CA1188142A - Method and apparatus for improving formation on a paper making machine - Google Patents
Method and apparatus for improving formation on a paper making machineInfo
- Publication number
- CA1188142A CA1188142A CA000418025A CA418025A CA1188142A CA 1188142 A CA1188142 A CA 1188142A CA 000418025 A CA000418025 A CA 000418025A CA 418025 A CA418025 A CA 418025A CA 1188142 A CA1188142 A CA 1188142A
- Authority
- CA
- Canada
- Prior art keywords
- foiling
- fabric
- blade
- stock
- blades
- 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
Classifications
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F1/00—Wet end of machines for making continuous webs of paper
- D21F1/48—Suction apparatus
- D21F1/483—Drainage foils and bars
-
- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
- D21F1/00—Wet end of machines for making continuous webs of paper
- D21F1/009—Fibre-rearranging devices
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Abstract
METHOD AND APPARATUS FOR IMPROVING
FORMATION ON A PAPER MAKING MACHINE
ABSTRACT OF THE DISCLOSURE
A system of foils for a Fourdrinier paper making machine having periodic variability in their surfaces across the width of the machine so as to cause ridges, in the surface of the liquid stock, which oscillate as they travel down the forming section of the machine causing mixing of the stock and improved paper formation.
FORMATION ON A PAPER MAKING MACHINE
ABSTRACT OF THE DISCLOSURE
A system of foils for a Fourdrinier paper making machine having periodic variability in their surfaces across the width of the machine so as to cause ridges, in the surface of the liquid stock, which oscillate as they travel down the forming section of the machine causing mixing of the stock and improved paper formation.
Description
This invention relates to a process and apparatus for improving the formation of a paper web on a paper making machine.
In the operation of a typical paper making rnachine, the pulp stock which is a thin suspension of fibers and fillers, containing generally ahout 99.5% water, is flowed from a headbox slice onto the upstream surface of a rnoving endless screen belt (forming fabric) which is made of woven ¦ metal or plastic filaments. The fabric passes over a breast ¦ 10 roll at one end of the forrning section of the machine and a ¦ couch roll at the other end and between these two rolls the fabric travels in contact with spaced apart transverse dewatering foils and then over suction boxes where water is withdrawn from the pulp stock leaving a thin, self-support-ing formation of matted fibers on the surface of the fabric.
This sheet of formed fibers is lifted off the fabric at the couch roll at the downstream end of the forming section and is transferred to a press section and then to a dryer section to complete the dewatering. After travelling around the couch roll, the fabric belt is returned through a series of return rolls to the upstream end of the forming section where it travels around the breast roll and again passes under the slice to complete the cycle.
In spite of attempts ~o thoroughly mix the pulp stock in the headbox of the paper machine so that the fibers thereof will be uniformly dispersed, the fibers tend to agglomerate as they emerge from the slice and deposit on the fabric in clumps or flocs. If these flocs remai.n undis-persed -the finished paper will no-t be of uniform density.
Also, there is a tendency for stock fibers to become aligned in the machine direction which is de-trimental to S cross machine s-trength of the paper.
Severa] methods have been proposed and used to redistribute fibers in the pulp stock after it has been transferred to the forming wi:re and during the early stages of dewatering. A common method that has been used for many years to reduce flocculation is to provide a rapid shaking motion to the upstrearn end of the forming section of the machine. In other methods air and/or water -jets are sprayed on the wet stock either from above or below to rewet and agitate the stock and so redistribute the fibers. These methods have not proven entirely satisfactory particularly in the case of large, high speed machines where machinery required to shake the forming section is expensive and power consuming or when jets of air and/or water tend to force excessive amounts of the fibers and solids through the forming fabric and increases the amount of water which ultimately has to be withdrawn from the stock therefore requiring additional dewatering equipment which is usually power consuming.
It is known that flocculation occurs almost continuously in the formation zone while the pulp fibers are still in suspension and that deflocculation of the fibers is most effectively accomplished on slow running machines in which the wet pulp stock is subjected to almost continuous cross-machine shear by a shake mechanism during the forming cycle. On large machines running at high speed it is impossible -to attain adequate continuous cros.s-machine sheax due -to rapid passage of the wet pulp through the forming zone and -to di.ffi.culty in overcoming -the inertia of the large mass of machinery to provide sufficiently rapid cross-machine oscillation.
I It has been observed also that when ridges and ¦ gullies form in the sheet of stock discharged from the I slice and produce thick and thin sections alternately in the cross-machine direction, the ridges tend to dissipate when the stock lands on the forming fabric and, as they do, create a flow of stock in the cross-machine direction which , produces shear action within the layer of stock at the ' dissipating ridge also in this direction. This condition ¦ is most apparent in cases where intermittent ridges are produced by the action of a rectifier roll in the headbox immediately preceding the slice.
Further, and possibly due to the greater energy contained in the ridges, a wave action is promoted and there occurs an interchange where a ridge becomes a gully and vice versa as the wet pulp moves down the forming table of the machine. This interchange of phase is enhanced as the stock on the fabric passes over a dewatering element such as a table roll or a foil blade where the stock is subjected to the vacuum created thereon and even a more vigorous shearing action is promoted within the layer of stock. While this action is almost instantaneous in a high speed machine it does tend to counteract the continual flocculation of pulp fibers with the result that in the vicinity where variations in stock thickness have occurred, and particularly where there has been a longitudinal %
(machine direction) change oE phase as described above, agglomeration of pulp fibers i5 reduced and the formation oE the paper becomes more uniform.
Ano-ther known method of redistributing fibers in the pulp stock attempts to utilize the shearing action promoted by ridges by providing a serrated slice lip to induce a regular flow of ridges in -the headbox discharge.
This measure has not been entire:Ly effective because the ridges tend to dissipate too soon.
It is a feature of this invention to utilize the above mentioned phenomenon and induce controlled varia-tions in -thickness in the wet sheet of pulp stock on the forming fabric throughout the forming zone of a paper making machine to create cross-machine shear in the wet , 15 sheet for the purpose of deflocculating agglomerated fibers 'i of stock.
According to one aspect of the invention there is provided one or a plurality of dewatering foil blades that are specifically designed to provide cross-machine variations in dewatering of the pulp stock to promote like variations in the thickness of the sheet of wet pulp stock on the forming fabric.
The blade of the invention is generally similar to those normally installed in a fixed position to extend crosswise under and in contact with the forming fabric in the dewatering zone. The blade has a leading edge, a flat fabric supporting surface and a foiling surface set at a small divergent angle from the supporting surface. The foiling surface of the blade of the invention, however, is provided with repeti-t:ive machine direction non-foiling portions at intervals cross-wise of the machine direction so that uniform drainage induced by the foiling angle is interrupted and sections of wet pulp on the fabric passing over a non-foiling portion will not be dewatered ~o the same extent as sections passing over a foiling portion. The resulting interrupted drainage produces thick and thin sections in the wet pulp in the cross-machine direction and promote.s cross-direction shear ko beneficially influence fiber distribution. The foiling and non-foiling surfaces are formed integral in the downstream portion of the blade.
The foiling surface of a foil blade is defined as a surface diverging from the forming fabric by an angle of less than approximately 5 degrees.
The blade of the invention may be constructed of any suitable material that is chemically inert and which provides a wear resistant, low friction surface.
A preferred materi.al is high density polyethylene which is easily machinable. The preferred way of mounting the blade is generally referred to as a T-bar attachment and is described in detail in U.S. Patent No. 3,337,394.
Standard drainage foils may be replaced by blades of the invention at any location in the forming section to improve deflocculation thus providing an efficient, inexpensive and flexible method of improving formation on the paper making machine.
According to another broad aspect of the present invention, there is provided a fabric supporting blade for use in a wet section of a paper making machine ., and being positionable in suppor-ting relationship to a forming fabric in the wet end of the paper making machine.
The blade extends across the machine transversely of fabric travel and comprises a body having an upstream side and a downstream side. A leading edge is provided at the upstream side. A transverse continuous flat fabric contacting and supporting surface of constant width extends downstream from the leading edge. A
discontinuous foiling surface ex-tends downstream from the continuous flat surface~ The foiling surface in-cludes a plurality of foiling portions lying in a common plane which slopes downwardly and rearwardly from the plane of the continuous flat surface in divergi.ng re-lationO The foiling portions are separated from each other by intermediate slots extending parallel to one another and defining non-foiling portions and providing intermittent dewatering in a cross-machine direction to induce longitudinal ridges and gullies in a layer of wet stock as it is being dewatered for the purpose of causing lateral shear in the stock to effect a more thorough interlacing of the stock fibers to thereby improve formation.
According to another broad aspect of the pre-sent invention, there is provided a method of forming a web of paper on a forming fabric of a paper making machine. The method comprises positioning at least one fabric supporting blade under and in contact.with the forming fabric in a wet section thereof. The blade has a leading edge, a transverse flat fabric supporting sur-face of constant width, a downstream surface, and in the downstream surface, a plurality of uniform foiling surfaces interspersed by non-foiling surface in the cross-machine direction. The foiling surfaces e~tend from and converge with the downstream edge of the trans-.~ -- 7 verse flat Eabric su~porting surEace and diverge there-from at an angle less than 5 degrees. The foiling and non-foiling surfaces are formed integral in the down-stream surface oE the blade by slots extending parallel to one another transversely of the blade and extending from the contact and supporting surface and angulated downwardly to the downstream side of the blade relative to the foiling surfaces. The method also comprises depositing a layer of wet paper stock on the forming fabric upstream of the blade. The method further com-prises inducing, in the layer of wet stock, longitudinal alternate ridges and gullies as the pulp on the fabric is conveyed over the blade for causing lateral shear in the wet stock to effect a more thorough interlacing of fibers in the wet stock to thereby improve formation.
The invention will be better understood by the following description and the accompanying drawings which illustrate preferred embodiments and in which:
FIGUR~ 1 is a perspective view, illustrating schematically the forming section of a conventional paper making machine equipped with foil blades, some of which are modified according to the invention' FIGURE 2 shows end and side elevations of a portion of a foil blade modified according to one embo-diment of the invention, FIGURE 3 shows end and side elevations of a foil blade portion modified according to another embodi-ment of the invention' and figure ~ shows encl and side elevations of a foil blade por-tion modified according to yet another embodiment of the invention.
Referring to Figure 1, 10 is the side rail of the machine, 11 is the breast roll over which the forming fabric 12 passes, 13 is the headbox and 14 is the slice.
Numeral 15 designates a forming board and 16, 17 and 18 are detachable foil blades of the invention which ex-tend the width of the machine. Numerals 19 and 20 are conventional detachable Eoil blades shown here as they might be placed in a secondary dewatering stage. Nurneral ~ 21 denotes a conventional T-shaped rail upon which the ; individual blades may be mounted. At 22 is shown, generally, the layer of wet pulp stock on the fabric and ridges in the stock produced by the foil blades of the invention are shown as strokes running in the direction of the fabric which is shown by arrow 23. An attempt has been made to indicate phase changes in the ridges as they decay and reappear as gullies with adjacent new ridges on either side. A phase change is most likely to be seen at or just after a blade where a slight vacuum is produced which promotes the interchange as explained previously.
For example, as the stock 22 issues from the slice, small ridges are usually formed which soon dissipate. As the wet pulp passes over blade 16 which is slotted according to the invention, variations in dewatering are promoted and, as a result, ridges and gullies form in the stoc~.
The location of ridges will generally correspond to the location of non-foiling portions in the blade~ As the ._ g _ , . ~ . .. .
ridged pulp approaches the next b]ade in line, numeral 17, the interchange of r.idges and gullies (phase change) has commenced and is accelerated by the dewatering action as it passes over -this blade. Blade 17 may be a conventional blade or, as is shown in the drawing, another blade of the i.nvention, in which case, it would be preferable to offset the foiling portions in the cross-machine direction from those of the preceding blade to enhance -the above mentioned phase changeO
Other blades at locations 18, 19 and 20 may be blades of the invention or they may be conventional foil blades.
The preferred T-rail method of attachment all.ows considerable flexibility to be exercised in the deployment of blades to achieve optimum dewatering effi-ciency and fiber formation for any given stock and operating condition.
~ Referring to Figure 2, nurneral 20 is a blade of i the invention which has an upstream side 23, a leading edge 21, a flat fabric supporting surface 22 and, commenc-ing at the downstream edge 25 of the fabric supporting surface, a plurality of uniform foiling surfaces 26 interspersed in the cxoss-machine direction with a plurality of uniform non-foiling surfaces 27. The foiling surfaces 26 diverge downward from the downstream edge of the fabric supporting surface at an angle not exceeding 5 degrees to meet the downstream side of the blade body 24. The noll-foiling portions 27 in this embodiment are slots which have been cut at even spacing in the cross-machine direction in such a way that their bottom surfaces 28 diverge downwardly from the downstream edge of the Eabric support:ing surface a-t an angle exceeding the divergent angle of the foiling surfaces. The non-foiling slots open into the downstream side 24 of the blade.
Numeral 29 is a T-shaped recess in the bottom of the blade having opposed flanges for slidable attachment to a T-bar mounted on the frame of the machine. Numeral 30 is a section of the forming fabrlc which runs in contact with the support surface 22 in the direction of arrow 31. ~umeral 32 depicts the layer of wet pulp on the fabric and 33 a ridge forming in the pulp over a non-foiling slot in the blade.
Preferably, but not exclusively, the cross-machine width of the land areas of the foiling surfaces 26 may range from l/8 of an inch to 2 inches and the cross-machine width of the slots may range from l/8 of an inch to 3/4 of an inch. The overall width of the blade, in the machine direction, will be the same as any conven-tional foil blade and the blade will extend in the cross-machine direction a few inches beyond each edge of the forming fabric.
In Figure 3 the flat fabric supporting surface 42 extends to the downstream side of the blade and a plurality of identical foiling slots 47 is cut in the fabric supporting surEace, each slot having a flat sloping bottom 48 which diverges from the supporting surface at a common alignment shown at 49 which is parallel to and some distance downstream of the leading edge. The extensions of the fabric supporting surface provide intermitten1: non-foiling portions. The slope of the bottoms 48 of the foiling slots will be less than 5 degrees in order to produce the oi1ing action required -to induce intermittent dewatering in the cross-machine direction.
Preferably, but not exclusively, the cross-machine width of the land areas of the non-foiling portions may range from 1/~ of an inch to 2 inches and the cross-machine width of the foiling slo-ts may range from 1/8 of an inch to 3/4 of an inch.
In Figure 4 the downstream portion oE the fabric supporting surface 52 of blade 50 is slotted with a plurality of identical flat, slanting foiling sur~aces 57 which slope in the cross-machine direction and extend from a short distance downstream from the leading edge 51 to the downstream side 54 where the slots present a ' saw tooth appearance. The slanting slots provide for intermittent dewatering in uniformly varying degrees in the cross-machine direction. In this particular embodi-ment of the invention the maximum slope in the machine direction of each of the slanted slots would be less than 5 degrees and preferably, but not exclusively, the width of the slots in the cross-machine direction at the downstream side of the blade could range from about 1/2 of an inch to 2 inches.
In the preferred concept of this embodiment alternate blades may have slots which slope in the opposite direction.
It is not intended to limit the invention to foiling slots having rectangularly or triangularly oriented flat surfaces. The slots in the downstream surface of the foil of the invention may have curved surfaces to provide for varying degrees of dewatering crosswise of each slot.
In order to minimize uneven wear at the downstream portion of -the transverse fabric supporting surface which is continuous, it is recommended that the foil blades of the invention be provided with wear resistant inserts as described in detail in U.S. patent ; No. 3,446,702.
It is within the ambit of the presen-t invention to cover any obvious modifications of the examples of the preferred embodirnent described herein, provided .such modifications fall within the scope of -the appended clairns.
As a typical example of modifications, it is conceivable that the cross-section of the slots may take other confi-gurations than those shown in the drawings. For example, the foiling or non-foiling slots may be of triangular cross-section, semi-circular cross-section, or any o-ther suitable shape and they may be angled with respect to the machine direction. Also, these blades rnay be intermixed with conventional foil b]ades, throughout the wet section and the slot configuration of these blades may also vary one from the other.
In the operation of a typical paper making rnachine, the pulp stock which is a thin suspension of fibers and fillers, containing generally ahout 99.5% water, is flowed from a headbox slice onto the upstream surface of a rnoving endless screen belt (forming fabric) which is made of woven ¦ metal or plastic filaments. The fabric passes over a breast ¦ 10 roll at one end of the forrning section of the machine and a ¦ couch roll at the other end and between these two rolls the fabric travels in contact with spaced apart transverse dewatering foils and then over suction boxes where water is withdrawn from the pulp stock leaving a thin, self-support-ing formation of matted fibers on the surface of the fabric.
This sheet of formed fibers is lifted off the fabric at the couch roll at the downstream end of the forming section and is transferred to a press section and then to a dryer section to complete the dewatering. After travelling around the couch roll, the fabric belt is returned through a series of return rolls to the upstream end of the forming section where it travels around the breast roll and again passes under the slice to complete the cycle.
In spite of attempts ~o thoroughly mix the pulp stock in the headbox of the paper machine so that the fibers thereof will be uniformly dispersed, the fibers tend to agglomerate as they emerge from the slice and deposit on the fabric in clumps or flocs. If these flocs remai.n undis-persed -the finished paper will no-t be of uniform density.
Also, there is a tendency for stock fibers to become aligned in the machine direction which is de-trimental to S cross machine s-trength of the paper.
Severa] methods have been proposed and used to redistribute fibers in the pulp stock after it has been transferred to the forming wi:re and during the early stages of dewatering. A common method that has been used for many years to reduce flocculation is to provide a rapid shaking motion to the upstrearn end of the forming section of the machine. In other methods air and/or water -jets are sprayed on the wet stock either from above or below to rewet and agitate the stock and so redistribute the fibers. These methods have not proven entirely satisfactory particularly in the case of large, high speed machines where machinery required to shake the forming section is expensive and power consuming or when jets of air and/or water tend to force excessive amounts of the fibers and solids through the forming fabric and increases the amount of water which ultimately has to be withdrawn from the stock therefore requiring additional dewatering equipment which is usually power consuming.
It is known that flocculation occurs almost continuously in the formation zone while the pulp fibers are still in suspension and that deflocculation of the fibers is most effectively accomplished on slow running machines in which the wet pulp stock is subjected to almost continuous cross-machine shear by a shake mechanism during the forming cycle. On large machines running at high speed it is impossible -to attain adequate continuous cros.s-machine sheax due -to rapid passage of the wet pulp through the forming zone and -to di.ffi.culty in overcoming -the inertia of the large mass of machinery to provide sufficiently rapid cross-machine oscillation.
I It has been observed also that when ridges and ¦ gullies form in the sheet of stock discharged from the I slice and produce thick and thin sections alternately in the cross-machine direction, the ridges tend to dissipate when the stock lands on the forming fabric and, as they do, create a flow of stock in the cross-machine direction which , produces shear action within the layer of stock at the ' dissipating ridge also in this direction. This condition ¦ is most apparent in cases where intermittent ridges are produced by the action of a rectifier roll in the headbox immediately preceding the slice.
Further, and possibly due to the greater energy contained in the ridges, a wave action is promoted and there occurs an interchange where a ridge becomes a gully and vice versa as the wet pulp moves down the forming table of the machine. This interchange of phase is enhanced as the stock on the fabric passes over a dewatering element such as a table roll or a foil blade where the stock is subjected to the vacuum created thereon and even a more vigorous shearing action is promoted within the layer of stock. While this action is almost instantaneous in a high speed machine it does tend to counteract the continual flocculation of pulp fibers with the result that in the vicinity where variations in stock thickness have occurred, and particularly where there has been a longitudinal %
(machine direction) change oE phase as described above, agglomeration of pulp fibers i5 reduced and the formation oE the paper becomes more uniform.
Ano-ther known method of redistributing fibers in the pulp stock attempts to utilize the shearing action promoted by ridges by providing a serrated slice lip to induce a regular flow of ridges in -the headbox discharge.
This measure has not been entire:Ly effective because the ridges tend to dissipate too soon.
It is a feature of this invention to utilize the above mentioned phenomenon and induce controlled varia-tions in -thickness in the wet sheet of pulp stock on the forming fabric throughout the forming zone of a paper making machine to create cross-machine shear in the wet , 15 sheet for the purpose of deflocculating agglomerated fibers 'i of stock.
According to one aspect of the invention there is provided one or a plurality of dewatering foil blades that are specifically designed to provide cross-machine variations in dewatering of the pulp stock to promote like variations in the thickness of the sheet of wet pulp stock on the forming fabric.
The blade of the invention is generally similar to those normally installed in a fixed position to extend crosswise under and in contact with the forming fabric in the dewatering zone. The blade has a leading edge, a flat fabric supporting surface and a foiling surface set at a small divergent angle from the supporting surface. The foiling surface of the blade of the invention, however, is provided with repeti-t:ive machine direction non-foiling portions at intervals cross-wise of the machine direction so that uniform drainage induced by the foiling angle is interrupted and sections of wet pulp on the fabric passing over a non-foiling portion will not be dewatered ~o the same extent as sections passing over a foiling portion. The resulting interrupted drainage produces thick and thin sections in the wet pulp in the cross-machine direction and promote.s cross-direction shear ko beneficially influence fiber distribution. The foiling and non-foiling surfaces are formed integral in the downstream portion of the blade.
The foiling surface of a foil blade is defined as a surface diverging from the forming fabric by an angle of less than approximately 5 degrees.
The blade of the invention may be constructed of any suitable material that is chemically inert and which provides a wear resistant, low friction surface.
A preferred materi.al is high density polyethylene which is easily machinable. The preferred way of mounting the blade is generally referred to as a T-bar attachment and is described in detail in U.S. Patent No. 3,337,394.
Standard drainage foils may be replaced by blades of the invention at any location in the forming section to improve deflocculation thus providing an efficient, inexpensive and flexible method of improving formation on the paper making machine.
According to another broad aspect of the present invention, there is provided a fabric supporting blade for use in a wet section of a paper making machine ., and being positionable in suppor-ting relationship to a forming fabric in the wet end of the paper making machine.
The blade extends across the machine transversely of fabric travel and comprises a body having an upstream side and a downstream side. A leading edge is provided at the upstream side. A transverse continuous flat fabric contacting and supporting surface of constant width extends downstream from the leading edge. A
discontinuous foiling surface ex-tends downstream from the continuous flat surface~ The foiling surface in-cludes a plurality of foiling portions lying in a common plane which slopes downwardly and rearwardly from the plane of the continuous flat surface in divergi.ng re-lationO The foiling portions are separated from each other by intermediate slots extending parallel to one another and defining non-foiling portions and providing intermittent dewatering in a cross-machine direction to induce longitudinal ridges and gullies in a layer of wet stock as it is being dewatered for the purpose of causing lateral shear in the stock to effect a more thorough interlacing of the stock fibers to thereby improve formation.
According to another broad aspect of the pre-sent invention, there is provided a method of forming a web of paper on a forming fabric of a paper making machine. The method comprises positioning at least one fabric supporting blade under and in contact.with the forming fabric in a wet section thereof. The blade has a leading edge, a transverse flat fabric supporting sur-face of constant width, a downstream surface, and in the downstream surface, a plurality of uniform foiling surfaces interspersed by non-foiling surface in the cross-machine direction. The foiling surfaces e~tend from and converge with the downstream edge of the trans-.~ -- 7 verse flat Eabric su~porting surEace and diverge there-from at an angle less than 5 degrees. The foiling and non-foiling surfaces are formed integral in the down-stream surface oE the blade by slots extending parallel to one another transversely of the blade and extending from the contact and supporting surface and angulated downwardly to the downstream side of the blade relative to the foiling surfaces. The method also comprises depositing a layer of wet paper stock on the forming fabric upstream of the blade. The method further com-prises inducing, in the layer of wet stock, longitudinal alternate ridges and gullies as the pulp on the fabric is conveyed over the blade for causing lateral shear in the wet stock to effect a more thorough interlacing of fibers in the wet stock to thereby improve formation.
The invention will be better understood by the following description and the accompanying drawings which illustrate preferred embodiments and in which:
FIGUR~ 1 is a perspective view, illustrating schematically the forming section of a conventional paper making machine equipped with foil blades, some of which are modified according to the invention' FIGURE 2 shows end and side elevations of a portion of a foil blade modified according to one embo-diment of the invention, FIGURE 3 shows end and side elevations of a foil blade portion modified according to another embodi-ment of the invention' and figure ~ shows encl and side elevations of a foil blade por-tion modified according to yet another embodiment of the invention.
Referring to Figure 1, 10 is the side rail of the machine, 11 is the breast roll over which the forming fabric 12 passes, 13 is the headbox and 14 is the slice.
Numeral 15 designates a forming board and 16, 17 and 18 are detachable foil blades of the invention which ex-tend the width of the machine. Numerals 19 and 20 are conventional detachable Eoil blades shown here as they might be placed in a secondary dewatering stage. Nurneral ~ 21 denotes a conventional T-shaped rail upon which the ; individual blades may be mounted. At 22 is shown, generally, the layer of wet pulp stock on the fabric and ridges in the stock produced by the foil blades of the invention are shown as strokes running in the direction of the fabric which is shown by arrow 23. An attempt has been made to indicate phase changes in the ridges as they decay and reappear as gullies with adjacent new ridges on either side. A phase change is most likely to be seen at or just after a blade where a slight vacuum is produced which promotes the interchange as explained previously.
For example, as the stock 22 issues from the slice, small ridges are usually formed which soon dissipate. As the wet pulp passes over blade 16 which is slotted according to the invention, variations in dewatering are promoted and, as a result, ridges and gullies form in the stoc~.
The location of ridges will generally correspond to the location of non-foiling portions in the blade~ As the ._ g _ , . ~ . .. .
ridged pulp approaches the next b]ade in line, numeral 17, the interchange of r.idges and gullies (phase change) has commenced and is accelerated by the dewatering action as it passes over -this blade. Blade 17 may be a conventional blade or, as is shown in the drawing, another blade of the i.nvention, in which case, it would be preferable to offset the foiling portions in the cross-machine direction from those of the preceding blade to enhance -the above mentioned phase changeO
Other blades at locations 18, 19 and 20 may be blades of the invention or they may be conventional foil blades.
The preferred T-rail method of attachment all.ows considerable flexibility to be exercised in the deployment of blades to achieve optimum dewatering effi-ciency and fiber formation for any given stock and operating condition.
~ Referring to Figure 2, nurneral 20 is a blade of i the invention which has an upstream side 23, a leading edge 21, a flat fabric supporting surface 22 and, commenc-ing at the downstream edge 25 of the fabric supporting surface, a plurality of uniform foiling surfaces 26 interspersed in the cxoss-machine direction with a plurality of uniform non-foiling surfaces 27. The foiling surfaces 26 diverge downward from the downstream edge of the fabric supporting surface at an angle not exceeding 5 degrees to meet the downstream side of the blade body 24. The noll-foiling portions 27 in this embodiment are slots which have been cut at even spacing in the cross-machine direction in such a way that their bottom surfaces 28 diverge downwardly from the downstream edge of the Eabric support:ing surface a-t an angle exceeding the divergent angle of the foiling surfaces. The non-foiling slots open into the downstream side 24 of the blade.
Numeral 29 is a T-shaped recess in the bottom of the blade having opposed flanges for slidable attachment to a T-bar mounted on the frame of the machine. Numeral 30 is a section of the forming fabrlc which runs in contact with the support surface 22 in the direction of arrow 31. ~umeral 32 depicts the layer of wet pulp on the fabric and 33 a ridge forming in the pulp over a non-foiling slot in the blade.
Preferably, but not exclusively, the cross-machine width of the land areas of the foiling surfaces 26 may range from l/8 of an inch to 2 inches and the cross-machine width of the slots may range from l/8 of an inch to 3/4 of an inch. The overall width of the blade, in the machine direction, will be the same as any conven-tional foil blade and the blade will extend in the cross-machine direction a few inches beyond each edge of the forming fabric.
In Figure 3 the flat fabric supporting surface 42 extends to the downstream side of the blade and a plurality of identical foiling slots 47 is cut in the fabric supporting surEace, each slot having a flat sloping bottom 48 which diverges from the supporting surface at a common alignment shown at 49 which is parallel to and some distance downstream of the leading edge. The extensions of the fabric supporting surface provide intermitten1: non-foiling portions. The slope of the bottoms 48 of the foiling slots will be less than 5 degrees in order to produce the oi1ing action required -to induce intermittent dewatering in the cross-machine direction.
Preferably, but not exclusively, the cross-machine width of the land areas of the non-foiling portions may range from 1/~ of an inch to 2 inches and the cross-machine width of the foiling slo-ts may range from 1/8 of an inch to 3/4 of an inch.
In Figure 4 the downstream portion oE the fabric supporting surface 52 of blade 50 is slotted with a plurality of identical flat, slanting foiling sur~aces 57 which slope in the cross-machine direction and extend from a short distance downstream from the leading edge 51 to the downstream side 54 where the slots present a ' saw tooth appearance. The slanting slots provide for intermittent dewatering in uniformly varying degrees in the cross-machine direction. In this particular embodi-ment of the invention the maximum slope in the machine direction of each of the slanted slots would be less than 5 degrees and preferably, but not exclusively, the width of the slots in the cross-machine direction at the downstream side of the blade could range from about 1/2 of an inch to 2 inches.
In the preferred concept of this embodiment alternate blades may have slots which slope in the opposite direction.
It is not intended to limit the invention to foiling slots having rectangularly or triangularly oriented flat surfaces. The slots in the downstream surface of the foil of the invention may have curved surfaces to provide for varying degrees of dewatering crosswise of each slot.
In order to minimize uneven wear at the downstream portion of -the transverse fabric supporting surface which is continuous, it is recommended that the foil blades of the invention be provided with wear resistant inserts as described in detail in U.S. patent ; No. 3,446,702.
It is within the ambit of the presen-t invention to cover any obvious modifications of the examples of the preferred embodirnent described herein, provided .such modifications fall within the scope of -the appended clairns.
As a typical example of modifications, it is conceivable that the cross-section of the slots may take other confi-gurations than those shown in the drawings. For example, the foiling or non-foiling slots may be of triangular cross-section, semi-circular cross-section, or any o-ther suitable shape and they may be angled with respect to the machine direction. Also, these blades rnay be intermixed with conventional foil b]ades, throughout the wet section and the slot configuration of these blades may also vary one from the other.
Claims (14)
1. A fabric supporting blade for use in a wet section of a paper making machine and being positionable in supporting relationship to a forming fabric in the wet end of the paper making machine, said blade extending across said machine transversely of fabric travel and comprising a body having an upstream side and a downstream side, a lead-ing edge at said upstream side, a transverse continuous flat fabric contacting and supporting surface of constant width extending downstream from said leading edge, and a discon-tinuous foiling surface extending downstream from said continuous flat surface, said foiling surface including a plurality of foiling portions lying in a common plane which slopes downwardly and rearwardly from the plane of said continuous flat surface in diverging relation, said foiling portions being separated from each other by intermediate slots extending parallel to one another and defining non-foiling portions and providing intermittent dewatering in a cross-machine direction to induce longitudinal ridges and gullies in a layer of wet stock as it is being dewatered for the purpose of causing lateral shear in the stock to effect a more thorough interlacing of the stock fibers to thereby improve formation.
2. A fabric supporting blade as claimed in claim 1 wherein said slots have bottoms which slope downwardly and rearwardly at a greater angle than the slope of said foiling portions.
3. A fabric supporting blade as claimed in claim 2 wherein said slot bottoms diverge from said flat support surface at an angle greater than 5 degrees.
4. A fabric supporting blade as claimed in claim 3 wherein said foiling portions slope at an angle less than 5 degrees.
5. A fabric supporting blade as claimed in claim 1 wherein said openings of said slots are positioned one adja-cent the other, said slots extending from and convergent with the downstream edge of said transverse flat fabric supporting surface.
6. A fabric supporting blade as claimed in claim 1 wherein a plurality of said blades are disposed in a parallel spaced apart configuration under and in contact with said forming fabric in said wet end where fibers in said pulp stock are in suspension, and said foiling portions of con-secutive ones of said blades are offset from one another to enhance a machine direction change of phase of said gullies and ridges where said stock passes over said blades.
7. A fabric supporting blade as claimed in claim 1 wherein a plurality of said blades are disposed in a parallel spaced apart configuration under and in contact with said forming fabric in said wet end where fibers in said pulp stock are in suspension, consecutive ones of said blades having their slot slanted bottoms in opposite direction from the slanted bottoms of the slots of adjacent blades.
8. A method of forming a web of paper on a forming fabric of a paper making machine, said method comprising (i) positioning at least one fabric supporting blade under and in contact with said forming fabric in a wet section thereof; said blade having a leading edge, a trans-verse flat fabric supporting surface of constant width, a downstream surface and, in said downstream surface, a plu-rality of uniform foiling surfaces interspersed by non-foiling surface in the cross-machine direction, said foiling surfaces extending from and convergent with the downstream edge of said transverse flat fabric supporting surface and diverging therefrom at an angle less than 5 degrees, said foiling and non-foiling surfaces being formed integral in said downstream surface of said blade by slots extending parallel to one another transversely of said blade and ex-tending from said contact and supporting surface and angu-lated downwardly to said downstream side of said blade rela-tive to said foiling surfaces, (ii) depositing a layer of wet paper stock on said forming fabric upstream of said blade, (iii) inducing, in said layer of wet stock, longitudinal alternate ridges and gullies as said pulp on said fabric is conveyed over said blade for causing lateral shear in said wet stock to effect a more thorough interlacing of fibers in said wet stock to thereby improve formation.
9. A method as claimed in claim 8 wherein said step (i) comprises positioning a plurality of said fabric sup-porting blades under and in contact with said forming fabric with said foiling surfaces of consecutive ones of said blades being offset from one another to enhance a machine direction change of phase of said gullies and ridges where said wet stock passes over said blades.
10. A fabric supporting blade for use in a wet section of a paper making machine and being positionable in support-ing relationship to a forming fabric in the wet end of the paper making machine, said blade extending across said machine transversely of fabric travel and comprising a body having an upstream side and a downstream side, a leading edge at said upstream side, a transverse continuous flat fabric contacting and supporting surface of constant width extending downstream from said leading edge, and a dis-continuous foiling surface extending downstream from said continuous flat surface, said foiling surface including a plurality of foiling portions lying in a common plane, said foiling portions being separated from each other by inter-mediate slots extending parallel to one another and defining non-foiling portions and providing intermittent dewatering in a cross-machine direction to induce longitudinal ridges and gullies in a layer of wet stock as it is being dewatered for the purpose of causing lateral shear in the stock to effect a more thorough interlacing of the stock fibers to thereby improve formation, a plurality of said blades dis-posed in a parallel spaced apart configuration under and in contact with said forming fabric in said wet end where fibers in said pulp stock are in suspension, and said foiling portions of consecutive ones of said blades are offset from one another to enhance a machine direction change of phase of said gullies and ridges where said stock passes over said blades.
11. A fabric supporting blade as claimed in claim 10 wherein said openings of said slots are positioned one adjacent the other, said slots extending from and convergent with the downstream edge of said transverse flat fabric supporting surface.
12. A fabric supporting blade arrangement as claimed in claim 11 wherein consecutive ones of said blades have their slot slanted bottoms in opposite direction from the slanted bottoms of slots of adjacent blades.
13. A fabric supporting blade as claimed in claim 10 wherein said slot bottoms are flat and are slanted in said cross-machine direction and each slot has a single side wall.
14. A fabric supporting blade as claimed in claim 13 wherein said single side wall is perpendicular to said downstream surface.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US33907082A | 1982-01-13 | 1982-01-13 | |
| US339,070 | 1982-01-13 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1188142A true CA1188142A (en) | 1985-06-04 |
Family
ID=23327355
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000418025A Expired CA1188142A (en) | 1982-01-13 | 1982-12-17 | Method and apparatus for improving formation on a paper making machine |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1188142A (en) |
| GB (1) | GB2113264B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4532009A (en) * | 1983-04-01 | 1985-07-30 | Albany International | Forming board elements |
| DE3513320A1 (en) * | 1985-04-13 | 1986-10-23 | Feldmühle AG, 4000 Düsseldorf | SCREW BAR FOR A PAPER MACHINE |
| DE10327427A1 (en) * | 2003-06-18 | 2005-03-17 | Voith Paper Patent Gmbh | Device for improving the properties of a fibrous web produced in a sheet forming device |
| DE102018123406B3 (en) * | 2018-09-24 | 2019-12-05 | Voith Patent Gmbh | dehydrator |
-
1982
- 1982-12-17 CA CA000418025A patent/CA1188142A/en not_active Expired
-
1983
- 1983-01-05 GB GB08300144A patent/GB2113264B/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB2113264A (en) | 1983-08-03 |
| GB8300144D0 (en) | 1983-02-09 |
| GB2113264B (en) | 1986-02-26 |
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