchronously along substantially circular paths in opposite angular directions to move close one to the other so that said welding elements (18, 18) compress one against the other the edges of said tubular strip, forcing them to weld one to the other, and to move away to allow the passage between said welding elements (20, 20) of said strip containing a portion of product, characterized in that said driving means comprise at least a first and a second cylinder (24, 26) which can be actuated by means of a pressurized fluid provided between each of said welding elements (18, 18) and the respective mobile support (20, 20), said first and a second cylinders (24, 26) comprise a respective piston (25, 28) and a compression chamber (30, 32), containing said piston, integral respectively with the corresponding welding element (18, 18) and the corresponding support (20, 20) of the respective welding element (18, 18), each of said compression chambers (30, 32) containing a pressurized fluid for allowing that said welding elements (18, 18) are pressed one against the other for a certain longitudinal section when the circular paths of the welding elements cross, and in that the pressure increase which is generated inside the support cylinders chambers is discharged when said welding elements come into contact one with the other, and each of said pressure chambers have a connection for the pressurized fluid with a plenum element, so as to discharge therein said pressure increase, a regulator (46) being provided for regulating the fluid pressure inside said plenum element (42). A device for sealing bags or packages according claim 1, characterized in that the fluid inside the inside said pressure chambers (30, 32) is at a predefined lower pressure level when the welding elements (18, 18) enter into contact and wherein the fluid pressure inside said pressure chambers (30, 32) is increased, after impact between the welding element (18, 18) has taken place, to obtain a greater welding pressure. A device for sealing bags or packages according to any of previous claim 1 and 2, characterized in that of comprising means (50) for setting the pressure which said regulator admits in the plenum (42). A device for sealing bags or packages according to any of previous claims, characterized in that said cylinders (24, 26) are preferably pneumatic cylinders and the pressurized fluid is preferably compressed air. A device for sealing bags or packages according to any of previous claims, characterized in that the stems (27, 29) of the pistons (25, 28) supporting the welding elements (18, 18) are guided and supported by means of respective bushes (31, 33) on the support elements (20, 20).

Inventors: SIMIONATO PAOLO, SIMIONATO, PAOLO
Applicants: SIMIONATO SPA, SIMIONATO S.P.A.
Application year: 1996
Main classification: B65B51
IPC codes: B65B51