EP2067895B1 - Forming fabric for use in a paper making machine - Google Patents

Abstract

The screen (1) has longitudinal threads (4, 5) divided in the ratio of number of threads in a longitudinal thread layer (3) on a machine side and a thread layer (2) on a paper side. Binding cross threads (10, 11) are bound in the thread layers (2, 3). Fiber support index (FSI) of the screen ranges between 230 to 250, and rectangular shaped flow-through openings are formed on the paper side. Diameter of the threads in the longitudinal thread layer on the machine side ranges between 0.15 to 0.25 millimeter. A part of the threads consists of polyethylene terephthalate (PET) material. Air permeability of the screen ranges between 5700 to 10600 meter cube or meter square/hour. The total fill degree of the longitudinal threads is 85 percent.

Description

The invention relates to a forming fabric for use in the forming of a paper machine with a paper and a machine side and extending in the intended direction longitudinal yarns and transverse to extending transverse yarns, wherein the longitudinal yarns in the number-of-yarn ratio of 1: 1 in a machine-side longitudinal yarn layer and a paper-side longitudinal thread layer are divided and embed the binding cross threads in both longitudinal thread layers.

Forming screens are used in the sheet forming area of a paper machine. It is about several tens of meters long and several meters wide, endless fabric belts that are guided over rollers such that they form a substantially flat surface on top. On this surface, a fiber pulp is fed to the beginning of the running path, which is dewatered down through the forming fabric, while the fibers attach to the top of the forming fabric and thus form a paper web. At the end of the Formiersiebes is then still very sensitive Paper web taken from a press belt and then fed to the press section for further drainage and the Trockepartie purposes of thermal drying.

For fabric construction of forming fabrics, a variety of different fabric constructions have been proposed. The present invention relates to a type of fabric in which the longitudinal threads are warp threads and are arranged in two longitudinal thread layers with the thread count ratio 1: 1 arranged one above the other longitudinal threads. Such Formiersiebe are for example from the EP 1 362 142 B1 , of the WO 2004/094719 A1 and the WO 2005/001197 A1 known. The connection of the longitudinal thread layers is done via binding cross threads, which integrate both in the machine side and in the paper-side longitudinal thread layer. In addition to these Bindequerfäden also other transverse threads may be present, which incorporate exclusively in the paper-side longitudinal thread layer and / or exclusively in the machine-side longitudinal thread layer. The aforementioned type of fabric is characterized by a good compromise between the conflicting demands for on the one hand good fiber support - in the EP 1 362 142 B1 For this purpose, an FSI value of 185 or 188 is specified - and on the other hand, high drainage performance.

Basically, forming fabrics today are made from plastic filaments formed as monofilaments. In the process, more and more high-strength plastics are gaining acceptance in order to achieve the same strength, especially in the longitudinal direction smaller thread diameter and thus a lower Längsfadenfüllgrad and consequently a higher permeability to be able to realize (see. WO 03/046277 A1 in a non-generic forming fabric with two transverse thread layers and binding warp threads). In this type of fabric, the Längsfadenfüllgrad is usually at least 100%, sometimes far above (see. WO 2006/034576 A1 ; WO 01/27385 A1 ; EP 0 998 607 B1 ; WO 2004/013410 A1 ), despite the use of high-strength longitudinal or warp threads. In some cases, even lower length fill levels are specified (cf. US 4,314,589 ; EP 0010 311 ; US 4,379,735 ), although this type of tissue is not comparable with the generic type of tissue in this respect. In the non-generic types of tissue air permeabilities between 7 500 to 10 500 m ³ / m ² / h (WO 2004/013410 A1) and 3 500 to 8 200 m ³ / m ^m / h (see. WO 01/27385 A1 ) achieved.

Despite the progress achieved in the meantime, there is still room for improvement in order to increase the efficiency of forming fabrics in terms of their fiber support property on the one hand and dewatering performance on the other and thus to obtain a paper web at the end of the forming fabric which has a low moisture content and high fiber density and thus strength , Such improvements have the consequence that the subsequent sections of the paper machine relieved or high dryness achieved and paper breaks are avoided. The invention is therefore based on the object, a forming fabric in such a way that at the end of the forming fabric, a paper web is obtained, which has a higher strength and a lower degree of moisture.

According to the invention, this object is achieved by a forming fabric which has a fiber subservience index (FSI) which is in the range from 230 to 250 and has an air permeability which, measured at 100 Pa in each case, lies in the range from 5700 to 10,600 m ³ / m ² / h (corresponding to 350-650 cfm, measured at 127 Pa), preferably in the range 6500 to 8200 m ³ / m ² / h (corresponding to 400-500 cfm, measured at 127 Pa). The basic idea of the invention is therefore to design the fabric structure of the forming fabric in such a way that excellent fiber support is achieved while maintaining strength and despite very high air permeability and thus dewatering effect, so that only a small proportion of fibers is lost during dewatering and one over the Surface uniform paper web relatively good strength forms. It should be noted that not only the number of longitudinal and transverse threads per cm is included in the calculation of the fiber support index, but also two coefficients, which depend on the type of integration of the longitudinal and transverse threads and their contribution to the fiber support, ie the fiber support index indirectly also says something about the fabric construction of the forming fabric.

wobei
a - Koeffizient für den Unterstützungsbeitrag der Längsfäden;
Nm = Anzahl der Längsfäden pro cm in Querrichtung auf der Papierseite des Formiersiebes;
b = Koeffizient für den Unterstützungebeitrag der Querfäden;
Nc = Anzahl der Querfäden pro cm in Längsrichtung auf der Papierseite des Formiersiebes.The fiber support index is calculated according to the publication "Approved Standard Meauring Method" of the Papier-Machine Clothing Association, 19, rue de la République, 45000 Orléans / France, June 2004 according to the following formula: $$\mathrm{FSI}=1.693\left(\mathrm{ax\; Nm}+2\mathrm{xbx\; Nc}\right).$$

in which
a - coefficient for the contribution of longitudinal yarns;
Nm = number of longitudinal threads per cm in the transverse direction on the paper side of the forming fabric;
b = coefficient for the contribution of the transverse threads;
Nc = number of transverse threads per cm in the longitudinal direction on the paper side of the forming fabric.

The coefficients a and b depend on the weave and can be taken from a table included in the pre-cited document.

Air permeability is also measured as indicated in the document cited using differential pressures of 100 and 127 Pa, respectively (see above).

In an embodiment of the invention, it is provided that the distribution of longitudinal and transverse threads is such that there are on the paper side between 1200 and 1600 flow openings per cm of surface of the forming fabric. The course of the thread and the structure of the thread should be such that the through-openings have a rectangular shape with a ratio of the extent in the longitudinal direction to the extension in the transverse direction of 1: 1.8 to 1: 3.4. In this way, there is a good drainage effect with high fiber retention.

According to a further feature of the invention, it is provided that the degree of filling of the longitudinal threads in the paper-side longitudinal thread layer is at most 32% in order to achieve a high degree of openness in this longitudinal thread layer. Overall, the degree of filling of the longitudinal threads should be a maximum of 90%, preferably a maximum of 85% and thus significantly lower than in the prior art forming fabrics of this genus.

According to a further feature of the invention, it is provided that the diameter of the longitudinal threads at least in the paper-side longitudinal thread layer is in the range of 0.08 to 0.12 mm, preferably 0.11 mm, and the diameter of the longitudinal threads in the machine-side longitudinal thread layer preferably in Range of 0.15 or 0.25 mm. Because of this comparatively small diameter of the longitudinal threads, in particular in the paper-side length of the thread layer, a low degree of fullness can nevertheless be achieved realize specific number of threads, ie you get a relatively open, but still providing a good fiber retention tissue. In order to satisfy high strength requirements despite the small diameter, the longitudinal threads should be made of a high-strength plastic, for example PET (polyethylene terephthalate) having an intrinsic viscosity (IV) of at least 0.8 dl / g and a modulus of elasticity of at least 10 N / mm ² and / or PEN (polyethylene naphthalate).

A good compromise between dewatering effect on the one hand and fiber retention on the other hand is achieved when the number of longitudinal threads in the range of 50 to 60 threads per cm in the transverse direction. in terms of the number of transverse threads, it should be in the range of 100 to 110 threads per cm in the longitudinal direction.

In principle, a forming fabric according to the invention - as far as the transverse yarns are concerned - can be realized solely with transverse binding yarns, that is to say with (first) transverse yarns which integrate into both longitudinal yarn layers and thus establish a connection between these layers. However, the fiber retention can be improved if, in addition, second transverse threads are present, which are exclusively incorporated into the paper-side longitudinal thread layer and expediently alternate with the binding transverse threads in a specific regular mode. Preferably, the second transverse threads should be taken alone Create plain weave with the longitudinal threads of the paper-side longitudinal thread layer.

According to a further feature of the invention, it is provided that the binding transverse threads are arranged side by side in groups of at least two binding transverse threads, wherein one of the binding transverse threads binds into the machine-side longitudinal thread layer if the other binding transverse thread or the other binding transverse threads binds or bind in the paper-side longitudinal thread layer. Within the groups of juxtaposed binding transverse threads, the binding cross threads should therefore be offset in the transverse direction of the forming fabric. However, they each have the same repeat, so bind in the same way both in the machine side and in the paper-side longitudinal thread position. Preferably, the respectively adjacent binding transverse threads with their repeat should be inserted into the paper-side longitudinal thread layer in such a way that their binding patterns in the transverse direction - ie along their extent - complement each other completely, preferably in such a way that the complementary embeddings result in a pattern on the paper side corresponding to that of the optionally existing second transverse threads corresponds, for example, also give a kind of plain weave.

It is also advantageous for the fiber support if the binding transverse threads bind in the machine-side longitudinal thread layer within a repeat with fewer longitudinal threads than in the paper-side longitudinal thread layers, preferably incorporate with no more than two longitudinal threads in the machine-side longitudinal thread layer. In the paper-side longitudinal thread layer, the binding transverse threads within a repeat suitably bind with more than three longitudinal threads.

According to a further feature of the invention, it is provided that third transverse threads are present, which integrate exclusively into the machine-side longitudinal thread layer. They are intended in particular to provide wear volume on the machine side of the forming fabric in favor of the protection of the longitudinal yarns in the machine-side longitudinal yarn layer. For this purpose, it is expedient if the third transverse threads float on the outside of the machine-side longitudinal thread layer over a plurality of longitudinal threads, wherein in each case the number of these longitudinal threads is greater than the number of longitudinal threads with which integrate the third transverse threads between two floats. Preferably, the floats should go over at least three, more preferably at least five longitudinal threads. Between the floats an integration with a single longitudinal thread of the machine-side longitudinal thread layer is sufficient.

With all range indications both in the description and in the claims, those values are meant and thus disclosed which lie between the respectively specified limit values for the ranges. They are therefore not explicitly mentioned.

In the drawing, the invention with reference to an embodiment is illustrated in more detail. It shows a section of the forming fabric 1 according to the invention in a cross section, ie transversely to the intended running direction.

The forming fabric 1 is a double-layered fabric with an upper, paper-side longitudinal thread layer 2 and a lower, machine-side longitudinal thread layer 3. Both longitudinal thread layers 2, 3 are of longitudinal or warp threads - by way of example denoted by 4 or 5 - in the thread number ratio of 1: 1, wherein in each case one longitudinal thread 4 of the paper-side longitudinal thread layer 2 is arranged exactly above a longitudinal thread 5 in the machine-side longitudinal thread layer 3, the longitudinal threads 4, 5 are thus in pairs above one another.

The diameter of the longitudinal threads 4 in the paper-side longitudinal thread layer 2 is 0.11 mm and the diameter of the longitudinal threads 5 in the machine-side longitudinal thread layer 3 0.18 mm. They consist of PEN. The number of longitudinal threads is 58 per cm in the transverse direction.

In the paper-side longitudinal thread layer 2, second transverse threads 6, 7 are integrated with the longitudinal threads 4 of this longitudinal thread layer 2 to form a plain weave. Perpendicular to the drawing plane each adjacent second transverse threads 6, 7 follow each other. The second Cross threads 6, 7 are made of PET, and they have a diameter of 0.11 mm.

Only in the machine-side longitudinal thread layer 3 third transverse threads are involved, of which only one can be seen here. The third transverse threads 8 each form over five longitudinal threads 5 going floats - exemplified with 9 - on the machine side of the forming fabric 1 and then bind each with a single longitudinal thread 5 a. The floats 9 represent abrasion material for the protection of the machine-side longitudinal thread layer 3, which is highly stressed by tension. The diameter of the third longitudinal threads is 0.22 mm. The material can be PET and / or PAM.

The longitudinal thread layers 2, 3 are joined by pairs of two binding transverse threads 10, 11, each adjacent to one another in the longitudinal direction. They have a diameter of 0.11 mm and are made of PET. They bind in the paper-side longitudinal thread layer 2 successively alternately above and below with longitudinal threads 4, then extend between the two longitudinal thread layers 2, 3 over three longitudinal threads 4 and 5 and then tie with a single longitudinal thread 5 in the machine-side longitudinal thread layer 3, before then float them again between the two longitudinal thread layers 2 and 3. They each have the same binding repeat, but are shifted to each other in the transverse direction - ie in the longitudinal direction - that the Binding pattern in the paper-side longitudinal thread layer 2 complement so that they together form a canvas pattern analogous to the second transverse threads 6, 7. In this way arises on the paper side of the forming fabric 1, a nearly uniform canvas pattern that provides a high fiber retention.

The degree of filling of the paper-side longitudinal thread layer 2 is 31%, the total degree of filling of the longitudinal threads 4, 5 82%. The number of transverse threads is 108 per cm in the longitudinal direction of the forming wire 1. This results in a high openness and thus a good drainage effect despite high fiber retention.

Claims (21)

1. A forming screen (1) for use in the forming section of a paper machine, comprising a paper and a machine side as well as longitudinal threads (4, 5) extending in the intended running direction and binding cross threads (10, 11) extending transversely thereto, wherein the longitudinal threads (4, 5) are divided in the ratio of the number of threads of 1:1 in a longitudinal thread layer (3) on the machine side and a longitudinal thread layer (2) on the paper side, and the binding cross threads (10, 11) bind in both longitudinal thread layers (2, 3), characterized in that the forming screen (1) has a fiber support index (FSI) which is in the range of 230 to 250 and an air permeability which is in the range of 5700 to 10600 m³/m²/h.
2. The forming screen according to claim 1, characterized in that the air permeability is in the range of 6500 to 8200 m³/m²/h.
3. The forming screen according to claim 1, characterized in that the forming screen (1) on the paper side has 1200 to 1600 flow-through openings per cm² surface of the forming screen (1).
4. The forming screen according to claim 1, characterized in that the flow-through openings are rectangular in shape with a ratio of the extension in running direction to the extension in transverse direction of 1:1,8 to 1:3,4.
5. The forming screen according to claim 1, characterized in that the fill degree of the longitudinal threads (4) in the longitudinal thread layer (2) on the paper side is maximum 32%.
6. The forming screen according to claim 1, characterized in that the total fill degree of all longitudinal threads (4, 5) is maximum 90%, preferably maximum 85%.
7. The forming screen according to claim 1, characterized in that the diameter of the longitudinal threads (4, 5), at least in the longitudinal thread layer (2) on the paper side, is in the range of 0.08 to 0.12 mm.
8. The forming screen according to claim 1, characterized in that the diameter of the longitudinal threads (5) in the longitudinal thread layer (3) on the machine side is in the range of 0.15 to 0.25 mm.
9. The forming screen according to claim 1, characterized in that at least a part of the longitudinal threads (4, 5) consist of PET with an intrinsic viscosity of at least 0.8 dl/g and an elasticity module of at least 10 N/mm².
10. The forming screen according to claim 1, characterized in that at least a part of the longitudinal threads (4, 5) consist of PEN.
11. The forming screen according to claim 1, characterized in that the number of longitudinal threads (4, 5) are in the range of 50 to 66 threads per cm in transverse direction.
12. The forming screen according to claim 1, characterized in that the number of cross threads (6, 7, 9, 10, 11) are in the range of 100 to 110 threads per cm in longitudinal direction.
13. The forming screen according to claim 1, characterized in that there are second cross threads (6, 7) which are only bound in the longitudinal thread layer (2) on the paper side.
14. The forming screen according to claim 13, characterized in that the second cross threads (6, 7), taken alone, form a plain weave with the longitudinal thread layer (2) on the paper side.
15. The forming screen according to claim 1, characterized in that the binding cross threads (10, 11) are arranged adjacent to one another to form groups of at least two binding cross threads (10, 11) each, whereby one of the binding cross threads (10, 11) binds in the longitudinal thread layer on the machine side when the other binding cross thread (11, 10) or the other binding cross threads bind in the longitudinal thread layer (2) on the paper side.
16. The forming screen according to claim 15, characterized in that the respectively adjacent binding cross threads (10, 11) bind in the longitudinal thread layer (2) on the paper side with their repeating staggered vis-à-vis one another in such a way that their binding patterns complement one another in transverse direction without a gap.
17. The forming screen according to claim 15, characterized in that the binding cross threads (10, 11) bind in the longitudinal thread layer (3) on the machine side within a repeating with less longitudinal threads (5) than in the longitudinal thread layer (2) on the paper side.
18. The forming screen according to claim 17, characterized in that the binding cross threads (10, 11) bind in the longitudinal thread layer (3) on the machine side within a repeating with not more than two longitudinal threads (5).
19. The forming screen according to claim 1, characterized in that there are third cross threads (8) which only bind in the longitudinal thread layer (3) on the machine side.
20. The forming screen according to claim 19, characterized in that the third cross threads (8) float on the outer side of the longitudinal thread layer (3) on the machine side over several longitudinal threads (5), wherein the number of these longitudinal threads (5) is always greater than the number of the longitudinal threads (5) with which the third cross threads (8) bind between two floatings (9).
21. The forming screen according to claim 20, characterized in that the third cross threads (8) float over more than three longitudinal threads (5) on the outside and, in between, only bind with one longitudinal thread (5).

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