Abstract:
A shrink system for a labelling system includes a return duct and a make up duct connected to the inlet of a fan. A valve regulates the temperature of air supplied to the inlet by varying the proportion of air flow between the return and make up ducts. The output of the fan is supplied to a nozzle configured to entrain ambient air with the outlet from the nozzle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 12/784,196 filed May 20, 2010, which claims priority from U.S. Provisional Application No. 61/179,994 filed on May 20, 2009, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to hot air systems for use in contouring shrinkable films to containers, commonly referred to as shrink systems. 
         [0003]    SUMMARY OF THE INVENTION 
         [0004]    It is well known to apply a label or covering to a container as it moves along a production line. In one known arrangement, the labels are wrapped around the container by applying glue to the leading and trailing edges and brought into engagement with the container as the container rotates. The label is drawn around the container and the glue applied to the trailing edge for secures the label on the container. 
         [0005]    Alternatively, sleeves may be preformed on a mandrel and slid onto the containers. The sleeve is dimensioned to allow relative sliding and must then be secured to the container. The application of labels allows standardised containers to be used for a range of products and reduces the warehousing and inventory necessary in a typical production facility. 
         [0006]    It is also known to use a heat sensitive material as a label so that the label can be made to conform to shape of the container. The label is applied in a conventional manner and then passed through a shrink system where an elevated temperature causes the material of the label to shrink and conform to the outer surface of the container. Many applications pass the container through an enclosed tunnel where the temperature is elevated by super saturated steam, hot air or infra-red radiant heat. This technique however may only be used when the contents of the containers are not likely to cause an explosion. Where the contents are volatile or under pressure, such as an aerosol, there is significant risk that the container may topple and be trapped within the tunnel. Prolonged exposure to the elevated temperature may then overheat the contents and cause an explosion. 
         [0007]    Where there is the potential for explosion therefore, the system must allow for visual observation of the containers as they pass through the heated zone. Accordingly, an open conveyor path is necessary. However, this in turn leads to an increased consumption of heating medium due to the need to replenish losses to the environment. These losses are increased by the movement of the containers at speed through the heating zone, which creates a disturbance and tends to dissipate the heated medium to the surrounding environment. 
         [0008]    U.S. Pat. No. 1,155,799 to Tetra Alfa Holdings shows a heat tunnel arrangement tor sealing the edge of a plastic bag. A pair of hot air plenums are located on either side of the passage through which the container moves and nozzles in the side walls of the hot air plenums supply the hot air to the plastic film. A suction box is located above the gap between the two hot air plenums and has inlets to suck the hot air from between the plenums. The hot air is returned through a duct for recirculation through the hot air plenums. To induce the flow of air within the closed loop, an injector is fed from a compressed air source to create the flow. Such an arrangement however is only suitable for small articles, such as the plastic bags shown, and does not lend itself to the labelling of larger containers such as beverage cans. Moreover, the use of an ejector to induce the flow of air through the nozzles is not compatible with the flow rates of air required in most applications. 
         [0009]    It is therefore an object of the present invention to provide a shrink system in which the above disadvantages are obviated or mitigated. 
         [0010]    In general terms, the present invention provides a shrink system in which heated air is applied to a container. The heated air is recovered and supplied to an inlet of a fan whose outlet supplies the heated air to the containers. The recovered air is combined with an ambient air duct and the proportions of ambient air and recovered are varied to maintain a predetermined temperature as the inlet to the fan. 
         [0011]    In a further aspect of the invention, the healed air is supplied to the container through a nozzle having convergent outer surfaces. The outer surfaces are arranged to induce a flow of air over the outer surface and entrain it with the air emitted from the nozzle. A plenum is located opposite the nozzle such that the air flowing from the nozzle and that entrained by the nozzle&#39;s airflow is constrained within the plenum. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which: 
           [0013]      FIG. 1  is a schematic representation of a container labelling and packaging production line. 
           [0014]      FIG. 2  is a perspective view of a shrink station incorporated into the production line of  FIG. 1 . 
           [0015]      FIG. 3  is a rear perspective view of the station shown in  FIG. 2 . 
           [0016]      FIG. 4  is a plan view of the station shown in  FIG. 2 . 
           [0017]      FIG. 5  is an exploded view of the station shown in  FIG. 2 . 
           [0018]      FIG. 6  is a section on the line VI-VI of  FIG. 2 . 
           [0019]      FIG. 7  is a perspective of a heating system used in the machine of  FIG. 2 . 
           [0020]      FIG. 8  is a view on the line VIII-VIII of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    Referring therefore to the drawings, a container labelling and packaging production line, generally indicated at  5  includes a labelling machine  9 , a shrink station  10  and an assembly station  11 . Filled containers (C) are fed to the labelling machine  9 . Labels (L) are applied to a filled container (C). The containers (C) pass from the labelling machine  9  through the shrink station  10  and are organized for placement in a package at the assembly station  11 . If necessary, accumulation stations are interposed between the labelling machine and the shrink system, and between the shrink system and assembly station  11 . The purpose of the shrink station  10  is to cause labels applied in the labelling station  9  to be heated and conform to the contours of the container (C) to which the labels are applied. For the purpose of the description, it will be assumed that the containers are a beverage can indicated at (C),  FIG. 6 , with upper and lower chines (D), (E) to which a label (L) is to conform. The label (L) is formed from a heat shrinkable material and carries indicia to decorate the external surface of the container (C). 
         [0022]    The containers (C) are delivered to the intake of the shrink station  10  along a conveyor  12 . At that time, the label (L) is formed as a cylinder adhered to the body of the container but with the upper and lower marginal edges spaced from the chines. The feed of container (C) through the station  10  is controlled by a worm assembly  14  that rotates about a horizontal axis to pick individual containers and separate them from adjacent containers as they are moved along the conveyor  12 . Movement of the containers through the station  10  continues under the guidance of a belt drive  16  that receives the containers (C) from the worm assembly and rolls them along a guide rail  18  located on the opposite side of the conveyor  12  to the belt drive  16 . The belt drive  16  discharges the containers (C) at the outlet of the station  10  from where they can he moved to the collection station  11 . 
         [0023]    As best seen in  FIG. 5 , the belt drive  16  consists of an endless belt  20  entrained about a pair of pullies  22  and supported by a backing rail  24  that extends between the two pullies  22 . One of the pullies  22  is driven by a motor  26  so that the belt engages the container (C) and rolls it along the guide rail  18 . 
         [0024]    A hot air system generally indicated  30  is located between the pullies  22 . The hot air system  30  includes two pairs of hot air nozzle assemblies  32 ,  34  each supplied with air from respective fans  36 ,  38 . A plenum  40  extends in a direction parallel to the conveyor  12  and the opposite side of the conveyor to the nozzle assemblies  32 ,  34  and collects air issued from the nozzle assemblies  32 ,  34  and returns it through return conduits  42 ,  44  respectively to respective ones of the fans  36 ,  38 . 
         [0025]    Each of the nozzle assemblies, fans and return conduits is similar and therefore only one will be described in detail. The fan  36  has an outlet  50  that is connected to a supply duct  52 . The supply duct  52  branches into two separate ducts  52   a ,  52   b  which are connected to respective upper and lower heater assemblies  54 ,  56 . Referring to  FIG. 6 , the heater assemblies  54 ,  56  each include a heater chamber  58  through which the air passes before entering a manifold  62 . The chamber  58  houses an electrical resistance heating element (not shown) to elevate the temperature of the air passing through the chamber  58 . The manifold  62  extends generally parallel to the conveyor  12  and has a pair of nozzles  64 ,  66  at opposite ends. Each of the nozzles  64 ,  66  has upper and lower surface  68 ,  70  respectively that converge in a direction toward the conveyor  12 . The upper and lower surfaces  68 ,  70  are generally triangular with the apex adjacent to the manifold  62  so that the nozzle  64 ,  66  define an elongate outlet  72  that is parallel to the path of movement of a container along the conveyor  12 . As an be seen in  FIG. 8 , the nozzles  64 ,  66  of the nozzle assemblies  32 ,  34  are positioned relative to one another to provide a substantially continuous outlet  72  between the guide pullies  22 . 
         [0026]    The heater assemblies  54 ,  56  are mounted on an adjustable column  74  through outriggers  76  that extend from a carriage  78 . An adjustment screw  80  cooperates with the carriage  78  to allow vertical adjustment of the heater assemblies  54 ,  56  relative to the conveyor to facilitate alignment with the chines (D), (E) of the container (B). Locking levers  82  secure the carriage  78  to the column  74  once the adjustment is made. 
         [0027]    The plenum chamber  40  extends between the pullies  22  on the opposite side of the conveyor  12  to the nozzle assemblies  32 ,  34 . The plenum chamber  40  has a trapezoidal cross section with a floor  92  and a roof  94  converging in a direction away from the conveyor  12 . An end wall  96  extends between the floor and roof and the roof  94  is pivoted by a hinge  98  to the end wall  96  so it may readily be opened to allow access to the conveyor. 
         [0028]    The conduits  42 ,  44  each include return ducts  100 ,  102  that are connected to apertures in the floor  92  and are connected to one another at a tee  104  to a common return line  106 . The return line  106  is connected to the inlet  108  of the respective one of the fans  36 ,  38  to supply return air to the fans. 
         [0029]    Between the tee  104  and the inlet  108 , a make up duct  110  is provided to draw external air into the return duct  106 . Air flow into the make up duct  110  is controlled by a butterfly valve  112 . 
         [0030]    The butterfly valve  112  has a valve member  114  that is movable by a motor  116  between a closed position in which flow through the duct  110  is prevented and an open position in which relatively unrestricted flow is permitted. The motor  116  is operable on the valve member  114  to vary the position of the valve member between the open and closed positions and thereby regulate the flow of air through the make up duct  110 . 
         [0031]    The motor  116  is controlled by a thermo couple  118  that is located adjacent to the inlet  108  and measures the temperature of air provided to the fan. By modulating the valve member  114 , the mixture of return and make up air may be regulated to adjust the temperature of the return air and maintain it below a predetermined level. A control  120  receives the signal indicative of the temperature from the thermo couple  118  and actuates the motor  116  to adjust the valve member so as to maintain the temperature at or about the set point. 
         [0032]    In operation, containers (C) are fed on the conveyor  12  to the worm assembly  14  where there are individually spaced along the conveyor. The worm assembly  14  delivers the container (C) to the belt drives  16  where the belt  20  engages the body of die container (C) and rotates it along the guide rail  18  past the nozzle assemblies  32 , 34 . 
         [0033]    As the container (C) passes the nozzle assemblies, the relative continuous heated air stream from the nozzles  64 ,  66  impinges upon the unsupported edges of the label L as the container rotates past the nozzles and the heat causes the material to shrink against the chines (D), (E). The container is then discharged by the belt drive into the assembly area. 
         [0034]    Air passing through the nozzle  64 ,  66  is projected transversely across the conveyor and is collected by the convergent walls of the plenum  90 . The air is drawn from the plenum  90  through the return ducts  100 ,  102  to the inlet  108  of the fan. The provision of the plenum  90  opposite the nozzles and the negative pressure within the plenum induced by the fans  36 ,  38  promotes the flow of air from the nozzles into the plenum so that the hot air may be reclaimed. The temperature of the air returned through the inlet is monitored by the thermo couple  118  and modulates the butterfly valve  112  to maintain the temperature below the set point. In this manner, the temperature returned to the fan is within the normal operating range of the fans  36 ,  38 . The temperature of air supplied by the fan through the outlet  50  is then elevated by the heaters  54 ,  56  but the energy supplied to maintain the desired temperature for impingement on the film may be reduced. In this manner, the energy consumption of the shrink station is significantly reduced without adversely impacting on the operation of the fans. 
         [0035]    To mitigate the heat losses further, the upper and lower surfaces  68 ,  70  of the nozzles  64 ,  66  are configured so that the air flowing from the outlet  72  induces a flow of air across the surfaces  68 ,  70  and into the plenum chamber. The air flow indicated by arrows in  FIG. 6 , minimizes the loss of heated air through convection and reduces the heat loss through radiation as the air passes across the containers. In a typical application, the included angle between the surfaces  68 ,  70  is 30 degrees and the height of the outlet  72  is 525 millimetres. The transverse dimensions of the surfaces  68 ,  70  is 355.6 millimetres and with allow of 18 mm 3  per second an effective induction of air over the surfaces is found to be generated. 
         [0036]    It will be seen therefore that the shrink station is effective to minimize loss of energy from the air as it is forced across the conveyor and by modulation of the air intake, the energy consumption used to elevate the temperature to that required to effect shrinkage on the film of the label is reduced.