Mining method

Abstract

The present disclosure provides a method of mining rock using a disc cutter comprising a cutter body with a diameter d, a plurality of tool holders mounted about a peripheral surface of the cutter body and a plurality of cutting elements attached to the tool holders, the method comprising cutting a slot with a slot depth D in the rock at a cutting position of the disc cutter, wherein a rotational speed of the disc cutter during cutting is greater than 60 rpm.

Description

[0001] MINING METHOD

[0002] FIELD OF THE INVENTION

[0003] This disclosure relates to a method of mining materials using a disc cutter. In particular, it relates to a method of mining rock using a disc cutter comprising cutter elements wherein a rotational speed of the disc cutter during cutting is greater than 60 rpm.

[0004] BACKGROUND

[0005] WO 2019 / 180164 Al, WO 2019 / 180169 Al and WO 2019 / 180170 Al each disclose a cutting assembly for use in above and below ground quarries and mines. The cutting assembly is typically used to extract slabs of rock from the ground, before the slabs are taken for further processing, such as polishing.

[0006] Each cutting assembly comprises a circular disc cutter, which is moveable between horizontal and vertical cutting orientations. Referring initially to Figures 1 and 2, a cutting assembly for slicing into natural formations 2 underground is indicated generally at 10. The cutting assembly forms part of a long wall mining system 1, commonly found in underground mines. The cutting assembly is a substitute for known shearer technology, which operates on amine floor 4, amidst a series of adjustable roof supports 6. As the shearer advances in the direction of mining, the roof supports 6 are positioned to uphold the mine roof 8 directly behind the shearer. Behind the roof supports 6, the mine roof 8 collapses in a relatively controlled manner. Typically, a gathering arm collects mined rock at the cutting face and transfers it onto a conveying system for subsequent removal from the mine.

[0007] As indicated in Figures 1 and 2, the cutting assembly 10 comprises a base unit 12, a pair of spaced apart support arms 14 extending from the base unit 12, a drive spindle 16 extending between and rotatably mounted to the pair of moveable support arms 14, and a plurality of disc cutters 18 fixed about the drive spindle 16. In a second example, indicated in Figures 3 and 4, a single support arm 14 extends from the base unit 12. The drive spindle 16 is supported centrally by the single support arm 14, and the plurality of disc cutters 18 is mounted to the drive spindle 16, distributed either side of the single support arm 14.

[0008] The base unit 12 functions as a transport system for the disc cutter 18. The base unit 12 is moveable to advance and retract the disc cutter 18 into and out of an operational position, in close proximity to the rock formation 2 to be cut. The speed at which the base unit 12 moves closer to the rock formation 2 is one of several variables determining the feed rate of the cutting assembly 10 into the rock formation 2. The base unit 12 (in concert with the roof supports 6) is also moveable sideways, from left to right and vice versa, along the long wall of the rock formation 2 to be mined.

[0009] Each support arm 14 is configured to be moveable into a first and a second cutting orientation. In the first cutting orientation, best seen in Figures 1 and 2, the drive spindle 16 is horizontal. As a result, cuts in the rock formation 2 made by the disc cutter 18 are correspondingly vertical. In the second cutting orientation, best seen in Figures 3 and 4, the drive spindle 16 is vertical. Consequently, cuts in the rock formation 2 made by the disc cutter 18 are correspondingly horizontal.

[0010] Each support arm 14 is moveable between a first operative position and a second operative position, in optionally each of the first and second cutting orientations, according to the depth of cut required. This is indicated by double end arrow A in Figure 2. For example, in the first operative position, the drive spindle 16 is lowered so as to be in close proximity to the mine floor 4 and in the second operative position, the drive spindle 16 is raised so as to be in close proximity to the mine roof 8.

[0011] In use, the disc cutter 18 is brought into contact with the rock formation 2 and rotation of the drive spindle 16, and therefore its disc cutter(s) 18, causes slicing of the rock formation 2. The cutting assembly 10 slices into the rock formation 2, for example, to create clean orthogonal cuts, the size of which depends on the size of the cutting elements 22 selected. The cut rock breakouts either under its own weight or with secondary wedge force, e.g. using a wedge- shaped tool.

[0012] Mining rock is a highly energy intensive processes. It is therefore important to perform such mining in such a way as to maximise the cutting efficiency, thereby reducing the energy requirement per unit mass of mined rock with associated environmental and cost benefits. The present inventors provide herein a method of mining rock with enhanced cutting efficiency.

[0013] STATEMENT OF INVENTION

[0014] In accordance with the invention, there is provided a method of mining rock using a disc cutter comprising a cutter body with a diameter d, a plurality of tool holders mounted about a peripheral surface of the cutter body and a plurality of cutting elements attached to the tool holders, the method comprising cutting a slot with a slot depth D in the rock at a cutting position of the disc cutter, wherein a rotational speed of the disc cutter during cutting is greater than 60 rpm.

[0015] As an option, one or more cutting elements are attached to each tool holder.

[0016] As an option, the cutting elements comprise poly crystalline diamond (PCD).

[0017] As an option, the cutting elements are poly crystalline diamond compacts (PDCs).

[0018] As an option, the rotational speed of the disc cutter during cutting is greater than 65 rpm.

[0019] As an option, the rotational speed of the disc cutter during cutting is greater than 70 rpm.

[0020] As an option, the rotational speed of the disc cutter during cutting is greater than 75 rpm.

[0021] As an option, the rotational speed of the disc cutter during cutting is greater than 80 rpm.

[0022] As an option, a ratio of the slot depth D to the diameter d of the cutter body is less than 0.50. As an option, the ratio of the slot depth D to the diameter d of the cutter body is less than 0.49.

[0023] As an option, the ratio of the slot depth D to the diameter d of the cutter body is less than 0.48.

[0024] As an option, the ratio of the slot depth D to the diameter d of the cutter body is less than 0.47.

[0025] As an option, the ratio of the slot depth D to the diameter d of the cutter body is less than 0.46.

[0026] As an option, the ratio of the slot depth D to the diameter d of the cutter body is less than 0.45.

[0027] As an option, the ratio of the slot depth D to the diameter d of the cutter body is less than 0.40.

[0028] As an option, the ratio of the slot depth D to the diameter d of the cutter body is at least 0.15.

[0029] As an option, the ratio of the slot depth D to the diameter d of the cutter body is at least 0.20.

[0030] As an option, the ratio of the slot depth D to the diameter d of the cutter body is at least 0.25.

[0031] As an option, the ratio of the slot depth D to the diameter d of the cutter body is at least 0.30.

[0032] As an option, the ratio of the slot depth D to the diameter d of the cutter body is at least 0.35.

[0033] As an option, a feed rate of the rock to the cutter body is from approximately 0.25 m / min to approximately 10 m / min.

[0034] As an option, a cutting width is from approximately 8 mm to approximately 70 mm.

[0035] As an option, the diameter, d, of the cutter body is from approximately 1.0 m to approximately 5.0 m.

[0036] As an option, the slot depth D is from approximately 150 mm to approximately 2500 mm. As an option, the rock has a Uniaxial Compressive Strength of from approximately 5 MPa to approximately 50 MPa.

[0037] As an option, a feed rate of the rock to the cutter body is <10 m / min.

[0038] As an option, the rock has a Uniaxial Compressive Strength of from approximately 50 MPa to approximately 100 MPa.

[0039] As an option, a feed rate of the rock to the cutter body is <6 m / min.

[0040] As an option, the rock has a Uniaxial Compressive Strength of from approximately 100 MPa to approximately 250 MPa.

[0041] As an option, a feed rate of the rock to the cutter body is <1 m / min.

[0042] BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The improved method of mining shall now be described by way of example and with reference to the accompanying drawings in which:

[0044] Figure 1 is a schematic plan view of an underground mine incorporating an example of a prior art cutting assembly as part of a long wall mining system, and in particular shows the cutting assembly in a horizontal orientation;

[0045] Figure 2 is a schematic end view of the long wall mining system of Figure 1;

[0046] Figure 3 is a schematic plan view of an underground mine incorporating a further example of a prior art cutting assembly as part of a long wall mining system, and in particular shows the cutting assembly in a vertical orientation;

[0047] Figure 4 is schematic end view of the long wall mining system of Figure 3; Figure 5 is a perspective view of an example disc cuter;

[0048] Figure 6 is a side view of a cuter body forming part of the disc cuter of Figure 5; and

[0049] Figure 7 shows a schematic of first and second slots cut into rock, and introduces parameters used to define the method of mining in accordance with the invention.

[0050] DETAILED DESCRIPTION

[0051] A disc cuter 18 such as the one shown in Figures 5 and 6 is used to cut into rock. The disc cuter 18 comprises a cuter body 20 with a diameter, d, and a thickness, t, a plurality of tool holders 24 mounted about a peripheral surface of the cuter body 20 and a plurality of cuting elements 22 mounted in the tool holders 24. The cuting elements 22 are arranged in a sequence within each repeating sets of tool holders 24. The cuting elements 22 may comprise poly crystalline diamond (PCD). For example, the cutting elements 22 may be poly crystalline diamond compacts (PDCs).

[0052] In use, the disc cuter 18 is rotated at speed and offered up to the rock. As the disc cuter 18 advances and engages with the rock, cuting begins and a first slot 26 is progressively formed in the rock 12 - see Figure 7. Once a target slot depth D, has been achieved, the disc cuter 10 is withdrawn from the slot. The disc cuter 18 is moved to a second cuting position, and the cuting operation repeated to form a second slot 28. The second slot 28 may to be to the left or right of the first slot 26 in the rock face, or alternatively, it may be above or below the first slot 26. The second slot 28 is spaced apart from the first slot 26 by distance S. The distance S equates to the spacing between slots 26, 28. The distance S and slot depth D are optimised based on the nature of the rock formation 2, and indirectly take into account the design of the cuter body 20. Third, fourth, fifth, etc. slots, as desired, can be cut in the same way.

[0053] The efficiency of the cuting depends on several factors, one of which is the rotational speed of the disc cuter during cutting. Higher rotational speeds lead to more rapid cuting of the rock. However, conventional carbide-based cuters are limited by the lack of strength of the carbide material. When cuting elements comprising PCD are used, higher rotational speeds can be reached, thereby improving cutting efficiency compared to conventional (e.g. carbide- based) cutters. The present inventors have found that a rotational speed of greater than 60 rpm is enabled by use of cutting elements comprising PCD, with a rotational speed of greater than 80 rpm particularly advantageous.

[0054] The diameter d of the cutter body 20 may be in the range of from approximately 1.0 m to approximately 5.0 m, for example, from approximately 1.0 m to approximately 4.0 m, for example from approximately 1.0 m to approximately 3.0 m, for example from approximately 1.0 m to approximately 2.0 m, for example from approximately 1.0 m to approximately 1.8 m. In one embodiment, the diameter d of the cutter body 20 is approximately 1.0 m. In another embodiment, the diameter d of the cutter body 20 is approximately 1.5 m. In a further embodiment, the diameter d of the cutter body 20 is approximately 1.75 m.

[0055] The slot depth D may be in the range of from approximately 150 mm to approximately 2500 mm, for example from approximately 150 mm to approximately 2000 mm, for example from approximately 150 mm to approximately 1500 mm, for example from approximately 150 mm to approximately 1000 mm, for example from approximately 150 mm to approximately 900 mm.

[0056] In general, the greater the slot depth D, the higher the cutting efficiency. However, as the slot depth D is increased, the torque and vibration on the cutter body are also increased, increasing the risk of inefficient excavation. There is therefore a balance to be had between slot depth D and the diameter d of the cutter body 20, and this can be characterised by the ratio of the slot depth D to the diameter d of the cutter 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 cutter body 20 may be from approximately 0.15 to approximately 0.50, or from approximately 0.15 to approximately 0.49, or from approximately 0.15 to approximately 0.48, or from approximately 0.15 to approximately 0.47, or from approximately 0.15 to approximately 0.46, or from approximately 0.20 to approximately 0.45, or from approximately 0.25 to approximately 0.40, or from approximately 0.30 to approximately 0.40, or from approximately 0.35 to approximately 0.40, or from approximately 0.32 to approximately 0.37, or from approximately 0.34 to approximately 0.36. In a particular example, the slot depth D is 340 mm and the diameter d of the cutter body 20 is 1000 mm, giving a ratio of slot depth D to diameter d of the cutter body of 0.34. In another particular example, the slot depth D is 540 mm and the diameter d of the cutter body 20 is 1500 mm, giving a ratio of slot depth D to diameter d of the cutter body of 0.36.

[0057] The slots have a width, i.e. the cutting width, W, which is less than the thickness, t, of the cutter body 20. The cutting width may be in the range of approximately 8 mm to approximately 70 mm, for example from approximately 16 mm to approximately 70 mm. In general terms, the higher the uniaxial compressive strength of the rock to be cut, the lower the recommended cutting width.

[0058] The feed rate of the rock is determined by the uniaxial compressive strength of the rock and the strength of the cutter. The faster the feed rate, the more efficient the cutting as the greater the output of cut rock per unit time. However, conventional carbide-based cutters cannot be used at as high feed rates as the diamond-based cutting elements described herein because they have insufficient strength and impact resistance, and therefore the overall cutting efficiency using carbide-based cutters is lower than a corresponding diamond-based cutting element. The present inventors have found that optimum cutting can be achieved where the feed rate of the rock to the cutter body 20 is from approximately 0.25 m / min to approximately 10 m / min, for example from approximately 1 m / min to approximately 10 m / min, for example from approximately 1 m / min to approximately 6 m / min, for example from approximately 6 m / min to approximately 10 m / min. The optimum feed rate depends on the strength of rock being cut.

[0059] According to the International Society for Rock Mechanics and Rock Engineering (ISRM), rock strength can be described as medium strength, high strength and very high strength, as shown in Table 1. More quantitively, Uniaxial Compressive Strength, also known as Unconfined Compressive Strength or UCS, is the most widely quoted parameter to describe the nature of rock and it is a significant factor to consider when designing for rock cutting. In short, strong rock requires higher forces to be applied before it will break. Examples of Medium Strength rock include concrete and sandstone. An example of High Strength rock is kimberlite. An example of Very High Strength rock is granite.

[0060] Table 1: extract taken from 'A review of rock cutting for underground mining: past, present and future', D. Vogt, published in The Journal of the Southern African Institute of Mining and Metallurgy, Volume 116, November 2016.

[0061] Where the rock has a uniaxial compressive strength of 5 MPa to 50 MPa, the optimum feed rate is <10 m / min, for example from approximately 0.25 m / min to approximately 10 m / min, for example, from approximately 1 m / min to approximately 10 m / min, for example, from approximately 2 m / min to approximately 10 m / min, for example from approximately 3 m / min to approximately 10 m / min, for example from approximately 4 m / min to approximately 10 m / min, for example from approximately 5 m / min to approximately 10 m / min, for example from approximately 6 m / min to approximately 10 m / min, for example from approximately 7 m / min to approximately 10 m / min, for example from approximately 8 m / min to approximately 10 m / min, for example from approximately 9 m / min to approximately 10 m / min.

[0062] Where the rock has a uniaxial compressive strength of 50 MPa to 100 MPa, the optimum feed rate is <6 m / min, for example from approximately 0.25 m / min to approximately 6 m / min, for example, from approximately 1 m / min to approximately 6 m / min, for example, from approximately 2 m / min to approximately 6 m / min, for example from approximately 3 m / min to approximately 6 m / min, for example from approximately 4 m / min to approximately 6 m / min, for example from approximately 5 m / min to approximately 6 m / min.

[0063] Where the rock has a uniaxial compressive strength of 100 MPa to 250 MPa, the optimum feed rate is <1 m / min, for example from approximately 0.25 m / min to approximately 1 m / min, for example, from approximately 0.50 m / min to approximately 1 m / min, for example, from approximately 0.75 m / min to approximately 1 m / min, for example from approximately 0.8 m / min to approximately 1 m / min, for example from approximately 0.9 m / min to approximately 1 m / min.

[0064] Example: Computer Simulation using Multiple Linear Regression Analysis of Laboratory Data The use of a PCD cutting disc is a relatively new technology in mining applications. The torque and torque fluctuation generated during the cutting process are key variables that affect mining performance and efficiency. Therefore, optimizing the ranges of these two variables is vital for designing corresponding mining equipment.

[0065] To this end, a multiple linear regression analysis was performed using Minitab. One multiple linear regression analysis was performed for the dependent variable torque, and one multiple linear regression analysis was performed for the dependent variable torque fluctuation.

[0066] The independent variables used in the regression analysis were as follows:

[0067] 1) The rotational speed (rpm) of the disc cutter during cutting

[0068] 2) The feed rate (mm / min) of the cutting assembly into the rock

[0069] 3) The cutting width (mm), i.e. the width of the slot cut into the rock by the cutter

[0070] 4) The slot depth (mm)

[0071] 5) The uniaxial compressive strength (UCS) (MPa) of the rock being cut.

[0072] First, multiple linear regression equations for torque and torque fluctuation were generated using laboratory data, and then the resulting equations were used to identify optimum mining conditions.

[0073] The laboratory data was obtained using a test rig. The test rig used a disc cutter as depicted in Fig. 5 comprising a cutter body with a diameter of 1.0 m, a plurality of tool holders mounted about a peripheral surface of the cutter body and a plurality of PDC cutting elements attached to the tool holders. 99 data sets obtained from the test rig were used to build the multiple linear regression equations. In the data sets, the rotational speed was from 30 rpm to 120 rpm, the feed rate was from 15 mm / min to 90 mm / min, the cutting width was from 15 mm to 70 mm, the slot depth was from 1 mm to 70 mm, and the UCS of the rock was either 200 MPa (granite) or 80 MPa (concrete).

[0074] As is conventional in the Minitab multiple linear regression analysis, unusual data points with large residuals and which are not well fit by the equation were removed from the analysis. However, as confirmed by the Minitab software, the remaining sample was sufficiently large (n = 63) to obtain a precise estimate of the strength of the relationship between the variables.

[0075] All the independent variables were found to have p-values that are less than the significance level of 0.05. The results therefore indicate that these independent variables have a statistically significant effect on the torque and torque fluctuation, which is consistent with the observations of the inventors in practice.

[0076] The values of R-sq for torque and torque fluctuation are 95.45% and 91.02% respectively, which indicates that the model can generate precise predictions for new observations.

[0077] Having generated a suitable model, the relationships between the independent variables and the dependent variables were studied.

[0078] Rotational speed

[0079] According to the regression model, the higher the rotational speed, the smaller the torque and the torque fluctuation, and the smoother the cutting. Specifically, when the rotational speed is greater than 80 rpm, the cutting effect will be significantly improved, though a notable improvement is seen from as low as 60 rpm. The use of such high rotational speeds is enabled by the use of cutting elements which comprise PCD, in this case PDC cutting elements.

[0080] The maximum rotational speed is only limited by the output power of the machine and the maximum rotational speed of the motor. Feed rate

[0081] The feed rate has a linear relationship with torque and torque fluctuations, and the maximum feed rate is limited by the strength and impact resistance of the cutter material. As noted above, lower cutting speeds are more suited to higher rock strengths, and vice versa.

[0082] Cutting width

[0083] The cutting width also has a linear relationship with torque and torque fluctuations. The minimum cutting width is limited by the strength of the disc cutter body, and the maximum cutting width is limited by the PCD strength and impact resistance.

[0084] Slot depth

[0085] In general, the greater the depth of cut, the higher the cutting efficiency. However, the required torque and vibration are also greater, and the requirements for the strength of the cutting disc are also higher. According to the present analysis, the ratio of slot depth to disc diameter should be approximately 0.35, so as to ensure smooth and reliable cutting without excessive vibration of the disc and high temperature.

[0086] While this 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 detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1. A method of mining rock using a disc cutter comprising a cutter body with a diameter d, a plurality of tool holders mounted about a peripheral surface of the cutter body and a plurality of cutting elements attached to the tool holders, the method comprising cutting a slot with a slot depth D in the rock at a cutting position of the disc cutter, wherein a rotational speed of the disc cutter during cutting is greater than 60 rpm.

2. The method of claim 1, wherein the cutting elements comprise poly crystalline diamond (PCD).

3. The method of claim 1 or claim 2, wherein the cutting elements are polycrystalline diamond compacts (PDCs).

4. The method of any one of claims 1 to 3, wherein the rotational speed of the disc cutter during cutting is greater than 65 rpm.

5. The method of claim 4, wherein the rotational speed of the disc cutter during cutting is greater than 70 rpm.

6. The method of claim 5, wherein the rotational speed of the disc cutter during cutting is greater than 75 rpm.

7. The method of claim 6, wherein the rotational speed of the disc cutter during cutting is greater than 80 rpm.

8. The method of any one of the preceding claims, wherein a ratio of the slot depth D to the diameter d of the cutter body is less than 0.50.

9. The method of claim 8, wherein the ratio of the slot depth D to the diameter d of the cutter body is less than 0.45.

10. The method of claim 9, wherein the ratio of the slot depth D to the diameter d of the cutter body is less than 0.40.

11. The method of any one of the preceding claims, wherein the ratio of the slot depth D to the diameter d of the cutter body is at least 0.15.

12. The method of claim 11, wherein the ratio of the slot depth D to the diameter d of the cutter body is at least 0.20.

13. The method of claim 12, wherein the ratio of the slot depth D to the diameter d of the cutter body is at least 0.25.

14. The method of claim 13, wherein the ratio of the slot depth D to the diameter d of the cutter body is at least 0.30.

15. The method of claim 14, wherein the ratio of the slot depth D to the diameter d of the cutter body is at least 0.35.

16. The method of any one of the preceding claims, wherein a feed rate of the rock to the cutter body is from approximately 0.25 m / min to approximately 10 m / min.

17. The method of any one of the preceding claims, wherein a cutting width is from approximately 8 mm to approximately 70 mm.

18. The method of any one of the preceding claims, wherein the diameter, d, of the cutter body is from approximately 1.0 m to approximately 5.0 m.

19. The method of any one of the preceding claims, wherein the slot depth D is from approximately 150 mm to approximately 2500 mm.

20. The method of any one of the preceding claims, wherein the rock has a Uniaxial Compressive Strength of 5 MPa to 50 MPa.

21. The method of claim 20, wherein a feed rate of the rock to the cutter body is <10 m / min.

22. The method of any one of claims 1 to 19, wherein the rock has a Uniaxial Compressive Strength of 50 MPa to 100 MPa.

23. The method of claim 22, wherein a feed rate of the rock to the cutter body is <6 m / min.

24. The method of any one of claims 1 to 19, wherein the rock has a Uniaxial Compressive Strength of 100 MPa to 250 MPa.

25. The method of claim 24, wherein a feed rate of the rock to the cutter body is <1 m / min.

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