EP2753751B1 - Pressing section of a machine for producing a fibrous web - Google Patents

Description

The invention relates to a press section of a machine for producing a fibrous web, in particular a paper, board or pulp web, with at least one press nip formed between a press roll and a counter roll, wherein the fibrous web before the press nip by means of a Abnahmesaugwalze of a preceding Covering can be transferred to an upper press felt and is guided by the press nip between the upper press felt and a lower fabric according to the preamble of claim 1. Such a press section is for example off DE-A-101 09 382 known.

Such a press section is known for example from the document EP 1072721 A1 , In the single press described there, the upper and lower press felt are moved together shortly after the web has been removed from the forming wire. The advantage of this solution is the excellent web guidance, since the web is guided in sandwich between the press felts before the press nip. The sandwich can be guided via a steam blow box for moisture cross profile influencing. However, the effect of the steam blow box is diminished by the fact that the steam is applied to the lower press felt and not directly to the fibrous web. Another disadvantage of this solution is that the long contact time of the fibrous web with a second wet felt can lead to increased rewetting of the web. The rewet can also take place unevenly across the width, so that additional moisture transverse profile errors arise.

Furthermore, there are also press sections, such as from DE 102004042637 A1 known, in which the fibrous web is guided hanging on the upper press felt to the press nip and the lower press felt is added to the counter roll. This arrangement is necessary if a steam blow box is to be installed, which blows directly onto the fibrous web. This is associated with an increased risk that before the press nip web disturbances occur, especially at heavier basis weight of the fibrous web.

The object of the invention is now to provide a press section, in particular for fibrous webs with a higher basis weight, which has excellent web running properties before the press nip, but nevertheless provides a free surface of the fibrous web, for example, for the effective use of a steam blow box.

The object is achieved in that after the Abnahmesaugwalze a stationary support member with the web-facing side of the upper press felt is in contact, that results in an approximately convex curved web travel for the fibrous web. Under approximately convex is also understood a polygonal shape of the support element, which results in approximately a convex track running path. The contact surface of the support member may be a continuous curved surface or composed of a plurality of shorter contact surfaces, as they result in a plurality of transverse to the web track arranged support strips composed. Because of the web tension of the fibrous web, the approximately convexly curved web run produces a normal force in the direction of press felt, so that the fibrous web follows the press felt without interference, without the lower press fabric having to be added to the sandwich in this area. By the solution according to the invention, folding away of the edges is prevented, as otherwise often occurs in heavier basis weights. The folding down of the edges is particularly critical, since in the case of a complete folding through the multi-folded web in fully loaded press nip large damage to the rollers and the felts can be caused. Experiments in the technical center have shown that even a straight web run of 500-1000 mm in length after the intake suction roll can lead to problems with falling edges. Often causes the leading of the lower clothing caused by the resulting air flow disturbances in the web and in particular flutter or lifting the edges. By the normal force generated by the support element these problems are reliably avoided.

Heavy or high basis weight fibrous webs have at least 100 g / m ² , preferably at least 120 g / m ² , more preferably at least 150 g / m ² considered.

The bottom fabric of the press nip may be a press felt, a semi-permeable belt or a water-impermeable transfer belt. The preceding string may be, for example, the wire of a sheet forming unit or the lower press sheet of a preceding press nip.

The straight pieces of the polygon along the web travel are preferably at most 350 mm long, more preferably at most 250 mm long, to achieve a sufficient convex curvature.

The support element should advantageously be so long that the fibrous web is safely guided until the start of the sandwich area, which is formed by the upper press felt and the lower covering. For example, by the support element until just before the beginning of the sandwich area or slightly beyond. This sandwich area can begin at the end of the support element, on a guide roller of the lower clothing or only on the counter-roller of the press nip. At least the approximately convexly curved web travel path should extend so far that the distance between the end of the approximately convexly curved web travel path and the beginning of the sandwich region formed by the upper press felt and the lower clothing is between 20 and 500 mm, preferably between 20 and 250 mm, more preferably between 20 and 100 mm. The end of the approximately convexly curved web travel path is the last contact line of the support element to the upper press felt. Of course, the approximately convexly curved web travel path can also protrude into the sandwich area. It should only be avoided that the distance between the guide roller of the lower clothing and the support element is too small, otherwise bugs or shreds, such as those arising during transfer, get stuck and lead to felt burns or other damage. Preferably, the distance between the Surface of the guide roller of the lower clothing and the contact surface of the support element at least 20 mm, preferably at least 40 mm.

However, it is preferred that the approximately convexly curved web travel path ends before the beginning of the sandwich region, in order to provide as much space as possible for a steam blower box.

The first contact surface of the support element to the upper press felt should be in the web running direction at most 350 mm, preferably at most 250 mm from the drain point A of the press felt on the Abnahmesaugwalze removed. As a result, a sufficiently rapid effect of the normal force is achieved after leaving the Abnahmesaugwalze.

The support member may comprise individual transverse to the machine direction support strips which are in contact with the press felt and thereby bring this on a polygonal track. The support member may also have a continuous curved covering, over which the press felt runs. The pad may have holes, grooves or recesses for reducing the contact surface and thus the friction. For lubrication, spray pipes or lubrication pockets can be present in front of or in the support element in order to apply water to the side of the press felt facing away from the web. As a material for the support strips, the contact surface of the support strips or the covering of the support element is particularly suitable ceramic.

Overall, it is advantageous if the distance from the Abnahmesaugwalze to the beginning of the sandwich area is as short as possible. In a preferred embodiment, the approximately convexly curved track running path has a length of more than 200 mm and at most 2000 mm, preferably at most 1300 mm, particularly preferably at most 1000 mm. This ensures adequate stabilization of the fibrous web.

Furthermore, it is advantageous if the support element is designed so that an effective radius of curvature for the approximately convexly curved track run between 150 and 10,000 mm, preferably between 500 and 5000 mm, and more preferably between 750 and 2500 mm. The effective radius of curvature can be determined when several points of contact between the support element and press felt are approximated by a circular path. An excessive deflection, ie too small a radius of curvature or "kink" in the web travel path should be avoided.

In order to achieve a good compromise between support of the web, length of the supported surface and minimization of friction and felt wear, it is advantageous if the support member per meter length of the approximately convexly curved web travel path at least four transverse to the machine direction support strips, with the upper Press felt come into contact. It is likewise advantageous if the support element has four to fifteen, preferably four to ten, cross-machine direction support strips that come into contact with the upper press felt.

The arrangement according to the invention is particularly suitable for a press section, in which the press nip following the support element is the second press nip of the press section and in particular is arranged after a first press nip, which is designed as a shoe press nip. The second press nip, especially after a shoe press nip, drains only relatively little. As a result, the press felts in the second press nip run drier and the adhesion of the fibrous web to the upper press felt is low. The risk of falling edges or web disturbances by Luftverwirbelungen when approaching the lower fabric is therefore particularly high.

On the other hand, the embodiment according to the invention is also well suited in the event that the support element is arranged in front of the first press nip of the press section, in particular if this is the only press nip of the press section. Before the first press nip the fibrous web has only a low dry content, between 16 and 23%, and is therefore still quite heavy. Therefore, especially at higher basis weight, the edges tend to fold.

In order to keep the friction as low as possible and to reduce the energy consumption of the press section and the drives, it is advantageous not to directly or indirectly to suck the support element and not otherwise act on negative pressure. The curved track guide and the normal force generated thereby in most cases sufficient for the stabilization.

Alternatively, the support element to increase the stabilizing effect and to improve the transfer of the fibrous web may be subjected to negative pressure. For example, by being directly connected to an exhaust or being indirectly sucked by the Abnahmesaugwalze or by a suction effect is generated on the support element via a corresponding supplied with compressed air nozzle. If the support element is sucked by the removal suction roll, the intermediate space must be sealed by way of corresponding side shields and sealing blades running transversely to the direction of web travel. The negative pressure measured on the side of the upper press felt remote from the web in the region of the support element is preferably between 0.5 and 20 kPa, more preferably between 0.5 and 10 kPa and particularly preferably between 1 and 5 kPa. Thus, the stabilization is improved without causing too much friction and wear.

In a very particularly preferred embodiment, a steam blower box, which can inflate steam onto the fibrous web, is provided on the side of the upper press felt opposite the support element and / or the suction roll. Due to the very stable web guide on the upper press felt, even under critical boundary conditions, such as with a very high basis weight, the lower clothing can be introduced later, which creates sufficient space for the installation of the steam blow box. At high basis weights, the use of a steam blow box with the press sections according to the prior art is not yet possible. The heating of the fibrous web by the steam blower box is particularly attractive because more water can be squeezed out in the press nip and thus less water must be evaporated in the subsequent drying section.

Compact steam blow boxes are particularly suitable for the press section according to the invention. The box length of the steam blow box in the web running direction should be at most 1000 mm, preferably at most 500 mm, particularly preferably at most 350 mm.

A good and intensive warming of the fibrous web is achieved if the nozzle openings of the steam blow box, from which the steam flows out, have a diameter between 1 and 10 mm.

In order to produce a sufficient web tension in the fibrous web, it is helpful to design the drives of the press section such that a differential speed of between 0.3 and 2%, preferably between 0.5 and 1.5%, of the upper press felt can be set to the preceding clothing ,

in Fig.1

eine Pressenpartie nach dem Stand der Technik für die Herstellung von Faserstoffbahnen mit höherem Flächengewicht

in Fig.2

eine Pressenpartie nach dem Stand der Technik für die Herstellung von Faserstoffbahnen mit niedrigerem Flächengewicht

in Fig.3

eine bevorzugte Ausführung einer erfindungsgemäßen Pressenpartie mit Dampfblaskasten

in Fig.4

eine Detailansicht einer weiteren bevorzugten Ausführung

in Fig.5

eine weitere Detailansicht einer weiteren bevorzugten Ausführung

in Fig.6

eine Detailansicht noch einer bevorzugten Ausführung

in Fig.7

eine Detailansicht noch einer bevorzugten Ausführung

By way of embodiments , further advantageous features of the invention will be explained with reference to the drawings. they show

in Fig.1

a press section of the prior art for the production of fibrous webs with a higher basis weight

in Fig.2

a prior art press section for the production of lower basis weight fibrous webs

in Fig.3

a preferred embodiment of a press section according to the invention with steam blower box

in Fig.4

a detailed view of another preferred embodiment

in Fig.5

a further detailed view of another preferred embodiment

in Fig.6

a detailed view of a still preferred embodiment

in Fig.7

a detailed view of a still preferred embodiment

The figures are described in more detail below.

Fig.1 and Fig.2 show tandem presses according to the prior art.

Fig.1 shows a version for heavy varieties. The web travel path on the first and on the second press nip is the same. The fibrous web 1 is taken over by means of the Abnahmesaugwalze 14,15 on the upper press felt 2,3 of the press nips. Immediately thereafter, the lower press felt 5,6 is added, so that the fibrous web 1 is guided in sandwich between the felts for press nip between the shoe press roll 10,11 and the counter-roller 12,13. After the press nip, the fibrous web 1 is held on the lower press felt 5, 6 by means of the suction felt guide roll 17, 18. The fibrous web 1 is always carried by a press felt or guided between two press felts. It is, except directly on the suction roll, never out of the way hanging.

Fig.2 shows a variant for lighter grades, which are not prone to problems with drooping edges, but are rather critical with respect to rewetting by the press felts. Here, the lower Pressfliz is 5,6 only on the counter-roller 12,13 added to the fibrous web 1. To increase the web temperature or to correct the moisture cross profile, a steam blower box 40 can blow directly onto the fibrous web.

In Figure 3 a preferred embodiment of the press section according to the invention is shown, in which the support element is arranged in front of the second press nip. It should be noted that additionally or alternatively, a corresponding support element may be provided in the upper press felt before the first press nip. After the first press nip, which is formed by the shoe press roll 10 and the counter roll 12, the fibrous web 1 is held by means of Saugfilzleitwalze 17 on the lower press felt 5 and then taken over by means of Abnahmesaugwalze 15 on the upper press felt 3. The standing support element 30 is brought into contact with the web-facing side of the upper press felt 3 in such a way that an approximately convexly curved web travel path results for the fibrous web 1. The contact surface of the support member 30 may be a continuous curved surface or composed of a plurality of shorter contact surfaces, as they result in a plurality of transverse to the web track arranged support strips composed. Under approximately convex also a polygonal shape of the support member 30 is understood, the approximately one convex web track results. Due to the web tension of the fibrous web 1, a normal force in the direction of press felt 3 is produced by the approximately convexly curved web run, so that the fibrous web 1 follows the press felt 3 without interference, without the lower press cover 6 having to be added to the sandwich in this area. The solution according to the invention reliably prevents folding down of the edges which is critical in the case of heavier basis weights and nevertheless provides a sufficiently long free surface of the fibrous web 1, so that a steam blower box 41 can be installed which can apply steam directly to the fibrous web 1. At the end of the curved web path, the lower press fabric 6 is brought to the sandwich, so that the fibrous web 1 between the two press felts 3 and 6 to the second press nip formed by the shoe roll 11 and the backing roll 13. Overall, it is advantageous if the distance from the Abnahmesaugwalze 15 to the beginning of the sandwich area is as short as possible. Also, the sandwich area should be kept as short as possible, just just as long as Wasserammeiwannen and other necessary elements can be structurally accommodated. Due to the effective use of the steam blow box 41, the dewatering of the fibrous web 1 in the second press nip is significantly improved. Especially with heavy grades, this is necessary to achieve higher production speeds and the required higher dewatering volume.

Figure 4 shows a detail of a preferred embodiment of the support element. The fibrous web 1 is taken over by the Abnahmesaugwalze 19 of the preceding fabric 7, which may be a lower press felt or a forming wire on the upper press felt 8. The support element 31 has six support strips 34 which predetermine the approximately convexly curved web travel path for the upper press section 8 and the fibrous web 1. The support member 31 may be unabsucked or carried out with suction. The first contact line C of the support element to the upper press felt follows shortly after the flow point A. In the region of the approximately convexly curved web travel path from C to D, the generated normal force is indicated as arrows.

The further detail view in Figure 5 shows a support member 32 which is designed so that there is a short distance from the drain point A to the first contact line C and a short distance from the end D of the approximately convexly curved Bahnlaufweges to the beginning of the sandwich area B. As a result, an excellent stabilization of the web run is given and yet there is no risk that the fabric or the support element will be damaged if pass through batches or shreds during the transfer. Via a seal 33, the support member 32 is connected to the Abnahmesaugwalze 19 so that at least no air is drawn into the region of approximately convexly curved web travel path. If the suction box of the Abnahmesaugwalze 19 is positioned accordingly, the support member can be indirectly drawn from the Abnahmesaugwalze 19 with.

Figure 6 represents in a detailed view of another embodiment of the invention in which the beginning B of the sandwich area is located in front of the end D of the approximately convexly curved web travel path. It is important to ensure that the distance between the surface of the guide roller 27 and the press felt 8 contacting parts of the support member 32 is sufficiently large, so that bats or shreds can pass through.

In Figure 7 a detail view of yet another embodiment of the invention is shown, in which also the beginning B of the sandwich area before the end D of the approximately convex curved web travel path. By avoiding a support strip 34 in the direct area of the guide roller 27 it is achieved that the distance between the surface of the guide roller 27 and the support element 35 is sufficiently large so that batches or shreds can pass through. The sieve sandwich can escape, since no rigid parts of the support element touch the press felt 8 in this area.

LIST OF REFERENCE NUMBERS

1

Fibrous web

2, 3, 8

Upper press felt

4

dryer

5, 6, 9

lower press cover

7

previous covering

10, 11

press roll

12, 13

backing roll

14, 15, 19

pick-up suction

16

Removal suction roll in the dryer section

17.18

Saugflizleitwalze

20,21,22,23,24,25,26,27

guide roll

30,31,32,35

support elements

33

seal

34

support strips

A

Expiration point of acceptance suction roll

B

Beginning of the sandwich area

C

first contact line to the upper press felt

D

End of the approximately convexly curved web travel path

Claims (15)

1. Pressing section of a machine for producing a fibrous web (1), in particular a paper, cardboard or pulp web, having at least one pressure nip which is formed between a press roll (10, 11) and a mating roll (12, 13), it being possible for the fibrous web (1) to be transferred upstream of the pressure nip with the aid of a suction pick-up roll (14, 15, 19) from a preceding fabric (5, 7) to an upper press felt (2, 3, 8), and the said fibrous web (1) being guided through the pressure nip between the upper press felt (2, 3, 8) and a lower fabric (5, 6, 9), a stationary supporting element (30, 31, 32) being in contact with that side of the upper press felt (2, 3, 8) which faces away from the web downstream of the suction pick-up roll (14, 15, 19) and upstream of the pressure nip in such a way this results in an approximately convexly curved web running path for the fibrous web (1), characterized in that the supporting element (30, 31, 32) has a first contact line (C) with the upper press felt (2, 3, 8), which contact line (C) lies upstream in the web running direction of the start (B) of a sandwich region which is formed by the upper press felt (2, 3, 8) and the lower fabric (5, 6, 9).
2. Pressing section according to Claim 1, characterized in that the approximately convexly curved web running path extends at least to such an extent that the spacing between the end (D) of the approximately convexly curved web running path and the start (B) of the sandwich region which is formed by the upper press felt (2, 3, 8) and the lower fabric (5, 6, 9) is between 20 and 500 mm, preferably between 20 and 250 mm, particularly preferably between 20 and 100 mm.
3. Pressing section according to either of the preceding claims, characterized in that the supporting element has the first contact line (C) with the upper press felt (2, 3, 8), which first contact line (C) is at most 350 mm, preferably at most 250 mm, away from the running-off point (A) of the press felt on the suction pick-up roll (14, 15, 19) in the web running direction.
4. Pressing section according to one of the preceding claims, characterized in that the approximately convexly curved web running path (C to D) has a length of more than 200 mm and at most 2000 mm, preferably at most 1300 mm, particularly preferably at most 1000 mm.
5. Pressing section according to one of the preceding claims, characterized in that the supporting element (30, 31, 32) is designed in such a way that an effective curvature radius of between 150 and 10 000 mm, preferably between 500 and 5000 mm and particularly preferably between 750 and 2500 mm results for the approximately convexly curved web running path.
6. Pressing section according to one of the preceding claims, characterized in that, per metre length of the approximately convexly curved web running path, the supporting element (30, 31, 32) has at least four supporting bars (34) which are arranged transversely with respect to the machine running direction and come into contact with the upper press felt (2, 3, 8), and/or in that the supporting element (30, 31, 32) has from four to fifteen, preferably from four to ten supporting bars (34) which are arranged transversely with respect to the machine running direction and come into contact with the upper press felt (2, 3, 8).
7. Pressing section according to one of the preceding claims, characterized in that the pressure nip is the second pressure nip of the pressing section and is arranged, in particular, downstream of a first pressure nip which is configured as a shoe pressure nip.
8. Pressing section according to one of Claims 1 to 6, characterized in that the pressure nip is the first pressure nip of the pressing section and, in particular, the only pressure nip of the pressing section.
9. Pressing section according to one of the preceding claims, characterized in that the supporting element (30, 31, 32) is not evacuated directly or indirectly and is not loaded with vacuum.
10. Pressing section according to one of the preceding Claims 1 to 8, characterized in that the supporting element (30, 31, 32) is loaded with vacuum by being connected directly to a suction means or being evacuated indirectly by the suction pick-up roll (14, 15, 19), or by a suction effect being generated on the supporting element (30, 31, 32) via a corresponding foil nozzle which is supplied with compressed air.
11. Pressing section according to Claim 10, characterized in that the vacuum which is measured in the region of the supporting element (30, 31, 32) on that side of the upper press felt (2, 3, 8) which faces away from the web lies between 0.5 and 20 kPa, preferably between 0.5 and 10 kPa and particularly preferably between 1 and 5 kPa.
12. Pressing section according to one of the preceding claims, characterized in that a steam blower box (41) which can blow steam onto the fibrous web is provided on that side of the upper press felt (2, 3, 8) which lies opposite the supporting element (30, 31, 32) and/or the suction roll (14, 15, 19).
13. Pressing section according to Claim 12, characterized in that the box length of the steam blower box (41) is at most 1000 mm, preferably at most 500 mm, particularly preferably at most 350 mm in the web running direction.
14. Pressing section according to Claim 12 or 13, characterized in that the nozzle openings of the steam blower box (41), from which the steam flows, have a diameter of between 1 and 10 mm.
15. Pressing section according to one of the preceding claims, characterized in that the drives of the pressing section are configured in such a way that a differential speed of between 0.3 and 2%, preferably between 0.5 and 1.5% from the upper press felt (2, 3, 8) to the preceding fabric (5, 7) can be set.

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