Patent Publication Number: US-7721473-B2

Title: Dragline excavator bucket

Description:
FIELD OF THE INVENTION 
   This invention relates to a suspension system for a bucket for a dragline excavator and to buckets so suspended and a dragline excavator having such a system. 
   BACKGROUND OF THE INVENTION 
   Dragline excavators may be categorised as falling within one of two general types; so-called “Conventional” draglines and Universal Dig Dump (“UDD”) draglines. A Conventional dragline employs a single hoist rope and, to enable angular adjustment of the dragline bucket, a dump rope connects the drag rope to the forward end of the bucket by way of a pulley that, in turn, is connected with the hoist rope. By way of contrast, a UDD dragline employs two, forward and rearward, hoist ropes that are rigged to be operated independently of one another and, thus, without any interconnecting dump rope. 
   In the case of the Conventional dragline, the single hoist rope is connected to opposite side walls of the bucket by way of splayed hoist chains. Similarly, in the case of the UDD dragline, the rearward hoist rope is connected to opposite side walls of the bucket by way of splayed hoist chains. In each case the hoist chains are connected to lower, rearward regions of the respective side walls of the bucket by way of axially aligned trunnions. Also, in each case and in order to provide for clearance between the spayed hoist chains and the side walls of the bucket during tilting/turning of the bucket about the axis of the trunnions, a spreader bar is employed to increase the size of the effective splay angle between the hoist chains, and the effective width of the bucket is reduced (i.e., the side walls are tapered inwardly) in the region in which interference might occur between the hoist chains and the side walls of the bucket. 
   Depending upon the type of dragline and the bucket size employed in any given case, the spreader bar typically has a weight within the range 500 kg to 2,000 kg, and this creates two problems. It imposes a commensurate weight reduction on the bucket payload during each operating cycle, and bucket damage is regularly experienced due to collisions occurring between the spreader bar and the bucket during excavating operations. Also, with the bucket width being reduced to avoid interference with the hoist chains, the payload volume is reduced commensurately during each operating cycle. 
   Three different approaches are known to have been taken toward obviating the need for the spreader bar and thereby minimising the above mentioned problems. In one case the hoist chain trunnions have been moved toward the upper rim of the side walls of the bucket, but this has created problems with load dumping as a consequence of the tilting axis of the bucket being shifted to a level above that of the centre of gravity of the bucket. In another case, the hoist chain trunnions have been moved into the interior of the bucket, but this has resulted in a reduction in the payload capacity of the bucket and interference with the hoist chains. In the third case the hoist chain trunnions have been moved to the rear wall of the bucket but positioned at or below the level of the centre of gravity of the bucket and angled to correspond approximately with the splay angle of hoist chains. This results in excessive wear due to the trunnion axes being inclined with respect to the tilting axis of the bucket. 
   SUMMARY OF THE PRESENT INVENTION 
   Broadly defined, the present invention provides a dragline excavator bucket having two spaced-apart pivot arms pivotally connected to a rear wall of the bucket and connectable to a pair of splayed hoist chains. Each of the pivot arms is pivotal about a pivot axis that extends transverse to the bucket and substantially parallel to the rear wall and is located below the rim of the rear wall, and the pivot arms are shaped to permit relative movement of the bucket and the pivot arms through an angle greater than 90° whereby the bucket may be moved from a substantially vertical disposition to a carry angle greater than 0° to the horizontal. 
   Each of the pivot arms may optionally have any shape that accommodates the relative movement of the bucket and the pivot arms through the angle greater than 90° and which, therefore, avoids the possibility of interference between the pivot arms and the bucket. Thus, each pivot arm may be formed, for example, with two arm portions that are separated by an obtuse included angle. As a further example, each pivot arm may have an arcuate (i.e., “boomerang”) shape and be dimensioned to extend around the rim of the bucket wall with clearance between the pivot arm and the rim of the bucket wall when the bucket is in a carry position. 
   The two pivot arms desirably share a common pivot axis and, in such case, the position of the common pivot axis may optionally be determined on a case-by-case basis to take into account the operational requirements of the bucket; for example for “chop cutting” a 75° high wall and/or “bottom” excavation. In one embodiment of the invention the common pivot axis is located on a line passing through the rear wall of the bucket and the centre of gravity (“CG”) of the bucket when unladen. More specifically, the pivot axis may be located slightly above the CG, and in a particular embodiment of the invention the pivot axis may be located above the level of the CG and on a line that makes an angle α of less than about 15° to the floor of the bucket. The angle α desirably is between 0° and 15°. 
   The invention may optionally be embodied in both Conventional and UDD draglines but it has greater application and can more usefully be embodied in UDD draglines; that is with one hoist rope connected with the pivot arms at the rearward end of the bucket and with the second hoist rope connected, typically by splayed hoist chains, to the front “ring” of the bucket. 
   The invention will be more fully understood from the following description of an illustrative embodiment of a bucket for use in a UDD dragline excavator. The description is provided with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings— 
       FIG. 1  is a diagrammatic representation of a UDD dragline excavator modified to include an embodiment of the invention and in an operational (e.g., strip mining) environment, 
       FIG. 2  is a perspective view of a bucket component of the dragline excavator, 
       FIG. 3A  shows a scrap end view of one pivot arm of the bucket, as seen in the direction of arrow  3  shown in  FIG. 2 , 
       FIG. 3B  shows a scrap end view of an alternative form of pivot arm, again as seen in the direction of arrow  3  in  FIG. 2 , 
       FIG. 4  shows a side view of the bucket when suspended in working relationship to a near-vertical wall of an excavation site, and 
       FIG. 5  shows a side view of the bucket when suspended in a carry position above a horizontal floor of an excavation site. 
   

   DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENT OF THE INVENTION 
   As illustrated in  FIG. 1 , the dragline excavator comprises a dragline bucket  10  which is suspended from a truss-structured boom  11  by forward and rearward hoist ropes  12  and  13  and which is connected to power plant  14  by a drag rope  15 . The bucket  10  is manoeuvred by means of the hoist and drag ropes  12 ,  13  and  14  during excavating and dumping operations. For example the bucket can be manoeuvred during so-called chop cutting as indicated in  FIG. 4  during excavation, during carry operations as indicated in  FIG. 5  and also during dumping operations, for example to the side or behind the excavation site. The boom  11  might typically have a length of 120 m. and the bucket might typically have a width of 4.5 m. and a carrying capacity of 54 m 3 . 
   The bucket  11  is constructed in a generally conventional way, in that it includes a fully cast front ring  16  which includes an arch bar  17  with which the forward hoist rope  12  is shackle-connected by way of splayed hoist chains  18 . Replaceable excavator teeth  19  are mounted to the front ring  16 , and the drag rope  15  is connected with forwardly projecting lugs  16 A of the front ring by way of splayed drag chains  20 . 
   Extending rearwardly from the front ring  16  are a bucket floor  21 , and parallel side walls  22  that taper downwardly to a rear (or end) wall  23  which has a height in the region of 50% to 70% of that of the side walls. 
   By way of contrast with prior art excavator buckets, the bucket as illustrated in  FIGS. 2 to 5  has a pair of spaced-apart pivot arms  24  pivotally connected to the rear wall  23  of the bucket. The pivot arms are connected with the rear hoist rope  13  by way of splayed hoist chains  25 , an equaliser connector  26  and a hoist link-socket assembly  27 . The two pivot arms  24  are mounted by way of pivot pins  28  to lug portions  28 A of the rear wall  23  and they are pivotal about a common pivot axis  29  that is located below the rim  30  of the rear wall of the bucket. The pivot axis  29  extends in a horizontal direction (i.e., parallel with the transverse direction of the bucket floor  21 ) and, hence, parallel with the axis about which the bucket tilts (i.e., rotates) in moving between set angles for dig, carry and dump modes of operation. 
   The pivot arms  24  are shaped (as seen in side elevation) to permit movement of the bucket  10 , relative to the pivot arms, through an angle greater than 90°, so that the bucket may be moved from the substantially vertical disposition shown in  FIG. 4  to a carry angle δ greater than 0° and normally between 0° and ˜20° to the horizontal, as shown in  FIG. 5 . Thus, as illustrated, each pivot arm  24  has a boomerang (or arcuate) shape and is dimensioned to extend around the rim  30  of the rear wall of the bucket with clearance (between the pivot arm and the bucket rim) when the bucket is in the extreme carry position. 
   In the illustrated embodiment of the invention, the common pivot axis  29  of the pivot arms  24  is located at a level slightly above the (unladen) CG of the bucket and on a line that makes an angle α of between 0° and 15° (and more normally between 1° and ˜5°) to the floor  21  of the bucket. 
   As seen in end elevation ( FIGS. 3A and 3B ), the alternative types of the pivot arms  24  (i.e., pivot arms  24 A and  24 B) have portions  31  of their length inclined inwardly to match the splay angle of the hoist chains  25 .