Abstract:
The present invention relates to a method for welding at least one foil in a packaging process using a welding assembly, comprising the steps of directing the foil into the welding assembly, holding the foil in at least one holding point of the welding assembly, welding the foil in at least one welding point of the welding assembly, and where a part of the foil is accumulated between the at least one holding point and the at least one welding point prior to welding the foil in the welding point. The present invention further relates to a welding assembly employing this method.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method for accumulating foil prior to welding. The foil is used for packaging and wrapping compressible and incompressible objects. 
       BACKGROUND 
       [0002]    Packaging and wrapping of products using foil is widely used in many industries. Such packed or wrapped products could be for the building industry and range from building materials such as plaster plates to glass or mineral wool. One of the primary requirements for the packaging of such products is naturally that the material wrapped around the products serves to protect the products until it is purposely broken. 
         [0003]    When wrapping insulation materials, such as glass or mineral wool, the foil is often used as a mean for maintaining a compression of normally a stack of insulation objects. The insulation objects are compressed and then wrapped in un-stretched or stretched foil, which is joined by welding. The welding is made by a welding assembly comprising two pairs of resilient jaws, between which a knife for cutting the foil is placed. Further, between the knife and the resilient jaws two pairs of welding beams for welding the foil are positioned. When the objects to be packed have been wrapped in the foil, the foil is stretched and held between the resilient jaws and at the same time clamped between the welding beams. Hereafter the foil is cut and welded at the same time. 
         [0004]    To reduce the production costs, it is desired to reduce the amount of foil used per package. This is done by using thinner foils in the existing production facilities. However, using thinner foil is encumbered with one major problem. Regardless of the foil thickness, the thermal stress applied to the stretched foil during welding will release the tension present in the foil. This will lead the foil to creep and consequently lead to a thinning of the foil between the resilient jaws and the welding beam. When using thin foils, the thinning can reduce the yield strength of the foil below the required level or be so severe that the foil is reduced to only thin threads. There is therefore a great risk that the packaging process fails or that the finished package is torn or breaks open unintentionally. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention relates to a method for welding at least one foil in a packaging process using a welding assembly comprising the steps of directing the foil into the welding assembly, holding the foil in at least one holding point of the welding assembly, welding the foil in at least one welding point of the welding assembly, and where a part of the foil is accumulated between the at least one holding point and the at least one welding point prior to welding the foil in the welding point. When the foil is welded the foil is drawn or crept towards the welding point, due to the heat in this point. Since a part of the foil has been accumulated between the welding point and the holding point, only the excess foil here is drawn towards the welding. Hereby it is avoided that the foil is over-stretched or that the welding will be too weak. Thinning of the foil between the welding point and the holding point will therefore not occur. Thus, the risk of breakage of the foil due to weaknesses in the foil and/or welding is reduced or eliminated. A packaging process using this method will therefore not fail nor will the finished package be torn or break open unintentionally. 
         [0006]    In another embodiment the method further comprises the step of cutting the foil during welding of the foil. When using continuous foil this is particular advantageous, as this enables a continuous packaging process. 
         [0007]    In a further embodiment the method comprises the step of clamping the foil in the at least one welding point prior to holding the foil in the at least one holding point. This is advantageous as it makes it possible to direct foil towards the welding point prior to holding the foil in the holding point, whereby foil will be accumulated between the welding point and the holding point. 
         [0008]    In yet another embodiment the method comprises the step of clamping the foil in the welding point offset from the holding point of the foil ( 112 ), and then aligning the at least one welding point with the at least one holding point. By having the welding point and the holding point offset from each other and subsequently aligning these two points, foil can be accumulated between these two points. The length of the accumulated foil can be max. the distance between the welding point and the holding point. This distance can advantageously be adjusted according to e.g. the welding and/or foil properties. 
         [0009]    The present invention further relates to a welding assembly for welding at least one foil comprising welding means for welding the foil, and where the welding assembly further comprises holding means for holding the foil while welding, and where the welding assembly comprises accumulation means for accumulating a part of the foil between at least one welding point of the welding means and the holding point of the holding means, prior to welding the foil. The welding assembly is advantageous in that the accumulation means ensures that a part of the foil can be accumulated between the welding point and the holding point. While welding, the foil will be drawn or crept towards the welding point of the welding means, but without weakening or breaking the foil both during and after the welding process. 
         [0010]    In another embodiment the welding assembly comprises cutting means for cutting the foil. This is advantageous in that the welding assembly can be used in e.g. a continuous packaging process using continuous foils. 
         [0011]    In a further embodiment the welding means of the welding assembly comprises a welding beam, at least one welding bar and a welding support. This is advantageous in that the foil can be clamped in a welding point by the welding beam and the welding, support, and further that the foil can be welded in the same welding point. In addition, the welding point can be moved independently of the holding means. 
         [0012]    In yet another embodiment the holding means of the welding assembly comprises an upper jaw, a lower jaw and at least one resilient member. This is advantageous in that the foil can be held firmly prior to and during the welding process. By having at least one resilient member it is ensured that the foil maintains its position, thus the foil cannot slide in the holding point. 
         [0013]    In another embodiment the accumulation means of the welding assembly is a pneumatic cylinder. Here the advantages are as mentioned above. 
         [0014]    The present invention further relates to the use of a welding assembly as mentioned above employing the method for welding at least one foil in a packaging process also mentioned above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In the following, preferred embodiments of the invention will be described referring to the figures, where  FIGS. 1   a - f  illustrate a number of method steps of accumulating foil prior to welding the foil. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0016]    The welding assembly  100  comprises holding means, welding means, cutting means and accumulation means. The holding means comprises an upper jaw  102  and a lower jaw  104 . The lower jaw  104  comprises a resilient member  105 , in which the two protrusions of the upper jaw  102  can form a recess or groove. The jaws  102 ,  104  can be moved vertically up and down and can hold the foil  112  in the holding point  124 ,  125 . The welding means of the welding assembly  100  comprises a welding beam  106  and a welding support  108 . The welding beam  106  and the welding support  108  are placed in between the jaws of the upper jaw  102  and the lower jaw  104 , respectively. The welding support  108  can be moved vertically up and down, independently of the lower jaw  104 . This movement can be enabled by accumulation means (not shown), such as a pneumatic cylinder. The welding beam  106  can be moved vertically up and down relative to the upper jaw  102 . This relative movement is limited to the clearance  118  of the upper jaw  102 . For illustrative purposes, the clearance  118  is only depicted in  FIG. 1   a . The welding beam  106  comprises two welding bars  107 ,  109 , which can be heated e.g. by directing a current there through. When the welding beam  106  and the welding support  108  are brought together they clamp the foil  112  in the welding point  122 ,  123 . The welding assembly  100  further comprises cutting means comprising a knife  110  for cutting the foil  112 . The knife  110  can be moved vertically up and down independently of the welding support  108 . The width of both the jaws  102 ,  104 , the welding beam  106 , and the welding support  108  span at least the width of the foil, but does not have to be continuous. The knife  110  also spans at least the width of the foil. 
         [0017]    In one embodiment the foil is welded using the welding assembly  100  according to the following method. The method relates to the joining of at least two foils. The at least two foils can originate from the same roll of foil but also be from two different rolls of foil. For the sake of simplicity the at least two foils are depicted and referenced as one foil  112 . The foil  112  used can be un-stretched or pre-stretched. The latter concerns a foil that has been stretched to such an extent that it is plastically deformed. This means that the foil cannot be stretched any further without breaking it. 
         [0018]    As illustrated in  FIG. 1   a , the foil  112  is directed or led in between the upper and lower jaws  102 ,  104  and the welding beam  106  and the welding support  108 , which have been positioned so that they form a space there between. As depicted in  FIG. 1   a , the welding beam  106  is positioned vertically higher than the jaws of the upper jaw  102 . The welding support  108  is then directed upwards towards the welding bars  107 ,  109 , whereby the foil  112  is clamped in the welding point  122 ,  123 , see  FIG. 1   b . This upward movement of the welding support  108  could be enabled by using accumulation means (not shown), such as actuating a pneumatic cylinder. The upper jaw  102  and thereby also the welding beam  106  are then moved downwards towards the lower jaw  104  and the resilient member  105 . The downwards movement of the welding beam  106  can take place as the pressure in the pneumatic cylinder (accumulation mean) in the welding support  108  is reduced or removed. The foil  112  is now held between both upper and lower jaw  102 ,  104  in the holding point  124 ,  125  and clamped between the welding beam  106  and the welding support  108  in the welding point  122 ,  123 . In the space between the holding point  124 ,  125  and the welding point  122 ,  123 , accumulated foil  112  is now placed. The foil  112  in this confined space will typically fold in e.g. an S- or Z-shape. As illustrated in  FIG. 1   d , the foil  112  is hereafter cut by moving the knife  110  (cutting means) upwards and at the same time welded in the welding point  122 ,  123 . Due to the heat, the accumulated foil  112  on both sides of the welding point  122 ,  123  is drawn or crept towards the welding point  122 ,  123 . If the foil  112  is pre-stretched (plastically deformed or stretched), the foil  112  will during welding creep or be drawn more towards the welding point  122 ,  123 , than an un-stretched foil  112 . In order to provide the best possible welding, the welding support  108  can be pressed against the welding bars  107 ,  109  during and after welding. 
         [0019]    This is done by activating the pneumatic cylinder of the welding support  108 . Hereby it can be ensured that e.g. the transition from the performed welding and the regular foil  112  is such that the foil  112  does not break if the foil  112  is exposed to e.g. a force across the foil  112 . 
         [0020]    The steps of the method described can vary both in terms of how they are performed and the sequence of them. Thus the foil can be accumulated in many other ways between the holding point  124 ,  125  and the welding point  122 ,  123 , using different accumulation means. This could e.g. be by moving the holding means and the welding means according to another method or sequence of steps. The foil could also be pre-accumulated before it is led in between the holding and the welding point. The accumulation means could also be an element or apparatus that conveys foil towards the welding point, e.g. when the welding means clamps the foil and before the foil is held in the holding point by the holding means. 
         [0021]    The knife  110  which can be moved vertically up and down independently of the welding support  108  makes it possible to actually weld the foil  112  before cutting the foil  112  ensuring that the foil  112  has the time to be welded before cutting and further that the foil is not stressed while cutting. The possibility of independently moving the knife  110  makes it possible to ensure the correct timing between welding and cutting. The timing could depend on the amount of foil to be welded as well as the type of foil to be welded. Further, the independent movement up and down of the knife  112  as well as the vertical space within said welding support  108  makes it possible to control the extent of up and downwards movement to ensure that the foil  112  gets cut, which again could depend on the type of foil. 
       REFERENCES 
       [0000]    
       
           100  welding assembly 
           102  upper jaw 
           104  lower jaw 
           105  resilient member 
           106  upper welding beam 
           107  welding bar 
           108  welding support 
           109  welding bar 
           110  knife 
           112  foil 
           118  clearance for moving the welding beam  106  relative to the upper jaw  102   
           120  direction of movement of the foil  112   
           122 ,  123  welding point of the welding means ( 106 ,  107 ,  108 ,  109 ) 
           124 ,  125  holding point of the holding means ( 102 ,  104 ,  105 )