Screen cylinder with axially variable wear-resistant coating thickness

Abstract

The screen cylinder includes a cylindrical screening medium having an inlet side and an outlet side. The screening medium is formed of a plurality of axially extending wedge wire bars spaced apart in the circumferential direction, each having an inlet surface facing the inlet side. The axially extending wedge wire bars have an abrasion-resistant coating on their inlet surfaces. The abrasion-resistant coating is substantially uniform in thickness on the inlet surface at individual axial positions, but is thicker on the inlet surface facing the outlet end of the screening medium on the bar compared to the abrasion-resistant coating located on the bar facing the inlet end of the screening medium.

Description

Technical Field

[0001] This application claims priority to International Application PCT / IB2023 / 050553, filed on January 23, 2023. The entire disclosure of this application is incorporated herein by reference.

[0002] This application generally relates to a screen cylinder for removing excessive solid contaminants from a solid suspension in a liquid such as pulp, particularly a screen cylinder having improved wear resistance characteristics, and a method for manufacturing and using such a screen cylinder.

Background Art

[0003] Papermaking involves the processing or manufacture of pulp, which is a solid suspension in a liquid of fibers such as cellulose fibers or other fibers. Pulp often contains various contaminants such as wood chips, fiber bundles, metal pieces, cured adhesives, or other contaminants. This is particularly true when paper is made from recycled paper as a raw material for pulp, as there may be a high likelihood of cured adhesives, metal pieces, and plastic particles in such recycled paper pulp. If these contaminants are not removed, they are likely to degrade the quality of the paper and / or disrupt the papermaking process.

[0004] To remove contaminants containing excessive particles or fibers, pulp is often screened. Screening may also be used to separate pulp into streams with different fiber size distributions. Pulp screening can be achieved by introducing the pulp into a pulp screen, where an acceptable portion of the pulp passes through openings such as slots within the screen. Excessive solid contaminants or other unacceptable portions of the pulp do not pass through the slots or openings within the screen and are discharged as rejects through an outlet from the outflow end of the screen. Pulp screens may also be used to remove excessive solid contaminants and other solid contaminants from slurries and solid suspensions other than pulp.

[0005] Pulp screening can be achieved using a screen cylinder located within a pulp screen. The screen cylinder can screen many types of fibers, including, but not limited to, cellulose fibers, cotton fibers, glass fibers, or other fibers. The screen cylinder can be an inward-flow screen cylinder, where the acceptable portion of the solid suspension flows radially inward through the screen cylinder, or an outward-flow screen cylinder, where the acceptable portion of the solid suspension flows radially outward through the screen cylinder. The pulp screen may include a rotor or other device capable of accelerating the pulp suspension to create a desired flow state at the inlet of the screen cylinder aperture, and also to create pressure pulsations that cause blockages to flow back out of the screen cylinder aperture. Each of these actions restricts the passage of contaminants and undesirable pulp while facilitating the passage of acceptable pulp through the screen slots. Some screen cylinders utilize a solid metal cylinder with multiple holes or slots that are drilled or milled. However, to improve the throughput of the pulp screening process, a screen cylinder comprising a plurality of longitudinally contoured wedge wire bars, wherein the wedge wire bars form a plurality of slots between them that extend over most of the length of the screen cylinder, is generally preferred for pulp screening.

[0006] These wedge wire screen cylinders are typically made by arranging multiple wedge wire bars in a cylindrical shape. The slots formed between the wedge wire bars allow the desired pulp to pass through, while preventing undesirable pulp or other contaminants from passing through as well. Therefore, the slot size of the screen cylinder is selected based on the parameters of the pulp and the desired results. However, pulp is abrasive, and after some use, the screen cylinder and the bars that form it will wear down. Wear on the screen cylinder can affect the performance and / or efficiency of the screen cylinder.

[0007] The bars forming the slots in screen cylinders have been coated with wear-resistant coatings, such as chromium, to help minimize wear on the bars and, consequently, the cylinders. Chromium coatings are applied using an electroplating process in which the cylinder is immersed in a bath of chromic acid and other chemical components. During the electroplating process, the cylinder acts as the cathode, and thus chromium is deposited on the wedge wire bar. However, consistent chromium coating on the bar surface can be challenging due to variations in various factors in the electroplating process, including the flow of current, the temperature of the acid bath, the gap between the anode and cathode (i.e., the cylinder), and the chemical strength of the acid bath. 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).

[0008] In either case, the screen cylinder tends to wear unevenly, most typically with the majority of wear occurring towards the outlet end of the screen cylinder. The outlet end of the screen cylinder, which is towards or near the reject outlet, can wear at a higher rate than the inlet end of the screen cylinder because a higher concentration of reject flows through the outlet end. It is not uncommon for the screen cylinder to wear prematurely because the surface near the outlet end of the wedge wire bar is worn, while the surface near the inlet end of the same bar is not. In such situations, even if only the end of the screening medium near the outlet end of the screen cylinder is worn, it may be necessary to replace the entire screening medium in the screen cylinder.

[0009] Therefore, it is desirable to realize a screen cylinder having a screen medium that can withstand wear at an increasing rate toward the outlet end of the screen cylinder and toward the wedge wire bar surface adjacent to the outlet end. Furthermore, it is desirable to utilize an abrasion-resistant coating that can be applied by spraying without adversely affecting several properties of the screening medium, such as the uniformity of the bar's cross-sectional shape along with the slot width. [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Therefore, there is a continuing need for screen cylinders having a wear-resistant coating, where the coating is preferentially applied to specific desired locations on the bars and / or sections of the screen cylinder, such as a thicker coating at or near the outlet end of the screen cylinder, without adversely affecting several specific properties of the screening medium, such as the uniformity of the bar's cross-sectional shape along with the slot width. In addition, whatever coating is used, it is preferable that the coating, when viewed axially, has substantially uniform thickness in the cross-section of the bar's width in the direction along the bar's inlet surface. Thus, such uniformity does not substantially alter the cross-sectional shape along the bar's inlet surface when viewed in such a direction. [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 axially extending slots spaced circumferentially between axially extending wedge wire bars. The axially extending bars of the screening medium have an inlet surface facing the inlet side. The screen cylinder and the screening medium have an inlet end and an outlet end opposite the inlet end in the axial direction. The axially extending bars include an abrasion-resistant coating on the inlet surface of the screening medium. The abrasion-resistant coating is thicker on the bar toward the outlet end of the screening medium compared to the abrasion-resistant coating located on the bar toward the inlet end of the screening medium. Each bar in the screen cylinder has an abrasion-resistant coating that is thicker toward the outlet end of the screening medium compared to the coating located on each bar toward the inlet end of the screening medium. The abrasion-resistant coating forms a substantially uniform coating area between the area on the inlet surface of the bar adjacent to the first slot and the area on the inlet surface of the bar adjacent to the second slot. Substantially uniform coating regions at multiple axial positions of the bar have a substantially uniform thickness along the inflow surface in the circumferential direction perpendicular to the axial direction, while the substantially uniform coating regions have increasing thickness at multiple axial positions along the axial direction or along the bar. The wear-resistant coating is preferably a spray-type wear-resistant coating with a hardness harder than the base material. The wear-resistant coating is typically a high-speed oxygen fuel coating, preferably formed as a homogeneous layer of a single coating that can be formed in multiple sublayers, for example, without the use of other coatings including chromium, with each sublayer consisting of a similar coating material.

[0012] A screen cylinder may include a plurality of irregularly shaped wedge wire bars aligned longitudinally and connected to at least one support ring at the mounting ends of the bars. Each bar typically extends along the length of the screen cylinder. Each bar includes an inlet surface facing away from at least one support ring, a first slot surface extending from the inlet surface to the mounting end of the bar opposite the inlet surface, and a second slot surface on the opposite side of the first slot surface extending from the inlet surface to the mounting end of the bar. The first slot surface of one bar and the second slot surface of another adjacent bar may define a slot. The wear-resistant coating can be applied to the inlet surface of a bar by using a spray nozzle and passing the spray nozzle multiple times along the length of the bar while the screen cylinder is rotating or between incremental rotations of the screen cylinder, resulting in spray paths of the spray nozzle where the wear-resistant coating is sprayed onto the inlet surface of the bar between the passes of the spray nozzle. The wear-resistant coating forms a substantially uniform coating area between the area on the inlet surface of the bar adjacent to the first slot and the area on the inlet surface of the bar adjacent to the second slot. The substantially uniform coating area at multiple axial positions of the bar has a substantially uniform thickness along the inlet surface in the circumferential direction perpendicular to the axial direction, while the substantially uniform coating area has increasing thickness at multiple axial positions along the bar or in the axial direction. The wear-resistant coating is applied on the bar such that it becomes thicker towards the outlet end of the screening medium compared to the wear-resistant coating located on the bar toward the inlet end of the screening medium. In other words, the wear-resistant coating on each and all of the bars of the screen cylinder has a coating that becomes thicker toward the outlet end of the screen cylinder.

[0013] A further aspect of the present disclosure provides a method for manufacturing a screen cylinder. The method comprises forming a cylindrical screening medium having an inlet side and an outlet side, wherein the screening medium has a plurality of axially extending slots arranged circumferentially spaced, formed between axially extending bars, the axially extending bars of the screening medium having an inlet surface facing the inlet side. The screen cylinder and the screening medium include an inlet end and an outlet end axially opposite the inlet end. The method also comprises applying an abrasion-resistant coating to the inlet surface of the axially extending bars of the screening medium. The abrasion-resistant coating forms a substantially uniform coating area between a region on the inlet surface of the bar adjacent to a first slot and a region on the inlet surface of the bar adjacent to a second slot. The substantially uniform coating area at a plurality of axial positions of the bar has a substantially uniform thickness along the inlet surface in a circumferential direction perpendicular to the axial direction, while the substantially uniform coating area has increasing thickness at a plurality of axial positions in the axial direction or along the bar. The wear-resistant coating on each bar is thicker towards the outflow end of the screening medium compared to the wear-resistant coating located on the bar toward the inflow end of the screening medium. The screen cylinder can be formed using a wedge wire bar, which provides a shaped bar including a mounting end and an inflow surface facing the opposite direction from the mounting end. The wedge wire bar may further include a first slotted surface extending from the inflow surface to the mounting end of the wedge wire bar, and a second slotted surface on the opposite side of the first slotted surface extending from the inflow surface to the mounting end.

[0014] In some embodiments of the screen cylinder, the substantially uniform coating area has a thickness variation of 20 percent or less of the average thickness, preferably 15 percent or less of the average thickness, preferably 10 percent or less of the average thickness, and / or more preferably 5 percent or less of the average thickness, along the inflow surface in a direction perpendicular to the axial direction. The wear-resistant coating comprises a material with greater hardness than the base material of the bar. The axially extending slots of the screen cylinder may have a slot width defined by the minimum distance between adjacent bars in the area between the bars not coated with the wear-resistant coating, and the slot width is not reduced by the wear-resistant coating in that area. The minimum distance between the coated areas of adjacent bars is preferably greater than or equal to the slot width defined by the minimum distance between adjacent bars in the area between the bars not coated with the wear-resistant coating. The slot width is preferably not reduced by or not coated by the wear-resistant coating.

[0015] The substantially uniform coating area on the bar's inlet surface can begin anywhere within 0 mm to 0.7 mm from the upper ridge, but in some embodiments, it should be as close to the upper ridge as possible, including the upper ridge. The substantially uniform coating area can extend to any location at least within 0 mm to 0.7 mm from the transition area, but in some embodiments, it should be as close to the transition area as possible, including the transition area. Therefore, it is preferable that the substantially uniform coating area is between 0.7 mm or less to the upper ridge (including the upper ridge) and 0.7 mm or less to the transition area (including the transition). The upper ridge area is the area between the first slot surface of the bar and the bar's inlet surface, and the transition area is the area between the second slot surface of the bar and the bar's inlet surface.

[0016] In embodiments of a screen cylinder and a method for manufacturing a screen cylinder, the thickness of the wear-resistant coating increases along the axial length of the bar from the inlet end to the outlet end. The thickness of the wear-resistant coating can be progressively increased along the axial length of the bar from the inlet end to the outlet end. The thickness of the wear-resistant coating may be progressively increased along the axial length of the bar from the inlet end to the outlet end at a linear rate or a rate greater than linear. The thickness of the wear-resistant coating may be progressively increased along the axial length of the bar from the inlet end to the outlet end at a rate less than linear. The thickness of the wear-resistant coating may change in steps and increase progressively from the inlet end to the outlet end in the outlet direction along the axial length of the bar. The thickness of the wear-resistant coating may change in a corrugated shape and increase progressively from the inlet end to the outlet direction along the axial length of the bar. The thickness of the wear-resistant coating may increase from a nominal thickness of 30 microns or more to a nominal thickness of 300 microns or less. The thickness of the wear-resistant coating may increase from a nominal thickness of 75 microns or more to a nominal thickness of 150 microns or less.

[0017] The abrasion-resistant coating is preferably sprayed onto the inlet surfaces of bars extending axially through the screening medium using a spray nozzle. The spray nozzle is moved axially in spray passes within a screen cylinder, and the cylinder rotates to apply the abrasion-resistant coating to each inlet surface of the axially extending bars of the screening medium. To vary the thickness of the abrasion-resistant coating along each bar, the number of passes of the spray nozzle or the speed of the passes can be varied while spraying the abrasion-resistant coating. Each spray pass can deposit an additional layer of the abrasion-resistant coating along each of the bars. By increasing the number and / or duration of passes toward the outlet end of the cylinder, the overall thickness of the coating on each bar toward the outlet end of the cylinder can be increased compared to toward the inlet end.

[0018] This method can be performed while the screen cylinder rotates and sprays the wear-resistant coating. The rotation speed of the screen cylinder can be varied based on the position of the spray nozzle. The thickness of the wear-resistant coating can be increased from 30 microns or more to 300 microns or less. The thickness of the wear-resistant coating can be increased from 75 microns or more to 150 microns or less.

[0019] The above general description and the following detailed description illustrate various embodiments and provide an overview or framework for understanding the nature and characteristics of the subject matter of the claims. However, the present invention is by no means limited to the specific embodiments disclosed.

[0020] The accompanying drawings are included herein and constitute part of this specification. The drawings illustrate various embodiments described herein and, together with the description, serve to illustrate the principles and operation of aspects of the present invention. [Brief explanation of the drawing]

[0021] [Figure 1] This figure schematically shows a front perspective view of a screen cylinder according to one or more embodiments described herein. [Figure 2] This figure schematically shows a partial perspective view of the screen cylinder of Figure 1, illustrating a plurality of irregularly shaped or contoured bars connected to a support ring of the screen cylinder, according to one or more embodiments described herein. [Figure 3] Figure 1 shows a schematic cross-sectional view of the five irregularly shaped bars of the screen cylinder, where the irregularly shaped bars have an abrasion-resistant coating on the inlet surface. [Figure 4](A) A schematic side view representation of a wedge wire bar having a wear-resistant coating whose thickness increases towards the outlet end of the screen cylinder, with the coating increasing linearly, according to one or more embodiments of the present invention described herein. (B) A schematic side view representation of a wedge wire bar having a wear-resistant coating whose thickness increases towards the outlet end of the screen cylinder, with the coating increasing more than linearly, according to one or more embodiments of the present invention described herein. (C) A schematic side view representation of a wedge wire bar having a wear-resistant coating whose thickness increases towards the outlet end of the screen cylinder, with the coating increasing stepwise, according to one or more embodiments of the present invention described herein. (D) A schematic side view representation of a wedge wire bar having a wear-resistant coating whose thickness increases towards the outlet end of the screen cylinder, with the coating increasing in a wave shape, according to one or more embodiments of the present invention described herein. [Figure 5] A cutaway view 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 surface of the bar. [Figure 6] A front perspective view of a screen cylinder on a rotatable platform together with a robotic arm having a spray nozzle used for applying a wear-resistant coating. [Figure 7] A schematic representation of a technique for varying the thickness of a wear-resistant coating applied to the inlet surface of a bar on a screen cylinder by varying the length of the path of the spray nozzle. [Figure 8] A cross-sectional view of a wedge wire shaped bar in the axial direction according to another embodiment of the present invention.

Mode for Carrying Out the Invention

[0022] The details of the screen cylinder described herein are derived from an example of a typical screen cylinder, but the screen cylinder may have different structures and characteristics. For example, depending on the screen cylinder, a structural backing plate can be incorporated outside the screen cylinder to support the structure of the screen cylinder. Such a structure is shown and described in U.S. Patent No. 5,200,072, issued April 6, 1993, which is hereby incorporated by reference in its entirety. The structural backing plate can reduce the support rings on the screen cylinder. In any case, the advantages and features of the invention described herein can be achieved and used in various types of screen cylinders, including but not limited to screen cylinders with or without a structural backing plate.

[0023] Here, a detailed reference is made to an embodiment of a screen cylinder having a profiled wedge wire bar, examples of which are shown in the accompanying drawings. Throughout the drawings, the same reference numerals are used to refer to the same or similar members.

[0024] Referring to FIG. 1, an example of a 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 the opposite axial end. Pulp or a similar fibrous suspension enters the cylinder at the inlet end 8, and a reject stream (including undesirable components) exits the cylinder at the outlet end 6. The accept, i.e., the desired pulp, passes radially through the screening medium and is recovered for later use or further processing.

[0025] The screen cylinder 10 may include a plurality of shaped wedge wire bars 12, which are aligned longitudinally and connected to at least one support ring 14 at the mounting ends of the plurality of shaped bars 12. The shaped bars form a slotted cylindrical wall 16. Referring to Figures 2 and 3, each of the shaped bars 12 may include an inlet surface 32 facing away from the support ring 14, a first slot surface 33 extending from the inlet surface 32 to the mounting end 30 of the shaped bar 12, and a second slot surface 35 opposite the first slot surface 33 and extending from the inlet surface 32 to the mounting end 30 of the shaped bar 12. The first slot surface 33 of one shaped bar and the second slot surface 35 of another adjacent shaped bar may define a slot 20 (Figure 3). Each of the shaped bars may include an abrasion-resistant coating as part of at least the inlet surface of the shaped bar 12 and at least on the inlet surface. The wear-resistant coating has a thickness that increases towards the outlet end of the screen cylinder. The inlet surface 32 of the bar is located on the inlet side of the screening medium and the cylinder. The mounting end 30 of the bar is located on the outlet side of the screening medium and the cylinder.

[0026] During the operation of the screen cylinder 10, the acceptable portion of the pulp or other solid suspension flows through the slots 20 (see Figure 3) of the slotted cylindrical wall 16. The wear-resistant coating applied to the shaped bar 12 can reduce wear on the shaped bar 12 caused by the abrasive solid components of the pulp. Reducing wear on the bar and its inlet surface 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 surface of the bar located near the outlet tends to wear at an increasing rate, leading to the need to replace the entire screen cylinder. Therefore, reducing wear toward the outlet end of the screen cylinder 10 over time can extend the service life of the screen cylinder.

[0027] The terms relating to direction used herein, such as up, down, right, left, front, back, top, and bottom, are intended only in relation to the diagrams depicted and the coordinate axes given therein, and are not intended to imply absolute orientation. Furthermore, references to thickness, including the thickness of the wear-resistant coating, include and refer to the nominal thickness, which is the desired thickness. Also, when we say that the wear-resistant coating is substantially uniform, as described herein, the actual coating thickness can vary by up to 20% from the average thickness. For example, an average thickness of 100 microns for the coating can vary by up to 20 percent, and the thickness may still be substantially uniform. Additionally, some areas of the inlet surface, particularly near the slot surface, may not be coated.

[0028] As used herein, the singular forms “a, an” and “the” include multiple referents unless otherwise explicitly indicated by the context. Therefore, for example, a reference to an “a” component includes embodiments having two or more such components unless otherwise explicitly indicated by the context.

[0029] As used herein, the terms “longitudinal” or “axial” may refer to a direction or orientation generally parallel to the central axis of the screen cylinder.

[0030] As used herein, the term “radial direction” may refer to a direction along any radius extending outward from the central axis of the screen cylinder (Figure 1).

[0031] As used herein, the terms “inflow” and “outflow” may refer to the relative positions of features with respect to the direction of flow of a solid suspension or slurry, as inflow when entering a slot and outflow when exiting a slot. In the case of the wedge wire bars of this disclosure, the flow of the solid suspension generally proceeds from the inflow face 32 of the wedge bar 12 to the outflow attachment end 30 of the wedge bar 12. Therefore, for example, “inflow direction” or “towards the inflow direction” refers to a direction radially away from the inflow face, opposite to or upstream of the flow direction. However, “outflow direction” or “towards the outflow direction” refers to a direction radially away from the inflow face, opposite to the inflow direction, in or downstream of the flow direction. “Upstream” and “downstream” refer to relative flow positions of the solid suspension as it moves from upstream to downstream. For a screen cylinder, the inflow end refers to the end of the screen cylinder into which the pulp enters, and the outflow end refers to the end out which the rejected pulp exits. Furthermore, the flow direction described above refers to the overall flow motion averaged over space and time, taking into account the possibility of recirculation of the flow through the cylinder and instantaneous flow reversals such as the reverse flow action of the slots.

[0032] As used herein, the terms “solid impurities” or “excessive solid impurities” may refer to solid objects that are not intended to be present in a solid suspension or slurry and are undesirable, such as fiber bundles, metal fragments, dried adhesives, plastic fragments, or other impurities, and can be distinguished from solid components intended to be present in a solid suspension, such as fibers.

[0033] Referring to Figures 1 and 2, a screen cylinder 10 containing a plurality of wedge wire shaped bars 12 is schematically depicted. The screen cylinder 10 includes a plurality of support rings 14. The screen cylinder 10 contains a plurality of such bars 12, which are aligned longitudinally and connected to at least one support ring 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. Although not shown in the drawings herein, screen cylinders typically contain a rotor inside to produce pressure pulsations that accelerate the suspension circumferentially and facilitate the flow of pulp through the slots of the screen cylinder. Details relating to the structure of screen cylinders and their operation can be found in U.S. Patents 7,188,733, 7,856,718, and 5,200,072, the entirety of each of these patents is incorporated herein by reference.

[0034] Each of the bars 12 can be aligned longitudinally and, together with each of the other bars 12, arranged circumferentially at specific radial intervals around the central axis of the screen cylinder 10. The bars 12 can be arranged side by side along the circular inner or outer circumference of the support ring 14 to form a slotted cylindrical wall 16. The slotted cylindrical wall 16 formed by multiple bars 12 may include slots 20 defined between each adjacent pair of bars 12. The slots 20 may extend longitudinally in the screen cylinder 10 between two annular end flanges.

[0035] By having slots 20 extending along the length of the screen cylinder 10, a screen cylinder 10 with multiple shaped bars 12 can generally increase the open area through which an acceptable pulp or other solid suspension can flow. The screen cylinder 10 is depicted in Figures 1 and 2 as an outward-flow screen cylinder 10 through which the acceptable solid suspension flows radially outward (Figure 3). However, the features of this disclosure can also be used in conjunction with an inward-flow screen cylinder or any other type of pressure screen device utilizing multiple shaped bars. The screen cylinder 10 may be operable to separate solid contaminants from a solid suspension.

[0036] Referring to Figure 3, a cross-sectional view of one embodiment of a shaped bar 12 attached to a support ring 14 of a screen cylinder is shown. Each of the bars 12 may have a mounting end 30 connected to the support ring 14. Each of the bars 12 may have an inlet surface 32 facing primarily away from at least one support ring 14. The inlet surfaces 32 of multiple bars 12 form the slotted cylindrical wall 16 of the screen cylinder 10 (Figure 1). Referring further to Figure 3, each of the bars 12 may have a first slot surface 33 extending from the inlet surface 32 to the mounting end 30 of the shaped bar 12, which is opposite the inlet surface 32. Each of the shaped bars 12 may have a second slot surface 35 on the opposite side of the first slot surface 33, extending from the inlet surface 32 to the mounting end 30 of the shaped bar 12. The first slot surface 33 and the second slot surface 35 face toward the support ring 14, away from the inlet surface 32. The first slot surface 33 of one irregularly shaped bar 12 and the second slot surface 35 of another adjacent irregularly shaped bar 12 define one of the slots 20 of the screen cylinder 10. When two irregularly shaped bars 12 are adjacent, the first slot surface 33 of the first irregularly shaped bar and the second slot surface 35 of the second irregularly shaped bar define a slot 20, provided that no other irregularly shaped bars are positioned between the first and second irregularly shaped bars. The slot width is defined as the closest distance between the first slot surface 33 and the second slot surface 35 of the adjacent bars.

[0037] The first slot surface 33 may have a flat surface shape, and the second slot surface 35 may also have a flat surface shape. The first slot surface 33 may intersect the inlet surface 32 at an upper ridge 39, which protrudes radially away from the support ring 14, for example inward, toward adjacent bars located counterclockwise from the upper ridge 39. The upper ridge 39 may include a curved or angular portion between the inlet surface 32 and the first slot surface 33. Downstream from the first slot surface 33, the bar side surface has a slight change in contour between the upper ridge 39 and the mounting end 30. The second slot surface 35 may intersect the inlet surface 32 of the irregularly shaped bar 12 at a radially downward ridge or transition region 38 that connects to the inlet surface 32. Downstream from the transition region 38 and the second slot surface 35 of the irregularly shaped bar 12, the bar side surface may connect to the bar mounting end 30. As previously mentioned, the flow of the solid suspension through the slot 20 generally proceeds from the inlet surface 32 of the irregularly shaped bar 12 toward the mounting end 30. The transition region 38 connects the second slot surface 35 to the surface 32 facing the inflow material, with corners or curves between them. However, the wedge wire bar may have shapes other than those depicted in Figure 3. For example, the inlet surface 32, the first slot surface 33, and the second slot surface 35 may have any suitable shape for manufacturing a screen cylinder for removing excess solid contaminants from slurries and solid suspensions.

[0038] In the case of a screen cylinder 10 for screening paper pulp, the slots 20 can have a slot width of 80 microns (0.08 mm) or more, for example, 0.08 mm to 1.5 mm. However, in applications in other industries, the spacing between the shaped bars 12 and the slot width may be larger or smaller depending on the specific industrial application. The slot width of the slots 20 should be constant along the longitudinal length of the shaped bars 12.

[0039] Referring to Figure 3, the wear-resistant coating 50 is located on the inlet surface 32 of the bar 12, as part of the inlet surface 32. Figure 3 shows a cross-sectional view of a section of the bar in the axial direction. However, Figure 3 only depicts one side of the bar at the same axial position and, for simplicity, does not depict the section of increased-thickness coating located toward the outlet end of the cylinder. Wear can cause erosion of the inlet surface 32, thereby impairing its hydrodynamic performance and reducing flow through the screen cylinder. As the inlet surface wears, its contour or cross-sectional shape changes, which can reduce the screen's hydraulic capacity and make the slots more prone to clogging. Contour wear generally increases in the axial direction. Consequently, screen cylinders without a wear-resistant coating may have a shorter service life when used to remove solid contaminants from solid suspensions of cellulose fibers or other solid components. In some cases, the service life may be as short as just a few months. In this embodiment, the wear-resistant coating 50 is applied along the entire length of the bar 12, but its thickness increases near and towards the outflow end 6 of the bar 12 and the screen cylinder 10. However, at any given axial position, preferably at all axial positions, the thickness of the bar is substantially uniform in the direction perpendicular to the axial direction (as shown in Figure 3). In other embodiments, the wear-resistant coating may not be applied to the region of the bar 12 near the inflow end 8. Thus, the wear-resistant coating on the inflow surface prevents premature wear of the surface. However, the coating is not applied to the slot surfaces 33, 35 of the bar in such a manner that it reduces the minimum width of the slot 20, i.e., the “slot width” which is typically defined as the minimum distance between the first slot surface 33 and the second slot surface 35, located between point 34 on the first slot surface and the transition region 38, respectively.

[0040] Each of the irregularly shaped bars 12 can be formed from a base material 46 coated with an abrasion-resistant coating. The base material 46 may be a rigid metal that is strong enough to withstand pressure pulses and other mechanical loads from the rotor without deforming or fracturing. In some embodiments, the base material 46 may be stainless steel, such as 304L stainless steel or 316L stainless steel. The base material 46 without the abrasion-resistant coating 50 may have a hardness value lower than that of the abrasion-resistant coating 50. For example, the base material 46 may have a hardness of less than 500HV0.05.

[0041] Referring to Figures 4A to 4D, several examples of axial cross-sectional shapes for the gradient of the wear-resistant coating according to an embodiment of the present invention are shown. The wear-resistant coating 50 is coated onto each base material 46 of the shaped bars 12 in the screen cylinder using a shape consistent with that shown in Figures 4A to 4D. However, Figures 4A to 4D show an exaggerated thickness of the coating 50 for illustrative purposes. The wear-resistant coating 50 is sprayed onto the inlet surface 32 of the shaped bar. As previously mentioned, the adjacent inlet surface 32 and outlet end of the screen cylinder may be the areas that experience the greatest wear. Therefore, the maximum effect of the wear-resistant coating 50 should occur at this location on the screen cylinder, i.e., at and toward or near the outlet end. The wear-resistant coating 50 may have a thickness profile sufficient to protect the outlet end of the screen cylinder from premature or excessive wear.

[0042] Figure 4A shows the linear axial gradient of the wear-resistant coating 50. Here, the coating thickness increases at a linear rate toward the outlet end of the screen cylinder 6. The axial thickness increase rate can be selected based on the properties of the fibrous suspension being screened, the parameters of the screen cylinder, and the variation in the wear rate toward the outlet end of the screen cylinder. For example, the thickness can increase from 0 microns at the inlet to 100 microns at the outlet, or from 50 microns at the inlet to 150 microns at the outlet. In another embodiment of the linear shape, there may be a section with a constant coating thickness, for example 50 microns, starting at the cylinder inlet and extending over one-third of the cylinder length, followed by a section where the coating thickness increases linearly from 50 microns to 150 microns, followed by a section extending to the outlet over the last one-third of the cylinder length, with a constant coating thickness of 150 microns.

[0043] Furthermore, Figure 4B shows a non-linear increase in the axial gradient of the wear-resistant coating 50. Here, the thickness of the coating increases at a rate non-linear, for example, a power-law or exponential rate, toward the outlet end of the screen cylinder 6. The rate of increase in the gradient of the thickness can be selected based on the properties of the fibrous suspension being screened, the parameters of the screen cylinder, and the variation in the wear rate toward the outlet end of the screen cylinder. For example, the thickness can increase from 0 microns at the inlet to 10 microns at a distance of one-third of the length from the inlet, then from 10 microns to 40 microns over the second third of the length of the cylinder, and finally from 40 microns to 100 microns over the last third of the length of the cylinder. In another embodiment of the gradient shape, there may be a section at the cylinder inlet with a constant coating thickness of, for example, 30 microns, which may extend over a quarter of the length of the cylinder; a subsequent section where the coating thickness increases from 30 microns to 40 microns over the next quarter of the length of the cylinder; a subsequent section where the coating thickness increases from 40 microns to 70 microns over the next quarter of the length of the cylinder; and a subsequent section where the coating thickness increases from 70 microns to 130 microns over the last quarter of the length of the cylinder.

[0044] Furthermore, Figure 4C shows the gradual increase in the axial gradient of the wear-resistant coating 50. Here, the thickness of the coating increases in a gradual rate, shape, and / or pattern toward the outlet end of the screen cylinder 6. The frequency, distance, and / or number of axial steps can be selected based on the characteristics of the fibrous suspension being screened, the parameters of the screen cylinder, and the variation in the wear rate toward the outlet end 6 of the screen cylinder 10. In addition, the increase in height or thickness for each step can also be selected based on the characteristics of the fibrous suspension being screened, the parameters of the screen cylinder, and the variation in the wear rate toward the outlet end of the screen cylinder. For example, in one embodiment, the thickness may be 50 microns in the first step extending over the first quarter of the length of the cylinder starting at the inlet, then the thickness increases to 75 microns in the second step extending over the next half of the length of the cylinder, and finally the thickness increases to 125 microns in the third step extending over the last quarter of the length of the cylinder.

[0045] Figure 5D shows the increasing axial gradient of the wave shape of the wear-resistant coating 50. Here, the thickness of the coating increases with respect to the screen cylinder 6 in proportion, shape, and / or pattern of the curved or wave shape. The length, frequency, shape, distance, and / or number of axial curves or waves can be selected based on the properties of the fibrous suspension being screened, the parameters of the screen cylinder, and the variation in the wear rate toward the outlet end of the screen cylinder. In addition, the increase in the height or thickness of each curve or wave can also be selected based on the properties of the fibrous suspension being screened, the parameters of the screen cylinder, and the variation in the wear rate toward the outlet end of the screen cylinder. For example, in one possible embodiment, the initial coating thickness may be 30 microns at the inlet end of the cylinder, increasing to 50 microns at the end of the first quarter of the cylinder's length, then decreasing to 40 microns during the second quarter of the cylinder's length, then increasing to 80 microns at the end of the second quarter of the cylinder's length, then decreasing to 70 microns during the third quarter of the cylinder's length, then increasing to 120 microns at the end of the third quarter of the cylinder's length, and finally decreasing to 110 microns before increasing to 150 microns at the outlet end of the cylinder.

[0046] In addition, the axial gradient pattern may include combinations of gradients as shown in Figures 4A to 4D. For example, the axial gradient of the coating may include linear shapes combined with stepped, gradient, and wave shapes, or any combination or arrangement of these shapes, across portions of the bar with different axial lengths. For example, the linear slope shown in Figure 4A may be made to have some step-like features as shown in Figure 4C, and the steps shown in Figure 4C may be made so as not to have sharp, distinct axial surfaces at each step increase.

[0047] For example, but not limited to, the wear-resistant coating 50 may have a thickness of 5 microns or more, 10 microns or more, 15 microns or more, or even 20 microns or more. In embodiments, the wear-resistant coating 50 may have a thickness of 5 to 300 microns, 5 to 250 microns, 5 to 200 microns, 5 to 100 microns, 5 to 50 microns, 5 to 30 microns, 10 to 300 microns, 10 to 100 microns, or 10 to 50 microns. In some embodiments, the wear-resistant coating 50 may have a thickness exceeding 300 microns without departing from the scope of the present disclosure. For example, the wear-resistant coating may be progressively increased in thickness from about 5 microns to 300 microns.

[0048] The wear-resistant coating 50 can have sufficient hardness to reduce wear on the wedge wire bar 12 during the operation of the screen cylinder 10. The wear-resistant coating 50 can have a hardness greater than that of the base material 46 of the bar 12. For example, the wear-resistant coating 50 can have a hardness greater than that of cold-rolled stainless steel, which has a hardness of approximately 400HV0.05. The wear-resistant coating 50 can have a hardness value between 500HV0.05 and 1200HV0.05. The hardness value can be determined by measurement performed according to a standard Vickers hardness test method.

[0049] Referring to Figures 5 and 6, a system for applying an abrasion-resistant coating to a screen cylinder 10 is shown. In this system, a robotic arm 52 includes a spray nozzle 54 at its tip. The spray nozzle 54 is adapted to spray the abrasion-resistant coating 50 onto the inlet side of the screen cylinder and onto the inlet surface 32 of the bar. The robotic arm 52 is oriented so that the spray nozzle 54 can move axially within the screen cylinder 10 along its entire inner axial length. In some embodiments, the spray nozzle 54 may not be able to move along its entire inner axial length, in which case the cylinder is coated along about half of its length, then rotated 180 degrees to coat the remaining half. The spray nozzle 54 moves at least axially and radially relative to the screen cylinder 10. The spray nozzle sprays the abrasion-resistant coating, for example, in the shape of a thin cylindrical plume, typically with a diameter of about 7 mm. Each pass deposits a coating layer, for example, about 10 microns thick. The thickness of the wear-resistant coating 50 and its axial gradient or cross-sectional shape can be controlled by varying the length, number, and / or speed of the passes along the axial length of the cylinder. In one embodiment, the screen cylinder 10 can be rotated using a rotating platform 56 while the spray nozzle 54 applies the coating 50.

[0050] Here, with reference to Figure 7, the technique for applying the wear-resistant coating 50 is described. Using this technique, the spray nozzle is coated with a thickness of 10 microns in each axial pass. Between each axial pass, the screen cylinder 10 may or may not rotate around its central axis. Initially, the screen cylinder 10 is oriented so that the outlet end 6 is located at the top or starting point of each spray pass. A first series of axial passes A occurs, in which the spray nozzle 54 moves along the entire axial length of the screen cylinder 10. Next, a second series of axial passes B occurs, but the length of each pass in the second series of axial passes is shorter than the length of each pass in the first series of axial passes. Then, a third series of axial passes C occurs, but the length of each pass in the third series of axial passes is shorter than the length of each pass in the second series of axial passes. Next, a fourth series of axial passes D occurs, but the length of each pass in the fourth series of axial passes is shorter than the length of each pass in the third series of axial passes. Next, a fifth series of axial passes E occurs, where the length of each pass in the fifth series of axial passes is shorter than the length of each pass in the fourth series of axial passes. Then, a sixth series of axial passes F occurs, where the length of each pass in the movement of the sixth series of axial passes is shorter than the length of each pass in the fifth series of axial passes. Each series of axial passes may include one or more axial passes, where one cycle is considered a continuous pass in the opposite direction, depending on the desired axial cross-sectional shape thickness. Each series of axial passes may, if necessary, result in a stepped or wavy shape. Additionally, to customize the axial gradient of the wear-resistant coating, an additional series of spray passes with continuously decreasing lengths may be performed. The screen cylinder may be rotated around its central axis between and / or between the axial passes of the spray nozzle.

[0051] Furthermore, by programming the rotational speed of the screen cylinder and / or the axial speed of the spray nozzle 54 while the spray nozzle is being coated, various different axial gradient profiles with increasing thickness can be achieved. Also, by decreasing the axial travel speed of the spray nozzle and / or the rotational speed of the screen cylinder towards the exit end of the screen cylinder, various different axial gradient profiles with increasing thickness can be achieved. The rotational speed of the screen cylinder and / or the length or speed of the spray nozzle's path can be changed or adjusted indefinitely to achieve various axial gradient profiles with increasing thickness. For example, the rotational speed of the screen cylinder may vary based on the axial position of the spray nozzle.

[0052] Preferably, forming the wear-resistant coating 50 may include applying the wear-resistant coating 50 only to the inlet surface 32 of the irregularly shaped bar 12. Applying the wear-resistant coating 50 may include any of the coating processes considered herein, and the wear-resistant coating 50 may be formed using any of the materials considered herein. In some embodiments, applying the wear-resistant coating to at least the inlet surface 32 may include a thermal spraying process. In some embodiments, the thermal spraying process may include a high-speed oxygen fuel (HVOF) process.

[0053] The bar 12 forming the screening medium is preferably coated on its inlet or surface 32 using high-velocity 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 an abrasion-resistant coating to the inlet side of the bar. This technique causes the coating to bond integrally with the bar surface. The coating adheres closely to the bar surface and gives rise to a dense crystalline grain structure.

[0054] The wear-resistant coating 50 can be, for example, a hard metal coating containing tungsten carbide and / or chromium carbide. Basic elements such as Ti, V, Nb, Mo, Ta, and Hf can also exist as carbides and can be used in carbide-containing wear-resistant coatings. Carbides of cobalt, chromium, and nickel can also be used in wear-resistant coatings. Screen cylinder bars can be coated with a wear-resistant coating by thermal spraying. The coating material is offset completely or partially to a molten or plastic state and finely dispersed as a particulate mist by a gas flow, then sprayed onto the bar to be coated via a nozzle 54. As it cools, the coating is formed from particles mechanically adhering to the surface of the bar to be coated. Any material with a stable molten state can be used as the coating material, such as metals, ceramics, or alloys thereof. Various thermal spraying methods for wear-resistant coating materials include flame spraying, arc spraying, plasma spraying, vacuum plasma spraying, high-velocity flame spraying, detonation spraying, and explosion spraying. For example, high-velocity flame spraying (HVOF, HVAF) can be used to form hard metal coatings, such as WC-Co(Cr) and Cr3C2-NiCr. The wear-resistant coatings can exhibit hardnesses ranging from 500HV0.05 to 1200HV0.05. Hardness values ​​can be determined by measurements performed according to standard Vickers hardness test methods.

[0055] Using such techniques, a coating 50 with optimal hardness, wear resistance, and fracture toughness can be achieved. Wear-resistant, sprayable hard metal coatings may contain other hard particles, such as nitrides, oxides, or borides, in addition to carbides.

[0056] 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-side surface 32 or face of the bar at one or more predefined angles to the inlet-side 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 can be set to 90 degrees with respect to a flat, inclined portion of the inlet surface. However, other spray angles may be used, and / or, for example, the angle of the spray nozzle 54 may change during subsequent spray passes.

[0057] An inclination angle of approximately 90 degrees for the spray nozzle 54 or head relative to the flat inclined surface of the inlet is generally preferred. Preferably, multiple passes of the spray nozzle or head are made across the screen to achieve the desired coating profile. Multiple passes of the nozzle or spray head are made across the screening medium to achieve the required coating profile.

[0058] Referring to Figure 8, the substantial uniformity of thickness at the inlet surface of the bar is shown. This thickness uniformity is confirmed in a section of the bar perpendicular to the axial direction, similar to the cross-sectional view. However, Figure 8 only depicts one piece of the bar at the same axial position and, for simplicity, does not depict the portion of the coating with increased thickness located toward the outlet end of the cylinder. Also, when viewed from axial a, the coating region on the inlet surface of the bar at a particular axial position has an average thickness. However, the uniformity of the coating region at any or all axial positions can vary by up to 20%, preferably up to 15%, preferably up to 10%, and most preferably up to 5% (including all amounts from 0 to 5%) of the average thickness. Thus, as used herein, substantial uniformity means that the thickness of the coating region varies by up to 20%, preferably up to 15%, preferably up to 10%, and more preferably up to 5% (including all amounts from 0 to 5%) of the average thickness. Also, from the region adjacent to the transition region 38 to the region adjacent to the upper ridge 39, the thickness may actually decrease slightly, but still remain substantial uniform. At any given axial position of the bar 12, preferably at all axial positions of the bar 12, the coating 50 is substantially uniform in the circumferential direction perpendicular to the axial direction (as shown in Figures 3 and 8). The bar 12 can also be coated along its entire length or a portion of its entire length in the axial direction.

[0059] Furthermore, as can be seen in Figure 8, the substantially uniform coating area 50 may not extend across the entire width of the inlet surface 32. In other words, the wear-resistant coating may have some non-uniformity at the edges of the inlet surface 32. This non-uniformity can occur if the coating 50 is applied one sublayer at a time in individual passes (the thickness of the coating deposited in each pass is about 10 microns thick) (the individual sublayers may not be perfectly aligned with the previously applied sublayers). The sublayers combine to form a coating area having the total thickness of the final layer as shown herein. The substantially uniform coating area may begin at the inlet surface 32 of the bar adjacent to the upper ridge 39 and may extend within 0.0 to 0.7 mm from the upper ridge 39. Preferably, the substantially uniform coating area begins within 0.0 to 0.5 mm of the upper ridge 39, more preferably within 0.0 to 0.2 mm from the upper ridge 39. However, it is sometimes most preferable for the substantially uniform coating area 50 to begin at the upper ridge 39 itself, so that there is no area between the upper ridge 39 and the substantially uniform coating area. The substantially uniform coating area 50 then extends in a direction perpendicular to the axial direction on the inlet surface 32, for example, circumferentially with respect to the screen cylinder, until it ends at the inlet surface 32 of the bar adjacent to a second slot located within 0.0 to 0.7 mm from the transition area 38. Preferably, the substantially uniform coating area begins within 0.0 to 0.5 mm of the transition area 38, more preferably within 0.0 to 0.2 mm of the transition area 38. However, it is sometimes most preferable for the substantially uniform coating area to begin at the transition area 38 itself, so that there is no area between the transition area 38 and the substantially uniform coating area. A typical wedge wire bar 12 for pulp screening has a width of about 3.2 mm at its inlet surface. The most common wedge wire bars have a width of 2.6 to 3.6 mm. However, when used for pulp screening, some bars have a narrow inlet width of 2.3 mm, while others have a wide inlet width of 5.0 mm.A substantially uniform coating area may begin and end near the upper ridge 39 and the transition area 38, as described above, across all possible widths on the bar's inlet surface, including the range of 2.3 to 5.0 mm. The substantially uniform coating area can be most uniform in the flat sections of the inlet surface by maintaining the nozzle (not shown) for spraying the wear-resistant coating at a constant angle to the flat surface on the bar's inlet surface. For example, the inclined flat surface of the coating area 50 shown in Figure 8 can be made most uniform by maintaining the spray nozzle at a constant angle to it when applying the coating 50.

[0060] Furthermore, the axially extending slots have a slot width 20 defined by the minimum distance between adjacent bars in the region between the bars that is not coated with the wear-resistant coating. Preferably, the wear-resistant coating 50 is not applied to the slot surface, particularly at the location of the slots, and the presence of any wear-resistant coating in the region does not substantially reduce the slot width. Also, to prevent the application of the wear-resistant coating from reducing the effective slot width 20 between adjacent bars, it is preferable that the minimum distance between regions of adjacent bars on which any coating material is present is greater than or equal to the minimum slot width 20. In this regard, the application of the wear-resistant coating 50 (or any overspray thereof) on the first slot surface 33 or the second slot surface 35, particularly upstream and slightly downstream of the slot width 20 at points 34 and 38, should be avoided.

[0061] As previously discussed herein, a screen cylinder 10 comprising a shaped bar 12 having an abrasion-resistant coating 50 can be used in the paper industry to process solid 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 this disclosure having a coated shaped bar 12 can be used to screen solid suspensions and / or slurries to remove excessive solid contaminants in mining and drilling applications, food preparation and processing operations, water treatment processes, coating operations, and other industries.

[0062] This specification describes various embodiments of the shaped bar 12 for the screen cylinder 10 and methods for manufacturing and using the shaped bar 12. It should be understood that each of these embodiments and techniques can be used individually or in combination with one or more embodiments and techniques. Those skilled in the art will see that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the subject matter of the claims. Accordingly, this specification is intended to encompass various modifications and variations of the embodiments described herein, provided that such modifications and variations fall within the scope of the appended claims and their equivalents.

[0063] Unless otherwise expressly stated, no method described herein is intended to be construed as requiring its steps to be performed in a specific order, nor is any apparatus intended to require a particular orientation. Therefore, if a claim for a method does not actually describe the order in which its steps should be followed, or if a claim for an apparatus does not actually describe the order or orientation of its individual components, or if it is not otherwise specifically stated in the claim or specification that the steps are limited to a particular order, or if no specific order or orientation of the components of the apparatus is described, no order or orientation is intended to be inferred in any respect.

Claims

1. A screening medium having an inlet side and an outlet side, wherein the screening medium is cylindrical and formed by a plurality of axially extending slots arranged at circumferential intervals between axially extending bars, the axially extending bars of the screening medium having an inlet surface facing the inlet side, and the inlet surface extends in the longitudinal direction in the axial direction and in the width direction in the circumferential direction relative to the screening medium Equipped with, The screening medium has an inlet end and an outlet end opposite the inlet end in the axial direction, and the axially extending bar extends from the inlet end to the outlet end. A screen cylinder wherein the axially extending bar includes a spray-on abrasion-resistant coating on the inlet surface of the screening medium, the abrasion-resistant coating forms a substantially uniform coating region between a region on the inlet surface of the bar adjacent to a first slot and a region on the inlet surface of the bar adjacent to a second slot, (i) the substantially uniform coating region at a plurality of axial positions has a substantially uniform thickness along the inlet surface in a direction perpendicular to the axial direction, while (ii) the substantially uniform coating region increases in thickness at a plurality of axial positions along the axial direction, so that the abrasion-resistant coating on the bar becomes thicker toward the outlet end of the screening medium compared to the abrasion-resistant coating located on the bar toward the inlet end of the screening medium.

2. The screen cylinder according to claim 1, wherein the substantially uniform coating area has a thickness variation of 20 percent or less of the average thickness, preferably 15 percent or less of the average thickness, preferably 10 percent or less of the average thickness, and / or more preferably 5 percent or less of the average thickness, along the inflow surface in a direction perpendicular to the axial direction.

3. The screen cylinder according to claim 1 or 2, wherein the wear-resistant coating in the substantially uniform coating area includes a material that is harder than the base material of the bar.

4. The axially extending slot has a slot width defined by the minimum distance between adjacent bars in the region between the bars that is not coated with the wear-resistant coating, and the slot width is not reduced by the wear-resistant coating in that region, according to any one of claims 1 to 3.

5. The screen cylinder according to any one of claims 1 to 4, wherein the minimum distance between the coated areas of adjacent bars is greater than or equal to the slot width defined by the minimum distance between adjacent bars in the area between the bars that is not coated with the wear-resistant coating, and the slot width is not reduced by the wear-resistant coating in the area.

6. The screen cylinder according to any one of claims 1 to 5, wherein the substantially uniform coating region begins at a position within 0.0 to 0.7 mm, preferably within 0.0 to 0.5 mm, more preferably within 0.0 to 0.2 mm from the upper raised region on the inlet surface of the bar adjacent to the first slot, the upper raised region being the region between the first slot surface of the bar and the inlet surface of the bar, and the substantially uniform coating region extends to the inlet surface of the bar adjacent to the second slot at a position within 0.0 to 0.7 mm, preferably within 0.0 to 0.5 mm, more preferably within 0.0 to 0.2 mm from the transition region, the transition region being the region between the second slot surface of the bar and the inlet surface of the bar.

7. The screen cylinder according to any one of claims 1 to 6, wherein the thickness of the wear-resistant coating increases gradually in the axial direction from the inlet end to the outlet end along the axial length of the bar.

8. The screen cylinder according to any one of claims 1 to 7, wherein the thickness of the wear-resistant coating increases linearly and gradually in the axial direction along the axial length of the bar, from the portion of the bar toward the inlet end to the outlet end.

9. The screen cylinder according to any one of claims 1 to 7, wherein the wear-resistant coating increases progressively in a stepped shape along the axial length of the bar, from the portion of the bar toward the inlet end to the outlet.

10. The screen cylinder according to any one of claims 1 to 5, wherein the thickness increases in a wave-like shape in the axial direction along the axial length of the bar, from the portion of the bar toward the inlet end to the outlet.

11. The screen cylinder according to any one of claims 1 to 9, wherein the thickness of the substantially uniform coating region increases in the axial direction from a thickness of 30 microns or more to a thickness of 300 microns or less, preferably from a thickness of 75 microns or more to a thickness of 150 microns or less.

12. A method for manufacturing a screen cylinder, The present invention relates to forming a screening medium having an inlet side and an outlet side, wherein the screening medium is cylindrical and has a plurality of axially extending slots spaced apart in the circumferential direction, formed between axially extending bars, the axially extending bars of the screening medium each have an inlet surface facing the inlet side, and the inlet surface extends in the longitudinal direction in the axial direction and in the width direction in the circumferential direction relative to the screening medium. Includes, The screening medium includes an inlet end and an outlet end opposite the inlet end in the axial direction, The aforementioned method, The invention provides a method for applying an abrasion-resistant coating by spraying onto the inlet surface of a bar extending in the axial direction of the screening medium, wherein the abrasion-resistant coating forms a substantially uniform coating region between the region on the inlet surface of the bar adjacent to the first slot and the region on the inlet surface of the bar adjacent to the second slot, (i) the substantially uniform coating region at multiple axial positions has a substantially uniform thickness along the inlet surface in a direction perpendicular to the axial direction, while (ii) the substantially uniform coating region increases in thickness at multiple axial positions along the axial direction, so that the abrasion-resistant coating on the bar becomes thicker toward the outlet end of the screening medium compared to the abrasion-resistant coating located on the bar toward the inlet end of the screening medium. Methods that include...

13. Applying an abrasion-resistant coating is, Using a spray nozzle, the wear-resistant coating is sprayed onto the inlet surface of the axially extending bar of the screening medium. The spray nozzle is passed axially along the screen cylinder to apply the wear-resistant coating to the inlet surface of the axially extending bar of the screening medium. The thickness of the wear-resistant coating is varied by changing the number, length, and / or speed of the spray nozzle passes while the wear-resistant coating is being sprayed. The method according to claim 12, including the method described in claim 12.

14. The method according to claim 11 or 12, wherein the substantially uniform thickness along the inflow surface in a direction perpendicular to the axial direction varies by an amount of 20 percent or less from the average thickness, preferably by an amount of 15 percent or less from the average thickness, preferably by an amount of 10 percent or less from the average thickness, and / or more preferably by an amount of 5 percent or less from the average thickness.

15. The method according to any one of claims 11 to 13, wherein the axially extending slot has a slot width defined by the minimum distance between adjacent bars in the region between the bars that is not coated with the wear-resistant coating, and the slot width is not reduced by the wear-resistant coating in the region.

16. A cylinder according to any one of claims 11 to 14, wherein the minimum distance between the coated areas of adjacent bars is greater than or equal to the slot width defined by the minimum distance between adjacent bars in the area between the bars that is not coated with the wear-resistant coating, and the slot width is not reduced by the wear-resistant coating in the area.

17. The method according to any one of claims 11 to 15, wherein the wear-resistant coating includes a material having a greater hardness than the base material of the bar.

18. The method according to any one of claims 11 to 17, wherein the substantially uniform coating region begins at a position within 0.0 to 0.7 mm, preferably within 0.0 to 0.5 mm, more preferably within 0.0 to 0.2 mm from the upper raised region on the inlet surface of the bar adjacent to the first slot, the upper raised region being the region between the first slot surface of the bar and the inlet surface of the bar, and the substantially uniform coating region extends to the inlet surface of the bar adjacent to the second slot at a position within 0.0 to 0.7 mm, preferably within 0.0 to 0.5 mm, more preferably within 0.0 to 0.2 mm from the transition region, the transition region being the region between the second slot surface of the bar and the inlet surface of the bar.

19. The method according to any one of claims 13 to 18, wherein the thickness of the substantially uniform coating area gradually increases in the axial direction from the inlet end to the outlet end along the axial length of the bar.

20. The method according to any one of claims 13 to 19, wherein the substantially uniform coating area increases in thickness from 30 microns or more to 300 microns or less in the axial direction, or from 75 microns or more to 150 microns or less in the axial direction.

21. The method according to any one of claims 11 to 20, wherein the screen cylinder rotates while the wear-resistant coating is being sprayed.

22. The method according to any one of claims 11 to 21, wherein the rotational speed of the screen cylinder is changed based on the position of the spray nozzle.

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