Drying group of a machine for producing a fibrous web

Abstract

Drying group of a machine for producing a fibrous web comprising at least one drying cylinder (1), at least one suction deflection roller (2), an air-permeable drying fabric guided over the drying cylinder and the suction deflection roller, at least one stabilizing device (3), several deflection rollers (4) and means for tensioning the drying fabric, wherein the at least one stabilizing device has at least one sealing device (3.3) against the associated drying cylinder and a sealing device (3.41) against the suction deflection roller, and wherein at least one suction area is arranged between the at least one sealing device against the drying cylinder and the sealing device against the suction deflection roller, and wherein a free length f of the drying fabric between the drying cylinder and the subsequent suction deflection roller is in a range of 420 - 700 mm, and a distance d between the drying cylinder and the subsequent suction deflection roller is at least 50 mm, and wherein a vacuum in the suction area is at least 2500 Pa, and wherein a tension of the drying fabric is in a range of 5 - 8 KN / m.

Description

[0001] The invention relates to a drying group of a machine for producing a fibrous web, in particular a paper, cardboard or tissue web, wherein the drying group comprises at least one drying cylinder, at least one suction deflection roller, an air-permeable drying fabric guided over the at least one drying cylinder and the at least one suction deflection roller, at least one stabilizing device and a plurality of deflection rollers.

[0002] Dryer groups of this type are known from the prior art. EP 1 979 534 B1 discloses such a dryer group. The stabilizing device of the disclosed dryer group comprises two seals to seal a suction area located in the region where the dryer fabric runs freely from a drying cylinder to the downstream suction deflection roller. The negative pressure of at least 1000 Pa in the suction area leads to undesirable deflection of the dryer fabric. To keep the deflection of the dryer fabric within a tolerable range, EP 1 979 534 B1 proposes keeping the distance over which the dryer fabric runs freely within a range of 80–400 mm, preferably within a range of 100–250 mm. For typical sizes of drying cylinder (1800 - 1830 mm) and suction deflection roller (1200 - 1500 mm), the gap between the drying cylinder and the suction deflection roller is less than 20 mm.Due to the small distance between the drying cylinder and the suction deflection roller, mechanical damage to the drying cylinder and / or the suction deflection roller can occur, for example, if the fiber web breaks or if the fiber web is incorrectly transferred due to "packing" of the drying cylinder or "paper lumps".

[0003] The object of the invention is to provide an alternative drying group in which the deflection of the drying wire can be kept within a tolerable range, whereby the risk of the described mechanical damage is reduced.

[0004] The object is achieved according to the invention by an embodiment according to the independent claim. Further advantageous embodiments of the present invention can be found in the subclaims.

[0005] The invention is explained below with reference to the figures. The figures show in detail: Fig. 1: Dry group Fig. 2: Section of a drying group according to the invention Fig. 3: Section of a drying group according to the invention

[0006] Fig. Figure 1 shows a schematic representation of an example of a drying group as used in numerous variations in machines for producing a fibrous web. Generally, such drying groups comprise at least one drying cylinder, at least one suction deflection roll, an air-permeable drying fabric guided over the at least one drying cylinder and the at least one suction deflection roll, at least one stabilizing device, and several deflection rolls. Fig. The drying group shown in Figure 1 comprises five drying cylinders, one of which is designated 1, five suction deflection rollers, one of which is designated 2, five stabilizing devices, one of which is designated 3, four deflection pulleys, one of which is designated 4, and a drying fabric, which is designated 7. The machine direction is indicated by the arrow marked MD. The drying fabric is under tension. For this purpose, the drying group comprises means for tensioning the drying fabric. These means generally consist of at least one deflection pulley which can be moved perpendicularly, i.e. laterally, to its axis of rotation. The drying fabric is put under tension by the lateral movement of the respective deflection pulley relative to the laterally fixed drying cylinders, suction deflection rollers and deflection pulleys, the laterally movable deflection pulley being fixed once the desired drying fabric tension has been reached.

[0007] Fig. Figure 2 shows a section of a drying group according to the invention. The section shows the area between two drying cylinders and the elements in between: a suction deflection roll and a stabilizing device. The designations correspond to those in Fig. 1. The arrows indicate the direction of rotation of the respective elements. The air-permeable dryer fabric, which is guided over the drying cylinders and the suction deflection roller 2, is only shown in the areas where it runs freely and is indicated by the two dashed lines. The fibrous web is in Fig. 2 not shown. Ideally, the fibrous web runs parallel to the dryer fabric and is arranged on the side of the dryer fabric facing the surfaces of the drying cylinders. A plurality of openings are arranged in the casing of the suction deflection roller, connecting the interior of the suction deflection roller with the exterior.

[0008] The length of the area in the running direction of the dryer fabric in which it runs freely between a drying cylinder 1 and the downstream suction deflection roller 2 is f. The length f is referred to below as the "free length." The minimum distance between the surface of a drying cylinder 1 and the surface of the downstream suction deflection roller 2 is d. The minimum distance d is referred to below as the "distance."

[0009] A stabilizing device 3 is assigned to a drying cylinder 1 and the downstream suction deflection roller 2. The stabilizing device 3 has the task of providing at least one suction area, and wherein a suction area serves to suck the fibrous web onto the dryer fabric in the area in which the dryer fabric runs freely by means of a negative pressure in this suction area. In this way, a stable transfer of the fibrous web from the drying cylinder 1 to the downstream suction deflection roller is ensured. To provide the at least one suction area, the stabilizing device 3 comprises at least two sealing devices. One sealing device is designated 3.3 and seals the stabilizing device 3 against the preceding drying cylinder 1. Another sealing device is designated 3.41 and seals the stabilizing device 3 against the suction deflection roller 2. The suction area is formed by the sealing device 3.3, a portion of the surface of the preceding drying cylinder 1, the free area of ​​the drying fabric between the preceding drying cylinder 1 and the suction deflection roller 2, a portion of the surface of the suction deflection roller 2, the sealing device 3.41, and a portion of the housing of the stabilizing device 3. In short, the suction area is arranged between the sealing device 3.3 directed toward the drying cylinder 1 and the sealing device 3.41 directed toward the suction deflection roller 2. To discharge the air extracted from the suction area, the suction area is connected to a chamber in the stabilizing device 3. The chamber is designated 3.1.

[0010] In a further embodiment, the stabilizing device 3 comprises a further sealing device which seals the stabilizing device 3 against the preceding drying cylinder 1. The further sealing device is located between the sealing device 3.3 and the sealing device 3.41, so that there is an upper sealing device (3.3) towards the drying cylinder and a lower sealing device (in Fig. 2 not shown) to the drying cylinder. The additional sealing device ensures that the Fig. 2 is divided into two separate extraction zones. The upper extraction zone has a higher vacuum than the lower extraction zone, as the upper extraction zone is used to lift the fibrous web from the drying cylinder, while the lower extraction zone sucks the already lifted fibrous web onto the drying screen. This division further minimizes the screen deflection. Fig. In the embodiment shown in Figure 2 with only one suction area towards the drying cylinder, this suction area serves to provide the two functions mentioned.

[0011] The inventors have recognized that the combination of features specified below can ensure that the screen deflection is kept within a tolerable range and, at the same time, the operation of the drying group is reliable and robust against mechanical damage, e.g. in the event of a tear in the fiber web and packing of drying cylinders.

[0012] The free length f is in a range of 420–700 mm, or particularly preferably in a range of 450–700 mm. The distance d is at least 50 mm. The tension of the drying screen is in a range of 5–8 kN / m. The vacuum in the at least one extraction area is at least 2500 Pa.

[0013] It is advantageous if the sealing device 3.41 is designed as a blade. It is also advantageous if the distance between the cutting edge of the blade and the drying screen is in the range of 20-50 mm, preferably in the range of 25-40 mm. The distance is measured perpendicular to the drying screen surface.

[0014] Optionally, the stabilizing device 3 can also be used to vacuum the suction deflection roller 2. For this purpose, the stabilizing device 3 comprises, as shown in Fig. 2 shows a further sealing device, designated 3.42, which seals the stabilizing device 3 against the suction deflection roller 2. A further, second chamber, designated 3.2, is arranged inside the stabilizing device 3. The two chambers 3.2 and 3.1 are separated from one another by an intermediate wall. The second chamber 3.2, the sealing device 3.41, a part of the surface of the suction deflection roller 2, and the sealing device 3.42 form a further suction area. In short, one can say that the further suction area is arranged between the sealing device 3.41 and the sealing device 3.42. A region of the suction deflection roller 2, which is arranged between the sealing device 3.41 and the sealing device 3.42, is suctioned via the further suction area.The suction creates a vacuum inside the suction deflection roller 2, which sucks the fibrous web through the openings in the casing of the suction deflection roller 2 to the casing surface. The air-permeable drying fabric is located between the fibrous web and the casing surface of the suction deflection roller.

[0015] Fig. 3 shows the Fig.2 in a larger context, i.e. together with other elements which play a role in the two suction areas shown. To simplify the illustration, the drying screen is not shown. The arrangement shown comprises means for providing a first negative pressure, which are designated 5.1. The means 5.1 for providing a first negative pressure are connected to the first chamber 3.1, so that the provided first negative pressure can act in the first suction area. Furthermore, the arrangement shown optionally comprises means for providing a second negative pressure, which are designated 5.2. The means 5.2 for providing a second negative pressure are connected to the second chamber 3.2, so that the provided second negative pressure can act in the second suction area. The connecting lines between the means 5.1 and 5.2 and the chambers 3.2 and 3.1 are schematically indicated by the dashed lines. These lines can also be multiple or branched lines. For example, a line or line branch can lead into each of the lateral end faces of the chambers. The illustrated arrangement comprises a control device, designated 6, which is designed to control means 5.1 and 5.2 to adjust the provided negative pressures. List of reference symbols 1 drying cylinder 2 suction deflection rollers 3 Stabilization device 3.1 First Chamber 3.2 Second Chamber 3.3 Sealing device against drying cylinder 3.41 Sealing device against suction deflection roller 3.42 Sealing device against suction deflection roller 4 pulley 5.1 Means for providing an initial negative pressure 5.2 Means for providing a second negative pressure 6 Control device 7 Drying sieve QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] EP 1 979 534 B1

[0002]

Claims

[1] Drying group of a machine for producing a fibrous web comprising at least one drying cylinder (1), at least one suction deflection roller (2) following the at least one drying cylinder (1), an air-permeable drying fabric guided over the at least one drying cylinder (1) and the at least one suction deflection roller (2), at least one stabilizing device (3) associated with the at least one drying cylinder (1) and the at least one suction deflection roller (2), a plurality of deflection rollers (4) and means for tensioning the drying fabric, wherein the at least one stabilizing device (3) comprises at least one sealing device (3.3) against the associated drying cylinder (1) and a sealing device (3.41) against the suction deflection roller (2), and wherein at least one suction region is arranged between the at least one sealing device (3.3) against the drying cylinder (1) and the sealing device (3.41) against the suction deflection roller (2), characterized bythat a free length f of the drying fabric between the drying cylinder (1) and the following suction deflection roller (2) is in a range of 420 - 700 mm, and a distance d between the drying cylinder (1) and the following suction deflection roller (2) is at least 50 mm, and wherein a vacuum in at least one suction area is at least 2500 Pa, and wherein a tension of the drying fabric is in a range of 5 - 8 KN / m. [2] Drying group according to claim 1, wherein the sealing device (3.41) for the suction deflection roller (2) is designed as a blade. [3] Drying group according to claim 2, wherein a distance of the cutting edge of the blade and the drying screen is in a range of 20 - 50 mm. [4] Drying group according to claim 2, wherein a distance of the cutting edge of the blade and the drying screen is in a range of 25 - 40 mm. [5] Drying group according to one of the preceding claims, wherein the at least one stabilizing device (3) comprises a further sealing device (3.42) against the suction deflection roller (2), and wherein a second suction area is arranged between the first sealing device (3.41) against the suction deflection roller (2) and the further sealing device (3.42) against the suction deflection roller (2).

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