EP0852273A2 - Dewatering press - Google Patents

Abstract

The press section for a fibre web, especially for the production of paper or cardboard, has an extended press gap (3) between a press belt (4) at a shoe press unit (5) and a counter surface (6). The web (1) has a dwell time of ≤ 12 mu seconds in the extended press gap (3).

Description

The invention relates to a dewatering press of a machine for manufacturing a fibrous web, in particular paper and / or cardboard web, with at least an extended nip in the web running direction, which is between a rotating flexible press belt of a Schunpreßeinheit and a counter surface against which the flexible press belt by at least one of the shoe press unit assigned press shoe is pressable, the press nip length at least in essentially by the length of the press shoe measured in the web running direction Shoe press unit is determined, and the fibrous web with at least one drainage belt runs through the extended press nip.

Such drainage presses have been around for a long time, for example from the DE-PS 22 62 201, DE-PS 34 10 172 or EP-PS 258 169 known and in Commitment. Due to the long dwell time of the fibrous web in the press nip, this could Drainage result can be significantly improved. However, they always require larger press areas of the long press nips also ever higher contact forces to ensure a certain pressure. This leads to a very high technical effort and thus also at considerable costs.

The aim of the invention is therefore a dewatering press of the type mentioned Kind to create a sufficient with the least possible technical effort good drainage of the fibrous web guaranteed.

According to the invention the object was achieved by the dewatering press described in claim 1 solved, the subclaims special forms of performance represent. By realizing that within a dwell time of 12 ms, especially the most essential part of the possible drainage capacity of 6 ms is reached, one is able to expand the press nip and thus to limit the press shoe in the direction of web travel. The dwell time is generally the length of the press nip and the speed of the fibrous web certainly.

As for the drainage process, i.e. H. squeezing the water out of the Fibrous web in the dewatering belt a minimal pressure available Optimization of the press shoe length also results in a minimization the contact pressure to be applied by the shoe press unit.

For this purpose, it was determined that for effective dewatering, depending on the dry content of the fibrous web, a pressing pressure of more than (T _abs x 100) ³ N / m ² (T _abs - absolute dry content at the beginning of the press nip, for example T _abs = 0.2 at 20% input dry matter) is required. In this context, it has been found that the pressure should be greater than 500 KN / m ² .

On the other hand, in order to achieve an acceptable drainage rate in the Press nip, of course, also to ensure a minimum dwell time. This lies at 2 ms, preferably even at 4 ms.

There are many options for the design of the press nip, including several Drainage belts can run through the press nip. On the one hand can the extended nip of a flexible press belt Shoe press unit are formed, which against a cylindrical and under Circumference-controlled roll is pressed, the press shoe the shoe press unit has a concave contact surface. On the other hand, the Press nip can also be formed by two shoe press units, the press surface is preferably flat.

In addition, the press shoe can one or both shoe press units from several Smaller ones arranged axially and / or in the web running direction Press shoes exist. At least some of the smaller press shoes can be used be designed to be independent of each other.

To determine the press nip length and thus also the dwell time, the section or sections of the press nip in which the press pressure is greater than (T _abs x 100) ³ N / m ² and in particular greater than 500 KN / m ² are particularly decisive.

Figur 1

einen verlängerten Preßspalt 3 zwischen einer Schuhpreßeinheit 5 mit einem Preßschuh 7 und einer zylindrischen Gegenwalze 9;

Figur 2

einen verlängerten Preßspalt 3 zwischen einer Schuhpreßeinheit 5 mit zwei kleineren Preßschuhen 7' und einer zylindrischen Gegenwalze 9;

Figur 3

einen verlängerten Preßspalt 3 zwischen einer Schuhpreßeinheit 5 mit zwei kleineren Preßschuhen 7' und einer weiteren Schuhpreßeinheit 5 mit einem Preßschuh 7;

Figur 4

einen Druckverlauf im Preßspalt gemäß Figur 1;

Figur 5

einen Druckverlauf im Preßspalt gemäß Figur 2 und

Figur 6

einen Druckverlauf im Preßspalt gemäß Figur 3.

The invention will be explained in more detail below using three exemplary embodiments. The attached drawing shows:

Figure 1

an extended press nip 3 between a shoe press unit 5 with a press shoe 7 and a cylindrical counter roll 9;

Figure 2

an extended press nip 3 between a shoe press unit 5 with two smaller press shoes 7 'and a cylindrical counter roll 9;

Figure 3

an elongated press nip 3 between a shoe press unit 5 with two smaller press shoes 7 'and a further shoe press unit 5 with a press shoe 7;

Figure 4

a pressure curve in the press nip according to Figure 1;

Figure 5

a pressure curve in the press nip according to Figure 2 and

Figure 6

3 shows a pressure curve in the press nip according to FIG. 3.

Common to all of the exemplary embodiments is that the dewatering press consists of at least one press nip 3 which is elongated in the web running direction 2 and which is formed between a rotating flexible and water-impermeable press belt 4 of a shoe press unit 5 and a counter surface 6 against which the flexible press belt 4 by at least one of the shoe press unit 5 assigned press shoe 7 or 7 'can be pressed. The press nip length l _p is essentially determined by the press shoe length of the shoe press unit 5 measured in the web running direction 2. The fibrous web 1 runs together with at least one water-absorbing drainage belt 8 through the extended press nip 3.

The exact structural design of the shoe press units 5 and the counter roller 9 are generally known and can also be used, for example, in the introduction to the description mentioned documents are taken. The pressure the press shoes 7 and 7 'is preferably hydraulic and the lubrication between the press shoes 7 and 7 'and the press belts 4 hydrodynamically and / or hydrostatic.

While in Figure 1 a press shoe 7 with a concave contact surface Shoe press unit 5 the press belt 4 against a cylindrical counter roller 9 Formation of an extended press nip 3 presses there are two in Figure 2 in the direction of web travel 2 spaced apart and here also independent of each other controllable pressing small press shoes 7 '. Figure 3 in turn shows the formation a flat press nip 3 by means of two shoe press units 5, one of which Shoe press unit 5 a press shoe 7 and the other two smaller press shoes 7 '. About the press shoes 7 and 7 'is a flexible endless and water-impermeable drainage tape 4 out.

In addition, only one in FIGS. 1 and 2 and one on both in FIG Sides of the fibrous web 1 arranged and water-absorbing drainage belt 8, for example in the form of a felt, passed through the press nip 3. This is only intended to indicate the various design options, the concrete form of implementation of several factors, such. B. the paper type and depends on the dryness. At the present time usual speeds v from 600 to 1500 m / min mostly press shoes 7 with a length of 25 to 35 cm. That especially at higher speeds v Used press shoes 7 lead to the mentioned Disadvantages.

Based on the knowledge that the most essential part of the dewatering process after a dwell time t _{w of} the fibrous web 1 in the extended press nip 3 of less than 12 ms, in particular even of 6 ms, a minimization of the press nip length l _{p is} made possible, which also leads to a Minimization of the contact pressure of the shoe press unit 5 leads. This not only has an energy saving but also a cost saving. which is based on the constructive design of the shoe press unit 5.

On the other hand, in order to achieve a sufficiently large drainage capacity but also a minimum dwell time of 2 ms, in particular 4 ms, is required.

Mainly when the press shoe 7 of a shoe press unit 5, as shown in FIGS. 2 and 3, consists of a plurality of smaller press shoes 7 ′ arranged side by side in the web running direction 2 with the very deep pressure sinks possibly present between them (FIGS. 2 and 5). if the press shoe 7 forms pressure sinks in the web running direction 2 or else has a smaller pressure gradient at the inlet and / or outlet of the press nip 3, a more precise determination of the press nip length l _p may be necessary or advantageous.

Starting from the recognition that an effective drainage, depending on the dry content of the fibrous web only at a pressing pressure p of _(abs T x 100) ³ N / m ² is effected, forming the p over this pressure _min exposed portions l _p1, l _p2 of Press nips 3 the press nip length decisive for the calculation of the dwell time l p = l p1 + l p2 . ( t w = l p / v = (l p1 + l p2 ) / v )

The dry content of the fibrous web 1 is generally between 0.2 and 0.6 at the inlet of the press nip 3. It is furthermore advantageous if the press nip length l _{p is determined} by the sections l _p1 , l _{p2 of} the press nip 7, in which the press pressure p is also greater than p _min = 500 KN / m ² .

Claims (9)

Dewatering press of a machine for producing a fibrous web (1), in particular paper and / or cardboard web, with at least one press nip (3) which is extended in the web running direction (2) and which is between a rotating flexible press belt (4) of a shoe press unit (5) and a counter surface (6) against which the flexible press belt (4) can be pressed by at least one press shoe (7) assigned to the shoe press unit (5), the press nip length (l _p ) being at least essentially determined by the press shoe length measured in the web running direction (2) Shoe press unit is determined, and the fibrous web (1) with at least one drainage belt (8) runs through the extended press nip (3),
characterized,
that the residence time t _{w of} the fibrous web (1) in the extended press nip (3) is less than 12 ms. Dewatering press according to claim 1,
characterized,
that the residence time of the fibrous web (1) in the extended press nip (3) is less than 6 ms. Dewatering press according to claim 1 or 2,
characterized,
that the residence time of the fibrous web (1) in the extended press nip (3) is greater than 2 ms, preferably greater than 4 ms. Dewatering press according to one of claims 1 to 3,
characterized,
that the counter surface (6) is formed by a roller (9), the press shoe (7) of the shoe press unit (5) forming a concave contact surface. Dewatering press according to one of claims 1 to 3,
characterized,
that the counter surface (6) is formed by a further shoe press unit (5), the contact surface preferably being flat. Dewatering press according to one of claims 1 to 5,
characterized,
that at least the press shoe (7) of a shoe press unit (5) consists of a plurality of smaller press shoes (7 ') arranged axially and / or in the web running direction (2). Dewatering press according to claim 6,
characterized,
that at least some of the smaller press shoes (7 ') can be pressed independently of one another. Drainage press according to one of claims 1 to 7,
characterized,
that the press nip length (l _p ) is essentially determined by the section or sections (l _p1 , l _p2 ) of the press nip (3) in which the press pressure p is greater than p min = (T Section x 100) 3rd N / m 2nd (T _abs - absolute dryness at the beginning of the press nip). Drainage press according to one of claims 1 to 8,
characterized,
that the press nip length (l _p ) is essentially determined by the section or sections (l _p1 , l _p2 ) of the press nip (3), in which the press pressure p is greater than p _min = 500 KN / m ² .

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