Basic structure and covering

Abstract

The invention relates to a basic structure for a covering, in particular a press felt for a machine for producing a fibre web, comprising a first ply having first MD yarns and first CD yarns and a second ply having second MD yarns and second CD yarns, wherein the first ply is disposed above the second ply. The first CD yarns have a smaller diameter than the second CD yarns and the yarn thickness of the first CD yarns is greater than the yarn thickness of the second CD yarns.

Description

[0001] Basic structure and covering

[0002] The invention relates to a basic structure for a covering according to the preamble of claim 1 and to a covering using such a basic structure.

[0003] Various fabrics are used in the production of fibrous webs such as paper, cardboard, or pulp. Press felts, in particular, are typically constructed with a base structure—usually a load-bearing structure—to which additional functional layers, such as nonwoven layers, can be attached. Woven base structures are the most common.

[0004] In many applications, it is desirable for the base structure to have properties—for example, with regard to its storage volume—that cannot easily be achieved with a single layer of fabric. In these cases, the base structures are manufactured from several fabrics arranged one above the other.

[0005] To produce the woven base structures, one or more endless fabric loops are required. For a long time, these fabric loops were manufactured exclusively as endless circular fabrics. Recently, however, structures have also been used that utilize flat fabrics made endless by joining the front edges. One such basic structure is described, for example, in EP 3 960 932 A1.

[0006] Round woven fabrics and flat woven fabrics have their specific advantages and disadvantages when used in basic structures. Round woven fabrics exhibit high tensile strength and a high degree of uniformity due to the lack of seams or joints. However, their production is very complex due to the more complex weaving process. Furthermore, the exact length of the subsequent covering must be known during the weaving process. Flat woven fabrics, on the other hand, are very quick and inexpensive to produce. They can also be manufactured as rolls, which are then cut to size for the required covering. However, the joints naturally represent potential weak points, which can become visible as markings in the fiber web.

[0007] The object of the invention is to further improve the known multi-layer coverings.

[0008] The problem is completely solved by a basic structure according to the characterizing part of claim 1 and a covering according to claim 14.

[0009] Further advantageous embodiments of the present invention can be found in the subclaims.

[0010] A basic structure for a clothing, in particular a press felt for a machine for producing a fibrous web, comprising a first fabric layer with first MD threads and first CD threads and a second fabric layer with second MD threads and second CD threads, wherein the first fabric layer is arranged above the second fabric layer.

[0011] According to the invention, it is provided that the first CD threads have a smaller diameter than the second CD threads and the thread density of the first CD threads is higher than the thread density of the second CD threads.

[0012] A fabric layer is referred to as 'above' another fabric layer if, when used as intended, it is arranged closer to the paper-contacting upper side of the covering. It is particularly possible for this fabric layer to be arranged 'directly above' the other fabric layer, and for the two fabric layers to touch each other completely or partially. Alternatively, it can also be provided that other components of the basic structure, e.g., nonwoven layers, films, or even further fabric layers, etc., are arranged between the two fabric layers. In the case of CD threads with a circular cross-section, their diameter can be clearly determined as a circle diameter.

[0013] For CD threads that do not have a circular cross-section, as well as for the use of twisted CD threads, a "fictitious diameter" shall be used as the diameter for the purposes of this application. This fictitious diameter corresponds to the diameter of a circle with the same area as the cross-sectional area of ​​the thread, or the sum of the cross-sectional areas of the filaments of the twisted yarn.

[0014] According to this definition, the fictitious diameter D for a thread made of 4 filaments with a diameter d=2r is calculated:

[0015] Cross-sectional area of ​​a filament Ar=r 2 * TT

[0016] Cross-sectional area of ​​four filaments = 4 Ar = 4 r 2 * TT = (2 r) 2 TT Fictitious diameter D = 2d = 4r

[0017] When this application states that the diameters of the first CD threads are smaller than the diameters of the second CD threads, this should be understood to mean that the diameters of all first CD threads are smaller than the diameters of all second CD threads. This criterion should be considered met even if individual CD threads, which in total constitute less than 5% of the CD threads, violate this criterion.

[0018] This can be achieved, for example, by providing individual very thick CD threads in the first fabric layer or individual very thin CD threads in the second fabric layer in order to be able to adapt the properties of the covering (such as fiber anchoring or permeability) in the region of the seam, for example in the case of seam felts.

[0019] In preferred embodiments, the first fabric layer and the second fabric layer may not be woven together. The two fabric layers are then not layers of a multi-layer fabric, but rather form a laminate of two largely independent layers. This is very advantageous for basic structures according to aspects of the present invention, among other things, because it allows both the diameters and the thread density of the two layers to be varied independently of one another and adapted to requirements.

[0020] The thread density is defined as the number of threads per unit length.

[0021] Advantageously, it can be provided that the diameter of the first CD threads is a maximum of 90% of the diameter of the second CD threads.

[0022] Furthermore, it may be advantageous if the thread density of the first CD threads is at least 3%, in particular at least 5% or at least 10%, in particular at least 15%, preferably at least 20% higher than the thread density of the second CD threads. Alternatively or additionally, the thread density of the first CD threads may be a maximum of 80%, in particular a maximum of 60%, higher than the thread density of the second CD threads.

[0023] Another advantage of the different thread densities of the two layers is that it can suppress the moiré effect. A difference of less than 3% often does not guarantee sufficient suppression of the moiré effect.

[0024] The thread density of the first CD threads can be between 20 and 200 threads / 10cm, preferably between 50 and 100 threads / 10cm.

[0025] Today, in multi-layer basic structures, the different layers are usually made from the same fabric.

[0026] In circular weaves, the CD threads of the basic structure are the loom's warp threads. Since changing the warp system is very complex and requires a long downtime of the loom, a quick change of the CD threads is hardly possible in circular weaves.

[0027] When using flat woven fabrics—as shown, for example, in EP 3 960 932 A1—there is the advantage that the CD threads of the basic structure are the weft threads of the loom. Changing the weft threads is significantly easier than changing the warp system. However, a major advantage of using flat woven fabrics is that these fabrics can be pre-produced on a roll, regardless of the dimensions of the subsequent covering, and then cut from this roll in the required quantity. If different CD threads are used for the different fabric layers, this advantage is lost. Therefore, the use of similar fabric layers also seems advisable when using flat woven fabrics.

[0028] However, the inventor has now recognized that by specifically adapting the CD thread structures, advantages in the clothing, especially in press felts, can be achieved that outweigh these disadvantages.

[0029] The smaller diameter of the CD threads and the higher thread density in the first layer lead to an increase in the number of contact points, a finer structure and a lower roughness.

[0030] This results in an improved and more homogeneous pressure distribution of the fabric layer onto the nonwoven layer above it, and thus ultimately onto the paper web. A reduced tendency to mark can also be observed.

[0031] In particular, it can be advantageous if the basic structure does not have any further fabric layers above the first fabric layer.

[0032] In the lower fabric layer, the use of coarser CD threads and reduced thread density leads to a more open structure and enables a fabric construction with increased permeability towards the running side, which in particular enables felts with improved dewatering performance.

[0033] In addition, the structures that are more open towards the running side can reduce the tendency to become dirty.

[0034] Finally, coarser CD threads in the second fabric layer can also improve the wear properties of the base structure. It can be particularly advantageous if the base structure has no further fabric layers below the second fabric layer.

[0035] A further advantage of basic structures according to aspects of the invention is that the anchoring of nonwoven fibers is improved compared to identical fabric layers.

[0036] In principle, both the first and second fabric layers can be made of circular weave. However, this is quite complex, as different warp systems must be used, as described above.

[0037] Therefore, the invention is particularly advantageous if the first fabric layer and / or the second fabric layer comprises or consists of a flat fabric.

[0038] Various versions are possible here:

[0039] 1.) Hybrid basic structure: One fabric layer is a round fabric, the other

[0040] The fabric layer consists of a flat weave. Since the CD threads of the round weave are difficult to adjust, the ratio of thread diameters and thread densities is conveniently adjusted via the flat weave.

[0041] The hybrid structure can be designed in such a way that the first fabric layer is a circular weave, shielding the connection point of the front edges from the paper side by the circular weave. This can be advantageous if the paper grade to be produced is highly susceptible to these seam marks.

[0042] Alternatively, the hybrid structure can also be designed in such a way that the first fabric layer is designed as a flat fabric.

[0043] 2.) Endless structure made of two flat fabrics.

[0044] Such structures are described, for example, in EP 3 960 932 A1. Both the first fabric layer and the second fabric layer each consist of a separate flat fabric, which is made endless by joining the front edges.

[0045] 3.) Seam structure

[0046] In this case, a single flat fabric is folded and stacked to form a two-layer structure with seam loops at the two folds. The first fabric layer and the second fabric layer in this basic structure are part of a single flat fabric. Although the two fabric layers are connected to each other at the folds, they are not interwoven within the meaning of this application. By appropriately alternating the CD threads at the subsequent folds, the ratio of thread diameter to thread density according to the invention can be achieved.

[0047] Such a structure is described in document EP2198083 B1.

[0048] The applicant's document WO21028116 A1 shows a further development of this technology, in which the basic structure does not consist of a single piece of flat fabric, but of several flat fabrics arranged one behind the other, two of which are designed as loop elements.

[0049] All of these structures are suitable for use as a basic structure according to aspects of the invention.

[0050] Often all first CD threads will be identical and / or all second CD threads will be identical.

[0051] Alternatively, different threads can be used for the first CD threads and / or the second CD threads. For example, CD threads with different diameters can be used.

[0052] Furthermore, it can be advantageous, for example, if both filaments and twisted yarns are used as first CD threads in the first fabric layer and / or as second CD threads in the second fabric layer. These can, in particular, also be arranged alternately, so that twist-filament-twist-filament are always arranged alternately. Different ratios of twisted yarns to monofilaments can be provided, such as 3:1, 2:1; 3:2, 1:1, 2:3, 1:2 or 1:3. It has been shown that such an alternating arrangement of filaments and twisted yarns, especially in the first fabric layer, can significantly improve the fiber anchoring of nonwoven fibers.

[0053] It can be particularly advantageous if the first and second layers have the same ratio of thread and monofilaments, for example 2:1.

[0054] A variety of structures are possible for the MD threads of the two fabric layers. While the MD threads can also be twisted, it is often advantageous for all MD threads of the two fabric layers to be filaments.

[0055] The MD threads of the first fabric layer and / or the second fabric layer can in particular have a diameter between 0.2 mm and 1 mm

[0056] The MD thread density of the first fabric layer and / or the second fabric layer can be between 20 and 200 threads per 10 cm.

[0057] It can be provided that the first fabric layer and the second fabric layer have the same MD threads or at least the MD threads that have substantially the same thread cross-section.

[0058] In advantageous embodiments, it can be provided that the diameter of the MD threads of the first fabric layer and / or the second fabric layer is between 0.24 mm and 0.6 mm, preferably between 0.3 mm and 0.5 mm.

[0059] The advantage of a two-layer base structure, in contrast to single-layer structures, is that the MD threads of both layers contribute to absorbing tensile forces in the MD direction. This allows the MD threads of the individual layers to be kept thinner, and in particular to have diameters of 0.6 mm, 0.5 mm, or less. Furthermore, MD threads with diameters over 0.6 mm impart greater rigidity to the base structure, which makes handling the structure more difficult during further processing, e.g., into felt, and during later use. However, particularly with regard to the designs described under "3.) Seam structure," it can also be advantageous not to choose a thread diameter that is too thin for the MD threads, since forming the seam loops and later threading a pintle through them is difficult with MD threads that are too thin. An MD thread diameter of at least 0.24 mm, or even better, at least 0.3 mm, has proven advantageous here.

[0060] Alternatively, it can be provided that the first fabric layer and the second fabric layer have different MD threads.

[0061] The invention is explained in more detail below using three examples. The invention is not limited to these examples.

[0062] Example 1:

[0063] In this example, the diameter of the first CD threads is approximately 78% of the diameter of the second CD threads (0.35 / 0.45 *100 ~ 77.8)

[0064] The CD thread density of the first fabric layer is approximately 23% greater than the CD thread density of the second fabric layer (85 / 69 ~ 1.23).

[0065] Example 2:

[0066] In this example, both the first CD threads and the second CD threads are made as twisted yarns.

[0067] As described, the diameter of a thread is to be determined using the cross-sectional area of ​​the individual filaments:

[0068] • A filament with a diameter of 0.2 mm has a cross-sectional area of ​​approximately 0.03142 mm 2 on.

[0069] • The three filaments of the first fabric layer therefore have a cross-sectional area of ​​3 x 0.03142 = 0.09426 mm 2 on.

[0070] • The cross-sectional area of ​​0.09426 mm 2 corresponds to a circle with a diameter of approximately 0.346 mm (=fictitious diameter of the first CD threads)

[0071] • Analogously, the fictitious diameter of the second CD thread is 0.4 mm

[0072] • Thus, the (fictitious) diameter of the first CD threads is approximately 86.6% of the (fictitious) diameter of the second CD threads.

[0073] Example 3:

[0074] In this example, the system of first CD threads consists of different threads. Both a 0.35 mm filament and a 0.2 mm x 3 thread are provided here, which are woven alternately, for example. Since the notional diameter of the second CD threads is 0.4 mm, as shown, the (notional / real) diameters of all first CD threads (0.35 mm and 0.346 mm) are smaller than the notional diameter of the second CD threads. Furthermore, the invention relates to a clothing, in particular a press felt for a machine for producing a fibrous web, wherein the clothing has a basic structure according to one aspect of the invention.

[0075] The covering can also be made of seam felt.

[0076] To produce a press felt, one or more layers of nonwoven fibers are usually arranged on the top side of the covering - and possibly also on the underside of the covering - and are attached by needling.

Claims

Patent claims 1 . Basic structure for a clothing, in particular a press felt for a machine for producing a fibrous web, comprising a first fabric layer with first MD threads and first CD threads and a second fabric layer with second MD threads and second CD threads, wherein the first fabric layer is arranged above the second fabric layer, characterized in that the first CD threads have a smaller diameter than the second CD threads and the thread density of the first CD threads is higher than the thread density of the second CD threads.

2. Basic structure according to claim 1, characterized in that the first fabric layer and the second fabric layer are not woven together.

3. Basic structure according to one of the preceding claims, characterized in that the diameter of the first CD threads is a maximum of 90% of the diameter of the second CD threads.

4. Basic structure according to one of the preceding claims, characterized in that the thread density of the first CD threads is at least 3%, in particular at least 10%, preferably at least 15% higher than the thread density of the second CD threads.

5. Basic structure according to one of the preceding claims, characterized in that the basic structure has no further fabric layers above the first fabric layer.

6. Basic structure according to one of the preceding claims, characterized in that the basic structure has no further fabric layers below the second fabric layer.

7. Basic structure according to one of the preceding claims, characterized in that the first fabric layer and / or the second fabric layer comprises or consists of a flat fabric.

8. Basic structure according to one of the preceding claims, characterized in that all first CD threads and / or all second CD threads are identical.

9. Basic structure according to one of the preceding claims, characterized in that the first CD threads consist of different threads and / or the second CD threads consist of different threads.

10. Basic structure according to claim 9, characterized in that both filaments and twisted yarns are used as first CD threads and / or as second CD threads 11. Basic structure according to claim 10, characterized in that in the first fabric layer and / or the second fabric layer the ratio of twisted yarns to monofilaments is 3:1, 2:1, 3:2, 1:1, 2:3, 1:2 or 1:

3.

12. Basic structure according to one of the preceding claims, characterized in that the first fabric layer and the second fabric layer have the same MD threads or at least the MD threads which have substantially the same thread cross-section.

13. Basic structure according to one of the preceding claims, characterized in that the diameter of the MD threads of the first fabric layer and / or the second fabric layer is between 0.24 mm and 0.6 mm, preferably between 0.3 mm and 0.5 mm.

14. Clothing, in particular press felt for a machine for producing a fibrous web, characterized in that the clothing has a basic structure according to one of the preceding claims.

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