EP0030490A1 - Double-ply fabrics for paper machines - Google Patents

Abstract

A double layer forming fabric for use in a paper-making machine has a warp ratio of at least six strands and a shute ratio of at least twelve strands. The warp strands bind with the lower layer at locations distributed according to a satin weave pattern whose ratio is equal to the warp ratio; the warp strands bind with the upper layer at locations distributed according to a pattern whose aggregated ratio is equal to the warp ratio and which is constituted by the association of several weave patterns each having a warp ratio lower to 6 strands. There are at least two shute strands of the upper layer between two successive points where a warp strand comes down from the paper contacting face across the upper layer and then comes up again, respectively.

Description

The invention relates to forming fabrics for paper machines, of the type commonly called "double layer" comprising two layers of weft yarns and one layer of warp threads and having a warp ratio of at least 6 threads (US-A -4 171 009). The term "paper machine" is to be interpreted in a broad sense, as encompassing any machine for making sheets of paper pulp, cellulose for paper pulp, paper itself, kraft or cardboard and non-woven woven on a dry or wet table; moreover, the invention applies whether the sheet is formed on an endless fabric, between two endless fabrics or between an endless fabric and cylinders.

It is known that several types of fabrics are used on paper machines: they are generally designated, in the paper industry, by the names "single layer", "double layer" and "triple layer". Single layer fabrics include a single layer of longitudinal wires and a single layer of transverse wires; double layer fabrics have a single layer of warp thread binding, by weaving, two layers of weft thread, more or less superimposed in pairs and having the same number of transverse threads per unit length in the upper layer (on the side where the canvas supports the paper) and in the lower layer (on the side where the canvas is in contact with the elements of the paper machine). In general, these fabrics are woven flat, then joined together, so that the warp threads constitute the longitudinal threads on the paper machine. Triple-layer fabrics use two layers of longitudinal threads which are distinguished from one another, in particular by their evolution in the fabric: one of the layers evolves mainly on the paper side, the other mainly on the machine side. In addition, the two layers generally differ from one another, for example by the diameter of the threads which constitute them, their nature, the number of threads per unit of width and the embuvage in weaving.

Double-layer fabrics have many advantages over single-layer fabrics, including higher stiffness and longer life. They tend, for many applications, to replace single-layer fabrics. On the other hand, triple-layer fabrics are little used, because the presence in the fabric of two kinds of staple threads evolving in a different way considerably complicates weaving and requires looms with at least two beams.

It is also known that the threads constituting a canvas for a paper machine can be metallic or made of plastic. Plastic fabrics have a longer lifespan than metallic fabrics, due to the better resistance of plastic bristles to abrasion. But different weaving weaves must be adopted, given the flexibility of the plastic hairs and they result in a mark on the paper distinctly different from that produced by the metallic fabrics and which is not acceptable for certain types of paper, especially those intended for rotogravure printing.

The present invention aims to provide a plastic fabric that better meets those previously known to the requirements of practice, in particular in that it combines the favorable characteristics of conventional double layer fabrics, in particular a long service life on the machine and a low brittleness. the sinking, with the weak mark which has so far been the prerogative of the metallic fabrics.

To this end, the invention proposes in particular a double layer canvas of the kind defined above having an overall weft ratio of at least 12 threads, in which: the bonding points of the warp threads with the lower layer (intended to be placed on the machine side) are distributed in a satin whose ratio is equal to the overall chain ratio; the binding points with the weft threads of the upper layer (intended to be placed on the paper side) have a ratio equal to the overall warp ratio, but constituted by the juxtaposition of two or three weaves with ratio in a chain less than 6; and between each place where a warp thread descends through the upper layer and that where it goes up further through this same layer, there are at least two weft threads of the upper layer.

The term "overall warp ratio" denotes above the number of yarns of the smallest group of warp yarns the evolution of which is repeated in an identical manner in the weft direction, while the "overall weft ratio" is the corresponding number of wefts in the warp direction. The term "chain ratio", when applied to the tying points, designates the number of threads of the smallest group of chain threads for which the tying points are repeated in the form of identical patterns.

This arrangement makes it possible to fully preserve the advantages of known double-layer fabrics having high overall warp and weft ratios, in particular the increased longevity due to the presence, on the machine side, of protruding weft threads and forming long floats, while having a weak mark, which these same previous fabrics did not allow which incorporated, paper side, ties distributed in the form of regular or irregular satins with high ratio. It can be seen that, in the fabric according to the invention, a distribution of the binding stitches is maintained according to a satin pattern, with large weft floats, on the machine side, while, on the paper side, there are a large number of simple binding points which constitute as many points of contact between the canvas and the sheet of paper. The fact that there are at least two weft threads of the upper layer between the place where the same warp thread descends from the face on the paper side, then rises again towards this face, ensures a good distribution of the binding points warp yarns with the weft yarns of the upper layer and reduces to a permissible value the level difference between the warp yarn loops and the weft yarn loops, paper side. This result is obtained even more completely by limiting the float of the weft threads to four warp threads paper side to prevent them from being pushed too strongly towards the outside of the canvas on this side and have a projection which would lead to an unacceptable mark.

• - sergéde trois, de quatre ou de cinq,
• - croisé de deux et deux, ou deux et trois,
• - satin de quatre irrégulier, dit satin turc, ou satin de cinq régulier.

As examples of weaves usable on the paper side and having a warp ratio of less than 6, the following may be mentioned in particular, which will be combined so that their juxtaposition corresponds to the cumulative ratios of the binding points with the weft yarns of the upper layer:

• - sergee of three, four or five,
• - cross of two and two, or two and three,
• - irregular four satin, said Turkish satin, or regular five satin.

An overall chain ratio of 8 threads seems, at present, to constitute the most satisfactory compromise between a high ratio, favorable to a high resistance of the fabric, on the one hand, the ease of manufacture and the use of 'a trade that does not have an excessive number of harnesses, on the other hand.

In all cases, it will be noted that the canvas can be produced with a conventional weaving loom comprising a single beam, by techniques well mastered at the present time.

As in the case of conventional double-layer fabrics, such as for example those described in US-A-4 171 009 to which reference may be made, the longitudinal and transverse threads are chosen from the group consisting of multi- threads. synthetic filament and monofilament, used alone or in combination with metallic threads; the wires may or may not be coated or sheathed. They can all be identical in the same canvas or combined. As for the filling coefficient of the warp threads, it will generally be 1.05 at least. Finally, although it is generally advantageous to. constitute the fabrics according to the invention by flat weaving, then joining together, the weft threads then being the transverse threads in the machine direction, it is also possible, in particular for certain fabrications, to carry out the endless canvas by circular weaving, which avoids the need for a later joining.

• - la figure la est une représentation schématique des armures de liage des fils de chaîne et des fils de trame d'une première toile,
• - la figure lb montre schématiquement les liages entre un fil de chaine et les fils de trame des deux couches dans une toile suivant la figure la,
• - la figure 2, similaire à la figure 1, illustre une condition à remplir pour réduire la marque de la toile sur le papier,
• - la figure 3, similaire à la figure la, montre une autre toile suivant l'invention,
• - les figures 4a et 4b, similaires aux figures la et lb, montrent un autre mode de mise en oeuvre,
• - les figures 5 à 9, similaires à la figure la, montrent d'autres modes de mise en oeuvre encore.

The invention will be better understood on reading the following description of particular embodiments given by way of nonlimiting examples. The description refers to the accompanying drawings, in which:

• FIG. 1a is a schematic representation of the weaving armor of the warp threads and the weft threads of a first fabric,
• FIG. 1b schematically shows the bindings between a warp yarn and the weft yarns of the two layers in a fabric according to FIG.
• FIG. 2, similar to FIG. 1, illustrates a condition to be fulfilled in order to reduce the mark of the canvas on the paper,
• FIG. 3, similar to FIG. 1a, shows another canvas according to the invention,
• FIGS. 4a and 4b, similar to FIGS. 1a and 1b, show another mode of implementation,
• - Figures 5 to 9, similar to Figure la, show yet other modes of implementation.

• - aucun signe n'est marqué si le fil de chaine passe entre les deux nappes de fils de trame superposés,
• - une croix " X " est marquée si le fil de chaine passe au-dessus de la nappe supérieure de fils de trame, formant le liage avec la couche supérieure des fils de trame,
• - un cercle " 0 " est marqué si le fil de chaine passe au-dessous de la nappe inférieure de fils de trame, formant un point de liage avec la couche inférieure de fils de trame.

In all the figures showing the armor diagrammatically, the warp threads and the pairs of superimposed weft threads are represented by solid lines. At each crossing of the warp and weft threads,

• - no sign is marked if the warp thread passes between the two layers of superimposed weft threads,
• - a cross "X" is marked if the warp thread passes over the upper ply of weft threads, forming the bond with the upper layer of the weft threads,
• - a circle "0" is marked if the warp thread passes below the lower ply of weft threads, forming a bonding point with the lower layer of weft threads.

In the embodiment shown in FIGS. 1a and 1b, the bonding points of the lower layer of weft threads 10 with the warp threads 11 are arranged in an irregular satin six, while the points for bonding the weft threads 12 of the upper layer with the warp threads 11 are distributed in two twills of three juxtaposed (chain ratio of three) leading to a cumulative chain ratio of 6. FIG. 1b clearly shows that there is, on the machine side, a chain ratio of 6 with a single binding point, hence the presence of large floats on the weft threads 10 in contact with the elements of the machine. On the paper side, it can be seen that the high number of simple tying points between warp threads 11 and weft threads 12 multiplies the points of contact between the sheet of paper and the canvas.

As indicated above, the difference in level D (Figure 2) between the warp yarn loops 11 and the weft yarn loops 12 should be as small as possible to reduce the mark. In practice, the permissible level difference D generally does not exceed 0.02 mm. This result is achieved, in the case illustrated in FIGS. 1 a and 1 b, because the weft floats on the paper side cover only two warp threads, so that they are not pushed too strongly towards the outside of the side canvas. paper. It can also be seen, in FIGS. 1b and 2, that two weft threads 12 of the upper layer are interposed between the place where a warp thread 11 descends from the face on the paper side and that where it goes up towards this face. In practice, this number of two wires will constitute a minimum. It is possible to provide more threads from the upper layer, it being understood that the warp thread can trap only weft threads 12 from the upper layer, as shown in FIG. 2, or also trap threads 10 from the lower layer, in particular when a number of weft threads 12 greater than two is interposed between the point of descent and the point of rise of the warp thread 11.

In the embodiment shown in Figure 3 (where the elements corresponding to those of Figure la are designated by the same reference number), the overall chain ratio is 7, while the overall ratio we trim is fourteen. The weft threads 12 of the upper layer are linked to the warp threads 11 in a twill of three plus a twill of four juxtaposed, which leads to a cumulative warp ratio of seven. The weft threads 10 of the lower layer are linked to the warp threads 11 following an irregular satin of seven.

The embodiment illustrated in Figures 4a and 4b belongs to the group of those who seem to constitute the most favorable compromise between the simplicity of the looms and the ease of weaving (which implies a number of harnesses as low as possible in the loom and an even ratio ) and a high ratio, which allows both long floats on the machine side and a paper side split into several weaves with low overall chain ratio. The fabric shown in FIGS. 4a and 4b has an overall warp ratio of 8. The links of the warp threads 11 with the weft threads 12 of the upper layer are carried out in two twills of four juxtaposes, leading to a warp ratio cumulative of 8. The weft threads 10 of the lower layer are linked to the warp threads 11 according to a regular satin of eight, with a notch of 5.

FIG. 5 shows a fabric the overall warp ratio of which is still 8. The weft threads 12 of the upper layer are linked to the warp threads 11 in two satins of four irregular or juxtaposed Turkish satin. The weft threads 10 of the lower layer are linked to the warp threads according to a regular satin of eight with a notch of ₃ .

In the embodiment of FIG. 6, the weft threads 12 of the upper layer are linked to the warp threads 11 in a twill of five and a twill of four juxtaposed, which leads to a cumulative warp ratio of 9. The weft threads 10 of the lower layer are linked to the warp threads according to an irregular satin new.

In the case of FIG. 7, the weft threads 12 of the upper layer are linked to the warp threads in three twills of three juxtaposed, leading to a cumulative warp ratio of 9. The weft threads 10 of the lower layer are linked to the warp threads 11 following a satin of 9 regular with release 4.

In the case of FIG. 8, the weft threads 12 of the upper layer are linked to the warp threads in two twills of 5 juxtaposed, leading to a cumulative warp ratio of 10. The weft threads 10 of the lower layer are linked to the warp threads 11 following a satin of 10 irregulars with alternating recesses of 7 and 5.

Finally, in the case of FIG. 9, the weft yarns 12 of the upper layer are linked to the warp yarns 11 according to two satins of five regulars with juxtaposed notches 3, leading to a cumulative warp ratio of 10. The yarns of weft 10 of the lower layer are linked to the warp threads 11 according to a regular satin of 10 with a notch of 3.

In all the cases which have been illustrated, it can be seen that the number of bonding points of the warp threads 11 with the weft threads 12 of the upper layer is at least twice the number of binding points of these warp threads 11 with the weft threads 10 of the lower layer. In the case of FIG. 1b, it can be seen that there are two upper bindings for a lower binding. It is the same in the case of FIGS. 3, 4, 5, .6, 8 and 9. But, in the case of FIG. 7, there are three upper bindings for a lower binding.

The fabrics according to the invention will, in most cases, be produced by flat weaving, then joined together. This arrangement, which leads to a fabric, the weft threads of which are placed transversely on the machine, has the advantage of leading to high transverse rigidity and to a longer service life, the wear bearing first on the threads. transverse, in particular of the lower layer. However, in certain cases, it may be necessary to produce the fabric by circular weaving, the weft threads then being placed longitudinally.

The invention is obviously not limited to the particular embodiments which have been shown and described by way of examples and it should be understood that the scope of this patent extends to any variant remaining within the framework of equivalences.

Claims (9)

1. Double layer forming fabric for a paper machine, comprising two layers of weft threads (10, 12) and a layer of warp threads (11) and having an overall warp ratio of at least six threads, characterized in that that it has an overall weft ratio of at least twelve threads; in that the bonding points of the warp threads with the lower layer (10) are distributed in a satin weave whose ratio is equal to the overall warp ratio; in that the bonding points of the warp threads (11) with the weft threads of the upper layer (12) are distributed in an arrangement having a cumulative ratio equal to the overall warp number, but formed by the juxtaposition of two or three armor with chain ratio less than six; and in that between each place where a warp thread (11) descends through the upper layer and that where it goes up further through this same upper layer, there are at least two weft threads of the upper layer (12 ). 2. Canvas according to claim 1, characterized in that the weft threads (12) have, in contact with the paper, floats whose length does not exceed four warp threads. 3. Canvas according to claim 1 or 2, characterized in that the number of bonding points of the warp threads (11) with the weft threads of the upper layer (12) is at least double the number of binding points of the warp yarns with the weft yarns of the lower layer. 4. Double layer canvas for a paper machine comprising two layers of weft threads and a layer of warp threads, having an overall warp ratio of eight threads, characterized in that the bonding points of the warp threads (11) with the weft threads of the lower layer (10) are distributed in a satin ratio of eight, in that the bonding points of the warp threads with the weft threads of the upper layer have a ratio equal to eight but have a distribution constituted by the juxtaposition of two armours of four, having each a warp ratio of four, and in that, between each place where a warp thread descends through the upper layer and that where it goes up further through this same layer, there are three wefts of the upper layer (Figures 4a and 4b). 5. Canvas according to any one of the preceding claims, characterized in that the warp threads are linked to the weft threads of the upper layer in two twills of four juxtaposed (FIGS. 4a and 4b). 6. Canvas according to any one of claims 1 to 4, characterized in that the warp threads are linked with the weft threads of the upper layer in two satins of four juxtaposed irregulars (FIG. 5). 7. Canvas according to any one of the preceding claims, characterized in that at least some of the longitudinal and transverse threads are chosen from the group consisting of synthetic multifilament threads, synthetic monofilament threads, coated or not, sheathed or not. 8. Canvas according to any one of the preceding claims, characterized in that the filling coefficient is at least 1.05. 9. Canvas according to any one of the preceding claims, characterized in that it is produced by flat weaving and joining, the weft threads being arranged transversely to the machine and the warp threads longitudinally.

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