EP1305472A1

EP1305472A1 - Endless belt

Info

Publication number: EP1305472A1
Application number: EP01980227A
Authority: EP
Inventors: Thomas Augscheller; Ulrich Begemann
Original assignee: Voith Paper Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2000-07-31
Filing date: 2001-07-31
Publication date: 2003-05-02
Also published as: WO2002010510A1

Abstract

The invention relates to an endless belt, especially made of felt or sieve, for a machine for producing and/or upgrading a web (1, 11, 21) of paper, paperboard, tissue or other fibers. The inventive belt is characterized in that it has an increased adhesive power in adhesive zones (3, 14, 24) that extend opposite the marginal zones (4, 12) of the fiber web (1, 11, 21).

Description

endless belt

The invention relates generally to an endless belt, in particular felt or screen, for a machine for producing and / or finishing a paper, cardboard, tissue or other fibrous web.

It relates, inter alia, to a compressible, water-absorbing and endless press felt for use in press sections for dewatering paper, cardboard, tissue or other fibrous webs, and to a method for producing the same, and also to a forming wire of a former for forming a machine for producing a paper , Cardboard, tissue or other fibrous web, which transfers the fibrous web to a subsequent machine unit and continues the edge strips of the fibrous web separated before the transfer of the fibrous web also after the transfer of the fibrous web, and finally a dryer fabric of a dryer section of a machine for the manufacture and / / or finishing a paper, cardboard, tissue or other fibrous web which guides the fibrous web and partially wraps around at least one heated rotating drying cylinder, the fibrous web coming into contact with the drying cylinder.

Particularly in the case of press nips with press felts arranged on both sides of the fibrous web, guide problems with regard to the fibrous web often occur after the press nip (after a press felt has been removed). This is especially true when the fibrous web has a relatively high dry content. As a result, web edge lifts can occur, which in turn can lead to wrinkling, tearing or even tearing of the fibrous web.

So far, this has been countered by suctioning the press felt on the side facing away from the fibrous web in the endangered area. However, this is constructively and energetically very complex.

The fiber web is dewatered and formed in the former, and is guided by at least one forming wire. The forming wire is permeable to air and water and usually passes the fibrous web to a press felt of a subsequent press section for further dewatering of the fibrous web.

The fibrous web formed in the former is generally wider than necessary, since only the homogeneously formed middle part of the fibrous web is treated further in the following machine unit. Therefore, before the transfer of the fibrous web, the edge strips are cut off using a water jet.

To dry the fibrous web, it is guided in drying groups in the dryer section, generally supported by a dryer fabric, over guide rollers and heated drying cylinders. The fibrous web comes into contact with the smooth surface of the drying cylinders. Because of the resulting adhesion of the fibrous web to the drying cylinder, the fibrous web tends to run with the drying cylinder when the drying wire is removed. This is particularly problematic when the fibrous web has a high moisture content, ie at the beginning of the dryer section. To counteract this, the dryer groups are designed to be very short at the beginning of the dryer section and trains, i.e. differential speeds, are built up between the dryer groups. This is not only complex, but also strains the fibrous web.

An object of the invention is therefore to improve the guidance of the fibrous web on the press felt with simple means. Another object of the invention is to ensure that the edge strips adhere to the forming wire even after the middle part has been transferred, even at high machine speeds. Finally, the invention has for its object to counteract the adhesion of the fibrous web to the drying cylinder with the simplest possible means.

According to the invention, these objects are generally achieved in that the endless belt in question has increased adhesion in adhesive regions which run opposite the edge regions of the fibrous web.

According to the invention, the object arising with respect to the press felt was therefore achieved in that the press felt has increased adhesion in adhesive areas which run opposite the edge areas of the fibrous web. This leads to improved adhesion of the edge areas and thus also the entire fibrous web to the press felt. Although the adhesive areas can cause qualitative differences in the edge areas of the fibrous web, this is irrelevant since the edge areas are generally separated in the subsequent machine units anyway. To achieve good adhesion, it is also sufficient from the aspect of minimizing the bleed if the adhesive areas of the press felt each cover an edge area of the fibrous web with a width of between 2 and 25 cm.

However, alone or in combination with the solution described above, it is also possible for the press felt to have increased air permeability in adhesive areas which run opposite the edge areas of the fibrous web. The reduced flow resistance improves the effectiveness of suction devices on the edge regions of the fibrous web, the suction devices being arranged, for example in the form of suction boxes or suction rolls, on the side of the press felt opposite the fibrous web. With regard to the design, the press felt can be designed like a sieve in the adhesive areas and / or have larger pores.

One way to increase the adhesion of the press felt is to coat or soak the press felt in the adhesive area at least on the side in contact with the fibrous web with a polymer, preferably polyurethane or polyamide. With regard to the production, it is advantageous if the adhesive area is treated with a liquid polymer and, after it has cured, aftertreated, in particular ground and / or embossed.

Another solution to improve the adhesion is that the press felt in the adhesive area has at least on the surface touching the fibrous web of fine nonwoven fibers than between the adhesive areas, the diameter of which is preferably less than 27 micrometers and / or has chemically treated nonwoven fibers. In addition to this or as an independent variant, it is also possible that the press felt in Adhesion area, at least on the surface contacting the fibrous web, has a larger number of nonwoven fibers than on the surface between the adhesion areas.

In all solutions, however, the thickness of the press felt in the adhesive area in the loaded state should deviate from the thickness between the adhesive areas by a maximum of 1 mm, preferably a maximum of 0.5 mm. This limits the impact on the quality of the fibrous web, especially the edge areas. In this context, it is also advantageous if the compressibility of the press felt in the thickness direction and / or the longitudinal extension of the press felt under tension across the width of the press felt is as equal as possible.

According to the invention, the problem arising with respect to the forming wire is achieved accordingly in that the forming wire has increased adhesion in adhesive areas which run opposite the edge areas of the fibrous web. This leads to an improved adhesion of the edge strips to the forming wire, so that there is little scrapping.

One possibility of increasing the adhesion is that the forming wire has a lower air permeability in the adhesive areas than in the main area in between. Preferably, the forming wire should even be air-impermeable in the adhesive areas. This makes rear ventilation more difficult and thus detachment of the edge strips.

For this purpose, the forming wire should be filled with a polymer, preferably polyurethane, in the adhesive areas. Adhesion can also be increased in that the forming wire has a smooth surface in the adhesive areas on the side facing the fibrous web.

Due to the good adhesion, the adhesive areas do not have to cover the entire width of the edge strips. Preferably less than 60%, in particular less than 40%, of the width of the edge strips is usually sufficient.

When using such a forming wire in a former, at least one scraper and / or water and / or air nozzle should be assigned to the adhesive areas after the transfer of the fibrous web to remove the edge strips from the adhesive areas.

In cases in which the former is formed by two forming screens, usually arranged one above the other, between which the fibrous web runs, only one, preferably the forming screen, which transfers the fibrous web to the next machine unit, should have adhesive areas. This is generally the lower forming wire.

According to the invention, the problem arising with respect to the dryer fabric is achieved in that the dryer fabric has increased adhesion in adhesive areas which run opposite the edge areas of the fibrous web. The knowledge was taken into account that in particular the edge areas of the fibrous web adhere more strongly to the drying cylinder. It is therefore sufficient to arrange adhesive areas opposite the edges of the fibrous web. The adhesive areas of the dryer fabric should each cover an edge area of the fibrous web with a width of 30 to 100 mm.

One possibility of increasing the adhesion is that the dry sieve has a smooth surface in the adhesive areas on the side facing the fibrous web. On its own or in combination with the smooth surface, it is also possible for the dry sieve to have less air permeability in the adhesive areas than in the main area in between. The adhesive areas should preferably even be air-impermeable.

This design of the adhesive areas is made possible in particular by filling the dryer fabric in the adhesive areas with a polymer, preferably polyurethane.

The impairment of the air permeability in the adhesive areas hinders rear ventilation and thus increases the adhesion of the fibrous web to the dryer fabric. On the other hand, however, this affects the evaporation and thus the drying of the fibrous web in the edge areas. However, this can be tolerated in the marginal areas, since these are later cut off anyway and / or tend to over-dry anyway.

Dryer screens designed in this way should be used in particular in dryer groups in the dryer section in which only one side of the fibrous web comes into contact with heated drying cylinders. This is essentially due to the fact that in these dryer groups the fibrous web does not have to be transferred between dryer fabrics. The invention should be explained in more detail below on the basis of various exemplary embodiments with reference to the drawing; in this show:

1 shows a cross section through the edge of a press felt,

2 shows a schematic cross section through an end region of a former,

Fig. 3 shows a cross section through a forming wire with fibrous web and

Fig. 4 shows a cross section through the edge of a dryer fabric.

In the following, reference is made to FIG. 1, in which a cross section through the edge of a press felt 2 is shown.

In particular in press sections of paper machines for dewatering paper webs with two long press nips through which a, usually separate, endlessly circulating press felt 2 runs on both sides of the fibrous web 1, problems arise when guiding the fibrous web 1, especially at high speeds. The fibrous web 1 already reaches a relatively high dry content after the first press nip, which reduces the adhesion to the press felt 2. Of course, this only becomes a problem when the press felt 2 is guided away on the other side of the fibrous web 1. The low adhesion of the fibrous web 1 to the press felt 2 often leads to the web edges of the fibrous web 1 being lifted off. This in turn results in web flutter or web breaks. To solve this problem, a press felt 2 is used in addition to a suction of the leading press felt 2 or above all on its own, which has increased adhesion in adhesive areas 3, which run in relation to the edge areas 4 of the fibrous web 1. Since this is usually associated with a changed surface structure in the adhesive area 3 of the press felt 2, impairments in the quality of the fibrous web 1 in the edge area 4 cannot be ruled out. However, for good adhesion of the fibrous web 1 to the press felt 2, it is sufficient if the adhesive regions 3 of the press felt 2 each cover an edge region 4 of the fibrous web 1 with a width of approximately 10 to 15 cm. Since these edge areas 4 are cut off anyway in subsequent units of the paper machine, at the latest when winding up, this impairment of the quality has no consequences.

To increase the adhesion, the surface of the press felt 2 which comes into contact with the fibrous web 1 is coated in the adhesive region 3, which here extends to the end of the press felt 2, with polyurethane. The polyurethane also penetrates into the press felt 2.

After the polyurethane has been thermally or chemically cured, elevations of this coating are ground off and the surface of the coating is roughened by means of an embossing roller. A too smooth adhesive area 3 could result in excessive adhesion of the fibrous web 1, which leads to difficulties in dispensing the fibrous web 1.

Since this coating with a polymer 5 leads to a thickening of the adhesive areas 3 of the press felt 2, action to ensure that the thickness of the press felt 2 in the adhesive area 3 in the unloaded state is a maximum of 0.5 mm greater than between the adhesive areas 3. In addition, with the polymer 5 and the penetration of the press felt 2 by this polymer 5, it should be noted that the compressibility of the press felt 2 in the thickness direction and / or the longitudinal expansion of the press felt 2 under tension across the width of the press felt 2 is as equal as possible.

The coating with the polymer 5 can cause the press felts

2 become impermeable to water in the detention area 3 and can no longer absorb water. Because of the following edge trimming, however, these moist, narrow edge regions 4 also have no disadvantages.

Instead of the coating with the polymer 5, the adhesion in the adhesive area 3 can also be improved in that the press felt 2 in the adhesive area

3 at least on the surface touching the fibrous web 1 has finer nonwoven fibers than between the adhesive areas 3, the diameter of which is preferably less than 27 μm and / or has chemically treated nonwoven fibers and / or the press felt 2 in the adhesive area 3 at least on the fibrous web 1 touching surface has a greater number of nonwoven fibers than on the surface between the adhesive areas 3. This also leads to a changed surface structure in the adhesive areas 3 of the press felt 2.

In the following, reference is made to FIGS. 2 and 3, in which a schematic cross section through an end region of a former or a partial step through a former screen 13 with a fibrous web 11 is shown. The former of a paper machine for dewatering and forming the fibrous web 11, that is to say specifically the paper web here, is formed by two superimposed, continuously rotating forming screens 13, 18, between which the fibrous web 11 lies.

The forming wires 13, 18 guided over guide rollers 21 are separated from one another at the end of the forming device, the fibrous web 11 running with the lower forming wire 13.

The edge strips 12 are then separated from the homogeneous part of the fibrous web 11 by means of water jet nozzles 22. The fibrous web 11 is then taken over by a press felt 19 of the following press section which wraps around a suction guide roller 20 for further dewatering.

The lower former 13 has adhesive areas 14 with increased adhesion compared to the edge strips 12. For this purpose, the adhesive areas 14 of the forming wire 13 are filled with polyurethane. While the main area 15 of the forming wire 13 is air-permeable for dewatering the fibrous web 11, the adhesive areas 14 are air-impermeable. In addition, the surface of the adhesive areas 14 facing the edge strips 12 is smooth. Both measures result in the edge strips 12 adhering securely to the forming wire 13 even after the fibrous web 11 has been released.

Only later is the detachment of the edge strips 12 from the forming wire 13 by means of a scraper 16 and the removal into the pulper. Thereafter, the forming wire 13, in particular the adhesive areas, is cleaned 14 instead of water nozzles 17, impurities and the spray water being absorbed by a suction bell 23.

In the following, reference is made to FIG. 4, in which a cross section through the edge of a dryer fabric 22 is shown.

The fibrous web 21 runs for drying in the single-tier dryer group of a dryer section from the dryer fabric 22, alternately over guide rollers and heated, rotating dryer cylinders 23, whereby it comes into contact with the dryer cylinders 23.

In order to be able to guide the fibrous web 21 relatively easily and safely away from the drying cylinder 23 after the partial wrapping, the drying wire 2 has an increased adhesion in adhesive areas 24 which run opposite the edge areas of the fibrous web 21.

For this purpose, the dryer fabric 22 is filled with polyurethane in the adhesive areas 24. The adhesive areas 24 are not only airtight, but also smooth in relation to the fibrous web 21.

Since, in particular, the edge regions of the fibrous web 21 tend to adhere to the smooth drying cylinder 23, it is sufficient if the adhesive regions 24 each cover an edge region of the fibrous web 21 with a width between 30 and 100 mm. LIST OF REFERENCE NUMBERS

Fibrous web

press felt

adhesion area

border area

polymer

Fibrous web

edge strips

forming wire

adhesion area

main area

scraper

water jets

forming wire

Press felt sucked guide roller

guide roll

water jet

suction cup

Claims

claims

1. endless belt, in particular felt (2) or sieve (13, 22), for a machine for producing and / or finishing a paper, cardboard, tissue or other fibrous web (1, 11, 21), characterized in that the endless belt (2, 13, 22) has increased adhesion in adhesive areas (3, 14, 24) which run opposite to the edge areas (4, 12) of the fibrous web (1, 11, 21).

2. Continuous belt according to claim 1, characterized in that it is formed by a compressible, water-absorbing and endless press felt (2) for use in press sections for dewatering paper, cardboard, tissue or other fibrous webs (1).

3. Endless belt (2) according to claim 2, characterized in that the adhesive areas (3) of the press felt (2) each cover an edge area (4) of the fibrous web (1) with a width between 2-25 cm.

4. endless belt (2) according to claim 2 or 3, characterized in that the press felt (2) in the adhesive region (3) at least on the fiber Web (1) touching side is coated with a polymer (5), preferably polyamide.

5. A process for the production of the endless belt or press felt (2) according to claim 4, characterized in that the adhesive area is treated with a liquid polymer (5) and after curing the same is treated, in particular ground and / or embossed.

6. endless belt according to claim 2 or 3, characterized in that the press felt (2) in the adhesive area (3) at least on the fibrous web (1) contacting surface has finer nonwoven fibers than between the adhesive areas (3), the diameter of which is preferably less than 27 is μm and / or has chemically treated nonwoven fibers.

7. endless belt (2) according to one of claims 2, 3 or 6, characterized in that the press felt (2) in the adhesive region (3) at least on the, the fibrous web (1) contacting surface a larger number of non-woven fibers than on the surface between the adhesive areas (3).

8. endless belt (2) according to any one of claims 2 to 7, characterized in that the thickness of the press felt (2) in the adhesive region (3) in the loaded Zu- stood a maximum of 1 mm, preferably a maximum of 0.5 mm from the thickness between the adhesive areas (3).

9. Continuous belt according to one of claims 2 to 8, characterized in that the compressibility of the press felt (2) in the thickness direction and / or the longitudinal expansion of the press felt (2) under tension across the width of the press felt (2) is as equal as possible.

10. endless belt, in particular felt (2) or sieve (13, 22), for a machine for producing and / or finishing a paper, cardboard, tissue or other fibrous web (1, 11, 21), in particular according to one of the Claims 2 to 9, characterized in that it is formed by a compressible, water-absorbing and endless press felt (2) for use in press sections for dewatering paper, cardboard, tissue or other fibrous webs (1) and in that the press felt (2 ) in adhesive areas (3), which run in relation to the edge areas (4) of the fibrous web (1), has an increased air permeability.

11. Endless belt according to claim 1, characterized in that it is formed by a forming wire (13) of a former for forming a sheet for a machine for producing a paper, cardboard, tissue or other fibrous web (11) which forms the fibrous web (11 ) passes to a subsequent machine unit and the edge strips separated before the transfer of the fibrous web (11) (12) of the fibrous web (11) continues after the transfer of the fibrous web (11).

12. endless belt (13) according to claim 11, characterized in that the forming wire (13) in the adhesive areas (14) has a lower air permeability than in the intermediate main area (15).

13. Continuous belt (13) according to claim 11 or 12, characterized in that the forming wire (13) in the adhesive areas (14) is air-impermeable.

14. Endless belt (13) according to one of claims 11 to 13, characterized in that the forming wire (13) is filled with a polymer in the adhesive area (14).

15. Endless belt (13) according to any one of claims 11 to 14, characterized in that the forming wire (13) has a smooth surface in the adhesive areas (14) on the side facing the fibrous web (11).

16. Shaper with a forming wire (13) according to one of claims 11 to 15, characterized in that the adhesive areas (14) of the forming wire (13) after the transfer be assigned to the fibrous web (11) scraper (16) and / or water (17) and / or air nozzles for removing the edge strips (12) from the adhesive areas (14).

17. Shaper according to claim 16, characterized in that the shaper is formed by two superimposed forming screens (13, 18), between which the fibrous web (11) extends, preferably only the shaping screen (13) which the fibrous web (11) passes to the next machine unit, has adhesive areas (14).

18. Shaper according to one of claims 11 to 17, characterized in that the adhesive areas (14) cover only a part of the edge strips (12), preferably less than 60%, in particular less than 40%, of the width of the edge strip (12).

19. Endless belt according to claim 1, characterized in that it is formed by a dryer fabric (22) of a dryer section of a machine for producing and / or finishing a paper, cardboard, tissue or other fibrous web (21) which is the fibrous web (21) leads and at least partially wraps around a heated, rotating drying cylinder (23), the fibrous web (21) coming into contact with the drying cylinder (23).

20. Endless belt (22) according to claim 19, characterized in that the adhesive areas (24) of the dryer fabric (22) each cover an edge area of the fibrous web (21) with a width of 30 to 100 mm.

21. Endless belt (2) according to claim 19 or 20, characterized in that the dryer fabric (22) in the adhesive areas (24) is filled with a polymer.

22. endless belt (22) according to one of claims 19 to 21, characterized in that the drying fabric (22) in the adhesive areas (24) has a lower air permeability than in the intermediate main area (25).

23. Endless belt (2) according to one of claims 19 to 22, characterized in that the dryer fabric (22) is made air-impermeable in the adhesive areas (24).

24. Endless belt (22) according to one of claims 19 to 23, characterized in that the drying wire (22) has a smooth surface in the adhesive areas (24) on the side facing the fibrous web (21).

5. Use of the endless belt or dryer fabric (22) formed according to one of claims 19 to 24, in dryer groups of the dryer section in which only one side of the fibrous web (21) comes into contact with heated drying cylinders (23).