WO2000068518A1

WO2000068518A1 - Method and apparatus for enhancing dragline dump rope life

Info

Publication number: WO2000068518A1
Application number: PCT/AU2000/000425
Authority: WO
Inventors: Viet Kinh Luan Mai; Jamil Srour
Original assignee: Bhp Innovation Pty Ltd.
Priority date: 1999-05-07
Filing date: 2000-05-08
Publication date: 2000-11-16
Also published as: AUPQ026999A0

Abstract

A suspension assembly (1) for a dragline bucket (2) includes: at least one hoist line (7) secured to a hitch (6); a hoist chain assembly (3) secured at an upper end to the hitch (6) and at lower ends to trunnions (4) on opposing sides of the bucket (2); at least one drag line (11, 12) secured to an open front of the bucket (2); a dump block (21) secured to the hitch (6) which includes at least one sheave (40); and a plurality of dump ropes (17, 18), each dump rope having a first end attached directly or indirectly to the at least one drag line (11, 12) and a second end attached to the bucket (2). Each dump rope (17, 18) passes over the or one of the sheaves (40) included in the dump block (21), so that tension in the dump ropes (17, 18) is less than in an equivalent single-dump-rope system, their size is correspondingly smaller, and longer dump rope life is obtained.

Description

METHOD AND APPARATUS FOR ENHANCING DRAGLINE DUMP ROPE LIFE

TECHNICAL FIELD This invention concerns dragline excavators of the type used in surface coal mining and similar activities and particularly concerns improvements to the rigging of buckets of such excavators. DESCRIPTION OF PRIOR ART

In surface coal mining, overburden is removed from above one or more coal seams so that the seam(s) may be extracted, and one type of machine often used for such overburden removal is a dragline excavator, more commonly known simply as a "dragline". A dragline is a mobile machine with a structure able to rotate about a vertical axis and including in that structure an operator's cab, and with an angled crane-like boom secured to the rotating structure. An open-fronted bucket is supported by a bucket suspension arrangement which includes one or more hoist lines running from a point on the boom and one or more drag lines running from the rotating structure. Paid-out lengths of the hoist and drag lines are variable by hoist and drag winches, respectively, in the rotating structure. The bucket is supported by hoist chains secured at their upper ends to the hoist line(s) and at their lower ends to trunnions on opposing sides of the bucket. The bucket suspension also includes one or more dump ropes, each of which is attached at one end, directly or indirectly, to the drag line(s) and at the other end to the bucket and runs over a sheave in a dump block between the ends of the dump rope, the or each dump block usually being attached to a hitch which connects the hoist chain assembly and the hoist lines. The dump rope is arranged to enable the bucket to be held in an attitude in which material contained within it is retained so long as some tension is maintained in the drag rope, and to allow the bucket to rotate about its trunnions so that material falls from its open front, when drag rope tension is released. Draglines of this general type are also used for other activities, such as general earth moving and canal cleaning.

Dump ropes of draglines are subject to repeated bending as they pass over their dump sheaves and after a certain number of dig-dump cycles typically fail as a result of such bending, unless replaced first. Deterioration of dump ropes is often accelerated by the presence, in the bucket's working area, of abrasive rock dust and fragments. In large draglines, such as those used in surface coal mining, replacing a failed dump rope, or replacing an apparently sound one as a preventative measure is an operation which takes considerable time and so may represent a substantial loss of production. Dump ropes in this situation may require replacement after less, and often substantially less, than two weeks' normal use.

Dump ropes are often made not from new rope but from lengths of used drag or hoist line rope, and so historically have been seen as comparatively cheap and expendable items, with very little development specifically directed to enhancing their life being carried out. However, the pressure to reduce maintenance costs and loss of production in high-production environments such as surface coal mining has led in recent years to recognition of the desirability of enhancing dump rope life. Enhanced dump rope life is an object of the present invention.

There is also an increased concern with safety, and by increasing dump rope life with preplanned replacement, the risk of accidental breakages of dump ropes may be reduced, and with it the risk of damage to the dragline and danger to personnel working on or around the dragline.

It is known that by careful design or adjustment of conventional rigging to reduce dump rope tension, dump rope life may be enhanced, and in practice this is usually the first approach used when dump rope life is found unsatisfactorily short. One example of such an adjustment is to locate the hoist chain trunnions closer than usual to the centre of gravity of the bucket and its payload. However, this can lead to longer dumping time with a consequent negative effect on production, or even to spillage from the rear of the bucket. Another approach is to use a longer- than-usual dump rope, but this can also lead to production loss, through spillage of overburden from the front of the bucket. There are therefore limits to the improvement available by this means.

One recent approach to the problem, described in Australian Patent No. 77474/98, is to provide a dump sheave of larger than usual diameter so that the severity of bending of the dump rope around the sheave is less than normal and the rope's life is accordingly enhanced. Clearance requirements on the rigging, imposed by the need at all times to avoid contact between the bucket and the dump block, require that the hoist chains be secured to extensions of a shaft of the dump sheave. A disadvantage of this arrangement is believed to be that the dump block is not free to align itself to the dump rope if the dump rope leaves a central plane of the bucket, as can often happen. This may lead temporarily to large fleet angles between the dump rope and dump block, with consequent rapid wear. The present invention at least alleviates this problem.

It is possible to eliminate the dump rope altogether, as proposed in US Patent 5400530 (Schmidt) and Australian Patent 618582 (Martin, Swick) which describe unconventional buckets. These buckets have largely failed to find favour with dragline users, possibly because of their use of moving parts, and require investment in new buckets, which are substantial capital items. It is desirable to alleviate the problem without buying such major items as buckets, and that is a further object of the invention.

Indeed, it is desirable to use standard buckets and as much standard rigging hardware as possible, and it is an object of the invention that it be applicable to standard buckets and rigging with only limited modification thereof.

An indirect approach is to provide a dump block which, while, not affecting dump rope life in itself, does permit more rapid changeover of the dump rope when required. US Patent No. 5,636,460 and Australian Patent No 623556 describe dump blocks which enable a dump rope to be removed and another one to be fitted by allowing side access to the periphery of the sheave so that no threading of rope through the block is necessary, and presocketed ropes can be used.

It is known in the art to provide multiple dump ropes, each rope having its own dump block. This arrangement is normally used for very large buckets where single dump ropes would be impractically large and difficult to handle during maintenance. In such an arrangement, the tension in each dump rope may be less than the tension that would exist in an equivalent single dump rope. However, such arrangements, apart from complexity and cost, have the following important disadvantage.

Draglines have a so-called rated suspended load, being a maximum allowed value of the combined weight of the bucket, rigging and its payload of excavated material. The weight of extra dump block(s) and the extra components associated with them in general reduces the payload that can be carried without exceeding the rated suspended load. In other words, a lesser proportion of the allowed suspended load can be payload in machines with multiple dump ropes and multiple dump blocks. This may offset any incidental improvement due to longer dump rope life. It is therefore not known in the art to attempt to enhance dump rope life by the use of extra dump ropes and dump blocks. BRIEF SUMMARY OF THE INVENTION

According to the invention there is provided a suspension assembly for a dragline bucket including: at least one hoist line secured to a hitch; a hoist chain assembly secured at an upper end to the hitch and at lower ends to trunnions on opposing sides of the bucket; at least one drag line secured to an open front of the bucket; a dump block secured to the hitch and including at least one sheave; and a plurality of dump ropes each dump rope having a first end attached directly or indirectly to the at least one drag line and a second end attached to the bucket, wherein each dump rope passes over the or one of the sheaves included in the dump block.

The essence of this invention is that multiple dump ropes are included in a bucket suspension, so that the load required to be taken by a dump rope is shared between several ropes, but with the dump ropes sharing the same dump block. Sharing of the dump rope loads leads to lesser tension in each one, by comparison to conventional single- or multiple-dump-rope arrangements, allowing enhanced dump rope life, while the use of a single dump block for several dump ropes, instead of multiple dump blocks, may lead to a lower suspension weight than multiple- dump-block arrangements. The suspension assembly is preferably so arranged that when the dragline bucket is suspended stationary on the hoist and drag lines, the dump ropes are substantially parallel along substantially their entire lengths. This is to alleviate or avoid dump rope wear or damage due to excessive fleet angles between the dump ropes and the sheave or sheaves. It is particularly preferred that the suspension assembly further includes tension equalizer means adapted to maintain at least approximately equal tensions in the dump ropes during use of the dragline bucket. The tension equalizer means may include a yoke to which are attached either first or second ends of a pair of the dump ropes with a point on the yoke substantially equidistant from those ends being pivotally attached via attachment mean to the at least one drag line or to the bucket, as the case may be. Most draglines use buckets rigged with either one or two dump ropes, in the latter case with two dump blocks. In both cases, a twin dump rope suspension according to the invention is the simplest possible and may be advantageous, in the first case because of the improvement in dump rope life and in the second because of the suspended weight saving associated with use of a single dump block, which can allow higher suspended loads or faster hoisting. In twin dump rope systems acording to the invention, the dump block may include two sheaves of substantially equal pitch diameter. Alternatively, the number of sheaves included in the dump block may be one, with that sheave defining two peripheral grooves of substantially equal pitch diameter each adapted to receive one of the dump ropes. In a further aspect, the invention provides a suspension assembly for a dragline bucket including: at least one hoist line; at least one drag line connected to an open front of the bucket; a hoist chain assembly connected at an upper end by first connecting means to the at least one hoist line and at lower ends to trunnions on the bucket; a dump block including at least one sheave and secured to said first connecting means; and a plurality of dump ropes, each dump rope having a first end connected by second connecting means to a said drag line and a second end connected to the bucket, wherein each dump rope passes over the or a said sheave.

The dump block may be included in the first connecting means. Alternatively however, the first connecting means may also include a hitch having separate connection points for the hoist chain assembly, the at least one hoist line and the dump block.

In yet a further aspect, the invention provides a dump block for use in a dragline bucket suspension assembly, including at least one sheave and formed on said at least one sheave a plurality of peripheral grooves, each said groove adapted to receive one of a plurality of dump ropes of the bucket suspension assembly.

There may be a plurality of sheaves each having at least one of said peripheral grooves thereon. In a particularly preferred arrangement, the dump block may include parts movable between first and second positions thereof, wherein when said parts are in said first positions, a said dump rope is separable laterally from said dump block and when said parts are in said second positions, such lateral separation is prevented by said parts. A further invention directed to alleviation of the same problem of extending dump rope life will now be disclosed in summary.

The further invention provides a method for modification of a suspension assembly of a dragline bucket wherein the bucket has an open front sides, a floor and a back wall and the suspension assembly includes: at least one hoist line secured to a hitch; a hoist chain assembly secured at an upper end to the hitch and at lower ends to coaxial trunnions on opposing sides of the bucket; at least one drag line secured to an open front of the bucket; a dump block secured to the hitch and including a sheave; and a dump rope having a first end attached directly or indirectly to the at least one drag line and a second end attached to the bucket and between the first and second ends passing over the sheave, the method including the step of: relocating the hoist trunnions on the sides of the bucket forwardly towards the open front of the bucket relative to their original positions so as to reduce the degree of tension in the dump rope required to avoid dumping of material from the front of the bucket without causing said degree of tension to fall to zero when the bucket is normally loaded. By reducing the tension in the dump rope during carrying of a payload, relocation of the hoist trunnions increases the life of the dump rope. The method preferably further includes the step of providing a flexible line, such as a wire rope or chain, having first and second ends, the first end being secured to a point on the back wall of the bucket and the second end being secured to the hitch, and the line being of such length as to limit rearward overbalancing of, and spillage from, the bucket. In essence, providing such a line avoids rearward overbalancing of the bucket, with consequent spillage of payload, in the case of payloads which are so distributed in the bucket that the combined centre of gravity of payload and bucket would otherwise be far enough towards the rear of the bucket for such overbalancing to occur, with trunnions relocated in the way disclosed above.

The method may also include the step of relocating the hoist trunnions downwardly towards the floor of the bucket relative to their original position. This has the advantage that the weight of the bucket has a greater moment arm about the trunnons during dumping, partially offsetting any increase in dumping time due to the forward relocation of the trunnions.

In particular, the hoist trunnions after relocation on the sides of the bucket may be located on a first plane which includes the combined centre of gravity of the bucket and the payload and which is inclined backwardly and downwardly at about 45 degrees to a second plane which includes the trunnion axes and the combined centre of gravity of the bucket and the payload. A lower figure preferably 35 degrees may also be used.

In another aspect, the further invention provides a suspension assembly for an open-fronted dragline bucket having sides, a floor and a back wall, the suspension assembly including: at least one hoist line secured to a hitch; a hoist chain assembly secured at an upper end to the hitch and at lower ends to coaxial trunnions on opposing sides of the bucket; at least one drag line secured to an open front of the bucket; a dump block secured to the hitch and including a sheave; and a dump rope having a first end attached directly or indirectly to the at least one drag line and a second end attached to the bucket and between the first and second ends passing over the sheave, the suspension assembly further including a flexible line, such as a wire rope or chain, having first and second ends, the first end being secured to a point on the back wall of the bucket and the second end being secured to the hitch, and the line being of such length as to limit rearward overbalancing of, and spillage from, the bucket. Non-limiting embodiments of the two inventions will now be described in more detail by reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a dragline bucket and its rigging, the rigging being according to the invention.

Figure 2 is a perspective view of a dump block, as shown in Figure 1.

Figure 3 is a diametral cross-sectional view of the dump block shown in Figure 2 taken at the position marked "A" in Figure 2.

Figure 4 is a perspective view of a portion of the bucket rigging shown in Figure 1.

Figure 5 is a perspective view of a portion of the bucket rigging shown in Figure 1.

Figure 6 is a diametral cross-sectional view of the dump block shown in Figure 6 taken at the position marked "B" in Figure 7. Figure 7 is an alternative dump block usable in rigging according to the invention.

Figure 8 is a perspective view of a dragline bucket and its rigging, the rigging being alternative rigging according to the invention.

Figure 9 is a side view of a loaded dragline bucket and its rigging, modified according to the further invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a suspension assembly 1 (i.e. rigging) for a dragline bucket 2 according to the invention. The bucket 2 is open-fronted and suspended on a hoist chain assembly 3, which is attached to hoist trunnions 4 on sides 5 of the bucket 2. The hoist chain assembly 3 is secured also to a hitch 6, which in turn is attached to wire rope hoist lines 7, and includes a spreader bar 70 to prevent lower hoist chains 71 from contacting the bucket 2. A tension equalizing link 8 (known as a "banana link") ensures at least approximate equality of tension in the hoist lines 7. Left and right drag chains 9, 10 are attached to the bucket 2 and, via drag sockets 13 and 14 of a type well known in the art, to left and right wire rope drag lines 1 1 , 12 respectively. As best seen in Figure 4, dump ropes 17 and 18 terminate in sockets 19 and

20 of a type well known in the art. The sockets 19 and 20 are pivotally secured by pins 54 to a tension equalizing yoke 16. The yoke 16 is pivotally secured by a pin 55 within a clevis fitting 33. The clevis fitting 33 is in turn pivotally secured by a pin 56 to tangs 57 on an arch 15 at the front of the bucket. The pin 55 is parallel to, and equidistant from, each of the pins 54. This arrangement allows the bucket 2 to be carried at various angles relative to the dump ropes 17 and 18 without bending them. The yoke 16 can pivot about the pin 55 to equalize the tensions in the dump ropes 17 and 18, at least approximately. The dump ropes 17 and 18 pass through a single dump block 21 , which is connected to the hitch 6, and then forward to sockets 22 and 23 of known type. As best seen in Figure 5, the sockets 22 and 23 are pivotally secured by pins 50 to a tension equalizing yoke 24. The tension equalizing yoke 24 is pivotally secured by a pin 51 to a connector 52 which in turn is pinned by a pin 26 to an equalizer bar 25 of known type. The pin 51 is parallel to, and equidistant from, each of the pins 50. The equalizer bar 25 is attached by shackles 27 and 28 to dump chains 29 and 30. The dump chains 29 and 30 are in turn attached to the drag sockets 13 and 14. The yoke 24 can pivot about pin 51 to equalize the tensions in the dump ropes 17 and 18, at least approximately. The dump ropes 17 and 18 are of substantially equal length. The provision of the two tension equalizing yokes 16 and 24 is intended to give the best possible assurance of equal tensions in the two dump dopes 17 and 18. However, it would also be possible to Use only one tension equalizing yoke such as either 16 or 24, the dump ropes 17 and 18 at their other ends being connected to the arch 15 or equalizer bar 25 (as the case may be) by conventional means such as would be known to those skilled in the art.

The bucket rigging 1 is in most respects conventional. However, what is not conventional is the presence of the two dump ropes 17 and 18 running through the single dump block 21 , and the arrangements disclosed above for ensuring equal tension in the dump ropes 17 and 18. The dump ropes 17 and 18 are substantially parallel along their respective whole lengths. It will be apparent to persons skilled in the art of bucket rigging, that the double dump ropes 17 and 18 and the single block

21 may be used in otherwise conventional buckets and rigging, by simply being substituted for an equivalent single dump rope and its dump block. This is a convenience to owners of such conventional buckets and rigging.

Reducing tension per unit cross-sectional area in a wire rope subject to repeated bending over a sheave is known to extend its fatigue life. So too is reducing the ratio of the diameter of the wire rope to the diameter of the sheave. By distributing loads between the two dump ropes 17 and 18 rather than a single dump rope, the tension in each is less than in a conventional single dump rope, so that a smaller rope can be used with about the same tension per unit cross-sectional area and a reduced ratio of rope diameter to sheave diameter. Accordingly, with suitable selection of rope size and type and sheave diameter, enhanced dump rope life is obtainable.

When the bucket 2 and rigging 1 are held stationary and clear of the ground, a vertical plane of symmetry (not explicitly shown) lies midway between the hoist lines 7, between the drag lines 11 and 12 and between the dump ropes 17 and 18. This plane of symmetry also bisects the bucket 2 longitudinally. In operation, however, it is possible for this symmetry to be disturbed. This can occur, for example, if the dragline (not shown) is already swinging as the bucket 2, full of dug material, is broken free from the ground by operation of the hoist lines 7 and the drag lines 11 and 12. Like conventional dump blocks, the dump block 21 is mounted to the hitch 6 in such a way that it may freely swing out of the plane of symmetry if the dump ropes 17 and 18 cease to be parallel to the plane of symmetry. This is important because fleet angles between the dump ropes 17 and 18 and the dump block 21 are thus kept small in such circumstances, with consequent avoidance of excessive wear of the ropes 17 and 18. As shown in Figure 2, the dump block 21 has an elongated ring 34 through which passes a pin 35 which is in turn retained in the hitch 6, this arrangement providing the necessary freedom of movement of the dump block 21. Other arrangements are of course possible as will be apparent to persons skilled in the art.

Figure 3 is a diametrally sectional view taken at a diameter identified by the phantom line marked "A" in Figure 2 and shows that the dump block 21 has a single sheave 40 mounted on an axle 41 between two cheek plates 42 and 43. The sheave 40 has two peripheral grooves 44 and 45, shaped to receive the dump ropes 17 and 18 respectively. A guide 46 has recesses 47 and 48 shaped to ensure that the dump ropes 17 and 18 are constrained to stay in their respective grooves 44 and 45. The particular construction of the dump block 21 shown is not intended to be limiting, as developments known in the art may be adapted readily to twin-groove dump blocks by persons skilled in the art. In particular, the constructions shown in US Patent 5,636,460 and Australian Patent 623556, which allow for easier and faster changing of dump ropes, may readily be adapted to twin-groove versions so that the dump ropes 17 and 18 need not be threaded through the block 21 and then socketed, but may be -pre-socketed and fed in laterally, in essentially the manner shown in those patents. Pre-socketing can further reduce the dragline downtime involved in installing new dump ropes.

Another possibility would be to provide two separate sheaves in a single dump block instead of a single twin-groove sheave. It is thought that this may in some circumstances lead to better equalization of tension between the two dump ropes. Figures 6 and 7 show, in a view exactly equivalent to Figure 3, an alternative dump block 60 generally similar to the block 21 but having twin sheaves 61 and 62 mounted to a shaft 63. It will be readily apparent that side-access to the sheaves in the manner described in US Patent 5,636,460 or the manner described in Australian Patent 623556 could also be provided in a twin-sheave dump block, to speed changeover and to enable the use of presocketed dump ropes. This is shown in Figures 6 and 7 where two doors 64 are hingeably connected to side plates 65 of the block 60. The doors 64 may be locked closed by bolts 66, or, for replacement of dump ropes, opened to the positions shown in phantom lines in Figure 6. The side plates 65 are secured to a central plate 66 between the two sheaves 61 and 62 by through-bolts 67. The doors 64 have formations 68 which when the doors are closed ensure that the ropes 17 and 18 remain on their respective sheaves 61 and 62.

Through the use of the twin dump ropes 17 and 18 and the single dump block 21 , a weight saving can be obtained compared to the provision of twin dump ropes and twin dump blocks and the necessary additional mounting components. For example, the dump block 21 shown in Figure 3 effectively serves as two dump blocks but has only one pair of cheek plates 42 and 43 and one mounting ring 34. Thus, rigging according to the invention should be able to be made more productive than a conventional double dump rope system, not only through lower maintenance times and production losses due to enhanced dump rope life, but through reducing to a lesser degree the ratio of payload to rated suspended load.

Figure 8 shows a further bucket suspension 90 according to the invention. This is in every respect the same as the suspension assembly 1 except that the hitch 6 and the dump block 21 of the assembly 1 are not present. Instead there is a single component 91 , which combines a dump block 92 (corresponding to the dump block 21 in Figure 1) and rigidly connected thereto a hitch plate 93 (corresponding to the hitch 6 in Figure 1). The further invention will now be described.

Referring to Figure 9, there is shown in side elevation an open-fronted dragline bucket 101 having sides 102, a back wall 103, a floor 104, and an arch 105. The bucket carries a load of material 106. The bucket 101 is supported by rigging 107 which includes a hoist line 108 secured to a hitch 109, to which in turn are secured a hoist chain assembly 110 and a conventional dump block 111.

A dump rope 112 is secured to the bucket 101 at the arch 105 and at its other end (not shown) to drag lines (not shown) which are extensions of drag chains 113 which are secured to the front of the bucket 101. The hoist chain assembly 110 is secured to the bucket at coaxial hoist trunnions 114 on sides 102, so that, for dumping, the bucket 101 rotates about the trunnions 114 when the dump rope 112 is slackened (which occurs when the drag lines are paid out). The combination of bucket 101 and its payload 106 has a centre of gravity whose position in elevation is shown at 115 in the Figure although it of course generally lies on or close to a central plane of symmetry of the bucket 101. It will be noted that the centre of gravity 115 is so located relative to the trunnions 114 that a positive tension in the dump rope 112 is required to prevent the bucket 101 rotating clockwise (in Figure 9) to dump its payload 106. In normal practice, the centre of gravity 115 is located sufficiently far forward of the trunnions 114 even with an unusual or irregular load 106 to avoid rearward overbalancing of the bucket 101. Moreover, a sufficiently far forward location of the centre of gravity 115 ensures satisfactorily rapid dumping by giving an adequate value of the torque exerted by the combined weight of the bucket 101 and payload 106 about the trunnions 114. The bucket 101 is provided with a further, non-conventional component, namely a wire rope line 116 with end sockets 117 and 118 which are attached respectively to the back wall 103 of the bucket (at a central location transversely of the bucket 101) and to the hitch 109. According to the method of the further invention, the hoist trunnions 114 are moved forwardly on the sides 102 of the bucket 101 to a position shown by the point 114', so that the hoist chain assembly 110 can be mounted in a position such as that illustrated by the chain dotted line 110'. The line 116 is also provided in the method, and has a length such that in normal operation (i.e.carrying payloads) it is slack. In this further-forward position of the hoist chain assembly 110', the fraction of the combined weight of the bucket 101 and payload 106 supported by the dump rope 112 is reduced and the proportion supported by the hoist chain assembly 110' is correspondingly increased. A lower tension in the dump rope 112 during each cycle is known to extend its life, as expressed in terms of the average number of dig-dump cycles before failure.

However, useful improvements in dump rope life require that the line 110' be very close (as seen in elevation) to the centre of gravity 115, and closer than any position that would be used in ordinary practice. In fact, rearward overbalancing of the loaded bucket 101 becomes a risk for at least some payloads 106 and dumping time is significantly increased. The length of the line 116 is chosen so that if rearward overbalancing does occur, it is prevented from leading to any significant actual loss of payload 106 over the back wall 103 of the bucket 101. Only in a case of rearward overbalancing would the line 116 become taut. In such cases, a competent operator would be able to cause dumping by, for example, a rapid "jerk" upward of the hoist line. However, the choice of trunnion position 114' and the length of the line 116 are such that this is the exception, most dumps being normal but slower than in a conventional case.

To at least partially offset the increase in dump time, it may be practical in some cases to move the position of the trunnions 114' not only forwardly along the bucket 101 but downwardly towards the floor 104, in each case relative to their conventional positions 114. The downward movement has the effect that as rotation of the bucket 101 takes place in dumping, the torque (clockwise in the figure) of the weight of the bucket about the trunnions 114' is larger than it otherwise would be, leading to faster dumping.

Some computer modelling studies for such cases have shown that it may be desirable for the trunnion position 114' to be on a line 121 (seen in elevation) passing through the combined centre of gravity 115 and sloping backwardly and downwardly from a line 120 (seen in elevation) between the original trunnion position 114 and the combined centre of gravity 115 such that the angle "A" in Figure 4 is about 35 degrees. A figure of about 45 degrees could also be used.

It will be recognized by persons skilled in the art that many variations to the inventions herein disclosed are possible without departing from their scope.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A suspension assembly for a dragline bucket including: at least one hoist line secured to a hitch; a hoist chain assembly secured at an upper end to the hitch and at lower ends to trunnions on opposing sides of the bucket; at least one drag line secured to an open front of the bucket; a dump block secured to the hitch and including at least one sheave; and a plurality of dump ropes, each dump rope having a first end attached directly or indirectly to the at least one drag line and a second end attached to the bucket, wherein each dump rope passes over the or one of the sheaves included in the dump block.

2. A suspension assembly according to Claim 1 wherein when the dragline bucket is hanging stationary on the hoist and drag lines, the dump ropes are substantially parallel along substantially their entire lengths.

3. A suspension assembly according to Claim 1 or 2 further including tension equalizer means adapted to maintain at least approximately equal tensions in the dump ropes during use of the dragline bucket.

4. A suspension assembly according to Claim 3 wherein the tension equalizer means includes a first yoke to which are attached the first ends of a pair of the dump ropes and wherein a point on the first yoke substantially equidistant from the first ends of each one of the pair of dump ropes is pivotally attached to attachment means which are in turn attached to the at least one drag line.

5. A suspension assembly according to Claim 4 wherein the number of drag lines is two and wherein the attachment means includes an equalizer bar having left and right ends respectively connected via dump chains to left and right ones of the drag lines and to which equalizer bar the first yoke is pivotally attached at a point equidistant from the left and right ends.

6. A suspension assembly according to Claim 4 or 5 wherein the tension equalizer means includes a second yoke to which are attached the second ends of said pair of the dump ropes and wherein a point on the second yoke substantially equidistant from the second ends of each one of said pair of dump ropes is attached via second attachment means to the bucket.

7. A suspension assembly according to Claim 3 wherein the tension equalizer means includes a second yoke to which are attached the second ends of a pair of the dump ropes and wherein a point on the second yoke substantially equidistant from the second ends of each one of the pair of dump ropes is attached via second attachment means to the bucket.

8. A suspension assembly according to any one of Claims 1 to 7 wherein the number of dump ropes is two.

9. A suspension assembly according to Claim 8 wherein the number of sheaves included in the dump block is two and the sheaves are of substantially equal pitch diameter.

10. A suspension assembly according to Claim 9 wherein the dump block further includes guide means adapted to maintain each dump rope in place on its respective sheave.

11. A suspension assembly according to Claim 8 wherein the number of sheaves included in the dump block is one, wherein that sheave defines two peripheral grooves each adapted to receive one of the dump ropes and wherein the pitch diameters of the two grooves are substantially equal.

12. A suspension assembly according to Claim 11 wherein the dump block further includes guide means adapted to maintain each dump rope in place in its respective peripheral groove of the sheave.

13. A suspension assembly for a dragline bucket including: at least one hoist line; at least one drag line connected to an open front of the bucket; a hoist chain assembly connected at an upper end by first connecting means to the at least one hoist line and at lower ends to trunnions on the bucket; a dump block including at least one sheave and secured to said first connecting means; and a plurality of dump ropes, each dump rope having a first end connected by second connecting means to a said drag line and a second end connected to the bucket, wherein each dump rope passes over the or a said sheave.

14. A suspension assembly according to claim 13 wherein the dump block is included in the first connecting means.

15. A suspension assembly according to claim 13 wherein the first connecting means includes a hitch having separate connection points for the hoist chain assembly, the at least one hoist line and the dump block.

16. A suspension assembly according to claim 13 wherein the dump block includes parts movable between first and second positions thereof, wherein when said parts are in said first positions, a said dump rope is separable laterally from said dump block and when said parts are in said second positions, said dump rope is captive in and movable lengthwise through said dump block.

17. A dump block for use in a dragline bucket suspension assembly, including at least one sheave and formed on said at least one sheave a plurality of peripheral grooves, each said groove adapted to receive one of a plurality of dump ropes of the bucket suspension assembly.

18. A dump block according to claim 17 including a plurality of sheaves each having at least one of said peripheral grooves thereon.

19. A dump block according to claim 17 or 18 including parts movable between first and second positions thereof, wherein when said parts are in said first positions, a said dump rope is separable laterally from said dump block and when said parts are in said second positions, such lateral separation is prevented by said parts.