Method of mining using disc cutter

Abstract

There is provided a method of mining rock using a disc cutter comprising a cutter body having a diameter d and a thickness t, a plurality of cutter holders mounted around a peripheral surface of the cutter body, and a plurality of cutting elements attached to the cutter holders, the method comprises the steps of: cutting a first slot in the rock at a first cutting location of the disc cutter; moving the disc cutter to a second cutting position, the second cutting position being left or right of the first cutting position, and cutting a second slot in the rock such that the second slot is spaced apart from the first slot by a distance S, at least one of the first slot and the second slot having a slot depth D, and wherein the ratio of the slot depth D to the distance S is in the range of 2 to 16.

Description

Technical Field

[0001] The present disclosure relates to a method of mining materials using a disc cutter. In particular, the present disclosure relates to a method of mining rock using a disc cutter including a polycrystalline diamond cutter. More specifically, the present disclosure relates to a method of mining cubic blocks from materials such as kimberlite and granite. Background Art

[0002] GB 2589736 discloses a disc cutter 10, which comprises a cutter body 14, a plurality of cutter holders 16, and a plurality of cutting elements 18 mounted to the cutter holders 16, as shown in FIGS. 1 and 2. The cutting elements 18 are arranged in the cutter holders 16 in a sequence that reduces the cutting force during use. In a particular embodiment, six or more disc cutters 10 are arranged on mutually driven spindles and are regularly spaced apart from each other. The spacing of the disc cutters 10 is selected according to the required cutting depth in the target rock formation and the mechanical properties of the rock.

[0003] The problem with this arrangement is that it is difficult to achieve perfect synchronization of the cutting of the various disc cutters as they engage the rock. No part of the rock will have exactly the same mechanical properties as an adjacent part of the rock, so some disc cutters cut with relative ease while others face greater resistance. This, therefore, causes problems controlling the cutting assembly, leading to downtime and mechanical failure. It can also result in inconsistent slot depths.

[0004] The object of the present invention is to address the above problems. Summary of the invention

[0005] According to a first aspect of the present invention, there is provided a method for mining rock using a disc cutter, the disc cutter comprising a cutter body having a diameter d and a thickness t, a plurality of cutter holders mounted around a peripheral surface of the cutter body, and a plurality of cutting elements attached to (e.g. mounted in) the cutter holders, the method comprising the following steps:

[0006] - cutting a first slot in the rock at a first cutting position of the disc cutter,

[0007] - moving the disc cutter to a second cutting position, for example to the left or to the right of the first cutting position, and

[0008] - cutting a second slot in the rock such that the second slot is spaced apart from the first slot by a distance S, at least one of the first slot and the second slot having a slot depth D, and wherein a ratio of the slot depth D to the distance S is in the range of 2 to 16.

[0009] According to a second aspect of the invention, there is provided a method for mining rock using a disc cutter, the disc cutter comprising a cutter body having a diameter d, a plurality of cutter holders mounted around a peripheral surface of the cutter body, and a plurality of cutting elements attached to the cutter holders (e.g., mounted in the cutter holders), the method comprising cutting a slot depth D in the rock at a cutting position of the disc cutter, wherein a ratio of the slot depth D to the diameter d of the cutter body is about 0.15 to about 0.50.

[0010] As an option, the ratio of the slot depth D to the diameter d of the tool body is about 0.15, about 0.20, about 0.25, about 0.30 or about 0.35 to about 0.49, about 0.48, about 0.47, about 0.46, about 0.45 or about 0.40.

[0011] As an option, the ratio of the slot depth D to the diameter d of the tool body is about 0.15 to about 0.50, or about 0.15 to about 0.49, or about 0.15 to about 0.48, or about 0.15 to about 0.47, or about 0.15 to about 0.46, or about 0.20 to about 0.45, or about 0.25 to about 0.40, or about 0.30 to about 0.40, or about 0.35 to about 0.40, or about 0.32 to about 0.37, or about 0.34 to about 0.37, or about 0.34 to about 0.36.

[0012] Further preferred and / or optional features of the first and second aspects of the invention are provided in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The improved mining method will now be described by way of example and with reference to the accompanying drawings, in which:

[0014] FIG1 shows a perspective view of a disc cutter of the prior art;

[0015] FIG2 shows a partial expanded view of the disc cutter of FIG1 ;

[0016] Figure 3 A schematic diagram of a first slot and a second slot cut into a rock is shown and parameters for defining a mining method according to the invention are introduced;

[0017] Figure 4 is a graph of the computer-simulated force (N) required to break concrete at the bottom of the slot, taking into account the slot spacing (mm) and the slot depth (mm);

[0018] Figure 5 is a graph of the force (N) required to break granite at the bottom of the slots, taking into account the slot spacing (mm) and the slot depth (mm);

[0019] Figure 6 is a graph showing the maximum principal stress at different heights of the slot;

[0020] Figure 7 is a graph showing the maximum principal stress at different hammer impact angles;

[0021] Figure 8a , Figure 8b and Figure 8c A finite element analysis image of an indentation formed in a first slot by a particular type of rock breaking tool, particularly a stress region around the indentation where a crack propagates from the indentation to a second slot;

[0022] Fig. 9 is a plan view of an example of a rock breaking tool;

[0023] Fig.10 It is used in mining environment Fig. 9 Stereoscopic image of rock crushing tools;

[0024] Fig.11 is a perspective view of another example of a rock breaking tool;

[0025] Fig.12 It is used in mining environment Fig.11 A stereoscopic view of a rock crushing tool; and

[0026] Fig.13 is a schematic plan view of another example of a rock breaking tool for use in a mining environment. DETAILED DESCRIPTION

[0027] As shown in Figures 1 and 2, a disc cutter 10 is used to cut into a rock 12. The disc cutter 10 includes a cutter body 14 having a diameter d and a thickness t, a plurality of tool holders 16 mounted around the peripheral surface of the cutter body 14, and a plurality of cutting elements 18 mounted in the tool holders 16. The cutting elements 18 are sequentially arranged in each set of repeated tool holders 16. The cutting elements 18 include polycrystalline diamond.

[0028] In use, the disc cutter 10 is rotated at a certain speed and is fed until it reaches the rock 12. As the disc cutter advances and engages the rock 12, cutting begins and a first slot 20 is gradually formed in the rock 12 (see Figure 3). Once the target slot depth D is reached, the disc cutter 10 is withdrawn from the slot. The disc cutter 10 is moved to a second cutting position, and the cutting operation is repeated to form a second slot 22. The second slot 22 may be to the left or right of the first slot 20 in the rock face, or alternatively, may be above or below the first slot 20. The second slot 22 is spaced a distance S from the first slot 20. The distance S is equal to the spacing between the slots 20, 22. In order to minimize the energy required for subsequent rock crushing, the ratio of the slot depth D to the distance S must be in the range of 2 to 16. This range has been confirmed based on the computer simulation work described below. The distance S and the slot depth D are optimized based on the properties of the rock 12, and indirectly take into account the design of the tool body 12.

[0029] The diameter of the tool body 14 is in the range of about 1.0 m to about 5.0 m (e.g., about 1.0 m to about 4.0 m, for example, about 1.0 m to about 3.0 m, for example, about 1.0 m to about 2.0 m, for example, about 1.0 m to about 1.8 m, for example, 1.0 m to 1.8 m). In one embodiment, the diameter of the tool body 14 is 1.0 m. In another embodiment, the diameter of the tool body 14 is 1.5 m. In yet another embodiment, the diameter of the tool body 14 is 1.75 m.

[0030] The first slot and / or the second slot has a width W that is less than the thickness t of the tool body 14. The slots 20, 22 have a width in the range of 20 mm to 80 mm. In practice, for rock materials having an unconfined compressive strength (UnconfinedCompressiveStrength) exceeding 200 MPa, a slot width of 20 mm is recommended. Similarly, for rock materials having an unconfined compressive strength in the range of 150 MPa to 200 MPa, a slot width of 40 mm is recommended. For rock materials having an unconfined compressive strength in the range of 60 MPa to 150 MPa, a slot width of 60 mm is recommended. For rock materials having an unconfined compressive strength in the range of 30 MPa to 60 MPa, a slot width of 80 mm is recommended. An alternative term for unconfined compressive strength is uniaxial compressive strength (Uniaxial Compressive Strength).

[0031] Computer simulation using finite element analysis

[0032] According to the International Society of Rock Mechanics and Rock Engineering (ISRM), rock strength can be described as moderate, high, and very high, as shown in Table 1. More quantitatively, uniaxial compressive strength or UCS is the most widely cited parameter describing the properties of rock and is an important factor to consider when designing for rock cutting. Simply put, strong rock requires a higher force to be applied before it breaks. Examples of moderately strong rocks include concrete and sandstone. An example of a high-strength rock is kimberlite. An example of a very high-strength rock is granite.

[0033] Concrete and granite, representing two extremes, are specifically considered in this disclosure.

[0034]

[0035] Table 1: Extract from D. Vogt’s ‘A review of rock cutting for underground mining: past, present and future’, The Journal of the Southern African Institute of Mining and Metallurgy, Vol. 116, November 2016.

[0036] In the study, slot depth D and distance (also referred to as 'spacing') S were explored. The selection of D and S will directly affect the load required for the rock 12 to be broken from the base 24 of the slot, near its bottom surface. The loading condition is a horizontal force applied to the top edge of the slot, generally indicated at 26. The output variable is the maximum principal stress. It should also be noted that for the purposes of this study, the rock damage initiation criterion is defined as when the maximum principal stress reaches the uniaxial compressive strength.

[0037] The simulation results for concrete and granite are provided in Tables 2 and 3, respectively. Figure 4 and Figure 5 The same results are also shown in .

[0038]

[0039] Table 2

[0040]

[0041]

[0042] Table 3

[0043] Similar simulations were performed for kimberlite with uniaxial compressive strengths between 50 MPa and 100 MPa, but the results are not presented here.

[0044] As the ratio of depth D to distance S drops below 2, the loads required to break rock using the rock breaking tool 28 become too high to implement, requiring increasingly higher energy expenditures to drive the disc cutter 10 and produce the cuts. Ratios above 15 are not achievable using currently available disc cutters of the sizes described herein.

[0045] The rock breaking tool 28 may take one of several different forms. The tool 28 may be a wedge tool such as Figure 3 The wedge tool shown. As the wedge tool is gradually inserted into the slots 20, 22, bending forces are generated at the base of the slots 20, 22, which ultimately cause the rock 12 to break. Alternatively, the rock breaking tool 28 can be configured to create an indentation in the rock. Other configurations of the rock breaking tool are described in more detail below. It should be noted that the rock breaking tool 28 is completely optional and is not necessary for the present invention. When the ratio of the depth D to the distance S becomes too high, the rock may be broken under its own load and vibration. Therefore, the rock breaking tool 28 is not required in all cases. However, it is preferred to use one of them because when the rock is broken in other ways, it tends to do so in an uncontrolled manner, resulting in greater waste.

[0046] In general, the greater the slot depth D, the more efficient the cutting. However, as the slot depth D increases, the torque and vibration on the tool body also increase, thereby increasing the risk of inefficient excavation. Therefore, there is a balance between the slot depth D and the diameter d of the tool body 20, and this can be characterized by the ratio of the slot depth D to the diameter d of the tool body 20. For efficient cutting, this parameter is ideally at least 0.15, 0.20, 0.25, 0.30 or 0.35 and / or less than 0.50, 0.49, 0.48, 0.47, 0.46, 0.45 or 0.40. For example, the ratio of the slot depth D to the diameter d of the tool body 20 can be about 0.15 to about 0.50, or about 0.15 to about 0.49, or about 0.15 to about 0.48, or about 0.15 to about 0.47, or about 0.15 to about 0.46, or about 0.20 to about 0.45, or about 0.25 to about 0.40, or about 0.30 to about 0.40, or about 0.35 to about 0.40, or about 0.32 to about 0.37, or about 0.34 to about 0.37, or about 0.34 to about 0.36.

[0047] A slot depth D of 340 mm can be achieved in practice using a cutter body 14 having a diameter of 1.0 m. This gives a ratio of slot depth D to cutter body diameter d of 0.34. A slot depth D of 540 mm can be achieved in practice using a cutter body 14 having a diameter of 1.5 m. This gives a ratio of slot depth D to cutter body diameter d of 0.36. A slot depth D of 740 mm can be achieved in practice using a cutter body 14 having a diameter of 1.75 m (giving a ratio of slot depth D to cutter body diameter d of 0.42); however, during initial field testing with the same size diameters, a slot depth D of 640 mm (giving a ratio of slot depth D to cutter body diameter d of 0.37) was considered to be preferred.

[0048] Because failure at the base 24 of the slot (ie, furthest from the opening into the slot) is likely to be due to tensile stress, and the ratio of uniaxial compressive strength to tensile stress is about 10, the actual force (load, kN) required may be as low as 1 / 10.

[0049] In actual mining applications, locations where damage may occur include the following conditions:

[0050] When the stress at the load contact point exceeds the uniaxial compressive strength of the rock material;

[0051] When the tensile stress exceeds the maximum tensile strength (usually at the bottom of the slot); and

[0052] · There are micro cracks.

[0053] Therefore, the principle for selecting the slot size is that the stress at the load contact point should not exceed the uniaxial compressive strength of the rock material, otherwise the rock will break at the load point.

[0054] The stress at the load contact point depends on the shape of the rock breaking tool 28 (eg a wedge tool) and its contact area; and the load conditions, such as the angle of incidence and whether they are dynamic or not.

[0055] As part of the investigation the height of the load contact point within the slots 20, 22 was also investigated. This was to try and identify the best position to apply the rock breaking tool 28 after the slots were formed.

[0056] Found:

[0057] The load at the top position may produce the maximum bending stress at the bottom / base of the slot; and

[0058] • When the height decreases, the bending stress decreases linearly.

[0059] Figure 6It is shown that different loads need to be applied to break the rock at different locations of the rock. The 'height of the slot' is measured at the edge away from the opening of the slot, towards the bottom of the slot. The results show that the closer to the edge of the rock 12 (near arrow 26), the smaller the required load. However, in practice, the best position is not necessarily at the top of the slot 20, 22, because the impact of the rock breaking tool 28 may cause damage to the rock 12 at this point. The best contact position may actually be at a lower position deeper into the slot. Preferably, the rock breaking tool 28 contacts the rock at a position located at least 15% of the way into the slot. If the position is less than 15% of the way into the slot 20, 22, undesirable damage is more likely to occur because the rock strength at the edge is significantly reduced due to unrestricted real-world conditions.

[0060] The study also included exploring the load required to break the rock at different incident angles. Specifically, the relationship between the bending stress at the bottom of the slot and the variable load angle was considered. Figure 7 The results are shown in , where an 'angle of impact' of zero represents a condition where the load of the rock breaking tool 28 is applied horizontally.

[0061] Found:

[0062] Horizontal loads will produce the maximum bending stress. As the angle increases, the bottom bending stress will decrease accordingly, such as Figure 7 shown.

[0063] The final area of ​​research is to investigate how dents affect crack initiation and propagation, see Figure 8a , Figure 8b and Figure 8c A hammer (a type of rock breaking tool 28) is used to form one or more indentations 30 in the rock. Based on the simulations, it has been found that:

[0064] The crack tends to propagate in the direction of the indentation; and

[0065] The spacing between the indents and the depth of the indents substantially affect the crack propagation between the indents.

[0066] It is therefore preferred that a notch 30 is formed in each of the first slot 20 and the second slot 22, the two notches facing each other. In this way, by controlling the spacing between a pair of first and second slots 20, 22, cracks can be predictably initiated and promoted to extend between the notches 30. They also reduce the required crushing force. The or each indent 30 may be formed to a depth of up to 95% of the distance S, or up to 90% of the distance S, or up to 85% of the distance S, or up to 80% of the distance S, or up to 75% of the distance S, or up to 70% of the distance S, or up to 65% of the distance S, or up to 60% of the distance S, or up to 55% of the distance S, or up to 50% of the distance S, or up to 45% of the distance S, or up to 40% of the distance S, or up to 35% of the distance S, or up to 30% of the distance S, or up to 25% of the distance S, or up to 20% of the distance S, or up to 15% of the distance S, or up to 10% of the distance S, or up to 5% of the distance S. Preferably, the or each indent 30 is formed to a depth of 20% of the distance S. These factors help facilitate recovery of rock above the fracture propagation line in substantially cubic blocks.

[0067] The expression 'facing towards each other' is intended to mean that the cross-section of the indentation decreases in the direction the indentation faces. For example, if the indentation is conical, the direction in which the apex points is the direction the indentation faces. Figure 8a The hemispherical indentation shown faces the right side of the page.

[0068] Preferably, the or each indentation 30 is formed at or near the bottom surface of the slot 20 , 22 .

[0069] As previously mentioned, the rock breaking tool 28 may be configured in several other ways.

[0070] exist Fig. 9 and Fig.10 In the example shown, the rock breaking tool 28, 300 includes an elongated tool body 302 having a longitudinal axis and a tool head 304 at one end of the tool body 302. The tool head 304 includes one or more projections 306 extending from its surface. To facilitate rock breaking, the rock breaking tool 28, 300 is at least partially inserted into the slot 20, 22. The rock breaking tool 28, 300 is slowly rotated about the longitudinal axis from the insertion orientation to the rock breaking orientation. In this way, the tool head 304, or more specifically (multiple) projections 306, thereby impact at least one adjacent rock column 12. This impact can be sufficient to generate cracks in the rock 12, which facilitates the subsequent recovery of the broken rock formation. This slow rotation rock breaking advantageously breaks the rock at the base of the slot 20, 22 using a minimum of energy. Optionally, the tool head 304 is configured to impact on two adjacent rock columns 12.

[0071] exist Fig.11 and Fig.12 In the example shown, the rock breaking tool 28, 400 includes a tool head 402, wherein the tool head 402 includes an elongated disc carrier 404, a base 406, and one or more micro disc cutters 408 supported by the disc carrier 404. The disc carrier 404 and the micro disc cutters 408 are thus movable relative to the base 406. Preferably, the tool head 402 includes three or more micro disc cutters 408 spaced apart along the base 406. The micro disc cutters 408 preferably include a carbide material. Unlike the main disc cutter 10, the micro disc cutters 408 have a compressed pyramidal shape with a rounded base and a low height.

[0072] Each micro-disc cutter 408 may extend in a plane orthogonal to the longitudinal plane of the base 406. Alternatively, each micro-disc cutter 408 may extend in a plane that forms an angle relative to the longitudinal plane of the base 406, the rock breaking tool 28, 400 being configured such that the angle is adjustable. Once at least partially inserted into the slot 20, 22, the rock breaking tool 28, 400 is operable to cut into the rock column using the micro-disc cutters 408 on the tool head 402. In this manner, fractures in the rock 12 may be initiated at multiple locations, which facilitates subsequent recovery of the broken rock formation. This particular method for rock breaking advantageously uses minimal energy to break rock in a predetermined direction.

[0073] exist Fig.13 In the example shown, the rock breaking tool 28 has a tool head 500, which includes one or more impact elements 502, which can be actuated to extend outwardly and retract inwardly, for example using a hydraulic expander. (Multiple) impact elements 502 can include superhard impact tips 504. In use, (multiple) impact elements 502 are fired from the tool head 500 toward the adjacent rock 12, that is, quickly deployed. This can cause the above-mentioned indentations in the rock 12. The impact of the impact tip 504 and the resulting indentation can be sufficient to initiate cracks and subsequent expansion. Similarly, this helps to subsequently recover the broken rock formation. Optionally, two opposing impact elements 502 are fired toward the rock column 12 on either side of the slot 20, 22.

[0074] Alternatively, if Fig.13 As seen in FIG. 1 , multiple tool heads may be employed to actuate at multiple depths within the slots 20 , 22 to force the rock 12 to fracture.

[0075] In summary, the inventors have developed an improved mining method that minimizes the energy required to break rock, particularly in hard rock mining.

[0076] While the invention has been particularly shown and described with reference to embodiments, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the scope of the invention as defined by the following claims.

Claims

1. A method for mining rock using a disc cutter, the disc cutter comprising a cutter body having a diameter d and a thickness t, a plurality of tool holders mounted around a peripheral surface of the cutter body, and a plurality of cutting elements attached to the tool holders, the method comprising the following steps: - cutting a first slot in the rock at a first cutting position of the disc cutter, - moving the disc cutter to a second cutting position, and - cutting a second slot in the rock such that the second slot is spaced apart from the first slot by a distance S, at least one of the first slot and the second slot having a slot depth D, and wherein a ratio of the slot depth D to the distance S is in the range of 2 to 16.

2. The method of claim 1, wherein: The second cutting position is on the left or right side of the first cutting position.

3. The method of claim 1, wherein: The second cutting position is above or below the first cutting position.

4. A method as claimed in any one of the preceding claims, wherein: The slot depth D is in the range of 300 mm to 800 mm.

5. The method of claim 4, wherein: The slot depth D is in the range of 300 mm to 400 mm.

6. The method of claim 4, wherein: The slot depth D is in the range of 500 mm to 600 mm.

7. The method of claim 4, wherein: The slot depth D is in the range of 700 mm to 800 mm.

8. A method as claimed in any one of the preceding claims, wherein The diameter d of the tool body is in the range of 1.0 m to 5.0 m.

9. The method of claim 8, wherein: The diameter d of the tool body is 1.0 m.

10. The method of claim 8, wherein: The diameter d of the tool body is 1.5 m.

11. The method of claim 8, wherein: The diameter d of the tool body is 1.75 m.

12. A method as claimed in any one of the preceding claims, wherein: The distance S is in the range of 50 mm to 200 mm.

13. A method as claimed in any one of the preceding claims, wherein: The uniaxial compressive strength of the rock is 25 MPa to 50 MPa.

14. The method according to any one of claims 1 to 12, wherein: The uniaxial compressive strength of the rock is 50 MPa to 100 MPa.

15. The method according to any one of claims 1 to 12, wherein: The uniaxial compressive strength of the rock is 100 MPa to 250 MPa.

16. A method as claimed in any one of the preceding claims, wherein: The first slot and / or the second slot has a width W, and the width is in the range of 20 mm to 80 mm.

17. The method of claim 16, wherein: The width of the slot is 20 mm to 40 mm, and the unconfined compressive strength of the rock is 200 MPa or greater.

18. The method of claim 16, wherein: The width of the slot is 40 mm to 60 mm, and the unconfined compressive strength of the rock is 150 MPa to 200 MPa.

19. The method of claim 16, wherein: The width of the slot is 60 mm to 80 mm, and the unconfined compressive strength of the rock is 60 MPa to 150 MPa.

20. The method of claim 16, wherein: The width of the slot is 60 mm to 80 mm, and the unconfined compressive strength of the rock is 30 MPa to 60 MPa.

21. A method as claimed in any preceding claim, further comprising at least partially inserting a rock breaking tool into the first slot and the second slot.

22. A method as claimed in any one of the preceding claims, wherein: The method further includes forming an indentation in the rock adjacent to the first slot and / or the second slot.

23. The method of claim 22, wherein: The depth of the indentation is as much as 20% of the distance S.

24. The method of claim 22 or 23, wherein: The indentation is formed at a location in the or each slot which is measured away from the opening of the slot and which is equal to at least 15% of the depth of the slot.

25. The method of claim 24, wherein: The or each indentation is formed at or adjacent a bottom surface of the slot.

26. A method as claimed in any one of claims 22 to 25, comprising forming an indentation in the rock adjacent the first slot and in the rock adjacent the second slot, wherein: The indentations face each other.

27. A method of mining rock using a disc cutter, the disc cutter comprising a cutter body having a diameter d, a plurality of cutter holders mounted around a peripheral surface of the cutter body, and a plurality of cutting elements attached to the cutter holders, the method comprising cutting a slot depth D in the rock at a cutting position of the disc cutter, wherein: A ratio of the slot depth D to the diameter d of the tool body is about 0.15 to about 0.

50.

28. The method of claim 27, wherein: A ratio of the slot depth D to the diameter d of the tool body is about 0.35 to about 0.40.

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