Patent Application
20070068591
This application is directed generally to papermaking, and 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 dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.
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. Likewise, directional references to the vertical relationship of the yarns in the fabric (e.g., above, below, top, bottom, beneath, etc.) assume that the papermaking surface of the fabric is the top of the fabric and the machine side surface of the fabric is the bottom of the fabric.
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. A number of auto-joining machines are now commercially available, which for certain fabrics may be used to automate at least part of the joining process. 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 basic weaving 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. Both weaving methods described hereinabove 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 are important considerations in papermaking, especially for the forming section of the papermaking machine, where the wet web is initially formed. Additionally, the forming fabrics should exhibit good stability when they are run at high speeds on the papermaking machines, and preferably are highly permeable to reduce the amount of water retained in the web when it is transferred to the press section of the paper machine. In both tissue and fine paper applications (i.e., paper for use in quality printing, carbonizing, cigarettes, electrical condensers, and like) the papermaking surface comprises a very finely woven or fine wire mesh structure.
Typically, finely woven fabrics such as those used in fine paper and tissue applications include at least some relatively small diameter machine direction or cross machine direction yarns. Regrettably, however, such yarns tend to be delicate, leading to a short surface life for the fabric. Moreover, the use of smaller yarns can also adversely affect the mechanical stability of the fabric (especially in terms of skew resistance, narrowing propensity and stiffness), which may negatively impact both the service life and the performance of the fabric.
To combat these problems associated with fine weave fabrics, 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 which employ one set of machine direction yarns which interweave with two sets of cross machine direction yarns to form a fabric having a fine paper forming surface and a more durable machine side surface. These fabrics form part of a class of fabrics which are generally referred to as “double layer” fabrics. Similarly, fabrics have been constructed which include two sets of machine direction yarns and two sets of cross machine direction yarns that form a fine mesh paperside fabric layer and a separate, coarser machine side fabric layer. In these fabrics, which are part of a class of fabrics generally referred to as “triple layer” fabrics, the two fabric layers are typically bound together by separate stitching yarns. However, they may also be bound together using yarns from one or more of the sets of bottom and top cross machine direction and machine direction yarns. As double and triple layer fabrics include additional sets of yarn as compared to single layer fabrics, these fabrics typically have a higher “caliper” (i.e., they are thicker) than comparable single layer fabrics. An illustrative double layer fabric is shown in U.S. Pat. No. 4,423,755 to Thompson, and illustrative triple layer fabrics are shown in U.S. Pat. No. 4,501,303 to Osterberg, U.S. Pat. No. 5,152,326 to Vohringer, U.S. Pat. Nos. 5,437,315 and 5,967,195 to Ward, and U.S. Pat. No. 6,745,797 to Troughton.
U.S. Pat. No. 6,896,009 and co-pending and co-assigned U.S. patent application Ser. No. 11/207,277, filed Aug. 18, 2005 describe a number of exemplary multi-layer forming fabrics that are “warped-stitched.” In some instances such fabrics may be easier to manufacture than weft-stitched forming fabrics and/or may have desirable performance properties. However, there is still a demand for additional types of warp-stitched fabrics to meet the vast array of papermaking needs.
As a first aspect, embodiments of the present invention are directed to a papermaking fabric, comprising a series of repeat units, each of the repeat units including: a set of top MD yarns; a set of top CMD yarns interwoven with the set of top MD yarns; a first set of bottom MD yarns, the first set of bottom MD yarns arranged in pairs; a second set of bottom MD yarns, the second set of bottom MD yarns arranged as single yarns; a set of bottom CMD yarns interwoven with the first and second sets of bottom MD yarns; and a set of pairs of MD stitching yarns interwoven with the top and bottom CMD yarns, each pair of MD stitching yarns sandwiching a respective immediately adjacent bottom MD yarn of the second set. Each of the yarns of a pair of the first set of bottom MD yarns interweaves with the bottom CMD yarns in the same pattern.
As a second aspect, embodiments of the present invention are directed to a papermaking fabric, comprising a series of repeat units, each of the repeat units including: a set of top MD yarns; a set of top CMD yarns interwoven with the set of top MD yarns; a first set of bottom MD yarns, the first set of bottom MD yarns arranged in pairs; a second set of bottom MD yarns, the second set of bottom MD yarns arranged as single yarns; a set of bottom CMD yarns interwoven with the first and second sets of bottom MD yarns; and a set of pairs of MD stitching yarns interwoven with the top and bottom CMD yarns, each pair of MD stitching yarns sandwiching a respective immediately adjacent bottom MD yarn of the second set. Each of the yarns of a pair of the first set of bottom MD yarns interweaves with the bottom CMD yarns in the same pattern. Also, each pair of bottom MD yarns of the first set is positioned beneath a top MD yarn.
As a third aspect, embodiments of the present invention are direction to a papermaking fabric, comprising a series of repeat units, each of the repeat units including: a set of top machine direction (MD) yarns; a set of top cross machine direction (CMD) yarns interwoven with the set of top MD yarns; a first set of bottom MD yarns, each of the yearns of the first set having a flattened cross-section; a second set of bottom MD yarns, the second set of bottom MD yarns arranged as single yarns; a set of bottom CMD yarns interwoven with the first and second sets of bottom MD yarns; and a set of pairs of MD stitching yarns interwoven with the top and bottom CMD yarns, each pair of MD stitching yarns sandwiching a respective immediately adjacent bottom MD yarn of the second set.
As a fourth aspect, embodiments of the present invention are directed to a method of making paper, comprising the steps of: (a) providing a papermaking fabric, the fabric comprising: a set of top MD yarns; a set of top CMD yarns interwoven with the set of top MD yarns; a first set of bottom MD yarns, the first set of bottom MD yarns arranged in pairs; a second set of bottom MD yarns, the second set of bottom MD yarns arranged as single yarns; a set of bottom CMD yarns interwoven with the first and second sets of bottom MD yarns; and a set of pairs of MD stitching yarns interwoven with the top and bottom CMD yarns, each pair of MD stitching yarns sandwiching a respective immediately adjacent bottom MD yarn of the second set; wherein each of the yarns of a pair of the first set of bottom MD yarns interweaves with the bottom CMD yarns in the same pattern; (b) depositing paper stock on the papermaking fabric; and (c) removing moisture from the papermaking stock.
The present invention will be described more particularly hereinafter with reference to the accompanying drawings. The invention is not intended to be limited to the illustrated embodiments; rather, these embodiments are intended to fully and completely disclose the invention to those skilled in this art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity.
Well-known functions or constructions may not be described in detail for brevity and/or clarity.
As used herein the expression “and/or” includes any and all combinations of one or more of the associated listed items.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Although the figures below only show single repeat units of the fabrics illustrated therein, those of skill in the art will appreciate that in commercial applications the repeat units shown in the figures would be repeated many times, in both the machine and cross machine directions, to form a large fabric suitable for use on a papermaking machine.
Turning now to
As can be seen in
As can be seen in
Each pair of stitching yarns is offset from its neighboring stitching yarn pairs by two top CMD yarns. This can be seen by examination of
The bottom layer of the fabric 10 is illustrated in
The paired bottom MD yarns, which are located beneath a corresponding top MD yarn, interweave as a pair with the bottom CMD yarns in a repeating “over 2/under 1” sequence. For example, referring to
Referring again to
A repeat unit of another fabric according to embodiments of the present invention is designated broadly at 110 and is illustrated in
As can be seen in
As can be seen in
Each pair of stitching yarns is offset from its neighboring stitching yarn pairs by four top CMD yarns. This can be seen by examination of
The bottom layer of the fabric 110 is illustrated in
Referring again to
It can be seen that, in the illustrated embodiment, the paired “a” bottom MD yarns are smaller in diameter than the paired “b” bottom MD yarns. It may be desirable in some embodiments for the “a” yarns to match the diameter of the stitching yarns, such that the paired knuckles of (a) the paired bottom MD yarns and (b) the pair knuckles of the unpaired bottom MD yarns and the stitching yarns are the same dimension. Those sklled in this art will appreciate that, in other embodiments (such as those of
A repeat unit of a further fabric according to embodiments of the present invention is designated broadly at 210 and is illustrated in
As can be seen in
As can be seen in
Each pair of stitching yarns is offset from its neighboring stitching yarn pairs by two top CMD yarns. This can be seen by examination of
The bottom layer of the fabric 210 is illustrated in
Referring again to
Each pair of paired bottom MD yarns is offset from its neighboring paired bottom MD yarns by one bottom CMD yarn. For example, paired bottom MD yarns 251a, 251b pass under bottom CMD yarn 275, and paired bottom MD yarns 252a, 252b pass under bottom CMD yarn 276, which is offset from bottom CMD yarn 276 by one bottom CMD yarn. Each unpaired bottom MD yarn is also offset from its neighboring unpaired bottom MD yarn by one bottom CMD yarn. For example, unpaired bottom MD yarn 261 forms a knuckle under bottom CMD yarn 273, and unpaired bottom CMD yarn 262 forms a knuckle under bottom CMD yarn 274, which is offset from bottom CMD yarn 273 by one bottom CMD yarn. As a result, the pairs of knuckles formed by the paired bottom MD yarns on the bottom surface form one diagonal thereon, and the pairs of knuckles formed by an unpaired bottom MD yarn and a stitching yarn form a second diagonal on the bottom surface. The knuckles formed by the paired bottom MD yarns are offset from the knuckles formed by an unpaired bottom MD yarn and a stitching yarn are offset from each other by two bottom CMD yarns.
As can be seen in
The form of the yarns utilized in fabrics of the present invention can vary, depending upon the desired properties of the final papermaker's fabric. For example, the yarns may be monofilament yarns, flattened monofilament yarns as described above, multifilament 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 papermaker's fabric. For example, the yarns may be formed of polyester, polyarnide (nylon), polypropylene, aramid, or the like. The skilled artisan should select a yarn material according to the particular application of the final fabric. In particular, round monofilament yarns formed of polyester or polyarnide are preferred.
Fabrics such as those illustrated above can demonstrate improved seam strength compared to similar prior fabrics, which may permit the use of fewer ends for joining the fabric. Also, increases in fabric open area and/or permeability can be achieved.
Pursuant to another aspect of the present invention, methods of making paper are provided. Pursuant to these methods, one of the exemplary papermaker's forming fabrics described herein is provided, and paper is then made by applying paper stock to the forming fabric and by then removing moisture from the paper stock. As the details of how the paper stock is applied to the forming fabric and how moisture is removed from the paper stock is well understood by those of skill in the art, additional details regarding this aspect of the present invention need not be provided herein.
The foregoing embodiments are illustrative of the present invention, and are not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.
