CA1081658A - Two-ply crowned-and-tensioned anti-clogging screen system - Google Patents
Two-ply crowned-and-tensioned anti-clogging screen systemInfo
- Publication number
- CA1081658A CA1081658A CA276,989A CA276989A CA1081658A CA 1081658 A CA1081658 A CA 1081658A CA 276989 A CA276989 A CA 276989A CA 1081658 A CA1081658 A CA 1081658A
- Authority
- CA
- Canada
- Prior art keywords
- screen
- screen cloth
- cloths
- strands
- openings
- Prior art date
- Legal status (The legal status 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 status listed.)
- Expired
Links
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- Combined Means For Separation Of Solids (AREA)
Abstract
NON-CLOGGING SCREEN APPARATUS
ABSTRACT OF THE DISCLOSURE
A vibratory screening apparatus has a pair of screen cloths in close face to face abutment with the strands or wires of the lower screen cloth generally intersecting the openings of the upper screen cloth to prevent "blinding" of the upper screen cloth by reason of the tendency of the strands of the lower screen cloth to prevent engagement of particles in the upper screen cloth of a size which would tend to clog the openings of the upper screen cloth. The mesh size of the lower screen cloth may be equal to the mesh size of the upper screen cloth or slightly larger than the upper screen cloth openings up to about fifty per cent larger. The superposed screen cloths may rest upon a much coarser mesh screen which serves merely as a structural support for the screen cloths and does not perform a screening function, the coarser mesh screen having upper edges defining a transverse arch for supporting the screen cloths in an upwardly arched formation so that the longitudinal strands of one screen are held securely against the transverse strands of the other screen and vice versa.
ABSTRACT OF THE DISCLOSURE
A vibratory screening apparatus has a pair of screen cloths in close face to face abutment with the strands or wires of the lower screen cloth generally intersecting the openings of the upper screen cloth to prevent "blinding" of the upper screen cloth by reason of the tendency of the strands of the lower screen cloth to prevent engagement of particles in the upper screen cloth of a size which would tend to clog the openings of the upper screen cloth. The mesh size of the lower screen cloth may be equal to the mesh size of the upper screen cloth or slightly larger than the upper screen cloth openings up to about fifty per cent larger. The superposed screen cloths may rest upon a much coarser mesh screen which serves merely as a structural support for the screen cloths and does not perform a screening function, the coarser mesh screen having upper edges defining a transverse arch for supporting the screen cloths in an upwardly arched formation so that the longitudinal strands of one screen are held securely against the transverse strands of the other screen and vice versa.
Description
~0~165~
This invention relates to industrial screening equipment -and more particularly to novel non-clogging screen cloth assemblies.
A very pressing problem exists in the screening art, particularly when screening finely divided material, due to the tendency of the material being screened to clog the openings in the screen cloth. This condition is sometimes referred to in the art as "blinding" of the screen surface.
This blinding of the screen cloth greatly impairs the effectiveness of the screening capacity of the apparatus and may even reduce such capacity substantially to zero.
Various methods have been employed to remove particles which have become wedged in the openings of the screen cloth as by shaking or the like, but none of these expedi-ents has proved effective with particles of certain shapes.
It is conventional in the art to provide a backing or supporting screen beneath the primary screen cloth but such backing screens have openings a number of times greater than the openings in the screen cloth and are provided for structural support of the screen cloth and do not of themselves perform any screening function.
The present invention resides in a vibratory screening apparatus for finely divided material and includes a pair of screen cloths in close face to face abutment for receiving material to be screened thereon, the upper screen cloth being of approximately 20 mesh or finer and the openings in the screen cloths being at least twice as wide as the diameters of the strands forming the screen cloths.
A frame supports the screen cloths, the lower screen cloth having openings therein at least as large as the openings in the upper screen cloth but not in excess of fifty per-cent larger than the openings in the upper screen cloth - ~08165~
and with the majorlty of the openings in the upper screen cloth intersected by the strands of the lower abutting screen cloth. The frame includes a transverse series of spaced parallel longitudinally extending stringers whose upper edges define a transverse arch for supporting the screen cloths in upwardly arched formation so that the longitudinal wires of one screen are held securely against the transverse strands of the other screen and vice versa to lock the strands of one screen into the strands of the other in such a manner that the plane defining the upper surfaces of the lower screen is above the plane defining the lower surfaces of the upper screen. Thus, the strands of the lower screen effectively prevents a generally spheroidal particle from becoming lodged in an opening of the upper screen, the convex surfaces further serving to effectively prevent relative vertical movement of the screen cloths during vibration thereof.
The present invention provides, therefore, a novel screen cloth structure which solves the clogging or "blinding" problem in a new manner by preventing the wedging of particles in the screen openings rather than by attempting to dislodge particles after they have become wedged in the screen openings. This is accomplished by using a sandwich comprising the pair of screen cloths in immediate vertical juxtaposition. This is not to be confused with the backing screen referred above and in fact a third very much coarser backing screen could be used beneath the pair of screen cloths referred to here.
. ~
108165~
1 The mesh size of the screen cloths per se may be approxi-mately the same although, for reasons which will appear later herein, it will generally be preferable to use a screen cloth of slightly larger mesh size beneath the top screen clo-th.
In pursuing t~e principles of the present invention -the openings in the screen cloths will be at least twice the width of the wire diameters and preferably at least two and a half times the wire diameter or more. Accordingly, when a particle of a size which might wedge into -the opening of -the top screen cloth tends to enter an opening therein it comes into contact wi-th a wire of the lower screen cloth and is thus prevented from getting into a wedging position.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a fragmentary top plan view of the left-hand por-tion of a screen frame constructed according to one form of the present invention;
Fig. 2 is a fragmentary view taken similarly to Fig. 1 bu-t on an enlarged scale and rota-ted through 90 degrees relative to Fig. l;
Fig. 3 is a transverse cross-sectional view through the left-hand side of the screen s-tructure of Figs. 1 and 2 on a generally vertical plane;
Fig. 4 is a much enlarged top plan view of one form of -the screen arrangement of the presen-t invention;
Fig. 5 is a transverse cross-sectional view through the screen structure of Fig. 4;
Fig. 6 is a view similar to Fig. 4 but showing the screen members in different relative positions, and Fig. 7 is a view similar to Fig. 5 but showing the embodi-ment of Fig. 6.
DESCRI_TION OF THE ILLUSTRATED EMBODIMENT
The general framing and support structure of the screen illustrated herein by way of example is conventional and comprises 1081~
a rectangular frame lO having a rigid screen support structure comprising a series of parallel stringer members 11 which extend longitudinally with respect to the direction of movement of material along the screen. So-called bulkhead members 12 extend parallel to each other between stringers 11 and are welded at their ends to the stringers ll. The bulkheads and stringers are arranged to present an upwardly arched surface in a transverse direction so that the screen elements are stretched over the top surface of the arch thus formed, as fragmentarily indicated in Fig. 3. It is to be understood that all of the foregoing is conventional in screening apparatus of the type here under consideration.
The top and bottom screen cloths which are sandwiched together are indicated at 14 and 15 in Fig. 3 and are jointly wrapped into a return-bent channel member 16 at their side edges. Flanges 17 are fixed to the side edges of frame lO and a rail member 20 has a flange portion 21 which engages the return-bent member 16, as clearly shown in Fig. 3, and draws the same generally outwardly and downwardly by virtue of a bolt and nut connection 22 between rail member 20 and flange 17. A much coarser backing screen 24 underlies the two screen cloths 14 and 15 and the return-bent member 16 and rests upon the top surface of frame lO and upon the stringers and bulkheads of the screen frame. In the present instance a cushioning strip 26 is interposed between frame lO and backing screen 24.
As indicated earlier herein, ~he backing screen is a conventional expedient for supporting relatively fine screen cloths and has openings a number of times greater than the screen element openings and performs no screening function but serves entirely as a support for the screen cloths.
`
~08~65~Y
The strands forming the screen cloths are termed wires in the following description, but clearly the terminology is not to be taken as relating only to metallic strands. In the instance illustrated in Figs.
4 and 5 the upper and lower screen cloths 14 and 15 are of the same mesh size and in - 4a -~, 108165~
1 such illustrated instance the wires of the lower screen cloth are arranged to be staggered with respect to the wires of the upper screen cloth so that each lower screen cloth wire lies approximately halfway between two superposed wires of the upper screen cloth. In alternative arrangements the wires of the lower screen cloth may be offset somewhat from this centered arrangement although such lower wires should be sufficien-tly offset from the upper wires -to engage and dislodge par-ticles which might tend to blind the upper screen openings or, in fact, to prevent the engagement of such particles in the upper screen openings.
By way of example, Figs. 6 and 7 show an instance wherein `~
the lower screen cloth is substantially offse-t from the centered arrangement illustrated in Figs. 4 and 5. Since the screen ~ -cloths of Figs. 6 and 7 are otherwise identical with -those of Figs. 4 and 5 like numerals have been applied -to -the several parts in Figs. 6 and 7.
In many, if not most, instances the lower screen cloth may be of a somewhat larger mesh than the upper screen cloth but not of such degree as to leave a major portion of the openings of the upper screen cloth without underlying wires of the ;
lower screen cloth.
This relationship between mesh size and registry of the wires of the two screen cloths is subjec-t to considerable varia-tion and is in general empirically determined by the type of material being screened and the general shapes and contours of the particles of such material.
While the relationship between the mesh size of the two screen cloths varies in accordance with various operating con-ditions and the type and size of material being screened, the mesh size of the lower screen cloth will in general vary between a minimum mesh size which is equal to that of the upper screen clo-th and a maximum mesh size which is about 50/O greater -than ~8165~
1 the mesh size of the upper screen cloth. In all cases the openings in the screen cloths will be of a wid-th at least twice the diameter of the wires of the screen cloth as to both the upper and lower screen cloths.
In Fig. 5 it will be noted that the actual effective mesh size would be as indicated by the dimension B indicating -the space between a wire of lower screen 15 and the adjacent corres-ponding wire of upper screen 14. This dimension will be greater and more nearly approach the particle size opening of the upper screen cloth when the wires of the lower screen cloth are off-set with respect to the wires of the upper screen cloth but not centered therebeneath as in Fig. 5. Where a larger mesh screen is employed in the lower screen cloth 15 dimension B will be variable across -the surfaces of the two screen cloths.
Merely by way of example, it will be noted that wire 28 of lower screen cloth 15 prevents lodgment of a particle A in the opening of upper screen cloth 14. With particle A resting on wire 28 of screen 15 as in Fig. 5, there will be a slight lateral clearance between particle A and the two adjacent wires of screen 14 so that there is no tendency of particle A to be-come lodged between such -two wires. There is no -tendency of particles to lodge in the space indicated by the dimension B
due to the slight relative movement between the screens which is a natural result of the rapid vertical vibration to which the screen cloths are subject during screening operations, such vertical vibrations -tending to cause the upper screen cloth to move upwardly slightly away from the lower screen cloth and back toward the same during vibrational movements. Also, because of the arched condition of the screen cloths, -there is a very slight relative movement of the two screen cloths in their plane of extent as -the screen is vibrated.
Preferred embodiments of -the presen-t invention have been described herein and shown in the accompanying drawings to ~081658 1 illustrate the underlying principles of the invention but it is to be understood that numerous modifications may be made with-out departing from the broad spirit and scope of the invention.
"
,' , ; `
:
This invention relates to industrial screening equipment -and more particularly to novel non-clogging screen cloth assemblies.
A very pressing problem exists in the screening art, particularly when screening finely divided material, due to the tendency of the material being screened to clog the openings in the screen cloth. This condition is sometimes referred to in the art as "blinding" of the screen surface.
This blinding of the screen cloth greatly impairs the effectiveness of the screening capacity of the apparatus and may even reduce such capacity substantially to zero.
Various methods have been employed to remove particles which have become wedged in the openings of the screen cloth as by shaking or the like, but none of these expedi-ents has proved effective with particles of certain shapes.
It is conventional in the art to provide a backing or supporting screen beneath the primary screen cloth but such backing screens have openings a number of times greater than the openings in the screen cloth and are provided for structural support of the screen cloth and do not of themselves perform any screening function.
The present invention resides in a vibratory screening apparatus for finely divided material and includes a pair of screen cloths in close face to face abutment for receiving material to be screened thereon, the upper screen cloth being of approximately 20 mesh or finer and the openings in the screen cloths being at least twice as wide as the diameters of the strands forming the screen cloths.
A frame supports the screen cloths, the lower screen cloth having openings therein at least as large as the openings in the upper screen cloth but not in excess of fifty per-cent larger than the openings in the upper screen cloth - ~08165~
and with the majorlty of the openings in the upper screen cloth intersected by the strands of the lower abutting screen cloth. The frame includes a transverse series of spaced parallel longitudinally extending stringers whose upper edges define a transverse arch for supporting the screen cloths in upwardly arched formation so that the longitudinal wires of one screen are held securely against the transverse strands of the other screen and vice versa to lock the strands of one screen into the strands of the other in such a manner that the plane defining the upper surfaces of the lower screen is above the plane defining the lower surfaces of the upper screen. Thus, the strands of the lower screen effectively prevents a generally spheroidal particle from becoming lodged in an opening of the upper screen, the convex surfaces further serving to effectively prevent relative vertical movement of the screen cloths during vibration thereof.
The present invention provides, therefore, a novel screen cloth structure which solves the clogging or "blinding" problem in a new manner by preventing the wedging of particles in the screen openings rather than by attempting to dislodge particles after they have become wedged in the screen openings. This is accomplished by using a sandwich comprising the pair of screen cloths in immediate vertical juxtaposition. This is not to be confused with the backing screen referred above and in fact a third very much coarser backing screen could be used beneath the pair of screen cloths referred to here.
. ~
108165~
1 The mesh size of the screen cloths per se may be approxi-mately the same although, for reasons which will appear later herein, it will generally be preferable to use a screen cloth of slightly larger mesh size beneath the top screen clo-th.
In pursuing t~e principles of the present invention -the openings in the screen cloths will be at least twice the width of the wire diameters and preferably at least two and a half times the wire diameter or more. Accordingly, when a particle of a size which might wedge into -the opening of -the top screen cloth tends to enter an opening therein it comes into contact wi-th a wire of the lower screen cloth and is thus prevented from getting into a wedging position.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a fragmentary top plan view of the left-hand por-tion of a screen frame constructed according to one form of the present invention;
Fig. 2 is a fragmentary view taken similarly to Fig. 1 bu-t on an enlarged scale and rota-ted through 90 degrees relative to Fig. l;
Fig. 3 is a transverse cross-sectional view through the left-hand side of the screen s-tructure of Figs. 1 and 2 on a generally vertical plane;
Fig. 4 is a much enlarged top plan view of one form of -the screen arrangement of the presen-t invention;
Fig. 5 is a transverse cross-sectional view through the screen structure of Fig. 4;
Fig. 6 is a view similar to Fig. 4 but showing the screen members in different relative positions, and Fig. 7 is a view similar to Fig. 5 but showing the embodi-ment of Fig. 6.
DESCRI_TION OF THE ILLUSTRATED EMBODIMENT
The general framing and support structure of the screen illustrated herein by way of example is conventional and comprises 1081~
a rectangular frame lO having a rigid screen support structure comprising a series of parallel stringer members 11 which extend longitudinally with respect to the direction of movement of material along the screen. So-called bulkhead members 12 extend parallel to each other between stringers 11 and are welded at their ends to the stringers ll. The bulkheads and stringers are arranged to present an upwardly arched surface in a transverse direction so that the screen elements are stretched over the top surface of the arch thus formed, as fragmentarily indicated in Fig. 3. It is to be understood that all of the foregoing is conventional in screening apparatus of the type here under consideration.
The top and bottom screen cloths which are sandwiched together are indicated at 14 and 15 in Fig. 3 and are jointly wrapped into a return-bent channel member 16 at their side edges. Flanges 17 are fixed to the side edges of frame lO and a rail member 20 has a flange portion 21 which engages the return-bent member 16, as clearly shown in Fig. 3, and draws the same generally outwardly and downwardly by virtue of a bolt and nut connection 22 between rail member 20 and flange 17. A much coarser backing screen 24 underlies the two screen cloths 14 and 15 and the return-bent member 16 and rests upon the top surface of frame lO and upon the stringers and bulkheads of the screen frame. In the present instance a cushioning strip 26 is interposed between frame lO and backing screen 24.
As indicated earlier herein, ~he backing screen is a conventional expedient for supporting relatively fine screen cloths and has openings a number of times greater than the screen element openings and performs no screening function but serves entirely as a support for the screen cloths.
`
~08~65~Y
The strands forming the screen cloths are termed wires in the following description, but clearly the terminology is not to be taken as relating only to metallic strands. In the instance illustrated in Figs.
4 and 5 the upper and lower screen cloths 14 and 15 are of the same mesh size and in - 4a -~, 108165~
1 such illustrated instance the wires of the lower screen cloth are arranged to be staggered with respect to the wires of the upper screen cloth so that each lower screen cloth wire lies approximately halfway between two superposed wires of the upper screen cloth. In alternative arrangements the wires of the lower screen cloth may be offset somewhat from this centered arrangement although such lower wires should be sufficien-tly offset from the upper wires -to engage and dislodge par-ticles which might tend to blind the upper screen openings or, in fact, to prevent the engagement of such particles in the upper screen openings.
By way of example, Figs. 6 and 7 show an instance wherein `~
the lower screen cloth is substantially offse-t from the centered arrangement illustrated in Figs. 4 and 5. Since the screen ~ -cloths of Figs. 6 and 7 are otherwise identical with -those of Figs. 4 and 5 like numerals have been applied -to -the several parts in Figs. 6 and 7.
In many, if not most, instances the lower screen cloth may be of a somewhat larger mesh than the upper screen cloth but not of such degree as to leave a major portion of the openings of the upper screen cloth without underlying wires of the ;
lower screen cloth.
This relationship between mesh size and registry of the wires of the two screen cloths is subjec-t to considerable varia-tion and is in general empirically determined by the type of material being screened and the general shapes and contours of the particles of such material.
While the relationship between the mesh size of the two screen cloths varies in accordance with various operating con-ditions and the type and size of material being screened, the mesh size of the lower screen cloth will in general vary between a minimum mesh size which is equal to that of the upper screen clo-th and a maximum mesh size which is about 50/O greater -than ~8165~
1 the mesh size of the upper screen cloth. In all cases the openings in the screen cloths will be of a wid-th at least twice the diameter of the wires of the screen cloth as to both the upper and lower screen cloths.
In Fig. 5 it will be noted that the actual effective mesh size would be as indicated by the dimension B indicating -the space between a wire of lower screen 15 and the adjacent corres-ponding wire of upper screen 14. This dimension will be greater and more nearly approach the particle size opening of the upper screen cloth when the wires of the lower screen cloth are off-set with respect to the wires of the upper screen cloth but not centered therebeneath as in Fig. 5. Where a larger mesh screen is employed in the lower screen cloth 15 dimension B will be variable across -the surfaces of the two screen cloths.
Merely by way of example, it will be noted that wire 28 of lower screen cloth 15 prevents lodgment of a particle A in the opening of upper screen cloth 14. With particle A resting on wire 28 of screen 15 as in Fig. 5, there will be a slight lateral clearance between particle A and the two adjacent wires of screen 14 so that there is no tendency of particle A to be-come lodged between such -two wires. There is no -tendency of particles to lodge in the space indicated by the dimension B
due to the slight relative movement between the screens which is a natural result of the rapid vertical vibration to which the screen cloths are subject during screening operations, such vertical vibrations -tending to cause the upper screen cloth to move upwardly slightly away from the lower screen cloth and back toward the same during vibrational movements. Also, because of the arched condition of the screen cloths, -there is a very slight relative movement of the two screen cloths in their plane of extent as -the screen is vibrated.
Preferred embodiments of -the presen-t invention have been described herein and shown in the accompanying drawings to ~081658 1 illustrate the underlying principles of the invention but it is to be understood that numerous modifications may be made with-out departing from the broad spirit and scope of the invention.
"
,' , ; `
:
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a vibratory screening apparatus for finely divided material, a pair of screen cloths in close face to face abutment for receiving material to be screened thereon, the upper screen cloth being of approximately 20 mesh or finer and the openings in the screen cloths being at least twice as wide as the diameters of strands forming the screen cloths thereof, a frame for supporting said screen cloths, the lower screen cloth having openings therein at least as large as the openings in the upper screen cloth but not in excess of fifty per cent larger than the openings in the upper screen cloth and with the majority of the openings in the upper screen cloth intersected by the strands of the lower abutting screen cloth, said frame including a transverse series of spaced parallel longitudinally extending stringers whose upper edges define a transverse arch for supporting said screen cloths in upwardly arched formation, whereby the longitudinal strands of one screen are held securely against the transverse strands of the other screen and vice versa to lock the strands of one screen into the strands of the other in such manner that the plane defining the upper surfaces of the lower screen is above the plane defining the lower surfaces of the upper screen whereby the strands of said lower screen effectively prevents a generally spheroidal particle from becoming lodged in an opening of said upper screen, said convex surfaces further serving to effectively prevent relative vertical movement of said screen cloths during vibration thereof.
2. Screening apparatus according to claim 1 wherein a backing screen of a mesh at least several times coarser than the mesh of the screen cloths underlies the lower screen cloth to support the screen cloths.
3. Screening apparatus according to claim 1 wherein the upper and lower screen cloths are of the same mesh size and wherein the wires of the lower screen cloth are offset in at least one horizontal direction with respect to the strands of the upper screen cloth.
4. Screening apparatus according to claim 1 wherein the lower screen cloth is of a larger mesh size than the upper screen cloth but wherein the openings in the lower screen cloth are less than about fifty per cent larger than the openings in the upper screen cloth.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA276,989A CA1081658A (en) | 1977-04-26 | 1977-04-26 | Two-ply crowned-and-tensioned anti-clogging screen system |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA276,989A CA1081658A (en) | 1977-04-26 | 1977-04-26 | Two-ply crowned-and-tensioned anti-clogging screen system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1081658A true CA1081658A (en) | 1980-07-15 |
Family
ID=4108501
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA276,989A Expired CA1081658A (en) | 1977-04-26 | 1977-04-26 | Two-ply crowned-and-tensioned anti-clogging screen system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1081658A (en) |
-
1977
- 1977-04-26 CA CA276,989A patent/CA1081658A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |