Patent Publication Number: US-6990760-B1

Title: Lip for an excavation bucket

Description:
BACKGROUND OF THE INVENTION 
   THIS invention relates to excavation buckets, and more specifically to a lip for an excavation bucket. 
   Excavation buckets such as dragline buckets generally have a lip welded to the front of the bucket for supporting a plurality of ground-engaging tools. These lips are usually formed from a single, rolled steel or cast steel plate with a straight front edge, and include a plurality of nosepiece castings which are fixed to the lip so as to project from the front edge of the lip. Ground-engaging tools are mechanically attached to the nosepieces, typically by means of adaptor castings. 
   The castings tend to be relatively heavy and consequently contribute significantly to the overall mass of the lip. Since the total mass of a loaded dragline bucket is limited by the dragline rated suspended load (RSL), it is desirable to reduce the mass of the bucket so as to allow for an increase in the bucket load and hence the productivity of the dragline. 
   A further disadvantage associated with conventional lips for dragline buckets is that the nosepiece castings have to be welded to the lip with transverse welds that extend across the upper and lower surfaces of the lip, and these welds reduce the fatigue strength of the lip. 
   SUMMARY OF THE INVENTION 
   According to the invention there is provided a lip for an excavation bucket including a lower plate defining a plurality of integral projections along a front edge thereof, and an upper plate joined to the lower plate so as to form a laminated structure, the upper plate defining a plurality of integral projections which together with the projections on the lower plate form tool attachment formations in a serrated front edge of the laminated structure for supporting ground-engaging tools on the lip. 
   Preferably, at least one additional plate is sandwiched between the upper plate and the lower plate. In this case, the additional plate or plates may be designed to project from the upper and lower plates between adjacent tool attachment formations and may include apertures for attaching shrouds to the lip between the tool attachment formations. 
   Typically, the lip includes one additional plate between the upper and lower plates, and the additional plate defines openings along its length for reducing the mass of this plate. 
   In a particularly preferred embodiment, the projections on the upper and lower plates are bent out of the planes of these plates so that the tool attachment formations are inclined relative to the plane of the lip. 
   Preferably, the upper plate, the lower plate and the additional plate are fabricated from rolled steel plate and are subsequently welded together. 
   In one arrangement, the lip curves upwardly at each lateral end thereof so that welds at these lateral ends are located out of areas of high stress in use. 
   The invention also extends to an excavation bucket including a lip as described above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: 
       FIG. 1  shows a top view of a lip according to the present invention; 
       FIG. 2  shows a front view of the lip illustrated in  FIG. 1 ; and 
       FIG. 3  shows a cross-sectional view along the line  3 — 3  in FIG.  1 . 
   

   DESCRIPTION OF AN EMBODIMENT 
     FIG. 1  of the drawings illustrates a top view of a lip for an excavation bucket according to the present invention. The lip is designated generally with the reference numeral  10  and is formed from three steel plates which are welded together in a manner which is described in more detail below. 
   With reference also to  FIG. 3  of the accompanying drawings, the steel plates forming the lip  10  include a lower plate  12 , an upper plate  14  and a central plate  16  which is sandwiched between the lower and upper plates, as shown. The lower plate and the central plate are formed from a high strength steel having a minimum yield strength of 700 N/mm 2 , typically WELDOX™ 700D, and the upper plate is formed from an abrasion resistant steel with a minimum hardness of 40 Rockwell C, typically HARDOX™ 400. 
   The lower plate  12  defines eight integral projections  18  (see  FIG. 2 ) which are formed by cutting recesses into a front edge of this plate. The projections are inclined downwardly out of the plane of the plate  12 , as shown most clearly in FIG.  3 . The upper plate  14  also defines eight integral projections  20  which correspond with the projections  18  on the lower plate and which are inclined downwardly out of the plane of the upper plate, as illustrated. To facilitate the welding of the plates, the peripheral edges of the upper and lower plates are seen to include bevel surfaces  21 . 
   The central plate  16  includes six openings  22  for reducing the mass of this plate and is machined so as to accommodate the inclined projections  20  on the upper plate. Along a front edge of the central plate  16  eight projections  24  are provided which are arranged to correspond with the projections  18  and  20 , and the plate  16  defines seven apertures  26  between adjacent projections  24  which are arranged to receive connection pins for securing seven shrouds to the lip  10 . The rear edge  27  of the central plate  16  tapers inwardly, as shown in  FIG. 3 , to facilitate welding of this plate to the upper and lower plates. 
   In this embodiment of the invention, the lip  10  is assembled in the following manner. First, the three plates  12 ,  14  and  16  are formed separately by fabricating three rolled steel plates. During fabrication, the plates are profiled in a flame-cutting machine, the central plate is machined as required, and the projections  18  and  20  on the upper and lower plates are bent relative to these plates. The three plates are then placed one above the other, as illustrated in  FIG. 3 , with the central plate sandwiched between the upper and lower plates, and are pressed together in a press to ensure proper engagement. Thereafter, the plates are welded together with welds (not illustrated) that extend along the bevel surfaces  21  around the periphery of the plates, or at least a substantial portion of the periphery of the plates, to form a laminated structure. 
   The lip formed from the three plates  12 ,  14  and  16  includes a serrated front edge  28  which defines eight tool attachment formations  30  (see  FIG. 1 ) for supporting ground-engaging tools (not shown). Typically, the ground-engaging tools are welded to the tool attachment formations as wear elements that can be replaced when worn. 
   Seven shrouds (not shown) are then connected to the lip between the tool attachment formations  30  with connection pins (also not shown) which are arranged to engage in the apertures  26 . 
   In this embodiment of the invention, the lip is welded to a dragline bucket but it should be appreciated that the lip could also be connected to various other types of excavation buckets. In  FIG. 2 , the lip  10  is seen to curve upwardly at each side edge thereof so that lateral edges  32  of the lip can be welded directly to cheek plates on the dragline bucket out of areas of high stress in use. 
   One advantage of the lip according to the embodiment of the invention described above is that it is relatively light when compared with conventional lips for dragline buckets. This is mainly due to the fact that ground-engaging tools are welded directly to the tool attachment formations and consequently there is no need for nosepiece castings or adaptor castings which tend to be fairly heavy. Also, the openings  22  in the central plate  16  serve to reduce the overall mass of the lip. This lip mass reduction is important because it allows for a larger bucket load and consequently an increase in the productivity of the dragline. 
   A further advantage of the lip of the invention is that there are no welds on the upper or lower surface of the lip since all of the welds on the plate  14  extend around the periphery of this plate. In conventional lips for dragline buckets it is necessary to have transverse welds on the upper and lower surfaces of the lip in order to connect the nosepiece castings to the lip. The absence of these transverse welds on the lip of the invention allows for a lip with increased fatigue strength.