Dragline Bucket Rigging System
An assembly and method for using a flexible tensile member as part of the rigging for a dragline bucket. The tensile member includes a stranded core surrounded by one or more armoring layers or devices. The stranded core produces excellent strength in tension. The armor layer(s) provides a lower but still sufficient strength in compression. The compression strength is sufficient to eliminate plastic deformation of the core strands when the tensile member is bent around or dragged across an edge. The armor layer(s) also protects against battering, cutting, abrading, compression, and shearing forces. This resistance greatly reduces the likelihood of heavy items—such as the yoke, dump block, and spreader bar—damaging the tensile member when the bucket assembly is laid on the ground.
This non-provisional patent application claims the benefit of two earlier-filed provisional applications. The first provisional application was assigned Ser. No. 61/708,326. The second provisional application was assigned Ser. No. 61/878,147. All three applications list the same inventor.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot Applicable.
MICROFICHE APPENDIXNot Applicable
BACKGROUND OF THE INVENTION1. Field of the Invention
This invention relates to the Held of mining and excavation equipment. More specifically, the invention comprises an improved rigging system for dragline buckets that reduces the need for heavy chains.
2. Description of the Related Art
In order to understand the significance of the present invention, it is important to have some understanding of conventional dragline bucket rigging.
In operation, the bucket is swung into position and then dropped into the material that is to be removed. The mouth of the bucket is typically given a downward pitch during the drop operation so that it digs into the material. The bucket is then dragged back toward the boom crane. As it is dragged along the bucket's mouth scoops in a load of material.
Once the bucket is full, the boom crane is used to pull the bucket assembly free of the material. The boom crane then swings the bucket toward the area where the scooped material is to be deposited. When the bucket assembly reaches the deposit area, a dumping mechanism causes the bucket to pitch downward. The contents of the bucket then spill from the bucket's mouth. Once the bucket is empty, the cycle repeats.
Bucket 24 and its contents are primarily suspended by a pair of lift trunnion assemblies 22—with a trunnion assembly being located on each side of the bucket. A lower hoist chain 20 connects each trunnion to spreader bar 18. An upper hoist chain 16 connects each side of the spreader bar to yoke 48.
The term “yoke” refers to the component that connects the upper hoist chains to the tensile members used to lift the entire bucket assembly, ft is also typically used to connect the chains to the dump block assembly. It can take on many shapes and forms. In the example of
The yoke may be a single large casting or it may be an assembly of several pieces. The term should be broadly construed to mean anything that connects the bucket assembly rigging to the lifting cables leading to the boom on the crane.
As stated previously, the lift ropes connect the bucket assembly to the boom of the crane. Yoke 48 also provides an attachment point for dump block 28. As the name suggests, a mechanism incorporating the dump block is used to change the bucket from its scooping configuration to its dumping configuration. When this mechanism is actuated, the bucket pivots downward about the two trunnion assemblies. The mouth of the bucket pitches downward and the tail of the bucket rises. Once the bucket's contents are completely dumped, the dumping mechanism is reversed and the bucket is returned to its digging orientation.
Still referring to
The reader will note that a clump rope 26 passes from the drag socket 34, around dump block 28 and connects to the upper portion of arch 32. The dump rope is used to regulate the transition of the bucket between its digging and dumping orientations.
The bucket assembly is operated in a brutal environment. The bucket is typically dropped into an ore deposit containing rocks and other abrasive materials. Chains have traditionally been used near the bucket itself because of the extreme forces applied and the abrasive action of the material being dug. The chains shown in the assembly may be comparable in size to the termination chains used on a large ship. For example, each link may be well in excess of 1 foot (30+ centimeters) long.
Such chains are quite heavy. They must be serviced and replaced quite often as well. The size and weight of the chains make them difficult and dangerous to handle. In addition, the chains rapidly elongate while in use—primarily because of link-to-link abrasion. This elongation alters the dumping geometry of the bucket assembly and reduces its performance. In addition, the elongation of the lifting chains reduces the maximum height to which the bucket assembly may be lifted. The reduction in lift height reduces the amount of material that the drag-line assembly can move. It would be advantageous to replace the chains with a lighter and less cumbersome material. It would also be advantageous to replace the chains with a tensile member that does not elongate significantly.
The reader will note mat the cables used are free of the actual dropping and dragging operations—being above spreader bar 18.
A dragline bucket assembly must be periodically laid on the ground for servicing, shift changes, or other reasons. When the bucket assembly is placed on the ground and the boom is lowered, the lifting rigging fails over the bucket in random and unpredictable ways.
Tensile member 46 is flexible enough to lay across top rail 38 as shown. Spreader bar 18 and dump block 28 have both fallen on top of tensile member 46 and “pinched” it against top rail 38. Tensile member 46 may also be dragged along top rail 38 while being subjected to other forces. The spreader bar may weigh several tons and even the dump block assembly may exceed one ton in weight. Thus, the reader will perceive that even though tensile member 46 lies above the dropping and digging operations it is still subjected to extreme battering, bending, cutting, and compression forces when the bucket is laid down. Further, the orientation of the “pile” of heavy components created when the bucket is laid down is random and impossible to consistently predict.
Thus, even though it is possible to use a flexible tensile member in the upper hoist assembly, a conventional flexible tensile member is not likely to survive the full range of bucket operations. Some flexible designs have been evaluated over the years but no such design has ever been able to successfully compete with chain.
The advantages of using such a tensile member are promising, however. Any reduction in the weight of the bucket rigging means that a larger bucket can be used (for a given, crane lifting capacity) and more fill material can be carried with each scoop. Any reduction in the stretching tendency of the tensile members used means that the assembly produces a more consistent bucket fill and soil mound height, thus increasing productivity. Any reduction in metal-to-metal wear increases the lifespan of a component and reduces the frequency of component replacement. Any reduction in the use of chain reduces the safety hazards inherent in the use of chain. Thus, a new type of flexible tensile member assembly that is able to withstand all the dragline bucket operations would be advantageous. A new type of flexible tensile member assembly that is able to employ modern synthetic materials would further reduce the weight of the rigging and provide an even greater advantage.
BRIEF SUMMARY OF THE PRESENT INVENTIONThe present invention comprises an assembly and method for using a flexible tensile member as part of the rigging for a dragline bucket. The tensile member includes a stranded core surrounded by one or more armoring layers or devices. The stranded core produces excellent strength in tension. The armor layer(s) provides a lower but still sufficient strength in compression. The compression strength is sufficient to eliminate plastic deformation of the core strands when, the tensile member is bent around or dragged across an edge. The armor layer(s) also protects against battering, cutting, abrading, compression, and shearing forces. This resistance greatly reduces the likelihood of heavy items—such as the yoke, dump block, and spreader bar—damaging the tensile member when the bucket assembly is laid on the ground.
However, as shown in
A group of core strands carries the tensile load within each tensile member 46 (The construction will be explained in more detail subsequently). Every group of core strands has a “critical radius.” If the group is bent around a radius that is smaller than this critical radius, at least some of the strands within the group will be plastically deformed. An important objective of the present invention is ensuring that the core strands of each tensile member do not undergo a bend that it tighter than the applicable critical radius during normal operations.
Dragline rigging undergoes two different classes of operation that may be deemed “normal.” The first class involves the actions of moving the bucket, digging with the bucket, and dumping the bucket. The second class involves lowering the bucket to the ground and setting the associated rigging on the ground so that the bucket and rigging may be inspected and/or serviced. The forces placed on the rigging may be quite different for these two classes of operation.
The improvement in the prior art collapsing sequence of the bucket rigging does not mean that a tensile member 46 will never come to rest beneath, a heavy component or be pinched or pulled against an edge. In many cases the upper hoist rigging will be required to bend around bucket top rail 38, which is often quite sharp. The rigging will experience these forces while it is still under some tension. Thus, it is still preferable to provide some “armoring” to protect the tensile members. One may therefore generalize a preferred tensile member as (1) possessing excellent strength in tension; (2) possessing a lower but still, sufficient strength in compression (sufficient to eliminate the likelihood of the tensile member undergoing a damaging sharp bend); (3) possessing resistance to lateral battering and bending forces: and (4) possessing some flexibility to allow the assembly to move as it needs in order to collapse to the ground.
The reader may naturally wonder whether the tensile elements shown as tensile members 46 could simply be made completely rigid. Some flexibility in the tensile members 46 is still desirable for many operation reasons. The bucket is often dropped onto lateral slopes and uneven ground. Flexibility in the rigging allows for energy absorption. A rigid structure may also suspend heavy components off the ground when the bucket is laid down for inspection and repair. This is an unsafe condition. The present invention therefore employs tensile members for the upper hoist assembly that can bend and flex, but which retain enough rigidity to prevent the tensile members bending into a bend radius small enough to plastically deform the core strands.
These goals may be achieved using a wide variety of structures.
Filler layer is preferably selected for its compressive strength and toughness. However, it should be more pliable than either the stranded core or the armor layer. It is preferable for the filler layer to provide cushioning, both to blunt the impact of lateral blows and to help create larger bend radii for the core strands. Suitable materials include cross-linking urethane, synthetic rubber, natural rubber, gel material, and closed or open-celled foams. In fact, if the end fittings and armor layer provide suitable sealing, the compressive layer may even be a gas such as air or nitrogen. Such fillers may also be used to provide a barrier against harmful debris that have penetrated the armoring layer.
Returning to
As stated previously, a portion of the tensile members will often tend to fall off the back or side of the bucket at some point. Part of the tensile member will then be draped across the edge of the bucket and may in fact be dragged along or pulled sharply over the edge. An idealized assembly such as shown in
Clevis receiver 60 is provided on the spreader bar. Termination 64 includes a tang which, slides into the clevis-receiver. A Cross pin 62 is then passed through aligned transverse holes in the clevis-receiver and the termination. The cross pin is typically retained in position by a welded tab, cottar key, or similar element.
Those skilled in the art will rapidly appreciate that termination 64 is thereby made free to pivot about cross pin 62. However, the existence of the pinned joint means that the termination can only easily rotate in a plane that is transverse to the pin. This constraint likewise promotes the flexing of the cable within bending plane 66.
Returning now to
In addition to the preferred rigidity the proposed tensile member also needs to possess “armoring” able to withstand various lateral forces, sharp edges, and blows. One way to provide both rigidity and armoring is the use of overmolding. The term “overmolding” refers to molding a suitable molded material (such as a polymer) over the top of the exterior surfaces of a previously-created assembly. The overmolded layer provides rigidity and armoring.
Once the assembly of stranded core 54 and the two terminations 64 is completed, the assembly is placed into a mold cavity. A suitable molding compound is then injected around the assembly. The molding compound transitions from a liquid to a solid to form flexible overmold 70. The material used for the flexible overmold should provide suitable impact cushioning, cut resistance, abrasion resistance, and the desired compressive strength (the bend-limiting feature). Various natural and synthetic rubbers may be used for this purpose. HDPE may also be used. In some embodiments the overmold may be created as multiple layers bonded together.
The flexible overmold includes transverse holes aligning with the two transverse openings 69. From the exterior, the assembly may appear to be a unified piece made of the overmold material as the internal components will often not be visible. However, the use of stranded core 54 allows the assembly to carry a tensile load that is at least an order of magnitude greater than would be possible using the overmolding material alone (and will in most cases be several orders of magnitude greater).
The use of overmolding also allows the creation of a “pre-bent” shape if desired. The embodiment of
The stranded core could be made in many additional ways. It could be made as a spliced rope, a fiber sling, a round rope sling or grommet, a steel cable, and a composite of multiple materials and/or multiple tensile members. Any of these constructions could be made into an overmolded assembly.
As discussed previously, it may be preferable in some embodiments to have significant compressive resistance.
Since the bend-limited tensile member assembly will be replacing a prior art chain, it may be advantageous to provide additional degrees of freedom proximate the end connections (chain generally having several degrees of freedom).
Tension spring 90 applies a torque to the lower termination in the view. Compression device 92 (a block of compressible material) likewise applies a torque to the upper termination. The tension and compression devices may be mechanical springs, air struts, or even active actuators. When the dragline bucket assembly is supported by lift ropes 14, each tensile member 46 is pulled taut and the torsional forces applied by the components 90, 92 are negligible. Of course, these devices could also be used as bend limiters in the opposing directions.
Of course, it may be desirable in some applications to provide more than two tensile members connecting the spreader bar and yoke.
Finally, although, the preceding embodiments have shown bend-limited tensile members with a constantly-bending structure (and uniform armoring) this need not always be the case.
Although the preceding description contains significant detail, it should not be construed as limiting the scope of the invention but rather as providing illustrations of the preferred embodiments of the invention. Thus, the language used in the claims shall define the invention rather than the specific embodiments provided.
Claims
1. A dragline bucket assembly, comprising:
- a. a bucket having a first lateral side and a second lateral side;
- b. a spreader bar having a first end and a second end;
- c. a first lower tensile member connecting said first lateral side of said bucket to said first end of said spreader bar;
- d. a second lower tensile member connecting said second lateral side of said bucket to said second end of said spreader bar;
- e. a yoke;
- f. a first upper tensile member connecting said first end of said spreader bar to said yoke;
- g. a second upper tensile member connecting said second end of said spreader bar to said yoke;
- h. wherein said first upper tensile member includes, i. a flexible stranded core, having a critical bending radius ii. an armor layer, iii. a bend-limiting element;
- i. wherein said second upper tensile member includes, i. a flexible stranded core, having a critical bending radius ii. an armor layer, iii. a bend-limiting element;
- j. wherein said bend-limiting element in said first upper tensile member is sufficiently stiff to prevent said stranded core of said first upper tensile member being bent to a radius that is less than said critical bending radius during the operation of said dragline bucket assembly; and
- k. wherein said bend-limiting element in said second upper tensile member is sufficiently stiff to prevent said stranded core of said second upper tensile member being bent to a radius that is less than said critical bending radius during the operation of said dragline bucket assembly
2. A dragline bucket assembly as recited in claim 1, wherein said flexible core in each of said upper tensile members includes a plurality of synthetic strands, with a termination being attached to each end of said plurality of synthetic strands.
3. A dragline bucket assembly as recited in claim 1, wherein said flexible core in each, of said upper tensile members includes a plurality of steel strands, with a termination being attached to each end of said plurality of steel strands.
4. A dragline bucket assembly as recited in claim 2, wherein each of said terminations is connected to said spreader bar by a cross pin, with said cross pins limiting a rotation of said terminations.
5. A dragline bucket assembly as recited in claim 3, wherein each of said terminations is connected to said spreader bar by a cross pin, with said cross pins limiting a rotation of said terminations.
6. A dragline bucket assembly as recited in claim J, wherein said bend-limiting elements comprise a thick layer of high-density polymer surrounding said flexible stranded core.
7. A dragline bucket assembly as recited in claim 1, wherein said bend-limiting elements comprise a leaf spring connected in parallel with at least one flexible stranded core.
8. A dragline bucket assembly as recited in claim 2, wherein each upper tensile member further includes an articulation block.
9. A dragline bucket assembly as recited in claim 2, wherein said articulation block comprises a length of chain.
10. A dragline bucket assembly as recited in claim 1, wherein said dragline bucket assembly further comprises a biasing element connecting said first upper tensile member to said spreader bar.
11. A dragline bucket assembly, comprising:
- a. a bucket having a first lateral side, a second lateral side, and a top rail;
- b. a spreader bar having a first end and a second end;
- c. a first lower tensile member connecting said first lateral side of said bucket to said first end of said spreader bar;
- d. a second lower tensile member connecting said second lateral side of said bucket to said second end of said spreader bar;
- e. a yoke;
- f. a first upper tensile member connecting said first end of said spreader bar to said yoke;
- g. a second upper tensile member connecting said second end of said spreader bar to said yoke;
- h. wherein said first upper tensile member includes, i. a flexible stranded core, having a critical bend radius ii. a bend-limiting element;
- i. wherein said second upper tensile member includes, i. a flexible stranded core, having a critical bend radius ii. a bend-limiting element;
- j. wherein said bend-limiting element in said first upper tensile member is sufficiently stiff to prevent said stranded core of said first upper tensile member being bent to a radius that is less than said critical bending radius when said first upper tensile member is bent over said top rail of said bucket; and
- k. wherein said bend-limiting element in said second upper tensile member is sufficiently stiff to prevent said stranded core of said second upper tensile member being bent to a radius that is less than said critical bending radius when said first upper tensile member is bent over said top rail of said bucket.
12. A dragline bucket assembly as recited, in claim 11, wherein said flexible core in each of said upper tensile members includes a plurality of synthetic strands, with a termination being attached to each, end of said plurality of synthetic strands.
13. A dragline bucket assembly as recited in claim 11, wherein said flexible core in each of said upper tensile members includes a plurality of steel strands, with a termination being attached to each end of said plurality of steel strands.
14. A dragline bucket assembly as recited in claim 12, wherein each of said terminations is connected to said spreader bar by a cross pin, with said cross pins limiting a rotation of said terminations.
15. A dragline bucket assembly as recited in claim 13, wherein each of said terminations is connected to said spreader bar by a cross pin, with said cross pins limiting a rotation of said terminations.
16. A dragline bucket assembly as recited in claim 11, wherein said bend-limiting elements comprise a thick layer of high-density polymer surrounding said flexible stranded core.
17. A dragline bucket assembly as recited in claim 11, wherein said bend-limiting elements comprise a leaf spring connected in parallel with at least one flexible stranded core.
18. A dragline bucket assembly as recited in claim 12, wherein each upper tensile member further includes an articulation block.
19. A dragline bucket assembly as recited in claim 12, wherein said articulation block comprises a length of chain.
20. A dragline bucket assembly as recited in claim 11, wherein said dragline bucket assembly further comprises a biasing element connecting said first upper tensile member to said spreader bar.
Type: Application
Filed: Oct 1, 2013
Publication Date: Apr 3, 2014
Inventor: Richard V. Campbell (Tallahassee, FL)
Application Number: 14/043,333
International Classification: E02F 3/60 (20060101);