Wear-resistant element

Abstract

A wear-resistant element 7 for a comminuting device comprising an attachment portion 18 and a wear-resistant portion 17 arranged along a longitudinal axis. The attachment portion 1 has an attachment e

Description

Field of the Invention This disclosure relates generally to the field of wear-resistant elements such as high-pressure grinding roller studs, for a comminuting device, for example, a high-pressure grinding roller. Such rollers are typically used for crushing rocks and minerals. Background 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. The first roller 1 is allowed to move linearly in a direction normal to the direction of the material feed. The first roller is usually biased to a particular position relative to the second roller by springs or hydraulic cylinders. 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. The use of counter-rotating rollers 1,2 allows the particle size reduction to be a continuous operation rather than a batch operation. The rollers 1,2 may have a flat surface, but in some examples (such as that shown in Figure 2) the rollers have a plurality of studs 5 disposed on the surface. Studs have the advantage of increasing the pressure where they contact the feed material and protecting the roller itself. The studs are typically made from a hard material such as cemented tungsten carbide and provide an effective roller surface. After continuous use for a period of time, the studs show signs of wear. The feed material 3 usually falls through the gap at the middle of the rollers, as shown in Figure 3. This leads to uneven wear, and the gap between the effective roller surfaces at the middle of the rollers becomes larger than the gap towards the ends of the rollers. The same situation occurs where studs are not used (as shown in Figure 3, with the gap 6 between the rollers being larger towards the middle). This reduces the efficiency of the rollers. In cases where studs are not used, the entire roller must be replaced. In cases where studs are used, the studs must either be replaced, or selectively ground down towards the ends of the rollers to ensure that the effective roller surfaces become flat again. Either way, this is a time-consuming and expensive operation. It is an object of the invention to provide an easy to manufacture option of a wear-resistant element, such as a stud, for a comminuting device, such as a high-pressure grinding roller, which requires less materials and is therefore more sustainable. Summary of the invention According to a first aspect of the invention, there is provided a wear-resistant element for a comminuting device, wherein the wear-resistant element comprises an attachment portion and a wear-resistant portion arranged along a longitudinal axis; wherein the attachment portion has an attachment end configured to connect to a comminuting device and an opposing first connection end; wherein the we ar-resista nt portion has a grinding surface configured to protrude from a wear surface of a comminuting device and an opposing second connection end; wherein the first connection end is configured to connect to the second connection end such that the attachment end of the attachment portion and the grinding surface of the wearresistant portion are at opposing longitudinal extremities of the wear-resistant element; wherein the first connection end comprises a cut-out portion which extends along the longitudinal axis and the second connection end does not comprise a protrusion which corresponds to the cut-out portion of the first connection end; and / or wherein the second connection end comprises a cut-out portion which extends along the longitudinal axis and the first connection end does not comprise a protrusion which corresponds to the cut-out portion of the second connection end. As an option, the wear-resistant element further comprises a connecting means between the first connection end and the second connection end. As an option, the first connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to a cut-out portion of the second connection end, and wherein said protrusions extend through the connecting means. As an option, the first connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to a cut-out portion of the second connection end, and wherein said protrusions extend through the connecting means and directly contact the second connection end. As an option, the second connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to a cut-out portion of the first connection end, and wherein said protrusions extend through the connecting means. As an option, the second connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to a cut-out portion of the first connection end, and wherein said protrusions extend through the connecting means and directly contact the second connection end. As an option, the protrusions on the first connection end are equiangularly arranged about the longitudinal axis. As an option, there are 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 protrusions on the first connection end. As an option, the protrusions on the second connection end are equiangularly arranged about the longitudinal axis. As an option, there are 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 protrusions on the second connection end. As an option, the second connection end comprises a cut-out portion which extends along the longitudinal axis. As an option, the connecting means at least partially fills the cut-out portion of the first connection end. As an option, the connecting means at least partially fills the cut-out portion of the second connection end. As an option, the connecting means is a braze layer. As an option, the cut-out portion of the first connection end has a cylindrical portion adjacent the connecting means and connected to a conical portion ora truncated conical portion. As an option, the cut-out portion of the second connection end has a cylindrical portion adjacent the connecting means and connected to a conical portion or a truncated conical portion. As an option, the wear-resistant element is a high-pressure grinding roller stud. As an option, the wear-resistant element is substantially cylindrical. As an option, the attachment portion comprises a first material having a first hardness, and wherein the wear-resistant portion comprises a second material having a second hardness. As an option, the hardness of the second material is greater than that of the first material. As an option, the first material comprises a steel and the second material comprises a cemented tungsten carbide. As an option, the first material has a Vickers hardness of between 100 and 500 HV30, and the second material has a Vickers hardness of between 900 and 1400 HV30. As an option, the wear resistant portion and the attachment portion have corresponding diameters and are provided in a volumetric ratio of about 1:1,2:1,3:1,4:1, or 5:1. As an option, the wear resistant portion and the attachment portion have corresponding diameters and are provided in a volumetric ratio of from about 1:1 to about 5:1. As an option, the attachment end is configured to attach to the roller by any one of the following techniques: gluing, brazing, press-fitting, shrink fitting, threaded connection and / or mechanical connection. As an option, the attachment portion further comprises a first side wall connecting the attachment end to the first connection end. As an option, the wear resistant portion further comprises a second side wall connecting the grinding surface to the second connection end. As an option, the wear resistant portion further comprises one or more circumferentially extending recesses provided in the second side wall. As an option, the cut-out portion of the first connection end and / or the cut-out portion of the second connection end has the form of a blind hole. As an option, the cut-out portion of the first connection end and / or the cut-out portion of the second connection end has the form of a through hole. As an option, the cut-out portion of the first connection end has the form of a through hole. As an option, the cut-out portion of the first connection end has the form of a blind hole. As an option, the cut-out portion of the second connection end has the form of a through hole. As an option, the cut-out portion of the second connection end has the form of a blind hole. According to a second aspect of the invention, there is provided a high-pressure grinding roller comprising a cylindrical roller having a circumferential surface, and a plurality of wear-resistant elements as described herein attached to the circumferential surface. As an option, the high-pressure grinding roller comprises a first plurality of wear-resistant elements located at a first location on the circumferential surface and a second plurality of wear-resistant elements located at a second location on the circumferential surface, each element of the first plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a first volumetric ratio, each element of the second plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a second volumetric ratio, the first and second volumetric ratios being substantially different to each other. As an option, the high-pressure grinding roller comprises a third plurality of wear-resistant elements located at a third location on the circumferential surface, each element of the third plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a third volumetric ratio, the third volumetric ratio being substantially different from the first and second volumetric ratios. As an option, each wear-resistant element is attached to the roller by any one of the following techniques: gluing, brazing, press-fitting, shrink fitting, threaded connection, and mechanical connection. According to a third aspect of the invention, there is provided a method of manufacturing a high-pressure grinding roller as described herein, the method comprising: providing a plurality of wear-resistant portions and attachment portions of wear resistant elements in a pre-defined volumetric ratio, joining together the wear-resistant portions and attachment portions of wear resistant elements using a connecting means, and attaching the plurality of wear resistant elements to the circumferential surface of the high-pressure grinding roller. According to a fourth aspect of the invention, there is provided a method of manufacturing a wear-resistant element, for example, a wear-resistant element as described herein, comprising: providing an attachment portion, wherein the attachment portion has an attachment end configured to connect to a comminuting device and an opposing first connection end, wherein the attachment portion further comprises a first side wall connecting the attachment end to the first connection end; and providing a wear-resistant portion comprising a plurality of protrusions, wherein the wearresistant portion has a grinding surface configured to protrude from a wear surface of a comminuting device and an opposing second connection end, wherein the wear resistant portion further comprises a second side wall connecting the grinding surface to the second connection end; wherein the first connection end is configured to connect to the second connection end such that the attachment end of the attachment portion and the grinding surface of the wearresistant portion are at opposing longitudinal extremities of the wear-resistant element; wherein the first connection end comprises a cut-out portion which extends along the longitudinal axis and the second connection end does not comprise a protrusion which corresponds to the cut-out portion of the first connection end; and / or wherein the second connection end comprises a cut-out portion which extends along the longitudinal axis and the first connection end does not comprise a protrusion which corresponds to the cut-out portion of the second connection end; wherein the second connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to the cut-out portion of the first connection end; placing a braze material in the cut-out portion of the attachment portion and / or in the cut-out portion of the wear-resistant portion; positioning the plurality of protrusions of the second connection end on the first connection end such that the first side wall of the attachment portion is in longitudinal alignment with the second side wall of the wear resistant portion; attaching the protrusions to the attachment portion to form a pre-connection assembly; and heating the pre-connection assembly so as to form a braze layer between the wear-resistant portion and the attachment portion, wherein the plurality of protrusions extends through the braze layer, thereby forming a wear-resistant element. As an option, the first connection end further comprises a plurality of protrusions. According to a fifth aspect of the invention, there is provided a method of manufacturing a wear-resistant element, for example, a wear-resistant element as described herein, comprising: providing an attachment portion, wherein the attachment portion has an attachment end configured to connect to a comminuting device and an opposing first connection end, wherein the attachment portion further comprises a first side wall connecting the attachment end to the first connection end; and providing a wear-resistant portion, wherein the wear-resistant portion has a grinding surface configured to protrude from a wear surface of a comminuting device and an opposing second connection end, wherein the wear resistant portion further comprises a second side wall connecting the grinding surface to the second connection end; wherein the first connection end is configured to connect to the second connection end such that the attachment end of the attachment portion and the grinding surface of the wearresistant portion are at opposing longitudinal extremities of the wear-resistant element; wherein the first connection end comprises a cut-out portion which extends along the longitudinal axis; wherein the first connection end comprises a plurality of protrusions; placing a braze material in the cut-out portion of the attachment portion; positioning the second connection end on the plurality of protrusions of the first connection end such that the first side wall of the attachment portion is in longitudinal alignment with the second side wall of the wear resistant portion; attaching the protrusions to the wear-resistant portion to form a pre-connection assembly; and heating the pre-connection assembly so as to form a braze layer between the wear-resistant portion and the attachment portion, wherein the plurality of protrusions extends through the braze layer, thereby forming a wear-resistant element. As an option, the second connection end further comprises a plurality of protrusions. According to a sixth aspect of the invention, there is provided a method of manufacturing a wear-resistant element, for example, a wear-resistant element as described herein, comprising: providing an attachment portion, wherein the attachment portion has an attachment end configured to connect to a comminuting device and an opposing first connection end, wherein the attachment portion further comprises a first side wall connecting the attachment end to the first connection end; and providing a wear-resistant portion, wherein the wear-resistant portion has a grinding surface configured to protrude from a wear surface of a comminuting device and an opposing second connection end, wherein the wear resistant portion further comprises a second side wall connecting the grinding surface to the second connection end; wherein the first connection end is configured to connect to the second connection end such that the attachment end of the attachment portion and the grinding surface of the wearresistant portion are at opposing longitudinal extremities of the wear-resistant element; wherein the second connection end comprises a cut-out portion which extends along the longitudinal axis; wherein the second connection end comprises a plurality of protrusions; placing a braze material in the cut-out portion of the wear-resistant portion; positioning the first connection end on the plurality of protrusions of the second connection end such that the first side wall of the attachment portion is in longitudinal alignment with the second side wall of the wear resistant portion; attaching the protrusions to the wear-resistant portion to form a pre-connection assembly; and heating the pre-connection assembly so as to form a braze layer between the wear-resistant portion and the attachment portion, wherein the plurality of protrusions extends through the braze layer, thereby forming a wear-resistant element. As an option, the method of the fourth, fifth or sixth aspects does not comprise a step of grinding the attachment portion after the brazing step. 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 illustrates schematically a known high-pressure grinding roller apparatus; Figure 2 shows rollers comprising studs; Figure 3 illustrates schematically a plan view of a pair of rollers after use; Figure 4 is a side elevation view of a first exemplary high-pressure grinding roller stud; Figure 5 is a side elevation view of a second exemplary high-pressure grinding roller stud; Figure 6 is a side elevation view of a third exemplary high-pressure grinding roller stud; Figure 7 is a side elevation view of a fourth exemplary high-pressure grinding roller stud; Figure 8 is a cross-sectional view of one embodiment of the high-pressure grinding roller stud of Figure 4; Figure 9 is a cross-sectional view of another embodiment of the high-pressure grinding roller stud of Figure 4; Figure 10 is a top plan view of an attachment portion of the high-pressure grinding roller stud of any of Figures 4 to 9; Figure 11 is a cross-sectional view of another embodiment of the high-pressure grinding roller stud of Figure 4; Figure 12 is a cross-sectional view of another embodiment of the high-pressure grinding roller stud of Figure 4; Figure 13 is a cross-sectional view of another embodiment of the high-pressure grinding roller stud of Figure 4; Figure 14 is a side elevation view of a wear-resistant portion of a high-pressure grinding roller stud; Figure 15 is a bottom plan view of a wear-resistant portion of the high-pressure grinding roller stud of Figure 14; Figure 16 is a bottom plan view of an alternative embodiment of a wear-resistant portion of a high-pressure grinding roller stud; Figure 17 is a side elevation view of a fifth exemplary high-pressure grinding roller stud; Figure 18 is a side elevation view of the fifth exemplary high-pressure grinding roller stud after brazing; Figure 19 is a cross-sectional view of the high-pressure grinding roller stud of Figure 18; Figure 20 is a cross-sectional view of another embodiment of the high-pressure grinding roller stud of Figure 18; Figure 21 is a cross-sectional view of another embodiment of the high-pressure grinding roller stud of Figure 18; Figure 22 is a schematic cross-section view of a high-pressure grinding roller incorporating an exemplary grinding roller stud; Figure 23 is a schematic cross-section view of a high-pressure grinding roller incorporating an exemplary high-pressure grinding roller stud which includes a circumferentially extending recess; Figure 24 is a schematic cross-section view of the high-pressure grinding roller of Figure 19 showing wear; Figure 25 is a flow diagram showing a first method of manufacturing a wear-resistant element according to the invention; Figure 26 is a flow diagram showing a second method of manufacturing a wear-resistant element according to the invention; and Figure 27 is a flow diagram showing a third method of manufacturing a wear-resistant element according to the invention. In the drawings, similar parts have been assigned similar reference numerals. Detailed Description Referring to Figure 4, a high-pressure grinding roller stud 7 is provided. The high-pressure grinding roller stud 7 is elongate and has a central longitudinal axis L. The high-pressure grinding roller stud 7 comprises a wear-resistant portion 17 and an attachment portion 18 joined by connecting means 19. The attachment portion 18 comprises a first material and the wear-resistant portion 17 comprises a second material. Preferably, the attachment portion 18 consists of a first (bulk) material and the wear-resistant portion 17 consists of a second (bulk) material. Wear resistance of the first and second materials is substantially different to each other. Hardness is used as an indirect measure (or proxy) for wear resistance. The first material may have a Vickers hardness of 100 to 500 HV30. The second material may have a Vickers hardness of 900 to 1400 HV30. The wear resistance of the wear-resistant portion 17 is higher than the wear resistance of the attachment portion 18. Preferably, the material of the wear-resistant portion 17 is a cemented metal carbide, for example a cemented tungsten carbide, and the material of the attachment portion 18 is a steel. The wear-resistant portion 17 is preferably a tungsten carbide grade of material with an 8 to 20 wt.% cobalt content. The medium grain size in the structure may be 2 to 5 pm. The attachment portion 18 may be a standard tool or construction steel. The stud 7 is substantially cylindrical, and typically circular in axial cross-section. Thus, each of the wear-resistant portion 17 and the attachment portion 18 is also circular in axial crosssection. The length of the stud 7 is typically up to 70 mm. Preferably, the length of each stud is between 20 and 80 mm. More preferably, the length of each stud is between 40 and 70 mm. The wear-resistant portion 17 and the attachment portion 18 may be joined by connecting means 19 using any one or more of the following techniques: brazing (e.g. silver braze, copper braze, brass braze and the like), gluing (e.g. epoxy, 2 component glue and the like), friction welding, welding, laser welding or threaded connection. In one embodiment, as indicated in Figure 4, the volumetric ratio of the wear resistant portion 17 to the attachment portion 18 is approximately 1:1. In another embodiment, as indicated in Figure 5, the volumetric ratio of the wear resistant portion 17 to the attachment portion 18 is approximately 2:1. Thus, each of the wear-resistant portion 17 and the attachment portion 18 is cylindrical with two different lengths. In another embodiment, as indicated in Figure 6, the volumetric ratio of the wear-resistant portion 17 to the attachment portion 18 is approximately 3:1. In a further embodiment, as indicated in Figure 7, the volumetric ratio of the we ar-resista nt portion 17 to the attachment portion 18 is approximately 4:1. The volumetric ratio is influenced by the strength of the joining technique used. For example, with a strong braze as the connecting means 19, the attachment portion 18 may be made longer than it could be otherwise because it is able to withstand the applied forces during use when the connecting means 19 of the stud 7 is no longer directly supported within a roller 12. A volumetric ratio of 5:1 is also envisaged. In all of these embodiments, the diameter of the wear-resistant portion 17 corresponds to that of the attachment portion 18. The attachment portion 18 has an attachment end 9 configured to connect to a comminuting device and an opposing first connection end 24. The attachment end 9 and the first connection end 24 are connected by a first side wall 10a. The wear resistant portion 17 has a grinding surface 8 arranged to contact the material to be ground. A second connection end 25 is located at the opposite end of the wear resistant portion 17 to the grinding surface 8. The grinding surface 8 and the second connection end 25 are connected by a second side wall 10b. The wear-resistant portion 17 includes the grinding surface 8 and the attachment portion 18 includes the attachment end 9. As shown in the schematic cross-sectional view of Figure 8, in one embodiment, the attachment portion 18 comprises a cut-out portion 20. The cut-out portion 20 extends along the longitudinal axis L from the first connection end 24 towards the attachment end 9. In the embodiment depicted in Figure 8, the cut-out portion 20 is in the form of a blind hole in the attachment portion 18, wherein the blind hole faces the second connection end 25 of the wearresistant portion 17. However, in the embodiment depicted in Figure 9, the cut-out portion 20 is in the form of a through hole which extends through the attachment portion 18. Specifically, the through hole extends from the first connection end 24 to the attachment end 9. It has been found that when a through hole is used as the cut-out portion 20 in the attachment portion 18, a better flow of braze material is enabled which results in a stronger braze connection than when a blind hole is used as the cut-out portion 20 in the attachment portion 18. Furthermore, use of a through hole prevents build-up of gas pressure in the cut-out portion during brazing. A top plan view of the attachment portion 18 of the embodiments of Figures 8 and 9 is shown in Figure 10. As can be seen, the cut-out portion 20 has a circular cross-section and is coaxial with the cylindrical body of the attachment portion 18. While a circular cross-section is shown in Figure 10, the shape of the cross-section of the cut-out portion 20 is not particularly limited, though simpler shapes are simpler to machine. In this embodiment, the cut-out portion 20 has a cylindrical profile. The cut-out portion 20 may have a stepped or tapered profile. Where the cut-out portion 20 is a blind hole, the cut-out portion 20 may have an initial portion adjacent to the connecting means 19 with a cylindrical profile and a further conical portion which tapers to a point. Alternatively, the further conical portion may have the form of a truncated cone, terminating in a flat planar surface. The cut-out portion 20, or the bore of the cut-out portion 20, may have a longest linear axial dimension of from 5% of the longest linear axial dimension of the attachment portion to 70% of the longest linear axial dimension of the attachment portion, for example from 10% of the longest linear axial dimension of the attachment portion to 60% of the longest linear axial dimension of the attachment portion, for example from 15% of the longest linear axial dimension of the attachment portion to 50% of the longest linear axial dimension of the attachment portion, for example from 20% of the longest linear axial dimension of the attachment portion to 40% of the longest linear axial dimension of the attachment portion, for example from 30% of the longest linear axial dimension of the attachment portion to 40% of the longest linear axial dimension of the attachment portion. The cut-out portion 20 may have a longest linear axial dimension of at least 5%, or at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 30%, or at least 35% of the longest linear axial dimension of the attachment portion. The cut-out portion 20 may have a longest linear axial dimension of at most 70%, or at most 65%, or at most 60%, or at most 55%, or at most 50%, or at most 45%, or at most 40% of the longest linear axial dimension of the attachment portion. For example, where both the attachment portion 18 and the cut-out portion 20 are cylindrical and the attachment portion 18 has a diameter of 20 mm and the cut-out portion has a diameter of 7 mm, then the longest linear axial dimension (i.e. the diameter) of the cut-out portion 20 would be 35% of the longest linear axial dimension (i.e. the diameter) of the attachment portion 18. When the cut-out portion 20 is in the form of a blind hole, the maximum length of the cut-out portion 20, measured along the longitudinal axis, may be from 5% of the total length of the attachment portion, measured along the longitudinal axis, to 95% of the total length of the attachment portion, measured along the longitudinal axis, for example from 10% of the total length of the attachment portion, measured along the longitudinal axis, to 90% of the total length of the attachment portion, for example from 15% of the total length of the attachment portion, measured along the longitudinal axis, to 85% of the total length of the attachment portion, for example from 20% of the total length of the attachment portion, measured along the longitudinal axis, to 80% of the total length of the attachment portion, measured along the longitudinal axis, for example from 25% of the total length of the attachment portion, measured along the longitudinal axis, to 75% of the total length of the attachment portion, measured along the longitudinal axis, for example from 30% of the total length of the attachment portion, measured along the longitudinal axis, to 70% of the total length of the attachment portion, measured along the longitudinal axis, for example from 35% of the total length of the attachment portion, measured along the longitudinal axis, to 65% of the total length of the attachment portion, measured along the longitudinal axis, for example from 40% of the total length of the attachment portion, measured along the longitudinal axis, to 60% of the total length of the attachment portion, measured along the longitudinal axis, for example from 45% of the total length of the attachment portion, measured along the longitudinal axis, to 55% of the total length of the attachment portion, measured along the longitudinal axis. The maximum length of the cut-out portion 20, measured along the longitudinal axis, may be at least 5%, or at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 30%, or at least 35%, or at least 40%, or at least 45% of the total length of the attachment portion, measured along the longitudinal axis. The maximum length of the cut-out portion 20, measured along the longitudinal axis, may be at most 95%, or at most 90%, or at most 85%, or at most 80%, or at most 75%, or at most 70%, or at most 65%, or at most 60%, or at most 55%, or at most 50% of the total length of the attachment portion, measured along the longitudinal axis. For example, where both the total length of the attachment portion 18 is 25 mm and the maximum length of the cut-out portion 20 as measured along the longitudinal axis is 15 mm, then the maximum length of the cut-out portion 20 would be 60% of the total length of the attachment portion 18. As depicted in Figure 11, as an alternative to the embodiment of Figure 8, instead of having a cut-out portion 20 in the attachment portion 18, a cut-out portion 21 can be provided in the wear-resistant portion 17. In this embodiment, the cut-out portion 21 is in the form of a blind hole in the we ar-resista nt portion 17, wherein the blind hole faces the first connection end 24 of the attachment portion 18. While in principle cut-out portion 21 could also be provided in the form of a through hole, in practice this is not favoured as a through hole in the wearresistant portion 17 would greatly reduce the lifetime of the wear-resistant portion 17. The cutout portion 21 extends along the longitudinal axis L. In this embodiment, the cut-out portion 21 has a circular cross-section and is coaxial with the cylindrical body of the wear-resistant portion 17. However, the shape of the cross-section of the cut-out portion 21 is not particularly limited, though simplershapes are simpler to machine. In this embodiment, the cut-out portion 21 has a cylindrical profile. The cut-out portion 21 may have a stepped or tapered profile. The cut-out portion 21 may have an initial portion adjacent to the connecting means 19 with a cylindrical profile and which adjoins a further conical portion which tapers to a point. Alternatively, the further conical portion may have the form of a truncated cone, terminating in a flat planar surface. The cut-out portion 21, or the bore of the cut-out portion 21, may have a longest linear axial dimension of from 5% of the longest linear axial dimension of the wear-resistant portion to 70% of the longest linear axial dimension of the wear-resistant portion, for example from 10% of the longest linear axial dimension of the wear-resistant portion to 60% of the longest linear axial dimension of the wear-resistant portion, for example from 15% of the longest linear axial dimension of the wear-resistant portion to 50% of the longest linear axial dimension of the wear-resistant portion, for example from 20% of the longest linear axial dimension of the wearresistant portion to 40% of the longest linear axial dimension of the we ar-resista nt portion, for example from 30% of the longest linear axial dimension of the wear-resistant portion to 40% of the longest linear axial dimension of the wear-resistant portion. The cut-out portion 21 may have a longest linear axial dimension of at least 5%, or at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 30%, or at least 35% of the longest linear axial dimension of the wear-resistant portion. The cut-out portion 21 may have a longest linear axial dimension of at most 70%, or at most 65%, or at most 60%, or at most 55%, or at most 50%, or at most 45%, or at most 40% of the longest linear axial dimension of the wear-resistant portion. For example, where both the wear-resistant portion 18 and the cut-out portion 21 are cylindrical and the wear-resistant portion 17 has a diameter of 20 mm and the cut-out portion 21 has a diameter of 7 mm, then the longest linear axial dimension (i.e. the diameter) of the cut-out portion 21 would be 35% of the longest linear axial dimension (i.e. the diameter) of the wearresistant portion 17. The maximum length of the cut-out portion 21, measured along the longitudinal axis, may be from 5% of the total length of the wear-resistant portion, measured along the longitudinal axis, to 95% of the total length of the wear-resistant portion, measured along the longitudinal axis, for example from 10% of the total length of the wear-resistant portion, measured along the longitudinal axis, to 90% of the total length of the wear-resistant portion, for example from 15% of the total length of the wear-resistant portion, measured along the longitudinal axis, to 85% of the total length of the wear-resistant portion, for example from 20% of the total length of the wear-resistant portion, measured along the longitudinal axis, to 80% of the total length of the wear-resistant portion, measured along the longitudinal axis, for example from 25% of the total length of the wear-resistant portion, measured along the longitudinal axis, to 75% of the total length of the wear-resistant portion, measured along the longitudinal axis, for example from 30% of the total length of the wear-resistant portion, measured along the longitudinal axis, to 70% of the total length of the wear-resistant portion, measured along the longitudinal axis, for example from 35% of the total length of the wear-resistant portion, measured along the longitudinal axis, to 65% of the total length of the wear-resistant portion, measured along the longitudinal axis, for example from 40% of the total length of the wear-resistant portion, measured along the longitudinal axis, to 60% of the total length of the wear-resistant portion, measured along the longitudinal axis, for example from 45% of the total length of the wearresistant portion, measured along the longitudinal axis, to 55% of the total length of the wearresistant portion, measured along the longitudinal axis. The maximum length of the cut-out portion 21, measured along the longitudinal axis, may be at least 5%, or at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 30%, or at least 35%, or at least 40%, or at least 45% of the total length of the wear-resistant portion, measured along the longitudinal axis. The maximum length of the cut-out portion 20, measured along the longitudinal axis, may be at most 95%, or at most 90%, or at most 85%, or at most 80%, or at most 75%, or at most 70%, or at most 65%, or at most 60%, or at most 55%, or at most 50% of the total length of the wear-resistant portion, measured along the longitudinal axis. For example, where both the total length of the wear-resistant portion 17 is 25 mm and the maximum length of the cut-out portion 21 as measured along the longitudinal axis is 15 mm, then the maximum length of the cut-out portion 21 would be 60% of the total length of the wear-resistant portion 17. Typically, where there is a cut-out portion 21, its total length is at most 50% of the total length of the wear-resistant portion, because removal of too much of the wear-resistant portion by formation of a cut-out 21 could weaken the wear-resistant portion to the point where it can no longer properly perform its function. As depicted in Figure 12, in a further embodiment both the attachment portion 18 comprises a cut-out portion 20 as described above and the wear-resistant portion 17 comprises a cut-out portion 21 as described above. While in this embodiment the cut-out portions 20, 21 are mirror images of each other, this is not necessary. Preferably the bores of the cut-out portions 20, 21 correspond with each other, but the length and cross-sectional shape of the cut-out portions 20, 21 can be adapted and altered as required. For example, and as shown in Figure 13, the cut-out portion 21 is likely to be a lower proportion of the wear-resistant portion 17 than the cut-out portion 20 is of the attachment portion 18, because removal of too much of the wearresistant portion by formation of a cut-out 21 could weaken the we ar-resista nt portion to the point where it can no longer properly perform its function. The cut-out portions 20, 21 may have differing depths and / or diameters, so long as at least a portion of the cut-out portions 20, 21 overlap. An example of this is shown in Figure 13, where cut-out portion 20 has a larger diameter and a greater depth than cut-out portion 21. The use of cut-out portion 20 and / or cut-out portion 21 advantageously allows the provision of a robust, fit-for-purpose high-pressure grinding roller stud which is more sustainable as less material is required. Furthermore, and as detailed below, the provision of a cut-out portion provides an improved method of manufacturing the high-pressure grinding roller stud. As depicted in Figure 14, the second connection end 25, i.e. the connection end of the wearresistant portion 17, may comprise a plurality of protrusions 22 which do not correspond to a cut-out portion 20 of the first connection end 24, and wherein said protrusions 22 extend into the connecting means 19. In this embodiment, the protrusions 22 extend through the connecting means 19 and directly contact the first connection end 24. As an example, these protrusions 22 can be spaced evenly around the periphery of the second connection end 25. Such an arrangement is depicted in Figure 15, which shows six protrusions 22 evenly spaced around the periphery of the second connection end 25. Specifically, the protrusions 22 are equiangularly arranged on the second connection end 25 about the central longitudinal axis L. In this embodiment, the angular spacing $ between adjacent protrusions 22 is 60 degrees since there are 6 protrusions 22. In another embodiment, (not shown), the angular spacing $ between the adjacent protrusions 22 is 120 degrees since there are 3 protrusions 22. Any number of protrusions 22 may be arranged on the second connection end 25, as long as none of them correspond to a cut-out portion 20 in the attachment portion 18. For example, the number of protrusions 22 may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12. The protrusions 22 help to create a small gap Gi (as shown in Figure 17) between the wear-resistant portion 17 and the attachment portion 18. For example, the gap Gi may be from 0.1 mm to 1 mm, for example from 0.1 mm to 0.5 mm, for example from 0.2 mm to 0.4 mm. Where the wear-resistant portion 17 and the attachment portion 18 are joined by brazing, the protrusions 22 further increase the surface area of the wear-resistant portion 17 against which the braze bonds, yet further enhancing the shear strength of the join. When the plurality of protrusions 22 is provided, the first and second connection ends 24, 25 face each other but, aside from any protrusions 22, they do not abut one another. In the embodiment shown in Figure 15, the wear-resistant portion 17 does not comprise a cutout portion 21. However, the plurality of protrusions 22 can be combined with a cut-out portion 21 in the wear-resistant portion 17, as depicted in Figure 16. While in the embodiments disclosed herein the protrusions 22 are on the wear-resistant portion 17, they could also (i.e. in addition to the wear-resistant portion 17) or alternatively be on the attachment portion 18. Protrusions 22 on the attachment portion 18 can be arranged in the same way as those on the wear-resistant portion 17. If protrusions 22 are present on both the wear-resistant portion 17 and the attachment portion 18, they would typically be arranged so that none of the protrusions on the wear-resistant portion 17 are in contact with any of the protrusions on the attachment portion 18. In the embodiment depicted in Figure 17, there is a plurality of protrusions 22 on the wearresistant portion 17 (only one is labelled on the Figure for simplicity, but four are visible). Figure 17 depicts the wear-resistant element 7 in an assembled position prior to joining of the wear-resistant portion 17 and the attachment portion 18 by a bonding layer which forms the connecting means 19, in this case a braze layer. A schematic depiction of the embodiment of Figure 17 after brazing is shown in Figure 18, where the connecting means 19 is formed of a braze layer. A cross-sectional view of the brazed wear-resistant element is shown in Figure 19. Here, the protrusions 22 can be seen penetrating the connecting means 19. Additionally, it can be seen that some of the braze used to form the connecting means 19 has partially filled the cut-out portion 20. Thus, in the brazed wear-resistant element, there is a void formed from the remains of cut-out portion 20, which is effectively capped by a braze plug. A similar void formation may also be observed in the above embodiment in which the wear-resistant portion 18 also comprises a cut-out portion 21. Advantageously, the combination of the above-mentioned plurality of protrusions 22 and cutout portion 20 and / or cut-out portion 21 facilitates a simpler manufacturing process for the stud. Where there is a planar interface between the wear-resistant portion 17 and the attachment portion 18, it is necessary to provide some means for pre-positioning of the wearresistant portion 17 and the attachment portion 18 prior to brazing. This can, for example, take the form of a circumferential peripheral ridge provided on the attachment portion 18 into which the wear-resistant portion 17 can be seated. However, the disadvantage of the provision of such a circumferential peripheral ridge is that it must be removed post-brazing, for example by grinding, and this adds a laborious step to the manufacturing process. The provision of the plurality of protrusions 22 allows the pre-positioning to be performed using a simple technique such as resistance welding to create a weak bond between the plurality of protrusions 22 and the attachment portion 18 and / or the wear resistant portion 17 (depending on where the plurality of protrusions 22 are positioned). Placing the braze inside the cut-out portion 20 and / or the cut-out portion 21 allows this welding process, which requires direct contact between the plurality of protrusions 22 and the attachment portion 18 and / or the wear resistant portion 17, to occur, and the braze is then ready for the subsequent brazing step. The stud 7 is typically inverted during the brazing process, such that the attachment portion 18 is above the wear-resistant portion 17. Thus, the combination of the plurality of protrusions 22 and the cut-out portion 20 and / or the cut-out portion 21 facilitates manufacturing of the composite stud, thereby providing time savings. As shown in Figure 20, instead of a cut-out portion 20 in the form of a blind hole as depicted in Figure 19, the cut-out portion 20 may be in the form of a through hole. As noted above, the provision of the cut-out portion 20 in the form of a through hole helps to provide a stronger braze connection between the attachment portion 18 and the wear-resistant portion 17. As shown in Figure 21, instead of a cut-out portion 20 in the form of a blind hole as depicted in Figure 19, the cut-out portion 20 may be in the form of a through hole, and the we ar-resista nt portion 17 may further comprise a cut-out portion 21 in the form of a blind hole. Optionally, as indicated in Figures 23 and 24, a circumferential recess 11 may extend around the second side wall 10b. However, the circumferential recess 11 is not essential to the invention and may be omitted. A recess 11 enables the selective removal of the grinding surface 8 to reveal a fresh grinding surface adjacent the recess when the initial grinding surface is removed. Turning now to Figure 22, in use, the stud 7 is attached to a high-pressure grinding roller 12 toward the attachment end 9. The stud 7 is received into and seated within a pocket in the surface of the roller 12. Such attachment may be by any suitable means, such as gluing, brazing, shrink fitting, press fitting and so on. A plurality of studs is attached to the grinding roller 12 such that the grinding surface 8 of each stud 7 is at a desired height, and the plurality of grinding surfaces 8 forms an effective roller surface, as indicated in Figure 22. The effective surface of the roller 12 is indicated by dashed line 13. Preferably, the proportion of the stud 7 seated below the surface of the grinding roller 12 is at least 80% of the total volume of the stud 7. The proportion of the stud 7 seated below the surface of the grinding roller 12 may be at least 40%, preferably at least 50%, more preferably at least 60% and optionally above 70% of the total volume of the stud 7. This proportion is influenced by the technique used to produce the connection by the connecting means 19. As discussed above, after a period of use, the studs 7 towards the middle of the grinding roller 12 are likely to have been subjected to more wear than the studs 7 towards the ends of the grinding roller, and so the effective grinding surface is no longer flat (or the desired shape profile). This is illustrated in Figure 23. The studs 14 towards the centre of the roller 12 experience more wear than the studs at either end of the roller 12, and so the effective surface is increasingly no longer flat and gradually resembles the curved surface shown in Figure 3. In addition to stud wear, the roller 12, which is typically steel, also experiences wear and lower portions of the stud 7 gradually become exposed. Consequently, the connecting means 19 is preferably located beneath the surface of the roller 19. It is useful to tailor the ratio of the wear-resistant portion 17 and the attachment portion 18 according to the position of the stud 7 along the length of the roller 12. The studs 7 located towards the centre of the roller 14 may include a greater proportion of wear-resistant portion 17 to attachment portion 18 than the studs 7 located towards the ends of the roller 12. For example, the studs 7 towards the centre of the roller 12 may comprise wear-resistant portion 17 and attachment portion 18 in a volumetric ratio of 3:1, whereas the studs 7 located towards the ends of the roller 12 may be present in a volumetric ratio of 1:1 since they will experience less wear. Note that while the effective roller surface 16 is shown as being substantially flat and parallel to the axis of rotation of the roller 12, a profiled effective grinding surface may be implemented instead. A flow diagram summarising a first method of manufacturing a wear-resistant element, for example, the above-mentioned composite stud, is shown in Figure 25. The first method has the steps S1-S4. S1. Providing an attachment portion (i.e. of a wear-resistant element) comprising a first connection end, wherein the first connection end comprises a cut-out portion, and a wearresistant portion comprises a second connection end which comprises a plurality of protrusions which do not correspond to the cut-out portion of the first connection end. The attachment portion has an attachment end configured to connect to a comminuting device and which opposes the first connection end. The attachment portion further comprises a first side wall connecting the attachment end to the first connection end. The wear-resistant portion has a grinding surface configured to protrude from a wear surface of a comminuting device and an opposing second connection end. The wear resistant portion further comprises a second side wall connecting the grinding surface to the second connection end. The first connection end is configured to connect to the second connection end such that the attachment end of the attachment portion and the grinding surface of the wear-resistant portion are at opposing longitudinal extremities of the wear-resistant element. The cut-out portion of the first connection end extends along the longitudinal axis. As detailed above, the cut-out portion may be a blind hole or a through hole. The second connection end does not comprise a protrusion which corresponds to the cut-out portion of the first connection end. S2. Placing a braze material in the cut-out portion of the attachment portion. The braze material may be in any suitable form, for example, the form of a rod. S3. Positioning the plurality of protrusions of the second connection end on the first connection end. This step is done such that the first side wall of the attachment portion is in longitudinal alignment with the second side wall of the wear resistant portion. S4. Attaching the protrusions to the attachment portion, for example, by resistance welding, to form a pre-connection assembly. S5. Heating the pre-connection assembly so as to form a braze layer between the wearresistant portion and the attachment portion, wherein the plurality of protrusions extends through the braze layer, thereby forming a wear-resistant element. In an alternative embodiment of the first method, the second connection end rather than the first connection end comprises a cut-out portion, the first connection end rather than the second connection end comprises a plurality of protrusions which do not correspond to the cut-out portion of the second connection end, and the braze material is placed in the cut-out portion of the second connection end. As detailed above, the cut-out portion may be a blind hole or a through hole. A second example method of manufacturing a wear-resistant element is shown in Figure 26. Instead of the plurality of protrusions being provided on the wear-resistant portion, they can instead be provided on the attachment portion. S1. Providing an attachment portion comprising a first connection end and a we ar-resista nt portion comprising a second connection end, wherein the first connection end comprises a cut-out portion and a plurality of protrusions. S2. Placing a braze material in the cut-out portion of the attachment portion (as above). S3. Positioning the second connection end of the wear resistant portion on the plurality of protrusions on the first connection end of the attachment portion. This step is done such that the first side wall of the attachment portion is in longitudinal alignment with the second side wall of the wear resistant portion. S4. Attaching the protrusions to the wear-resistant portion, for example, by resistance welding, to form a pre-connection assembly. S5. Heating the pre-connection assembly so as to form a braze layer between the wearresistant portion and the attachment portion, wherein the plurality of protrusions extends through the braze layer, thereby forming a wear-resistant element. In an alternative embodiment of the second method, the second connection end rather than the first connection end comprises a cut-out portion, the second connection end rather than the first connection end comprises a plurality of protrusions, and the braze material is placed in the cut-out portion of the second connection end. In a third exemplary method, as outlined in Figure 27, a plurality of protrusions can be provided on both the attachment portion and the wear-resistant portion. In an alternative embodiment of the third method, the second connection end rather than the first connection end comprises a cut-out portion. In any of the above methods, both the first and second connection ends may comprise cutout portions. In such an embodiment, the braze material may either be placed in the cut-out portion of only one of the first and second connection ends, or it may be placed in both cutout portions. As detailed above, the cut-out portion(s) may be a blind hole or a through hole. In all of the above methods, it is advantageously not required to perform a grinding step to remove any locating means from the attachment portion after the brazing step. This simplifies the manufacturing method. The high-pressure grinding roller stud as described herein enables the provision of a more sustainable high-pressure grinding roller than what has been previously available. Furthermore, each composite stud has a better fit in the steel cylinder of the high-pressure grinding roller because the portion of the stud in contact with the roller will have a much more closely matched hardness to the steel than a stud with higher wear resistance (and therefore hardness). The combination of materials in the stud provides a visual indicator of wear marking too, useful as a maintenance control function, enabling operators to better determine when the roller surface needs to be redressed. Lastly, combination material studs also provide for the higher utilisation of tungsten carbide. 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. For example, other types of material could be used, such as hardened steel, and the stud may have a shape other than cylindrical as described in the examples. Claims 1. A wear-resistant element for a comminuting device, wherein the wear-resistant element comprises an attachment portion and a we ar-resista nt portion arranged along a longitudinal axis; wherein the attachment portion has an attachment end configured to connect to a comminuting device and an opposing first connection end; wherein the wear-resistant portion has a grinding surface configured to protrude from a wear surface of a comminuting device and an opposing second connection end; wherein the first connection end is configured to connect to the second connection end such that the attachment end of the attachment portion and the grinding surface of the wearresistant portion are at opposing longitudinal extremities of the wear-resistant element; wherein the second connection end comprises a cut-out portion which extends along the longitudinal axis and the first connection end does not comprise a protrusion which corresponds to the cut-out portion of the second connection end. 2. The wear-resistant element of claim 1, further comprising a connecting means between the first connection end and the second connection end. 3. The wear-resistant element of claim 2, wherein the first connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to a cut-out portion of the second connection end, and wherein said protrusions extend through the connecting means. 4. The wear-resistant element of claim 2 or claim 3, wherein the second connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to a cut-out portion of the first connection end, and wherein said protrusions extend through the connecting means. 5. The we ar-resista nt element of claim 3 or claim 4, wherein the protrusions on the first connection end are equiangularly arranged about the longitudinal axis. 6. The wear-resistant element of claim 4 or claim 5, wherein the protrusions on the second connection end are equiangularly arranged about the longitudinal axis. 7. The wear-resistant element of any one of the preceding claims, wherein the first connection end comprises a cut-out portion which extends along the longitudinal axis. 8. The wear-resistant element of any one of claims 2 to 7, wherein the connecting means at least partially fills the cut-out portion of the second connection end. 9. The wear-resistant element of claim 7 or claim 8, wherein the connecting means at least partially fills the cut-out portion of the first connection end. 10. The wear-resistant element of any one of claims 2 to 9, wherein the connecting means is a braze layer. 11. The wear-resistant element of any one of the preceding claims, wherein the cut-out portion of the second connection end has a cylindrical portion adjacent the connecting means and connected to a conical portion ora truncated conical portion. 12. The wear-resistant element of any one of the preceding claims, wherein the wearresistant element is a high-pressure grinding roller stud. 13. The wear-resistant element of any one of the preceding claims, wherein the wearresistant element is substantially cylindrical. 14. The wear-resistant element of any one of the preceding claims, wherein the attachment portion comprises a first material having a first hardness, and wherein the we ar-resista nt portion comprises a second material having a second hardness; wherein the hardness of the second material is greater than that of the first material. 15. The wear-resistant element of claim 14, wherein the first material comprises a steel and the second material comprises a cemented tungsten carbide. 16. The wear-resistant element of claim 14 or claim 15, wherein the first material has a Vickers hardness of between 100 and 500 HV30, and the second material has a Vickers hardness of between 900 and 1400 HV30. 17. The wear-resistant element of any of the preceding claims, wherein the wear resistant portion and the attachment portion have corresponding diameters and are provided in a volumetric ratio of from 1:1 to 5:1. 18. The insert of any one of the preceding claims, wherein the cut-out portion of the second connection end has the form of a blind hole. 19. The insert of any one of the preceding claims, wherein the cut-out portion of the second end has the form of a through hole. 20. The insert of any one of the preceding claims, wherein the cut-out portion of the first connection end has the form of a blind hole. 21. The insert of any one of the preceding claims, wherein the cut-out portion of the first connection end has the form of a through hole. 22. A high-pressure grinding roller comprising a cylindrical roller having a circumferential surface, and a plurality of wear-resistant elements as claimed in any one of the preceding claims attached to the circumferential surface. 23. A high-pressure grinding roller as claimed in claim 22, comprising a first plurality of wear-resistant elements located at a first location on the circumferential surface and a second plurality of wear-resistant elements located at a second location on the circumferential surface, each element of the first plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a first volumetric ratio, each element of the second plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a second volumetric ratio, the first and second volumetric ratios being substantially different to each other. 24. A high-pressure grinding roller as claimed in claim 23, comprising a third plurality of wear-resistant elements located at a third location on the circumferential surface, each element of the third plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a third volumetric ratio, the third volumetric ratio being substantially different from the first and second volumetric ratios. 25. A high-pressure grinding roller as claimed in any one of claims 22 to 24, wherein each wear-resistant element is attached to the roller by any one of the following techniques: gluing, brazing, press-fitting, shrink fitting, threaded connection, and mechanical connection. Amendments to the claims have been filled as follows Claims 1. A wear-resistant element for a comminuting device, wherein the wear-resistant element comprises an attachment portion and a we ar-resista nt portion arranged along a longitudinal axis; wherein the attachment portion has an attachment end configured to connect to a comminuting device and an opposing first connection end; wherein the wear-resistant portion has a grinding surface configured to protrude from a wear surface of a comminuting device and an opposing second connection end; wherein the first connection end is configured to connect to the second connection end such that the attachment end of the attachment portion and the grinding surface of the wearresistant portion are at opposing longitudinal extremities of the wear-resistant element; wherein the second connection end comprises a cut-out portion which extends along the longitudinal axis and the first connection end does not comprise a protrusion which corresponds to the cut-out portion of the second connection end; wherein the wear-resistant element further comprises a connecting means between the first connection end and the second connection end; and wherein the second connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to a cut-out portion of the first connection end, and wherein said protrusions extend through the connecting means. 2. The wear-resistant element of claim 1, wherein the first connection end comprises a plurality of protrusions, wherein said protrusions do not correspond to a cut-out portion of the second connection end, and wherein said protrusions extend through the connecting means. 3. The wear-resistant element of claim 2, wherein the protrusions on the first connection end are equiangularly arranged about the longitudinal axis. 4. The wear-resistant element of any one of the preceding claims, wherein the protrusions on the second connection end are equiangularly arranged about the longitudinal axis. 5. The wear-resistant element of any one of the preceding claims, wherein the first connection end comprises a cut-out portion which extends along the longitudinal axis. 6. The wear-resistant element of any one of the preceding claims, wherein the connecting means at least partially fills the cut-out portion of the second connection end. 7. The wear-resistant element of claim 5 or claim 6, wherein the connecting means at least partially fills the cut-out portion of the first connection end. 8. The wear-resistant element of any one of the preceding claims, wherein the connecting means is a braze layer. 9. The wear-resistant element of any one of the preceding claims, wherein the cut-out portion of the second connection end has a cylindrical portion adjacent the connecting means and connected to a conical portion ora truncated conical portion. 10. The wear-resistant element of any one of the preceding claims, wherein the wearresistant element is a high-pressure grinding roller stud. 11. The wear-resistant element of any one of the preceding claims, wherein the wearresistant element is substantially cylindrical. 12. The wear-resistant element of any one of the preceding claims, wherein the attachment portion comprises a first material having a first hardness, and wherein the we ar-resista nt portion comprises a second material having a second hardness; wherein the hardness of the second material is greater than that of the first material. 13. The wear-resistant element of claim 12, wherein the first material comprises a steel and the second material comprises a cemented tungsten carbide. 14. The wear-resistant element of claim 12 or claim 13, wherein the first material has a Vickers hardness of between 100 and 500 HV30, and the second material has a Vickers hardness of between 900 and 1400 HV30. 15. The wear-resistant element of any of the preceding claims, wherein the wear resistant portion and the attachment portion have corresponding diameters and are provided in a volumetric ratio of from 1:1 to 5:1. 16. The wear-resistant element of any one of the preceding claims, wherein the cut-out portion of the second connection end has the form of a blind hole. 17. The wear-resistant element of any one of claims 1 to 15, wherein the cut-out portion of the second connection end has the form of a through hole. 18. The wear-resistant element of any one of claims 5 to 17, wherein the cut-out portion of the first connection end has the form of a blind hole. 19. The wear-resistant element of any one of claims 5 to 17, wherein the cut-out portion of the first connection end has the form of a through hole. 20. A high-pressure grinding roller comprising a cylindrical roller having a circumferential surface, and a plurality of wear-resistant elements as claimed in any one of the preceding claims attached to the circumferential surface. 21. A high-pressure grinding roller as claimed in claim 20, comprising a first plurality of wear-resistant elements located at a first location on the circumferential surface and a second plurality of wear-resistant elements located at a second location on the circumferential surface, each element of the first plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a first volumetric ratio, each element of the second plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a second volumetric ratio, the first and second volumetric ratios being substantially different to each other. 22. A high-pressure grinding roller as claimed in claim 21, comprising a third plurality of wear-resistant elements located at a third location on the circumferential surface, each element of the third plurality of wear-resistant elements having a wear resistant portion and an attachment portion with corresponding diameters and provided in a third volumetric ratio, the third volumetric ratio being substantially different from the first and second volumetric ratios. 23. A high-pressure grinding roller as claimed in any one of claims 20 to 22, wherein each wear-resistant element is attached to the roller by any one of the following techniques: gluing, brazing, press-fitting, shrink fitting, threaded connection, and mechanical connection.

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