Abstract:
The invention concerns a sealing clip ( 10 ) for bags, foil tubes or the like, said sealing clip ( 10 ) comprising a wire section, a pre-curved clip base ( 12 ) and two clip legs ( 14 ) adjoining the latter on both sides. The two clip legs taper constantly from their clip base ends to their free ends. The invention also concerns a wire section for sealing clips of this type which tapers constantly towards both ends. The invention finally concerns a matrix ( 30 ) for sealing the sealing clip and having two slide channels ( 36, 38 ) which each narrow conically from an inlet point.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a sealing clip comprised of a wire section for bags, film tubes or the like, having a pre-bent clip base and two clip legs adjoining the latter on both sides. The invention furthermore relates to a wire section for the sealing clip and to a matrix having two sliding grooves for closing the sealing clip. 
     Simple sealing clips consisting of a wire section can be produced in that an endless wire is supplied to a sealing machine, a portion is cut off from the wire in the sealing machine, and the wire section is then for instance bent around a bag neck to be closed. It is likewise known to supply to a sealing machine not an endless wire, but wire sections already cut through. The wire sections may be straight or prebent to form a U. For magazining purposes, these wire sections are generally fixed one beside the other on a carrier strap, so that they form a magazine strand. The advantage of such sealing clips formed of a wire section resides in the easy manufacture of these sealing clips. The tightness of the closures which can be achieved with the known sealing clips formed of a wire section is, however, not satisfactory. 
     As a tool for closing the above-mentioned sealing clips there are usually used sealing machines which have a stamp and a matrix. The sealing clip pre-bent to form a U is first of all transferred from a magazine to the stamp and non-rotatingly guided. Subsequently, stamp and matrix are moved towards each other. During this movement, the sealing clip surrounds the packaging material gathered to form a neck. Then, the free ends of the legs of the sealing clip are the first to reach the matrix and in the course of the further movement are guided by sliding grooves in the matrix. In the process, the legs of the sealing clip are plastically deformed, so that there is finally obtained a more or less circularly closed sealing clip. 
     There are known matrixes which have two semicircular sliding grooves arranged parallel to each other. The main plane of the two sliding grooves is slightly inclined with respect to the main plane of the sealing clip, so that each sliding groove has an inlet point which lies in the main plane of the sealing clip. Main plane is understood to be that plane in which extends the center line of a sliding groove or the sealing clip. When the sealing clip guided by a stamp is moved towards the matrix for closure, each of the free leg ends enters one of the sliding grooves at a respective inlet point and is guided by the same on a helical path produced by the inclination of the sliding grooves. As a result, the two free ends of the sealing clip slide past each other during closure, so that upon closure they laterally overlap each other and rest against each other in parallel. 
     It is the object underlying the invention to provide a sealing clip comprised of a wire section, with which tighter closures can be achieved than with the sealing clips known so far. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, the solution of this object consists in a sealing clip as described above, which is characterized in that during closure the two clip legs taper constantly from their clip base ends to their free ends. This is based on the knowledge that during closure a sealing clip made of wire with a uniform cross-section always bends particularly in the vicinity of the arc sections between the legs and the clip base, because there the bending load is largest. Therefore, sealing clips consisting of a wire section of uniform cross-section never take on the circular shape ideal for tight closures. Since the wire cross-section of the inventive sealing clip tapers towards the legs, there is a much more uniform distribution of the bending load over the entire length of the legs, so that during closure the sealing clip approximately takes on the ideal circular shape. 
     DETAILED DESCRIPTION 
     Preferably, the clip base and the clip legs of the sealing clip have a round cross-section. Such sealing clip can be produced easily and inexpensively from a piece of round wire, which is partly stretched, so that the tapering legs are obtained. 
     In a preferred embodiment of the sealing clip the clip base has been preformed to form a circular arc. Preforming the clip base to form a circular arc promotes the approach of the sealing clip to the ideal circular shape during closure. 
     There is furthermore preferred a sealing clip which has a projection at the outer radius of the clip base. By means of such projection the sealing clip can be non-rotatingly guided in the stamp during closure. 
     The solution of the object underlying the invention also comprises a wire section for the inventive sealing clips which is characterized in that the wire section tapers constantly towards both ends. Such wire section solves the inventive object in particular in conjunction with those machines to which straight, not pre-bent wire sections are supplied. In this case, the individual wire sections are only pre-bent to form a U in the sealing machine (DE 41 20 440). 
     In the case of a straight wire section it is particularly advantageous when the cross-section of the wire section decreases constantly from the middle of the wire section to both ends, so that the wire section already tapers towards both sides in the vicinity of its future clip base. In this way, it is already during preforming that the wire section is subjected to a uniform bending load in the vicinity of the clip base, so that it easily takes on the shape of a circular arc. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     In accordance with the invention, a matrix as described above also contributes to the solution of the object, where the two sliding grooves of said matrix each narrow conically from an inlet point. Such matrix has the advantage that the tapering clip legs of the inventive sealing clip can be moved towards each other more tightly during closure than by means of conventional matrixes. In addition, the matrix can be designed more narrow, so that for the matrix only a smaller space must be provided in the sealing machine. Sealing clips closed by means of the inventive matrix require less space on the packaging casing gathered to form a neck, so that less packaging casing material is required for closure. 
     In a preferred embodiment of the matrix, the matrix is designed such that the centers of curvature of the sliding grooves are offset with respect to the center of the recess laterally reversed and their parallel axes are inclined less with respect to the axis of the recess than with respect to the axis of the rib. The result is that during closure the tapered ends of the clip legs are urged more firmly against the packaging casing gathered to form a neck and also laterally against each other. 
     Embodiments of the invention will now be explained with reference to the drawings, wherein: 
     FIG. 1 shows a sealing clip in accordance with the invention with tapering legs and round cross-section; 
     FIG. 2 shows a modification of the sealing clip in accordance with FIG. 1 with a circular-arc-shaped clip base with projection; 
     FIG. 3 shows a wire section for the sealing clips in accordance with FIGS. 1 and 2; 
     FIG. 4 shows a variant of the wire section in accordance with FIG. 3; 
     FIGS. 5 a  to  c  show various views or partial sections of a known matrix for closing the sealing clips in accordance with FIGS. 1 and 2; 
     FIG. 6 shows a closed sealing clip in accordance with the prior art in a side view (and top view); 
     FIGS. 7 a  to  c  show a novel matrix in a top view and partial section; 
     FIG. 8 shows a sealing clip closed by means of the matrix in accordance with FIG. 7 with tapering legs. 
    
    
     The variant of a sealing clip  10  shown in FIG. 1 has a preformed clip base  12  to which a leg  14  is each joined on both sides. Clip base  12  and leg  14  each have a round cross-section. In the case of the legs  14 , the same decreases constantly from their clip base ends to their free ends. When closing the sealing clip in accordance with FIG. 1, the conically tapering legs  14  ideally each form a carrier of the same bending load, so that they become uniformly round during closure. 
     It is provided that the leg ends are guided such during closure that they slide past each other, so that the free ends of the legs  14  in part laterally overlap each other upon closure. A sealing clip  10  closed in this way only to a small extent tends to unbend itself under the influence of the internal pressure exerted by the packaging material. In addition, different neck diameters are compensated in that the leg ends correspondingly overlap each other to different extents upon closure. In this way, a large bandwidth of different neck diameters can be covered with one sealing clip geometry. This simplifies stockkeeping, as only few variants of the sealing clip  10  must be kept in store. 
     FIG. 2 shows a variant of the sealing clip  10  in accordance with FIG. 1, where the clip base  12 ′ is not flattened in its middle, but has the shape of a circular arc. In addition, the clip base  12 ′ is provided with a projection  16  at its outer radius, which allows to precisely guide the sealing clip  10 ′ during closure, in that the projection  16  engages in a corresponding groove of a closing tool. This prevents in particular a rotation of the sealing clip  10 ′ during closure. 
     It can also be taken from FIG. 2 that the clip base  12 ′ and the legs  14 ′ do not have a round cross-section, but—with the exception of the area of the projection  16 —a hexagonal one. 
     FIGS. 3 and 4 each show a wire section  20  and  20 ′, respectively, from which sealing clips of the kind shown in FIG. 1 or similar sealing clips can be formed. The wire section  20  in accordance with FIG. 3 has a cylindrical center piece, to which end portions  24  conically tapering towards their ends are joined on both sides. The center piece  22  should be preformed to form a U, so that it forms a clip base as for instance that of the sealing clip  10  in accordance with FIG.  1 . The end portions  24  of the wire section  20  then form the legs  14  of the sealing clip  10 . 
     Preforming the wire section  20  to obtain the open sealing clip  10  can be effected outside the sealing machine, for instance at the location of the sealing clip manufacturer. The sealing clip is then supplied to the sealing machine in the preformed condition—possibly as part of a magazine strand. 
     Preforming the sealing clip  10  can, however, also be effected inside the sealing machine before the actual closing operation. In the latter case, a wire section is supplied to the sealing machine in the stretched condition. For this case, the wire section  201  in accordance with FIG. 4 is particularly suited. The wire section  20 ′ tapers constantly from its middle to its two ends. Thus, it virtually comprises only two conical end portions  24 ′; a cylindrical center piece  22  as in the wire section  20  is omitted. In this way, the middle portion of the wire section  20 ′, which forms the future clip base  12 , already represents a carrier of the same bending load, which easily takes on a uniformly round shape when it is preformed in the sealing machine. The end portions of the wire section  20 ′, which form the clip legs  24 ′, remain stretched. They are only bent around the neck to be closed when the sealing clip is closed. Since the clip legs  24 ′ also represent a carrier of uniform bending load, they also take on the ideal shape of a circular arc when they are closed. 
     FIGS. 5 a  to  c  show a known matrix  30  of a tool for closing sealing clips in accordance with FIGS. 1 and 2. FIGS. 5 b  and  5   c  represent the sections illustrated in FIG. 5 a.    
     The matrix  30  has an impression in the form of a partly cylindrical recess  32 . In the wall  34  thereof there have been milled two directly adjacent sliding grooves  36  and  38  extending parallel to each other. Both sliding grooves  36 ,  38  have the shape of a circular arc of the same radius, are also keyed in cross-section and between each other form a rib  35 . In addition, the centers of both circular arcs lie on a common central axis  40 , which intersects the cylinder axis  42  of the recess  32 . The central axis  40  is inclined with respect to the cylinder axis  42  such (for instance under an angle of 12°) that the inlet points  44  and  46  of the sliding grooves  36 ,  38 , i.e. their vertices, approximately lie in the central plane  48  of the matrix  30  extending vertically to the cylinder axis  42 . The production of both sliding grooves  36 ,  38  is now effected by means of an integral milling cutter, which has been swivelled by the above-mentioned angle of inclination about the vertical axis defined by the intersection of the cylinder axis  42  with the central plane  48 . 
     For closing a sealing clip  10 , the same is supplied from a stamp onto the matrix  30 . The free leg ends of the sealing clip  10  move into the two sliding grooves  36 ,  38  at the inlet points  44 ,  46  and during the further movement of the stamp are guided by the sliding grooves  36 ,  38  to the outlet points  45 ,  47 . The clip legs  14  of the sealing clip  10  are bent to form a circular arc and at the same time are moved past each other in parallel by the sliding grooves  36 ,  38 , so that the closed sealing clip in accordance with the prior art takes on the shape illustrated in FIG. 6 with laterally overlapping leg ends resting against each other in parallel. 
     If the matrix  30  of FIG. 5 would, however, be used for closing the sealing clip  10  of FIG. 1, the tapering clip leg ends would not be brought together go closely, that in the end they laterally rest against each other. 
     For closing the sealing clip  10  in accordance with FIG. 1, there is therefore preferably used the matrix  30 ′ illustrated in FIG.  7 . The matrix  30 ′ also has two sliding grooves  36 ′ and  38 ′, whose main planes  37 ′,  39 ′ extend parallel to each other, but as compared to FIG.  5 —with unchanged inclination of the rib  35 ′—are inclined legs with respect to the central plane  48 ′. At the same time, the centers M 2  and M 3  as well as the axes of rotation  40 ′,  40 ″—vertical to the main planes  37 ′,  39 ′—are offset with respect to each other in parallel, namely laterally reversed towards both sides of the axis  40 , which extends under the same angle with respect to the axes of rotation  40 ′,  40 ″ which the rib  35 ′ includes with the main planes  37 ′,  39 ′. 
     This fact as well as the production of the sliding grooves  36 ′,  38 ′ by means of individual milling cutters offset with respect to each other by the distance M 2 -M 3  does not alter the fact that the inlet points  44 ′ and  46 ′ of the sliding grooves  36 ′,  38 ′ lie in the central plane  48 ′. In contrast to the sliding grooves of the known matrixes (e.g. matrix  30  of FIG.  5 ), however, the sliding grooves  36 ′ and  38 ′ narrow constantly from their inlet points  44 ′ and  46 ′, so that in the ideal case the width of the sliding grooves  36 ′ and  38 ′ corresponds to the respective width of the conically tapering clip legs  14  of the sealing clip  10 . As a result, the clip legs  14  are brought together more closely during closure, and when the sealing clip  10  is closed, they closely rest against each other laterally. This reduction of the width of the sliding grooves from the inlet point to the outlet point (with which corresponds the “swivelling back” of their main planes  37 ′,  39 ′ towards the central plane  48 ′) leads to the fact that the width of the matrix  30 ′—transverse to the central plane  48 ′—can be clearly smaller than that of the known matrix  30  (FIG.  5 ), which has the advantages described above. It is furthermore advantageous that due to the above-described geometry each sliding groove tapers off towards its outlet point of a reduced depth, with the further consequence that during closure the legs  14  of the sealing clip  10  are urged more firmly against the packaging casing neck to be closed. 
     One of the many conceivable modifications of the matrixes  30  and  30 ′ resides in providing sliding grooves which do not extend on a circular path, but on a helical path, so that the respective inlet point of a sliding groove lies on a larger radius than the corresponding end point of the sliding groove. 
     By means of the above described and other variations of the matrix, the shape of the closed sealing clip can be adapted to all kinds of applications. 
     FIG. 8 shows a side view of the result of a closing operation, when a sealing clip in accordance with FIG. 4 is processed with a matrix in accordance with FIG.  7 .