EP1774091A1

EP1774091A1 - Drying fabric

Info

Publication number: EP1774091A1
Application number: EP05770265A
Authority: EP
Inventors: Rauno Enqvist; Marja Ojanen; Juhani Saari
Original assignee: Tamfelt Oyj AB
Current assignee: Metso Fabrics PMC Oy
Priority date: 2004-08-04
Filing date: 2005-08-03
Publication date: 2007-04-18
Also published as: WO2006013232A1; FI20045287A; FI116911B; FI20045287A0; EP1774091A4

Abstract

The invention relates to a drying fabric having an independent top fabric (11) and bottom fabric (12). The top fabric is woven of longitudinal (14) and trans- verse (15) monofilament yarns. The bottom fabric is woven of longitudinal yarns (16) and transverse soft yarns (17). The soft yarns densify the structure of the bottom fabric, whereby the bottom fabric serves as a filtering layer. The top fabric made of monofilament yarns protects the bottom fabric from me- chanical stress.

Description

DRYING FABRIC

BACKGROUND OF THE INVENTION

[0001] The invention relates to a drying fabric that has a roll side surface and a paper web side surface and is woven of several longitudinal yarns in the machine direction and several transverse yarns in the cross- machine direction.

[0002] Drying fabrics are used in the drying section of a paper ma¬ chine to lead the paper web to be dried through the drying section. A drying fabric is made of yarns that endure high temperatures and moisture by using suitable weaves so that the drying fabric has a specific permeability, specific aerodynamic properties and a specific smoothness. When a paper web is re- fed on a paper machine after a shutdown, for instance, the end of the paper web can first be fed through the paper machine as a relatively narrow strip, and only after the end of the paper web has been fed through the paper ma¬ chine or a part thereof, it is spread to the normal run width of the paper ma¬ chine. During the feeding of the paper web, any excess web is cut away with a water jet, and only the section necessary for feeding the web is fed through the drying section of the paper machine. The jet used in cutting the paper web needs to be relatively strong so as to cut the paper web. Such a strong water jet may, however, damage the drying fabric and its yarns below the paper web. In addition, the water jet may push fibres of the paper web through the struc¬ ture of the drying fabric and clog the structure. A problem with the present dry¬ ing fabrics is that they are poorly suited for paper machines that use a cutting water jet during the feeding of the web.

BRIEF DESCRIPTION OF THE INVENTION

[0003] It is an object of the present invention to provide a novel and improved drying fabric.

[0004] The drying fabric of the invention is characterized in that it has at least a top fabric and a bottom fabric on top of each other with the top fabric on the paper side and the bottom fabric on the roll side, that the top fab¬ ric and bottom fabric are independent fabric layers that comprise their own longitudinal yarns and transverse yarns, that the top fabric and bottom fabric are woven at the same time in a weaving machine, and that the fabric layers are fastened to each other with several binding yarns, that the top fabric com¬ prises only monofilament yarns, whereby the top fabric is arranged to form a fabric layer protecting the bottom fabric, that the transverse yarns of the bottom fabric are soft yarns that are arranged to densify the structure of the bottom fabric, and that the air permeability of the bottom fabric is substantially lower than that of the top fabric, whereby the bottom fabric is arranged to form a fil¬ tering layer in the drying fabric.

[0005] The essential idea of the invention is that the drying fabric has at least two independent fabric layers arranged on top of each other, namely a top fabric and a bottom fabric. The top fabric is woven of longitudinal and transverse monofilament yarns. The bottom fabric is woven of longitudinal and transverse yarns, and the transverse yarns are soft yarns that densify the structure of the bottom fabric in respect of air permeability.

[0006] The invention provides the advantage that the top fabric made of monofilament yarns is capable of receiving mechanical stresses, such as wear and the pressure impact of water jet cutting. The bottom fabric, in turn, has a clearly denser structure than the top fabric, whereby it prevents the penetration of the fibres of the paper web and impurities inside the drying fab¬ ric and to the back, from which it is difficult to wash off the fibres and impuri¬ ties. Thus, the fabric layers of the drying fabric of the invention have their own tasks: the top fabric serves as a protective layer and the bottom fabric as a filtering layer. In the drying fabric of the invention, the fibres and impurities cannot penetrate deep into the structure of the drying fabric, but remain on the paper side of the drying fabric, from which they can be washed away with nor¬ mal washing devices belonging to the paper machine that are usually arranged to wash the paper side surface of the drying fabric. The washing is further fa¬ cilitated by the fact that the paper side of the drying fabric has monofilament yarns, from which impurities can easily be cleaned.

[0007] The essential idea of an embodiment of the invention is that the soft transverse yarns of the bottom fabric are multifilament yarns, spun yarns, thermoforming yarns, or yarns forming through weaving forces. With such yarns, it is possible to form a very dense woven fabric.

[0008] The essential idea of an embodiment of the invention is that there are several transverse filling yarns between the top fabric and bottom fabric to further densify the structure of the drying fabric.

[0009] The essential idea of an embodiment of the invention is that the longitudinal yarns of the top fabric are flat in cross-profile, for instance oval or rectangular yarns. Such yarns are capable of receiving the pressure impact of water jet cutting and of protecting the bottom fabric when the end of the pa¬ per web is fed.

[0010] The essential idea of an embodiment of the invention is that the top fabric and bottom fabric are single-layer structures with transverse yarns in one layer, and that the top layer and bottom layer have a two-shed weave structure.

BRIEF DESCRIPTION OF THE FIGURES

[0011] The invention is described in greater detail in the attached drawings, in which

[0012] Figure 1 is a schematic view of web feeding in a paper ma¬ chine,

[0013] Figure 2 is a schematic view of a drying fabric of the inven¬ tion seen in the cross-machine direction CMD, and

[0014] Figure 3 is a schematic view of a microscopic image of the bottom fabric of the drying fabric of the invention.

[0015] In the figures, some embodiments of the invention are shown simplified for the sake of clarity. Similar parts are marked with the same refer¬ ence numbers in the figures.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

[0016] Figure 1 shows in a highly simplified manner how a web end 1 can be fed through the drying section 2 of a paper machine. A relatively nar¬ row strip, i.e. the web end 1 , can be cut from a normal width web 4 with a wa¬ ter jet cutter 3, the strip being easier to feed through the rolls 5, reels, and other components of the drying section 2 than a normal width web 4. Thus, the section 6 cut away from the paper web can be led into a discharge channel 7 and on for further use. For the sake of clarity, the figure does not show the dry¬ ing fabric that supports the paper web through the drying section 2. The water jet cutter 3 can be moved in the cross-machine direction CMD of the drying section 2 supported by a guide bar 8, for instance. After the paper web end 1 is fed through the drying section 2, the web is spread. The water jet cutter 3 is then moved in direction A toward the other edge of the drying section 2, and the cutting point 9 moves in direction A and the width of the paper web in¬ creases. The web is spread to its normal run width, after which the water jet cutter 3 can be disconnected. [0017] A problem detected during web spreading is that the strong water jet penetrates through the paper web and may damage the drying fabric below the paper web and especially the yarns on the web-side surface. In ad¬ dition, the strong water jet may push fibres of the paper web inside the struc¬ ture of the drying fabric at cutting point 9, whereby the drying fabric may clog at the cutting point 9. Thus, during web feeding, a damaged section may form in the drying fabric at the cutting point 9, which may impede web feeding and runnability and further cause marking on the paper web. During web spread¬ ing, when the water jet is moved in cross direction, the drying fabric may clog between the web end 1 and the other edge. A new drying fabric installed dur¬ ing a service shutdown may thus lose its properties prematurely, and the ser¬ vice life of the fabric may be shortened.

[0018] Figure 2 shows a drying fabric 10 of the invention seen in the cross-machine direction CMD. The drying fabric 10 has a paper-side surface P, against which the paper web 4 being dried can be arranged in the drying section 2. On the opposite side of the drying fabric 10, there is a roll side sur¬ face T that can be arranged against the paper machine. The drying fabric 10 may have at least two fabrics on top of each other, namely a top fabric 11 on the paper side and a bottom fabric 12 at the back T. The top fabric 11 and the bottom fabric 12 may be woven in a weaving machine, and they may both comprise their own yarn systems, i.e. longitudinal MD yarns and transverse CMD yarns. A woven drying fabric 10 may be sufficiently firm and stable, which enhances the runnability of the drying fabric 10 in the drying section 2. The top fabric 11 and bottom fabric 12 may be woven at the same time in the same weaving machine, and the fabrics 11 , 12 may be connected to each other with one or more yarns. For the sake of clarity, in Figure 2, the fabric layers 11 , 12 are separated from each other in the rightmost section of the fabric. The drying fabric 10 can be woven so that the longitudinal MD yarns are warp yarns and the transverse CMD yarns are weft yarns. Between the fabric layers 11 , 12, there may be several transverse filling yarns 13 that densify the structure of the drying fabric 10. The cross-profile of the filling yarns 13 may be round, or in some cases, the filling yarns may be flat. During weaving, the filling yarns may be arranged so that they do not at all cross with the yarns of the top fabric 11 and bottom fabric 12.

[0019] The top fabric 11 may be woven of several longitudinal MD yarns 14 and several transverse CMD yarns 15. The yarns 14, 15 of the top fabric 11 may be monofilament yarns that endure well wear and mechanical stress. Further, the surface of the monofilament yarn is smooth. This way, the top fabric 11 woven of monofilament yarns can form a layer protecting the bot¬ tom fabric 12 on the paper side P of the drying fabric 10. In addition, the top fabric 11 woven of monofilament yarns is, due to its smoothness, easily clean- able, whereby the service life of the drying fabric 10 becomes long. Further, the longitudinal yarns 14 of the top fabric 11 may be flat in cross-profile, for instance oval, rectangular, or rectangular with rounded corners. With the flat yarns, the surface of the top fabric 11 becomes even smoother, whereby dirt comes off it easily. In addition, flat yarns provide a smooth surface that does not mark and has good aerodynamic properties. The transverse yarns 15 of the top fabric 11 may be round in cross-profile. The top fabric 11 may be a sin¬ gle-layer structure with transverse yarns 15 on one layer. However, it is also possible to form a two-layer or multi-layer top fabric 11 with transverse yarns 15 on two or more layers. The top fabric 11 of Figure 2 has a two-shed weave, i.e. the longitudinal yarn 14 runs alternately over and under one transverse yarn 15. Alternatively, it is possible to use a 3-, 4-, 5-shed, or multi-shed weave in the top fabric 11 as necessary.

[0020] The bottom fabric 12 of the drying fabric 10 can be woven of several longitudinal MD yarns 16 and several transverse CMD yarns 17. The longitudinal yarns 16 may be monofilament yarns with a flat cross-profile, for example oval, rectangular or rectangular with rounded corners. The transverse yarns 17 may for instance be multifilament yarns, staple fibre yarn, spun yarn, bi-component yarn, hollow yarn, or some other soft yarn that can densify the structure of the bottom fabric 12 and give the fabric filtering properties. The soft yarn may also be a thermoplastic yarn or a yarn forming through weaving forces. The weave of the bottom fabric 12 may be a two-shed weave, i.e. the longitudinal yarn 16 runs alternately over and under one transverse yarn 17. Alternatively, it is possible to use a 3-, 4-, 5-shed, or multi-shed weave in the bottom fabric 12 as necessary. The bottom fabric 12 may be a single-layer structure with transverse soft yarns 17 on one layer. However, it is also possi¬ ble to form a two-layer or multi-layer bottom fabric 12 with transverse yarns 17 on two or more layers. Then, at least one layer of the bottom fabric 12 com¬ prises soft transverse yarns 17 that densify the structure.

[0021] The top fabric 11 and bottom fabric 12 may be connected to each other with several longitudinal yarns 16 of the bottom fabric 12 that may be arranged to run via the transverse yarn 15 of the top fabric 11. In this case, the longitudinal yarn 16 thus also serves as a binding yarn. All the yarns 16 or only some of the yarns 16 can be used in the binding. It is also possible to ar¬ range the connection between the fabrics 11 and 12 with the longitudinal yarns 14 of the top fabric 11 , or with some of the longitudinal yarns 14. Further, transverse yarns, for instance the transverse yarns 15 of the top fabric 11 , can be used for binding. The binding of the fabric layers can thus be done with binding wefts or binding warps, and further, the yarns used in binding may also belong to the yarn systems of the fabric layers or be separate yarn systems.

[0022] The top fabric 11 of the drying fabric 10 may mechanically and chemically protect the bottom fabric 12 below it. The top fabric 11 or the yarns 14, 15 used in it may be treated with an agent improving self-cleansing, such as polytetrafluoroethylene (PTFE). Further, the top fabric 11 or the yarns 14, 15 used in it can be treated with a hydrophobic or hydrophilic material as necessary.

[0023] At least the following yarn materials can be used in the dry¬ ing fabric 10: polyester (PES), polyamide (PA), polyphenylene sulphide (PPS), polyetheretherketone (PEEK), polyethylene terephthalate (PET), polymethyl- ene cyclohexylene terephthalate (PCTA), polyurethane (PU), and polyethylene naphthalate (PEN).

Example 1

[0024] A drying fabric was woven with two overlapping fabrics at¬ tached to each other during weaving, namely a top fabric and bottom fabric that were bound to each other with the transverse yarns of the top fabric during weaving. The following yarns were used in the weaving:

- the top fabric had one layer and the weave was a two-shed weave,

- the bottom fabric had one layer and the weave was a two-shed weave,

- the warps in the surface and bottom fabrics were flat monofila¬ ments of 0.3 * 0.6 mm,

- the wefts in the top fabric were monofilaments with a diameter of 0.4 mm,

- the wefts, i.e. the filtering yarns, in the bottom fabric were 440 tex, 100 twists, - the filling wefts between the surface and bottom fabrics were monofilaments with a diameter of 0.6 mm,

- the warp density was 240/10 cm,

- the weft density was 162/10 cm (3 * 56 wefts),

- the air permeability of the drying fabric was 1 ,600 m³/m²h, 100 Pa,

- the thickness of the drying fabric was 1.5 mm.

[0025] Figure 3 shows a microscopic image of a bottom fabric 12 of a drying fabric of the invention. It is possible to measure from the figure the width of the soft transverse yarns, i.e. in this case that of the wefts, the width of the section between the wefts, and to calculate the weft coverage on the basis thereof. In this case, the weft coverage is over 50%, which is substantially higher than in prior-art drying fabrics, in which the corresponding coverage is typically below 30%.

[0026] The transverse yarn coverage of the top fabric of the drying fabric of the invention is preferably below 25% and its air permeability is below 15,000 m³/m²h, 100 Pa. Further, the soft transverse yarn coverage of the bot¬ tom fabric of the drying fabric of the invention is over 50% and its air permeability is below 3,500 m³/m²h, 100 Pa.

[0027] The drawings and the related description are only intended to illustrate the idea of the invention. The invention may vary in detail within the scope of the claims.

Claims

1. A drying fabric that has a roll side surface (T) and a paper web side surface (P) and is woven of several longitudinal yarns in the machine direction (MD) and several transverse yarns in the cross-machine direction (CMD), characterized in that the drying fabric (10) has at least a top fabric (11) and a bottom fab¬ ric (12) on top of each other with the top fabric (11) on the paper side (P) and the bottom fabric (12) on the roll side (T), the top fabric (11) and bottom fabric (12) are independent fabric lay¬ ers that comprise their own longitudinal yarns (14; 16) and transverse yarns (15; 17), the top fabric (11) and bottom fabric (12) are woven at the same time in a weaving machine, and the fabric layers are fastened to each other with several binding yarns, the top fabric (11) comprises only monofilament yarns (14, 15), whereby the top fabric is arranged to form a fabric layer protecting the bottom fabric (12), the transverse yarns (17) of the bottom fabric (12) are soft yarns that are arranged to density the structure of the bottom fabric (12), and the air permeability of the bottom fabric (12) is substantially lower than that of the top fabric (11), whereby the bottom fabric (12) is arranged to form a filtering layer in the drying fabric (10).

2. A drying fabric as claimed in claim 1, characterized in that the transverse soft yarns of the bottom fabric (12) are of one of the following types: multifilament yarns, spun yarns, staple fibre yarns, bi- component yarns, hollow yarns, thermoforming yarns, yarns forming through weaving forces.

3. A drying fabric as claimed in claim 1 or 2, characterized in that between the top fabric (11) and bottom fabric (12), there are several transverse (CMD) filling yarns (13) that densify the structure of the drying fabric (10).

4. A drying fabric as claimed in claim 3, characterized in that the filling yarns (13) are arranged into the drying fabric without crossing with the yarns of the top fabric (11 ) and bottom fabric (12).

5. A drying fabric as claimed in any one of the preceding claims, characterized in that the longitudinal yarns (14) of the top fabric (11) are flat in cross- profile.

6. A drying fabric as claimed in any one of the preceding claims, characterized in that the top fabric (11) and bottom fabric (12) comprise a two-shed weave.

7. A drying fabric as claimed in any one of the preceding claims, characterized in that the air permeability of the drying fabric (10) is below 5,000 m³/m²h, 100Pa.

8. A drying fabric as claimed in any one of the preceding claims, characterized in that the coverage of the transverse soft yarns (17) of the bottom fabric (12) is over 50%.

9. A drying fabric as claimed in any one of the preceding claims 1 to 6, characterized in that the coverage of the transverse yarns (15) of the top fabric (11 ) is be¬ low 25%, the air permeability of the top fabric (11) is below 15,000 m³/m²h, 100Pa, the coverage of the transverse soft yarns (17) of the bottom fabric (12) is over 50%, and the air permeability of the bottom fabric (12) is below 3,500 m³/m²h, 100Pa.

10. A drying fabric as claimed in any one of the preceding claims, characterized in that the top fabric (11) is a single-layer structure with transverse yarns (15) in one layer, and the bottom fabric (12) is a single-layer structure with transverse yarns (17) in one layer.

11. A drying fabric as claimed in any one of the preceding claims 1 to 9, characterized in that at least one fabric layer (11, 12) of the drying fabric (10) has at least two layers.