WO1995005248A1 - Slotted screen for paper stock - Google Patents

Slotted screen for paper stock Download PDF

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Publication number
WO1995005248A1
WO1995005248A1 PCT/US1994/009243 US9409243W WO9505248A1 WO 1995005248 A1 WO1995005248 A1 WO 1995005248A1 US 9409243 W US9409243 W US 9409243W WO 9505248 A1 WO9505248 A1 WO 9505248A1
Authority
WO
WIPO (PCT)
Prior art keywords
slot
slots
screen
segments
ends
Prior art date
Application number
PCT/US1994/009243
Other languages
French (fr)
Inventor
James R. Jamieson
Gary S. Williamson
Original Assignee
The Black Clawson Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US10659293A priority Critical
Priority to US08/106,592 priority
Application filed by The Black Clawson Company filed Critical The Black Clawson Company
Publication of WO1995005248A1 publication Critical patent/WO1995005248A1/en

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B07SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07BSEPERATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, OR SIFTING OR BY USING GAS CURRENTS; OTHER SEPARATING BY DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
    • B07B1/00Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
    • B07B1/46Constructional details of screens in general; Cleaning or heating of screens
    • B07B1/4609Constructional details of screens in general; Cleaning or heating of screens constructional details of screening surfaces or meshes
    • B07B1/469Perforated sheet-like material
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D29/00Other filters with filtering elements stationary during filtration, e.g. pressure or suction filters, or filtering elements therefor
    • B01D29/11Other filters with filtering elements stationary during filtration, e.g. pressure or suction filters, or filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
    • B01D29/111Making filtering elements
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D29/00Other filters with filtering elements stationary during filtration, e.g. pressure or suction filters, or filtering elements therefor
    • B01D29/11Other filters with filtering elements stationary during filtration, e.g. pressure or suction filters, or filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
    • B01D29/13Supported filter elements
    • B01D29/15Supported filter elements arranged for inward flow filtration
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D29/00Other filters with filtering elements stationary during filtration, e.g. pressure or suction filters, or filtering elements therefor
    • B01D29/11Other filters with filtering elements stationary during filtration, e.g. pressure or suction filters, or filtering elements therefor with bag, cage, hose, tube, sleeve or like filtering elements
    • B01D29/13Supported filter elements
    • B01D29/23Supported filter elements arranged for outward flow filtration
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B07SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07BSEPERATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, OR SIFTING OR BY USING GAS CURRENTS; OTHER SEPARATING BY DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
    • B07B1/00Sieving, screening, sifting, or sorting solid materials using networks, gratings, grids, or the like
    • B07B1/18Drum screens
    • DTEXTILES; PAPER
    • D21PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21DTREATMENT OF THE MATERIALS BEFORE PASSING TO THE PAPER-MAKING MACHINE
    • D21D5/00Purification of the pulp suspension by mechanical means; Apparatus therefor
    • D21D5/02Straining or screening the pulp
    • D21D5/16Cylinders and plates for screens
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2201/00Details relating to filtering apparatus
    • B01D2201/18Filters characterised by the openings or pores
    • B01D2201/184Special form, dimension of the openings, pores of the filtering elements

Abstract

A slotted cylindrical screen basket (10) for screening a slurry of papermaking stock is formed with axially extending slots (25) which are arranged so that terminal ends of slots or slot (25a, b, c) segments are not circumferentially aligned, for the purpose of distributing loads throughout a wider portion of the screen body. The terminal ends (30) of the slots may be staggered relative to each other.

Description

SLOTTED SCREEN FOR PAPER STOCK

This invention is directed to screen plates, cylindrical screen baskets and the like for the screening of papermaking stock, and more particularly to such a screen in which the openings therethrough are defined by a plurality of slots which are staggered and/or interrupted, for the purpose of improving the screen strength and reducing stress concentrations.

Slotted screens, such as plates and baskets, have commonly been formed with slot patterns in the form of rows of parallel slots. In cylindrical screens these rows extend circumferentially of the screen. The terminal ends of the slots in any given pattern are circumferentially aligned along a common imaginary line, and the adjacent slots are formed of the same length. Such slotted screens have been nighly successful in the screening of papermaking stock, and examples of slotted screen baskets or cylinders are shown in Chupka et al, U. S. Patent No. 4,795,560. Another example of a screen basket having rows of parallel slots is shown in Nelson, U. S. Patent No. 3,713,541 issued January 30, 1973.

In the conventional screen construction, the individual screening slots extend generally axially of the axis of the cylinder screen and in annular zones separated by stiffening ribs. Therefore, the material between adjacent slots is in the form of a rectangle and, when bending, behaves similarly to that of a beam which has fixed end conditions. In this structure, the strength of the screen is highly dependent upon the circumferential stiffening ribs.

In the conventional design, such as shown in U. S. patent 4,795,560, the internal bending loads are transferred by the rectangular beam structures formed between the slots to the circumferential ribs, or to the screen end flanges, and take the form of circumferential loop loads. This is an inefficient load transfer mechanism and as a result of this, and the increasing need for longer slots and more open area, structural failure can occur. This is particularly due to the fact that the high stress concentrations are located at the ends of the slots. Failure can be the result of high cycle metal fatigue.

The conventional cylindrical screen or screen basket is now used for the purpose of screening papermaking stock which includes or consists of reclaimed or secondary fibers. Due to the fact that this stock is much dirtier than stock made from virgin pulp fibers, for effective screening it has become necessary to make such screens with increasingly smaller openings. While, for clean papermaking stock, slot widths in the order of 0.012 to 0.020 inch have been satisfactory, now screens with narrower slot widths are required for the screening of "dirty" pulp suspensions. The fact that the slots are narrower than before has also increased the stress concentration at the ends of the slots. In a cylindrical screen, when the slots terminate at a common axial location or position on the screen, the stress increase is cumulative and localized.

A need exists for a slotted screen design and/or arrangement of screen slots in which structural loads as well as concentrations are broken up and the overall stress state is reduced. This invention preferably utilizes the teachings of U. S. Patent No. 4,795,560, incorporated herein by reference. In the '560 patent, a screen cylinder basket or screen plate is slotted using a directed laser beam. Slot walls or openings are formed which extend generally along straight lines from an inlet surface to an outlet surface, in which the walls are formed of a thin layer of recast metal material from the laser cutting, at the exposed surface. This presents a very hard interface to the flow of stock therethrough and provides a slot with an exposed wall surface which is free of machine and tool marks. Slot cutting by a laser permits the forming of slots which are substantially narrow than slots which can be readily or conveniently cut by mechanical sawing operations. Thus, slots of 0.005 inch in width and less may now be formed.

This invention provides a slotted screen for screening papermaking stock in which generally linearly extending slots are individually interrupted along their respective lengths, thereby forming slot segments and non-slotted land areas between adjacent slot segments. Preferably, such land areas have a dimension in the slot direction substantially less than the length of any portion or segment of the slot.

In the slotting of a screen, such as a cylindrical screen basket, such interruptions in a slot may readily be accomplished by turning off the laser and permitting the basket and laser head to move relative to each other for a short distance corresponding to the intermediate land area, and then turning the laser back on again. In this manner, a slot is caused to have a plurality of intermediate interruptions, thereby reducing the length of any particular slot segment to a dimension substantially less than that of a conventional non- interrupted slot, and thereby reducing the actual stress at the terminal ends by dividing the stresses along the length of the effective slot.

The uninterrupted segments or land areas are preferably staggered with respect to the position of the land areas formed in an adjacent slot. This staggered geometry of the land areas results in additional structural stiffness to form a structure which approaches the characteristic of a shell, as opposed to the characteristic of a plurality of parallel discrete beams. Thus, the loading on the circumferential ribs is reduced, permitting the use of thinner wall material and/or smaller reinforcing rings, in the design of a cylindrical screen basket.

Also, the terminal ends of the slots may be staggered in axial relation to adjacent slots, as distinguished from the conventional practice of terminating slots along a common imaginary circumferential line. This arrangement has the desirable result of distributing structural stress over a wider area of basket material, approaching the structural characteristics of a uniform plate, as opposed to a beam. An important aspect of the invention resides in the fact that neighboring slots are not in direct side- by-side alignment. The land areas between slot segments and slot segments themselves may be staggered. The staggering may be random, and the respective length of slot segments may be randomized. Further, the slots may extend in any convenient direction with respect to a screen dimension, and in the case of a cylindrical screen, the slots may extend conventionally axially, or may be formed in more complex patterns such as curved or inclined to the axis or even circumferential of the axial.

The use of segmented slots or shorter slot segments with a greater number of land areas therebetween provides a greater strength to the overall screen plate, as compared to conventional slot pattern arrangements. Also, the invention makes possible the use of a thinner slotted wall, and permits the use of faster cutting speeds with correspondingly lower cost of manufacture. Alternatively, the staggered arrangements of slot segments can be employed to permit a greater slotted open area without dangerously reducing the total strength of the screen.

The invention may be considered as a screen or screen plate for the sc: eening of a slurry of papermaking stock in which the screen has or is formed with a plurality of screening slots extending through a wall of the screen, characterized by generally linear or parallel extending slots in side-by-side relation in which linearly aligned slot segments or slot ends are separated by land areas and the slot segments have ends which are staggered with respect to each other so that adjacent land areas between slots or slot segments are not aligned directly in side-by-side relationship. The land areas between the ends of aligned segments have a dimension in the direction of slot extension which is less than the length of a slot segment.

A further aspect of the invention resides in screening apparatus for screening papermaking stock in which a screen plate, which may be cylindrical, has a multiplicity of slots extending therethrough in parallel or uniform spaced relation, and at least some of the slots are formed as individual slot segments which are in lengthwise spaced relation to define a row of slots, and characterized by slot segments which are staggered lengthwise with respect to adjacent slot segments in the row, with the result that land areas in the row are correspondingly staggered lengthwise of the row with land areas on either side thereof.

Fig. 1 is a perspective view of a cylindrical screen basket to which this invention may be applied;

Fig. 2 is a fragmentary plan view illustrating a slot pattern made in accordance with this invention; Fig. 3 is a fragmentary enlarged sectional view through a portion of the basket wall taken generally along line 3—3 of Fig. 2;

Fig. 4 illustrates a plan view of an alternative slotting pattern in accordance with this invention; and

Fig. 5 is a fragmentary sectional view showing a weld bead layout for a cylindrical screen basket made in accordance with this invention. A cylindrical centrifugally cast screen basket to which this invention is applied is illustrated generally at 10 in Fig. 1. The basket 10, which may have a diameter of 24 inches and a height of 26 inches as an example, is formed with a body 11 including a pair of end flanges 12 and 13 and a plurality of intermediate stiffening ribs or rings 15. The wall thickness of the body 11, between the end flanges and between the individual stiffening ribs, has a uniform wall thickness which may be in the order of about 3/8". As described in the above identified '560 Patent, the screen basket 10 as illustrated in Fig. 1 is centrifugally cast and finished on the inside and the outside surfaces to provide a highly accurate and uniform wall thickness throughout. It is understood, however, that the principles and teachings of this invention may be applied to non- cylindrical screens and plates, such as conical screens, and may also be applied to flat screen plates, with advantage.

The annular slot zones 18 defined between the stiffening ribs 15, and between a rib and one of the end flanges 12 and 13, are formed with generally axially extending slots 25, preferably at a relatively uniform slot density, and are spaced to allow for the placement of parallel wear bars or weld beads therebetween, such as the beads 20 as illustrated in the sectional view of Fig. 5. These beads 20, which are preferably applied to the inner or inlet surface, after slot cutting, may be made in accordance with the teachings of the above '560 patent. It is preferred that the slots be laser cut also as described in patent '560.

The parallel and axially extending slots 25 are interrupted and broken into individual slot segments represented for the purpose of illustration by segments 25a, 25b, and 25c. The segments are in linear alignment with each other, and define small non-slotted land areas 27 therebetween, shown in the sectional view of Fig. 3. The land areas 27 have a dimension in the direction of slot extensions which is less than the length of a slot segment. It will be noted in viewing Fig. 2 that the slot segment arrangement of each alternate slot 25 is axially staggered with respect to that of the slot on either side thereof, with the result that the land areas 27 between segment sections are likewise staggered so that they do not form a continuous circumferential row. Thus, in a typical arrangement, while one slot may have longer sections, as illustrated by the sections 25a and 25b, an adjacent slot may be formed as two longer segments 25d and a shorter segment 25e. As previously noted, the provision of the non- aligned land areas in the wall of the screen provides a substantially stiffer structure and reduces the amount of stress which much otherwise be carried by the beams defined between the slots to the intermediate ribs and/or end flanges, and provides a structural stiffness which may be attributed to the staggered geometry relation of the slots.

It may also be noted that stress concentrations at the terminal ends of a single long slot (extending between ribs or between a rib and an end flange), are divided at corresponding intermediate locations, so that the total stress concentration at the end of any particular slot segment is substantially less than for the slot total . A further optional form of the invention is illustrated in Fig. 2 in which the slot segments 25c extend axially beyond the laterally adjacent slot segment illustrated at 25d. The ends of the slots 25 are thus staggered at the end flange 12 in the zone 18a. Stresses are distributed by the staggered arrangement of the slot ends.

A further advantage is that the fatigue limits of the metal are not exceeded at the small radii of curvature which occur at the terminal ends of very narrow slots or slot segments.

The zones 18 may be slotted substantially identically to each other or may be formed with different slot patterns characterized by individual slot segments separated by land regions, in which the land region of one slot is not directly opposite the land region of an adjacent slot. It is also not necessary for the slots, or at least all of them, to extend parallel to the axis, in the embodiment of a screen cylinder. The slot segments may extend circumferentially or at an angle of other than 90" to the screen axis.

Fig. 4 illustrates a modified arrangement which enjoys certain advantages of the invention in which the terminal ends 30 of non-segmented slots 35 are staggered in relation to each other. The terminal ends are shown positioned relatively adjacent to one of the reinforcing rings or end flanges. By staggering the terminal ends, the stress loadings are similarly staggered to provide a shell affect to the structure as in the case of the staggered land areas in the pattern of Figs. 1 and 2. The remaining structure will behave as a series of parallel beams between adjacent slots.

The pattern illustrated in Fig. 4 could be particularly useful in extending the life of screen baskets which have conventionally wide slots in the 0.015 to 0.030 inch range such as formed by conventional saw cut methods, but which otherwise would terminate along common circumferential locations.

It will therefore be seen that this invention provides an improved screen, illustrated in the preferred embodiment in the form of a cylindrical screen basket, in which generally circumferentially extending slots arranged along slot zones, between strengthening ribs and end flanges, and in which the slots are staggered and/or segmented, and the segments are staggered or offset and so as to provide a suspended distribution of loads and reduce total stress concentrations. While the preferred embodiments have been disclosed and discussed in connection with a centrifugal cast screen in which the slots are cut by laser, it will be readily apparent that the techniques and concepts disclosed herein can be used with advantage in conventional screen construction and to screen plates to extend the life of the screens.

Claims

1. A screen, such as a screen plate or cylinder, for screening a slurry of papermaking stock, in which said screen has a plurality of screening slots formed in a slot zone, which slots extend through a wall of said screen, characterized by: a plurality of generally linearly extending slots which are interrupted intermediate their terminal ends by non-slotted land areas thereby forming linearly aligned slot segments separated by at least one land area, said land area having a dimension in the direction of slot extension less than the length a said slot segment.
2. A screen according to claim 1 in which a plurality of said slots are positioned in said zone in generally parallel, side-by-side relation and in which adjacent slot segments are staggered with respect to each other so that adjacent said land areas between slot segments are not aligned in side-by-side relation.
3. A screen according to claim 1 in which the terminal ends of at least some of said slots are staggered with respect to the position of terminal ends of others of said slots.
4. A slotted screen for screening papermaking stock in which a screen body has a plurality of generally parallel slots extending through the thickness of the screen body and terminating at slot ends, characterized by ends staggered in relation to the ends of others of said slots.
5. A screen according to claim 4 in which at least some of said slots are segments of a longer slot, which segments are in linear alignment with others of said segments forming a non-slotted land area between aligned segments.
6. A screen according to claim 4 in which said body is shaped in the form of a cylinder, means defining at least a top flange and a bottom flange on said body and in which said slots extend axially of said cylinder and said slot ends terminate in said staggered relation adjacent at least one of said flanges.
7. A screen according to claim 5 further characterized by at least some of said slots being interrupted intermediate their said ends by non-slotted land areas thereby forming slot segments on either side of said land areas.
8. A screen according to claim 7 in which said land areas have a dimension in the direction of slot extension less than the length of a slot segment.
PCT/US1994/009243 1993-08-16 1994-08-16 Slotted screen for paper stock WO1995005248A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
US10659293A true 1993-08-16 1993-08-16
US08/106,592 1993-08-16

Publications (1)

Publication Number Publication Date
WO1995005248A1 true WO1995005248A1 (en) 1995-02-23

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PCT/US1994/009243 WO1995005248A1 (en) 1993-08-16 1994-08-16 Slotted screen for paper stock

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000041822A1 (en) * 1999-01-11 2000-07-20 Tuboscope I/P Inc. Screen assembly for use in a vibratory shaker

Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US255325A (en) * 1882-03-21 Oastler
US313037A (en) * 1885-02-24 Screen-plate or pulp-strainer for paper-making machines
US704004A (en) * 1899-03-06 1902-07-08 George W Cross Screen.
US887557A (en) * 1906-03-02 1908-05-12 William A Werckle Corn-grader.
US4017387A (en) * 1975-08-11 1977-04-12 The Black Clawson Company Screening apparatus
US4309284A (en) * 1979-08-30 1982-01-05 Mitsubishi Jukogyo Kabushiki Kaisha Screen device for paper material
US4473466A (en) * 1982-03-03 1984-09-25 Isenmann Drahterzeugnisse Gmbh Flat sieve element
US4795560A (en) * 1987-04-16 1989-01-03 The Black Clawson Company Screen plates
US4885090A (en) * 1987-04-16 1989-12-05 The Black Clawson Company Screen plates
US5059324A (en) * 1990-11-15 1991-10-22 Chen Tzau Ha Centrifugal pulp screen
US5064537A (en) * 1987-04-16 1991-11-12 The Black Clawson Company Seamless screen cylinder with laser cut openings

Patent Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US255325A (en) * 1882-03-21 Oastler
US313037A (en) * 1885-02-24 Screen-plate or pulp-strainer for paper-making machines
US704004A (en) * 1899-03-06 1902-07-08 George W Cross Screen.
US887557A (en) * 1906-03-02 1908-05-12 William A Werckle Corn-grader.
US4017387A (en) * 1975-08-11 1977-04-12 The Black Clawson Company Screening apparatus
US4309284A (en) * 1979-08-30 1982-01-05 Mitsubishi Jukogyo Kabushiki Kaisha Screen device for paper material
US4473466A (en) * 1982-03-03 1984-09-25 Isenmann Drahterzeugnisse Gmbh Flat sieve element
US4795560A (en) * 1987-04-16 1989-01-03 The Black Clawson Company Screen plates
US4885090A (en) * 1987-04-16 1989-12-05 The Black Clawson Company Screen plates
US5064537A (en) * 1987-04-16 1991-11-12 The Black Clawson Company Seamless screen cylinder with laser cut openings
US5059324A (en) * 1990-11-15 1991-10-22 Chen Tzau Ha Centrifugal pulp screen

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
CROSS ENGINEERING CO., 1927 (No Month), "Perforated Sheet Metals", pages 2, 11-13, 19-21, 28 and 33. *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000041822A1 (en) * 1999-01-11 2000-07-20 Tuboscope I/P Inc. Screen assembly for use in a vibratory shaker

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