Abstract:
In a method to seal/lock a strap ( 44 ) including a metal strap ( 44   d ) which is fitted at least in the zone of seal with a protective layer ( 44   c ), the packing strap is laid in the form of a loop around the package and is held, in particular, clamped, in place before and/or during production of the seal. The seal is implemented on the packing strap ( 44 ) by resistance welding and the protective layer ( 44   c ) of the packing strap ( 44 ) shall be pierced before and/or during production of the seal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims the benefit of priority of International Application No. PCT/IB2006/003759, filed Dec. 22, 2006, entitled “METHOD AND DEVICE FOR STRAPPING GOODS”. 
   TECHNICAL FIELD 
   The disclosure relates to a method creating a seal for a packing (looping) strap fitted with a metal strap, in particular a metal steel strap, said strap being fitted with a protective coat at least in the zone of said seal, the packing strap being placed in the form of a strap loop around the package and being kept in place in a predetermined manner prior to and/or during the creation of said seal, for instance being clamped in place by at least one strap clamp. The disclosure also relates to strapping equipment to strap a package and comprising a metal packing strap fitted with a protective coating, said equipment being fitted with a sealing device to create a seal allowing joining together two superposed strap plies of a packing strap loop. 
   BACKGROUND 
   To appropriately ship packages, it has long been known to strap such packages with one or several packing straps that are sealed by strapping equipment to said packages. To ship heavy-industry goods, usually, though not exclusively, the above cited metal straps and in particular steel straps are used. To prevent such steel straps from rusting, they are ever more frequently fitted with a protective coat that typically may be an enamel or the like or a wax. 
   The strapping equipment of the art is fitted with a strap guide and a drive to guide said strap around the package. As a rule, the strapping equipment also comprises a tensioner to allow appropriately tensioning the strap loop placed around the particular package. A clamping system of said strapping equipment allows sealing said strap loop to the material to be packed to be used in the ensuing connection procedure at the package. Thereupon, the strap loop shall be locked/sealed in place in a zone of said loop where two strap plies are superposed on each other. 
   In a first known procedure of the art, said seal is implemented on packing straps of the above kind by using an additional sealing element placed around the said overlapping strap ends and then being plastically deformed. This procedure however incurs the drawback of requiring an additional sealing element, typically a lead seal. Moreover, this kind of seal may not always withstand high stresses. The same reservations apply to other strapping techniques that do not use sealing elements, for instance resorting to notched sealing elements. 
   Also the European patent document EP 0 621 181 B1 discloses a procedure using a tungsten inert gas procedure to permanently join together the two strap ends without resort to another sealing element. This procedure, however, may be considered disadvantageous in that an inert gas must be used to for seal. No other need for inert gas existing in many enterprises that use such strapping equipment, the latter alone must justify inert gas logistics and supplies for strapping. 
   Besides the above cited tungsten inert gas welding procedure, other appropriate procedures to create an seal on protectively coated straps are known and appropriate, namely those joining the two strap plies by resort to notches. However the ensuing restricted load capacity of such connections and the relatively large area of damage to the said protective layer and to the metal strap may be considered disadvantageous. 
   Lastly, the German patent document 929 059 discloses connecting to each other two strap ends by resistance welding. In this procedure, resistance welding is used wherein two electrodes will directly contact the metal surfaces of the two strap plies which in turn also make electrical contact with each other. Electric contact between the two electrodes by means of the two strap plies is easily established. Said German patent document 929 059 is dated from the year 1959. At that time only uncoated steel straps were used, consequently the objective of the German patent document 929 059 has been inappropriate to packing straps fitted with a protective coating. 
   Indeed the most diverse procedures relating to other applications, for instance pressure welding techniques such as gas pressure welding or ultrasonic welding also are known. However the coatings of the packing straps also always are an impediment in such welding procedures, they ought to be considered basically inappropriate. 
   SUMMARY 
   Accordingly, there is a need to create a method and equipment for a strap seal where the straps are fitted with an external protective coating, in particular an enamel or the like or a wax coating. In particular, disclosed embodiments of the present invention create especially high load resistance with minimal damage to the protective coating. 
   A method for creating a seal uses resistance welding at the packing strap, said method in accordance with disclosed embodiments of the present invention, in particular, including mechanically piercing the strap protective coating in the area of said seal before or during its implementation. Accordingly, the disclosed embodiments of the present invention are also based on the insight that, contrary to prevailing expert opinion, it is quite feasible to seal to each other straps fitted with typically electrically non-conducting protective coatings using resistance welding. The resistance welding procedures of the disclosed embodiments of the present invention allow making seals of high load strength. 
   Because the electrically non-conducting protective layers preclude generating currents adequate for welding, especially between the strap plies, the protective layer of the disclosed embodiments of the present invention may be expelled locally from a minute area in order to set up electrical contact between an electrically conducting component of the strapping equipment and the metal strap. It was found that with this localized damage to the protective layer, no serious degradation of the packing strip need be feared, for instance from rusting. 
   The electric contact between the welding apparatus and the metal strap required for resistance welding may be attained in a number of ways. A first embodiment of the present method pierces the protective layer within the zone of the anticipated welding site. In particular this may be done by generating a bulge in at least one of the strap plies as required for projection resistance welding. In the process, at the plastically deformed welding site of the metal strip, the protective layer tears open. Thereupon, the damaged site may be used both to generate the first electrically conducting contact between the seal and the strap plies and as the site of connection/seal. 
   In another embodiment, said two sites of piercing of the protective layer may be a distance apart. Preferably the minimum of one site where predetermined piercing of, i.e. damage to the protective layer is made, shall be situated very near to at least one of the welding sites. Preferably such piercing shall be implemented at both strap plies, in particular at two plies which are externally accessible and, with regard to the direction of the packing strap, at least substantially at the same site of the two plies. 
   In particular, with regard to spot welding, first an electrical shunt or bypass circuit or current detour shall be generated. This terminology denotes that initially an electrical current is generated through the strap along a path that at least partly deviates from the path of that current which shall implement the weld joint. Preferably, the current detour passes through an electrode member into a first strap ply to the first element with which piercing of the protective layer is implemented in the same strap ply. Accordingly, both the first electrode member and the first element to be discussed below make contact with this strap ply. In an embodiment, said first element may be electrically conducting per se and can make electrical contact with the second element by means of the strapping equipment, the second element also being used to damage or pierce the protective coat at the second strap site. Consequently, the second element shall preferably make contact with the metal strap and the current is able to pass through the second strap site from the second element to a second electrode in turn connected to a power source. In this embodiment of a detour circuit, both the first and preferably also the second element shall be electrically conducting. 
   A strap clamp, which typically is used to seal the strap prior to and/or during production of the seal, does touch the strap and therefore, the clamp elements of the strap clamp may be used in an appropriate embodiment of the present invention to pierce the protective layer. In this process the contact surface of the protective layer as well as the pressure at which the clamp elements are forced against the strap plies may be respectively so shaped and selected that the protective layer shall be pierced by the strap clamp. Where conventional seals were used heretofore, damaging the protective layer was considered a drawback and was carefully avoided. 
   The spot-welding procedure of disclosed embodiments of the present invention may be used at little technical and logistic complexity while nevertheless offering high operational reliability. This technical problem is solved by strapping equipment which is characterized in that the sealing system is a resistance welder which comprises at least two electrodes that may be hooked up to a power source and at least one piercing element allowing piercing the protective layer of at least one of the strap plies in order to thereby allow electrical contact between the metal band and the piercing element. 
   In another aspect of the present invention, having independent significance, the strapping equipment includes a module usually termed “strapping head”. All those mechanical components, or a part of them, which are required to advance the strap, to generate the strap tension, to seal the strap during production of the seal, to cut off the strap and to implement the seal, may be combined compactly in this strapping head. In accordance with disclosed embodiments of the present invention, an electric power element of the resistance welder preferably shall be configured as a whole immediately next to electrode members of the resistance welder. This configuration offers the advantage in particular that one or more welding cables between said power element and the minimum of one electrode member may be kept short and the cross-section of the welding cable(s) need not be excessively large. Moreover, electric losses are reduced thereby and cooling shall be minimized. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein: 
       FIG. 1  is a perspective of strapping equipment in accordance with an embodiment of the invention, 
       FIG. 2  shows a strapping head of the strapping equipment of  FIG. 1 , 
       FIG. 3  is a first elevation of a partial view of the strapping head of  FIG. 2 , 
       FIG. 4  is a second elevation of a partial view of the strapping head of  FIGS. 2 and 3 , 
       FIG. 5  shows a control shaft of the strapping head with part of the drive lever actuated by the control shaft, 
       FIG. 6  is a further perspective partial view of the strapping head, 
       FIG. 7  is a longitudinal section of the apparatus shown in  FIG. 6 , 
       FIGS. 8-13  a schematized strapping method in accordance with a further embodiment of the invention, and 
       FIG. 14  shows a partial section of a first electrode and a second clamp of the strapping head, further, by means of a solid line, a detour current. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiment illustrated. 
   It should be further understood that the title of this section of this specification, namely, “Detailed Description of the Invention”, relates to a requirement of the United States Patent Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein. 
     FIG. 1  shows strapping equipment  1  comprising a control console  2 , a supply receptacle  3  to store and to dispense the packing strap, a strapping head  5  to advance said strap, to tension a strap loop and further to implement a packing strap seal. Moreover the strapping equipment is fitted with a strap guide  6  whereby the strap is automatically moved by the machine along a predetermined path on and around a package  7 . All components except the strapping head  5  are conventional in strapping equipment. 
   The strapping head  5  is mounted jointly with the guide  6  on a framework  8  and shown separately in  FIG. 2 , and also comprises a strap drive  10  known per se. Said drive may be fitted with in particular with one or several pairs of rollers  11 ,  12 ;  13 ,  14  and optionally with further individual deflection rollers of which at least one is motor driven to advance or pull back the strap, which is guided between said rollers. 
   A welding and clamping unit  16  is integrated into the strapping head  5  which further comprises a welding power source  15 . To control the operations of said unit  16  and to synchronize them, use is made of a control shaft  17  shown in  FIGS. 3 and 4  which is actuated in a manner not elucidated further by a drive  18 . For that purpose the welding and clamping unit  16  is fitted at one of its end faces with a belt wheel  19  operationally connected in a manner not elucidated further here by a toothed belt to the drive  18 . An electric motor, of the drive  18 , for instance a stepping motor, powers the control shaft  17  by means of omitted toothed belts. Said motor in turn is controlled by the strapping head control  2 . 
   As shown in particular in  FIGS. 5 ,  6 , and  7 , various control cams  22 , 23 , 24 , 25  and by an eccentric cam  21  are fixed irrotationally relative to and on the control shaft  17  and are each associated with one of the control levers  28 ,  29 ,  30 ,  31 . Each of the levers  28 - 32  is operationally connected to a first and a second spot welding electrode  35 ,  36  and also to each of two strap clamps  38 ,  39 . The lever  31  drives a cutting blade  40  to cut off the packing strap  44 . The control levers may carry out the drive motions for the component linked to them. Moreover, a further control cam generates an inward or outward pivoting motion of a pivoting plate  43  of the welding and clamping unit. 
   To reduce wear, the levers  28 - 32  each may be fitted with a roller  45  implementing the contact with the particular control cam  22 - 25  or the eccentric cam  21 . Alternatively too, one or several of the levers  28 - 32  shall not be fitted with such roller(s) but are in direct contact with the associated control cam  21 - 25 . Each lever  28 - 32  is configured on a pivot shaft  46  running parallel to the axis  17   a  of the control shaft  17 , the levers  28 - 32  carrying out pivoting motions about said axis due to the particular associated control cam or eccentric cam. Each lever  28 - 32  is fitted with its own compression spring  47  forcing it against its associated control cam or eccentric cam. Said springs assure reliable contact between the control cams and the levers. 
   The pivot plate  43  is pivotally connected ( FIGS. 3 and 4 ) to two static support plates  48 ,  49  which are configured apart from and parallel to each other. Two coupling levers  51 ,  52  of the pivot plate  43  are connected for that purpose by pivot pins  53 ,  54  to the support plates  48 ,  49 . One of the coupling levers  51  makes contact by one contact end with a further control cam  55  of the control shaft  17 . This control shaft  55  predetermines the timing of the inward and outward pivoting motions as well as the dwell time of the pivot plate  43  in the particular position. Lower clamp elements  38   a ,  39   a  of the two strap clamps  38 ,  39 , and a lower electrode member  35   a ,  36   a  or one common lower electrode member of the two or more electrodes  35 ,  36 , are configured on said pivot plate  43 . The configuration of the upper electrode members  35   b ,  36   b  which jointly with the lower electrode members  35   a ,  36   a  constitute the electrodes  35 ,  36  are elucidated further below. 
   The components implementing the operations of the welding and clamping unit  16  are mounted to the control levers  28 - 32 . As shown more clearly in  FIGS. 5 through 7 , upper clamp elements  38   b ,  39   b  of a first and second strap clamp  38 ,  39  are mounted on the lower sides of two external levers  28 ,  32  respectively. The two upper clamp elements  38   b ,  39   b  each cooperate respectively with the lower clamp element  38   a ,  39   a  mounted on the pivot plate  43  of the first and second strap clamps. The upper clamp element  39   b  of the second strap clamp  39  is connected in electrically conducting manner by means of the lever  28 , further by the pivot shaft  46  resting on the support plate  48  and by the pivot plate  43 , with the lower clamp element  39   a  of the same strap clamp  39 . 
   The upper clamp elements  38   b ,  39   b  are moved toward the particular associated lower clamp elements  38   a ,  39   a  at given times and, following a given dwell time, shall then be moved back. The clamp elements  39   a ,  39   b  in particular are fitted with metallic, sharp-edged notching elements such as teeth or sharp tips of sufficient size to pierce the protective layer of the packing strap  44 . 
   The first and second electrodes  35 ,  36  each comprising the upper and the lower electrode member  35   a ,  35   b ;  36   a ,  36   b  are configured between the two strap clamps  38 ,  39  ( FIG. 7 ). The two upper electrode members  35   b ,  36   b  are guided up-and-down relative to the pivot plate by a lever  29 ,  30 . Both upper electrode members  35   b ,  36   b  comprise a cavity  57  which is part of a water cooling system for them. Each upper electrode member  35   b ,  36   b  is connected electrically by one of the two welding cables  56  to a transformer  15   a  ( FIG. 2 ). Said transformer in turn is connected to a thyristor system  15   b  which by means of a plug connection box  15   c  can be connected to an electric power source. The transformer  15   a , the thyristor system  15   b  and the connection box are all part of the resistance welder electric power supply. 
   Lastly the cutoff blade is situated between the upper electrode member  36   b  of the second electrode  36  and the upper clamp element of the first strap clamp  38 . 
   A strap stop  58  is linked to a rocker  59  which in turn is displaceable to-and-fro by means of a further control cam  60  of the control shaft  17 . The strap stop may be moved in this manner into the path of the packing strap when the strap loop is being deployed. By means of optical sensors not shown in further detail, the arrival of the strap end at the strapping head may be detected during the advance of said strap and said advance may thus be stopped. In the event of detection malfunction, the strap impinges the strap stop whereby the advance of the packing strap shall also be stopped. 
   The sequence of a strapping method in accordance with an embodiment of the invention is elucidated as follows in relation to  FIGS. 8 through 14 . To implement strapping (looping) and seal, first the pivot plate  43  is pivoted into its welding position underneath the upper electrode members  35   b ,  36   b . In that position the pivot plate  43  is configured immediately above the package  7 . Next the control  2  powers the strap drive  10 . As a result the packing strap  44  is drawn from the supply receptacle  3  and moved through the strap guide  6 . The packing strap under consideration is fitted with a protective layer, in particular a coat of enamel or the like or wax. Various straps of this kind were welded within the scope of the invention, for instance the strap 0204012 (19×0.90) “paint/wax” made by the enterprise Magnus at Dinslaken (Germany), the strap 085207 (19×0.60) of the enterprise Steel at Swansea, the strap Liljendals (19×0.40) “paint/wax” of the enterprise Liljendals Bruk AB and the strap 1114.680 (19×8.0) enamel NF of the enterprise Burserud. 
   Accordingly, the packing strap rests loosely as a loop around the package  7 , the end zone of said strap resting against the strap stop  58  moved into a front stop position, or stopping shortly before it. As a result the packing strap  44  is situated in the region between the strap stop  58  and approximately the cutting blade  40  in the form of two plies  44   a ,  44   b  above the pivot plate  43 . Thereupon, the first clamp  38  is used to clamp only a single ply segment of said strap in the region of the pivot plate. Next a backward motion of the packing strap  44  can be implemented by means of the strap drive in the direction of the arrow  62 . Due to the clamping action of the first clamp  38 , the packing strap  44  may rest stretched tautly against the package  7 . This state is shown in  FIG. 8 . 
   Next, the second clamp  39  is actuated as shown in  FIG. 9 , whereby the upper clamp element  39   b  is displaced toward the pivot plate  43  and the packing strap is compressed between the upper and lower clamp elements  39   a ,  39   b . Accordingly, the second clamp  39  clamps a double ply segment of the packing strap  43 . The clamping stress is selected so large that the metal notching elements of both of the upper and lower clamp elements  39   a ,  39   b  of the second strap clamp  39  pierce the protective layer as far as the inner metal strap of both strap plies  44   a ,  44   b . The clamp elements  39   a ,  39   b  are now each in electrical contact with one of the strap plies  44   a ,  44   b.    
   As shown in  FIG. 10 , the cutting blade  40  is actuated next to sever the upper strap ply  44   b  between the second electrode  36  and the first clamp  38 . 
   Thereupon, the upper electrode member  35   b  of the first electrode  35  may be lowered on the double ply packing strap  44 , whereby the two strap plies  44   a ,  44   b  are compressed against each other. In the region of the first electrode  35 , the upper electrode member  35   b  rests on the upper strap ply  44   b  and the lower electrode member  35   a  supports the lower strap ply  44   a.    
   In this state of the strapping head, a preheating current is applied by the welding power source  15  to the first electrode  35 . However, the superposed protective layers preclude a direct current path from one strap ply  44   b  to the other strap ply  44   a . Because the upper and lower clamp elements  39   a ,  39   b  of the second clamp  39  pierced the protective layer  44   c  and preferably now make contact by their notching elements  41 ,  42  with the metal strap  44   d , the preheating current passes through the upper electrode member  35   b  through the upper strap ply  44   b  to the upper clamp element  39   b . By means of the support plates  48 ,  49 , of the levers  51 ,  52  and the pivot plate  43 , said current then reaches the lower clamp element  39   a  of the second clamp  39 . At that point the current passes into the lower strap ply  44   a  and then through the electrode member  35   a  of the first electrode closes the current loop  64  termed herein as the shunt path or bypass circuit or current detour. 
   The above preheating current is, for instance 2,500 amp, and is applied during a predetermined time interval wherein the enamel or protective layer  44   c  of the packing strap  44  will be heated. It was observed that such heating suffices to lower to such an extent the electric resistance between the two strap plies  44   a ,  44   b  that, following said heating the current will pass directly between the two electrode members  35   a ,  35   b  through the two strap plies without taking the detour present at the higher electric resistance through the clamp elements  39   a ,  39   b . Accordingly, the control now can switch to a welding current which is substantially higher than that of the preheating procedure, namely being, for instance, between 6,000 and 7,000 amp. The time interval during which the preheating current is applied, and hence the time required until the electrical resistance of the strap plies has dropped so much that the current shall pass straight from one into the other strap ply, essentially depends both on the amplitude of the preheating current and on the nature of the protective layer. Optimal conditions may be ascertained for any packing strap by running a few tests wherein said parameters will be varied. 
   At the time or shortly thereafter of said switchover, the detour is substantially eliminated and the welding current between the two electrode members  35   a ,  35   b  will melt the strap material within an approximately circular spot. In a manner already known, the material of the two strap plies  44   a ,  44   b  will combine and shall solidify after the welding current has been shut off. In this manner a first weld connection has been made. 
   Immediately after the upper electrode member  35   b  of the first electrode has been raised off the packing strap  44  by its control lever, then, as shown in  FIG. 12 , the upper electrode member  36   b  of the second electrode  36  will be lowered onto the strap  44  to generate a second weld connection/seal. Exactly as for the case before that of the first electrode  35 , the two strap plies  44   a ,  44   b  are compressed by the electrode members  36   a ,  36   b . Optionally, in this case too a preheating current may be first applied to the second electrode  36  of an amplitude sufficient to generate another detour path. As regards the detour path preceding the second weld connection, the said detour current may pass by means of the upper electrode member  36   a  through the first weld connection into the lower strap ply  44   a  and from there through the lower electrode member  36   a . Another current path also is conceivable, for instance again through one of the strap clamps. 
   Preferably however, a welding current higher than the preheating current shall be applied to the case of the second electrode  36 . Because of the prior heating and the ensuing reduction in electrical resistance in particular between the two strap plies  44   a ,  44   b , the welding current is able to pass directly through the two strap plies between the two electrode members  36   a ,  36   b . By means of a melting process, material commingling between two plies and cooling of said material of both plies after the welding current has been shut off and by raising the upper electrode member off the packing strap, a second welding connection/seal has been created. Finally, the seal is released from applied loads by pivoting away the pivot plate  43  ( FIG. 13 ). Strapping (looping) is now completed. 
   In further, omitted embodiment modes, more or fewer than two spot weld connections per seal also may be generated. Moreover the said seals may assume shapes different from circular spot weld connections. 
   All patents referred to herein, are incorporated herein by reference, whether or not specifically done so within the text of this disclosure. 
   In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. 
   From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims