Abstract:
A thermoshrinking tunnel oven for making thermoshrinking plastic material film packages comprises a bottom plate and a top plate having openings for allowing thermoshrinking hot air to pass therethrough, the cross-sections of the openings being controlled by perforated sliders which are independently slidably mounted on the plates. 
     With respect to conventional tunnel ovens, the inventive tunnel oven and method have the advantage that they provide thermoshrinking material packages of even aspect and devoid of unevennesses.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a tunnel oven for making thermoshrinking material films packages. 
     The invention also relates to a packaging method for providing packages, the method being carried out in the inventive tunnel oven. 
     More specifically, the field of the invention is that of the tunnel ovens used for making thermoshrinking material film packages, for example for packaging bottles, cans and the like. 
     Prior systems for packaging articles in general, such as bottles, cans and so on, in thermoshrinking plastic material films, provide to use heated tunnel ovens, inside which the packages as preliminarily enveloped by the mentioned thermoshrinking film are conveyed. 
     The oven tunnel is heated by hot air jets, oriented against the articles to be packaged. 
     The size of the tunnel oven is so selected as to be compatible to the size of the articles to be packaged, to provide an efficient heating and thermo-shrinking process. 
     The above mentioned prior solutions are however affected by several drawbacks. 
     At first, the thermoshrinking plastic material films have usually an uneven thickness, which is conventionally modified by the application of decorations or advertisement patterns, which are randomly printed on the film surfaces. 
     Thus, the aspect of the obtained packages is frequently altered, thereby reflecting an unproper packaging process. 
     Furthermore, the requirement of designing the oven tunnels with a size related to that of the articles to be packaged represents a great limitation preventing the same oven from being used for articles of different size, i.e. having a size different from that for which the tunnel oven has been constructed. 
     A further drawback of the tunnel ovens of the prior art is that the film material enveloping the packaged articles tend to adhere to the chain conveying means of the oven, thereby hindering a proper hot air flow, and leaving undesired marks on the bottoms of the packaged articles, and, moreover, undesirably depositing plastic material debris on the oven conveying chains. 
     SUMMARY OF THE INVENTION 
     Accordingly, the aim of the present invention is to improve prior tunnel ovens, for making packages devoid of surface unevennesses to be used for a broad range of the article to be packaged size. 
     The above aim, as well as yet other objects, are achieved by tunnel oven and packaging method as respectively defined by claims  1  and  23 . 
     Preferred embodiments of the tunnel oven and packaging method according to the present invention are defined by the subclaims. 
     With respect to the prior art, the tunnel oven and packaging method according to the present invention provide the advantage of providing thermoshrinking material packages devoid of surface unevennesses, and of even aspect, owing to the use of controlling means for controlling the air flows. 
     The invention provides moreover that it allows to process, in the same tunnel oven, packages of differently sized articles. 
     Furthermore, the provision of control systems for controlling the temperature of the air flow and for cleaning the article conveying chains, provides packages devoid of surface defects. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The tunnel oven and packaging method according to the present invention will be disclosed in a more detailed manner hereinafter with reference to a preferred embodiment thereof, which is illustrated, by way of an indicative, but not limitative example, in the figures of the accompanying drawings, where: 
     FIG. 1 is a perspective view of the overall tunnel oven according to the present invention; 
     FIG. 2 is a front view illustrating the tunnel oven shown in FIG. 1; 
     FIG. 3 illustrates a detail of the cleaning device for cleaning the chain conveying means of the tunnel oven shown in FIG. 1; 
     FIG. 4 is a schematic view illustrating the tunnel oven of FIG. 1, with the top covering removed therefrom, in order to show the hot air bottom flow outlets; 
     FIG. 5 is a broken away view of the tunnel oven of FIG. 1, specifically showing the deflection outlets or ports for deflecting the hot air top flows toward the oven fan; 
     FIG. 6 illustrates the arrangement of the hot air side outlets of the tunnel oven shown in FIG. 2; 
     FIG. 7 illustrates the conveying device for conveying the hot air flows to the top portion of the tunnel oven; 
     FIG. 8 illustrates the arrangement of the cooling fans of the chain conveying means at the front portion of the tunnel oven shown in FIG. 1; 
     FIG. 9 illustrates a modified embodiment of the tunnel oven shown in FIG. 8; 
     FIG. 10 illustrates a detail of a control device for controlling the bottom air flows of the oven tunnel shown in FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The tunnel oven according to the present invention has been generally indicated in FIG. 1 by the reference number  1 . 
     Said tunnel oven comprises a bottom supporting base  2 , supporting a covering element  3  defining, with said bottom base  2 , the thermoshrinking chamber  4  of the tunnel oven. 
     Said bottom base  2  comprises a chain conveyor  5 , provided for receiving a plurality of articles  6  to be packaged (in FIG. 1 said articles comprising bottles) which are preliminarily enveloped by a thermoshrinking material film  7 . 
     Immediately under the package  16  bearing surface, a plurality of fans  8  are provided on the chain conveying means  5 . 
     As is clearly shown in FIG. 4, the fans are arranged outside the covering element  3  and are designed for cooling down the chain conveying means  5 , thereby preventing the chain conveying means for achieving the thermoshrinking temperature of the film  7 . 
     The control means for controlling the hot air flows exiting the bottom portion of the tunnel oven and directed to the packages are shown in FIGS. 4,  8  and  10 . 
     More specifically, said hot air flow control means comprise a plate  9 , including a plurality of holes or slots  10 , said plate extending through the overall length of the tunnel oven  1 . 
     With said plate  9  are associated slider elements  11 , preferably in a overlapping relationship with respect to said plate, said slider elements adjoining one another in a slidable manner and comprising a plurality of holes  12  or perforations, registering with the holes  10  of said plate  9 . 
     The slider elements  11  on the plate  9  are driven, in the direction of the arrows F of FIG. 8, by a driving mechanism including corresponding shafts  13  and levers  14 , and in turn driven by corresponding driving knobs  15 . 
     Preferably, the driving knobs  15  controlling the displacement of the slider elements or drawers  11  are independently arranged on the base  2 , at both walls and on the two ends of the tunnel oven  1 . 
     Thus, by operating the mentioned driving knobs, it is possible to achieve two different positions of the slider elements or drawers  11  on the plate  9  and, more specifically: 
     1. a full opening position in which the holes  10  of the plate  9  are fully opened, and the holes  12  of the slider elements  11  are brought into registration with said holes  10 , and 
     2. a fully closing position, in which the holes  10  of the plate  9 , with the slider elements  11  are arranged so that the holes  12  thereof are fully offset with respect to the holes of said plate  9 . 
     In this connection it should be apparent that it would be possible to achieve intermediate adjustments, providing a partial closure of the holes  10  of the plate  9 . 
     The bottom base  2  of the tunnel  1  comprises a covering element  3  on which are mounted hot air circulating fans  17 . 
     As is clearly shown in FIG. 2, the fans  17  cause air to be directed inside the gap  18  of the covering element  3 , in which are arranged resistances  19  for heating said air. 
     The thus heated air flow is oriented toward the base  2  and is upward directed, starting from the bottom  20  of the thermoshrinking chamber  4 , by passing through the holes of the plate  9  and of the slider elements  11 . 
     The air flow provided by said fans  17  is also oriented in the direction of the perforated top plate  21  and perforated top slider element  22  assembly, having a construction and an arrangement analogous to those of the bottom plate  9  and bottom slider elements  11 , as thereinabove disclosed. 
     In particular, the top slider elements or drawers  22  comprises, at a respective end portion thereof, knobs  23  for driving said slider elements in the direction of the arrows F of FIG. 5, thereby closing, in a partial manner, the holes of the plate  21  for allowing air to enter the thermoshrinking chamber  4 . 
     In order to provide the air flow exiting from the bottom base  2  with a profile like that of the package  16 , the top slider elements  22  are so driven as to close the side surfaces of the plate  21 , while leaving open the central portion of said plate, corresponding to the position of the package  16 . 
     In this connection it should be apparent that the number of slider elements or drawers which are left open will depend on the size of the packages or number of the simultaneously processed packages. 
     For some applications, in which the top region of the packages  16  must not be affected by an excessive heat, the holes of the top plate  21  are fully closed by the slider elements  22 , and the air upward flowing from the bottom base  2  will be discharged through the openings  25  formed through the top portion of the side walls  24  of the covering element  3 . 
     In the modified embodiment shown in FIG.  6 , the air flow provided by the fans  17  is partially deflected by a baffle  26 , driven by a corresponding knob  27 , provided on the side walls  24  at the rear portion of the tunnel oven  1 , or processed packages outlet portions. 
     As shown in FIG. 2, the fans  17  draw air from the thermoshrinking chamber in the direction indicated by the arrows  29 , at a further fan  28 . 
     Then, as is shown in FIG. 7, the drawn air flow is at the start conveyed into a cyclone  30  and being then conveyed from the latter, by deflecting walls  31 , through the overall length of the gap  18  of the covering element  3  (see the arrows  32  of FIG.  2 ). 
     The top plate  21  and top slider element  22  system (see FIG. 5) can be arranged, at an adjustable height above the bottom base  2  supporting the chain conveying means  5 , by supporting brackets  33  which can slide in slots  34  formed on said side walls  24 . 
     The adjusted in height position of the plate  21  and of the slider elements  22  is locked by locking screws (not shown), operating between the walls  22  and brackets  33 . 
     This height is selected depending on the size of the packages  16  to be processed in the tunnel oven. 
     The cleaning of the chain conveying means  5  is performed by the cleaning device shown in FIG.  3 . 
     This cleaning device comprises a rotary brush  35  arranged at the package  16  inlet region. 
     For providing an efficient cleaning of the chain conveying means  5 , the cleaning brush  35  is advantageously adapted to rotate in a direction opposite to the sliding direction of the conveying chain. 
     The driving of the cleaning brush  35  is at a temporary driving and is controlled by a pneumatic cylinder  36  driving a brush supporting lever  37 . 
     The lever  37  supports moreover a gear wheel  38  coupled to the brush  35  and engaging with a corresponding gear wheel  39  for driving the chain conveying means. 
     Thus, as the lever  37  is driven, the two gear wheels  38  and  39  are mutually engaged, thereby causing the cleaning brush  35  to be moved toward the conveying chain  5 , to contact the latter. 
     The driving of the cylinder  36  is controlled by a preset controlling program. 
     Advantageously, on the package  16  outlet section, are provided a plurality of IR lamps  40 , arranged on the side walls  24  of the covering element  3 , as shown in FIG.  9 . 
     If a plurality of packages arranged on a plurality of rows are supplied, then the lamps  40  will be also arranged between a row of packages and another row thereof. 
     The mentioned lamps operate to concentrate the heat on the side walls of the packages, requiring a great amount of heat as necessary for properly extending the film. 
     The invention, as disclosed and shown in the figures of the accompanying drawings, is susceptible to several modifications and variations, without departing from the scope of the following claims. 
     Thus, for example, the plurality of bottom slider elements  11  and top slider elements  22  can be replaced by a single bottom slider element and a single top slider element, even arranged under the related plate, respectively  9  and  21 .