EP0030490B1 - 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 known as "double layer" comprising two layers of weft threads 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 manufacturing 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 cloth, between two endless cloths or between an endless cloth and cylinders.

We know 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 consist of a single layer of longitudinal threads and a single layer of transverse threads; 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 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 warp 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. However, different weaving weaves must be adopted, given the flexibility of the plastic bristles and they result in a mark on the paper which is clearly different from that produced by the metallic fabrics and which is not acceptable for certain types of paper, in particular those intended for gravure 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 provides in particular a double-layer fabric according to claims 1 or 4 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, the ratio of which is equal to the overall warp ratio; the bonding 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 warp ratio less than 6; and between each place where a warp thread descends through the upper layer and that where it rises further through this same layer, there are at least two weft threads of the upper layer.

The term "global warp ratio" designates above the number of threads in the smallest warp thread group whose evolution is repeated identically in the weft direction, while the "global warp ratio" is the corresponding number of weft threads in the warp direction. The term "chain ratio", when applied to the tying stitches, denotes the number of threads in the smallest group of warp threads for which the tying stitches are repeated in the form of identical patterns.

This arrangement makes it possible to fully retain 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 mark weak, which these same previous canvases do not allow which incorporated, on the paper side, ties distributed in the form of regular or irregular satins with a 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 is minus 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 bonding points of the warp threads with the weft of the upper layer and reduces to a permissible value the level difference between the warp thread loops and the weft thread loops, paper side. This result is obtained even more completely by limiting the float of the weft threads on the paper side to four warp threads to prevent them from being. pushed too strongly towards the outside of the fabric on this side and have a projection which would lead to an unacceptable mark.

• - sergé de 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 ciq 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:

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

An overall warp 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-filament and monofilament threads synthetic, used alone or in combination with yarn. metallic; 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 at least 1.05. Finally, although it is generally advantageous to constitute the fabrics according to the invention by flat weaving, then joining, 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 subsequent junction.

• - 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- 1 b montre schématiquement les liages entre un fil de chaîne et les fils de trame des deux couches dans une toile suivant la figure 1 a,
• ― 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 1a, montre une autre toile suivant l'invention,
• - les figures 4a et 4b, similaires aux figures 1 a et 1b, montrent un autre mode de mise en œevre,
• - les figures 5 à 9, similaires à la figure 1a, 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. 1 b schematically shows the bindings between a warp yarn and the weft yarns of the two layers in a fabric according to FIG. 1 a,
• 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. 1 a and 1b, show another mode of implementation,
• - Figures 5 to 9, similar to Figure 1a, show yet other modes of implementation.

• - aucun signe n'est marqué si le fil de chaîne passe entre les deux nappes de fils de trame superposés,
• - une croix »X« est marquée si le fil de chaîne 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 chaîne 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. 1 a and 1 b, 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 bonding points of the weft threads 12 of the upper layer with the warp threads 11 are distributed in two twists of three juxtaposed (chain ratio of three) leading to a cumulative chain ratio of 6. FIG. 1 b clearly shows that there is, side machine, a chain ratio of 6 with a single tying point, hence the presence of large floats on the weft son 10 in contact with the elements of the machine. On the paper side, it can be seen that the high number of simple binding 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 (FIG. 2) between the warp yarn loops 11 and the weft yarn loops 12 should be as low as possible to reduce the mark. In practice, the admissible 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 floats, of weft on the paper side cover only two warp threads, so that they are not pushed too strongly towards the outside of the canvas on the paper side. It can also be seen, in FIGS. 1 and 2, that two weft threads 12 of the upper layer are inserted 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 for more yarns from the upper layer, it being understood that the warp yarn can trap only weft yarns 12 from the upper layer, as shown in FIG. 2, or also trap weft yarns 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 1a are designated by the same reference number), the overall warp ratio is 7, while the overall weft ratio 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 linkages of the warp threads 11 with the weft threads 12 of the upper layer are carried out according to two twists of four juxtaposed, leading to a ratio of cumulative warp of 8. The weft yarns 10 of the lower layer are linked to the warp yarns 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 according to two irregularly shaped satins of four 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 in an irregular satin nine.

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 regular satin 9 with an unhooking 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 threads 12 of the upper layer are linked to the warp threads 11 according to two satins of five regulars with juxtaposed notches 3, leading to a cumulative warp ratio of 10. The threads 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 double the number of bonding 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. The same is true 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.

Claims (9)

1. Plastic double layer forming fabric for papermaking machine, comprising two layers of shute threads (10, 12) and a layer of warp threads (11) and having an aggregate warp ratio of at least six threads, wherein, between each location where a warp thread (11) comes down through the upper layer and that where it comes up further through that same upper layer, there are at least two shute threads of the upper layer (12), characterized in that said fabric has an aggregate shute ratio of at least twelve threads; the binding points of the warp threads with the lower layer (10) are distributed according to a satin pattern the ratio of which is equal to the aggregate warp ratio; the binding points of the warp threads (11) with the shute threads of the upper layer (12) are distributed according to a pattern having a cumulated ratio equal to the aggregate warp ratio, but constituted by two- or three juxtaposed weaving patterns each with a warp ratio lower than six.

2. A fabric according to claim 1, characterized in that the shute threads (12) have floats contacting the paper whose length does not exceed four warp threads.

3. A fabric according to claim 1 or 2, characterized in that the number of binding points of the warp threads (11) with the shute threads of the upper layer (12) is at least double the number of binding points of the warp threads with the shute threads in the lower layer.

4. Plastic double layer forming fabric for papermaking machine, comprising two layers of shute threads and a layer of warp threads, having an aggregate warp ratio of eight threads, characterized in that the binding points of the warp threads (11) with the shute threads of the lower layer (10) are distributed according to a satin weave pattern with a ratio of eight, the binding points of the warp threads with the shute threads of the upper layer have a ratio equal to eight but have a distribution constituted by the juxtaposition of two weave patterns of four, each having a warp ratio of four, and, betweeen each location where a warp thread passes down through the upper layer and the location where it passes up further through that same layer, there are three shute threads of the upper layer (Figures 4a and 4b).

5. A fabric according to any one of the preceding claims, characterized in that the binding points of the warp threads with the shute threads of the upper layer are distributed according to two juxtaposed four shaft twill wave patterns (Figures 4a and 4b).

6. A fabric according to any one of the preceding claims, characterized in that the binding points of the warp threads with the shute threads of the upper layer are distributed according to two juxtaposed irregular four shaft satin (12) weave patterns (Figure 5).

7. A fabric according to any one of the preceding claims, characterized in that some at least of the longitudinal and transversal threads are selected from the group consisting of synthetic multifilament strands and synthetic monofilament strands, coated or not, sheathed or not.

8. A fabric according to any one of the preceding claims, characterized in that the filling ratio is 1.05 at least.

9. A fabric according to any one of tire' preceding claims, characterized in that it is flat woven and rendered endless by splicing, the shute threads being arranged crosswise to machine running direction and the warp theads lengthwise.

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