US20040020549A1

US20040020549A1 - Endless fabric

Info

Publication number: US20040020549A1
Application number: US10/357,251
Authority: US
Inventors: Thomas Augscheller; Ulrich Begemann
Original assignee: Voith Paper Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2000-07-31
Filing date: 2003-01-31
Publication date: 2004-02-05
Also published as: DE10037367A1; DE20107844U1; DE20107846U1

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 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

This application corresponds to and claims foreign priority benefits under 35 U.S.C. 119 (a)-(d) or (f), or 365 (b) based upon German patent applications No. 100 37 367.4 filed Jul. 31, 2002, and No. 201 07 844.9 filed May 9, 2001, and No. 201 07 846.5 filed May 9, 2001.

The invention generally relates to an endless fabric, in particular a felt or a screen, for a machine for the manufacture and/or converting of a paper web, a card web, a tissue web or another fiber web.

It relates among other things to a compressible, water absorbing and endless pressing felt for use in pressing sections for the dewatering of paper webs, card webs, tissue webs or other fiber webs as well as to a method for the manufacture of the same, furthermore to a former screen of a former for the forming of a sheet of a machine for the manufacture of a paper web, a card web, a tissue web or another fiber web, said screen transferring the fiber web to a succeeding machine unit and also continuing to transport the edge strips of the fiber web separated prior to the transfer of the fiber web after the transfer of the fiber web, and finally to a drying screen of a drying section of a machine for the manufacture and/or converting of a paper web, a card web, a tissue web or another fiber web which guides the fiber web and partly surrounds at least one heated rotating dryer cylinder, with the fiber web coming into contact with the dryer cylinder.

In particular with press nips having pressing felts arranged at both sides of the fiber web, guide problems frequently occur after the press nip with respect to the fiber web (after the leading away of a pressing felt). This applies above all with relatively high dry contents of the fiber web. Consequently, web edge lifting can occur, which can in turn result in crease formation, tears or even tearing-off of the fiber web.

Previously, this has been countered by a suction of the pressing felt in the region at risk on the side remote from the fiber web. However, this is very expensive with respect to design and energy.

The dewatering and formation of the fiber web takes place in the former, with the fiber web being guided by at least one former screen. The former screen is permeable for air and water and usually transfers the fiber web to a pressing felt of a succeeding pressing section for the further dewatering of the fiber web.

The fiber web formed in the former is generally wider than necessary, since only the homogeneously formed center part of the fiber web is further treated in the following machine unit. The separation of the edge strip therefore takes place by means of a water jet prior to the transfer of the fiber web.

For the drying of the fiber web, it is guided in dryer groups of the drying section, generally supported by a drying screen, via guide rolls and heated dryer cylinders, with the fiber web coming into contact with the smooth surface of the dryer cylinder. Due to the adhesion of the fiber web to the dryer cylinder which thereby results, the fiber web tends to run with the dryer cylinder when the drying screen is guided away. This is in particular problematic with a high moisture content of the fiber web, i.e. at the start of the drying section.

To counteract this, the dryer groups are made very short at the start of the drying section and tensions, that is different speeds, are built up between the dryer groups. This is not only complex, it also strains the fiber web.

It is therefore an object of the invention, to improve the guiding of the fiber web at the pressing felt using simple means. A further object of the invention consists of ensuring that the edge strips also adhere to the former screen after the transfer of the center part to the former screen even at high machine speeds. Finally, it is the underlying object of the invention to counteract the adhesion of the fiber web to the dryer cylinder with means which are as simple as possible.

These objects are generally satisfied in accordance with the invention, in that the endless fabric in question has increased adhesion in adhesion zones which extend opposite the edge regions of the fiber web.

In accordance with the invention, the object set with respect to the pressing felt is satisfied in that the pressing belt has increased adhesion in adhesion zones extending opposite the edge regions of the fiber web. This results in improved adhesion of the edge regions and thus also of the whole fiber web at the pressing felt. The adhesion zones can admittedly cause differences in quality in the edge regions of the fiber web, but since the edge regions are generally anyway cut off in the following machine units, this is insignificant. It is sufficient for the achieving of good adhesion, also under the aspect of minimizing the trimmings, for the adhesion zones of the pressing felt to each cover one edge region of the fiber web with a width between 2 up to 25 cm.

However, it is also possible per se, or in combination with the aforesaid solution, for the pressing felt to have an increased air permeability in adhesion zones extending opposite the edge regions of the fiber web. The efficiency of suction devices on the edge regions of the fiber web improves due to the reduced flow resistance, with the suction devices being arranged, for example in the form of suction boxes or suction rolls, on the side of the pressing felt opposite the fiber web. With respect to design, the pressing felt can be designed like a screen and/or have larger pores.

A possibility of increasing the adhesion of the pressing felt lies in that fact that the pressing felt is coated or soaked with a polymer, preferably polyurethane or polyamide, in the adhesion zone at least on the side contacting the fiber web, with it being of advantage with respect to the manufacture for the adhesion zone to be treated with a liquid polymer and to be treated again, in particular ground and/or imprinted after the hardening thereof.

Another solution for the improvement of the adhesion lies in the fact that the pressing felt has finer mat fibers in the adhesion zone, at least at the surface contacting the fiber web, than between the adhesion zones, the diameter of said mat fibers preferably being smaller than 27 micrometers and/or having chemically treated mat fibers. Complementary to this, or as an independent variant, it is, however, also possible for the pressing felt to have a larger number of mat fibers in the adhesion zone, at least at the surface contacting the fiber web, than at the surface between the adhesion zones.

In all solutions, however, the thickness of the pressing felt in the adhesion zone in the loaded state should differ from the thickness between the adhesion zones by a maximum of 1 mm, preferably a maximum of 0.5 mm. This restricts the effects on the quality of the fiber web, in particular on the edge regions. In this connection, it is also of advantage for the compressibility of the pressing felt in the direction of thickness and/or the longitudinal extent of the pressing felt under tension to be as constant as possible over the width of the pressing felt.

In accordance with the invention, the object set with respect to the former screen is correspondingly satisfied in that the former screen has increased adhesion in adhesion zones which extend opposite the edge regions of the fiber web. This results in improved adhesion of the edge strips to the former screen such that there is no scrap flying.

A possibility of increasing the adhesion consists of the fact that the former screen has a lower air permeability in the adhesion zones than in the main region lying therebetween. The former screen should preferably even be made impermeable to air in the adhesion zones. This makes the rear ventilation, and thus the separation of the edge zones, more difficult.

For this purpose, the former screen should preferably be filled with a polymer, preferably polyurethane, in the adhesion zones.

The adhesion can also be increased in that the former screen has a smooth surface in the adhesion zones at the side facing the fiber web. Due to the good adhesion, the adhesion zones do not have to cover the whole width of the edge strips. Preferably less than 60%, in particular less than 40%, of the width of the edge strips is usually sufficient.

In the use of such a former screen in a former, at least one scraper and/or water nozzle and/or air nozzle should be associated with the adhesion zones after the transfer of the fiber web for the removal of the edge strips from the adhesion zones.

In cases in which the former is formed by two former screens which are usually arranged over one another and between which the fiber web extends, only one former screen, preferably the one which transfers the fiber web to the next machine unit, should have adhesion zones. This is generally the lower former screen.

In accordance with the invention, the object set with respect to the dryer screen is satisfied in that the dryer screen has increased adhesion in adhesion zones extending opposite the edge regions, with the fact being taken into account that in particular the edge regions of the fiber web adhere more pronouncedly to the dryer cylinder. It is therefore sufficient to arrange adhesion zones opposite the edges of the fiber web.

The adhesion zones of the dryer screen should each cover an edge region of the fiber web with a width from 300 to 100 mm.

A possibility of increasing the adhesion consists of the fact that the dryer screen has a smooth surface in the adhesion zones at the side facing the fiber web. It is further also possible per se, or in combination with the smooth surface, for the dryer screen to have a lower air permeability in the adhesion zones than in the main region lying therebetween. The adhesion zones should preferably even be made impermeable to air.

This design of the adhesion zones in particular becomes possible in that the dryer screen is filled with a polymer, preferably polyurethane, in the adhesion zones.

The impairment of the air permeability in the adhesion zones obstructs a rear ventilation and thus increases the adhesion of the fiber web to the dryer screen. On the other hand, however, this impairs the steaming out, and thus the drying, of the fiber webs in the edge regions. However, this can be accepted in the edge regions since these are anyway later cut off and/or usually anyway tend to overdrying.

Dryer screens designed in this manner should in particular be used in dryer groups of the drying section in which only one side of the fiber web comes into contact with heated dryer cylinders. This is substantially due to the fact that the fiber web does not have to be transferred between dryer screens in these dryer groups.

The invention should be explained in more detail below with reference to various embodiments and to the drawing, in which are shown: [0029]
FIG. 1 a cross-section through the edge of a pressing felt; [0030]
FIG. 2 a schematic cross-section through an end region of a former; [0031]
FIG. 3 a cross-section through a former screen with fiber web; and [0032]
FIG. 4 a cross section through the edge of a dryer screen.[0033]
Reference is made in the following to FIG. 1, in which a cross-section through the edge of a [0034] pressing felt 2 is shown.
In particular in pressing sections of paper making machines for the dewatering of paper webs using two long press nips, through which one respective, usually separate, endlessly circulating [0035] pressing felt 2 extends on both sides of the fiber web 1, problems result in the guiding of the fiber web 1 above all at high speeds. The fiber web 1 reaches a relatively high drying content after only the first press nip, which reduces the adhesion to the pressing felt 2. This naturally only becomes a problem when the pressing felt 2 is guided off at the other side of the fiber web 1. The low adhesion of the fiber web 1 to the pressing felt 2 often results in the lifting off of the web edges of the fiber web 1. This results in turn in web flutter or web tears.
To solve this problem, a [0036] pressing felt 2 is used in addition to a suction of the leading pressing felt 2, or above all on its own, which has increased adhesion in adhesion zones 3 extending opposite the edge regions 4 of the fiber web 1. Since this is usually associated with a changed surface structure in the adhesion zone 3 of the pressing felt 2, impairments in the quality of the fiber web 1 in the edge region 4 cannot be precluded. It is, however, sufficient for a good adhesion of the fiber web 1 to the pressing felt 2 for the adhesion zones 3 of the pressing felt 2 to each cover an edge region 4 of the fiber web 1 with a width of approximately 10 to 15 cm. Since these edge regions 4 are cut off in succeeding units of the paper making machine, at the latest on the wrapping up, this impairment of quality is without consequences.
To increase the adhesion, the surface of the [0037] pressing felt 2 coming into contact with the fiber web 1 in the adhesion zone 3, which extends here up to the end of the pressing felt 2, is coated with polyurethane, with the polyurethane also penetrating into the pressing felt 2.
After the thermal or chemical hardening of the polyurethane, the grinding off of elevations of this coating as well as a roughening of the surface of the coating takes place by means of an imprinting roll. Too smooth an adhesion zone [0038] 3 could have the consequence of too strong an adhesion of the fiber web 1, which results in difficulties in the handing over of the fiber web 1.
Since this coating with a polymer [0039] 5 results in a thickening of the adhesion zones 3 of the pressing felt 2, care must be taken, in particular in the subsequent treatment, that the thickness of the pressing felt 2 in the adhesion zone 3 in the unloaded state is at a maximum 0.5 mm larger than between the adhesion zones 3. It must moreover be observed in the polymer 5 and in the penetration of the pressing felt 2 by this polymer 5 that the compressibility of the pressing felt 2 in the thickness direction and/or the longitudinal extent of the pressing felt 2 under tension is as constant as possible over the width of the pressing felt 2.
The coating with the polymer [0040] 5 can result in the fact that the pressing felts 2 become impermeable to water in the adhesion zone 3 and can no longer absorb any water. However, due to the following trimming, these wetter, narrow edge regions 4 also do not bring along any disadvantages with them.
Instead of the coating with the polymer [0041] 5, the adhesion in the adhesion zone 3 can also be improved in that the pressing felt 2 in the adhesion zone 3 has finer mat fibers at least at the surface contacting the fiber web 1 than between the adhesion zones 3, whose diameter is preferably smaller than 27 μm, and/or has chemically treated mat fibers, and/or the pressing felt 2 in the adhesion zone 3 has a larger number of mat fibers at least at the surface contacting the fiber web 1 than at the surface between the adhesion zones 3. This also results in a changed surface structure in the adhesion zone 3 of the pressing felt 2.
Reference is made in the following to FIGS. 2 and 3 in which a schematic cross-section through an end region of a former or a part section through a [0042] former screen 13 with a fiber web 11 is shown.
The former of a paper making machine for the dewatering and forming of the [0043] fiber web 11, that is here specifically of the paper web, is formed by two endlessly circulating former screens 13, 18 which are arranged over one another and between which the fiber web 11 lies.
The [0044] former screens 13, 18 guided via guide rolls 13, 18 are separated from one another at the end of the former, with the fiber web 11 running along with the lower former screen 13.
The cutting off of the edge strips [0045] 12 from the homogeneous part of the fiber web 11 subsequently takes place via water jet nozzles 22. Subsequently, the fiber web 11 is taken over by a pressing felt 19 of the following pressing section wrapping around a guide roll 20 with suction for the further dewatering.
The lower [0046] former screen 13 has adhesion zones 14 of increased adhesion opposite the edge strips 12. For this purpose, the adhesion zones 14 of the former screen 13 are filled with polyurethane. While the main region 15 of the former screen 13 is permeable to air for the dewatering of the fiber web 11, the adhesion zones 14 are impermeable to air. In addition, the surface of the adhesion zones 14 facing the edge strips 12 is smooth. Both measures result in the fact that the edge strips 12 also adhere securely to the former screen 13 after the handing over of the fiber web 11.
The release of the edge strips [0047] 12 from the former screen 13 by means of a respective scraper 16 and the guiding away into the pulper only takes place later. A cleaning of the former screen 13, in particular of the adhesion zones 14, then takes place via water nozzles 17, with contaminants and the splashing water being taken up by a suction bell 23.
Reference is made in the following to FIG. 4 in which a cross-section through the edge of a [0048] dryer screen 22 is shown.
For the drying in the single-row dryer group of a drying section, the [0049] fiber web 21, guided by the dryer screen 22, runs alternately over guide rolls and heated rotating dryer cylinders 23, with it coming into contact with the dryer cylinders 23.
To be able to guide off the [0050] fiber web 21 relatively simply and reliably from the dryer cylinder 23 after the part wrapping around, the dryer screen 2 has increased adhesion in adhesion zones 24 extending opposite the edge regions of the fiber web 21.
For this purpose, the [0051] dryer screen 22 is filled with polyurethane in the adhesion zones 24. The adhesion zones 24 are not only impermeable to air, but are also smooth opposite the fiber web 21.
Since in particular the edge regions of the [0052] fiber web 21 tend to increased adhesion to the smooth dryer cylinder 23, it is sufficient for the adhesion zones 24 each to cover an edge region of the fiber web 21 with a width between 30 and 100 mm.

REFERENCE NUMERAL LIST

[0053] 1 fiber web
[0054] 2 pressing felt
[0055] 3 adhesion zone
[0056] 4 edge zone
[0057] 5 polymer
[0058] 11 fiber web
[0059] 12 edge strip
[0060] 13 former screen
[0061] 14 adhesion zone
[0062] 15 main region
[0063] 16 scraper
[0064] 17 water nozzles
[0065] 18 former screen
[0066] 19 pressing felt
[0067] 20 guide roll with suction
[0068] 21 guide roll
[0069] 22 water jet nozzle
[0070] 23 suction bell

Claims

1. An endless fabric, in particular a felt (2) or a screen (13, 22), for a machine for the manufacture and/or converting of a paper web, a card web, a tissue web or another fiber web (1, 11, 21), characterized in that the endless fabric (2, 13, 22) has increased adhesion in adhesion zones (3, 14, 24) extending opposite the edge regions (4, 12) of the fiber web (1, 11, 21).

2. An endless fabric in accordance with claim 1, characterized in that it is formed by a compressible, water absorbing and endless pressing felt (2) for use in pressing sections for the dewatering of paper webs, card webs, tissue webs or other fiber webs (1).

3. An endless fabric (2) in accordance with claim 2, characterized in that the adhesion zones (3) of the pressing felt (2) each cover an edge region (4) of the fiber web (1) with a width between 2-25 cm.

4. An endless fabric (2) in accordance with claim 2, characterized in that the pressing felt (2) is coated with a polymer (5), preferably polyamide, in the adhesion zone (3) at least on the side contacting the fiber web (1).

5. A method for the manufacture of the endless fabric or pressing felt (2) in accordance with claim 4, characterized in that the adhesion zone is treated with a liquid polymer (5), and treated again, in particular ground and/or imprinted, after the hardening thereof.

6. An endless fabric in accordance with claim 2, characterized in that the pressing felt (2) has finer mat fibers in the adhesion zone (3), at least at the surface contacting the fiber web (1), than between the adhesion zones (3), whose diameter is preferably smaller than 27 μm and/or has chemically treated mat fibers.

7. An endless fabric (2) in accordance with claim 2, characterized in that the pressing felt (2) has a larger number of mat fibers in the adhesion zone (3), at least at the surface contacting the fiber web (1), than at the surface between the adhesion zones (3).

8. An endless fabric (2) in accordance with claim 2, characterized in that the thickness of the pressing felt (2) in the adhesion zone (3) deviates in the loaded state by a maximum of 1 mm, preferably a maximum of 0.5 mm, from the thickness between the adhesion zones (3).

9. An endless fabric in accordance with claim 2, characterized in that the compressibility of the pressing felt (2) in the thickness direction and/or the longitudinal extent of the pressing felt (2) under tension is as constant as possible over the width of the pressing felt (2).

10. An endless fabric, in particular a felt (2) or a screen (13, 22) for a machine for the manufacture and/or converting of a paper web, a card web, a tissue web or another fiber web (1, 11, 21), in particular in accordance with claim 1, characterized in that it is formed by a compressible, water absorbing and endless pressing felt (2) for use in pressing sections for the dewatering of paper webs, card webs, tissue webs or other fiber webs (1); and in that the pressing felt (2) has an increased permeability for air in adhesion zones (3) extending opposite the edge regions (4) of the fiber web (1).

11. An endless fabric in accordance with claim 1, characterized in that it is formed by a former screen (13) of a former for the forming of a sheet of a machine for the manufacture of a paper web, of a card web, of a tissue web or of another fiber web (11), the screen transferring the fiber web (11) to a succeeding machine unit (11) and also continuing to guide the edge strips (12) of the fiber web (11) cut off prior to the transfer of the fiber web (11) after the transfer of the fiber web (11).

12. An endless fabric (13) in accordance with claim 11, characterized in that the former screen (13) has a lower permeability in the adhesion zones (14) than in the main region (15) therebetween.

13. An endless fabric (13) in accordance with claim 11, characterized in that the former screen (13) is impermeable to air in the adhesion zones (14).

14. An endless fabric (13) in accordance with claim 11, characterized in that the former screen (13) is filled with a polymer in the adhesion zone (14).

15. An endless fabric (13) in accordance with claim 11, characterized in that the former screen (13) has a smooth surface in the adhesion zones (14) on the side facing the fiber web (11).

16. A former comprising a former screen (13) in accordance with claim 11, characterized in that a scraper (16) and/or water nozzles (17) and/or air nozzles is/are associated with the adhesion zones (14) of the former screen (13) after the transfer of the fiber web (11) for the removal of the edge strips (12) from the adhesion zones (14).

17. A former in accordance with claim 16, characterized in that the former is formed by two former screens (13, 18) arranged over one another, between which the fiber web (11) extends, with preferably only the former screen (13) which transfers the fiber web (11) to the next machine unit having adhesion zones (14).

18. A former in accordance with claim 11, characterized in that the adhesion zones (14) only cover part of the edge strips (12), preferably less than 60%, in particular less than 40%, of the width of the edge strip (12).

19. An endless fabric in accordance with claim 1, characterized in that it is formed by a dryer screen (22) of a drying section of a machine for the manufacture and/or converting of a paper web, of a card web, of a tissue web, or of another fiber web (21), the screen guiding the fiber web (21) and at least partly wrapping around a heated, rotating dryer cylinder (23), with the fiber web (21) coming into contact with the dryer cylinder (23).

20. An endless fabric (22) in accordance with claim 19, characterized in that the adhesion zones (24) of the dryer screen (22) each cover an edge region of the fiber web (21) with a width from 30 to 100 mm.

21. An endless fabric (2) in accordance with claim 19, characterized in that the dryer screen (22) is filled with a polymer in the adhesion zones (24).

22. An endless fabric (22) in accordance with claim 19, characterized in that the dryer screen (22) has a lower air permeability in the adhesion zones (24) than in the main region (25) therebetween.

23. An endless fabric (2) in accordance with claim 19, characterized in that the dryer screen (22) is impermeable to air in the adhesion zones (24).

24. An endless fabric (22) in accordance with claim 19, characterized in that the dryer screen (22) has a smooth surface in the adhesion zones (24) on the side facing the fiber web (21).

25. Use of the endless fabric or of the dryer screen (22) made in accordance with claim 19 in dryer groups of the dryer section in which only one side of the fiber web (21) comes into contact with heated dryer cylinders (23).