Cheek plate

Abstract

Herein is disclosed a cheek plate (6) for a roller mill, the cheek plate comprising a wear face (9) configured to face an end of a roller in the roller mill, wherein the wear face comprises a superhard material, and a roller mill comprising the check plate.

Description

[0001] CHEEK PLATE

[0002] Field of the Invention

[0003] This disclosure relates generally to the field of cheek plates for roller mills, in particular high- pressure grinding roller mills, and roller mills comprising said cheek plates.

[0004] Background

[0005] High-pressure grinding roller (HPGR) milling is becoming a popular route for crushing rocks and minerals. As shown in Figure 1 , HPGR apparatus includes a first roller 1 and a second roller 2 with a gap between them. In use, the first and second rollers counter-rotate. A feed of material 3 is allowed to fall from a hopper through a gap between the first and second rollers 1 , 2.

[0006] The first roller 1 is allowed to move linearly in a direction normal to the direction of the material feed. The first roller 1 is usually biased to a particular position relative to the second roller 2 by springs or hydraulic cylinders.

[0007] As the material feed passes through the gap between the first and second rollers 1 , 2, compression causes the particles of the feed material 3 to fracture, and the resultant material 4 has a reduced particle size. This longitudinal region of closest approach between the first and second rollers 1 , 2 is referred to as the nip 5. To prevent escape of material at the ends of the rollers, it is necessary to use some form of confinement means. Two forms of confinement means are currently in use by manufacturers of HPGR systems, namely cheek plates and flanges (also referred to as rotating side plates). This disclosure relates to cheek plates. These are usually placed substantially perpendicular to the longitudinal axis of the nip at each end of the rollers. The flow of abrasive material is strongest at each end of the nip, and thus the portion of the cheek plate which faces this area is typically reinforced with a wearresistant material such as cemented tungsten carbide. However, even when reinforced, this part of the cheek plate wears out significantly faster than the rest of the cheek plate.

[0008] It is an object of the invention to provide an improved cheek plate for a roller mill which has a wear face which can better withstand strong flows of abrasive materials than those available in the state of the art. Summary of the invention

[0009] According to a first aspect of the invention, there is provided a cheek plate for a roller mill, the cheek plate comprising a wear face configured to face an end of a roller in the roller mill, wherein the wear face comprises a superhard material.

[0010] As an option, the wear face is configured to be placed substantially perpendicular to a longitudinal axis of a nip formed between two counter-rotating rollers in the roller mill.

[0011] As an option, the superhard material is or comprises diamond or polycrystalline boron nitride.

[0012] As an option, the diamond is polycrystalline diamond (PCD).

[0013] As an option, the wear face comprises a first plate, the first plate comprises one or more recesses, and the superhard material is mounted in at least one of the one or more recesses in the form of an insert.

[0014] As an option, the wear face has a centreline, and a packing density of the inserts increases closer to the centreline.

[0015] As an option, the wear face has a centreline, the first plate comprises a plurality of recesses, a superhard material insert is inserted into each of the plurality of recesses, and a packing density of the inserts increases closer to the centreline.

[0016] As an option, the inserts are arranged to form a repeating pattern on the surface of the wear face.

[0017] As an option, the first plate comprises a plurality of recesses, a superhard material insert is inserted into each of the plurality of recesses, and the inserts are arranged to form a repeating pattern on the surface of the wear face.

[0018] As an option, the inserts which are configured to be positioned closest to the nip have a larger diameter than those which are configured to be positioned further from the nip.

[0019] As an option, the first plate comprises a plurality of recesses (e.g. configured to receive an insert), and a superhard material insert is inserted into (e.g. substantially) all the recesses in the first plate (i.e. the plurality of recesses).

[0020] As an option, the first plate comprises a plurality of first recesses having a first diameter and a plurality of second recesses having a second diameter, wherein a first set of superhard material inserts are inserted into the plurality of first recesses and a second set of superhard material inserts are inserted into the plurality of second recesses, wherein the first diameter and the second diameter are different.

[0021] As an option, the first and second sets of inserts are arranged in corresponding and offset Bravais lattices.

[0022] As an option, the superhard material inserts are substantially cylindrical and are mounted in the recess such that the exposed surface of the superhard material insert is substantially flush with the surface of the wear face.

[0023] As an option, the superhard material inserts are substantially cylindrical and each of the superhard material inserts is mounted in one of the one or more or plurality of recesses such that the exposed surfaces of each of the superhard material inserts is substantially flush with the surface of the wear face.

[0024] As an option, the superhard material inserts comprise polycrystalline diamond mounted on a cemented carbide substrate, for example a cemented tungsten carbide substrate.

[0025] As an option, the wear face comprises a cemented carbide, for example a cemented tungsten carbide.

[0026] As an option, the first plate is mounted on a second plate.

[0027] As an option, the second plate comprises a steel, for example a stainless steel.

[0028] As an option, the wear face further comprises a pair of third plates which flank the first plate and which are mounted on the second plate and comprise a cemented carbide, preferably a cemented tungsten carbide.

[0029] As an option, the wear face comprises one or more plates formed of a superhard material.

[0030] As an option, the first plate is formed of at least two plates, each of which comprises a plurality of recesses, wherein a superhard material insert is inserted into the recesses of each of the at least two plates, and wherein the diameter of the superhard material inserts inserted into the recesses of the first of the at least two plates is different to the diameter of the superhard material inserts inserted into the recesses of the second of the at least two plates.

[0031] As an option, the cheek plate further comprises attachment means to attach the cheek plate to a roller mill.

[0032] As an option, the roller mill is a high-pressure grinding roller mill. According to a second aspect of the invention, there is provided a roller mill comprising: a first roller and a second roller, wherein the first roller and the second roller are configured to counter-rotate to form a longitudinal nip between the first and second rollers for crushing material; wherein the first and second rollers have corresponding first and second ends; and wherein the roller mill further comprises first and second cheek plates, each cheek plate as described herein; wherein the wear face of the first cheek plate is in contact with and orientated substantially perpendicular to the longitudinal nip and faces the first ends of the first and second rollers; and wherein the wear face of the second cheek plate is in contact with and orientated substantially perpendicular to the longitudinal nip and faces the second ends of the first and second rollers.

[0033] As an option, the roller mill is a high-pressure grinding roller mill.

[0034] According to a third aspect of the invention, there is provided a use of diamond in a cheek plate of a roller mill, preferably a high-pressure grinding roller mill.

[0035] As an option, the diamond is polycrystalline diamond (PCD).

[0036] Brief Description of the Drawings

[0037] The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

[0038] Figure 1 illustrates schematically a known high-pressure grinding roller apparatus;

[0039] Figure 2 is a schematic front view of a cheek plate in accordance with an embodiment of the invention;

[0040] Figure 3 is a schematic front view of another cheek plate in accordance with an embodiment of the invention;

[0041] Figure 4 is a schematic front view of another cheek plate in accordance with an embodiment of the invention;

[0042] Figure 5 illustrates schematically the mounting of the cheek plate with the rollers of a roller mill;

[0043] Figure 6 is a schematic front view of another cheek plate in accordance with an embodiment of the invention;

[0044] Figure 7 is a perspective view of a second portion of a cheek plate as defined herein; Figure 8 is a perspective view of an alternative embodiment of a second portion of a cheek plate as defined herein;

[0045] Figure 9 is a schematic cross-section of a first plate as defined herein showing a PCD / cemented tungsten carbide insert contained in a recess in the first plate;

[0046] Figure 10 is a schematic front view of a first plate as defined herein showing an arrangement of inserts;

[0047] Figure 11 is a schematic front view of a first plate as defined herein showing another arrangement of inserts;

[0048] Figure 12 is a schematic front view of a first plate as defined herein showing another arrangement of inserts;

[0049] Figure 13 is a schematic front view of a first plate as defined herein showing another arrangement of inserts;

[0050] Figure 14 is a schematic front view of a first plate as defined herein showing another arrangement of inserts;

[0051] Figure 15 is a schematic front view of a first plate as defined herein showing another arrangement of inserts;

[0052] Figure 16 is a schematic front view of a cheek plate in accordance with another embodiment of the invention;

[0053] Figure 17 is a schematic depiction of a further design for the second portion of the cheek plate; and

[0054] Figure 18 is a schematic depiction of a further design for the second portion of the cheek plate.

[0055] In the drawings, similar parts have been assigned similar reference numerals.

[0056] Detailed

[0057] Cheek plates for HPGR systems typically have an upper part which has curved or tapered sides, and a lower part which is typically substantially rectangular or square in profile and is placed adjacent to the nip. One cheek plate is placed as close as possible to one pair of ends of the rollers, while another cheek plate is placed as close as possible to the other pair of ends of the rollers. Contact between the rollers and the cheek plates is undesirable as this leads to wear on both the rollers and the cheek plates, while the gap between the roller ends and the cheek plates is minimised to reduce material loss as much as possible.

[0058] In modern HPGR systems, it is typical to have one roller which is fixed and one roller which can be skewed relative to the other roller. This skewing is used to address issues of uneven feed size distribution. As the use of fixed cheek plates limits the amount of skewing (because the skewed roller will, at a certain level of skewing, contact one of the cheek plates), adjustable cheek plates have been developed which can be moved to accommodate the roller skew, thereby maintaining a minimal distance between the cheek plate and the roller. Nevertheless, these adjustable cheek plates have the same general structure as the traditional static cheek plates.

[0059] A schematic representation of a front view of a cheek plate 6 according to the invention is shown in Figure 2. In this embodiment, the cheek plate comprises a first portion 7 and a second portion 8. The first portion 7 and the second portion 8 may be two, separate entities, or they may be integrally formed. Where the first portion 7 and the second portion 8 are two separate entities, they are typically positioned adjacent to one another.

[0060] In this embodiment, the first portion 7 has a longitudinal axis L and two concave edges 7c symmetric about the longitudinal axis L. The concave edges may have a radius of curvature which substantially conforms to that of the rollers. This conserves material and ensures that the cheek plates do not foul the equipment used to spin the rollers. The first portion 7 has an upper boundary 7a and a lower boundary 7b. The length of the upper boundary 7a (measured perpendicular to the longitudinal axis) is greater than the length of the lower boundary 7b (measured perpendicular to the longitudinal axis). The concave edges 7c extend from the upper boundary 7a towards the lower boundary 7b. The lower boundary 7b abuts or is adjacent to the second portion 8.

[0061] Another embodiment of a cheek plate 106 is depicted schematically in Figure 3. The cheek plate 106 comprises a first portion 107 and a second portion 8. The first portion 107 has an upper boundary 107a and a lower boundary 107b. The length of the upper boundary 107a (measured perpendicular to the longitudinal axis) is greater than the length of the lower boundary 107b (measured perpendicularto the longitudinal axis). The edge of the first portion 107 of the cheek plate 106 tapers linearly from the upper boundary towards the lower boundary. The lower boundary abuts or is adjacent to the second portion 8.

[0062] Another embodiment of a cheek plate 206 is depicted schematically in Figure 4. In this embodiment, to save material and to enable only half of the first portion to be changed at a time (if, for example, one half is subject to greater wear than the other), the cheek plate 206 comprises two first portions 207c and 207d and a second portion 8. Each first portion 207c, 207d has an upper boundary 207a and a lower boundary 207b. The length of the upper boundary 207a (measured perpendicular to the longitudinal axis) is greater than the length of the lower boundary 207b (measured perpendicular to the longitudinal axis). The outward edges of the first portions 207c, 207d of the cheek plate 206 taper linearly from the upper boundary 207a towards the lower boundary 207b. The lower boundaries 207a, 207b abut or are adjacent to the second portion 8.

[0063] The first portions 7, 107, 207c, 207d may further comprise a wear shield at the periphery of the concave edges as these may be subjected to wear from abrasive material ejected at the ends of the rollers. This wear shield may be formed of a superhard material such as those detailed below. Alternatively, this wear shield may be formed of a cemented carbide, for example a cemented tungsten carbide.

[0064] The second portion 8 has a wear face 9 which is configured to face an end of a roller in a roller mill. More specifically, the wear face is configured to be placed substantially perpendicular to a longitudinal axis of a nip formed between two counter-rotating rollers in the roller mill. As noted above, this is the area of most significant wear as this is where the flow of abrasive material is strongest.

[0065] In this invention, the wear face comprises a superhard material. The superhard material may comprise or consist of diamond. For example, the superhard material may comprise or consist of a diamond-based composite material. Examples of diamond-based composite materials are polycrystalline diamond (PCD) material (also referred to herein as polycrystalline diamond (PCD)), silicon carbide-bonded diamond (SCD) material and diamond enhanced carbide (DEC) material, all of which are described in more detail below. The superhard material may comprise or consist of a sintered polycrystalline super-hard material, such as polycrystalline diamond (PCD) material, polycrystalline cubic boron nitride (PCBN) material (as used herein, PCBN material comprises grains of cubic boron nitride (cBN) dispersed within a matrix comprising metal or ceramic material, and also referred to herein as polycrystalline boron nitride (PCBN)), or silicon carbide-bonded diamond (SCD) material (as used herein, unless otherwise specified, the term “diamond” will include both natural and fabricated diamond). The superhard material may comprise or consist of 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). Preferably, the superhard material comprises or consists of PCD material.

[0066] As used herein, fabricated diamond, which is also called man-made or synthetic diamond, is diamond material that has been manufactured. 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 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 as a solvent I 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. The catalyst material and / or solvent may have been removed by leaching with a strong aqueous acid, for example, by a method as detailed in GB2465175A, GB2499092A or WO2021136833A1 , the contents of which are incorporated herein by reference in their entirety.

[0067] The position of the cheek plate with respect to the rollers is depicted schematically in Figure 5 using the cheek plate of Figure 2 as an example. As can be seen, the concave edges of the first portion 7 of the cheek plate 6 broadly correspond to the curvature of the rollers 1 , 2. The first portion 7 is brought very close to the end of the rollers 1 ,2 so as to minimise escape of feed material to the greatest extent possible. As noted above, it is not essential that the concave edges of the cheek plate absolutely correspond to the curvature of the rollers 1 , 2, only that the curvature (or shape of the linear taper, as in the embodiments shown in Figures 3 and 4) is such that the cheek plate does not foul the mechanism used to spin the rollers. As noted above, instead of having curved edges, the first portion of the cheek plate could have straight edges to give an overall substantially triangular profile. In addition, and as shown above, the cheek plate does not have to be one integral body. If desired, the first portion can be divided into two parts, each of which has an edge has described above and which, when mounted in combination, provide the two required edges. The wear face 9 of the second portion 8 of the cheek plate 6 is placed substantially perpendicular to the longitudinal axis of the nip formed between the two counter-rotating rollers 1 , 2 in the roller mill such that it is positioned at the place where maximum wear occurs.

[0068] The wear face may be entirely formed of superhard material. For example, the second portion 8 could be entirely formed of a superhard material, or the second portion 8 could comprise a substrate which is coated with one or more layers of a superhard material to form the wear face 9.

[0069] Alternatively, as depicted in Figure 7, the wear face 9 may instead be formed of an array of superhard material inserts embedded in a substrate. This reduces the cost of using superhard material to form the wear face 9, while still providing a significant increase in wear resistance compared to a conventional cemented tungsten carbide wear face.

[0070] A schematic depiction of an example wear plate is depicted in Figure 7. In this embodiment, the wear face 9 is formed of a first plate 10 mounted on a second plate 11 . The first plate 10 may be attached to the second plate 11 by any one of the following techniques: gluing, brazing, press-fitting, shrink fitting, threaded connection and / or mechanical connection.

[0071] The first plate 10 comprises a plurality of recesses, and superhard material inserts 12 are mounted in the recesses (i.e. one insert is mounted in each of the plurality of recesses). In this embodiment, the inserts 12 are arranged to form a repeating pattern on the surface of the wear face 9. The superhard material inserts 12 are substantially cylindrical and are mounted in the recesses such that the exposed surface of the superhard material insert 12 is substantially flush with the surface of the wear face 9. While it is shown here that the inserts 12 are flush with the surface of the wear face 9, this is not essential and in an alternative embodiment the inserts 12 can be mounted so as to protrude from the wear face 9. In a still further alternative embodiment, the inserts 12 can be mounted to as to be sunken or recessed from the wear face 9.

[0072] Alternatively, as depicted in Figure 8, the wear face 9 may instead be formed of a series of plates formed of superhard material, i.e. any of the superhard materials listed above. A schematic depiction of an example wear plate is depicted in Figure 8. In this embodiment, instead of a first plate 10 into which inserts are mounted, the wear face 9 is formed of a series of plates 10a on a second plate 11 . The plates 10a may be attached to the second plate 11 by any one of the following techniques: gluing, brazing, press-fitting, shrink fitting, threaded connection and / or mechanical connection. The plates 10a may be separated by thin sheets of copper. The plates 10a may be entirely formed of a superhard material, or they may be formed of a superhard material backed with a cemented carbide, for example a cemented tungsten carbide. An optional further plate may be inserted between the superhard material plate 10a and the second plate 11 . This optional further plate may be formed of a cemented carbide, for example cemented tungsten carbide. The superhard material plate 10a may be brazed to this optional further plate.

[0073] In some embodiments, a combination of superhard material plates, as depicted in Figure 8, and plates comprising superhard inserts, as depicted in Figure 7, may be used to form the wear face 9. For example, the superhard material plates may be placed close to the nip, where there is most wear, with the plates which comprise inserts as described herein used around the periphery. The same second plate 9 can be used for both the superhard material plates and the plates which comprise inserts.

[0074] An exemplary insert 12 is depicted in Figure 9. As depicted in Figure 9, in this embodiment, the superhard material inserts 12 comprise a PCD layer 13 mounted on a cemented carbide (e.g. a cemented tungsten carbide) substrate 14. PCD could be replaced with PCBN, or any of the other superhard materials detailed above. In addition, the cemented carbide substrate may be omitted. The inserts may be attached to the recesses by any one of the following techniques: gluing, brazing, press-fitting, shrink fitting, threaded connection and / or mechanical connection. As noted above, the inserts can also be mounted so as to recede from or protrude from the surface of the wear face 9.

[0075] As can be best seen in Figure 10, in this embodiment the superhard material inserts are arranged such that the centres of each insert form a hexagonal Bravais lattice when viewed in a 2D projection. The inserts 12 may have a diameter D, measured as shown in Figure 10, of between 6 mm and 30 mm, for example between 8 mm and 100 mm, for example between 10 and 80 mm. While in Figure 10 the inserts are all depicted as having the same diameter, this is not necessary. In an alternative design, the inserts which are intended to be positioned most closely to the nip may be larger in diameter, and those which are intended to be positioned further away may be smaller in diameter.

[0076] The insert 12 may have a height of between 1 and 30 mm, for example between 5 and 25 mm, for example between 5 and 20 mm, for example between 5 and 10 mm.

[0077] In the above-mentioned embodiments, the second plate 11 is formed of stainless steel, though any suitable material may be used. The second plate comprises attachment means to attach the cheek plate to a roller mill. For example, the second plate may be attached to the roller mill by any one ofthe following techniques: gluing, brazing, press-fitting, shrink fitting, threaded connection and / or mechanical connection. In some embodiments, the cheek plate is adjustable so that it can be moved during grinding to ensure that the gap between the cheek plate and the roller is kept as low as possible even when the cheek plate has been worn.

[0078] While a particular pattern of inserts is depicted in the wear face 9 shown in Figures 7 and 10, the precise arrangement of the inserts can be varied. For example, as shown in Figure 11 , a lower density of inserts could be used in the same type of hexagonal Bravais lattice, or, as shown in Figure 12, the superhard material inserts can be arranged such that the centres of each insert form a cubic Bravais lattice when viewed in 2D projection.

[0079] As noted above, the most wear occurs at the part of the wear face which faces the nip. As such, the superhard materials can be arranged such that the highest area density of superhard material (when viewing the wear face as a 2D projection) is in the area of the wear face which faces the nip. A higher area density can be achieved in a number of ways. As one option, the spacing between the centre of the inserts can be kept constant, but larger diameter inserts can be used closer to the part of the wear face which faces the nip. Alternatively, the diameter of the inserts can be maintained constant, but the spacing between them can be reduced.

[0080] As a further option, inserts 12, 13 comprising different materials can be used as depicted in Figure 13. For example, as depicted schematically in Figure 13, inserts 12 of a first material may be arranged in a hexagonal Bravais lattice, and inserts 13 of a second material may be arranged in a hexagonal Bravais lattice with the same unit cell parameters but which is offset by half a unit cell a along the X axis. For example, a mixture of superhard materials could be used in the inserts, such as PCD and PCBN inserts, or some of the inserts could be superhard materials and some could be hard materials, such as a different grade of cemented tungsten carbide to the first plate.

[0081] While the insert shown in Figure 9 is cylindrical with a substantially planar working surface (working surface here referring to the part of the insert which is exposed to the nip when the insert is mounted in a check plate), other shapes may also be used. For example, the insert could have a working surface with a rounded geometry that is conical, hemispherical, domed, truncated, ballistic, or a combination thereof. Alternatively, the working surface may be hexagonal, quadrangular or octagonal in lateral cross-section. Such an embodiment is depicted in Figure 14, which shows an array of square inserts (i.e. inserts which are square in cross-section). A mixture of different insert shapes can also be used, with an example of such an arrangement depicted in Figure 15. Each insert may be chamfered, double chamfered or multiple chamfered. Such chamfering helps to reduce the risk of early failure of the insert.

[0082] While in the wear plate depicted in Figure 7 the first plate and the second plate have substantially the same width, height and depth as each other, this is not a requirement of the invention. A plurality of first plates may be attached to a single second plate, in a similar arrangement to that shown in Figure 8 for the plates without inserts. The plurality of first plates may all have the same pattern of inserts, or they may comprise different patterns and / or sizes of inserts. An advantage of having a plurality of first plates is that only those first plates subjected to the most wear need to be changed, rather than the whole plate, thereby reducing costs (this applies both to the superhard material plates and the plates with inserts). Alternatively, the wear face 9 can be made up of multiple wear plates.

[0083] In a further embodiment, as depicted in Figure 16, the wear face 9 further comprises a pair of third plates 14 which flank the first plate 10 and which are mounted on the second plate 11. These third plates 13 do not comprises a superhard material and instead comprise a wear resistant material such as a cemented carbide, preferably a cemented tungsten carbide. In this design, the superhard material inserts 12 are concentrated at the centre portion of the wear face 9 which will be positioned closest to the nip, with less wear-resistant cemented tungsten carbide plates used for the outer parts of the wear face 9 which are subjected to less wear. This reduces the amount of superhard material required, thereby reducing costs.

[0084] In an embodiment, the third plates 14 can be formed of a plurality of plate portions, each of which is mounted on a second plate 11 . A single second plate 11 can be used to support all of the first and third plates, or each first and third plate may have its own second plate. Alternatively, each first plate may have its own second plate, and the plurality of third plate portions on each side of the first plates may be supported by respective single second plates.

[0085] In an embodiment, the depth of the first plate(s) is greater than that of the third plates, and the first plates are mounted flush with the third plates to form the wear face. This is typically achieved by reducing the depth of the second plate(s) which support the first plate(s). The depth A of the first plate and the depth B of the second plate are indicated in Figure 7. The depth of the third plate is its analogous dimension. The advantage of this arrangement is that a greater depth of wear-resistant material is provided at the centre part of the wear face which is formed of the first plate(s), and which as noted above is subjected to most wear, while a lesser depth of wear-resistant material is provided by the third plates at the sides, thereby reducing costs by reducing the quantity of wear-resistant material (typically cemented tungsten carbide) which is used. In a further embodiment, instead of using carbide plates into which superhard material inserts have been inserted, as depicted above, superhard material plates can instead be used. For example, PCD plates could be used in place of carbide plates. However, while this enhances the wear resistance, it has the disadvantage of being more costly than the insert approach. As a further option, only the plates which are to be placed closest to the nip are formed of superhard material.

[0086] As depicted in Figure 17, the density of inserts can be varied across the wear face. In this embodiment, the second portion 8 has a wear face made of a series of plates 10, 110, 210, 310, 410. Plate 10 has larger diameter, less densely packed inserts 12 as it is further from the nip, while the diameters of inserts 112, 212, 312 and 412 become progressively smaller and more densely packed towards the part of the wear face which is designed to face the nip. For example, inserts 12, 112, 212, 312 and 412 could have diameters of 6 mm, 12 mm, 16 mm, 19 mm and 25 mm, respectively. This provides greater wear resistance at the part of the wear face which is subjected to the most wear. The provision of separate plates also allows for replacement of only part of the wear face, for example plate 410 may become worn more quickly than plate 10 due to their relative positions in the high-pressure grinding roller apparatus.

[0087] As shown in Figure 18, the concept depicted in Figure 17 can be combined with the concept depicted in Figure 16. This requires the use of less superhard material inserts, thereby reducing costs while ensuring maximum wear resistance is delivered where it is required.

[0088] It should be noted that the depictions in Figures 17 and 18 are merely schematic; in a real system, the number of inserts per plate would likely be higher, and the plates would typically be sized such that there was not a large gap between the inserts of one plate and the inserts of another plate.

[0089] The cheek plates as described herein can be mounted in a roller mill. The roller mill comprises a first roller and a second roller, wherein the first roller and the second roller are configured to counter-rotate to form a longitudinal nip between the first and second rollers for crushing material. The first and second rollers have corresponding first and second ends. The roller mill further comprises first and second cheek plates, each cheek plate as detailed above. In an alternative embodiment, only one cheek plate as described above is used, with the other cheek plate being a conventional one. The wear face of the first cheek plate is in contact with and orientated substantially perpendicular to the longitudinal nip and faces the first ends of the first and second rollers, and the wear face of the second cheek plate is in contact with and orientated substantially perpendicular to the longitudinal nip and faces the second ends of the first and second rollers. In a particular embodiment, the roller mill is a high-pressure grinding roller mill.

[0090] The present application also provides for the use of diamond in a cheek plate of a roller mill, preferably a high-pressure grinding roller mill. In an embodiment, the diamond is polycrystalline diamond (PCD).

[0091] The invention as set out in the appended claims has been shown and described with reference to embodiments. However, 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 cheek plate for a roller mill, the cheek plate comprising a wear face configured to face an end of a roller in the roller mill, wherein the wear face comprises a superhard material.

2. The cheek plate of claim 1 , wherein the wear face is configured to be placed substantially perpendicular to a longitudinal axis of a nip formed between two counter-rotating rollers in the roller mill.

3. The cheek plate of claim 1 or claim 2, wherein the superhard material is diamond or polycrystalline boron nitride.

4. The cheek plate of claim 3, wherein the diamond is polycrystalline diamond (PCD).

5. The cheek plate of any one of claims 1 to 4, wherein the wear face comprises a first plate, the first plate comprises one or more recesses, and the superhard material is mounted in at least one of the one or more recesses in the form of an insert.

6. The cheek plate of claim 5, wherein the wear face has a centreline, the first plate comprises a plurality of recesses, a superhard material insert is inserted into each of the plurality of recesses, and a packing density of the inserts increases closer to the centreline.

7. The cheek plate of claim 5 or claim 6, wherein the first plate comprises a plurality of recesses, a superhard material insert is inserted into each of the plurality of recesses, and the inserts are arranged to form a repeating pattern on the surface of the wear face.

8. The cheek plate of any one of claims 5 to 7, wherein the first plate comprises a plurality of recesses configured to receive an insert, and a superhard material insert is inserted into all of the plurality of recesses.

9. The cheek plate of any one of claims 5 to 8, wherein the first plate comprises a plurality of first recesses having a first diameter and a plurality of second recesses having a second diameter, wherein a first set of superhard material inserts are inserted into the plurality of first recesses and a second set of superhard material inserts are inserted into the plurality of second recesses, wherein the first diameter and the second diameter are different.

10. The cheek plate of claim 9, wherein the first and second sets of inserts are arranged in corresponding and offset Bravais lattices.11 . The cheek plate of any one of claims 5 to 10, wherein the superhard material inserts are substantially cylindrical and each of the superhard material inserts is mounted in one ofthe recesses such that the exposed surface of the superhard material insert is substantially flush with the surface of the wear face.

12. The cheek plate of any one of claims 5 to 11 , wherein the superhard material inserts comprise polycrystalline diamond mounted on a cemented carbide substrate.

13. The cheek plate of any one of the preceding claims, wherein the wear face comprises a cemented carbide, for example a cemented tungsten carbide.

14. The cheek plate of any one of claims 5 to 13, wherein the first plate is mounted on a second plate.

15. The cheek plate of claim 14, wherein the second plate comprises a steel, for example a stainless steel.

16. The cheek plate of claim 14 or claim 15, wherein the wear face further comprises a pair of third plates which flank the first plate and comprise a cemented carbide.

17. The cheek plate of claim 16, wherein the cemented carbide is a cemented tungsten carbide.

18. The cheek plate of any one of the preceding claims, wherein the wear face comprises one or more plates formed of a superhard material.

19. The cheek plate of any one of claims 5 to 18, wherein the first plate is formed of at least two plates, each of which comprises a plurality of recesses, wherein a superhard material insert is inserted into the recesses of each of the at least two plates, and wherein the diameter of the superhard material inserts inserted into the recesses of the first of the at least two plates is different to the diameter of the superhard material inserts inserted into the recesses of the second of the at least two plates.

20. The cheek plate of any one of the preceding claims, wherein the roller mill is a high- pressure grinding roller mill.

21. A roller mill comprising: a first roller and a second roller, wherein the first roller and the second roller are configured to counter-rotate to form a longitudinal nip between the first and second rollers for crushing material; wherein the first and second rollers have corresponding first and second ends;wherein the roller mill further comprises first and second cheek plates, each cheek plate according to any one of the preceding claims; wherein the wear face of the first cheek plate is in contact with and orientated substantially perpendicular to the longitudinal nip and faces the first ends of the first and second rollers; and wherein the wear face of the second cheek plate is in contact with and orientated substantially perpendicular to the longitudinal nip and faces the second ends of the first and second rollers.

22. The roller mill of claim 21 , wherein the roller mill is a high-pressure grinding roller mill.

23. Use of diamond in a cheek plate of a roller mill.

24. The use of claim 23, wherein the roller mill is a high-pressure grinding roller mill.

25. The use of claim 23 or claim 24, wherein the diamond is polycrystalline diamond (PCD).

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