Abstract:
Closure clips and a process for the production of closure clips of strip-form or wire-form material for the closure of tubular or bag-like packagings. In the process, a substantially wave-form profile with successive first and second apex points is stamped along the strip-form or wire-form material, the first apex point forming a clip bottom, flanks respectively adjoining the first apex point on each side thereof form clip limbs that are bent over in a U-shape and the second apex point forms limb ends that are bent over outwardly with respect to the U-shape at which two adjacent closure clips are separably connected. The strip-form or wire-form closure clip material is pierced inwardly with respect to the U-shape so that a raised material portion is formed at the limb inside.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention concerns a closure clip and a process for the production of closure clips of strip-form or wire-form material for closing tubular or bag-like packagings, wherein a substantially wave-form profile with successive first and second apex points is stamped along the strip-form or wire-form material. The first apex point forms a clip bottom, flanks respectively adjoining the first apex point on each side thereof form clip limbs which are bent over in a U-shape and the second apex point, with respect to the U-shape, forms outwardly bent-over limb ends at which two adjacent closure clips are separably connected. The invention further concerns a stamping tool for the production of closure clips in accordance with such a process.  
         [0002]     Closure clips of that kind are known for example from DE 3 148 757 A1, EP 0 337 301 A1 or EP 0 738 662 A1. Those closure clips (also referred to as clips) are used to close tubular or bag-shaped packagings filled with liquid to viscous-pasty or (in part) granular content, sausage cases or artificial cases, at one or both ends thereof. For that purpose, the clips, typically made from an aluminum wire extrusion, are pre-bent in a U-shape in a clip machine, as described above, and are fed to a first closure tool of the clip machine, the female die, in a condition of being joined together by means of connecting legs formed in the form of the bent limb ends. After the filled packaging has been constricted in portion-wise manner to form a plaited portion, for example, by means of a displacement member or by being twisted off and thus a portion (sausage) has been divided off, the foremost clip of the above-described line of clips is pressed against the plaited portion and clamped between that and the female die. Thereupon, by means of a second closure tool that moves towards the female die, the punch, the foremost clip is severed from the following line of clips in the region of the connecting leg and then closed around the plaited portion of the packaging material. In that situation, the bent limb ends are pressed against the outside of the clip limbs and bent around the plaited portion of the packaging material, the limb ends and leg portions being pressed in butting relationship against each other and are upset so that the result is a ring that compresses the plaited portion of the packaging material as closely as possible.  
         [0003]     The endeavor was and is to develop such closure clips in such a fashion that either with the material thickness remaining the same, an always greater retaining force and resistance to slipping is achieved in order to ensure that the closure effect is as firm and tight as possible or conversely, with the same quality of closure, it is possible to make a saving in terms of material. Particularly when using plastic skins, for example of PVC, polyamide, polyester or plastic-coated fiber skins that have a relatively smooth surface, the resistance to slipping is a major requirement.  
         [0004]     For that purpose DE 3 148 757 A1 proposes, for example, arranging a reinforcing bead that is disposed centrally with respect to the width of the strip of material, in the region of the clip bottom and the arcuate connecting portions provided at the transition to the clip limbs. The reinforcing bead increases in particular the resistance of the closure clip to its being bent open.  
         [0005]     EP 0 738 622 A1 proposes a different route, whereby the closure clips, on the inside, have one or more grooves in the longitudinal direction of the strip of material in order to reduce the risk of the clips slipping off. EP 0 337 301 A1, along the same line, further discloses closure clips that on the inside of the clip limbs and also on the clip bottom have a plurality of grooves that substantially provide surface coverage and are arranged in mutually crossing relationship. The knurled patterns produced in that way have a higher level of surface roughness in relation to the longitudinal grooves and further reduce the risk of slipping off.  
       SUMMARY OF THE INVENTION  
       [0006]     An object of the present invention is to further improve the retaining force in relation to the known closure clips and in particular to further increase the resistance to slipping, using simple means.  
         [0007]     In the case of a process of the kind set forth in the opening part of this specification, that object may be attained in that the strip-form or wire-form material is pierced inwardly, with respect to the U-shape, that is to say in the direction of the clip limbs.  
         [0008]     In that way, the closure clip acquires an opening or aperture therethrough with a thrown-up raised material portion on its inside towards the limbs. The raised material portion provides a stiffening effect and thus an increased level of flexural strength as the thickness of material (at least partially) increases in the plane of the clip as defined by the U-shape. At the same time, the pressure loading of the closure clip against the plaited packaging material portion enclosed thereby is increased in point fashion and thus the adhesion of the clip to the plaited portion is improved in comparison with a flat clip inside.  
         [0009]     The opening through the clip may also include a raised material portion with a burr is preferably formed on the inside of the closure clip, which faces towards the limbs. That means that the point pressure loading and thus the static friction of the closure clip are further increased. The burr formation is harmless in particular in relation to packaging materials that afford a high level of resistance to tearing.  
         [0010]     Preferably, the process provides that the strip-form or wire-form material is pierced approximately centrally in the region of the clip bottom.  
         [0011]     The closure clip thus retains its symmetry. That ensures a stable deformation process during the closure operation without tilting moments. The opening through the clip or a recessed configuration in opposite relationship to the raised material portion in the outside of the clip bottom can further be used to center the clip in the female die and to secure it to prevent it from turning or tilting during the closure operation by virtue of the die being provided with a corresponding projection that engages into the recessed configuration in the closure clip when it is fitted into the die.  
         [0012]     In the process according to the invention, the operation of piercing the strip-form or wire-form material is preferably effected during the operation of stamping the wave-form profile.  
         [0013]     In that way, the working steps of stamping a substantially wave-form profile on the one hand and forming a raised material portion or an opening through the clip on the other hand are performed in a common working step with the same tool. That fixes the position of the opening through the clip, in relation to the profile. The piercing operation is thus implemented in the form of a comparatively easy working step which is simple to perform.  
         [0014]     The raised material portion is preferably of a hump-shaped configuration in the closure clip. That provides that the point loading on the packaging material in the closed condition of the clip is still further increased. The hump shape according to the invention can be produced by using for example a pointed bar of substantially round, oval or square cross-section for the piercing operation (bar piercing).  
         [0015]     In accordance with a preferred development of the process, recesses are impressed in the strip-form or wire-form material in the region of the inside of the limbs of the closure clip in the longitudinal direction.  
         [0016]     If, when a clip in the closed condition, those recesses correspond to the oppositely disposed raised material portion, the plaited material around which the clip is closed is displaced by the raised material portion into the recess and the plaited portion of material is gripped in that way. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0017]     Further objects, features and advantages of the invention are described hereinafter by means of an embodiment by way of example with reference to the drawings in which:  
         [0018]      FIG. 1  shows a closure clip according to the invention as a plan view onto the plane of the clip,  
         [0019]      FIG. 2  shows a sectional side view of the closure clip of  FIG. 1  in the plane of the clip,  
         [0020]      FIG. 3  shows a closure clip according to the invention closed around the end of a sausage, and  
         [0021]      FIG. 4  shows an embodiment of a stamping tool according to the invention for the production of the closure clip. 
     
    
     DETAILED DESCRIPTION  
       [0022]     The closure clip  100  according to the invention as shown in  FIG. 1  has a clip bottom  110  and two clip limbs  112 ,  114  that are bent over in a U-shape on both sides of the clip bottom  110 . The limb ends  116 ,  118  are bent over outwardly and on their underside have recessed impressions  120 ,  122  that represent a desired bend location and which, when the clips are closed, allow the limb ends to be bent over more sharply. Centrally, the clip bottom  110  has a straight portion that is adjoined by arcuate connecting portions  124 ,  126  at the transition to the limbs  112 ,  114 . The straight portion serves to provide that the clip  100  when fitted into a female closure die does not tend to twist or tilt by virtue of forces which possibly non-uniformly act at the limb ends.  
         [0023]     In the case of the production process according to the invention the closure clip is preferably pierced during the operation of stamping the wave-form profile by means of a mandrel bar, from the outside, with respect to the U-shape. That results in an opening  128  through the clip and a raised material portion  130  that is thrown on the inside of the closure clip. That raised material portion  130  is of a substantially hump-shaped configuration so that it provides for a point loading on the plaited portion of the packaging material that is closed by the clip.  
         [0024]     Stabilization and/or centering of the closure clip in the female die in the closure operation is further enhanced by the opening  128  according to the invention if a corresponding projection is provided on the die, which in the inserted condition of the clip at least initially engages into the opening through the clip.  
         [0025]      FIG. 1  further indicates an adjacent closure clip  150  that adjoins the closure clip  100  at  154  and is joined to the limb end  118  of the closure clip  100 , with one of its limb ends also bent over outwardly. The connecting leg  152  formed in that way is severed upon or immediately prior to the closure operation by a shearing tool on the punch that approaches the female die from above.  
         [0026]     On the inside, the clip limbs  112 ,  114  have recesses  132 ,  134  that are impressed centrally with respect to the plane  136  of the clip and are thus disposed in opposite relationship to the raised material portion  130  in the closed condition of the clip, see the sectional views in  FIG. 2  and  FIG. 3 .  
         [0027]     In the closed condition the closure clip  100 ′ embraces a plaited portion  160  of the packaging material of the divided and packaged portion (sausage)  162  and holds it fast in the manner shown in  FIG. 3 . It is possible to clearly see therefrom, how the projection formed by the raised material portion  130  presses into the plaited portion  160  in point form and thus gathers it still more greatly in the plane of the clip. Furthermore the packaging material on the opposite side is urged into the recesses  132 ,  134  in the clip limbs  112 ,  114 . That provides for an additional clamping effect and increases the resistance to the clip closed around the plaited portion from slipping off.  
         [0028]     The resistance to the clip slipping off is further increased by the opening  128 , wherein packaging material is urged into the aperture thereof on the inside of the clip by virtue of the compression of the plaited portion  160  and forms a projection  164 .  
         [0029]     Finally the resistance to the clip slipping off can be still further increased by the burr formation on the inside of the opening  128  being enhanced. A sharp burr  138  at the inner edge of the opening  128  increases the (point) pressure loading on the plaited portion  160  and thus increases the friction between the closed clip  100 ′ and the packaging material plaited portion  160 . The magnitude of burr formation depends on the choice of the packaging material and in particular its resistance to tearing and cutting.  
         [0030]      FIG. 4  shows an embodiment of a stamping tool  200  according to the invention for the production of the closure clips  100 ,  100 ′. The stamping tool  200  comprises an upper tool or punch  210  and a lower tool or female die  212 . The upper tool  210  is reversibly displaceable in a vertical direction with respect to the lower tool  212 . It will be appreciated that the lower tool  212  can also be displaceable with respect to the upper tool  210  or the upper and bottom tools  210 ,  212  can be displaceable relative to each other. In the description hereinafter it is assumed that only the upper tool  210  is displaced.  
         [0031]     Both the upper tool and the lower tool  210 ,  212  have a total of three working or stamping tool portions  210   a,    212   a  and  210   b,    212   b  and  210   c,    212   c.  The three stamping tool portions  210   a,    212   a  and  210   b,    212   b  and  210   c,    212   c  are arranged at least equidistantly relative to each other in a horizontal orientation, that is to say in perpendicular relationship to the direction of displacement of the upper tool  210 .  
         [0032]     Each of the stamping tool portions  210   a,    212   a  and  210   b,    212   b  and  210   c,    212   c  in turn comprises an upper tool or punch  210   a,    210   b,    210   c  and a respective lower tool or female die  212   a,    212   b,    212   c.  The three stamping tool portions  210   a,    212   a  and  210   b,    212   b  and  210   c,    212   c  each serve for a respective working step that occur in succession in order to produce a closure clip  100 ,  100 ′ according to the invention from a flat strip material BM that is fed in  FIG. 4  from the right by means of an advance device (not further shown).  
         [0033]     The first stamping tool portion  210   a,    212   a  produces a basic shape in respect of the closure clip  100 ,  100 ′ by the punch  210   a  moving into the female die  212   a  and in so doing imparting to the corresponding portion of the flat strip material BM the basic shape of the closure clip  100 ,  100 ′ according to the invention as shown in  FIG. 1 .  
         [0034]     After the upper tool  210  has been retracted, the flat strip material BM is then advanced with the advance device to such an extent that the portion of the flat strip material BM that was worked in the first stamping tool portion  210 ,  212  is disposed in the region of the next stamping tool portion, that is to say, the second stamping tool portion  210   b,    212   b,  and can there be fitted into the female die  212   b.  An unworked portion of the flat strip material BM is now disposed over the first stamping tool portion  210   a,    212   b.    
         [0035]     Thereupon the upper tool  210  can be displaced in the direction of the lower tool  212  so that the closure clip  100 ,  100 ′, which was pre-shaped in the first stamping tool portion  210   a,    212   a,  experiences further working or deformation. In particular in that case, the impressions  120 ,  122  at the upper end of the closure clip  100 ,  100 ′ and the recesses  132 ,  134  are then shaped. At the same time, at the flat strip material BM that extends towards the right, the basic shape of a further closure clip  100 ,  100 ′ is again produced in the first stamping tool portion  210   a,    212   a.    
         [0036]     After the upper tool  210  has been moved away from or lifted off the lower tool  212 , the flat strip material BM, after removal from the female dies  212   a,    212   b,  is further displaced towards the left in such a way that the closure clip  100 ,  100 ′ that has been worked in the second stamping tool portion  210   b,    212   b  can be arranged in the third stamping tool portion  210   c,    212   c  and the closure clip  100 ,  100 ′ that was worked in the first stamping tool portion  210   a,    212   a  can be arranged in the second stamping tool portion  210   b,    212   b.  In addition, a further unworked portion of the flat strip material is disposed in the region of the first stamping tool  210   a,    212   a.  In the downward movement of the upper tool  210 , in the first stamping tool portion  210   a,    212   a,  the basic shape of a closure clip  100 ,  100 ′ is produced from the unworked portion of the flat strip material BM, the basic shape of a closure clip  100 ,  100 ′ produced in the first stamping tool portion  210   a,    212   a  in the preceding working step is produced in the above-described manner in the second stamping tool portion  210   b,    212   b  and the closure clip  100 ,  100 ′ produced in the second stamping tool portion  210   b,    212   b  in the preceding working step is further worked in the third stamping tool portion  210   c,    212   c.    
         [0037]     In particular, the raised material portion  130  and the opening  128  are now produced in the third stamping tool portion  210   c,    212   c  in the clip bottom  110 . The opening  128  is produced with a raised portion  212   d  that is disposed at the bottom of the female die  212   c  and the shape of which is matched to the opening  128  to be produced. Provided in the punch  210   c  of the third stamping tool portion  210   c,    212   c  is a corresponding recess  210   d,  which in the illustrated embodiment, extends into a through opening (not identified in greater detail) in the upper tool  210 . That opening serves, inter alia, to be able to remove lumps of material that have been caught in the recess  210   d  of the punch  210   c  of the third stamping tool portion  210   c,    212   c.    
         [0038]     After a finished portion of the flat strip material BM has left the third stamping tool portion  210   c,    212   c,  it can be cut off as a finished closure clip  100 ,  100 ′ by means of a cutting device (also not shown in greater detail).