CA1115177A

CA1115177A - Forming fabric for paper making and similar machines

Info

Publication number: CA1115177A
Application number: CA328,130A
Authority: CA
Inventors: Arne B. Johansson; Francisco Lorente Codorniu
Original assignee: Albany International Corp
Current assignee: Albany International Corp
Priority date: 1978-06-12
Filing date: 1979-05-23
Publication date: 1981-12-29
Also published as: GB2022638A; JPS5512892A; ATA328979A; CH640284A5; JPS6342040B2; NL188048B; GB2022638B; NL7904253A; AU4767279A; NO149853B; IT1118627B; SE420852B; BE876707A; AU519359B2; NZ190361A; NO791819L; FR2432575B1; ES8205096A1; BR7903629A; IT7967929A0

Abstract

ABSTRACT OF THE DISCLOSURE

A forming fabric for papermaking, cellulose and similar machines consisting of two complete weaves.
Each weave comprises one set of warp threads and one sat of weft threads. The two weaves are joined together by separate binder weft threads which are positioned between the two weaves and which inter-weave with threads from each set of warp threads.

Description

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BACKGROUND 0~ THE INVENTION
In the production of paper in papermachines, a slurry of fibres is discharged onto a fabric having a network-like structure The water is drained off from the fibrous mass through the opsnings in the fabric. On the upper face of the fabric, the fibras are formed into a sheet. As the flow-through of the water takes place at the points of the fabric where the yarn material of the fabric meshes does not bar the ; 10 flow, it is of utmost importance that these through--flow points are evenly distributed over the entire fabric area. The permeability of the forming fabric must be of a certain magnitude while at the same time the fabric surface must be very fine-meshed in order to " 15 avoid marking of the sheet being formed and loss of fibres. A fine-mesh fabric comprising thin threads is, however, less resistant to wear and 1BSS stable and as a consequence thereof its useful life is greatly reduced Up to the beginnings of the 1960's, only single layer fabrics of metal were used for the sheet formation. To some extent, metal screens wsre replaced by single-layer fabrics of synthetic fibre threads, the so-called synthetic fabrics, which are more wear-.' .

-resistant but less stable. On account of the reduced stability of such fabrics, these single-layer synthetic fabrics could not be used in large and high-speed machines. Only with the arrival nf so-called double-layer forming fabrics could synthetic fibre materials oe used to a larger extent in these large and high-speed paper machines. In machines of this kind, the forming fabric is exposed to considerable tensile stresses which the fabric must be capable of absorbing without stretching lengthwise or contracting crosswise to such a degree that the fabric can no longer be used for its intended purpose.
The so-called doubls-layer forming fabrics that - are in practical use consist of two layers of synthetic weft threads as well as synthetic warp threads inter-connecting the weft layers. In fabrics of this kind, the conflicting requirements on the one hand of a fine-mesh forming face comprising fine threads, and on the other hand of a wear face wherein the threads are coarser and more wear-resistant are met to some extent. This could be achieved by using threads of differing dimensions and/or different fibre materials in the two weft layers. However, these cunflicting ... .

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requirements cannot be met by the single thread layer in the opposite direction, viz. the warp thrsads that interconnect the weft layars. From a sheet--forming point of view these warp threads should preferably be as fine as possible but in their capacity as machins direction threads they must be capable of absorbing any tensile stresses that might occur without stretching to an unduly high degree.
Every expert designer in the field aims at providing a forming fabric which consists of two layers of complete fabrics, each one with its individual ssts of warp threads and weft threads, which fabrics are joined together. The part of the fabric that is closest to the material to be formed as a rule consists of fine threads arranged in a fine-mesh structure whereas the bottom part consists of coarse and more wear-resistant threads arrangsd in a more coarse-mesh structurs. The reason that this aim has been unattainable in practice depends on the difficulties 2û to interconnect the two wire parts without disturbing the arrangement of the fine-mesh fabric part to such a degree that the disturbance of the latter will reflect on the paper sheet in the form of marking.

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From the US Patent Specification No, 3 127 308 is already known a forming fabric which comprises one fine-mesh face closest to ths paper web and a coarse--mesh face serving as the wear side. These two fabric fa-ces are structured as complete weaves which arewoven together with one another. The Patent Speci-fication referrsd to suggests interweaving by inter-connection of the two fabric parts 61 and 62 by means of the coarse warp thread 61a. Another prior-art suggestion is to interweave the two complete fabrics by means of separate warp binder threads.
In these prior-art structures the two weaves thus are interconnected either by warp threads that are a part of one of the weaves, or by separate warp threads. During the manufacture of weaves of forming fabric type, the weft threads normally extend in a straight condition inside the weave body, whereas the warp threads have a sinuously curved configuration and form the very face of the fabric. However, by stretching the fabric it is possible to change the curvature in the subsequent heat-fixation process, whereby the sinuosity of the warp threads is reduced while the curvature of the weft threads is enhanced.
A process of this kind cannot, however, but to a small . . :

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sxtent eliminate the unevenness of the warp threads given to thsse threads during the weaving opsration.
When a warp thread in the fine-mesh fabric part is used as the interconnecting thread, this causes unevenness on the sensitive paper-facing side of the fabric, when this warp thread is to bind, at equal intervals, with the bottom side of the fabric.
If a warp thread in the coarse-mesh part of the fabric or a separate warp thread is used as the interconnecting thread, unevenness occurs on the paper-facing side of the fabric, when this thread is to bind with the fine-mesh fabric part which faces the paper web. These unevenness which is caused by interconnection with the aid of warp threads, is sufficient to cauæe a marking effect on paper of qualities that are particularly sensitive thereto, such as e g. newsprint paper.
In addition, interconnection by means of warp threads is considerably more complicated from a manufacturing-technical point of view, sincs the binder threads has a size in woven condition that differs from the rest of the warp threads, on account of the difference in geometrical configuration. ~inder warp threads therefore must be warped in a particular warp-beam and be driven at a different speed from ~, .

that of the r~st of th~ warp threads.
SUMMARY OF THE INVENTION
The subjsct invention concerns a forming fabric for papermaking, cellulose and similar machines and which fabric is of the kind comprising a first set of warp threads and a first set of weft threads which are interwoven to form a first complete weave, and a second set of warp threads and a second set of weft threads which are interwoven to form a second complete weave. It is characteristic of the invention that separats binder weft threads are used to interconnect said first weave and said second weave, which binder wsft threads are positioned between the two weaves and interweave with threads from said first and said second sets of warp threads.
9ecause the weft threads lie comparatively straight inside the weave body after and during the weaving, as mentioned abovs, the binder weft threads will also be in the same position, and the sinuous warp threads on both sides of the fabric will twine about these binder threads. The interweaving points proper therefore will be positioned inside the weave body and not, like in warp-bound structures, on the surface thereof. The surfaces of the fabric, and particularly the facs which is turned towards the web of material to be formed, will not be effected by the inter-~` weaving points. One has also found that fabrics wherein th~ face that is turned towards the material web is even and which are free of binding (or inter-weaving) point disturbancs in ths raw weave stage of the fabric, have a face that is more even and smoother also after exposure of the fabric to stretching during ; the heat-fixation process. The function of the binder , 10 threads in the fabri~ is merely to join together the top and bottom cloths. Their dimensions and material therefore could be different from the rest of the thread material. Prsferably, a finer and softer thread material is used for the binder thread.
ORIEF DESCRIPTION OF THE DRAWINGS
The invention will be described in closer detail ` in the following with reference to the accompanying schematical drawing of which Figs. 1 to 5 are sectional views along the warp threads and illustrate different 2û binding patterns.
DETAILED DESCRIPTION OF A PREFERRED EMSODIMENT
The forming wire in accordance with the invention is woven endless in the usual manner of the art or - joined endless. In the structure of the fabric when the fabric is wovan endless, the machine direction threads of the weave are wsft threads whereas the warp threads form the crosswise yarn system in the position of use of the fabric. In the fabric structure joined endless the situation is the reverse.
The embodiments shown in Figs. 1 to 3 illustrate a comparatively fine-mesh weave 1 which in position of use of the fabric is to face the material to be formed. This weave - in the following referred to as - 10 the top cloth - is woven in a two-shaft pattern which means that each warp thread 2 binds over every other weft thread 3a and beneath every other weft thread 3b.
A second and mora coarse-mesh weave 4, which is woven in a four-shaft twill weave pattern, forms the bottom cloth of the fabric. This bottom cloth 4 likewise comprises two complete thread systems, viz. warp thread 5, which weaves above three weft threads 6a in succession and below the fourth weft thread 6b. Between these two cloths 1 and 4 are woven weft threads 7 which bind or weave with the warp threads 2, 5 from the top as well as from the bottom cloths 1 and 4, respectively.
These binder weft threads 7 can be placed thinly or densely. In Fig. 1, the binder weft threads are , ::
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- comparatively thinly placad, more precisely following each twelfth w~ft thread in the top cloth 1.
Fig. 2 exemplifies a more dense position and Fig, 3 a further increased density of the binder weft threads 7.
The patterns of the top cloth 1 and the bottom cloth 4 may be varied in many ways, some of which are shown in Figs 4 and 5 by way of example. In Fig. 4, both cloths 1 and 4 are woven in a four-shaft pattern.
The embodiment of Fig. 5 is distinguished from thoss shown as examples earlier in that both cloths 1, 4 are woven in a three-shaft pattern and in that the ; ratio of weft density between the top and bottom cloths is 3 to 1 instead of 2 to 1 as illustrated in the other drawing figures.
` The binding patterns and the density ratios of the top and bottom cloths 1, 4 thus may be varied in a number of ways, and the density ratios of the cloths ; may also differ. The common feature of all is that the two cloths are anchored in a system of weft binder threads 7 that are interwoven with and between the cloths 1, 4. As these binder weft threads 7, like the other weft threads 3a, 3b, 6a, 6b, are comparatively straight, wh=rsas the w,rp threads 2, 5 ar~ sinuously '''' ' : . .
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curved, the binder weft threalis 7 will, after weaving, be positioned entir0ly inside the body of the double--layer fabric. These binder weft threads 7 thersfore will not b~ in contact with the sxternal parts of the fabric and therefore cannot, contrary to warp binder threads, disturb the regularity of the inter-weaving of the two yarn systems 2 and 3a, 3b of the top cloth 1.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. An improved forming fabric for use in papermaking, cullulose and similar machines, said fabric comprising a first set of warp threads and a first set of weft threads, said two sets of threads interwoven to form a first complete weave, and a second set of warp threads and a second set of weft threads, said two sets of threads interwoven to form a second complete weave, the improvement comprising separate binder weft threads to interconnect said first weave and said second weave, said binder weft threads positioned between said two weaves and interweaving with threads from said first and said second sets of warp threads.

2. An improved forming fabric as claimed in claim 1, wherein said binder weft threads have a diameter that is smaller than the diameter of the rest of the threads.