DE102011004565A1 - Press section of a machine for producing a fibrous web - Google Patents

Abstract

The invention relates to a press section for dewatering in a machine for producing a fibrous web (1), in particular a paper, cardboard or tissue web, with a shoe press nip (8) formed from a press roll (2) and a counter roll (3), wherein the pressing roller (2) has a circumferential flexible jacket, a supporting stationary yoke, a pressing element (4) and pressing devices, and wherein the pressing devices press the pressing element (4) onto the jacket (7) and thus the jacket (7) onto the counter roll ( 3) press on, and a collecting trough (20.1, 20.3, 20.4) is provided after the shoe press nip (8) in the web running direction; the jacket (7) is grooved, the length of the grooves in the circumferential direction being greater than the nip length (L), and in front of the shoe press nip (8) on the side of the press roller (2) is a collecting trough (10.1, 10.2, 10.3, 10.4 ) is provided so that a large amount of water splashes back against the direction of web travel from the shoe press nip and contributes to improving the drainage performance.

Description

The invention relates to a press section for dewatering in a machine for producing a fibrous web, in particular a paper, board or tissue web, with a shoe press nip formed from a press roll and a counter roll, wherein the press roll a rotating flexible jacket, a supporting stationary yoke, a pressing member and pressing means, and wherein the pressing means press the pressing member to the jacket and thus the jacket to the counter roll.

The fibrous web is passed through the nip together with a felt or between two felts. By the pressing force with which the press roll and the counter roll are pressed against each other, water from the web is pressed into the felt.

Such a press section is known for example from the document EP 1072721 A1 , which describes a press section with only a single shoe press nip. It is also described that after the shoe press nip on the press felt a channel for collecting the squeezed out water, which is thrown off the jacket of the press roll, is provided.

The shoe press nip has an extended compared to simple Walzenpressnips press zone. The nip length is synonymous with the length of the press zone, which is given by the pressing element, the so-called shoe. This results in the fibrous web when passing through the press a longer residence time in the nip, ie in the press zone. And thus more water can be squeezed out. In order to absorb the many water in the nip and to be able to transport it to the nipples, the jacket is provided with grooves or blind holes. For very high dewatering volumes, an ever-increasing storage volume is needed and therefore coats with blind holes or with a combination of blind holes and grooves are used. At the same time, however, the coat must not mark with its pattern, whereby the optimization is limited.

Under certain conditions u. a. too high pressing force or hydraulic overload of the press nip also leads to uncontrolled ejection of water from the nip, which is always avoided as undesirable, as a result, the moisture profile is adversely affected or the paper web is suppressed. According to popular opinion, the water in the nip should be pressed into the cavities of the shell and the felt and be thrown off the nip or sucked out of the felt. Up to now, coats with a large storage volume have always been developed for high dewatering volumes in order to achieve a low hydraulic pressure in the nip.

The object of the invention is now to provide an improved press section for efficient drainage of higher amounts of water with as few press nips.

The object is achieved in that the shell of the press roll is grooved, wherein the length of the grooves in the circumferential direction is greater than the nip length, and characterized in that in the web running direction in front of the shoe press nip on the side of the press roll a drip pan is provided. In the grooves of the shell, a high hydraulic pressure is generated, so that water also splashes against the web running direction in larger quantities from the nip. For this to be possible, the grooves in the web running direction must be longer than the nip length. In the embodiment of the press section according to the invention, the water is injected back evenly over the web width, so that no displacements and no uneven drainage occur. At the same time, the water jet must now also be collected in a suitable collecting trough, so that the water can not flow back onto the felt and thus no deterioration of the moisture cross profile occurs. By this additional unused drainage direction against the web running direction more water can be dissipated.

The width of the grooves transversely to the web running direction is preferably 0.5-2 mm, so there is no risk of marking the fibrous web. Furthermore, the jacket preferably has no blind holes in order to be able to use the effect as well as possible.

In pilot plant trials it was confirmed that the dewatering performance can be increased significantly and evenly - without quality problems in the fibrous web. By means of the press section according to the invention, the so-called tray drainage can be intensified in high-speed paper machines and can only be achieved at slow speeds. With trough drainage is called when the squeezed water is not transported mainly in felts from the nip and discharged to suction elements, but when the squeezed water transported in the storage volume of the shell and the backing roll from the nip and then spun in drip trays. This is particularly efficient because it reduces the rewet from a felt to the fibrous web.

Also for the quality of the fibrous web advantages can arise. Due to the increased drainage already at the beginning of the shoe press nip, the fibrous web can be stronger overall be compressed, resulting in some paper webs such. As newsprint or packaging paper is desired to achieve a high gap strength.

Particularly advantageous effect of the present invention, when the press section has only a single press nip and thus all water must be squeezed out in this shoe press nip. As a result, investment and operating costs can be saved, and nevertheless a high dewatering performance can be achieved.

But even if the press section has a further shoe press nip, which is preferably downstream of the shoe press nip according to the invention in the web running direction, for example in so-called tandem presses, the total dewatering performance can be increased and thus drying energy can be saved in a subsequent dryer section.

The invention can be used particularly positively in press sections in which the shoe press nip is designed for a pressing force of at least 600 kN / m, preferably of at least 800 kN / m, since particularly much water is obtained here.

In a preferred embodiment of the described press section, the press roll is arranged above the paper web and the counter roll below the paper web.

Overall, it is helpful if the shoe press nip is covered with two felts, a top felt and an underfelt, and the fibrous web between these two felts is passed through the nip. The felt or felts can also be designed as drainage tapes. The invention is also applicable if only one felt is present. Second, an impermeable belt may then be provided.

It is advantageous if the shoe press nip is covered with a first felt, which lies in the nip between the fibrous web and press roll and which is designed with a predominantly non-woven basic structure, a so-called scrim, wherein the basic structure at least two layers, preferably at least three Has layers. Due to the relatively tightly packed non-woven basic structure in contrast to fabrics, a low internal storage volume in the felt is achieved. This promotes the drainage of the water from the felt into the grooves of the shell and enhances backfeeding against the web running direction. Such a type of felt is also referred to as a tub drainage type. The basic structure should contain at least 2/3 non-woven portion and only a small amount of woven structure. The basic structure is responsible for the tensile strength of the felt in the web running direction and across the web running direction.

Furthermore, it is advantageous if the shoe press nip is covered with a second felt which lies in the nip between the fibrous web and the counter-roller and which is designed with a predominantly woven basic structure, the basic structure having at least two layers, preferably at least three layers. Due to the woven basic structure, the felt gets a higher inner storage volume. Such felts are also referred to as a tube trough dewatering type.

In a basic structure containing two layers of thread, a third layer may be provided, which is formed as a membrane, that is, as a perforated or perforated polymer film, or as a random web, that is, as a nonwoven without preferred fiber orientation. The third layer can be arranged between the two thread layers of the basic structure or above or below the two thread layers. If the third layer is a random web, it is also possible for one or both thread layers to be embedded in the random web.

Furthermore, a first felt together with the fibrous web and a second felt should wrap around the mating roll and at a length of at least 30 mm before the start of the nip, d. H. the press zone between press roll and counter roll. In addition, a second felt should wrap around the mating roll at an angle of at least 10 ° relative to the backing roll before the nip begins.

The drip pan should have a jammed edge, so that no water can flow back from the tub, and it should have a drain and preferably also a suction, so that the water and possibly also spray can be reliably dissipated. The trough preferably has a gradient behind the edge of the stowage, so that the water flows away from the shoe press nip. Furthermore, it makes sense for the removal of the large amount of water sprayed back against the web running direction, if the flow is so large that a quantity of water of at least 20 l per minute and per meter web width, preferably dissipated by at least 30 l per minute and per meter web width can be. Ie. at a web width of for example 8 m, this then corresponds to at least 160 l / min, preferably at least 240 l / min. With a basis weight of the web of 90 g / m ² and a web speed of 900 m / min, and a dry content increase of 22% to 45%, this corresponds to a proportion of more than 10%, preferably more than 16% based on the total in the press section squeezed amount of water.

The amount of water flowing back against the web running direction should preferably amount to at least 15%, particularly preferably at least 20%, of the total amount of water squeezed out upward.

In order to be able to catch as much of the back-splashed water, the drip tray should have an inlet edge which has at most 20 mm, preferably at most 10 mm distance from a first felt. This is made possible by a corresponding arrangement of the drip pan.

It is advantageous if the entire drip pan and / or the inlet edge is adjustable. For this purpose, suitable pivoting and adjusting devices can be provided.

By generating a larger pressure pulse at the beginning of the nip the back-injected amount of water can be increased. This is possible when the pressing element is designed so that a pressure profile with a steep gradient in the inlet third, ie in the first third of the nip length, is generated. The gradient G in the upstream third is described by the ratio of the pressure p to one third of the nip length to the peak pressure p _max in the pressure profile based on the ratio 1/3. G = (p _1/3 / p _max ) / (L _1/3 ) / L) = (p _1/3 / p _max ) / (1/3)

The gradient G should have a value of at least G = 1.35, preferably at least G = 1.50, particularly preferably at least G = 1.80.

The distribution of the squeezed amount of water upwards and downwards or forwards and backwards, however, depends strongly on the pressing force, the production speed and the basis weight of the fibrous web.

In the state of the art, it has hitherto always been advisable to have as gentle a rise as possible at the beginning of the pressure profile in order to avoid displacements and uneven drainage.

An additional possibility to contribute to a desired high hydraulic pressure in the grooves of the shell at the beginning of the shoe press nip is, when a smaller depth of the grooves is used of at most 1.5 mm, preferably at most 0.9 mm, particularly preferably 0, 7 mm.

Furthermore, a larger pressure pulse at the beginning can also be achieved if the pressing element is designed such that a two-zone pressure profile with two local pressure maxima can be generated, wherein the second pressure maximum in the web running direction should be higher than the first pressure maximum in order to achieve a good overall dewatering performance , Between the two pressure maxima, the pressure should be at least 5%, preferably at least 10%, particularly preferably at least 15% below the value of the first maximum pressure in a partial region.

The pressing element is preferably a continuous shoe width over the width of the web, which is pressed by a plurality of pressing elements, which are arranged side by side in the web running direction, is pressed. The pressing elements are generally preferred hydraulic pressure elements.

This results in the advantage that the pressure profile can be adapted to different operating conditions. These different operating conditions can be caused for example by changes in the basis weight of the fibrous web, the speed, the pressing force, the felt or the fiber raw material.

The pressing element can be advantageously pressed by at least two rows of pressing elements, which are arranged one behind the other in the web running direction. As a result, the pressure profile can be adjusted accordingly. This is especially true when a bending soft executed in the web running direction pressing element is used.

In order to achieve an even better adjustability, the pressing element can consist of two pressing elements which can be pressed against one another and are arranged one behind the other in the direction of web travel. In particular, when working with a pressure profile with two local pressure maxima, this solution is advantageous.

By way of embodiments, further advantageous features of the invention will be explained with reference to the drawings. They point in

1 a possible embodiment of a press section according to the invention

2 a section of an arrangement according to the invention

3 a further embodiment of a press section according to the invention

4 Yet another embodiment of a press section according to the invention

5a schematic plan view of a non-woven basic structure (a Geleges) with two layers

5b schematic plan view of a woven basic structure with two layers

5c schematic cross section of a felt with non-woven basic structure

6a Example of a steep pressure profile

6b Example of a two-zone pressure profile with two local pressure maxima

The figures are described in more detail below.

In the execution according to 1 becomes the shoe press nip 8th through the overhead press roll 2 and the underlying mating roll 3 educated. The pressing element shown here only in one piece 4 is pressed by the pressing elements, not shown, from the inside against the mantle and thus produces an extended press nip. The fibrous web 1 runs along with the first felt 5 and the second felt 6 through the press nip and is drained there. The special design of the grooved jacket of the press roll 2 already squeezed out at the beginning and sprayed against the web running direction water is in the drip tray 10.1 collected and over the drain 12.1 derived. Any accumulating spray is via the suction 14.1 aspirated. The drip pan can be swiveled and adjusted via the adjusting devices 15.1 and 16.1 , As a result, an exact alignment of the tip or inlet edge as close as possible to the felt 5 possible. With a suitable design of the inlet edge, this can also be in contact with the felt 5 be. So all the water that is injected back from the Nipeinlauf, is collected. The water in the further course of the shoe press nips 8th is pressed, after leaving the nip from the coat 7 the press roll 2 and from the felt 5 thrown off and in the further drip tray 20.1 collected and about the processes 22 . 22.1 derived. Again, there is a suction 24.1 intended. In addition, there is a cleaning spray pipe 28.1 and a Wasserabstreifeinrichtung 27.1 to the grooved coat 7 to condition well. Also the further drip tray 20.1 is with adjusting devices 25.1 . 26.1 equipped. In this example encloses the further drip tray 20.1 the press roll 2 on a large part of the circumference, as it is often found in conversions. As well as the counter roll 3 and the second felt 6 Water can be thrown off, even after the counter roll 3 below the felt 6 yet another, not shown here catch basin are provided.

2 shows a detail with details on the drip tray 10.2 , Shown is the rope edge 11 that prevents water from falling back onto the felt 5 and on the fibrous web 1 can flow, and the subsequent gradient to the end 12.2 , The leading edge 13 has a distance c from the first felt 5 , The second felt 6 wraps around the counter roll 3 at an angle α before the shoe press nips 8th , synonymous with the press zone between pressing element 4 or coat 7 the press roll 2 and the counter roll 3 , The first felt 5 wraps around with the fibrous web 1 and the second felt 6 the counter roll 3 on a length b.

3 represents a further embodiment of the invention, in which the drip pan 10.3 in front of the shoe press nip 8th with the drip tray 20.3 after the shoe press nip 8th Thus, the entire press roll is 2 enclosed. It is advantageous if, as shown in the illustration, both drip pans 10.3 . 20.3 are adjustable. Serve the adjustment 15.3 . 16.3 . 25.3 . 26.3 , Here, in addition, another catchment tray after the counter roll 3 on the bottom of the second felt 6 be provided.

4 shows yet another version with a drip tray 10.4 after the shoe press nip and another drip tray 20.4 in front of the shoe press nip, which is smaller, as you would expect in a new construction of a press section. This version can be built very compact.

In 5a and 5b Examples of a basic structure of a felt are shown. 5a shows a non-woven structure, a layer of two layers 9a . 9b , The layers are formed from threads which may consist of several monofilaments of twisted individual threads or consisting of multifilament threads or of multifilament threads. 5b shows in contrast a woven basic structure of a felt, also two-ply 9c . 9d , A basic structure with two layers of thread and a third layer, which is formed as a membrane, or as a random web, is not shown separately, but can also be provided according to the invention.

5c schematically represents a possible structure of a felt. In essence, a three-layer non-woven basic structure 9a ' . 9 b ' . 9e and on the top and bottom each have a nonwoven layer 9f . 9f ' , which itself can consist of several layers. It can be between the nonwoven layer 9f . 9f ' and the base structure also be provided further intermediate layers. Again, an additional membrane or a random web may be arranged in, on or under the basic structure, which are not shown.

In 6a is an example of a pressure profile p with steep gradient G shown in the upstream third. After one third of the Niplänge L becomes one Pressure p1 / 3 reached, which is disproportionate. The gradient G is defined as G = (p _1/3 / p _max ) / (1/3)

In an embodiment according to the invention, the pressing element is designed and pressed in such a way that a steep gradient G results in the inlet-side third with a value of at least G = 1.35, preferably at least G = 1.50, particularly preferably at least G = 1.80 ,

6b represents a possibility for a two-zone pressure profile p ', with a first local pressure _maximum p _max ' and a second local and simultaneously absolute pressure _maximum p _max ''. The first local pressure maximum ensures controlled back splash at the beginning of the nip. By varying the contact pressure of the first and second part of the pressing element, which together form the nip length L ', or a flexible pressing element with the nip length L', the height of the two local maxima can be controlled, so that an optimum dewatering is achieved. Here, too, a steep gradient G is preferably used. Between the first and the second local pressure maximum, there is a region in which the pressure is at least 5%, preferably at least 10%, particularly preferably at least 15% lower than the first pressure _maximum p _max '.

LIST OF REFERENCE NUMBERS

1

paper web

2

press roll

3

backing roll

4

Pressing element (so-called shoe)

5

first felt

6

second felt

7

Coat of the press roll

8th

shoe press nip

9a, 9c, 9a '

first location of the basic structure

9b, 9d, 9b '

second position of the basic structure

9e

third layer of the basic structure

9f, 9f '

Non-woven layer

10.1, 10.2, 10.3, 10.4

Drip tray in front of the shoe press nip

11

collecting edge

12.1, 12.2, 12.3, 12.4

procedure

13

leading edge

14.1, 14.3

suction

15.1, 15.3, 15.4

adjustment

16.1, 16.3, 16.4

further adjustment

20.1, 20.3, 20.4

further drip tray

22, 22.1, 22.3, 22.4

procedure

24.1, 24.3

suction

25.1, 25.3, 25.4

adjustment

26.1, 26.3, 26.4

further adjustment

27.1, 27.3, 27.4

water wiper

28.1, 28.3, 28.4

spray wand

α

Umschlingwinkel

b

Umschlinglänge

c

distance

G

Gradient of the pressure profile in the first third

L, L '

nip length

p, p '

pressure profile

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1072721 A1 [0003]

Claims (16)

Press section for dewatering in a machine for producing a fibrous web ( 1 ), in particular a paper, board or tissue web, with a shoe press nip ( 8th ) formed from a press roll ( 2 ) and a counter-roller ( 3 ), wherein the press roll ( 2 ) a circumferential flexible jacket, a supporting stationary yoke, a pressing element ( 4 ) and pressing devices, and wherein the pressing devices are the pressing element ( 4 ) to the coat ( 7 ) and thus the coat ( 7 ) to the counter roll ( 3 ), and wherein after the shoe press nip ( 8th ) in the web running direction a collecting tray ( 20.1 . 20.3 . 20.4 ) is characterized in that the jacket ( 7 ) is grooved, wherein the length of the grooves in the circumferential direction is greater than the nip length (L), and that in front of the shoe press nip ( 8th ) on the side of the press roll ( 2 ) a drip tray ( 10.1 . 10.2 . 10.3 . 10.4 ) is provided. Press section according to claim 1, characterized in that the press section only a single press nip namely the shoe press nip ( 8th ) having. Press section according to claim 1, characterized in that the press section has a further shoe press nip, which preferably in the web running direction after the shoe press nip ( 8th ) is arranged. Press section according to one of the preceding claims, characterized in that the shoe press nip ( 8th ) with a first felt ( 5 ) covered between fibrous web ( 1 ) and press roll ( 2 ), the first felt ( 5 ) is executed with a predominantly non-woven basic structure, a so-called scrim, and wherein the basic structure at least two layers ( 9a . 9b ), preferably at least three layers ( 9a ' . 9 b ' . 9e ) having. Press section according to one of the preceding claims, characterized in that the shoe press nip ( 8th ) with a second felt ( 6 ) covered between fibrous web ( 1 ) and counter roll ( 3 ), the second felt ( 6 ) is executed with a predominantly woven basic structure and wherein the basic structure at least two layers ( 9c . 9d ), preferably at least three layers. Press section according to one of the preceding claims, characterized in that a first felt ( 5 ) together with the fibrous web ( 1 ) and a second felt ( 6 ) the counter roll ( 3 ) already before the shoe press ( 8th ) between mating roll ( 2 ) and press roll ( 2 ), at a length (b) of at least 30 mm. Press section according to one of the preceding claims, characterized in that a second felt ( 6 ) the counter roll ( 3 ) already before the shoe press ( 8th ) between mating roll ( 3 ) and press roll ( 2 ) wraps around, and at an angle (α) of at least 10 ° with respect to the backing roll ( 3 ). Press section according to one of the preceding claims, characterized in that the collecting trough ( 10.1 . 10.2 . 10.3 . 10.4 ) a jammed edge ( 11 ) and a process ( 12.1 . 12.2 . 12.3 . 12.4 ) and preferably also a suction ( 14.1 . 14.3 ) having. Press section according to claim 8, characterized in that the sequence ( 12.1 . 12.2 . 12.3 . 12.4 ) is designed so large that a quantity of water of at least 20 l per minute and per meter of web width, preferably of at least 30 l per minute and per meter web width can be dissipated. Press section according to one of the preceding claims, characterized in that the collecting trough ( 10.1 . 10.2 . 10.3 . 10.4 ) an inlet edge ( 13 ), wherein the collecting trough is arranged or adjustable so that the inlet edge ( 13 ) at most 20 mm, preferably at most 10 mm distance to a first felt ( 5 ) Has. Press section according to one of the preceding claims, characterized in that the pressing element ( 4 ) is designed so that a pressure profile (p, p ') can be generated in the web running direction, which has a gradient G in the upstream third of at least G = 1.35, preferably at least G = 1.50, particularly preferably at least G = 1, 80 has. Press section according to one of the preceding claims, characterized in that the depth of the grooves of the shell ( 7 ) is at most 1.5 mm, preferably at most 0.9 mm, particularly preferably at most 0.7 mm. Press section according to one of the preceding claims, characterized in that the pressing element ( 4 ) is designed so that a two-zone pressure profile (p ') can be produced with two local pressure maxima, wherein the second maximum pressure in the web running direction is higher than the first pressure maximum. Press section according to claim 13, characterized in that the pressing element ( 4 ) is designed so that a pressure profile (p, p ') can be generated, wherein the pressure in a partial area between the first pressure maximum and the second pressure maximum at least 5%, preferably at least 10%, more preferably at least 15% below the first Maximum pressure is. Press section according to one of the preceding claims, characterized in that at least two rows of pressing elements, arranged in the web running direction one behind the other, are provided which hold the pressing element ( 4 ) to the coat ( 7 ) to press. Press section according to one of the preceding claims, characterized in that the pressing element ( 4 ) consists of two different pressable one another, in the web running direction successively arranged part-pressing elements.

Images