Classifications

• • 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
  • D21F9/003—Complete machines for making continuous webs of paper of the twin-wire type
• • 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
  • D21F1/02—Head boxes of Fourdrinier machines
• • 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
  • D21F1/02—Head boxes of Fourdrinier machines
  • D21F1/028—Details of the nozzle section

Definitions

• Dewatering arrangement adapted to use in a twin-wire dewatering section of a stock processing machine.
• the present invention relates to a dewatering arrangement adapted to use in a twin- wire dewatering section of a stock processing machine, comprising a single-ply head box for supplying stock through a nozzle with an inlet fed by a tube bank with tubes of non-circular cross-section, a closed loop first wire adapted to receive the stock from the head box on its upper surface and with pressure pulse generating blades mounted inside the loop, a closed loop second wire adapted to be fed on top of the first wire, and with pressure pulse generating blades mounted inside the loop, thereby pressing the stock between itself and the first wire.
• the fibre suspension is dewatered by the pressure generated below the tensioned, curved outer wire.
• the pressure event can include some fluctuations, but it is in principle mainly constant. This means that much of the fibre flocculation in the headbox jet will remain in the formed paper products.
• the fibre suspension is dewatered by pressure pulses, generated by local wire deflections over solid blades. These blades thus create a pulsating dewatering pressure, which can improve large-scale formation by floe stretching/breaking effects.
• the separate layers are placed one at a time on a first wire each by a separate headbox and dewatered each by a secondary wire supported and dewatered by blades on the upper side of the secondary wire and by movable blades on the lower side of the first wire.
• the dewatering is effected by pressure pulses like the dewatering process in the blade former previously mentioned.
• twin-wire dewatering is previously known which is a combination of initial roll dewatering (low sensitivity to jet instabilities and jet angle), and final blade dewatering (for large-scale formation improvement).
• the basic idea is to combine the advantages of the two dewatering principles, while avoiding their drawbacks.
• a similar problem with formation damages also occurs in paper board machines.
• the separate layers are placed one at a time on a first wire each by a separate headbox and dewatered each by a secondary wire supported and dewatered by blades on the upper side of the secondary wire and by movable blades on the lower side of the first wire.
• the pressure pulses from the blade dewatering can cause serious formation damages, like in the roll/blade forming case mentioned above.
• a tube bank delivering one individual jet from each tube in the bank, feeds the nozzle.
• the individual tubes are separated by solid boundaries, downstream of which flow wakes will form. These wakes gradually disappear along the nozzle contraction.
• the pressure will drop and the velocity profile across the nozzle will gradually get more even.
• the headbox nozzles In today's high speed printing paper machines (newsprint, SC paper, LWC paper and fine paper) of the roll/blade type, the headbox nozzles have a comparatively small inlet height, not above 130 mm. (This has enforced comparatively small slice openings, to avoid formation damages, in the order of 5 mm in newsprint production and 10 mm in copy paper production.) This small nozzle inlet height seriously limits the possibility to create an acceptable jet stability to avoid formation damages in machines using roll/blade forming.
• One aim of the present invention is thus to provide an apparatus capable of lessening the risk of formation damages. This aim is achieved by that the inlet height of the headbox nozzle, defined as the total tube bank height minus the total upstream thickness of eventual nozzle vanes, is at least 150 mm.
• a further advantageous embodiment of the present invention discloses an inlet height of the headbox nozzle that is at least 200 mm.
• a further advantageous embodiment of the present invention discloses an inlet height of the headbox nozzle that is at least 275 mm.
• An especially advantageous embodiment of the present invention discloses a roll/blade apparatus where the distance from the wire separation line on the roll to the first blade on the roll side of the wires is less than 100 mm.
• Fig. 1 discloses a headbox according to a dewatering arrangement of the present invention.
• Fig. 2 discloses a fundamental view of an apparatus according to a first embodiment of the present invention involving a roll/blade former.
• Fig. 3 discloses a detailed side view of a blade according to a dewatering arrangement of the present invention.
• Fig. 4 discloses a side view of a tip of a blade according to a dewatering arrangement of the present invention.
• Fig. 5 discloses a fundamental view of an apparatus according to a second embodiment of the present invention involving a paper board former.
• Fig. 2 discloses a part of a twin-wire forming apparatus with a forming roll 1 , a first wire 2 partly wrapped directly around the forming roll 1 , a second wire 3 wrapped around the forming roll lying on the first wire 2.
• a head box 4 is arranged with its opening directed substantially in the feeding direction of the wires 2, 3.
• the head box feeds stock to the nip between the wires 2, 3 wrapped around the forming roll 1.
• By changing the angle of the opening of the head box 4 against this nip it is possible to change the direction of the stock fed to the forming apparatus.
• the headbox 4 has a tube bank 6, from which is delivered one individual jet of fibre suspension from each tube 7 in the tube bank 6, which feeds a nozzle 8 in the headbox.
• the individual tubes 7 are separated by solid boundaries 9, to each of which is arranged a vane 14, downstream of which flow wakes will form. These wakes gradually disappear along the nozzle contraction. When the flow is accelerated along the nozzle 8, the pressure will drop and the velocity profile across the nozzle 8 will gradually get more even.
• the headbox 4 according to fig. 1 has a height of 320 mm and 9 solid vanes 14 of 5 mm upstream thickness each.
• the real inlet height is thus 275 mm, with which it was possible to avoid formation damages.
• the tubes of the headbox according to the present invention are thus tightly packed and show a non-circular, preferably an essentially rectangular or hexagonal form.
• a first blade 5 is arranged inside of the first wire 2.
• This blade is designed to support the first wire 2 and to avoid under pressure generation between the first wire 2 and the surface of the forming roll 1 by breaking the fluid capillary between the first wire 2 and the forming roll surface. If this happens early on any substantial force will not form from a local under pressure between roll and wire. This means that any substantial deformation of wire 2 leading to sheet damage will be avoided. This means in turn that the tip of the blade 5 will not be exposed to any significant radial force from the inner wire, thus not causing any significant blade wear by friction.
• the blade 5 is thus designed so that it supports the inner wire at a distance of at the most approx. 100 mm, and more preferably approx. 20-30 mm downstream of the separation line on the forming roll surface.
• the blade 5 has for geometrical reasons (the closeness to the roll nip) a very small thickness at its leading edge, of the magnitude of one millimeter, as can be understood from fig. 3. Such a blade gets thereby a low flexural rigidity, and will not be able to carry any loads from the inner wire. Therefore the blade 5 is designed so that the inner side has a curvature adjusted to support against the forming roll while the outer side is essentially plane to support the inner wire. Referring now to fig. 4, by choosing different tapering of the roll and wire side resp.
• the radial force generated by the flow deflections can be controlled.
• a higher value of the taper on the roll side gives a resulting force to the wire side.
• Minimum wear between the roll side of the blade 5 and the roll surface must be ensured.
• the blade tip must therefore be designed so that a suitable amount lubricating water is let through between the blade and the roll surface. This is effected by the taper (a, ⁇ ) on the roll side of the tip, see fig 4. As can be seen from the figure, this taper angle is ⁇ .
• Minimum wear between the wire side of the blade 5 and the first wire 2 is obtained by that a suitable water layer is let through between the wire and the blade 5. This is accomplished by a suitable tapering (b, ⁇ ) of the wire side of the tip of blade 5, see figure 3. As can be seen from the figure, this taper angle is ⁇ .
• the design of the blade and the headbox according the invention can, of course, be given different forms within the scope of the claims, and is not limited to the example above.
• the blade may be manufactured from ceramic, polymeric or metallic materials, or combinations thereof. Also other material combinations are possible.
• fig. 5 an apparatus for paper board forming is disclosed. The separate layers of stock are placed one at a time on a first wire 2 each by a separate headbox 4 and dewatered each by a separate secondary closed loop wire 3 supported and dewatered by stationary blades 12 on the upper side of the secondary wire 3 and by movable blades 13 on the lower side of the first wire 2.

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• 2005
  • 2005-02-28 SE SE0500446A patent/SE526969C2/sv not_active IP Right Cessation
• 2006
  • 2006-02-27 DE DE602006002027T patent/DE602006002027D1/de active Active
  • 2006-02-27 AT AT06716945T patent/ATE403028T1/de not_active IP Right Cessation
  • 2006-02-27 EP EP06716945A patent/EP1853759B1/de not_active Not-in-force
  • 2006-02-27 WO PCT/SE2006/000257 patent/WO2006091166A1/en active Application Filing

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