GB2299354A - An apparatus and method for shearing rock, rock-like material and mineral deposits with reduced drum chatter - Google Patents

Abstract

A rock shearing machine utilizing radial cutting tools 20 that experiences reduced drum chatter during operation. The radial cutting tools are arranged on a shearing drum 10 in a manner which stabilizes the vibration waves caused by drum chatter. Where less than all the possible tool positions are filled with tools, a number of blank tools 40 are interspersed among the radial tools. Further, the radial tools and blank tools may be arranged in a repeating pattern in order to reduce cutting force applied to radial cutting tools. This repeating pattern is utilized when drum chatter is less of a concern, such as when cutting coal or soft rock. The radial tools and blank tools may be positioned within a number of vanes and in such a manner that a radial tool in one vane will strike the surface to be cut as a radial tool in another vane remains in contact with the surface to be cut, thereby reducing the magnitude of vibration waves traveling through the drum.

Description

AN APPARATUS AND METHOD FOR SHEARING ROCK, ROCK-LIKE MATERIAL AND MINERAL DEPOSITS WITH REDUCED DRUM CHATTER BACKGROUND OF THE INVENTION The present invention generally pertains to a machine for shearing rock, rock-like material and mineral deposits.

The present invention is more particularly directed to an apparatus and method for reducing drum chatter associated with such shearing machines.

In order to efficiently cut through rock and rock-like material, most shearing machines incorporate a drum and a plurality of cutting implements which are utilized in concert. The mining industry utilizes these shearing machines. Within the mining industry, two types of cutting implements predominate -- conical cutting tools and radial cutting tools. Both types of tools are fastened to shearing drums via toolholders. An example of a mining shearing machine with conical tools is illustrated in FIG.

5.

In general, radial tools have performance characteristics superior to conical tools. Radial tools have approximately twice the clearance from the cutting surface to the toolholder than conical tools. As a result, the depth of cut from a radial tool is greater than from a conical tool.

Additionally, because the depth of cut for conical tools is shallower, the size of the cut material is smaller. In certain instances, the size of a mined mineral impacts upon its selling price. For example, if mining for coal, a smaller coal size negatively impacts the selling price, thus decreasing possible earnings.

Deeper cuts also create more extensive break outs - the loosening of material to either side of the cut. Because the depth of cut from conical tools is shallower, power consumption and equipment maintenance costs are generally higher when using conical tools. These higher power consumption and maintenance costs are exacerbated because the amount of force required to use conical tools is greater than radial tools.

Further, the use of conical bits not only increases power consumption and maintenance costs, it also increases the amount of dust and fines produced. Therefore, there are increased health risks associated with the use of conical tools.

Despite all of these performance deficiencies, conical tools are generally preferred over radial tools. This is due to the fact that conical tools are generally resistant to what is called drum chatter. Drum chatter is the vibration experienced in a shearing drum stemming from the rotation of the drum and the successive cuts made by individual cutting implements.

Conical tools are more resistant to drum chatter than radial tools because conical tools cut at optimal rake and clearance angles. A clearance angle is the angle between the cut surface and the edge of the tool closest to that surface. The rake angle is the angle between the surface to be cut and the edge of the tool closest to that surface.

As tools cut, they wear. As the tools wear, the rake and clearance angles change. As radial tools wear, the clearance angle approaches zero. Radial tools do not move relative to their toolholders, and so the front edge of the tools does not become as abraded, and hence, wears little or not at all. Thus, because a radial tool remains stationary relative to its toolholder, the rake angle remains static. Conical tools, on the other hand, rotate relative to their toolholders. As a consequence, as conical tools wear, both the clearance and rake angles change.

Due to their relative resistance to drum chatter, conical tools experience less breakage than radial tools, even though the force applied to conical tools is greater than that applied to radial tools. With a high degree of drum chatter, the shock experienced by an individual radial tool is high, and often greater than the ultimate strength of the tool, leading to its premature breakage. The most common failure mode being splitting or lost carbide tips.

The present invention alleviates at least the foregoing deficiencies in the current methods and apparatuses used for shearing rock, rock-like material and mineral deposits.

SUMMARY OF THE INVENTION An object of the present invention is to provide a shearing machine that includes all the enhanced performance characteristics of radial tools but with reduced drum chatter. This object is accomplished in the present invention by correcting cutting force imbalances along the drum face of the shearing drum, caused by the positioning of radial cutting tools thereon. The radial tools may be positioned in a number of vanes in a repeating pattern.

Further, the radial tools may be positioned such that the balance of strikes of individual radial tools upon a surface to be cut is improved, thus decreasing the severity of vibration waves traveling through the shearing drum.

A further object of the present invention is to provide blank tools to a shearing drum when cutting coal or soft rock. This object is accomplished in the present invention by providing blank tools and interspersing them among the radial tools on the outer circumference of the shearing drum.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-sectional side view of a preferred embodiment of a shearing drum according to the present invention with radial cutting tools and blank tools; FIG. 2a is a view from the tool leading edge of the radial cutting tool of FIG. 1; FIG. 2b is a side view of the radial cutting tool of FIG. 1; FIG. 3a is a top view of the blank tool of FIG. 1; FIG. 3b is a side view of the blank tool of FIG. 1; FIG. 4 is a development view (drum surface unrolled) of a preferred embodiment of the shearing drum of FIG. 1; and FIG. 5 is a side view of a prior art shearing drum utilizing conical cutting tools.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to FIG. 1, a shearing drum 10 according to a preferred embodiment of the present invention is shown in partial cross-section. The shearing drum 10 hays a drum face 11.

Affixed to shearing drum 10 are a number of radial cutting tools 20. Each radial tool 20 includes a tool leading edge 27 and a back edge 28. Further, each radial tool 20 may include a carbide tip 22 with a cutting edge 23. The carbide tip 22 is positioned generally at the point where the tool leading edge 27 meets the back edge 28, with the cutting edge 23 located closest to the tool leading edge 27. Radial tools 20 may further also include a tool shank 24. The tool shank 24 may further include a tool shank head 25.

Radial tools 20 are affixed to shearing drum 10 by way of toolholders 30. Toolholders 30 are positioned in recesses on the shearing drum 10 such that the outwardly facing surface of toolholder 30 is generally within the same plane as drum face 11. The toolholders 30 are affixed to shearing drum 10 by way of any suitable connection means that may withstand the substantial forces that will be directed upon them during operation. An example of such connection means is welding.

In a preferred embodiment of the present invention, radial tools 20 are connected to toolholders 30 by way of tool shanks 24 (FIGS. 2a, 2b). Due to the force directed toward the cutting edge 23 of the carbide tip 22 and the tool leading edge 27 of each radial tool 20 as drum 10 rotates in a cutting direction A, it is imperative that tool shanks 24 extend into toolholders 30 such that tool shank heads 25 are flush with the outwardly facing surface of toolholders 30. Therefore, the surface of each tool shank head 25 in contact with the outwardly facing surface of toolholder 30 is generally within the same plane as the drum face 11.If a radial tool 20 does not extend into toolholder 30 enough such that the tool shank head 25 is flush with the outwardly facing surface of the toolholder 30, the forces directed at the tool leading edge 27 and carbide tip 22 during cutting would be such that the radial tool 20 would likely experience metal fatigue and break at the tool shank 24.

Another preferred embodiment of the present invention includes the use of gripping cleats 26 located on the tool shank 24 (FIGS. 2a, 2b). The gripping cleats 26 are located laterally on tool shank 24. The toolholder 30 accepts the tool shank 24 and grips the gripping cleats 26, thereby affixing and positioning the radial tools 20 in the desired location with the tool shank head 25 flush with the outwardly facing surface of the toolholder 30.

A major. reason for drum chatter when using radial tools 20 in cutting operations is the presence of cutting force imbalances along the circumference of shearing drum 10.

These cutting force imbalances are due in part to the positioning of the radial tools 20.

In addressing the problem of cutting force imbalance, another preferred embodiment of the present invention includes the use of blank tools 40, as shown in FIG. 1.

Each blank tool 40 includes a tool head 42 and a tool shank 44. As shown in FIGS. 3a and 3b, the tool shank 44 may further include gripping cleats 46 which are gripped by toolholders 30 as disclosed above. The gripping cleats 46 may be the same as the gripping cleats 26 located on the radial tools 20. Further, the tool head 42 and tool shank 44 of blank tool 40 may be similar to the tool shank 24 and tool shank head 25 of radial tool 20. Each blank tool 40 is positioned within a toolholder 30 such that the tool head 42 is flush with the outwardly facing surface of the toolholder 30.

In this way, when it becomes necessary for all tool positions to be used to reduce drum chatter, they are available to be filled with radial tools 20. When less than all of the positions are needed to reduce drum chatter, the remainder are filled with blanks 40.

In another preferred embodiment of the present invention, radial tools 20 and blanks 40 are positioned on a number of vanes. A vane is a helix-shaped steel plate mounted to the drum 10. The vane serves as a supporting member for the toolholders 30 and the means for conveying the cut material away from the area being cut. As shown in FIG. 4, radial tools 20 and blanks 40 are positioned on a first vane 12, a second vane 14 and a third vane 16. First vane 12, second vane 14 and third vane 16 are located on the drum face 11 at an angle which is oblique to the longitudinal axis of the shearing drum 10. Further, each vane 12, 14, 16 is generally parallel to the other vanes.

Each vane 12, 14, 16 corkscrews around a certain percentage of the circumference of the shearing drum face 11. More particularly, in a preferred embodiment of the present invention it is envisioned that vanes 12, 14, 16 extend 250 around the circumference of the shearing drum 10. However, the present invention is not limited to any particular range of degrees of wrap around.

As noted above, drum chatter is caused when a cutting implement such as a radial tool 20 comes in contact with and cuts a material which has a certain amount of resistance to cutting. As the tool leading edge 27 and the cutting edge 23 of the carbide tip 22 of a radial tool 20 comes in contact with the material to be cut, a vibration occurs and the vibration wave travels through the shearing drum 10.

As the shearing drum 10 continues to rotate in cutting direction A, more radial tools 20 strike the material to be cut. One way to lessen the effects of drum chatter is to increase the number of individual radial tool strikes that occur, thereby balancing the vibration waves that travel throughout the shearing drum 10. Thus, another preferred embodiment of the present invention is to position the radial tools 20 along the drum face 11 in such a way that a radial tool 20 located in vane 12 will be in the same general plane as radial tools in vanes 14 and 16, where such a plane is generally parallel to the longitudinal axis of shearing drum 10.By positioning tools in this manner, as the shearing drum 10 continues to rotate in a cutting direction A, a radial tool 20 located in vane 12 will remain in contact with a surface to be cut as a radial tool 20 located in vane 14 also comes in contact with the surface to be cut. Thus, as the radial tool 20 in vane 12 moves away from the surface to be cut, the radial tool 20 in vane 14 remains in contact with that surface as a radial tool 20 in vane 16 comes in contact with the surface to be cut. In this way, the number of individual strikes is stabiled, thus lessening the magnitude of vibration waves traveling through the shearing drum 10.

A further preferred embodiment of the present invention, for use when cutting coal or soft rock, is to position radial tools 20 and blanks 40 on vanes 12, 14, 16 in a repeating pattern. Such a pattern will lessen the cutting force along the drum face 11 and down the length of drum 10. One such pattern that reduces the cutting force in a shearing drum 10 utilizing radial tools 20 is a pattern whereby two blanks 40 are positioned between two radial tools 20, as shown in FIG. 4. Patterns including radial tools 20 and blank tools 40 are used when drum chatter is not a concern, which is primarily when only coal or softer rock is being cut.

It can be seen by comparing FIGS. 1 and 5 that there is a fundamental difference in the positioning of conical tools 220 within toolholders 230 and radial tools 20 within toolholders 30. Radial tools 20 extend in a direction generally perpendicular to the drum face 11. Conical tools 220, on the other hand, extend out and are positioned in a direction generally parallel to the cutting direction A.

Due to this positioning, as a conical tool 220 comes in contact with a surface to be cut, the force directed upon the conical tool 220 is directed generally along the longitudinal axis of the tool. However, despite the fact that conical tools 220 are generally resistant to drum chatter, drum chatter is nevertheless experienced in shearing operations which utilize conical tools 220. Drum chatter reduces the working lives of respective mining machine components, especially toolholders and the toolholder weld joints. Further, vanes and vane weld joints may begin to crack from the drum chatter. Also, cutting heads, gear cases and gear trains wear excessively and cutting head motors and hydraulic jacks require more repair. Thus, maintenance costs are increased due to drum chatter.

However, due to the positioning of conical tools 220 within the toolholders 230, it would not be possible to place blank tools 40 within toolholders 230. If this were attempted, as the shearing drum 200 turns in the cutting direction A, the tool head 42 would come in contact with and would be abraded by the surface to be cut, thereby eventually fatiguing and breaking the toolholder 30.

Claims (16)

1. A machine suitable for use in shearing, rock, rock-like material or mineral deposits comprising: a number of radial cutting tools, said radial tools affixed to said drum; and a number of blank tools, said blank tools affixed to said drum.

2. A shearing machine as claimed in Claim 1, wherein said numbers of radial tools and blank tools are positioned on said drum in such a manner as to reduce drum chatter.

3. Ashearing machine as claimed in Claim 2, wherein said numbers of radial tools and blank tools are arranged in a repeating pattern on said drum.

4. Ashearing machine as claimed in Claim 3, wherein said radial tools and said blank tools are positioned on a number of vanes.

5. Ashearing machine as claimed in Claim 4, wherein each said vane extends at least 2500 around the circumference of said drum.

Ashearing machine as claimed in Claim 5, wherein each said vane is substantially parallel to each other said vane and wherein each said vane extends in a direction which corkscrews around the circumference of said drum.

Ashearing machine as claimed in Claim 6, wherein each said radial tool includes a carbide tip and wherein each said radial tool is positloned on said drum such that said carbide tip faces in a cutting direction of said drum and generally counter to said direction of each said vane.

8. Ashearing machine as claimed in Claim 7, wherein said repeating pattern on each said vane is that two of said blank tools are positioned between two of said radial tools.

9. Ashearing machine as claimed in Claim 8, wherein each said radial tool and blank tool is connected to said drum by a toolholder, each said toolholder recessed into said drum face.

10 A shearing machine as claimed in Claim 9, wherein each said radial tool and blank tool further comprises a tool shank, said tool shanks extending into and held in position by each said toolholder.

11. A shearing machine as claimed in Claim 10, wherein each said tool shank further comprises gripping cleats positioned laterally on said tool shank, said gripping cleats gripped by said toolholder.

12. A blank tool for use with a machine suitable for use in shearing rock, rock-like material or mineral deposits comprising: a tool head; and a tool shank

13. A blank tool as claimed in Claim 12 further comprising gripping cleats positioned laterally on said tool shank, said gripping cleats gripped by said toolholder.

14. A shearing machine as claimed in Claim 5, wherein said radial tools are positioned on said drum such that there are at least three tools generally in a line parallel to an axis of rotation of said drum and at least two cutting tools located on a common vane.

15. A method of shearing rock, rock-like material or mineral deposits comprising the steps of: providing a shearing machine including a drum having a drum face, a number of radial cutting tools affixed to said drum, and a number of blank tools affixed to said drum; operating said machine to rotate said drum; and engaging the rock with said cutting tools positioned on said rotating drum, to shear the rock.

16. Shearing machine for shearing rock, rock-like material or mineral deposits constructed arranged and adapted to operate substantially as hereinbefore described with reference to Figures 1 to 4 of the accompanying drawings.