Woven Wire Fabric

Abstract

A woven, phosphor bronze, wire fabric having weft strands of cylindrical cross section and warp strands of rectangular and slightly oval cross section, the warp and weft strands being made of 7 to 10 percent phosphor bronze material, with both the warp and weft strands having a hard temper in order to provide a wire fabric having improved flexural fatigue properties.

Description

BACKGROUND OF INVENTION

1. Field of Invention

This invention is directed toward an improved woven, phosphor bronze wire fabric used in papermaking machines, the fabric having improved flexural fatigue life in both the warp and weft strands forming the woven wire fabric.

The invention is more particularly directed toward an improved woven, phosphor bronze, wire fabric having improved flexural fatigue life and also increased tensile strength in the weft and warp directions in order to reduce the tendency of the wire fabric to split by cracking when used as a forming wire in certain types of paper machines where the wire fabric is subjected to greater than normal flexure. The increased flexural fatigue life and tensile strength in the improved wire fabric are obtained without reducing the drainage characteristics of the woven wire fabric for any given mesh count as compared with normal wire fabrics.

2. Description of Prior Art

Phosphor bronze wire fabrics generally in use are woven with warp or machine direction strands and weft or cross-machine direction strands which have a circular cross section. Phosphor bronze comprises a percentage of tin, approximately 0.4 percent phosphorus, with the remainder, copper. Phosphor bronze is a preferred material for both the warp and weft strands in fabrics used as forming wires since it has reasonably high tensile strength with good ductility. It is also corrosion resistant, has good abrasion-resistant qualities and adequate flexural fatigue resistance for bending conditions encountered during normal use of the fabric when it is used as a fourdrinier wire, for example. Generally, the warp strands in a forming wire are made of 8 percent phosphor bronze (8 percent denoting the percentage of tin in the phosphor bronze), and the weft strands are made of 6 percent phosphor bronze. The weft strands are also sometimes made from 3 percent phosphor bronze.

The warp strands in the woven fabric are generally mechanically worked to have a hard temper. The temper of the strands is measured by the grain size of the phosphor bronze material, and the smaller the grain size, the harder the temper. A strand with hard temper will generally have a grain size of less than 5 microns. In normal forming wires, the warp strands have a grain size of 4 microns. The weft strands do not have a hard temper and generally have a grain size of 14 microns. It is thus seen that the weft strands in an ordinary forming wire have a relatively soft temper in comparison to the warp strands as is apparent from their difference in grain size. With the weft having a relatively soft temper, the forming wire has a tendency to split before it has been used for its normal life when the forming wire is subjected to abnormal flexing. Even the warp strands, having a hard temper, can crack under abnormal flexing and cause the wire to split.

One example of abnormal flexing encountered with forming wires is in fourdrinier wires used in papermaking machines having a presser roll located adjacent the couch roll. Although many modern papermaking machines no longer use a presser roll adjacent the couch roll, there are still many older machines in use which were constructed on the open-draw principle and which require use of the presser roll in conjunction with the couch roll to aid in properly withdrawing the web of paper. The fourdrinier wire carrying the newly formed web passes between a nip formed by the presser roll and the couch roll. The wire, in passing through this nip, is forced into apertures in the couch roll by the presser roll thus repeatedly flexing the wire. The constant flexing or dimpling of the fourdrinier wire does not reduce the useful life of the wire where the machines run at their original design speed. However, to meet present-day production requirements, these machines are now run at speeds above their design speed requiring increased pressure from the presser roll. The increased pressure greatly increases the fatigue effect on the fourdrinier wire during its flexing or dimpling in passing between the presser roll and the couch roll. This causes the wire to tend to split by cracking of the weft strands before the wire has been used for a normal period of time. The splitting of the wire thus increases the cost of production of paper due to the downtime required to replace the wire.

Another example of abnormal flexing is encountered by forming wires used in the relatively new vertical-type papermaking machines. In vertical paper-forming machines, pulp stock is fed between vertical, substantially parallel runs, of two forming wires. The stock is fed between the wires at the top end of their vertical run, and the stock is drained laterally through the wires as the wires move downwardly. Drainage is assisted by passing the wires over deflectors, which deflectors flexurally stress the warp strands in the wire. The repeated flexure on the wires by the deflectors can cause cracking of the warp strands thus shortening the life of the wire.

The present invention provides an improved phosphor bronze wire fabric having increased useful life when used under operating conditions where increased flexing is encountered by either the warp or weft strands while still maintaining, or even slightly increasing, the drainage and tensile characteristics for the improved wire fabric when it has substantially the same size of strands and a mesh count as in ordinary wire fabrics.

In order to improve the flexural fatigue life of the phosphor bronze woven wire fabric, the weft strands are made of stronger phosphor bronze material, and both the warp and weft strands have a harder temper. However, a wire fabric made from hard temper warp strands having a circular cross section is extremely difficult to weave compared to the weaving of soft temper warp strands having a circular cross section of the same diameter, to obtain a fabric having substantially the same drainage properties as a fabric using circular warp strands.

It is known to use warp strands having a rectangular cross section, with the direction of the smaller dimension of the rectangular cross section extending perpendicular to the plane of the wire, to make wire fabrics having a "flat-surfaced" weave. By a "flat-surfaced" weave, it is meant a weave where the height or depth of the knuckles formed at the crossover points of the warp and weft strands is reduced when a rectangular warp, lying flat in the direction of the plane of the wire fabric, is used in place of a warp having a circular cross section. See U.S. Pat. No. 600,352, issued Mar. 8, 1898, J. C. Bell, inventor, for example.

It has also been known to obtain a finer fabric mesh using rectangular warps, since rectangular warps allow the weft to be beat up easier during weaving. The rectangular warps are flexible and thus more weft strands can be used per inch of fabric than when using warps of circular cross section. See U.S. Pat. No. 2,003,123, issued May 28, 1935, H. G. Specht, inventor.

The rectangular warp strands used have a ratio of the width, in the plane of the wire, to the thickness, transverse to the plane of the wire, exceeding 1.3:1. This ratio has been found to be the acceptable lower limit for providing a "flatter" wire or a finer wire where strength and/or drainage properties of the wire is not a critical factor.

To use rectangular warp wires having this minimum width to thickness ratio in phosphor bronze wires with a hard temper, while attempting to maintain the same strength and drainage characteristics obtained in a fabric using a circular warp of the same width as the rectangular warp, results in an unacceptable fabric. When the rectangular strands are woven into a wire fabric to have substantially the same drainage characteristics as a wire having circular warps, the resulting fabric is loose or "sleazy" whereby the warp and weft strands of the wire slip relatively to each other. At the same time, the tensile strength of the fabric is reduced. If the fabric is instead woven tight enough to overcome the problem of a loose weave, more weft strands are required than the number used in a fabric employing circular warps, whereby the drainage properties of fabric are reduced.

SUMMARY OF INVENTION

Applicant has unexpectedly discovered that an improved woven, phosphor bronze, wire fabric, having improved flexural fatigue life without reduction of drainage properties, can be made of warp and weft strands having a hard temper if rectangular or slightly oval warp strands are used having a ratio of width to thickness ranging between 1.05:1 and 1.15:1. Using such warp strands, the wire fabric, made of hard temper strands, can be woven on a standard weaving machine, and the wire fabric has improved flexural fatigue life and tensile strength properties, and further, has no reduction in drainage properties for a given mesh count and wire size as compared with a wire fabric with the same mesh count and wire size but using warps having a circular section.

The invention is particularly directed toward a woven, phosphor bronze, wire fabric for use in paper-forming operations in papermaking machines, the fabric comprising weft and warp strands of phosphor bronze material. The warp strands are rectangular or slightly oval in cross section having a ratio of width to thickness ranging between 1.05:1 and 1.15:1. Both weft and warp strands are tempered to have a grain size of less than 4 microns.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in detail having reference to the accompanying drawings, wherein:

FIG. 1 is a plan view of the woven, phosphor bronze, wire fabric; and

FIG. 2 is an enlarged partial cross section view of the fabric taken along line II--II in FIG. 1 showing the weft and flattened warp strands in detail.

DESCRIPTION OF PREFERRED EMBODIMENTS

The woven fabric 1, shown in FIG. 1, comprises weft or cross-machine direction strands 3 and warp or machine direction strands 5. The weft and warp strands 3, 5 are preferably woven in a standard semitwill weave pattern with each warp strand 5A passing under two weft strands 3A, 3B and over one weft strand 3C.

The warp strands 5 are tempered to have a grain size of 2 microns or less. The weft strands are tempered to have a grain size less than 5 microns. The grain size of the warp preferably is 1.5 microns and of the weft, 4 microns.

Both the warp and weft strands are made of phosphor bronze. The tin content of the phosphor bronze material for both the warp and weft can range between 7 percent and 10 percent. Preferably, the tin content of the warp and weft is 8 percent to 9 percent.

The warp strands 5 are rectangular or slightly oval in cross section, as shown in FIG. 2, to facilitate weaving of the wire. The major axis Y of the cross section of the warp strand is parallel to the plane of the woven wire fabric 1. The ratio of the width W of each warp strand along the major axis Y to its thickness T along the minor axis X ranges between 1.15:1 and 1.05:1, and preferably is 1.1:1.

The wire fabric can be woven into any standard mesh count ranging from 50 by 50 to 100 by 100 using weft strands having a diameter ranging between 0.015 and 0.004 in. and warp strands having a width, along the major axis, ranging from 0.013 to 0.004 in.

The following table illustrates, for comparison purposes, the relative physical differences between an ordinary woven wire fabric made of phosphor bronze material with warp strands of circular cross section having a hard temper with a grain size of 4 microns and weft strands of circular cross section having a soft temper with a grain size of 14 microns, as compared with a wire fabric of the present invention made with warp and weft strands having a hard temper and with the warp rectangular or slightly oval in cross section. The ordinary wire fabric is made of 6 percent phosphor bronze strands and the improved wire fabric is made of 8 percent phosphor bronze warp and weft strands. ---------------------------------------------------------------------------

Ordinary Improved Wire Wire __________________________________________________________________________ Mesh --in..sup..sup.-1 68.times.56 68.times.56 Warp Size --in. 0.0082 0.0082.times.0.0074 Weft Size Type --in. 0.0090 6% 0.0087 8% Warp Grain Size --microns 4 1.5 Weft Grain Size --microns 14 4.0 Warp Direction Tensile Strength --lb./in. 210 212 Weft Direction Tensile Strength --lb./in. 202 240 Weft Direction Flexural Fatigue Life --cycles 3,000 4,007 Warp Direction Flexural Fatigue Life --cycles 13,000 17,554 Drainage (as measured by a Frazier Permeometer) --c.f.m./sq.ft. 785 790 __________________________________________________________________________

It will be noted from the above table that the flexural fatigue life in both the weft and warp directions of the improved wire fabric has been increased approximately 30 percent or more. Further, the tensile strength in both the warp and weft directions has been increased with nearly a 20 percent increase in the weft direction even though a slightly smaller weft is used. It is equally important that the drainage characteristics of the improved wire fabric be at least the same as the ordinary wire fabric. As seen from the table, the drainage of the improved wire fabric is slightly increased over the ordinary fabric. If a wire fabric were to be woven using a rectangular warp with approximately a minimum ratio of width to thickness of 1.32:1, it would, because of the increased weft strands required to produce an acceptable tight fabric, have a much lower drainage. For example, a wire fabric woven from 0.0086".times.0.0065" rectangular warps and 0.009-inch diameter wefts, with a mesh count of 68.times.63, has a drainage of 620 c.f.m./sq.ft. as measured by a Frazier Permeometer.

Claims

We claim:

1. A woven, phosphor bronze, wire fabric having improved flexural fatigue life for use as a forming wire in papermaking machines, said fabric woven from weft and warp strands of phosphor bronze material, said warp strands having an oval cross section so as to have a ratio of width to thickness ranging between 1.15:1 and 1.05:1, both said weft and warp strands tempered to have a grain size less than 5 microns.

2. A woven wire fabric as claimed in claim 1, wherein both the warp and weft strands are made of phosphor bronze material having a tin content ranging from 7 to 10 percent.

3. A woven wire fabric as claimed in claim 2, wherein the warp strands have a grain size not exceeding 2 microns.

4. A woven wire fabric as claimed in claim 2, wherein the weft strands have a grain size of 4 microns.

5. A woven wire fabric as claimed in claim 2, wherein the ratio of width to thickness of the oval warp strands is 1.1:1.

6. A woven wire fabric as claimed in claim 1, wherein the ratio of width to thickness of the oval warp strands is 1.1:1, the weft strands having a grain size of 4 microns, the warp strands having a grain size of 1.5 microns, and the weft and warp strands being made of phosphor bronze material having a tin content ranging from 8 to 10 percent.