The screen cylinder includes a screening plate having contoured grooves along an inflow side and a backing cylinder having a plurality of openings therethrough and disposed on the outflow side of the screening cylinder. The contoured grooves are elongated in the axial direction and are closely circumferentially spaced one from the other about the screen cylinder. In one embodiment, circumferentially extending grooves are formed along the outflow side of the screening cylinder whereby pulp flows through the contoured grooves into the recesses and then through the openings of the backing cylinder. In another embodiment, the recesses are formed on the inflow side of the backing cylinder, the screening cylinder being provided with elongated slots along its outflow side in registry with the contoured slots. In this manner, increased flow capacity is provided. Additionally, the screening cylinder is removable when worn for replacement by a fresh screening cylinder which may then be secured to the backing cylinder.
|
18. A method of manufacturing a screen for use in screening for pulp, said screen being formed of a screening plate and a backing plate, said screening plate having first and second opposite faces, comprising the steps of:
(a) forming elongated, substantially parallel, grooves in said first face, each groove having a side face and a bottom;
(b) forming openings through the bottom of the grooves in said first face and into the screening plate to terminate within the screening plate short of said second face thereof;
(c) forming elongated grooves in the second face of said screening plate inclined relative to the longitudinal extent of the grooves formed in step (a) and to a depth to expose the openings formed in step (b) so that the openings extend entirely through said screening plate, and leave a plurality of ridges in the second face spaced one from the other there-along and extending in a direction inclined relative to the longitudinal extent of said grooves.
10. A screen plate for screening pulp flowing therethrough comprising:
a screening medium having a plurality of slots therethrough and extending generally parallel to one another, said slots having contoured portions on an inflow side of said screening medium; and
a structural backing plate having a plurality of openings therethrough;
said screening medium and said structural backing plate lying in registration one with the other and having respective opposed surfaces in engagement with ne another at an interface therebetween whereby said backing plate structurally supports said screening medium;
one of said screening medium and said backing plate having a plurality of recesses formed in its opposing surface and opening at the opposite surface of the other of said screening medium and said backing plate at the interface thereof establishing communication between the openings of said backing plate and said slots of said screening medium;
whereby pulp may flow sequentially through said slots, said recesses and said openings in said backing plate.
1. A screen cylinder comprising:
a generally cylindrical screening medium having a plurality of openings therethrough;
a generally cylindrical structural backing plate for structurally supporting said screening medium and having a plurality of openings therethrough; and
said screening medium and said structural backing plate lying concentrically one within the other and having respective opposed surfaces in engagement with one another at an interface therebetween whereby said backing plate structurally supports said screening medium;
one of said screening medium and said backing plate having a plurality of circumferentially extending recesses formed in its opposing surface and opening at the opposing surface of the other of said screening medium and said backing plate at the interface thereof establishing communication between the respective openings of said screening medium and said backing plate; and
a plurality of axially spaced projections spaced one from the other in the axial direction defining said recesses and projecting radially from one of said screening medium and said backing plate at said interface;
the openings in said screening medium being elongated and extending in a generally axial direction substantially normal to the circumferential extent of said recesses.
2. A screen cylinder according to
3. A screen cylinder according to
4. A screen cylinder according to
5. A screen cylinder according to
6. A screen cylinder according to
7. A screen cylinder according to
8. A screen cylinder according to
9. A screen cylinder according to
11. A screen plate according to
12. A screen cylinder according to
13. A screen cylinder plate according to
14. A screen cylinder plate according to
15. A screen cylinder plate according to claim 10 11 including means for releasably connecting said cylindrical screening medium and said cylinder backing cylinder plate one to the other.
16. A screen plate according to
17. A screen plate according to
20. A method according to
22. A method according to
23. A method according to claim 18 19 including the step of forming the screening plate into a cylindrical shape to form a metal screen cylinder.
0. 24. A screen cylinder according to
0. 25. A screen cylinder according to
0. 26. A screen cylinder according to
0. 27. A screen cylinder according to
0. 28. A screen cylinder according to
0. 29. A screen cylinder according to
0. 30. A screen cylinder according to
0. 31. A screen cylinder according to
0. 32. A screen plate according to
0. 33. A screen plate according to
0. 34. A screen plate according to
0. 35. A screen plate according to
0. 36. A screen plate according to
0. 37. A screen cylinder according to
0. 38. A screen cylinder according to
0. 39. A screen plate according to
|
The present invention relates to screen plates, e.g., screen cylinders and flat screen plates, for use, for example, in the pulp and paper industry for screening pulps and to methods for their manufacture.
In the formation of paper products from pulp, the pulp is typically screened such that impurities, such as sticks, shives and other undesirable pulp constituents, are removed. This screening process effectively separates the accept and reject portions of the pulp. Screening is generally performed using screen cylinders or flat plates, each of which is provided with openings therethrough for separating the accept and reject portions of the pulp.
In many such screens, whether flat or cylindrical, alternating grooves and ridges are provided in one of the surfaces of the screen. For example, see U.S. Pat. No. 4,529,520. These ridges and grooves are provided for adjusting the flow characteristics of the pulp passing through the screen. While these grooves and ridges have proven to be highly desirable, screens and cylinders with such surface configurations have not heretofore been readily and easily manufactured. For example, such screens are frequently formed by first providing a plurality of openings through a flat metal plate. A plurality of bars are then secured to the inflow side of the plate at longitudinally spaced positions therealong in parallel alignment one with the other to form the ridges and the grooves therebetween. In the case of a screen cylinder the bars are secured in a substantially axial direction. Particularly, the bars are conventionally welded along their opposite sides to the surface of the plate. The fabrication time and, hence, the cost of manufacture of screen plates of this type is quite substantial. Additionally, and importantly, the welds on the opposite sides of the bars occupy substantial space on the surface of the plate. The apertures through the plate are therefore oftentimes blocked by the welds and the number of screen apertures, holes or slots, is accordingly diminished. Welds along the bars also cause stress risers in the screen plate which is subject to heavy vibrations caused by high frequency pulses. Stress cracks and premature failures have frequently been observed in those areas. Additionally, in screen cylinders, rings are frequently secured on the outflow side of the screen cylinder to ensure the stiffness, rigidity and structural strength of the cylinder. Such rings have been secured by welding them circumferentially about the cylinder whereby the welds block a substantial number of screening openings decreasing the effective open area of the screen and consequently the screening throughput.
In conventional screen cylinders, only a limited percentage of the cylinder has screening slots, apertures and the like. This limits the flow through the screen and hence its capacity. It will be appreciated that it is not simply a matter of increasing the number of apertures through the screen plate to compensate for such reduced numbers because predetermined spacings between the apertures, holes or slots must be maintained to avoid the stapling phenomena which clogs the screen plate. Also, structural considerations have often been factors limiting screening capacity. Large bands of metal are often applied about the screen cylinder to provide structural strength and these effectively limit the effective number of openings.
Additionally, screen plates and cylinders used in the pulp and paper industry are subjected to high wear rates, even with hardened surface treatments, and are exposed to corrosive chemicals. In fact, it is not uncommon for plates of this type to completely wear out within weeks of their initial use, necessitating replacement with wholly new plates. These plates and cylinders are quite expensive.
Therefore, in accordance with the present invention, there are provided screen plates for use in the pulp and paper industry having substantially increased efficiency, flow capacity, and strength characteristics, as well as reduced manufacturing costs and fabrication times in comparison with prior methods of forming similar-type plates. Also, the present invention enables substantially reduced replacement costs of the screen plates when worn whereby the end-user does not need to bear the costs of a wholly new screen plate when replacing the worn plate.
Particularly, the present invention provides a screen formed of two separate layers. The first layer comprises a screening plate having narrow slots or small apertures and the second layer comprises a backing plate affording the screening plate the necessary structural strength for pressure screening in the pulp and paper environment.
For purposes of this description, the terms inflow and outflow surfaces designate the sides of the plates through which the flow enters and exits, respectively. The terms inflow and outflow will also refer to other features of the plates hereof, it being understood that the parts so designated lie on the respective entry and exit sides of the plate or elements thereof with reference to the direction of pulp flow. To form the screening plate, in accordance with a first preferred embodiment of the present invention, and preferably for screening low consistency pulps, the outflow face of a plate, for example, a flat plate, is provided with rows of grooves with parallel ridges or bands of material therebetween. The width of the grooves is many times the width of the resulting ridges or bands. Blind grooves are then formed in the opposite inflow face of the plate. These inflow grooves extend in a direction generally normal to the outflow grooves. These blind inflow grooves are preferably contoured and are formed in the plate to a depth such that the contoured grooves do not open through the plate, i.e., do not open through the bottoms of the outflow grooves. Slots are then formed through the bottoms of the contoured grooves and these slots open through the bottoms of the outflow grooves thereby establishing communication between the inflow and outflow sides of the plate. These slots also extend part way through the ridges or bands of material between the outflow grooves. Thus, on one side of the screening plate, for example, the inflow side, there are provided generally parallel extending contoured grooves each preferably having at least one inclined surface and which contoured grooves communicate with slots formed through the bottoms of the contoured grooves opening into the outflow grooves on the opposite side of the plate. The screening plate can be made of metal with the grooves and slots formed by machining, water jets, electric discharge mechanisms or by lasers. Additionally, materials other than metal may be utilized. For example, ceramics may be used because, as will become apparent from the ensuing description, the structural support for the screen plate is provided by a backing plate.
The backing plate in this first preferred embodiment of the present invention comprises a perforated plate having a plurality of relatively large openings in comparison with the slots through the screening plate. The size and number of the openings is, however, consistent with the requirement that the backing plate structurally supports the screening plate.
Where a flat screen plate is desired, the two flat plates are registered one with the other, with the backing plate disposed along the outflow side of the screening plate and secured one to the other, for example, by welding, soldering, riveting or adhesives. The backing plate thus engages the screening plate and forms a structural net-like supporting structure therefor.
To form a screen cylinder, the screening plate is preferably formed initially in a flat configuration as previously described. The plate is then rolled into a cylindrical configuration, the inflow contoured grooves preferably extending substantially parallel to the axis of the cylindrical plate and the outflow grooves extending circumferentially about the cylinder. (Of course, the inflow contoured grooves may extend circumferentially of the cylinder). The edges of the screening plate are then secured, for example, by welding to one another to form the screening plate. Where an outflow screen cylinder is desired, the backing plate is rolled into a cylindrical shape having an inside diameter slightly smaller than the outside diameter of the screening plate. The backing plate is then heated to expand it, thereby enabling the cylindrical screening plate to be received within the backing plate. The backing plate is then heat-shrunk onto the screening plate. The plates are then secured one to the other, e.g., by welding, although shrink-fitting one plate onto the other may be itself sufficient to secure the plates to one another.
With this construction, it will be appreciated that the stiffness, rigidity and structural strength of the backing plate is effectively transmitted to the screening plate. The ridges on the outflow side of the screening plate bear against the inflow surface of the backing plate and afford support in those areas of the screening plate spanning the outflow grooves in the screening plate. Note that this construction also eliminates the capacity reducing support rings previously required in screen cylinders of this type, further enabling an increase in capacity through an increase in the lengths of the slots and contoured grooves to substantially the full axial length of the screen cylinder.
In this preferred form of the invention, it will be appreciated that a substantial increase in capacity or throughput is provided, as well as a capability of replacing the screening plate, once worn, with a wholly new screening plate, without replacing the backing plate. With respect to the increased capacity, it will be appreciated that the contoured grooves in a screen cylinder of this type may extend substantially the full axial length of the cylinder, i.e., terminate just short of the ends of the cylinder. The slots through the base of the contoured grooves, likewise, are substantially coextensive in length with the contoured grooves. The contoured grooves and slots therefore open into the circumferentially extending grooves on the outflow side of the screening plate, i.e., into the annular recesses between the circumferentially grooved outflow surface of the screening plate and the inner inflow surface of the backing plate. Those grooves also open into the apertures formed in the backing plate. It will be appreciated that the flow capacity of the outflow grooves of the screening plate and the apertures in the backing plate are substantially greater than the flow capacity through the contoured grooves and slots of the screening plate. By forming the slots and contoured grooves substantially the length of the cylinder, without interruption, substantially increased throughput is provided in comparison with prior screen cylinders of this type. For example, in screen cylinders previously manufactured, wide bands of metal conventionally extend in circumferential and axial directions for purposes of affording structural support to the cylinder. Such bands substantially diminished the flow through capacity of the screen cylinder. Here, however, the ridges or bands of material between the grooves on the outflow side of the screening plate are relatively small inasmuch as they do not provide substantial structural support to the screening plate. The accepts essentially flow about the bands or ridges and they effectively do not see the bands or ridges. Also, the relatively narrow, circumferential bands are partially recessed in a radial outward direction when the blind slots are cut between the bases of the contoured and outflow grooves, thereby effectively eliminating blockage in those areas of the bands and enabling flow around the bands through the slot portions directly radially in front of the bands.
As noted previously, the screening plate can be replaced when worn by breaking the welds or other securing means between the backing and screening plates. By machining, or chemical treatment if adhesives are used, the worn screening plate may be removed from the backing plate. A new screening plate may then be disposed and secured to the backing plate similarly as previously described. It will be appreciated that the screening plate may be formed of much thinner material then screen plates have previously been formed where structural considerations were necessary. Thus, when the present screening plate has worn to the point where it needs replacement (corresponding to a point where the structural integrity of prior screen plates would be brought into question or when the contoured grooves are no longer effective), the screening plate may be removed from the backing plate and replaced. The cost of this replacement with what is, in effect, a substantially wholly new screen plate, is sharply reduced, e.g., approximately halved, in comparison with the cost of a wholly new screen cylinder. Additional cost savings may be effected by using different materials for the screen plate and backing plate. For example, a lower grade metal may be used for the structural backing plate than for the screening plate.
It will also be appreciated that the arrangement of cylindrical screening and backing plates may be reversed where an inflow configuration is desired. That is, the screening plate may lie radially outwardly of the backing plate with the contoured grooves on the radially outermost inflow surface of the screening plate. Furthermore, costs savings are achieved where special treatments to the screening plates are used and which are not required for use on the backing plate. Additionally, the backing plate may be fabricated inexpensively and placed in inventory, while awaiting orders from customers for particular screen cylinders having particular sized contoured grooves. Thus, upon a customer order, the screening plate may be fabricated and fit to the inventoried backing plate. Also, increased longevity is accomplished in the present invention by minimizing the fatigue factor in the screening plate. Thus, while the screening plate is subjected to compressive forces during use, its fatigue factor in the screening plate. Thus, while the screening plate is subjected to compressive forces during use, its fatigue factor is greatly reduced because it relies solely on the backing plate for structural support.
In another embodiment of the present invention, preferably for screening high consistency pulp and where an even stronger screening plate is desired, the outflow grooves of the screening plate may be formed as inflow grooves in the backing plate. In this embodiment, the backing plate may have a plurality of inflow grooves formed along its inflow surface. Blind apertures may be formed into its opposite surface and which open into the inflow grooves. The screening plate, in this latter embodiment, has a series of contoured grooves formed along its inflow surface. Along its opposite outflow surface, there is provided a plurality of blind slots in registry with the contoured grooves. Slots of reduced width are provided opening the bottom of the inflow contoured grooves into the outflow grooves and hence through the outflow surface of the screening plate. The screening plate and backing plate are then joined similarly as described above, in either flat or cylindrical configurations to form the desired flat or cylindrical screen plates. Thus, where a screen cylinder is being formed, it will be appreciated that the flow through the axially extending contoured grooves and slots enters the circumferentially extending grooves of the cylindrical backing plate and passes through its apertures.
In certain applications it is advantageous to angle one or both of the side faces of the contoured grooves of the screening plate and this can be accomplished simply by machining the side faces of the grooves to the appropriate angles. In this manner, one side of the contoured groove may, for instance, be formed perpendicularly to its base, while its opposite side is angled away from the base of the groove.
It will be also appreciated that the aggregate area of the openings through the screening plate is substantially increased in comparison with the aggregate area of the openings at like spacing provided through similar plates of the previously described prior art constructions. Thus, the present invention provides an increase in effective screen area of approximately 20 to 80% with respect to prior, similarly sized, plates. Further, the screen plates of the present invention may be manufactured at substantially reduced costs and fabrication times.
In the description of the invention in the specification and claims, the term “openings” will be used throughout. This term is used for convenience only, and is intended to encompass apertures of all shapes and sizes, including holes, slots, orifices and passageways.
In a preferred embodiment according to the present invention, there is provided a screen cylinder comprising a generally cylindrical screening medium having a plurality of openings therethrough, a generally cylindrical structural backing plate having a plurality of openings therethrough, with the screening medium and the structural backing plate lying concentrically one within the other and having respective opposed surfaces in engagement with one another at an interface therebetween whereby the backing plate structurally supports the screening medium. One of the screening medium and the backing plate has a plurality of circumferentially extending recesses formed in its opposing surface and which pen at the opposing surface of the other of the screening medium and the backing plate at the interface thereof establishing communicates between the respective openings of the screening medium and the backing plate.
In a further preferred embodiment according to the present invention, there is provided a screen plate for screening pulp flowing therethrough comprising a contoured screening medium having a plurality of elongated slots therethrough and extending generally parallel to one another, a structural backing plate having a plurality of openings therethrough, with the screening medium and the structural backing plate lying in registration one with the other and having respective opposed surfaces in engagement with one another at an interface therebetween whereby the backing plate structurally supports the screening medium. One of the screening medium and the backing plate has a plurality of recesses formed in its opposing surface which open at the opposing surface of the other of the screening medium and the backing plate at the interface thereof establishing communication between the respective openings of the screening medium and the backing plate, whereby pulp may flow sequentially through the contoured slots, the recesses and the openings in the backing plate.
In a further preferred embodiment according to the present invention, there is provided a method of manufacturing a screening plate for use in a screen plate for pulp, the screen plate being formed of a screening plate and a backing plate, the screening plate having first and second opposite faces, comprising the steps of (a) forming openings through the first face and into the body of the screening plate to terminate within the screening plate body and (b) forming grooves in the second face arranged to expose the openings formed in step (a) so that the openings extend entirely through the plate, and leave a plurality of ridges in the second face spaced one from the other therealong.
In a further preferred embodiment according to the present invention, there is provided a method of manufacturing a screening plate for use in a screen plate for pulp, the screen plate being formed of a screening plate and a backing plate, the screening plate having first and second opposite faces, comprising the steps of (a) forming elongated, substantially parallel, grooves in the first face, each groove being contoured and having at least two side faces and a bottom, (b) forming openings through the bottom of the grooves in the first face and into the screening plate to terminate within the screening plate short of the second face thereof (c) forming elongated grooves in the second face of the screening plate inclined relative to the longitudinal extent of the grooves formed in step (a) and to a depth to expose the openings formed in step (b) so that the openings extend entirely through the screening plate, and leave a plurality of ridges in the second face spaced one from the other therealong and extending in a direction inclined relative to the longitudinal extent of said contoured grooves.
In a further preferred embodiment according to the present invention, there is provided a method of manufacturing a screen cylinder including a discrete screening plate and a discrete backing plate comprising the steps of (a) rolling a backing plate to form a backing cylinder, (b) attaching the edges of the backing plate together to form a round cylinder, (c) r lling a screening plate to form a screening cylinder, (d) attaching the edges of the screening plate together to form a round cylinder, (e) inserting one of the screening cylinder and the backing cylinder inside the other of the cylinders and (f) shrink-fitting the cylinders into engagement one with the other.
In a further preferred embodiment according to the present invention, there is provided a method of fabricating screen cylinders for use in screening pulp and repairing a worn screen cylinder, comprising the steps of forming a screening cylinder having elongated contoured grooves along an inflow side thereof and slots through the screening cylinder for communicating pulp between inflow and outflow sides of the screening cylinder, forming a backing cylinder having a plurality of openings therethrough between inflow and outflow sides thereof, inserting one cylinder within the other cylinder, shrink-fitting the cylinders into engagement one with the other whereby the backing cylinder structurally supports the screening cylinder and enable flow of pulp through the contoured grooves and slots of the screening cylinder and the openings of the backing cylinder, subsequent to use and when worn, removing the screening cylinder from the backing cylinder, forming a second screening cylinder having elongated contoured grooves along an inflow side thereof and slots through the second screening cylinder for communicating pulp between inflow and outflow sides thereof, engaging the second screening cylinder and the backing cylinder one to the other whereby the backing cylinder structurally supports the second screening cylinder and enables flow of pulp through the contoured grooves and slots of the second screening cylinder and the openings of the backing cylinder.
Accordingly, it is a primary object of the present invention to provide novel and improved screen plates for use in the pulp and paper industry having increased efficiency and capacity for screening pulp with substantial reductions in cost and manufacturing time, as well as screen plates which can be replaced when worn at substantially reduced costs in comparison with providing a wholly new screen plate.
These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.
Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.
Referring now to
Referring to
In accordance with a preferred method of manufacture, the screening plate is initially in the form of a flat plate. Contoured grooves 16 are formed along the inflow surface of the flat screening plate 12 and blind slots 26 are then formed through the bases 20 of the contoured grooves. The opposite or outflow surface of the flat plate is then grooved in a direction perpendicular to the direction of the contoured grooves 16 and slots 26, the grooves 22 opening into the slots 26. Thereafter, the flat plate is rolled into cylinder form and welded along a vertical seam. The sequence f forming the groove and slot formations may be reversed.
Backing plate 14 structurally supports screen plate 12. Backing plate 14 is therefore constructed of a relatively thick metal plate provided with openings or apertures 28. The openings may be cylindrical or other shapes as desired and may be punched or drilled through the material.
Additionally, the arrangement of the openings in the backing plate may comprise any number of different arrangements. Preferably, however, the openings are formed so that their centers locate on the apices of equilateral triangles whereby the structural strength properties of the backing plate are optimized. With that arrangement of openings 28, a substantially net-like supporting structure is formed. It will be appreciated that the inside diameter of backing plate 14 is formed slightly smaller than the outside diameter of screening plate 12.
To interfit the screening and backing plates one with the other, the grooves, slots and openings in the screening and backing plates are formed while the plates lie in a flat configuration. Thereafter, the plates are rolled into cylindrical form and secured, for example, by welding, along their adjoining edges. The backing plate is then heated to expand it. When expanded, the screening plate is inserted within the expanded backing plate. The backing plate is then cooled to heat-shrink it onto the outer surface of the screening plate. Additionally, or in the alternative, the screening plate may be cooled and then inserted into the backing plate. In either event, when the plates reach room temperature, it will be appreciated that because the outside diameter of the screening plate is slightly larger than the inside diameter of the backing plate, the plates are rigidly secured one to the other. The plates may then be finally secured to one another, e.g., by welding, although rivets, screws, adhesives, solders or the like may be used.
Where an inflow cylinder is required, i.e., the screening plate lies on the outside of the backing plate, the inner diameter of the screening plate will be formed slightly smaller than the outer diameter of the interior backing plate. Thus, after rolling and securing the plates into their cylindrical form, the screening cylinder may be heated and the backing cylinder cooled. Once temperature-treated, the backing cylinder may be inserted within the screening cylinder and the plates brought to room temperature, whereby the plates are heat-shrunk one onto the other.
It will be appreciated that with reference to the outflow screen cylinder illustrated in
In operation the screen plate in accordance with the present invention demonstrates its superior performance when compared to the screen plates of the prior art. The most critical measure of the capacity or performance of a screen plate is its open area, i.e. the percentage of openings with respect to the entire plate area. The foregoing described structure is an optimal structure with regard to both open area and strength. While the open area of the substantially thin screening plate is very large when compared to conventional screen plates of this type, for instance the screen plates disclosed in U.S. Pat. No. 4,529,520, the strength of the screening plate is ensured by engaging the backing plate on the outflow side of the screening plate. The screening plate also has substantially wide and deep grooves 22 along its outflow surface for receiving the pulp flowing through the slots 20.
As discussed previously, conventional screen plates and cylinders employ structural backing ridges/rings arranged on the back side of a screen. These backing rings occupy a substantial area of the screen plate. Because openings cannot lie in those areas, substantially diminished flow capacity occurs. A typical value for the length of the slotted portion of an ordinary screen cylinder is about 50 to 70% of the entire length of the screen cylinder. The backing rings and end rings attached to both ends of the cylinder take the rest, 50 to 30%, of the length of the cylinder. The screen cylinder of this embodiment of the present invention is able to utilize typically 85 to 95% of the entire length of a screen cylinder due to the formation of continuous slots on the inflow side of the screening plate substantially corresponding in length to the axial extent of the cylinder. Additionally, increased flow capacity is provided because ridges 24 on the outflow side of the screening plate, corresponding to the backing rings of an ordinary screen plate/cylinder structure, are so narrow and are recessed back at 27 from the bases of grooves 22 that pulp fibers are able to pass ridges 24 without any substantial “throttling” in the flow velocity. The fibers essentially do not see the ridges 24 because of their narrow width and because the slot depth at 27 permits fibers in the slots 27 in registry with slots 26 to easily divert the fibers for passage around the remaining portions of the ridges 24.
After the screen cylinder, that is, the screening plate portion thereof, is worn to such an extent that it cannot be used efficiently any more, the screening cylinder may be removed from use and reworked for further use essentially as a wholly new screen cylinder. To accomplish this, the screening plate may be removed, e.g., cut along the welds between it and the backing cylinder, and removed from the latter. The backing cylinder may be checked for any necessary modifications or repair. A new screening plate is then formed and installed within the previously used backing plate (in the case of an outflow screen cylinder) or externally about the previously used backing plate (in the case of an inflow screen cylinder). Thus, the wholly new screening plate and the previously used backing plate are heat-shrunk onto one another and finally secured, for example, by welding, riveting, soldering or gluing, as previously described.
From the above, it will be appreciated that the backing plate may be reused many times with wholly new screening plates as each screen cylinder becomes worn and inefficient. Replacement of the screening cylinder therefore wastes a minimum of material inasmuch as the thicker and heavier backing plate is reused as the structural support for the wholly new screening cylinder and the screening plate may be formed of substantially reduced thickness.
Referring now to the second embodiment of a screen cylinder constructed in accordance with the present invention, there is illustrated in
Backing plate 14a, similarly as in the previous embodiment, is formed of a structural material. When the backing plate is in a flat form, grooves 40 are formed along one face, i.e., the inflow surface thereof, and in a direction such that, when the backing plate and screening plate form a screen cylinder, the grooves 40 will extend about the backing plate in a circumferential direction and lie axially spaced one from the other. Blind holes 28a are then formed through the flat backing plate from the opposite or outflow side thereof to open into the grooves 40. As in the prior embodiment, the openings may be cylindrical or other shapes, as desired, and may be punched or drilled through the material. Blind holes are used so that the material of the backing plate in the area of the ridges 42 formed between the grooves 40 is not removed. Preferably, the openings are formed so that their centers locate in the apices of equilateral triangles whereby the structural strength properties of the backing plate are optimized. Thus, a substantially structural net-like structure is formed. The flat backing plate may then be rolled into cylindrical form. For outflow screen cylinders as illustrated, the outer diameter of the screening cylinder is slightly larger than the inner diameter of the backing plate. In this manner, once the screening plate and backing plate are rolled into cylinders, the cylinders may be heat-shrunk one onto the other, as previously described. Additional welds or other securing means, such as solder, rivets or glue, may be provided to secure the screening cylinder and backing cylinder one to the other.
From a review of
Similarly as in the previous embodiment, improved capacity for flow through the plate is provided. Additionally, the screen plate 12a may be removed, when worn, from the backing plate 14a by breaking the welds or other securing means between the screening and backing cylinders and removing the screening plate from the backing plate. A wholly new screening plate may then be secured to the backing plate in the manner previously described.
It will be appreciated that in both embodiments of the present invention the screening plate may be heat-treated in a conventional manner to harden the metal. Also, the screening plate may be provided with a coating layer on its screening side, for example, by treating the surface by a laser or plating the surface with chromium, nickel and the like. While the screening plate is preferably formed of steel, other materials may be used, such as a ceramic. Also, a wedgewire screening plate may be used.
A comparison of the performance characteristics of a conventional screen cylinder is made below with respect to low and high consistency screen cylinders of the embodiments illustrated in
TABLE A1
FIGS.
FIGS.
Conv.
1-4
5-8
Slot Length
42
20 (18)
52
No. of Slot Rows
12
47
13
No. of Slots per Row
1040
1040
1040
Axial Slot Length [mm]
504
940
676
Total No. of Slots
12480
48880
13520
Effective Open Area [m2]
0.268
0.489
0.352
Effective Open Area [%]
8.07%
14.8%
10.6%
Improvement over Conventional [%]
—
82%
31%
In Table A2 below, each cylinder has a diameter and a height of 508 mm and 546 mm, respectively, a slot width of 0.2 mm and a slot pitch of 3.6 mm.
TABLE A2
FIGS.
FIGS.
Conv.
1-4
5-8
Slot Length
49
20 (18)
50
No. of Slot Rows
6
23
7
No. of Slots per Row
437
437
437
Axial Slot Length [mm]
294
460
350
Total No. of Slots
2622
10051
3059
Effective Open Area [m2]
0.0257
0.0402
0.0306
Effective Open Area [%]
3.18%
4.98%
3.79%
Improvement over Conventional [%]
—
56%
19%
From these tables, it will be appreciated that the effective open area of both screen cylinders of the embodiments hereof illustrated in
The following Table B represents a comparison of the strength of the cylinders hereof and a conventional cylinder of the same dimensions, slot width and pitch. Particularly the strength is given in terms of the deformation of a ridge between the slots in directions radially outwardly or inwardly and tangential of the screen cylinder, respectively, in response to a force applied radially from within or from outside the cylinder. In this example, the force applied is 100 kPa and 100% perfect contact between the inner and outer screen members is assumed.
TABLE B
Deformation (mm)
Conventional
FIGS. 4-8
Radial
0.340
0.200 (59%)
0.006 (2%)
Tangential
3.23
0.10 (3%)
0.06 (2%)
Thus, the deformation of the present cylinders is much less than in the conventional cylinders and is considerably less in the high strength cylinder of
It will be appreciated that, by the foregoing described method, fabrication costs and times are substantially reduced in comparison with the prior methods previously described. Additionally, this method enables approximately 20% to 80% greater effective screen area than afforded by screen plates manufactured by previous methods, while simultaneously affording increased strength. The capability of replacing only the screening plate portion of the screen cylinder whereby screen cylinder replacement costs is also afforded, together with the foregoing noted advantages.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
Frejborg, Frey Å., Halonen, Lassi J.
Patent | Priority | Assignee | Title |
7690097, | Jan 03 2006 | BAKER HUGHES, A GE COMPANY, LLC | Methods of assembling well screens |
8297445, | Nov 14 2007 | KADANT CANADA CORP | Screen basket |
8469198, | May 09 2005 | KADANT CANADA CORP | Screen basket with replaceable profiled bars |
8584865, | Mar 27 2009 | Voith Patent GmbH | Screen |
Patent | Priority | Assignee | Title |
2450838, | |||
2850165, | |||
3709186, | |||
3768648, | |||
3941703, | Dec 12 1973 | TRISLOT SYSTEMS N V , ROTERIJSTRAAT 134-136, WAREGEM, BELGIUM, A CORP OF BELGIUM | Wire screens |
4017387, | Aug 11 1975 | The Black Clawson Company | Screening apparatus |
4019987, | Jan 14 1976 | Extended area filters | |
4066555, | May 06 1976 | Rotary filter | |
4146296, | Oct 31 1977 | Viewing apparatus employing transparent viewing screen | |
4200537, | Nov 23 1977 | E. et M. Lamort | Apparatus for the purification of paper pulp |
4206574, | Sep 26 1978 | Hughes Aircraft Company | Lapping block for curved surfaces |
4257419, | Dec 14 1978 | AKTIEBOLAGET STILLE-WERNER, A LIMITED COMPANY OF SWEDEN | Suction-assisted hemorrhoid ligator |
4259136, | Jul 22 1977 | Escher Wyss Limited | Method of making a centrifuge screen |
4264438, | Mar 02 1979 | CAE SCREENPLATES INC | Screen drum and a method for its manufacture |
4276265, | Dec 26 1979 | WHEELABRATOR ENGINEERED SYSTEMS INC | Screen for collection and distribution of process streams |
4358370, | Apr 22 1980 | British Sidac Limited | Backwashable filter |
4529520, | Jan 26 1983 | ADVANCED FIBER TECHNOLOGIES AFT TRUST | Screen plate |
4676903, | Jan 26 1983 | AHLSTROM PROCESS EQUIPMENT INC | Screening apparatus |
4776957, | Jan 26 1983 | AHLSTROM PROCESS EQUIPMENT INC | Rotating element for a screening apparatus with a contour surface |
4818403, | Dec 24 1986 | Nagaoka Kanaami Kabushiki Kaisha | Double cylinder screen |
4832834, | Jul 11 1988 | Elastomer sieve screen | |
4836915, | Jan 26 1983 | A. Ahlstrom Corporation | High flow capacity barrier type screening apparatus |
4880540, | Jan 26 1983 | AHLSTROM PROCESS EQUIPMENT INC | Pulp screening apparatus |
4918807, | Oct 19 1988 | ADVANCED FIBER TECHNOLOGIES AFT TRUST | Screen and method of manufacture |
4950402, | Jan 26 1983 | A. Ahlstrom Corporation | Rotating element for a screening apparatus with a contour surface |
4958843, | Feb 02 1990 | Multi-purpose speed-away toy coaster vehicle and method therefor | |
4986900, | Apr 04 1989 | ADVANCED FIBER TECHNOLOGIES AFT TRUST | Sectional screen cylinder |
5011065, | Nov 14 1987 | J M VOITH GMBH, FRIEDEUSTR 10, D-7920 HEIDENHEIM, FEDERAL REPUBLIC OF GERMANY, A CO OF FEDERAL REPUBLIC OF GERMANY | Screen basket and method of manufacture |
5064537, | Apr 16 1987 | THERMO BLACK CLAWSON INC , A CORPORATION OF DELAWARE | Seamless screen cylinder with laser cut openings |
5147543, | Mar 07 1983 | A. Ahlstrom Corporation | Rotating element for a screening apparatus with a contour surface produced by a plurality of protrusions in the direction of the axial length of the cylindrical rotor |
5192438, | Mar 07 1983 | A. Ahlstrom Corporation | Rotating element for screening apparatus with a contour surface produced by a plurality of protrusions in the direction of the axial length of the rotor |
5200072, | Aug 16 1990 | ADVANCED FIBER TECHNOLOGIES AFT TRUST | Screen plates and methods of manufacture |
5607589, | Jun 06 1995 | ADVANCED FIBER TECHNOLOGIES AFT TRUST | Multiple contour screening |
5624558, | Aug 04 1994 | Aikawa Fiber Technologies Trust | Method and apparatus for screening a fiber suspension |
5718826, | May 26 1995 | Aikawa Fiber Technologies Trust | Screen and method of manufacture |
6021905, | May 26 1995 | Aikawa Fiber Technologies Trust | Screen cylinder with reinforcing rings and method of manufacture thereof |
DE2533240, | |||
EP79811, | |||
EP236843, | |||
EP294832, | |||
EP299258, | |||
EP471195, | |||
IT628633, | |||
WO9004675, | |||
WO9704474, |
Executed on | Assignor | Assignee | Conveyance | Frame | Reel | Doc |
Sep 12 2003 | Advanced Fiber Technologies (AFT) Trust | (assignment on the face of the patent) | / |
Date | Maintenance Fee Events |
Date | Maintenance Schedule |
Dec 18 2010 | 4 years fee payment window open |
Jun 18 2011 | 6 months grace period start (w surcharge) |
Dec 18 2011 | patent expiry (for year 4) |
Dec 18 2013 | 2 years to revive unintentionally abandoned end. (for year 4) |
Dec 18 2014 | 8 years fee payment window open |
Jun 18 2015 | 6 months grace period start (w surcharge) |
Dec 18 2015 | patent expiry (for year 8) |
Dec 18 2017 | 2 years to revive unintentionally abandoned end. (for year 8) |
Dec 18 2018 | 12 years fee payment window open |
Jun 18 2019 | 6 months grace period start (w surcharge) |
Dec 18 2019 | patent expiry (for year 12) |
Dec 18 2021 | 2 years to revive unintentionally abandoned end. (for year 12) |