WOVEN PAPERMAKING DRAINAGE FABRIC HAVING FOUR SHED WEAVE PATTERN AND WEFT ...

United States Patent im

Egan

[ii] 3,851,681 [45] Dec. 3, 1974

[54] WOVEN PAPERMAKING DRAINAGE
FABRIC HAVING FOUR SHED WEAVE
PATTERN AND WEFT THREADS OF
ALTERNATING DIAMETER

[75] Inventor: Cleon J. Egan, Kaukauna, Wis.

[73] Assignee: Albany International Corp.,

Appleton, Wis.

[22] Filed: Apr. 18, 1973 [21] Appl. No.: 352,320

[52] U.S. CI 139/420 R, 139/425 A, 162/348,

162/DIG. 1, 245/2, 245/8

[51] Int. CI D2H1/10

[58] Field of Search 162/348, DIG. 1;

139/383 A, 425 A, 420 R, 425 A; 245/2, 8

[56] References Cited

UNITED STATES PATENTS 1,616,222 2/1927 Harrigan 162/DIG. 1

2,554,034 5/1951 Koester et al 139/383 A

3,216,893 11/1965 Schuster.. 139/425 X

3,603,354 9/1971 Lee et al 139/383 A

3,681,193 8/1972 Nykopp 162/133 X

FOREIGN PATENTS OR APPLICATIONS

630,975 11/1961 Canada 139/425 A

Primary Examiner—Robert L. Lindsay, Jr.
Assistant Examiner—Richard H. Tushin
Attorney, Agent, or Firm—Ouarles & Brady

[57] ABSTRACT
A papermaking fabric woven from synthetic monofila-
ments is shown in which the warp threads pass under
one and then over three weft threads in a repeated
pattern, and the weft threads alternate in diameter to
develop a fabric wear surface that is uneven with the
average level of the smaller diameter weft threads
being receded into the fabric to a greater degree than
for the larger weft threads.

7 Claims, 4 Drawing Figures

WOVEN PAPERMAKING DRAINAGE FABRIC HAVING FOUR SHED WEAVE PATTERN AND WEFT THREADS OF ALTERNATING DIAMETER

BACKGROUND OF THE INVENTION 5

This invention relates to the field of papermaking fabrics, particularly as used on Fourdrinier machines.

In the manufacture of paper on a Fourdrinier machine a slurry of paper pulp is laid down on a large, 10 moving belt in the form of a woven open mesh fabric. Water is drained from the pulp through the fabric to form the pulp fibers into an initial paper web, which web is then transferred from the Fourdrinier machine to the dryer section of the papermaking apparatus. 15

Fourdrinier fabrics have been woven in a variety of weave patterns and from a large selection of materials. For many years they were woven from metal wire with soft brass for the recessed weft threads and bronzes for the warp threads which were exposed at their knuckles 20 on the wear side to take the primary wear. Other metals including stainless steel have been employed, and both single and multiple strands as well as hollow wires have been woven into Fourdrinier fabrics. Weave patterns have consisted of plane weaves, semi-twill weaves, and 25 a variety of four shed weaves. In recent years synthetic materials have been introduced into the art, and at times they have been intermixed with metal threads. Also, there has been some use of synthetic coated metal wires. 30

Synthetic threads can be selected from a variety of materials. Some of the earlier work used nylon for its abrasive resistant characteristics, but there has been a shift to polyesters which are nearly non-water absorbent and generally inert to paper pulp slurries. Both 35 monofilament and multi-strand synthetic threads have been used. One of the problems with synthetic materials is that they do not take a permanent set, as do metal threads, when crimped in the weaving process, and a variety of treating techniques have been developed to 40 dimensionally stabilize the synthetic fabrics after weaving.

A Fourdrinier fabric must satisfy a number of requirements in order to be suitable for papermaking. It must present a smooth surface on its upper or paper- 45 making side, in spite of the open mesh characteristic, so that the resulting paper web will not carry wire marking from the fabric. It must have proper water drainage rates and retain the finer pulp fibers on the surface, rather than to lose them in the draining water. It must function as a web forming medium in which paper fibers become intertwined with an adequate percentage in the cross machine direction. The under, or wear side should not groove suction boxes, machine 5^ rolls or foils. A fabric must also have adequate tensile strength to be drawn around and over the machine rolls at high speeds, and it should be dimensionally stable, without excessive stretch. Further, a fabric should lie smooth and not buckle or warp in any of its surface re- 6Q gions. The fabric should be woven in such a manner that adequate seams with requisite life and strength can be used to join the fabric ends into an endless belt.

A particular objective is to provide a fabric that will have a long life, for the down time involved in installing 6J and removing fabrics on a Fourdrinier machine is very costly. Metal fabrics had lives measured in days, and synthetic materials have lasted, in contrast, for weeks

and months. Hence, there has been a shift in the industry from the metal to the synthetic materials. Longer life has been the result of enhanced abrasion resistance and less wear from passing over suction boxes, machine rolls and foils. Also, the chemical inertness and resistance to corrosion has been a factor favoring synthetic materials.

In meeting the foregoing variety of requirements, each fabric must also be compatible with, and tailored for the particular papermaking machine on which it is to be used. Hence, results of weaves, patterns and materials successful in one installation may not necessarily be satisfactory in another application. Also to be considered is the fineness of the fabric mesh. Some weaves are as coarse as less than 10 warp threads to the inch, whereas other weaves have several hundred warp threads to the inch. Usually the number of weft threads per inch is somewhat less, but there are notable exceptions to this generalization.

Into this extensive background of weaving techniques and practices, the present invention introduces an uneven surface on the wear side of a fabric for the principal purpose of further improving fabric life.

SUMMARY OF THE INVENTION

The invention resides in a Fourdrinier fabric having weft threads of varying diameter with points along the smaller diameter wefts being at a different level in the fabric than the corresponding points of the larger diameter wefts to develop an uneven surface.

It is usual to have all the warp threads of one diameter and all the weft threads of another diameter. By introducing weft threads of alternating diameter the wear surface is made more uneven than in usual weaves. It may be an anomaly to speak of a fabric surface, when it is an open mesh and comprised of threads woven into knuckles at cross over points, and with the threads following a somewhat sinuous configuration which does not define a plane at all. Nonetheless, the term surface is used herein to denote the general contour as seen from one side or the other of the fabric, and the points along a thread are referred to as being at levels within the fabric meaning at a level, or height, within the maximum thickness of the fabric as measured from the outermost thread knuckle surfaces that define the outermost planes of the fabric.

It is not in of itself novel to use weft threads of varying diameter. In U.S. Pat. No. 3,216,893 this is done, but metal wefts alternate with plastic wefts in a plain weave, i.e., one over-one under, and the plastic weft are the larger in diameter in order to have all warp knuckle crests lie in a single plane on each side of the fabric. The goal there is to have a mono-plane on each fabric side that is composed of warp knuckles alone. That is a quite different objective from that of the present invention. Reinforcing strands of smaller diameter have been laid in a nonwoven relation alongside the warp threads of the selvedge area in U.S. Pat. No. 3,523,867, and in U.S. Pat. No. 1,616,222 a Fourdrinier fabric has larger than normal warp and weft threads at spaced intervals along the fabric to change drainage characteristics for developing water marks in the resulting paper. Neither of these practices is similar to the present invention.

In the invention the weft preferably alternate in diameter so that adjacent threads on one side of the fabric lie at different average levels in the fabric. This un