U.S. patent application number 10/543555 was filed with the patent office on 2006-05-25 for dragline bucket.
This patent application is currently assigned to CMTE DEVELOPMENT LIMITED. Invention is credited to Jeffrey Rowlands.
Application Number | 20060107556 10/543555 |
Document ID | / |
Family ID | 30005104 |
Filed Date | 2006-05-25 |
United States Patent
Application |
20060107556 |
Kind Code |
A1 |
Rowlands; Jeffrey |
May 25, 2006 |
Dragline bucket
Abstract
The invention provides for the design of a dragline bucket of
the type where there are separate front and rear hoist ropes
attached to front mounting points and rear mounting points
respectively. The front and rear hoist ropes can be independently
operated to vary the horizontal attitude of the bucket. The bucket
design methodology seeks to equalize the loads in the front and
rear hoist ropes during the major phases of the operating cycle
such as digging, hoisting and dumping, and this is typically
achieved by providing a bucket with comparatively shallow side
walls compared with the overall length of the bucket and the
positions at which the front and rear hoist ropes ultimately join
onto the bucket. The bucket typically has a flat floor and
relatively shallow side walls which may in some embodiments taper
downwardly from the rear section to the front section.
Inventors: |
Rowlands; Jeffrey;
(Queensland, AU) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
CMTE DEVELOPMENT LIMITED
|
Family ID: |
30005104 |
Appl. No.: |
10/543555 |
Filed: |
January 29, 2004 |
PCT Filed: |
January 29, 2004 |
PCT NO: |
PCT/AU04/00105 |
371 Date: |
July 27, 2005 |
Current U.S.
Class: |
37/398 |
Current CPC
Class: |
E02F 3/48 20130101; E02F
3/60 20130101 |
Class at
Publication: |
037/398 |
International
Class: |
E02F 3/60 20060101
E02F003/60 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 31, 2003 |
AU |
2003900403 |
Claims
1-12. (canceled)
13. A method of designing a bucket for a dragline of the type
wherein the attitude of the bucket is controllable by differential
movement of front and rear hoist ropes attached to front and rear
portions of the bucket respectively, said method including the
steps of: analysing the loads in both the front and rear hoist
ropes during digging, hoisting and dumping phases of the dragline
operating cycle; and optimising bucket parameters such that the
respective loads are equalized as far as possible over as much of
the cycle as possible.
14. A method as claimed in claim 13, when performed on a dragline
having two spaced apart boom point sheaves located at or adjacent
the distal end of a boom assembly, one sheave being positioned
closer to the distal end of the boom assembly than the other.
15. A method as claimed in claim 13, wherein the bucket parameters
are optimised such that the respective front and rear hoist rope
loads are within 30% of their mean value during a major part of the
hoisting phase of the operating cycle, being the time between the
point of disengagement of the bucket from the ground, and dumping
of the payload.
16. A method as claimed in claim 15, wherein the bucket parameters
are optimised such that the respective front and rear hoist rope
loads are within 20% of their mean value during a major part of the
hoisting phase of the operating cycle.
17. A method as claimed in claim 13 whereby the bucket parameters
include the positions at which the front and rear hoist ropes
ultimately join onto the bucket.
18. A bucket for a dragline assembly when designed in accordance
with the method as claimed in claim 13.
19. A bucket for a dragline assembly as claimed in claim 18,
including a base and side walls extending upwardly therefrom,
wherein the bucket has a height dimension shorter than a length
dimension, and wherein the height dimension at a front part of the
bucket is less than or equal to the height dimension at a rear part
of the bucket.
20. A bucket for a dragline assembly as claimed in claim 18,
wherein the bucket has a substantially flat base with two tapering
side walls along its length dimension.
21. A bucket for a dragline assembly as claimed in claim 18,
wherein the overall length dimension of the bucket is at least
twice the overall height dimension.
22. A bucket for a dragline assembly as claimed in claim 21,
wherein the length dimension is at least three times the height
dimension.
Description
FIELD OF THE INVENTION
This invention relates to a new type of bucket for a rigged
dragline assembly.
[0001] Draglines are large excavating machines designed to fill,
carry and dump loads of material, typically earth. Draglines are
often used in open cut coal mines to remove waste overburden
covering a shallow coal seam.
BACKGROUND OF THE INVENTION
[0002] FIG. 1 illustrates a typical large electric dragline in
accordance with the prior art. A conventional dragline includes a
rotatable support 1 mounted on a stationary base 2. An outwardly
projecting boom assembly 3 is mounted pivotally to the rotatable
support. Winches 6,9 are mounted on the support for retrieving or
releasing cables or ropes. Normally there are two main sets of
ropes or cables, hereinafter referred to as hoist ropes 4 and drag
ropes 5. Hoist ropes 4 extend from the hoist winch 6 mounted on the
support, up and outwardly along the boom, over pulleys or sheaves 7
mounted at the most distant point of the boom, down to a bucket and
rigging assembly 8. Drag ropes 5 extend from a drag winch 9 mounted
on the support 1, outwardly to the bucket and rigging assembly 8.
The bucket and rigging assembly consists of the bucket itself, and
the "Rigging" which refers to the total collection of chains,
ropes, cables and other components used to suspend the bucket.
[0003] A conventional dragline is equipped with a mechanism for
locomotion, typically being reciprocating support feet or crawler
tracks. FIG. 2 shows the typical components of the bucket and
rigging assembly in accordance with the prior art. While it is
acknowledged that there are variations on the arrangements and
names of components, the following definitions, familiar to any
person skilled in the art, will be used:
[0004] Drag ropes 5 which are used to pull the bucket while filling
(normally two).
[0005] Drag chains 10 which connect the drag ropes to the
bucket.
[0006] Hoist ropes 4 which are used to lift and carry the bucket
(normally two).
[0007] Hoist chains 11 (upper and lower) which connect the bucket
to the hoist ropes.
[0008] Spreader bar 12 which separates the left and right hoist
chains to allow the bucket to sit there between. It is situated at
the junction of the upper and lower hoist chains.
[0009] Dump rope 13 that allows the bucket to be picked up or
dumped by applying or releasing tension to the drag ropes.
[0010] Dump block 14 which is a pulley around which the dump rope
is free to move.
[0011] Dump chains 15 which are intermediate chains connecting the
dump rope to the leading end of the drag chains.
[0012] Miracle hitch 16 which is a three way link connecting the
hoist ropes, chains and dump block.
[0013] Drag three way link 17 that joins the drag ropes, drag
chains and dump chains.
[0014] Equaliser links 18 that equalise the loads between various
components and allow interconnection, e.g., from the two hoist
ropes to the single miracle hitch.
[0015] Rope sockets 19 that are used to terminate ropes and allow
their connection to other components.
[0016] Teeth and lip assembly 20 which is the leading (cutting)
edge of the bucket.
[0017] Basket 21 which is the main body of the bucket used to carry
payload.
[0018] Arch 22 which provides structural integrity to the bucket
and supplies a point to attach the dump rope.
[0019] Dump hitch 23 which is the point on the arch to which the
dump rope is attached.
[0020] Drag hitches 24 which are the points on the front of the
bucket to which the drag chains are connected.
[0021] Hoist trunnions 25 which are the points to which the lower
hoist chains are attached to the bucket.
[0022] Top rails 26 which are structural thickeners along the top
edges of the bucket.
[0023] Rear rail 27 which is a structural thickener along the top
edge of the rear of the bucket.
[0024] Other relevant definitions are:
[0025] "Carry Angle" which is the acute angle between the floor of
the bucket and the horizontal.
[0026] "Rated Suspended Load" (RSL) which is the maximum
recommended load that can be suspended from the hoist ropes.
[0027] "Boom Point"which is the most distant extreme of the boom 3
from the support 1. This point corresponds to the location of the
Boom Point Sheaves 7.
[0028] "Boom Point Radius" which is the horizontal radius measured
outwardly from the centre of rotation of the support 1 to a point
directly under the boom point sheaves 7.
[0029] The drag and hoist ropes may be retrieved or released from
their respective winches to move the bucket freely in space. The
rotatable support can "Swing" the upper dragline assembly and thus
bucket and rigging through a horizontal arc. The normal operation
of a dragline begins with the bucket freely suspended in space
above the ground. The bucket is then lowered to the ground and
positioned by releasing rope from the hoist winch and/or drag
winch. The bucket is then filled with material by retrieving drag
ropes onto the drag winch. At some point, the bucket may be lifted
or "Disengaged" from the ground by retrieving the hoist ropes. In
this operation, tension is developed in the dump rope 13 which
causes the front of the bucket to lift via the arch 22. A certain
volume of excavated material known as "Payload" is retained in the
bucket after disengaging. The bucket may then be moved to its dump
point by retrieving and releasing the hoist and drag ropes and/or
swinging the support 1. The payload is dumped by releasing drag
rope until the dump rope loses tension and allows the bucket to tip
forward. This operation can only occur under, or nearly under the
boom point sheaves. For a typical large electric dragline (e.g. BE
1370W or Marion 8050), the bucket capacity is approximately 47
cubic metres. The bucket weight is typically 40 tonnes. The
combined rigging weight is typically 20 tonnes. The RSL for these
machines is approximately 150 tonnes. Therefore, the manufacturers
recommend payloads of approximately 90 tonnes.
[0030] There are a number of limitations that conventional rigging
designs place on operating a dragline:
[0031] a) After filling the bucket, it cannot be disengaged from
the ground until the bucket is sufficiently close to the support 1
to allow enough tension to be developed in the dump rope to lift
the bucket arch. FIG. 3 shows that if the bucket is lifted too
early, the forward section of the payload is lost. This means that
the bucket must be "Over dragged" after it is full, to a point
where it can be lifted and retain a satisfactory payload. This adds
to cycle time, increases wear and reduces hoisting efficiency.
[0032] b) A dragline bucket can only dump at the perimeter defined
by the boom point radius. This is because the dump rope will only
become slack enough to drop the front of the bucket when the drag
rope tension is low, i.e., the drag ropes have been sufficiently
released. FIG. 4 shows this effect.
[0033] There are dynamic methods for dumping just inside and
outside of boom point radius, however these methods are not
recommended by the manufacturers.
[0034] Various proposals have been made to improve the control of
the orientation of the dragline bucket in a vertical plane i.e.
"carry angle" control by utilising differential control of the two
hoist ropes, one of which is operatively connected to the front of
the bucket, and the other operatively connected to the rear of the
bucket. By adjusting the position of one hoist rope relative to the
other, the vertical orientation of the bucket can be adjusted in
order to provide a dumping movement without relying on the dump
rope becoming slack with all of the disadvantages set out
above.
[0035] A construction of this type is described in International
Patent Application WO01/32994, where the carry angle of the bucket
is controlled by differential hoist rope movement with the hoist
rope entrained over two boom point sheaves. FIG. 5 shows the
multiple hoist rope dragline assembly described in WO01/32994. A
bucket 30 is suspended from two hoist ropes 31 and 32. The first
hoist rope 31 is connected to a forward part of the bucket. The
second hoist rope 32 is connected to a rear part of the bucket. Two
sheaves 33 and 34 are spaced one behind the other at the distal end
of boom 35. The first hoist rope 31 is entrained over the first
sheave 33, while the second hoist rope is entrained over the second
sheave 34. The two hoist ropes 31 and 32 in combination with drag
ropes 36 control movement of the bucket 30.
[0036] In a dragline assembly having front and rear hoist ropes, as
shown in FIG. 5, the payload is distributed between the two hoist
ropes. However, the payload is inevitably not distributed evenly
between the two hoist ropes. One hoist rope will usually bear more
load than the other.
[0037] The lifetime of a dragline hoist rope is proportional to the
peak cyclic stress experienced by it (stress being the load per
unit cross-sectional area of the rope, and peak cyclic stress being
the span between consecutive maximum and minimum stress states).
This relationship is defined by the "fatigue" lifetime as defined
in equation 1: Rope Fatigue Lifetime is proportional to 1/(Maximum
Cyclic Stress).sup.x eqn. 1 where x lies between 5 and 6. i.e. for
a 10% increase in maximum cyclic stress, rope life is reduced by
approximately a half. For a 50% increase in maximum cyclic stress,
rope life is reduced by approximately 90%.
[0038] Hence, in a dragline assembly having separate front and rear
hoist ropes, there is typically a large difference in lifetime
between the front and rear hoist ropes, since each rope has
differing maximum cyclic stress.
[0039] Hoist ropes having unequal lifetimes are highly undesirable
from a maintenance point of view. Replacement of a hoist rope is a
costly exercise, because it involves lengthy downtime of the
dragline assembly. Moreover, because of the expense of this
downtime, it is desirable to change both hoist ropes together.
However, if one hoist rope fatigues quicker than the other,
replacement of both ropes at the same time is inefficient since one
rope, having useful remaining lifetime, is unnecessarily
replaced.
[0040] It is, therefore, an object of the present invention to
provide a means for equalising, as far as possible, the loads
carried by each dragline in a multiple hoist rope dragline
assembly. It is a further object of the present invention to
provide a means for equalising, as far as possible, the hoist rope
lifetimes in a multiple hoist rope dragline assembly.
SUMMARY OF THE INVENTION
[0041] Accordingly, the present invention provides a method of
designing a bucket for a dragline assembly of the type wherein the
attitude of the bucket is controllable by differential movement of
front and rear hoist ropes attached to front and rear portions of
the bucket respectively, said method including the steps of:
[0042] analysing the loads in both the front and rear hoist ropes
during digging, hoisting and dumping phases of the dragline
operating cycle; and
[0043] optimising bucket parameters such that the respective loads
are equalized as far as possible over as much of the cycle as
possible.
[0044] Preferably the parameters include, but are not limited to:
[0045] (a) the positions of the points at which the front and rear
hoist ropes ultimately join the bucket; [0046] (b) the position of
the centre of gravity of the payload; [0047] (c) the position of
the centre of gravity of the bucket itself; and [0048] (d) the
carry angle of the bucket with respect to the horizontal.
[0049] Preferably, the method of designing a bucket is performed on
a dragline assembly having two spaced apart boom point sheaves
located at or adjacent the distal end of a boom assembly, one
sheave being positioned closer to the distal end of the boom
assembly than the other
[0050] Preferably, the bucket parameters are optimised such that
the respective front and rear hoist rope loads are within 30% of
their mean value during a major part of the hoisting phase of the
operating cycle, being the time between the point of disengagement
of the bucket from the ground, and dumping of the payload.
[0051] Preferably, the bucket parameters are optimised such that
the respective front and rear hoist rope loads are within 20% of
their mean value during a major part of the hoisting phase of the
operating cycle.
[0052] Preferably, the bucket parameters are optimised such that
the respective front and rear hoist rope loads are within 10% of
their mean value during a major part of the hoisting phase of the
operating cycle.
[0053] In a further aspect the invention provides a bucket for a
dragline assembly when designed in accordance with the method
above.
[0054] Preferably, the bucket includes a base and side walls
extending upwardly therefrom, wherein the bucket has a height
dimension shorter than a length dimension, and wherein the height
dimension at a front part of the bucket is less than or equal to
the height dimension at a rear part of the bucket.
[0055] Preferably, the bucket has a substantially flat base with
two tapering side walls along its length dimension.
[0056] Preferably, the overall length dimension of the bucket is at
least twice the overall height dimension.
[0057] Preferably, the length dimension is at least three times the
height dimension.
[0058] Preferably, the bucket does not include an arch between the
upper front portions of the bucket side walls.
[0059] The bucket of the present invention has generally shallow
sides which may be tapered from rear to front. This means that when
the bucket carries a payload, the centre of gravity of the combined
payload and bucket is shifted further towards the rear of the
bucket than in a conventional bucket design. This advantageously
tends to equalise the load carried by the front and rear hoist
ropes. This effect is illustrated in more detail below in the
Example and Comparative Example.
[0060] Preferably, the bucket has a substantially flat base with
two tapering side walls along its length dimension.
[0061] A further advantage of the bucket of the present invention
is that it has a short height dimension relative to its length
dimension and, preferably, its width dimension. Preferably, the
length dimension is at least twice the height dimension, more
preferably at least, or about, three times the height dimension.
This flat bucket geometry minimises the amount of bucket steel
required to constrain the payload and thus increases the efficiency
of the carrying operation, i.e. maximum payload for minimum
steel.
[0062] Preferably, the bucket includes attachment means at the
front and rear parts of the bucket for attachment to front and rear
hoist ropes respectively.
[0063] Preferably, the bucket includes attachment means at the
front part of the bucket for attachment to a drag rope/s.
[0064] The attachment means may be, for example, hooks or openings
in the bucket. Preferably, the attachment means for the rear hoist
rope comprise a single rope and/or chain attached to a central
point at the rear of the bucket, or a dual attachment to multiple
rear points via an intermediate "bridal" or "yoke" chain or rope.
The dual arrangement minimises the chance of the bucket twisting or
uncontrollably rotating in situations where the bucket is hanging
almost exclusively by the rear hoist rope, e.g. during dumping or
"chopping". Preferably, the attachment means for the front hoist
rope comprises a pair of flanges having a plurality of openings
therein, each flange extending upwards from respective side walls
forming the length of the bucket. Preferably, the attachment means
for the drag rope comprises a pair of flanges having a plurality of
openings therein, each flange extending in a forward direction from
respective side walls forming the length of the bucket.
[0065] Preferably, the bucket does not include an arch. As shown in
FIG. 2, traditional dragline buckets include an arch 22. The
incorporation of the arch 22 has the effect of shifting the centre
of gravity of the bucket towards the front part. The absence of an
arch, in this preferred embodiment of the present invention,
contributes to shifting the centre of gravity more towards the rear
of the bucket. In addition, the elimination of the arch reduces the
total bucket weight and thus increases the total payload that may
be carried without exceeding the machine's RSL.
[0066] Preferably, the bucket of the present invention is
substantially cuboid- or trapezoid-shaped, having an open top and
an open front section. Preferably, the side walls forming the
length of the bucket are flared outwards from the base, which
increases the volume of the bucket and helps to retain material in
the bucket.
[0067] Preferably, the bucket includes a scooping means for
scooping material into the bucket. Preferably, the scooping means
comprises a downwardly angled flange extending from a front part of
the base. These types of scooping flanges are known in dragline
bucket design. Preferably, the flange includes a plurality of
tapered fingers which define the flange's front leading edge. The
tapered fingers facilitate scooping of material (e.g. earth) into
the bucket.
[0068] Preferably, the bucket is used with a dragline assembly
including differential control means for adjusting the length of
one hoist rope relative to the other, thereby allowing control of
the angle of inclination of the bucket in a vertical plane.
[0069] Preferably, the first hoist rope is wound onto a first drum
located on the base, and the second hoist rope is wound onto a
second drum located on the base, the first and second drums being
independently rotatable to achieve differential control.
[0070] Preferably, the first and second boom sheaves are spaced
apart from each other by a fixed distance such that the first
sheave is located closer to the support than the second sheave.
This type of rigged dragline assembly (excluding the bucket of the
present invention) is described in more detail in WO01/32994.
[0071] In a further aspect, the present invention provides a method
of moving a payload, including the steps of
[0072] providing a rigged dragline assembly as described above;
[0073] depositing a payload into the bucket; and
[0074] adjusting the front and rear hoist ropes and/or the drag
rope(s) to move the payload in a desired manner.
[0075] Preferably, the front and rear hoist ropes are adjusted
independently to control the carry angle of the bucket, thereby
controlling the combined centre of gravity of the payload and
bucket. Thus, in addition to the bucket design being used to
distribute evenly the load between the front and rear hoist ropes,
the carry angle may also be used to facilitate even weight
distribution. A large carry angle will tend to shift the centre of
gravity towards the front hoist rope due to the extra payload being
carried on the front payload face, whereas a small carry angle will
tend to shift the centre of gravity towards the rear hoist rope due
to the loss of payload from the front payload face.
[0076] Hence, the present invention recognises the problem of
unequal loads between front and rear hoist ropes in the known
dragline assembly described in WO01/32994. Moreover, the present
invention recognises that this problem may be addressed by
optimising bucket design. In addition, the present invention allows
the payload to be varied to ensure that the total hoist rope load
is matched to the Rated Suspended Load (RSL) of the Dragline by
virtue of altering the bucket's carry angle to control the bucket
payload, yet still maintaining an even load distribution between
the two hoist ropes during the parts of the dragline cycle in which
maximum hoist rope loads are experienced.
[0077] Preferably, the analysis is performed on a dragline assembly
having two spaced apart boom point sheaves located at or adjacent
the distal end of a boom assembly, one sheave being positioned
closer to the distal end of the boom assembly than the other. This
type of boom arrangement is described in WO01/32994.
[0078] Preferably, the bucket parameters are optimised such that
the respective front and rear hoist rope loads are within 30% of
their mean value during a major part of the hoisting phase of the
cycle, more preferably within 20%, and more preferably within 10%.
The hoisting phase is defined as the time between the point of
disengagement and dumping of the payload in a typical dragline
assembly cycle.
[0079] Preferably, the major part of the hoisting phase comprises
at least 50% of the hoisting phase, more preferably at least 60%,
more preferably at least 70%, and more preferably at least 80%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0080] The present invention will now be described in more detail
with reference to the following Figures in which:--
[0081] FIG. 1 illustrates a conventional dragline;
[0082] FIG. 2 illustrates conventional components of a bucket and
rigging assembly;
[0083] FIG. 3 illustrates a disadvantage with a conventional
dragline;
[0084] FIG. 4 illustrates a conventional dragline dumping at the
boom point radius;
[0085] FIG. 5 illustrates a prior art dragline having front and a
rear hoist rope;
[0086] FIG. 6A is a front view of a bucket according to the present
invention;
[0087] FIG. 6B is a side elevation of FIG. 6A;
[0088] FIG. 6C is a perspective view of FIG. 6A;
[0089] FIG. 7 is a graph of hoist rope load over time for both
conventional and separate front and rear end hoist ropes; and
[0090] FIG. 8 is a similar graph to FIG. 7 showing the loads from a
bucket designed in accordance with the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0091] In a dragline assembly having front and rear hoist ropes as
shown in FIG. 5, the payload is distributed between the two hoist
ropes. The payload is inevitably not distributed evenly between the
two hoist ropes and the inventor of the present invention has
realised that this uneven distribution can be minimized by careful
bucket design.
[0092] This uneven distribution of rope load during hoisting is a
direct result of: [0093] (a) the positions of the points at which
the various ropes and chains ultimately join the bucket; [0094] (b)
the position of the centre of gravity of the payload; [0095] (c)
the position of the centre of gravity of the bucket itself; and
[0096] (d) the carry angle of the bucket with respect to the
horizontal.
[0097] In addition the rope load distribution may be uneven during
other parts of the dragline cycle such as dumping or when the
bucket is disengaged out of the ground.
[0098] This uneven distribution of rope load can be overcome by
providing a means for equalizing, as far as possible, the hoist
rope lifetimes in a multiple hoist rope dragline assembly.
[0099] The inventor of the present invention has realised that this
can be achieved by providing a bucket design that allows the total
hoist rope load to be matched to the Rated Suspended Load (RSL) of
the Dragline by virtue of altering the bucket's carry angle to
control the bucket payload, yet still approximate an even load
distribution between the hoist ropes during the parts of the
dragline cycle in which maximum hoist rope loads are
experienced.
[0100] The present invention recognises that in a typical multiple
hoist rope dragline assembly, having a front and a rear hoist rope,
the maximum load carried by the front hoist rope is often greater
than the maximum load carried by the rear hoist rope. Furthermore,
the present invention recognises the importance of bucket design in
equalising the loads carried by front and rear hoist ropes during
the parts of the dragline cycle in which maximum hoist rope loads
are experienced.
[0101] Typically, this can be achieved by carefully considering the
bucket parameters including those listed in items (a) to (d) above
when designing the bucket to be used with the dragline.
[0102] Referring to FIGS. 6A-6C, there is shown a bucket 100,
having a base 102 and side walls 103, 104 and 105 extending
upwardly therefrom. Two side walls 103 and 104 define a length of
the bucket, and one side wall 105 defines a width of the bucket.
From FIG. 6B, it can be seen that the bucket 1 has a length
dimension which is approximately three times the height
dimension.
[0103] The bucket 100 has a rear part 106 and a front part 107.
From FIG. 6B, it can be seen that the height of the bucket at the
rear part 106 is greater than the height of the bucket at the front
part 107. The effect of this tapering is that more payload is
carried in the rear part than the front part, meaning that when the
bucket is filled with a payload, the centre of gravity is located
towards the rear part of the bucket.
[0104] To facilitate construction and reduce weight in the bucket,
the rear corners 108 and 109 may be left open, braced by welded
rods across the top of the opening. These rods may also be used to
mount a bridle (not shown) for attachment to the rear hoist rope,
although the rear hoist rope may be attached to a single central
point on the rear wall 105 of the bucket.
[0105] At the front part of the bucket 1, a pair of flanges 110 and
111 extend upwards from respective side walls 103 and 104. Each
flange 110 and 111 has respective openings 112 and 113 for
attachment of a front hoist rope via an intermediate bridal or
yoke.
[0106] Also at the front part of the bucket 1, a pair of flanges
114 and 115 extend frontwards from respective side walls 103 and
104. Each flange 114 and 115 has respective openings 116 and 117
for attachment of a drag rope.
[0107] From FIG. 6A, it can been seen that side walls 103 and 104
are flared outwards from the base, facilitating retention of
material in the bucket. Hence, the bucket 100 is substantially
trapezoid-shaped, having an open top and an open front end.
[0108] The bucket 100 includes a downwardly angled flange 118
extending from a front part of the base 102. The flange 118 is
comprised of a plurality of fingers 119. The fingers 119 are
tapered to define a front leading edge 120 of the flange 118. As
with conventional dragline buckets, material may be scooped into
the bucket 100 using the flange 118 by dragging it along the
ground.
[0109] The efficacy of the bucket shown in FIGS. 6A-6B was compared
with a conventional bucket, as illustrated in FIGS. 1-5.
COMPARATIVE EXAMPLE
[0110] The hoist rope loads were measured for a typical prior art
bucket design (as shown in FIGS. 1-5) for two cases. The first
where the bucket was rigged with conventional hoist ropes, i.e.
side by side, and the second in the front/rear configuration using
a conventional bucket as described in WO01/32994. FIG. 7 shows the
hoist rope loads over time during the various stages of digging,
hoisting, dumping and return for the two cases. The trace
corresponding to the conventional hoist rope load represents
exactly half the total hoist load because there are actually two
identical ropes working together, joined by an "equalising bar" at
or near the bucket hitching point. This trace is used as a
reference for comparison for the individual front and rear hoist
ropes in the new invention.
[0111] It can be seen that during the hoist part of the dragline
cycle, the hoist rope loads for the front/rear configuration system
diverge significantly from the conventional trace. Since the peak
load for the front hoist rope during hoisting is greater than that
of the rear hoist rope, its lifetime is significantly shorter.
EXAMPLE
[0112] The loads on a front hoist rope and a rear hoist rope were
measured on a rigged dragline bucket assembly of the type shown in
FIGS. 6A, B and C. The total suspended load was matched to the
example of the conventionally designed bucket of prior art. FIG. 8
shows the hoist rope loads over time during the various stages of
digging, hoisting, dumping and return.
[0113] It can be seen that the peak front and rear hoist rope loads
are nearly equal during the hoisting part of the cycle, meaning
that they will have similar lifetimes.
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