PAPER MACHINE FABRIC AND USE OF SUCH FABRIC

Description

[0001] The invention relates to a fabric, in particular a forming fabric, for a machine for producing or processing a material web, in particular a tissue web, comprising a first fabric layer providing a web material contact side and formed by weaving first longitudinal threads running in the longitudinal direction of the fabric with first transverse threads running in the transverse direction of the fabric, and a second fabric layer providing a machine contact side and formed by weaving second longitudinal threads running in the longitudinal direction of the fabric with second transverse threads running in the transverse direction of the fabric, wherein the first fabric layer and the second fabric layer are connected to one another by binding threads, wherein the fabric has more first longitudinal threads than second longitudinal threads, but the number of first longitudinal threads is at most twice as large as the number of second longitudinal threads,and wherein the weave pattern of the fabric is repeated in repeats, and in each repeat, the second transverse threads form at least two contact flotations on the machine contact side. Furthermore, the invention relates to the use of such a fabric for the production of a tissue web.

[0002] Since such coverings are usually woven flat, the longitudinal threads are usually the warp threads and the cross threads the weft threads. However, if the covering is woven round, the situation is reversed.

[0003] Such a covering is known, for example, from WO 2008 / 068317 A1. By having more first longitudinal threads than second longitudinal threads, the first longitudinal threads can be finer than the second longitudinal threads, thus providing a particularly low-marking web material contact side. The tensile stresses to which the covering is exposed in the longitudinal direction can be primarily absorbed by the second longitudinal threads with a larger cross-section.

[0004] To protect the second longitudinal threads, which are subject to high tensile stress, from wear, the clothing is designed so that contact with the machine occurs primarily at the contact floats of the second transverse threads. Flat-woven clothings are referred to as "weft walkers." This means that the second transverse threads are particularly exposed to wear during normal use. Since it is generally assumed that local wear decreases as the contact area increases, the floats of the second transverse threads on the machine side are usually relatively long.

[0005] One problem observed with such known fabrics is that the transverse stability could be improved. Transverse stability is important to prevent the fabric from reducing its cross-machine dimension when subjected to tensile loads in the machine direction.

[0006] The publications US2009205740A1 and US2008196784A1 already disclose generic fabrics, namely the fabrics described above, in which all contact flotations of the second transverse threads have a maximum length of two. In other words, the second transverse threads per contact flotation are to be guided under only one second longitudinal thread or a maximum of two immediately adjacent second longitudinal threads. It has been shown that by reducing the contact flotation length and thus increasing the number of contact flotations compared to that present in the fabric from WO 2008 / 068317 A1, the transverse stability can be increased without, however, significantly or even measurably increasing the wear on the second transverse threads. This applies in particular when the fabric is used as intended as a forming fabric in tissue machines.It is assumed that this is due to the fact that no or only very small amounts of fillers are used in tissue production, and fillers have an abrasive effect on the fabric.

[0007] At the same time, the fact that there are more and shorter contact flotations than in the prior art results in the contact flotations being more closely bound together due to the tighter weave. In other words, the thickness of the fabric in the contact flotation area is reduced. This effect is suspected to be the cause of the improved transverse stability, which is reflected in increased wire width stability on the paper machine.

[0008] As a beneficial side effect, the closer connection also results in a reduction of the free volume within the covering, through which free volume unwanted drag water is transported.

[0009] Reducing the free volume within the fabric also facilitates dewatering of the material web transported on it. This is particularly advantageous when the material web is a fibrous web, especially tissue web, with a low specific weight per unit area. The production of such tissue webs requires forming fabrics with particularly fast dewatering.

[0010] However, the drainage performance of the coverings described in US2009205740A1 and US2008196784A1 could be even better.

[0011] It is the object of the present invention to solve this problem, ie to improve the drainage performance without compromising the running time and the transverse stability with the aforementioned advantages of such a covering.

[0012] The object is achieved by the device having the features according to claim 1. Further advantageous features are mentioned in the dependent claims.

[0013] According to the invention, the generic clothing is characterized in that the first longitudinal threads and the second longitudinal threads are arranged in several groups in each repeat, namely at least a first group and a second group, the first group being formed from a first longitudinal thread and a second longitudinal thread which are arranged exactly one above the other in the thickness direction of the clothing, while the second group is formed from two first longitudinal threads and a second longitudinal thread, neither of the two longitudinal threads of the second group being arranged exactly above the first longitudinal thread of the second group in the thickness direction of the clothing. This special arrangement of the first and second longitudinal threads makes it possible for water which has passed from the tissue web through the first fabric layer to also flow relatively easily and directly through the second fabric layer. This promotes rapid drainage.

[0014] This applies in particular when the first longitudinal threads and the second longitudinal threads are dimensioned and arranged relative to one another in such a way that, viewed projected in the thickness direction of the covering, they form at least one free longitudinal strip within a repeat, wherein such a strip is preferably formed everywhere where individual groups adjoin one another.

[0015] For the purposes of this invention, "exactly arranged one above the other" means that the first longitudinal thread—projected in the thickness direction of the covering—should not extend laterally beyond the second longitudinal thread. However, any minor local displacements that may occur should be disregarded here.

[0016] Preferably, a different number of first and second groups is provided in each repeat. Since the first and second groups have different drainage and thus marking behavior, it has been shown that the different number of first and second groups in the repeat can create an irregularity in the marking pattern, making the markings significantly less visible.

[0017] Furthermore, this design offers the possibility of influencing the dewatering behavior of the fabric. Therefore, in an advantageous development of this concept of the invention, it is proposed that the number of first groups differ from the number of second groups in the fabric. For example, if more first groups are used than second groups, a fabric with higher dewatering performance can be created than if more second groups are used than first groups. However, if, conversely, more second groups are used than first groups, this has the advantage that the fabric provides the fibrous web with more support points.

[0018] Especially with regard to a regular twill weave in the second fabric layer, this type of arrangement of the first and second longitudinal threads in different groups can specifically influence the appearance of the fibrous web, especially a tissue web, particularly through the interactions of the diagonally directed and longitudinally directed hydraulic markings. The term "hydraulic marking" refers to a disruption in the homogeneous flow of the white water through the fabric during dewatering and sheet formation, triggered by the presence of the longitudinal and transverse threads and their thread crossings.

[0019] To avoid overcomplicating the weave pattern, it is preferable for the second cross threads in each repeat to form a maximum of six contact flotations on the machine contact side. Typically, between two and four such contact flotations per repeat are sufficient.

[0020] It is also proposed that the binding threads always run in pairs next to each other in the cross-facing direction of the fabric, preferably alternating between the weave pattern on the side of the web material contact. Such fabrics are also referred to in the trade as SSB fabrics, where the abbreviation SSB stands for "sheet support binder."

[0021] In order to provide as many fiber support points as possible on the web contact side and thus design the clothing with as few markings as possible, it is proposed that the first fabric layer has a plain weave. It should be noted that the binding threads should be able to contribute to the weave pattern of the first layer. Thus, the plain weave is preferably achieved not only by the first longitudinal and the first transverse threads alone, but also by the binding threads, which further preferably also extend essentially in the transverse direction of the fabric. Alternatively, it is also possible for the first fabric layer to have a different weave, in particular a 3-shaft twill weave or 4-shaft twill weave or a weave derived therefrom. This is particularly advantageous if a certain structuring of the fibrous web is even desired, as is the case with tissue webs, for example.The binding threads can have essentially the same diameter as the first transverse threads and / or the first longitudinal threads. The term "essentially" in this context means that the diameters of these thread systems do not differ by more than 30%.

[0022] The second fabric layer, which does not come into contact with the material web, can have a plain weave or a twill weave. The twill weave is characterized by the diagonally running ridge it has. This ridge can continue across the entire covering without interruption, in which case it is referred to as a regular, uninterrupted twill weave, or it can exhibit certain deviations, in particular interruptions or offsets, in which case it is referred to as a broken or interrupted twill weave. Both types of twill weave have proven to be well suited to practical use for the covering according to the invention. Regular twill weaves result in thinner coverings than broken twill weaves, since interruptions in the twill ridge lead to a greater flotation height in this area.Regular twill weaves can reproduce the diagonal they form in the dewatered fibrous web through hydraulic interaction, which is advantageous when a structured fibrous web is desired. Broken twill burrs, on the other hand, generally exhibit less hydraulic marking in the dewatered fibrous web. Multi-burr twills with different burr widths can also optimize the hydraulic marking potential.

[0023] It should be noted that the binding threads are generally not taken into account when defining the weave pattern of the second layer, unlike the weave pattern of the first layer.

[0024] Furthermore, two adjacent contact flotations of a second transverse thread can be separated from each other by a maximum of two second longitudinal threads. Due to the numerous intersection points in the second fabric layer, its thickness can be relatively small, and the second longitudinal threads can also be protected from wear. In particular, the second fabric layer can be designed to be relatively flat, meaning that there are no significant protrusions on the web contact side that would be particularly exposed to wear.

[0025] In a further development of this idea, it can even be provided that two adjacent contact flotations of a second transverse thread are separated from each other by only one second longitudinal thread.

[0026] A further aspect of the present invention relates to the use of a previously described fabric according to the invention for producing a tissue web, wherein the advantages of the fabric according to the invention are particularly evident when the tissue web has a low specific weight per unit area, ie a specific weight per unit area of ​​at most 30 g / m 2<, preferably between 8 g / m 2< and 30 g / m 2<.

[0027] Advantageously, the fabric according to the invention is used as a forming fabric in a so-called crescent former of a tissue machine.

[0028] Further advantageous features of the invention are explained using exemplary embodiments with reference to the drawings. Fig. 1 schematic representation of a first embodiment of a covering according to the invention in cross section, which has three contact floatations of length two, two and one per repeat; Fig. 2schematic representation of only the first and second longitudinal threads of Fig. 1 , which are arranged in groups; Fig. 3a the weave pattern of a first variant of the second layer of the fabric of Figure 1 with a regular, uninterrupted twill weave; Fig. 3b the weave pattern of a second variant of the second layer of the fabric of Figure 1 , with an interrupted twill weave; Fig. 4 the weave pattern as in Figure 3a , but with slightly different numbering; Fig. 5 the complete weaving paths of all threads running in the cross direction of the covering, including the binding threads, of the covering according to the invention according to Figure 4 within a report; Fig. 6 the weave pattern of the second layer of a second embodiment of the covering according to the invention, which has four contact floatations per repeat, each with a length of one, with a plain weave; Fig. 7the complete weaving paths of all threads running in the cross direction of the covering, including the binding threads, of the covering according to the invention according to Figure 6 within a report; Fig. 8 the weave pattern of the second layer of a third embodiment of the covering according to the invention, which has four contact floatations per repeat with lengths two, one, two and one, with a regular, uninterrupted twill weave; Fig. 9 the weave pattern of the second layer of a fourth embodiment of the fabric according to the invention, which has four contact floatations per repeat with lengths of two, two, two and one, with a regular, uninterrupted twill weave; Fig. 10a-b the complete weaving paths of all threads running in the transverse direction of the covering, including the binding threads, of the covering according to the invention according to a third embodiment; Fig. 11 the weave pattern only of the second layer of the fabric of the third embodiment according to Figure 10a-bwith a regular, uninterrupted twill weave.

[0029] Figure 1 shows a schematic representation of a first embodiment of a covering 10 according to the invention in cross-section. The section plane shown is defined by the covering transverse direction CD and the thickness direction T. This embodiment is particularly characterized by having three contact flotations KF1, KF2, and KF3 per repeat, which have lengths of two, two, and one, respectively.

[0030] In Figure 1 you can see a track contact side (top in Figure 1 ) providing the first fabric layer L1 and a machine contact side arranged underneath (bottom in Figure 1) providing a second fabric layer L2. Both fabric layers L1 and L2 are connected to each other by pairs of binding threads extending essentially in the fabric transverse direction CD. The first fabric layer L1 comprises first transverse threads QF1, which are interwoven with first longitudinal threads LF1. As shown in Figure 1As shown, the first transverse threads QF1 can be woven with the first longitudinal threads LF1 to form the first fabric layer L1 using a plain weave. Similarly, the second fabric layer L2 comprises second transverse threads QF2 which are woven with second longitudinal threads LF2. The fabric 10 according to the invention further has the special feature that it comprises more first longitudinal threads LF1 than second longitudinal threads LF2, namely in this exemplary embodiment 1.5 times as many first longitudinal threads LF1 as second longitudinal threads LF2. Both the first longitudinal threads LF1 and the first transverse threads QF1 have a noticeably smaller cross-section than the second longitudinal threads LF2 and second transverse threads QF2, respectively. In this way, a particularly fine and low-marking paper contact surface can be provided by the first fabric layer L1, while the tensile loads acting on the covering 10 during intended use are primarily absorbed by the second fabric layer L2.

[0031] The second cross threads QF2 point on the machine contact side (bottom in Figure 1 ) of the covering 10, namely so-called contact flotations KF1, KF2, and KF3, which are all kept short, i.e., they are guided only under a second longitudinal thread or, at most, under two second longitudinal threads arranged directly next to one another. This has a beneficial effect on the transverse stability of the covering 10. The thickness of the covering 10 in the area of ​​the contact flotations KF1, KF2, and KF3 is reduced compared to the covering with longer contact flotations known from WO 2008 / 068317 A1.

[0032] Figure 2 shows in a schematic representation per repeat only the first longitudinal threads LF1 and the second longitudinal threads LF2 from Figure 1, but not the various transverse threads. This illustration makes it clear that the first longitudinal threads LF1 and the second longitudinal threads LF2 are arranged in each repeat in a plurality of groups G1 and G2, namely at least a first group G1 and a second group G2, the first group G1 being formed from a first longitudinal thread LF1 and a second longitudinal thread LF2, which are arranged exactly one above the other in the thickness direction T of the clothing 10, while the second group G2 is formed from two first longitudinal threads LF1 and a second longitudinal thread LF2, none of the two first longitudinal threads LF1 of the second group G2 being arranged exactly above the one second longitudinal thread LF2 of the second group G2 in the thickness direction T of the clothing 10. In the present exemplary embodiment, the two groups G1 and G2 alternate continuously with one another.The first longitudinal threads LF1 and the second longitudinal threads LF2 are dimensioned and arranged relative to one another such that, viewed projected in the thickness direction T of the fabric 10, they form at least one free longitudinal strip within a repeat pattern, with such a strip preferably being formed everywhere where different groups G1, G2 adjoin one another. The free longitudinal strips facilitate drainage from the material web on the material contact side (top in . Figure 1 ) to the machine contact side (bottom in Figure 1 ), which in Figure 2 is shown with dashed arrows. The term "free longitudinal strip" deliberately ignores the fact that the Figure 2not shown transverse threads can hinder the free drainage, or a straight drainage in the thickness direction T of the clothing 10 from the web contact side of the clothing 10 to the machine contact side of the clothing 10 at least in sections in the longitudinal direction of the clothing 10 (orthogonal to the image plane in Figure 1 or 2 ) contradicts.

[0033] The Figures 3a and 3b show two different variants of the weaving pattern of the second layer L2 of the covering 10 from the Figures 1 and 2The columns of this checkerboard representation of the weave pattern correspond to the second longitudinal threads LF2, whereas the rows correspond to the second transverse threads QF2. Where an "x" is shown in the boxes, the corresponding second transverse thread QF2 is guided above, i.e. towards the web contact side of the clothing 10, over a corresponding second longitudinal thread LF2. Conversely, where there is no "x" in the box or the box is empty, the corresponding second transverse thread QF2 is guided under the corresponding second longitudinal thread LF2 and thus forms a contact flotation KF1, KF2 or KF3 on the machine contact side of the clothing 10. Below the weave pattern, the course of the weaving path of a second transverse thread QF2, namely the second transverse thread with the number 1 in the weave pattern shown above, is shown again for illustration.

[0034] The two in the Figures 3a and 3bThe variants shown differ from each other in that the second layer L2 in the first variant is Figure 3a has a regular, uninterrupted twill weave, whereas the second layer L2 in the second variant according to Figure 3b has an interrupted twill weave. The ridge of the respective twill weave is indicated by a diagonal, dashed line in the Figures 3a and 3b In the second variant according to Figure 3b the 12 second cross threads QF2 of the repeat can be divided into 4 groups or sections of equal size, with each group or section having a regular, uninterrupted twill weave.

[0035] The Figures 4 and 5 show once again in more detail the weaving pattern of the first variant according to Figure 3a , where "more detailed" here means that in Figure 5the weaving paths of all threads in a repeat of the fabric 10 are shown, including the weaving paths of the first longitudinal threads LF1 and the first transverse threads QF1 of the first layer L1, as well as the weaving paths of the binding threads connecting the two layers L1 and L2. Accordingly, Figure 4 compared to Figure 3a to a different numbering of the second longitudinal threads LF2 and second transverse threads QF2 of the second layer L2, whereby the Figure 4 otherwise the Figure 3a corresponds. In Figure 5 Every second pair of threads extending essentially in the transverse direction is a pair of binding threads, with each binding thread from the pair of binding threads being represented by a dotted line. The binding threads, together with the first transverse threads QF1 and the first longitudinal threads LF1, form a plain weave on the web material contact side.

[0036] Figure 4shows that in the case of the first variant of the first embodiment, the second fabric layer L2 is also a multi-ridge twill, since there are two twill ridges of different widths.

[0037] The Figures 6 and 7 show the weaving paths of a second embodiment of the fabric according to the invention. This differs from the first embodiment primarily in that the second layer has four contact flotations per repeat, with each individual contact flotation having a length of one. Thus, the second layer has a plain weave. The representation of the second embodiment corresponds to that of the Figures 4 or 5 for the first embodiment.

[0038] Two further embodiments of the covering according to the invention are shown in the Figures 8 and 9 shown, whereby the representation of those in the Figures 3a and 3b corresponds, since here too only the weave pattern of the second layer per repeat is shown. The third embodiment according to Figure 8 is characterized by the fact that there are four contact floatations per repeat, which have the lengths two, one, two and one. The fourth embodiment according to Figure 9 is characterized by only three contact flotations, each with a length of two. In both the third and fourth embodiments, the second fabric layer has a regular, uninterrupted multi-ridge twill weave.

[0039] The Figures 10a , 10b and 11 describe a third, particularly preferred embodiment of the present invention. The Figures 10a and 10b show the entire course of the first transverse threads QF1, the second transverse threads QF2 and the binding threads relative to the first longitudinal threads LF1 and the second longitudinal threads LF2 in two complete repeats of the covering 10. In the Figures 10a and 10bThe first transverse threads QF1, the second transverse threads QF2 and the binding threads, which all extend in the transverse direction of the covering, are designated Weft 1 to Weft 40, whereas the first longitudinal threads LF1 and the second longitudinal threads are simply numbered 1 to 26. As can be seen from these figures, a complete repeat comprises eight first longitudinal threads LF1, namely the longitudinal threads numbered 1, 3, 4, 6, 8, 9, 11, and 13, whereas the longitudinal threads numbered 14, 16, 17, 19, 21, 22, 24, and 26 represent only a first repeat, and five second longitudinal threads LF2, namely the longitudinal threads numbered 2, 5, 7, 10, and 12, whereas the longitudinal threads numbered 15, 18, 20, 23, and 25 represent only a first repeat. Thus, the ratio of first longitudinal threads LF1 to second longitudinal threads LF2 is 8:5.This distinguishes the third embodiment from the first two, where this ratio was 3:2. This allows for the formation of particularly fine surfaces on the web material contact side.

[0040] Figure 11 shows, similar to this in Figure 4 As described for the first embodiment, only the weave pattern of the second fabric layer L2 is shown twice next to each other. In the present third embodiment, every second transverse thread QF2 of a complete repeat of the second layer L2 has two contact flotations, namely one of length 1 and one of length 2. Figure 11 As an example, a concrete weaving path is shown again, namely that of the second cross thread QF2 with the number 2, according to the top line in the checkerboard-like representation above.

[0041] How Figure 11As can be seen further, the second layer L2 has a regular, uninterrupted twill weave, although the widths of the ridges differ. Thus, this is also a multi-ridge body. List of reference symbols :

[0042] 10Covering CDCovering cross direction G1first group G2second group KF1first contact flotation KF2second contact flotation KF3third contact flotation L1first layer L2second layer LF1first longitudinal thread LF2second longitudinal thread QF1first transverse thread QF2second transverse thread TThickness direction

Claims

1. Clothing (10), in particular a forming screen, for a machine for producing or processing a material web, in particular a tissue web, comprising a first woven-fabric layer (L1) which provides a web material contact side and is formed by interweaving first longitudinal threads (LF1) that run in the clothing longitudinal direction and first transverse threads (QF1) that run in the clothing cross direction (CD), and a second woven-fabric layer (L2) which provides a machine contact side and is formed by interweaving second longitudinal threads (LF2) that run in the clothing longitudinal direction and second transverse threads (QF2) that run in the clothing cross direction (CD), wherein the first woven-fabric layer (L1) and the second woven-fabric layer (L2) are connected to one another by binding threads; wherein the clothing (10) has more first longitudinal threads (LF1) than second longitudinal threads (LF2), but the number of first longitudinal threads (LF1) is at most double the number of second longitudinal threads (LF2); and wherein the weaving pattern of the clothing (10) recurs in repeats, and the second transverse threads (QF2) in each repeat form at least two contact flotations (KF1, KF2, KF3) on the machine contact side; wherein all contact flotations (KF1, KF2, KF3) of the second transverse threads (QF2) have a length of at most two, characterized in that the first longitudinal threads (LF1) and the second longitudinal threads (LF2) in each repeat are disposed in a plurality of groups (G1, G2), specifically at least one first group (G1) and one second group (G2), wherein the first group (G1) is formed from one first longitudinal thread (LF1) and one second longitudinal thread (LF2) which are disposed exactly on top of one another in the thickness direction (T) of the clothing (10), while the second group (G2) is formed from two first longitudinal threads (LF1) and one second longitudinal thread (LF2), wherein none of the two first longitudinal threads (LF1) of the second group (G2) is disposed exactly above the one second longitudinal thread (LF2) of the second group (G2) in the thickness direction (T) of the clothing (10).

2. Clothing (10) according to Claim 1, characterized in that the first longitudinal threads (LF1) and the second longitudinal threads (LF2) are dimensioned and disposed relative to one another in such a manner that, when viewed projected in the thickness direction (T) of the clothing (10), said threads (LF1, LF2) within a repeat form at least one free longitudinal strip, wherein such a strip is preferably formed at all locations where different groups (G1, G2) are adjacent to one another.

3. Clothing (10) according to Claim 1 or 2, characterized in that the number of first groups (G1) differs from the number of second groups (G2) in the clothing (10).

4. Clothing (10) according to one of the preceding claims, characterized in that the second transverse threads (QF2) form at most six contact flotations (KF1, KF2, KF3) on the machine contact side in each repeat.

5. Clothing (10) according to one of the preceding claims, characterized in that the binding threads always run in pairs beside one another in the clothing cross direction (CD), wherein said binding threads, preferably in an alternating manner, continue a weaving pattern on the web material contact side.

6. Clothing (10) according to one of the preceding claims, characterized in that the first woven-fabric layer (L1) has a plain weave.

7. Clothing (10) according to one of Claims 1 to 5, characterized in that the first woven-fabric layer (L1) has a twill weave, in particular a 2 / 1 twill weave, or a 3 / 1 twill weave, preferably a broken or an interrupted twill weave.

8. Clothing (10) according to one of the preceding claims, characterized in that the second woven-fabric layer (L2) has a non-interrupted twill weave.

9. Clothing according to one of Claims 1 to 7, characterized in that the second woven-fabric layer (L2) has an interrupted twill weave.

10. Clothing (10) according to one of the preceding claims, characterized in that two neighboring contact flotations (KF1, KF2, KF3) of a second transverse thread (QF2) are mutually separated by at most two second longitudinal threads (LF2).

11. Clothing (10) according to Claim 10, characterized in that two neighboring contact flotations (KF1, KF2, KF3) of a second transverse thread (QF2) are always in each case mutually separated by only one second longitudinal thread (LF2).

12. Use of a clothing (10) according to one of the preceding claims for producing a tissue web, wherein the tissue web preferably has a specific area weight between 8 g / m2 and 30 g / m2.