Patent Publication Number: US-7900657-B2

Title: Jaw for sealless strapping machine

Description:
BACKGROUND OF THE INVENTION 
     The present invention is directed to a jaw for use in a sealless strapping machine for forming a sealless seal. More particularly, the present invention is directed to a one-piece jaw for forming a sealless seal. 
     Strapping machines are in widespread use. Typically, strapping machines are designed for use with metal (steel) or plastic strapping. In use, strapping is wrapped around the load, tensioned and sealed to itself. In use of metal strapping, the seal can be formed by use of a separate seal that is positioned around the strap and crimped onto the overlapping courses of strap. The seal can also be formed by gripping the strap material sections between a punch and the strapping machine jaw and cutting portions of the over- and under-lying courses of strap material into one another to interlock the strap courses. Such a seal is referred to as a sealless seal. 
     This action creates a locking action that provides additional strength to the strap, so that the tension in the band is maintained. The geometry of the jaw is highly engineered and does not lend itself to change. The jaws, by the nature of the design, experiences extremely high fluctuating stresses, that can result in fatigue failure if the maximum tensile stresses at the shear section exceeds half the shear yield strength. There are tremendous gains to be had if the stresses stay at or below ½ the yield strength. 
     Failure of the jaws can occur by fracture at the interface of the punch with the jaw structure. Again, this is due to the high localized stresses that are exhibited at this juncture. In order to address this, it has been thought that a build-up of material (e.g., making the jaw thicker) at the juncture would preclude or lessen the chances of the jaw failing. While this has increased the jaw life, it results in other undesirable characteristics, namely, the jaws have become too large and heavy and the space for the strap to move into the jaw area and for the strap to reside during the sealing operation is too small. 
     Another approach has been to use a two piece design that relies on improving wear performance through the use of two different materials (one for the bearing surface, e.g., the punches, and one for the bulk). Such as design lowers the shear cross sectional area that is subjected to the highest loads, and hence lowers fatigue life. 
     Known punches, e.g., bearing surfaces, are such as that shown in U.S. Pat. No. 6,554,030 to Cheung, et al. Each the fixed and movable punches include a plurality of punch heads. The punches are mounted to the jaw by fasteners to permit removing the punches for replacement, repair or maintenance. One drawback to this design is that the bearing surfaces (punches) are mounted to the jaw structure using fasteners, such as bolts. The bores or holes that are formed to secure the punches to the jaw structure also create areas that can be susceptible to failure. 
     Accordingly, there is a need for a jaw seal arrangement in which the jaw will not fail under load and that provides sufficient space in and around the punches for the positioning of strap in the jaw for sealing. 
     BRIEF SUMMARY OF THE INVENTION 
     A jaw for a sealless strapping machine includes a jaw element having a body that defines a linkage portion, a hook portion and a base portion. The hook portion extends transverse to the leg portion. 
     The linkage portion is contiguous with the hook portion which is contiguous with the base portion. The linkage, hook and base are formed from a single piece of material. 
     The jaw element includes a plurality of punches, preferably three punches (three peaks with two, intermediate valleys), that extend upwardly from the base portion to defining a juncture. Each punch is defined by a peak and a valley between the peak and the peak of an adjacent punch. The juncture of the punches and the base is formed as a relieved area. 
     The relived area defines a first transition between the punches and the base and second transition between the base and the support leg. The first and second transitions are formed having smooth radii, defining the relieved area. The transitions are formed parallel to a longitudinal direction of the jaw. 
     In a present jaw, the relieved area has a depth that is about equal to or greater than a depth of a valley as measured from its respective adjacent peaks to a base of the valley. The jaw can be configure such that the peaks have about equal heights and the valleys have about equal depths. 
     These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS 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 front view of a jaw assembly that has been formed, in part, in accordance with the principles of the present invention, the jaw assembly shown at a slight upward angle; 
         FIG. 2  is a side view of the jaw assembly of  FIG. 1 ; 
         FIG. 3  is a front perspective view of the jaw assembly; 
         FIG. 4  is a side view of the jaw assembly; 
         FIG. 5  is another perspective view of the jaw of the present invention, similar to that shown in  FIG. 3 ; and 
         FIG. 6  is a front view showing the relationship of the punches (peaks and valleys) to the base and the jaw. 
     
    
    
     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. 
     Referring to figures, there is shown a jaw assembly  10  having a relieved region  12  embodying the principles of the present invention. The jaw assembly  10  includes a body  14  having a linkage portion  16  (that portion that is operably connected to the strapping machine—not shown), a hook portion  18  that extends generally transverse to the linkage or leg portion  16  and a base portion  20 . The hook  18  extends transverse, toward an opposing hook portion (not shown). 
     The punches  22 , which are those portions of the jaw  10  that contact and punch (deform or cut) the strap, are formed on the base portion  20  and extend upwardly from the base  20 . The punches are defined by peaks  26  and valleys  28 . The assembly  10  is a contiguous, unitary element. That is, unlike known jaws which use separate, attached punches, the present jaw assembly  10  uses a unitary jaw element with the punches  22  formed as part of the jaw  10 . This precludes the need for holes or bores in the jaw structure (for mounting screws or bolts) that otherwise could weaken the jaw. 
     As best seen in  FIG. 6A , the juncture (indicated at  24 ) of the punches  22  and the base  20  is formed in counter-intuitive manner. Rather than a build-up of material at the juncture  24 , the material at the juncture  24  is relieved or removed and the transition from the punch  22  to the base  20  and the base  20  to the support leg  16  surfaces are formed having relatively large radii, thus forming the respective relieved areas  40 ,  42 . 
     As set forth above, the punches  22  are formed as raised areas or peaks  26  (for first contact with the strap), much like teeth, and root areas or valleys  28  between the raised areas  26 . The root areas  28  extend transverse to the longitudinal direction of the jaw A 10  and essentially divide the peaks  26  from one another. In the illustrated embodiment, there are three peaks  26   a,b,c . The peaks  26   a,b,c  are separated from the hook portion  18  at a transition area  30 . The transition area  30  extends parallel to the direction A 10  of the jaw  10  and transverse to the root areas  28 . The faces of the punches (e.g.,  22   a  and  22   b ) are angled slightly rearward from the peak  26  to the root  28 , to define a projected or crested front face (as indicated at  23 ). 
     A present jaw  10  includes a one-piece body made of high strength high fatigue material such as high alloy steel, for example, D2 or DC53 heat treated to hardness in excess of 62 RC. Referring to FIGS.  5  and  6 A-C, the jaw  10  includes a maximum possible metallic section (indicated at  32  in  FIG. 5 ), along the shear plane where shear stresses are highest and fatigue related failure occurs. This feature reduces the effective shear stress along the section. 
     The strapping surface  22  (the punch) dictates the strap strength and is formed by the peak and valley features  26 ,  28 . A smooth radius, indicated at  34  blends in the peak  26  and valley  28  features to the back face  36  with a radius R that seamlessly blends these features of the geometry. In a present jaw  10 , a sand blasted or shot blasting process is used to establish a compressive stresses at the surface of the fillet area. This improves fatigue life. 
     To ensure that static stresses are lowest at the shear section, the depth of the undercut d 38  preferably closely matches the peak to valley height h 26 . This is established by thinning the section  32 . To avoid any stress risers on this surface, the depth of the undercut d 38  is more than or approximately equal to the peak to valley height. That is, the radius at  34  is formed to a depth d 38  that is about at the valley  28  depth d 28  to (relieve stresses and to) prevent failure of the jaw  10 , while at the same time, retaining sufficient material to provide strength. The highest stresses are seen at the interface of the peaks  26  and the back face  36 . By eliminating the point junctures (of the peaks  26  and face  36 ), and creating a line interface, (see at  40 ), the highest stress areas are eliminated. 
     The present jaw can be used on, for example, an M40 strapping machine currently available from ITW Signode of Glenview, Ill. 
     All patents referred to herein, are hereby 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 all such modifications as fall within the scope of the invention.