Abstract
A pressure screen for use in a fiber web product process (10) has an inlet zone (12), a basket having an accept zone (14) and a reject zone (20). The pressure screen (10) has a housing (28) inside which a rotor (27) is located. The reject zone (20) of the pressure screen (10) has a cover (22) forming a rejects chamber (21) for the reject zone (20). The cover (22) of the rejects chamber (21) of the screen (10) is removable by a reopenable attachment means (25, 29) attached to the housing (28) of the screen (10).
Claims
1. A screen comprising: an inlet zone, a basket and accept zone and a reject zone, which screen further comprises a housing, inside which a rotor is located, wherein the reject zone of the screen comprises a cover forming a rejects chamber for the reject zone and wherein the cover of the rejects chamber of the screen is removable by a reopenable attachment means attached to the housing of the screen.
2. The screen of claim 1, wherein the attachment means are provided as a cast dished design and flange mounted.
3. The screen of claim 1 wherein the rejects chamber of the screen comprises at least one surface provided with a wear resistance coating.
4. The screen of claim 3 wherein the rejects chamber comprises a light rejects outlet and wherein the at least one surface provided with the wear resistance coating is located in an immediate vicinity of the light rejects outlet.
5. The screen of claim 3 wherein the wear resistance coating is applied by arc welding, laser welding or thermal spraying (Plasma, HVOF (High Velocity Oxygen Fuel), HVAF (High Velocity Air-Fuel), Arc Spraying of Flame Spraying).
6. The screen of claim 3 wherein the wear resistance coating is comprised of a material selected from a material alternatives group consisting of iron- or nickel-based alloys having hard carbides embedded in metal matrix (Arc and laser welding), oxide ceramics or Tungsten- or Chromium-based carbides.
7. The screen of claim 3 wherein the wear resistance coating has a coating thickness of at least 100 ?m.
8. The screen of claim 1 wherein the attachment means comprise openings and fasteners extending through the openings.
9. The screen of claim 8, wherein the openings are spaced apart along a circumference of the housing and the cover is removably fastened to the housing by the fasteners which extend through the openings.
10. The screen of claim 1 wherein the attachment means has a piloted fit (a rabbet).
11. The screen of claim 1 wherein the rejects chamber of the screen further comprises at least one hydrodynamic anti-wear vane.
12. The screen of claim 11 wherein the rejects chamber further comprises a light rejects outlet and the at least one hydrodynamic anti-wear vane is located at a distance from the light rejects outlet.
13. A method comprising use of the screen of claim 1 for screening a stock comprising recycled fiber material.
14. A pressure screen for use in a fiber web product process, the pressure screen comprising: a housing; a motor having a shaft which extends into the housing and supports a rotor within the housing for rotatable motion; a basket mounted to the shaft within the housing, having portions defining an accept zone; an inlet zone defined at a front of the housing; and a cover mounted to the housing and having portions which define a reject zone in communication with the accept zone, wherein the cover has portions defining a rejects chamber in the reject zone, and wherein a light rejects outlet communicates with the rejects chamber for the passage of light rejects out of the screen and wherein the cover is removably fastened to the housing.
15. The pressure screen for use in a fiber web product process of claim 14 wherein the rejects chamber of the cover has portions defining an inner wall, portions of which are provided with a wear resistance coating.
16. The pressure screen for use in a fiber web product process of claim 15 wherein the portions of the inner wall provided with the wear resistance coating is located in an immediate vicinity of the light rejects outlet.
17. The pressure screen for use in a fiber web product process of claim 16 wherein the wear resistance coating is comprised of a material selected from a group consisting of iron- or nickel-based alloys having hard carbides embedded in metal matrix, and oxide ceramics or Tungsten- or Chromium-based carbides.
18. The pressure screen for use in a fiber web product process of claim 14 wherein the cover has a flange and the housing has a flange, and wherein the cover is removably attached to the housing by fasteners which extend through aligned openings formed in the the flange of the cover and the flange of the housing.
19. The pressure screen for use in a fiber web product process of claim 14 wherein the cover has a flange which has a piloted fit with the housing defined by a rabbet.
20. The pressure screen for use in a fiber web product process of claim 14 wherein at least one hydrodynamic anti-wear vane is fixed to the cover within the rejects chamber spaced from the light rejects outlet.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Aspects of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of some example embodiments when read in connection with the accompanying drawings and in the following the invention is described in more detail referring to the accompanying drawings.
[0018] FIG. 1 is a perspective view, partially broken away in section, of an advantageous example of a screen according to the invention.
[0019] FIG. 2 is a side view, partially broken away in section of another advantageous example of a screen according to the invention.
[0020] FIG. 3A is an end view of a rejects zone of a screen according to the invention.
[0021] FIG. 3B is a cross-sectional view of the apparatus of FIG. 3A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] During the course of this description like numbers and signs will be used to identify like elements according to the different views which illustrate the invention. Repetition of some reference signs may have been omitted in the figures for clarity reasons.
[0023] In FIG. 1 is schematically shown an advantageous example of a screen 10, in which stock flow is from the inner diameter to the outer diameter of a basket 33 of the screen 10 and a rotor 27 is used to fluidize the pulp slurry on the inner diameter of the basket. The internal shell of the screen 10 has three functional zones: inlet zone 12, basket and accept zone 14 and reject zone 20. Power for the screen 10 is provided from a motor 18 via a shaft 19. The screen 10 comprises a housing 28 which receives the rotor 27 therein. The rotor has replaceable wear bars to fluidize the pulp slurry. The rotor 27 is overhung on the shaft 19, which extends through the rear of the screen 10 and into the housing 28. The shaft 19 is supported at the rear of the screen 10 by bearings 30. The screen 10 is advantageously equipped with a replaceable seal assembly located at the rear of the screen 10 where the shaft 19 passes through the screen shell. The screen 10 has a fabricated assembly. All parts in contact with stock are advantageously constructed of stainless steel. Access to the internals of the screen 10 is made through a hinged (bolted) access door 11. The screen 10 is designed with a horizontally mounted rotating assembly. The inlet 13 and accepts outlet 15 of the screen 10 are vertical. The heavy rejects outlet 16 and light rejects outlet 17 are, in the example of FIG. 1, located on the left-hand side of the screen 10 when viewed from the access door 11. In the inlet zone 12 heavy tramp material is removed prior to the screening of the pulp slurry. The inlet zone 12 is provided with the access door 11 for maintenance. The pulp slurry enters at the front top of the screen 10 through the tangentially mounted inlet 13. The stock flows in a clockwise direction, as viewed from the front, as it enters the inlet zone. Heavy rejectable material moves to the outside of the screen shell by centrifugal force. A junk trap is located in the inlet zone, to collect and isolate tramp material from the rotating assembly. Collected tramp material is removed through periodic cycling of a heavy rejects valve located in connection with the heavy rejects outlet 16. By means of the differential pressure between the interior of the screen 10 and the basket and the accepts zone 14 in the cover 22, the acceptable fibers are passed through the screen basket 33 and into the accept zone part of the basket and the accept zone 14 and accepted fibers are discharged through the accepts outlet 15 located midway on the screen basket of the basket and accepts zone 14. A rejects chamber 21 is formed by the cover 22 to provide the reject zone 20. The light reject outlet 17 of the rejects chamber 21, in the embodiment of FIG. 2, is advantageously positioned in the optimum location for the least resistance to flow. Light rejects will be discharged through the light reject outlet 17 of the rejects chamber 21 and heavy rejects will be discharged through a heavy rejects outlet 16 in the housing 28. The fiber mat, which forms over the screen basket, is re-fluidized with the pulsation generated by the rotor 27. The cover 22 with the reject chamber 21 is located at the rear of the screen 10. Material which does not pass through the screen basket will be discharged through the light rejects outlet 17 therefrom. The cover 22 is attached removably by attachment means to the housing 28 of the screen 10. The attachment means comprise removable external, more advantageously threaded, fasteners 29 mounted on openings 25, advantageously threaded, in the housing 28 of the screen and the cover 22 which forms the rejects chamber 21. Additionally, as shown in FIG. 2, the attachment means 25, 29 advantageously has a piloted fit (a rabbet) in order to maintain alignment of the cover 22 and the rejects chamber 21 with the housing 28 and the rest of the screen 10, when attached.
[0024] In FIG. 2 is schematically shown an advantageous example of a screen 10, in which stock flow is from the inner diameter to the outer diameter of a basket 33 of the screen 10 and a rotor 27 is used to fluidize the pulp slurry on the inner diameter of the basket formed inside a housing 28 of the screen 10. The internal shell of the screen 10 has three functional zones: an inlet zone 12, a basket and accept zone 14 and a reject zone 20. Power for the screen 10 is provided from a motor 18 via a shaft 19. The screen 10 comprises a housing 28 containing a rotor within which has replaceable wear bars located to fluidize the pulp slurry. The rotor 27 is overhung on the shaft 19, which extends through the rear of the screen 10. The shaft 19 is supported at the rear of the screen 10 by bearings 30. The screen 10 is advantageously equipped with a replaceable seal assembly located at the rear of the screen 10 where the shaft 19 passes through the screen shell. The screen 10 consists of a fabricated assembly. All parts in contact with stock are advantageously constructed of stainless steel. Access to the internals of the screen 10 is made through a hinged (bolted) access door 11. The screen 10 is designed with a horizontally mounted rotating assembly. The inlet and accepts outlet 13, 15 of the screen 10 are vertical. The heavy rejects and light rejects, outlets 16, 17 are in the example of the FIG. 2 located on the right-hand side of the screen 10 when viewed from the access door 11. In the inlet zone 12 heavy tramp material is removed prior to the screening of the pulp slurry. The inlet zone 12 is provided with the access door 11 for maintenance. The pulp slurry enters at the front top of the screen 10 through the tangentially mounted inlet 13. The stock flows in a clockwise direction, as viewed from the front, as it enters the inlet zone. Heavy rejectable material moves to the outside of the screen by centrifugal force. A junk trap is located in the inlet zone, to collect and isolate tramp material from the rotating assembly. Collected tramp material is removed through periodic cycling of the heavy rejects valve from the fiber slurry entering the screening in the basket and accept zone 14 via the inlet 13. By means of the differential pressure between the interior of the screen 10 and the basket and accepts zone 14 the acceptable fibers are passed through a screen basket 33 and into the accept zone part of the basket and the accept zone 14 and accepted fibers are discharged through the accepts outlet 15 located midway on the screen basket of the basket and accepts zone 14. Light rejects will be discharged through the light reject outlet 17 and heavy rejects will be discharged through a heavy rejects outlet 16. The fiber mat which forms over the screen basket is re-fluidized with the pulsation generated by the rotor 27. The reject zone 20 is located at the rear of the screen 10. Material which does not pass through the screen basket will be discharged through the light rejects outlet 17 therefrom. The rejects zone 20 is defined within a cover 22 which forms the rejects chamber 21. The cover 22 has a shaft opening for the shaft 19. The rejects chamber 21 within the cover of the screen 10 is removable by reopenable attachment means mounted in a cast dished design cover with a mounted flange, to facilitate replacement in the field. The cover 22 is attached removably by attachment means 25, 29 to the housing 28 of the screen 10. The attachment means 25, 29 comprise removable external, more advantageously threaded, fasteners 29 mounted on openings 25, advantageously threaded, in the housing 28 of the screen and the cover 20. The openings 25 are arranged spaced apart along the circumference of the housing 28 and the cover 22, advantageously to corresponding flange part 37 of the housing 28 and flange part 39 of the cover 20. The fasteners 29 are removably fastened through the openings 25 in the flange parts 37, 39. Preferably, the fasteners 29 are threaded and the openings 25 have respective threads. Additionally, the attachment means 25, 29 advantageously has a piloted fit (a rabbet) in order to maintain alignment of the cover 22 and the rejects chamber 21 with the housing 28 and the rest of the screen 10, when attached. The cover 22 with the rejects chamber 21 has at least one interior surface in an immediate vicinity of the light rejects outlet 17 provided with a wear resistance coating 26 i.e. a hard facing.
[0025] In FIGS. 3A-3B is very schematically shown an advantageous example of the cover 22 with the rejects zone 20 of the screen 10. The rejects zone 20 is defined within the cover 22 which forms the rejects chamber 21. The cover 22 has a shaft opening 23 for the shaft 19 (such as shown in FIG. 1). The rejects chamber 21 of the screen 10 is removable by reopenable attachment means which mounted the cast dished design and flange-mounted cover 22, to facilitate replacement in the field. The attachment means for the flange are located in bolt openings 25. The rejects chamber 21 of the screen 10 comprises at least one hydrodynamic anti-wear vane 24 attached on an inner wall 38 of the cover 22 at a distance from the light rejects outlet 17. The hydrodynamic anti-wear vanes 24 guide the flow inside the rejects chamber 21 hydrodynamically such that the particles of the reject flow causing wear are guided off from those surface parts that are susceptible to wear. Advantageously, more than one hydrodynamic anti-wear vane 24 is provided located at a radial distance from each other on the inner wall 38 of the cover 22 forming the rejects chamber 21. The cover 22 with the rejects chamber 21 has at least one surface in an immediate vicinity of the light rejects outlet 17 provided with a wear resistance coating 26, i.e. a hard facing.
[0026] As can be seen from the examples shown in the figures, the cover 22 with the rejects chamber 21 of the screen 10 is removable by operation of the reopenable attachment means which mounts a cast dished design and flange mounted, to facilitate replacement in the field. The cover 20 is attached removably by the attachment means 25, 29 to the housing 28 of the screen 10. The attachment means 25, 29 comprise removable external, more advantageously threaded, fasteners 29 mounted to extend through openings 25, advantageously threaded, in the housing 28 of the screen and the cover 20 forming the rejects chamber 21. The openings 25 are arranged spaced apart along the circumference of the housing 28 and the cover 22, advantageously to corresponding flange parts 37, 39. The fasteners 29 are to be mounted though the openings 25 removably. Preferably, the fasteners 29, such as shown in FIG. 2, are threaded and the openings 25 have respective threads. Additionally, the attachment means 25, 29 advantageously has a piloted fit (a rabbet) in order to maintain alignment of the cover 22 and the rejects chamber 21 with the housing 28 and the rest of the screen 10, when attached.
[0027] As can be seen from the examples of FIGS. 2 and 3A-3B the rejects chamber 21 of the screen 10 comprises at least one surface in an immediate vicinity of the light rejects outlet provided with a wear resistance coating 26 i.e. a hard facing. The internal surface 38 of the cover 22 of the reject chamber 21 is at least partly provided with the wear resistance coating 26. Preferably the internal surface 38 of the reject chamber 21 is provided with the wear resistance coating 27 at the light rejects outlet 27 and in the immediate vicinity of it. The wear resistance coating 26 may be applied on a surface, which is in the immediate vicinity of the light rejects outlet 17 of the reject chamber 26 of the screen 10. Additionally, the wear resistance coating may be provided on a surface of the reject chamber 21 forming an inner surface 40 of the outlet channel 17 for the light rejects.
[0028] The wear resistance coating may be applied on a surface which is in the immediate vicinity of the light rejects outlet of the reject chamber of the screen. Additionally, the wear resistance coating may be provided on a surface of the reject chamber forming an inner surface of a flow channel for the light rejects.
[0029] According to one preferable embodiment the wear resistance coating may be provided during a maintenance shutdown of the manufacture of paper, board, or the like.
[0030] The wear resistance coating may be in the form of solution, emulsion, or dispersion when it is applied on the surface to be coated. Alternatively, the wear resistance coating may be in the form of a powder comprising discrete particles, which are applied on the surface and attached to the surface, e.g. by melting. According to yet another alternative, the wear resistance coating is in the form of a continuous coating foil or film. The composition may be applied on the cleaned surface by spraying, pasting, spreading or by attaching the coating foil or film on the surface, for example by using curable adhesive.
[0031] According to one embodiment of the invention the wear resistance coating has a coating thickness of at least 100 ?m, in particular when thermal spraying is used as the coating process. According to one embodiment of the invention the wear resistance coating has a coating thickness of several millimeters, in particular when arc and laser welding is used as the coating process. The coating thickness of the wear resistance coating is preferably so thin that it does not disturb the flow patterns in the vicinity of the light rejects outlet. The coating thickness of the wear resistance coating is selected to provide a uniform coating layer which effectively protects the surface from wear.
[0032] The wear resistance coating is advantageously of metallic, ceramic or cermet material having good wear properties. Preferably, the wear resistance coating is applied by arc welding, laser welding or thermal spraying (Plasma, HVOF (High Velocity Oxygen Fuel), HVAF (High Velocity Air-Fuel), Arc Spraying of Flame Spraying). Preferably the wear resistance coating is selected from a material alternatives group consisting of iron- or nickel-based alloys having hard carbides embedded in metal matrix (Arc and laser welding), oxide (typically Al or Cr) ceramics (Thermal Spraying) or Tungsten- or Chromium-based carbides (Thermal spraying).
[0033] In the description in the foregoing, although some functions and elements have been described with reference to certain features, those functions and elements may be performable by other features whether described or not. Although features have been described with reference to certain embodiments or examples, those features may also be present in other embodiments or examples whether described or not. Above the invention has been described by referring to some advantageous examples only to which the invention is not to be narrowly limited. Many modifications and alterations are possible within the invention as defined in the following claims.
