Patent Grant
RE40066
The present invention relates generally to papermaking, and relates more specifically to fabrics employed in papermaking.
In the conventional fourdrinier papermaking process, a water slurry, or suspension, of cellulosic fibers (known as the paper “stock”) is fed onto the top of the upper run of an endless belt of woven wire and/or synthetic material that travels between two or more rolls. The belt, often referred to as a “forming fabric,” provides a papermaking surface on the upper surface of its upper run which operates as a filter to separate the cellulosic fibers of the paper stock from the aqueous medium, thereby forming a wet paper web. The aqueous medium drains through mesh openings of the forming fabric, known as drainage holes, by gravity or vacuum located on the lower surface of the upper run (i.e., the “machine side”) of the fabric.
After leaving the forming section, the paper web is transferred to a press section of the paper machine, where it is passed through the nips of one or more pairs of pressure rollers covered with another fabric, typically referred to as a “press felt.” Pressure from the rollers removes additional moisture from the web; the moisture removal is often enhanced by the presence of a “batt” layer of the press felt. The paper is then transferred to a drier section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.
Typically, papermaker's fabrics are manufactured as endless belts by one of two basic weaving techniques. In the first of these techniques, fabrics are flat woven by a flat weaving process, with their ends being joined to form an endless belt by any one of a number of well-known joining methods, such as dismantling and reweaving the ends together (commonly known as splicing), or sewing on a pin-seamable flap or a special foldback on each end, then reweaving these into pin-seamable loops. In a flat woven papermaker's fabric, the warp yarns extend in the machine direction and the filling yarns extend in the cross machine direction. In the second technique, fabrics are woven directly in the form of a continuous belt with an endless weaving process. In the endless weaving process, the warp yarns extend in the cross machine direction and the filling yarns extend in the machine direction. As used herein, the terms “machine direction” (MD) and “cross machine direction” (CMD) refer, respectively, to a direction aligned with the direction of travel of the papermakers' fabric on the papermaking machine, and a direction parallel to the fabric surface and traverse to the direction of travel. Both weaving methods described hereinbelow are well known in the art, and the term “endless belt” as used herein refers to belts made by either method.
Effective sheet and fiber support and an absence of wire marking are important considerations in papermaking, especially for the forming section of the papermaking machine, where the wet web is initially formed. Wire marking is particularly problematic in the formation of fine paper grades, as it affects a host of paper properties, such as sheet mark, porosity, see through, and pin holing. Wire marking is the result of individual cellulosic fibers being oriented within the paper web such that their ends reside within gaps between the individual threads or yarns of the forming fabric. This problem is generally addressed by providing a permeable fabric structure with a coplanar surface that allows paper fibers to bridge adjacent yarns of the fabric rather than penetrate the gaps between yarns. As used herein, “coplanar” means that the upper extremities of the yarns defining the paper-forming surface are at substantially the same elevation, such that at that level there is presented a substantially “planar” surface. Accordingly, fine paper grades intended for use in quality printing, carbonizing, cigarettes, electrical condensers, and like grades of fine paper have typically heretofore been formed on very finely woven or fine wire mesh forming fabrics.
Regretably, such finely woven forming fabrics often are delicate and lack dimensional stability in either or both of the machine and cross machine directions (particularly during operation), leading to a short service life for the fabric. In addition, a fine weave may adversely effect drainage properties of the fabric, thus rendering it less suitable as a forming fabric.
To combat these problems associated with fine weaves, multi-layer forming fabrics have been developed with fine-mesh yarns on the paper forming surface to facilitate paper formation and coarser-mesh yarns on the machine contact side to provide strength and durability. For example, fabrics have been constructed to include one fabric layer having a fine mesh, another fabric layer having a coarser mesh, and stitching yarns that bind the layers together. These fabrics, known as “triple layer” fabrics, are illustrated in U.S. Pat. No. 4,501,303 to Osterberg, U.S. Pat. No. 5,152,326 to Vohringer, and U.S. Pat. No. 5,437,315 to Ward.
Although these fabrics have performed successfully, they have some shortcomings that relate to the inclusion of the stitching yarns. In a typical triple layer forming fabric, one of more stitching yarns are positioned between some of the CMD yarns of the top and bottom layers and interwoven with the top and bottom MD yarns. In such a construction, portions of the stitching yarns form part of the papermaking surface of the fabric. As a result, the appearance of paper formed with the fabric can be affected (sometimes adversely) by the presence of the stitching yarns.
In addition, triple layer fabrics have proven to have problems with interlayer wear. As the fabric is used on a paper machine, the top and bottom layers tend to shift relative to one another, both in the machine direction and the cross machine direction, due to the tension imparted to the fabric by the rolls. This effect is exacerbated on paper machines, such as the so-called “high-wrap” machines, that include multiple rolls, including some which contact the top layer of the fabric. This shifting can cause the fabric to wear and decrease in thickness, which can adversely affect the drainage of the fabric and, accordingly, its performance in papermaking. In many instances, it is this interlayer wear, rather than the wear of the machine side surface of the fabric machine against the paper machine, that determines the longevity of the fabric.
Further, because the stitching yarns of a triple layer fabric have a different weave pattern than the top CMD yarns (i.e., they interweave with the bottom CMD yarns also, whereas the top CMD yarns to not), there can be differences in tension between the stitching yarns and the top CMD yarns. These differences can induce the fabric to distort out-of-plane, which can in turn reduce the quality of paper produced with the fabric.
Also, the stitching yarns of a triple layer fabric should be sufficiently strong and durable to bind the top and bottom layers and to resist the wear and abrasion conditions that the bottom layer experiences while in contact with the paper machine, yet should be delicate enough to produce high quality paper. This balance can be quite difficult to strike.
In view of the foregoing, it is an object of the present invention to provide a multi-layer forming fabric construction with little distortion in the top fabric layer.
It is also an object of the present invention to provide a multi-layer forming fabric construction that produces a high quality paper.
It is another object of the present invention to provide a multi-layer forming fabric construction that maintains the top and bottom layers in a tightly bound condition.
It is a further object of the present invention to provide a multi-layer forming fabric that addresses the problem of interlayer wear.
These and other objects are satisfied by the present invention, which relates to a multi-layer papermaker's forming fabric with stitching yarns integrated into the papermaking surface. The fabric is formed as a plurality of repeating units. Each of the repeating units comprises: a set of top machine direction yarns; a set of top cross-machine direction yarns interwoven with the set of top machine direction yarns; a set of bottom machine direction yarns; a set of bottom cross-machine direction yarns interwoven with the set of bottom machine direction yarns; and pairs of first and second stitching yarns. The stitching yarn pairs are positioned between pairs of top cross-machine direction yarns. The stitching yarns of each pair are interwoven with the top and bottom machine direction yarns such that, as a fiber support portion of the first stitching yarn is interweaving with the top machine direction yarns, a binding portion of the second stitching yarn is positioned below the top machine direction yarns, and such that as a fiber support portion of the second stitching yarn is interweaving with the top machine direction yarns, a binding portion of the first stitching yarn is positioned below the top machine direction yarns. The first and second stitching yarns cross each other as they pass below a transitional top machine direction yarn. Also, each of the binding portions of the first and second stitching yarns passes below at least one of the bottom machine direction yarns. In this configuration, the stitching yarns are completely integrated into the top, or papermaking, surface of the fabric, and therefore do not adversely impact the papermaking qualities of the fabric. Also, the relatively large number of stitching yarns provides reliable binding of the top and bottom layers of the fabric.
In two illustrated embodiments of the fabric, the stitching yarns are interwoven with the top MD and CMD yarns so that they form a plain weave papermaking surface. In this embodiment, it is preferred that the stitching yarns be interwoven as “reverse picks” (this term is defined in detail hereinbelow). In another illustrated embodiment, the stitching yarns are interwoven with the top MD and CMD yarns to form a 1×2 twill top surface. In these embalmments, the integration of the stitching yarns into the papermaking surface of the fabric addresses many of the problems associated with prior art triple layer fabrics, such as distortion of the papermaking surface and inadequate binding of the top and bottom layers.
The present invention will be described more particularly hereinafter with reference to the accompanying drawings. The invention is not intended to be to the illustrated embodiments; rather, these embodiments are intended to fully and completely disclose the invention to those skilled in this art.
A 20 harness multi-layer forming fabric, generally designated at 20, is illustrated in
Referring now to
The top layer (formed by the top MD yarns and the top CMD yarns) and the bottom layer (formed by the bottom MD yarns and the bottom CMD yarns) are stitched together with twenty stitching yarns, designated herein as pairs 61a, 61b through 70a, 70b. The stitching yarns are positioned in pairs between adjacent CMD yarns. For example, stitching yarns 61a and 61b are positioned between top CMD yarns 31 and 32 and between bottom CMD yarns 51 and 52. The stitching yarns interweave with the top MD yarns and bottom MD yarns to bind the top and bottom fabric layers together.
As can be seen in
The weaving pattern of the stitching yarns is exemplified in
As can be seen in
Referring back to
It can also be seen in
It has been discovered that this “reversed picks” configuration is particularly effective in masking the presence of stitching yarns in the top surface of the fabric. When a transitional yarn passes over the stitching yarns of a pair to form a top surface knuckle, that knuckle tends to receive less upwardly-directed support from the stitching yarns at that location than other locations on the top MD yarn where it passes over a stitching yarn or top CMD yarn. As a result, that knuckle tends to be positioned slightly lower than the other top MD knuckles. As seen in
Those skilled in this art will appreciate that the aforedescribed “reverse picks” configuration is created in the fabric by weaving the stitching yarns into the top and bottom MD yarns so that first an “a” stitching yarn immediately follows the waving of top and bottom CMD yarns (followed by a “b” stitching yarn), then a “b” stitching yarn immediately follows the next set of top and bottom CMD yarns (followed by an “a” stitching yarn). This pattern can be repeated throughout weaving. Although it is preferred that all of the stitching yarn pairs follow this pattern (i.e., that 50 percent of the stitching yarn pairs be “reversed”), some benefit can be obtained by reversing only a smaller percentage (for example 25, 33, or 40 percent) of the stitching yarn pairs.
Another embodiment of the present invention is illustrated in
Like the fabric 20, the top MD and CMD yarns of the fabric 100 are interwoven such that each top CMD yarn passes over and under alternate MD yarns, and so that every CMD yarn passes over and under to same MD yarns. These, in combination with the stitching yarn pairs, form a top papermaking surface that has a plain weave pattern (FIG. 3A). The bottom MD and CMD yarns are interwoven so that each bottom CMD yarn follows an “over 1/under 5” pattern relative to the bottom MD yarns, and so that the knuckles formed by the bottom MD yarns take a “broken twill” pattern, in which the knuckles formed under adjacent CMD yarns are first offset by two MD yarns in one direction, then by three MD yarns in the opposite direction. Thus, the knuckles form a zig-zag diagonal pattern (see FIG. 3B).
Each of the stitching yarns of the fabric 100 has a fiber support portion, which interweaves with the top MD yarns, and a binding portion, which stitches the bottom layer of the fabric. As in the fabric 20, these portions of the stitching yarns are separated at transitional top MD yarns, under which both stitching yarns of a pair pass under and cross. The fiber support portion of each stitching yarn is positioned above the binding portion of the other stitching yarn of its pair.
Each of the stitching yarns of the fabric 100 follows the same weave pattern in its fiber support portion as it interweaves with the top MD yarns, with each stitching yarn passing over three top MD yarns and under two top MD yarns in an alternating fashion. The stitching yarns pass over the top MD yarns passed under by the top CMD yarns, then pass over the top MD yarns passed under by the top CMD yarns, with the result that the top layer of the fabric 100 has a plain weave surface. Pairs of stitching yarns are interwoven with the top MD yarns such that each group of four adjacent stitching yarn pairs falls within a pattern in which the fiber support portions of three of the four pairs of stitching yarns are not offset from one another in the MD direction at all; i.e., the fiber support portions of each pass over the same top MD yarns. The fiber support portion of fourth pair of stitching yarns of the group is offset from the others within the group by two top MD yarns. For the fiber support portions of the next group of four yarn pairs, the entire group is offset by two top MD yarns in the direction opposite of the offset of the individual stitching yarn pair.
As an example of this pattern, the stitching yarns 188a, 189a, 190a, and 191a form a group of four stitching yarns in adjacent stitching yarn pairs. Of these, stitching yarns 188a, 190a, and 191a pass over top MD yarns 105, 107, and 109. Stitching yarn 189a passes over top MD yarns 107, 109, and 111, which represents a two MD yarn offset. The next group of four stitching yarn pairs would then begin with stitching yarn 191a, which passes over top MD yarns 103, 105 and 107; this represents a two top MD yarn offset in the direction opposite that of the offset of stitching yarn 189a. This pattern continues for each group of four stitching yarn pairs.
In its binding portion, each stitching yarn passes below five top MD yarns and above four bottom MD yarns while passing below one bottom MD yarn to stitch the top and bottom layers together. The bottom MD yarn stitched by the stitching yarn binding portion follows one of three different patterns; it is either the second, third or fourth bottom MD yarn reached by the stitching yarn after passing below a traditional top MD yarn. For example, stitching yarn 182a passes below bottom MD yarn 144, the second bottom MD yarn it approaches after passing below transitional top MD yarn 102. In contrast, stitching yarn 181a passes below bottom MD yarn 147, the third bottom MD yarn it approaches after passing below traditional top yarn 104, and stitching yarn 183a passes below bottom MD yarn 146, the fourth bottom MD yarn it approaches after passing below transitional top MD yarn 102.
Notably, the stitching yarns of each pair follow the same weave pattern in their binding portions as the other stitching yarn of that pair (i.e., like stitching yarn 183a, stitching yarn 183b also stitches the fourth bottom MD yarn it approaches after passing below a transitional top MD yarn). Also, it can be seen from
Like the stitching yarns of the fabric 20, the stitching yarns of the fabric 100 are also interwoven as “reverse picks.” The “reveres picks” nature of the fabric can be see in
Those skilled in the art will also appreciate that other plain weave patterns in which the stitching yarns are divided differently into fiber support portions and binding portions can be constructed. For example, the fabric can include a top layer in which each stitching yarn of a pair passes over two or four top MD yarns in its fiber support portion. As illustrated, the stitching yarns can pass over different numbers of top MD yarns, or can pass over the same number. Of course, appropriate adjustment of the positioning of the bottom knuckles in the binding portions of such stitching yarns should be made with changes to the stitching yarn pattern on the top surface.
Another embodiment of a multi-layer forming fabric of the present invention is illustrated in
As shown in
Referring now to
The top and bottom layers of the fabric 200 are bound together by the stitching yarns listed above, each of which has both a fiber support portion and a binding portion. As with the fabrics 20 and 100 described earlier, the fiber support portion and binding portion of each stitching yarn are divided by traditional top MD yarns below which stitching yarns of a pair cross each other. The fiber support portion of each stitching yarn follows an “over 2/under 1/over 2” pattern. In its binding portions, each stitching yarn passes between the top and bottom MD yarns with the exception of passing below one bottom MD yarn to stitch the top and bottom layers together. The bottom MD yarn that is stitched is located either two or three MD yarns away from the transitional MD yarns that separate the fiber support and binding portions of each stitching yarn.
This pattern is exemplified by stitching yarn 285a, the stitching pattern of which is illustrated in FIG. 6E. Stitching yarn 285a passes over top MD yarns 201 and 202, under top MD yarn 203, and over top MD yarns 204, 205 before passing below transitional top MD yarn 206. In its binding portion, stitching yarn 285a passes above bottom MD yarns 247 and 248, below bottom MD yarn 249 and above bottom MD yarns 250, 251 before passing below transitional top MD yarn 212 and above bottom MD yarn 252.
Pairs of stitching yarns are interwoven with the top MD yarns relative to one another such that their fiber support portions, the top MD yarns, and the top CMD yarns form a 1×2 twill pattern. Referring again to
Those skilled in this art will appreciate that fabrics of the present invention can be construed with other twill patterns in the top layer. For example, a fabric can have a 1×3 or 1×4 twill top layer. Any of these twill patterns can be a conventional twill, such as that of the fabric 100, or can take a broken twill pattern, such as those embodied in 4 or 5 harness satin single layer fabrics. Fabrics can also be constructed in which fiber support portions of stitching yarn pairs pass over different numbers of top MD yarns. In each instance, the skilled artisan should understand the appropriate modifications to the binding portions of the stitching yarns to accommodate differences in the fiber support portions.
Those skilled in this art will recognize that, although the plain weave and twill fabrics illustrated and described in detail herein are preferred, other fabric weaves, such as other twill weaves and satins, that employ pairs of stitching yarns integrated into the papermaking surface of a fabric with the top CMD yarns can also be made. Also, any number of configuration of the bottom layer in which stitching yarn pairs stitch the bottom MD yarns can be used. It is also contemplated that, rather than including a pair of stitching yarns between each pair of top CMD yarns, a fabric in which a pair of stitching yarns is included between every other pair of top CMD yarns can be constructed. In addition, although the illustrated fabrics have equal numbers of top and bottom MD and CMD yarns, this need not be the case for the present invention; other ratios, such as two top CMD yarns for each bottom CMD yarn, can also be employed.
The configurations of the individual yarns utilized in the fabrics of the present invention can vary, depending upon the desired properties of the final papermakers' fabric. For example, the yarns may be multifilament yarns, monofilament yarns, twisted multifilament or monofilament yarns, spun yarns, or any combination thereof Also, the materials comprising yarns employed in the fabric of the present invention may be those commonly used in papermakers' fabric. For example, the yarns may be formed of cotton, wool, polypropylene, polyester, aramid, nylon, or the like. The skilled artisan should select a yarn material according to the particular application of the final fabric.
Regarding yarn dimensions, the particular size of the yarns is typically governed by the size and spacing of the papermaking surface. Generally, the diameter of the top CMD yarns is about 25 to 75 percent of the diameter of the bottom CMD yarns, and the diameter of the top MD yarns is about equal to or smaller than the diameter of the top CMD yarns. In a typical fabric, the diameter of the top CMD yarns is between about 0.11 and 0.17 mm, the diameter of the top MD yarns is between about 0.11 and 0.15 mm, the diameter of the bottom CMD yarns is between about 0.20 and 0.40 mm, and the diameter of the bottom MD yarns is between about 0.17 and 0.25 mm. The diameter of the stitching yarns is typically between about 0.11 and 0.17 mm.
Yarns may also vary advantageously in modulus of elasticity. For example, stitching yarns that interweave with a fewer number of top MD yarns than its paired stitching yarn (such as the “b” yarns of fabric 20) may have a higher modulus of elasticity (typically between about 10 and 50 percent higher) than its paired stitching yarn.
As the foregoing discussion demonstrates, the fabrics of the present invention address problems encountered with prior art triple layer forming fabrics. The fabrics of the present invention integrate the stitching yarns into the top surface of the fabric, whether it be a plain weave, a twill, a satin, or other pattern, and therefore avoid the marring of the papermaking surface that can accompany stitching yarns that comprise less of the papermaking surface. The integration of the fabric attributable to the stitching yarns also greatly reduces (if not eliminating) interlayer wear. In addition, because the stitching yarns comprise such a large portion of the papermaking surface, the differences in tension between the top CMD yarns and the stitching yarns that can distort the papermaking surfaces of other fabric are less critical to the fabrics of the present invention. The destiny of the stitching yarns also provides a tighter and more reliable binding of the top and bottom layers of the fabric, which can provide the designer with a wider variety of yarn choices to balance paper forming properties, durability and wear.
The foregoing embodiments are illustrative of the present invention, and are not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3325909 | Clark | Jun 1967 | A |
| 4501303 | Osterberg | Feb 1985 | A |
| 4605585 | Johansson | Aug 1986 | A |
| 4739803 | Borel | Apr 1988 | A |
| 4759975 | Sutherland et al. | Jul 1988 | A |
| 4987929 | Wilson | Jan 1991 | A |
| 5152326 | Vohringer | Oct 1992 | A |
| 5518042 | Wilson | May 1996 | A |
| 5564475 | Wright | Oct 1996 | A |
| 5709250 | Ward et al. | Jan 1998 | A |
| RE35777 | Givin | Apr 1998 | E |
| 5826627 | Seabrook et al. | Oct 1998 | A |
| Number | Date | Country |
|---|---|---|
| 454 092 | Aug 1927 | DE |
| 454092 | Aug 1927 | DE |
| 0 224 276 | Dec 1986 | EP |
| 0224276 | Dec 1986 | EP |
| 0408040 | Nov 1990 | EP |
| 0 408 849 | Nov 1990 | EP |
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| 0 794 283 | Sep 1997 | EP |
| 0794283 | Sep 1997 | EP |
| 2 597 123 | Oct 1987 | FR |
| 2597123 | Oct 1987 | FR |
| WO8600099 | Mar 1986 | WO |
| WO 8600099 | Mar 1986 | WO |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 08905130 | Aug 1997 | US |
| Child | 09982917 | US |
