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WO2025031670A1 - Tamis de formage à bandes longitudinales non perforées - Google Patents

Tamis de formage à bandes longitudinales non perforées Download PDF

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Publication number
WO2025031670A1
WO2025031670A1 PCT/EP2024/068427 EP2024068427W WO2025031670A1 WO 2025031670 A1 WO2025031670 A1 WO 2025031670A1 EP 2024068427 W EP2024068427 W EP 2024068427W WO 2025031670 A1 WO2025031670 A1 WO 2025031670A1
Authority
WO
WIPO (PCT)
Prior art keywords
edge
strip
forming screen
unperforated
forming
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/EP2024/068427
Other languages
German (de)
English (en)
Inventor
Cedric FITZER
Uwe Köckritz
Jens Kallenberg
Reinhard Holl
Uemit-Yasae KAYMAK
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Voith Patent GmbH
Original Assignee
Voith Patent GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Voith Patent GmbH filed Critical Voith Patent GmbH
Publication of WO2025031670A1 publication Critical patent/WO2025031670A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F1/00—Wet end of machines for making continuous webs of paper
    • D21F1/0027—Screen-cloths
    • D21F1/0063—Perforated sheets

Definitions

  • the invention relates to a forming screen for a machine for producing a fibrous web, in particular a tissue web, wherein the forming screen is essentially formed from a perforated, preferably laser-perforated, substrate and has the shape of an endless belt extending in a longitudinal direction, with a first side edge and a second side edge opposite the first side edge, wherein the forming screen comprises a perforated useful area arranged between the first side edge and the second side edge, on which the fibrous web to be produced is formed when the forming screen is used as intended and which is spaced from the first side edge and the second side edge, and wherein the forming screen further comprises a first edge strip which is arranged between the first side edge and the useful area, and a second edge strip which is arranged between the second side edge and the useful area, wherein the first edge strip and the second edge strip are also perforated.
  • Machines for producing a fibrous web usually comprise a forming section in which a fibrous suspension consisting predominantly of water is applied to a forming screen by means of a so-called headbox, through which a considerable proportion of the water is drained away, while the fibers remain on the screen, where the so-called sheet formation takes place.
  • the rest of the machine then essentially only serves to dry the fibrous web.
  • it usually comprises a press section in which drying takes place by means of mechanical pressure, and a drying section in which drying takes place using heat.
  • Tissue webs are particularly light fibrous webs with a basis weight of no more than 25 g/m 2 . Typical basis weights of tissue webs, for example, are around 15 g/m 2 .
  • mechanical pressing often takes place against a heated Yankee cylinder.
  • substrate is generally understood to mean a plastic film material.
  • Figure 1 illustrates the perforation process by means of laser drilling according to US5837102.
  • Figure 1 shows only a section of a substrate 20' from which the forming screen is made.
  • the substrate comprises a first surface 22' and an opposite second surface 24', which is not visible in Figure 1.
  • the substrate 20' is perforated by means of a laser beam LB from a laser that is connected to a control unit in order 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. orthogonal to the first surface 22' and the opposite second surface, and thus connect the first surface 22' to the opposite second surface.
  • the substrate 20' can be stretched between two rollers R, as illustrated in Figure 2.
  • a substantially uniform arrangement of through-channels 30' is introduced into the substrate over the entire extent in the width direction WD of the substrate 20' between a first side edge 26' and a second side edge 28' opposite the first side edge 26'.
  • 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 faces the fibrous web during normal use of the forming screen, to the second surface 24', where the laser beam exits and which faces away from the fibrous web during normal operation of the forming screen.
  • the fiber suspension is applied from the headbox across the entire width of the forming fabric, although in the end only the fiber web in a smaller usable area between the side edges is used.
  • the formation at the edges of the forming fabric is often of lower quality, so these edges are removed.
  • edge jet nozzles in the forming section, with the help of which the edges are cut off using a water jet and fed into a pulper.
  • the remaining web in the middle usable area then essentially corresponds to the width of the finished fiber web at the end of the machine when it is rolled up there, whereby the shrinkage of the web caused by drying is not taken into account here.
  • the edge jet nozzles are maintenance-intensive, as fibers can easily accumulate on them, which, if they fall onto the fiber web as lumps, can lead to poor formation or even a web break in the machine.
  • the publication WO 2012/095251 A1 also discloses a perforated, in particular laser-perforated, film covering that can be used as a forming screen for a machine for producing a fibrous web. Between the perforated usable area of this film covering and the left or right side edge there is an edge area that has a lower perforation density than the usable area of the film covering. The respective edge area may also not be perforated at all. The purpose of these edge strips is to offer a high level of security against the edge of the covering tearing during the intended use of the covering.
  • the object of the present invention to provide a forming fabric and a method for producing a fibrous web which solves the problem described above.
  • the forming fabric should preferably be as simple to produce as possible and the maintenance effort during the production of the fibrous web should be kept as low as possible.
  • the object is achieved by the generic forming screen described at the beginning, which is particularly characterized in that a longitudinally extending, unperforated first separating strip is arranged between the first edge strip and the usable area and/or a longitudinally extending, unperforated second separating strip is arranged between the second edge strip and the usable area, wherein the unperforated first separating strip and/or the unperforated second separating strip has a width between 1 mm and 8 mm, preferably between 2 mm and 6 mm, more preferably between 3 mm and 5 mm.
  • the at least one unperforated separating strip ensures that no dewatering takes place in the area of this separating strip, so that no solidification or sheet formation of the fibrous web occurs there. This automatically limits the fibrous web in the usable area of the forming fabric. As a result, the use of edge jet nozzles can be completely dispensed with, which also eliminates the maintenance and cleaning work associated with these edge jet nozzles.
  • the solution according to the invention also has the advantage that the forming screen can be produced particularly quickly and easily. By leaving at least one separating strip unperforated, the energy and time required to create corresponding perforations is saved. Alternatively, it would also be conceivable to subsequently close the through-channels 30' in the substrate 20', which was previously described with regard to Figures 1 to 3 of the prior art, in particular by means of a coating, but this solution is more labor-intensive and therefore not preferred. In addition, coatings can be subject to wear due to abrasion.
  • the at least one unperforated separating strip has a certain width, i.e. a certain extent in the width direction of the forming fabric. This is the only way to ensure that no solidification or sheet formation occurs in the at least one unperforated separating strip, but without too much suspension being drained.
  • the forming fabric has an upper side facing the fibrous web in its intended use and a lower side facing away from the fibrous web, wherein the useful area comprises a plurality of through-channels that extend through the substrate and connect the upper side to the lower side, wherein the through-channels are non-cylindrical and have a cross-sectional area that decreases along a thickness direction of the substrate from the upper side to a central region of the substrate located between the upper side and the lower side, wherein an upper edge of at least one of the plurality of through-channels is in direct contact with an upper edge of at least one other adjacent through-channel of the plurality of through-channels in such a way that the upper edge of the at least one of the plurality of through-channels does not lie in one plane.
  • the first unperforated separating strip is spaced from the first side edge by between 20 mm and 160 mm, preferably between 35 mm and 115 mm, and/or the second unperforated separating strip is spaced from the second side edge by between 20 mm and 160 mm, preferably between 35 mm and 115 mm. This allows good formation results to be achieved without too much fiber suspension being removed from the first edge strip and/or second edge strip.
  • an unperforated first edge protection strip extending in the longitudinal direction of the forming screen is arranged between the first side edge and the perforated first edge strip
  • an unperforated second edge protection strip extending in the longitudinal direction of the forming screen is arranged between the second side edge and the perforated second edge strip
  • the first edge protection strip and the second edge protection strip each have a width between 1 mm and 5 mm, preferably between 1 mm and 3 mm, and are directly adjacent to the first and second side edges, respectively.
  • this increases the strength and dimensional stability of the forming screen, and on the other hand, it can be used to Forming fabric can be better protected against wear on the side edges, where the forming fabric often rubs against fixed components, such as a mechanical and/or pneumatic edge sensor, during normal use.
  • the first edge protection strip and the second edge protection strip are each coated with a protective layer.
  • the protective layer can extend over part of the first surface of the substrate and/or part of the second surface of the substrate and/or over the edge or a side edge in the thickness direction of the substrate. Preferably, all of the cases apply.
  • the respective protective layer extends beyond the unperforated first edge protection strip or the unperforated second edge protection strip into the area of the perforated first edge strip or the perforated second edge strip. This allows the material of the protective layer to flow into the perforations or passageways of the substrate, where, when it solidifies, it forms a positive connection with them. This results in particularly good adhesion of the protective layer to the substrate.
  • the respective protective layer can comprise a polyurethane or preferably even consist essentially of a polyurethane.
  • Polyurethane has proven to be particularly suitable for this purpose. In addition, it is relatively inexpensive and easy to process.
  • the substrate is formed from a film or from a laminate of several films, wherein the one film or several films are preferably stretched, wherein more preferably at least one stretching direction corresponds essentially to the longitudinal direction of the forming screen.
  • the stretching can take place uniaxially only in the longitudinal direction of the forming screen, or biaxially in two directions, wherein in this case one of the two stretching directions then preferably corresponds to the longitudinal direction of the forming screen.
  • the stretching gives the molecular chains from which the film is formed a preferred orientation. If a If a a tensile load is applied to the film in this direction, it can no longer stretch as much as would otherwise be the case without prior stretching.
  • the useful area has a substantially homogeneous permeability.
  • the first edge strip and the second edge strip can also have a substantially homogeneous permeability, which can, however, differ from the permeability of the useful area.
  • the clear width of the through channels of the edge strips can be selected to be larger than that in the useful area, so that in the first and second edge strips of the forming fabric, not only the water is drained through the through channels, but also the fibers from the applied fibrous suspension. This means that no solid edge strips are formed on the fibrous web in the first place. This process can be promoted by suction elements that suck the water and the fibers through the through channels.
  • first edge strip and the second edge strip have a substantially homogeneous permeability which essentially corresponds to the permeability of the useful area, and/or the first edge strip and the second edge strip have a perforation density which essentially corresponds to the perforation density of the useful area.
  • This also allows a paper web to form on the edge strips which, in terms of its formation, essentially corresponds to the paper web in the useful area and which can be easily lifted off the forming screen at the end of the forming section in order to be guided into a so-called pulper, for example.
  • the first and the second edge strips can comprise a plurality of through-channels which extend through the substrate and connect the upper side to the lower side, wherein the through-channels are non-cylindrical and have a cross-sectional area which decreases along a thickness direction of the substrate from the upper side to a central region of the substrate located between the upper side and the lower side, wherein an upper edge of at least one of the plurality of through-channels is connected to an upper edge of at least one other adjacent through-channel of the plurality of through-channels is in direct contact such that the upper edge of at least one of the plurality of through-channels is not in one plane.
  • a further aspect of the present invention relates to a machine for producing a fibrous web, in particular a tissue web, comprising a previously described forming screen according to the invention.
  • a forming section of the machine is free of a device for trimming the edges of the fibrous web.
  • Such a device can be dispensed with by using the forming screen according to the invention, in particular if it comprises both the first unperforated separating strip and the second unperforated separating strip.
  • the present invention further relates to a method for producing a fibrous web using a previously described forming fabric according to the invention and preferably in a previously described machine according to the invention, wherein a fibrous suspension is applied to the forming fabric essentially over the entire width of the forming fabric by means of a headbox and wherein the excess part of the fibrous suspension that is applied to the first edge strip and the second edge strip is discharged into a pulper.
  • the excess part of the fibrous suspension can be discharged essentially through the perforations in the first edge strip and the second edge strip.
  • Figure 4 a section of a forming fabric according to the invention.
  • Figure 5 a high magnification of the top of the forming fabric in Figure 4.
  • Figure 4 shows schematically a small section of a forming screen 10 according to the invention with a first side edge 26 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 at a distance from them there is a perforated useful area 32.
  • a fiber suspension is applied to an upper side of the forming fabric 10 across its entire width, whereby only the fiber suspension that is applied in the usable area 32 is used for the fiber web that is actually to be produced.
  • the first edge strip 34 and the second edge strip 36 are also perforated. The portion of the fiber suspension that is applied to the first edge strip 34 and the second edge strip 36 does not contribute to the finished fiber web. Instead, this portion of fibers is returned to a pulper.
  • a first unperforated separating strip 40 is located between the useful area 32 and the first edge strip 34.
  • a second unperforated separating strip 42 is also located between the useful area 32 and the second edge strip 36.
  • Both separating strips 40, 42 have a width of at least 2 mm, but no more than 6 mm. Since the two separating strips 40, 42 are unperforated, the fiber suspension is not drained on them and therefore no sheets are formed. This automatically results in a limitation of the fiber web that forms on the useful area 32 along the separating strips 40, 42, without the need for edge cutting nozzles, as in the prior art.
  • the through-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 fabric 10 is essentially formed, from a first surface 22, on which the fibrous material suspension is applied in normal use, to a second surface facing away from the first surface 22, similar to that shown in Figure 3.
  • the through-channels 30 can be so close to one another that their upper edges 44, i.e. the edges on the first surface of the substrate 20, at least partially overlap one another, whereas their lower edges 46, i.e. the edges on the second surface of the substrate 20, are noticeably spaced apart from one another.
  • Whether or not sheet formation occurs on the first edge strip 34 and the second edge strip 36 depends largely on how the perforations or through-channels are designed there.
  • the permeability of the first edge strip 34 and the second edge strip 36 differs from the permeability of the useful area 32 of the forming fabric 10.
  • a preferred embodiment of the forming fabric 10 according to the invention provides that the clear width of the through-channels in the two edge strips 34, 36 is noticeably larger than the clear width of the through-channels 30 in the useful area, so that not only the water but also the fibers can pass through the through-channels in the two edge strips 34, 36. In this case, sheet formation does not even occur there.
  • the through-channels in the two edge strips 34, 36 can or should be further apart from one another than the through-channels 30 in the usable area, in order not to negatively affect the required structural strength of the forming fabric 10 there or, if necessary, even to increase it there compared to the usable area.
  • an unperforated first edge protection strip 48 extending in the longitudinal direction LD of the forming fabric 10 can be arranged between the first side edge 26 and the perforated first edge strip 34, and an unperforated second edge protection strip 28 extending in the longitudinal direction LD of the forming fabric 10 can be arranged between the second side edge 28 and the perforated second edge strip 36, wherein the first edge protection strip 26 and the second edge protection strip 28 each have a width between 1 mm and 5 mm, preferably between 1 mm and 3 mm, and are directly connected to the first and second side edges 26, 28.
  • the edge protection strips 26, 28 primarily serve to protect the side edges 26, 28 of the forming fabric 10 against wear.
  • first edge protection strip 26 and the second edge protection strip 28 can each be coated with a protective layer, for example made of a polyurethane.
  • the protective layer preferably extends both over a part of the first surface 22 of the substrate 20 and over a part of the second surface of the substrate 20 and over the edge or side edge 26, 28 in the thickness direction TD of the substrate 20. It is particularly advantageous if the respective protective layer extends beyond the unperforated first edge protection strip 48 or the unperforated second edge protection strip 50 into the area of the perforated first edge strip 34 or the perforated second edge strip 36.
  • the protective layer can be applied with a width of 5 mm to 10 mm, so that it is wider than the unperforated first edge protection strip 48 or the unperforated second edge protection strip 42.
  • the total width of the forming fabric according to the invention is typically between 2.50 m and 3.00 m, or between 5.00 m and 6.00 m in the case of double-width machines.
  • the forming fabric according to the invention is preferably used in a machine for producing a tissue web. This machine, or at least the forming section thereof, can or should be free of a device for cutting the edges of the fibrous web or tissue web.

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Abstract

L'invention concerne un tamis de formage (10), qui est essentiellement constitué d'un substrat perforé (20) et qui prend la forme d'une bande continue s'étendant dans le sens longitudinal (LD), présentant un premier bord latéral (26) et un second bord latéral (28) opposé au premier bord latéral (26) ; le tamis de formage (10) comprend une région d'utilisation perforée (32) agencée entre le premier bord latéral (26) et le second bord latéral (28), sur laquelle est formée la bande de matériau fibreux à produire, lorsque le tamis de formage (10) est utilisé comme prévu, et espacée du premier bord latéral (26) et du second bord latéral (28) ; le tamis de formage (10) comporte en outre une première bande de chant (34) agencée entre le premier bord latéral (26) et la région d'utilisation (32), et une seconde bande de chant (36) agencée entre le second bord latéral (28) et la région d'utilisation (32) ; la première bande de chant (34) et la seconde bande de chant (36) étant également perforées, et une première bande de séparation non perforée (40), s'étendant dans le sens longitudinal (LD), étant agencée entre la première bande de chant (34) et la région d'utilisation (32), et/ou une seconde bande de séparation non perforée, s'étendant dans le sens longitudinal (LD), étant agencée entre la seconde bande de chant (36) et la région d'utilisation (32), la largeur de la première bande de séparation non perforée (40) et/ou de la seconde bande de séparation non perforée (42) étant comprise entre 1 mm et 8 mm ; le tamis de formage (10) comporte, lorsqu'il est utilisé comme prévu, un côté supérieur orienté vers la bande de matériau fibreux et un côté inférieur orienté à l'opposé de la bande de matériau fibreux ; la région d'utilisation (32) comporte une pluralité de canaux traversants qui s'étendent à travers le substrat (10) et qui relient le côté supérieur au côté inférieur, les canaux traversants étant non cylindriques et ayant une surface de section transversale qui se rétrécit le long du sens de l'épaisseur du substrat (20) depuis le côté supérieur jusqu'à une région centrale du substrat (20) située entre le côté supérieur et le côté inférieur ; un bord supérieur d'au moins un canal de la pluralité de canaux traversants (30) est en contact direct avec un bord supérieur d'au moins un autre canal traversant adjacent (30) de la pluralité de canaux traversants de sorte que le bord supérieur dudit au moins un canal de la pluralité de canaux traversants ne se trouve pas dans un plan.
PCT/EP2024/068427 2023-08-08 2024-07-01 Tamis de formage à bandes longitudinales non perforées Pending WO2025031670A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102023121031.9A DE102023121031A1 (de) 2023-08-08 2023-08-08 Formiersieb mit unperforierten Längsstreifen
DE102023121031.9 2023-08-08

Publications (1)

Publication Number Publication Date
WO2025031670A1 true WO2025031670A1 (fr) 2025-02-13

Family

ID=91853523

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2024/068427 Pending WO2025031670A1 (fr) 2023-08-08 2024-07-01 Tamis de formage à bandes longitudinales non perforées

Country Status (2)

Country Link
DE (1) DE102023121031A1 (fr)
WO (1) WO2025031670A1 (fr)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5837102A (en) 1997-04-24 1998-11-17 Voith Sulzer Paper Technology North America, Inc. Perforated and embossed sheet forming fabric
US6503602B1 (en) * 2000-07-26 2003-01-07 Astenjohnson, Inc. Dryer fabric with reinforced edges
DE102004037213A1 (de) * 2004-07-30 2006-03-23 Voith Paper Patent Gmbh Pressverfahren
WO2012095251A1 (fr) 2011-01-11 2012-07-19 Voith Patent Gmbh Habillage perforé de type feuille muni d'un bord résistant au déchirement
EP3839135A1 (fr) * 2019-12-19 2021-06-23 Voith Patent GmbH Toile pour machine à papier et son procédé de fabrication

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5837102A (en) 1997-04-24 1998-11-17 Voith Sulzer Paper Technology North America, Inc. Perforated and embossed sheet forming fabric
US6503602B1 (en) * 2000-07-26 2003-01-07 Astenjohnson, Inc. Dryer fabric with reinforced edges
DE102004037213A1 (de) * 2004-07-30 2006-03-23 Voith Paper Patent Gmbh Pressverfahren
WO2012095251A1 (fr) 2011-01-11 2012-07-19 Voith Patent Gmbh Habillage perforé de type feuille muni d'un bord résistant au déchirement
EP3839135A1 (fr) * 2019-12-19 2021-06-23 Voith Patent GmbH Toile pour machine à papier et son procédé de fabrication

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Publication number Publication date
DE102023121031A1 (de) 2025-02-13

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