GB2192907A

GB2192907A - Wire-cloth for paper-making machine

Info

Publication number: GB2192907A
Application number: GB08714185A
Authority: GB
Inventors: Valentin Andreevi Korobeinikov; Alexandr Mikhailovich Tomilov
Original assignee: PERM VNII TSELLYULOZNO BUMAZHN
Current assignee: PERM VNII TSELLYULOZNO BUMAZHN
Priority date: 1986-07-24
Filing date: 1987-06-17
Publication date: 1988-01-27
Also published as: SE8702933D0; FI872995A; SU1441840A1; FI872995A0; CS354887A1; SE8702933L; GB2192907B; FR2601976A1; GB8714185D0; SE464141B; DD282147A7

Abstract

The wire-cloth is intended for production of thin paper grades and is made of interwoven warp threads 1 and alternating main weft threads 2 and additional weft threads 3, with the weaving pattern repeat of the warp threads 1 equalling five, and the weaving pattern repeat of the weft threads 2,3 equalling ten. In the pattern repeat, each main weft thread 2 underlies one and overlies four successive warp threads 1, the points 4 of interweaving with the warp threads 1 being staggered every second warp thread 1. Each additional weft thread 3 passes under one warp thread, over two, under one and over one forming two interweaving points 5 and 6 with the warp threads 1, one 5 of these points being accommodated diagonally (a-a) intermediate the interweaving points 4. The threads are preferably of synthetic material. <IMAGE>

Description

SPECIFICATION Wire-cloth for paper-making machine The invention relates to a wire-cloth for a paper-making machine, particularly but not solely a wire-cloth made of synthetic material. Wirecloths according to the invention can be successfully used in production of thin grades of paper, such as newsprint.

There is known a single-ply wire-cloth for a paper-making machine, made of polymeric monofilaments, specifically polyester monofilaments, with the weaving pattern repeat of both the warp and weft threads equalling five course or picks (US-A-4161195). The wirecloth has a reinforced satin weave with the points of interweaving, respectively, at courses 1 and 2, 3 and 4, 5 and 1, 2 and 3, 4 and 5, i.e. a weft thread passes under two warp threads, then interweaves with the last one of them, and passes over three warp threads. The successive weft thread is woven similarly, but its interweaving is offset by two warp threads with respect to the preceding weft thread.

The known wire-clotch is characterised by high inverse relationship of its capacity of dehydration and its ability to retain paper fibres, which means that the weft density of the wire-cloth has to be increased in order to retain fine fibres thereon, which affects adversely its water-draining capacity and renders it unsuitable for production of paper grades containing a high percentage of fine fibres or fine fillers, i.e. paper grades of such kinds as newsprint, letterpress printing, paper, and other thin paper grades. This shortcoming can be detected in practically all synthetic wirecloths where weft threads are arranged in a single layer.

A high degree of dehydration (the waterdraining capacity) in combination with adequate ability to retain fine fibres is offered by two-ply wire cloths. However, experience of using two-ply wire-cloths has shown that they are prone to blocking of their meshes with fibres, which involves a considerable input of energy into their washing. Furthermore, the manufacture of wire-cloths of this type consumes an additional amount of weft threads.

There is further known a single-ply wire cloth of satin weave for a paper-making machine (DE-A-2517228) comprising interwoven warp and weft threads with the weaving pattern repeat of both the warp and weft threads equalling five, with a weft thread in the warp pattern repeat passing over four warp threads, being interwoven with the fifth warp thread and passing thereunder, and the first weft thread in the weft pattern repeat being interwoven with the first warp thread, the second weft thread being interwoven with the third warp thread, the third weft thread being interwoven with the fifth warp thread, the fourth weft thread being interwoven with the second warp thread, and the fifth warp thread being interconnected with the fourth warp thread.

The points of interweaving of adjacent weft threads with warp threads are staggered every second warp thread, the warp thread diameter being 0.20-0.25 mm, and the weft thread diameter being 0.22-0.28 mm.

Although this wire-cloth offers an enhanced dehydrating capacity while being adequately dense, its relationship of the ability to retain fine fibres with the water-draining capacity is practically the same as in any other single-ply wire-cloth. This wire-cloth is likewise all but unsuitable for forming thin grades of pap'er or grades with a high content of fine fibres and filler. This is caused by dehydration- being scant at the points of crossing (interweaving) of warp and weft threads, the bulk of the process of dewatering taking place in areas where warp and weft threads merely overlap.

Thus, the more points of overlapping and the less points of crossing or interweaving (i. e.

the links in the warp/weft system) a wire cloth has, the greater dehydration capacity it offers.

However, this growth of dehydration capacity leaves the ability to retain fine pulp practically unchanged. When the weft density of wire cloth is stepped up, its ability to retain fine fibres grows insignificantly, whereas the dehydration capacity drops sharply. Consequently, this could lead to a "flooding" situation in operation of a paper-making machine, i.e. a situation where the paper web at the end of the forming operation has insufficient dryness, and the working speed of the machine has to be slowed down to compensate for this insufficiency. A wire-cloth of satin weave being of the kind of single-ply wirecloths, it is tainted by the shortcoming of single-ply cloths, namely, the impossibility of stepping up the ability to retain fine fibres without adversely affecting the required dehydration capacity.

What is desired is a wire-cloth in which the interweaving of warp and weft threads enhances its ability to retain fine fibres on the cloth while maintaining its high dehydration capacity and securing such advantages of single-ply wire-cloths over two-ply ones as lower production cost and resistance to clocking of the meshes.

The present invention provides a wire-cloth for a paper-making machine, formed of interwoven warp threads, main weft threads and additional weft threads, with the weft weaving pattern repeat equalling ten and the warp weaving pattern repeat equalling five; the number of said additional weft threads in the pattern repeat corresponding to the number of the main weft threads; each main weft thread in the pattern repeat passing under one and over four warp threads, forming an interweaving point, the thus formed interweaving points of adjacent main weft threads with the warp threads being staggered every second warp thread, one said additional weft thread extending intermediate each two adjacent main weft-.

threads, passing in the warp repeat pattern under one, over two, under one and over one successive warp threads, forming two interweaving points with the warp threads, one of these points being accommodated diagonally intermediate-the two adjoining points of interweaving of the warp and main weft threads.

In a preferred embodiment of the invention, the additional weft threads are interwoven in the weft repeat pattern, respectively, with the second and fifth, second and fourth, first and fourth, first and third, third and fifth warp threads of the warp repeat pattern. It is expedient to have the additional weft threads made of monofilaments having a diameter equalling from 0.80 to 1.00 of the main weft thread diameter.

The introduction of an additional weft thread between two adjacent weft threads of the ''main satin weave" yields, in effect, a oneand-a-half-ply structure of the wire-cloth. This wire-cloth in accordance with the invention differs essentially from two-ply cloths because the weft threads (the main and additional ones) in it are arranged not one on top of the other, but in an offset or staggered relationship. Owing to this arrangement of the threads in the pattern repeat, the additional weft threads are prevailingly situated at the working or forming side of the wire-cloth, whereas the weft threads defining the "main satin weave" are prevailingly situated at its back side.Moreover, when the additional weft threads are made of a smaller diameter than the main weft threads, the water draining acpacity of the wire-cloth remains practically unaffected, i.e. not reduced. With the oneand-a-half-ply structure of the wire-cloth, its ability to retain fibres thereon is enhanced, as the mesh size of the wire-cloth is reduced, the weft density thereof is increased, but the "porosity" of the wire-cloth and its air-venting capacity influencing the draining capacity are not decreased, as the increased thickness of the wire-cloth is due to the growing volume of the inter-thread space, and the distribution of the filtering meshes takes place not in one and the same plane, but throughout the volume of the wire-cloth.The interweaving of the threads follows a diagonal pattern, which reduces the size of the meshes and augments the fibre-retaining ability, but at the same time resists blocking of the meshes with fibres.

The invention will be further described in connection with an embodiment of the invention in a wire-cloth for a paper-making machine, with reference to the accompanying drawings, wherein: Figure 1 illustrates schematically the weave pattern repeat of the wire-cloth; Figure 2 is a schematic sectional view taken along a main weft thread; Figure 3 is a schematic sectional view taken along an additional weft thread; Figure 4 is a schematic sectional view taken along a warp thread in a wire-cloth in which the additional weft threads have a diameter smaller than the diameter of the main weft threads; Figure 5 is a view similar to that shown in Figure 4, in a wire-cloth in which the additional weft threads have a diameter substantially equal to the diameter of the main weft threads.

The illustrated wire-cloth for 9 paper-making machine is made by interweaving synthetic filaments or threads in the form of warp threads 1 (Figure 1), main weft threads 2, and additional weft threads 3 alternating in the weave with the main weft threads 2, i.e. each additional weft thread 3 is accommodated intermediate two adjacent main weft threads 2.

The interweaving of the threads 1,2, and 3 follows a warp pattern repeat equalling five and a weft pattern repeat equalling ten. The weft pattern repeat is defined by five main weft threads 2,--2, alternating with five additional weft threads 3,35. Each main weft thread 2 (Figure 2) underlies one warp thread and overlies four warp threads, the interweaving points 4 (Figure 1), i.e. the crossing points of adjacent main weft threads 2 with the warp threads 1 being staggered diagonally every second warp thread 1 in the weft pattern repeat. Each additional weft thread 3 (Figure 3) extends in the warp pattern repeat under one warp thread, then over two warp threads, then under one warp thread, then over one warp thread, and so on.This weaving pattern yields for every additional weft thread 3 (Figure 1) two interweaving (crossing) points 5 and 6 of which one, e.g. the point 5, is situated intermediate the two adjoining points 4 of interweaving of the main weft threads 2 and warp threads 1, so that all the points 4 and 5 belong to one and the same diagonal line a-a.

The additional weft thread 3 is preferably made of a monofilament having a diameter equalling 0.80 to 1.00 of the diameter of the main weft thread 2. The selection of a specific diameter of the additional weft threads 3 and of the main weft threads 2 is governed by the grade of paper to be f ormed. Should, however, the diameter of the additional weft threads 3 be taken greater than the diameter of the main weft threads 2, the paper formed might show weft markings adversely affecting its quality; on the other hand, if the diameter of the additional weft threads 3 was less than 0.80 of the diameter of the main weft threads 2, the strength of the wire-cloth might be impaired and its service life curtailed.

With the threads 1,2 and 3 interwoven in manufacture, the wire-cloth acquires in crosssection the appearance shown in Figures 4 and 5, with the weft threads 2 and 3-either of different thickness as in Figure 4 or of substantially the same thickness as in Figure being staggered in the wire-cloth relative to one another, defining one-and-a-half plies of a wire-cloth of satin weave.

In the embodiment of the weft pattern repeat illustrated, the additional weft thread 3a (Figure 1) is interwoven with the second 12 and fifth 15 warp threads of the warp pattern repeat, the additional weft threads 32 is interwoven with the second 12 and fourth 14 warp threads, the additional weft thread 33 is interwoven with the first 1, and fourth 14 warp thread,s the additional weft threads 34 is interwoven with the first 1, and third 13 warp threads, and the additional weft threads 35 is interwoven with the third 13 and fifth 15 warp threads of the warp pattern repeat.

Thus, a wire-cloth of the disclosed structure has an increased weft density owing to the additional weft threads being staggered relative to the main weft threads. The arrangement of the weft threads (the main and additional ones) in one-and-a-half plies steps up the bulk of the wire-cloth, the volume of the inter-thread space and, correspondingly, the number of the meshes on the surface of the wire-cloth. The paper-forming side of a wirecloth of this structure is defined by intersections of the warp threads and additional weft threads, whereas the back side of the wirecloth is defined by intersections of the main weft thread in the transverse direction, which is of essential importance for resistance of the wire-cloth to rubbing wear. This structure precludes unwanted marking of a paper web by the wire-cloth and reduces significantly the rate of dropping-through of fine fibres, thus providing for forming on this wire-cloth fine grades of paper from liquid pulp with an increased content of the filler and fine fibres.

Claims

1. A wire-cloth for a paper-making machine, formed of interwoven warp threads, main weft threads, and additional weft threads, with the weft weaving pattern repeat equalling ten and the warp weaving pattern repeat equalling five; the number of the additional weft threads in the pattern repeat equalling the number of the main weft threads; each main weft thread in the pattern repeat passing over four warp threads and under one, forming an interweaving point, the thus formed interweaving points of adjacent main weft threads with the warp threads being staggered every second warp thread; one additional weft thread extending intermediate each two adjacent main weft threads, passing in the warp repeat pattern under one, over two, under one, and over one successive warp thread, forming two interweaving points with the warp threads, one of these points being accommodated diagonally intermediate the two adjoining points of interweaving of the warp and main weft threads.

2. A wire-cloth as claimed in claim 1, wherein the additional weft threads are interwoven in the weft repeat pattern, respectively with the second and fifth, second and fourth, fifth and fourth, first and third, third and fifth warp threads of the warp repeat pattern.

3. A wire-cloth as claimed in claim 1 or 2, wherein each additional weft thread is made of a monofilament of a diameter equalling 0.80 to 1.00 of the diameter of the main weft thread.

4. A wire-cloth for a paper-making machine, substantially as described with reference to, and as shown in, the accompanying drawings.

5. A paper-making machine including a wirecloth according to any preceding claim.