Method and device for treating a fibrous material web in a long nip pressing unit

Abstract

A method for treating a pulp web in a paper or tissue machine with an extended-nip press unit. This extended-nip press unit includes a shoe press roll with a revolving press belt and a backing roll, where the pulp web is dewatered in the extended press nip between the backing roll and the press belt and where the pulp web is carried on the revolving press belt of the press roll after the extended press nip to a transfer fabric that receives the pulp web. The transfer fabric is guided over a stationary transfer device in the transfer area. A corresponding device for treating the pulp web.

Claims

1. A method for treating a pulp web (1) in a paper or tissue machine (2) in an extended-nip press unit (3) with a press roll (4) having a rotating press belt (5), and a backing roll (6), the press roll (4) being a shoe press roll, comprising the steps of: dewatering the pulp web (1) in an extended press nip (7) between the press belt (5) of the press roll (4) and the backing roll (6) to yield a dewatered pulp web, transferring the dewatered pulp web (1) directly to the rotating press belt (5) of the press roll (4) after the extended press nip (7), passing the dewatered pulp web (1) from the press belt (5) to a transfer fabric (9) in a transfer area (8), wherein the transfer fabric (9) is guided over a stationary transfer device (10) in the transfer area (8).

2. The method according to claim 1, comprising a step of applying suction to the transfer device (10) in the transfer area (8) to support transfer of the pulp web (1) to the transfer fabric (9).

3. The method according to claim 1, characterized in that the transfer device (10) and the transfer fabric (9) running over the press belt (5) of the press roll (4) is inserted radially into the press belt (5) of the press roll (4) a radial insertion between (i) a position touching the press belt with no gap between the transfer fabric (9) and the press belt (5) to define a first position, and (ii) a position inward from the first position by 20 mm to define a radial insertion of 20 mm.

4. The method according to claim 3, characterized in that depth of the radial insertion of the transfer device (10) into the press belt (5) of the press roll (4) in the transfer area (8) is set via a setting device (11) outside the press roll (4).

5. The method according to claim 1, characterized in that the pulp web (1) is transferred from the press belt (5) to a permeable structured transfer fabric (9) in the transfer area (8).

6. The method according to claim 2, characterized in that the pulp web (1) is transferred from the press belt (5) to a permeable transfer fabric (9) in the transfer area (8).

7. The method according to claim 1, characterized in that the pulp web (1) moves in a running direction and is transferred to the transfer fabric (9) in the transfer area (8) over a thickness of less than 10 mm measured in the running direction.

8. The method according to claim 1, characterized in that the transfer fabric (9) moves at a lower speed than the press belt (5) when the pulp web (1) is transferred from the press belt (5) to the transfer fabric (9).

9. The method according to claim 1, wherein supporting elements (12, 13) are positioned on a side (15) of the press roll (4) opposite the pulp web (1) before and after the transfer area (8), the supporting elements (12, 13) being configured to support the press belt (5) of the press roll (4).

10. The method according to claim 9, characterized in that the supporting elements (12, 13) press radially outwards from the press belt (5) of the press roll (4) and the transfer fabric (9) running over the press belt (5) of the press roll (4) is inserted radially into the press belt (5) of the press roll (4) a radial insertion between (i) a position touching the press belt with no gap between the transfer fabric (9) and the press belt (5) to define a first position, and (ii) a position inward from the first position by 20 mm to define a radial insertion of 20 mm.

11. The method according to claim 1, characterized in that the pulp web (1) is guided onto the transfer fabric (9) via a suction device (14) to secure the pulp web (1) onto the transfer fabric (9) after transfer from the press belt (5) of the press roll (4).

12. A press arrangement for treating a pulp web (1) in a paper or tissue machine (2), comprising: an extended-nip press unit (3) comprising an extended press nip (7) through which the pulp web (1) is guided, the extended-nip press unit (3) further including a press roll (4) with revolving press belt (5) and a backing roll (6), the press roll (4) being a shoe press roll, wherein after the extended press nip (7) of the extended-nip press unit (3), the pulp web (1) is guided directly on the rotating press belt (5) of the press roll (4) to a transfer fabric (9) which receives the pulp web (1) in a transfer area (8), and the transfer fabric (9) is guided over a stationary transfer device (10) in the transfer area (8).

13. The press arrangement according to claim 12, wherein the press belt (5) of the press roll (4) is not supported in the transfer area (8) on a side opposite the pulp web (1).

14. The press arrangement according to claim 13, comprising supporting elements (12, 13) that are lubricated hydrostatically or hydrodynamically or both hydrostatically and hydrodynamically positioned inside the press belt (5) before and after the transfer area (8).

15. The press arrangement according to claim 12, characterized in that the stationary transfer device (10) in the transfer area (8) is a slotted suction device (10).

16. The press arrangement according to claim 15, wherein the slotted suction device (10) has a curved area (18) in front of an inlet side suction slot edge (17).

17. The press arrangement according to claim 12, wherein the transfer fabric (9) runs onto the transfer device (10) before transfer of the pulp web (1) from the press belt (5) of the press roll (4).

18. The press arrangement according to claim 14, characterized in that a circumferential angle (α) between the supporting element (12) in front of the transfer area (8) and the transfer area (8) is less than 15° as viewed from a center axis of the press roll (19), and a circumferential angle (β) between the transfer area (8) and the supporting element (13) after the transfer area (8) is less than 30° as viewed from the center axis of the press roll (19).

19. The press arrangement according to claim 12, characterized in that an angle (γ) between the transfer fabric (9) guided into the transfer area (8) and a tangent (20) to the press belt (5) is greater than zero degrees in the transfer area (8), thereby preventing or reducing likelihood of the transfer fabric (9) from wrapping round the press belt (5) in front of the transfer area (8).

20. The press arrangement according to claim 12, characterized in that an angle (δ) between the transfer fabric (9) carried out from the transfer area (8) and a tangent (21) to the press belt (5) in the transfer area (8) is greater than zero degrees, thereby preventing or reducing likelihood of the transfer fabric (9) from wrapping around the press belt (5) after the transfer area (8).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is described on the basis of drawings. In these drawings:

(2) FIG. 1 shows a tissue machine with the disclosed press and transfer arrangement;

(3) FIG. 2 shows a detailed view of the disclosed transfer arrangement;

(4) FIG. 3 shows a detailed view of the transfer area;

(5) FIG. 4 shows a detailed view of a stationary transfer device over which the transfer fabric is carried;

(6) FIG. 5 shows another embodiment of the disclosed stationary transfer device;

(7) FIG. 6 shows a view of a Fujifilm impression (Ultra Extreme Low Pressure 5 L W) of the transfer area of a transfer arrangement with a 900 mm wide transfer fabric;

(8) FIG. 7 shows a Fujifilm impression (Ultra Extreme Low Pressure 5 L W) of the transfer area of a transfer arrangement, and

(9) FIG. 8 shows an enlarged view of the press roll and the backing roll, and web being transferred from the clothing to the press belt of the press roll.

DETAILED DESCRIPTION

(10) Identical reference figures in the individual figures refer to the same components.

(11) FIG. 1 illustrates a tissue machine 2 with the press arrangement according to the disclosure.

(12) The pulp suspension is fed to the forming unit through a headbox 22 and leaves the headbox 22 between a breast roll 24 and a forming roll 23. Another fabric 25 is wrapped round the breast roll 24. In the forming unit, the pulp suspension is dewatered so that a material web 1 forms on the clothing 26. The clothing 26 is preferably a felt that conveys the pulp web 1 to a shoe press roll (press roll) 4.

(13) The press arrangement according includes an extended-nip press unit 3, which contains a press roll 4 with a revolving press belt 5 and a backing roll 6. An extended press nip 7 is formed between the press roll 4 and the backing roll 6.

(14) The disclosed press arrangement operates as follows:

(15) The pulp web 1 is carried through the extended press nip 7 on the felt 26. The felt 26 absorbs moisture from the pulp web 1 in the extended press nip 7. Immediately after the extended press nip 7, the felt 26 is separated from the pulp web 1 so that re-wetting of the pulp web is avoided.

(16) As shown most clearly in FIG. 8, after the extended press nip 7, the pulp web 1 no longer runs on the felt 26, but on the press belt 5 of the press roll 4. The press belt 5 transfers the pulp web 1 to a transfer fabric 9 in a transfer area 8. Transfer of the pulp web to the transfer fabric 9 is assisted by the transfer device 10, to which suction is applied. The transfer fabric 9 in the present example is structured and permeable.

(17) In the present example, another web treatment step is applied to the pulp web 1 in the transfer area 8, namely creping. For this purpose, the surface of the transfer fabric 9 moves through the transfer area 8 a little slower (lower relative speed) than the press belt 5, causing the pulp web 1 to be compressed slightly and creped when it is transferred to the transfer fabric 9.

(18) Mechanical dewatering in the extended-nip press unit 3 is followed by thermal drying on a Yankee dryer 27, from which the dry pulp web 1 is scraped off with the aid of a doctor, for example.

(19) Conditioning of the transfer fabric 9 should be conducted in such a way that there is no or only very little wetting of the transfer fabric 9 by the conditioning process. Thus, conditioning can be performed with compressed air, for example, or a pressurized air blade. If water is used for conditioning, it must be guaranteed that the transfer fabric 9 is dried or dried by suction before the pulp web 1 is placed on it again.

(20) In order to secure the pulp web 1 to the transfer fabric 9, it is also advantageous if the pulp web 1 is secured to the transfer fabric 9 after the pulp web 1 is transferred from the press belt 5 to the transfer fabric 9. It can be secured by guiding the pulp web 1 on the transfer fabric 9 over a vacuum box 14, where the vacuum at the vacuum box 14 holds the pulp web 1 on the transfer fabric 9 by suction.

(21) FIG. 2 shows a detailed view of the area where the pulp web 1 is transferred to the transfer fabric 9. The pulp web 1 on the press belt 5 is transferred to the transfer fabric 9 in the transfer area 8. This transfer is assisted by the transfer device 10, to which suction is applied. As can be seen, the press belt 5 is not supported in the transfer area 8. That means that no supporting elements are provided in the transfer area 8 on the side 15 of the press belt 5 opposite the pulp web 1. With the press roll 4, a first supporting element 12 for the press belt 5 is provided before the transfer area 8. The angle α between the supporting element 12 in front of the transfer area 8 and the transfer area 8, viewed from the press roll axis (center of the press roll) 19, is less than 15° here, for example 6°.

(22) With press roll 4, a second supporting element 13 on which the press belt 5 is supported is provided after the transfer area 8. The angle β between the supporting element 13 and the transfer area 8 is less than 30° here.

(23) The transfer fabric 9 is not wrapped round the press belt 5 beforehand or afterwards in the transfer area 8. In this sense, the angle γ between the transfer fabric 9 carried into the transfer area 8 over the stationary transfer device 10 and the tangent 20 to the press belt 5 in the transfer area 8 is greater than zero degrees, meaning that there is no contact between the transfer fabric 9, pulp web 1 and press belt 5 until the transfer area 8. Similarly, the angle δ between the transfer fabric 9 carried out of the transfer area 8 and the tangent 21 to the press belt 5 is greater than zero degrees in the transfer area 8, with the result that the transfer fabric 9 is not wrapped round the press belt 5 after the transfer area 8 and there is only contact between the transfer fabric 8, pulp web 1 and press belt 5 in the transfer area 8.

(24) The radial depth of insertion by the stationary transfer device 10 into the press belt 5 of the press roll 4 is set by the setting device 11 outside the press roll 4. For example, the stationary transfer device 10 can be secured to a pivoting lever arm 29 on the frame, where it is possible to insert it radially into the press belt 5 in accordance with the center of rotation 30 of the lever arm—taking the center point 19 of the press roll 4 as reference. The setting device 11 has an adjusting screw 28 that is used to set the depth of insertion of the transfer device 10.

(25) FIG. 3 shows the transfer area 8 from FIG. 2 in detail. As can be seen, the transfer device 10 is designed as a slotted suction device. Suction is applied through the suction slot 16 to the transfer fabric 9 between a first 17 and second suction slot edge 31. The slotted suction device 10 has a curved area 18 in front of the first suction slot edge 17 on the inlet side. The effective length of the curved area 18 up to the first suction slot edge 17 is less than 30 mm, for example, preferably less than 15 mm. Contact between the stationary transfer device 10 and the transfer fabric 9, the pulp web 1 and the press belt 5 takes place in the curved area 18 in front of the first suction slot edge 17 on the inlet side, where the transfer area 8 is also in the curved section 18 in front of the first suction slot edge 17 on the inlet side. In the present example, the suction slot 16 of the transfer device 10 is already outside the transfer area 8, which means that the transfer fabric 9 no longer touches the press belt 5 in the area of the suction slot 16. After this, the transfer fabric 9 runs over the outlet area 32 of the transfer device 10.

(26) The transfer device is shown in FIG. 4. The suction slot 16 is 15 mm wide here. The transfer fabric 9 preferably runs onto the transfer device 10 in the curved area 18 in front of the first suction slot edge 17. The curved area 18 is 12 mm long here.

(27) FIG. 5 shows another possible embodiment of the transfer device 10. Unlike FIG. 4, the outlet area 32 of the transfer device has a downward sloping design.

(28) FIG. 6 shows a Fujifilm impression 33 (Ultra Extreme Low Pressure 5 L W) of the transfer area 8 of a transfer arrangement designed according to the disclosure; For this purpose, the pressure-sensitive Fujifilm is inserted into the gap between the press belt 5 under pneumatic pressure and the transfer fabric 9 with the transfer device 10 upright and swung down. Then the stationary transfer device 10 with transfer fabric 9 is brought into the operating position against the press belt 5 under pneumatic pressure. Depending on the contact between the components—stationary transfer device 10, transfer fabric 9, Fujifilm and press belt 5—the pressure-sensitive film changes color. A change of color indicates contact and the changed color indicates the transfer area. The Fujifilm impression 33 shows a transfer area 8 with a length of less than 5 mm in the running direction of the pulp web 1, within which the pulp web 1 is transferred from the press belt 5 of the press roll 4 to the transfer fabric 9. The length of contact between the transfer fabric 9 and the press belt 5 perpendicular to the running direction (at right angles to the machine running direction) of the pulp web 1 is 900 mm in this case, corresponding to the width of the transfer fabric of 900 mm in this case.

(29) FIG. 7 shows a detailed section of the Fujifilm impression 33 (Ultra Extreme Low Pressure 5 L W) from the full impression illustrated in FIG. 6. A scale is provided so that it can be quantified more easily. The scale reads in running direction of the pulp web 1 in units of one centimetre. As the changed colour indicates the transfer area 8, it can be seen easily that there is a transfer area 8 with a length of less than 5 mm in running direction of the pulp web 1 in the section of the Fujifilm impression 33 shown.

REFERENCE NUMERALS

(30) 1 Pulp web 2 Paper or tissue machine 3 Extended-nip press unit 4 Press roll 5 Press belt 6 Backing roll 7 Extended press nip 8 Transfer area 9 Transfer fabric 10 Transfer device 11 Setting device 12 First supporting element 13 Second supporting element 14 Suction device 15 Opposite side 16 Suction slot 17 First suction slot edge 18 Curved area 19 Press roll center 20 Tangent 1 21 Tangent 2 22 Headbox 23 Forming roll 24 Breast roll 25 Outer clothing 26 Felt 27 Yankee 28 Adjusting screw 29 Lever arm 30 Fulcrum point of lever arm 31 Second suction slot edge 32 Outlet area 33 Fujifilm impression Angle α, β, γ, δ