Abstract:
Method and relevant equipment for achieving stabilising ventilated coverings for palletised loads (P) with plastic film; the method comprising a first phase, or step, where the plastic film is applied to the load (P) to achieve a stabilising covering, and a following phase, or step, where the stabilising covering is perforated, making a plurality of holes to aerate the load (P) The equipment for carrying forth the method comprises at least one mobile supporting structure ( 33 ), that alternately approaches, and moves away, from the palletised load (P), and which has a plurality of perforating punches ( 4 ), each one making a hole in said covering of the palletised load (P).

Description:
FIELD OF THE INVENTION  
       [0001]     This invention refers to a method and the relevant equipment, for achieving stabilising ventilated coverings for palletised loads, with plastic film.  
       BACKGROUND OF THE INVENTION  
       [0002]     It is commonly known that to transport a load, it is put on a pallet and then wrapped, sometimes the pallet too, with a plastic film that holds the load firm, stabilising it during handling and can even protect it against water and dust.  
         [0003]     Today different methods are used to apply said stabilising film.  
         [0004]     One of such methods entails covering the palletised load with a plastic film, like a large cover. Said cover can be heat shrunk plastic, heated so it shrinks and adheres perfectly to the palletised load, or it can be a cover made with an elastic material that expands when it is being fitted, adhering elastically to the palletised load. Yet another method entails wrapping the palletised load with an extensible plastic strip, pulled taut, wrapping it tightly.  
         [0005]     The second method can be achieved using a wrapping machine that comprises a reel of film moving vertically and which wraps the plastic film helicoidally around the outside of the palletised load as it turns on a swivel platform; or, with a different wrapping machine whose reel of film moves both vertically and with a planetary motion around the palletised load that stays still.  
         [0006]     Regardless of the method used, however, there is one particular problem with such stabilising coverings which arises when the loads contain objects whose temperature is below the dew point temperature of the surrounding environment, typical of liquid containers—bottles or bricks.  
         [0007]     In these cases, in fact, the humidity in the air trapped inside the stabilising covering condensates on the surface of said containers which, getting wet, can deteriorate (i.e. bricks) or can wet other objects of the load or other packaging elements, damaging them.  
         [0008]     To solve this drawback, pre-perforated covering materials are now used (heat shrunk wrapping, elastic wrapping or extensible film) to ensure natural aeration of the load with no condensation.  
         [0009]     Said pre-perforated covering materials however, are more expensive (because they need perforating), less resistant compared to the usual, non perforated covering materials and afford less stability to the palletised load in general; pre-perforated material is preferred only when it is essential to avoid condensation, as mentioned above.  
         [0010]     For these reasons, when palletised loads subject to the formation of condensate and others that are not subject are on the same packing line, the above described covering materials have to be alternated various times which creates difficulties in managing the process as well as increasing production times and equipment costs.  
         [0011]     Besides these drawbacks, peculiar to all pre-perforated covering materials, there are others specific to extensible pre-perforated films.  
         [0012]     One of these drawbacks is that there are normally problems when pulling such pre-perforated films tight, undermining the stabilising effect they have on the wrapped load. Yet another drawback is that since the palletised load is normally wrapped with several layers of pre-perforated film, this film cannot always guarantee aeration holes in the stabilising covering as they could be closed by the outer most layers.  
       BRIEF SUMMARY OF THE INVENTION  
       [0013]     The purpose of this invention is to solve the drawbacks of known techniques with a simple, rational and cost-effective solution.  
         [0014]     Generally speaking, this objective is attained with a method for achieving stabilising ventilated coverings for palletised loads using plastic film, comprising a first phase, or step where the plastic film is applied to the load to achieve a stabilising covering (according to traditional methods) followed by a second phase, or step, where the stabilising covering is perforated, making a plurality of holes to aerate the load.  
         [0015]     Thanks to this solution, the palletised load can be advantageously covered with the usual, non perforated covering materials that are more economical and resistant compared to pre-perforated materials. In addition, it is no longer necessary to alternate the different types of covering materials on the same packing line, simplifying process management and a reduction in costs.  
         [0016]     According to a preferred form of embodiment of the method, the stabilising covering is applied by wrapping a plastic film around the palletised load several times and then all the layers, on at least one side of the load, are perforated simultaneously.  
         [0017]     To make each aeration hole in the stabilising covering, it is preferable to use a heat source that softens the stabilising covering, melting it locally. In this way, each aeration hole has an edge thickened by a ridge of melted plastic which, as it cools, prevents the hole from expanding which would weaken the stabilising covering; this makes the film far more resistant to tears compared to a film that is perforated mechanically. In addition, if the stabilising covering is applied by wrapping a plastic film around the load several times, the layers thus obtained are sealed together by the melted (and hardened) edges of the holes. By using this method the stabilising covering is not weakened by the aeration holes as is the case if perforation is simply mechanical but, to the contrary, the sealing of said layers renders the whole wrapping stronger and the plastic film cannot unwind when the load is being handled.  
         [0018]     The invention also makes an equipment available for perforating the stabilising covering of palletised loads, achieved with plastic film.  
         [0019]     Said equipment comprises at least one mobile supporting structure that alternately approaches, and moves away, from the palletised load and which has a plurality of perforating punches, each one making a hole in said covering of the palletised load.  
         [0020]     According to a preferred form of embodiment of the invention, each one of said perforating punches has a heatable head that softens the stabilising covering locally so that, by means of a mechanical action, the perforating punch can then perforate said stabilising covering.  
         [0021]     In particular, as mentioned previously, when the perforating punch is facing a portion of the stabilising covering formed by several overlapping layers of plastic film, the heat of the heatable head also seals said layers together, improving the wrapping of the palletised load.  
         [0022]     According to the invention, the perforating equipment includes means to stop the supporting structure when the latter, as it approaches the palletised load, reaches a set distance from the palletised load, allowing the perforating punches to make the holes in the stabilising covering. In particular, according to a preferred form of embodiment of the invention, said stopping means include a proximity sensor integral with the supporting structure and which, as it touches the palletised load, causes the supporting structure to stop.  
         [0023]     In this way, the approaching movement of the supporting structure is not constant but can adapt effectively and automatically to the different dimensions of palletised loads and to their position in relation to the perforating equipment.  
         [0024]     According to the invention, the perforating punches are fixed to the supporting structure through securing means so their position can be varied on the structure. Thus it is advantageously possible to adjust the position of the perforating punches so the aeration holes can be made in the stabilising covering where there is no risk of damaging the load under it like, for instance, in gaps between one object and another as in the case of non-continuous loads such as bottles or the like.  
         [0025]     In addition, according to the invention, the supporting structure oscillates on a rotational axis orthogonal to its direction of movement, preferably according to a horizontal axis, fitted with a pair of stop elements on sides opposite said rotational axis, their job being to go against the palletised load when the supporting side reaches the forward position.  
         [0026]     Thanks to this solution, the supporting structure can always place itself parallel to the side of the palletised load it is facing and, therefore, position the perforating punches correctly in relation to the stabilising covering.  
         [0027]     Further characteristics and advantages of the invention will appear evident from the following description of a form of embodiment according to this invention, illustrated by way of non limiting example in the attached drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]      FIG. 1  is a perspective front view of an equipment according to the invention;  
         [0029]      FIG. 2  is a perspective rear view of the equipment in  FIG. 1 ;  
         [0030]      FIG. 3  is a plan view of the equipment in  FIG. 1 ;  
         [0031]      FIG. 4  is the section of tracing IV-IV shown in  FIG. 3 ; and  
         [0032]      FIG. 5  is an enlarged detail of  FIG. 1 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     The enclosed figures illustrate an equipment that makes aeration holes in the stabilising covering, obtained by wrapping palletised loads P with an extensible plastic film.  
         [0034]     In the example given, said equipment configures as a perforation station  1  of an industrial packing line, to be placed downstream the palletised loads P wrapping station; it could, however, also be used in the actual wrapping station and start working straight after the wrapping machine so the palletised load P needs no further handling.  
         [0035]     The station  1  comprises a conveyor device  2  fitted with three sliding belts  20  on which the palletised loads P stand—their job being to move the loads in a straight feeding line A—and a perforating machine  3  on the side of said conveyor device  2 .  
         [0036]     The perforating machine  3  consists of a fixed base  30  on which the sliding frame  31  is mounted which, operated by a jack  32 , moves with a reciprocating motion in a straight line B orthogonal to the feeding direction A of the palletised loads P.  
         [0037]     A substantially vertical supporting side  33  on the front of the frame  31 , that is, on the side facing the conveyor device  2  and which follows the movement of the frame  31 , can selectively approach or move away from the palletised loads P.  
         [0038]     In particular, said supporting side  33  is hinged to the frame  31  so it can oscillate in relation to the latter, turning around a rotational axis C, horizontal and orthogonal to the direction of movement B of the frame  31 ; said oscillation is limited by a pair of opposing stops  42  positioned on an intermediate cross bar  43  fixed to the frame  31  (see  FIGS. 2 and 4 ).  
         [0039]     In detail, the supporting side  33  comprises a perimeter frame  34  stiffened by a pair of horizontal beams  35  and closed at the rear by a panel  36 , plus a set of vertical rods  37  with their ends connected to the top and bottom of said perimeter frame  34 .  
         [0040]     A row of perforating punches  4  is fixed to each vertical rod  37  projecting from the supporting side  33 , facing the palletised loads P.  
         [0041]     In the example shown, said perforating punches  4  are elongated elements, each fitted with a heatable head  40  with a controlled and adjustable temperature (using a thermostat). They are pushed against the stabilising covering of the palletised loads P to make the hole.  
         [0042]     Said perforating punches  4  can however be different like, for instance, a cutter or perforating head.  
         [0043]     In detail, the ends of the vertical rods  37  are secured to the perimeter frame  34  by sliding joints  38  that engage inside the horizontal guides  39  fixed to the top and bottom of the perimeter frame  34  so that the rows of perforating punches  4  can alternately approach/move away; in addition, said perforating punches  4  are, in turn, fixed to the vertical rods  37  with clamp devices  41  so their reciprocal vertical distance can be varied.  
         [0044]     The supporting side  33  also includes a pair of horizontal stop bars  5  on the opposite side of the horizontal axis hinge C that connects the supporting side  33  to the frame  31 .  
         [0045]     The purpose of said stop bars  5  is to go against the palletised load P as the supporting side  33  approaches so as to define the correct position of the perforating punches  4  in relation to the stabilising covering and to make the supporting side  33  oscillate around the rotational axis C if its inclination does not coincide with that of the side of the palletised load P facing it.  
         [0046]     In detail, the stop bars  5  are connected to the perimeter frame  34  of the supporting side  33 , each one by means of a pair of sliding joints  50  that, engaging in a vertical guide  51 , make it possible to adjust their position and reciprocal distance.  
         [0047]     In addition, each stop bar  5  supports its own proximity sensor  52 , preferably a microswitch that, when it comes into contact with the palletised load P, emits an electrical signal that is sent to the control means (not shown) of the perforating machine  3 .  
         [0048]     In particular, when both microswitches  52  emit said signal, the supporting side  33  stops instantly and retracts from the palletised load P. As the supporting side  33  stops, a timer can be operated which, appropriately set, makes it move back after a certain length of time, sufficient for the heatable heads  40  of the perforating punches  4  to make the holes in the palletised load&#39;s P wrapping.  
         [0049]     When using, before starting the process, the position of the perforating punches  4  on the supporting side  33  needs to be adjusted according to the form, type and layout of the load on the pallet so said punches  4  cannot accidentally damage the load during perforation.  
         [0050]     The palletised loads P wrapped previously with the extensible plastic film are positioned on the conveyor device  2  one at a time.  
         [0051]     Said palletised loads P are normally parallelepiped in shape and, therefore, positioned on the conveyor device  2  so two opposite sides are parallel with the feeding direction A.  
         [0052]     The conveyor device  2  moves the palletised loads P forward intermittently so that for each feeding phase a palletised load P is in the perforating position, that is, in a suitable position for the perforating machine  3 .  
         [0053]     In the example shown, the perforating position for the palletised load P is in front of the perforating machine  3  so that one of its opposite sides, parallel with feeding direction A, faces the supporting side  33  and, hence, the perforating punches  4  projecting from the latter.  
         [0054]     During the stopping time of the palletised load P the jack  32  operates the frame  31  so that said supporting side  33  makes an approach stroke towards the palletised load P.  
         [0055]     When the perforating punches  4  move close the stabilising covering, it is locally softened by the heatable heads  40  so that when the supporting side  33  moves forward again, the perforating punches  4  can mechanically perforate the film.  
         [0056]     In this way, when a perforating punch  4  is facing a portion of the stabilising covering made of several overlapping layers of plastic film, the heat of the heatable head  40  also seals said layers together locally, strengthening the wrapping of the palletised load P even more; in addition, said head also creates an edge of melted plastic material around the hole that, cooling down, strengthens it.  
         [0057]     When the stop bars  5  come into contact with the side of the palletised load P, the perforating punches  4  have already made the holes in the stabilising covering.  
         [0058]     In particular, when said side of the palletised load P slants differently from the normal inclination of the supporting side  33 , the contact of the stop bars  5  is not simultaneous and therefore the first stop bar  5  that comes into contact with the palletised load P makes the supporting side  33  rotate, gradually becoming parallel with the side it faces, until the second stop bar  5  also comes into contact with the palletised load P.  
         [0059]     The instant both microswitches  52  on the stop bars  5  send the signal of contact, the frame  31  stops moving forward and, if used, the timer starts, defining the time needed by the perforating punches  4  to finish the holes in the stabilising covering.  
         [0060]     The jack  32  is then operated again, retracting the frame  31  and moving the supporting side  33  away for a new feeding phase of the conveyor device  2  that moves the palletised load P away with its perforated wrapping, placing a new palletised load P in the perforating position.  
         [0061]     Obviously the solutions described above are not the only possibilities.  
         [0062]     For example, the perforating equipment could be made of a plurality of perforating machines  3  that make aeration holes on several sides of the palletised load P simultaneously.  
         [0063]     In particular, according to a preferred form of embodiment of the invention, the perforating station  1  could comprise two perforating machines  3 , opposite each other and positioned on opposite sides of the conveyor device  2 , working simultaneously on both sides of the palletised load P, parallel with the feeding direction A.  
         [0064]     In addition, according to an alternative form of embodiment of the invention, the supporting side  33  of perforating machine  3  could have just one vertical row of perforating punches  4  and the feeding system could be made to move the palletised loads P forward in steps shorter than their length.  
         [0065]     In this way in fact, by making the supporting side  33  perform one approach stroke each time the palletised load P stops, it would be possible to make all the aeration holes in the stabilising covering even using a device that is very simple and small in size.  
         [0066]     Many practical-application changes can be made to the invention described above without losing sight of the inventive idea as claimed below.