DRAINAGE FOIL FOR USE IN AN INSTALLATION FOR PRODUCING A PAPER WEB WITH A FABRIC BELT, WHICH CAN BE MOVED OVER A MULTIPLICITY OF DRAINAGE FOILS ORIENTED TRANSVERSELY TO ITS DIRECTION OF MOVEMENT

Abstract

A drainage foil for use in an installation for producing a paper web with a fabric belt, which can be moved over a multiplicity of drainage foils oriented transversely to a direction of movement. A surface of the drainage foil is formed with a defined profiling, which has elevations and/or depressions. The vertical extent of the profiling is at least 0.1 mm.

Claims

1. A drainage foil for use in an installation for producing a paper web with a fabric belt, the fabric belt being moved over a multiplicity of drainage foils oriented transversely to a direction of movement, the drainage foil comprising: a drainage foil body having a surface formed with a defined profiling, said defined profiling having elevations and/or depressions, and a vertical extent of said defined profiling is at least 0.1 mm.

2. The drainage foil according to claim 1, wherein said elevations and said depressions define said defined profiling and/or are distributed in a defined manner over said surface.

3. The drainage foil according to claim 1, wherein said drainage foil body has ceramic plates disposed beside one another and defining said surface of said drainage foil body, said elevations and/or said depressions are formed on a surface of said ceramic plates, wherein the vertical extent of said defined profiling is at least 0.1 mm.

4. The drainage foil according to claim 1, wherein the vertical extent of the defined profiling is up to 3.0 mm.

5. The drainage foil according to claim 1, wherein said surface is formed with said defined profiling oriented in a longitudinal extent of said drainage foil body or enclosing an acute angle with said drainage foil body in a form of ribs that are triangular in cross section.

6. The drainage foil according to claim 1, wherein said surface is formed with said defined profiling oriented in a longitudinal extent of said drainage foil body or enclosing an acute angle with said drainage foil body in a form of bars that are rectangular in cross section and rectangular grooves.

7. The drainage foil according to claim 1, wherein said surface is formed with said defined profiling oriented in a longitudinal extent of said drainage foil body or enclosing an acute angle with said drainage foil body in a form of bars that are wave-shaped in cross section.

8. The drainage foil according to claim 3, wherein said defined profiling of said ceramic plates disposed beside one another are offset with respect to one another transversely to a longitudinal direction of said drainage foil body.

9. The drainage foil according to claim 6, wherein a longitudinal extent of said elevations and/or said depressions enclose an angle of 0 to 80 with a longitudinal extent of said drainage foil body.

10. The drainage foil according to claim 1, wherein said defined profiling is formed by cut-outs formed in said surface and are concave in cross section and are disposed at a distance from one another or by cylindrical holes.

11. The drainage foil according to claim 1, wherein said surface has a convex curvature in a section transverse to a longitudinal extent of said drainage foil body.

12. The drainage foil according to claim 11, wherein said convex curvature has a radius of 100 mm to 500 mm.

13. The drainage foil according to claim 1, wherein said surface has side edges that are rounded in cross section with a radius of 0.5 mm to 5 mm.

14. The drainage foil according to claim 1, wherein the vertical extent of the profiling is up to 1.6 mm.

15. The drainage foil according to claim 1, wherein the vertical extent of the profiling is between 0.2 mm and 0.8 mm.

16. The drainage foil according to claim 6, wherein a longitudinal extent of said elevations and/or said depressions enclose an angle of 30 to 55 with the longitudinal extent of said drainage foil body.

17. The drainage foil according to claim 11, wherein said convex curvature has a radius of 200 mm to 350 mm.

18. The drainage foil according to claim 1, wherein said surface has side edges that are rounded in cross section with a radius of 1 mm to 3 mm.

19. A kit for an installation for producing a paper web, comprising: a supporting frame configured to be detachable fixed on a suction box of the installation; and drainage foils disposed on said supporting frame, said drainage foils each containing a drainage foil body having a surface formed with a defined profiling, said defined profiling having elevations and/or depressions, and a vertical extent of said defined profiling is at least 0.1 mm.

20. An installation for producing a paper web, comprising: a plurality of drainage foils each containing a drainage foil body having a surface formed with a defined profiling, said defined profiling having elevations and/or depressions, and a vertical extent of said defined profiling is at least 0.1 mm; and a fabric belt being moved over said plurality of drainage foils extending transversely to a direction of movement.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0017] FIG. 1 is a diagrammatic, sectional view of an installation for producing a paper web with a fabric belt, which is moved over drainage foils and a suction box located underneath, in a section located in the longitudinal direction of the movement of the fabric belt;

[0018] FIG. 1A is an illustration of detail X from FIG. 1 on a scale highly enlarged with respect to FIG. 1;

[0019] FIG. 2 is a perspective view of a first embodiment of a drainage foil according to the invention in an axonometric illustration;

[0020] FIG. 3 is a cross-sectional view of the drainage foil according to FIG. 2 on a scale highly enlarged with respect to FIG. 2;

[0021] FIG. 3A is an illustration corresponding to FIG. 1A to explain a mode of action of the drainage foil according to FIG. 3, on a scale highly enlarged with respect to FIG. 3;

[0022] FIGS. 4, 4A and 4B are cross-sectional views of three further embodiments of the drainage foil according to the invention;

[0023] FIG. 5 is a plan view of a further embodiment of a drainage foil according to the invention;

[0024] FIG. 5A is a cross-section view taken along the line V-V from FIG. 5;

[0025] FIG. 6 is a plan view of another embodiment of the drainage foil according to the invention;

[0026] FIG. 6A is a sectional view taken along the line VI-VI from FIG. 6;

[0027] FIG. 6B is a sectional view of yet another embodiment of the drainage foil according to the invention;

[0028] FIG. 7 is a sectional view of the drainage foil according to the invention according to FIG. 2 and on a scale enlarged with respect to FIG. 2;

[0029] FIG. 8 is a sectional view of a section of an installation for producing a paper web, formed with drainage foils according to the invention, with a fabric belt moved over the drainage foils and with a further formation of the surfaces of the drainage foils; and

[0030] FIG. 8A is a sectional view showing a detail Y from FIG. 8, on a scale highly enlarged with respect to FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Referring now to the figures of the drawings in detail and first, particularly to FIG. 1 thereof, there is shown a section of a fabric belt 1 in an installation for producing a paper web, on which a layer of a fibrous stock 2 is found and which is moved in the direction of arrow M over a group of drainage foils 3. The fibrous stock 2 is sprayed onto the fabric belt 1 at the start of the latter. The drainage foils 3 are each formed on their upper side with an overlay 4 made of a wear-resistant material. Underneath the drainage foils 3 there is a suction box 5, in an interior 51 of which there is a vacuum of about 2 mbar to 700 mbar. The drainage foils 3 are located on a supporting frame 52, which is detachably fixed to the upper side of the suction box 5.

[0032] The fabric belt 1, which extends over a length of up to about 50 m and can have a width of 2 m up to 12 m, is moved over the drainage foils 3 at a speed of, for example, 1 m/s to 40 m/s by means of transport rolls located in the installation.

[0033] The drainage foils 3 are usually but not necessarily produced from acid-resistant stainless steel, from a plastic, e.g. from polyethylene, or from a glass fiber reinforced plastic. The suction box 5 is generally likewise produced from acid-resistant stainless steel. The overlays 4 found on the supporting bars 3 are preferably plates made of a ceramic material, e.g. Al oxide (hardness HV 0.5 18,000 N/mm.sup.2), Zr oxide (hardness HV 0.5 12,700 N/mm.sup.2), Si nitride (hardness HV 0.5 18,800 N/mm.sup.2), Si carbide (hardness HV 0.5 28,150 N/mm.sup.2).

[0034] As a result of the vacuum prevailing in the interior 51 of the suction box 5, a suction force is exerted on the fibrous stock 2, by which liquid 6 contained in the latter is extracted. The liquid 6 escaping from the fibrous stock 2 passes through the fabric belt 1 and reaches the underside of the fabric belt 1, from which, during the movement of the fabric belt 1 over the drainage foils 3, it is stripped off the latter and reaches the suction box 5, through which it is led away.

[0035] FIG. 1A illustrates the drainage foil 3 having the wear-resistant overlay 4 and the fabric belt 1 moved over the latter, on which the fibrous stock 2 is found. As can be seen herefrom, the fabric belt 1, which consists of a fabric, e.g. of polyamide or of polyester, has warp threads 1a oriented in the longitudinal direction of the fabric belt 1 and weft threads 1b oriented in the transverse direction of the fabric belt 1.

[0036] During the movement of the fabric belt 1 over the drainage foils 3 in the direction of the arrow M, during which the fabric belt 1 rests on the surface of the overlays 4 of the drainage foils 3, high frictional resistances occur, which have to be overcome by the transport rolls found in the fabric belt installation in order to move the fabric belt 1. In addition, in this case, high wear of the fabric belt 1 and of the drainage foils 3 and of the overlays 4 is caused, which means that the fabric belt 1 and the drainage foils 3 have only short service lives. During the movement of the fabric belt 1 over the drainage foils 3, bow waves 61 are formed in the liquid 6 that has escaped from the fabric belt 1, in front of the weft threads 1b resting on the drainage foils 3.

[0037] According to the prior art, the drainage foils 3 can be formed on their upper side, facing the fabric belt 1 in the operating position, with a multiplicity of ceramic plates, which have lengths of, for example, 12 mm to 230 mm in the direction of the drainage foils and widths of, for example, 12 mm to 100 mm transverse to the drainage foils, and also heights of, for example, 2 mm to 10 mm. The hardnesses of the ceramic plates are preferably HVO,5 12,700 N/mm.sup.2 to HVO,5 28,150 N/mm.sup.2. In order to keep the frictional resistances which occur during the movement of a fabric belt 2 over the drainage foils 3 as low as possible, the surfaces of the drainage foils 3, in particular the ceramic plates 4, are plane-ground according to the prior art, having surface roughness values Ra of 0.15 m to 0.7 m.

[0038] FIG. 2 shows a drainage foil 3 according to the invention. The drainage foil 3 differs from a drainage foil according to the prior art in the fact that the ceramic plates 41 found on its upper side are formed with elevations and/or depressions on their upper side facing the fabric belt 1 in an installation for producing a paper web, wherein the height difference of the elevations with respect to the depressions is 0.1 mm to 1.6 mm. The elevations and depressions in embodiments of the invention that are particularly preferred and described below in various variants have a profiling with a defined cross-sectional shape and distribution over the surface of the ceramic plates 4. The dimensions and the material of the ceramic plates 41 are preferably those according to the above-described known prior art.

[0039] FIG. 3 illustrates a first embodiment of the ceramic plate 41 found on a drainage foil 3 according to the invention, which is formed with a profiling on its surface. The ceramic plate 41, which in the direction of movement M of the fabric belt 1 has a width B of, for example, 8 mm to 70 mm, preferably of 12 mm to 25 mm, and a height of, for example, 2 mm to 10 mm, is provided on its surface with ribs 42 extending in the longitudinal direction of the drainage foil 3, triangular or saw-tooth-like in cross section and having upper edges 45, wherein depressions 43 are found in the regions of the flanks located between the edges 45. The width B1 of a rib 42 is, for example, 1 mm to 16 mm, preferably 2 mm to 6 mm, and the height difference T between the edges 45 of the ribs 42 and the bottom of the depressions 43 is at least 0.1 mm, preferably up to 1.6 mm, particularly preferably 0.2 mm to 0.8 mm. The lateral regions 44 of the ceramic plate 41, which have a width A of, for example, 1 mm to 8 mm, preferably of 2 mm to 6 mm, are likewise formed flatly. Thus, the surface of the ceramic plate 41 is formed with a defined profiling according to the invention, consisting of elevations and depressions, wherein the ribs 42 that are saw-tooth-like in cross section form the elevations with the edges 45, and the regions of the flanks of the saw-tooth-like ribs 42 located between the edges 45 form the depressions 43.

[0040] The described formation of the surface of the drainage foils 3, in particular of the surfaces of the ceramic plates 41, particularly preferably but not necessarily with a defined profiled surface, is based on the finding that, as a result of the relatively large elevations and depressions formed according to the invention, the frictional resistances occurring during the movement of the fabric belt 1 over the drainage foils are reduced down to about 50%, which means firstly that a significant reduction in the drive power for the fabric belt 1 can be achieved and secondly the service lives of the fabric belt 1 and of the drainage foils 3 are substantially prolonged.

[0041] As can be seen from FIG. 3A, which corresponds to the illustration of FIG. 1A, this action is achieved in that first the fabric belt 1 in the regions of the depressions 43 does not rest on the surface of the drainage foil 3 or the surfaces of the ceramic plates 41, which means that no frictional resistances occur in these regions, and that, second, because of the movement of the fabric belt 1, bow waves 61 occur in the liquid 6 found in the depressions 43, by means of which the fabric belt 1 in the regions of the elevations 42, in particular the edges 45, is lifted over the latter, and by means of which liquid gets between the elevations and the fabric belt 1, by means of which the frictional resistances between the elevations and the fabric belt 1 are reduced highly.

[0042] FIG. 4 illustrates a further embodiment of the ceramic plate 41a profiled in a defined manner according to the invention and having a width B, in which, between the lateral regions 44a which form the elevations and which have a width A of, for example, 1 mm to 8 mm, preferably of 2 mm to 6 mm, there is a depression 43a, the depth of which with respect to the lateral regions 44a is at least 0.1 mm to preferably 2.5 mm, particularly preferably 0.2 mm to 0.8 mm.

[0043] In the further embodiment, illustrated in FIG. 4A, of the ceramic plate 41b according to the invention having a width B, elevations in the form of ribs 42b of rectangular cross section and depressions in the form of rectangular grooves 43b, which have widths B2 and B3 of, for example, 1 mm to 10 mm, preferably 2 mm to 8 mm, are located between the lateral regions 44b having a width A, wherein the height difference T2 between the elevations formed by the ribs 42b and the depressions formed by the grooves 43b is at least 0.1 mm to preferably 3.0 mm, particularly preferably 0.2 mm to 0.8 mm.

[0044] In the further embodiment, illustrated in FIG. 4B, of the ceramic plate 41c according to the invention having a width B, there is a wave-like profiling with ribs 42c and depressions 43c that are concave in cross section located in between two lateral regions 44c having a width A, wherein the distance B4 between two depressions 43c is, for example, 1 mm to 20 mm, preferably 2 mm to 8 mm, and the height difference T3 between the upper sides of the ribs 42c and the bottoms of the depressions 43c is at least 0.1 mm to preferably 3.0 mm, particularly preferably 0.2 mm to 0.8 mm.

[0045] The elevations 44a, 42b, 42c and depressions 43a, 43b, 43c of the embodiments of the invention illustrated in FIG. 4 to FIG. 4B are oriented in the longitudinal direction of the drainage foil 3 and preferably extend over the entire length of the ceramic plates 41a, 41b, 41c.

[0046] In the further embodiment of a ceramic plate 41d according to the invention, illustrated in FIG. 5 and FIG. 5A, the defined profiling is formed by elevations in the form of rectangular ribs 42d and depressions located in between in the form of rectangular grooves 43d, which have widths B5 and B6 of, for example, 1 mm to 10 mm, preferably of about 2 mm to 8 mm, and a height difference T4 of at least 0.1 mm to preferably 3.0 mm, particularly preferably of 0.2 mm to 0.8 mm. The longitudinal extent of the ribs 42d and the depressions 43d found in between encloses an angle W1 of 0 to 80, preferably of 30 to 55, with the longitudinal extent of the drainage foil 3.

[0047] In the further embodiments of two ceramic plates 41e, 41f, according to the invention, illustrated in FIG. 6, FIG. 6A and FIG. 6B, the plates are formed with profilings in the form of concave cut-outs 43e and cylindrical cut-outs 43f located close beside one another on a substantially flat surface, possibly somewhat curved as described below, which are spaced apart from one another. The distances B7 between the centers of two cut-outs 43e and 43f located beside one another are, in this case for example, 1 mm to 20 mm, preferably 2 mm to 12 mm, and the depths T5 of the cut-outs are at least 0.1 mm to preferably 3.0 mm, particularly preferably 0.2 mm to 0.8 mm.

[0048] The cut-outs can also have another shape, both in plan view and also in cross section, in particular an elongate or elliptical shape.

[0049] The ceramic plate 41g according to the invention illustrated in FIG. 7 corresponds to the embodiment according to FIG. 3, having ribs 42g that are saw-tooth-like in cross section and having edges 45g which form the elevations, and depressions 43g in the regions of the flanks of the saw-tooth-like ribs 42g, wherein the lateral regions 44g having a width F of, for example, 1 mm to 20 mm, preferably of 2 mm to 8 mm, are formed so as to fall obliquely toward the outside with an angle of, for example, 2 to 10, preferably of 3 to 6, and, in addition, the outer edges are rounded with a radius R of, for example, 0.5 mm to 5 mm, preferably of 1 mm to 3 mm.

[0050] A further embodiment of a drainage foil according to the invention is now explained. According to the known prior art, the surfaces of drainage foils are formed flat and the surfaces of drainage foils found on suction boxes are located in a common plane. However, as a result of the fact that a suction action is exerted by the suction boxes on the fabric belt in the interspaces found between the drainage foils, the fabric belt is drawn into the interspaces found between the drainage foils. In this way, the two lateral regions of the surfaces of the drainage foils, in particular of the overlays of a wear-resistant material found on the latter, for example ceramic plates, are loaded more highly than is the case for the central regions of the surfaces of the drainage foils, located in between.

[0051] In order to achieve a uniform pressure distribution over the width of the drainage foils 3a, as can be seen from FIG. 8 and FIG. 8A, the surfaces of the ceramic plates 4a found on the drainage foils 3a have a curvature or are formed convexly in cross section, which means that the fabric belt 1 overall assumes a wave-like course. The drainage foils 3a are located on a supporting frame 52a, which is detachably fixed to the suction box 5.

[0052] As can also be seen from FIG. 8A, the radius R1 of the curved surfaces of convex cross section of the ceramic plates 4a located on the drainage foils 3a is, for example, 100 mm to 500 mm, preferably 200 mm to 350 mm. In addition, the side edges of the drainage foils 3a are rounded, the radius R2 of the rounding of the side edges being, for example, 0.5 mm to 5 mm, preferably 1 mm to 3 mm.

[0053] By means of such a formation of the surfaces of the drainage foils 3a, in particular of ceramic plates 4a found on the latter, a uniform distribution of the pressure exerted by the fabric belt 1 over the width of the drainage foils 3a is effected, which likewise means firstly that the frictional resistances and secondly the wear of the fabric belt 1 and of the drainage foils 3a are reduced.

[0054] This further formation of the drainage foils 3a is in particular combined with the profiling of the surface of the drainage foils, which can be provided with a wear-resistant overlay 4a, e.g. with ceramic plates, as is explained above by using FIG. 2 to FIG. 7.

[0055] The formation of drainage foils according to the invention is in particular advantageous in those drainage foils which are located on a suction box.

[0056] The drainage foils can be provided with overlays of ceramic plates. However, the drainage foils can also be produced overall from polyethylene, not being coated with ceramic plates. In addition, the surfaces, in this case, are formed with a profiling in the form of elevations and/or depressions with a vertical extent of at least 0.1 mm to preferably 3.0 mm.

[0057] As soon as the elevations have been ground off by the use of the drainage foils, the surfaces are re-machined to the effect that the height differences between the elevations and depressions required for the specified action are reproduced.

[0058] All the embodiments described in conjunction with overlays of a wear-resistant material, in particular ceramic, can also be used within the context of the invention in drainage foils which have overlays of another material, in particular materials not having such good wear properties, and likewise in drainage foils which have no overlays, in which the elevations and depressions are applied to or formed directly on the drainage foils.

[0059] All the embodiments illustrated and described can be combined wholly or partly with one another and with embodiments which have not actually been illustrated and described.