MXPA99007338A - Abrasion resistant surface coatings and method of forming same - Google Patents

Abstract

Hardfacing for a sugar mill roller is disclosed including a wear resistant material supported by a mild steel matrix and applied to the outer surface of the sugar mill roller. A method of hardfacing a sugar mill roller is also disclosed wherein a mild steel weld pool is formed on the surface of said roller, a particulate wear resistant material is impinged on the weld pool, and the weld pool is allowed to solidify. A method of applying a hardfacing capping to a ridge profile of a sugar mill roller is also disclosed, wherein hardfacing composition comprising a mild steel matrix material is progressively laid up by welding and a particulate abrasion resistant material is continuously impinged thereon. Preferably, the ridge profile includes a base portion and one or more elongate projections extending away from the base portion, and one or more beads of hardfacing composition are applied to the base portion against the sides of the or each projection in successive layers until the height of the or each projection is substantially reached. It is further preferred that is at least one further bead of hardfacing composite is applied to the or each responsive projection to substantially encapsulate same.

Description

SURFACE COATINGS RESISTANT TO ABRASION AND METHOD TO FORM THEMSELVES Technical Field This invention relates to mill rollers and abrasion resistant surface coatings for mill rolls, as well as to the method for constructing mill rolls and forming abrasion resistant surface coatings on mill rolls. The invention has particular application to sugar mill rolls and, for illustrative purposes, reference will be made to said application. However, it should be understood that the invention will have use in other applications where improved mill rolls are required. BACKGROUND TECHNIQUE In the sugar industry, sugar cane is usually crushed between rolls arranged in pairs or in groups of three. Generally, the rollers have a plurality of machined reliefs extending circumferentially around the rollers that form a surface of alternate bridges and valleys. The slots are normally spaced apart along the roller, however, it will be appreciated that in some applications, it may be convenient to have separate slots non-uniformly. The slotted arrangement provides support for the sugarcane fiber as it passes between the rollers, the groove of an upper roller being operatively aligned with its opposing roller ridges or lower rollers. A sugar mill roll is usually constructed as a cast roller mounted on an arrow and rotated by drive means. The wear-resistant material is sometimes provided on the cover of the grooved roller bearings, but only in intermittent places around the circumference of the roller. This approach has been partially taken because it was thought that the intermittent application of the abrasion resistant material produced the best gripping surface for grinding sugarcane. Normally, conventional bonding material is used, including, for example, high speed steel, austenitic manganese steel, iron with high austenitic chromium content, cobalt or copper based alloys, or nickel-chromium-boron alloys, according to the practices exhibited in Jones, FD, & Horton, H L, Machinery's Handbook. ISBN 0-831 1 - 1 155-0. Additionally, for example, the abrasion resistant material such as small pieces of tungsten carbide can be placed in the matrix to form a mixed cementation material in the cementation materials listed in this reference or in mild steel or stainless steel welding. After a period of use, the sugar mill rolls need to be renewed due to the uniform wear of the mixed cement materials of the cane and / or the bagasse between the rollers. In order to remove said roller, according to traditional practices, the entire roller is removed from the mill, broken and re-cooked in a new roa'iiio. This process is expensive in terms of replacing the entire roller and requires significant downtime for the sugar mill to replace the roller. There are also heavy transport costs to remove and supply the rollers to the site. The present invention helps to improve one or more prior disadvantages and to provide a roller having a wear resistant surface and forming method, some of which will be reliable and efficient to use. DESCRIPTION OF THE INVENTION In view of the foregoing, this invention, in one aspect, largely resides in a sugar mill roll that includes: a roller body in substantially circular cross section having a plurality of machined reliefs, operating circumferentially, formed to be substantially parallel and spaced apart along a substantial portion of said roller body, each of the machined reliefs including one or more planar portions and a ridge over said one or more planar portions, each ridge including a plurality of plies welding, supporting a wear-resistant material in them.

Preferably, each machined relief includes two or multiple flat portions, separated by a wall portion and one or more of the welding layers are supported on the flat portions against the wall portion. It is also preferred that the roller body is formed of gray cast iron, and that the ridge cap includes a first weld layer of stainless steel and it is further preferred that the first layer includes wear resistant material. In another aspect, this invention broadly relates to a method for applying the cementation to a sugar mill roll, the method including: providing a roll body of substantially circular section; machining a plurality of reliefs operating circumferentially on said roller body, the reliefs being substantially parallel and axially spaced along a substantial portion of the roller body, each relief including one or more planar portions, and on each of said reliefs , forming a solder matrix on, or each innermost flat portion by successfully applying solder on, the pre-layer until a ridge is formed substantially in the whole part surrounding the roller body, at least some of said solder layers having wear-resistant material in particles supported therein. Preferably, a wall portion is machined on each relief so as to provide one or more planar portions on each side of the wall portion and the weld is applied against each side of the wall portion in successive layers until it is substantially reached. the height of the wall portion. Welding should be applied by any suitable welding process, however, inert metallic gas welding (gim) or inert gas welding of tungsten (tig) is used, and the weld combination is applied first, or each flat portion is formed of a stainless steel welding bar without wearing the wear resistant material added thereto and successive layers of a mild steel welding bar are formed in which said respective successive welding combinations are incised with a wear resistant material in particles. The layers are placed one on top of the other until a desired profile covering is formed substantially in all parts around each relief. In another aspect, this invention resides broadly in a sugar mill roll including a roll body formed in accordance with the method as described above. However, it will be appreciated that cementation can be applied to substrates other than sugar mill rolls. In another aspect, this invention relates broadly to a roller assembly including: a mounting arrow; a plurality of cover portions, each cover portion being mountable on said mounting arrow and configured to abut in order to form a roller cover; each of said cover portions having an external perimeter and an internal diameter of a dimension that allows the hermetic coupling of said roller cover over said mounting arrow, and a wear resistant surface applied to the external perimeter. The roller lids may have a substantially uniform external surface for receiving the luting, but preferably, the lids of the roller include a plurality of grooves extending circumferentially around the outer perimeter as described above. The roller assembly is preferably circular in section, although it will be appreciated that other sections may be used, such as elliptical or bone-shaped interengaging sections. The wear resistant surface preferably has the shape of a wear resistant weld applied to the outer perimeter as described above. Preferably, at least some of the reliefs between the grooves include a lid portion with an abrasion resistant material on each lid portion. The roller cover can include cover portions that can be connected to form an annular cover element, or can be comprised of a unitary annular cover element, each cover element being able to abut to form the roller assembly such as, for example, a sugar mill roll. In sugar mill applications, the groove profile is selected to be similar in size and cross-sectional shape to the slot profile of cast sugar mill rolls, which generally have a gap between 15 mm and 80 mm, but more commonly, a separation of either 25 mm, 37.5 mm or 50 mm. Preferably, the groove profile includes relief profiles including an elongated projection and a flat area on each side of the elongated projection of the successive layers of welding can be applied sequentially, allowing time between the respective layers to cool the weld. Suitably, the first weld layer on each side of the projection is applied to the respective planar areas. The elongated projection is of an adequate thickness to function as a dam preventing the weld from falling on the other flat area. The application combination of the weld layers is adapted to produce a weld profile that when solidified is of substantially triangular cross-section. The combination of welding torch angle, profile of pre-machined roller teeth, roller rotational speed (welding surface velocity), raw materials, preheating welding consumables and specific provide the finished profile allows a Sugar mill roll is used in a condition such as welding. This is preferably done while rotating the roller with its longitudinal axis in the horizontal plane. In another aspect, this invention largely resides in a method for applying a mixed cementing material to a sugar roller, said method including rolling said roller at a suitable circumferential speed for the application of the mixed cementing material, whereby the mixed material Cementing is applied continuously around the entire circumference of the roller. Preferably, a plurality of beads of mixed cementation material is applied around the roll. It is also preferred that the cement beads be applied in parallel relation along the distal edge portions of the relieves normally provided on the sugar mill rolls. The roller preferably includes cover portions as defined above. The cover portions can be formed of machined solid metal, such as steel, rolled or cast. Where the cover portion is formed by rolling, the mixed cementation material can be applied before or after forming. Preferably, the wear resistant cementation is made using ARM-2 welding manufactured and supplied by Abrasion Resistant Materials Pty Ltd, at a suitable current, normally, from 200 to 260 amps, and at a suitable potential, normally, from 22 to 26 volts. in a "gim" atmosphere at a sufficient linear regime to coat the net area required for welding. This wire conforms to ES2901 Part 1 1970A18 and AWS A5.18 E70S-6.

Sand may be added in the melted solder combination during the welding process, by any suitable means, and preferably has 12/35 mesh size. Surprisingly, it has been found that the abrasion resistant cementation material provided as described above provides a superior clamping surface for the sugar cane mill. In addition, the sand improves with use and it is thought that this is at least partly due to the acid juices, preferably releasing part of the matrix and providing a more pronounced profile of the hard tungsten carbide particles that are fastened to the fiber mat on contact. It is also thought that there is a contribution to the erosion of the frictional wear of the bagasse on the matrix. In a further preferred form suitable for use as a crushing roller of the sugar cane mill, the roller cover includes fixing means for attaching to the mounting shaft. For example, where the roll cap has the shape of arcuate segments, pairs of semicircular or triplet section pieces can be provided each having segments with internal radii at 120 °, and so on. The segments may abut to form a roller end cap that is removable and replaceable on the mounting arrow to form the sugar cane roll. The mounting arrow is suitably adapted to receive the segments by providing complementary fixing means which can be operatively coupled with the fixing means on the respective segments. The fixing means may include, for example, one or more flange portions arranged circumferentially around the inner arc of the circumference at each respective end of each roll cap. Each flange portion may further include an opening extending therethrough in a coaxial direction and through which the fastening means, such as a bolt, screw or the like, can pass to hold the roller cap to the mounting arrow through the corresponding openings on the mounting arrow. However, preferably, a sleeve with a flattened portion extending axially along its entire length is provided, the sleeve being adapted to fit over the arrow and receive the cemented covers that include a complementary internal plane over their respective internal holes. The end caps of the roller are fixed, by applying bolts, on the ends of the sleeve. In another aspect, this invention relates broadly to a method for forming a roller assembly including: providing a mounting arrow; forming a plurality of cover portions; mounting each cover portion to the mounting arrow in abutting relationship to form a roller cover, and applying a wear resistant surface to the outer perimeter of at least some of the cover portions. Preferably, the wear resistant surface is applied to the cover portions before being mounted on the mounting shaft. The cover portions may be raised in temperature relative to the temperature of the mounting arrow in order to provide sealing engagement of the cover portions on the mounting shaft. For example, the cover portions may include an internal diameter of one dimension that allows for sealing engagement of the cover portion on the mounting arrow by heating said cover portion to a temperature sufficient to expand the cover for engagement around the arrow , so it can adjoin a plurality of said covers along the arrow. Where cover portions are provided in arcuate portions, they are suitably circumferentially connected to form respective annular covers. In a preferred embodiment, each cover portion includes a plurality of grooves extending circumferentially around the respective outer perimeter as described above. In another aspect, this invention largely resides in a cementation for a sugar mill roll, said cementation including a wear resistant material supported by a mild steel matrix and applied to the other outer surface of a sugar mill roll.

BEST MODE FOR CARRYING OUT THE INVENTION In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein: Figure 1 is a developed view of a set of cemented rollers mounted on a bearing shaft; Figure 2 is an end view of the roller assembly of Figure 1; Figure 3 is a section on A-A of Figure 2 showing part of the roller assembly; Figure 4 is a sectional detail view of the abrasion-resistant material applied to lids of the grooves of the roller of Figures 1 to 3; Figure 5 is a detailed view of an alternative application of the abrasion resistant material of Figure 4; Figures 6 to 9 are detailed sectional views of alternative preferred embodiments of relief profiles for the application of the mixed cementation material; Figure 10 is a sectional detail view of the wear profile of the bridge of Figure 6, after a normal partial cycle of use, and Figure 11 is a collective diagramatic representation of self-grinding of the wear profile of Figure 10 Referring to Figures 1, 2 and 3, a roller assembly 10 includes a plurality of roller cover sections, one of which is normally shown at 11 in Figure 1, each mounted on a collar 18 that at its once, it is mounted on an arrow 12. In order to hold the roller cover sections 11 on the arrow 11 and the sleeve 18, two respective end cover sections 13 are provided. Each of the outer cover section 13 and the cover section 11 includes a plane 19 which engages a complementary key 20 on the sleeve 18 to prevent the cover sections 11 from rotating on the sleeve 18. Referring to FIG. Figure 3, each of the end cover section 13 and the cover section 11, includes a plurality of reliefs normally shown at 21 and interposed therebetween, a plurality of grooves normally shown at 22 extending circumferentially around their respective external perimeters. With reference to Figure 4, a portion of an end or center cover section 13 or 14 is shown in the sectional view. Each relief 21 includes a relief cover portion 31 on which a plurality of abrasion resistant solders 33 are provided, to provide the abrasion weld cover 32. In this embodiment, the slots 22 are not plugged with the welding material.

Referring to Figure 5, the reliefs 21 and the grooves 22 are provided with a plurality of abrasion resistant welds 33 in a manner similar to that provided on the abrasion resistant welding cap 32 shown in Figure 4. However, the entire surface of the reliefs 21 and the grooves 22 , are provided with the abrasion resistant welds 33 to form an abrasion resistant welding liner 34. Referring to Figures 6 to 9, a relief profile 23 has a variety of shapes as shown. In Figures 6 to 9, the welding material is represented by a triangle and dot filling pattern. The following combinations with respect to the welding process are critical to creating the weld profile so that when the molten solder solidifies, the final weld shape has a substantially triangular cross section. The combination of the angle of the welding torch, the tooth profile of the pre-machined roller, the rotational speed of the roller (welding surface velocity), raw materials, preheating and specific welding consumables, provide the finished profile of a mill roller of sugar to be used as such a condition. This it is preferably performed while the roller rotates with its longitudinal axis in the horizontal plane. The shape shown in Figures 4 and 5 are very difficult to form otherwise with the inert gas metal carbide (gim) cemented except by elemvando the roller of the horizontal and tilting it on its longitudinal axis. It will be appreciated that preferred pre-machined shapes may vary from those shown in Figs. 6 to 9. It is preferred that the relief profiles 23 be substantially symmetrical, however, it will be appreciated that in some applications, where a non-symmetrical weld profile is required or desired, a symmetrical relief profile may be appropriate. However, the relief profile 23 includes a base portion 24 and one or more projections 25. The relief profile 23 shown in Figure 7 is the preferred option for general applications, however, the relief profile 23 shown in figure 23 is preferred for rollers of longer spacings. In each case, the welding layers 1 to 9 are successively applied as required for the relief profile 23. Another way of describing the profile of the relief 23 in Figures 6 to 9, is as a base portion 24 having a or more stepped or inclined reductions in cross section. It is thought that the dispersion of tungsten carbide through the matrix and the weld adhesion of multi-step layers for the roll and for each layer, give an advantage to each of the profiles of the relief 23 shown in Figures 6 to 9. Clearly, the dimensions could be provided in scale to adapt larger profiles of larger rollers. Larger separating rollers may also need the same machined profiles on the teeth to achieve similar results. The relief profile 23 in Figure 6 is a minimum weld pitch profile of nine; the relief profile 23 in Figure 7 is a minimum weld pitch profile of seven and the respective relief profiles 23 in Figures 8 and 9 are for a minimum weld pitch profile of seven or nine, or a profile minimum welding pitch of five, respectively. Although the successive welding beads are generally applied in numerical order as given in Figure 7, the order can change to 1, 4, 2, 5, 3, 6 and then 7. A similar method can be applied to Figure 8 with successive welding beads applied on the alternate sides of the projection 25. The relief profiles 23 described above have been applied to a normal gray cast iron roller, despite the expected difficulties in the relatively high carbon content of the iron. casting affecting the welded profile by diffusion of carbon in the weld. Referring to Figure 10, the relief profile 23 has a weathered to worn surface shown at 26, with more of the base portion 24 using that of the lid portion 27. It has been found that a portion is formed below the section 18 in the experimental tests of the invention on the grinding of the sugarcane after grinding a million tons of cane. In addition, it has also been surprisingly found that the wear-resistant coating of the present invention increases its hold on the bagasse, in addition to which it appears that the substrate into which the carbide is embedded partially detaches from the surface of the lid portion 27. , exposing the angular sand of the carbide material to hold onto the bagasse. Accordingly, as shown in FIG. 11, a portion of the sugar mill roll 40 has a pulley profile generally shown at 41. A cementitious composition of the present invention is applied to the relief stops typically shown in FIG. 42. An enlarged portion 45 is shown in the separate views at 51, 52, 53, and 54. The enlarged portion includes a surface 46 of mild steel imbibed with tungsten carbide sand, some of which is exposed and is normally shown at 47. As the surface of the weathered cementation, some of the sand 47 is detached from the die, the surface being shown in dashed lines at 48 in the views 52, 53 and 54. The surface 46 wears or peels off to expose new sands as shown at 50 in views 53 and 54. In order that this invention can be more easily understood and have a practical effect, reference will now be made to an example of the invention having the process specifications of welding as follows: The rotating speed of the roller to apply welding layers was in the range of 21.7 mm to 22.3 mm per second for the solder of the layer of lard and the layers of cemented. The rotation speed of the roller to apply final crown welding was 19.35 mm at 20.02 mm per second. The weld blowing angle was 18 ° from the vertical when applied to the upper (ie, horizontal) perimeter of the roller. This can also vary up to 25 ° to weld the lower layers in the machined relief profile 23 as shown in Figure 6. The current was on a scale of 200 A to 300 A and the voltage of 22 V to 26 V in ARM - 1 and 1 and 2 wires. These wires are 0.9 mm wires that conform to BS2901 Part 1 1970A18 and AWS AS.18 E70S-6. The preheating temperature of gray cast iron rollers was 100 ° C + 5 ° C before welding. The ARM 1 wire is made of mild steel and the ARM 2 wire is made of 309L stainless steel. An additional technique can be used where the ARM-2 wire is used as a sandfree coating of ARM STD 1 tungsten carbide in the weld. Next, the ARM-1 wire with ARM STD 1 of tungsten carbide sand is immediately welded onto the first layer of butter by the second layer creating a unique matrix and metallurgical weld. This affects the shape of the weld bead and the cooling characteristics and seems to affect the solidification (opposite to melting) of the tungsten carbide in the weld combination. This produces a superior bond to the gray cast iron rollers and in particular reduces the problem of longitudinal cracking under the bead in the area affected by the heat.

In use, the abrasion resistant surface of this invention can be applied to a sugar mill roll. Although it will be appreciated that the mixed cementation material can be applied to a solid roll according to the present invention, instead of replacing the entire sugar mill roll when it wears out, the roll covers can be unscrewed from a roll drum and they are replaced by the replacement cylindrical portions.

The worn roller caps can be recycled by separating the mixed cementation materials and the substrate according to any known process. Occasionally, one or more cover sections of a roller may wear out more than the rest. In such a case, only the worn cover sections can be replaced, reducing the cost of roll maintenance. Of course, it will be understood that the foregoing was given only by way of illustrative example of the invention and that all such modifications and variations thereto as will be apparent to those skilled in the art are considered to fall within the broad scope and scope of the invention. the invention in accordance with the following claims.

Claims (8)

1. CLAIMS 1. A sugar mill roll including: a roller body of substantially circular cross section having a plurality of machined reliefs operating circuentially shaped to be substantially parallel and spaced apart along a substantial portion of said roller body , each machined relief including one or more planar portions and a ridge over said one or more planar portions, each ridge including a plurality of weld layers bearing thereon a wear resistant material. A sugar mill roll according to claim 1, wherein said machined relief includes two, or a multiple of two, flat portions, separated by a wall portion and one or more of said welding layers are supported on the respective ones of said flat portions against the wall portion. 3. A sugar mill roll according to claim 1 or claim 2, wherein the roller body is formed of gray cast iron and said ridge includes a first weld layer of stainless steel. 4. A sugar mill roll according to claim 3, wherein the first layer includes material not resistant to wear. 5. A method for applying cemented to a sugar mill roll, the method comprising: providing a roll body of substantially circular cross-section; machining a plurality of reliefs running circuentially on said roller body, the reliefs being substantially parallel and axially spaced along a substantial portion of the roller body, each relief including one or more flat portions, and on said relief, forming a welding matrix on the, or each internal flat portion by successively applying welding, on the previous layer until a desired profile ridge is formed substantially throughout the roller body, at least one of said welding layers having wear resistant material in particles supported in them. A method according to claim 5, which includes machining a wall portion on each relief in a manner that provides one or more flat portions on each side of the wall portion, and applying solder to each side of the wall portion in successive layers until the height of the wall portion is substantially reached. A method according to claim 8, which includes applying one or more additional layers of welding to each respective relief to substantially encapsulate the wall portion. A method according to any of claims 5 to 7, wherein the welding is applied by welding of metallic inert gas (gim) or inert gas welding of tungsten (git), characterized in that the welding combination is applied first a, or each flat portion is formed of, a stainless steel welding rod without any wear resistant material added thereto and the successive layers are formed of a mild steel welding rod used to form the respective welding combinations coincident with the wear-resistant material in particles, until a ridge of the desired profile is formed in substantially the entire part around the relief. 9. A sugar mill roll including a roller body formed according to the method of any of claims 5 to 8.