Patent Grant
12123141
The present invention relates to a screen cylinder that is particularly suitable for screening, filtering, fractionating, or sorting cellulose pulp or fibre suspensions of the pulp and paper industry or other similar suspensions. The present invention relates more particularly to screening devices, which are usually cylindrical though also conical shapes are known. Such screening devices have basically two optional constructions. A first one comprises a plurality of screen wires positioned substantially axially and at a small spacing parallel to each other. The plurality of screen wires forms a screening surface facing the pulp or fibre suspension to be screened and adjacent wires form screening openings therebetween allowing an accept portion of the pulp or fibre suspension to flow therethrough. The second construction comprises a drilled or slotted sheet metal plate bent to a circular, or in broader terms, rotationally symmetrical shape.
The pulp screening process is most typically directed to the removal of oversize contaminants from a slurry of pulp fibres. Screening is often accomplished by a series of screening operations, with each successive operation generally having smaller apertures. In this way, the first screening operation, which may be called coarse screening, will remove very large, aggressive contaminants. Flakes of pulp can also be broken apart in this operation, which is a process called deflaking, to yield useful fibre. This coarse screening operation requires very durable screen rotor and screen cylinder constructions so that they can survive the impact of large and/or aggressive contaminants such as rocks, sand, knots, metal pieces, etc. Once these contaminants are removed and the flakes are dispersed, the pulp can pass to a so-called fine screening operation that is specifically engineered to make a more precise separation between the smaller debris and the pulp fibres. Nowadays both wedge-wire screen cylinders and drilled or slotted sheet-metal cylinders may be found in the various screening operations. A typical wedge-wire screen cylinder, illustrated schematically in
U.S. Pat. No. 5,472,095 discloses a screen cylinder formed of longitudinal, i.e. axially-oriented wedge wires separated by gaps or screening openings, and support rings extending around the circumference of the cylinder to support the wedge wires, as well as longitudinal strips or disruptor bars whose outer surfaces (i.e. surfaces away from the support rings) are at a greater distance from the support rings than are those of the wedge wires.
The above mentioned US-patent also shows so-called contours, i.e. regularly appearing “hills and valleys”, that are created on the feed-side face or screening surface of the screen cylinder by the shape of the individual wedge-wire cross-sections. Similar contours may also be found at the feed-side face of drilled or slotted screen cylinders as shown in U.S. Pat. No. 4,529,520. The phrase ‘profiled screen plate’ is sometimes used to refer to the contoured surface. These contours are intended to increase screen capacity by one or more of the following actions: 1) creating turbulence in the feed-side flow to disperse fibre flocs, and to remove any material that is immobilized at the slot entry, 2) streamlining the flow stream that passes through the slots, and 3) moving the location of the flow bifurcation point away from the slot entry to a location where fibres are less likely to accumulate.
Disruptor bars used in connection with both drilled or slotted screen cylinders and screen cylinders made of wedge wires are typically square or rectangular in cross-section and are most commonly separately formed and attached by their foot part to the feed-side face of the screen cylinder, the feed-side face being either formed of the surface of drilled/slotted sheet-metal plate or by the assembly of wedge wires. The disruptor bars may also act to induce turbulence, but their intent is directed mainly to one or more of the following actions: 1) dispersing fibre flakes to their constituent fibres in the so-called “deflaking” process, 2) breaking up any large agglomeration of strings and other large contaminants, 3) protecting the wedge wires from large contaminants that might otherwise strike and damage the wedge wires and 4) for inclined and spiral disruptor bars, directing the large contaminants to the reject outlet of the screen.
An essential part of the action of a disruptor bar is the presence of an active edge, which is the corner edge of the bar where the flow impinges, and which provides the localized force to the impinging large contaminants, agglomerations or flakes that will cause them to be weakened or broken apart. For a typical disruptor bar in a typical screen, where the flow is driven by the rotor and is largely circumferential, there is only one active edge.
JP2003/201691 discloses a screen cylinder formed of a plurality of screen wires or wedge wires connected to a plurality of locking portions, i.e. notches, in support rings.
U.S. Pat. No. 4,846,971 discloses a sieve which is produced by mechanical interfit between screen wires and support members, with both the screen wires and the support members being provided with notches which fit together when the screen cylinder is assembled.
There are problems with the current practice, i.e. the current design of coarse screen cylinders with wedge wires, as well as drilled and milled screen cylinders, and with disruptor bars. In many cases the problems exist to the extent that the coarse screen cylinder is manufactured without disruptor bars. The main problems that are addressed by the current invention are as follows:
Deflaking can be difficult to measure, and it may be difficult to observe any significant degree of deflaking with cylinders that have relatively few disruptor bars. Increasing the number of disruptor bars is thought to increase the degree of deflaking but at the expense of a significant increase in power consumption.
Runnability is a term used to describe the ability of the screen to maintain capacity even with the inevitable fluctuations in the debris content, fibre character, pulp consistency and other process variables. The disruptor bars, along with the screen contours and screen rotor action, are part of the approach to increasing runnability, for example in breaking up an agglomeration of large, stringy debris, but improvements in runnability can be difficult to measure, and in some cases, the simple rectangular shape of the disruptor bar may not provide the turbulence and fluid action needed.
The large, aggressive contaminants that are typical of coarse screening applications will impact the active edge of the typical current disruptor bars, which are typically separately formed and welded to the surface of the screen cylinder, and in some cases the large impacts can cause welds to crack and the bars to break.
The presence of the disruptor bars can lead to flow patterns such as bound vortices that may lead to accelerated wear immediately downstream of the disruptor bar. This wear may lead to slots becoming wider, thus allowing oversize debris to pass. In the extreme, the screen cylinder will wear through completely, weakening the cylinder and allowing even more debris to pass.
An object of the present invention is to provide a screen cylinder to overcome at least one of the above problems as well as to alleviate the above disadvantages.
The object of the invention is achieved by an arrangement which is characterized by what is stated in the independent claim. The preferred embodiments of the invention are disclosed in the dependent claims.
The invention is based on the idea of a screen cylinder, which possesses at least one disruptor bar having a complex 3-dimensional shape.
An advantage of the screen cylinders of the present invention is that the specifically-designed at least one disruptor bar generates a favourable flow pattern as well as provides additional support and strength to the screen cylinder. The at least one disruptor bar may also be shaped to avoid the downstream bound vortex and the accelerated wear in that location.
A screen cylinder of the present invention comprises a cylindrical screening media provided with perforations, end rings fastened to opposite axial ends of the cylindrical screening media, the cylindrical screening media having a feed-side face and an exit-side face, the feed-side and said exit-side faces extending in a circumferential direction, and the cylindrical screening media being provided with at least one disruptor bar at the feed-side face thereof, the disruptor bar extending in a mainly longitudinal direction on the cylindrical screening media, the at least one disruptor bar having a foot part and a head part, the foot part and the head part forming radially-opposite ends of the disruptor bar, the at least one disruptor bar being formed separately from and fastened to the cylindrical screening media by means of its foot part, the screen cylinder further comprising two or more active edges (E1, E2, E3, E4, E5, E6) provided in a cross-section of the head part of the at least one disruptor bar, the cross-section being taken in a direction perpendicular to a longitudinal axis of the at least one disruptor bar. These two or more active edges may present themselves relative to a circumferential flow, but they may also present themselves to the axial or some other direction of the flow, respecting the other flow components and turbulent flows which will cause motion other than in a simple circumferential direction.
In another embodiment of the invention, the two or more active edges (E1, E2, E3) are formed by a surface facing, at least in part, towards the circumferential direction of flow and a surface facing, at least in part, towards the radial direction (perpendicular to the flow direction) away from the screening media.
In another embodiment of the invention the two or more active edges (E4, E5, E6) are formed by a surface facing, at least in part, in the circumferential direction away from the direction of flow and a surface facing, at least in part, towards the radial direction (perpendicular to the flow direction) away from the screening media.
In another embodiment of the invention the two or more active edges (E1, E2, E3, E4, E5, E6) extend in the longitudinal direction of the at least one disruptor bar.
In another embodiment of the invention the active edges at the head part of the at least one disruptor bar are at least partially-raised above the generally cylindrical feed-side face of the cylindrical screening media.
In another embodiment of the invention the at least one disruptor bar is formed of at least two parts fastened to one another.
The at least one disruptor bar may be connected to the screen cylinder in several different ways. Different ways to connect the at least one disruptor bar provide additional strength and support to the screen cylinder depending on the need.
In one embodiment of the invention the wedge wires are supported by a plurality of support rings forming a support structure to support the wedgewire screening media, each support ring having a notched circumference with notches for the wedge wires.
In another embodiment of the invention the at least one disruptor bar is fastened on the feed-side face of the screening media.
In another embodiment of the invention the at least one disruptor bar is attached onto the wedge wires.
In another embodiment of the invention said at least one disruptor bar is attached, at its foot part, to the end rings, preferably to notches in the end rings.
In another embodiment of the invention the at least one disruptor bar is fastened to the support ring between wedge wires, preferably to a notch in the support ring.
In at least one embodiment, the disruptor bar is distinct and formed separately from, and attached to, a support structure via support rings, the wedge wire, or on the face of a drilled or slotted screening medium.
In another aspect, the invention includes a disruptor bar for a screen cylinder of the type having a cylindrical screening media provided with perforations, where the end rings are fastened to opposite axial ends of the cylindrical screening media, and the cylindrical screening media has a feed-side face and an exit-side face, the feed-side and said exit-side faces extending in a circumferential direction. The at least one distributor bar is to be mounted at the feed-side face of the cylindrical screening media and extending in a mainly longitudinal direction on the cylindrical screening media. The at least one disruptor bar having a foot part and a head part, the foot part and the head part forming radially opposite ends of the disruptor bar, the at least one disruptor bar to be fastened to the cylindrical screening media by means of its foot part, the distributor bar further comprising two or more active edges (E1, E2, E3, E4, E5, E6) provided in a cross-section of the head part of the at least one disruptor bar, the cross-section being taken in a direction perpendicular to a longitudinal axis of the at least one disruptor bar.
In one or more embodiments, the distributor bar may include some or all of the aforementioned features discussed above and herein, in any combination.
In at least one embodiment, the at least one disruptor bar is configured to be attached onto the wedge wires.
In at least one embodiment, the at least one disruptor bar is configured to be fastened to the support ring between wedge wires.
In at least one embodiment, the disruptor bar is configured wherein the foot part fits within a notch in the support ring of the screen cylinder.
In at least one embodiment, the disruptor bar is configured wherein the foot part is configured to fit within a notch in one or more of the end rings of the screen cylinder.
In at least one embodiment, the disruptor bar is distinct and formed separately from, and attached to, a support structure via support rings or on the screening media.
In the following, the present invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which
a and 2b illustrate schematically a conventional prior art outflow wedge wire screen cylinder 10 comprising five coaxial annular support structures 12, 14′, 14″, 14′″ and 16, and wedge wires 18 fastened to the support structures, the support structures 14′, 14″ and 14′″ having a radially notched circumference 20 and a radially solid circumference 22. Support structures 12 and 16 are the top and the bottom support structures or top and bottom end rings and support structures 14′, 14″ and 14′″ are normally called support rings that form a support structure and support the wedge wires or the perforated sheet metal plate between the end rings. The actual number of support rings 14 depends on the length of the screen cylinder and may easily exceed 10. A plurality of wedge wires 18 is connected or clamped to notches 24 in the annular support rings 14′, 14″, 14′″ so that the plurality of wedge wires 18 extend to a first predetermined distance from a radially notched circumference 20 of the support rings 14 and so that gaps or screening openings or slots 26 are formed between two adjacent wedge wires 18. In
In another optional screen cylinder construction, the disruptor bars 30, or rather their foot parts, are fastened on the screen surface, i.e. either on the feed-side face of the wedge wires (see
In order to provide the most durable construction, the coarse screen cylinder has traditionally been made with relatively large (typically 1.8 mm) holes that may be recessed within a contoured screen cylinder surface (see for instance U.S. Pat. No. 4,529,520). More recently, slotted (the most popular alternative of which are wedge-wire) cylinders have come into use. The slot widths in these cylinders are also relatively large (typically 0.5 mm) compared with fine screen cylinders, but they remove a greater amount of contaminants compared to the drilled cylinders with large holes. The contours featured in either the drilled or slotted cylinders are typically deeper, i.e. more aggressive, than used in fine screen cylinders, to promote a greater degree of fibre passage.
These coarse screen cylinders may also be distinguished by the presence of disruptor bars on the feed-side face of the screening media. The performance of these disruptor bars are believed to do one or more of the following, which is to: 1) increase deflaking by the collision of flakes with the leading, which is to say the active, edge of the disruptor bars, 2) break-up agglomerations of “stringy” debris such as plastic tape and other large recycled contaminants, and 3) create large-scale turbulence that prevents the slots or holes from plugging and thus increases screen capacity.
Coarse screen cylinders with disruptor bars may feature either: 1) many disruptor bars with a drilled or slotted screening media, where the disruptor bars remove the need to have small-scale contours adjacent the individual slots or rows of holes, or 2) a more limited number of disruptor bars that are welded onto the feed-side face of the screening media with either plug welds or gusset welds on either side of the foot part of the disruptor bar. The disruptor bars are typically fastened on the feed-side face of the screening media.
The screen cylinder of the present invention discloses disruptor bars having a complex, three-dimensional shape. In practice, the cross-section of a disruptor bar is designed to have more than one leading or active edge when seen in the circumferential direction, i.e. in the direction of movement of the fiber suspension in relation to the screen cylinder or, in other words, with the active edges facing the predominantly circumferential flow of fibre suspension. Additionally, the cross-sectional shape of the disruptor bar may vary in the longitudinal direction of the disruptor bar. This disruptor bar shape addresses previously-listed problems.
A screen cylinder of the present invention comprises a screening media, i.e. either a cylindrical drilled/slotted sheet metal screening media or a screening media made of wedge wires supported to a cylindrical form by means of a support structure, and disruptor bars running in the longitudinal direction of the screening media, i.e. either in axial or in somewhat inclined direction, (i.e. between +/−30 degrees from the axis), to the screen cylinder. Both the drilled or slotted screening media and the screening media made of the wedge wires usually have a surface structure that is typical for screen cylinders known in the prior art. The disruptor bars, on their part, have, at their head part, more than one active edge receiving or facing the fibre suspension moving along the feed-side face of the screen cylinder, and possibly also a cross-section that varies in the axial and/or circumferential direction of the screen cylinder. The cross section may vary continuously for the entire length and/or width of the disruptor bar, or may vary only partially along the length and/or width of the disruptor bar. The head parts of the disruptor bars further at least partly extend beyond, i.e. are raised from, the feed-side face of the screen cylinder in a direction away from the supporting structures. Another way of expressing the extension is to say that the head parts of the disruptor bars extend farther away from the radially-notched circumference of the support structures than do the wedge wires. The disruptor bars used for a single screen cylinder may all have the same structure and shape, but the disruptor bars may as well be a combination of the disruptor bars having different kinds of cross-sections or configurations, as disclosed herein including in the following Figures.
Each disruptor bar according to the present invention includes more than one active edge within a single disruptor bar. Such active edges may be leading edges when seen in the direction of circumferential movement of fibre suspension, or edges pointing in radial direction away from the screening media. This addresses the problem of deflaking without increasing the number of disruptor bars and the associated power consumption. A single disruptor bar of the present invention may be formed of several parts or elements that are welded to one another such that the disruptor bar has at least two sharp active edges. There may be variations of the constituent disruptor bars. For example, if the disruptor bar is formed of three parts or elements attached to each other, the first and middle parts may be generally rectangular or square (sharp cornered) but the last part (in the direction of flow) may be sloped to provide a gentle transition and to avoid the creation of bound vortices which cause unwanted downstream wear.
The complex disruptor bar shape having two or more active edges, and possibly changes in its cross-section, also generates more complex flow patterns and more effective wake turbulence than a simple rectangular disruptor bar. These more-complex flow patterns are more effective in breaking up any debris agglomerations and in maintaining the slots free from plugging with pulp and debris.
It is believed that extreme wear of disruptor bars of a conventional screen cylinder results from “bound vortices” that exist immediately downstream of a simple rectangular disruptor bar and are interrupted only with the periodic passage of the rotor. A more complex disruptor bar shape reduces or eliminates these patterns. In addition, the trailing edge of the complex disruptor bar-shape could be sloped rather than fashioned as a step to reduce wear.
In an embodiment of the present invention, the foot part of the disruptor bar is anchored directly into the support structures of the screen cylinder. In such a case, the screen cylinder is typically constructed of: 1) a cylindrical screening media formed of adjacent wedge wires and support rings, which serve a dual purpose of arranging the wedge wires to have appropriate screening slots therebetween and to support the wedge wires in cylindrical form, and 2) end-rings that are used to connect the cylinder to the pulp screen housing. Thus the disruptor bars are provided between the wedge wires and fastened at their foot part to support rings such that they form interruptions in the otherwise substantially-cylindrical screening face. The support structures of the present invention comprise usually support rings and end rings, but they may also relate to, for example, a shell-type screen cylinder design.
In another embodiment of the present invention the foot part of the disruptor bar is anchored, for example, on the screening media of the screen cylinder. In that case the screen cylinder is typically constructed of 1) a screening media, i.e. either a cylindrical drilled or slotted sheet metal plate or a cylindrical media formed of adjacent wedge wires, and support rings which may be welded onto the drilled plate or serve a dual purpose of arranging the wedge wires, and 2) end-rings that are used to connect the cylinder to screen body. Thus the disruptor bars form interruptions in the otherwise substantially cylindrical screening face.
The inventive screen cylinder construction addresses the following problems.
Disruptor bar breakage and detachment is minimized or alleviated by using a direct and mechanical connection of the disruptor bar to the much stronger support rings. In this manner, the strength of the disruptor bar is not dependent merely on the applied weld and a welded connection of the disruptor bar to the irregular inner surface of the screen cylinder. The weld that is applied to the back of the disruptor bar may function only to connect the pieces together and not to absorb the applied load of impinging debris or debris trapped between the rotor and cylinder.
A second strength benefit is that the proposed design eliminates the possibility of impinging material becoming wedged beneath a welded disruptor bar when either plug welds are used or a gusset weld is not applied along the full length of the disruptor bar.
A third strength benefit is that the integrated disruptor bars transmit load between the screen cylinder end-rings. An issue with the current wedge-wire screen cylinder design is that any torsional, compressive or other load that is applied to the overall cylinder and that is resisted by the cylinder end-rings must be transmitted by the wires. This can lead to fatigue and failure of the relatively small wires. By also having proposed disruptor bars that are anchored to the support rings, there would be several of these much more substantial mechanical members connecting the end-rings of the cylinder, transmitting any extraordinary mechanical loads and avoiding the fatigue and failure of the wires. The design of the present invention may also be applied to fine screen applications where the issue is a worn screen body or other situation that presents mechanical challenges, however, the disruptor bar would not extend above the height of the wires.
Thus, to construct a disruptor bar fulfilling the requirements of the present invention, i.e. the disruptor bar having at least two active leading edges, at least two disruptor bar elements of
The elements of
It is easy to understand when viewing elements of
The disruptor bars, or actually parts of the disruptor bars, of the present invention, especially those having a more challenging configuration, like for instance those discussed in
The bar 308 of
The bar 310 of
As was already discussed in connection with
Thus,
As to the present invention: in
In
And in
Although the invention is above described with reference to specific illustrated embodiments, it is emphasized that it also covers equivalents to the disclosed features, as well as changes and variants obvious to a man skilled in the art, and the scope of the invention is only limited by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20195686 | Aug 2019 | FI | national |
The present disclosure is a continuation of U.S. patent application Ser. No. 17/023,485, filed on Sep. 17, 2020, which claims priority to International Application No. PCT/FI2020/050521, filed on Aug. 6, 2020, and Finnish Patent Application No. 20195686, filed on Aug. 16, 2019. The disclosures of each of the prior applications are incorporated herein by reference in their entirety.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3667615 | Likness | Jun 1972 | A |
| 4529520 | Lampenius | Jul 1985 | A |
| 4846971 | Lamort | Jul 1989 | A |
| 5472095 | Malm | Dec 1995 | A |
| 11846070 | Martineau | Dec 2023 | B2 |
| Number | Date | Country |
|---|---|---|
| 2178683 | Apr 1997 | CA |
| 2965065 | Jul 2010 | CA |
| 2003201691 | Jul 2003 | JP |
| 201546346 | Dec 2015 | TW |
| Entry |
|---|
| Search Report for Finnish Patent Application No. 20195686 dated Mar. 4, 2020. |
| Office Action for Finnish Patent Application No. 20195686 date Mar. 4, 2020. |
| International Search Report and Written Opinion for PCT/FI2020/050521 and mailed on Nov. 19, 2020. |
| Number | Date | Country | |
|---|---|---|---|
| 20240044077 A1 | Feb 2024 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17023485 | Sep 2020 | US |
| Child | 18485663 | US | |
| Parent | PCT/FI2020/050521 | Aug 2020 | WO |
| Child | 17023485 | US |
