Abstract:
A laminar staple comprising two walls arranged at an angle and two ribs which protrude laterally from the walls; the walls and the ribs form a substantially W-shaped profile which has a cutting edge at one end and a striking edge at the opposite end; the staple is peculiar in that the ribs enclose, by means of their respective walls, an angle whose value decreases from the cutting edge to the striking edge.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a laminar staple for corner jointing profiled strips, particularly for manufacturing frames, frameworks and the like. 
     In the manufacture of borders, frames or similar frameworks made of wood it is known to corner-joint the strips by using laminar staples which are inserted so as to straddle the jointing plane formed by arranging the appropriately chamfered ends of the strips mutually adjacent. 
     In particular, laminar staples are commercially available which comprise a steel lamina folded so as to form two mutually perpendicular walls and two end ribs or ridges which are perpendicular to the walls and protrude outward, so that the staple assumes a substantially W-shaped profile. Staples of this kind are disclosed in U.S. Pat. Nos. 29,957, 4,681,498 and 5,336,038 and in French patents no. 2,318,715 and 2,525,949. 
     To mutually joint two profiled strips, cut for example at an angle of 45° in order to be arranged at right angles to each other, said W-shaped staples are inserted so as to straddle the jointing plane formed by arranging the strips mutually adjacent, so that the edge formed by the perpendicular walls and arranged on the centerline plane of the staple lies on the joint. In order to facilitate insertion, one of the edges having a W-shaped profile of the staples is sharp. 
     In order to make the joint of the strips as invisible as possible, there is a trend to use staples which are as high as possible in relation to the height of the strips. However, using high staples facilitates the onset of cracks in the exposed surface of the strips. It has been observed that the cracks decrease as the angle formed by the ribs with respect to the walls of the staples increases. However, as this angle increases the force with which the strips are mutually fastened decreases, producing a wider and accordingly more visible jointing line. 
     SUMMARY OF THE INVENTION 
     The aim of the present invention is to provide a new kind of staple which allows to substantially eliminate the danger of strip cracking during the insertion of the staples without thereby detracting from the quality of the joint. 
     Within the scope of this aim, an object of the present invention is to provide a staple which can be inserted by means of conventional stapling machines. 
     This aim and this object are achieved by a laminar staple comprising two walls arranged at an angle and two ribs which protrude laterally from said walls, said walls and said ribs forming a substantially W-shaped profile which has a sharp edge at one end and a striking edge at the opposite end, characterized in that said ribs enclose, by means of their respective walls, planar angles whose values decrease from said sharp edge to said striking edge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further characteristics and advantages of the present invention will become apparent from the following detailed description on the basis of the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a staple according to a first embodiment; 
     FIG. 2 is a perspective view of the staple of FIG. 1, taken from a different angle; 
     FIG. 3 is a view of the profile of the staple of FIGS. 1 and 2; 
     FIG. 4 is an enlarged-scale view of the detail shown circled in FIG. 3; 
     FIGS. 5,  6  and  7  are a front view, a profile view and a perspective view of a first embodiment of the staple; 
     FIGS. 8,  9  and  10  are a front view, a profile view and a perspective view of a second embodiment of the staple; 
     FIGS. 11,  12  and  13  are a front view, a profile view and a perspective view of a third embodiment of the staple; 
     FIGS. 14,  15  and  16  are a front view, a profile view and a perspective view of a fourth embodiment of the staple; 
     FIGS. 17,  18  and  19  are a front view, a profile view and a perspective view of a fifth embodiment of the staple; 
     FIGS. 20,  21 ,  22  and  23  are a front view, a profile view, a perspective view and a side view of a sixth embodiment of the staple; 
     FIGS. 24,  25  and  26  are a front view, a profile view and a perspective view of a seventh embodiment of the staple; 
     FIGS. 27,  28  and  29  are a front view, a profile view and a perspective view of an eighth embodiment of the staple; 
     FIGS. 30,  31 ,  32  and  33  are a front view, a profile view, a perspective view and a side view of a ninth embodiment of the staple; 
     FIGS. 34,  35 ,  36  and  37  are a front view, a profile view, a perspective view and a side view of a tenth embodiment of the staple; 
     FIGS. 38 and 39 are a profile view and a front view of a ribbon composed of staples according to FIGS. 8-10; 
     FIGS. 40 and 41 are a profile view and a front view of another ribbon composed of staples according to FIGS. 17-19; and finally 
     FIG. 42 is a view of a pack composed of staples according to FIGS.  30 - 33 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to the above figures, the staple is generally designated by the reference numeral  1  and is composed of a rectangular steel lamina which is folded in half so as to form two rectangular and mutually perpendicular walls  2  and  3  forming a central edge  4  which coincides with the centerline plane P. The border portions of the walls  2  and  3  are in turn folded at an angle with respect to the walls  2  and  3 , so as to form two ribs  5  and  6  which protrude outward with respect to the right angle enclosed by the walls  2  and  3  and give the staple a W-shaped profile. 
     The insertion edge of the staples has a sharp region  7  formed by lateral or bilateral sharpening. 
     In order to be usable in a stapling machine, the staples  1  are grouped so as to be mutually adjacent, thus forming a pack, and are held together with the aid of suitable adhesives. 
     The planes of the ribs  5  and  6  and of the walls  2  and  3  form respective edges  8  and  9  which are mutually parallel and lateral with respect to the central edge  4 ; along said edges  8  and  9 , the angle enclosed by the walls  2  and  3  and by the ribs  5  and  6  gradually decreases from one end of the staple to the other. More precisely, the planar angle α defined at the sharp region  7  is greater than the planar angle β formed at the end of the staple that lies opposite the sharp region  7 , i.e., the striking edge  10  on which the striking mass of the stapling machine acts. 
     The ribs  5  and  6  further have a width which increases from the sharp region  7  toward the striking edge  10  while keeping the lateral edges  11  and  12  mutually parallel. By way of this shaping of the ribs  5  and  6 , the staple assumes a more open profile which facilitates insertion in strips and prevents cracking of said strips. 
     The portion of the ribs  5  and  6  located proximate to the striking edge  10 , by maintaining an angle β which is narrower than α, produces a traction force on the strips which tends to mutually fasten them, forming a neater joint than obtained with conventional staples. Further, the risk of cracking on the exposed surface of the strips is reduced substantially. 
     The described staple is susceptible of numerous modifications and variations. 
     FIGS. 5-7 illustrate a staple in which a rectangular wall  13  is interposed between the walls  2  and  3 , forming with them edges  14  and  15  which are parallel to the edges  8  and  9 . 
     FIGS. 8-10 are views of a staple in which the walls  2  and  3  are trapezoidal, so as to form two lateral edges  8  and  9  which diverge toward the sharp region  7 . The angle of the edge  4  is constant. 
     FIGS. 11-13 are views of a staple which differs from the one shown in FIGS. 8-10 in that instead of the central edge there is a wall  28  which is interposed between the walls  2  and  3 . The wall  28  is rectangular, so as to form parallel edges  15  and  16 . The edges  8  and  9  diverge toward the sharp region  7  and the angle formed by the extensions of the walls  2  and  3  toward the center of the staple decreases toward the striking edge  10 . 
     FIGS. 14-16 are views of a staple which is similar to the one of FIGS. 8-10 but in which the lateral edges  11  and  12  diverge toward the sharp region  7 . The angle of the edge  4  is constant. 
     FIGS. 17-19 are views of a staple with walls  2  and  3  shaped like a parallelogram and an intermediate wall  17  which is shaped like an isosceles trapezoid and which, by means of the walls  2  and  3 , forms two edges  18  and  19  which diverge toward the sharp portion  7  but form a constant angle. 
     FIGS. 20-23 are views of a staple in which each rib  5  and  6  has two portions which form different angles with respect to each other and with respect to the walls  2  and  3  but have aligned outer edges. In this manner, the lateral edges formed by the walls  2  and  3  and by the portions  20  and  21  of the ribs are each composed of two mutually angled portions  22  and  23 . 
     FIGS. 24-26 are views of a staple which is similar to the one of FIGS. 1-4 but in which the angle of the central edge  4  is greater, so that the staple is substantially flatter. 
     FIGS. 27-29 are views of a staple which is similar to the one of FIGS. 24-26 but in which the edges  8  and  9  are not parallel to the central edge  4  and the angle formed by the walls  2  and  3  decreases toward the striking edge. 
     FIGS. 30-33 are views of a staple in which the outer edges of the ribs  5  and  6 , like the lateral edges formed by the walls  2  and  3  with the ribs  5  and  6 , have two mutually angled portions  24  and  25 , of which the portion  25  is parallel to the central edge. 
     FIGS. 34-37 are views of a staple similar to those of FIGS. 30-33, but in which the portions  25  of the edges of the ribs are not parallel but are inclined with respect to the central edge. 
     FIGS. 38,  39  and  40 ,  41  are views of two ribbons  26  and  27  formed by joining staples as shown in FIGS. 8-10 and  17 - 19  respectively. The embodiments of FIGS. 38-41 are particularly adapted for use in automatic stapling machines. 
     However, in order to allow the staples to be usable in stapling machines it is also possible to group the staples  1  face to face in a stack, so that they are mutually adjacent, forming a pack and holding them together by means of suitable adhesives, as shown in FIG. 42, which is a view of a pack composed of staples of the type shown in FIGS. 30-33. 
     The disclosures in Italian Patent Application No. BO99A000440 from which this application claims priority are incorporated herein by reference.