EP0656967A1

EP0656967A1 - Forming web.

Info

Publication number: EP0656967A1
Application number: EP93919118A
Authority: EP
Inventors: Daniel Zimmermann; Liam Maher
Original assignee: Siebtuchfabrik AG
Current assignee: Siebtuchfabrik AG
Priority date: 1992-08-25
Filing date: 1993-08-20
Publication date: 1995-06-14
Anticipated expiration: 2013-08-20
Also published as: FI97156B; CA2142283A1; FI950813A0; NO950703D0; US5613527A; ATE144804T1; DK0656967T3; FI950813A; FI97156C; ES2094563T3; DE9211391U1; DE59304370D1; EP0656967B1; WO1994004748A1; CA2142283C; NO950703L; BR9306955A; NO305091B1

Abstract

PCT No. PCT/EP93/02234 Sec. 371 Date Feb. 10, 1995 Sec. 102(e) Date Feb. 10, 1995 PCT Filed Aug. 20, 1993 PCT Pub. No. WO94/04748 PCT Pub. Date Mar. 3, 1994A paper machine forming screen has a paper side and a machine side. A plurality of synthetic longitudinally extending machine direction threads are provided. A plurality of synthetic cross threads extend generally transverse to the machine direction threads, and the cross threads are disposed in first and second groups and at least of the cross threads have a flattened cross section. The first group threads are disposed in a plane of the paper side and have a repeat floating over a number of the machine direction threads. The second group threads form a plane on the machine side. The flattened cross threads extend parallel to the paper side plane, a distance from about 1.2 to about 2.2 times the distance by which the flattened cross threads extend transverse to the paper side plane.

Description

description

Forming fabric

The invention relates to a forming fabric for the sheet formation section of a paper machine, consisting of a more than single-layer, in particular flat-woven, fabric made of plastic threads with longitudinal threads extending in the machine direction and transverse threads extending transversely thereto, a first group of transverse threads lying in the plane of the paper side and there Floated over longitudinal threads, the number of which is at least as large as the number of transverse threads over which the longitudinal threads float on the paper side, and the plane d machine side being formed exclusively by a second group of transverse threads.

A conventional paper machine essentially consists of three consecutive lots. In the individual batches, the paper web is dewatered or dried in different ways. The paper web is supported and guided by so-called paper machine clothing.

In the first section, the so-called sheet formation section, a forming screen is used for this. The liquid to pulpy fibrous material is applied to this. By

The effect of gravity, supported by suction boxes generating negative pressure, the fiber material is dewatered to such an extent that at the end of the forming wire there is a coherent, if still very sensitive, paper web with a high liquid content. This is then removed from the forming wire and led to the second section, the so-called press section . There the paper web is rolled between the rollers for the purpose of drainage exposed to high pressure. It is supported by press felts, which generally consist of a base fabric and a non-woven fabric needled on it at least on the paper side. In the third section, the drying section, the paper web is essentially thermally dewatered by being passed over heated drying cylinders almost without pressure. It is supported by so-called dryer fabrics, which dryer fabrics can be designed as a fabric or as wire link belts.

Due to the different types of dewatering in the individual batches of the paper machine, different requirements are imposed on the paper machine clothing used - forming fabric, press felt and drying fabric - therefore, their structure is fundamentally very different. This applies in particular to their water permeability, fabric thickness, durability etc. In principle, paper machine clothing used in one lot can never be used in another lot

In this respect, special requirements are placed on forming fabrics. This is based on the fact that foraging screens serve primarily to form a paper web z from a liquid mass, so that there is not already a coherent paper web - as in the press and dryer sections. When designing a forming fabric, the behavior of the individual fibers in relation to the forming fabric must therefore be taken into account, a requirement that naturally does not arise in the press and dryer section because of the paper web already formed there. The demands are often conflicting, meaning that they can only be met by compromise. For example, a forming fabric must have a good separating effect, that is to say hold the paper fibers on the paper-side surface of the forming fabric on the one hand and effect good drainage on the other. The property called fiber retention, the fibers on the Holding the forming fabric must also be combined with the ability to prevent parts of the fibers from being drawn into the forming fabric and thereby creating a sheat-sealing. The latter not only results in a reduction in dewatering performance, but also makes sheet removal at the end of the forming wire more difficult due to the interlocking with it.

Another very important requirement, especially with forming fabrics, is to achieve the longest possible service life. In contrast to the paper machine clothing used in the press and dryer section, a forming fabric is not only guided over deflection rollers, but also over fixed machine parts with the result that great frictional forces act there. Particularly when it comes to suction boxes, in which a vacuum is generated to support gravity drainage, the forming fabric is in contact with machine parts with considerable contact pressure and rubs over them. This is taken into account by using particularly resistant plastic materials on the machine side and by decoupling the paper-side and machine-side structure. Special transverse threads are then provided as abrasion material on the machine side, which then only form the plane of the machine side. These transverse threads protect the longitudinal threads, which are highly stressed by the longitudinal tension in the forming wire, from abrasion and thus an impairment of their strength.

A generic paper machine sieve is disclosed, for example, in EP-A-0 390 005. It has long floating cross threads on the machine side that only form the plane of the machine side and thus protect the longitudinal threads from abrasion. On the paper side, longitudinal and transverse threads are bound in such a way that a monoplane surface is created if possible. Both the longitudinal and the transverse threads have a circular cross section in a conventional manner. This has one Series of disadvantages.

The support of the individual fibers is not satisfactory on the paper side. The conical gaps in the opening due to the round cross-sections have the consequence that some of the fibers are drawn into the inside of the sieve, whereby at least one toothing between tissue and fibers which is harmful for the paper removal is produced. This also results in a high surface roughness of the paper and poor printability. Another disadvantage is that dynamic pressure fluctuations, which occur in the water being carried when driving over machine parts of the wet end, easily penetrate to the paper web and lead to markings there.

On the machine side, a sufficient abrasion volume can only be made available by using relatively thick transverse threads. However, their flexibility is limited, which is why the longitudinal threads are pressed down close to the plane of the machine side when they are integrated with these transverse threads and are therefore subject to wear relatively quickly. It is even more serious that the sieving properties change considerably and at different speeds when the transverse threads forming the machine side wear out. Due to the long floatation and the rigidity of these transverse threads, there is an arcuate course between the bindings, with the result that the contact surface changes constantly and unevenly in both the longitudinal and transverse directions of the thread during abrasion.

Proposals have been known for a long time to use flattened longitudinal threads in forming fabrics. These proposals initially only related to single-layer forming fabric and here primarily to metal screens (cf. US-A-2 003 123; US-A-3 139 119; US-A-3 143 150; US-A-3 545 705 ; US-A-3,632,068). After the advent of synthetic threads Existing forming fabrics, the use of flattened longitudinal threads has also become known for these fabrics (US-A-4 143 557). Recently, proposals have also been made to provide flattened longitudinal threads in multi-layer, in particular two and three-layer forming fabrics (GB-A-2 157 328; US-A-4 815 499). According to the information in these writings, a number of advantages were expected.

Insofar as they relate to metal sieves, however, they cannot easily be transferred to plastic sieves, since the behavior of metal wires in a woven fabric structure differs greatly from that of the plastic threads. The same applies to the difference between single and multi-layer fabrics. More generally, it can be said that the use of flattened longitudinal threads has little or no influence on the essential properties of a forming fabric. Since the longitudinal threads are stretched even with multi-layer forming fabrics due to the thermosetting that is basically carried out on plastic screens and then have only a slight amount of cranking and mainly run inside the screen, the greater flexibility of the flattened longitudinal threads is due to their low height - this is only achieved anyway , if the cross-sectional area remains the same or less than round threads - hardly advantageous.

The invention has for its object to develop a forming fabric of the generic type so that significantly improved conditions with regard to the web formation and with regard to the abrasion properties are created.

According to the invention, this object is achieved by a forming fabric with the following features:

(a) at least some of the transverse threads have a flattened cross-section; (b) the flattened transverse threads are arranged in such a way that their cross-sectional extent in the tissue plane is greater than transverse to the tissue plane;

(c) the ratio between cross-sectional extent in the tissue plane to cross-sectional extent transverse to the tissue plane is between 1.2 and 2.5, preferably 1.2 and 1.8;

This combination of features is based on the knowledge that the use of flattened transverse threads means that the properties of a forming fabric can be influenced much more and considerably more versatile. This is based on the consideration that is already part of the invention that the transverse threads, particularly after heat setting, have significantly more pronounced crankings than the longitudinal threads. Provided the cross-sectional areas are the same, the flattened transverse threads are considerably more supple and therefore adapt better to the course of the longitudinal threads in the cranks. As a result, the thickness of a forming fabric can be optimized in wide areas with a view to the sometimes contradicting demands for good drainage performance, the provision of large abrasion volumes and the size of the free internal volume and adapt it to the respective requirements in the paper machine concerned. This opens up possibilities for tailoring and adapting a forming fabric to a specific paper machine, which could not be achieved with forming fabrics consisting of round threads and only to an insignificant extent with forming fabrics containing flattened longitudinal threads. These possibilities have apparently not been recognized for decades, because the professional world, as far as the use of flattened threads in forming fabrics is concerned, has been stuck with the idea that such threads only make sense when arranged in the longitudinal direction. It is particularly preferred if some or all of the transverse threads of the first group lying in the plane of the paper side are flattened. Since the flattened transverse threads on the paper side extend transversely to the main direction of the fiber of the paper stock, this results in optimal fiber support with a significantly reduced risk that some of the fibers slide into the inside of the wire. The flattened cross threads act like small, transversal plateaus, which effectively take the pulp fibers with them and, because they are oriented in the running direction, provide them with optimal support without the risk of slipping. The toothing effect that occurs with round threads is largely avoided and in this way the sheet removal at the end of the sheet formation section is considerably facilitated.

The basic idea of the invention can also be realized in forming fabric, in which the first group of transverse threads consists of at least two subgroups of transverse threads, of which a first subgroup forms normal transverse threads and a second subgroup forms filling transverse threads. The filling transverse threads can have floats that go over more longitudinal threads than the longest floats of the normal transverse threads, as a result of which the above-described transverse plateau effect is particularly pronounced. Of course there is the possibility of giving the normal transverse threads and the filling transverse threads cross-sectional areas and / or cross-sectional shapes that differ from one another.

The above-described effect is particularly evident when the transverse threads float over a number of longitudinal threads that are greater than the number of transverse threads over which the longitudinal threads float. As a result, a distinctive transverse structure is produced from a large number of transverse plateaus, which give the accumulated fibers optimum support precisely because of their orientation, primarily in the running direction. The floats of the flattened cross threads can be designed according to the respective requirements. In the case of a one-and-a-half-layer fabric, the longest floats should go over at least four longitudinal threads, in a double-layer fabric over at least three longitudinal threads and in a three-layer fabric over at least one longitudinal thread.

According to a further feature of the invention, it is provided that the flattened transverse threads of the first group have a fiber support width which is at least 9% larger than that of a circular thread of the same cross-sectional area. The fiber support width should preferably even be at least 15% and particularly advantageously at least 30. The fiber support width is to be understood as the width of a flat thread surface, that is to say when 10% of its height, ie the extent transverse to the plane of the fabric, is removed from the paper side of the respective transverse thread.

According to a further feature of the invention it is provided that the degree of coverage of the transverse threads of the first group in one and a half and double-layer fabrics without filling transverse threads is at least 32%, better still 37% and preferably at least 4 or even 47%, better still 52%. The degree of coverage is defined as the product of the previously defined fiber support width (in cm), the number of threads (thread density) per cm screen length and the number 100. If different types of threads are used for the first group of transverse threads, separate degrees of coverage are determined for each thread type. The total degree of coverage then corresponds to the sum of the degrees of coverage of the individual types of transverse threads. In the case of two-layer fabrics with filling cross threads or at least three-layer fabrics, the degree of coverage should be at least 40, better still 50 or even 55% and preferably 60%. Using the basic idea of the present invention, further advantages can be achieved if part or all of the transverse threads of the second group, which form the plane of the machine side, are flattened.

Such a design has the advantage that the essential properties of the forming fabric no longer change so strongly and then in a much more uniform manner than in forming fabrics in which these transverse threads are designed as round threads. On the one hand, this is due to the fact that the contact surface of the forming fabric does not change as much during abrasion or - with rectangular transverse threads - practically does not change and that the transverse threads nestle better against the underside of the forming fabric because of their greater flexibility, i.e. they do not protrude as much . The latter has the consequence that the length of the abrasion surface changes only insignificantly over time. Optimization options are also opened up here. While maintaining the thickness of the forming fabric, considerably more abrasion volume can be made available. On the other hand, the thickness of the forming fabric can be reduced with the same abrasion volume. Precisely because the transverse threads of the second group protrude on the machine side, these transverse threads can be used to exert a strong influence on the one hand with regard to the abrasion volume and on the other hand with regard to the thickness of the sieve.

The transverse threads of the second group should float over at least four longitudinal threads in the case of a fabric with one and a half layers and over at least five longitudinal threads in the case of a double-layer fabric. In the case of a double-layer fabric, a differentiation can be made according to the number of shafts in the transverse threads. With a number of fourteen shafts, the transverse threads of the second group should float over at least ten longitudinal threads and with a number of sixteen shafts over at least twelve longitudinal threads.

With the flattened cross threads of the second group, this should The ratio of the maximum to the standard abrasion surface is a maximum of 2.9, better still 2.2 and preferably 1.7 or even better 1.4. The abrasion surface of a thread floating on the machine side is referred to as its machine-side contact surface with the elements of the paper machine. The maximum abrasion area means the largest contact area which arises in the course of wear of the transverse threads. The contact surface is defined as the standard abrasion surface, which occurs after removal of 10% of the height of the respective transverse thread, that is to say the extension of the relevant thread transverse to the tissue plane.

As far as the degree of coverage is concerned, it should be over 52% for transverse threads of the second group, better still over 62%, if the fabric is one and a half layers. In the case of a double-layer fabric without filler cross threads in the first group, the degree of coverage of the cross threads in the second group should be over 40%, better still over 45%, and in the case of a double-layer fabric with filler cross threads in the first group over 32%, preferably over 37%. In the case of a three-layer fabric in which the ratio of the number of transverse threads of the first group to that of the transverse threads of the second group is 1: 1, the degree of coverage should be over 45%, better still over 50%. In the case of a three-layer fabric in which the ratio of the number of cross threads of the first group to that of the cross threads of the second group is 3: 2, the degree of coverage should be over 42%, better still over 46%. In the case of a three-layer fabric in which the ratio of the number of transverse threads of the first group to that of the transverse threads of the second group is 2: 1, the degree of coverage should be at least 39%, better still 42%.

There is also the possibility of combining the transverse threads flattened according to the invention with such longitudinal threads. The flattened longitudinal threads should be arranged so that their cross-sectional extent in the tissue plane is greater than transverse to the tissue plane and daε The ratio between the cross-sectional extent in the tissue plane to the cross-sectional extent transverse to the tissue plane is between 1.2 and 2.2. The flattened longitudinal threads should have an area of 0.015 to 0.226 mm ² .

The flattened transverse threads of the first group expediently have an area of 0.013 to 0.195 mm ² , the second group an area of 0.022 to 0.4 mm ² .

The flattened threads can have any cross-sectional shape, provided that the conditions of the basic idea of the invention are observed. Particularly suitable are oval, in particular elliptical and, above all, rectangular cross sections, the latter preferably with chamfered edges. However, other thread shapes can also be used, for example trapezoidal or rhomboidal ones.

The forming fabric according to the invention can also be set within very wide limits with regard to its open inner volume. There can be an optimal compromise between the drainage performance on the one hand and the so-called on the other

Water dragging can be achieved. In this case, the value should few as 54 mm 3 / cm ^2, preferably less than 46 mm 3 / cm ^2, are not exceeded. However, it can d

Tissue can be differentiated as follows:

₃₃

- for a one-and-a-half-layer fabric less than 54 mm / cm ² , preferably less than 46 mm / cm ² ;

3

- in the case of a double-layer fabric, less than 38 mm / cm ² ,

3 preferably less than 33 mm / cm ² ;

- for a double-layer fabric with a first group of

Cross threads from normal cross threads and filling cross threads less than

53 mm 3 / cm ² , preferably less than 44 mm 3 / cm ² ; - for a three-layer fabric with a ratio of

Thread counts from the first to the second group of cross threads from

3 2: 1 less than 60ram / cm ² , preferably less than

3 55 mm / cm ² ;

- for a three-layer fabric with a ratio of

Thread counts from the first to the second group of cross threads from

3 1: 1 less than 40 mm / cm ² , preferably less than

3 38 mm / cm.

The surface unit, which is designated "cm ² ", extends in the tissue plane.

Insofar as the fabric is at least three layers and the layers are connected to one another by binding threads, it is also recommended to use di binding threads with a flattened cross-section with a cross-sectional extent of the tissue plane that is larger than transverse to it. The cross-sectional area should go from 0.013 to 0.069 mm ² .

In the drawing, the invention is illustrated in more detail using exemplary embodiments. Show it:

Figure (1) a one and a half-layer forming screen in

Longitudinal section;

Figure (2) the forming fabric according to Figure (1) in cross section;

Figure (3) a two-layer forming fabric in

Longitudinal section;

Figure (4) a three-layer forming fabric in

Longitudinal section;

Figure (5) with a two-layer forming fabric Filling cross threads in longitudinal section;

Figure (6) another two-layer forming fabric with filling cross threads in longitudinal section;

Figure (7) a further two-layer forming fabric in longitudinal section;

Figure (8) is a representation of the support of

Paper fibers for circular and rectangular, flattened cross threads.

The one and a half-layer forming screen (1) shown in the figures (1) and (2) has longitudinal threads (2) which are circular in cross section and which extend in the machine direction (MD). The forming fabric (1) also has a first group of transverse threads (3) with a likewise circular cross section. Below this is a second group of transverse threads (4), which have a rectangular cross section, the extent transverse to the plane of the forming fabric (1) being less than in its plane.

The integration of the longitudinal threads (2) and the first group of transverse threads (3) is such that a monoplane top, i.e. H. Paper side arises. A longitudinal thread (2) binds every fifth transverse thread (3) of the first group. The transverse threads (3) of the first group float over four longitudinal threads before they tie in with one longitudinal thread (2) (see FIG. 2). This creates a distinctive transverse structure on the paper side of the forming fabric (1), i. H. the transverse floats of the transverse threads (3) of the first group dominate the paper side.

The second group of transverse threads (4) floats to the machine side over a total of nine longitudinal threads (2) before these transverse threads (4) bind with a longitudinal thread (2). Since di transverse threads (4) are the same compared to a round transverse thread Cross-sectional area are significantly more flexible, they have no arc shape. Rather, because of their conformability, they run straight between the ties with the longitudinal threads. This fact and the rectangular cross-section have the consequence that the abrasion surface, ie the surface with which the forming fabric (1) rubs over the stationary parts of the paper machine, changes with increasing wear. The change in sieve thickness per unit of time is less than when using cross threads of round cross-section and remains essentially constant. This means that the sieving properties change only slightly and then only very uniformly while the forming sieve (1) is running.

The exemplary embodiment of a two-layer forming fabric (5) shown in FIG. (3) has round longitudinal threads (6) as well as a first group of transverse threads (7) on the paper side and a second group of transverse threads (8) on the machine side. In each case one cross thread (7) of the first group lies above a cross thread (8) of the second group. In contrast to the exemplary embodiment according to FIGS. 1 and 2, the transverse threads 7, 8 of both groups have a rectangular, flattened cross section. The longitudinal threads (6) float first over two transverse threads (7) of the first group on the paper side, then between three transverse threads (7, 8) of the first and the second group and then tie in with a transverse thread (8) of the second group.

Because of their flattened cross-sections, the transverse threads (7) of the first group form transversely directed plateaus for the support of the paper stock fibers mainly oriented in the running direction of the forming sieves (5). Compared to circular transverse threads of the same cross-sectional area, the transverse threads (7) of the first group have a lower height, which results in flatter crankings for the longitudinal threads (6). This reduces the risk of wire markings and ensures better length constancy of the forming wire (5) on the paper machine. The same also applies to the transverse threads (8) of the second group. Their abrasion properties correspond to the transverse threads (4) in the exemplary embodiment according to FIGS. (1) and (2).

In Figure (4), a forming fabric (9) is shown, which is three layers. It has longitudinal threads (10) on the paper side which bind in plain weave with a first group of transverse threads (11). Both the longitudinal threads (10) and the transverse threads (11) have a circular cross section. Machine-side longitudinal threads (12) of likewise round cross-section run below the paper-side longitudinal threads (10). They tie in with a second group of transverse threads (13) which run on the machine side and thereby protect the longitudinal threads (10, 12) from wear. The transverse threads of the second group (13) have a rectangular cross section. Their cross-sectional area is larger than that of the transverse threads (11) of the first group. The ratio of the number of transverse threads (11) in the first group to that of the transverse threads (13) in the second group is 2: 1. Within the scope of the invention, there is also the possibility of providing flattened, in particular rectangular, cross sections for the transverse threads (11) of the first group. The use of flattened cross-sectional shapes reduces the thickness of the forming sieve (9) compared to embodiments with round cross-sections of the same cross-sectional area.

FIG. (5) shows a two-layer forming fabric (14), which has a first group of transverse threads in the upper position, normal transverse threads (15) alternating with filling transverse threads (16) in this group. They each have a circular cross-section. The lower, machine-side layer is formed by a second group of long floating cross threads (17) with a rectangular cross-section. Both groups of transverse threads (15, 16, 17) are bound by longitudinal threads (18), each of which floats on the paper side via two normal transverse threads (15) and a filling transverse thread (16) and each incorporates a transverse thread (17) from the second group on the machine side. Each Adjacent longitudinal threads (18) are offset by three transverse threads (15, 16) from the first group in the machine direction.

The forming screen (19) shown in Figure (6) is similar in structure to the forming screen (14) according to Figure (5). It is accordingly constructed in two layers and has alternating normal transverse threads (20) and filling transverse threads (21), which form the first group of transverse threads running on the paper side. Both have a flattened rectangular cross section.

The lower layer is formed by a second group of transverse threads (22), which in this case have a circular cross-section and are integrated on the machine side with a long float. The longitudinal threads (23) float in the same way as in the embodiment according to FIG. (5).

While in the embodiment according to FIG. (4) importance was attached to constant and uniformly changing abrasion properties through the use of rectangular cross threads (17) from the second group, the rectangular cross sections of the normal and fill cross threads (20, 21) ensure in the embodiment according to FIG (6) an improved fiber support, in particular when these transverse threads (20, 21) dominate on the paper side and produce a transverse rib structure there. The possibilities of design optimization depending on the requirements in the paper machine in question are shown here in particular. The flattened cross-sections have a freely selectable parameter more than round cross-sections, which increases the design options taking into account the diverse requirements that are currently placed on a forming fabric.

The embodiment shown in FIG. (7) is also a two-layer forming fabric (24), but without filler cross threads. A first group of cross threads (25) with round cross-section forms the upper layer. The lower layer is formed by a second group of transverse threads (26), which have a rectangular cross section and are integrated in a long float. In the machine direction, longitudinal threads (27) which float on the paper side each over two transverse threads (25) of the first group and each incorporate one transverse thread (26) of the second group on the machine side. Adjacent longitudinal threads (27) are each offset by three transverse threads (25) of the first group in the machine direction. By using transverse threads (26) of the second group with a rectangular cross-section, the screen thickness is considerably reduced compared to a forming screen, in which the transverse threads of the second group have a round cross-section with the same cross-sectional area.

FIG. (8) shows in cross-section two transverse threads (28, 29) lying next to one another with a round cross-section, and in each case two transverse threads (30, 31) lying next to each other with a rectangular cross-section. The round transverse threads (28, 29) and the rectangular transverse threads (30, 31) have the same horizontal dimensions and matching cross-sectional areas. The minimum distances between the round cross threads (28, 29) correspond to the distances of the rectangular cross sections (30, 31).

Paper pulp (32, 33) is supported on the round transverse threads (28, 29). They are oriented in the machine direction due to the difference in speed between the fiber headbox and the paper machine screen. The support is unsatisfactory because there is a tendency for the pulp fibers (32, 33) to be drawn in by the dewatering stream and the negative pressure into the upwardly conically opening column between the round transverse threads (28, 29). This creates problems with the drainage and due to the toothing effect during the later sheet removal.

Paper fibers (34, 35) are also deposited on the rectangular transverse threads (30, 31). Although the gap between the rectangular cross threads (30, 31) is the same size as between the round cross threads (28, 29), it becomes clear that the support of the pulp fibers (34, 35) is considerably improved. The paper fibers (34, 35) are no longer drawn into the gap between the transverse threads (30, 31), so they do not interfere with the drainage. There is also no interlocking with the transverse threads (30, 31) that could impair the sheet removal.

Otherwise, the definition of the fiber support width (FIBER SUPPORT WIDTH) can be explained on the basis of FIG. It results when 10% of the height of the thread is taken from the top of the thread. In the case of the rectangular transverse threads (30, 31), this corresponds to

The width of the width of these transverse threads (30, 31) is in the case of the round transverse threads (28, 29)

Fiber support width - each indicated by the length of the arrows - considerably smaller than the diameter of the transverse threads (28, 29) and thus also as the fiber support width of the rectangular transverse threads (30, 31).

Claims

Claims forming screen

1. forming fabric for the sheet formation section of a paper machine, consisting of a more than single-layer, in particular flat-woven, fabric made of plastic threads with longitudinal threads extending in the machine direction and transverse threads extending transversely thereto, a first group of transverse threads lying in the plane of the paper side and floating there over longitudinal threads , the number of which is at least as large as the number of transverse threads over which the longitudinal threads float on the paper side, and the plane of the machine side being formed exclusively by a second group of transverse threads, characterized by the following features:

(a) at least some of the transverse threads (4, 7, 8, 13, 17, 20, 21, 26, 30, 31) have a flattened cross-section;

(b) the flattened transverse threads (4, 7, 8, 13, 17, 20, 21, 26 30, 31) are arranged in such a way that their cross-sectional dimensions in the tissue plane are greater than transversely to the tissue plane;

(c) the ratio between cross-sectional extent in the tissue plane to cross-sectional extent transverse to the tissue plane is between 1.2 and 2.2, preferably 1.2 and 1.8;

2. forming fabric according to claim (1), characterized in that flattened transverse threads (7, 20, 21) belong to the first group of transverse threads (7, 20, 21).

3. forming fabric according to claim (2), characterized in that all transverse threads (7, 20, 21) of the first group are flattened.

4. forming fabric according to claim (2) or (3), characterized in that the first group of transverse threads consists of at least two subgroups of transverse threads, of which a first subgroup of normal transverse threads (15, 20) and a second subgroup of filling transverse threads (16, 21st ) form.

5. forming fabric according to claim (4), characterized in that the filling transverse threads (16, 21) have floats that go over more longitudinal threads (23) al the longest floats of the normal transverse threads (15, 20).

6. forming fabric according to claim (4) or (5), characterized in that the normal transverse threads (15, 20) and the filling transverse threads (16, 21) each have different cross-sectional areas and / or cross-sectional shapes.

7. forming fabric according to one of claims (2) to (6), characterized in that the transverse threads (3, 7, 11, 15, 16, 20, 21, 25) of the first group over a number of longitudinal threads (2, 6 , 12, 18, 23, 27) float that is greater than the number of transverse threads (3, 7, 11, 15, 16, 20, 21, 25) over which the longitudinal threads (2, 6, 12, 18, 23, 27) float.

8. forming fabric according to one of claims (2) biε (7), characterized in that in the case of a one-and-a-half-layer fabric, the transverse threads (3) of the first group float with their longest floats over at least four longitudinal threads (2).

9. forming fabric according to one of claims (2) to (7), characterized in that in the case of a double-layer fabric, the transverse threads (6, 15, 16, 20, 21, 25) of the first group float with their longest floats over at least three longitudinal threads (6, 18, 23, 27).

10. forming fabric according to one of claims (2) to (7), characterized in that d transverse threads (11) of the first group go over at least one longitudinal thread (12) in a three-layer fabric.

11. forming fabric according to one of claims (2) biε (8), characterized in that the flattened transverse threads (7, 20, 21) of the first group have a fiber support width which is at least 9% larger than that of a circular thread of the same cross-sectional area.

12. forming fabric according to one of claims (2) to (11), characterized in that the degree of coverage of the transverse threads (3, 7, 25) of the first group is at least 32% in one and a half and double-layer fabrics without filling transverse threads.

13. Forming sieve according to one of claims (2) to (11), characterized in that the degree of coverage of the transverse threads (11, 15, 16, 20, 21) of the first group in fabrics which have two layers with filling transverse threads (16, 21) or are at least three layers, is at least 40%.

14. forming fabric according to one of claims (1) to (13), characterized in that transverse threads (4, 8, 13, 17, 26) d second group are flattened.

15. forming fabric according to claim (14), characterized in that all transverse threads (4, 8, 13, 17, 26) of the second group are flattened.

16. forming fabric according to claim (14) or (15), characterized in that the transverse threads (4) of the second group float in a one and a half-layer fabric over at least four longitudinal threads (2).

17. forming fabric according to claim (14) or (15), characterized in that the transverse threads (8, 17, 22, 26) of the second group float in a double-layer fabric over at least five longitudinal threads (6, 18, 23, 27).

18. forming fabric according to claim (17), characterized in that in a double-layer fabric, the transverse threads (17, 22, 27) of the second group with a shaft number of fourteen over at least ten longitudinal threads (18 23) and with a shaft number of sixteen over at least float twelve longitudinal threads (27).

19. Forming sieve according to one of claims (14) to (17), characterized in that floating in a three-layer fabric di transverse threads of the second group float over longitudinal threads, the number of each floating being 1 less than the number of shafts of these transverse threads.

20. Forming sieve according to one of the claims (14) to (19), characterized in that in the flattened transverse threads (4, 8, 13, 17, 26) of the second group, the ratio of the maximum to the standard abrasion surface is a maximum of 2.9 .

21. Forming screen according to one of the claims (14) to 20 (20), characterized in that the degree of coverage of the transverse threads (4) of the second group is over 52% for a one-and-a-half layer fabric.

22. forming fabric according to one of claims (14) to (20), characterized in that the degree of coverage of the transverse threads (8, 17, 22, 26) of the second group in one double-layer fabric without fill cross threads in the first group over 40% and with fill cross threads (16, 21) in the first group over 32%.

23. forming fabric according to one of claims (14) to (20), characterized in that the degree of coverage of the transverse threads (13) of the second group in a three-layer fabric, in which the ratio of the number of transverse threads of the first group to that of the transverse threads of second group is 1: 1, is over 45%, and for a three-layer fabric in which the ratio of the number of transverse threads of the first group to that of the second group of transverse threads is 3: 2, is over 42%, and for a three-layer Fabric in which the ratio of the number of transverse threads (11) of the first group to that of the transverse threads (13) of the second group is 2: 1 is over 39%.

24. Forming fabric according to one of claims (1) to (23), characterized in that at least some of the longitudinal threads have a flattened cross section, the flattened longitudinal threads being arranged such that their cross-sectional extent in the fabric plane is greater than transverse to the fabric plane and the ratio between the cross-sectional extent in the tissue plane to the cross-sectional extent transverse to the tissue plane is between 1.2 and 2.2.

25. Forming wire according to claim (24), characterized in that all the longitudinal threads are flattened εin

26. Forming sieve according to claim (25), characterized in that the flattened longitudinal threads have an area of 0.15 to 0.226 mm ² .

27. forming fabric according to one of claims (1) to (25), characterized in that the flattened transverse threads (7, 20, 21) of the first group have an area of 0.013 to 0.195 mm ² .

28. Forming fabric according to one of claims (1) to (27), characterized in that the flattened transverse threads (4, 8, 13, 17, 22, 26) of the second group have an area of 0.022 to 0.4 mm ² .

29. Forming sieve according to one of claims (1) to (28), characterized in that the flattened threads (4, 7, 8 13, 17, 20, 21, 26) have oval or rectangular cross-section.

30. forming fabric according to one of claims (1) to (29), characterized in that the open inner volume of the

3 tissue less than 54 mm / cm ² , preferably less than

3 is 46 mm / cm ² .

31. forming fabric according to claim (30), characterized in that the open inner volume of the fabric

(a) less than for a one and a half ply fabric

55 mm 3 / cm ² , preferably less than 66 mm3 / cm ² ,

(b) less than for a double layer fabric

38 mm 3 / cm ^2, preferably alive ^'s less alε 33 mm3 / ^cm2,

(c) in the case of a double-layer fabric with a first group of transverse threads made of normal transverse threads and filling transverse threads

3 less than 53 mm / cm ² , preferably less than

44 mm / cm ² ,

(d) for a three-layer fabric

(aa) with a ratio of the thread counts of the first to the second group of cross threads of 2: 1 less

3 than 60 mm / cm ² , preferably less than

55 mm / cm ² ,

(bb) with a ratio of the thread numbers of the first to the second group of transverse threads of 1: 1 less

3 than 40 mm / cm ² , preferably less than

38 mm / cm ² .

is.

32. forming fabric according to one of claims (1) to (31), characterized in that the fabric is at least three layers and the layers are connected to one another by binding threads, the binding threads also having a flattened cross-section with a cross-sectional extent in the tissue plane which is larger than across it.

33. forming fabric according to claim (32), characterized in that the cross-sectional area of the binding threads is between 0.012 and 0.062 mm ² .