[1] The present invention relates to a method for producing a wear-resistant roller for processing very abrasive materials, such as crude ore, by which method a layer of wear-resistant material is provided on at least a part of the surface of the roller where high resistance to wear is needed. The wear-resistant roller may for example be used in a high-pressure roller press, in a vertical roller mill or in similar equipment for processing of particulate material.

[2] A wear-resistant roller of the aforementioned kind is known from US6086003. In this

US patent a wear-resistant layer consisting of two different powder metallurgical steels is applied on the surface of a roller by means of diffusion welding. The advantage of using powder metallurgical steels is that a surface with a very high content of hard phases and a high toughness can be achieved due to a fine microstructure and small well-distributed carbides. The powder metallurgical technology furthermore allows for a composition of hard phases which is difficult or impossible to achieve by other techniques. Hexagonal tiles are preformed using a first material and placed on the surface of a roller covering the largest area of the surface and a second material is placed between the tiles. Whereas the first material has a very high content of carbides and thus a high wear resistance, the second material has a lower content of carbides and therefore a higher wear rate but also a higher toughness, i.e. high resistance to crack propagation. This difference in wear and mechanical properties of the two materials will ensure that an autogenous wear protection is obtained and that fractures in the surface due to tramp metal etc. are avoided. The diffusion welding technique used is Hot Isostatic Pressing (HIP) where the metallurgical powder is consolidated to 100% density by applying a pressure above 1000 bar and a temperature above 1000 ⁰ C. The high pressure of the HIP process is a significant disadvantage as the equipment for the process must be designed to withstand such a high pressure. At present the diameter of the roller is limited to 1500 mm in diameter due to the equipment for the HIP process.

[3] The European patent 0516952B 1 describes a roller press in which the rollers comprise a plurality of cylindrical pins embedded in the crushing surface. The cylindrical pins, which are made of wear-resistant material, are inserted in drilled holes in the crushing surface of the roller and secured by means of a shrink fit connection or a similar arrangement. A part of the pins protrudes from the surface of the roller. Given that the pins and holes must fit each other exactly in order to withstand the high loads occurring during operation they must be manufactured with a relatively high degree of precision and since the entire circumference of the roller is covered with pins it is a very time-consuming process to manufacture such a roller. As a consequence hereof, the manufacture of such rollers involves significant costs.

[4] It is the object of the present invention to provide a wear-resistant roller by means of which the described disadvantages are eliminated or reduced.

[5] This is obtained by a wear-resistant roller of the kind mentioned in the introduction, and being characterized in that said layer of wear-resistant material comprises a flexible band being at least partially saturated with wear-resistant particles, where said flexible band, without any need for heating, is formed and fitted to the curvature of the surface of the roller for subsequent bonding to the roller by means of a sintering process.

[6] In this way it will be relatively easy and fast to manufacture a wear-resistant roller and it will be possible to manufacture rollers with a very large diameter, without being limited by equipment which must be capable of withstanding high pressures.

[7] The bands are described as being flexible since they can be shaped and easily cut prior to sintering. The flexibility is provided since the bands are saturated with a mixture of metal powder which is not influenced by neither handling nor pre-cutting the band before sintering. Typically, the powder mixture consists of braze material and wear-resistant particles. The wear-resistant particles may be cemented tungsten carbides.

[8] Due to the composition of the flexible band it will not be necessary to use a high pressure during the sintering process. The sintering process may take place in an inert atmosphere with a pressure below one atmosphere. This eliminates the need for a special design of the sintering equipment with capability to withstand high pressure making it easy to build large furnaces for large diameter rollers. The formulation of metal powders contained in the flexible bands is such that a good diffusion to the substrate as well as sintering of the band itself is readily achieved without elevated pressure. This however entails a certain porosity of the final surface, but this is acceptable in the present field of application.

[9] Normally it is very time-consuming and expensive to achieve a texture with holes or grooves on a hard and wear-resistant surface on a roller due to the machining required. By using a flexible band prepared with the wanted texture the time needed and thus the cost for obtaining the texture of the surface of the roller will be significantly reduced. Therefore it is preferred that the flexible band is provided with a number of holes and/ or grooves prior being formed and fitted to the curvature of the surface of the roller. Before the flexible band is sintered to the roller it is easy to provide the flexible band with holes or grooves, which means that this is a very fast and effective way of achieving a desired texture on the surface of the wear-resistant roller. The holes or grooves may be provided to the flexible band by means of a rolling technique. [10] During operation of the roller the holes or grooves in the surface of the roller will be efficiently filled with fine particles of the crushed materials. The fines become compacted in the holes or grooves entailing an efficient retention on the surface. The effect is referred to as autogenous wear protection since the crushed materials wears against itself. The autogenous layer builds up naturally during operation of a roller press, but may be further enforced by favourable layout of the holes or grooves. The autogenous effect impedes further wear of the holes or grooves filled with fines and also contributes to an increased throughput due to increased fiction between the materials to be processed and the materials in the holes or grooves. Thus an optimal texture of the surface of the roller would have significant advantages for the operation given its importance for reducing wear and for increasing the production.

[11] In principle the holes or grooves in the flexible band may have any conceivable shapes as long as the texture of the layer of sintered wear-resistant material offers suitable protection for the roller and/or establishes an autogenous wear protection. For example the holes may have a polygonal or oval shape and the grooves may for example have a zig-zag shape in the axial direction of the roller or around the circumference of the roller. It is preferred that the area of the holes or grooves in the surface of the finished wear-resistant roller exceed the area in the surface without holes or grooves. The holes or grooves may go through the whole layer of flexible band or just extend a small distance into the band. However, it is preferred that the flexible band is provided with through-going cylindrical holes since these will effectively establish the autogenous wear protection and they are easy and fast to cut in the flexible band.

[12] In another embodiment more layers of flexible bands are bonded to the roller. The layers are bonded on top of each other and the thickness of the layers may vary. Multiple layers will increase the lifetime of the roller. It is preferred that only the outermost layer is provided with holes or grooves. In this way the roller material onto which the layers are provided will not be subjected to wear until the innermost layer of flexible band is worn down. The roller should preferably be provided with two layers of flexible band where the inner layer has a greater ductility than the outer layer, with the outer layer having a higher hardness than the inner layer. In this way the harder outer layer provides good protection against wear and the inner layer, which not is subject to severe wear, is very resistant to crack propagation.

[13] In a further embodiment a buffer layer prior to sintering is provided between the flexible band and the roller. In this way it is possible to achieve an even stronger bond between the roller and the flexible band when the wear-resistant layer is sintered to the roller. In addition to this a greater variety of materials for both the roller and the flexible band will be available since to some degree the buffer layer may compensate for the properties of the two materials.

[14] In a yet further embodiment the flexible band is divided into more sections which are fixed to the roller in either circumferential or axial direction of the roller.

[15] In another embodiment the roller is a hollow cylinder divided into a number of annular sections on each of which the flexible band is formed, fitted and sintered for subsequently being shrink- fitted to a roller body. In this way the annular sections can be produced in specialized workshops and be transported to another location, e.g. the site where the rollers are in operation, for being shrink- fitted to the roller body. It may also be possible to change a worn-out or damaged annular section on site if it is shrink- fitted to the roller body.

[16] The invention will now be explained in greater detail with reference to the drawing, being diagrammatical, and where

[17] Fig. Ia, Fig. Ib and Fig. Ic show embodiments of rollers provided with flexible bands according to the invention.

[18] Fig. 2a and Fig. 2b show a cross-sectional view of the outer part of a wear-resistant roller.

[19] Fig. 3 shows an embodiment of a wear-resistant roller surface.

[20] Fig. 4 shows flexible bands according to the invention fixed to the surface of a number of roller tyres.

[21] Fig. Ia shows a wear-resistant roller for processing abrasive materials. The roller 1 is provided with a flexible band 2 being at least partially saturated with wear-resistant particles. The flexible band 2 is formed and fitted, without any need for heating, to the curvature of the surface of the roller 1 and subsequently bonded to the roller 1 by means of a sintering process. Prior sintering holes 5 are provided in the flexible band 2 in order to establish an autogenous wear protection during the operation of the wear- resistant roller. Fig. Ib shows an embodiment of a wear-resistant roller where the flexible band 2 is divided into multiple sections and fixed to the roller 1 in the circumferential direction of the roller surface. Fig. Ic also shows a wear-resistant roller where the flexible band is divided into multiple sections but in this embodiment the sections of flexible band 2 are much smaller and fixed in the axial direction of the roller surface.

[22] Fig. 2a shows a cross-sectional view of the outer part of a wear-resistant roller. An inner layer of flexible band 3 and an outer layer of flexible band 2 are fixed to the roller 1. A buffer layer 4 is provided between the roller 1 and the inner layer of flexible band 3. In this way it is possible to achieve an even stronger bond between the roller 1 and the inner layer of flexible band 3 when the wear-resistant layers of flexible band 2,3 are sintered to the roller 1. The layers of flexible band 2,3 are bonded on top of each other and the thickness of the layers may vary. The outer layer of flexible band 2 is provided with holes 5 before sintering. Prior to sintering it is very easy to provide the flexible band 2 with holes 5, which means it is a fast and effective way of achieving a desired texture on the surface of the wear-resistant roller. During operation of the wear-resistant roller the holes 5 will be filled with fine particles of crushed material. The fine material will become compacted in the holes whereby an autogenous wear protection is established. In this way the roller 1, onto which the layers of flexible band 2,3 are fixed, will not be subjected to wear until the inner layer of flexible band 3 (and the buffer layer 4) is worn down. The inner layer of flexible band 3 has a greater ductility than the outer layer of flexible band 2 and the outer layer of flexible band 2 has a higher hardness than the inner layer of flexible band 3. In this way the harder outer layer of flexible band 2 provides good protection against wear and the inner layer of flexible band 3, which not is subject to severe wear, is very resistant to crack propagation. Fig. 2b also shows a cross-sectional view of the outer part of a wear- resistant roller. In this embodiment only one layer of flexible band 2 is bonded to the roller 1. The holes 5 only extend a small distance into the layer of flexible band 2. In this way the roller will not be subject to wear before the flexible band 2 is worn down. This might be a preferred embodiment if only one layer of flexible band 2 is used.

[23] Fig. 3 shows an embodiment of a section of two flexible bands 2,3 on top of each other wherein a combination of holes 5 and grooves 6 are cut in the outer layer of the flexible band 2. The flexible bands 2,3 are shown prior being formed and fitted to the curvature of the surface of the roller and prior to being bonded to the roller 1 by means of a sintering process. The holes 5 and the grooves 6, which have a zig-zag shape, extend through the whole layer of the flexible band 2. In other embodiments the holes 5 and/or grooves 6 may just extend a small distance into the flexible band 2.

[24] Fig. 4 shows an embodiment where the roller is a hollow cylinder divided into a number of annular sections 7 on each of which the flexible band 2 is formed, fitted and sintered whereafter the annular sections 7 are shrink- fitted to a roller body. In this way the annular sections 7 can be produced in specialized workshops and be transported to another location for being shrink-fitted to a roller body. Furthermore, it will also be possible to change a worn down or damaged annular section 7 on site if it is shrink- fitted to the roller body.