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
  • D21F1/009—Fibre-rearranging devices
• • 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
  • D21F1/52—Suction boxes without rolls
  • D21F1/523—Covers thereof
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
  • D21F9/00—Complete machines for making continuous webs of paper
  • D21F9/02—Complete machines for making continuous webs of paper of the Fourdrinier type

Definitions

• This invention is concerned with paper making machines of the type having a "flat wire” or “open wire” forming section, which includes means to remove water from the stock by the use of suction.
• an aqueous slurry known as the stock which contains both fibers and other substances in an amount of from about 0.1% to 1.5% by weight, is fed from a head box slice onto a single moving forming fabric. Water is progressively removed from the stock through the forming fabric in what is known as the "forming section" of the paper making machine. In this forming section, a variety of drainage devices are used, until the stock contains from about 2% to about 4% by weight of solid material.
• a conventional open wire forming section includes a forming fabric which is supported at the head box slice end by a breast roll, which is followed in sequence by a "forming board” and a series of drainage devices, which may be drainage foils or table rolls, and suction boxes. More recently, forming sections have included a forming board followed by suction boxes of the type described by Johnson, in U.S. Patent 4,140,573. These suction boxes heretofore have been distributed along the length of the forming section with gaps, or undrained spaces, in between them.
• Justus recommends to use a vacuum level ranging from a low level of effectively zero in a suction box adjacent the head box slice rising to a figure of 2 inches of mercury at the 3% point, that is a value of about 70 cms of water. It has been discovered that this is also a mistake, and that with dewatering devices somewhat similar to those advocated by Justus a far lower level of vacuum is often sufficient, rising from a very low level adjacent the head box slice to a value of no more than 50 cms of water at the end of the forming section. It has been discovered that much lower levels of vacuum than those suggested by Justus can be used with great benefit in retention and wire mark provided the above mentioned agitation or kick-up can be achieved.
• Values for FPR can range from 30 % in the case of papers with a high filler content to over 90% for some long fibered grades.
• FPR can range from 30 % in the case of papers with a high filler content to over 90% for some long fibered grades.
• factors affect the FPR including the type of stock, the kind of forming fabric, the use of chemical retention aids, the amount of stock agitation, the amount of suction used in forming the paper, and particularly the velocity induced in the stock by that suction while forming. Improving retention from 45% to 70% reduces the consistency of the recirculating white water considerably if the amount of slice opening is left unchanged. (By "consistency” in this context is meant the total suspended solids content in percent by weight in the stock or in the white water, as appropriate). This has beneficial effects on the entire paper mill and reduces the amount of fiber and filler loss.
• this invention provides a process for improving paper formation in a paper making machine having an open surface forming section, including at least a travelling continuous forming fabric which passes over a breast-roll adjacent a head box having a head box slice through which aqueous stock is deposited onto the forming fabric, and a plurality of stock dewatering devices beneath the forming fabric which are provided with white water drainage means, in which forming section the solids content of the stock deposited from the head box through the head box slice onto the forming fabric rises from an initial low value to a value of from about 2% to about 4%, comprising the steps of:
• a dewatering device comprising a continuous vacuum assisted suction box including a plurality of chambers to each which a controlled level of vacuum is applied, which includes a foraminous top support surface for the forming fabric, and which provides a vacuum tight seal between the forming fabric and the evacuated chambers of the suction box;
• the vacuum in the suction box is controlled in such a way that it rises in a stepwise fashion in the separate sections of the box along the length of the forming section, from the initial low value of below 5 cms water gauge to a maximum value of no more than 50 cms water gauge. Desirably there are as many vacuum levels as possible, preferably more than three, and most preferably at least five.
• this invention provides in a paper making machine having an open surface forming section, including at least a travelling continuous forming fabric which passes over a breast-roll adjacent a head box having a head box slice through which aqueous stock is deposited onto the forming fabric, and a plurality of stock dewatering devices beneath the forming fabric which are provided with white water drainage means, in which forming section the solids content of the stock deposited from the head box through the head box slice onto the forming fabric rises from an initial low value to a value of from about 2% to about 4%, an apparatus for stock dewatering consisting essentially of in combination:-
• a suction box comprising a plurality of evacuated chambers, each of which is provided with a vacuum tight drainage means, located in the forming section adjacent the head box slice and extending continuously for the length of the forming section;
• a foraminous surface on the suction box adapted to support the forming fabric, to provide apertures through which the forming fabric drains under the influence of the vacuum in the suction box, to provide a path through which the forming fabric moves which will cause a controlled level of uniformly spaced periodic harmonic agitation within the stock on the forming fabric; and to provide a vacuum tight seal between the forming fabric and the evacuated chambers of the suction box;
• a vacuum control means whereby the vacuum in the evacuated chambers of the suction box is controlled to a value that rises progressively along the suction box for the length of the forming section from an initial low value of less than 5 cms water gauge adjacent the head box slice, to a maximum value of no more than 50 cms water gauge at the end of the forming section.
• the suction box comprises a plurality of contiguously adjacent suction boxes, each of which is the full width of the forming section.
• a series of vacuum-tight transverse divisions can be provided in a single large suction box.
• the suction box comprises a sequence of separated drainage chambers, to each of which a controlled level of vacuum is applied, rising stepwise from a level of no more than 5 cms water gauge adjacent the head box slice to no more than 50 cms * water gauge at the other end of the suction box, that is at the end of the forming section.
• Each drainage chamber is also provided with a separate vacuum-tight drainage means.
• the foraminous surface comprises a slotted type fabric-supporting cover comprising a series of spaced apart forming fabric-supporting blades having generally planar top surfaces transverse to the direction of travel of the fabric in a common essentially horizontal plane providing therebetween suction-accessible gaps in which the forming fabric is substantially unsupported and is drawn downward to form stock-agitating undulations in said gaps, the cover including water seal-forming blades disposed intermediately in the gaps between the fabric-supporting blades and having top surfaces transverse to the direction of travel of the fabric at a lower level than the top surfaces of the fabric-supporting blades, and at least forming water seals at the downward undulations of the forming fabric thereby interrupting the suction temporarily to limit drainage while causing vertical agitation of fibers on the fabric passing through the forming section.
• the fabric supporting blades are spaced apart equally from each other for the length of the forming section. This provides the desired and required agitation in the stock, since the forming fabric and the paper stock thereon undulate in a periodic or harmonic manner for the length of the forming section.
• this invention provides in a paper making machine having an open surface forming section, including at least a travelling continuous forming fabric which passes over a breast-roll adjacent a head box having a head box slice through which aqueous stock is deposited onto the forming fabric, and a plurality of stock dewatering devices beneath the forming fabric which are provided with white water drainage means, in which forming section the solids content of the stock deposited from the head box through the head box slice onto the forming fabric rises from an initial low value to a value of from about 2% to about 4%, an apparatus for stock dewatering consisting essentially of in combination:-
• a relatively short foraminous dewatering device adjacent the head box slice consisting essentially of a forming board section, including at least one forming board, situated adjacent the slice, and a foil section adjacent to the forming board section, which includes a plurality of foils, in which foil section each foil comprises a flat support surface, and a trailing portion (in the direction of forming fabric travel) diverging from the plane of the fabric at an angle greater than zero degrees and less than five degrees;
• suction box adjacent the dewatering device extending for the remainder of the length of the forming section, which suction box consists essentially of either a single box provided with transverse vacuum tight divisions each provided with a vacuum supply means and a water drainage means or a plurality of drainage boxes each extending the full width of the forming fabric, which are placed contiguously with each other thereby effectively having a common dividing wall, and which are each provided with a vacuum supply means and a water drainage means;
• a foraminous surface on the suction box adapted to support the forming fabric consisting essentially of a slotted-type fabric cover comprising a series of uniformly spaced forming fabric-supporting blades having a generally planar top surface transverse to the direction of travel of the fabric in a common essentially horizontal plane providing therebetween suction-accessible gaps in which the forming fabric is substantially unsupported and is drawn downward to form stock-agitating undulations in said gaps, said cover including water seal forming blades disposed intermediately in said gaps between the fabric supporting blades and having top surfaces transverse to the direction of travel of the fabric at a lower level than the top surfaces of the fabric supporting blades and at least forming water seals at the downward undulations of the forming fabric, thereby interrupting the suction temporarily to limit drainage while causing vertical agitation of fibers on the fabric passing through the forming section; and wherein both the first, the last, and any intermediate support-blades placed over either an internal transverse vacuum tight division or a pair of contiguous transverse walls
• a vacuum control means whereby the vacuum in the suction box is controlled to a value that rises discretively stepwise along the length of the suction box from a low value of less than 5 cms water gauge adjacent the foraminous dewatering device to a maximum value of no more than 50 cms water gauge at the end of the forming section.
• this invention provides a process for improving paper formation in a paper making machine having an open surface forming section, including at least a travelling continuous forming fabric which passes over a breast-roll adjacent a head box having a head box slice through which aqueous stock is deposited onto the forming fabric, and a plurality of stock dewatering devices beneath the forming fabric which are provided with white water drainage means, in which forming section the solids content of the stock deposited from the head box through the head box slice onto the forming fabric rises from an initial low value to a value of from about 2% to about 4%, comprising the steps of:
• the short foraminous dewatering device can also provide a path causing changes in level in the forming fabric thereby initiating a controlled level of agitation in the stock before it reaches the foraminous surface of the suction box.
• the short foraminous dewatering device includes both a forming board adjacent to the head box slice, and a foil section (between the forming board and the suction box), wherein the foil section may comprise up to four fifths of the area drained by the short foraminous dewatering device.
• each foil comprises a flat support surface, and a trailing portion (in the direction of forming fabric travel) diverging from the plane of the fabric at an angle greater than 0° and less than 5°.
• the foils generally are grouped above drainage boxes of a suitable size.
• the separate foils are also so placed as to contribute toward controlled agitation of the stock on the forming fabric.
• the combination of forming boards and foil section comprises no more than about 20% of the length of the forming zone.
• the suction box either is a plurality of contiguously adjacent suction boxes (each of which is the full width of the forming section), or is provided with a series of vacuum-tight-transverse divisions to provide a series of separated drainage chambers to each of which a controlled level of vacuum is applied.
• the applied vacuum will thus rise in a stepwise fashion in the suction box from an initial low value of no more than 5 cms water gauge up to a maximum of no more than 50 cms water gauge at the end of the forming section.
• Such a mode of construction readily permits control of the applied level of vacuum.
• this invention provides a process for improving stock formation on a paper making machine, including the steps of:
• a relatively short foraminous dewatering device comprising in combination a forming board section, adjacent the head box slice, and a foil unit section in which section each foil comprises a flat support surface, and a trailing portion (in the direction of forming fabric travel) diverging from the plane of the fabric at an angle greater than zero degrees and less than 5 degrees;
• Figure 1 shows diagram atically the initial part of a conventional paper making machine
• Figure 2 shows a conventional foil blade
• Figure 3 shows a so-called Isoflo unit
• Figure 4 shows schematically harmonic stock agitation associated with a series of foils
• Figure 5 shows diagrammatically a paper making machine modified according to one aspect of this invention
• Figure 6 shows a modification to the machine of Figure 5.
• Figure 7 shows a detail of Figure 5.
• FIG. 1 the forming section of a conventional open surface paper making machine is shown, incorporating a forming fabric 1, which moves in the direction of the arrows shown at 1A and IB.
• the forming fabric moves over a breast roll 2, and various tensioning and idling rollers 3.
• the stock is deposited onto the forming fabric 1 from the head box shown diagrammatically at 4, through a slice 5, which extends across the forming fabric 1.
• Beneath the forming fabric in the dewatering zone are placed a sequence of drainage devices 6, 7, 8, 9, 10, 11 and 12, provided with white water drains
• the first of these drainage devices, 6, comprises a forming board
• the second, 7, comprises an open foil unit, and the remainder are so-called Isoflo units (Trade Mark).
• Boxes 8 to 12 are also provided with a controlled vacuum, through the vacuum pipes 20, 21, 22, 23 and 24 respectively.
• the vacuum applied will typically range from zero to 5 cms water gauge in box 8, to no more than 50 cms water gauge in box 12; the white water drains 15,
• the drainage and suction boxes are separated by the spans marked a, b, c, d, e and f which represent undrained areas, apart from any water which may happen to drain through under gravity. In the machine shown, these spans represent nearly 30% of the total area of the forming section.
• the drainage elements 25 are conventional foil blades broadly conforming to the design shown in section in Figure 2. These foils comprise a supporting bar 28 with a tee-shaped head, onto which is slid the foil blade proper, 29. This includes a flat face 30 onto which the forming fabric 1 rests, and a divergent trailing face 31. In the figure the divergent angle Z is shown exaggerated for clarity. Generally it is far smaller than it is shown, ranging from about 1 degree to about 5 degrees, with angles of 2 to 2.5 degrees being commonly used. As the forming fabric moves over the foil in the direction of the arrow 32, as a consequence of hydraulic phenomena created in the nip provided by the trailing face 31, water is sucked from the stock through the forming fabric.
• FIG. 3 which corresponds broadly to Johnson's Figure 4
• FIG 3 which corresponds broadly to Johnson's Figure 4
• the static devices 26 and 27 differ in two separate ways.
• the top faces of all of these devices which bear against the forming fabric 1 are generally planar and either in the plane of the forming fabric (devices 26) or a little below it (devices 27).
• the vertical lowering of the devices 27 is indicated at A, which is exaggerated for clarity. In practise, this distance generally will range from about 0.5 mm to about 5.0 mm.
• the forming fabric in moving over such a foraminous surface undulates between successive devices 26, and the intervening devices 27 are so placed vertically as to provide a water seal to the underside of the forming fabric. Sealing elements, not shown, are also provided along the sides of the boxes in between the drainage devices, parallel to the sides of the forming fabric. Water is drawn from the stock through the forming fabric by the application of vacuum to the box.
• FIG 4 shows diagrammatically the harmonic, or periodic, stock agitation that can be generated by a regular and uniform spacing of the vertical pulses generated by foil blades supporting a forming fabric.
• a small section of the forming fabric 1 is shown moving in the direction of arrow 1A.
• the forming fabric passes over a series of foil blades all uniformly spaced apart by the distance Y, as indicated between foil blades 45 and 46 mounted on the tee bars 41 and 42. Because the stock agitation is generated by vertical movement of the forming fabric caused by the foil blades, which are each spaced apart by the constant distance Y, the area of vertical stock agitation shown by 48 is followed by another area 50.
• the quiescent zone 49 is followed by another quiescent zone 51, following the area 50.
• both the areas of vertical agitation 48 and 50 and the zones of quiescence 49 and 51 are each spaced apart at the same distance Y.
• vertical agitation of the stock still occurs at the location 52 (which is differently shaded in Figure 4 to emphasize that there is no foil blade on tee bar 43), although the amplitude of the agitation at the location 52 is somewhat less than is obtained with a foil blade in place on tee bar 43.
• the occurrence of this activity in the vicinity of the tee bar 43 (which has no foil blade) is referred to as occurring at a "ghost blade".
• spacing of the various support surfaces for the forming fabric can be used to generate, to optimize and to control the agitation occurring in the stock on the forming fabric.
• the dewatering support surfaces can be placed to control the vertical movement which is initiated by earlier drainage devices.
• FIG. 5 Two possible ways of utilizing this invention are shown in Figures 5 and 6.
• Each of these figures shows essentially the same portion of a paper making machine as is shown in Figure 1, but with certain differences.
• the forming fabric 1 passes over the rollers 3, around the breast roll 2, and then past the head box slice 5, at which point the stock is deposited onto it. Drainage is initiated by the forming board section on box 6, and continued by the foils associated with box 7; it is to be noted that boxes 6 and 7 are still separated by the gap a.
• the remainder of the forming section comprises a single extended suction box 100, which is separated into the sequence of separate chambers 8, 9, 10, 11 and 12, either by using a single continuous suction box with dividers, or by using a plurality of smaller boxes, butting up closely to each other.
• These suction units also differ from the arrangement shown in Figure 3 in another way.
• the first support surface 26 is an upper one, and is followed by a lower one, 27.
• the last support surface in the box is also an upper one.
• the first is that it will still leave an equivalent length of forming fabric (corresponding substantially to the eliminated gap length) effectively unused, unless the somewhat drastic step of reducing overall machine length is also taken.
• the second is that although the same amount of water is being removed from the stock, the use of an overall shorter forming section means that water is being removed more rapidly, than is the case if the length of the forming section is retained unchanged. It appears to be advantageous to retain the forming section length, since removing the same amount of water over a longer length of forming fabric reduces the rate at which that water is removed. Decreasing the drainage rate generally improves the quality of the paper being made, since better paper mat formation occurs and wire marking is lessened. Further, the FPR figures also improve; it appears to be feasible to obtain an improvement of the order of 20% with the method of this invention.

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• Paper (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
• Centrifugal Separators (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23428083

Family Applications (1)

Country Status (7)

Citations (4)

Family Cites Families (4)

• 1990
  • 1990-06-07 EP EP19900908880 patent/EP0476002B1/en not_active Expired - Lifetime
  • 1990-06-07 WO PCT/CA1990/000185 patent/WO1990015187A1/en active IP Right Grant
  • 1990-06-07 JP JP2507885A patent/JP2581615B2/ja not_active Expired - Fee Related
  • 1990-06-07 CA CA 2057932 patent/CA2057932C/en not_active Expired - Fee Related
  • 1990-06-07 DE DE90908880T patent/DE69005304T2/de not_active Expired - Fee Related
  • 1990-06-07 AU AU57250/90A patent/AU633105B2/en not_active Ceased
• 1991
  • 1991-12-05 FI FI915763A patent/FI915763A0/fi unknown

Patent Citations (4)

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