Cutting element

Abstract

Herein is disclosed a cutting element 1 for use in a method of undercut mining comprising: a substrate, and a superhard tip 2 having a largest diameter of at least 16 mm and an exposed surface, wherei

Description

FIELD OF THE INVENTION This disclosure relates generally to a cutting element for use in a method of undercut mining, an undercutting disc cutter, an actuating disc cutter head, and use of the cutting element, undercutting disc cutter or actuating disc cutter head in a method of mining. BACKGROUND In modern mining, the principal modes of operation are drill-and-blast and mechanical excavation. In drill-and-blast, a series of holes are drilled into the rock to be mined. Explosives are then packed into these holes and a controlled explosion performed to break up the rock. The broken rock is then collected. In mechanical excavation, the rock is removed using mechanical equipment, such as a continuous miner. Mechanical excavation provides a less hazardous working environment than drill-and-blast due to, for example, the lack of requirement for explosives. Mechanical excavation is the dominant mode of mining for softer rocks and materials such as coal. However, hard rock mining is still dominated by drill-and-blast. One of the primary reasons for this is that the cutting elements typically used for mechanical excavation do not have sufficient wear resistance and toughness to cut hard rock, or, where they do, they tend to fail relatively rapidly. It is an aim of the invention to provide a cutting element for use in a method of undercut mining that addresses the above-mentioned problem. SUMMARY OF THE INVENTION The present inventors have surprisingly found that a cutting element of a particular diameter and exposed surface area has a significantly increased wear resistance and toughness, thereby increasing the amount of hard rock which can be removed in a method of undercut mining. The present disclosure provides a cutting element for use in a method of undercut mining comprising a substrate, and a superhard tip having a largest diameter of at least 16 mm and an exposed surface, wherein the exposed surface has a surface area of at least 200 mm2. As an option, the surface area is at least 250 mm2. As an option, the surface area is at least 300 mm2. As an option, the surface area is at least 350 mm2. As an option, the surface area is at least 400 mm2. For example, the surface area is at least 450 mm2, or at least 500 mm2, or at least 550 mm2, or at least 600 mm2, or at least 700 mm2, or at least 750 mm2, or at least 800 mm2, or at least 850 mm2, or at least 900 mm2, or at least 950 mm2. As an option, the surface area is at most 250 mm2, or at most 300 mm2, or at most 350 mm2, or at most 400 mm2, or at most 450 mm2, or at most 500 mm2, or at most 550 mm2, or at most 600 mm2, or at most 700 mm2, or at most 750 mm2, or at most 800 mm2, or at most 850 mm2, or at most 900 mm2, or at least 950 mm2, or at most 1000 mm2. As an option, the surface area is from approximately 200 mm2 to approximately 1000 mm2, or from approximately 250 mm2 to approximately 1000 mm2, or from approximately 300 mm2 to approximately 1000 mm2, or from approximately 350 mm2 to approximately 1000 mm2, or from approximately 400 mm2 to approximately 1000 mm2, or from approximately 400 mm2 to approximately 950 mm2, or from approximately 400 mm2 to approximately 900 mm2, or from approximately 400 mm2 to approximately 850 mm2, or from approximately 400 mm2 to approximately 800 mm2, or from approximately 400 mm2 to approximately 750 mm2, or from approximately 400 mm2 to approximately 700 mm2, or from approximately 400 mm2 to approximately 650 mm2, or from approximately 400 mm2 to approximately 600 mm2, or from approximately 400 mm2 to approximately 550 mm2, or from approximately 400 mm2 to approximately 500 mm2, or from approximately 400 mm2 to approximately 450 mm2. As an option, the largest diameter of the superhard tip is at most 30 mm. As an option, the largest diameter of the superhard tip is at most 29 mm, or at most 28 mm, or at most 27 mm, or at most 26 mm, or at most 25 mm, or at most 24 mm, or at most 23 mm, or at most 22 mm, or at most 21 mm, or at most 20 mm, or at most 19 mm, or at most 18 mm. As an option, the largest diameter of the superhard tip is from approximately 16 mm to approximately 30 mm, or from approximately 16 mm to approximately 29 mm, or from approximately 16 mm to approximately 28 mm, or from approximately 16 mm to approximately 27 mm, or from approximately 16 mm to approximately 26 mm, or from approximately 16 mm to approximately 25 mm, or from approximately 16 mm to approximately 24 mm, or from approximately 16 mm to approximately 23 mm, or from approximately 16 mm to approximately 22 mm, or from approximately 16 mm to approximately 21 mm, or from approximately 16 mm to approximately 20 mm, or from approximately 16 mm to approximately 19 mm, or from approximately 16 mm to approximately 18 mm. As an option, the largest diameter of the superhard tip is from approximately 17 mm to approximately 30 mm, or from approximately 17 mm to approximately 29 mm, or from approximately 17 mm to approximately 28 mm, or from approximately 17 mm to approximately 27 mm, or from approximately 17 mm to approximately 26 mm, or from approximately 17 mm to approximately 25 mm, or from approximately 17 mm to approximately 24 mm, or from approximately 17 mm to approximately 23 mm, or from approximately 17 mm to approximately 22 mm, or from approximately 17 mm to approximately 21 mm, or from approximately 17 mm to approximately 20 mm, or from approximately 17 mm to approximately 19 mm, or from approximately 17 mm to approximately 18 mm. As an option, the surface area of the exposed surface is at most 1000 mm2 As an option, the superhard material comprises or consists of polycrystalline diamond (PCD). As an option, the superhard material comprises or consists of polycrystalline boron nitride (PCBN). As an option, the superhard material comprises or consists of diamond enhanced carbide (DEC) material. As an option, the ratio of the diameter of the superhard tip to the height of the superhard tip is at least 1.75. As an option, the ratio of the diameter of the superhard tip to the height of the superhard tip is at least 1.75, or at least 2, or at least 2.5, or at least 3, or at least 3.5, or at least 4, or at least 4.5, or at least 5, or at least 5.5, or at least 6, or at least 6.5, or at least 7, or at least 7.5, or at least 8, or at least 8.5, or at least 9, or at least 9.5. As an option, the ratio of the diameter of the superhard tip to the height of the superhard tip is at most 10. As an option, the ratio of the diameter of the superhard tip to the height of the superhard tip is at most 5. As an option, the ratio of the diameter of the superhard tip to the height of the superhard tip is at most 2.5. As an option, the ratio of the diameter of the superhard tip to the height of the superhard tip is at most 10, or at most 9.5, or at most 9, or at most 8.5, or at most 8, or at most 7.5, or at most 7, or at most 6.5, or at most 6, or at most 5.5, or at most 5, or at most 4.5, or at most 4, or at most 3.5, or at most 3, or at most 2.5, or at most 2. As an option, the ratio of the diameter of the superhard tip to the height of the superhard tip is from approximately 1.75 to approximately 10, or from approximately 1.75 to approximately 5, or from approximately 1.75 to approximately 2.5. As an option, the largest diameter of the superhard tip is from approximately 16 mm to approximately 18 mm, preferably from approximately 17 mm to approximately 18 mm. As an option, the ratio of the diameter of the superhard tip to the height of the superhard tip is from approximately 1.75 to approximately 2.5 or 5, and the largest diameter of the superhard tip is from approximately 16 mm to approximately 18 mm, preferably from approximately 17 mm to approximately 18 mm. As an option, the superhard tip has rotational symmetry about a main central axis, the superhard tip having an apex area and, on a plane on which the main central axis lies, a convex curved side wall extending between the apex area and the substrate. As an option, the apex area is a planar apex area. As an option, the curved side wall has a varying radius of curvature. As an option, the superhard tip has a substantially conical profile. The present disclosure further provides an undercutting disc cutter, which comprises one or more cutting elements as defined herein. The present disclosure further provides an actuating disc cutter head, which comprises one or more undercutting disc cutters as described herein. As an option, the actuating disc cutter head further comprises a motor connected to a shaft, the shaft being connected to an actuator, the actuator being connected to an undercutting disc cutter. The present disclosure further provides a use of the cutting element as described herein, the undercutting disc cutter as described herein or the actuating disc cutter head as described herein in a method of mining. As an option, the method of mining is a method of undercut mining. As an option, the method is a method of mining of hard rock. As an option, the hard rock has a uniaxial compressive strength of greater than 100 MPa. As an option, the hard rock has a uniaxial compressive strength of at most 450 MPa. As an option, the hard rock has a Cerchar abrasivity index (CAI) of at least 3. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an embodiment of a cutting element according to the invention; Figure 2 is a schematic representation of the cutting element depicted in Figure 1; Figure 3 is a schematic representation of a rock face; Figure 4 is a schematic representation of a further embodiment of a cutting element according to the invention; Figure 5 is a schematic representation of a further embodiment of a cutting element according to the invention; Figure 6 is a schematic representation of a further embodiment of a cutting element according to the invention; Figure 7 is a schematic representation of a further embodiment of a cutting element according to the invention; Figure 8 is a schematic representation of a further embodiment of a cutting element according to the invention; Figure 9 is a schematic representation of a further embodiment of a cutting element according to the invention; Figure 10 is a schematic representation of an undercutting disc cutter according to an embodiment of the invention; Figure 11 is a schematic representation of an actuating disc cutter head according to an embodiment of the invention; and Figure 12 is a schematic representation of the actuation of the actuating disc cutter head shown in Figure 11 with respect to a rock face. DETAILED DESCRIPTION Exemplary cutting element 1 is depicted in Figures 1 and 2. Cutting element 1 comprises a PCD tip 2 and a substrate 3. In cutting element 1, the PCD tip is in the general form of a layer defining a generally planar working surface. The interface between the substrate 3 and the PCD tip 2 in the example shown in Figure 1 is planar. PCD tip 2 has a largest diameter of at least 16 mm. In this example, the PCD tip 2 has a diameter of 17.5 mm. The largest diameter d of the tip is measured perpendicular to a longitudinal axis of rotation I as depicted in Figure 2. The exposed surface area of the superhard tip is at least 200 mm2. By exposed surface area is meant all of the surface area of the PCD tip that is exposed when the cutting element is attached to the substrate. Exposed surface area does not include the surface area of the PCD tip which interfaces with the substrate. Cutting element 1 is for use in a method of undercut mining. Herein “undercut mining” is understood to be a method of mining where during cutting the primary motion of the cutting element is in a plane which is generally parallel to the surface of the material being cut, as opposed to the primary motion of the cutting element during cutting being in a plane which is generally orthogonal to the surface of the material being cut. This can be illustrated using Figure 3, which depicts a rock face 15 where the surface being cut S is generally parallel to the xy plane. In a method of undercut mining of surface S, the primary motion of the cutting element would be in the xy plane. There may also be secondary motion of the cutting element, such as in the yz plane (for example, caused by actuation as described herein). This contrasts with a method of mining where the primary motion of the cutting element is in the xz or yz planes, i.e. orthogonal to the surface being cut S. The term “generally” is used here as the cutting element may be tilted to a degree and therefore not in a plane precisely parallel to the surface of the material being cut. The angle of tilt may be, for example up to 15 degrees from the parallel plane. An example of undercut mining as defined herein is mining using an undercutting disc cutter. Here, during cutting the undercutting disc cutter body would be aligned parallel to the yx plane shown in Figure 3, rather than being aligned parallel to the yz plane. The height h of the PCD tip 2 is measured along the longitudinal axis I as depicted in Figure 2. The ratio of the diameter of the PCD tip 2 to the height h of the superhard tip is ideally at least 1.75 and at most 10. In this example, the height h of the PCD tip 2 is 8 mm and the diameter d is 17.5 mm, and therefore the ratio of the diameter of the PCD tip 2 to the height h of the superhard tip is 2.19. In other words, the PCD tip 2 is approximately twice as wide as it is tall. This shape is advantageous when cutting rock as blunter tools have a smaller bending moment and are therefore less prone to breaking than sharper tools. In addition, a blunter tool has a larger contact area which decreases the forces on the PCD tip and creates less stress on the rock during cutting. The shape of the PCD tip can be varied so long as the largest diameter d is larger than 16 mm and the exposed surface area of the superhard tip is at least 200 mm3. Exemplary cutting elements are depicted in Figures 4 to 9 and described below. Exemplary cutting elements 11 and 21 are depicted in Figures 4 and 5. Cutting elements 11,21 comprise a PCD tip 2 and a substrate 3. In both cutting elements 11 and 21, the PCD tip 2 is in the general form of a layer defining a generally dome-like working surface. The interface between the substrate 3 and the PCD tip 2 in the example shown in Figure 4 is planar, while the interface between the substrate 3 and the PCD tip 2 in the example shown in Figure 5 is non-planar. Further exemplary cutting elements 31 and 41 are depicted in Figures 6 and 7. Cutting elements 31, 41 comprise a PCD tip 2 and a substrate 3. In both cutting elements 31 and 41, the PCD tip 2 has the general shape of a rounded or blunted cone. As shown in Figure 6, the conical part of the tip 2 may be inclined at an angle of about 42 degrees with respect to a longitudinal axis L. The interface between the substrate 3 and the PCD tip 2 in the example shown in Figure 6 is planar, while the interface between the substrate 3 and the PCD tip 2 in the example shown in Figure 7 is non-planar. A further exemplary cutting element 51 is depicted in Figure 8. Cutting element 51 comprises a PCD tip 2 and a substrate 3. The PCD tip 2 has rotational symmetry about a main central axis. PCD tip 2 comprises a planar apex area 2a at the apex of the PCD tip 2. The PCD tip 2, when viewed in side elevation has a curved convex side wall 2b extending between the planar apex area 2a and the substrate 3. The curved convex side wall 2b has a varying radius of curvature. PCD tip 2 has a truncated conical working surface. In this example, PCD tip 2 has a largest diameter d of 17.5 mm, a height h of 8 mm, and an exposed surface area of 443 mm3. In the embodiments disclosed herein, the tip 2 comprises or consists of polycrystalline diamond (PCD) material. As used herein, polycrystalline diamond (PCD) material comprises an aggregation of a plurality of diamond grains, a substantial portion of which are directly inter-bonded with each other and in which the content of diamond is at least about 80 volume per cent of the PCD material. Interstices between the diamond grains may be at least partly filled with a filler material that may comprise catalyst material for synthetic diamond, or they may be substantially empty. As used herein, a catalyst material (which may also be referred to a solvent / catalyst material) for synthetic diamond is capable of promoting the growth of synthetic diamond grains and or the direct inter-growth of synthetic or natural diamond grains at a temperature and pressure at which synthetic or natural diamond is thermodynamically stable. Examples of catalyst materials for diamond are Fe, Ni, Co and Mn, and certain alloys including these. Bodies comprising PCD material may comprise at least a region from which catalyst material has been removed from the interstices, leaving interstitial voids between the diamond grains. Other superhard materials may also be used in combination with or instead of PCD in the superhard tips 2 of the cutting elements of the present disclosure. For example, the superhard tip 2 may comprise or consist of composite material comprising diamond and / or cubic boron nitride (cBN) grains dispersed within a matrix, which may comprise or consist of cemented carbide material, alloy material, super-alloy material (such as Ni-based super-alloy material), ceramic material, cermet material, intermetallic phase material. As used herein, PCBN material comprises grains of cubic boron nitride (cBN) dispersed within a matrix, which may comprise metal, alloys, intermetallic materials, Ni-based super-alloy material or ceramic material, for example. In some examples the tip 2 may comprise polycrystalline cBN (PCBN) material and / or silicon carbide bonded diamond (SCD) composite material. In some examples, the superhard tip 2 may comprise a polycrystalline diamond body comprising a plurality of bonded together diamond grains forming a matrix phase, a plurality of interstitial regions interposed between the bonded together diamond grains, and a carbonate material disposed within the interstitial regions as described in WO 2014 / 078620 A1, the entire contents of which are hereby incorporated herein by reference. The carbonate material may be, for example, magnesium carbonate or calcium carbonate. The working surface of the superhard tip 2 may be pointed, rounded or truncated in a known manner. As such, the superhard tip 2 may be generally circular, generally rectangular, generally pyramidal, generally conical, generally asymmetric, or combinations thereof, or similar. Some examples of superhard tip 2 shapes are shown in Figures 1, 2 and 4 to 9. Further examples of tip shapes are given in EP 2795062 B1, GB 2490795 A, and WO 2018 / 162442 A1, the entire contents of which are incorporated herein by reference. As noted above, the superhard tip 2 is joined to a substrate 3. The substrate 3 may be formed of a cemented metal carbide, for example cemented tungsten carbide. The substrate may further comprise from approximately 5 vol.% to approximately 20 vol.% of a metallic binder, such as Co, Ni or Fe. In some examples, the substrate may comprise or consist of cemented tungsten carbide material including at least about 5 weight per cent and at most about 10 weight per cent binder material comprising cobalt. In some examples, the substrate may comprise cemented carbide material having Rockwell hardness of at least 88 HRa, transverse rupture strength of at least about 2,500 MPa, magnetic moment of at least 8 G cm3 / g and at most 16 G cm3 / g and coercivity of at least 6 kA / m and at most 14 kA / m. The superhard tip 2 may be joined to the substrate 3 by means of a join layer comprising braze alloy material. Exemplary join layers comprising braze alloy material and configurations of the interface between the superhard tip 2 and the substrate 3 are detailed in WO 2020 / 161218 A1, the entire contents of which are incorporated herein by reference. As another example, the superhard tip 2 may be metallurgically bonded to the substrate 3. Exemplary superhard tips 2 metallurgically bonded to substrates 3 are detailed in WO 2013 / 087773 A1 and WO 2013 / 092346 A2, the entire contents of which are incorporated herein by reference. One or more interlayers may be inserted between the superhard tip 2 and the substrate 3. An example of this is depicted in Figure 9. Cutting element 61 is the same as cutting element 51 described above, except that it further comprises an interlayer 4. Due to the presence of the interlayer 4, the height h of the superhard tip 2 is reduced to 7 mm. Such an interlayer 4 could be included in any of the cutting elements disclosed herein. While the interlayer 4 depicted in Figure 9 completely separates the superhard tip 2 and the substrate 3, embodiments are also envisaged in which the interlayer 4 only partially separates the superhard tip 2 and the substrate 3. For example, there may be a peripheral portion where the superhard tip 2 and the substrate 3 remain in direct contact, and a central portion where there is an interlayer 4 between the superhard tip 2 and the substrate 3. The interlayer may comprise a bonded mass of superhard abrasive particles and refractory particles wherein the size of the superhard abrasive particles is the same as or less than that of the refractory particles. In the interlayer the superhard abrasive particles and the refractory particles will generally be present as discrete entities with little or no or substantially no intergrowth or direct particle-to-particle bonding. A bonding phase may also be present. This bonding phase may comprise or consist of nickel, cobalt, iron or alloys containing one or more of these metals. The interlayer may comprise a composite material formed of non-interbonded grains of super hard material, preferably diamond grains with, for example, any one or more of oxides, nitrides, carbides, silicides, carbonitrides, and / or oxycarbides of any one or more transition metals including titanium, zirconium, vanadium, hafnium, tantalum, niobium, chromium, molybdenum, tungsten, copper, manganese, and / or rhenium or an alloy thereof. The amount of superhard abrasive particle in the interlayer may generally be in the range of about 10 vol.% to about 90 vol.%. The superhard abrasive may be cubic boron nitride but would typically be diamond. A mixture of superhard abrasive particles may be present in the interlayer. The refractory particles may be carbide, nitride, or boride. Carbide particles are preferred. In some example arrangements, the interlayer is formed of a diamond enhanced carbide (DEC) material, such as that described in GB2459272A, the entirety of which is incorporated herein by reference. Diamond enhanced carbide refers to any composite material that comprises particulates of diamond or other super-hard phase, such as cubic boron nitride (cBN) and at least one other hard phase (typically including a carbide, such as WC), wherein these particles are held together by means of a binder phase, preferably a metallic binder phase which is typically a transition metal (for example Co). Additionally or alternatively, the superhard tip 2 may comprise or consist of diamond enhanced carbide (DEC) material as described herein. The size of the superhard abrasive particles may be the same as or less than that of the refractory particles. When the size of the superhard abrasive particles is less than that of the refractory particles, they will generally have a size of about 10 microns, preferably about 5 microns or less than that of the refractory particles. The thickness of the interlayer may be in the range from about 100 to about 2000 microns, typically from about 200 to about 500 microns. An exemplary undercutting disc cutter 70 is depicted in Figure 10. Undercutting disc cutter 70 comprises a disc body 5, an opening 6 and cutting elements 7. Cutting elements 1, 11, 21, 31, 41, 51 and 61 may be used as cutting elements 7 in undercutting disc cutter 70. The undercutting disc cutter 70 may form part of an actuating disc cutter head as depicted in Figures 11 and 12. Motor 10 drives shaft 9 which is connected to actuator 8. Actuators is connected to undercutting disc cutter 70 and is configured to actuate the undercutting disc cutter 70 as it cuts the rock. Where there are multiple undercutting disc cutters 70, one or more of them can be actuated by the same actuator 8, or each undercutting disc cutter 70 may have its own actuator 8. One or more shafts 9 and motors 10 may be used as appropriate. The actuator 8 may be connected to the or multiple undercutting disc cutters 70 by means of suitable adaptors. The precise nature of the actuator and the amplitude of the actuation can be tuned to provide optimal rock cutting. For example, the actuator may be an eccentric cam. In another example, the actuator may be a drive shaft comprising multiple lobes configured to vary the position of the undercutting disc cutter with respect to the rock face. As shown in Figure 12, the effect of such actuation is to produce movement M with respect to the rock face 15 to be cut. Movement M generates a hammering motion on the rock face perpendicular to the direction of cut, weakening the rock and further improving the cutting process. While the schematic in Figure 12 shows the undercutting disc cutter parallel to the rock face 15 to be cut, the undercutting disc cutter may impact the rock face 15 at a tilt angle. For example, the tilt angle may be up to 15 degrees. A critical aspect of optimal rock cutting is the diameter and exposed surface area of the cutting elements. The inventors have found that a truncated cutting element (i.e. as depicted in Figure 8 and described above) with a largest PCD tip diameter of 17.5 mm and an exposed surface area of 443 mm2 shows a 4% improvement in wear (measured by a pin-on-disc wear test) and a 30% increase in fracture toughness compared to an analogous cutting element with a largest PCD tip diameter of 15 mm and an exposed surface area of 356 mm2. As a result of the improved wear and toughness of the tip with a larger diameter and exposed surface area, the volume of rock which can be mined by an undercutting disc cutter or an actuating disc cutter head comprising the cutting element of the present disclosure is significantly higher than that which can be achieved using smaller tip cutting elements. The undercutting disc cutter or the actuating disc cutter head may be used in a method of mining of hard rock. Uniaxial compressive strength (UCS) is a commonly used parameter to define the mechanical properties of rocks. Hard rock is rock which has a uniaxial compressive strength of greater than 100 MPa. Examples of 5 hard rock include kimberlite and granite. The uniaxial compressive strength may be at most 450 MPa. The Cerchar abrasivity index (CAI) is a standard measurement of the abrasiveness of hard rock. In view of the enhanced properties of the cutting elements disclosed herein, the hard rock to be cut may have a Cerchar abrasivity index (CAI) of at least 3. 10 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

1. A cutting element for use in a method of undercut mining comprising: a substrate, anda superhard tip having a largest diameter of from 16 mm to 18 mm and an exposed surface,wherein the exposed surface has a surface area of at least 400 mm2, and wherein the ratio of the diameter of the superhard tip to the height of the superhard tip is at most 2.5.

2. The cutting element according to claim 1, wherein the surface area of the exposed surface is at most 1000 mm2.

3. The cutting element according to any claim 1 or claim 2, wherein the superhard material comprises polycrystalline diamond (PCD).

4. The cutting element according to any one of the preceding claims, wherein the ratio of the diameter of the superhard tip to the height of the superhard tip is at least 1.75.

5. The cutting element according to any one of the preceding claims, wherein the largest diameter of the superhard tip is from 17 mm to 18 mm.

6. The cutting element according to any one of the preceding claims, wherein the superhard tip has rotational symmetry about a main central axis, the superhard tip having an apex area and, on a plane on which the main central axis lies, a convex curved side wall extending between the apex area and the substrate.

7. The cutting element according to claim 6, wherein the apex area is a planar apex area.

8. The cutting element according to claim 6 or claim 7, wherein the curved side wall has a varying radius of curvature.

9. The cutting element according to any one of claims 1 to 7, wherein the superhard tip has a substantially conical profile.

10. An undercutting disc cutter, which comprises one or more cutting elements as defined in any one of the preceding claims.

11. An actuating disc cutter head, which comprises one or more undercutting disc cutters as defined in claim 10.

12. Use of the cutting element of any one of claims 1 to 9, the undercutting disc cutter of claim 10 or the actuating disc cutter head of claim 11 in a method of mining.

13. The use of claim 12, wherein the method of mining is a method of undercut mining.

14. The use of claim 12 or claim 13, wherein the method is a method of mining of hard rock.

15. The use of any one of claims 12 to 14, wherein the hard rock has a uniaxial compressive strength of greater than 100 MPa.

16. The use of any one of claims 12 to 15, wherein the hard rock has a uniaxial compressive strength of at most 450 MPa.

17. The use of any one of claims 12 to 16, wherein the hard rock has a Cerchar abrasivity index (CAI) of at least 3.

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