EP2764157B1 - Papermaking fabric - Google Patents

Description

The present invention relates to a multi-ply papermaking fabric, e.g. a sheet forming screen of a paper machine, in particular a forming screen as used in the process of papermaking in the sheet forming zone of a wet end of a paper machine for dewatering / filtration of a pulp suspension or a paper pulp. Such screens are primarily used for high quality, low paper weight graphic papers and high printability requirements. These papers can be produced with so-called gap formers or Gap-Foruiern with speeds up to 2000 m / min. High demands are placed on the mechanical stability, the drainage performance, the fiber support, the freedom from marking and the running time of the sieve.

An essential process within papermaking is the formation of the sheet (= sheet formation) which takes place by dewatering a pulp suspension or a paper pulp by means of filtration in the sheet forming zone of the wet end of a paper machine using a so-called sheet forming screen.

Pulp suspension can be understood as meaning a mixture of wood or cellulose fibers, fillers and chemical auxiliaries suspended in water.

In order to be able to produce a sheet of paper that is as uniform as possible, it is necessary to increase or adjust the water content of the pulp suspension to approximately 99% immediately before sheet formation. This ensures that the fibers can distribute evenly in the water, which has an advantageous effect on the quality of the sheet to be formed.

Within the foliation zone, i. during the sheet forming process, the water content is reduced to about 80% by the above-mentioned filtration process. The paper fibers and the fillers and auxiliaries remain evenly distributed in the form of a non-woven fabric on the papermachine fabric.

While in the past drainage was mainly by a paper machine screen applied to a fourdrinier machine, today twin-wire machines are predominantly used, e.g. in the form of a so-called gap former (in English "Gap-Former"). These twin-wire machines are characterized in that the pulp suspension is injected into a gap formed between two paper machine wires, so that the dewatering can take place simultaneously through both wires, whereby the filtration process and thus also the production speed of the paper machine can be significantly accelerated. Today paper machines are available for paper grades with low basis weights that can produce at speeds of more than 2000 m / min.

The extreme demands placed on the paper to be produced and the conditions prevailing in the paper machine require specially designed sheet forming screens which at the same time have high fiber support, high openness and high mechanical stability. In addition, for the area of graphic papers, a slight tendency to marrow of the fabric is required, ie a high uniformity of the sheet forming screen.

In recent years, multi-layer paper machine screens have been proven for such applications, which have two differently shaped sides, which are adapted to the particular application. such Sieves have a paper side formed by the top of a top fabric. The paper page is commonly referred to as Sieboberseite and is responsible for the formation of the paper sheet. In addition, these sieves have a running side, which is formed by the underside of a lower fabric. The running side, which can also be referred to as the underside of the screen, comes into contact with the elements of the paper machine. The respective sieve side has a direction of the machine and a transverse direction, whereby the machine direction (in English MD for "machine direction") is understood to mean the running direction of the paper web and thus also the running direction of the paper machine screen, and the transverse direction (in English CMD for "cross machine direction "), sometimes also called cross-machine direction, which is in the plane of the papermachine fabric rotated by 90 °, ie, the direction transverse to the direction of the paper and the screen direction.

Due to the very special structure of modern paper machine screens, neither paper nor running side, nor machine and transverse direction can usually be exchanged, since otherwise the functioning of the screen is not guaranteed or not sufficiently ensured. For example, on the running side, the machine direction threads (= longitudinal threads), which realize the circulation of the screen, are protected against wear by clearly protruding or protruding transverse threads. On the paper side, for example, by providing a balanced ratio of longitudinal and transverse threads, a good storage option for the paper fibers can be ensured. With regard to the fiber support but also with regard to the tendency of the screen to mark, the simplest and at the same time oldest foundation bond of textile technology, the so-called plain weave, has proven itself for the upper fabric and thus for the paper side. In this bond, whose bond repeat (= smallest repeating unit of Binding) of exactly two warp threads (usually the warp threads form the longitudinal threads / machine direction threads of the wire) and two weft threads (usually the weft threads form the transverse threads of the wire), the threads become intimately intimate and uniform connected to a tissue. As suitable as the plain weave for the formation of a paper sheet and thus for the paper side, so little is it usually suitable for the running side .. If a paper machine screen equipped with a canvas paper side, so it may be advisable to a second, the Running side of the mesh forming fabric layer below the plain weave, which gives the screen sufficient stability and wear potential.

A particular challenge in this case is the connection of the two layers (i.e., the paper side forming Öbergewebes with the running side forming lower fabric), u.a. This is because the plain weave, which is favorable for the paper side, has extremely unfavorable requirements for such a layered connection.

In the prior art, different approaches for the connection of two fabric layers are described, of which one approach provides for the use of additional, separate binding threads, which extend in the longitudinal or transverse direction. According to this approach, two finished, fully formed fabric layers are connected to each other via separate, non-woven binding threads, which binding threads do not contribute to the construction of the respective fabric layer binding / are needed. The two fabric layers consist of longitudinal threads and transverse threads, which extend exclusively in the respective fabric layer and thereby completely generate the respective fabric layer pattern or the respective fabric layer weave. This procedure is described eg in CA 1 115 177 A1 where separate binding weft threads used, which bind with warp threads of the upper fabric and warp threads of the lower tissue, and DE 39 28 484 A1 , in which separate warp threads are used as connecting threads. Further examples are in DE 42 29 828 A1 . WO 93/00472 and EP 0 136 284 A2 to find. The separate binding threads are usually made thinner than the respective fabric layer forming threads (see, eg CA 1 115 177 A1 ), since the binding threads must be added to the fabric structure in addition to the fabric-forming threads, with little space for such separate binding threads, especially in a plain weave. Otherwise, the originally homogeneous structure of the binding would be disturbed by the binding threads, so that in particular in the provided on the paper side plain weave defects would be created that cause marks in the paper. In practice, however, it has been shown that the thin binding threads, especially in paper machines that process a high proportion of abrasive fillers or whose construction loads the screens strongly on bending in the machine direction, wear and break quite quickly, so that subsequently the two fabric layers first move and later separate. Of course, can not produce high quality paper with such a modified fabric / sieve.

An alternative to this is the use of tissue-own threads for connecting the layers. The threads used for the layer connection serve on the one hand to connect the layers, for which they switch back and forth between the layers, and on the other hand form the upper fabric or the lower fabric with. It can be used as connecting threads, different thread own threads, ie transverse and / or longitudinal threads of the upper and / or the lower fabric, the different binding threads bring different Siebeigenschaften with it.

Furthermore, it is known to use two transverse threads, which cooperate as a so-called. Functional transverse thread pair. One or both of the transverse threads of a functional pair run alternately in the upper and lower tissues. The two transverse threads of a functional pair can form a virtually uninterrupted transverse thread of a paper-side plain weave, ie an upper composite transverse thread. Those portions of the thread of the functional pair that are not currently required for the formation of the paper-side virtually uninterrupted transverse thread run inside the fabric and can be used to attach the lower fabric to the upper fabric. At the same time, the thread section tying the lower fabric can, for example, at the same time complete the lower fabric or its binding. For example, an upper transverse thread can be arranged between two functional transverse thread pairs, which exclusively completes the plain weave (ie which runs only in the upper fabric), but has no binding function. Exemplary embodiments of this approach can be found for example in EP 0 097 966 A2 . EP 794 283 A1 . WO 99/06630 A1 . WO 99/06632 A1 and WO 02/14601 A1 ,

Alternatively, the connection of the layers can be effected by so-called functional longitudinal thread pairs. For example, be on EP 0 069 101 and EP 093 096 referenced, which show a layer connection via functional longitudinal thread pairs.

A papermaker's fabric according to the preamble of claim 1 is known, for example DE 32 24 236 A1 ,

The object of the present invention is to provide a sheet forming screen of a multi-layered fabric which at least partially, esp. Completely meet the requirements described above, ie, for example, a high fiber support, a low Markierneigung, has a suitable mechanical stability and a stable layer connection.

To achieve this object, the invention provides a papermaking fabric according to claim 1. Further embodiments of the sieve according to the invention are described in the dependent claims.

The sieve according to the invention is formed by an upper transverse thread-bonded, in particular, weft-bound, multi-layered fabric, ie by a multi-layered fabric whose upper layer (preferably exclusively) is connected to the lower layer by means of upper transverse threads. The fabric used for the sieve thus belongs to the group of tissues whose layers are connected by means of tissue-own threads. The connecting upper transverse threads contribute on the one hand to the layer connection and on the other hand to the completion / formation of the upper fabric layer or its binding.

The wire according to the invention has on the paper side a high fineness to ensure proper fiber support. Due to the uniform design of the paper side, the tendency to mark is low. The running side can be a ggü. the paper side has increased openness for a good drainage behavior and a reduced tendency to clog the fabric with fibers and contaminants. The running side in particular has a high mechanical stability against elongation. The internal wear and ultimately a ply separation can be avoided or greatly reduced in the multilayer sheet forming screen whose fabric layers are interconnected by upper transverse threads.

According to the invention, therefore, a fine fabric with a very homogeneous design can be used for sheet formation and tied to a stable and coarser lower fabric. The upper fabric is made in a binding that is comparable to a plain weave and thus optimal for Production of graphic paper is suitable. In particular, the lower tissue is coarser in the longitudinal and transverse directions and thus offers the following advantages: solids which may have penetrated into the tissue through the upper tissue are not retained in the lower tissue; the drainage performance of the screen is determined solely by the paper side; the lower tissue is so open that its influence is subordinate to the total flow. The coarse lower fabric is used in particular to optimize the overall screen in terms of mechanical stability and wear resistance and fabric thickness.

According to the invention, the paper-side fabric is thus constructed relatively fine and homogeneous. The running side fabric layer can be made more robust and with higher openness, esp. With relatively thick warp and weft threads, which contribute to a higher mechanical strength. There is a stable connection of upper and lower tissue through a special design of the paper-side transverse threads with a binding zone. As a result, depending on the application, a convenient binding frequency can be set.

The papermaker's fabric according to the invention has an upper fabric layer which is formed of a plurality of upper longitudinal yarns extending exclusively in the upper fabric layer and a plurality of upper transverse yarns interwoven with the upper longitudinal yarn and either completely or predominantly in the upper fabric layer run. The interwoven upper transverse threads and upper longitudinal threads together form an upper binding, ie an overlapping pattern of the upper fabric layer. Characteristic of this upper binding is the upper weave repeat (see below), a pattern that repeats continuously on the paper side, reflecting the course of the upper transverse threads with respect to the upper longitudinal threads.

The papermaking fabric of the present invention further has a lower fabric layer formed of a plurality of lower longitudinal yarns extending exclusively in the lower fabric layer and a plurality of lower transverse yarns interwoven with the lower longitudinal yarns and extending exclusively in the lower fabric layer. The interwoven lower transverse threads and lower longitudinal threads together form a lower binding, i. an overlapping pattern of the lower fabric layer. Characteristic of this lower binding is the lower weave repeat, on the run side, constantly repeating pattern.

The lower longitudinal threads may have a larger diameter than the upper longitudinal threads, and the lower transverse threads may have a larger diameter than the upper transverse threads. The underside of the screen coming into contact with the paper machine can thus be made robust, whereas the upper side of the screen coming into contact with the fiber suspension can be formed finely. Since the lower longitudinal threads and the lower transverse threads do not change to the upper layer, the fine paper side is not disturbed by the robust lower threads. The comparatively thin upper transverse threads, which change to the lower layer, disturb the lower binding only slightly. Further, the comparatively thick lower transverse threads protrude lower than the upper transverse threads during their stay in the lower layer, whereby the upper transverse threads are shielded from the lower transverse threads.

The ratio of upper longitudinal threads to lower longitudinal threads in the entire fabric is eg greater than or equal to 1, eg greater than 1. For example, the ratio may be 3 to 2 or alternatively 1 to 1. Preferred is the ratio of 3 to 2, which is the formation of a fine top and a coarse bottom favored. In addition, with this ratio, the lower transverse threads) are made particularly thick, while still a sufficiently open bottom can be achieved.

The tissue may e.g. have a repeating overall repeat in which the ratio of upper longitudinal threads to lower longitudinal threads 9 to 6 or 9 to 9.

The ratio of upper transverse threads to lower transverse threads in the entire fabric may be e.g. greater than 1, e.g. 2 to 1. This also favors the formation of a fine top and a coarse bottom.

The tissue may e.g. have a repeating overall repeat in which the ratio of upper transverse threads to lower transverse threads is 6 to 3 or 12 to 6.

The tissue may e.g. have a repeating overall repeat in which the ratio of upper longitudinal threads to upper transverse threads is 9 to 12 or 9 to 9 or 9 to 6. This represents in each case a balanced ratio of upper longitudinal threads to upper transverse threads, with which a fine upper side can be formed.

The respective upper weave repeat has nine upper longitudinal threads and three upper transverse threads according to the invention. Each of the three upper transverse threads of each upper weave repeat has the following course: under one upper longitudinal thread, over the next upper longitudinal thread, under the next upper longitudinal thread, over the next upper longitudinal thread, under the four next, successive upper longitudinal thread and over the next upper one longitudinal thread. In this case, the course (or the starting point thereof) of the respective upper transverse thread relative to the course of the adjacent upper transverse thread in the transverse direction is arranged offset by three upper longitudinal threads.

The upper transverse threads repeat the course described in the transverse direction continuously and immediately successive, so that the respective upper transverse thread is interwoven with the upper longitudinal threads of the fabric in the manner of a plain weave, whereby regularly a so-called binding zone is formed, in which the upper transverse thread between the Fabric layer or in the lower fabric layer runs, depending on whether it is designed as a connecting upper transverse thread or not. The respective binding zone extends over a distance of four upper longitudinal threads, and between two adjacent binding zones of an upper transverse thread five upper longitudinal threads are arranged.

For connecting the layers, at least some of the upper transverse threads are formed as connecting transverse threads in the fabric. For this purpose, the upper transverse threads have a so-called binding zone, which is formed by the thread section which extends below the four upper longitudinal threads. To connect the upper fabric layer with the lower fabric layer some or all upper transverse threads can temporarily change during its course under the four successive upper longitudinal threads, ie in the binding zone, in the lower fabric layer and there at least undergo a lower longitudinal thread, thereby the lower longitudinal thread and thus attaching the lower tissue to the upper tissue.

In the respective overall repeat of the fabric (repeating weave pattern of the entire fabric, formed from upper longitudinal and transverse threads as well as lower longitudinal and transverse threads), at least one of the upper transverse threads should therefore be formed as connecting transverse thread. Such a connecting upper transverse thread binds along its course through the tissue in the transverse direction repeatedly (in each binding zone) one or more lower longitudinal threads to the upper Fabric layer, whereby the two layers are joined together.

For example, in the respective overall repeat of the fabric, each lower longitudinal thread can be connected to the upper fabric layer at least once, ie, for example, exactly once (see the second embodiment according to FIG FIG. 5 ) or exactly twice (see the second embodiment according to FIG. 6 ). Each connection can be made by a separate upper transverse thread. The fact that in the respective total repeat of the fabric by means of the upper transverse threads of each lower longitudinal thread is at least once connected to the upper fabric layer, a stable layer connection and thus a long life of the screen can be achieved.

But there may also be upper Bindungsrapporte whose upper transverse threads are all formed as non-connecting upper transverse threads. However, this reduces the number of layer connections in the respective overall repeat.

For many applications, it may be preferred that at least one of the three upper transverse threads of each upper weave repeat is formed as a connecting transverse thread. More preferably, at least two, in particular each of the three upper transverse threads of each upper weave repeat are formed as connecting transverse thread.

The number of layer connections in the respective overall repeat can be set appropriately as needed or in case of use.

The respective connecting upper transverse thread can be used to connect the upper fabric layer with the lower fabric layer during its course under the four successive Upper longitudinal threads undercut exactly one lower longitudinal thread or exactly two consecutive lower longitudinal threads.

The combination of upper fabric layer and lower fabric layer can be done exclusively with the above-described upper connecting transverse threads. That is, no separate binding threads are needed for the integrity of the fabric.

The upper fabric layer can therefore consist exclusively of a plurality of adjacent upper binding repeats. That is, in this case no further threads are arranged between the individual upper binding briefs. Also, the respective upper Bindüngsrapport consist solely of the nine upper longitudinal threads and the three upper transverse threads.

The lower transverse threads may be so verwöben with the lower longitudinal threads that they form a dreischäftige or sechschäftige binding in the lower fabric layer, in which the course of the respective lower transverse thread after three or six lower longitudinal threads constantly repeated. These are examples with which a coarse and open running side can be achieved. The respective lower transverse thread may, for example, initially run over a lower longitudinal thread and then under the two subsequent lower longitudinal threads, and the respective lower transverse thread may, for example, initially run over a lower longitudinal thread and then under the five subsequent lower longitudinal threads If the respective total repeat has nine lower longitudinal threads, then the lower fabric layer can be designed, for example, as three-layered or neo-strong.

Preferably, the longitudinal threads are formed as warp threads and the transverse threads as weft threads.

Further variations of the inventive sieve will become apparent from the following description of exemplary embodiments.

• Als Längsfäden werden Fäden des Siebes/Gewebes bezeichnet, die in Längsrichtung bzw. Längserstreckung des Siebs verlaufen und im Betrieb in Laufrichtung der Papiermaschine angeordnet sind. Beim flach gewebten Sieb sind die Längsfäden durch die Kettfäden des Webstuhls gebildet. Rundgewebe hingegen realisieren die Längsfäden mit den Schüssen.

Here are some terms used in this application:

• As longitudinal yarns threads of the screen / fabric are referred to, which extend in the longitudinal direction or longitudinal extent of the screen and are arranged in operation in the running direction of the paper machine. In the flat woven screen, the longitudinal threads are formed by the warp threads of the loom. Round fabrics, on the other hand, realize the longitudinal threads with the wefts.

As transverse threads, threads of the screen / fabric are referred to, which extend in the transverse direction of the screen and are arranged transversely to the running direction of the paper machine during operation. In the flat woven screen, the transverse threads are formed by the shots. Round fabrics, on the other hand, realize the transverse threads with the chains of the loom.

The fabric layer is understood to be a single-layer fabric consisting of interwoven transverse threads and longitudinal thread (or chains and wefts).

The upper fabric or the upper fabric layer is usually a particularly fine fabric layer from which usually the paper side (≈ outwardly facing, upper side of the upper fabric) of the screen is formed, on which the paper fiber layer is formed. The upper fabric is on the "logical top" of the screen.

The lower fabric or the lower fabric layer is an i.d.R. particularly robust trained fabric layer, from the i.d.R. the running side (= outwardly facing, lower side of the lower fabric) of the wire is formed, which comes into direct contact with the wear generating drive and dewatering elements of the paper machine.

Upper longitudinal threads are such threads that are exclusively in the upper fabric and are interwoven there with running in the upper fabric transverse threads. Upper longitudinal threads never leave the upper fabric, i. they do not change into the lower tissue.

Upper transverse threads are threads that are at least predominantly in the upper fabric and are interwoven there with the upper longitudinal threads. Upper transverse threads in the sense of this application can thus either run exclusively in the upper tissue or temporarily change into the lower tissue. At least a part of the upper transverse threads changes into the lower tissue in order to bind it to the upper tissue.

Lower longitudinal threads are those threads that are located exclusively in the lower fabric and are interwoven there with running in the lower fabric transverse threads. Lower longitudinal threads never leave the lower tissue, i. they do not change into the upper tissue.

Lower transverse threads are those threads that are exclusively in the lower fabric and are interwoven there with the lower longitudinal threads. Lower transverse threads never leave the lower tissue, i. they do not change into the upper tissue.

The weave repeat of the upper weave or the so-called upper weave repeat is a recurrent pattern or one of itself repeating unit in the upper fabric of interwoven upper longitudinal threads and upper transverse threads, in particular the smallest repeating unit in the upper fabric. In plan view of the upper fabric or the paper side of the screen a plurality of such upper binding repeats in the longitudinal and transverse direction of the screen can be seen and especially in the transverse direction (but preferably also in the longitudinal direction) strung together directly. The upper weave repeat therefore represents in particular the recurring overlapping pattern of the upper fabric formed in the plan view of the upper fabric by the upper longitudinal threads and upper transverse threads. If one of the upper transverse threads temporarily changes into the lower fabric, the exact course of the upper transverse thread in the lower fabric has the upper binding repeat no influence; because the upper transverse thread runs during this time always under the upper longitudinal threads. In other words, the upper weave repeat relates to the course of the upper transverse threads with respect to the upper longitudinal threads and the resulting overlapping pattern; The course of the upper transverse threads with respect to the lower longitudinal threads has no meaning for the determination of the upper binding repeat.

Analogously, a binding repeat of the lower tissue or a so-called lower binding repeat can be defined / specified.

The overall repeat of the fabric is a recurrent weave pattern / overlap pattern of the entire fabric, especially the smallest repeating unit of the entire fabric, taking into account the course of all the threads (upper and lower longitudinal threads, upper and lower transverse threads). With knowledge of the total repeat, therefore, the complete fabric or sieve can be produced. That is, the sieve or the tissue may consist of a plurality of immediately juxtaposed total repeats.

A longitudinal thread repeat is the smallest repetitive unit of longitudinal threads in the entire fabric.

Analogously, a transverse thread repeat means the smallest repeating unit of transverse threads in the entire fabric.

• Fig. 1 eine Draufsicht auf einen vollständigen oberen Bindungsrapport eines erfindungsgemäßen Siebs in schematischer Darstellung,
• Fig. 2 ein Foto, welches in vergrößerter Ansicht einen Ausschnitt der Papierseite eines erfindungsgemäßen Siebs zeigt, welche aus einer Vielzahl von aneinander angrenzenden oberen Bindungsrapporten besteht, d.h. eine Draufsicht auf die Oberseite eines erfindungsgemäßen Siebs bzw. dessen obere/papierseitige Gewebelage, wobei die untere/laufseitige Gewebelage aus Gründen der Übersichtlichkeit weggelassen/weggeschnitten wurde,
• Fig. 3 das Foto aus Figur 2, wobei ein einzelner oberer Bindungsrapport (durchgezogene Linien) sowie die acht diesen umgebenden oberen Bindungsrapporte (gestrichelte Linien) hervorgehoben sind,
• Fig. 4 verschiedene alternative Verläufe für die drei oberen Querfäden des oberen Bindungsrapports aus Fig. 1 innerhalb des gesamten Gewebes, d.h. bzgl. der oberen und unteren Gewebelage/Längsfäden,
• Fig. 5 den Gesamtrapports eines Siebs gemäß einer ersten Ausführungsform der Erfindung in schematischer Darstellung und
• Fig. 6 den Gesamtrapport eines Siebs gemäß einer zweiten Ausführungsform der Erfindung in schematischer Darstellung.

In the following the invention will be explained in more detail with reference to various embodiments with reference to the drawing. In the drawing show:

• Fig. 1 a top view of a complete upper binding repeat of a sieve according to the invention in a schematic representation,
• Fig. 2 a photo which shows in enlarged view a section of the paper side of a sieve according to the invention, which consists of a plurality of adjacent upper Bindungsrapporten, ie a plan view of the top of a sieve according to the invention or its upper / paper-side fabric layer, the lower / running side fabric layer has been omitted / cut away for reasons of clarity,
• Fig. 3 the photo off FIG. 2 in which a single upper bond repeat (solid lines) and the eight upper binding replicas surrounding it (dashed lines) are highlighted,
• Fig. 4 various alternative courses for the three upper transverse threads of the upper binding repeat Fig. 1 within the entire fabric, ie with respect to the upper and lower fabric layers / longitudinal threads,
• Fig. 5 the overall repeat of a sieve according to a first embodiment of the invention in a schematic representation and
• Fig. 6 the overall repeat of a sieve according to a second embodiment of the invention in a schematic representation.

Fig. 1 shows a complete upper binding repeat of a sieve according to the invention in a schematic representation with a view from above. This upper binding repeat is repeated on the sieve top side, ie the sieve top has a plurality of such identically formed upper binding repeats.

As the Figures 2 and 3 For example, the paper side of a screen according to the invention can consist of a plurality of such upper binding reports, which are arranged directly adjacent to one another. Ie, to the in Fig. 1 The upper binding repeat shown on the paper side of the sieve then eight immediately adjacent identically formed upper binding repeats are arranged (at the four corners and above, below, right and left).

In the FIGS. 1 to 3 the longitudinal threads run vertically and the transverse threads horizontally.

The upper binding repeat consists of 9 longitudinal threads (1, 2, 3, .., 9) and 3 transverse threads (21, 22, 23). In FIG. 3 the longitudinal threads and transverse threads of an adjacent repeat are provided with one or two "'".

In FIG. 1 represents - as usual in textile technology - each square is an intersection of a longitudinal thread (eg warp thread) and a transverse thread (eg weft thread). If the square is provided with a cross, the longitudinal thread runs over the transverse thread or the transverse thread under the longitudinal thread, otherwise the longitudinal thread runs under the transverse thread. In FIG. 3 the circle indicates that the longitudinal thread runs under the transverse thread or the transverse thread over the longitudinal thread.

As in FIG. 1 is shown, the courses of the three upper transverse threads 21-23 respect. The nine upper longitudinal threads 1-9 are basically the same in the upper binding repeat. In particular, each upper transverse thread 21-23 passes first under an upper longitudinal thread, then over the next upper longitudinal thread, then under the next upper longitudinal thread, then over the next upper longitudinal thread, then below four consecutive upper longitudinal threads and finally over the next upper longitudinal thread.

For example, the upper transverse thread 21 runs in Fig. 1 first under the upper longitudinal thread 1, then over the upper longitudinal thread 2, then under the upper longitudinal thread 3, then over the upper longitudinal thread 4, then below the four successive upper longitudinal threads 5 to 8 and finally over the upper longitudinal thread 9. Subsequently, the transverse thread repeats 21 this course. That is, in the in FIG. 1 not shown upper binding repeat immediately to the right of the upper binding repeat shown repeats the upper transverse thread 21 the described course, etc .; see especially the FIG. 3 ,

The upper transverse thread 22 has the same course, but its course or the starting point thereof is shifted relative to that of the upper transverse thread 21 by three upper longitudinal threads to the right. Thus begins the course described above (once under, once over, once under, once over, 4 times under, once over) for the upper transverse thread 22 at the upper longitudinal thread 4, ie, the upper transverse thread 22 initially passes under the upper longitudinal thread 4, then over the upper longitudinal thread 5, then under the upper longitudinal thread 6, then over the upper longitudinal thread 7, then below the four consecutive upper longitudinal threads 8, 9, 1, 2 and finally, above the upper longitudinal thread 3. It is noted that in textile technology for determining the course of the thread in a repeat "over edge / corner" is counted. This is justified insofar as another repeat immediately adjoins the repeat W shown transverse direction.

The upper transverse thread 23 has the course described above (once below, once over it, once under it, once over it, 4 times under, once over it), but its course relative to the adjacent upper transverse thread 22 is shifted by three upper longitudinal threads to the right. Thus, the course described above for the upper transverse thread 23 begins at the upper longitudinal thread 7, ie, the upper transverse thread 23 extends first under the upper longitudinal thread 7, then over the upper longitudinal thread 8, then below the upper longitudinal thread 9, then over the upper longitudinal thread 1, then below the four successive upper longitudinal threads 2 to 5 and finally over the upper longitudinal thread. 6

In summary, in the upper binding repeat the course of the respective upper Qüerfadens relative to the course of the adjacent upper transverse thread in the transverse direction offset by three upper longitudinal threads, which in textile technology usually as. Slope is called. That is, according to the invention, the pitch of the upper transverse threads is three in the upper binding repeat and on the paper side, respectively.

As already explained, the paper side of the screen according to the invention is made up of a multiplicity of upper binding reports according to FIG Fig. 1 educated. This clarifies FIG. 2 and particularly FIG. 3 in which one of the upper binding repeats is identified by a rectangle of solid lines. The eight upper bond repeats immediately adjacent to this upper bond repeat are shown with dashed rectangles, with six of the eight adjacent upper binding repeats in Fig. 2 or 3 are shown only partially. Other than the "X" in Fig. 1 , gives the "o" in FIG. 3 assume that the upper cross thread overflows the upper longitudinal thread (or that the upper longitudinal thread runs under the upper cross thread).

As also in the Figures 2 and 3 can be clearly seen, the upper longitudinal threads are next to each other substantially parallel to each other and spaced from each other. The upper transverse threads are also arranged side by side substantially parallel to each other, so do not form functional pairs. The upper transverse threads can in principle likewise be arranged at a distance from one another, but in sections they touch each other.

According to the invention, at least some of the upper transverse threads are formed as connecting transverse threads in the fabric. Connecting transverse threads serve to connect the upper fabric layer to the lower fabric layer. According to the invention, this connection takes place during the course of an upper transverse thread below the four successive upper longitudinal threads. The upper transverse thread changes temporarily into the lower fabric layer in order to undermine there one or more lower longitudinal threads and thereby bind to the upper fabric.

In other words, the sieve according to the invention is a so-called. Wound-bonded or cross-thread-bonded multilayer fabric, in particular a pure weft-bound or cross-thread-bonded multilayer fabric, i. a fabric without further connecting threads.

FIG. 4 shows alternative embodiments or courses of the upper transverse threads 21 to 23 from FIG. 1 within the entire fabric - ie with respect to upper and lower fabric layers. Shown is the course of an upper one Transverse thread over a distance of nine upper longitudinal threads; the respective course is repeated in the fabric in the transverse direction constantly and directly, ie, the transverse thread 21 is formed for example of a plurality of immediately successive thread sections, each of the course 21a or alternatively each of the course 21b or alternatively the course 21c or alternatively respectively the course 21d correspond.

The courses of the threads 21a to 21d with respect to the upper fabric or with respect to the upper longitudinal threads are identical and correspond to the above-described course of the thread 21 (including the starting point). Analogously, the course of the threads 22a to 22d with respect to the upper fabric corresponds to the course of the thread 22, etc.

With the index "a" marked threads are formed as pure upper transverse threads, which extend exclusively in the upper fabric and do not contribute to a layer connection.

The threads marked with the index "b", "c" or "d", however, are formed as connecting transverse threads, which contribute to a connection of the layers.

The threads with the index "b" and "c" bind within a so-called binding zone, which is formed by the cross-thread section running under the four successive upper longitudinal threads, exactly one lower longitudinal thread on the upper fabric layer or undercut this. The threads with the index "b" bind in the transverse direction - viewed from left to right - with the respective first lower longitudinal thread 13, 15 and 11. That is, these threads change in the binding zone immediately down into the lower fabric layer to the connect the first possible lower longitudinal thread to the upper fabric. The threads with the index "c" on the other hand, they bind in the transverse direction - viewed from left to right - with the respective second lower longitudinal thread 14, 10 or 12, ie, these threads overflow the first possible lower longitudinal thread and only bind the subsequent lower longitudinal thread to the upper fabric.

The threads with the index "d" bind within the binding zone exactly two lower longitudinal threads on the upper fabric layer or undercut them.

For a respective upper binding repeat or for three longitudinally adjacent upper transverse threads, the in FIG. 4 shown upper transverse thread courses are arbitrarily combined with each other as long as from each group exactly one thread is selected, ie it can be any thread from the first group (21a-21d) with any thread of the second group (22a-22d) and any thread of third group (23a-23d) are combined. For example, one or more of the top binding repeats may look like FIG. 3 or three longitudinally adjacent upper transverse threads FIG. 3 be formed from the threads 21c, 22c, 23c, or from the threads 21b, 22b, 23b, or from the threads 21a, 22a, 23a (so it is also possible that one or more upper binding repeats, but not all, exclusively from non-connecting upper transverse threads are formed), or from the threads 21a, 22b, 23c.

As already mentioned, according to the invention, at least some of the upper transverse threads are formed as connecting transverse threads in the fabric. Thus, at least some of the upper binding repeats, e.g. all upper binding repeats, one or more connecting upper transverse threads "b", "c" or "d".

In the respective overall repeat, the respective upper binding repeat can thus be put together arbitrarily, as long as from each group "21", "22", "23" exactly one thread is selected, whereby the upper binding repeats can be put together differently (see eg the Figures 5 and 6 ), and wherein at least one of the upper binding repeats has at least one connecting upper transverse thread, so that in the tissue a plurality of connecting threads or in the Gesamtrapport the fabric at least one connecting thread is present.

Against this background, two exemplary embodiments of the invention will now be described.

The following is with reference to FIG. 5 the overall repeat (ie a complete weave repeat of the fabric) of a fabric according to a first embodiment of the invention is described. A sieve according to the invention can thus be produced by juxtaposing a plurality of such total repeats or consisting of a plurality of such total repeats.

The in FIG. 5 The overall repeat shown has nine upper longitudinal threads 1-9 and six lower longitudinal threads 10-15, which are here each formed as warp threads and run exclusively in the upper or the lower fabric layer. The upper warp threads 1-9 are thinner than the lower warp threads 10-15. The warp or longitudinal thread ratio of paper side / upper fabric to running side / lower fabric in the total repeat and in the fabric is therefore 9 to 6 and 3 to 2, respectively.

Furthermore, the in. FIG. 5 shown overall repeat twelve upper transverse threads 21-23 and six lower transverse threads 31-36. The transverse threads are each formed here as weft threads. The lower transverse threads 31-36 run exclusively in the lower fabric layer. The upper transverse threads change between the two layers of fabric, so they are all as connecting transverse threads formed, however, extend predominantly in the upper fabric layer and form there together with the upper longitudinal threads of the upper fabric and its binding. The upper weft threads are thinner than the lower weft threads 31-36. The weft or transverse thread ratio of paper side / upper fabric to running side / lower fabric in the total repeat and in the fabric is accordingly 12 to 6 and 2 to 1, respectively.

In the overall repeat, each upper transverse thread 21-23 has the same relation to the upper longitudinal threads 1-9 FIG. 1 described course of once under, once over it, once under it, once over it, 4 times under it, once over it. The transverse thread pitch in the overall repeat is three. The respective transverse thread course is repeated in the tissue in the transverse direction constantly. In the fabric, therefore, each upper transverse thread together with the upper longitudinal thread on the paper side forms a plain weave (once under, over, etc.) which is repeatedly interrupted along each upper transverse thread along a distance of four upper longitudinal threads to form a binding zone is.

In the overall repeat, the twelve upper transverse threads together with the nine upper longitudinal threads form four upper binding repeats ac, df, gi, jl. The three upper transverse threads 21, 22, 23 of the upper weave repeat ac and the three upper transverse threads, 21, 22, 23 of FIG upper binding repeats gi are in each case formed as "b" threads, which undercut the first of two lower longitudinal threads in their binding zone and thereby bind to the upper fabric. The three upper transverse threads 21, 22, 23 of the upper binding repeat df and the three upper transverse threads 21, 22, 23 of the upper binding repeat jk are each formed as "c" threads, which undercut in their binding zone the second of two lower longitudinal thread and thereby bind to the upper fabric.

The course of the transverse threads in the fabric section a-f is identical to the course of the transverse threads in the fabric section g-l. The twelve upper transverse threads thus form, together with the new upper longitudinal threads, two upper Querfadenrapporte a-f, g-l.

According to the first embodiment, the six lower transverse threads 31-36 together with the six lower longitudinal threads 10 to 15 form a relatively open and coarse lower fabric or a relatively open and rough running side. The six lower transverse threads 31-36 and the six lower longitudinal threads 10 to 15 form in the total repeat exactly one lower weave repeat. In the lower binding repeat, each lower transverse thread undergoes five consecutive lower longitudinal threads and then overflows a lower longitudinal thread; see, e.g. the lower longitudinal thread 36. Each lower transverse thread overflows another lower longitudinal thread. The: lower fabric is here in the transverse direction so 6-schäftig trained, i. the course of the respective lower transverse thread is repeated after six longitudinal threads.

In the in FIG. 5 In the embodiment shown, the lower fabric is tethered to the upper fabric twelve times within a total repeat, once by each upper transverse thread. Each lower longitudinal thread is tied twice, namely by two different upper transverse threads. Since the upper transverse threads are made thinner than the lower transverse threads, the lower binding (or the overlapping pattern formed by the lower transverse and longitudinal threads) is not significantly disturbed by the upper transverse threads temporarily submerged in the lower fabric. In addition, the lower transverse threads shield the upper transverse threads. It can be so at the same time form a stable layer connection and a fine, homogeneous paper side.

The following is with reference to FIG. 6 the overall repeat of a sieve according to a second embodiment of the invention described. A sieve according to the invention may consist of a plurality of such total repeats.

The in FIG. 6 shown overall repeat has nine upper longitudinal threads 1-9 and six lower longitudinal threads 10-15, which are each formed as warp threads and extend exclusively in the upper and the lower fabric layer. The upper longitudinal threads 1-9 are thinner than the lower longitudinal threads 10-15. The warp or longitudinal thread ratio of upper fabric to lower fabric in the total repeat and in the fabric is thus again 9 to 6 or 3 to 2.

Furthermore, the in FIG. 6 shown Gesamtrapport six upper transverse threads 21-23 and three lower transverse threads 41-43. The transverse threads are again formed as weft threads. The lower transverse threads 41-43 run exclusively in the lower fabric layer. The upper transverse threads each change between the two layers of fabric, so they are all formed as connecting transverse threads, but each extending predominantly in the upper fabric layer. The upper transverse threads are thinner than the lower transverse threads 41-43. The weft or transverse thread ratio from paper side to lower fabric in the overall repeat and in the fabric is 6 to 3 and 2 to 1, respectively.

Each upper transverse thread 21-23 has respect to the upper longitudinal threads 1-9 with respect to FIG. 1 described course of once under, once over it, once under it, once over it, 4 times under it, once over it. The transverse thread pitch in the overall repeat or in the tissue is again three.

The six upper transverse threads together with the nine upper longitudinal threads in the overall repeat form two upper binding repeats a-c, d-f. The three upper transverse threads 21, 22, 23 of the upper weave repeat a-c are each formed as "b" yarns, and the three upper transverse yarns 21, 22, 23 of the upper weave repeat d-f are each formed as "c" yarns.

According to the second embodiment, the three lower transverse threads 41-43 together with the six lower longitudinal threads 10 to 15 form a relatively open and coarse lower fabric. The three lower transverse threads 41-43 and the six lower longitudinal threads 10 to 15 form exactly one lower weave repeat in the overall repeat. In the lower weave repeat, each lower transverse thread first undergoes two successive lower longitudinal threads., Then overflows a lower longitudinal thread, again undergoing two successive lower longitudinal threads, and then overflows a lower longitudinal thread; see, e.g. The lower longitudinal thread 42. Each lower transverse thread overflows two other lower longitudinal threads, so that each lower longitudinal thread is overrun in the lower binding repeat of a lower transverse thread. The lower fabric is transversely 3-formed here, i. the course of the respective lower transverse thread is repeated after three longitudinal threads.

In the in FIG. 6 In the embodiment shown, the lower fabric is tied six times to the upper fabric within the overall repeat, once by each upper transverse thread. Each lower longitudinal thread is connected once in the overall repeat. Also with the overall repeat after FIG. 6 At the same time a stable layer connection and a fine, homogeneous paper side can be achieved.

• eine hohe Feinheit der Papierseite zur Gewährleistung einer zweckmäßigen bzw. hohen Faserunterstützung;
• eine hohe Gleichmäßigkeit der Papierseite zur Reduzierung der Markierneigung des Siebs;
• eine Laufseite mit einer hohen Offenheit zur Erzielung eines zweckmäßigen bzw. guten Entwässerungsverhaltens und einer reduzierten Neigung des Gewebes zur Verstopfung mit Fasern und Verunreinigungen;
• eine Laufseite mit einer hohen mechanischen Stabilität, z.B. gegen Dehnung;
• eine Vermeidung bzw. Reduzierung von innerem Verschleiß, wodurch eine Trennung der Lagen vermieden/hinausgezögert werden kann, so dass die Lebenszeit des Siebs hoch ist.

With the sieve according to the invention, for example a sieve with a total repeat after FIG. 5 or FIG. 6 , numerous beneficial properties are achieved or at least made possible, inter alia, the following properties:

• a high degree of fineness of the paper side to ensure appropriate or high fiber support;
• a high uniformity of the paper side to reduce the tendency of the screen to sag;
• a high openness side for good drainage and a reduced tendency of the fabric to become clogged with fibers and contaminants;
• a running side with a high mechanical stability, eg against elongation;
• avoidance or reduction of internal wear, whereby a separation of the layers can be avoided / delayed, so that the lifetime of the screen is high.

In other words, a fine upper fabric having a homogeneous design can be used for sheet formation and tied to a more stable and coarser lower fabric. The upper fabric is designed in a binding that is comparable in terms of their sheet-forming properties with a plain weave and thus optimally suited for the production of graphic paper. The lower fabric may be coarser in the longitudinal and transverse directions than the upper fabric and thus offer the following advantages: any solids which have penetrated through the upper fabric into the fabric / sieve are not / hardly retained in the lower fabric; the drainage performance of the sieve is exclusively determined by the Paper side or the upper fabric determines, ie, the lower fabric is formed open so that its influence is subordinate to the total flow. According to the invention, the coarse lower fabric can therefore be used to optimize the screen in terms of mechanical stability, wear resistance and fabric thickness.

Thus, a very fine and homogeneous paper-side fabric layer is achieved (esp. In comparison to the running side), whereas the running side fabric layer can be performed with higher openness and relatively thick longitudinal and transverse threads, which can contribute to a high mechanical strength. At the same time, a particularly stable connection of upper fabric layer and lower fabric layer is made possible; generally by a weft or transverse thread-bound formation of the screen and in particular by a special design of the paper side / upper transverse threads with a binding zone. The upper transverse threads each have a course that corresponds in sections to a plain weave, wherein binder zones are created in which the respective upper transverse thread runs under four successive upper longitudinal threads. These bonding zones can be used to tie the lower fabric layer to the upper fabric layer. As a result, a high binding frequency and thus a high stability of the sieve can be achieved. For example, can be achieved with the inventive sieve - compared to known sieves - an increase in the binding frequency by up to 33%, using the same number of threads and the same arithmetic fiber support index (FSI Beran).

Claims (11)

1. Paper machine screen, in particular sheet forming screen, formed as a multi-layer fabric, in particular a two-layer fabric,

   having an upper fabric layer and a lower fabric layer, wherein the upper fabric layer comprises a plurality of upper longitudinal threads (1-9) extending exclusively in the upper fabric layer, and a plurality of upper transverse threads (21-23) being interwoven with the upper longitudinal threads and respectively extending at least mainly in the upper fabric layer,

   wherein the lower fabric layer comprises a plurality of lower longitudinal threads (10-15) extending exclusively in the lower fabric layer, and a plurality of lower transverse threads (31-36) being interwoven with the lower longitudinal threads and extending exclusively in the lower fabric layer,

   characterized in that,

   the upper fabric layer has, on its upper side, a repeating upper weave repeat formed by nine upper longitudinal threads (1-9) and three upper transverse threads (21-23),

   the three upper transverse threads (21-23) of the upper weave repeat respectively have the following course in the upper weave repeat: under one upper longitudinal thread, over the next upper longitudinal thread, under the next upper longitudinal thread, over the next upper longitudinal thread, under the four next upper longitudinal threads arranged next to each other and over the subsequent upper longitudinal thread,

   in the upper weave repeat, the course of the respective upper transverse thread (21-23) is arranged offset in transverse direction by three upper longitudinal threads (1-9) to the course of the adjacently arranged upper transverse thread, and

   in the fabric, at least some of the upper transverse threads (21-23) are formed as binding transverse threads that, during their course under the four upper longitudinal threads arranged next to each other, temporarily change into the lower fabric layer where they extend under at least one lower longitudinal thread, for binding the upper fabric layer to the lower fabric layer.
2. Paper machine screen according to claim 1, wherein the lower longitudinal threads (10-15) have a greater diameter than the upper longitudinal threads (1-9) and/or

   wherein the lower transverse threads (31-36) have a greater diameter than the upper transverse threads (21-23).
3. Paper machine screen according to claim 1 or 2, wherein the ratio of upper longitudinal threads (1-9) to lower longitudinal threads in the entire fabric is 3 to 2 or 1 to 1 and/or

   wherein the fabric comprises or consists of a repeating total repeat in which the ratio of upper longitudinal threads (1-9) to lower longitudinal threads (10-15) is 9 to 6 or is 9 to 9.
4. Paper machine screen according to one of the preceding claims, wherein the ratio of upper transverse threads (21-23) to lower transverse threads (31-36) in the entire fabric is 2 to 1 and/or

   wherein the fabric comprises or consists of a repeating total repeat in which the ratio of upper transverse threads (21-23) to lower transverse threads (31-36) is 6 to 3 or is 12 to 6.
5. Paper machine screen according to one of the preceding claims, wherein at least one of the three upper transverse threads (21-23) of each upper weave repeat is formed as a binding transverse thread that, during its course under the four upper longitudinal threads arranged next to each other, temporarily changes into the lower fabric layer where it extends under at least one lower longitudinal thread, for binding the upper fabric layer to the lower fabric layer.
6. Paper machine screen according to claim 5, wherein at least two, in particular each of the three upper transverse threads (21-23) of each upper weave repeat is formed as a binding transverse thread.
7. Paper machine screen according to one of the preceding claims, wherein the respective binding upper transverse thread (21-23) for connecting the upper fabric layer to the lower fabric layer extends under exactly one lower longitudinal thread (1-9) or exactly two lower longitudinal threads (1-9) arranged next to each other, during its course under the four upper longitudinal threads arranged next to each other.
8. Paper machine screen according to one of the preceding claims, wherein the connection between the upper fabric layer and the lower fabric layer is exclusively performed by the upper binding transverse threads (21-23).
9. Paper machine screen according to one of the preceding claims, wherein the upper fabric layer exclusively consists of a plurality of upper weave repeats adjacent to each other and/or

   wherein the respective upper weave repeat exclusively consists of the nine upper longitudinal threads (1-9) and the three upper transverse threads (21-23).
10. Paper machine screen according to one of the preceding claims, wherein the lower transverse threads (31-36) are interwoven with the lower longitudinal threads (10-15) in such a way that they form, in the lower fabric layer, a three-shaft-weave or a six-shaft-weave, in which the course of the respective lower transverse thread is repeated after three or six longitudinal threads respectively,

    wherein the respective lower transverse thread (31-36) with the three-shaft-weave in particular first extends over a lower longitudinal thread and then extends under the following two lower transverse threads, and wherein the respective lower transverse thread (31-36) with the six-shaft-weave in particular first extends over a lower longitudinal thread and then extends under the following five lower longitudinal threads.
11. Paper machine screen according to one of the preceding claims, wherein the longitudinal threads (1-9, 10-15) are formed as warp threads and the transverse threads (21-23, 31-36) are formed as weft threads.

Images