The present invention relates to a wear-resistant roller for crushing of particulate material, such as crude ore for use in the cement or minerals industry comprising a roller body, a wear surface on the roller body. The wear surface comprises welding beads comprising different fractions of hard phase materials. Furthermore, the welding beads have fractions of hard phase materials which are higher in central portions compared to peripheral portions. Also the invention relates to a method of forming such a wear surface on a roller body.
Covering roller bodies with a wear surface comprising wear-resistant materials is well-known in the art of milling. The wear surface may comprise wear-resistant materials implemented by wear-resistant studs implemented in the surface or as in wear-resistant rollers of the above-mentioned kind comprise welding beads with high contents of carbide. Carbides have long been known to have a hardness close to that of diamond and has consequently been used extensively for cutting or grinding in situations requiring extreme resistance to wear and abrasions. Welding beads comprising wear and abrasion resistant materials welded on a roller is often referred to as hardfacing of the roller. Using studded technologies is often too expensive either to install or maintain, and often also inadequate when working with very high pressures such as in roller mills or roller crushers due to failure of attachment to the roller body. The wear-resistant material of which the studs are made is very expensive and since a part of each stud is embedded in the roller for fastening the stud, and only a smaller portion of the stud protrudes from the roller surface and is actually utilized as wear-resistant material, most of the expensive material is not subjected to wear, which is a poor utilization of the wear-resistant material.
Hardfacing on the other hand has the advantage of being less expensive, fairly easy to maintain and capability of withstanding extremely high pressures. However, a well-known disadvantage of hardfacing is the decrease in grinding effectiveness as a consequence of un-even wear of the wear surface of the roller across the width of the roller. To ensure a reasonable service lifetime of the roller between consecutive hardfacing, the hardfacing technology has conventionally been limited to using expensive high wear-resistant materials.
Therefore it would be advantageous to be able to use hard-faced surfaces while maintaining a more even wear distribution of the wear surface of the roller to optimize the wear resistance of the roller, maintain a high grinding efficiency to increase the service life of the roller.
It is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide an improved wear-resistant roller of the kind mentioned in the introduction, wherein the wear surface comprises a high fraction of hard phase materials in a central portion of the wear surface and a lower fraction of hard phase material in a peripheral portion of the wear surface seen in the axial direction of the roller. Also, it is an object of the present invention to provide a method of forming a wear surface on a roller body characterized in welding a first welding bead to a central portion of a wear-resistant roller, said first welding bead comprising a first secondary fraction of carbide material, welding a second welding bead to a peripheral portion of the wear-resistant roller, said second welding bead comprising a second secondary fraction of carbide material, said second fraction of carbide material being lower than said first secondary fraction of carbide material.
The above objects, together with numerous other objects, advantages, and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by a wear-resistant roller for crushing of particulate material, such as crude ore for use in the cement or minerals industry, comprising a roller body, a wear surface on the roller body having an axial extension in an axial direction of the roller and a radial extension in a radial direction of the roller, and the wear surface comprising a primary fraction of matrix material and a secondary fraction of hard phase material suspended in the matrix material, wherein the secondary fraction of hard phase material in a central portion of the wear surface is higher than the secondary fraction of hard phase material in a peripheral portion of the wear surface seen in the axial direction of the roller.
The advantage of having lower contents of hard phase materials in peripheral portions of the wear surface is that they wear off as quickly as the central portions which are exposed to much higher wear, since the grinding pressure is higher in the central portions.
In one embodiment of the invention, a distal portion of the wear surface comprises a higher fraction of hard phase material than a proximal portion of the wear surface seen in the radial direction of the roller.
In another embodiment of the invention, the wear surface comprises a plurality of central portions of the wear surface, wherein said plurality of central portions comprise secondary fractions of hard phase material being higher than the secondary fraction of hard phase material in a peripheral portion of the wear surface.
In an embodiment of the invention, the wear surface comprises a plurality of distal portions of the wear surface, wherein said plurality of distal portions comprise secondary fractions of hard phase material being higher than the secondary fraction of hard phase material in the proximal portion of the wear surface.
In an embodiment of the invention, the wear surface is made from a plurality of Plasma Transfer Arc (PTA) welding beads comprising at least two different secondary fractions of hard phase material.
In an embodiment of the invention, the wear surface is made from a plurality of laser cladded deposits comprising at least two different secondary fractions of hard phase material.
Laser cladding is a method of depositing material by which a powdered or wire feedstock material is melted and consolidated by use of a laser in order to coat the roller with a wear surface having different fractions of hard phase material in different portions of the wear surface.
In an embodiment of the invention, the wear surface is made from a matrix of Plasma Transfer Arc (PTA) welding beads comprising a plurality of different secondary fractions of hard phase material.
In an embodiment of the invention, the wear surface is made from a plurality of Plasma Transfer Arc (PTA) welding beads comprising a plurality of different secondary fractions of hard phase material continuously changing from a high concentration level to a low concentration level of secondary fractions of hard phase material.
In an embodiment of the invention, the primary fraction of matrix material is selected from a group consisting of Nickel, Iron, Cobalt and alloys thereof.
In an embodiment of the invention, the secondary fraction of hard phase material is selected from a group consisting of Wolfram Carbide, Titanium Carbide, Vanadium Carbide, Niobium Carbide, Silicon Carbide, Boron Carbide, Chromium Carbide, Tantalum Carbide, Aluminium Oxide and solid solutions thereof.
In an embodiment of the invention, the central part of the wear surface preferably comprises 40-75%, or more preferably 50-72% or even more preferably 55-70% of the secondary fraction of hard phase material and wherein the peripheral portion preferably comprises 30-50%, or more preferably 35-45% or even more preferably 38-42% of secondary fraction of hard phase material.
In an embodiment of the invention, wherein the distal part of the wear surface preferably comprises 40-75%, or more preferably 50-72% or even more preferably 55-70% of the secondary fraction of hard phase material and wherein the proximal portion preferably comprises 30-50%, or more preferably 35-45% or even more preferably 38-42% of secondary fraction of hard phase material.
In an embodiment of the invention, the wear surface comprises a series of circumferential welding beads comprising at least two different secondary fractions of hard phase material.
In an embodiment of the invention, the welding beads preferably have a width of preferably 8 mm to 24 mm, or more preferably a width of from 10 mm to 22 mm or even more preferably a width of from 12 mm to 20 mm.
According to an embodiment of the invention, a roller mill comprises a feed of material, at least one wear-resistant roller as described above for comminution of the feed of material, and the mill being a roller press or a vertical mill.
In an embodiment of the invention, the wear surface comprises a plurality of central portions of the wear surface, wherein said plurality of central portions comprise secondary fractions of hard phase material being higher than the secondary fraction of hard phase material in a peripheral portion of the wear surface, and wherein the secondary fractions of hard phase material continuously increases from the highest fraction being in the most central portion to the lowest fraction being in the most peripheral portion of the central portions.
In an embodiment of the invention, the wear surface comprises a plurality of distal portions of the wear surface, wherein said plurality of distal portions comprise secondary fractions of hard phase material being higher than the secondary fraction of hard phase material in a proximal portion of the wear surface, and wherein the secondary fractions of hard phase material continuously increases from the highest fraction being in the most distal portion to the lowest fraction being in the most proximal portion of the distal portions.
In a method of forming a wear surface on a roller body according to the invention, the method comprises the steps of welding a first welding bead to a central portion of a wear-resistant roller, said first welding bead comprising a first secondary fraction of carbide material and welding a second welding bead to a peripheral portion of the wear-resistant roller, said second welding bead comprising a second secondary fraction of carbide material, said second fraction of carbide material being lower than said first secondary fraction of carbide material.
In an embodiment of the method according to the invention, the method further comprising the steps of welding a third welding bead to a distal portion of the wear-resistant roller, said third welding bead comprising a third secondary fraction of carbide material, welding a forth welding bead to a proximal portion of the wear-resistant roller, said forth welding bead comprising a forth secondary fraction of carbide material, said forth fraction of carbide material being lower than said third secondary fraction of carbide material.
The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which
Hardfacing is the deposition of thick coatings of hard, wear-resistant materials on a worn or new component surface that is subject to wear during operation.
More also indicated in
Proximal indicates close to the centre of the roller, whereas distal indicates close to the grinding surface of the roller. Central indicates the mid-section of the roller, whereas peripheral indicates closer to the edge of the wear surface roller in the axial direction of the roller.
Further, as seen in
Advantageous welding bead widths preferably lie in the range of 8 mm to 24 mm, or more preferably a width of from 10 mm to 22 mm or even more preferably a width of from 12 mm to 20 mm.
The wear-resistant roller 1 according to the invention may be implemented in a roller press 10, a vertical mill 11 or other appropriate grinding apparatus or comminution devices. Perspective views of a roller press 10 and a vertical mill 11 are shown in
In a method of forming a wear surface on a roller body according to the invention a first step comprises welding a first welding bead to a central portion of a wear-resistant roller, said first welding bead comprising a first secondary fraction of hard phase material. After the first welding bead a second welding bead is welded to the roller body, a second welding bead is welded to a peripheral portion of the wear-resistant roller, said second welding bead comprising a second secondary fraction of hard phase material, said second fraction of hard phase material being lower than said first secondary fraction of hard phase material. The difference in secondary fraction of hard phase material partial overlap ensures re-heating of the overlapping volume thereby increasing the wear resistance in this volume by up-concentration of carbides in the lower parts of the overlapping volume close to the roller body.
In a method of forming a wear surface on a roller body according to the invention, the method comprises the steps of welding a third welding bead to a distal portion of the wear-resistant roller, said third welding bead comprising a third secondary fraction of hard phase material, and welding a forth welding bead to a proximal portion of the wear-resistant roller, said forth welding bead comprising a forth secondary fraction of hard phase material, said forth fraction of hard phase material being lower than said third secondary fraction of hard phase material.
The wear surface may comprise a series of circumferential welding beads, wherein neighbouring circumferential welding beads have different secondary fractions of HPM and substantially follow the circumferential direction of the wear-resistant roller. However, in some embodiments of the invention the welding beads instead of having a linear shape have a sinusoidal shape, a zigzag shape or a step-function shape in the circumferential direction.
Vertical mills are common machines for grinding various mineral ores and are widely used within cement production. Vertical mills are characterized by having a horizontal grinding table, which is driven by a gear and motor unit. A number of vertical rollers are positioned on top of the grinding table along its periphery, as seen in
Due to the rolling dynamics between the grinding table and vertical rollers, an asymmetric wear profile appears on both counteracting surfaces, as seen in
Number | Date | Country | Kind |
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PA 2014 70818 | Dec 2014 | DK | national |
Filing Document | Filing Date | Country | Kind |
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PCT/DK2015/050371 | 12/1/2015 | WO | 00 |