Perforated clothing with edge protection layer
By applying a protective layer through perforations and using unperforated strips, the adhesion issue is resolved, ensuring reliable wear protection and uniform fiber web formation in fibrous web production machines.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- VOITH PATENT GMBH
- Filing Date
- 2025-12-09
- Publication Date
- 2026-07-23
Smart Images
Figure EP2025085976_23072026_PF_FP_ABST
Abstract
Description
[0001] 1 file: 28729 WO / PFF
[0002] Perforated
[0003]
[0004] with edge protection layer
[0005] The invention relates to a covering for a machine for producing a fibrous web, in particular a paper, cardboard or tissue web, wherein the covering is essentially formed from a perforated substrate and has the form of an endless band extending in a longitudinal direction, with a first side edge and a second side edge opposite the first side edge, wherein a perforated first edge strip extending in the longitudinal direction of the covering is provided immediately adjacent to the first side edge and wherein a perforated second edge strip extending in the longitudinal direction of the covering is provided immediately adjacent to the second side edge, wherein the first edge strip and the second edge strip are each at least partially coated with a protective layer.
[0006] Machines for producing fibrous webs, such as paper, cardboard, or tissue, typically include a forming section in which a fiber suspension consisting primarily of water is applied to a forming wire by means of a headbox. A significant portion of the water is drained through the wire, while the fibers remain on the wire, where sheet formation occurs. The remainder of the machine then serves essentially only to dry the fibrous web. For this purpose, it generally comprises a press section with at least one rotating press felt, in which drying takes place by mechanical pressure, and a dryer section with at least one rotating drying screen, in which drying is achieved by heat.
[0007] Traditionally, and still today, most of these screens are manufactured using filaments, particularly through weaving or spiralizing. However, this manufacturing process is time-consuming. Therefore, it has been suggested in the past to use perforated substrates instead of woven or spiralized screens. The term "substrate" generally refers to a plastic film material. For the production of forming screens, it is advantageous to use a laser for perforating the substrate. (2 File: 28729 WO / PFF)
[0008] Substrates are used because they can produce very fine perforations. The substrate can also be die-cut to create a dry sieve.
[0009] This idea was already described in publication US5837102, the contents of which are referenced here. Figure 1 illustrates the laser drilling perforation process according to US5837102. Figure 1 shows only a section of a substrate 20' from which the forming screen is manufactured. The substrate comprises a first surface 22' and an opposing second surface 24', which is not visible in Figure 1. The substrate 20' is perforated by a laser beam LB from a laser connected to a control unit to drill a plurality of through-channels 30' into the substrate 20'. The through-channels 30' extend in the thickness direction TD of the substrate 20', i.e., orthogonally to the first surface 22' and the opposing second surface, thus connecting the first surface 22' to the opposing second surface.
[0010] In laser perforation, the substrate 20' can be clamped between two rollers R, as illustrated in Figure 2. A substantially uniform arrangement of through-channels 30' is introduced into the substrate along its entire width WD, between a first side edge 26' and a second side edge 28' opposite the first side edge 26'. As shown in Figure 3, the through-channels can have a cross-sectional shape that changes in the thickness direction TD of the substrate 20', in particular a cross-sectional shape that tapers from the first surface 22', where the laser beam enters and which, in normal use of the forming screen, faces the fiber web, to the second surface 24', where the laser beam exits and which, in normal operation of the forming screen, faces away from the fiber web.
[0011] A generic covering described above is known, for example, from the applicant's publication WO 2012 / 095251 A1. Figure 10 therein shows how an abrasion-resistant coating, for example made of a polymer resin such as polyurethane, is applied to one side of a perforated edge strip of a perforated substrate. The perforations in this area can be closed or partially closed.3 File: 28729 WO / PFF
[0012] The problem with this type of covering, known from the prior art, is that the adhesion of the protective layer to the surface of the substrate is not always satisfactory, and this can lead to unwanted detachment of the protective layer during normal operation of the covering.
[0013] It is therefore an object of the present invention to provide a covering and a manufacturing method for such a covering which solve the problem described above. The covering should be as easy to manufacture as possible and its edges should be reliably protected against wear by a firmly adhering protective layer.
[0014] This problem is solved by the features of the independent claims. The dependent claims relate to advantageous further developments of the invention. Specifically, the problem is solved by the generic covering described at the outset, which is particularly distinguished by the fact that the respective protective layer extends over a portion of the upper surface of the covering facing the fiber web during intended operation, over a portion of the underside of the covering facing away from the upper surface, and over the first or second side edge of the covering, wherein the material of the respective protective layer on the underside of the covering and the material of the respective protective layer on the upper surface of the covering are not only separated by the material of the respective protective layer at the first or second side edge.The protective layer is not only connected to the second edge of the covering, but also by material of the respective protective layer, which extends through or fills at least some of the channels of the perforated first or second edge strip of the covering. This does not result in a particularly good, and especially not a form-fitting, adhesion of the protective layer to the perforated substrate.
[0015] An advantageous embodiment of the present invention provides that the covering has a perforated usable area arranged between the perforated first edge strip and the perforated second edge strip, which comprises a plurality of through-channels extending through the substrate and connecting the top with the bottom, wherein the usable area is an im4 Akte: 28729 WO / PFF
[0016] The substrate exhibits essentially homogeneous permeability, and the perforated first edge strip and the perforated second edge strip also exhibit essentially homogeneous permeability, which corresponds essentially to the permeability of the usable area. This makes it possible to perforate the entire substrate during production using essentially identical process parameters. It also makes it possible to produce the perforated substrate in advance and cut it to size for further processing, depending on the width of the machine on which the finished covering is to be used. Particularly when using the covering as a forming screen, it is advantageous for the usable area to have essentially homogeneous permeability in order to achieve the most uniform formation of the fiber web possible.
[0017] The respective protective layer can have a width between 4 mm and 12 mm, preferably between 5 mm and 10 mm if the covering is a forming screen, or it can have a width between 20 mm and 45 mm, preferably between 25 mm and 40 mm if the covering is a drying screen.
[0018] It is preferred that the respective protective layer comprises an extrudable material, preferably consisting essentially of an extrudable material. In this way, the material can be applied to the covering relatively easily in a liquid or paste-like state, flowing into the affected passageways of the perforated part of the covering, where it then solidifies.
[0019] The protective layer can be made of polyurethane or, preferably, consist primarily of polyurethane. Polyurethane has proven particularly suitable for this purpose. It is also relatively inexpensive and easy to process. However, if the screen is a dry screen, other materials such as silicone, acrylates, and epoxy resins, which offer higher temperature resistance, are preferred.
[0020] An advantageous embodiment of the present invention provides that the substrate is formed from a film or from a laminate of several films, wherein the one film or the several films are preferably stretched, furthermore 5 File: 28729 WO / PFF
[0021] Preferably, at least one stretching direction corresponds essentially to the longitudinal direction of the covering. The stretching can only occur uniaxially in the longitudinal direction of the covering. Through stretching, the molecular chains from which the film is formed acquire a preferred orientation. If a tensile load later acts on the film in precisely this direction, it can no longer stretch as much as it would otherwise do without prior stretching.
[0022] To further increase the tensile strength of the covering in its longitudinal direction, it may also be advantageous if at least partially, preferably completely, a yarn- or band-shaped edge reinforcement element is embedded in the respective protective layer.
[0023] In one embodiment of the present invention, the screen is a stamped drying screen.
[0024] In another, alternative embodiment, the covering according to the invention is a forming sieve, in particular a laser-drilled forming sieve.
[0025] In the latter case, it is particularly advantageous if the through-channels of the usable area are non-cylindrical and have a cross-sectional area that decreases along a thickness direction of the substrate from the top surface to a middle region of the substrate located between the top and bottom surfaces, wherein an upper edge of at least one of the multiple through-channels is in direct contact with an upper edge of at least one other adjacent through-channel such that the upper edge of the at least one of the multiple through-channels does not lie in a plane. By having the upper edges of adjacent through-channels quasi-touch or intersect, a very close arrangement of through-channels can be achieved, resulting in a very fine formation of the fiber web.
[0026] A preferred embodiment of the present invention provides that a longitudinally extending, unperforated first separating strip is arranged between the perforated first edge strip and the usable area and / or between 6 File: 28729 WO / PFF
[0027] A second, unperforated separating strip extending longitudinally is arranged between the perforated second edge strip and the usable area.
[0028] The inclusion of at least one unperforated separating strip prevents dewatering in that area, thus preventing the fiber web from becoming compacted or flake-like. This automatically limits the fiber web within the working area of the forming screen. Consequently, the use of edge jet nozzles is unnecessary, eliminating the associated maintenance and cleaning requirements.
[0029] Furthermore, this solution also has the advantage that the forming sieve can be produced particularly quickly and easily. By leaving at least one separating strip unperforated, the energy and time required to create the necessary perforations are saved.
[0030] Tests have shown that it is important for the at least one unperforated separating strip to have a specific width, i.e., a specific extent in the width direction of the forming sieve. This is the only way to ensure that no solidification or sheeting occurs in the at least one unperforated separating strip, without, however, allowing too much suspension to remain undrained. The latter can cause problems if the suspension flows into the working area. Therefore, the unperforated first separating strip and / or the unperforated second separating strip should have a width between 1 mm and 8 mm, preferably between 2 mm and 6 mm, and more preferably between 3 mm and 5 mm.
[0031] Preferably, the unperforated first separating strip is spaced between 20 mm and 160 mm from the first side edge, and / or the unperforated second separating strip is spaced between 20 mm and 160 mm from the second side edge. This allows for good formation results without removing too much fiber suspension from the first and / or second edge strip.
[0032] Another aspect of the present invention relates to a method for producing a covering, preferably a covering according to the invention as described above, comprising the following steps: a) providing a substrate, made of 7 File: 28729 WO / PFF
[0033] the covering is to be substantially formed; b) perforating the substrate, wherein at least a first edge strip immediately adjacent to a first lateral edge of the covering and extending in the longitudinal direction of the covering, and a second edge strip immediately adjacent to the second lateral edge and extending in the longitudinal direction of the covering, are also perforated; and c) at least partially coating the first edge strip and the second edge strip with a protective layer; wherein in step c) the protective layer is applied to the first edge strip and to the second edge strip by extruding an extrudable material, preferably a polyurethane, through dies such that the respective protective layer extends over a portion of a top surface of the covering facing the fiber web during intended operation,extending over part of the underside of the covering, opposite the top side, and over the first or second edge of the covering, wherein the material of the respective protective layer on the underside of the covering and the material of the respective protective layer on the top side of the covering are connected to each other not only by the material of the respective protective layer at the first or second edge of the covering, but also by material of the respective protective layer which extends through or fills at least some of the passage channels of the perforated first or second edge strip of the covering.
[0034] For example, each protective layer can be applied to the covering simultaneously from above and below using extrusion dies.
[0035] The present invention is illustrated below with reference to schematic figures not drawn to scale. These show:
[0036] Figure 4: a section of a covering according to the invention;
[0037] Figure 5: a strong magnification of the top of the covering in Figure 4; and Figure 6: a cross-section through part of the covering along line VI - VI in Figure 4.
[0038] Figure 4 schematically shows a small section of a covering 10 according to the invention, in this example a forming screen 10, with a first side edge 268 File: 28729 WO / PFF
[0039] and a second side edge 28 opposite the first side edge 26 in the width direction WD of the forming screen 10. Between the two side edges 26, 28 and spaced apart from them is a perforated working area 32. In the intended use of the forming screen 10, a fiber suspension is applied to one upper side of the forming screen 10 across its entire width, but only the fiber suspension applied in the working area 32 is used for the fiber web actually to be produced. Between the working area 32 and the first side edge 26 is a first edge strip 48 of the forming screen 10, and between the working area 32 and the second side edge 28 is a second edge strip 50 of the forming screen. The first edge strip 48 and the second edge strip 50 are also perforated.The portion of the fiber suspension applied to the first edge strip 48 and the second edge strip 50 does not contribute to the finished fiber web. Instead, this portion of fibers is returned to a pulper.
[0040] Between the working area 32 and the first edge strip 48 is a first unperforated separating strip 40. Likewise, between the working area 32 and the second edge strip 50 is a second unperforated separating strip 42. Both separating strips 40 and 42 have a width of at least 2 mm but no more than 6 mm. Since the two separating strips 40 and 42 are unperforated, the fiber suspension is not dewatered on them, and therefore no sheets form. This automatically results in the fiber web forming on the working area 32 being bounded along the separating strips 40 and 42, without the need for edge-cutting nozzles.
[0041] In the usable area 32, the passage channels 30 preferably have a cross-sectional shape that changes, in particular tapers, in the thickness direction TD of a substrate 20, from which the forming screen 10 is substantially formed, from a first surface 22, on which the fiber suspension is applied in the intended use, to a second surface facing away from the first surface 22, similar to that shown in Figure 3. As shown in Figure 5, which is an enlargement of section V in Figure 4, the passage channels 30 can be positioned so close together that their upper edges 44, i.e., the edges on the first surface of the substrate 20, at least partially overlap each other.9 File: 28729 WO / PFF
[0042] The two surfaces overlap, whereas their lower edges 46, i.e., the edges on the second surface of the substrate 20, are noticeably spaced apart. This results in an egg-crate-like topography on the upper surface of the forming screen 10 facing the fiber web in the working area. Only small areas, if any, remain of the originally essentially flat first surface 22 of the substrate 20. In addition, the clear width of the passage channels 30 in the working area 32 is very small, allowing for good filtration of the fiber suspension applied to the forming screen 10. In other words, a significant proportion of the water from the fiber suspension passes through the passage channels 30, while the fibers are retained on the upper surface of the forming screen 10 in the working area 32, where they then form sheets. The result is a very fine formation of the fiber web.
[0043] Whether or not sheeting occurs on the first edge strip 48 and the second edge strip 50 depends largely on the design of the perforations or through-channels there. In a preferred embodiment, the two edge regions 48, 50 have the same permeability as the usable area 32.
[0044] In an alternative embodiment, the permeability of the first edge strip 48 and the second edge strip 50 differs from the permeability of the working area 32 of the forming screen 10. The clear width of the passage channels in the two edge strips 48, 50 can be significantly larger than the clear width of the passage channels 30 in the working area 32, allowing not only water but also fibers to pass through the passage channels in the two edge strips 48, 50. In this case, leaf formation does not occur there in the first place. Simultaneously, the passage channels in the two edge strips 48, 50 can be spaced further apart than the passage channels 30 in the working area 32, in order to avoid negatively impacting the required structural strength of the forming screen 10 there, or even to increase it if necessary compared to the working area 32.
[0045] To provide very good wear protection, the first edge strip 48 and the second edge strip 50 are each coated with a protective layer 52, for example made of 10 File: 28729 WO / PFF
[0046] coated with polyurethane. As shown in Figure 6, which shows a cross-section through a part of the substrate 20 according to section line VI-VI in Figure 4, the protective layer 52 extends over a part of the first surface 22 of the substrate 20, as well as over a part of the second surface 24 of the substrate 20, and over the edge or side margin 26, 28 in the thickness direction TD of the substrate 20. According to the invention, the material of the respective protective layer 52 on the underside of the covering 10 and the material of the respective protective layer 52 on the top side of the covering 10 are connected to each other not only by the material of the respective protective layer 52 at the first side margin 26 or second side margin 28 of the covering 10, but also by material of the respective protective layer 52 which extends through at least some passage channels 30 of the perforated first edge strip 48 or second edge strip 50 of the covering 10.this fills... The material of the protective layer enters the perforations or...
[0047] The protective layer forms a positive connection with the substrate 20 through the channels 30 into which it flowed and solidified. This results in particularly good adhesion of the protective layer to the substrate. For example, the protective layer can be applied with a width of 5 mm to 10 mm.11 File: 28729 WO / PFF
[0048]
[0049] 10 screens, e.g. forming screen 20, 20' substrate
[0050] 22, 22' first surface
[0051] 24' , 24 second surface
[0052] 26, 26' first side margin
[0053] 28, 28' second side margin
[0054] 30, 30' through channel
[0055] 32 Usable area
[0056] 40 Unperforated first separating strip 42 Unperforated second separating strip 44 Upper edge
[0057] 46 bottom edge
[0058] 48 perforated first edge strip 50 perforated second edge strip 52 protective layer
[0059] LB laser beam
[0060] LD longitudinal direction
[0061] R roller
[0062] TD Thickness Direction
[0063] WD width direction
Claims
12 files: 28729 WO / PFF 1. Fabric (10) for a machine for producing a fibrous web, in particular paper, cardboard or tissue web, wherein the fabric (10) is essentially formed from a perforated substrate (20) and has the form of an endless strip extending in a longitudinal direction (LD), with a first side edge (26) and a second side edge (28) opposite the first side edge (26), wherein a perforated first edge strip (48) extending in the longitudinal direction (LD) of the covering (10) is provided immediately adjacent to the first side edge (26) and wherein a perforated second edge strip (50) extending in the longitudinal direction (LD) of the covering (10) is provided immediately adjacent to the second side edge (28), wherein the first edge strip (48) and the second edge strip (50) are each at least partially coated with a protective layer (52), characterized in that the respective protective layer (52) extends over a part of a top side of the covering (10) facing the fiber web during intended operation, over a part of a bottom side of the covering (10) facing away from the top side, and over the first side edge (26) or over the second side edge (28) of the covering (10), wherein the material of the respective protective layer (52) on the bottom side of the covering (10) and the material of the respective protective layer (52) on the top side of the covering (10) are connected to each other not only by the material of the respective protective layer (52) at the first side edge (26) or second side edge (28) of the covering (10), but also by material of the respective protective layer (52) which extends through or fills at least some passage channels (30) of the perforated first edge strip (48) or second edge strip (50) of the covering (10).
2. Covering (10) according to claim 1 , characterized in that the covering (10) has a perforated usable area (32) arranged between the perforated first edge strip (48) and the perforated second edge strip (50), which has a plurality 13 File: 28729 WO / PFF comprising passage channels (30) extending through the substrate (20) and connecting the top to the bottom, wherein the usable area (32) has a substantially homogeneous permeability and wherein the perforated first edge strip (48) and the perforated second edge strip (50) also have a substantially homogeneous permeability, which is substantially the same as the permeability of the usable area (32).
3. Covering (10) according to claim 1 or 2, characterized in that the respective protective layer (52) has a width between 4 mm and 12 mm, preferably between 5 mm and 10 mm, if the covering is a forming screen, or that the respective protective layer (52) has a width between 20 mm and 45 mm, preferably between 25 mm and 40 mm, if the covering is a drying screen.
4. Covering (10) according to one of the preceding claims, characterized in that the respective protective layer (52) comprises an extrudable material, preferably consisting essentially of an extrudable material.
5. Covering (10) according to one of the preceding claims, characterized in that the respective protective layer (52) comprises polyurethane and / or silicone and / or acrylate and / or epoxy resin, preferably consisting substantially of polyurethane and / or silicone and / or acrylate and / or epoxy resin.
6. Covering (10) according to one of the preceding claims, characterized in that the substrate (20) is formed from a film or from a laminate of several films, wherein the one film or the several films are preferably stretched, wherein at least one stretching direction preferably corresponds substantially to the longitudinal direction (LD) of the covering (10).14 File: 28729 WO / PFF 7. Covering (10) according to one of the preceding claims, characterized in that at least partially, preferably completely, a yarn- or band-shaped edge reinforcement element is embedded in the respective protective layer (52).
8. Covering (10) according to one of the preceding claims, characterized in that the covering (10) is a stamped drying screen.
9. Covering (10) according to one of claims 1 to 7, characterized in that the covering (10) is a laser-drilled forming screen.
10. Covering (10) according to claim 9 and further at least according to claim 2, characterized in that the through-channels (30) of the usable area (32) are non-cylindrical and have a cross-sectional area that decreases along a thickness direction (TD) of the substrate (20) from the top to a central area of the substrate (20) located between the top and the bottom, wherein an upper edge (44) of at least one of the multiple through-channels (30) is in direct contact with an upper edge (44) of at least one other adjacent through-channel (30) of the multiple through-channels (30) such that the upper edge (44) of the at least one of the multiple through-channels (30) does not lie in a plane.
11. Covering (10) according to claim 10, characterized in that an unperforated first separating strip (40) extending longitudinally (LD) is arranged between the perforated first edge strip (48) and the usable area (32) and / or that an unperforated second separating strip (42) extending longitudinally (LD) is arranged between the perforated second edge strip (50) and the usable area (32).15 File: 28729 WO / PFF 12. Covering (10) according to claim 11, characterized in that the unperforated first separating strip (40) is spaced between 20 mm and 160 mm from the first side edge (26) and / or that the unperforated second separating strip (42) is spaced between 20 mm and 160 mm from the second side edge (28).
13. Covering (10) according to claim 11 or 12, characterized in that the unperforated first separating strip (40) and / or the unperforated second separating strip (42) have a width between 1 mm and 8 mm, preferably between 2 mm and 6 mm, more preferably between 3 mm and 5 mm.
14. Method for producing a covering (10), preferably a covering (10) according to one of the preceding claims, comprising the following steps: a) Providing a substrate (20) from which the covering (10) is to be substantially formed; b) Perforating the substrate (20), wherein at least a first edge strip (48) immediately adjacent to a first side edge (26) of the covering (10) and extending in the longitudinal direction (LD) of the covering (10) and a second edge strip (50) immediately adjacent to the second side edge (28) and extending in the longitudinal direction (LD) of the covering (10) are also perforated; and c) at least partially coating the first edge strip (48) and the second edge strip (50) with a protective layer (52) each; characterized in that in step c) the protective layer (52) is applied to the first edge strip (48) and to the second edge strip (50) by extruding an extrudable material, preferably a polyurethane, through dies such that the respective protective layer (52) extends over a part of a top surface of the covering (10) facing the fiber web in the intended operation, over a part of a bottom surface of the covering (10) facing away from the top surface, and over the first side edge (26) or over the second side edge (28) of the covering (10), wherein the material of the respective protective layer (52) on the bottom surface of the covering (10) and the16 File: 28729 WO / PFF The material of the respective protective layer (52) on the upper side of the covering (10) is connected not only by the material of the respective protective layer (52) at the first side edge (26) or second side edge (28) of the covering (10), but also by material of the respective protective layer (52) which extends through or fills at least some passage channels (30) of the perforated first edge strip (48) or second edge strip (50) of the covering.