Basic Structure and Covering

This application is a continuation, under 35 U.S.C. § 120, of copending International Patent Application PCT/EP2023/086017, filed Dec. 15, 2023, which designated the United States; this application also claims the priority, under 35 U.S.C. § 119, of German Patent Application DE 10 2022 134 296.4, filed December 21. 2022; the prior applications are herewith incorporated by reference in their entirety.

The invention relates to a basic structure for a covering, in particular a press felt for a machine for producing a fiber web, including a first ply having first MD (Machine Direction) yarns and first CD (Cross-Machine Direction) yarns and a second ply having second MD yarns and second CD yarns, wherein the first ply is disposed above the second ply. The invention also relates to a covering using such a basic structure.

Various coverings are utilized in the production of fiber webs, such as, for example, paper, cardboard, or cellulose webs. In that regard, press felts in particular are commonly constructed such that they have a basic structure, which is usually load-carrying, to which further functional layers, such as, for example, non-woven layers, may be fastened. In that regard, woven basic structures are the most widespread.

In many applications, it is desirable for the basic structure to have properties, for example with respect to its storage volume, which cannot be readily achieved by a single ply. In those cases, the basic structures are produced from several fabrics which are disposed one above the other.

In that regard, to produce the woven basic structures, one or more continuous fabric loops are needed. For a long time, those fabric loops were manufactured exclusively as continuous circular-woven fabrics. Recently, however, structures have also been utilized in which flat-woven fabrics are used which are rendered continuous by connecting the front edges. Such a basic structure is described, for example, in European Patent Application EP 3 960 932 A1, corresponding to U.S. Pat. No. 11, 834,789 B2.

When utilized in basic structures, circular-woven fabrics and flat-woven fabrics have their specific advantages and disadvantages. As an example, circular-woven fabrics have high tensile strength, as well as high uniformity due to the absence of seam or connection points. However, their production is very complex due to the more elaborate weaving process. In addition, the exact length of the later covering must already be known during the weaving process.

In comparison, flat-woven fabrics are very quick and inexpensive to produce. In addition, they may be produced as rolled goods, which are then correspondingly finished for the covering needed. For that purpose, the connection points naturally constitute potential weak points which may become visible as marks in the fiber web.

It is accordingly an object of the invention to provide a basic structure and a covering, which overcome the hereinafore-mentioned disadvantages of the heretofore-known basic structures and coverings of this general type and which further improve the known multi-layer coverings.

With the foregoing and other objects in view there is provided, in accordance with the invention, a basic structure for a covering, in particular a press felt for a machine for producing a fiber 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 density of the first CD yarns is greater than the yarn density of the second CD yarns.

With the objects of the invention in view, there is concomitantly provided a covering, in particular a press felt for a machine for producing a fiber web, the covering comprising the basic structure according to the invention.

Further advantageous embodiments of the present invention can be found in the dependent claims.

In this regard, a ply is referred to as being “above” another ply if, when used as intended, it is disposed closer to the paper-contacting top side of the covering. In this regard, it is possible in particular for this ply to be disposed “directly above” the other ply and for the two plies to come into contact completely or partially. Alternatively, it may also be provided that other constituents of the basic structure, e.g., non-woven layers, films, or even further plies, etc., are disposed between the two plies.

In the case of CD yarns with a circular cross-section, their diameter is clearly determinable as the circular diameter.

In the case of CD yarns which do not have a circular cross-section and in the case of the use of twisted CD yarns, a “hypothetical diameter” is to be used as the diameter within the scope of this application. This hypothetical diameter corresponds to the diameter of a circle which has the same surface area as the cross-sectional area of the yarn or the sum of the cross-sectional areas of the filaments of the twist.

As an example, according to this definition, for a twist of 4 filaments with a diameter d=2r, the hypothetical diameter D is calculated as:

If, within the scope of this application, the diameters of the first CD yarns are cited to be smaller than the diameters of the second CD yarns, then this should be understood to mean that the diameters of all of the first CD yarns are smaller than the diameters of all of the second CD yarns. This criterion should also be considered to be met if individual CD yarns, which in sum, however, account for less than 5% of the CD yarns, violate this criterion.

This may occur, for example, by providing individual very thick CD yarns in the first ply or a few very thin CD yarns in the second ply to be able to adapt the properties of the covering (such as, e.g., fiber anchoring or permeability), for example, in the case of seam felts in the region of the seam.

In preferred embodiments, it may be provided that the first ply and the second ply are not interwoven. The two plies are then not layers of a multi-layer fabric, but 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 both the diameters and the yarn densities of the two layers thereby may be varied independently of one another and may be adapted to the requirements.

In this regard, the yarn density is defined as the number of yarns per unit of length.

Advantageously, it may be provided that the diameter of the first CD yarns is a maximum of 90% of the diameter of the second CD yarns.

Moreover, it may be advantageous if the yarn density of the first CD yarns 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 yarn density of the second CD yarns. Alternatively or additionally, it may be provided that the yarn density of the first CD yarns is a maximum of 80%, in particular a maximum of 60%, higher than the yarn density of the second CD yarns.

A further advantage of the different yarn densities of the two layers is that the Moiré effect may be suppressed thereby. In this regard, a difference of less than 3% often does not ensure sufficient suppression of the Moiré effect.

In this regard, the yarn density of the first CD yarns may be between 20 and 200 yarns/10 cm, preferably between 50 and 100 yarns/10 cm.

Nowadays, in the case of multi-layer basic structures, the various layers are commonly produced from the same fabric.

In the case of circular-woven fabrics, the CD yarns of the basic structure are the warp yarns of the loom. Since switching the warp system is very complex and entails a long standstill of the loom, a short-term change of the CD yarns is hardly possible in the case of circular-woven fabrics.

When flat-woven fabrics are used, as shown, e.g., in European Patent Application EP 3 960 932 A1, corresponding to U.S. Pat. No. 11, 834,789 B2, there is the advantage that the CD yarns of the basic structure are the weft yarns of the loom. Switching the weft yarns is much easier to realize than switching the warp system. However, a great advantage of the use of flat-woven fabrics is precisely that these fabrics may be pre-produced onto a roll independently of the dimension of the later covering and may then be cut off from this roll in the amount needed. If different CD yarns are used for the various plies, this advantage is lost. Thus, utilizing identical plies appears to be necessary even when flat-woven fabrics are used.

However, the inventor has now recognized that, by using a specific adaptation of the CD yarn structures, advantages in the covering, in particular in press felts, may be achieved which exceed these disadvantages.

The smaller diameter of the CD yarns and the higher yarn density in the first layer lead to an increase in the number of contact points, finer structuring, and lower roughness.

This causes an improved and more homogeneous pressure distribution of the ply onto a non-woven layer disposed above it and, as a result, ultimately onto the paper web. Reduced marking tendency may also be observed.

In particular, it may be advantageous herein if the basic structure does not have any further plies above the first ply.

In the lower ply, utilizing coarser CD yarns and reduced yarn densities leads to a more open structure and enables a fabric configuration with increased permeability towards the running side, which in particular enables felts with an improved dewatering performance.

In addition, the structures which are more open towards the running side may reduce soiling tendency.

Finally, the coarser CD yarns in the second ply may also improve the wear properties of the basic structure.

In particular, it may be advantageous herein if the basic structure does not have any further plies below the second ply.

A further advantage of basic structures according to aspects of the invention is that the anchoring of non-woven fibers is improved compared to identical plies.

In principle, both the first ply and the second ply may be in the form of a circular-woven fabric. However, this is quite complex since different warp systems have to be used for this purpose, as described.

Therefore, the invention is particularly advantageous if the first ply and/or the second ply include or are formed of a flat-woven fabric.

Here, various embodiments are possible:

One ply is a circular-woven fabric, the other ply is formed of a flat-woven fabric. Since the CD yarns of the circular-woven fabric are difficult to change, the ratio of the yarn diameters and yarn densities is expediently adjusted via the flat-woven fabric.

In this regard, the hybrid structure may be in such a form that the first ply is in the form of a circular-woven fabric, whereby the connection point of the front edges is shielded from the paper side by the circular-woven fabric. This may be advantageous if the type of paper to be produced is very susceptible to these seam marks.

Alternatively, the hybrid structure may also be in such a form that the first ply is in the form of a flat-woven fabric.

2.) Continuous Structure made of Two Flat-Woven Fabrics:

Such structures are described, for example, in European Patent Application EP 3 960 932 A1, corresponding to U.S. Pat. No. 11, 834,789 B2. In this regard, both the first ply and the second ply each are formed of one separate flat-woven fabric, which is rendered continuous by connecting the front edges.

Herein, by folding and depositing on top of one another, a single flat-woven fabric becomes a two-layer structure having seam loops at the two folding points. In this basic structure, the first ply and the second ply are part of a single flat-woven fabric. Although the two plies are connected to one another at the folding points in this case, they are not interwoven for the purposes of this application. The ratio of yarn diameters and yarn densities according to the invention may be achieved by suitably switching the CD yarns at the later folding points.

Such a structure is described in European Patent EP 2 198 083 B1, corresponding to U.S. Pat. No. 7,892,402 B2.

Applicant's International Publication WO 2021/028116 A1, corresponding to U.S. Pat. No. 11,952,717 B2, shows a development of this technology in which the basic structure is not formed of a single piece of flat-woven fabric but of several flat-woven fabrics disposed one behind the other, two of which are in the form of loop elements.

All of these structures are suitable to be used for a basic structure according to aspects of the invention.

Often, all of the first CD yarns will be identical and/or all of the second CD yarns will be identical.

Alternatively, it may also be provided that different yarns are used for the first CD yarns and/or the second CD yarns. In this regard, for example, CD yarns with different diameters may be used.

Moreover, it may be advantageous, for example, if both filaments and twists are used as the first CD yarns in the first ply and/or as the second CD yarns in the second ply. In particular, they may also be disposed alternately so that twist/filament/twist/filament are disposed in a constantly alternating manner. Different ratios of twists to monofilaments may be provided, such as, e.g., 3:1, 2:1; 3:2, 1:1, 2:3, 1:2, or 1:3. It has been found that such an alternate arrangement of filaments and twists, especially in the first ply, may significantly improve the fiber anchoring of non-woven fibers.