EP2678471B1 - Press section of a machine for producing a fibrous web - Google Patents

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 by 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, i.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 object is further achieved according to the invention by 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.

By generating a larger pressure pulse at the beginning of the nip the back-injected amount of water can be increased. This is possible by the pressing element according to the invention 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 after one third of the nip length to the peak pressure p _max in the pressure profile based on the ratio 1/3. $$\mathrm{G}=\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_{1/3}/{\mathrm{p}}_{\mathrm{Max}}\right)/\left({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">L</figure-callout>}}_{1/3}/\mathrm{L}\right)=\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_{1/3}/{\mathrm{p}}_{\mathrm{Max}}\right)/\left(1/3\right)$$

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 width of the grooves transversely to the web running direction is preferably 0.5-2 mm, so that there is no danger of marking the fibrous web. Furthermore, the Mantel prefers no blind holes 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 is transported in the storage volume of the shell and the backing roll from the nip and then thrown into 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 dewatering already at the beginning of the shoe press nip, the fibrous web can be more compacted overall, which in some paper webs such. Newsprint or packaging paper is desired to achieve a high nip strength.

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. Through the woven basic structure of 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 backing roll, at a length of at least 30 mm prior to the beginning of the nip, i. 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. That is, 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.

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. This allows the pressure profile adjusted accordingly become. 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.

Fig.1

eine mögliche erfindungsgemäße Ausführung einer Pressenpartie

Fig.2

einen Ausschnitt einer erfindungsgemäßen Anordnung

Fig.3

eine weitere erfindungsgemäße Ausführung einer Pressenpartie

Fig.4

noch eine weitere erfindungsgemäße Ausführung einer Pressenpartie

Fig.5a

schematische Draufsicht einer nicht-gewebten Grundstruktur (eines Geleges) mit zwei Lagen

Fig.5b

schematische Draufsicht einer gewebten Grundstruktur mit zwei Lagen

Fig.5c

schematischen Querschnitt eines Filzes mit nicht-gewebter Grundstruktur

Fig.6a

Beispiel für ein steiles Druckprofil

Fig.6b

Beispiel für ein zweizoniges Druckprofil mit zwei lokalen Druckmaxima

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

Fig.1

a possible embodiment of a press section according to the invention

Fig.2

a section of an arrangement according to the invention

Figure 3

a further embodiment of a press section according to the invention

Figure 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

5 b

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

Figure 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 Fig.1 the shoe press nip 8 is formed by the upper press roll 2 and the lower counter roll 3. The pressing element 4 shown here only in one piece 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 together with the first felt 5 and the second felt 6 through the press nip and is dehydrated there. The pressed out by the special design of the grooved jacket of the press roll 2 already at the beginning and sprayed back against the web running direction water is in collected the drip pan 10.1 and derived via the drain 12.1. Any resulting spray mist is sucked out via the exhaust 14.1. The drip pan is pivotable and adjustable via the adjusting 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 is possible. With a suitable embodiment of the leading edge, this can also be in contact with the felt 5. So all the water that is injected back from the Nipeinlauf, is collected. The water which is pressed out in the further course of the shoe press nips 8 is thrown off the jacket 7 of the press roll 2 and the felt 5 after leaving the nip and collected in the further drip pan 20.1 and discharged via the processes 22, 22.1. Again, a suction 24.1 is provided. In addition, there is a cleaning spray pipe 28.1 and a water wiper 27.1 to well condition the grooved jacket 7. The further collecting trough 20.1 is equipped with adjusting devices 25.1, 26.1. In this example, the further collecting trough 20.1 surrounds the pressing roller 2 on a large part of the circumference, as is often found in conversions.
Since the counter-roller 3 and the second felt 6 eject water, even after the counter-roller 3 below the felt 6 yet another, not shown here collecting tray can be provided.

Fig.2 shows a section with details of the drip pan 10.2. Shown is the storage edge 11, which prevents water can flow back to the felt 5 and the fibrous web 1, and the adjoining slope until the expiry 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 beginning of the shoe press nips 8, synonymous with the press zone between the pressing element 4 and coat 7 of the press roll 2 and the counter roll 3. Der first felt 5 wraps together with the fibrous web 1 and the second felt 6, the counter roll 3 over a length b.

Figure 3 represented a further embodiment of the invention, in which the drip pan 10.3 is combined in front of the shoe press nip 8 with the drip pan 20.3 after the shoe press nip 8. Thus, the entire press roller 2 enclosed. It is advantageous if, as shown in the illustration, both collecting trays 10.3, 20.3 are adjustable. Serve the adjustment 15.3, 16.3, 25.3, 26.3.
Here, too, a further collecting trough can be additionally provided after the counter-roller 3 on the underside of the second felt 6.

Figure 4 shows yet another embodiment with a drip pan 10.4 after the shoe press nip and another drip pan 20.4 in front of the shoe press nip, which is smaller, as you could provide for a new construction of a press section. This version can be built very compact.

In Fig. 5a and 5b Examples of a basic structure of a felt are shown.
5a shows a nonwoven structure, a scrim 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.
5 b 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 construction of a felt. In essence, a three-layer non-woven basic structure 9a ', 9b', 9e and on the top and bottom each have a nonwoven layer 9f, 9f ', which itself may consist of several layers. It can be provided between the nonwoven layer 9f, 9f 'and the basic structure also 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.

Das Presselement wird bei einer erfindungsgemäßen Ausgestaltung so ausgeführt und so angepresst, dass sich ein steiler Gradient G im einlaufseitigen Drittel mit einem Wert von mindestens G=1,35 , bevorzugt mindestens G=1,50 , besonders bevorzugt mindestens G=1,80 ergibt.In 6a is an example of a pressure profile p with steep gradient G shown in the upstream third. After one third of the nip length L, a pressure p1 / 3 is reached, which is disproportionate. The gradient G is defined as $$\mathrm{G}=\left({\mathrm{<figure-callout\; id="1"\; label="p"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">p</figure-callout>}}_{1/3}/{\mathrm{p}}_{\mathrm{Max}}\right)/\left(1/3\right)$$

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 ,

Figure 6b represents a possibility for a two-zone pressure profile p ', with a first local pressure _maximum p _max ' and a second local and at the same time absolute pressure _maximum p _max . "The first local pressure maximum ensures the controlled back-splash at the beginning of the nip and the 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 optimal dewatering is achieved, Here too, a steep gradient G is preferably used Between the first and the second local pressure maximum, there is an area 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

Claims (14)

1. Pressing section of a machine for producing a fibrous web (1), for dewatering, in particular, a paper, cardboard or tissue web, having a shoe pressure nip (8) formed from a press roll (2) and a counter-roll (3), the press roll (2) having a circulating flexible shell (7), a supporting stationary yoke, a pressing element (4) and pressure devices, and the pressure devices pressing the pressing element (4) onto the shell (7) and therefore the shell (7) onto the counter-roll (3), and a collecting trough (20.1, 20.3, 20.4) being provided downstream of the shoe pressure nip (8) in the web running direction, and a collecting trough (10.1, 10.2, 10.3, 10.4) being provided upstream of the shoe pressure nip (8) on the side of the press roll (2), the shell (7) being grooved, characterized in that the pressing section has only a single pressure nip, namely the shoe pressure nip (8), and the length of the grooves in the circumferential direction is greater than the nip length (L), and the pressing element (4) is configured in such a way that a pressure profile (p, p') can be generated in the web running direction, which pressure profile (p, p') has a gradient G in the inlet-side third of at least G = 1.35, it being defined that G = (p_1/3/p_max) / (1/3), p_1/3 being the pressure after a third of the nip length (L), and p_max being the peak pressure in the pressure profile (p, p').
2. Pressing section according to claim 1, characterized in that the shoe pressure nip (8) is covered with a first felt (5) which lies between the fibrous web (1) and the press roll (2), the first felt (5) being configured with a predominantly nonwoven base structure, what is known as a roving, and the base structure having at least two layers (9a, 9b), preferably at least three layers (9a', 9b', 9e).
3. Pressing section according to either of the preceding claims, characterized in that the shoe pressure nip (8) is covered with a second felt (6) which lies between the fibrous web (1) and the counter-roll (3), the second felt (6) being configured with a predominantly woven base structure, and the base structure having at least two layers (9c, 9d), preferably at least three layers.
4. Pressing 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), already wraps around the counter-roll (3) before the beginning of the shoe pressure nip (8) between the counter-roll (3) and the press-roll (2), to be precise over a length (b) of at least 30 mm.
5. Pressing section according to Claim 3 or 4, characterized in that the second felt (6) already wraps around the counter-roll (3) before the beginning of the shoe pressure nip (8) between the counter-roll (3) and the press roll (2), to be precise at an angle (α) of at least 10° in relation to the counter-roll (3).
6. Pressing section according to one of the preceding claims, characterized in that the collecting trough (10.1, 10.2, 10.3, 10.4) which is arranged upstream of the shoe pressure nip (8) has an accumulation edge (11) and an outlet (12.1, 12.2, 12.3, 12.4) and preferably also an extraction means (14.1).
7. Pressing section according to Claim 6, characterized in that the outlet (12.1, 12.2, 12.3, 12.4) is configured to be so great that a water quantity of at least 20 l per minute and per metre of web width, preferably of at least 30 l per minute and per metre of web width, can be discharged.
8. Pressing section according to one of the preceding claims, characterized in that the collecting trough (10.1, 10.2, 10.3, 10.4) which is arranged upstream of the shoe pressure nip (8) comprises an inlet edge (13), the collecting trough being arranged or adjustable in such a way that the inlet edge (13) is at a spacing from a first felt (5) of at most 20 mm, preferably of at most 10 mm.
9. Pressing section according to one of the preceding claims, characterized in that the pressing element (4) is configured in such a way that a pressure profile (p, p') can be generated in the web running direction, which pressure profile (p, p') has a gradient G in the inlet-side third of at least G = 1.50, preferably at least G = 1.80.
10. Pressing 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.
11. Pressing section according to one of the preceding claims, characterized in that the pressing element (4) is configured in such a way that a two-zone pressure profile (p') with two local pressure maxima can be generated, the second pressure maximum in the web running direction being higher than the first pressure maximum.
12. Pressing section according to Claim 11, characterized in that the pressing element (4) is configured in such a way that a pressure profile (p, p') can be generated, in which the pressure in a part range between the first pressure maximum and the second pressure maximum lies at least 5%, preferably at least 10%, particularly preferably at least 15% below the first pressure maximum.
13. Pressing section according to one of the preceding claims, characterized in that at least two rows of pressure elements are provided such that they are arranged behind one another in the web running direction, which two rows of pressure elements press the pressing element (4) onto the shell (7).
14. Pressing section according to one of the preceding claims, characterized in that the pressing element (4) consists of two partial pressing elements which can be pressed in a different manner from one another and are arranged behind one another in the web running direction.

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