WO2021254745A1

WO2021254745A1 - Method for the variable setting of the dewatering performance of a pressing device

Info

Publication number: WO2021254745A1
Application number: PCT/EP2021/064038
Authority: WO
Inventors: Kjell Karlsson; Natalie OSTI; Kerst Aengeneyndt
Original assignee: Voith Patent Gmbh
Priority date: 2020-06-19
Filing date: 2021-05-26
Publication date: 2021-12-23
Also published as: EP4168623B1; EP4168623A1; DE102020116216A1

Abstract

The invention relates to a method for the variable setting of the dewatering performance of a pressing device for a machine for producing a fibrous web, such as a paper, tissue or cardboard web, wherein the dewatering performance of the pressing device is set in a variable manner by way of variation of the (in particular, currently) available dewatering volume of the pressing device. Furthermore, the invention relates to a roll cover for a pressing device, to a pressing device of this kind, and to a machine for producing a fibrous web, such as a paper, tissue or cardboard web, comprising a pressing device of this type.

Description

Method for the variable adjustment of the drainage capacity of a

Pressing device

The invention relates to a method for the variable adjustment of the dewatering performance of a pressing device for a machine for producing a fibrous web, such as a paper, tissue or cardboard web. The invention also relates to a roll cover for a pressing device, a pressing device of the same type and a machine for producing a fibrous web, such as a paper, tissue or cardboard web, comprising such a pressing device

When producing fibrous webs such as paper, tissue or cardboard webs on appropriate machines, the deposited, still moist fibrous web must be dewatered. This is first done mechanically on appropriate pressing devices.

Such a press device of a machine for producing a fibrous web usually comprises at least one press felt, a press roll and a counter roll, the latter two together forming a press nip. The fibrous web together with the press felt can be passed through this press nip. The press felt is designed in such a way that it has a first cavity volume for absorbing water from the fibrous web. The press roll is assigned a roll cover which has dewatering openings which define a second cavity volume for receiving water from the fibrous web. The two cavity volumes of the press felt and press roll are also called the dewatering volumes of the press device. This available drainage volume significantly influences the drainage performance of the press device. If a comparatively small drainage volume is available in the press nip, the drainage capacity of the press device will also be lower. The invention relates to such generic pressing devices. Due to natural wear and tear, with increasing service life and aging, the cavity volumes of both the press felt and the press roll decrease. The void volumes are further reduced by fillers, cellulose fibers and chemical and mechanical damage that settle in them.

There are different solutions in the prior art to counteract the reduction of the cavity volumes, in particular of press felts. For example, press felts with fibers that can be detached over the course of the operating time have been proposed in order to enlarge the void volume again. So far, however, these solutions have not been convincing. It is also known to provide a “buffer” of cavity volume for newly manufactured press felts. The production of the press felt creates a comparatively large cavity volume, which can then become clogged over time during operation. A reduction in the void volume thus takes place automatically and inexorably during operation. So far, it has not been able to meet the requirements of dewatering of fibrous webs with different grammages or different types to be produced one after the other with the same press felt. The object of the invention is to avoid the disadvantages of the prior art. The aim is to create the possibility of actively influencing the dewatering performance of the press device during operation and, for example, to set it in a targeted or optional manner. The object is achieved according to the invention by an embodiment in accordance with the independent claims. Further advantageous features of the embodiment according to the invention can be found in the subclaims.

The inventors have achieved the object by making the dewatering volume of such a pressing device variably adjustable. This means that this can optionally be changed during normal operation of the press device or the machine. This can take place, for example, in that the first and / or the second cavity volume is / are actively changed. If the drainage capacity is to be reduced, one and / or both cavity volumes is / are reduced. Conversely, if the drainage capacity is to be increased again from a lower value, the corresponding cavity volume is increased again based on this.

In the context of the invention, set variably means that the drainage capacity is changed or can be changed. The dewatering performance can be changed by reducing the dewatering volume of the press device. Conversely, the dewatering performance can be increased by increasing the dewatering volume of the press device. According to the invention, the corresponding cavity volume can only be reduced with respect to the actually present, that is to say available, cavity volume.

The hollow volume of the press felt or of the roll cover of the press roll is understood to mean the sum of all volumes which are used to absorb water from the fibrous web during normal operation of the press device / machine. In the case of the roller cover, it is the sum of all individual drainage openings that are made in the roller cover. In the case of press felts, the drainage openings for absorbing water are formed by the fibers of the press felt itself. Intended operation is to be understood as that operation of the press device or machine in which the press device dehydrates the fibrous web or the machine produces the fibrous web. If only the operation of the pressing device is mentioned, then the intended operation is meant.

The dewatering volume of the pressing device is preferably composed of the first cavity volume for absorbing water from the fibrous web, which from a press felt of the press device is made available and / or a second cavity volume, which is made available by a roll cover of a press roll, which comprises dewatering openings for receiving water from the fibrous web. In principle, the first void volume of the press felt and / or the second void volume of the roll cover of the press roll could be adjusted within the meaning of the invention.

One idea of the invention is therefore to vary the second cavity volume of the roll cover of the press roll without having to remove the roll cover or the roll carrying it from the press device. The adjustment of the cavity volume can also take place when the pressing device is at a standstill.

The dewatering volume is preferably set by setting the void volume for absorbing water from the fibrous web, namely the void volume of the roll cover. The void volume of the dewatering openings of roll covers can usually be changed with simpler means than those of press felts.

The invention also relates to a roll cover for a press device for a machine for producing a fibrous web, such as paper, tissue or cardboard web, the roll cover having drainage openings on its radially outermost lateral surface which define a second cavity volume for absorbing water from the fibrous web, wherein the roller cover is set up in such a way that the second cavity volume is variably adjustable.

The invention also relates to a press device of a machine for producing a fibrous web, such as paper, tissue or cardboard web, the press device comprising a press felt with a first cavity volume for absorbing water from the fibrous web, a press roll and a counter roll which together form a press nip form, through which the fibrous web and the press felt can be passed, wherein the press roll is assigned a roll cover which has dewatering openings that provide a second cavity volume Define uptake of water from the fibrous web, the pressing device being assigned means for adjusting the dewatering volume of the pressing device. The means for adjusting the drainage volume can preferably be designed in such a way that the second cavity volume, that is to say that of the

Drainage openings of the roll cover can be changed, in particular by introducing cross-sectional constrictions into the drainage openings, the second cavity volume being optionally adjustable between a maximum value at which there is no cross-sectional constriction of the drainage openings and a minimum value at which the cross-section of the drainage openings are narrowed. The maximum value relates to the actual void volume physically present with the press felt / roll cover. Starting from this value, the void volume cannot be increased, but only reduced with regard to a minimum value.

The means can preferably be set up in such a way that the

Drainage openings are provided in the roll cover channels and the roll cover is designed to be elastic in such a way that when the channels are pressurized with a pressure medium, they are deformed and a

Cross-sectional constriction towards a minimum value of the second cavity volume can be generated.

Another advantageous possibility of making the second cavity volume changeable is to introduce one or more thread-like inserts into the grooves of the roll cover. These thread-like inserts can be inserted into the roll cover along the grooves and reduce the available cavity volume of the groove or roll cover. Such thread-like inserts can be removed again when the machine is at a standstill, as a result of which the cavity volume can be increased again. Among other things, it is possible to make the grooves in the roller cover deeper than required for the application. The so much available cavity volume is filled via the thread-like deposits. When the roller is in operation, the roller cover wears and the groove depth and the cavity volume of the grooves decrease. If this loss of (second) cavity volume is too great, the operator can very easily and quickly remove the thread-like deposits when the systems are at a regular standstill, thereby gaining new cavity volume. In this way, the service life of such a roller can be massively extended before it has to be removed and the roller cover reworked.

Suitable thread-like inserts can comprise or consist of a monofilament, a multifilament or a twisted thread. Materials that do not swell or hardly swell on contact with water can be used as the material. In this way, a very precise setting of the volume reduction is obtained. A polyester thread, especially a polyester thread, can be used for this, for example. If necessary, it can be advantageous to fix such thread-like inserts in the groove by means of a suitable adhesion promoter.

However, it can also be advantageous to use materials which swell significantly on contact with water. Polyamides are suitable for this, for example. Such a polyamide thread can then simply be introduced into the grooves in the dry state. Contact with water when the roller is in operation or in a special swelling step increases the volume of the thread so that it holds securely in the groove by itself. A bonding agent can then be completely or partially dispensed with. Another advantageous possibility is to provide the thread-like inlays with a suitable impregnation. In particular, these inserts can be provided with an impregnation which, after the thread-like insert has been introduced, foams under appropriate conditions (moisture, pressure, temperature, radiation, etc.). The resulting foam layer in the groove can make the hydraulic pressure in the groove more even.

Such thread-like deposits are usually inserted at the factory before the roller is installed. But it is also possible to build these inserts into an already installed roller, whereby the cavity volume can also be reduced during operation.

Finally, the invention relates to a machine comprising a press device according to the invention, the machine preferably being set up in such a way that it carries out a method according to the invention.

The grooves in the roll cover can extend in the circumferential direction of the roll cover or run spirally over the outer surface of the roll cover. The drainage openings in the form of e.g. grooves and / or bores can be machined.

The roll cover according to the invention can also be implemented in the form of a press jacket of a shoe press.

On the basis of exemplary embodiments, further advantageous features of the invention are explained with reference to the drawings. The features mentioned can not only be implemented advantageously in the combination shown, but can also be combined individually with one another. The figures show in detail: FIG. 1 a partially sectioned, schematic side view of a

Pressing device with a roll cover according to an embodiment of the present invention. 2 to 4 conceivable embodiments of a roll cover, each seen in a section through its longitudinal axis; 1 shows, in a partially sectioned, schematic side view, an embodiment of a press device according to the invention, which in the present case comprises a press roll 12, such as a shoe press roll, and a counter roll 14. Press roll 12 and counter roll 14 are arranged parallel to one another with regard to their longitudinal axes. Together they form a press nip 22 or limit one.

While the counter roll 14 here consists of a cylindrically designed roll rotating about its longitudinal axis with a roll cover, the shoe press roll 12 is composed of a shoe 16, a standing yoke 18 carrying this and a press cover 20. Shoe 16 and yoke 18 are in

Arranged in a fixed manner with respect to the counter roller 14 or the press cover 20. That means they don't rotate. In this case, the shoe 16 is supported by the yoke 18 and is pressed against the radially innermost surface of the press jacket 20 that runs around it relative to it via hydraulic press elements (not shown). The press jacket 20, which surrounds the shoe 16 and yoke 18 in the circumferential direction, rotates about its longitudinal axis in the opposite direction of rotation to the counter roll 14. The concave design of the shoe 16 on its side facing the counter roll 14 results in a comparatively long press nip 22. The press device 10 is particularly suitable for the mechanical dewatering of fibrous webs 24. When the press device is in operation, a fibrous web 24 with one or two press felts 26, 26 ′ is passed through the press nip 22. In the present case there are exactly two press felts 26, 26 'that sandwich the fibrous web 24 between them. When passing through the press nip 22, a pressure is exerted indirectly in the press nip 22 on the fibrous web 24 through the press felts 26, 26 '. This is done in that the radially outermost surface of the counter roller 14 on the one hand and the radially outermost Surface of the press jacket 20 come directly into contact with the corresponding press felts 26, 26 '. The liquid emerging from the fibrous web 24 is temporarily absorbed by the press felts 26, 26 'and the dewatering openings 6 (see FIGS. 2 to 4) provided in the press jacket or roll cover surface. After leaving the press nip 22, the liquid taken up by the drainage openings 6 of the press jacket 20 is thrown off before the press jacket 20 re-enters the press nip 22. In addition, the water taken up by the press felt 26, 26 'can be removed with suction elements after it has left the press nip 22

In a further embodiment of the invention not shown in the figures, the press felts 26, 26 'can be dispensed with. In such a case, the fibrous web 24 is in direct contact on the one hand with the press jacket 20 and on the other hand with the counter roll 14, which together form a press nip. The latter can then be designed as a heated drying cylinder. In the context of the invention, the press cover 20 corresponds to a roll cover 8 which has corresponding grooves and / or bores as drainage openings 6.

As already mentioned, a modification of the embodiment shown in FIG. 1 would also be conceivable in which, instead of the shoe press roll 12, a conventional press roll comprising a roll cover 8 according to the invention with corresponding drainage openings 6, such as grooves and / or bores, is provided. Regardless of the two embodiments presented, the roller cover 8, as shown in the following figures, can be designed according to the invention.

In FIGS. 2, 3a, 3b and 4, different embodiments of the invention are each shown in a partially shown cross section, not to scale, through the axis of rotation of the roll cover. The illustration in FIG. 2a shows a detail from a roller cover 8. This comprises a plurality of drainage openings in the form of grooves on its radially outermost lateral surface. All of the volumes of the plurality of drainage openings 6 taken together, which are capable of absorbing water from the fibrous web 24 in the press nip 22, are referred to as the second flea volume in the sense of the invention. According to the idea of FIG. 2, the dewatering performance of the pressing device 10 is influenced in that the second volume of the flea space is changed. This can be done in that, for example, part of the drainage openings 6, here for example the grooves, is filled. The filling can be done by introducing a filling material into the drainage openings 6. The backfilling can take place when the pressing device 10 is at a standstill. The filling material can be introduced into the drainage openings 6 in a non-positive, positive and / or cohesive manner, for example when the pressing device 10 is at a standstill, that is, when it is not in operation. The filler material can be threads or it can comprise threads. The filling material can basically be removed. However, it could also resolve itself during the operation of the pressing device 10.

Another idea is shown in the illustration of FIGS. 3a and 3b. There a part of the actually present, that is to say available, second flea space volume of the roll cover can be changed in that the cross section of the drainage openings 6 is changed in a targeted manner. This can be done in that channels 4 are embedded in the roller cover 8 and can be acted upon by a fluid. The channels 4 are thus made in one piece with the roller cover 8. The channels 4 are delimited by a wall which at the same time represents a part of the wall of the drainage openings 6, which is able to absorb the water from the fibrous web 24. If the roller cover 8 is formed from a polymer which behaves elastically, then as a result of the application of pressure with the fluid it can elastically deform, that is to say expand. This increases the volume of the channel 4, whereas the volume of the corresponding drainage opening 6, which is delimited by the wall of the channel 4, is reduced. This reduces the cross section of the drainage openings 6 when pressure is applied. If the pressure is removed and the channel 4 relieved, the wall of the channel 4 can return to its original position and the cross section of the corresponding drainage opening 6 increases again, up to the original value before the application of pressure. The material of the wall of the channel 4 can be restored by a corresponding elastic polymer of the roll cover 8. For pressure actuation, the channels 4 can be connected in a fluid-conducting manner to a corresponding fluid pressure source (not shown here). A delivery device, such as a pump, could be provided between the fluid pressure source and the channels 4 in order to supply fluid from the fluid pressure source to the channels. The pressure in the channels 4, the volume of the channels 4 and the dewatering performance determined thereby can then be transmitted to a control or determined by such.

According to FIG. 3 a, the channel 4 is located radially on the inside, at the base of the drainage opening 6. In contrast, according to the embodiment of FIG. However, a single channel 4 could also be provided on one end face of the drainage opening 6. Combinations of the configurations from FIGS. 3a and 3b would also be conceivable. The alternative according to FIG. 4 is essentially based on a combination of the objects of FIGS. 2, 3a and 3b. This means that a separate channel 4 is introduced into a drainage opening 6 as a filler material, but which is not formed in one piece with the roller cover 8. The channel 4, like the filling material, can also be introduced into the drainage opening 6 in a non-positive, positive or material fit. This has the advantage that it can be removed again as soon as it is damaged or the roller cover 8 is worn. Then the channel 4 in a new roller cover 8 can be reused. Here, too, the channel 4 can be actuated by pressure by means of a fluid, as explained in connection with FIGS. 3a and 3b.

The drainage openings 6, as shown in FIGS. 2 to 4, do not have to have the rectangular cross section shown. Any cross-sectional shape can be selected. The same applies, of course, to channels 4.

The embodiments of FIGS. 2 to 4 have in common that the dewatering performance of the pressing device 10 can be influenced in that the dewatering volume of the pressing device is actively, that is to say, optionally changed. This happens because the drainage openings 6, for example, only temporarily, i.e. for a certain period of time, and this clogging can be removed later.

It is conceivable that the channels or the filler material are or can be introduced in all or only in a part of the drainage openings 6 arranged distributed over the jacket surface. For example, the dewatering performance can be set in a defined manner along the axis of rotation of the roll cover 8 or over the circumference of the roll cover 8.

Although the invention has only been described with reference to the figures with regard to the second flea space volume, it is fundamentally possible to vary the first flea space volume, e.g. of a press felt of the pressing device, or a combination of both, i.e. first and second flea space volumes.

Claims

1. A method for the variable setting of the dewatering performance of a press device (10) for a machine for producing a fibrous web (24), such as paper, tissue or cardboard web, the dewatering performance of the pressing device (10) by varying the available dewatering volume of the pressing device (10) is set variably.

2. The method according to claim 1, characterized in that the

Dewatering volume of the pressing device (10) consists of a first cavity volume for receiving water from the fibrous web (24), which is made available by a press felt (26, 26 ') of the pressing device (10) and / or a second cavity volume, which is provided by a roll cover (8) of a press roll (12) is made available, which comprises drainage openings (6) for receiving water from the fibrous web (24).

3. The method according to claim 2, characterized in that the pressing device (10) in addition to the press roller (12) also a

Comprises counter roll (14), the press roll (12) and counter roll (14) together forming a press nip (22) through which the fibrous web (24) and the press felt (26, 26 ‘) can be passed.

4. The method according to any one of claims 1 to 3, characterized in that the drainage volume is set variably during normal operation of the pressing device (10).

5. The method according to any one of the preceding claims, characterized in that the adjustment of the drainage volume solely by adjusting the second cavity volume for receiving Water from the fibrous web (24), namely that of the roll cover (8), takes place.

6. Roller cover (8) for a pressing device (10) for a machine for producing a fibrous web (24), such as paper, tissue or

Cardboard web, comprising a plurality of drainage openings (6), the drainage openings (6) being arranged on the radially outermost lateral surface of the roll cover (8) and being optionally adjustable with regard to their cross-section

7. Pressing device (10) of a machine for producing a

Fibrous web, such as paper, tissue or cardboard web, wherein the pressing device (10) comprises a press felt (26, 26 ') with a first cavity volume for absorbing water from the fibrous web (24), a press roll (12) and a counter roll (14 ), which together form a press nip (22) through which the fibrous web (24) and the press felt (26, 26 ') can be passed, the press roll (12) being assigned a roll cover (8) which has dewatering openings (6) which define a second cavity volume for receiving water from the fibrous web (24), the pressing device (10) being assigned means for adjusting the dewatering volume of the pressing device (10).

8. Pressing device (10) according to claim 7, characterized in that the means for adjusting the drainage volume are designed such that the second cavity volume, which is of the

Drainage openings (6) of the roll cover (8) are made available, can be changed, in particular by introducing cross-sectional constrictions in the drainage openings (6), the second cavity volume between a maximum value at which there is no cross-sectional constriction of the drainage openings (6) and a minimum value at which the drainage openings (6) are narrowed in terms of their cross-section, can be optionally set.

9. Pressing device (10) according to claim 8, characterized in that the means are set up such that the drainage openings (6) of the roll cover (8) are assigned channels (4) and the roll cover (8) is designed so elastic that through Pressurization of the channels (4) with a pressure medium, this deformation and a cross-sectional constriction to a minimum value of the second cavity volume can be generated in order to reduce the second cavity volume and thus the drainage capacity of the pressing device (10).

10. Pressing device (10) according to one of claims 8 or 9, characterized in that drainage openings (6) are provided in the form of one or more grooves, and thread-like inserts are introduced into the grooves as means for adjusting the drainage volume.

11. Machine for producing a fibrous web (24), such as paper, tissue or cardboard web, comprising a pressing device (10), preferably according to one of claims 7 to 9, wherein the machine is preferably set up in such a way that this is a method according to a the claims 1 to 5 carries out.