EP2264243B1 - Method and device for treating a strip of fibrous material in a long nip press unit - Google Patents

Description

The invention relates to a method for treating a fibrous web in a paper or board machine in a Langnip press unit with a press roll, which is formed as a shoe press roll and having a rotating press shell and a counter roll, wherein the fibrous web in an extended press nip between the counter roll and the press roll of the press roll is dewatered. The invention also relates to a pressing arrangement with which the method according to the invention is carried out.

In conventional processes for paper and tissue production, the mechanical dewatering of a fibrous web before the thermal drying by a direct contact pressure of the fibrous web against a drying cylinder (Yankee cylinder). Such a manufacturing method is in the DE 102 33 920 A1 described. In these paper or tissue machines, however, the mechanical pressure or the achievable line load is limited because it is pressed against the Yankee drying cylinder. By an upstream press step, as for example in the EP 1 075 567 B1 is described, the mechanical dehydration takes place in a press unit independent of the Yankee cylinder. Optimum pressing conditions can be set here, because you no longer press against the drying cylinder and thus are not limited by the load limits of the drying cylinder. The mechanical dewatering can be significantly improved by this upstream pressing step, which is preferably carried out with a long-nip press unit, in particular a shoe press. The expense for the thermal drying is reduced, which leads to energy savings.

The EP 1 397 553 B1 describes a process for making a fibrous web in which the fibrous web is dewatered by a shoe press before being transferred to a thermal drying through-hole (TAD).

The WO 97/15718 A1 and the DE 10 2005 060 379 A1 reveal shoe presses through which the fibrous web is guided and dewatered. Here, the continuation of the fibrous web takes place after the extended press nip directly on the mating roll of the shoe press.

The DE 196 42 046 A1 describes an apparatus and a method for dewatering a fibrous web. In one embodiment mentioned here, the fibrous web is transferred from a wire to a shoe press roll and guided on the shoe press roll through the extended press nip.

In conventional paperboard manufacturing processes, one or more separate pressing steps for mechanical dewatering prior to thermal drying are prior art. Such a press arrangement is for example in the EP 0 954 634 B1 described. Again, the pressing steps are often performed with one or more Langnip press units, such as shoe presses.

For dewatering in a long-nip press unit, such as a shoe press, the fibrous web is passed on a felt through an extended press nip formed by a shoe press roll having a rotating press shell and a counter roll. After the extended press nip, the felt is separated as quickly as possible from the fibrous web. The fibrous web is then carried on either a string, which was also passed through the extended press nip, or by the backing roll.

The press cover of Langnip press units has contact with a covering in conventional systems in the extended press nip and serves only for mechanical dewatering.
The further transport of the fibrous web is always realized by other components.

The aim of the present invention is to disclose a method for the treatment of a fibrous web, in which the dewatering and the further transport of the fibrous web is to be realized without an intervening web transfer. In addition, a simpler and more compact construction of a press arrangement for a paper or board machine is to be disclosed.

In the method according to the invention, after the extended press nip on the rotating press jacket of the press roll, the fibrous web is guided to a transfer region in which the fibrous web is transferred from the press cover to a transfer element. Thus, the rotating press cover not only fulfills its function as a pressing element, but also serves as a means for further transport of the fibrous web after mechanical dewatering. A transfer fabric, which is performed in addition to the felt in some embodiments by the extended press nip, is thus superfluous. In addition, the fibrous web adheres very well to the flexible press jacket due to the pressure. When transferring the fibrous web from the press cover onto a transfer element, further advantages result, which will be explained below. According to the invention, the fibrous web is guided on a felt to and through the extended press nip. The felt absorbs the moisture from the fibrous web in the extended press nip. To avoid rewetting of the fibrous web, it makes sense if the felt is separated from the fibrous web immediately after the extended press nip.

It is favorable if, in the transfer area, the fibrous web is transferred from the press cover to a transfer cover. In this case, the press cover can be partially wrapped in the transfer area of the transfer cover. This results in a prolonged transfer area, through which a reliable web transfer is ensured.
The web transfer from the press cover can also be done directly on a roller.

The transfer of the fibrous web to the transfer element can be supported by a suctioned roller.

In a further embodiment of the invention, the press jacket of the press roll is stabilized by an overpressure in the interior of the press roll. By this stabilization, a smooth running of the press jacket can be ensured, this also has a positive effect on the life of the press jacket.

It is advantageous if the felt on which the fibrous web is guided through the extended press nip, has a three-dimensional structure, wherein the fibrous web is pressed in the extended press nip in this three-dimensional structure. The fibrous web can thus escape during the pressing process in the three-dimensional structure of the felt. The pressing is done selectively and not flat, achieving better quality properties than for example in conventional tissue is possible.

If the transfer of the fibrous web from the press cover to the transfer element is carried out with a speed difference between press cover and transfer element, a further treatment step of the fibrous web can be realized at the same time. If the transfer element moves in the transfer area at a lower relative speed than the press cover, creping of the fibrous web occurs during the transfer from the press cover to the transfer element. It is also conceivable that the transfer element moves at a higher relative speed than the press cover, thereby a tensile force can be exerted on the fibrous web in the web running direction.

In a favorable embodiment of the invention, the press cover is cleaned after the transfer of the fibrous web to the transfer element by a cleaning device. This ensures that no impurities or fibrous web remnants adhere to the press cover when it is passed through the press nip again.

In a further favorable embodiment of the method, an interface regulation mixture is applied to the surface of the press jacket before the press cover passes through the extended press nip. The application can be carried out for example by a spray bar, which sprays the Grenzflächenregulierungsgemisch on the press cover. By this process step, the surface adhesion of the fibrous web can be well regulated on the press cover

The dewatering of the fibrous web in the press nip can also be improved by heating the fibrous web with the aid of a steam blower box arranged in front of the extended press nip (change in viscosity).

The invention also relates to a press arrangement of a paper or board machine with which the method according to the invention is carried out. In the press arrangement according to the invention, the fibrous web is guided through an extended press nip of a L.angnip press unit, wherein the long nip press unit has a press roll with a rotating press cover and a counter roll. The fibrous web is, following the extended press nip on the press cover of the shoe press roll to a transfer element, which takes over the fibrous web, out. According to the invention, the press roll is a shoe press roll and the fibrous web is guided on a felt to and through the extended press nip.

Advantageously, the transfer element is a transfer fabric, which may be structured or unstructured. The press cover may be partially wrapped in the transfer area of the transfer cover. A permeable transfer cover also offers the advantage that the fibrous web transfer from the press cover to the transfer cover is assisted by suction devices which suck the fibrous web through the transfer cover.

A good web transfer can also be realized if an extended transfer nip for fibrous web transfer is formed between the transfer element and the press roll. Advantageously, the length of the extended transfer gap between press cover and transfer element is adjustable, thereby the web transfer can be optimally adjusted depending on the fibrous web type and the machine speed. This extended transfer nip, which may preferably also be drained, extends the transfer area, as a result of which a reliable web transfer can also be realized.

It is particularly advantageous if the position of a felt guide roller, which deflects the felt after the extended press nip, is adjustable so that thereby the contact surface or contact length after the extended press nip between the felt and the fibrous web is adjustable.

By enlarging this contact surface, it is possible to ensure that the felt travels a little longer along the fibrous web, this favors the passage of the fibrous web on the press cover or the transfer of the fibrous web onto the press cover. On the other hand, by reducing the contact area between the felt and the fibrous web, it is possible to achieve a particularly rapid separation of the felt from the fibrous web after the press nip and thus to prevent or minimize liquid moistening. In addition, for the transfer of a Einfädelstreifens first as large a contact surface can be realized so that the Einfädelstreifen safely runs along the press cover. After threading and widening out ^of: fibrous web, this contact area can be reduced, so that the re-wetting of the fiber web is minimized.

• Fig. 1 eine Papiermaschine mit Schuhpressentechnologie zur Herstellung von Tissuepapier nach dem Stand der Technik
• Fig. 2 eine Pressenpartie einer Kartonmaschine nach dem Stand der Technik
• Fig. 3 eine Tissuemaschine mit der erfindungsgemäßen Pressanordnung
• Fig. 4 eine Detailansicht der erfindungsgemäßen Pressanordnung
• Fig. 5 eine Kartonmaschine mit der erfindungsgemäßen Pressanordnung
• Fig. 6 den Verlauf eines konventionellen und eines Langnip-Pressprofils Gleiche Bezugszeichen in den einzelnen Figuren bezeichnen gleiche Bauteile.

In the following the invention will be described with reference to drawings.
It shows:

• Fig. 1 a paper machine with shoe press technology for the production of tissue paper according to the prior art
• Fig. 2 a press section of a cardboard machine according to the prior art
• Fig. 3 a tissue machine with the pressing arrangement according to the invention
• Fig. 4 a detailed view of the pressing arrangement according to the invention
• Fig. 5 a board machine with the pressing arrangement according to the invention
• Fig. 6 the course of a conventional and a long-nip press profile The same reference numerals in the individual figures designate the same components.

In Fig. 1 a conventional tissue machine with shoe press technology is shown. About a headbox 1, the pulp suspension is fed to the forming unit, it occurs between a breast roll 4 and a forming roller 5 from the headbox 1 from. The breast roll 4 is wrapped by an outer fabric 2. In the forming unit, the pulp suspension is dewatered so far that forms a fibrous web 9 on the fabric 3. The fabric 3 is preferably a felt which conveys the fibrous web 9 to a shoe press roll 6. Between the shoe press roll 6 and the Yankee cylinder 7, an extended press nip is formed in which the fibrous web is mechanically dewatered and transferred to the Yankee cylinder 7. At the Yankee cylinder 7, the thermal drying of the fibrous web 9 takes place. A scraper 8 releases the dry fibrous web 9 from the Yankee cylinder 7. Due to the direct contact pressure of the fibrous web 9 to the Yankee cylinder 7, the mechanical drainage is limited, since the shoe press roll 6 can not press any strength for reasons of stability to the Yankee cylinder 7. Most of the maximum line load is limited to 170 kN / m.

The inventive pressing arrangement, the mechanical dewatering of the fibrous web 9 relative to the pressing arrangement in Fig. 1 be increased considerably.

Fig. 2 schematically shows a press section 11 of a board machine according to the prior art. The press section 11 is arranged after a wet end 10 and before the dryer section 12. The fibrous web 9 is passed through the wire 13 of the wet end 10 to the press section 11. The web transfer to the press felt 14a is supported by the evacuated takeover roll 15. In the press section 11, the fibrous web 9 is mechanically dewatered by the two shoe presses 16a and 16b. The shoe presses 16a, 16b each consist of a shoe press roll 18a, 18b and a counter roll 17a, 17b.

Between the shoe press rollers 18a, 18b and the counter rollers 17a, 17b, an extended press nip is formed, in which the fibrous web 9 is mechanically dewatered. The moisture from the fibrous web 9 is thereby received by the press felts 14a, 14b, 14c and 14d, which are also performed together with the fibrous web 9 through the extended press nips.

After the mechanical dewatering, the fibrous web 9 is transferred by means of the transfer roller 22 to the dryer wire 21 of the dryer section 12. In the drying section 12, the fibrous web 9 is guided through the drying wire 21 meandering over the drying cylinder 19 and the suction rolls 20 and thereby thermally dried.

In Fig. 3 Now a Tissuemaschine is shown with the pressing arrangement according to the invention. It consists of a long-nip press unit 29, which has a press roll 24 with rotating press cover 25 and a counter-roller 23. Between the press roll 24 and the counter roll 23, an extended press nip 26 is formed.
The press arrangement according to the invention now works in the following way: The fibrous web 9 is guided on the felt 33 through the extended press nip 26. In the extended press nip 26, the felt 33 absorbs moisture from the fibrous web 9. The felt 33 has a three-dimensional structure in the present example. The fibrous web 9 can thereby escape during the pressing process in the three-dimensional structure of the felt 33. The pressure is thus punctiform and not flat. The felt 33 is separated from the fibrous web 9 immediately after the extended press nip 26 in order to avoid rewetting.

After the extended press nip 26, the fibrous web no longer runs on the felt 33 but on the press cover 25 on. The press cover 25 transfers the fibrous web 9 onto a transfer element 31 in a transfer region 30. In the present example, the transfer element 31 is a transfer cover 27. But the transfer element can also be a roller which takes over the fibrous web 9 from the press cover 25. This roller can also be drained.
The fibrous web transfer to the transfer fabric 27 is supported by the drawn roll 28. Between the evacuated roll 28 and the press roll 24, an extended transfer nip 32 is formed.

The transfer fabric 27 is permeable in the present example, of course, the use of a non-permeable transfer fabric 27 is conceivable. The transfer fabric 27 may have a smooth or a textured surface.

In the transfer region 30, a further web treatment step of the fibrous web 9 can be carried out, namely a creping or stretching of the fibrous web 9. For a crepe, the surface of the transfer fabric 27 moves slightly slower (lower relative speed) through the extended transfer nip 32 than the press cover 25, thus the fibrous web 9 is slightly compressed or creped during the transfer to the transfer fabric. Conversely, it is also possible to apply tensile forces to the fibrous web 9, which lead to an expansion of the fibrous web 9. For this purpose, the transfer cover 27 moves slightly faster (higher relative speed) than the press cover. A faster-moving transfer cover 27 can also have a positive effect on the fibrous web transfer.

The conditioning of the transfer fabric 27 should be such that there is no or only a very small humidification of the transfer fabric 27 through the conditioning process. Therefore, the conditioning can be carried out for example with compressed air or a compressed air sword. When conditioning with water, it must be ensured that the transfer fabric 27 is dried or sucked dry before it again takes over the fibrous web 9.

To stabilize the fibrous web 9 on the transfer fabric 27, it may be advantageous if the region in which the transfer fabric 27 transports the fibrous web 9 is continuously evacuated.
Following the mechanical dewatering in the long-nip press unit 29, the thermal drying takes place on a Yankee cylinder 7, from which the dry fibrous web 9 is scraped off with the aid of a scraper 8.

In Fig. 3 also the adjustable felt guide 40 is shown. By this adjustable Filzleitwalze 40, the exit angle of the felt 33 can be adjusted from the long-nip press unit 29, for example by +/- 15 °. Thereby, the contact surface or the contact length of the felt 33 with the fibrous web 9 after the extended press nip 26 is adjustable. The adjustability of the felt guide roll 40 is represented by a double arrow.
By enlarging this contact surface or contact length, it is possible to ensure that the felt 33 runs along the press cover 25 for a little longer, the fibrous web 9 being clamped between the felt 33 and the press cover 25. A reduction in this contact surface between the felt 33 and the fibrous web 9 causes a particularly rapid separation of the felt 33 from the fibrous web 9 after the extended press nip 26. To transfer a Einfädelstreifens first as large a contact surface is realized are, so that the threading securely runs along the press cover 25. After threading and spreading the fibrous web 9, this contact surface can be reduced so that the rewet of the fibrous web 9 is minimized.

Through the steam blower box 36, the fibrous web can be heated.

In Fig. 4 the long-nip press unit 29 according to the invention is shown in more detail. It can clearly be seen the extended press nip 26 between the press cover 25 of the press roll 24 and the backing roll 23. Also recognizes the extended transfer nip 32 between the press cover 25 of the press roll 24 and the transfer fabric 27. The press roll 24 is designed as a shoe press roll.

The extended transfer nip 32 is formed by the transfer fabric 27 being pressed against the press cover 25 by a roller, in the present case by a drawn roller 28, the press cover 25 in the transfer region 30 substantially following the surface contour of the roller 28. The support and guide surface of the press roll 24 for the press cover 25 is formed in the transfer region 30 so that the press cover 25 is pressed in this area to the center axis 39 of the press roller 24, similar to the case in the region of the extended press nip 26. By changing the immersion depth of the press jacket 25, the length of the extended transfer nip 32 can be changed.

In the interior of the press roll 24, an overpressure is applied, by means of which the circulating press jacket 25 is stabilized. The end faces of the press roll 24 have corresponding sealing cover.

The backing roll 23 of the long-nip press unit 29 may have grooves in the cross-machine direction to improve the drainage. The grooves should be as narrow as possible and be arranged as close together as possible, this can significantly improve the drainage. A groove width smaller than 0.5 mm, especially smaller than 0.4 mm, and a groove number of 5 or more grooves per cm in the circumferential direction of the backing roll 23 is desirable. The surface of the mantle roll 23 may for example be made of a hard elastomer or of metal, in these materials, the grooves can be incorporated well.

In Fig. 4 are cleaning means 34 for cleaning the press jacket 25 after the transfer area 30 is provided. The cleaning devices 34 may be one or more scrapers or spray nozzles for a cleaning fluid such as water or air. The cleaning device 34 can also be used for the web removal during the transfer of the fibrous web 9. The fibrous web 9 can be removed from the press cover 25, for example, be scraped, and a Pulper are fed until the web run has stabilized and the fibrous web 9 of the dryer section can be supplied.

In addition, an interface regulation mixture can be applied to the surface of the press jacket 25 before the press cover 25 passes through the extended press nip 26. The application can be carried out for example by a spray bar 35 with spray nozzles which spray the Grenzflächenregulierungsgemisch on the press cover 25. By this method step, the surface adhesion of the fibrous web 9 can be influenced on the press cover 25.
Interfacial control mixtures include, but are not limited to, all fluids used to surface finish Yankee cylinders 7, as well as TAD chemicals.

The dewatering of the fibrous web 9 in the extended press nip 26 can also be improved by heating the fibrous web 9, for example by means of a steam blower box 36, which is arranged in front of the extended press nip 26.
The adjustable felt guide roll 40 is also shown.

Fig. 5 shows a board machine according to Fig. 2 However, this time with the long-nip press unit 29 according to the invention. The transfer of the fibrous web 9 from the press cover 25 is effected directly onto the dryer wire 21 of the dryer section 12. The fibrous web transfer in the extended transfer nip 32 is assisted by the drawn-through roller 28. The length of the extended transfer nip 32 can be controlled by the immersion depth of the evacuated roll 28 into the nip roll 24.

A comparison with Fig. 2 shows that the press felt 14c is no longer needed in the board machine according to the invention.

In the extended press nip 26, a precisely defined press profile can act on the fibrous web 9. Such a press profile of a Langnip press unit 29 is in Fig. 6 shown as curve 37. Curve 38 shows a press profile of a press unit with standard rollers without extended press nip 26. The adjustable felt guide 40 also allows adjustment of the contact surface or the contact length between felt 33 and fibrous web 9 after the extended press nip 26th
Again, a steam blower box (not shown) may be provided for heating the fibrous web 9 in front of the extended press nip 26.

In the long-nip press unit 29, the smallest possible pressing pressure on the fibrous web 9 should preferably act on entry of the fibrous web 9 into the extended press nip 26. This pressing pressure then rises slowly, as can be clearly seen from the curve 37 in FIG Fig. 6 is apparent. By this gentle increase of the pressing pressure, the specific volume (bulk) of the fibrous web 9 is maintained. With increasing dry content of the fibrous web 9, the pressing pressure for further dewatering can be increased, without thereby the bulk is significantly affected. At a dry content of 40 to 50%, the pressing pressure reaches a maximum. At the end of the extended press nip 26, the pressing pressure should drop as quickly as possible, since this largely prevents or minimizes rewetting of the fibrous web 9 by the felt 33.

The embodiments shown in the drawings represent only a preferred embodiment of the invention. The invention also includes other embodiments in which, for example, the press cover 25 is partially wrapped in the transfer region 30 by the transfer fabric 27. This also forms an extended transfer nip 32 for the transfer of the fibrous web 9. It is also conceivable that the transfer element (31) is a roller.

Claims (14)

1. Process for treating a pulp web (9) in a paper or board machine in a long-nip pressing unit (29) with a press roll (24) that is designed as a shoe press roll and has a rotating pressing shell (25) and a opposing roll (23), where the pulp web (9) is dewatered in an extended press nip (26) between the opposing roll (23) and the pressing shell (25) of the press roll (24) and where the pulp web (9) is guided after the extended press nip (26) on the rotating pressing shell (25) of the press roll (24) to a transfer zone (30) in which the pulp web (9) from the pressing shell (25) is passed to a transfer element (31, 27), characterised by the pulp web (9) being carried on a felt (33) to and through the extended press nip (26).
2. Process according to Claim 1, characterised by the pulp web (9) being passed from the pressing shell (25) to a transfer fabric (27) in the transfer zone (30).
3. Process according to one of Claims 1 or 2, characterised by transfer of the pulp web (9) to the transfer element (31, 27) being assisted by a roll to which suction is applied.
4. Process according to one of Claims 1 to 3, characterised by the felt (33) being separated from the pulp web (9) immediately after the extended press nip (26).
5. Process according to one of Claims 1 to 4, characterised by the felt (33) having a three-dimensional structure and by the pulp web (9) being pressed into this three-dimensional structure in the extended press nip (26).
6. Process according to one of the preceding claims, characterised by the transfer element (31, 27) having a speed differential towards the pressing shell (25) when the pulp web (9) is passed from the pressing shell (25) to the transfer element (31, 27).
7. Process according to one of the preceding Claims, characterised by the pulp web (9) being heated by means of a steam blow box (36) located in front of the extended press nip (26).
8. Press arrangement of a paper or board machine for treating a pulp web (9), where the pulp web (9) is fed through an extended press nip (26) of a long-nip pressing unit (29), where the long-nip pressing unit (29) contains a press roll (24) designed as a shoe press roll with a rotating pressing shell (25) and an opposing roll (23), where the pulp web (9) is guided after the extended press nip (26) on the pressing shell (25) of the press roll (24) to a transfer element (31, 27) that receives the pulp web (9), characterised by the pulp web (9) being carried on a felt (33) to and through the extended press nip (26).
9. Press arrangement according to Claim 8, characterised by the transfer element (31, 27) being a transfer fabric (27).
10. Press arrangement according to Claim 9, characterised by the transfer fabric (27) being structured.
11. Press arrangement according to one of Claims 9 or 10, characterised by the transfer fabric (27) being permeable.
12. Press arrangement according to one of Claims 8 to 11, characterised by there being an extended transfer gap (32) for pulp web transfer between the pressing shell (25) and the transfer element (31, 27).
13. Press arrangement according to Claim 12, characterised by suction being applied to the extended transfer gap (32) between pressing shell (25) and transfer element (31, 27).
14. Press arrangement according to one of Claims 8 to 13, characterised by the position of a felt roll (40) round which the felt (33) is deflected after the extended press nip (26) being able to be set in such a way that the contact area between the felt (33) and the pulp web (9) after the extended press nip (26) can be adjusted as a result.

Images