WO1999001608A1

WO1999001608A1 - Headbox of a papermachine/board machine

Info

Publication number: WO1999001608A1
Application number: PCT/FI1998/000534
Authority: WO
Inventors: Salah Skali Lami; Petri Nyberg
Original assignee: Centre Technique Industriel, Dit 'centre Technique De L'industrie Des Papiers, Cartons Et Celluloses'; Valmet Corporation
Priority date: 1997-06-30
Filing date: 1998-06-18
Publication date: 1999-01-14
Also published as: FI972812A0; FI102091B; AU7771998A; DE19882511T1; FI102091B1; JP2002507257A

Abstract

A headbox of a paper/board machine comprises an inlet header (10), an intermediate part (20), feed means (70a, 70b, 70c, 70d) for dilution liquid, a turbulence generator (30), and a slice cone (40), as well as a slice opening (41) from which a fibre suspension is passed into a gap (G) between a breast roll (50) and a forming roll (60). The turbulence generator (30) comprises a first cylinder (31) revolving in the direction of the pulp flow and a first stationary curved plate (32) fitted on a common central axis (C1), a first curved flow duct (33) being formed between said first cylinder and said first curved plate. The turbulence generator further comprises a second cylinder (34) revolving in the direction of the pulp flow and a second stationary curved plate (35) fitted on a common central axis (C2) which is parallel to the first central axis (C1), a second curved flow duct (36) being formed between said second cylinder and said second curved plate. The mantle faces (31a, 34a) of the cylinders (31, 34) are formed of a regular radial wave line. Large fibre flocs are dispersed by means of the first cylinder (31) and small fibre flocs are dispersed by means of the second cylinder (34).

Description

Headbox of a paper machine/board machine

The invention relates to the headbox of a paper or board machine defined in the preamble of claim 1.

The function of a headbox in a paper or board machine is, firstly, to spread paper pulp slurry emerging initially from one pipe into a homogeneous flow having a width of a paper web and moving forward as a uniform front, secondly, to form out of the spread flow front a homogeneous pulp slurry jet which is uniform in velocity, direction, consistency and thickness and in which both short and long fibres as well as fines and fillers are evenly distributed and which has adequate turbulence.

Adequate turbulence is produced by means of a turbulence generator which, in conventional hydraulic headboxes, comprises a densely constructed tube bank. In the turbulence generator, the pulp flow is passed through standing stationary ducts, in which connection the increased velocity of flow and the design of walls cause strong microturbulence which disperses fibre floes.

In the turbulent tube flow, a zone is formed close to the wall of the tube where the velocity of flow is lower than in the middle of the tube. In this zone situated close to the wall, the consistency of the pulp flow is also slightly lower than in the middle of the tube. Since the number of this kind of tubes in the largest headboxes of paper or board machines is 2500, it causes disturbances in the forming of the web in a wire section of a paper or board machine.

With a view to achieving these objectives, a number of different headbox arrange- ments are known from prior art. One such arrangement is disclosed in FI Patent

Application 961547 (based on international patent application PCT/FR95/01028).

The publication discloses an arrangement in which a pulp flow is passed into a first outer curved duct and therefrom further into a second inner curved duct, the inner wall of the second curved duct consisting of the outer mantle of a rotating cylinder. The inner wall of the first curved duct constitutes the outer wall of the second curved duct. The initial part of the first curved duct is constituted by a straight outer wall extending parallel to the feed direction of the fibre suspension and by a curved inner wall, the height of the flow path for liquid defined between said walls being gradually reduced. After this initial portion, the first curved duct continues so that its height remains the same for almost a full circle, and ends at a wall which turns the flow direction of the liquid, and guides the liquid from an opening in the inner wall of the first curved duct into the second curved duct, where the liquid moves in a direction opposite to the flow direction of the first curved duct. At the end of the second curved duct, the liquid is passed into a slice cone and therefrom further through a slice opening out of the headbox. The mantle line of the cylinder associated with the inner duct corresponds to a radial sine-shaped path, whose wavelength is about 2-10 times the average length of fibres. The aim of this headbox arrangement is to produce large eddies in the outer stationary duct for dispersing big fibre floes and to produce small eddies in the inner duct associated with the rotating cylinder for dispersing small fibre floes.

In the arrangement described in the above-mentioned FI Patent Application 961547, the first stationary outer curved duct is, however, not a sufficiently efficient turbulence member for high-consistency pulp. For this reason, the fibres are able to be flocked in some place, with the result that the formed fibre floe begins to collect more fibres and their aggregation causes a risk of blockage. It is difficult and expensive to manufacture this kind of stationary curved duct because of the high pressure which has to be used in supply of pulp.

FI Patent Publication 91649 discloses a headbox provided with a movable means that comes into contact with a pulp flow. The movable means aims at providing turbu- lence in the pulp flow. In one embodiment, this movable means is constituted by two revolving cylinders whose mantle faces are arranged to form a part of the wall guiding the pulp flow. One cylinder forms a part of the lower wall guiding the pulp flow and the other cylinder forms, in a similar way, a part of the upper wall guiding the pulp flow. The faces of the cylinders may be, for example, smooth. It is, however, also possible to use different coating materials. The directions of rotation of the cylinders may be either in the direction of the pulp flow or opposite to the direction of the pulp flow.

The arrangement in accordance with the above-mentioned FI Patent Publication 91649 does not provide sufficiently efficient turbulence. In the embodiment in which two revolving cylinders are employed, turbulence is mainly produced by the friction forces between the cylinder mantle and the pulp suspension and between the wall of the duct and the pulp suspension.

The arrangement of the invention provides an essential improvement over the above- mentioned prior-art arrangements.

The main characteristic features of the arrangement in accordance with the invention are set forth in the characterizing clause of claim 1.

By means of the headbox in accordance with the invention it is possible to eliminate velocity and consistency disturbances in the turbulence produced by means of standing, stationary ducts and occurring at the edges of the tube flow. The boundary of the tube flow in the turbulence created between a stationary plate and a cylinder which revolves in the direction of the flow, and follows a regular wave line, and has a peripheral speed higher than that of the pulp flow, is only the face of the stationary plate. The face of the stationary plate is always the surface side in the paper web and, thus, in the paper web there occur no disturbances caused by turbulence that is produced by means of standing, stationary ducts. In the structure in accordance with the invention, the pulp flow is not divided into compartments in the cross direction but, instead, turbulence of higher intensity is generated than that produced by standing, stationary ducts. The turbulence may be regulated by changing the speed of rotation of the cylinder. The structure in accordance with the invention also facilitates the function of the slice of the headbox. The cylinders revolving in the direction of flow and provided with a regular radial wave line on their mantle face also operate to some extent as pumps for the pulp flow, but most of the energy they provide for the pulp flow is transferred to turbulence.

The construction in accordance with the invention provides a simpler headbox structure, which is easier to manufacture and which is therefore also less expensive.

In the headbox in accordance with the invention it is possible to use a feed consist- ency of about 1-4 % for the fibre suspension to be fed from the slice opening of the headbox into a gap between a breast roll and a forming roll. The feed consistency higher than normal enabled to be used in the headbox in accordance with the invention leads to the fact that smaller total pulp amounts are needed and, thus, also smaller mixing boxes and pumps. In addition, the need for deaeration and centrifugal cleaning is reduced.

The high velocity and the small total pulp amount achieved by the headbox in accordance with the invention lead, in turn, to the fact that the pulp jet discharging from the slice opening applies a smaller impulse to the forming wire and, consequently, the service life of the wire becomes longer. The smaller total pulp amount also leads to the fact that the need for dewatering at the beginning of the web former in particular is reduced and, thus, the need for water treatment capacity is also reduced. The arrangement in accordance with the invention also enables the speed of a paper or board machine to be increased. Also, the formation and the strength properties of paper remain good by means of the arrangement in accordance with the invention.

In the following, the headbox in accordance with the invention will be described with reference to the figures of the accompanying drawings, to the details of which the invention is not exclusively confined. Figure 1 is a schematic sectional view from the side of a headbox in accordance with the invention.

Figure 2 shows the form of the turbulent flow in the turbulence generator in the headbox in accordance with the invention.

Figure 3 is a schematic longitudinal sectional view of the cylinders of the turbulence generator in the headbox in accordance with the invention.

The headbox of the invention shown in Fig. 1 comprises an inlet header 10 by means of which a pulp suspension is supplied into the headbox across the headbox in the cross direction. The inlet header 10 is followed by an intermediate part 20 by means of which the flow of the pulp suspension is further equalized and made calmer. The intermediate part 20 is followed by a turbulence generator 30 and a slice cone 40 as well as a slice opening 41, from which the fibre suspension is passed, across the headbox in the cross direction, into a gap G between a breast roll 50 and a forming roll 60.

As the inlet header 10 is used a normal inlet header 10 known per se in which the flow cross-sectional area of the fibre suspension decreases in the cross direction of the headbox.

The intermediate part 20 comprises a substantially horizontal bank of tubes 21,22 and a duct 23 directed downwards from the horizontal plane and narrowing in the height direction. The tube bank is constituted by tubes 21,22 situated adjacent to one another across the headbox in the cross direction, in which connection the diameter of the tubes 21 opening into the inlet header 10 is smaller than the diameter of the tubes 22 opening into the narrowing duct 23. The outlet opening of the narrowing duct 23 , which also extends across the headbox in the cross direction, opens into the turbulence generator 30. By the arrangement in accordance with the invention, the tube bank 21,22 may be made less dense than at present. The turbulence generator comprises a first revolving cylinder 31 and a second revolving cylinder 34 mounted above it. The second cylinder 34 is situated above the first cylinder 31 such that the vertical planes drawn to the parallel centre axes Cι , C₂ of the cylinders 31 , 34 are situated in a horizontal plane at a distance from each other. The diameter of the first cylinder 31 is preferably about 1—4 times larger than the diameter of the second cylinder 34, and the rotation directions P_j, P₂ of the cylinders 31,34 coincide with the flow direction P of the fibre suspension.

A first curve-shaped duct 33 extends around the first cylinder 31 of the turbulence generator, the inner wall of said duct 33 being constituted by the outer mantle of the first cylinder 31 and the outer wall of said duct 33 being constituted by a first curved plate 32, whose centre axis coincides with the centre axis C^ of the first cylinder 31. Similarly, a second curve-shaped duct 36 extends around the second cylinder 34, the inner wall of said duct 36 being constituted by the outer mantle of the second cylinder 34 and the outer wall of said duct 36 being constituted by a second curved plate 35, whose centre axis coincides with the centre axis C2 of the second cylinder 34. The above-mentioned outlet opening of the narrowing duct 23 situated in the intermediate part 20 opens into the inlet opening of said first curved duct 33, which inlet opening is situated below the horizontal plane drawn to the centre axis C^ of the first cylinder 31. Both of the curved ducts 33, 36 extend across the headbox in the cross direction.

The outer wall of the first curved duct 33 changes at the vertical plane drawn to the uppermost point on the outer face of the mantle of the first cylinder 31 into a substantially horizontal guide face 33a which ends slightly before the vertical plane drawn to the lowermost point on the outer face of the mantle of the second cylinder 34. The purpose of the guide face 33a is to guide the fibre suspension substantially tangentially to the outer face of the mantle of the first cylinder 31 onto the outer face of the mantle of the second cylinder 34. The outer wall of the second curved duct 36 also joins the slice cone 40 such that the fibre suspension is passed into the slice cone 40 tangentially to the outer face of the mantle of the second cylinder 34. The slice cone 40 comprises a first stationary cone 40a and a second adjustable cone 40b ending at the slice opening 41.

The length α^ of the first curved duct 33 is about 90—360°, preferably about 225—315°. The length α₂ of the second curved duct 34 is about 45—270°, preferably about 135—225°. By means of the length of the duct it is possible to affect the time during which the fibre suspension is subjected to the treatment of the revolving cylinder. Furthermore, the length of the duct affects the forces applied by the fibre suspension flowing in the duct to the axle of the cylinder. A shorter duct causes a greater unequal force on the cylinder axle than a longer duct.

Figs. 2 and 3 show the mantle lines of the cylinders 31,34 and the form of turbulences generated in the ducts 33,36.

The mantle line 31a of the first cylinder 31 is formed of a radial regular wave line, preferably of a path following a sine wave. The mantle line in the shape of a sine wave produces in the fibre suspension turbulence that is advantageous in shape. The wavelength λ_j of the sine-shaped mantle line of the first cylinder 31 is 5—20 times the average length of the fibres. The height h^ of the first curved flow duct 33 from the median of the sine wave constituting the mantle line of the first cylinder 31 to the concave inner face of the first curved plate 32 is about 6—20 times the average length of the fibres and constant over the entire length γ of the flow duct. The peripheral speed of the first cylinder 31 revolving in the flow direction is about 1.5- 4 times higher than the peripheral speed of the fibre suspension flow.

The mantle line 34a of the second cylinder 34 is also formed of a radial regular wave line, preferably of a path following a sine wave. The wavelength λ2 of the sine-shaped mantle line of the second cylinder 34 is about 1—10 times the average length of the fibres. The height h2 of the second curved flow duct 36 from the median of the sine wave constituting the mantle line of the second cylinder 34 to the concave inner face of the second curved plate 35 is about 1—10 times the average length of the fibres and constant over the entire length o^ °f the flow duct. The peripheral speed of the second cylinder 34 revolving in the flow direction is about 1.5—4 times higher than the peripheral speed of the fibre suspension flow.

The larger fibre floes in the fibre suspension are dispersed and the pulp flow is equalized in the first curved duct 33 by the joint action of the first revolving cylinder 31 and the first curved plate 32. The purpose of this first cylinder 31 and the first duct 33 associated therewith is to improve the conditions of operation of the second cylinder 34 and the second duct 36 associated therewith.

Small fibre floes are dispersed in the second curved duct 36 by the joint action of the second cylinder 34 and the second curved plate 35. The function of this second cylinder 34 and the associated duct 36 is to create small-scale turbulence, which ensures that the slice part of the headbox will have good operating conditions.

Fig. 1 shows that the headbox in accordance with the invention further comprises means 70a, 70b, 70c, 70d for regulating consistency at different points of the headbox. Dilution liquid may be fed either into the first tube bank 21 of the intermediate part 20, the means 70a, or into the initial end of the narrowing duct 23 of the intermediate part, the means 70b, or into the initial end of the first curved duct 33, the means 70c, or into the initial end of the second curved duct 36, the means 70d. The means 70a, 70b, 70c, 70d for regulation of consistency are shown only schematically in the figure. The means for regulation of consistency comprise a header (not shown in the figure) for a dilution liquid extending across the headbox in the cross direction, flow ducts provided with valves leading from said header to different width points of the headbox.

The flow rate of each flow duct can be regulated individually by means of the valves associated with the regulation of consistency, whereby the grammage profile of the fibre suspension can be regulated across the headbox in the cross direction, i.e. across the machine width. Such consistency regulation enabling the grammage profile of the fibre suspension to be regulated constitutes an important part in present-day headboxes. From the point of view of mixing, the best regulation of consistency is attained if the means 70c for regulation of consistency are situated at the initial end of the first curved duct 33. From the point of view of small resolution, the best regulation of consistency is, in turn, attained by placing the means 70d for regulation of consist- ency at the initial end of the second curved duct 36.

Fig. 3 shows a radial regular wave pattern of the mantle lines 3 la, 34a of the cylinders 31,34. The figure also shows sealing 80 of the end faces of the cylinders 31,34 in accordance with the invention. The seal elements 80 of the end faces of the cylinders 31,34 are situated in the immediate vicinity of the mantle face or on the mantle face. By this means, the entry of pulp between the end faces of the cylinders 31, 34 and the side walls of the headbox is eliminated. If pulp is able to enter between the end faces of the cylinders 31,34 and the side walls of the headbox, it gives rise to a harmful pumping effect on the edge area.

In the following, claims are presented, and the details of the invention may differ from what has been stated above by way of example only.

Claims

1. A headbox of a paper/board machine, comprising an inlet header (10), an intermediate part (20), means (70a, 70b, 70c, 70d) for regulation of consistency, a turbulence generator (30), and a slice cone (40), as well as a slice opening (41) from which a fibre suspension is passed into a gap (G) between a breast roll (50) and a forming roll (60), characterized in that the turbulence generator (30) comprises:

- a first revolving cylinder (31) and a first stationary curved plate (32) fitted on a common central axis (C_j), in which connection a first curved flow duct (33) for the pulp suspension is formed between the outer face of the mantle of the first cylinder (31) and the concave inner face of the first curved plate (32), which flow duct (33) extends across the headbox in the cross direction,

ΓÇö a second revolving cylinder (34) and a second stationary curved plate (35) fitted on a common central axis (C₂) which is parallel to the central axis (C of the first cylinder (31) and of the first curved plate (32), in which connection a second curved flow duct (36) for the pulp suspension is formed between the outer face of the mantle of the second cylinder (34) and the concave inner face of the second curved plate (35), which flow duct (36) extends across the headbox in the cross direction, and that ΓÇö the mantle lines (3 la, 34a) of the first (31) and the second (34) cylinder are formed of radial regular wave lines.

2. A headbox as claimed in claim 1, characterized in that the length (╬▒_j) of the first curved flow duct (33) of the pulp suspension is about 90┬░ -360┬░, preferably about 225 ┬░-315┬░.

3. A headbox as claimed in claim 1 or 2, characterized in that the length (o^) of the second curved flow duct (36) of the pulp suspension is about 45┬░ ΓÇö 360┬░, preferably about 135┬░ -225┬░.

4. A headbox as claimed in any one of claims 1 to 3, characterized in that the mantle line of the first revolving cylinder (31) is formed of a radial sine wave whose wavelength (╬╗^) is about 5 to 20 times the average length of the fibres.

5. A headbox as claimed in any one of claims 1 to 4, characterized in that the mantle line of the second revolving cylinder (34) is formed of a radial sine wave whose wavelength (╬╗₂) is about 1 to 10 times the average length of the fibres.

6. A headbox as claimed in any one of claims 1 to 5, characterized in that the peripheral speed of the first revolving cylinder (31) is about 1.5 to 4 times higher than the peripheral speed of the fibre suspension flow.

7. A headbox as claimed in any one of claims 1 to 6, characterized in that the peripheral speed of the second revolving cylinder (34) is about 1.5 to 4 times higher than the peripheral speed of the fibre suspension flow.

8. A headbox as claimed in any one of claims 1 to 7, characterized in that the height (h_j) of the first curved flow duct (33), measured from the median of the regular wave line forming the mantle line of the first cylinder (31) to the concave inner face of the first curved plate (32), is about 6 to 20 times the average length of the fibres and constant over the entire length of the flow duct (33).

9. A headbox as claimed in any one of claims 1 to 8, characterized in that the height (h₂) of the second curved flow duct (36), measured from the median of the regular wave line forming the mantle line of the second cylinder (34) to the concave inner face of the second curved plate (35), is about 1 to 10 times the average length of the fibres and constant over the entire length of the flow duct (36).

10. A headbox as claimed in any one of claims 1 to 9, characterized in that the feed means (70a) for regulation of consistency spaced from one another in the cross direction of the headbox open into a first tube bank (21) of the intermediate part (20).

11. A headbox as claimed in any one of claims 1 to 9, characterized in that the feed means (70b) for regulation of consistency spaced from one another in the cross direction of the headbox open into the initial part of a narrowing duct (23) of the intermediate part (20).

12. A headbox as claimed in any one of claims 1 to 9, characterized in that the feed means (70c) for regulation of consistency spaced from one another in the cross direction of the headbox open into the initial part of the first curved flow duct (33).

13. A headbox as claimed in any one of claims 1 to 9, characterized in that the feed means (70d) for regulation of consistency spaced from one another in the cross direction of the headbox open into the initial part of the second curved flow duct (36).

14. A headbox as claimed in any one of claims 1 to 13, characterized in that the cylinders (31,34) are sealed by means of seal members (80) at both end flanges thereof to the side walls of the headbox such that the seal members (80) are situated on the end flanges of the cylinders (31,34) in the immediate vicinity of the mantle faces of the cylinders (31,34).