Screen cylinder with bars configured to receive abrasion-resistant spray coating

Abstract

The screen cylinder includes a cylindrical screen medium having an inlet side and an outlet side. The screen medium is formed of a plurality of axially extending wedge wire bars spaced circumferentially, each wedge wire bar having an inlet surface facing the inlet side. The axially extending wedge wire bars have a cross-sectional shape optimized for applying a spray-type abrasion-resistant coating to their inlet surfaces.

Description

Technical Field

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

Background Art

[0002] 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 is a high likelihood that cured adhesives, metal pieces, and plastic particles may be present in such recycled pulp. If these contaminants are not removed, they are likely to degrade the quality of the paper and / or interfere with the papermaking process.

[0003] 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 the 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 at 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.

[0004] 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 is generally preferred for pulp screening, which includes a plurality of irregularly shaped wedge wire bars arranged longitudinally, wherein the wedge wire bars form a plurality of slots between them that extend over most of the length of the screen cylinder.

[0005] These wedge wire screen cylinders are typically constructed by arranging multiple wedge wire bars in a cylindrical shape. The slots formed between the wedge wire bars allow desirable pulp to pass through, while preventing undesirable pulp or other impurities from passing through. Therefore, the slot size of the screen cylinder is selected based on the parameters of the pulp and the desired outcome. However, pulp is abrasive, and after some use, the screen cylinder and the bars forming it will wear down. Wear on the screen cylinder can affect its performance and / or efficiency.

[0006] 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).

[0007] High-speed thermal coatings are typically sprayed onto bars using high pressure and high-speed nozzles. The spray can be difficult to control, potentially resulting in the coating being applied to undesirable areas of the screen cylinder and bars. For example, high-speed sprays can deflect from one bar surface to an adjacent surface, resulting in so-called "overspray." Overspray of abrasion-resistant coatings, including deflection of the coating to an adjacent surface, can create limitations that affect the flow through the slot. Alternatively, the spray may not reach or provide sufficient protection against abrasion to the desired area. For instance, an abrasion-resistant coating applied to a bar near a bar ridge where excessive abrasion may occur may not receive adequate coating. In another example, an area on the inlet surface near a transition area may not receive adequate coating because the coating spray is effectively obstructed by the adjacent bar ridge. [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, it is desirable to realize a screen cylinder and a method for manufacturing and using it, in which the wear-resistant coating is applied in such a way that the resulting coating is located in the desired locations on the bar and not elsewhere, minimizing the effects of overspray, and / or reduces wear on the screen cylinder, optimizes the life of the screen cylinder, and provides a coating pattern or shape on the screen cylinder bar that results in hydrodynamic conditions essential for good screening performance.

[0009] Furthermore, the shape of the wedge wire bar, i.e., the shape including their inlet faces and sides, which include side portions that form internal slots through which pulp or other solid suspensions in a liquid pass, can be optimized to reduce overspray and eliminate or minimize the deposition of spray-applied abrasion-resistant coating in undesirable locations on the bar, including in or near the bar slots, or even on the sides of the bar. Such shapes, together with other features and techniques disclosed herein, facilitate maximizing the overall deposition efficiency of the coating, maximizing the coating thickness on the inlet faces near the bar ridges, and minimizing areas on the bar inlet faces opposite the ridges that may not otherwise receive sufficient coating. In addition, the technique of spraying the abrasion-resistant coating onto the bar can be optimized to reduce overspray and eliminate or minimize the deposition of spray-applied abrasion-resistant coating in undesirable locations on the bar, including in or near the bar slots, or even on the sides of the bar, maximizing the coating thickness on the inlet faces near the bar ridges, and minimizing areas on the bar inlet faces opposite the ridges that may not otherwise receive sufficient coating.

[0010] Therefore, there is a continuing need for screen cylinders having a wear-resistant coating, where the coating is 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 the deposition and retention of the spray material on the desired surface. [Means for solving the problem]

[0011] According to one or more embodiments, 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 wedge wire bar having an inlet surface facing away from at least one support ring, a first side extending from the inlet surface to the mounting end of the bar opposite the inlet surface, and a second side opposite the first side extending from the inlet surface to the mounting end of the bar. Each axially extending wedge wire has an inlet surface shape optimized for spraying its inlet surface with an abrasion-resistant coating. Each bar is formed of a base material and each has an inlet surface, 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 another adjacent bar can define a slot. A transition region connects the second slot surface to the inlet surface. A raised portion is located between the inlet-side surface and the first slot surface. The raised portion is located at a radial distance greater from the support ring than the radial distance from the support ring to the transition region, and ii) the raised portion extends circumferentially at or beyond the position of the first slot surface that defines the slot width. The wedge wire bar is shaped and configured such that the angle formed between i) a first plane extending axially and radially from the center of the cylindrical screening medium to the circumferential position where the raised portion of the first bar is closest to an adjacent opposing bar, and ii) a second plane extending axially on the same plane from the inlet-side surface at the position where the inlet-side surface intersects with the transition region of an adjacent bar facing the first bar, is 80 degrees or more. Furthermore, this angle is preferably 90 degrees or less, and therefore the preferred angle is 80 to 90 degrees.

[0012] A portion of the axially extending bar includes a spray-on abrasion-resistant coating across the base material and on the surface facing the screening medium inflow. Preferably, the abrasion-resistant coating does not form a layer extending beyond the first plane and / or planes coplanar from the first slot surface at the location defining the narrowest dimension of the slot between the first slot surface of the 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 inflow-side surface of the axially extending bar may comprise a first region of the inflow-side surface adjacent to the transition region, which extends toward the raised portion and includes a concave surface region, and a second region of the inflow-side surface adjacent to the first region, which includes a convex surface region.

[0014] The first region extends toward the bulge and forms a concave surface region, which includes a region of increasing slope, meaning that a point on a plane tangential to the inlet surface region moves radially further away from the support ring at a rate that increases as the point moves circumferentially from the transition region toward the bulge. The second region of the inlet-side 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 bulge above it, which has a smaller slope 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 inlet surface region. The slope can progressively increase in the first region and / or progressively decrease in the second region. The first and second regions each preferably do not exhibit a negative slope. The cross-sectional shape of the inlet surface may resemble the shape of a smooth, continuous wave. The inclination of the inlet surface is preferably less than 30 degrees at all points on the inlet surface.

[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 a flat surface, but it can also be inclined. For example, the first and second regions can form relatively flat regions on the inflow side with a relatively constant incline.

[0016] The wear-resistant coating is preferably applied using a high-speed thermal spray process such as a high-speed 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 base material is preferably less than 20 percent, ideally less than 10 percent. The wear-resistant coating may contain 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. The wear-resistant coating can exhibit a hardness of 0.05 to 1200 HV. The hardness value can be determined by measurement performed according to a standard Vickers hardness test.

[0017] The axially extending bar has a mounting end on the outlet side. The mounting end is secured to a notch in the ring to form a screen cylinder.

[0018] In yet another embodiment, the screen cylinder includes a cylindrical screening medium having a plurality of axially extending slots spaced circumferentially between axially extending bars. The screening medium has an inlet side and an outlet side opposite to it. Each bar has an inlet side face, a first side having a first slot surface, and a second side having a second slot surface opposite to the first slot surface. The inlet side face lies between the first side and the first slot surface and the second side and the second slot surface. There is a ridge between the inlet side face and the first side and the first slot surface. The inlet side face of the axially extending bar extends from a transition region adjacent to the second slot surface. The inlet side face includes a first region of the inlet side face adjacent to the transition region and a second region of the inlet side face adjacent to the first region, which includes a convex surface region. The first region extends toward the ridge and includes a concave surface region. The first region has a region where the slope increases. The transition region connects the second side surface and the second slot surface to the inflow side surface. The second region of the inflow surface has a region toward a raised area where the slope decreases. The raised area is located i) at a radial distance greater from the support ring than the radial distance from the support ring to the transition region, and ii) the raised area extends circumferentially at or beyond the position of the first slot surface that defines the slot width. The second region may have a surface adjacent to the raised area above it, which has a slope smaller than the slope of the second region adjacent to the first region. The slopes of the first and second regions can be increased and decreased, respectively. The slopes can be increased and decreased progressively, respectively. The first region adjacent to the transition region can generally form a flat surface. The second region adjacent to the raised area can also form a flat region. The region between the first region adjacent to the transition region and the second region adjacent to the raised portion may also be a flat surface or it may be inclined. For example, the first and second regions form a relatively flat region on the inflow-side surface with a relatively constant incline. Subsequently, a spray-type abrasion-resistant coating is applied to the inflow-side surface of the screening medium and the inflow surface of the bar.Preferably, the wear-resistant coating does not form a layer on the bar that extends circumferentially beyond the raised portion and the transition region of the adjacent bar facing the raised portion.

[0019] The abrasion-resistant coating is preferably sprayed onto the inlet surface of a bar extending axially through the screening medium using a spray nozzle. The spray nozzle is moved axially in a spray pass within a screen cylinder to apply the abrasion-resistant coating to the inlet surface of the bar extending axially through the screening medium. The spray angle of the sprayed coating material applied onto the bar can be changed by changing the angle of the spray nozzle circumferentially with respect to the inlet side of the screening medium. For example, the angle of the spray nozzle with respect to the inlet surface of the bar can be changed during or between spray passes of the spray nozzle. By changing the angle of the spray nozzle, the spraying of the abrasion-resistant coating onto the inlet surface of the bar can be optimized and overspray can be reduced. The angle of the spray nozzle can be changed circumferentially by about 5 to 31 degrees, preferably 5 to 14 degrees. The spray angle of the spray nozzle is changed by rotating the spray nozzle circumferentially in the direction from the transition region of a bar to the raised portion of the same bar. Each increment of rotation of the spray nozzle angle should be 0 to 3 degrees, preferably 1 to 2 degrees. The angle is measured clockwise or counterclockwise 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, when spraying the coating can be changed. Such changes may occur for different spray passes or within a spray pass. Such changes can be used, if desired, to alter the local thickness of the wear-resistant coating within or between spray passes.

[0020] The abrasion-resistant coating can be applied while the screen cylinder rotates, moving the spray nozzle through the axial pass and spraying the coating. The rotation speed of the screen cylinder can be kept constant, which facilitates the deposition of a consistent layer of the coating. Alternatively, the rotation speed of the cylinder can be varied based on the position of the spray nozzle. The number of spray passes can be up to approximately 7 to 30 passes, where each pass is defined as the time it takes for the spray to traverse the length of the screen cylinder. In each pass, the spray nozzle can deposit a coating with a thickness of approximately 10 microns.

[0021] 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 any particular embodiment disclosed.

[0022] The accompanying drawings are included in this specification 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 invention. [Brief explanation of the drawing]

[0023] [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 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 irregularly shaped bar of the screen cylinder, and the irregularly shaped bar has an abrasion-resistant coating on its inlet surface. [Figure 4]A side cross-sectional view of a pair of wedge wire bars mounted on a support ring and within the screen of FIG. 1, having a wear-resistant coating, according to one or more embodiments of the invention shown and described herein, the side cross-sectional view of the wedge wire bar having a slot between a first slot surface of one bar and a second slot surface of an adjacent bar. [Figure 5] A view showing a side cross-sectional view of three bars within the screen cylinder of FIG. 1, according to one or more embodiments of the invention shown and described herein, where a wear-resistant coating is not formed on the base material. [Figure 6] (a) A schematic representation of a spray nozzle for one or more wedge wire bars for applying a wear-resistant coating on the inlet surface of the bar and the angle of the spray nozzle that can be changed during its path for applying a wear-resistant coating on the inlet surface of the bar. (b) A schematic representation of a spray nozzle for one or more wedge wire bars for applying a wear-resistant coating on the inlet surface of the bar and the angle of the spray nozzle that can be changed during its path for applying a wear-resistant coating on the inlet surface of the bar. [Figure 7] A view of a screen cylinder having a robot arm, the robot arm having at its end a spray nozzle for spraying a wear-resistant coating on the inlet surface of the bar. [Figure 8] A view showing a cut-away cross-section of a screen cylinder on a rotatable platform together with a robot arm having a spray nozzle used for applying a wear-resistant coating. [Figure 9] A schematic representation of the change in the circumferential spray angle for applying a wear-resistant coating on the bars of the screen cylinder of FIG. 1. [Figure 10] A view showing a magnified cross-section of a part of the bar of FIG. 9, where three constituent layers form part of the coating on the bar and are applied at the spray angle referred to in FIG. 9.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Herein, an embodiment of a screen cylinder having a modified wedge wire bar is given in detail, an example of which is shown in the accompanying drawings. Throughout the drawings, the same reference numerals are used to refer to the same or similar components.

[0025] 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 depicted figures and the coordinate axes provided therein, and are not intended to imply absolute orientation. Furthermore, references to thickness, including the thickness of abrasion-resistant coatings, refer to nominal thickness, which, when referring to abrasion-resistant coatings, may not be uniform, but rather have some variation from the desired or nominal thickness. For example, a coating with a nominal thickness of 100 microns may vary by 10-15%, and the thickness may not be perfectly uniform.

[0026] 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.

[0027] 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.

[0028] 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).

[0029] As used herein, the term “circumferential direction” may refer, depending on the context, to a clockwise or counterclockwise direction around the central axis of the screen cylinder.

[0030] 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, with inflow being the point of entry into a slot and outflow being the point of exiting a slot. In the case of the wedge wire bars of this disclosure, the flow of the solid suspension in liquid generally proceeds from the inflow surface 32 of the wedge wire bar 12 to the outflow attachment end 30 of the wedge wire bar 12. Thus, for example, “inflow direction” or “towards the inflow direction” refers to the upstream direction of flow. However, “outflow direction” or “towards the outflow direction” refers to the downstream direction of flow, opposite to the inflow direction. “Upstream” and “downstream” refer to relative flow positions of each other where the overall time-averaged flow of the solid suspension 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.

[0031] Furthermore, the terms “solid impurities” or “excessive solid impurities” may refer to solid objects such as fiber bundles, metal fragments, dried adhesives, or other impurities that are not intended and undesirable to be present in a solid suspension or slurry, and can be distinguished from solid components intended to be present in a liquid-solid suspension, such as pulp fibers.

[0032] Referring to Figure 1, an inlet-type 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 similar fibrous suspension enters the cylinder at the inlet end 8, and reject (containing high concentrations of undesirable components) exits the cylinder at the outlet end 6. The receipt, containing the vast majority of desirable pulp with reduced concentrations of undesirable components, passes radially through the screening medium and is recovered for later use. Referring to Figures 1 and 2, the clean cylinder 10 includes a plurality of wedge wire bars 12, which are 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. Although not shown in the drawings herein, the screen cylinder is typically accompanied by a rotor that provides pressure pulsations to facilitate the flow of pulp through the slots of the screen cylinder. Details relating to the structure and operation of screen cylinders can be found in U.S. Patents No. 7,188,733, No. 7,856,718, and No. 5,200,072, the entirety of each of these patents is incorporated herein by reference.

[0033] Referring to Figures 2 and 3 and a partial view of the slotted cylindrical wall 16, each shaped bar 12 may include an inlet surface 32 facing away from the support ring 14 in the inlet direction, a first side surface 33 having a first slot surface 34 extending from the inlet surface 32 to the mounting end 30 of the shaped bar 12, and a second side surface 35 opposite to the first slot surface 34 and having a second slot surface 36 extending from the inlet surface 32 to the mounting end 30 of the shaped bar 12. The first slot surface of one shaped bar and the second slot surface of another adjacent shaped bar define a slot 20 (Figures 3 and 4). Each of the shaped bars may include an abrasion-resistant coating 50 on at least the inlet surface 32 of the shaped bar 12. The inlet surface 32 of the bar is located on the inlet side of the screening medium and cylinder. The mounting end of the bar is located on the outlet side of the screening medium and cylinder. During the operation of the screen cylinder 10, the acceptable portion of the pulp or other solid suspension flows radially outward through the slots 20 (see Figure 3) of the slotted cylindrical wall 16. The wear-resistant coating 50 applied to the shaped bars 12 can reduce wear on the shaped bars 12 caused by the abrasive solid components of the pulp. Reducing wear on the bars and their inlet surfaces, especially the portions 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 surfaces of the bars tend to wear at an increasing rate, leading to the need to replace the entire screen cylinder. Therefore, by reducing wear on the screen cylinder 10 over time, the service life of the screen cylinder can be extended.

[0034] The details of the screen cylinder described herein represent a typical example of a screen cylinder, but screen cylinders may differ 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 structure of the screen cylinder. Such a structure is shown and described in U.S. Patent No. 5,200,072. The structural backing plate can 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 applicable in various types of screen cylinders, including screen cylinders with or without structural backing plates, but are not limited to these.

[0035] Referring to Figures 1 to 3, each of the bars 12 is aligned longitudinally and spaced circumferentially with each of the other bars 12 around the central axis of the screen cylinder 10. The bars 12 are 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 the multiple bars 12 includes slots 20 defined between each adjacent pair of bars 12. The slots 20 can extend over most of the length of the screen cylinder 10 between the two annular end flanges.

[0036] By having slots 20 that extend over most of the length of the screen cylinder 10, the screen cylinder 10 can generally increase the open area through which acceptable pulp or other solid suspensions 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. However, the features of this disclosure can also be used with inward-flow screen cylinders or any other type of pulp screening apparatus that utilizes multiple shaped bars. Also, in order to clearly illustrate the features, the drawings shown are not to scale, and the size of the slots 20 is exaggerated to appear larger than in drawings at the appropriate scale.

[0037] 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 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 2). Referring further to Figure 3, each of the bars 12 may have a first side surface 33 extending from the raised portion 39 and 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 bar 12 may have a second side surface 35 on the opposite side of the first side surface 33, extending from the inlet surface 32 to the mounting end 30 of the shaped bar 12. The first side surface 33 includes a first slotted surface portion 34. Furthermore, the second side surface 35 includes a second slot surface portion 36. The first slot surface 34 of one irregularly shaped bar 12 and the second slot surface 36 of another adjacent irregularly shaped bar 12 define one of the slots 20 of the screen cylinder 10. When the two irregularly shaped bars 12 are adjacent, the first slot surface 34 of the first irregularly shaped bar and the second slot surface 36 of the second irregularly shaped bar facing the first bar define the slot width, i.e., the closest distance between the first irregularly shaped bar and the second irregularly shaped bar.

[0038] Referring to Figures 3 and 4, the first slot surface 34 may have a flat profile, and the second slot surface 36 may also have a flat profile. The first side surface 33 intersects the inlet surface 32 at an upper ridge 39, which projects radially inward toward the adjacent bar located counterclockwise (or to the right, as shown in Figures 3 and 4). The upper ridge 39 is in the form of a corner or curve between the first side surface 33 and the inlet surface 32. Downstream from the first slot surface 34, the first side surface 33 of the bar has a slight change in profile between the upper ridge 39 and the mounting end 30. However, in other embodiments, there may be no change in profile, or there may be a different change in profile. The second slot surface 36 may intersect the inlet surface 32 of the irregularly shaped bar 12 at a radially lower ridge or transition region 38 that connects to the inlet surface 32. The transition region is typically in the form of a corner or curve between the inlet surface 32 and the second slot surface 36 of the second side surface 35. The upper ridge 39 is located at a radial distance further upstream, for example, in the case of an outlet cylinder as shown in Figures 1 to 4, at a radial distance smaller than the radial distance of the transition region 38, and the upper ridge 39 extends at or past the circumferential position near the position where the transition region 38 of the adjacent bar intersects with the second slot surface 36 and / or second side surface 35 of the adjacent bar. Downstream of the transition region 38 and second slot surface 36 of the shaped bar 12, the second side surface 35 of the bar connects to the mounting end 30 of the bar. As previously mentioned, the flow of the solid suspension through the slot 20 is generally from the inlet surface 32 of the shaped bar 12 towards the mounting end 30.

[0039] In the case of a screen cylinder 10 for screening paper pulp, the slots 20 can have a slot width of any width between 0.08 mm and 0.50 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.

[0040] The wear-resistant coating 50 is located on the inlet surface 32 of the bar 12. The wear-resistant coating 50 can 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 bar. Details of the wear-resistant coating and its application to the bar are described in more detail herein.

[0041] Each of the irregularly shaped bars 12 can be formed from a base material 46 (Figure 4) to which a wear-resistant coating is applied. The base material 46 may be a rigid metal that is strong enough to withstand pressure pulses 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 wear-resistant coating 50 may have a hardness value lower than that of the wear-resistant coating 50. For example, the base material 46 may have a hardness of less than 500HV0.05.

[0042] Referring to Figure 4, the wear-resistant coating 50 is applied to the base material 46 of the shaped bar 12 on the inlet surface. The axially extending wedge wire bar has a cross-sectional shape and inlet surface shape optimized for applying a spray-on wear-resistant coating to its inlet surface using a high-speed thermal spray technique such as HVOF. The wear-resistant coating 50 is sprayed onto the inlet surface 32 of the shaped bar. The inlet surface 32 of the bar in the screen cylinder is likely to experience the greatest wear from the flow of the solid suspension. Preferably, the wear-resistant coating 50 does not extend beyond the plane 200 that extends coplanar from the first slot surface 34 at the position 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. Preferably, the wear-resistant coating 50 does not extend beyond the raised portion 39. The features and techniques disclosed herein facilitate minimizing overspray and minimizing the extent to which the coating material extends beyond the plane 200 and the raised portion 39 or into the slot 20.

[0043] Referring to Figure 5, a cross-sectional view of an uncoated bar in the screen cylinder 10, formed from the base material 46, is shown. The shape of the bar is optimized to receive a spray-type wear-resistant coating while minimizing the coating applied to the surface defining the slots above the first slot surface 34 adjacent to the raised portion 39. For example, the base material forming the inflow-side face of an 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 inflow-side face 32. The first region 132 of the inflow-side face is adjacent to the transition region 38. The first region 132 extends toward the raised portion 39 and has a concave surface region. The second region 134 of the inflow-side face is adjacent to the first region and includes a convex surface region.

[0044] The first region 132 has an increasing slope in the circumferential direction. The second region 134 on the inflow-side surface adjacent to the first region, which forms a convex surface region, has a decreasing slope. The slope of each region is measured at a point on a plane tangential to the inflow surface region from the support ring. The first and second regions preferably do not 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 bulge 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 bulge can also form a relatively flat surface, although this region is sloped. Thus, the first and second regions form a relatively flat region between them on the inflow-side surface with a relatively constant slope. The cross-sectional shape of the inflow surface may resemble a smooth, continuous wave shape, or a shape that approximates a wave shape but has several flat regions. Therefore, the concave and / or convex regions on the inlet surface of the bar include and / or can 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 may also be a flat surface, but it may be inclined. For example, the first and second regions can form relatively flat regions on the inflow side with a relatively constant incline.

[0046] The orientation and shape of the bars are optimized to allow for spray-applied abrasion-resistant coating. For example, the angles formed by the bars and their surfaces, combined with the angle used to spray the abrasion-resistant coating (including changing the angle), help minimize unwanted deposition of the abrasion-resistant coating on the slot surfaces 34, 36 and sides 33, 35 of the bars. This unwanted deposition can occur when the spray coating is deflected away from the bar surface as it is applied. To minimize this effect, the raised portion of each bar extends circumferentially near, onto, or beyond the first slot surface of the same bar. Additionally, the first region 132 and the second region are formed as a concave and convex surface, respectively. The shape of these surfaces and the spray angle used to apply the abrasion-resistant coating help minimize and / or prevent the coating from deflecting onto adjacent bars, particularly the first sides 33 and first slot surfaces of such adjacent bars. Furthermore, such shapes, along with other features and techniques disclosed herein, facilitate maximizing the overall deposition efficiency of the coating, maximizing the coating thickness on the inflow surface near the raised portions 39 and minimizing the area on the inflow surface near transition areas that may not receive coating. For example, by using the wire configurations and shapes disclosed herein, along with changing the spray angle of the wear-resistant coating applied to the bars, the coating thickness on the inflow surface near the raised portions 39 (where excessive wear may occur) can be maximized, and the area on the inflow surface near transition areas that may not receive sufficient coating (because they are effectively obstructed by the raised portions of adjacent bars) can be minimized.

[0047] Referring further to Figure 5, a preferred configuration of the bar before the abrasion-resistant coating is applied 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 medium to the circumferential position 142 on the bar where the upper ridge 39 of the bar is closest to an adjacent opposing bar. For example, the outermost circumferential position of the upper ridge 39 in the clockwise direction in Figure 5. In addition, a line from a second plane 144 is shown. The second plane 144 extends coplanar from the inlet-side surface 32 to the position 146 where this surface intersects with the transition region 38. The angle θ between the first plane 136 and the second plane 144 should be 80 degrees or more, preferably 80 to 90 degrees. Also, the inclination of the inlet surface as viewed from a cross-section, such as shown in Figure 5, should be less than 30 degrees at any point. In other words, the inclination of the inlet surface 32 should always be less than 30 degrees. Furthermore, the inclination of the inlet surface 32 from a point adjacent to the transition region 38 should preferably be between 0 and 10 degrees. Similarly, the inclination of the inlet surface 32 adjacent to the upper ridge 39 should preferably be between 0 and 10 degrees. The inclination of the inlet surface 32 between the region adjacent to the transition region 38 and the upper ridge 39 should increase from 0 to 10 degrees, up to a maximum of 29 degrees. The inclination of the inlet surface 32 is measured as an angle α between i) a line perpendicular to a plane extending axially and radially from the center of the cylindrical screening medium, and ii) a line tangential to the position or point on the inlet surface 32 where the inclination is determined. The first 10 to 15 percent of the inlet surface 32 from the transition region preferably has an inclination of 0 to 10 degrees, and the latter 20 to 23 percent of the inlet surface 32 adjacent to the upper ridge 39 also preferably has an inclination of 0 to 10 degrees. Furthermore, the region between the first 10-15 percent of the inlet surface 32 and the latter 20-23 percent of the inlet surface 32 preferably has a slope between 0-10 degrees and 29 degrees.

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

[0049] The bar 12 forming the screening medium is preferably coated on all or substantially all of its inlet surface 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 surface 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.

[0050] The wear-resistant coating is applied to the inlet surface to form a final coating with a nominal thickness of preferably 75 to 300 microns, more preferably 75 to 150 microns, and even more preferably about 120 to 150 microns. The variation in the thickness of the wear-resistant coating is preferably less than 20 percent, ideally less than 10 percent. In some embodiments, the wear-resistant coating 50 can have a thickness of any value between 50 and 300 microns without departing from the scope of the present disclosure. Thus, the nominal thickness of the final coating can be any thickness between 5 and 300 microns (including any thickness in between).

[0051] The wear-resistant coating 50 should 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 should 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 is approximately 400HV0.05. The wear-resistant coating 50 can have a hardness value of 500HV0.05 to 1200HV0.05. The hardness value can be determined by measurement performed according to a standard Vickers hardness test method. The wear-resistant coating 50 should be applied to a relatively smooth inlet surface to reduce resistance to the flow of solid suspension through the screen cylinder 10.

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

[0053] Referring to Figures 6a, 6b, 7, 8, and 9, 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 end. The spray nozzle 54 is adapted to spray coating material onto the inlet surface 32 of a bar to form an abrasion-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 within the interior of the screen cylinder 10. The robotic arm 52 can move the entire length of the cylinder if possible. Alternatively, the robotic arm may move a portion of the length of the cylinder to coat only a portion of the cylinder, and then the cylinder may be reversed so that the robotic arm can move the remaining length of the cylinder to coat any remaining desired portion of the bar. The spray nozzle 54 is circumferentially rotatable and optionally moves at least axially, and also in the axial plane relative to the radial direction of the screen cylinder 10. The spray nozzle sprays the abrasion-resistant coating in a path, for example, about 3 to 7 millimeters wide. Each pass deposits a layer of coating, for example, about 10 microns thick. By changing the angle of the spray nozzle in the axial plane for different spray passes along the axial length of the cylinder, the wear-resistant coating 50 can be deposited at a desired location on the bar, particularly on its inlet surface. Overspray of the wear-resistant coating to undesirable areas, such as the first side and the first slot surface, can be minimized, and thus the resulting layer of coating on such areas can be minimized. In one embodiment, the screen cylinder 10 can be rotated using a rotating platform 56 while the spray nozzle 54 is coating and forming the coated surface 50.

[0054] Here, with reference to Figure 8, the technique for applying the wear-resistant coating 50 is described. Using this technique, the spray nozzle 54 is coated with a thickness of 10 microns 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 the axial passes of the spray nozzle. Alternatively, 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 Figure 7, the cylinder 10 can rotate on the platform 56 while the coating is being applied. While the cylinder is rotating, the spray nozzle 54 travels the entire axial length of the screen cylinder 10 from the first end to the second end, and then from the second end back to the first end, resulting in a first series of axial passes. The wear-resistant coating is continuously sprayed onto the bar during the axial passes of the spray nozzle 54. For simplicity, this specification describes a series of axial passes 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, a series of axial passes may include two or more passes, if desired.

[0056] Referring now to Figure 9, a schematic diagram is shown of one example of a preferred variation in the circumferential spray angle of the nozzle 54, as previously described with reference to Figures 6a and 6b. In this example, there are 10 spray passes that occur while the cylinder rotates at a speed at which the bar 12 moves at a specific inflow surface velocity. In addition, the nozzle moves axially at a specific speed with each rotation of the screen cylinder. As a result, the pattern to which the wear-resistant coating is applied forms a relatively tight helix along the inflow surface of the screen cylinder. The first axial spray pass of the nozzle occurs at a spray angle of 5 degrees. After each spray pass, the angle of the spray nozzle rotates circumferentially by 1 degree from the transition region 38 of the bar to its raised portion 39, which corresponds to counterclockwise in Figure 9. Thus, the 10th pass occurs at a spray angle of 14 degrees (as defined above). As a result, there are 10 spray passes, with each spray pass having a spray angle that is 1 degree larger for all such angles from 5 to 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 the final wear-resistant coating can be achieved. In addition, the thickness of each layer of coating deposited per pass can be changed by varying the rotation speed of the screen cylinder and / or the axial speed of the spray nozzle.

[0057] Referring here to Figure 10, the first three layers 340, 440, and 540 of the wear-resistant coating applied to the inlet surface of an axially extending bar are shown. Because each layer is applied at a different spray angle, the layers are neither identical nor uniform in shape. Similarly, although the coating is generally relatively uniform in thickness, the edges of the resulting coating 50 in or near the transition region and ridges may be sloped. The first layer 340 of the coating is sprayed onto the inlet surface 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 surface 32, particularly the orientation of the bar including the transition region 38, the first region 132, the second region 134, and the ridges 39 (as shown in Figure 5), and the resulting slot width, result in a configuration that minimizes unwanted overspray of the wear-resistant coating onto the slot surface of the bar and the sides of the bar. For example, the wear-resistant coating is deflected little to no from the inlet surface 32 of one bar onto the first side surface 33 or slot surface of the adjacent bar. In addition, the raised portion 39 of each bar effectively acts as a mask, preventing the spray of the wear-resistant coating near the raised area of ​​the bar from entering the slot area, transition area, and second slot surface of the adjacent bar. For example, the raised portion 39 of the first bar in Figure 10 prevents the spray from the nozzle from accumulating on the transition area 38 of the second bar, thereby keeping the first layer of coating 340 away from the slot surface. Furthermore, as described above, by changing the spray angle for the second layer 440 and the third layer 540 of the coating by 1 degree each, each layer starts further away from the transition area and accumulates on the inlet surface. In addition, this results in smoother edges for the final wear-resistant coating. Furthermore, the spray angle changes from 5 to 14 degrees between each spray path, and this, combined with the shape of the inlet surface and the edge of the bar, reduces the deflection of the spray from the inlet surface to unwanted areas.

[0058] The wear-resistant coating 50 can be, for example, a hard metal coating containing tungsten carbide 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. Any material having a stable molten state, such as metals, ceramics, or alloys thereof, 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 flame spraying, and detonation spraying / explosive 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.

[0059] 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.

[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-side surface 32 or face of the bar at one or more predefined angles 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 angles of the spray nozzles or heads may be adjustable and 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, a screen cylinder 10 comprising a shaped bar 12 having an abrasion-resistant coating 50 can be used in the paper industry to process liquid solid suspensions of cellulose or other fibers in pulp, as described herein. 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 cylindrical screening medium having a plurality of axially extending slots arranged at circumferential intervals between axially extending bars, the screening medium having an inlet side and an outlet side opposite to the inlet side. Equipped with, Each of the aforementioned bars is formed from a base material, and the base material is The inflow side and, A first side having a first slot surface that defines a slot, A second side having a second slot surface opposite to the first side defining an adjacent slot, wherein the slot width is defined as the closest distance between the first side of the bar and the second side of the adjacent bar, Includes, The inflow side surface is located between the first side surface and the second side surface. The aforementioned base material is A transition region connecting the second slot surface to the inflow side surface, The raised portion between the inflow side surface and the first side surface, Includes, The raised portion is characterized in that i) it is located at a radial distance in the inflow direction greater than the radial distance of the transition region, and ii) it extends circumferentially at or beyond the position of the first side surface defining the slot width. i) A first plane extending axially and radially from the center of the cylindrical screening medium to the circumferential position where the raised portion of the first bar is closest to an adjacent opposing bar, and ii) A second plane extending on the same plane from the inflow side surface to the position where the inflow side surface intersects with the transition region of an adjacent bar facing the first bar, wherein the angle formed by these planes is 80 degrees or more. i) The inclination of the inlet-side surface, measured between a line perpendicular to a plane extending axially and radially from the center of the cylindrical screening medium and ii) a line tangential to a position on the inlet surface, is less than 30 degrees at all positions on the inlet surface. A screen cylinder characterized in that a portion of the axially extending bar includes a spray-type wear-resistant coating on the inlet side of the screening medium across the base material.

2. The screen cylinder according to claim 1, wherein the wear-resistant coating does not form a layer on the bar that extends beyond the first plane.

3. The base material forming the inflow side surface of the bar extending in the axial direction is A first region of the inflow-side surface adjacent to the transition region, which extends toward the raised portion and includes a concave surface region, A second region of the inflow-side surface adjacent to the first region, which includes a convex surface region, A screen cylinder according to claim 1 or 2, comprising:

4. The first region extending toward the raised portion, which forms the concave surface region, includes a region in which the inclination increases in the circumferential direction, and each inclination of the concave surface region is measured at a point on a plane tangential to the surface region from the support ring. The screen cylinder according to any one of claims 1 to 3, wherein the second region of the inflow-side surface adjacent to the first region, which forms the convex surface region, includes a region where the inclination decreases, each inclination of the convex surface region is measured at a point on a plane tangential to the surface region from the support ring, and the second region has a surface adjacent to the raised portion having a smaller inclination than the inclination of the second region adjacent to the first region.

5. The screen cylinder according to any one of claims 1 to 4, wherein the first region and the second region each do not exhibit a negative slope.

6. The screen cylinder according to any one of claims 1 to 4, wherein the first region and the second region form a relatively flat region with a relatively constant slope on the inlet-side surface.

7. The screen cylinder according to any one of claims 1 to 5, wherein the wear-resistant coating has a thickness of 75 to 300 microns.

8. The screen cylinder according to any one of claims 1 to 6, wherein the thickness of the wear-resistant coating varies by less than 20 percent.

9. The screen cylinder according to any one of claims 1 to 8, wherein the wear-resistant coating includes tungsten carbide, chromium carbide, titanium nitride, chromium nitride, electroless nickel plating, ceramic coating, alumina, or a combination thereof.

10. The abrasion-resistant coating has a hardness of 500HV 0.05 or higher, as described in any one of claims 1 to 9.

11. The screen cylinder according to claim 10, wherein the wear-resistant coating has a hardness of 900HV0.05 or higher.

12. The screen cylinder according to claim 2, wherein the angle formed by the first plane and the second plane is 80 to 90 degrees.

13. A cylindrical screening medium having a plurality of axially extending slots arranged at circumferential intervals between axially extending bars, the screening medium having an inlet side and an outlet side opposite to the inlet side. Equipped with, Each of the bars has an inlet-side surface, a first side surface having a first slot surface, and a second side surface having a second slot surface on the opposite side of the first slot surface, wherein the inlet-side surface has a second side surface located between the first side surface and the second side surface, and a raised portion located between the inlet-side surface and the first slot surface. The inlet-side surface of the bar extending in the axial direction is A transition region adjacent to the second slot surface, the transition region connecting the second slot surface to the inflow side surface, A first region of the inflow-side surface adjacent to the transition region, extending toward the raised portion, including a concave surface region, and having a region extending toward the raised portion with increasing inclination, wherein the inclination is measured between i) a line perpendicular to a plane extending axially and radially from the center of the cylindrical screening medium and ii) a line tangential to a position or point on the inflow surface, A second region of the inflow-side surface adjacent to the first region, which includes a convex surface region, having a region that extends toward the raised portion where the slope decreases, and the slope is measured at a point on a plane tangential to the surface region from the support ring, Includes, The raised portion is located i) at a radial distance in the inflow direction greater than the radial distance of the transition region, and ii) extends circumferentially at or beyond the position where the transition region of the adjacent bar intersects with the second slot surface of the adjacent bar. A screen cylinder characterized in that the inclination of the surface facing the inlet side is less than 30 degrees at all positions on the inlet surface.

14. The screen cylinder according to claim 13, wherein the inlet-side surface of the screening medium and the inlet surface of the bar are coated with a spray-type wear-resistant coating.

15. The screen cylinder according to claim 14, wherein the wear-resistant coating has a thickness of 75 to 300 microns.

16. The screen cylinder according to any one of claims 1 to 15, wherein the first region and the second region form a relatively flat region with a relatively constant slope on the inlet-side surface.

17. The screen cylinder according to any one of claims 14 to 16, wherein the wear-resistant coating includes tungsten carbide, chromium carbide, titanium nitride, chromium nitride, electroless nickel plating, ceramic coating, alumina, or a combination thereof.

18. The abrasion-resistant coating has a hardness of 500HV 0.05 or higher, as described in any one of claims 14 to 17.

19. The screen cylinder according to claim 18, wherein the wear-resistant coating has a hardness of 900HV0.05 or higher.

20. The screen cylinder according to any one of claims 14 to 19, wherein the wear-resistant coating does not form a layer on the bar that extends circumferentially beyond the raised portion and the transition region of the adjacent bar facing the raised portion.

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