Spraying wear resistant coating on screen drum by changing spray angle

Abstract

The screen drum comprises a cylindrical screening medium consisting of a plurality of circumferentially spaced, axially extending wedge screws having an inflow surface facing an inflow side. An axially extending wedge screw has an optimized profile shape to spray a wear resistant coating onto its inflow surface using a nozzle. In order to spray the coating, the angle of the nozzle varies in the circumferential direction with respect to the inflow side of the screening medium in order to vary the spray angle of the nozzle in order to spray the coating on the rod material.

Description

Technical Field

[0001] This application generally relates to a screen cylinder for removing oversized solid contaminants from a liquid-solid suspension such as pulp, in particular a screen cylinder made of wedge-shaped screw rods, which has a structure optimized for receiving a sprayed wear-resistant coating, and this application also relates to a method for spraying a wear-resistant coating. Background Art

[0002] Papermaking involves the processing or production of pulp, which is a liquid-solid suspension of fibers such as cellulose fibers or other fibers. Pulp typically includes various contaminants such as wood chips, fiber bundles, metal fragments, hardened adhesives or other contaminants. This is especially the case when the pulp source for papermaking is recycled paper, as hardened adhesives, metal fragments and plastic particles may be present in such recycled pulp. If these contaminants are not removed, it is very likely to reduce the quality of the paper and / or interfere with the papermaking process.

[0003] To remove contaminants including oversized particles or fibers, the pulp is usually screened. The screening process can also be used to fractionate the pulp into pulp 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. Oversized solid contaminants or other unacceptable portions in the pulp will not be able to pass through the slots or openings within the screen and are discharged as waste through the outlet at the outflow end of the screen. In addition to pulp, pulp screens can also be used to remove oversized solid contaminants and other solid contaminants from slurries and solid suspensions.

[0004] Pulp screening can be accomplished using a screen cylinder located within the pulp screen. The screen cylinder can screen various types of fibers such as, but not limited to, cellulose fibers, cotton fibers, glass fibers or other fibers. The screen cylinder can be an inward-flowing screen cylinder, where the acceptable portion of the solid suspension flows radially inward through the screen cylinder, or an outward-flowing screen cylinder, where the acceptable portion of the solid suspension flows radially outward through the screen cylinder. The pulp screen can include a rotor or other device that can be operated to accelerate the pulp suspension to create desired flow conditions at the inlet of the screen cylinder holes and to generate pressure pulsations for backwashing blockages in the screen cylinder holes. Each of these actions can facilitate the passage of acceptable pulp through the screening slots while restricting the passage of contaminants and undesired pulp. Some screen cylinders use solid metal cylinders with multiple holes or slots drilled or milled into them. However, to increase the throughput of the pulp screening process, pulp screening generally preferably includes a screen cylinder with a plurality of longitudinally arranged profiled wedge-shaped screw rods that form a plurality of slots over most of the length of the screen cylinder.

[0005] These wedge wire screen cylinders are typically made by arranging a plurality of wedge-shaped wire rods in a cylindrical shape. The slots formed between the wedge-shaped wire rods allow the desired pulp to pass therethrough while preventing the undesired pulp or other contaminants from passing therethrough. Accordingly, the size of the screen cylinder slots is selected based on pulp parameters and such desired results. However, the pulp is abrasive and over time can cause wear to the screen cylinder and the screen rods that make up the screen cylinder. Wear of the screen cylinder can affect the performance and / or efficiency of the screen cylinder.

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

[0007] High velocity thermal coatings are typically sprayed onto the surface of the rods using high pressure and high velocity nozzles. Spraying can be difficult to control and may result in the coating being sprayed onto undesired locations on the screen cylinder and screen rods. For example, high velocity spraying may deviate from the surface of the screen rod and be sprayed onto adjacent surfaces, causing so-called "overspray". Overspray of the wear-resistant coating, including the coating that deviates onto adjacent surfaces, can cause restrictions that affect the flow through the slots. Alternatively, the spraying may not reach the desired wear-resistant areas or may not be applied to the desired extent. For example, on the inflow surface near the ridges of the rods where excessive wear may occur, the wear-resistant coating sprayed onto the rods may not be adequately sprayed. In another example, areas on the inflow surface near the transition region may not receive sufficient coating because the coating spray is effectively blocked by the ridges of adjacent rods.

[0008] Accordingly, it is desirable to obtain a screen cylinder and a process for producing and using the screen cylinder in which the wear-resistant coating is applied in such a way that the coating is applied to the desired locations on the rods and not to other locations, minimizing the effects of overspray, and / or providing a coating pattern or shape on the rods of the screen cylinder to reduce screen cylinder wear, optimize the life of the screen cylinder, and create the hydrodynamic conditions necessary for good screening capacity.

[0009] In addition, the shape of the wedge screw, including its inlet surface and side surfaces, including the side portions where grooves are formed internally for the flow of pulp or other liquid-solid suspensions, can be optimized to reduce overspray and eliminate or minimize the deposition of the sprayed wear-resistant coating on undesired locations of the rod, including on or near the grooves or even on the side surfaces of the rod. Further, such shapes, along with other features and techniques disclosed herein, help to maximize the overall deposition efficiency of the coating, maximize the coating thickness on the inlet surface near the ridges of the rod, and minimize the areas on the inlet surface of the rod opposite the ridges, which may not receive sufficient coating. Additionally, the techniques for spraying the wear-resistant coating onto the rod can be optimized to: reduce overspray and eliminate or minimize the deposition of the sprayed wear-resistant coating on undesired locations of the rod, including on or near the grooves or even on the side surfaces of the rod, maximize the coating thickness on the inlet surface near the ridges of the rod, and minimize the areas on the inlet surface of the rod opposite the ridges, which may not receive sufficient coating. Summary of the Invention

[0010] Accordingly, there is a current need for a sieve drum having a wear-resistant coating, in which the coating is applied in a more controllable manner and is applied to specific desired locations on the sieve rods and / or sieve drum portions of the sieve drum, while minimizing overspray and maximizing the deposition and retention of the sprayed material on the desired surfaces.

[0011] According to one or more aspects, a screen cylinder includes a cylindrical screening medium having an inlet side and an outlet side. The screening medium is composed of a plurality of circumferentially spaced, axially extending wedge-shaped rods having an inlet surface remote from at least one support ring, a first side surface extending from the inlet surface to the attachment end of the rod opposite the inlet surface, and a second side surface opposite the first side surface and extending from the inlet surface to the attachment end of the rod. Each axially extending wedge-shaped rod has an optimized inlet surface shape for spraying a wear-resistant coating on its inlet surface. Each wedge-shaped rod is made of a base material, and each wedge-shaped rod has an inlet surface, a first side surface having a first groove surface, and a second side surface having a second groove surface opposite the first side surface. The first groove surface of one rod and the second groove surface of an adjacent rod may define a groove. A transition region connects the second groove surface to the inlet surface. A ridge is located between the inlet surface and the first groove surface. The ridge is located at: i) a radial distance from the support ring greater than the radial distance from the support ring to the transition region; ii) a position where the ridge extends at a circumferential position of the first groove surface or passing through the first groove surface, which position defines the groove width. The shape and configuration of the wedge-shaped rod are such that the angle formed by the following two planes is greater than or equal to 80 degrees: i) a first plane extending axially and radially from the center of the cylindrical screening medium to the circumferential position where the ridge of the first rod is closest to the adjacent rod; and ii) a second plane extending axially and coplanarly from the inlet surface at the junction of the inlet surface and the transition region of the adjacent rod facing the first rod. Moreover, this angle is preferably 90 degrees or less, and thus, the preferred angle is between 80 degrees and 90 degrees.

[0012] A portion of the axially extending rod includes a wear-resistant coating sprayed on the surface of the base material and on the inlet surface of the screening medium. The wear-resistant coating preferably does not form a layer extending beyond the first plane and / or a plane extending coplanarly from the first groove surface, where the plane is at the position defining the narrowest dimension of the groove between the first groove surface of the first rod and the second groove surface of the adjacent rod facing the first groove surface of the first rod.

[0013] The base material forming the inlet surface of the axially extending rod may include a first region of the inlet surface near the transition region, the first region extending towards the ridge and including a concave region; and a second region of the inlet surface adjacent to the first region, the second region including a convex region.

[0014] The first region extends towards the ridge and forms a concave region, which includes a region with an increasing slope. That is, when a point moves from the transition region towards the ridge in the circumferential direction, the points on the plane tangent to the inflow surface region will radially move away from the support ring at an increasing rate. The second region of the inflow surface is adjacent to the first region, forms a convex region, and includes a region with a decreasing slope. The second region has a surface near the ridge, and the slope on this surface is less than the slope of the second region near the first region. Each slope is measured at a point on the plane tangent to the inflow surface region. The slope can gradually increase in the first region and / or gradually decrease in the second region. Preferably, neither the first region nor the second region has a negative slope. The profile of the inflow surface can be similar to a smooth continuous waveform.

[0015] In some aspects, the first region near the transition region can form a substantially flat surface. The width of this substantially flat region near the transition region can be less than about 50% of the maximum width of the rod, preferably less than about 20% of the maximum width of the rod. Additionally, this flat surface can be orthogonal to the radius of the sieve cylinder. The second region near the ridge can also form a substantially flat region. The width of this substantially flat region near the ridge can be less than about 50% of the maximum width of the rod, preferably less than about 20% of the maximum width of the rod. Additionally, this flat surface can be orthogonal to the radius of the sieve cylinder. The region between the first region near the transition region and the second region near the ridge can also be a flat surface but is inclined. For example, the first region and the second region can form a relatively flat region with a relatively constant slope on the inflow surface.

[0016] The wear-resistant coating preferably uses a high-velocity thermal spraying process, such as the high-velocity oxygen fuel (HVOF) process, and its coating thickness is preferably between 75 - 300 microns. Moreover, the thickness variation of the wear-resistant coating on the substrate material and normal to the substrate material is preferably less than 20%, preferably less than 10%. The wear-resistant coating can include tungsten carbide and / or chromium carbide. Basic elements such as titanium, vanadium, niobium, molybdenum, tantalum, and hafnium can also appear as carbides and can be used in carbide-containing wear-resistant coatings. Carbides of cobalt, chromium, and nickel can also be used in the wear-resistant coating. The hardness of the wear-resistant coating can be between 500 HV0.05 and 1200 HV0.05. The hardness value can be determined by measuring according to the standard Vickers hardness test method.

[0017] The axially extending rod includes an attachment end on the outflow side. The attachment end is fixed to the annular notch to form the sieve cylinder.

[0018] In another aspect, the sieve tube includes a cylindrical screening medium having a plurality of circumferentially spaced, axially extending slots formed between axially extending rods. The screening medium has an inlet side and an opposite outlet side. Each rod has an inlet face, a first side surface having a first slot surface, and a second side surface having a second slot surface opposite the first slot surface. The inlet face is located between the first side surface and the first slot surface, and between the second side surface and the second slot surface. There is a ridge between the inlet face and the first side surface and the first slot surface. The inlet face of the axially extending rod extends from a transition region near the second slot surface. The inlet face includes a first region of the inlet face near the transition region, and a second region of the inlet face adjacent to the first region and including a convex surface region. The first region extends towards the ridge and includes a concave surface region. The first region has a region of increasing slope. The transition region connects the second side surface and the second slot surface to the inlet face. The second region of the inlet surface has a region towards the ridge where the slope gradually decreases. The ridge is located at: i) a radial distance from the support ring greater than the radial distance from the support ring to the transition zone; ii) a position where the ridge extends at a circumferential position on or passing through the first slot surface that defines the slot width. The second region may have a surface near the ridge with a slope less than that of the second region near the first region. The slopes of the first region and the second region may increase and decrease respectively. The slopes may increase and decrease gradually respectively. The first region near the transition region may form a substantially flat surface. The second region near the ridge may also form a flat region. The region between the first region near the transition region and the second region near the ridge may also be a flat surface but be inclined. For example, the first region and the second region form relatively flat regions on the inlet face of the screening medium and the inlet face of the rods. Subsequently, a wear-resistant coating is sprayed on the inlet face of the screening medium and the inlet face of the rods. The wear-resistant coating preferably does not form a layer on the rods that extends circumferentially beyond the ridge and the transition region of the adjacent rods facing the ridge.

[0019] Preferably, a nozzle is used to spray the wear-resistant coating on the inflow surface of the axially extending rod of the screening medium. The nozzle moves axially and sprays inside the sieve drum, spraying the wear-resistant coating on the inflow surface of the axially extending rod of the screening medium. The nozzle angle can be changed in the circumferential direction relative to the inflow side of the screening medium to change the spraying angle of the sprayed coating material onto the rod. For example, the angle relative to the inflow surface of the rod can be changed during the spraying of the nozzle or between two sprayings. Changing the nozzle angle optimizes the wear-resistant coating sprayed onto the inflow surface of the rod and reduces overspray. The angle of the nozzle can vary between approximately 5 and 31 degrees in the circumferential direction, preferably between 5 and 14 degrees. The nozzle angle rotates circumferentially in the direction from the transition region of the rod to the ridge of the same rod to change the spraying angle of the nozzle. Each incremental rotation of the nozzle angle should be between 0 and 3 degrees, preferably 1 to 2 degrees. The direction of angle measurement is clockwise or counterclockwise from the nozzle to the central axis of the sieve drum. When spraying the coating, the number of passes or the passing speed of the nozzle can be changed. Moreover, such changes can occur during different spraying processes or during a single spraying process. If necessary, such changes can be used to change the local thickness of the wear-resistant coating during or between spraying processes.

[0020] When axially passing through and spraying the wear-resistant coating, the nozzle can be moved while rotating the sieve drum. The rotation speed of the sieve drum can be kept constant, which helps to deposit a uniform coating. Alternatively, the rotation speed of the sieve drum can vary according to the position of the nozzle. The number of spraying passes (each spraying is spraying through the length of the sieve drum) can be up to about 7 to 30 times. Each time of spraying, the nozzle can deposit a coating with a thickness of about 10 microns.

[0021] The foregoing general description and the following detailed description describe various embodiments and provide an overview or framework for understanding the nature and characteristics of the subject matter claimed in the present invention. However, the present invention is in no way limited to the specific embodiments disclosed. Description of the Drawings

[0022] The accompanying drawings are included in this specification and form a part of this specification. The drawings illustrate various embodiments described herein and, together with the specification, are used to explain the principles and operations of various aspects of the present invention.

[0023] Figure 1 A front perspective view of a sieve drum according to one or more embodiments shown and described herein is schematically depicted.

[0024] Figure 2 Schematically depicted according to one or more embodiments shown and described herein Figure 1 A partial perspective view of the middle sieve drum, which shows a plurality of profiles coupled to the support ring of the sieve drum.

[0025] Figure 3Schematically depicts Figure 1 A cross-sectional view of the profile of the middle sieve cylinder, the profile having a wear-resistant coating on its inflow surface.

[0026] Figure 4 Schematically depicts a pair of wedge-shaped screw rods according to one or more embodiments of the invention as shown and described herein, installed on a support ring and Figure 1 in a sieve mesh, the pair of wedge-shaped screw rods having a wear-resistant coating, with a groove between the first groove surface of one rod and the second groove surface of the adjacent rod.

[0027] Figure 5 Depicts according to one or more embodiments of the invention as shown and described herein Figure 1 A side cross-sectional view of three rod materials inside the sieve cylinder, which do not form a wear-resistant coating on the base metal.

[0028] Figure 6 a and Figure 6 b depict a schematic view of a nozzle relative to one or more wedge-shaped screw rods, wherein the nozzle applies a wear-resistant coating to the inflow surface of the rod material, and the angle of the nozzle can be changed as the nozzle passes through to apply the wear-resistant coating to the inflow surface of the rod material.

[0029] Figure 7 Depicts a view of a sieve cylinder with a robotic arm, the end of the robotic arm having a nozzle for spraying a wear-resistant coating onto the inflow surface of the rod material.

[0030] Figure 8 Depicts a cross-sectional view of a sieve cylinder located on a rotatable platform, the platform having a robotic arm with a nozzle for spraying a wear-resistant coating.

[0031] Figure 9 Depicts Figure 1 A schematic diagram of the change in the circumferential spraying angle when spraying a wear-resistant coating on the rod material of the sieve cylinder.

[0032] Figure 10 Depicts Figure 9 A close-up cross-sectional view of a part of the rod material in, which has three component layers, on which a part of the coating is formed, and is sprayed at the spraying angle mentioned in Figure 9 Detailed Description

[0033] Embodiments of a sieve cylinder with profiled wedge-shaped screw rods will now be described in detail, examples of which are shown in the accompanying drawings. Throughout the drawings, the same reference numerals will refer to the same or similar components.

[0034] ​The directional terms used in this document, such as up, down, right, left, front, back, top, bottom, only refer to the drawn figures and the coordinate axes provided in the figures, and are not intended to limit the absolute direction. In addition, when referring to thickness (including the thickness of the wear-resistant coating), it includes and refers to the nominal thickness. That is, when referring to the wear-resistant coating, its thickness may not be uniform, but may have some differences from the desired thickness or nominal thickness. For example, a coating with a nominal thickness of 100 microns may vary by 10% to 15%, and the thickness is not exactly the same.

[0035] As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, "a" component includes aspects having two or more such components unless the context clearly dictates otherwise.

[0036] As used herein, the term "longitudinal" or "axial" may refer to an orientation or direction generally parallel to the central axis of the sieve cylinder.

[0037] As used herein, the term "radial" may refer to a direction along any radius extending outward from the central axis of the sieve cylinder ( Figure 1 ).

[0038] As used herein, the term "circumferential" refers to the clockwise or counterclockwise direction, which can be the clockwise or counterclockwise direction around the central axis of the sieve cylinder according to the present invention.

[0039] As used herein, the terms "inflow" and "outflow" may refer to the relative position of a feature with respect to the flow direction of the solid suspension or slurry, i.e., it is inflow when entering the trough and outflow when exiting the trough. For the wedge-shaped lead screw of the present disclosure, the flow direction of the liquid-solid suspension is generally from the inflow surface 32 of the profile 12 to the outflow attachment end 30 of the profile 12. Thus, for example, "inflow direction" or "towards the inflow direction" refers to the upstream direction of the flow direction. However, "outflow direction" or "towards the outflow direction" refers to the downstream direction of the flow direction, opposite to the inflow direction. "Upstream" and "downstream" refer to the relative flow positions of each other in the normal and average flow of the solid suspension from upstream to downstream. For the sieve cylinder, the inflow end refers to the end where the pulp enters the sieve cylinder, and the outflow end refers to the end where the waste pulp flows out.

[0040] In addition, the term "solid contaminant" or "oversized solid contaminant" may refer to solid objects such as fiber bundles, metal fragments, hardened adhesives, or other contaminants that are not intended to be present and are not desired in the solid suspension or slurry, and can be distinguished from the solid components (such as pulp fibers) intended to be present in the liquid-solid suspension.

[0041] Reference Figure 1, showing an inflow type screen cylinder 10 according to an embodiment of the present disclosure. The screen cylinder includes an inflow end 8 at its axial end and an outflow end 6 at its other axial end. Pulp or a similar fibrous suspension enters the screen cylinder at the inflow end 8, and waste (including higher concentration of undesired components) flows out of the screen cylinder at the outflow end 6. The received material, including most of the desired pulp, together with the lower concentration of undesired components, flows radially through the screening medium and is collected for standby. Refer to Figure 1 and Figure 2 , the screen cylinder 10 includes a plurality of wedge-shaped screw rods 12 that are longitudinally aligned and coupled to a plurality of support rings 14 at the attachment ends 30 of the rods 12. The screen cylinder 10 may also include an annular end flange at either axial end of the screen cylinder 10. Although not shown in the drawings herein, the screen cylinder will generally be equipped with a rotor to generate pressure pulsations that are used to facilitate the flow of pulp through the slots of the screen cylinder. Details of the construction and operating principle of the screen cylinder can be found in U.S. Patent Nos. 7,188,733, 7,856,718, and 5,200,072, the entire contents of each of the above patents being incorporated herein by reference.

[0042] Refer to Figure 2 and Figure 3 and a view of a portion of the slotted cylindrical wall 16, each profile 12 may include an inflow surface 32, a first side surface 33, and a second side surface 35. The inflow surface 32 faces away from the support ring 14 in the inflow direction. The first side surface 33 has a first groove surface 34 that extends from the inflow surface 32 to the attachment end 30 of the profile 12. The second side surface 35 has a second groove surface 36 that is opposite to the first groove surface 34 and extends from the inflow surface 32 to the attachment end 30 of the profile 12. The first groove surface of one profile and the second groove surface of an adjacent profile define the slot 20 ( Figure 3 and Figure 4 ). Each profile may include a wear-resistant coating 50 on at least the inflow surface 32 of the profile 12. The inflow surface 32 of the rod is located on the inflow side of the screening medium and the screen cylinder. The attachment end of the rod is located on the outflow side of the screening medium and the screen cylinder. During the operation of the screen cylinder 10, the acceptable portion of the pulp or other solid suspension flows radially outward through the slot 20 on the slotted screen cylinder wall 16 (see Figure 3 ). The wear-resistant coating 50 sprayed onto the profile 12 can reduce the wear caused to the profile 12 by the abrasive solid components in the pulp. Reducing the wear of the rod and its inflow surface, especially the wear at those parts towards the outlet end of the screen cylinder, can help maintain the performance and efficiency of the screen cylinder 10 in the long term, because the wear rate of the inflow surface of the rod tends to increase, resulting in the need to replace the entire screen cylinder. Therefore, reducing the long-term wear of the screen cylinder 10 can extend the service life of the screen cylinder.

[0043] Although the specific details of the screen cylinder described herein are examples of typical screen cylinders, the structure and characteristics of the screen cylinder may vary. For example, some screen cylinders may have a structural base plate on the outer side of the screen cylinder to support the structure of the screen cylinder. U.S. Patent No. 5,200,072 shows and describes such a structure. The structural back plate can reduce the support rings on the screen cylinder. In any case, the advantages and features of the invention described herein can be implemented and used in different types of screen cylinders, including but not limited to screen cylinders with or without a structural back plate.

[0044] Reference Figures 1 to 3 , each of the rods 12 is circumferentially spaced apart and longitudinally aligned with each other rod 12 about the central axis of the screen cylinder 10. The rods 12 are arranged side by side along the annular inner or outer peripheral surface of the support ring 14 to form a slotted cylindrical wall 16. The slotted cylindrical wall 16 formed by the plurality of rods 12 includes slots 20 defined between each pair of adjacent rods 12. The slots 20 may extend over most of the length of the screen cylinder 10 between two annular end flanges.

[0045] Through the slots 20 that extend over most of the length of the screen cylinder 10, the screen cylinder 10 can generally provide a larger opening area through which an acceptable pulp or other solid suspension can flow. In Figure 1 and Figure 2 the screen cylinder 10 is depicted as an outward-flowing screen cylinder 10 in which an acceptable solid suspension generally flows radially outwardly through the slots 20. However, the features of the present disclosure can also be used for an inward-flowing screen cylinder or any other type of pulp screening device utilizing multiple profiles. Additionally, the accompanying drawings are not drawn to scale in order to clearly show these features, and the dimensions of the slots 20 are enlarged so as to appear larger than would be appropriate in a drawing at scale.

[0046] Reference Figure 3 , a cross-sectional view of one embodiment of the profile 12 mounted on the support ring 14 of the screen cylinder is depicted. Each of the rods 12 has an attachment end 30 that is coupled to the support ring 14. Each of the rods 12 may have an inlet surface 32 that is remote from at least one support ring 14. The inlet surfaces 32 of the plurality of rods 12 form the slotted cylindrical wall 16 of the screen cylinder 10 ( Figure 2 ). Still referring to Figure 3, each of the bars 12 may include a first side surface 33 that extends from the ridge 39 and the inflow surface 32 to the attachment end 30 of the profile 12 opposite the inflow surface 32. Each of the profiles 12 may include a second side surface 35 that is located on the side opposite the first side surface 33 and extends from the inflow surface 32 to the attachment end 30 of the profile 12. The first side surface 33 includes a first groove surface portion 34 located therein. And the second side surface 35 includes a second groove surface portion 36 located therein. The first groove surface 34 of one profile 12 and the second groove surface 36 of another adjacent profile 12 define one of the grooves 20 of the sieve cylinder 10. When two profiles 12 are adjacent, the first groove surface 34 of the first profile and the second groove surface 36 of the second profile facing the first bar define the groove width, i.e., the closest distance between the first profile and the second profile.

[0047] Reference Figure 3 and Figure 4 , the first groove surface 34 may have a flat profile, and the second groove surface 36 may also have a flat profile. The first side surface 33 meets the inflow surface 32 at the upper ridge 39, which projects radially inward and projects towards the adjacent bar located in its counterclockwise direction (or as shown on the right side as in Figure 3 and Figure 4 ). The upper ridge 39 is a corner or bend between the first side surface 33 and the inflow surface 32. Downstream of the first groove surface 34, the first side surface 33 has a slight profile change between the upper ridge 39 and the attachment end 30. However, in other embodiments, there may be no profile change or there may be different profile changes. The second groove surface 36 may meet the inflow surface 32 of the profile 12 at a ridge radially below or at a transition region 38 connecting to the inflow surface 32. The transition region is generally a corner or bend between the inflow surface 32 and the second groove surface 36 of the second side surface 35. The upper ridge 39 is located at a more upstream radial distance. For example, for an outflow cylinder as shown in Figures 1 to 4 , its radial distance is less than the radial distance of the transition region 38, and the upper ridge 39 extends at a circumferential position close to, located at, or passing through the transition region 38 of the adjacent bar and meeting the second groove surface 36 and / or the second side surface 35 of the adjacent bar. Downstream of the transition region 38 and the second groove surface 36 of the profile 12, the second side surface 35 of the bar is connected to the attachment end 30 of the bar. As discussed above, the flow of solid suspensions through the grooves 20 generally flows from the inflow surface 32 of the profile 12 towards the attachment end 30.

[0048] For the sieve cylinder 10 used for screening pulp, the slot width of the slot 20 can be between 0.08 and 0.50 millimeters. However, for applications in other industries, the spacing between the profiles 12 and the slot width can be larger or smaller, depending on the specific industrial application. The slot width of the slot 20 should be consistent along the longitudinal length of the profile 12.

[0049] The wear-resistant coating 50 is located on the inflow surface 32 of the rod 12. The wear-resistant coating 50 can be sprayed on each of the rods 12 and the entire length of the sieve cylinder 10. In other embodiments, the coating can be sprayed on various parts of the rod. Details of the wear-resistant coating and its application on the rod will be described in detail below.

[0050] Each of the profiles 12 can be formed from a base metal 46 ( Figure 4 ), and a wear-resistant coating is sprayed on the base metal 46. The base metal 46 can be a rigid metal whose strength is sufficient to withstand the pressure pulses from the rotor without deformation or fracture. In some embodiments, the base metal 46 can be stainless steel, such as 304L stainless steel or 316L stainless steel. The hardness value of the base metal 46 without the wear-resistant coating 50 can be lower than the hardness value of the wear-resistant coating 50. For example, the hardness of the base metal 46 can be lower than 500 HV0.05.

[0051] Reference Figure 4 , the wear-resistant coating 50 is coated on the base metal 46 of the profile 12 on the inflow surface. The axially extending wedge-shaped screw rod has a profile shape and an inflow surface shape that are optimized for spraying a wear-resistant coating on its inflow surface using a high-speed thermal spraying technique such as HVOF. The wear-resistant coating 50 is sprayed on the inflow surface 32 of the profile. The inflow surface 32 of the rod in the sieve cylinder is likely to be subject to the greatest wear due to the flow of the solid suspension. The wear-resistant coating 50 preferably does not extend beyond the plane 200 that extends coplanarly from the first slot surface 34. The position of the plane 200 defines the narrowest dimension of the slot between the first slot surface of the first rod and the second slot surface of the adjacent rod, and the second slot surface of the adjacent rod faces the first slot surface of the first rod. The wear-resistant coating 50 preferably does not extend beyond the ridge 39. The features and techniques disclosed herein help to minimize overspray and minimize the extension of the coating material beyond the plane 200 and the ridge 39 or into the slot 20.

[0052] Reference Figure 5, shows a cross-sectional view of an uncoated rod in the sieve tube 10, which is made of a base material 46. The shape of the rod is optimized to receive a sprayed wear-resistant coating while minimizing the coating being sprayed on the surface defining the groove near the ridge 39 on the first groove surface 34. For example, the base material material of the axially extending rod facing the inflow surface includes a transition region 38 near the second groove surface 36. The transition region 38 connects the second groove surface 36 to the inflow surface 32. A first region 132 of the inflow surface is near the transition region 38. The first region 132 extends towards the ridge 39 and has a curved surface region. A second region 134 of the inflow surface is adjacent to the first region and includes a raised surface region.

[0053] The slope of the first region 132 increases in the circumferential direction. The slope of the second region 134 of the inflow surface adjacent to the first region, which forms the raised surface region, decreases. The slope of each region is measured at a point on a plane tangent to the inflow surface region of the support ring. Both the first region and the second region preferably do not exhibit a negative slope. The portion of the first region near the transition zone may form a substantially flat surface. The portion of the second region near the ridge may also form a relatively flat area. The region between the first region near the transition region and the second region near the ridge may also form a relatively flat surface, but this region is inclined. Thus, the first region and the second region form a relatively flat region therebetween on the inflow surface with a relatively constant slope. The profile of the inflow surface may resemble a smooth continuous wave shape, or a shape approximating a wave shape but having some flat regions. Thus, the concave and / or convex surfaces on the inflow surface of the rod may include flat regions and / or be formed by flat regions.

[0054] For example, in some aspects, the first region near the transition region may form a substantially flat surface. The substantially flat region near the transition region may be less than about 50% of the maximum width of the rod, and preferably less than about 20% of the maximum width of the rod. Additionally, the flat surface may be orthogonal to the radius of the sieve tube. The second region near the ridge may also form a substantially flat region. The substantially flat region near the ridge may be less than about 50% of the maximum width of the rod, and preferably less than about 20% of the maximum width of the rod. Additionally, the flat surface may be orthogonal to the radius of the sieve tube. The region between the first region near the transition region and the second region near the ridge may also be a flat surface, but with a certain inclination. For example, the first region and the second region may form a relatively flat region with a relatively constant slope on the surface in the inflow direction.

[0055] Optimize the orientation and shape of the rod to spray a wear-resistant coating. For example, the angle formed by the rod and its surface, plus the angle (including angle changes) for spraying the wear-resistant coating, helps to minimize unnecessary deposition of the wear-resistant coating on the groove surfaces 34, 36 and the side surfaces 33, 35 of the rod. This unnecessary deposition may be caused by the sprayed coating deviating from the surface of the rod during spraying. To minimize this effect, the ridge of each rod is circumferentially close to, located at, or passes through the first groove surface of the same rod. In addition, the first region 132 and the second region are formed by a concave surface and a convex surface respectively. The shape of these surfaces and the spraying angle for spraying the wear-resistant coating help to minimize and / or prevent the coating from shifting onto adjacent rods, especially onto the first side surface 33 and the first groove surface of adjacent rods. In addition, this shape and other features and techniques disclosed herein help to maximize the overall deposition efficiency of the coating, maximize the coating thickness on the inflow surface near the ridge 39, and minimize the areas on the inflow surface near the transition region that may not receive the coating. For example, by using the lead screw configuration and shape disclosed herein and changing the spraying angle of the wear-resistant coating on the spraying rod, the coating thickness on the inflow surface (where excessive wear may occur) near the ridge 39 can be maximized, and the areas on the inflow surface near the transition region that may not receive sufficient coating (because this region is effectively blocked by the ridges of adjacent rods) can be minimized.

[0056] Still referring to Figure 5 , a preferred configuration of the rod before spraying the wear-resistant coating is shown. For example, a line from the 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 rod, at which the ridges 39 of the rod are closest to adjacent rods. For example, Figure 5 shows the circumferentially outermost position of the ridge 39 in the clockwise direction. In addition, a line from the second plane 144 is also shown. The second plane 144 extends coplanarly from the inflow surface 32 to the position 146 at which the second plane 144 extends coplanarly with the inflow surface 32. The angle Ɵ between the first plane 136 and the second plane 144 should be greater than or equal to 80 degrees, preferably between 80 and 90 degrees.

[0057] Preferably, the wear-resistant coating 50 is only sprayed on the inflow surface 32 of the profile 12. Spraying the wear-resistant coating 50 can include any of the spraying processes discussed herein, and the wear-resistant coating 50 can be any of the materials discussed herein. Preferably, spraying the wear-resistant coating on at least the inflow surface 32 can include a thermal spraying process. In some embodiments, the thermal spraying process can include a high velocity oxy-fuel (HVOF) process.

[0058] The rod 12 forming the screening medium is preferably coated on all or substantially all of its inflow surface or surface 32 using high velocity flame spraying under the combustion of liquid or gaseous fuel. A high velocity flame nozzle such as a high velocity oxygen fuel (HVOF) nozzle is used to spray a wear-resistant coating onto the inflow side surface of the rod. This technique enables the coating to be tightly bonded to the rod surface. The coating is highly adherent to the rod surface and forms a dense grain structure on the rod surface.

[0059] The wear-resistant coating is sprayed onto the inflow surface to form a final coating, the nominal thickness of which is preferably between 75 - 300 microns, and more preferably between 75 - 150 microns, even more preferably about 120 - 150 microns. The thickness of the wear-resistant coating preferably varies by less than twenty percent, and most desirably by less than ten percent. In certain embodiments, the wear-resistant coating 50 can have any thickness between 50 - 300 microns without departing from the scope of the present disclosure. Thus, the nominal thickness of the final coating can be between 5 and 300 microns, including any and all thicknesses therebetween.

[0060] The hardness of the wear-resistant coating 50 should be sufficient to reduce the wear of the wedge-shaped screw during the operation of the sieve drum 10. The hardness of the wear-resistant coating 50 should be greater than the hardness of the base metal 46 of the rod 12. For example, the hardness value of the wear-resistant coating 50 can be greater than the hardness value of cold-rolled stainless steel (about 400 HV0.05). The hardness value of the wear-resistant coating 50 can be between 500 HV0.05 and 1200 HV0.05. The hardness value can be determined by measurements conducted in accordance with the standard Vickers hardness test method. The inflow surface of the wear-resistant coating 50 should have a relatively smooth wear-resistant coating to reduce the resistance of the solid suspension flowing through the sieve drum 10.

[0061] Reference Figure 6 a and Figure 6 b show the variability of the nozzle 54, which is capable of rotating in the circumferential direction and relative to the inflow surface 32 of the axially extending rod 12. The nozzle 54 employs well-known high velocity thermal spraying techniques to eject a stream of wear-resistant coating at high velocity through its opening or orifice. The spraying liquid emerges as a fine cylindrical stream when ejected from the nozzle 54, typically having a diameter of about 7 mm, and the coating is more concentrated at the center of the stream with a diameter of about 3 mm. Thus, the spray angle formed by the nozzle 54 represents the difference between the spray direction of the nozzle and the spray direction when the nozzle is collinear with the cylindrical centerline. For example, the spray angle can be defined by the angle between: 1) a line 207 at the center of the spray stream ejected from the nozzle and 2) a radial line 206 starting from the central axis of the sieve drum. Thus, if the nozzle is directed in the same direction collinear with the radial line 206, the spray angle is generally referred to as zero degrees. Figure 6 a shows such a zero-degree spray angle. However, the nozzle can be rotated clockwise / counterclockwise to change the spray angle. For example, as Figure 6As shown in b, a spray angle of approximately 14 degrees is shown.

[0062] Reference Figure 6 a, Figure 6 b, Figure 7 , Figure 8 and Figure 9 , shows a system for spraying a wear-resistant coating onto a sieve drum 10. In this system, the robotic arm 52 includes a nozzle 54 at its end. The nozzle 54 is adapted to spray the coating material so as to spray the wear-resistant coating 50 onto the inflow surface 32 of the rod at the inflow side of the sieve drum. The robotic arm 52 is oriented to allow the nozzle 54 to travel axially inside the sieve drum 10. If possible, the robotic arm 52 can travel the entire length of the sieve drum. Alternatively, the robotic arm can travel a portion of the length of the sieve drum to spray only a portion of the sieve drum, and then the sieve drum can be flipped so that the robotic arm can travel the remaining length of the sieve drum and spray any remaining desired portions of the rod. The nozzle 54 can rotate in the circumferential direction, can also move at least in the axial direction, and optionally move in the axial plane relative to the radial direction of the sieve drum 10. The nozzle sprays the wear-resistant coating on a path, for example, about 3 to 7 millimeters wide. For example, a coating about 10 microns thick is deposited each pass. By changing the angle of the nozzle along different spray paths along the axial length of the sieve drum in the axial plane, the wear-resistant coating 50 can be deposited at the desired position of the rod, especially the inflow surface of the rod. Moreover, overspray of the wear-resistant coating in non-ideal areas such as the first side surface and the first groove surface can be minimized, so that forming a coating in these areas can minimize costs. In one embodiment, the sieve drum 10 can be rotated using a rotating platform 56 while the nozzle 54 sprays the coating to form the coated surface 50.

[0063] Reference Figure 8 , now a technique for spraying the wear-resistant coating 50 will be described. Using this technique, the nozzle 54 sprays a 10-micron-thick coating each axial pass. The sieve drum 10 can be rotated during each axial pass. However, it may not be necessary to rotate the sieve drum during the axial pass of the nozzle. In addition, the sieve drum can be rotated between one or more axial passes or a series of axial passes of the nozzle, rather than during the axial pass.

[0064] Return to Figure 7, the sieve drum 10 can rotate on the platform 56 when spraying the coating. When the drum rotates, a first series of axial passes are made, during which the nozzle 54 travels the entire axial length of the sieve drum 10 from the first end to the second end and then from the second end to the first end. During the axial pass of the nozzle 54, the wear-resistant coating is continuously sprayed onto the rod. Briefly, this text describes a series of axial pass cycles as a first pass from the first end to the second end and then a second cycle from the second end back to the first end. However, if desired, a series of axial pass cycles can include more than two passes.

[0065] Now referring to Figure 9 , an example of a preferred variation of the spray angle of the nozzle 54 in the circumferential direction is shown, as described previously with reference to Figure 6 Figs. 6a and 6b. In this example, there are 10 spraying passes while the sieve drum rotates at a constant speed, where the rod 12 moves at a specific inflow surface speed. Additionally, in each rotation of the sieve drum, the nozzle rotates axially at a specific speed. This results in a relatively tight helical spray pattern of the wear-resistant coating along the inflow surface of the sieve drum. The first axial spray pass of the nozzle is made at a spray angle of 5 degrees. After each spraying pass, the angle of the nozzle rotates one degree in the circumferential direction from the transition region 38 of the rod towards its ridge 39, i.e., Figure 9 in the counterclockwise direction as defined in

[0066] Now referring to Figure 10 , the figure shows the first three wear-resistant coatings 340, 440, and 540 sprayed on the inflow surface of the axially extended rod. Since each layer is sprayed at a different spray angle, the shapes of the layers are not exactly the same or consistent. Similarly, although the thickness of the coating is generally relatively uniform, the two ends of the coating 50 at or near the transition region and the ridge may be inclined. The first layer of coating 340 is sprayed onto the inflow surface of the rod at a first spray angle of approximately 5 degrees, the second spray angle is 6 degrees, and the third spray angle is 7 degrees. These spray angles, combined with the shape of the inflow surface 32, particularly the transition region 38, the first region 132, the second region 134, and the ridge 39 (as Figure 5as shown), and the orientation of the rod stock, including the resulting groove width, minimizes unnecessary overspray of the wear-resistant coating on the groove surface and the side surface of the rod stock. For example, little or no wear-resistant coating will deflect from the inflow surface 32 of the rod stock onto the first side surface 33 or the groove surface of an adjacent rod stock. Additionally, the ridges 39 of each rod stock effectively act as a shield, blocking the wear-resistant coating spray near the ridge area of the rod stock from entering the groove area, transition area, and second groove surface of an adjacent rod stock. For example, Figure 10 the ridge 39 of the first rod stock in Figure 10 will prevent the spray ejected from the nozzle from depositing on the transition area 38 of the second rod stock, so that the first layer of coating 340 will be away from the groove surface. Additionally, as described above, by changing the spraying angles of the second layer of coating 440 and the third layer of coating 540 by one degree each, each layer of coating will start depositing on the inflow surface from a position farther away from the transition area. Additionally, this can also make the edge of the final wear-resistant coating smooth. Additionally, the spraying angles between each spraying pass vary from 5 degrees to 14 degrees, combined with the shape of the inflow surface and the spray bar edge, which can result in less deflection of the spray from the inflow surface to unwanted areas during spraying.

[0067] For example, the wear-resistant coating 50 can be a hard metal coating containing tungsten carbide or chromium carbide. Basic elements such as Ti, V, Nb, Mo, Ta, and Hf can also occur as carbides and can be included in the wear-resistant coating containing carbides. Carbides of cobalt, chromium, and nickel can also be used for the wear-resistant coating. The screen cylinder rods can be coated with the wear-resistant coating by thermal spraying methods. Any material with a stable molten state, such as metals, ceramics, or their alloys, can be used as the coating material. Various thermal spraying methods for wear-resistant coating materials include flame spraying, arc spraying, plasma spraying, vacuum plasma spraying, high-velocity oxy-fuel spraying, and detonation spraying. For example, high-velocity oxy-fuel spraying (HVOF, HVAF) can be used to form hard metal coatings such as WC-Co(Cr) and Cr3C2NiCr.

[0068] Using these techniques, a coating 50 with optimal hardness, wear resistance, and fracture toughness can be obtained. The wear-resistant thermally sprayed hard metal coating can also contain other hard particles such as nitrides, oxides, or borides in addition to carbides.

[0069] The substrate material of the rod stock 12 is typically stainless steel, but it can also be composed of other metals and alloys. Preferably, the wear-resistant coating 50 is applied to the inflow side surface 32 or the rod stock surface at one or more predetermined angles relative to the inflow side surface 32 or the rod stock surface to ensure the desired coating profile. The wear-resistant coating can be sprayed by one or more nozzles or a nozzle 54 with multiple spray heads. The angle of the nozzle or spray head is adjustable and can be determined as the case may be. For example, the angle of the nozzle 54 can be changed during subsequent spraying processes.

[0070] As described above, the screen cylinder 10, including the profile 12 having the wear-resistant coating 50, can be used to process liquid-solid suspensions of cellulose or other fibers in the pulp and paper industry. However, the screen cylinder 10 may not be limited to use in the pulp and paper industry. For example, the screen cylinder 10 of the present disclosure having the coated profile 12 can be used to screen solid suspensions and / or slurries to remove oversized solid contaminants in mining and drilling equipment, food preparation and processing operations, water treatment processes, coating operations, and other industries.

[0071] Although various embodiments of the profile 12 for the screen cylinder 10 and methods of manufacturing and using the profile 12 are described herein, it should be understood that each of these embodiments and techniques can be used alone or in combination with one or more embodiments and techniques. It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Accordingly, this specification is intended to cover modifications and variations of the various embodiments described herein as long as these modifications and variations come within the scope of the appended claims and their equivalents.

[0072] Unless otherwise expressly stated, no method set forth herein is to be construed as requiring that its steps be performed in a particular order, nor is any apparatus to be construed as requiring a particular orientation in its use. Accordingly, if a method claim does not actually recite an order to be followed by its steps, or any apparatus claim does not actually recite an order or orientation of individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a particular order, or that an apparatus component is to be limited to a particular order or orientation, no order or orientation is, in any way, to be inferred.

Claims

1. A method for manufacturing a screen cylinder, the method comprising: forming a cylindrical screening medium by arranging a plurality of circumferentially spaced, axially extending rods with slots therebetween, the screening medium having an inlet side and an outlet side, wherein a single rod has: an inlet surface, a first slot surface, and a second slot surface opposite the first slot surface, wherein the inlet surface is located between the first slot surface and the second slot surface; applying a wear-resistant coating on the inlet surface of the rod using a nozzle by causing the nozzle to pass along the length of the screening medium a plurality of times to generate a spraying pass of the nozzle, wherein during each pass of the nozzle, the wear-resistant coating is sprayed onto the inlet surface of the rod by the nozzle; and, changing an angle of the nozzle relative to the inlet side of the screening medium in a circumferential direction to change a spraying angle at which the nozzle sprays the coating on the rod.

2. The method according to claim 1, wherein the wear-resistant coating is sprayed using high-velocity thermal spraying.

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

4. The method according to claims 1-3, wherein the wear-resistant coating comprises one or more of: tungsten carbide, chromium carbide, nickel carbide, or a combination thereof.

5. The method according to claims 1-4, wherein after one spraying pass of the nozzle, the angle of the spraying pass is changed.

6. The method according to claims 1-5, wherein the angle at which the nozzle passes is changed by circumferentially rotating the nozzle in a direction from a transition region near the second slot surface of the rod towards a ridge near the first slot surface of the same rod, the ridge being more radially towards the inlet surface than the transition region.

7. The method according to claims 1-6, comprising, after one spraying pass, rotating the nozzle in a direction less than 3 degrees towards the circumferential direction from the second slot surface of the rod to the first slot surface of the same rod to change the angle of the nozzle.

8. The method according to claims 1-7, comprising rotating the screening medium relative to the nozzle while passing the nozzle and spraying the wear-resistant coating.

9. The method according to claims 1-8, wherein the wear-resistant coating sprayed onto the inlet surface of the rod forms a final wear-resistant coating with a relatively stable thickness along the inlet surface, wherein the thickness of the final coating is between 75-300 microns.

10. The method according to claims 1-9, wherein the final wear-resistant coating is absent between the first slot surface and the second slot surface.

11. A method for manufacturing a screen cylinder, the method comprising: forming a cylindrical screening medium by arranging a plurality of circumferentially spaced, axially extending rods with slots therebetween, the screening medium having an inlet side and an outlet side; Generating a spraying pass of the nozzle by causing the nozzle to pass along the length of the screening medium multiple times, applying a wear-resistant coating on the inflow surface of the rod using the nozzle, wherein during each pass of the nozzle, the wear-resistant coating is sprayed on the inflow surface of the rod through the nozzle; and wherein by circumferentially rotating the nozzle from a transition region adjacent to the second groove surface of the rod towards a ridge of the first groove surface close to the same rod, an angle formed by the nozzle is changed, the radial distance of the ridge towards the inflow direction is greater than the radial distance of the transition region by a total of 0 to 35 degrees, and the radial distance of the ridge towards the inflow direction is greater than the radial distance towards the transition region.

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

13. The method according to claims 11-12, wherein the wear-resistant coating comprises one or more of the following: tungsten carbide, chromium carbide, nickel carbide, or a combination thereof.

14. The method according to claims 11-13, wherein the wear-resistant coating is sprayed using high-velocity thermal spraying.

15. The method according to claims 11-14, wherein the final wear-resistant coating is absent between the first groove surface and the second groove surface.

16. The method according to claims 11-15, comprising changing the direction of the nozzle by an angle of less than 3 degrees from the second groove surface of the rod to the first groove surface of the same rod towards the circumferential direction after one spraying pass.

17. The method according to claims 11-15, wherein the angle formed by the nozzle in the circumferential direction is changed by a total of 5 to 15 degrees.

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