Wear-resistant spray coating of screen cylinder by changing spray angle

Abstract

The screen cylinder includes a cylindrical screen media formed of a plurality of circumferentially spaced, axially extending wedge wire bars, the wedge wire bars having an inlet face facing the inlet side. The axially extending wedge wire bars have a cross-sectional shape optimized for applying a spray-type wear-resistant coating to their inlet faces using spray nozzles. To apply the coating, the angle of the spray nozzles is varied circumferentially relative to the inlet side of the screening media to vary the nozzle spray angle to apply the coating sprayed onto the bars.

Description

[Technical Field]

[0001] The present invention relates generally to a screen cylinder for removing excess solid contaminants from a solid-in-liquid suspension such as pulp, and in particular to a screen cylinder made from wedge wire bars having a configuration optimized for receiving a spray-on wear-resistant coating, and a method for applying the wear-resistant coating. [Background technology]

[0002] Papermaking involves the processing or production of pulp, which is a solid suspension of fibers, such as cellulose or other fibers, in a liquid. Pulp often contains various contaminants, such as wood chips, fiber bundles, metal pieces, hardened glue, or other contaminants. This is especially true when paper is made from recycled paper as the raw material for the pulp, as hardened glue, metal pieces, and plastic particles may be present in such recycled paper pulp. If not removed, these contaminants can reduce the quality of the paper and / or disrupt the papermaking process.

[0003] Pulp is often screened to remove contaminants, including oversized particles or fibers. Screening may also be used to separate pulp into streams with different fiber size distributions. Pulp screening can be accomplished by introducing the pulp into a pulp screen, where an acceptable portion of the pulp passes through openings, such as slots, in the screen. Oversized solid contaminants or other unacceptable portions of the pulp do not pass through the slots or openings in the screen and are discharged as rejects from the outflow end of the screen via an outlet. Pulp screens may also be used to remove oversized and other solid contaminants from slurries and solid suspensions other than pulp.

[0004] Pulp screening can be accomplished using a screen cylinder located within a pulp screen. The screen cylinder can screen many types of fibers, including, but not limited to, cellulose, cotton, glass, or other fibers. The screen cylinder can be an inward-flow screen cylinder, in which an acceptable portion of the solids suspension flows radially inward through the screen cylinder, or an outward-flow screen cylinder, in which an acceptable portion of the solids suspension flows radially outward through the screen cylinder. The pulp screen can include a rotor or other device operable to accelerate the pulp suspension to create desirable flow conditions at the entrance to the screen cylinder apertures and to create pressure pulps that flush blockages back through the screen cylinder apertures. Each of these actions restricts the passage of contaminants and undesirable pulp while promoting the passage of acceptable pulp through the screen slots. Some screen cylinders utilize a solid metal cylinder with multiple holes or slots drilled or milled into it. However, to increase the throughput of the pulp screening process, a screen cylinder comprising a plurality of longitudinally arranged profiled wedge wire bars, the wedge wire bars defining a plurality of slots therebetween that extend the majority of the length of the screen cylinder, is generally preferred for pulp screening.

[0005] These wedge wire screen cylinders are typically made from multiple wedge wire bars arranged in a cylindrical shape. The slots formed between the wedge wire bars allow the desired pulp to pass therethrough while preventing undesired pulp or other contaminants from passing therethrough. Therefore, the slot size of the screen cylinder is selected based on the pulp parameters and the desired results. However, pulp is abrasive, and after some use, the screen cylinder and the bars forming it will wear out. Screen cylinder wear can affect the performance and / or efficiency of the screen cylinder.

[0006] The bars forming the slots of screen cylinders have been coated with wear-resistant coatings, such as chromium, to help minimize wear on the bars and, therefore, the cylinders. The chromium coating is applied using an electroplating process in which the cylinder is immersed in a bath of chromic acid and other chemical components. The cylinder acts as the cathode during the electroplating process, thus depositing chromium on the wedge wire bar. However, due to variations in various factors in the electroplating process, including current flow, temperature of the acid bath, gap between the anode and cathode (i.e., the cylinder), and chemical strength of the acid bath, it can be difficult to consistently apply a chromium coating to the surface of the bar. Wear-resistant coatings can also be applied to the bars by known coating or spraying methods, including, but not limited to, high-velocity oxygen fuel (HVOF) spraying, plasma spraying, laser spraying, chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD).

[0007] High-velocity thermal coatings are typically sprayed onto the bars using high-pressure, high-velocity nozzles. The spray can be difficult to control, potentially resulting in unwanted placement of the coating on the screen cylinder and bars. For example, high-velocity spray can deflect from the bar surface onto adjacent surfaces, resulting in so-called "overspray." Overspray of the wear-resistant coating, including deflection of the coating onto adjacent surfaces, can create restrictions that affect flow through the slots. Alternatively, the spray may not reach areas where wear protection is desired, or may not be applied to the required extent. For example, a wear-resistant coating applied to a bar on the inlet face near a ridge on the bar, where excessive wear may occur, may not receive sufficient coating. In another example, an area on the inlet face near the transition region may not receive sufficient coating because the coating spray is effectively blocked by the ridges on the adjacent bar. Summary of the Invention [Problem to be solved by the invention]

[0008] It would therefore be desirable to have a screen cylinder and methods of making and using the same in which an abrasion resistant coating is applied in such a way that the resulting coating is located in desired locations on the bar and not in other locations, minimizes the effects of overspray, and / or provides a coating pattern or shape on the screen cylinder bar that reduces wear on the screen cylinder, optimizes the life of the screen cylinder, and provides hydrodynamic conditions essential for good screening capacity.

[0009] Additionally, the shape of the wedge wire bars, including their inlet and side faces, including side portions forming slots therein through which pulp or other solids-in-liquid suspensions pass, can be optimized to reduce overspray and eliminate or minimize deposition of sprayed-on wear-resistant coatings in undesirable locations on the bars, including at or near the bar slots, or even on the sides of the bars. Such shapes, along with other features and techniques disclosed herein, also facilitate maximizing the overall coating deposition efficiency, maximizing coating thickness on the inlet face near the bar's ridges and minimizing areas on the bar's inlet face opposite the ridges that might otherwise receive insufficient coating. Additionally, techniques for spraying the wear-resistant coating onto the bars can be optimized to reduce overspray and eliminate or minimize deposition of sprayed-on wear-resistant coatings in undesirable locations on the bars, including at or near the bar's slots, or even on the sides of the bars, maximizing coating thickness on the inlet face near the bar's ridges and minimizing areas on the bar's inlet face opposite the ridges that might otherwise receive insufficient coating.

[0010] Thus, there is a continuing need for screen cylinders having wear-resistant coatings that can be applied in a more controlled manner to specific desired locations on the bars and / or sections of the screen cylinder, while minimizing overspray and maximizing deposition and retention of spray material on the desired surfaces. [Means for solving the problem]

[0011] According to one or more embodiments, a screen cylinder includes a cylindrical screening medium having an inlet side and an outlet side. The screening medium is formed of a plurality of circumferentially spaced, axially extending wedge wire bars. Each wedge wire bar has an inlet side facing away from at least one support ring, a first side extending from the inlet side to an attachment end of the bar opposite the inlet side, and a second side extending from the inlet side to the attachment end of the bar opposite the first side. Each axially extending wedge wire has an inlet side shape optimized for spraying a wear-resistant coating on its inlet side. Each bar is formed of a base material and has an inlet side, a first side having a first slot surface, and a second side having a second slot surface opposite the first side. The first slot surface of one bar and the second slot surface of an adjacent bar can define a slot. A transition region connects the second slot surface to the inlet side. A ridge is located between the inlet face and the first slot surface. The ridge i) is located at a radial distance farther from the support ring than the radial distance from the support ring to the transition region, and ii) the ridge extends circumferentially at or beyond the first slot surface that defines the slot width. The wedge wire bar is shaped and configured such that an angle formed between: i) a first plane extending axially and radially from the center of the cylindrical screening media to a circumferential location where the ridge of the first bar is closest to the adjacent opposing bar; and ii) a second plane extending coplanarly axially from the inlet face where the inlet face intersects with the transition region of the adjacent bar facing the first bar is 80 degrees or greater. This angle is preferably 90 degrees or less, with a preferred angle being between 80 and 90 degrees.

[0012] A portion of the axially extending bars includes a spray-on wear-resistant coating over the matrix on the inlet-side surface of the screening media, the wear-resistant coating preferably not forming a layer extending beyond the first plane and / or a plane coplanar with the first slot surface at a location defining the narrowest dimension of the slot between the first slot surface of a first bar and the second slot surface of an adjacent bar facing the first slot surface of the first bar.

[0013] The base material forming the inlet face of the axially extending bar can include a first region of the inlet face adjacent the transition region, the first region extending toward the ridge and including a concave surface region, and a second region of the inlet face adjacent the first region including a convex surface region.

[0014] The first region extends toward the ridge and forms a concave surface region, which includes a region of increasing slope; in other words, a point on a plane tangential to the inflow surface region moves radially further away from the support ring at an increasing rate as the point moves circumferentially from the transition region toward the ridge. A second region of the inflow surface adjacent to the first region forms a convex surface region and includes a region of decreasing slope. The second region has a surface adjacent to the ridge that has a slope less than the slope of the second region adjacent to the first region. Each slope is measured at a point on a plane tangential to the inflow surface region. The slope can be gradually increasing in the first region and / or gradually decreasing in the second region. The first and second regions each preferably do not exhibit a negative slope. The cross-sectional shape of the inflow surface may resemble a smooth, continuous wave shape.

[0015] In some embodiments, the first region adjacent to the transition region can form a generally flat surface. This generally flat region adjacent to the transition region can be less than about 50 percent of the maximum width of the bar, preferably less than about 20 percent of the maximum width of the bar. This flat surface can also be oriented perpendicular to the radius of the screen cylinder. The second region adjacent to the ridge can also form a generally flat region. This generally flat region adjacent to the ridge can be less than about 50 percent of the maximum width of the bar, preferably less than about 20 percent of the maximum width of the bar. This flat surface can also be oriented perpendicular to the radius of the screen cylinder. The region between the first region adjacent to the transition region and the second region adjacent to the ridge can also be flat, but can also be sloped. For example, the first region and the second region can form a relatively flat region on an inlet surface with a relatively constant slope.

[0016] The wear-resistant coating is preferably applied using a high-velocity thermal spray process, such as a high-velocity oxygen-fuel (HVOF) process, and the coating is preferably 75 to 300 microns thick. The thickness of the wear-resistant coating on and perpendicular to the substrate preferably varies by less than 20 percent, ideally less than 10 percent. The wear-resistant coating can contain tungsten carbide and / or chromium carbide. For example, base elements such as Ti, V, Nb, Mo, Ta, and Hf can also exist as carbides and be used in carbide-containing wear-resistant coatings. Carbides of cobalt, chromium, and nickel can also be used in wear-resistant coatings. The wear-resistant coating can exhibit a hardness of 500 HV 0.05 to 1200 HV 0.05. Hardness values ​​can be determined by measurements performed according to standard Vickers hardness testing methods.

[0017] The axially extending bars have attachment ends on the outlet side that are secured to the cutouts in the rings to form the screen cylinder.

[0018] In yet another embodiment, a screen cylinder includes a cylindrical screening medium having a plurality of circumferentially spaced, axially extending slots formed between axially extending bars. The screening medium has an inlet side and an opposite outlet side. Each bar has an inlet side surface, a first side surface having a first slot surface, and a second side surface having a second slot surface opposite the first slot surface. The inlet side surface is between the first side surface and the first slot surface and the second side surface and the second slot surface. A ridge is located between the inlet side surface and the first side surface and the first slot surface. The inlet side surfaces of the axially extending bars extend from a transition region adjacent to the second slot surface. The inlet side surface includes a first region of the inlet side surface adjacent to the transition region and a second region of the inlet side surface adjacent to the first region including a convex surface region. The first region extends toward the ridge and includes a concave surface region. The first region has a region of increasing slope. The transition region connects the second side surface and the second slot surface to the inlet face. The second region of the inlet face has a region toward the ridge where the slope decreases. The ridge is i) located at a radial distance farther from the support ring than the radial distance from the support ring to the transition region, and ii) the ridge extends circumferentially at or beyond the first slot surface that defines the slot width. The second region can have a surface adjacent to the ridge that has a slope less than the slope of the second region adjacent to the first region. The slopes of the first and second regions can increase and decrease, respectively. The slopes can increase and decrease gradually, respectively. The first region adjacent to the transition region can form a generally flat surface. The second region adjacent to the ridge can also form a flat region. The region between the first region adjacent to the transition region and the second region adjacent to the ridge can also be flat or sloped. For example, the first and second regions may form a relatively flat area on a relatively constant slope of the inlet face of the screening media. A spray-on wear-resistant coating is then applied to the inlet face of the screening media and the inlet face of the bars.The wear resistant coating preferably does not form a layer on the bar that extends circumferentially beyond the ridge and the transition region of the adjacent bar facing the ridge.

[0019] The abrasion-resistant coating is preferably sprayed onto the inlet face of the axially extending bars of the screening media using a spray nozzle. The spray nozzle is moved axially within the screen cylinder in a spray pass to apply the abrasion-resistant coating onto the inlet face of the axially extending bars of the screening media. The angle of the spray nozzle can be varied circumferentially relative to the inlet side of the screening media to vary the spray angle of the sprayed coating material onto the bars. For example, the angle of the spray nozzle relative to the inlet face of the bars can be varied during or between spray passes of the spray nozzle. Varying the spray nozzle angle optimizes spray of the abrasion-resistant coating onto the inlet face of the bars and reduces overspray. The spray nozzle angle can be varied circumferentially by approximately 5 to 31 degrees, preferably 5 to 14 degrees. The spray nozzle angle is rotated circumferentially from the transition region of one bar to the ridge of the same bar to vary the spray angle of the spray nozzle. Each incremental rotation of the spray nozzle angle should be 0 to 3 degrees, preferably 1 to 2 degrees. The angle is measured in a clockwise or counterclockwise direction from the nozzle to the central axis of the screen cylinder. The number of passes of the spray nozzle or the speed of the passes can be varied when spraying the coating, and such variations can occur for different spray passes or during a spray pass. Such variations can be used to vary the local thickness of the abrasion-resistant coating during or between spray passes, if desired.

[0020] The wear-resistant coating can be applied while the screen cylinder rotates while the spray nozzle moves through the axial passes and sprays the wear-resistant coating. The rotational speed of the screen cylinder can be kept constant, which can facilitate depositing a consistent layer of coating. Alternatively, the rotational speed of the cylinder can vary based on the position of the spray nozzle. The number of spray passes can be up to approximately 7 to 30 passes, with each pass defined as when the spray traverses the length of the screen cylinder. With each pass, the spray nozzle can deposit a coating approximately 10 microns thick.

[0021] Although the foregoing general description and the following detailed description describe various embodiments and provide an overview or framework for understanding the nature and character of the claimed subject matter, the invention is in no way limited to the particular embodiments disclosed.

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments described herein and, together with the description, serve to explain the principles and operation of aspects of the invention. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 schematically illustrates a front perspective view of a screen cylinder according to one or more embodiments shown and described herein. [Figure 2] FIG. 2 is a schematic diagram illustrating a perspective view of a portion of the screen cylinder of FIG. 1 showing a plurality of profiled bars connected to a support ring of the screen cylinder according to one or more embodiments shown and described herein. [Figure 3] 2 is a schematic cross-sectional view of a profiled bar of the screen cylinder of FIG. 1, the profiled bar having a wear-resistant coating on the inlet face of the profiled bar; FIG. [Figure 4]FIG. 2 is a schematic cross-sectional side view of a pair of wedge wire bars having a wear-resistant coating mounted on a support ring and within the screen of FIG. 1, wherein the wedge wire bars have a slot between a first slot surface of one bar and a second slot surface of an adjacent bar, in accordance with one or more embodiments of the invention shown and described herein. [Figure 5] FIG. 2 illustrates a cross-sectional side view of three bars in the screen cylinder of FIG. 1 without a wear-resistant coating formed on the base material in accordance with one or more embodiments of the present invention shown and described herein. [Figure 6] (a) A schematic representation of a spray nozzle relative to one or more wedge wire bars for applying a wear resistant coating onto the inlet face of the bar and the angle of the spray nozzle that can be changed during its pass to apply a wear resistant coating onto the inlet face of the bar, (b) A schematic representation of a spray nozzle relative to one or more wedge wire bars for applying a wear resistant coating onto the inlet face of the bar and the angle of the spray nozzle that can be changed during its pass to apply a wear resistant coating onto the inlet face of the bar. [Figure 7] FIG. 1 is a diagram of a screen cylinder equipped with a robotic arm having a spray nozzle at its end for spraying a wear-resistant coating onto the inlet face of the bars. [Figure 8] FIG. 1 shows a cutaway view of a screen cylinder on a rotatable platform along with a robotic arm with a spray nozzle used to apply the wear-resistant coating. [Figure 9] FIG. 2 shows a schematic representation of the variation of circumferential spray angle for applying a wear-resistant coating onto the bars of the screen cylinder of FIG. 1. [Figure 10] FIG. 10 shows an enlarged cross-sectional view of a portion of the bar of FIG. 9, with three constituent layers forming part of the coating on the bar and applied at the spray angles noted in FIG. 9. DETAILED DESCRIPTION OF THE INVENTION

[0024] Reference will now be made in detail to embodiments of the screen cylinder having profiled wedge wire bars, examples of which are illustrated in the accompanying drawings, wherein the same reference numerals are used throughout to refer to the same or similar parts.

[0025] As used herein, directional terms, such as up, down, right, left, front, back, top, and bottom, refer only to the depicted figures and coordinate axes provided therein and are not intended to imply absolute orientation. Additionally, references to thickness, including the thickness of an abrasion-resistant coating, include and refer to a nominal thickness, which, when referring to an abrasion-resistant coating, may not be uniform, but rather may have some variation from a desired or nominal thickness. For example, a coating with a nominal thickness of 100 microns may vary 10-15% and not be perfectly uniform in thickness.

[0026] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a" element includes aspects having two or more such elements unless the context clearly dictates otherwise.

[0027] The terms "longitudinal" or "axial" as used herein may refer to an orientation or direction generally parallel to the central axis of the screen cylinder.

[0028] The term "radial" as used herein may refer to a direction along any radius extending outward from the central axis of the screen cylinder (FIG. 1).

[0029] As used herein, the term "circumferential" refers to a clockwise or counterclockwise direction, as the case may be, about the central axis of the screen cylinder.

[0030] As used herein, the terms "inlet" and "outlet" may refer to the relative location of a feature with respect to the direction of flow of a solids suspension or slurry, as the inlet when entering the slot and the outlet when exiting the slot. For the wedge wire bar of the present disclosure, the flow of the solids-in-liquid suspension generally is from the inlet face 32 of the profiled bar 12 toward the outlet mounting end 30 of the profiled bar 12. Thus, for example, "inlet direction" or "toward the inlet direction" refers to the upstream direction of the flow. However, "outlet direction" or "toward the outlet direction" refers to the downstream direction of the flow, which is opposite the inlet direction. "Upstream" and "downstream" refer to the relative flow locations of the overall time-averaged flow of the solids suspension moving from upstream to downstream. For a screen cylinder, the inlet end refers to the end of the screen cylinder where pulp enters, and the outlet end refers to the end where reject pulp exits.

[0031] The terms "solid contaminants" or "excessive solid contaminants" may also refer to solid objects such as fiber bundles, metal pieces, hardened adhesives, or other contaminants that are not intended to be present in a solid suspension or slurry and are undesirable, and can be distinguished from solid components intended to be present in a solid-in-liquid suspension, such as pulp fibers.

[0032] Referring to FIG. 1 , a flow-through screen cylinder 10 according to an embodiment of the present disclosure is shown. The screen cylinder includes an inlet end 8 at its axial end and an outlet end 6 at its opposite axial end. Pulp or a similar fibrous suspension enters the cylinder at the inlet end 8, and rejects (containing high concentrations of undesirable components) exit the cylinder at the outlet end 6. The acceptor, containing a preponderance of desirable pulp with reduced concentrations of undesirable components, passes radially through the screening media and is collected for later use. Referring to FIGS. 1 and 2 , the clean cylinder 10 includes a plurality of wedge wire bars 12 aligned longitudinally and connected to a plurality of support rings 14 at the mounting ends 30 of the bars 12. The screen cylinder 10 may also include annular end flanges at both axial ends of the screen cylinder 10. While not shown in the drawings herein, the screen cylinder typically includes a rotor that provides pressure pulsations to promote pulp flow through the slots in the screen cylinder. Details regarding the construction of screen cylinders and their operation can be found in U.S. Patent Nos. 7,188,733, 7,856,718, and 5,200,072, the entire contents of each of which are incorporated herein by reference.

[0033] 2 and 3 and the illustration of a portion of the slotted cylindrical wall 16, each profiled bar 12 can include an inflow surface 32 facing away from the support ring 14 in the inflow direction, a first side 33 having a first slot surface 34 extending from the inflow surface 32 to the attachment end 30 of the profiled bar 12, and a second side 35 opposite the first slot surface 34 and having a second slot surface 36 extending from the inflow surface 32 to the attachment end 30 of the profiled bar 12. The first slot surface of one profiled bar and the second slot surface of an adjacent profiled bar define a slot 20 (FIGS. 3 and 4). Each profiled bar can include a wear-resistant coating 50 on at least the inflow surface 32 of the profiled bar 12. The inflow surface 32 of the bar is located on the inflow side of the screening media and the cylinder. The attachment end of the bar is located on the outflow side of the screening media and the cylinder. During operation of the screen cylinder 10, an acceptable portion of the pulp or other solid suspension flows radially outward through the slots 20 (see FIG. 3 ) in the slotted cylindrical wall 16. The wear-resistant coating 50 applied to the profiled bars 12 can reduce wear on the profiled bars 12 caused by the abrasive solid components of the pulp. Reducing wear on the bars and their inlet faces, particularly those located toward the outlet end of the screen cylinder, can help maintain the performance and efficiency of the screen cylinder 10 over time, as the inlet faces of the bars tend to wear at an increasing rate, resulting in the need to replace the entire screen cylinder. Therefore, reducing wear on the screen cylinder 10 over time can extend the useful life of the screen cylinder.

[0034] The details of the screen cylinder described herein are an example of a typical screen cylinder, but screen cylinders may vary in structure and features. For example, some screen cylinders may incorporate a structural backing plate on the outside of the screen cylinder to support the screen cylinder's structure. Such a structure is shown and described in U.S. Pat. No. 5,200,072. The structural backing plate may reduce the number of support rings on the screen cylinder. In any case, the advantages and features of the present invention described herein are achievable and usable with various types of screen cylinders, including, but not limited to, screen cylinders with or without structural backing plates.

[0035] 1-3, each of the bars 12 is longitudinally aligned and circumferentially spaced apart from each other bar 12 about the central axis of the screen cylinder 10. The bars 12 are arranged side-by-side along the circular inner or outer periphery of the support ring 14 to form a slotted cylindrical wall 16. The slotted cylindrical wall 16 formed by the plurality of bars 12 includes slots 20 defined between each adjacent pair of bars 12. The slots 20 may extend for a majority of the length of the screen cylinder 10 between two annular end flanges.

[0036] By having slots 20 extending through most of the length of the screen cylinder 10, the screen cylinder 10 generally provides an increased open area through which acceptable pulp or other solids suspension can flow. The screen cylinder 10 is depicted in FIGS. 1 and 2 as an outward-flow screen cylinder 10 in which acceptable solids suspension flows radially outward through the slots 20. However, the features of the present disclosure can also be used with inward-flow screen cylinders or any other type of pulp screening device utilizing multiple profiled bars. Also, to allow the features to be clearly shown, the illustrated drawings are not to scale, and the size of the slots 20 has been exaggerated to appear larger than in drawings to the appropriate scale.

[0037] Referring to FIG. 3, a cross-sectional view of one embodiment of profiled bars 12 mounted on a support ring 14 of a screen cylinder is depicted. Each of the bars 12 can have an attachment end 30 connected to the support ring 14. Each of the bars 12 can have an inlet flow face 32 facing away from at least one support ring 14. The inlet flow faces 32 of the plurality of bars 12 form the slotted cylindrical wall 16 ( FIG. 2 ) of the screen cylinder 10. Still referring to FIG. 3, each of the bars 12 can have a first side 33 extending from the ridge 39 and the inlet flow face 32 to the attachment end 30 of the profiled bar 12 opposite the inlet flow face 32. Each of the profiled bars 12 can have a second side 35 opposite the first side 33, extending from the inlet flow face 32 to the attachment end 30 of the profiled bar 12. The first side 33 includes a first slot surface portion 34. The second side 35 also includes a second slot surface portion 36. The first slot surface 34 of one profiled bar 12 and the second slot surface 36 of another adjacent profiled bar 12 define one of the slots 20 in the screen cylinder 10. When two profiled bars 12 are adjacent, the first slot surface 34 of the first profiled bar and the second slot surface 36 of the second profiled bar facing the first bar define the slot width, i.e., the closest distance between the first profiled bar and the second profiled bar.

[0038] 3 and 4, the first slot surface 34 can have a flat profile, and the second slot surface 36 can also have a flat profile. The first side 33 meets the inlet flow face 32 at an upper ridge 39 that projects radially inward toward the adjacent bar, located counterclockwise therefrom (or to the right as shown in FIGS. 3 and 4). The upper ridge 39 is in the form of a corner or curvature between the first side 33 and the inlet flow face 32. Downstream from the first slot surface 34, the first side 33 of the bar has a slight change in profile between the upper ridge 39 and the attachment end 30. However, in other embodiments, there may be no change in profile, or a different change in profile. The second slot surface 36 can meet the inlet flow face 32 of the profiled bar 12 at a radially lower ridge or transition region 38 that connects to the inlet flow face 32. The transition region is typically in the form of a corner or curvature between the inlet face 32 and the second slot surface 36 of the second side 35. The upper ridge 39 is located at a radial distance further upstream—for example, in the case of an outlet cylinder such as that shown in FIGS. 1-4 , a radial distance less than that of the transition region 38—and the upper ridge 39 extends circumferentially near, at, or past the location where the transition region 38 of an adjacent bar meets the second slot surface 36 and / or second side 35 of the adjacent bar. Downstream of the transition region 38 and second slot surface 36 of the profiled bar 12, the second side 35 of the bar connects to the bar's attachment end 30. As previously mentioned, the flow of solids suspension through the slot 20 is generally from the inlet face 32 of the profiled bar 12 toward the attachment end 30.

[0039] For a screen cylinder 10 for screening paper pulp, the slots 20 can have a slot width that is anywhere from 0.08 mm to 0.50 mm. However, for applications in other industries, the spacing between the profiled bars 12 and the slot width may be larger or smaller depending on the particular industrial application. The slot width of the slots 20 should be constant along the longitudinal length of the profiled bars 12.

[0040] A wear-resistant coating 50 is located on the inlet face 32 of the bars 12. The wear-resistant 50 coating may be applied to each of the bars 12 and the entire length of the screen cylinder 10. In other embodiments, the coating may be applied to sections of the bars. Details of wear-resistant coatings and their application to the bars are described in more detail herein.

[0041] Each of the profiled bars 12 can be formed from a base material 46 to which a wear-resistant coating is applied (FIG. 4). The base material 46 can be a rigid metal having sufficient strength to withstand pressure pulses from the rotor without deforming or fracturing. In some embodiments, the base material 46 can be stainless steel, such as 304L stainless steel or 316L stainless steel. The base material 46 without the wear-resistant coating 50 can have a hardness value that is lower than the hardness value of the wear-resistant coating 50. For example, the base material 46 can have a hardness of less than 500HV0.05.

[0042] Referring to FIG. 4, a wear-resistant coating 50 is applied to the base material 46 of the profiled bar 12 on its inlet face. The axially extending wedge wire bar has a cross-sectional shape and inlet face geometry optimized for spray-on application of a wear-resistant coating to its inlet face using a high-velocity thermal spray technique, such as HVOF. The wear-resistant coating 50 is sprayed onto the inlet face 32 of the profiled bar. The inlet face 32 of the bar within the screen cylinder is likely to experience the greatest wear from the flow of solid suspension. The wear-resistant coating 50 preferably does not extend beyond a plane 200 coplanar with the first slot surface 34 at a location defining the narrowest dimension of the slot between the first slot surface of the first bar and the second slot surface of the adjacent bar facing the first slot surface of the first bar. The wear-resistant coating 50 preferably does not extend beyond the ridge 39. The features and techniques disclosed herein facilitate minimizing overspray and minimizing the extension of coating material beyond flat surface 200 and ridges 39 or into slot 20.

[0043] Referring to FIG. 5, a cross-sectional view of an uncoated bar in the screen cylinder 10 is shown, formed from a matrix 46. The bar's shape is optimized to receive a spray-on wear-resistant coating while minimizing the coating on the slot-defining surfaces above the first slot surface 34 adjacent the ridge 39. For example, the matrix forming the inlet face of the axially extending bar includes a transition region 38 adjacent to the second slot surface 36. The transition region 38 connects the second slot surface 36 to the inlet face 32. A first region 132 of the inlet face is adjacent to the transition region 38. The first region 132 extends toward the ridge 39 and has a concave surface area. A second region 134 of the inlet face is adjacent to the first region and includes a convex surface area.

[0044] The first region 132 has an increasing slope in the circumferential direction. A second region 134 of the inlet face adjacent to the first region, forming a convex surface region, has a decreasing slope. The slope of each region is measured at a point on a plane tangent to the inlet face region from the support ring. The first and second regions preferably do not each exhibit a negative slope. A portion of the first region adjacent to the transition region can form a generally flat surface. A portion of the second region adjacent to the ridge can also form a relatively flat region. The region between the first region adjacent to the transition region and the second region adjacent to the ridge can also form a relatively flat surface, but this region is sloped. Thus, the first and second regions form a relatively flat region between them on the inlet face with a relatively constant slope. The cross-sectional shape of the inlet face can resemble a smooth, continuous wave shape or a shape that approximates a wave shape but has several flat regions. Thus, the concave and / or convex regions on the inlet flow face of the bar may include and / or be formed by flat regions.

[0045] For example, in some embodiments, the first region adjacent to the transition region can form a generally flat surface. This generally flat region adjacent to the transition region can be less than about 50 percent of the maximum width of the bar, preferably less than about 20 percent of the maximum width of the bar. This flat surface can also be oriented perpendicular to the radius of the screen cylinder. The second region adjacent to the ridge can also form a generally flat region. This generally flat region adjacent to the ridge can be less than about 50 percent of the maximum width of the bar, preferably about 20 percent of the maximum width of the bar. This flat surface can also be oriented perpendicular to the radius of the screen cylinder. The region between the first region adjacent to the transition region and the second region adjacent to the ridge can also be flat, but can also be sloped. For example, the first region and the second region can form a relatively flat region on an inlet surface with a relatively constant slope.

[0046] The orientation and shape of the bars are optimized to allow for spray-on wear-resistant coating. For example, the angles formed by the bars and their surfaces, combined with the angle used to spray the wear-resistant coating, including varying angles, help minimize unwanted deposition of the wear-resistant coating on the bar's slot surfaces 34, 36 and side surfaces 33, 35. This unwanted deposition can result from the spray-on coating deflecting from the bar's surface as it is applied. To minimize this effect, the ridges on each bar extend circumferentially near, at, or beyond the first slot surface of the same bar. Additionally, the first and second regions 132 and 133 are formed with concave and convex surfaces, respectively. The shape of these surfaces and the spray angle used to apply the wear-resistant coating help minimize and / or prevent the coating from deflecting onto adjacent bars, particularly the first side surfaces 33 and first slot surfaces of such adjacent bars. Additionally, such a shape, along with other features and techniques disclosed herein, facilitates maximizing the overall deposition efficiency of the coating, maximizing the coating thickness on the inlet face near the ridges 39 and minimizing the area on the inlet face near the transition region that may not receive the coating. For example, the wire configurations and shapes disclosed herein, along with modifying the spray angle of the wear-resistant coating applied to the bars, can be used to maximize the coating thickness on the inlet face near the ridges 39 (where excessive wear may occur) and minimize the area on the inlet face near the transition region that may not otherwise receive sufficient coating (because it is effectively blocked by the ridges of adjacent bars).

[0047] Referring further to FIG. 5, a preferred configuration of the bar prior to application of the wear-resistant coating is shown. For example, a line from a first plane 136 is shown. The first plane 136 extends axially and radially from the center of the cylindrical screening media to a circumferential location 142 on the bar where the ridge 39 of the bar is closest to the adjacent opposing bar. For example, this is the outermost circumferential location of the ridge 39 in the clockwise direction in FIG. 5. In addition, a line from a second plane 144 is shown. The second plane 144 extends coplanarly from the inlet face 32 to a location 146 where the second plane intersects with the transition region 38. The angle θ between the first plane 136 and the second plane 144 should be greater than or equal to 80 degrees, and preferably between 80 and 90 degrees.

[0048] Preferably, the wear-resistant coating 50 is sprayed only onto the inflow surface 32 of the profiled bar 12. Applying the wear-resistant coating 50 can include any of the coating processes discussed herein, and the wear-resistant coating 50 can be any of the materials discussed herein. Preferably, applying the wear-resistant coating to at least the inflow surface 32 can include a thermal spray process. In some embodiments, the thermal spray process can include a high velocity oxygen fuel (HVOF) process.

[0049] The bars 12 forming the screening media are preferably coated on all or nearly all of the inlet face or surfaces 32 using high velocity oxygen flame spraying under the combustion of a liquid or gaseous fuel. A high velocity flame nozzle, such as a high velocity oxygen flame (HVOF), is used to apply a wear-resistant coating to the inlet face of the bar. This technique results in the coating being integrally bonded to the bar surface. The coating adheres to the bar surface and provides a dense grain structure thereon.

[0050] The abrasion-resistant coating is preferably applied to the inlet face to form a final coating having a nominal thickness of 75 to 300 microns, more preferably 75 to 150 microns, and even more preferably about 120 to 150 microns. The thickness of the abrasion-resistant coating preferably varies by less than 20 percent, and ideally by less than 10 percent. In some embodiments, the abrasion-resistant coating 50 can have a thickness of any value between 50 and 300 microns without departing from the scope of this disclosure. Thus, the nominal thickness of the final coating can be any thickness between 5 microns and 300 microns, including any and all thicknesses therebetween.

[0051] The wear-resistant coating 50 should have sufficient hardness to reduce wear on the wedge wire bar 12 during operation of the screen cylinder 10. The wear-resistant coating 50 should have a hardness greater than that of the base material 46 of the bar 12. For example, the wear-resistant coating 50 may have a hardness greater than that of cold-rolled stainless steel, which is approximately 400 HV 0.05. The wear-resistant coating 50 may have a hardness value between 500 HV 0.05 and 1200 HV 0.05. The hardness value may be determined by measurements performed according to the standard Vickers hardness test method. The wear-resistant coating 50 should be located on a relatively smooth inlet surface to reduce resistance to the flow of the solid suspension through the screen cylinder 10.

[0052] 6a and 6b, the variability of the spray nozzle 54, which can rotate circumferentially relative to the inlet face 32 of the axially extending bar 12, is illustrated. The spray nozzle 54 sprays a plume of wear-resistant coating at high velocity from its opening or orifice using known high-velocity thermal spraying techniques. The spray exits the nozzle 54 in the form of a thin, cylindrical plume, typically about 7 mm in diameter, with a higher concentration of coating within the center of the plume, which is about 3 mm in diameter. Thus, the nozzle 54 produces a spray angle that represents the difference from the direction of the spray exiting the nozzle compared to the direction of the spray if the nozzle were collinear with a line from the center of the cylinder. For example, the spray angle can be defined by the angle between 1) the center line 207 of the spray plume exiting the nozzle and 2) a radial line 206 from the central axis of the cylinder. Thus, when the nozzle is pointed in the same direction, collinear with the radial line 206, the spray angle is generally said to be zero degrees. FIG. 6a illustrates such a zero-degree spray angle. However, the spray nozzle can be rotated clockwise / counterclockwise to change the spray angle. For example, as shown in Figure 6b, a spray angle of approximately 14 degrees is shown.

[0053] 6a, 6b, 7, 8, and 9, a system for applying a wear-resistant coating to a screen cylinder 10 is shown. In this system, a robotic arm 52 includes a spray nozzle 54 at its end. The spray nozzle 54 is adapted to spray a coating material onto the inlet face 32 of the bar to form a wear-resistant coating 50 on the inlet side of the screen cylinder. The robotic arm 52 is oriented so that the spray nozzle 54 can move axially inside the screen cylinder 10. The robotic arm 52 can move the entire length of the cylinder, if possible. Alternatively, the robotic arm can move a portion of the length of the cylinder to coat only a portion of the cylinder, and then reverse the cylinder so that the robotic arm can move the remaining length of the cylinder to coat any remaining desired portions of the bar. The spray nozzle 54 is circumferentially rotatable and moves at least axially, optionally also in an axial plane relative to the radial direction of the screen cylinder 10. The spray nozzle sprays the wear-resistant coating in a path, e.g., approximately 3 to 7 millimeters wide. Each pass deposits a layer of coating, for example, approximately 10 microns thick. By varying the angle of the spray nozzles in the axial plane for different spray passes along the axial length of the cylinder, the wear-resistant coating 50 can be deposited at desired locations on the bars, particularly on their inlet faces. Overspray of the wear-resistant coating onto undesired areas, such as the first side and first slot surfaces, can also be minimized, thus minimizing the resulting coating layer on such areas. In one embodiment, a rotating platform 56 can be used to rotate the screen cylinder 10 while the spray nozzles 54 apply the coating to form the coating surface 50.

[0054] A technique for applying the wear-resistant coating 50 will now be described with reference to FIG. 8. Using this technique, the spray nozzle 54 applies a 10 micron thick coating in each axial pass. The screen cylinder 10 can be rotated during each axial pass. However, it may not be necessary to rotate the screen cylinder during an axial pass of the spray nozzle. Also, the screen cylinder may be rotated between passes rather than during one or more axial passes or a series of axial passes of the spray nozzle.

[0055] Referring again to FIG. 7 , the cylinder 10 can rotate on the platform 56 while the coating is being applied. While the cylinder is rotating, a first series of axial passes occurs in which the spray nozzle 54 travels the axial length of the screen cylinder 10 from the first end to the second end, and then from the second end to the first end. The wear-resistant coating is sprayed continuously onto the bars during each axial pass of the spray nozzle 54. For simplicity, the cycle of axial passes will be described herein as a first pass from the first end to the second end, followed by a second pass in the reverse direction from the second end to the first end. However, the cycle of axial passes may include more than one pass, if desired.

[0056] Referring now to FIG. 9, a schematic diagram of one example of a preferred variation in the spray angle of the nozzle 54 in the circumferential direction, as previously described with reference to FIGS. 6a and 6b, is shown. In this example, there are ten spray passes that occur while the cylinder rotates at a speed at which the bar 12 moves at a particular inlet face velocity. In addition, the nozzle moves axially at a particular speed with each rotation of the screen cylinder. This results in a wear-resistant coating pattern that forms a relatively tight spiral along the inlet face of the screen cylinder. The nozzle's first axial spray pass occurs at a spray angle of 5 degrees. After each spray pass, the spray nozzle angle rotates circumferentially by one degree from the bar's transition region 38 to its ridge 39, which corresponds to a counterclockwise rotation in FIG. 9. Thus, the tenth pass occurs at a spray angle of 14 degrees (as defined above). This results in ten spray passes, with each spray pass increasing by one degree for all such angles between 5 and 14 degrees. In this example, each spray pass deposits a layer of coating approximately 10 microns thick, resulting in a wear-resistant coating of approximately 100 microns. However, by increasing or decreasing the number of passes, different thicknesses of final wear-resistant coating can be achieved. Additionally, the thickness of each layer of coating deposited per pass can be altered by varying the speed of rotation of the screen cylinder and / or the axial speed of the spray nozzle.

[0057] Referring now to FIG. 10, the first three layers 340, 440, and 540 of a wear-resistant coating applied to the inlet face of an axially extending bar are shown. Because each layer is applied at a different spray angle, the layers are not identical or uniform in shape. Similarly, the coating is generally relatively uniform in thickness, although the resulting edges of the coating 50 at or near the transition region and ridges may be angled. The first layer 340 of the coating is sprayed onto the inlet face of the bar at a first spray angle of approximately 5 degrees, the second layer at 6 degrees, and the third layer at 7 degrees. These spray angles, along with the shape of the inlet face 32—particularly the transition region 38, first region 132, second region 134, and ridge 39 (as shown in FIG. 5)—and the orientation of the bar, including the resulting slot width, result in a configuration that minimizes unwanted overspray of the wear-resistant coating onto the bar slot surfaces and sides of the bar. For example, little or no wear-resistant coating is deflected from the inlet flow face 32 of a bar onto the first side 33 or slot surface of an adjacent bar. Additionally, the ridges 39 of each bar effectively act as a mask, blocking the spray of the wear-resistant coating near the ridge area of ​​the bar from entering the slot area, transition area, and second slot surface of the adjacent bar. For example, the ridges 39 of the first bar in FIG. 10 block the spray exiting the nozzle from depositing in the transition area 38 of the second bar, thereby moving the first layer of coating 340 away from the slot surface. Additionally, as discussed above, by varying the spray angle for the second and third layers 440 and 540 of the coating by one degree, each layer is deposited on the inlet flow face starting further away from the transition area. This also results in smoother edges for the final wear-resistant coating. Additionally, the spray angle varies from 5 to 14 degrees between each spray pass, which, combined with the shape of the inlet face and bar edges, reduces deflection of spray from the inlet face into unwanted areas.

[0058] The wear-resistant coating 50 can be, for example, a hard metal coating containing tungsten carbide or chromium carbide. For example, basic elements such as Ti, V, Nb, Mo, Ta, and Hf can also exist as carbides and be used in carbide-containing wear-resistant coatings. Cobalt, chromium, and nickel carbides can also be used in wear-resistant coatings. The screen cylinder bar can be coated with a wear-resistant coating by thermal spraying. Any material with a stable molten state, such as metal, ceramic, or their alloys, can be used as the coating material. Various thermal spraying methods for wear-resistant coating materials include flame spraying, arc spraying, plasma spraying, vacuum plasma spraying, high-velocity fuel spraying, and detonation spraying. For example, high-velocity fuel spraying (HVOF, HVAF) can be used to form hard metal coatings, such as WC-Co(Cr) and Cr3C2-NiCr.

[0059] Using such techniques, a coating 50 with optimum hardness, wear resistance, and fracture toughness can be achieved. Wear-resistant, thermally sprayable hard metal coatings can include other hard particles in addition to carbides, such as nitrides, oxides, or borides.

[0060] The base material of the bar 12 is typically stainless steel, but may be composed of other metals and alloys. Preferably, the wear-resistant coating 50 is applied to the inlet surface 32 or face of the bar at one or more predefined angles relative to the inlet surface 32 or face of the bar to ensure a desired coating profile. The wear-resistant coating may be applied by one or more spray nozzles or a nozzle with multiple spray heads 54. The angle of the spray nozzle or head may be adjustable or may change depending on the situation. For example, the angle of the spray nozzle 54 may change between subsequent spray passes.

[0061] As previously discussed herein, the screen cylinder 10 including the shaped bars 12 with the wear-resistant coating 50 can be used in the paper industry to process solid-in-liquid suspensions of cellulose or other fibers in pulp. However, the screen cylinder 10 may not be limited to use in the pulp and paper industry. For example, the screen cylinder 10 of the present disclosure having coated shaped bars 12 can be used to screen solid suspensions and / or slurries to remove oversized solid contaminants in mining and drilling applications, food preparation and processing operations, water treatment processes, coating operations, and other industries.

[0062] While various embodiments of the shaped bar 12 for the screen cylinder 10 and methods for making and using the shaped bar 12 have been described herein, it should be understood that it is contemplated that each of these embodiments and techniques can be used separately or in combination with one or more other embodiments and techniques. It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Accordingly, it is intended that this specification cover modifications and variations of the various embodiments described herein, provided such modifications and variations come within the scope of the appended claims and their equivalents.

[0063] Unless expressly stated otherwise, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a particular order, or that any particular orientation of any apparatus be required. Thus, where a method claim does not actually recite the order in which its steps should be followed, or an apparatus claim does not actually recite an order or orientation for individual components, or unless the claim or specification specifically states that the steps are limited to a particular order, or where no particular order or orientation for the apparatus components is recited, it is absolutely not intended that any order or orientation should be inferred in any respect.

Claims

1. 1. A method for manufacturing a screen cylinder, comprising: forming a cylindrical screening medium by arranging a plurality of circumferentially spaced, axially extending bars having slots therebetween, the screening medium having an inlet side and an outlet side, each bar having an inlet face, a first slot surface, and a second slot surface opposite the first slot surface, the inlet face being between the first slot surface and the second slot surface; applying a wear-resistant coating onto the inlet flow face of the bar using a spray nozzle by passing the spray nozzle multiple times along the length of the screening media to provide a spray pass of the spray nozzle, the wear-resistant coating being sprayed through the spray nozzle onto the inlet flow face of the bar during the pass of the spray nozzle; Varying the angle of the spray nozzle relative to the inlet side of the screening media in the circumferential direction to vary the spray angle of the nozzle applying the coating to the bar; A method comprising:

2. The method of claim 1 , wherein the wear-resistant coating is applied using high velocity thermal spraying.

3. 3. The method of claim 1 or 2, wherein the wear-resistant coating comprises one or more of tungsten, carbide, chromium, nickel, cobalt, boron, titanium, vanadium, niobium, molybdenum, tantalum, hafnium, or combinations thereof.

4. 4. The method of claim 1, wherein the wear-resistant coating comprises one or more of tungsten carbide, chromium carbide, nickel carbide, or combinations thereof.

5. 5. The method of claim 1, wherein changing the angle of the spray path occurs after one spray pass of the spray nozzle.

6. 6. The method of claim 1, wherein the angle of the spray path is varied by circumferentially rotating the spray nozzle in a direction from a transition region adjacent the second slot surface of a bar toward a ridge adjacent the first slot surface of the same bar, the ridge being located a radial distance toward the inflow direction than the transition region.

7. 7. The method of claim 1, comprising changing the angle of the spray nozzle by rotating the spray nozzle circumferentially less than 3 degrees from the second slot surface of one bar to the first slot surface of the bar after one spray pass.

8. 8. The method of any one of claims 1 to 7, comprising rotating the cylindrical screening media relative to the spray nozzle while spraying the wear-resistant coating past the spray nozzle.

9. 9. The method of claim 1, wherein the wear resistant coating sprayed onto the inflow face of the bar forms a final wear resistant coating of relatively constant thickness along the inflow face, the final coating thickness being between 75 and 300 microns.

10. 10. The method of claim 1, wherein a final wear resistant coating is absent from the first slot surface and the second slot surface of the bar.

11. 1. A method for manufacturing a screen cylinder, comprising: forming a cylindrical screening media by arranging a plurality of circumferentially spaced, axially extending bars having slots therebetween, the screening media having an inlet side and an outlet side; applying a wear-resistant coating onto the inlet flow face of the bar using a spray nozzle by passing the spray nozzle multiple times along the length of the screening media to provide a spray pass of the spray nozzle, the wear-resistant coating being sprayed through the spray nozzle onto the inlet flow face of the bar during the pass of the spray nozzle; Including, the angle formed by the spray nozzle is varied by rotating the spray nozzle circumferentially from a transition region adjacent a second slot surface of a bar to a ridge adjacent a first slot surface of the same bar, the ridge being located a total radial distance of 0 to 35 degrees toward the inflow direction from the transition region, and the ridge being located a total radial distance of 0 to 35 degrees toward the inflow direction from the transition region.

12. The method of claim 11 , wherein the wear-resistant coating comprises tungsten, carbide, chromium, nickel, cobalt, boron, titanium, vanadium, niobium, molybdenum, tantalum, hafnium, or a combination thereof.

13. 13. The method of claim 11 or 12, wherein the wear-resistant coating comprises tungsten carbide, chromium carbide, nickel carbide, or a combination thereof.

14. 14. The method of any one of claims 11 to 13, wherein the wear resistant coating is applied using high velocity thermal spraying.

15. 15. The method of any one of claims 11 to 14, wherein a final wear resistant coating is absent from the first slot surface and the second slot surface of the bar.

16. 16. The method of any one of claims 11 to 15, comprising changing the angle of the spray nozzle circumferentially by less than 3 degrees from the second slot surface of a bar to the first slot surface of the same bar after one spray pass.

17. 16. The method of any one of claims 11 to 15, wherein the angle formed by the spray nozzle is varied by a total of 5 to 15 degrees in the circumferential direction.

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