Abstract:
An apparatus for shrinking a shrink film onto a package formation includes a shrink tunnel-system having gas conductors that direct hot gas into the tunnel&#39;s interior along first and second flow-directions that are opposite to each other and parallel to a direction in which the package formation is conveyed through the shrink tunnel.

Description:
RELATED APPLICATIONS 
       [0001]    This application is the national stage under  35  USC 371 of PCT/EP2013/002472, filed on Aug. 16, 2013, which claims the benefit of the Feb. 22, 2013 priority date of German application 10 2013 101 782.7, the contents of which are herein incorporated by reference. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to shrink-wrapping, and in particular, to a shrink-tunnel system with an improved flow behavior and an associated method for shrinking a shrink film onto package formations. 
       BACKGROUND 
       [0003]    Shrink tunnel-systems for shrinking a shrink film onto package formations are well known. 
         [0004]    The process of shrinking the shrink film includes loosely wrapping a package formation in shrink film and applying a flow of hot air to it. The flow is oriented onto the side of the package formation to seal the ends of the shrink film overlapping at that point so that they are welded or otherwise bonded to each other. 
         [0005]    In known shrink-wrap methods undesired edge folding occurs. This results in messy shrink-wrapping with wrinkles that detract from the appearance of the finished product. 
       SUMMARY 
       [0006]    A disadvantage of known shrink-tunnel systems is that flow arrives at the package formation in an uncontrolled manner. As a result, the level of effectiveness of the shrink-on process depends on the form of the package formation. Sometimes, undesired edge folding of the shrink film can occur as a result. 
         [0007]    The invention provides a shrink-tunnel system and an associated method that improves the effectiveness of known shrink-wrapping methods and that also reduces energy consumption. 
         [0008]    In one aspect, the invention features an apparatus for shrinking a shrink film onto a package formation. Such an apparatus includes a shrink tunnel-system that has a tunnel housing, a conveyor, and air conductors. The tunnel housing encloses a tunnel interior through which the conveyor moves a package formation wrapped with shrink film along a conveying direction. The air conductors direct hot air into the tunnel interior along a first flow-direction that is parallel to the conveying direction and also in a second flow-direction that is opposite the first flow-direction. 
         [0009]    In some embodiments, some of the air conductors direct hot air into the tunnel interior in the first flow-direction while others direct it in the second flow-direction. 
         [0010]    In yet other embodiments, an average flow within the tunnel housing is equal to zero during operation, wherein the average flow is a volume integral of a flow field within the tunnel interior. 
         [0011]    In other embodiments, the tunnel interior has an inlet zone and an outlet zone that adjoins the inlet zone. In these embodiments, air conductors in a first set of air conductors are disposed in the inlet zone and air conductors in a second set of air conductors are disposed in the outlet zone. The air conductors in the first set introduce the flow in the first flow-direction, and air conductors in the second set introduce the flow in the second flow-direction. 
         [0012]    In yet other embodiments, the air conductors are configured to cause flow to rise constantly along the conveying direction. 
         [0013]    Alternative embodiments include lateral tunnel-walls. These include embodiments in which air conductors are arranged on those walls, embodiments in which the tunnel-walls at least in part form the air conductors, and those in which the air conductors are integrated into the lateral tunnel-walls. 
         [0014]    In additional embodiments, the air conductors are configured to cause the flow to be distributed evenly along a height of the tunnel interior. 
         [0015]    Yet other embodiments have a lateral tunnel-wall that at least in part defines the tunnel interior. In these embodiments, the air conductors comprise a set of openings in the lateral tunnel-wall. In some of these embodiments, a first opening from the set directs hot air along the first flow-direction, and a second opening from the set directs hot air along the second flow-direction. Also among these embodiments are those in which an area that protrudes into the tunnel interior surrounds each opening. In some embodiments, the protruding area has a structural feature that indicates that it has been embossed. Such features may include particular patterns of deformation and stress associated with the use of an embossing tool that would not be present if, for example, the area had been cast. Other embodiments include a set of nozzles in the lateral tunnel-wall, with each nozzle being formed by an opening and a protruding area surrounding that opening. 
         [0016]    In other embodiments, an opening in a lateral tunnel-wall includes a structural feature that indicates that it was made by a laser. Such a feature may include, for example, the presence of re-solidified metal showing flow marks indicative of having been cut by laser. 
         [0017]    In other embodiments, the tunnel housing defines an axis, the openings in the set of openings have diameters, each opening has a position along the axis, diameters of the openings vary as a function of a position of the opening on the axis, and the diameters increase monotonically with position. In other words, as one proceeds down the tunnel, the openings become progressively larger. 
         [0018]    Although the openings are often circular, in some embodiments, the openings include slots. These slots are adjacent to the conveyor. 
         [0019]    Yet other embodiments feature a lateral tunnel-wall that at least in part defines the tunnel interior, and that includes a metal panel. In these embodiments, the air conductors are openings formed in the metal panel. In some of these embodiments, there is a structural feature indicative first opening having been made by a metal punch. For example, the edges of the opening may be slightly deformed to indicate the occurrence of a force exerted by the punch. 
         [0020]    In another aspect, the invention features a method for shrinking a shrink film onto a package formation. Such a method includes moving a package formation that has been loosely wrapped with shrink film through a tunnel interior along a conveying direction, and, while the package formation is in the tunnel interior, exposing the package formation to flow of hot gas, such as hot air, that is directed along a first direction and to flow that is directed along a second direction that is opposite to the first direction, wherein the first direction is parallel to the conveying direction. 
         [0021]    In some practices, exposing the package formation to flow that is directed along a first direction and to flow that is directed along a second direction that is opposite to the first direction comprises passing the package formation through an inlet zone, at the inlet zone, exposing the package formation to the flow that is directed along the first direction, passing the package formation through an outlet zone, and, at the outlet zone, exposing the package formation to the hot-air flow that is directed along the second direction, 
         [0022]    In other practices, exposing the package formation to hot-air flow that is directed along a first direction comprises causing hot air to enter the tunnel interior through air conductors provided on lateral walls that at least in part define the tunnel interior. 
         [0023]    In yet another aspect, the invention features a shrink tunnel-system having air conductors that direct hot air into the tunnel&#39;s interior along first and second flow-directions that are opposite to each other and parallel to a direction in which the package formation is conveyed through the shrink tunnel. 
         [0024]    A significant aspect of the shrink-tunnel system according to the invention arises from having air conductors that introduce hot air-flow into the tunnel&#39;s interior with a first flow-direction oriented along the conveying direction and a second flow-direction oriented against the conveying direction. The targeted feed of the hot-air flow into the tunnel interior and thus onto the package formations wrapped with the shrink film tends to avoid the formation of defective shrink points. This results in a clear improvement in the quality of the shrink process. This is particularly advantageous with printed films, where the overall printed design depends on proper wrapping. There also arises a perceptible reduction in energy consumption. 
         [0025]    Because the air conductors are to direct the hot-air flow in first and second flow-directions, it is practical to generate the hot-air flow centrally and to introduce it into the tunnel interior by the air conductors with a specified flow-direction. 
         [0026]    The shrink tunnel&#39;s interior is preferably divided into an inlet zone and an adjoining outlet zone. First air conductors in the inlet zone introduce the hot-air flow with a first flow-direction, and second air-conductors in the outlet zone introduce the hot-air flow with a second flow-direction. In the inlet zone, a rear free-end of the shrink film is laid on the package formation and a front free-end of the shrink film is lifted off the package formation. Conversely, in the outlet zone, the front free-end of the shrink film is laid on the package formation and the rear free-end of the shrink film is lifted off the package formation. Due to this directed application of the shrink film with the hot-air flow, a considerable improvement in the shrink result arises. 
         [0027]    The air conductors are advantageously designed in such a way that the hot-air flow introduced into the tunnel interior rises constantly in the conveying direction. The air conductors are advantageously designed to generate a hot-air flow that is distributed evenly over the height of the tunnel interior. These measures improve the quality of the shrinking process. 
         [0028]    In some embodiments, two lateral tunnel-walls bound the tunnel&#39;s interior. The air conductors are arranged along the lateral tunnel-walls. Among these embodiments are those in which the air conductors are at least partially formed by the lateral tunnel-walls themselves, as well as those in which the air conductors are integrated into the lateral tunnel-walls. 
         [0029]    In some embodiments, the lateral tunnel-walls are made of metal panels that have a multiplicity of openings to introduce the hot-air flow into the tunnel interior. These form the air conductors. In these embodiments, the openings are formed so as to impose a first or second flow-direction on the hot air emerging through the openings. The area of the lateral walls around the openings has a bowed contour that bows outward into the tunnel&#39;s interior. This results in a nozzle structure formed by the openings and the areas of the lateral tunnel-walls around them. 
         [0030]    Preferably, a metal punch or laser makes the openings and an embossing tool makes the bowed contour of the area around the openings. 
         [0031]    In some embodiments, the diameter of the openings increases along the tunnel interior. Due to the described design of the lateral tunnel-walls according to the invention, the air conductors are simple and inexpensive to manufacture. 
         [0032]    In another embodiment, openings next to the conveyor are shaped like slots. This provides superior lifting of the shrink film&#39;s free ends and thus leads to a better shrink result. 
         [0033]    In another aspect, the invention features a method for shrinking a shrink film onto a package formation in a shrink-tunnel system comprising a tunnel interior, in which the package formations that have been loosely wrapped with shrink film are moved in a conveying direction through the tunnel&#39;s interior by at least one conveyor and exposed to a flow of hot-air within the tunnel&#39;s interior. A significant aspect of the method lies in the fact that at least one hot-air flow is applied to the package formations wrapped with the shrink film, said air-flow having a first flow-direction oriented along the conveying direction and a second flow-direction oriented against the conveying direction. 
         [0034]    A particularly advantageous practice includes moving the package formation through an inlet zone of the tunnel&#39;s interior and through an outlet zone next to the inlet zone. In the inlet zone, the hot-air flows with a first flow-direction. In the outlet zone, the hot-air flows with a second flow-direction. Air conductors along the tunnel&#39;s lateral walls direct the hot air in the first and second flow-directions. 
         [0035]    As used herein, the expressions “substantially,” “approximately,” and “around” mean deviations from an exact value in each case by ±10%, preferably by ±5% and/or deviations in the form of changes that are not significant for function. 
         [0036]    Although the specification refers specifically to air as a medium of heat transfer within the shrink tunnel, it is to be understood that any gas or gas mixture can be used. The claims are thus in no way limited to air. 
         [0037]    Further developments, benefits and application possibilities of the invention arise also from the following description of examples of embodiments and from the figures. Moreover, all characteristics described and/or illustrated individually or in any combination are categorically the subject of the invention, regardless of their inclusion in the claims or reference to them. The content of the claims is also an integral part of the description. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0038]    These and other features of the invention will be apparent from the following detailed description and the accompanying figures, in which: 
           [0039]      FIG. 1  shows a simplified schematic longitudinal section through a shrink-tunnel system according to the invention, 
           [0040]      FIG. 2  shows a view from above a lateral wall of the tunnel housing shown in  FIG. 1 , 
           [0041]      FIG. 3  shows a section along the axis I-I through the lateral wall shown in  FIG. 2 , 
           [0042]      FIG. 4  shows a simplified schematic cross-section through the shrink-tunnel system of  FIG. 1 , 
           [0043]      FIG. 5  shows a view from above an alternative embodiment of the lateral wall shown in  FIG. 2 , and 
           [0044]      FIG. 6  shows a section along the axis II-II through the lateral wall shown in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0045]      FIGS. 1 and 3  show a shrink-tunnel system  1  for shrinking a shrink film  2  onto a package formation  3 . 
         [0046]    As used herein, a package formation  3  includes sets of packaged goods that are to be packaged with shrink film. Examples include sets of containers, bottles, cans or similar individual packages that, upon being bound together by shrink film  2 , form a packaging unit  4  or a cluster pack. In some embodiments, the shrink film  2  is a printed film. 
         [0047]    The shrink-tunnel system  1  includes a tunnel housing  5 . In some embodiments, the tunnel housing  5  has multiple parts. In either case, the tunnel housing  5  defines a tunnel interior  6  that is separated from the exterior by at least first and second lateral tunnel-walls  5 . 1 ,  5 . 2  opposite each other, and a top and bottom tunnel-wall  5 . 3 ,  5 . 4 . In some embodiments, the tunnel-walls  5 . 1 - 5 . 4  are held in the tunnel housing  5 . In other embodiments, the tunnel-walls  5 . 1 - 5 . 4  at least in part form the tunnel housing  5 . 
         [0048]    Referring to  FIG. 1 , a conveyor  7  carries a package formation  3  that has been loosely wrapped with shrink film  2 . The conveyor  7  carries this package formation  3  through a tunnel inlet  5   a  and into an inlet zone EZ within the tunnel interior  6 . It continues carrying the package formation into an adjoining outlet zone EZ and on out through a tunnel outlet  5   b.  In some embodiments, the conveyor  7  is a conveyor belt. 
         [0049]    Within the tunnel interior  6 , the package formation  3  encounters a flow  8  of hot air. This hot-air flow  8  shrinks the shrink film  2  tightly so that the resulting packaging unit  4  approximates the external shape of the package formation  3 . 
         [0050]    Hot air used for the hot-air flow  8  comes from a heating/blower arrangement  9 ,  9 ′, which is preferably located above the tunnel interior  6 . A pipe distribution system  10  feeds this hot air into the tunnel interior  6  through first openings  11  and second openings  12 . The first openings  11  are in the lateral tunnel-walls  5 . 1 ,  5 . 2 . The second openings  12  are in the bottom tunnel wall  5 . 4 . 
         [0051]    The heating/blower arrangement  9 ,  9 ′ draws partially-cooled hot air from the tunnel interior  6  through an extractor opening  13  in the top tunnel wall  5 . 3 , as shown in  FIG. 1 . The heating/blower arrangement  9 ,  9 ′ then heats this partially-cooled hot air all over again and recirculates it. Preferably, the hot air is heated to a temperature in the range of approximately 320° F. to 450° F. for shrinking the shrink film  2 . 
         [0052]    The shrink-tunnel system  1  includes first and second air-conductors  14 ,  15  for providing a targeted hot-air flow  8  onto the shrink film  2 . The first air-conductor  14  introduces hot-air flow  8  along a first flow-direction SR 1  that is oriented along the conveying direction TR. The second air-conductor  15  introduces a hot-air flow  8  along a second flow-direction SR 2  that is oriented opposite the conveying direction TR. In the transitional area between the inlet zone EZ and the outlet zone AZ, the direction of hot-air flow  8  changes. 
         [0053]    The first and second air-conductors  14 ,  15  are designed to generate a constantly-rising hot-air flow  8  with a specified direction along the inlet and outlet zone EZ, AZ. To achieve this, the first and/or second air-conductors  14 ,  15  are preferably arranged along the lateral tunnel-wall  5 . 1 ,  5 . 2 . In alternative embodiments, they are partially formed by the lateral tunnel-wall  5 . 1 ,  5 . 2  itself. In yet other embodiments, they are integrated into the lateral tunnel-wall  5 . 1 ,  5 . 2 . The air conductors  14 ,  15  are preferably also configured to generate a hot-air flow  8  that is evenly distributed along a vertical direction, at least over the height of the packaging units  4  if not over the height of the tunnel interior  6 . 
         [0054]    Within the tunnel interior  6  is a lower air-layer zone under the conveyor  7 . The pipe distribution system  10  directs some hot air into this zone. This air exits the lower air-layer zone through the second openings  12  in a direction perpendicular to the conveying direction TR and directed toward the top tunnel wall  5 . 3 . 
         [0055]    It is particularly advantageous to apply the oriented hot-air flow  8  to the ends of the shrink film  2  that project laterally over the package formations. These ends will be referred to herein as the “free ends.” 
         [0056]    Preferably, the hot-air flow  8  is applied in alternation. In this way, the free ends are turned over such that they come to rest on the open faces  3 ′ of the package formation  3 , namely those that are not wrapped with the shrink film  2 . 
         [0057]    Because the flow-directions SR 1 , SR 2  are oriented in opposite directions, the free ends of the shrink film  2  that are oriented in the conveying direction TR and the free ends of the shrink film  2  that are on the opposite end, which are thus oriented against the conveying direction TR, are turned over on the faces  3 ′ of the package formation  3  in an optimum manner. As a result, they can be shrunk on with reduced wrinkle formation. In this context, a window-like opening  4 ′ arises, which provides a view of the section of the package formation not enclosed by the shrink film  2 . 
         [0058]    As shown in  FIG. 1 , a package formation  3  enclosed by the shrink film  2  is fed to the shrink-tunnel system  1  in such a way that a first open face  3 ′ of the package formation  3  faces the first lateral tunnel-walls  5 . 1  and a second open face  3 ′ faces the second lateral tunnel wall  5 . 2 . This direction causes hot-air flow  8  to have a velocity vector that is generally tangential to the open faces  3 ′ of the package formation  3 . 
         [0059]    In some embodiments, the lateral tunnel-walls  5 . 1 ,  5 . 2  are metal panels that have a multiplicity of first openings  11  to supply hot-air flow  8  into the tunnel interior  6 . These openings  11  thus form the first and second air-conductors  14 ,  15 . 
         [0060]    Within the inlet zone EZ, the first openings  11  are shaped to direct hot-air flow  8  emerging therefrom along either a first flow-direction SR 1 . These collectively define the first air-conductor  14 . Within the outlet zone AZ, the first openings  11  are shaped to direct hot-air flow  8  emerging therefrom along the second flow-direction SR 2 . These collectively define the second air-conductor  15 . 
         [0061]    Referring to  FIGS. 2 and 3 , in a preferred embodiment, a first opening  11  is made through the lateral tunnel-walls  5 . 1 ,  5 . 2 . This can be carried out by metal punching or by a laser. Next, an embossing tool embosses an area  16  around the first opening  11 . The resulting embossed area  16  has an outwardly bowed contour that protrudes into the tunnel interior  6 . The position of the opening  11  within the area  16  determines the direction in which hot-air flow  8  exits the opening  11 . 
         [0062]    The spacings and the diameters of the first openings  11  are selected to control the magnitude of the hot-air flow  8  needed for the shrink process. The first openings  11  are preferably arranged in a matrix of rows and columns on the lateral tunnel-walls  5 . 1 ,  5 . 2 . 
         [0063]    The bowed contour of the areas  16  can be circular or oval. The location of the opening  11  within the bowed area can also vary. For example, the first openings  11  can be made to lie near an edge of the bowed areas  16 . This will tend to increase the tangential component of the velocity vector at the cost of the normal component thereof. 
         [0064]      FIG. 2  shows a view facing a lateral tunnel-wall  5 . 1 ,  5 . 2  in which openings  11  have been embossed to direct flow along the first direction SR 1 .  FIG. 3  shows a section along the line I-I through the lateral tunnel-wall  5 . 1 ,  5 . 2  in  FIG. 2 . The first openings  11  together with the bowed areas  16  thus form a nozzle-like structure. 
         [0065]    Within the inlet zone EZ, the first openings  11  are shaped to direct gas flow  8  in a first flow-direction SR 1 . Meanwhile, within the outlet zone AZ, the first openings  11  are shaped to direct gas flow  8  in in a second flow-direction SR 2  against the conveying direction TR. 
         [0066]    In some embodiments, the diameters of the nozzle-like first openings  11  are not all the same. In particular, the diameters increase in the conveying direction TR so that the volume of hot-air flow  8  introduced into the tunnel interior  6  by the first openings  11  increases in the conveying direction TR. Advantageously, in this way, the hot-air flow  8  is applied to the shrink films  2  alternately in and against the conveying direction TR, and thus the front or reverse of the shrink film  2  is raised from the package formation  3 . This improves the result of the shrinking process. 
         [0067]      FIG. 4  shows a cross-section through the shrink-tunnel system  1 . In general, a package formation  3  will have four free-ends. A first and second free-end will face the first lateral-wall  5 . 1  and a third and fourth free-end will face the second lateral-wall  5 . 2 . The package formation  3  is always oriented such that the first and third free-ends are closest to the tunnel inlet  6   a  and the second and fourth free-ends are closest to the tunnel outlet  6   b.    
         [0068]    While the package formation  3  is in the inlet zone EZ, the flow  8  is in the conveying direction TR. This flow  8  will tend to fold the first and third free-ends towards the package formation  3  and to lift the second and fourth free-ends away from the package formation  3 . 
         [0069]    In the transitional area between the inlet zone EZ and the outlet zone AZ, the direction of the flow  8  changes. In the outlet zone AZ, a hot-air flow  8  oriented against the conveying direction TR is now applied to the package formation  3 . The second and fourth free-ends of the shrinking film  2  are thus blown against the conveying direction TR and folded onto the package formation  3 . 
         [0070]    In some embodiments, such as that shown in  FIG. 1 , a first heating/blower arrangement  9  serves the inlet zone EZ and a second heating/blower arrangement  9 ′ serves the outlet zone AZ. 
         [0071]    The first heating/blower arrangement  9  has a first blower unit  9 . 1  and a first heating unit  9 . 2 . At the end of the inlet zone EZ, the first blower unit  9 . 1  draws air out of the tunnel interior  6  through a first extractor opening  13  and feeds it to the first heating unit  9 . 1  for heating. The pipe distribution system  10  then routes the heated air from the first heating unit  9 . 1  to the first openings  11  provided in the inlet zone EZ so that the hot air can be fed back into the tunnel interior  6 . 
         [0072]    Similarly, the second heating/blower arrangement  9 ′ has a second blower unit  9 . 1 ′ and a second heating unit  9 . 2 ′. At the end of the outlet zone AZ, the second blower unit  9 . 1 ′ draws air out of the tunnel interior  6  through a second extractor opening  13 , and feed it to the second heating unit  9 . 2 ′ for heating. The pipe distribution system  10  then routes the heated air from the second heating unit  9 . 2 ′ to the first openings  11  arranged in the outlet zone AZ so that the hot air can be fed back into the tunnel interior  6 . 
         [0073]    In some embodiments, the shrink-tunnel system  1  includes a temperature sensor for sensing the temperature of the hot air or of the gas flow  8  in the tunnel interior  6 . This measured temperature can then be used to adjust heating/blower arrangements  9 ,  9 ′ accordingly. 
         [0074]    In a further embodiment, shown in  FIGS. 5 and 6 , the first openings  11  that are closest to the conveyor  7  are slot-shaped openings  11 ′. Each slot-shaped opening  11 ′ on the first lateral tunnel-wall  5 . 1  has a corresponding slot-shaped opening on the second lateral tunnel-wall  5 . 2  that lies on the opposite side of the conveyor  7 . A slot-shaped openings  11 ′ is made by punching a rectangular hole in a lateral tunnel-wall  5 . 1 ,  5 . 2  while leaving behind a guide panel section  17  that can be bent to direct flow in a desired direction, as shown in  FIG. 6 . 
         [0075]    Slot-shaped openings  11 ′ along conveyor  7  permit targeted application of the free ends of the shrink film  2  projecting on the front face. In particular, the section of the free ends of the shrink film  2  oriented in the direction of the conveyor  6  is raised and routed in the direction of the front face  3 ′ of the package formation  3 . 
         [0076]    The invention has been described above using various embodiments as examples. However, other embodiments are possible without departing from the scope of the invention as defined by the attached claims.