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

Definitions

• the invention concerns a gap-roll former in a paper machine, comprising a headbox, which feeds a stock suspension jet into the forming gap defined by the forming wires, and of which forming wires one wire is a covering wire guided by its guide rolls, and the other wire is a carrying wire guided by its guide rolls, along with which carrying wire the paper web follows after the twin-wire zone defined by said forming wires, and in which twin- wire zone there are dewatering and web formation elements, and which twin-wire zone starts directly after the forming gap on a curve sector of the first forming roll.
• the principal object of the present invention is to provide a novel gap-roll former in which, on a curve sector of the former roll directly following after the forming gap, the dewatering, in particular its distribution between the inner wire and the outer wire, can be controlled better than in the prior art.
• the invention is mainly characterized in that on the curve sector of the twin-wire zone on the first forming roll there are at least two successive suction/pressure zones, by whose means a pressure effect that varies in the direction of progress of the paper web can be applied through the perforated mantle of the first forming roll to the paper web that is being formed, so that the dewatering process on said curve sector can be controlled.
• a former roll which comprises at least two successive pressure zones and by whose means it is possible to act upon the structure of the paper in the z-direction, in particular upon the structure of the middle layer in the paper, more efficiently.
• a former in accordance with the invention, it is possible to manufacture a paper, in particular a fine paper, which has improved properties, for example Scott Bold.
• the wrap angle of the twin-wire zone on the first former roll can, as a rule, be dimensioned optimally, because it is possible to use said wrap angles larger than in the prior art and, in this way, the range of basis weight in the former can be made wider than in the prior art.
• Figure 1 shows an embodiment of a roll-gap former in accordance with the invention in which the twin- wire zone is vertical and rises from the bottom upwards.
• Figure 2 is a schematic side view of a twin-wire zone formed in connection with the first forming roll and of suction/pressure zones fitted in the forming roll.
• Figure 3 is a schematic illustration of the effect of the vacuum present in the suction/pressure zone of the first forming roll on the height of the water column present in the perforations in the forming roll.
• Figure 4 is a schematic illustration of the initial part of the twin-wire forming zone.
• Figure 5 is a graphic illustration of the pressure profiles on the first forming roll with a low wrap angle and with a high wrap angle.
• a preferred environment of application of the invention will be described, which environment is a gap- roll former, whose twin- wire zone rises from the bottom upwards vertically, and the first former roll or forming roll 11 is placed inside the loop of the covering wire 10.
• the invention can also be applied to a number of other gap-roll formers, for example to formers in which the first forming roll 11 is placed inside the loop of the carrying wire 20 and/or the twin-wire zone is horizontal, upwards or downwards inclined.
• a stock suspension J is fed through the slice cone 35 of the headbox 30 into the forming gap G defined by the wires 10 and 20.
• the slice cone 35 of the headbox includes vanes 36, which extend to the vicinity of the slice opening and provide the stock jet J with an adequate level of micro-turbulence as it is discharged into the forming gap G.
• the forming gap G is defined between the carrying wire 20 coming from the guide roll 21 and the covering wire 10 curved on the first forming roll 11. After the forming gap G, there starts directly a twin- wire curve sector a, in which there are at least two suction/pressure zones 1 la, 1 lb one 4 after the other.
• the latter zone lib extends preferably at least partly into the opening wedge space or nip N 0 placed between the mantle 12a of the forming roll 11 and the wires 10,20.
• the covering wire 10 is guided by its guide rolls 18, and the carrying wire 20 is guided by its guide rolls 21 and 28.
• the diameter D ⁇ of the first forming roll 11 is, as a rule, in a range Di ⁇ 1200...2000 mm, preferably in a range D, « 1400.. J800 mm.
• the first forming roll 11 is followed by a first forming shoe 22, which has a ribbed deck 22a with a curve radius R ⁇ .
• a MB unit (loading-element unit) 50 there follows a MB unit (loading-element unit) 50, and after that a second forming shoe 24 provided with a curved ribbed deck 24a, and after this a second forming roll 29.
• the loading element 13 of the MB unit 50 is placed inside the loop of the covering wire 10
• the support element 23 is placed inside the loop of the carrying wire 20, but corresponding elements can also be placed inside the opposite wire loops 20,10.
• the first forming roll 11 is placed inside the loop of the covering wire 10
• the second, upper forming roll 29 is placed inside the loop of the carrying wire 20.
• Both forming rolls 11,29 can also be placed inside the same wire loop.
• the suction zone 29a of the second forming roll 29 ensures that, after it, the web W follows the carrying wire 20, which is guided by the guide rolls 28 and on which the web W is carried onto a pick-up roll 41.
• On the suction zone 41a of this roll 41 the web W is transferred onto a pick-up fabric 40, which carries the web W into the press section (not shown).
• a vacuum is present in the first zone 11a, so that draining of water takes place to some extent also through the covering wire 10.
• the suction sector 11a is followed by a narrow pressure sector lib, in whose area draining of water takes place through the carrying wire 20 only.
• the first forming roll 11 is provided with three successive zones HaJ lbJlc, whose pressure levels can be regulated by means of a suction/ - pressure device 60 by the intermediate of the ducts 60a,60b,60c.
• the zones llaJlb, l ie are defined by sealing ribs 12c fitted inside the mantle 12a of the forming roll 11, which ribs run against the inner face of the mantle 12a.
• a suitable pressure +P a in the next zone a pressure ⁇ P b , and in the last zone a pressure ⁇ P C .
• Said pressures P a ,P b ,P c are, as a rule, chosen in a range -40... +20 kPa, preferably in a range -25... + 10 kPa.
• the last zone 1 lc is placed after the line K on which the wires 10,20 are separated from the roll mantle 12, on a narrow sector, preferably so that, by means of the pressure P c present in the zone lie, the vacuum that tends to be induced otherwise in the opening wedge-shaped nip space N 0 between the roll mantle and the wires 10,20 is eliminated or reduced (vacuum zone a 12 in Fig. 5).
• Fig. 5 is a graphic illustration of the dewatering taking place on the curve sector a of the forming roll 11 in a gap-roll former as shown in Fig. 4; the vertical axis represents the dewatering pressure ve, and the horizontal axis represents the wrap angle of the twin-wire zone on the forming roll 11.
• This vacuum peak -P kl can be so high that it exceeds the cavitation limit and causes destruction of the fibre mesh that is being formed. In the present invention, this can be prevented by means of a pressure zone 1 lb, He as shown in Fig.
• the dewatering can be partly controlled by means of choice of the ratio of the speed of the slice jet J to the speed of the wires 10,20. Since, in particular in the area of the curve sector a, a thin fibre mat is drained quite rapidly on both faces of the wires 10,20 whereas the middle layer remains more freely mobile, by means of choice of said speed ratio, the middle layer can be either decelerated or accelerated in relation to said drained outer layers. In this way it is possible to act upon the properties of the web, in particular upon the formation of layers in the orientation in the z-direction.

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Priority Applications (3)

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Publications (1)

Family

ID=8551436

Family Applications (1)

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Cited By (1)

Citations (4)

• 1998
  • 1998-04-01 FI FI980743A patent/FI980743A/fi unknown
• 1999
  • 1999-03-29 WO PCT/FI1999/000255 patent/WO1999050498A1/fi active Application Filing
  • 1999-03-29 BR BR9909424-0A patent/BR9909424A/pt not_active Application Discontinuation
  • 1999-03-29 AU AU30382/99A patent/AU3038299A/en not_active Abandoned
  • 1999-03-29 DE DE19983087T patent/DE19983087T1/de not_active Withdrawn

Patent Citations (4)

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