EP2199458A1 - Forming fabric - Google Patents

Abstract

The forming fabric (1) has a textile sheet material (2) formed from fiber and knit fabric. Connecting threads (15) extend perpendicular to a running direction (A) and are inserted on paper sides (3) of the sheet material for forming a paper web. The connecting threads are released between dewatering surfaces continuously extending along an extension of the threads and a plane of the threads. The threads have a breadth of 0.49 mm in a projection perpendicular to plane of the sheet material and cover 50 percentages of an entire surface of the sheet material.

Description

The invention relates to a forming fabric for dewatering a paper web in the sheet forming area of a paper machine, with a carrier web of a fabric, wire link belt and / or knitted fabric, placed on the paper web intended for the construction of the paper web transverse to the intended direction extending transverse threads at least partially spaced and without Incorporation are attached to the carrier web to her, the transverse threads between them drainage areas, which are continuous along the extension of the transverse threads in the plane thereof.

Forming screens are used in the sheet forming area of a paper machine. It is about 10m long and several meters wide, endless belts that are guided over rollers such that they form paper-side substantially flat surfaces. In the case of a wire, a fiber pulp is applied to this surface or, in the case of a twin-wire former, a fiber pulp is injected between the two wires. Under the influence of gravity and suction devices is dehydrated by the sieve (s), wherein the fibers formed by wire filaments form gradually to the paper web. At the end of the forming section, the then still very sensitive paper web is taken over by a press belt and then the press section for further drainage and finally the drying section supplied for thermal drying.

For forming fabrics are almost exclusively used fabric usually formed as monofilaments plastic threads. In the past, a large number of different fabric constructions have been proposed. The main objectives in the construction of such fabrics are, on the one hand, good fiber retention on the paper side provided for the construction of the paper web and, on the other hand, good drainage performance. The retention of the fibers strongly influences the properties and quality of the paper web, while the dewatering performance has an influence on the moisture content and the fiber density and thus on the strength of the paper web, with the result that the subsequent sections of the paper machines relieve pressure and achieve high degrees of drying and ultimately also paper breaks be avoided. Examples of fabric constructions which are suitable for forming fabrics, the EP 1 362 142 B1 . WO 2004/094719 A1 and WO 2005/001197 A1 remove. However, knitted fabrics or wire-link belts can also be used as carriers (see FIG WO 99/41447 ) or combinations of woven, knitted fabric and / or wire link band.

The objective, on the one hand to obtain a good fiber retention and on the other hand a high dewatering performance, is in a certain contradiction, because a good fiber retention requires a relatively dense fabric structure, while a high drainage performance requires a sieve that is as open as possible. To achieve the best possible compromise asymmetric fabric structures are therefore realized, in which on the one hand the integration of the longitudinal and transverse threads on the paper side is such that a good fiber support is provided, but on the other hand, the fabric is formed inside open so that a good Drainage effect is achieved. This leads to relatively complex, mostly multi-layered tissue types.

In the EP 1 719 834 A1 a generic papermachine clothing is disclosed, which should also find use as a forming fabric. It has a carrier web which may be formed as a film, fine fabric or non-woven or combinations thereof. In one embodiment ( FIG. 1 ) are on the paper web side transverse threads and machine side longitudinal threads placed on the carrier web formed as a film and fixed to the carrier web by fusing, gluing or positive connection. The additional thread layer layers formed thereby are intended to create a reinforcing structure with the aim of improving the dimensional stability of the carrier web. Accordingly, filaments with a relatively large cross section between 0.5 and 10 mm in width are proposed for the filament scrims. The distance between the longitudinal and transverse threads of the scrim is a multiple of the width. This is apparently done with the intent of the properties of the carrier web in particular with regard to fiber retention and drainage performance to disturb as little as possible by the additional threads.

In addition, it has been proposed in the past, in forming fabrics textile carrier webs, in which the longitudinal and transverse threads are integrated, ie in particular woven or knitted fabric to avoid superimposed by several layers of yarn layers with parallel and spaced apart threads superimposed and each other be connected at the crossing points. So is out of the GB 1 224 629 A1 a forming fabric is known, which is composed of three or four layers of such scrim, wherein on a central longitudinal thread scrim paper side and machine side ever a Querfadengelege is launched. In one embodiment, a further Längsfadengelege may additionally be provided on the machine side. The scrims are connected to each other via adhesive strips which fill the spaces between the transverse threads in the region of the longitudinal threads of the central longitudinal thread scrim. This creates window-like, self-contained drainage channels.

Further examples of papermachine clothing, which are constructed exclusively from yarn layers, are the EP 1 359 251 A1 and EP 1 357 223 A1 refer to. These paper machine clothing are intended primarily for use as dryer fabrics, as is already apparent gives the dimensions of the threads indicated in the documents.

Forming fabrics made of yarns have not become relevant in practice. Tissues are still used in which the best possible compromise between fiber retention on the one hand and drainage performance on the other hand is sought through variations in tissue structure. The invention has for its object to provide a forming fabric that holds considerable improvements in terms of these two properties.

1. a) die Querfäden haben in der Projektion senkrecht zur Ebene der Trägerbahn eine Breite von höchstens 0,49 mm;
2. b) die Querfäden decken die Gesamtfläche der Trägerbahn in der Projektion senkrecht zu deren Ebene zu mindestens 50%, besser mehr als 50% ab.

This object is achieved according to the invention in a forming fabric of the type mentioned by the following features:

1. a) the transverse threads have in the projection perpendicular to the plane of the carrier web a width of at most 0.49 mm;
2. b) the transverse threads cover the total area of the carrier web in the projection perpendicular to its plane to at least 50%, better more than 50%.

The basic idea of the invention is to arrange a transverse thread layer with relatively thin transverse threads on the paper side of the carrier web, but in such a high number that a pronounced transverse thread structure with small distances between the individual transverse threads results on the paper side. By limiting the transverse thread width on the one hand and the high coverage of the carrier web on the other hand results in a cross-thread density, as they would not be reached by means of a fabric or knit, certainly not in a wire link belt. This causes an extremely good fiber retention. On the other hand, despite the high coverage of the carrier web remain a variety of along the transverse threads continuous slit-like drainage surfaces, which ensures a very uniform and effective over the entire surface drainage of the building on the transverse threads paper web, especially - as opposed to fabrics - interfere with no longitudinal threads.

A significant advantage of the invention is that in the construction of the carrier web no compromise must be made, since the fiber retention is taken over solely by the attached transverse threads. The carrier web can therefore be optimized to achieve the highest possible dewatering performance, i. The fabric structure can be made relatively simple and very open, which can also save costs. Accordingly, with the forming fabric according to the invention a clear separation of functions between the carrier web as a constituent element and the transverse thread layer as a fiber-supporting element is produced.

In an embodiment of the invention, it is provided that the transverse threads extend over the entire width of the carrier web, but at least across the width of the headbox.

The transverse threads may extend parallel to each other to obtain a uniform surface texture. In addition, all transverse threads can be spaced from each other, preferably with a distance of at least 0.001 mm. For manufacturing reasons, the transverse threads can run straight. However, this does not exclude other courses, for example a wave-shaped course. It is expedient that the transverse threads extend parallel to each other.

The transverse threads need not extend at right angles to the direction of the Formieriebes, even if this is appropriate. You can also extend at an angle of 60 ° to 120 °, preferably from 85 ° to 95 ° to the direction of the Formiersiebes.

In order to obtain the most uniform possible surface structure, the distances between the transverse threads should be equal to one another. Nevertheless, the invention opens up the possibility of alternating groups of transverse threads with different distances and / or widths and / or cross-sectional geometries while observing the above boundary conditions. For example, threads with different diameters may follow alternately, but it is also possible for a certain number of threads with a first diameter, then a certain number of threads with a second diameter to follow one another in groups, the numbers also being the same or different could be. In that regard, the respective requirements can be taken into account as optimally as possible.

The width of the transverse threads should be at least 0.05 mm. Preferably, the upper limit of 0.49 mm should not be fully utilized, i. the width of the transverse threads is suitably in the range of 0.08 to 0.3 mm, preferably 0.08 to 0.15 mm.

The coverage of the carrier web by the transverse threads is advantageously more than 60%, preferably more than 2/3 of the total area of the carrier web, more preferably at least 75%. In order to obtain good drainage properties, it is expedient that the coverage is not greater than 90% of the total area of the carrier web.

The advantage of the forming fabric according to the invention, in the design of the carrier web to be relatively free, can be used to give the paper side of the carrier web a longitudinal yarn structure, ie with the proportion of longitudinal yarns of the carrier web extending in the plane of the paper side of the carrier web , in the projection perpendicular to the plane of the carrier web, a surface coverage between 40% and 90%, preferably 50% to 70%, better still cause 60% to 65% of the total surface of the carrier web.

The attachment of the transverse threads on the carrier web should be punctiform, preferably only on longitudinal threads of the carrier web be to disturb as little as possible the drainage of the paper web by fixing the transverse threads. For this purpose, above all, the welding and the bonding, both types of attachment can also be combined with each other. Particularly advantageous is the welding by means of a laser beam, as has already been used in dry screens, consisting of pure thread layers, applied (see. EP 1 359 251 A1 ). For this purpose, the transverse threads should have the property of absorbing laser energy and being able to be brought to melting temperature by absorbed laser energy at least at the surface. In this way, the transverse threads with the carrier web can be selectively welded under the action of a laser beam. The laser-absorbing property of the transverse threads can be effected by a suitable additive which is incorporated into the transverse threads, be it distributed over the cross-section or only in the region of the lateral surface (cf. EP 1 359 251 A1 ).

Another possibility is that threads are used for the carrier web, which are able to absorb laser energy, while the transverse thread layer is made of material which absorbs virtually no laser energy.

A selective connection of the transverse threads on the carrier web can also take place using a preferably elastic adhesive. In this case, so little adhesive should be applied that there is no impairment of the drainage performance.

The carrier web consists of a single-layer or multi-layered woven and / or knitted fabric and / or of a wire link band which consists of a multiplicity of wire spirals which extend side by side transversely to the running direction and which are hingedly connected to one another via coupling wires (cf. EP 0 524 478 B1 ; DE 24 19 751 A1 ). Preferably, no further scrim is to be present except for the paper-side transverse thread layer. The carrier web can be manufactured as an endless tube, either round woven or formed from narrow strips. In the latter case, the strips are spirally wound transversely to the intended running direction, wherein the strips are connected to one another at the longitudinal edges, so that a closed, endless tube is formed as a carrier web (cf. EP 1 209 283 A1 ). Alternatively, however, the carrier web can finally be produced, wherein the transversely extending end edges are formed so that they can be connected to form a Steckdrahtnaht (see. EP 0 011 977 B1 ; EP 0 262 467 B1 ; EP 0 108 733 B1 ; EP 0 925, 394 B1 ). The thereby to be connected loops on the front edges of the forming fabric can be formed from the longitudinal threads themselves. Alternatively, in the front edges but also eyelets forming spirals can be used.

With all this, it is important that the drainage properties in the seam area are no different than the rest Area. Therefore, should also extend over the seam at least one transverse thread, if necessary, several transverse threads. If necessary, the transverse threads should also be made wider than the other transverse threads in order to achieve a permeability which is constant over the surface.

The transverse threads may have any cross section, expediently a round, but also a non-circular cross section. In the latter case, they may for example be oval, rectangular, square, hexagonal or star-shaped, with rounded edges, or have a different geometric cross-sectional shape. The transverse threads are preferably monofilaments, but may also be twines or combinations thereof. As monofilaments also hollow monofilaments can be used, which can be adapted by pressure and heat in the form. The same applies to the threads of the carrier web. Here also monofilaments, multifilaments, threads or other thread forms, such as stranded or braided threads or combinations thereof may be used. For these threads, the above-mentioned cross-sectional shapes are also in question.

As the material for the threads, the plastic materials commonly used for forming fabrics are proposed, in particular PET, PBT, PA, PP, PPS or mixtures thereof.

Figur 1

einen Längsschnitt durch ein erstes Formiersieb und

Figur 2

einen Längsschnitt durch ein zweites Formiersieb im Nahtbereich.

In the drawing, the invention is illustrated by means of exemplary embodiments. Show it:

FIG. 1

a longitudinal section through a first Formiersieb and

FIG. 2

a longitudinal section through a second forming fabric in the seam area.

This in FIG. 1 forming fabric 1 shown consists of a web formed as a web 2 and a force applied to the paper side 3 transverse thread layer 4th

The carrier web 2 has two layers 5, 6 with transverse threads - respectively by way of example denoted by 7 and 8 respectively - which are formed as a monofilament thread, wherein two transverse threads 7, 8 are in pairs one above the other. The transverse threads 7, 8 are bound by longitudinal threads 9 to 14, which consist of monofilaments and / or monofilament threads and have different course. The front longitudinally lying in this view two longitudinal threads 9, 10 float on the paper side 3 of the carrier web 2 via three adjacent transverse threads 7 and then bind a subsequent transverse thread 7 of the top layer 5 below, before they float again over three transverse threads 7. These two longitudinal threads 9, 10 in the longitudinal direction (arrow A), ie the intended direction of the Formieriebes 1 offset by two transverse threads 7.

The underlying four further longitudinal threads 11, 12, 13, 14 have a different course. They bind an upper transverse thread 7 on the paper side 3, pass through the interior of the carrier web 2 between a pair of adjacent transverse threads 7, 8 and tie the subsequent transverse thread 8 on the machine side of the carrier web 2 at the bottom before then again through the interior of the Carrier web 2 between an adjacent pair of transverse threads 7, 8 go and incorporate a subsequent upper transverse thread 7 at the top. In this way, the transverse thread layers 5, 6 are connected to each other. Two adjacent of these longitudinal threads 11, 12, 13, 14 are offset in the longitudinal direction (arrow A) of the forming fabric 1 by a respective transverse thread 7, 8.

The transverse thread layer 4 consists of a multiplicity of transverse threads-denoted by 15 by way of example-in this case a round cross-section which runs parallel to one another over the entire width of the carrier web 2 and has the same distances from each other. The diameter corresponds to the width B of the transverse threads 15 in the projection perpendicular to the plane of the carrier web 2. The distances are smaller than the diameter of the transverse threads 15, so that the cover of the carrier web 2 by the transverse threads 15 is higher than 50%. The transverse threads 15 are formed as monofilaments and are straight and at right angles to the direction of the Formieriebes 1. The attachment of the transverse threads 15 to the carrier web 2 is selectively at the floats on the paper side 3 longitudinal threads 9, 10 by welding or by adhesive.

FIG. 2 shows a further embodiment of a forming fabric 21 according to the invention. The forming fabric 21 also consists of a carrier web 22, on the paper side 23, a transverse thread layer 24 is placed.

The carrier web 2 is formed as a double-layered fabric, which has an upper layer 25 with transverse threads - designated 26 by way of example - and a lower layer 27 with transverse threads - designated by way of example with 28 - has. In this case, the transverse threads 26, 28 are monofilaments. The transverse threads 26, 28 are bound by longitudinal threads 29, 30, 31, 32 of which only two longitudinal threads 29, 30 and 31, 32 are shown here on each side. All longitudinal threads 29, 30, 31, 32 bind the transverse threads 26, 28 in cranks - exemplified by 33 - a, each longitudinal thread 29, 30, 31, 32 after incorporating a transverse thread 26 in the upper layer 25 a transverse thread 28 in the lower layer 27 binds, wherein it passes through the interior of the carrier web between a pair of superimposed transverse threads 26, 28.

In the section shown, the carrier web 22 ends in end edges. At both end edges forms - viewed perpendicular to the plane of the drawing - each have a longitudinal thread 29 and 31 seam loops 36 and 37, while the respective underlying longitudinal threads 30, 32 form tight loops 38, 39 to an additional filling thread 40 and 41. All longitudinal threads 29, 30, 31, 32 are after training The seam loops 36, 37 and the tight loops 38, 39 weaved back into the fabric of the carrier web 2 and meet there - which is not shown here - on shortened ends of the respective adjacent longitudinal thread.

The seam loops 36, 37 serve to produce a plug wire seam. For this they are - as shown - brought into meshing overlap, so that a channel 42 is formed parallel to the end edges of the carrier web 22, through which a pintle 43 is inserted as a coupling. This results in an endless Formiersieb 21. By pulling the plug wire 43 from the channel 42, the connection of the end edges can be solved again. Regarding further details of this seam is on the EP 0 262 764 B1 Referenced.

The transverse thread layer 24 also consists here of a plurality of transverse threads - designated by way of example by 45 -. They have oval cross-section of the width B and extend parallel to each other and over the entire width of the carrier web 22. They have the same distances from each other, wherein the distances are significantly less than in the forming fabric 1 and only a fraction of the width B of the transverse threads 45 amount. The transverse threads 45 are likewise formed as monofilaments and extend straight and at right angles to the running direction (arrow C) of the forming fabric 21. The attachment of the transverse threads 45 to the carrier web 22 is also here selectively at the offsets 33 of the longitudinal threads 29, 30, 31, 32. The connection can be made by welding or by adhesive.

As can be seen, transverse threads 45 are also present in the seam area. The transverse thread 45 located perpendicularly above the pintle wire 43 is expediently connected only to the seam loops 36 on the left-hand end edge. In this way, the seam can be closed and also released again, without said transverse thread 45 being a hindrance.

The above-cited prior art documents are expressly incorporated herein by reference for the full content of the present description. Furthermore, all of the features set out above belong to the invention, and they are each independently disclosed in isolation, in which context they stand.

Claims (15)

Forming screen (1, 21) for dewatering a paper web in the sheet forming area of a paper machine, with a textile carrier web (2, 22) of a fabric, wire link belt and / or knitted fabric, on whose provided for the construction of the paper web paper side (3, 23) transversely to the intended running direction (arrows A, C) extending transverse threads (15, 45) placed at least partially spaced and without involvement with the carrier web (2, 22) are attached to her, the transverse threads (15, 45) between them drainage areas, which are continuous along the extent of the transverse threads (15, 45) and in their plane, characterized by the following features: a) the transverse threads (15, 45) have in the projection perpendicular to the plane of the carrier web (2, 22) has a width (B) of at most 0.49 mm; b) the transverse threads (15, 45) cover the total area of the carrier web (2, 22) in the projection perpendicular to the plane of at least 50%. Forming fabric according to claim 1, characterized in that the transverse threads (15, 45) extend over the entire width of the carrier web (2, 22). Forming fabric according to one of claims 1 to 2, characterized in that all the transverse threads (15, 45) are spaced from each other, preferably with a distance of at least 0.001 mm. Forming fabric according to one of claims 1 to 3, characterized in that the transverse threads (15, 45) run straight and / or extend parallel to each other. Forming fabric according to one of claims 1 to 4, characterized in that the transverse threads (15, 45) to the running direction of the forming fabric (1, 21) at an angle of 60 ° to 120 °, preferably from 85 ° to 95 ° and even better extend at an angle of 90 °. Forming fabric according to one of claims 1 to 5, characterized in that the distances between the transverse threads (15, 45) are equal to each other. Forming fabric according to one of claims 1 to 4, characterized in that alternate groups of transverse threads (15, 45) with different distances and / or widths and / or cross-sectional geometries. Forming fabric according to one of claims 1 to 6, characterized in that the width (B) of the transverse threads (15, 45) is at least 0.05 mm, more preferably 0.08 mm to 0.3 mm, preferably 0.08 mm to 0 , 15 mm. Forming fabric according to one of claims 1 to 8, characterized in that the cover by the transverse threads (15, 45) in the projection perpendicular to the plane over 60% of the total area of the carrier web (2, 22), preferably at least 75%. Forming fabric according to one of claims 1 to 9, characterized in that the cover by the transverse threads (15, 45) in the projection perpendicular to the plane of the carrier web (2, 22) is at most 90% of the total area of the carrier web (2, 22). Forming fabric according to one of claims 1 to 10, characterized in that the proportion of longitudinal threads (9, 10) of the carrier web (2) extending in the plane of the paper side (3) of the carrier web (2), in the projection perpendicular to Level of the carrier web (2, 22) a surface coverage between 40% to 90%, preferably 50% to 70%, more preferably 60% to 65% of the total area of the carrier web (2, 22) causes. Forming fabric according to one of claims 1 to 11, characterized in that the transverse threads (15, 45) on the carrier web (2, 22) are fixed selectively. Forming fabric according to one of claims 1 to 12, characterized in that the transverse threads (15, 45) and / or the threads (7 to 14, 26, 28, 29 to 32) of the carrier web (2, 22) have the property of laser energy and can be brought to melting temperature by absorbed laser energy at least at the surface and that the transverse threads (15, 45) are spot welded to the carrier web (2, 22), and / or that the transverse threads (15, 45) on the carrier web (15) 2, 22) are selectively secured using an adhesive. Forming fabric according to one of claims 1 to 13, characterized in that the forming fabric (1, 21) end edges, which are connected to each other via a seam (36, 37, 43). Forming fabric according to one of the claims 14, characterized in that at least one transverse thread (45) also extends over the seam (36, 37, 43).

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