Patent Publication Number: US-2009235560-A1

Title: Dragline buckets

Description:
FIELD OF THE INVENTION 
     This invention relates to dragline buckets. 
     BACKGROUND OF THE INVENTION 
     Although there are many factors affecting the productivity of a dragline, the efficiency and effectiveness of the bucket during the dig cycle (that is, fill carry and dump) has a big influence on the overall productivity of the dragline. Previous inventions have been aimed at increasing the efficiency and effectiveness of the bucket during the fill component of the dig cycle. However, there is room for further improvement in that area and there is also room for improvements in other areas. 
     A large amount of energy is required to pull a dragline bucket through spoil during the fill phase and to carry the bucket and the spoil to the dump site. Some of the energy is used in moving the bucket itself and some to moving the spoil contained in the bucket. Thus it is desirable to maximise the ratio of mass of spoil, that is, the payload, to the mass of the bucket. It is also desirable to retain as much of the spoil as possible which has entered the bucket during the fill phase through the carry phase to the dump site. The present invention is aimed at providing a dragline bucket which is more efficient than previously known buckets at least in some circumstances. 
     DISCLOSURE OF THE INVENTION 
     With the foregoing in view, the invention in one aspect resides broadly in a dragline bucket comprising: 
     a floor having a ground engaging leading edge, a rear wall extending upward from said floor and spaced rearward from said leading edge, and two spaced apart side walls extending upward from said floor and forward from said rear wall, the upper edges of said rear wall and said side walls defining an open top and the height from said floor of at least a portion of said side walls forward of said rear wall being substantially less than the height of said side walls adjacent said rear wall. 
     In another aspect, the invention resides broadly in a dragline bucket comprising: 
     a floor having a ground engaging leading edge; 
     a rear wall extending upward from said floor and spaced rearward from said leading edge; 
     two spaced apart side walls extending upward from said floor and forward from said rear wall, the upper edges of said rear wall and said side walls defining an open top; and 
     a lifting arch operatively connected to said floor and/or said side walls forward of said rear wall, said leading edge and said lifting arch defining a mouth through which spoil may enter, the height from said floor of at least a portion of said side walls between said rear wall and said lifting arch being substantially less than the height of said rear wall from said floor. 
     In yet another aspect, the invention resides broadly in a dragline bucket comprising: 
     a floor having a ground engaging leading edge; 
     a rear wall spaced from said leading edge and extending upwards from said floor and curving forward at opposite sides of its centre to meet two spaced apart side walls also extending upward from said floor and forward from said rear wall, the upper edges of said rear wall and said side walls defining an open top. 
     In yet another aspect, the invention resides broadly in a dragline bucket comprising: 
     a floor having a ground engaging leading edge; 
     a rear wall spaced from said leading edge and extending upwards from said floor and curving forward meet two spaced apart side walls also extending upward from said floor and forward from said rear wall, the upper edges of said rear wall and said side walls defining an open top; and 
     a lifting arch operatively connected to said floor and/or said side walls forward of said rear wall, said leading edge and said lifting arch defining a mouth through which spoil may enter. 
     Preferably, said side walls and said rear wall terminate in a top rail running therealong from the lifting arch on one side of the mouth to the lifting arch on the other side of the mouth. However, if desired the top rail could be spaced above the side walls along said portion of lower height. In such case, stiffening ribs, gussets or the like may be added to the side walls if desired to increase its strength. 
     Preferably, the upper edges of said side walls slope downward at a predetermined angle from the upper edge of said rear wall towards the leading edge of said floor to respective predetermined points. It is preferred that the predetermined angle is the angle enclosed by a straight line joining the upper edge of the rear wall (at the points where the respective side walls meet the rear wall) to the leading edge or a point just in front of or just behind the leading edge. Although theoretically the height of the side walls could fall to zero at the leading edge, preferably, the predetermined points are selected to achieve desired energy efficiency while at the same time maintaining sufficient strength. In one presently preferred form, the respective predetermined points are where the height of the side walls is about half that of the rear wall (at the points where the respective side walls meet the rear wall). In one particularly preferred form, at that point the side walls then curve upwards towards the lifting arch. Typically a plurality of spaced apart teeth will be fitted to the floor along the leading edge in known manner to improve ground cutting performance and in such cases the preferred points to which the straight line referred to above is drawn may vary according to the particular bucket or the particular teeth being used. 
     In another form, the invention resides broadly in a method of operating a dragline, including: 
     providing a dragline having a dragline bucket as previously described; 
     dragging the bucket through spoil in a forward direction to substantially fill a front portion of the bucket and then lifting the ground engaging leading edge while continuing dragging in the forward direction to tilt the front of the bucket upwards whereby spoil accumulated adjacent the mouth of the bucket moves towards the rear wall of the bucket; 
     tilting the bucket to a predetermined carry angle; 
     lifting the bucket to a desired height; 
     carrying the bucket to a dump site; and 
     dumping the spoil at the dump site. 
     Advantageously, the method according to the invention reduces the amount of load on the drag rope which will be connected to the side walls for pulling the bucket forward. 
     Terms such as horizontal, vertical, upper, lower, front, rear, side and the like are used herein for the purpose of describing the invention from the perspective of its normal at rest position and are not intended to limit the invention to use in any particular orientation. The term spoil is intended to encompass virgin ground and ground which has been dug or stockpiled. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be more easily understood and put into practical effect, reference will now be made to the accompanying drawings wherein: 
         FIG. 1  is a pictorial representation of a conventional dragline bucket; 
         FIG. 2  is a plan of the dragline bucket of  FIG. 1 ; 
         FIG. 3   a  is a schematic sectional side elevation of a conventional dragline bucket showing various spoil shear plane lines during the fill phase of a dig cycle; 
         FIG. 3   b  is a schematic sectional side elevation of the dragline bucket of  FIG. 3   a  showing the initial fill line at the end of the fill phase of the dig cycle; 
         FIG. 3   c  is a schematic sectional side elevation of the dragline bucket of  FIG. 3   a  showing the initial fill line and the retained fill line after spilling or settling while being lifted at the end of the fill phase; 
         FIG. 3   d  is a schematic sectional side elevation of the dragline bucket of  FIG. 3   a  at commencement of the carry phase showing the settled fill line; 
         FIG. 4  is a pictorial representation of a dragline bucket according to the invention; 
         FIG. 5   a  is a plan of the bucket of  FIG. 4 ; 
         FIG. 5   b  is a side elevation of the bucket of  FIG. 4 ; 
         FIG. 6   a  is a schematic sectional side elevation of the bucket of  FIG. 4  showing various spoil shear planes during the fill phase of a dig cycle; 
         FIG. 6   b  is a schematic sectional side elevation of the dragline bucket of  FIG. 4  towards the end of the fill phase; 
         FIG. 6   c  is a schematic sectional side elevation of the dragline bucket of  FIG. 4  showing the initial fill line and the retained fill line after spilling or settling while being lifted at the end of the fill phase; 
         FIG. 6   d  is a schematic sectional side elevation of the dragline bucket of  FIG. 4  during the carry phase showing the settled fill line; 
         FIG. 6   e  is a schematic sectional side elevation of the dragline bucket of  FIG. 4  being carried at a greater carry angle than that in  FIG. 6   d ; and 
         FIG. 6   f  is a schematic sectional side elevation of the dragline bucket of  FIG. 4  showing the settled fill line for the carry angle of  FIG. 6   e  with the settled line from  FIG. 6   d  superimposed. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     The dragline bucket  10  illustrated in  FIG. 1  has a floor  11  with a ground engaging leading edge  12  to which a plurality of spaced apart teeth  13  are fitted in known manner, a rear wall  14  extending upward from the floor and spaced rearward of the leading edge which is contiguous with two spaced apart side walls  16  and  17  which also extend upward from the floor and forward from the rear wall, the rear wall terminating at its upper edge  18  in a rear top rail  19  and the side walls terminating at their upper edges  21  and  22  in side top rails  23  and  24  respectively, the top rails defining an open top  26 . 
     A lifting arch  27  is connected to the forward end portions of the side walls and to the floor (via the side walls) for connecting the bucket to the lift cable of the dragline in known manner. It will be appreciated that the leading edge  12  together with the side walls and the lifting arch define a mouth  28  through which spoil may enter the bucket. Lifting lugs  29  and  31  are welded to the outer face of the side walls towards the rear wall for attaching lifting chains also for connection to the dragline cable. Similarly, drag lugs  32  and  33  are connected to the forward ends of the side walls below the lifting arch for connection to the drag chain of the dragline in known manner. 
     It will be appreciated that the top rails  19 ,  23  and  24  of the conventional bucket all lie in the same plane, that being a plane substantially parallel to the plane containing the surface of the body of the floor of the bucket (which is generally horizontal when at rest on level ground). Additionally, the rear wall meets the floor substantially at right angles with only a slightly rounded bottom corner and the rear wall meets the side walls substantially at right angles, the two side walls being substantially parallel and the floor being substantially rectangular. 
     It is understood in the mining industry that dragline buckets fill in accordance with what is known as the “shear zone theory”. Under the shear zone theory as illustrated in  FIGS. 3   a  to  3   d , as the bucket starts to fill while it is pulled through the virgin spoil an initial laminar layer  41  of spoil forms over the floor of the bucket. Then, as filling continues, the virgin spoil immediately in front of the leading edge shears upwardly over the laminar layer  41  and progressively creates shear zones  42 ,  43  and so on, until the end of the fill phase of the dig cycle to form the mound of spoil  44  as seen in  FIG. 3   b . As can also be seen in  FIG. 3   b , the mound  44  within the bucket is biased towards the leading edge  12 . The bias is due to the bucket “bulldozing” the virgin spoil  40  towards the end of the fill phase as evidenced by the upper surface  46  (shown in phantom) being moved upwards in front of the leading edge. It is believed that particles of clay in the spoil tend to bind together at the front of the bucket thereby increasing the density of the spoil in that area. The virgin spoil in front of the bucket helps hold the spoil  44  in the bucket. 
     As the shear zones  42 ,  43 , etc, are formed, the shearing action causes the spoil towards the front of the bucket to be compacted and hence denser in front of the peak  47  of the heap  44  then the spoil behind the peak. Thus, a given volume of spoil forward of the peak will be heavier then the same volume reward of the peak. 
     As can be seen in  FIG. 3   b , at the end of the drag phase, a portion  47  of the heap is above the top rail and a space  52  remains behind the mound  44  although in other drag phases, the space may be filled. As the bucket is lifted while still in a horizontal attitude, a movement known as “nodding” occurs in which the bucket tilts forward and back and causes spoil from the peak (and forward of the peak) to shear and fall over the leading edge. That lost spoil is typically denser than most other spoil in the bucket for reasons mentioned previously. The bucket is then titled to a desired carry angle prior to being swung to a dump site. The carry angle typically places the floor at 32° to 38° to the horizontal as generally indicated in  FIG. 3   d.    
     The bucket  110  of the present invention as illustrated in  FIG. 4  is similar to the conventional bucket  10  just described in many respects and accordingly corresponding numbers will be used to reference corresponding features except prefaced by a “1”. Thus, it will be seen that bucket  110  has a floor  111  with a leading ground engaging edge  112  having spaced apart teeth  113  mounted thereto, a rear wall  114  extending upward from the floor and spaced rearward of the leading edge, two spaced apart side walls  116  and  117  also extending upward from the floor, the upper edge of the rear wall terminating in a rear top rail  119  and the upper edges of the side rails  116  and  117  terminating in side tops rails  123  and  124  respectively. A lifting arch  127  is mounted to the side walls and the floor in the same manner as in the conventional bucket shown in  FIG. 1  and lifting lugs and drag lugs are provided in the same manner. However, in the bucket  110 , the rear wall curves outwards from the side walls such that the centre of the rear wall is further behind the leading edge than the ends of the rear wall. It will also be seen that the rear wall is higher in the centre and curves downwards to the points where it meets the respective sidewalls. 
     It will also be seen that the height of the side walls of the bucket  110  from the floor is not constant as in conventional bucket  10 , but rather the upper edges slope forward from the rear top rail at an angle α to a straight line drawn from the rear top rail to the ground engaging leading edge for a point approximately halfway along the length of the floor. At that point, the side walls are approximately half the height of the rear wall and from there, the side walls curve upwardly in an arc towards the top of the lifting arch in a manner selected to achieve sufficient structural integrity. Testing has demonstrated that the optimum carry angle of the dragline bucket, represented by the angle between the floor  111  and the horizontal to be equal to or greater than the angle α as will be discussed in more detail later. 
     As can be seen in  FIG. 6   a , the shear zone theory applies to the initial fill stages in the same manner as previously described in relation to conventional buckets in relation to shear zones  141 ,  142 ,  143  and so on. However, when the bucket is filled according to the method broadly described earlier, the peak  147  of the mound  144  is further forward than in the conventional bucket relative to the leading edge with more spoil in the zone of higher density. Moreover, as the bucket is titled further back as illustrated in  FIG. 6   c , spoil therein settles to the general shape of the mound  148  shown therein. One advantage of progressively angling the bucket  110  from the horizontal to the desired carry angle during the fill phase is that more of the filled spoil is retained during the fill phase and in the transition between the fill phase and the carry phase (that is the initial lift after filling) than with conventional buckets using conventional digging methods. Thus, buckets constructed according to the present invention and used according to the method described earlier are less likely to suffer the spoil losses due to “nodding” and will have a greater ratio of retained spoil payload to bucket weight than conventional buckets. It is also believed that buckets according to the present invention have higher drag efficiency due to less drag friction. 
     In use, bucket  110  commences digging in the horizontal attitude illustrated in  FIG. 6   a  and after a mound forms to the level  147  shown in  FIG. 6   b , the bucket is tilted or rolled back slightly by lifting the lifting arch and thus the leading edge  112 . As the bucket moves, the arch is lifted higher thus tilting the bucket back further to the desired carry angle as it fills to the level  148  shown in  FIG. 6   c  and then as the bucket is lifted further for the carry phase, the mound settles to the form  149  shown generally in  FIG. 6   d . Under this method, the face of the virgin spoil will tend to form an arc and the bucket will tend to follow the arc during each dig cycle. Depending on the type of spoil being dug, the bucket can be tilted further back and be carried at a steeper carry angle to prevent loss of filled spoil over the leading edge as shown by levels  150  and  151  in  FIGS. 6   e  and  6   f . it will be appreciated that the reduced height of the side walls of the bucket results in a decrease in energy consumption during the fill phase because spoil movement in the fill phase is not as constrained by the side walls as in previously known buckets. 
     The foregoing description has been given by way of illustrative example of the invention and all modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as defined by the appended claims.