Patent Publication Number: US-6701696-B1

Title: Packaging machine of the tunnel type for carrying out packaging with a heat-shrinkable film

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an improvement in a packaging machine using a heat-shrinkable film and provided with a shrinkage tunnel. 
     In the known art packaging machines using heat-shrinkable films are known and they comprise a frame for sealing of the film surrounding the product to be packaged and a shrinkage tunnel providing circulation of hot air in a continuous cycle. 
     A conveyor belt carries out passage through the tunnel of the products wrapped in the film already sealed by means of the frame. The film grazed by the hot air circulating within the tunnel shrinks on the product thereby packaging it. 
     In these shrinkage tunnels, air circulation through the electrical heating elements takes place in a continuous manner and temperature adjustment is carried out by a probe measuring the air temperature and sending a signal to an appropriate thermoregulator adjusting the heating power of the electrical heating elements. 
     This way of operating involves a high energy consumption and a high thermal pollution in the work environment due to continuous emission of hot air. On the other hand, if air heating is reduced, film shrinkage becomes unsatisfactory. It is a general aim of the present invention to obviate the above mentioned drawbacks by providing a packaging machine of the above type, which allows high energy saving while keeping a satisfactory heat-shrinkage of the film. 
     SUMMARY OF THE INVENTION 
     In view of the above aim, in accordance with the invention a packaging machine using a heat-shrinkable film has been devised which comprises a frame for peripheral sealing of a film segment and a tunnel disposed alongside the frame in which means is arranged for circulation of the air heated by electrical heating elements for shrinkage of the sealed film which is introduced into the tunnel, characterised in that it comprises means for detecting a condition associable with the presence in the machine of a product wrapped in a film to be shrunk, the detecting means, upon detection of said condition, producing a signal for temporary actuation of the hot-air circulation means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For better explaining the innovatory principles of the present invention and the advantages it offers over the known art, a possible embodiment applying said principles will be described hereinafter, by way of non-limiting example, with the aid of the accompanying drawings. In the drawings: 
     FIG. 1 is a diagrammatic perspective view of a packaging machine embodied by the invention; 
     FIG. 2 is a cross-sectional view of the machine in FIG. 1, taken along line II—II in FIG. 3; FIG. 
     FIG. 3 is a view partly in longitudinal section of the machine in FIG. 1, taken along line III—III in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings, a packaging machine generally identified by  10  comprises a sealing region  11  and a heat-shrinkage region  12 , connected with each other by a conveyor belt  13  made up of a perforated netting. The sealing region comprises a frame  14  hinged at  15 , to be moved close to a fixed counter-frame or abutment  16  provided with sealing blades  35  at the upper part thereof. Frame  14  surrounds a support table  17  along three sides thereof, on which table the products or items  18  to be packaged by means of a heat-shrinkage film  19  unwound from a supply bobbin  20  are disposed. The film is longitudinally folded to surround the product at the upper and lower parts thereof and the open sides of the film are sealed by the action of the sealing blades  16  disposed on the front side and the upstream side (relative to the film feeding direction) of table  17 . 
     As also clearly shown in FIGS. 2 and 3, the shrinkage region comprises a hot-air shrinkage chamber or tunnel  21  in which a rest surface is present which consists of the upper part of the conveyor belt  13  passing through the chamber to convey the items wrapped in the film between an entry opening  22  and an exit opening  23 . The two openings are advantageously closed by depending flexible bands  24 ,  25  enabling passage of the items while reducing dispersion of hot air to the outside of the chamber. 
     The chamber is defined at the upper part thereof by a cover or vault  26  advantageously made at least partly of a transparent material, so as to enable sight of the shrinkage process taking place inside it. 
     In the shrinkage chamber there is a fan  27  causing circulation of air within the chamber itself, making it pass through heat-adjusted electrical heating elements  28 . Advantageously, the heating elements  28  are held in a baghouse  29  communicating at the lower and upper parts thereof with the shrinkage chamber. The upper opening of baghouse  29  is closed by a shutter or flap  30  driven for opening by an actuator  31  (an electromagnet, for example). Fan  27  and actuator  31  are operated by a control box or timer  32  receiving an enable signal  33  to operation by a control means  34 . The control means  34  is operated for signalling that an item to be packaged is about to be or has been inserted into the shrinkage chamber. In other words, there is the presence of means  34  for detecting a condition associable with the presence in the machine of a product wrapped in a film to be shrunk; the detecting means, on detection of said condition, produces a signal  33  for temporary actuation of the means  27  for hot-air circulation. 
     In accordance with the described embodiment, the control means is embodied by a sensor or microswitch  34  detecting closure and subsequent re-opening of the sealing frame  14 . This microswitch can be the same element switching on the synchronised-pulse heating of the sealing blades present in the frame. Since closure of the frame enables the sealing operation preceding the shrinkage operation to be carried out, the signal emitted by microswitch  34  is of relevance for starting a timely hot-air circulation in the tunnel. The control box or timer  32  will keep fan  27  and actuator  31  in operation over a predetermined period of time sufficient to achieve shrinkage of the film on the product. 
     This time may comprise the estimated time for introduction of the product into the tunnel and passage of the product therethrough until reaching of the tunnel exit. This time can be adjusted depending on requirements. By virtue of the transparency of tunnel  26  the shrinkage process can be watched while it is being carried out and the exactness of the set time can be checked with the possibility of adjusting it, if necessary. 
     In use, on starting of the packaging machine the net-type conveyor belt  13  is set in motion. Simultaneously, the thermostat-controlled electrical heating elements  28  within the heat baghouse  29  get hot until they reach the optimal temperature for heating of the air circulating within the tunnel. 
     By operating the sealing frame downwardly, sensor  34  enables heating of the sealing blades  26  for carrying out sealing of the film onto the item. When sealing has been completed, by lifting the frame to its rest position sensor  34  drives the control box  32  to start operation of the circulation fan and to open the heat baghouse. Meanwhile, the item can be introduced into the tunnel by means of the conveyor, so that at the tunnel exit  23  it appears conveniently packaged in the film shrunk thereon. 
     At this point it is apparent that the intended purposes have been achieved by supplying a packaging machine provided with a shrinkage tunnel in which the hot air circulation is not continuous, as it happened in the known art, but is only present when required for packaging of a product introduced into the tunnel itself, which will bring about a very important energy saving and a reduced environmental impact. 
     Obviously, the above description of an embodiment applying the innovatory principles of the present invention is given by way of example only and therefore must not be considered as a limitation of the scope of the invention as herein claimed. 
     For instance, the air-circulation fan can be also positioned at the tunnel top instead of being provided at the bottom. In addition, the sensor for starting the hot-air circulation can be also made in a different manner from the preferred embodiment shown. For instance, placement of a sensor provided with a photoelectric barrier may be envisaged at the entry opening of the tunnel for detecting passage of the product disposed on the belt. The sealing frame can be made in different ways: for example, the sealing blades may be fitted in the movable portion of the frame, instead of being arranged in the fixed one. The blades themselves may be accomplished both by pulsed heating and hot wire heating.