MAST HEAD FOR A DRAGLINE
A mast head assembly for a dragline comprises an elongated body for connecting to a mast of a dragline. The elongated body includes side plates on opposite sides of the body. The side plates have suspension lugs and chord and lacing stubs for attaching cables from the mast head to the boom of a dragline. At least one of the cord stubs is located above and to the rear of a first chord stub. The chord and lacing stubs are positioned on the side plates so that the maximum stress in the mast head assembly is where the chord stub connects to the original chord. The highest remaining stress is located at the point where the upper/rear chord stub connects to the original chord.
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This application claims the benefit of and priority to U.S. Provisional Application No. 61/623,949, which was filed on Apr. 13, 2012, and International Application no. PCT/US2012/035646, which was filed on Apr. 27, 2012, both of which are incorporated herein by reference in their entirety.
TECHNICAL FIELDThis disclosure relates to a mast head assembly for a dragline.
BACKGROUNDDraglines are an important excavating tool used in many surface mining operations worldwide. These highly productive machines operate 24 hours a day, seven days a week and are able to reach depths of 79.8 m (262 ft) with capacities up to 116.2 m3 (152 yd3). Offering the lowest material removal cost per tonne (ton) and an average operating life of 40 years, draglines are the most productive and versatile machine in the industry.
Draglines, the largest single-bucket excavators in existence today, are used primarily for the removal of overburden in long-life surface coal mines.
The mast head box on draglines have been problematic after several years of use, and generally require lengthy repairs followed by increasingly frequent cracking. Instead of performing frequent repairs, the disclosed device is a new mast head box design.
SUMMARYThe disclosed device is a mast head assembly for a dragline. The mast head assembly comprises an elongated body for connecting to a mast of a dragline. The elongated body includes side plates on opposite sides of the body. The side plates have suspension lugs and chord and lacing stubs for attaching cables from the mast head to the boom of a dragline. At least one of the cord stubs is located above and to the rear of a first chord stub. The chord and lacing stubs are positioned on the side plates so that the maximum stress in the mast head assembly is where the chord stub connects to the original chord. The highest remaining stress is located at the point where the upper/rear chord stub connects to the original chord.
The disclosure will become more fully understood from the following detailed description, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements, in which:
Before turning to the figures, which illustrate the exemplary embodiments in detail, it should be understood that the present application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting.
The disclosed information and analysis was done on a model 1570W dragline manufactured by Bucyrus, now Caterpillar. This model had the following general capacities: bucket capacities—48 to 61 m3 (63 to 80 yd3); boom lengths—94 to 105 m (310 to 345 ft); maximum allowable load—142,900 to 181,400 kg (315,000 to 400,000 lbs); maximum working weight—3,630,000 kg (8,000,000 lbs). However, the disclosed device has general applicability to other draglines as well.
After an initial analysis it was deemed necessary to perform an entire beam analysis of the mast in order to map displacements and rotations to the smaller, more detailed model. To provide an accurate and fair comparison, the original and the upgrade were analyzed with identical boundary conditions and loads. The loads were determined by reviewing historical boom and mast analysis models. Additionally, both designs were analyzed at the maximum and minimum loads that would be experienced while digging to obtain a stress range for fatigue analysis.
As evident in
The disclosed device is a mast head assembly 100 for a dragline. The mast head assembly 100 comprises an elongated body 110 for connecting to a mast of a dragline. The elongated body 110 includes side plates 108 on opposite sides of the body 110. The side plates 108 have suspension lugs 106 for attaching cables from the mast head to the boom of a dragline. At least one of the chord stubs 114 is located above and to the rear of a first chord stub. Lacing stubs 112 are positioned on the side plates 108 so that the maximum stress in the mast head assembly 100 is where the chord stub 114 connects to the original chord 116. The highest remaining stress is located at the point where the upper/rear chord stub 114 connects to the original chord 116.
The upgrade design 100 improves the original design and should eliminate problems with machines that have frequent mast head cracking issues. The loading and deflections used in the analysis are worse than actually experienced by the mast head. The area with the shortest fatigue life for the original design lasted only 0.18 years, whereas the upgrade design 100 shows a shortest fatigue life of 3.57 years. This demonstrates a life increase of 19 times longer. Since the original design has lasted the customer 10-20 years, it is deduced that the upgrade 100 should last the life of the dragline. The increase in fatigue life is a result of a reduced max stress and a reduced stress range. The max stress for the original peaked at 80 ksi in the chord and lacing connection to the box, compared to 40 ksi for the upgrade 100. It should be noted that the max stress in the upgrade 100 is where the chord stub 114 connects to the original chord 116, and cannot be improved without changing the upper chord 116 near the tip of the mast. After studying the effects of thickening the wall of the chord 116 near the mast head box 110, it was determined that the best solution is to use the original chord 116, as a thicker chord wall creates a higher stress at the joint between the chord stub 114 and the bottom plate 104 of the mast head box 110.
An analysis was performed to compare the original design with feedback from the field, in order to develop an effective upgrade (e.g., mast head 100). Once the original analysis matched the problems reported from the field, the loads and boundary conditions were applied to the upgrade design 100. Based on results from a preliminary analysis, the upgrade 100 was then iterated to a final design to minimize stress, and provide a longer fatigue life.
After an initial analysis was performed on the original design, it was apparent that a beam analysis of the entire mast would be necessary to determine the displacements and rotations at the boundaries of the detailed analysis model. The beam analysis (see
The beam analysis model of the entire mast was assembled using the VAX information from the original analysis of 1570W Lot 43, which has a very similar mast to Lot 45. The only difference between the Lot 43 and Lot 45 masts was one chord thickness that was adjusted for this analysis. The Lot 43 VAX information was exported to Excel, adjusted to the Lot 45 design, and then imported into Ansys from the Excel file. Ansys was able to take the information for each beam element, such as end points, cross sectional area, and material to build a 3-D stick model of the mast as shown in
Both the original and upgrade detailed analysis models were designed as assemblies in SolidWorks (see
The mast head box 110, chords 116, and lacings 118 were modeled as one component for simplification of the meshing process (shown in
The first attempt at the mast head analysis used only the mast head box 110 and a very small portion of the mast chords, and lacing 118. The cut plane of the chords 116 was fixed, and the cut plane of the lacing 118 was given a symmetry constraint. This proved insufficient, and so an entire beam analysis of the mast was completed. Each location was given a displacement and rotation in each the X, Y, and Z direction. The upgrade model was constrained identically to the original model.
Once the beam analysis of the mast was completed, cut planes were taken to coincide with the boundaries of the detailed analysis model shown in
The data from Tables 1 and 2 was then inserted into both the original and upgrade detailed analysis models as shown in
Since the analysis assemblies were made of few components, only a few contacts are required to adequately setup the model. As shown in
The mast head box 110 also has no penetration contacts setup between the round and flat surfaces of the pin 120 and the hubs 102. This allows the pin 120 to pull away from the hub 102, but does not allow the pin 120 to pass through the hub 102. Additionally, there is a 0.050″ gap between the face of the link hub and the face of the pin hub 102. This allows the pin 120 to pull towards the centerline of the mast until those faces contact each other.
Two loading cases were used for this analysis. The max load case uses the highest load per suspension cable throughout any of the load cases and combines them into one conservative load case. The max load case values are taken from the original Lot 43 analysis. The minimum load case is actually the bucket on ground load case for the Lot 52 machine which has a different boom and mast angle, therefore creating a lower minimum load than actually occurs on the Lot 45 dragline.
By using a max load greater than the actual loads, and a minimum load less than the actual loads, a larger stress range is created for the fatigue analysis shown later. The maximum and minimum loads are shown in
The beam analysis model has a very simple mesh. The elements are simple beam elements, with one element used to represent each piece of chord 116 or lacing 118. The element shapes are further defined by the cross sectional area, rotational inertia values, material properties, and other information provided within the original VAX analysis. The beam element mesh is shown in
Mesh sizes and expansion ratios were applied as listed below:
The mesh shown in
Mesh sizes and expansion ratios were applied as listed below:
The mesh shown in
The displacement plot in
As shown in
The maximum stress location shown in
The results from the original design analysis match fairly closely with the actual failures that are experienced in the field. See
One discrepancy between the original design analysis and the field feedback is the lack of stress at Point 8 in our analysis model.
The results from the upgrade design analysis show that the proposed design will greatly reduce stress in all of the areas of concern. See
It should be noted that locations 3, 8, 10, and 11 are not on the diagrams because those geometries have been removed from the upgraded design 100. The other points are located in the same places as on the original design for comparison purposes.
With the upgraded design 100 all of these high stress locations have been engineered to withstand the loads that are applied to the mast head box 110. As is evident from reviewing
The Life in years was calculated using the Life in cycles (B10) divided by the number of cycles per year. The equation for Life in cycles (B10) is below:
Because the loads used in the analysis were for extreme situations the fatigue life in years is much shorter than actual. For this reason, a Life Improvement Ratio was used. By taking the Shortest Life of any location for the original design and the upgrade design 100, the expected life improvement for the mast head was calculated in the last row of the table. The expected life improvement ratio is 19× the original life, which was approximately 10-20 years. The new design 100 can be expected to outlive the rest of the dragline.
The original design frequently experiences cracking at the top of the intermediate lug. The finite element analysis that was performed did not show a high stress at this location. There are two possible theories to explain this discrepancy.
One theory is that the ropes are oscillating at a much higher frequency than once per dig cycle, thus causing the plate to experience many more load cycles than the rest of the mast head box. This theory is perhaps part of the real issue, but is very difficult to analyze.
The second theory is that the stress range in the plate is larger than shown because of the potential for positive and negative stresses due to bending on the plate as the loads change within the upper and lower intermediate ropes.
The analysis was performed with the same boundary conditions and mesh as the original design, but the loads were changed in order to simulate various loads in the intermediate ropes. The loads used were the maximum and minimum loads used in the original analysis. However, they were switched so that the maximum Upper Intermediate load was combined with the minimum Lower Intermediate load, and vice-versa. This was an attempt to see if there was reversed bending occurring in the intermediate lug plate as the upper and lower rope loads vary throughout the digging cycle.
The resulting stress plots are almost identical for the two load sets. However, another detail was observed. Instead of viewing only the Von Mises Stresses for the intermediate lug plate, the first (tension) and third (compression) principal stresses were viewed.
This additional load case provides some explanation for why the intermediate lug plate has cracking issues, yet has a relatively low Von Mises Stress. The other explanation, which may compound the issue, is that there are many more cycles at this location due to the frequency of the ropes oscillating.
The highest remaining stress in the upgrade design 100 is located at the point where the upper/rear chord stub 114 connects to the original chord 116. The only way to improve this stress is to replace the original mast chord with a heavier walled chord. The purpose of this additional load case is to determine the wall thickness and length of replacement chord that would be required to successfully lower the stress at the connection joint.
All of the loads and boundary conditions were left at the maximum load situation, while the thickness of the chord 116 was changed to get the desired stress reduction. The heavy walled chord was extended to the joint where item 17 and 18 connect on drawing E004737. The runs that were performed are listed below.
Attempt 2 had the lowest stress at the stub to chord connection. However, the original has the lowest stress at the stub to bottom plate connection. Based on the stress listed above, using the original chord 116 is the most favorable option for providing the longest fatigue life.
Keeping the original 0.625″ chord wall will reduce the stress at the connection between the stub 114 and bottom plate 104 of the mast head box 110. This will keep the stress level to a comparable level at the stub to bottom plate connection.
The construction and arrangement of the mast head for a dragline, as shown in the various exemplary embodiments, are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. Some elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process, logical algorithm, or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed mast head for a dragline. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed mast head for a dragline. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.
Claims
1. A mast head assembly for a dragline comprising:
- an elongated body for connecting to a mast of a dragline;
- said body having opposing side plates and chord and lacing stubs;
- said side plates having suspension lugs for attaching cables from the mast head to the boom of a dragline;
- said lacing stubs positioned on said side plates to provide structural stability;
- at least one of said chord stubs located above and to the rear of a first chord stub;
- wherein the highest remaining stress is located at the point where the upper/rear chord stub connects to the original chord.
2. A mast head for a dragline comprising:
- an elongated body configured to connect to a mast of the dragline, the mast having at least one chord member and at least one lacing member;
- the body having opposing side plates, a top plate and a bottom plate,
- a suspension lug extending from each side plate and configured to receive cables supporting a boom of the dragline;
- a lacing stub disposed on at least one of the side plates and configured to connect with the lacing member; and
- at least one chord stub disposed on the bottom plate and configured to connect with the chord member.
3. The mast head of claim 2, wherein the side plates are substantially parallel to one another, and the suspension lugs extend from the side plates in a substantially coplanar manner.
4. The mast head of claim 3, wherein the suspension lugs are integral extensions of the side plates.
5. The mast head of claim 3, wherein the suspension lugs each include an opening, and the openings are substantially axially aligned with one another.
6. The mast head of claim 2, wherein each of the side plates include an angled portion that converge toward one another proximate the bottom plate to form a tapered region of the mast head.
7. The mast head of claim 6, wherein the lacing stub is disposed on one of the angled portions.
8. The mast head of claim 7, wherein the at least one chord member comprises a first chord member and a second chord member, and the at least one chord stub comprises a first chord stub and a second chord stub disposed on the bottom plate, and wherein the first chord stub is configured to connect with the first chord member and the second chord stub is configured to connect with the second chord member.
9. The mast head of claim 8, wherein the at least one chord member further comprises a third chord member and a fourth chord member, and further comprising a second mast head having:
- an elongated body having opposing side plates, a top plate and a bottom plate, the side plates each having an angled portion that converge toward one another proximate the bottom plate,
- a suspension lug extending from each side plate and configured to receive cables supporting a boom of the dragline;
- a lacing stub disposed on one of the angled portions and configured to connect with another lacing member; and
- a third chord stub disposed on the bottom plate and configured to connect with the third chord member, and a fourth chord stub disposed on the bottom plate and configured to connect with the fourth chord member.
10. The mast head of claim 2, wherein the lacing member and the chord member each have a longitudinal axis configured to intersect with one another at an intersection location, and wherein the elongated body substantially envelops the intersection location.
11. The mast head of claim 2, wherein each side wall further comprises a hub formed therein, each hub being substantially free of support gussets.
12. A dragline for mining, comprising:
- a boom;
- a mast having at least one chord member and at least one lacing member; and
- at least one mast head, comprising: an elongated body connected to the mast and having opposing side plates, a top plate and a bottom plate; a suspension lug extending from each side plate and configured to receive cables supporting the boom; a lacing stub disposed on at least one of the side plates and configured to connect with the lacing member; and at least one chord stub disposed on the bottom plate and configured to connect with the chord member.
13. The mast head assembly of claim 1, wherein the side plates are substantially parallel to one another, and the suspension lugs extend from the side plates in a substantially coplanar manner.
14. The mast head assembly of claim 13, wherein the suspension lugs are integral extensions of the side plates.
15. The mast head assembly of claim 13, wherein the suspension lugs each include an opening, and the openings are substantially axially aligned with one another.
16. The mast head assembly of claim 1, wherein each of the side plates include an angled portion that converge toward one another to form a tapered region of the mast head assembly, and wherein the lacing stub is disposed on one of the angled portions.
17. The mast head assembly of claim 1, wherein the mast includes one or more chord members and one or more lacing members, wherein at least one of the lacing stubs is configured to connect with at least one of the lacing members and the upper rear chord stub is configured to connect with at least one of the chord members.
18. The mast head assembly of claim 17, wherein the mast includes a first chord member and a second chord member, and the at least one chord stub comprises a first chord stub and a second chord stub disposed on the bottom plate, and wherein the first chord stub is configured to connect with the first chord member and the second chord stub is configured to connect with the second chord member.
19. The mast head assembly of claim 17, wherein the lacing members and the chord members each have a longitudinal axis configured to intersect with one another at an intersection location, and wherein the elongated body substantially envelops the intersection location.
20. The mast head assembly of claim 1, wherein each side wall further comprises a hub formed therein, each hub being substantially free of support gussets.
Type: Application
Filed: Apr 27, 2012
Publication Date: Jun 25, 2015
Applicant:
Inventors: Brian Niggemann (Racine, WI), Gregory N. Feld (Franklin, WI)
Application Number: 14/391,979