EP0608534B1 - Wet press for a papermaking machine - Google Patents

Abstract

The invention relates to a wet press for a papermaking machine for drying a wet paper web by pressing; - having a plurality of press rolls (9-13); - the press rolls form, respectively in pairs, a press nip with each other; - the paper web (4) is supported continuously by an envelope surface of a press roll on its path from the first to the last press nip of the press; The invention is characterised by the following features: - at leat four successive press nips are provided; - the press rolls (10, 11), which together form a felt-less second press nip (II), each have a closed envelope surface. <IMAGE>

Description

The invention relates to a wet press for a paper machine. Reference is made to the preamble of claim 1.

A press of this type has become known from US-A-4,556,451. This press comprises four press rolls which form an uninterrupted chain with one another, so that the paper web always wraps around a press roll on a part of its circumference as it passes through the press, and that a total of three press nips are formed. The four-roll press mentioned is preceded by a two-roll press which takes over the paper web coming from the wire of the paper machine.

A large number of press sections of various configurations have become known. US-A-2 694 348 describes a press section in which the paper web is first removed from the paper machine screen by means of a felt belt and is passed with this felt belt through a first two-roll press. A second felt, which also runs through the aforementioned two-roll press, takes over the paper web and guides it through a second two-roll press. The paper web is then removed from a third felt belt which passes through the second two-roll press; this third felt belt guides the paper web through a third two-roll press two-roll press. through, and further through a fourth This press section thus has a total of four press nips. Felt tapes are thus simultaneously passed through all press nips with the paper web. Between the individual press nips, the paper web is transported by the felts mentioned, namely on a route on which the felt web bridges a free path with the paper web located thereon or attached to it.

In general, the aim is to adapt wet presses or entire wet press sections to the high requirements of fast-running paper machines. Wet presses should generally have a high pressing efficiency, take up as little space as possible, especially when viewed in the running direction of the paper web and in the horizontal direction, and they should also have an inexpensive construction.

From DE-U-90 11 940 a wet press section according to the preamble of claim 1 is known, which is characterized by a compact design and a high drainage capacity.

With increasing speed of the paper machine there is the problem that the dewatering performance of the press section has to be increased, which cannot be done without increasing the number of press nips. However, this requires more space in the running direction of the paper machine. However, the increasing speed of modern paper machines also has other technical problems, e.g. when starting up the paper machine after a standstill, when a narrow paper strip has to be passed through the press section. Furthermore, the risk of tearing off the paper web increases with increasing speed of the paper machine. Another problem is the marking of the press felts in the still wet paper web. Finally, the wear of the press felts increases with increasing machine speed and with increasing line pressures in the press nips, so that these have to be replaced more frequently with new felts, which of course drives up the costs.

These problems were not optimally solved with the known devices according to the prior art. The invention is therefore based on the object of designing a wet press in accordance with the preamble of claim 1 in such a way that with high pressing efficiency and high Speeds a correct transfer of the narrow transfer strip or the completely wide paper web is ensured that the marking of sieves or borehole patterns of suction rolls in the damp paper web is reduced or is avoided, and that the felt wear is reduced.

This object is solved by the characterizing features of claim 1.

Figur 1

zeigt eine Pressenpartie mit einer Fünf-Walzen-Presse, die zwei Schuh-Preßwalzen enthält.

Figur 2

zeigt eine Pressenpartie mit einer Vier-Walzen-Presse, die eine Schuhpresse aufweist.

Figur 3

zeigt eine Pressenpartie, die u.a. eine Fünf-Walzen-Presse enthält; eine dieser Walzen ist wiederum eine Schuh-Preßwalze.

Figur 4

zeigt eine Pressenpartie mit einer Fünf-Walzen-Presse, die zwei Schuh-Preßwalzen enthält.

The invention is explained in more detail with reference to the drawing. The following is shown in detail:

Figure 1

shows a press section with a five-roll press that contains two shoe press rolls.

Figure 2

shows a press section with a four-roll press, which has a shoe press.

Figure 3

shows a press section, which includes a five-roll press; one of these rollers is in turn a shoe press roller.

Figure 4

shows a press section with a five-roll press that contains two shoe press rolls.

The following elements can be seen in detail in FIG. 1: A belt-shaped screen 1, which rotates in the direction of the arrow, wraps around a suction roller 2 and a deflection roller 3. The screen 1 carries a paper web 4, which is shown in broken lines.

A first felt 5 can also be seen, which is also designed as an endless loop. The felt 5 wraps around a number of guide rollers, of which the guide roller 6, the suction guide roller 7 and the guide roller 8 are shown, and also a press roller 9, which is part of the press.

Press roll 9 forms with a further press roll 10 a first press point I. Press roll 9 is a shoe press roll with a pressure shoe 9. 1 shown only schematically, with which a relatively long press nip is produced, as seen in the direction of wire travel. The contact shoe 9.1 is, in a known manner, displaceable in the radial direction relative to a stationary support body, not shown, so that the pressing force acting in the pressing point I can be varied. Through the press point I runs a tubular and flexible press jacket sliding over the pressure shoe; its outer surface can have fine recesses (eg blind holes) for temporarily storing water (the recesses are symbolically represented by a dashed line). Press roll 10 is followed by a third press roll 11. The two press rolls 10 and 11 touched by the paper web 4 form together a feltless second press nip II. Press roll 11 is adjustably mounted in the sense of double arrow 11 'for the purpose of varying the press force in press nip II. Press roller 11 is followed by a fourth press roller 12, which is also a shoe press roller with a pressure shoe 12.1. The rollers 11 and 12 together form a third press nip III. A fifth press roll 13, which is designed as a suction press roll, forms with press roll 11 a fourth press nip IV. Press roll 13 can be set against press roll 11 in the sense of the double arrow 13.1 or moved away from it, so that press nip IV is not required depending on the operating conditions.

Press roll 12 is located within the endless loop of a second press felt 14, which in turn is looped around guide rolls 15, 16, 17, etc. The flexible press jacket of the press roll 12 can also have fine recesses on its outside, especially if a relatively thin and finely woven press felt 14 is used, the water absorption capacity of which is relatively low.

Press roll 13 is located within the endless loop of a third press felt 18. This is guided around guide rolls, as around guide rolls 19, 20.

A dryer section is connected to the wet press in the usual way. In the present case, it is a single-tier dryer section. This includes a variety drying cylinders 21, 22, a plurality of deflection suction rolls 23, etc., each arranged between two drying cylinders, and a drying wire 24 with guide rolls 25, 26, etc. At the beginning of the drying section there is a deflection suction roll 27. This serves to remove the paper web 4 from the third press felt 18 to take off.

As can be seen, there are other elements, but they are not of primary importance for the invention. These include, for example, a scraper 10.1, which is assigned to the press roll 10, a scraper 11.1, which is assigned to the press roll 11, a reject discharge channel 10.2, which is located below the press roll 10.

As can be seen, the course of the paper web 4 is as follows: The paper web 4 is first removed from the wire 1 by means of the first press felt 5 and the pick-up roller 7. It then hangs at the bottom of the first press felt 5. Together with this, it passes through the first press nip I, then leaves the press felt 5, remains on the circumference of the press roll 10 until it reaches the second press nip II, then remains on the circumference of the press roll 11 until it is reached of the third press nip III and - if appropriate - the fourth press nip IV, and is then transferred by means of the deflection suction roll 13 to the third press felt 18, from which it is removed by the deflection suction roll 27 and passed through the dryer section with the dryer wire 24.

It is important here that the paper web 4 always adheres to the outer surface of one of the press rolls involved as it passes through the wet press, so that tearing off is practically impossible on this critical section of the paper web run.

It is also important that the press roll 10 has a relatively soft jacket, while the press roll 11 has a relatively hard coat. The change from the felted press nip I, formed from a shoe press, to the feltless press nip II, formed from completely smooth (closed) jacket surfaces, and further to the felted press nip III, again formed from a shoe press, has proven to be particularly favorable. Press felt 18 is expediently formed from a relatively fine fabric, so that the paper web 4 at the last press nip IV (if there is one) receives relatively little marking by the press felt 18. In other words: the underside of the paper web 4 remains relatively smooth on contact with the press felt 18.

The configuration shown in FIG. 2 is similar to that of FIG. 1. A part of the wire section with the wire 1, the wire suction roll 2, the deflecting roller 3, and the paper web 4 carried along on the wire 1 can again be seen. Here, too, a first press felt 5 is provided, which presses the paper web 4 through a first Press nip I passes between the rollers 9 and 10. Roll 9 is a press roll with a smooth, i.e. closed outer surface. Deviating from this, the outer surface of the roller 9 (for temporarily storing water) can also be provided with fine recesses, e.g. Circumferential grooves. The rest of the structure of the press is also very similar to that shown in FIG. 1. However, the fifth press roll 13 is a roll with a closed outer surface. The paper web 4 is delivered from the press roll 13 to the drying wire 24, the deflection suction roll 27 ensuring a reliable transfer.

The configuration shown in Figure 3 is designed up to the pick-up roller 7 analogous to the two previous configurations. This is followed by an upstream press with a press nip Ia, formed from two press rolls 30 and 31. Press roll 30 has a suction zone 30a in order to securely feed paper web 4 to press nip Ia to lead. Press roller 31 has a suction zone 31.1 in order to safely transfer the paper web 4 onto a second press felt 11 '.

As can be seen, the subsequent press again comprises five press rolls, namely rolls 9, 10, 11, 12 and 13. The roll 9 (with a smooth or grooved surface) is also located in the loop of the felt 11 '. Together with roller 10, it forms a press nip I. The rollers 10 and 11 together form a press nip II; the rollers 11 and 12 together form a press nip III; the rollers 11 and 13 together form a fourth press nip IV.

The roller 12 is located within the loop of a third press felt 17. The roller 13 is at the same time a suction deflecting roller and is used to transfer the paper web 4 onto a dryer fabric 18 of the downstream dryer section. The dryer section and its elements do not need to be described here, since they basically have the same structure as the dryer sections of the other two configurations.

Also in this press according to the invention, comprising the press rolls 9-13, the paper web 4 always follows the circumferences of the press rolls involved from the first press nip I to the last press nip IV. It never runs free. Here, too, the second press nip II of this press is formed from a roller with a relatively soft shell - here roller 10 - and from a roller with a hard shell - here roller 11. The roller 10 with a soft jacket is again arranged in front of the roller 11 with a hard jacket, as seen in the direction of travel of the paper web 4. Roller 12 (with a press jacket which is smooth on the outside or provided with recesses) is in turn a shoe press roller with a shoe 12.1.

The configuration shown in Figure 4 is the Similar to the first two configurations according to FIGS. 1 and 2, as here too the five-roll press shown is the only press and no two-roll press is connected upstream. However, it goes without saying that this could also be different. Another press could be connected upstream and another press could also be connected downstream.

One recognizes the five press rolls 9, 10, 11, 12, 13, which together form a total of four press nips I, II, III, IV. The first press roller 10 in contact with paper is now, in contrast to FIGS. 1 and 2, a shoe press roller, the tubular and flexible circumferential press jacket of which must therefore always be smooth. The roller 10 has a radially movable (and having a concave pressing surface) press shoe 10a, which forms the press nip I together with the preferably grooved press roll 9. In addition, the shoe press roll 10 has a radially movable bar 10b at the press nip II, preferably with a convex press surface. This bar 10b is used to open or close the press nip II and to vary the pressing force in the press nip II. Thanks to the movable bar 10b, the press roll 11 need not be adjustable, in contrast to the exemplary embodiments according to FIGS. 1 to 3. In other words: The four press rolls 9 to 12 can all be supported essentially rigidly on a foundation or on a machine frame. This results in an extremely simple and space-saving arrangement of the entire wet press.

As can be seen, the paper web 4 is removed from the screen 1 by means of the press felt 5 and the pick-up roller 7 and passed through the first press nip I with the felt 5. In contrast, the paper web 4 runs through the second press nip II alone, ie without felt. With press nip III it is again like with press nip I; here too, paper web 4 and a felt 14 run through it together Press nip. With press nip IV it is again like with press nip II: the paper web 4 runs alone through this press nip. This alternating path - first with felt, then without felt, then again with felt, and finally without felt - is very advantageous. Pressing out with felt allows a relatively intensive dewatering, but has the disadvantage of marking the felt fabric in the moist paper web, while the downstream press nip without felt ensures a smoothing of this previous felt marking.

A spray tube 13.1 is assigned to the press roller 13. It applies a water spray over the entire width of the roller to the outer surface of the roller 13 just before the press nip IV. This can, if necessary, ensure that the paper web continues to run behind the press nip IV with the roller 13. A scraper 13.2 cleans the outer surface of the roller 13.

Claims (7)

1. Wet press for a papermaking machine for pressing out a wet length of paper;

   1.1   with a plurality of press rollers;

   1.2   respective pairs of the press rollers form a press gap;

   1.3   the length of paper is on its way from the first to the last press gap of the press always supported by the casing surface of a press roller;

   1.4   at least four successive press gaps (I - IV) are provided;

   1.5   the press rollers (10, 11), which together form a feltfree second press gap (II), each have a sealed casing surface;

   characterised by the following features:

   1.6   the second press gap (II) is formed a press roller (10) of a relatively soft casing and a press roller (11) of a relatively hard casing;

   1.7   the press roller (10) with the soft casing is arranged in front of the press roller (11) with the hard casing, as seen in the moving direction of the length of paper (4).
2. Wet press according to Claim 1, characterised in that the fourth press gap (IV) is also formed by two press rollers (11, 13) with sealed casing surfaces.
3. Wet press according to one of Claims 1 - 2, characterised in that at least one of the press gaps is formed by a shoe press.
4. Wet press according to Claim 3, characterised in that the first and the third press gap are formed by a shoe press.
5. Wet press according to one of Claims 1 - 4, characterised in that at least one of the rollers (13) with sealed casing surface is associated with a spray pipe (13.1), which is arranged in front of the press gap (IV) formed by this roller and sprays moisture onto the casing surface of the roller (13).
6. Wet press according to Claim 1, characterised by the following features:

   a) the feltfree second press gap (II) is formed by a shoe-press roller (10), the flexible peripheral press casing of which comprises a smooth outer surface, and a normal press roller (11) with a smooth sealed casing surface;

   b) the shoe-press roller (10) has a concave press shoe (10a), which forms with a felted press roller (9) a first press gap (I), as well as a ledge (10b), which forms with a smooth press roller (11) a feltfree second press gap (II).
7. Wet press according to one of Claims 1 to 6, characterised in that the felt (5) which runs through the first press gap (I) runs in front of said press gap (I) over a pickup roller (7) for the purpose of pickup of the length of paper (4) from a sieve (1).

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