HK1178104B - Bimaterial elongated insert member for a grinding roll - Google Patents

Description

Bi-material elongated insert member for a grinding roll

Technical Field

The invention relates to an elongated insert member for a grinding roll for heavy wear operation. The invention also relates to cassettes and segments for grinding rolls, grinding rolls and rolling mills.

Background

When crushing or comminuting material using inter-particle crushing, two counter-rotating mounted rollers separated from each other by a gap form a pull-in pinch where the material is pulled in, forced or gravity fed and crushed against each other. The benefit of interparticle crushing is that effective crushing can be achieved, even with very small particle sizes, with reduced energy consumption compared to many other comminution techniques. In addition, the noise level during processing is substantially reduced compared to other comminution techniques.

The present invention relates to an improved wear resistant element for a roller construction using inter-particle crushing and single particle crushing, wherein during crushing or comminution of material large wear conditions exist between two rollers in the roller construction. The outer surface of the roll is subjected to very high pressures, wherein high wear occurs thereby. Such wear has been addressed by measures of different shapes and coatings of the roll surfaces exposed to wear.

EP-699479 discloses a roll for a high-pressure roll press with reduced size of the compression of the particulate material, having a hard surface with nub pins which are resistant to wear and suitable for spontaneous wear protection. Nub pins, which have a long potential life even under high pressure loads, have a radially inner pin portion that is easily welded to the roll surface and a harder radially outer pin portion that protectively covers the radially inner pin portion.

There are problems associated with the above-described techniques. Due to the large pressure exerted on the roller, wear-resistant nub-pins inserted into the surface area of the roller must be able to cope with the large pressure without failure. However, uniform nub pins as described in EP-699479 wear away at an unsatisfactory rate. The edges of the nub-pins are particularly exposed and have a tendency to prematurely break, accelerating the wear rate of the nub-pins.

Disclosure of Invention

It is an object of the present invention to provide an improvement of the above-mentioned techniques and prior art. More particularly, it is an object of the present invention to provide an improved insert member for a grinding roller such that the outer surface of the grinding roller is given a high wear resistance. Furthermore, it is an object of the invention to provide cassettes and segments for grinding rolls, grinding rolls and rolling mills.

These and other objects and advantages will become apparent from the following description of the invention, which is achieved by an elongated insert member for a grinding roll for heavy wear operation according to the independent claim.

An elongated insert member for a grinding roll for heavy wear operation is provided. The elongated insertion member includes: a core formed of a first material having a first hardness, the core extending in a longitudinal direction of the elongated insert; and a body formed of a second material having a second hardness, the body surrounding the core. Wherein the first hardness is greater than the second hardness. . This is advantageous in that an insert part with such a structure has a considerable reliability compared to hard metal nails according to the prior art. Due to the more ductile body of the insert member, a hard metal grade with less binding content may be used, making the insert member more wear resistant. This in turn leads to a reduced amount of insert member failure which in current grinding rolls incorporating wear resistant insert members leads to failure during use. The more ductile body of the insert further weakens the premature rupture of the edge of the insert which is particularly susceptible to wear. When the insert part is worn, the malleable but tough body will be worn away fairly quickly on top of the insert part, exposing the core. Thus, the top of the insert part to be subjected to wear will consist of a hard and wear-resistant core surrounded in the radial direction by a harder but ductile body. Since the surface of the body subject to wear is much smaller than the surface of the core subject to wear, the body and the core will wear away at about the same rate. As mentioned above, the body of the insert member may also function to protect the more sensitive edges of the core. Another advantage of having a hard but more ductile body is that the insert member is made less likely to become dislodged from the grinding roll due to the elasticity that is created between the insert member and the grinding roll when connected.

The first material may have a first toughness and the second material a second toughness, the first toughness being less than the second toughness, facilitating further strengthening of the more ductile body.

The first material may be selected from the group comprising a metallic material, a ceramic material or a combination of a metallic material and a ceramic material, which is advantageous in that such material is very wear resistant.

The second material may be selected from the group comprising a metallic material, a ceramic material or a combination of a metallic material and a ceramic material, which is advantageous in that such material is very wear resistant.

The first material may have a preferred hardness of from at least 600HV to 1200 HV. This is a particularly preferred hardness of the core of the insert part.

The second material has a preferred hardness of from at least 400HV to 1200 HV. This is a particularly preferred hardness of the body of the insert member.

The cross-section of the insertion part may be cylindrical and the insertion part may have the shape of a pin. This simple shape makes it easy to manufacture the insert part.

The core may be cylindrical, which is a simple shape, making it easy to manufacture an insert part with such a core.

The geometric central axis of the core and the geometric central axis of the insert member may be misaligned. The core may extend along the entire length of the insert part in the longitudinal direction.

The core may extend in a longitudinal direction from a top end of the insert member and along a portion of a length of the insert member.

Thus, depending on the type of material to be crushed or comminuted, the insert part may be adapted to different shapes and sizes to obtain the characteristics required for a certain crushing operation.

The outer surface of the insert member may be shaped, which has the advantage that a non-uniform surface is provided on the roller, thereby improving the pull-in of the material to be comminuted. Furthermore, the material to be crushed or pulverized fills the space created between the insertion parts, thus forming a spontaneous protection of the roller, is maintained thanks to the non-uniform surface of the insertion parts.

According to a second aspect thereof, the invention relates to a cassette for a grinding roller for heavy wear operation, comprising a plurality of insert parts according to the above-mentioned features.

According to a third aspect thereof, the invention relates to a segment of a grinding roller for heavy wear operation, comprising a plurality of insert parts or cassettes according to the above-mentioned features.

According to a fourth aspect thereof, the invention relates to a grinding roller for heavy wear operation, comprising a plurality of insert parts, cassettes or segments according to the above-mentioned features.

According to a fifth aspect thereof, the present invention relates to a rolling mill for crushing a pile of material, comprising at least one grinding roller according to the above-mentioned characteristics.

According to a sixth aspect of the invention, the invention relates to a method for increasing the wear resistance of a high pressure grinding roll. The method comprises the following steps: manufacturing a grinding roll, arranging at least one groove to a circumference of the grinding roll, manufacturing at least one insert member, and arranging and connecting the at least one insert member to the at least one groove, wherein the step of manufacturing the at least one insert member comprises: arranging a core formed of a first material having a first hardness in a body formed of a second material having a second hardness, the core extending in the longitudinal direction of the at least one insert part and the body surrounding the core, wherein the first hardness is greater than the second hardness. This is advantageous in that it results in a reliable connection of the at least one insert part to the grinding roller, thereby ensuring a high wear resistance of the envelope surface of the grinding roller.

In general, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, device, component, means, etc" are to be interpreted openly as referring to at least one of the element, device, component, means, etc., unless explicitly stated otherwise. Furthermore, the term "toughness" is used throughout this application to refer to "fracture toughness" and "including" is used throughout this application to refer to "including, but not limited to". The term "milling" is meant to include "comminution".

Drawings

The above and other objects, features and advantages of the present invention will be better understood by the following illustrative and non-limiting detailed description of preferred embodiments of the invention with reference to the accompanying drawings, in which like reference numerals will be used for like elements, and in which:

figures 1a-l are perspective views of an insert part according to twelve different embodiments of the invention,

figure 2 is a perspective view of a cassette for a grinding roller comprising a plurality of insert members,

figure 3 is a perspective view of a segment for a grinding roller comprising a plurality of cassettes or insert parts,

FIG. 4 is a perspective view of a grinding roll comprising a plurality of segments, cassettes or insert members,

FIG. 5 is a perspective view of a rolling mill including at least one grinding roll, an

Fig. 6 is a perspective view of an insert member according to a ninth embodiment of the invention.

Detailed Description

Fig. 1a illustrates an insert member 1 for a grinding roll for heavy wear operation according to a first embodiment of the invention. The cross-section of the insert part 1 is cylindrical and the insert part has the shape of a pin. The insert member 1 has a core 2 formed of a first material having a first hardness. The core 2 is cylindrical and extends in the longitudinal direction of the insert member 1. The geometric axis of the core 2 is aligned with the geometric axis of the insert member 1. The insert member 1 further has a body 3 formed of a second material having a second hardness, which completely surrounds the core 2. The first hardness is greater than the second hardness. The first material, that is to say the material of the core 2 of the insert part 1, is preferably composed of a metallic material, a ceramic material or a combination of a metallic material and a ceramic material. However, other material solutions for the core 2 of the insert part 1 are naturally also possible. The first material has a preferred hardness of from at least 600HV to 1200 HV. The second material, that is to say the material of the body 3 of the insert part 1, is preferably composed of a metallic material, a ceramic material or a combination of a metallic material and a ceramic material. However, other material solutions for the core 3 of the insert part 1 are naturally also possible. The second material has a preferred hardness of from 400HV to 1200 HV. In a preferred embodiment of the invention, the first material has a first toughness and the second material has a second toughness, the first toughness being less than the second toughness.

In fig. 1b, an insert part 1 according to a second embodiment of the invention is illustrated. The core 2 is cylindrical and extends in the longitudinal direction along the entire length of the insert part 1. The geometric axis of the core 2 is aligned with the geometric axis of the insert member. The body 3 of the insert member 1 radially surrounds the core 2. When standing in the vertical direction, the core 2 is thus exposed at the top and bottom of the insert member 1.

Fig. 1c illustrates an insert member 1 according to a third embodiment of the invention. The core 2 is cylindrical and extends in the longitudinal direction of the insert member 1. The geometric axis of the core 2 is offset or displaced relative to the geometric axis of the insert member 1. The body 3 of the insert member 1 completely surrounds the core 2. In fig. 1d, an insert part 1 according to a fourth embodiment of the invention is illustrated. The core 2 is cylindrical and extends from the top of the insert 1 and along part of the length of the insert in the longitudinal direction. The geometric axis of the core 2 is aligned with the geometric axis of the insert member 1. The body 3 of the insert member 1 radially surrounds the core 2. When standing in the vertical direction, the core 2 is exposed at the top of the insertion part 1.

Fig. 1e illustrates an insert member 1 according to a fifth embodiment of the invention. The core 2 is cylindrical and extends in the longitudinal direction of the insert member 1. The geometric axis of the core 2 is aligned with the geometric axis of the insert member 1. The body 3 of the insert member 1 completely surrounds the core 2. The outer surface 4 of the insert part 1 is shaped. That is, the outer surface 4 of the insert members 1 is provided with projections to help retain the material to be crushed or comminuted in the spaces created between the insert members 1 when disposed on a roller to create and maintain a protective autogenous layer during use of the roller. The projection may be formed integrally with the body 3 or may be provided as a sleeve arranged on said body.

Fig. 1f illustrates an insert member 1 according to a sixth embodiment of the invention. The core 2 is cylindrical and extends in the longitudinal direction of the insert member 1. The geometric axis of the core 2 is aligned with the geometric axis of the insert member 1. The body 3 of the insert member 1 completely surrounds the core 2. The entire body 2 is covered with a surface layer or coating. The surface layer or coating may be obtained by soaking the insert 1 into a liquid coating and allowing it to dry on or react with the insert surface. The coating or surface layer may also be obtained by mechanical or physical processes, for example by deposition or carburization.

Fig. 1g illustrates an insert member 1 according to a seventh embodiment of the invention. The body 3 has the form of a hollow tube having an annular cross-sectional shape. Thus, the center of the insert part 1 is a hollow and hollow space, which will be filled with the material to be ground during grinding. A plurality of circular cores 2 are inserted into the ring-shaped body 3. The core 2 has parallel longitudinal axes.

Fig. 1h illustrates an insert member 1 according to an eighth embodiment of the invention. The insert part has a circular cross section and a plurality of annular cores 2 of an insert body 3. The cores 2 are parallel and they are of the same size, i.e. their cross-sectional area is the same. However, in embodiments utilizing multiple cores in a single body, it is not necessary that all of the cores be the same size. The cores may be different from each other and have different lengths, cross-sectional forms and/or cross-sectional areas. Furthermore, the core may be made of different materials. This increases the possibilities of adapting the insert part properties for different materials to be ground and/or for different positions on the surface of the grinding roller.

Fig. 1i illustrates an insert member 1 according to a ninth embodiment of the invention. The insert member has a circular cross-section. The circular core 2 is inserted into the center of the circular body 3 so that the longitudinal axes of the core 2 and the body 3 are parallel and overlap each other. The insert member 1 further comprises an intermediate layer arranged between the core 2 and the body 3. The intermediate layer may improve the mechanical properties of the insert 1 or it may improve the attachment of the core 2 to the body 3. The insert 1 further comprises a coating on the outer surface of the body 3. The coating may also improve the mechanical properties of the insert member 1 or the attachment of the insert member 1 to the grinding roll. The intermediate layer and the coating layer may be of the same or different materials.

An insert member 1 according to a tenth embodiment of the invention is illustrated in fig. 1 j. The insertion member 1 has a body 3 in the form of a hollow tube having a circular cross-sectional shape. The core 2 is arranged on the inner surface of the body 3, and the core 2 is thus also in the form of a hollow tube having an annular cross-sectional shape. The center of the insert member 1 is a hollow and hollow space defined by the core material 1.

Fig. 1k illustrates an insert part 1 according to an eleventh embodiment of the invention. The core 2 is cylindrical and extends substantially in a diagonal direction of the insert member 1 when standing. The geometric axis of the core 2 is thus angled with respect to the geometric axis of the insert part 1. The angle of the geometric axis of the core with respect to the geometric axis of the insert part may naturally vary. The body 3 of the insert member 1 completely surrounds the core 2. However, the core 2 may be exposed at the top and bottom of the insert member 1. Furthermore, the core 2 may naturally have different sizes and shapes. When crushing material using a grinding roller having an insert member, it is possible for the material to be crushed to strike the insert member diagonally from the top of the insert member. By orienting the core 2 of the insert member 1 at different angles with respect to the insert member 1, in particular, the wear resistance of the insert member may be improved in directions of the insert member that are believed to be largely exposed to wear. Naturally, different sizes and shapes of the insert part 1 are also possible.

Fig. 1l illustrates an insert member 1 according to a twelfth embodiment of the invention. The cross-sections of the insert member 1 and the core body 2 are rectangular. The core 2 extends in the longitudinal direction of the insert member 1. The geometric axis of the core 2 is aligned with the geometric axis of the insert member 1. The body 3 of the insert member 1 completely surrounds the core 2.

A cassette 5 for a grinding roller 6 is illustrated in fig. 2. The cartridge 5 includes a plurality of insertion members 1. The cassette 5 will be connected to the envelope surface of the grinding roller 6, thereby facilitating both the installation and possible replacement or servicing of the insert member 1. The outer surface 7 of the cassette 5 surrounding the insert part 1 may be coated or treated, e.g. carburized, to be more wear resistant.

Fig. 3 shows a segment 8 for heavily worn operating grinding roller 6. The segment 8 comprises a plurality of insertion parts 1. The segments 8 will be connected to the envelope surface of the grating roller 6, thereby facilitating both the installation and possible replacement or servicing of the insert member 1. The outer surface 9 of the segment 8 surrounding the insert part 1 may be coated or treated, e.g. carburized, to be more wear resistant.

In fig. 4 a grinding roller 6 for heavy wear operation is illustrated. The grinding roller 6 comprises a plurality of insert parts 1. The insert part 1 is to be attached to the envelope surface of the grating roller 6. The insert part 1 can be connected to the envelope surface of the grinding roller 6 in many different ways. For example, the above-described cassette 4 and segments 8 may be used to facilitate mounting of the insert member 1. Another possibility is to use a binding ring. The outer surface 10 of the roller 5 surrounding the insert 1 (or cassette, segment, coupling ring, etc.) may be coated or treated, e.g. carburized, for better wear resistance.

The insert parts can be fixed in the envelope surface of the grinding roller or in cassettes or segments by different techniques. Thus, the individual insert elements can be fixed, for example, by shrink fitting, welding, gluing, clamping, wedging or screwing.

Fig. 5 illustrates a rolling mill 11 for crushing a pile of material. The rolling mill 11 comprises two grinding rolls 6. During use, the insert part 1 of the grinding roll 6 connected to the rolling mill 11 will be subjected to wear. When the insert member 1 is subjected to wear, the malleable but tough body 3 will wear fairly quickly on top of the insert member 1, exposing the core 2. Thus, the top of the insert part 1, which will be subjected to wear, will be constituted by a hard and wear resistant core 2, the core 2 being surrounded in the radial direction by a harder but ductile body 3. Since the surface of the body 3 to be subjected to wear is much smaller than the surface of the core 2 to be subjected to wear, the body 3 and the core 2 will wear at about the same rate. This will result in a longer service life of the insert part and thus of the grinding roller 8.

In order to further extend the service life of the grinding roller 6, the latter can be provided with a wear-resistant layer on the envelope surface, which wear-resistant layer covers the space formed on the grinding roller 6 between the insert parts 1. The wear resistant layer reduces wear caused under the autogenous layer formed between the insert parts 1 and also prevents wear of the surface in case of failure of the insert parts 1. For example, the wear layer may be made of a tool steel material.

In fig. 6, an insert member 1 according to a ninth embodiment is illustrated. In this embodiment, the first and second materials are of the same material type. That is, the entire insert member 1 is made of one material type. Thus, both materials may contain particles of a single, specific material type, but the particle size may be different in both materials. The body 3 may thus be formed of a first material comprising particles larger than the particles of the second material forming the core 2 to obtain the same effect as the other embodiments of the insert member 1. Therefore, the hardness of the core 2 is greater than that of the body 3, and the toughness of the core 2 is less than that of the body 3. The core 2 is cylindrical and extends in the longitudinal direction of the insert member 1. The geometric axis of the core 2 is aligned with the geometric axis of the insert member 1. The body 3 of the insert member 1 completely surrounds the core 2.

In use, the two grinding rollers are arranged substantially parallel to each other with a gap between them. The crushed material is fed into the gap, typically jammed in the feed, but possibly only by gravity, and crushed between the grinding rollers. In the interparticle crushing, only a partial crushing work is performed by the crushing surfaces of the grinding rollers, and a partial crushing takes place in a material bed formed between the grinding rollers when the particles in the material bed grind each other. The space between the insert parts will be filled with crushed material, forming a protective wear layer. Thus, the wear on the actual envelope surface is reduced, extending the working life of the grinding roller.

The first material of the core and the second material of the body may have the same chemical composition, i.e. they may be chemically identical but differ in their physical properties (e.g. vickers hardness and/or fracture toughness). The difference in physical properties may be achieved by different treatments of the first and second materials, for example by hardening.

The body may be made of a material having a vickers hardness value in the range of 400HV-1200HV, and the core may be made of a material having a vickers hardness value of at least 600HV-1200 HV. According to one embodiment of the invention, the body has a Vickers hardness of at least 600HV and the core has a Vickers hardness of at least 1000 HV. Preferably, the body has a Vickers hardness of at least 1000HV, whereby the core has a Vickers hardness of at least 1200 HV. The hardness of the core is always higher than that of the body, thus providing improved wear resistance and fracture toughness during grinding of hard and abrasive mineral materials.

The first material used to make the core has a typical fracture toughness that is lower than the fracture toughness of the second material. Fracture toughness on the first material is typically < 18MN/m^3/2Usually in the range of 10-18MN/m^3/2More typically in the range of 11-16MN/m^3/2Preferably between 12 and 14MN/m^3/2In the range of (1). Typically, the wear resistance of the first material is higher than the wear resistance of the second material. The first material may be a composite of metal and ceramic, so called cermet or cemented carbide, where the metal acts as a binder. For example, a typical binder may be diamond, and the binder content may be 0-20% by weight. Other metals that may be used as binders are drill-based alloys, nickel and nickel-based alloys, titanium and titanium-based alloys, iron-based alloys, and molybdenum-based alloys. The ceramic material may be any suitable carbide material, such as tungsten carbide (WC), titanium carbide (TiC), Vanadium Carbide (VC), chromium carbide (CrC), tantalum carbide (TaC), a mixture of two or more carbides, or a mixture of two or more ceramic materials. The first material is alsoMay be a metal oxide such as a partially stabilized zirconia or aluminum oxide, or a metal nitride or metal boride. The first material may also be a ceramic cemented carbide material.

According to one embodiment of the invention, the second material used for manufacturing the body has at least 14MN/m^3/2Typically in the range of 15-30MN/m^3/2More typically in the range of 16-25MN/m^3/2More preferably in the range of 18-25MN/m^3/2In the range of (1). The second material may be a composite of metal and ceramic, so called cermet or cemented carbide, where the metal acts as a binder. For example, a typical binder may be diamond, and the binder content may be 10-25% by weight. Other metals that may be used as binders are drill-based alloys, nickel and nickel-based alloys, titanium and titanium-based alloys, iron-based alloys, and molybdenum-based alloys. The ceramic material may be any suitable carbide material, such as tungsten carbide (WC), titanium carbide (TiC), Vanadium Carbide (VC), chromium carbide (CrC), tantalum carbide (TaC), a mixture of two or more carbides, or a mixture of two or more ceramic materials. The second material may also be a metal oxide, such as a partially stabilized zirconia or aluminum oxide, or a metal nitride or metal boride. The second material may also be an industrial diamond or tool steel, preferably a tool steel. Tool steel is herein understood to be an iron-based material comprising carbides, such as chromium carbide, vanadium carbide, niobium carbide, tungsten carbide or any combination thereof. Examples of tool steel types are carburized steel, tempered steel, high speed steel, spray formed steel or cast iron. The vickers hardness of the tool steel is typically at least 400HV, more typically at least 500HV, more preferably at least 600 HV. The amount of carbides in the tool steel is at least 5% by volume, typically more than 10% by volume, preferably more than 20% by volume.

According to a preferred embodiment of the invention, the body is made of a material which is a cermet or a hard metal, while the core is also made of a cermet or a hard metal. According to another preferred embodiment of the invention, the body is made of a material being tool steel and the core is made of a material being cermet or hard metal.

According to another preferred embodiment of the invention, the hardness of the body varies throughout the body. The hardness may, for example, increase continuously from the outer surface of the body to the center of the body, independently of the core inserted into the body.

The core may also be made of a plurality of individual core components. For example, the core may comprise a plurality of cylindrical components that have been sequentially arranged into the body. In this manner, the core is discontinuous, but the core includes a plurality of discontinuities where one core component ends and a second core component begins. The ends of the individual core components may be in contact with each other or may have material between them. The discontinuities of the core make the core more resistant to cracking, but the core retains its increased resistance to wear. The core may comprise 2-4 individual core components.

The cross-sectional shape of the core may be circular, elongated, triangular, quadrilateral, parallelogram, polygonal, or irregular. The cross-sectional shape and area of the core is generally constant throughout the length of the core. However, in some implementations it is possible that the diameter and cross-sectional area decrease from the first end towards the second end of the core, whereby the core has a truncated cone shape. It is also possible that the core is T-shaped.

Typically, the insert member has a length of 25-100 mm, typically 30-80 mm, more typically 30-60 mm, and an overall diameter in the range of 10-60 mm. The diameter of the core is typically 2-50 mm. It is also possible that the body comprises a plurality of parallel cores. A single body may comprise, for example, 2-6, typically 2-4 parallel cores. The parallel cores may have a diameter in the range of 5-30 mm. When the insert member has a plurality of parallel cores, the mechanical reliability thereof is improved even if the single core is thinner than the core used in the insert member including only the single core. The multiple cores provide the advantage that even if one core would be damaged or destroyed, the strength of the insert part remains at an acceptable level due to the other unbroken cores. An insert part with a plurality of cores can be used, for example, for protecting the edge of a grinding roller.

The cross-section of the insert part may be circular, elongated, triangular, quadrangular, parallelogram, polygonal or irregular. The flow of the material to be crushed can be controlled so that the material is distributed more evenly in the axial direction of the grinding roller. For example, the elongated insert members may be positioned at an angular relationship to a centerline of the grinding roll such that the insert members direct the material being ground away from a central portion of the grinding roll toward both ends of the grinding roll. It is also possible to improve the crushing result by using insert parts with different cross-sectional shapes at different positions of the grinding roller.

It is also possible that the body has the shape of a hollow tube, torus or ring. The core may be arranged in a tube, annulus or annular wall, or the core may form a core layer on the inner wall of the body. During the grinding process, the hollow space inside the insert is filled with the material to be ground, thereby providing autogenous protection.

In one embodiment, the insert member has a plurality of cores, each having a spherical shape.

According to an embodiment of the invention, the insert part further comprises a surface layer or coating, the surface layer or coating enveloping at least a part of the body. The surface layer or coating may be a different material than the body, or the outer surface of the body may have been treated or processed in a manner that provides the outer surface of the body with different properties and/or properties than the majority of the material of the body. For example, the surface of the body may be carburized. The surface layer or coating may improve the wear resistance of the insert member or it may improve its bonding to the grinding roller. It is also possible that the core components comprise corresponding surface layers or coatings, improving the mechanical properties of the core or its bonding to the body. In the case where the surface layer or coating is disposed on the outer surface of the core prior to insertion of the core into the body, the surface layer or coating will become an intermediate layer between the core and the body.

In one embodiment of the invention, one or more intermediate layers may be disposed between the body and the core. The material of the intermediate layer may be chemically different from both the core and the body. The material of the intermediate layer may also be chemically similar to the core and/or body material, but in this case the material of the intermediate layer is physically different from the core and/or body. A plurality of intermediate layers may be disposed on the surface of the core one layer at a time before inserting the intermediate layers and attaching the intermediate layers to the body.

The core and body may be attached to each other in any suitable way that provides sufficient strength for attachment. Where both the body and the core are made of composite metals, ceramics, cermets, they are typically sintered together. Where the body is made of tool steel and the core is made of composite metal, ceramic, cermet, they are joined together using an adhesive, a press fit, an interference fit or brazing. Suitable adhesives are epoxy-based adhesives, preferably two-component epoxy adhesives. In press fitting, the core is pressed into a recess in the body, the recess having a diameter slightly smaller than the core. In order to adapt each grinding roller to different types of wear, the pattern of the insert members along the grinding roller to which it is connected may vary.

The grinding rolls may have a diameter of 0.15 to 5 metres, typically 1.0 to 2.5 metres, and may be up to 2.0 metres long in the axial direction. The grinding roller may be refined, forged, cast or hot isostatic pressed steel and the grinding roller may be extended by hot forming such as ring forging). The material of the grinding roll has a vickers hardness that is the same as or less than the vickers hardness value of the body. The grinding roller comprises roller ends extending from the edges of the roller towards the centre of the grinding roller and having a length of 10-20% of the total length of the grinding roller. Positioned between these roller ends is a central portion of the grinding roller, which central portion comprises 60-80% of the total length of the grinding roller. Typically, the volume flow of the material to be ground in the central portion of the grinding roller is higher than the volume flow of the material to be ground in the end portions of the roller. The peripheral speed of the grinding roller is usually 1 to 2 m/s during grinding. Grinding rolls are used in high pressure grinding units comprising two counter-rotating rolls that crush the material between them under a great water pressure.

According to one embodiment of the invention, the grinding roller is covered with a wear-resistant surface layer, which is produced by hot isostatic pressing, spray forming, induction hardening, hybrid casting or welding. The surface of the grinding roller may also be surface treated by, for example, carburizing, nitrating, or a combination thereof. By arranging a wear resistant surface layer on the roll surface between the insert parts, the risk of wear under autogenous layers that may form during grinding can be reduced. The surface layer also prevents catastrophic wear of the roll surface in the event of an accidental insert failure and also protects the roll surface in the event that no autogenous layer is formed during grinding. For example, if one or several insert members are damaged and/or broken during grinding, the wear resistant layer gives the process operator more time to notice and react to insert member failure before the grinding roll surface is irreparably damaged. The grinding roller comprises at least one, preferably a plurality of, recesses for insert members, which insert members comprise a core and a body surrounding the core. The insert member may be attached to the groove of the grinding roller using an adhesive, brazing, shrink fitting, welding, press fit, interference fit, or mechanical connection. Adhesives that can be used for bonding are epoxy adhesives, in particular two-component epoxy adhesives. In many embodiments, the adhesive bond provides a quick, inexpensive, and simple method of bonding the insert member to the grinding roll. There are also lower requirements for removing the insert and the groove size. Adhesive bonding also enables replacement of damaged and/or worn insert components. For example, a temperature-sensitive adhesive can be used, whereby heating the roller at the location of the insert causes decomposition of the adhesive and makes it possible to remove the insert from the recess and replace it with a new insert.

The depth of the grooves in the grinding roll is generally such that the insert members extend beyond the surface of the roll by a length typically in the range of 5 to 20 mm, more typically in the range of 5 to 15 mm. This enables the formation of a self-abrasion resistant protection from the crushed material when the crushed material can be deposited between the insert parts. The depth of the groove may also be such that the end of the insert member is in the same plane as the surface of the main roller.

It is possible to define the insert member footprint on the grinding roll. The insert part coverage areas in these are defined as the ratio of the sum of the cross-sectional areas of the insert parts over a defined surface area of the grinding roller to this defined surface area of the grinding roller, set in percentages. The insert covers at least 20%, typically at least 30%, and not more than 100%, and typically less than 90% of the area. The insert member coverage area may vary on or along the roll surface, and is typically selected such that a autogenous layer of the material being ground is formed between the insert members. The insert member coverage area may also be selected so as to obtain even wear of the roller surface. Typically, the insert member is higher in the central portion of the grinding roller and lower in the end portions of the roller.

According to a second aspect of the invention, a cassette for heavily worn operating grinding rollers is provided, comprising a plurality of insert members according to the above-mentioned features.

According to a third aspect of the invention, a segment of a grinding roller for heavy wear operation is provided, comprising a plurality of insert parts or cassettes according to the above-mentioned features.

According to a fourth aspect of the invention, a grinding roll for heavy wear operation is provided, comprising a plurality of insert members, cassettes or segments according to the above-mentioned features.

According to a fifth aspect of the present invention, there is provided a rolling mill for crushing a pile of material, comprising at least one grinding roller according to the above-mentioned features.

According to a sixth aspect of the present invention, a method for improving the wear resistance of a high pressure grinding roll is provided.

The invention has mainly been described above with reference to some embodiments. However, a person skilled in the art will readily appreciate that other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended claims.

Thus, the size and shape of the insert member, body and core according to the present invention may vary in many different embodiments without departing from the scope of the present invention.

Claims (18)

1. An elongated insert member (1) for a grinding roll (6) for heavy wear operation, comprising:

a core (2) formed of a first material having a first hardness, the core (2) extending in a longitudinal direction of the elongated insertion part (1), and

a body (3) formed of a second material having a second hardness, the body (3) surrounding the core (2), wherein the first hardness is greater than the second hardness.

2. The elongated insertion member (1) according to claim 1, wherein the first material has a first toughness and the second material has a second toughness, and wherein the first toughness is smaller than the second toughness.

3. The elongated insertion member (1) according to claim 1 or 2, wherein said first material is selected from the group comprising a metallic material, a ceramic material or a combination of a metallic material and a ceramic material.

4. The elongated insertion member (1) according to claim 1 or 2, wherein said second material is selected from the group comprising a metallic material, a ceramic material or a combination of a metallic material and a ceramic material.

5. The elongated insertion member (1) according to claim 1 or 2, wherein the hardness of the first material is in the range from at least 600HV to 1200 HV.

6. The elongated insertion member (1) according to claim 1 or 2, wherein the hardness of the second material is in the range from at least 400HV to 1200 HV.

7. The elongated insertion member (1) according to claim 1 or 2, wherein the cross-section of the elongated insertion member (1) is circular.

8. The elongated insertion member (1) according to claim 1 or 2, wherein the elongated insertion member (1) has the shape of a pin.

9. The elongated insertion member (1) according to claim 1 or 2, wherein the core (2) is cylindrical.

10. The elongated insert member (1) according to claim 1 or 2, wherein the geometric centre axis of the core (2) is not aligned with the geometric centre axis of the elongated insert member (1).

11. The elongated insertion member (1) according to claim 1 or 2, wherein the core (2) extends in a longitudinal direction along the entire length of the elongated insertion member (1).

12. The elongated insertion member (1) according to claim 1 or 2, wherein the core (2) extends in a longitudinal direction from a tip of the elongated insertion member (1) and along a part of the length of the elongated insertion member (1).

13. The elongated insertion member (1) according to claim 1 or 2, wherein the outer surface (4) of the elongated insertion member (1) is shaped.

14. A cassette (5) for a grinding roller for heavy wear operation, comprising a plurality of elongated insert members (1) according to any one of claims 1-13.

15. Segment (8) of a grinding roll for heavy wear operation, comprising a plurality of elongated insert parts (1) according to any one of claims 1-13 or a plurality of cassettes (5) according to claim 14.

16. A grinding roll (6) for heavy wear operations, comprising a plurality of elongated insert members (1) according to any one of claims 1-13, a plurality of cassettes (5) according to claim 14 or a plurality of segments (8) according to claim 15.

17. A rolling mill (11) for crushing a pile of material, comprising at least one grinding roller (6) according to claim 16.

18. A method for increasing the wear resistance of a high pressure grinding roll comprising the steps of:

the manufacture of the grinding roller is carried out,

arranging at least one groove to the circumference of the grinding roller,

manufacturing at least one insert part, and

arranging and connecting the at least one insert member to the at least one recess, wherein the step of manufacturing the at least one insert member comprises:

arranging a core formed of a first material having a first hardness in a body formed of a second material having a second hardness, the core extending in the longitudinal direction of the at least one insert part and the body surrounding the core, wherein the first hardness is greater than the second hardness.