WO2004085741A1

WO2004085741A1 - Machine direction yarn stitched triple layer papermaker's forming fabrics

Info

Publication number: WO2004085741A1
Application number: PCT/US2004/008311
Authority: WO
Inventors: Kevin J. Ward
Original assignee: Weavexx Corporation
Priority date: 2003-03-19
Filing date: 2004-03-18
Publication date: 2004-10-07
Also published as: KR20050117569A; US20070157987A1; KR100768490B1; AU2004223463B2; US6959737B2; AU2004223463A1; US20050121097A1; CN1761788A; EP1604064A1; CA2519224A1; US6896009B2; US20040182464A1; US7441566B2; MXPA05009853A; JP2006520862A; BRPI0408426A

Abstract

Triple layer papermaker's forming fabrics having a set of top MD yarns that are interwoven exclusively with a set of top CMD yarns to form at least part of a top fabric layer and a set of bottom MD yarns that are interwoven exclusively with a set of bottom CMD yarns to form at least part of a bottom fabric layer are provided. These fabrics further include a set of stitching MD yarn pairs. The stitching MD yarns that comprise each such pair weave in both the top fabric layer and the bottom fabric layer such that at locations where the first yarn in the pair weaves in the top fabric layer the second yarn in the pair drops down into the bottom fabric layer. In embodiments of the present invention, each stitching MD yarn may also be woven so as to form side-by-side machine direction knuckles on the bottom surface of the bottom fabric layer with a bottom MD yarn. In other embodiments of the invention, at least some of the top CMD yarns that the stitching MD yarns of the stitching MD yarn pairs pass over immediately before dropping down into the bottom fabric layer have a larger diameter and/or a higher modulus than the remainder of the top CMD yarns.

Description

MACHINE DIRECTION YARN STITCHED TRIPLE LAYER PAPERMAKER'S FORMING FABRICS

RELATED APPLICATION

This application is a continuation-in-part of U.S. Patent Application No. 10/391,827, filed March 19, 2003, the disclosure of which are hereby incorporated herein in its entirety.

FIELD OF THE INVENTION The present invention relates generally to papermaking. and relates more specifically to forming fabrics employed in papermaking.

BACKGROUND OF THE INVENTION

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 papeπr aking 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 yams 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 yams 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. Patent No. 4,423,755 to Thompson, and illustrative triple layer fabrics are shown in U.S. Patent No. 4,501,303 to Osterberg, U.S. Patent No. 5,152,326 to Vohringer, U.S. Patent No. 5,437,315 to Ward and U.S. Patent No. 5,967,195 to Ward.

SUMMARY OF THE INVENTION

The present invention relates to machine direction yam stitched triple layer papermaker's forming fabrics which can exhibit relatively good drainage, permeability and machine direction yarn stacking characteristics, and in some instances may have reduced diagonal marking. In one embodiment of the present invention, a triple layer papermaker's fabric includes: a set of top CMD yams; a set of top MD yams interwoven exclusively with the top CMD yarns to form at least part of a top fabric layer having a papermaking surface; a set of bottom CMD yarns; a set of bottom MD yams interwoven exclusively with the bottom CMD yarns to form at least part of a bottom fabric layer having a machine side surface, the bottom MD yarns forming bottom MD knuckles as they pass below bottom CMD yarns; and a pair of additional MD yams disposed on either side of each top MD yam, wherein the first yarn of each pair of additional MD ya s weaves exclusively in the top fabric layer and the second yam of each pair of additional MD yarns completes the weave of the first yam of each pair of additional MD yams on the papermaking surface and also weaves with the bottom fabric layer beneath a bottom CMD yam to form a bottom MD stitching yam knuckle so as to bind the top fabric layer and the bottom fabric layers together. Each bottom stitching yarn knuckle is formed below a bottom CMD yarn under which an adjacent bottom MD yarn forms a bottom MD knuckle. In another embodiment of the present invention, a triple layer papermaker's forming fabric includes: a set of top CMD yams; a set of top MD yams interwoven exclusively with the top CMD yams to form at least part of a top fabric layer having a papermaking surface; a set of bottom CMD yams; a set of bottom MD yams interwoven exclusively with the bottom CMD yams to form at least part of a bottom fabric layer having a machine side surface, the bottom MD yarns forming bottom MD knuckles as they pass below bottom CMD yarns; and a pair of additional MD yarns disposed on either side of each top MD yarn, wherein the first yam of each pair of additional MD yams weaves exclusively in the top fabric layer and the second yarn of each pair of additional MD yams completes the weave of the first yam of each pair of additional MD yams on the papermaking surface and also weaves with the bottom fabric layer beneath a bottom CMD yarn to form a bottom MD stitching yarn knuckle so as to bind the top fabric layer and the bottom fabric layers together. In this embodiment, each of the additional MD yams forms knuckles by passing over the top CMD yams, and wherein the number of knuckles formed by the first yam of each pair of additional MD yams differs from the number of knuckles formed by the second yarn of each pair. Another aspect of the present invention includes methods of using a triple layer papermaker's forming fabric as described above for making paper.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a top view of the top fabric layer of an embodiment of a 16 harness triple layer forming fabric of the present invention.

Figure 2 is a top view of the bottom fabric layer of the triple layer forming fabric of Figure 1.

Figures 3A-3P are machine direction section views taken along the lines 3 A- 3 A through 3P-3P of Figures 1 and 2. Figure 4 is a top view of the top fabric layer of another embodiment of a 16 harness triple layer forming fabric of the present invention.

Figure 5 is a top view of the bottom fabric layer of the triple layer forming fabric of Figure 4.

Figures 6A-6D are machine direction section views taken along the lines 6A- 6A through 6D-6D of Figures 4 and 5.

Figure 7 is a top view of the top fabric layer of another embodiment of a 16 harness triple layer forming fabric of the present invention.

Figure 8 is a top view of the bottom fabric layer of the triple layer forming fabric of Figure 7. Figures 9A-9D are machine direction section views taken along the lines 9A-

9A through 9D-9D of Figures 7 and 8. Figure 10 is a top view of the top fabric layer of a 20 harness triple layer forming fabric of the present invention.

Figure 11 is a top view of the bottom fabric layer of the triple layer forming fabric of Figure 10. Figures 12A-12E are machine direction section views taken along the lines

12A-12A through 12D-12D of Figures 10 and 11.

Figure 13 is atop view of the top fabric layer of another embodiment of a 16 harness triple layer forming fabric of the present invention.

Figure 14 is a top view of the bottom fabric layer of the triple layer forming fabric of Figure 13.

Figures 15A-15D are machine direction section views taken along the lines 15A-15A through 15D-15D of Figures 13 and 14.

Figure 16 is atop view of the top fabric layer of another embodiment of a 12 harness triple layer fomiing fabric of the present invention. Figure 17 is a bottom view of the bottom fabric layer of the triple layer forming fabric of Figure 16.

Figures 18A-18B are machine direction section views taken along the lines 18A-18A through 18D-18D of Figures 16 and 17.

Figure 19 is a top view of the top fabric layer of another embodiment of a 24 harness triple layer forming fabric of the present invention.

Figure 20 is a bottom view of the bottom fabric layer of the triple layer forming fabric of Figure 19.

Figures 21A-21D are machine direction section views taken along the lines 21 A-21 A through 21D-21D of Figures 19 and 20. Figure 22 is a top view of the top fabric layer of another embodiment of an 8 harness triple layer forming fabric of the present invention.

Figure 23 is a bottom view of the bottom fabric layer of the triple layer forming fabric of Figure 22.

Figures 24A-24B are machine direction section views taken along the lines 24A-24A through 24D-24D of Figures 22 and 23.

Figure 25 is a top view of the top fabric layer of another embodiment of an eight harness triple layer forming fabric of the present invention. Figure 26 is a bottom view of the bottom fabric layer of the triple layer forming fabric of Figure 16.

Figures 27A-27D are machine direction section views taken along the lines 27-27A through 27D-27D of Figures 25 and 26.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments or other embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the figures, the dimensions of some components may be exaggerated for clarity.

One aspect of the present invention is directed to machine direction yam stitched triple layer papermaker's forming fabrics that include both a top fabric layer and a bottom fabric layer. These fabrics are "true" triple layer fabrics in that they include sets of machine direction yams and cross machine direction yams that only weave in the top fabric layer, as well as sets of machine direction yams and cross machine direction yams that only weave in the bottom fabric layer. The fabrics also include pairs of adjacent machine direction yams that together replace the equivalent of a single machine direction yam in the weave pattern on the papermaking surface. These yarns are woven such that when one yarn in the pair is weaving in the top fabric layer so as to complete the weave pattern on the papermaking surface, the second yam in the pair weaves below the papermaking surface. Throughout the fabric, these yams trade these positions. At least one of the yams in the pair also drops down to the bottom fabric layer at one or more points so as to bind the top and bottom fabric layers together. Herein, these yam pairs are referred to as "stitching MD yarn pairs" (even in those embodiments in which only one yam of the pair actually "stitches" with the bottom fabric layer). Individual yarns from these yam pairs are typically referred to as a "stitching MD yarn." An embodiment of the machine direction yam stitched triple layer fabrics of the present invention is illustrated in Figures 1-3 and designated broadly at 100. Figure 1 depicts a top view of the top fabric layer 102 of the triple layer fabric 100 (i.e., a view of the papermaking surface) while Figure 2 depicts a top view of the bottom fabric layer 104 of fabric 100 (i.e., a view of the fabric 100 with the yams that weave exclusively in the top fabric layer 102 removed). Figures 3A-3P depict the paths of each of the machine direction yams in one repeat unit of the fabric 100. The triple layer fabric 100 of Figures 1-3 is woven on 16 harnesses, and hence a single repeat of the fabric encompasses 16 machine direction yams. While Figures 1 and 2 only show a single repeat unit of the fabric, those of skill in the art will appreciate that in commercial applications the repeat unit shown in Figures 1 and 2 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.

As seen in Figure 1, the repeat unit of the top fabric layer 102 includes a set of top MD yarns 110-113 and a set of top CMD yams 130-145 that are interwoven together. The top fabric layer further includes a set of four stitching MD yam pairs 120, 124; 121, 125; 122, 126; 123, 127 that also interweave with the top CMD yarns 130-145. As shown in Figure 1, a stitching MD yarn pair, such as for example, stitching MD yam pair 120, 124, is provided between each pair of adjacent top MD yarns, such as yams 110-111. Each stitching MD yarn pair (such as pair 120, 124) is woven such that while one of the yams of the pair (e.g., yam 120) weaves in the top fabric layer 102 to complete the weave pattern in the top fabric layer 102, the other of the stitching MD yams (e.g., yam 124) drops down into the bottom fabric layer 104 to bind the top fabric layer 102 and the bottom fabric layer 104 together. In this manner, the stitching MD yam pairs 120, 124; 121, 125; 122, 126; 123, 127 both complete the weave of the top layer fabric 102 and also serve to bind the top and bottom fabric layers 102, 104 together.

As shown in Figure 1, the yams comprising the set of top CMD yams 130- 145 are interwoven with the set of top layer MD yams 110-113 and the stitching MD yam pairs 120, 124; 121, 125; 122, 126; 123, 127 in a lxl or "plain weave" pattern, meaning that each of the top CMD yams 130-145 alternatively pass below one, and then above the next, of the machine direction yams that at that point are weaving in the papermaking surface. For example, top CMD yarn 130 passes below top MD yam 110, above stitching MD yam 120, below top MD yarn 111, above stitching MD yam 121, below top MD yam 112, above stitching MD yarn 122, below top MD yarn 113, and above stitching MD yarn 127. The other top CMD yams 131-145 follow an identical "over one/under one" pattern, although this pattern is offset by one machine direction yam for adjacent top CMD yams 130-145.

Referring now to Figure 2, a repeat unit of the top surface of the bottom fabric layer 104 of the fabric 100 is shown. The repeat unit includes a set of bottom MD yarns 150-153 which are interwoven with a set of bottom CMD yams 160-167. The repeat unit further includes the stitching MD yam pairs 120, 124; 121, 125; 122, 126; 123, 127 which are described above.

As shown best in Figure 2, the bottom CMD yams 160-167 may be constructed using relatively large diameter yams that are well suited to sustain the wear caused by the friction between the machine side surface of the fabric 100 and the papermaking machine during use of the fabric 100. As can be seen in Figure 2, the weave pattern of fabric 100 provides relatively long cross machine direction "floats" on the machine side surface, meaning that when viewing the machine side surface (i.e., the bottom surface) of the bottom fabric layer 104, the CMD yarns pass or "float" above large numbers of adjacent machine direction yarns. This may be advantageous in that it allows the larger, sturdier bottom CMD yarns 160-167 to primarily contact the papermaking machine.

As noted above, in the fabric depicted in Figures 1 and 2, the top fabric layer 102 (pictured in Figure 1) and the bottom fabric layer 104 (pictured in Figure 2) are bound together by the stitching MD yarn pairs 120, 124; 121, 125; 122, 126; 123, 127. In Figure 1, only those portions of the stitching MD yams 120-127 which weave with the top fabric layer 102 are depicted. In Figure 2, the entirety of the stitching MD yams 120-127 are shown, but those portions of the stitching warp yam that weave in the top fabric layer are shown using dotted lines.

Figures 3A-3P depict the individual machine direction yam paths of each of the sixteen MD yams in one repeat of the fabric 100. As shown in Figures 3 A, 3E, 31 and 3M, the top MD yams 110-113 are woven in identical over-one/under-one patterns with the top CMD yarns 130-145. These top MD yams 110-113 do not weave with the bottom fabric layer 104. As shown in Figures 3B, 3F, 3J and 3K, the bottom MD yarns 150-153 are woven with the bottom CMD yams 160-167 in an over-four/under-one/over-two/under-one pattern, meaning that each bottom MD yam 150-153 passes over four yams in the set of bottom CMD yams 160-167, below the next bottom CMD yam, above the next two bottom CMD yarns, and below the next bottom CMD yarn in each repeat unit of the fabric. For example, as shown in Figure 3F, bottom MD yam 151 passes above bottom CMD yams 165-167 and 160, below bottom CMD yam 161, above bottom CMD yams 162-163, and below bottom CMD yam 164. The other bottom CMD yams 150, 152-153 follow a similar "over- four/under-one/over-two/under-one pattern" weave pattern, although this pattern is offset by two bottom CMD ya s 160-167 for each adjacent bottom MD yarn 151- 153.

Figures 3C, 3G, 3K and 3O depict the individual machine direction yarn paths for stitching MD yarns 120, 121, 122 and 123, respectively. As shown, yarns 120-123 are woven in identical patterns with the top CMD yams 130-145 and the bottom CMD yarns 160-167, with each stitching MD yam 120-123 offset by two bottom CMD yarns (and hence four top CMD yarns) with respect to the stitching MD yarns 120-123 adjacent to it. As shown, for example, in Figure 3C, stitching MD yarns 120-123 weave with the top CMD yams 130-145 in an under-one/over- one/under-one/over-one/under-one/over-one/under-one/over-one/ under-one/over- one/under-six pattern. The stitching MD yarns also interweave with the bottom CMD yarns 160-167 in an over-seven/under-one pattern.

Figures 3D, 3H, 3L and 3P depict the individual machine direction yam paths for stitching MD yams 124, 125, 126 and 127, respectively. As shown, yarns 124- 127 are woven in identical patterns with the top CMD yams 130-145 and the bottom CMD yams 160-167, with each stitching MD yarn 124-127 offset by two bottom CMD yams (and hence four top CMD yams) with respect to the stitching MD yams 124-127 adjacent to it. As shown, for example, in Figure 3D, stitching MD yarns 120-123 weave with the top CMD yams 130-145 in an under-eleven/over-one/under- one/over-one/under-one/over-one pattern.. The stitching MD yams 124-127 also interweave with the bottom CMD yams 160-167 in an over-seven/under-one pattern. As can be seen from Figures 1-3, only 50% of the machine direction yams in the fabric 100 weave in both the top fabric layer 102 and the bottom fabric layer 104. As a result of this configuration, improved "stacking" of the yarns running in the machine direction may be obtained. Specifically, the top MD yams 110-113 may be arranged so that they are substantially directly above the bottom MD yams 150-153. Such an arrangement can provide desirable straight through drainage so that water reaching the top surface of the top fabric layer 102 meets relatively large drainage holes between the yams that go straight through to the bottom of the bottom fabric layer 104. Such an arrangement can provide improved water drainage and easier cleaning, which is a desired fabric feature in many papermaking applications.

Additionally, by having less than 100% of the machine direction yams weaving in both the top and bottom fabric layers 102, 104, it is generally possible to increase permeability and uniformity as compared to an equivalent fabric formed with 67% or 100% of the machine direction yams configured as stitching yams such as the fabrics claimed in U.S. Patent No. 6,202,705 or German patent WO 02/00996-02 Al . These features are also desirable in numerous papermaking applications.

As can also be seen in Figure 2, each bottom MD yarn 150-153 alternatively comes together with or "couples" with the stitching MD yams 120-127 that are adjacent to it on each side. Thus, for example, bottom MD yam 151 couples with stitching MD yarn 121 in the vicinity of bottom CMD yam 164, while it couples with stitching MD yam 124 in the vicinity of bottom CMD yarn 161. The pairing occurs proximate the locations where the bottom MD yarns 150-153 pass below the bottom CMD yarns 160-167 such that they are in a position to be protected from coming in contact with the papermaking machine. Often, when two adjacent yams "couple" in this manner persons of skill in the art refer to the two yams as "pairing" at the locations where the yarns come together in the weave. However, to avoid confusion given the references to "stitching MD yam pairs" in this application, the word "couples" will be used to describe situations where two yams come together within the weave. The coupling arrangement that occurs between the bottom MD yams 150-153 and the stitching MD yarns 120-127 may have several beneficial effects in certain applications. First, by coupling at these locations each individual yam may come into less contact with the papermaking machine since the yams tend to act to protect each other. This may advantageously extend the life of the fabric, as a potential failure point for the fabric is wear of the MD yams that come in contact with the papermaking machine. Additionally, having two MD yarns coupled at the locations where the MD yams float below the CMD yams potentially acts to increase the upward force on the bottom CMD yarn at that location. This increased upward force helps to "bury" the machine side MD yarn floats up into the bottom fabric layer 104, which further may help to reduce the machine-induced wear on the bottom MD yams 150-153 and the stitching MD yams 120-127. Third, as best seen in Figure 2, a relatively large drainage hole is provided adjacent each location where the coupling occurs. These larger drainage holes may serve to facilitate drainage of water from the fabric 100.

In the embodiment of Figures 1-3, all of the stitching MD yams 120-127 weave in both the top and bottom fabric layers 102, 104 to stitch the fabric layers together. It will be appreciated that not all of the stitching MD yams need to perform such a stitching function, as is made clear in the description of the following fabric.

Another fabric 200 constructed according to the teachings of the present invention is illustrated in Figures 4-6. Figure 4 depicts a top view of the top fabric layer 202 of the triple layer fabric 200 (i.e., a view of the papermaking surface) while Figure 5 depicts a top view of the bottom fabric layer 204 of fabric 200 (i.e., a view of the fabric 200 with the yams that weave exclusively in the top fabric layer 202 removed). Figures 6A-6D depict the weave pattern of top MD yarn 210, bottom MD yarn 250, and stitching MD yarns 224 and 220, respectively. Those of skill in the art will appreciate that in commercial applications the depicted portion of the fabric would be repeated many times, in both the machine and cross machine directions. As seen in Figure 4 the top fabric layer 202 includes a set of top MD yams 210-213 and a set of top CMD yams 230-245 that are interwoven together. The top fabric layer further includes a set of four stitching MD yarn pairs 220, 224; 221, 225; 222, 226; 223, 227 that also interweave with the top CMD yams 230-245. As shown in Figure 4, a stitching MD yam pair, such as for example, stitching MD yarn pair 220, 224, is provided between each pair of adjacent top MD yams (e.g., yams 210- 211). The stitching MD yam pairs are woven such that while one of the yams in the pair (e.g., yam 220) weaves in the top fabric layer 202 to complete the weave pattern in the top fabric layer 202, the other yarn of the pair (e.g., yarn 224) drops below the papermaking surface. As best seen in Figures 6C and 6D, in the embodiment of fabric 200, only one of the two yams in each stitching MD yarn pair (e.g., yam 224 in stitching MD yarn pair 220, 224) drops down into the bottom fabric layer 204 to bind the top fabric layer 202 and the bottom fabric layer 204 together. The other yarn in the stitching MD yarn pair (e.g., yarn 220) drops below the papermaking surface and travels between the top fabric layer 202 and the bottom fabric layer 204 at positions in the weave where the second yam in the stitching MD yam pair (e.g., yam 224) travels up to the papermaking surface to complete the weave of the top fabric layer 202.

Referring now to Figure 5, the machine side surface of the bottom fabric layer 204 is shown. The bottom fabric layer 204 includes a set of bottom MD yams 250- 253 which are interwoven with a set of bottom CMD yarns 260-267. The repeat unit further includes stitching MD yams 224-227 which, as noted above, weave in both the top fabric layer 202 and the bottom fabric layer 204 to bind the fabric layers together. As shown in Figure 5, the bottom CMD yams 260-267 of fabric 200 may be constructed using relatively large diameter yams that are well suited to sustain the wear caused by the papermaking machine during use of the fabric 200. As can also be seen in Figure 5, the weave pattern of fabric 200 provides relatively long cross machine direction "floats" on the machine side surface.

Figures 6A-6D depict the individual machine direction yarn paths of representative machine direction yams in the fabric 200. Figure 6A depicts the machine direction yam paths for top MD yam 210. Top MD yams 211-213 are woven in identical weave patterns. As shown in Figure 6 A, each of these top MD yams 210-213 are woven in over-one/under-one patterns with the top CMD yarns 230-245, and do not weave with any yams in the bottom fabric layer 204.

Figure 6B depicts the machine direction yarn path of bottom MD yarn 250. As shown in Figure 6B, bottom MD yarn 250 weaves with the bottom CMD yarns 260-267 in an over-three/under-one/over-three/under-one pattern - i.e., it passes over bottom CMD yarns 267, 260-261, passes under bottom CMD yam 262, passes over ' bottom CMD yarns 263-265 and passes under bottom CMD yarn 266 in each repeat of the fabric. The other bottom MD yams 251-253 follow a similar "over- toee/under-one/over-three/under-one pattern" weave pattern, although the starting point for the pattern is offset by two bottom CMD yams 260-267 for each adjacent bottom MD yam 250-253.

Figure 6C depicts the machine direction yam path of stitching MD yarn 224. As shown in Figure 6C, stitching MD yarn 224 is woven in an over-three/under- one/over-three/under-one pattern with respect to the bottom CMD yams 260-267, and is woven in a over-seven under-one/over-seven under-one pattern with respect to the top CMD yams 230-245. Stitching MD yarns 225-227 follow the same patterns with respect to the bottom CMD yams 260-267 and the top CMD yams 230-245 as stitching MD yam 224, except that the starting point for the pattern is offset by two bottom CMD yams 260-267 (and hence four top CMD yams 230-245) for each adjacent stitching MD yam 224-227.

Figure 6D depicts the machine direction yam path of stitching MD yarn 220. As shown in Figure 6D, stitching MD yam 220 is woven in an under-one/over- one/under-three/over-one/under-one/over-one/under-one/over-one/under-three/over- one/under-one/over-one pattern with respect to the top CMD yarns 230-245. Stitching MD yam 220 does not weave with the bottom CMD yams 260-267. Stitching MD yarns 221-223 follow the same patterns with respect to the top CMD yams 230-245 as stitching MD yam 220, except that the starting point for the pattern is offset by four top CMD yams 230-245 for each adjacent stitching MD yam 220- 223.

As shown in Figures 6C and 6D, the stitching MD yam pairs 220, 224; 221, 225; 222, 226; 223, 227 weave in a "dropped knuckle pattern" to complete the weave in the papermaking surface. By "dropped knuckle pattern" it is meant that one of the yarns in each pair (yams 220-223) substantially completes the weave in the papermaking surface, but occasionally the yam skips one of the knuckles where it crosses over a top CMD yarn in its over-one/under-one pattern so as to allow the other yarn of the pair (yams 224-227) to interlace with the top fabric layer. The dropped knuckle pattern may be advantageous in various applications as fine paper, newsprint and brown paper applications.

Pursuant to another aspect of the present invention, it will be realized that the position of the stitching MD yams in the fabric may have a significant impact on fabric performance. For example, in the fabric 100 of Figures 1-3, stitching MD yams 124-127 may be woven off the same warp beam as bottom MD yams 150-153 and stitching MD yams 120-123 may be woven off the same warp beam as top MD yams 110-113. As can best be seen in Figure 1, with this weaving configuration, in each stitching MD yam pair the stitching MD yams that form five knuckles per repeat on the papermaking surface (yams 124-127) fall slightly to the left (from the vantage point of Figure 1) of the stitching yams that form three knuckles per repeat on the papermaking surface (yarns 120-123). Thus, for example, in Figure 1 stitching MD yarn 120 falls slightly to the left of stitching MD yam 124. Figure 7 depicts a top view of the top fabric layer 302 of a triple layer fabric

300 having the reverse weave on the stitching MD yarns. As seen in Figure 7, the repeat unit of the top fabric layer 302 includes a set of top MD yams 310-313 and a set of top CMD yarns 330-345 that are interwoven together. The top fabric layer further includes a set of four stitching MD yam pairs 320, 324; 321, 325; 322, 326; 323, 327 that also interweave with the top CMD yams 330-345 and that are provided between each pair of adjacent top MD yarns. The stitching MD yam pairs are woven such that while one of the yarns in the pair (e.g., yarn 320) weaves in the top fabric layer 302 to complete the weave pattern in the top fabric layer 302, the other yam of the pair (e.g., yam 324) drops below the papemiaking surface. Figure 8 depicts a repeat unit of the machine side surface of the bottom fabric layer 304 of the fabric 300. The repeat unit includes a set of bottom MD yams 350- 353 which are interwoven with a set of bottom CMD yams 360-367. The repeat unit further includes stitching MD yams 320-327 which, as noted above, weave in both the top fabric layer 302 and the bottom fabric layer 304 to bind the fabric layers together. Figures 9A-9D depict the individual machine direction yam paths of representative machine direction yams in the fabric 300. As shown in Figure 9A, top MD yam 310, as well as top MD yams 311-313, are woven in over-one/under-one patterns with the top CMD yams 330-345, and do not weave with any yams in the bottom fabric layer 304. Figure 9B depicts the machine direction yam path of bottom MD yarn 350.

As shown in Figure 9B, bottom MD yarn 350 weaves with the bottom CMD yarns 360-367 in an over-four/under-one/over-two/under-one pattern - i.e., it passes over bottom CMD yams 367, 360-362, passes under bottom CMD yam 363, passes over bottom CMD yarns 364-365 and passes under bottom CMD yam 366 in each repeat of the fabric. The other bottom MD yams 351-353 follow a similar "over-four/under- one/over-two/under-one pattern" weave pattern, although the starting point for the pattern is offset by two bottom CMD yams 360-367 for each adjacent bottom MD yarn 350-353.

Figure 9C depicts the machine direction yam path of stitching MD yam 320. As shown in Figure 9C, stitching MD yam 320 is woven in an over-seven/under-one pattern with respect to the bottom CMD yams 360-367, and is woven in an under- eleven/over-one/under-one/over-one/under-one/over-one pattern with respect to the top CMD yarns 330-345. Stitching MD yams 321-323 follow the same patterns with respect to the bottom CMD yams 360-367 and the top CMD yams 330-345 as stitching MD yam 320, except that the starting point for the pattern is offset by two bottom CMD yams 360-367 (and hence four top CMD yams 330-345) for each adj acent stitching MD yam 324-327.

Figure 9D depicts the machine direction yarn path of stitching MD yarn 324. As shown in Figure 9D, stitching MD yam 324 is woven in an under-one/over- one/under-one/over-one/under-one/over-one/under-one/over-one/under-one/over- one/under-six pattern with respect to the top CMD yams 330-345. Stitching MD yam 324 weaves with the bottom CMD yarns 360-367 in an over seven/under-one pattern. Stitching MD yams 325-327 follow the same patterns with respect to the top CMD yarns 330-345 as stitching MD yam 324, except that the starting point for the pattern is offset by four top CMD yams 330-345 for each adjacent stitching MD yam 324- 327. The fabric 300 depicted in Figures 7-9 is very similar to the fabric 100 depicted in Figures 1-3, the only difference being that the positions of the stitching MD yam pairs are reversed in the two fabrics. Thus, in fabric 100, the stitching MD yarns 120-123 that form five knuckles per repeat on the papermaking surface fall to the left (from the vantage point of Figure 1) of the stitching MD yarns 124-127 that form three knuckles per repeat on the papermaking surface, while in fabric 300 the stitching MD yams 324-327 that form five knuckles per repeat on the papermaking surface fall to the right (from the vantage point of Figure 7) of the stitching MD yams 320-323 that form three knuckles per repeat on the papermaking surface.

As shown best in Figure 8, reversing the position of the stitching MD yams can result in a significant change in positioning of the yams in the bottom fabric layer 304. In particular, the machine direction yams weaving in the bottom fabric layer 304 take more of a zig-zag pattern (as compared to the bottom fabric layer 104 depicted in Figure 2), which can improve the straight through drainage in fabric 300. The zigzag pattern results because each stitching MD yarn tends to couple with a specific bottom MD yam, namely the bottom MD yarn that passes underneath the same bottom CMD yam as does the stitching MD yam. In the fabric 300, each bottom MD yam and the stitching MD yam with which it pairs are separated by one other stitching MD yarn. As a result, each bottom MD yam and the stitching MD yams with which it alternatively couples must travel farther across the fabric to perform the alternative coupling, thereby providing more of a zig-zag pattern. By way of example, bottom MD yarn 351 couples with stitching MD yam 320 where those two yarns pass under bottom CMD yarn 361. As shown in Figure 8, stitching MD yam 324 lies between (and above) bottom MD yam 351 and stitching MD yam 320. As a result, bottom MD yam 351 tends to bend heavily to the left and stitching MD yam 320 tends to bend heavily to the right so that the two yams may couple together at the location where they both pass beneath bottom CMD yarn 361. Likewise, stitching MD yarn 321 lies between (and above) bottom MD yarn 351 and stitching MD yam 325. Bottom MD yam 351 thus tends to bend heavily to the right and stitching MD yarn 325 tends to bend heavily to the left so that the two yams may couple together at the location where they both pass beneath bottom CMD yam 364. This tendency of the bottom MD yams and the stitching MD yams (at locations where they weave in the bottom fabric layer) to lean first to the left and then to the right results in the zigzag pattern.

Note that in fabric 300, the stitching MD yams in each stitching MD yarn pair are pulled toward each other by the forces that cause those yarns to couple with the bottom MD yams. As a result, the stitching MD yarns tend to align themselves approximately halfway between the bottom MD yams (except at the locations where they couple with a bottom MD yarn), which provides for improved straight through drainage in the fabric. In contrast, in the fabric 100 of Figures 1-3, the stitching MD yarns in each stitching MD yam pair are pulled away from each other toward the bottom MD yam which they are adjacent to.

The principles of the present invention can be extended to fabrics woven with different repeat patterns. For instance, a triple layer fabric 400 according to the present invention woven on 20 harnesses is depicted in Figures 10-12. Figure 10 depicts a top view of the top fabric layer 402 of the triple layer fabric 400 (i.e., a view of the papermaking surface) while Figure 11 depicts atop view of the bottom fabric layer 404 of fabric 400 (i.e., a view of the fabric 400 with the yams that weave exclusively in the top fabric layer 402 removed). Figures 12A-12D depict the weave pattern of top MD yam 410, bottom MD yarn 450, and stitching MD yams 420 and 425, respectively. The triple layer fabric of Figures 10-12 is woven on twenty harnesses, and hence a single repeat of the fabric encompasses twenty machine direction yams. While Figures 10 and 11 only show a single repeat unit of the fabric, those of skill in the art will appreciate that in commercial applications the depicted portion would be repeated many times, in both the machine and cross machine directions.

As seen in Figure 10, the repeat unit of the top fabric layer 402 includes a set of top MD yams 410-414 and a set of top CMD yams 430-439 that are interwoven together. The top fabric layer further includes a set of five stitching MD yam pairs 420, 425; 421, 426; 422, 427; 423, 428; 424, 429 that also interweave with the top CMD yarns 430-439. As shown in Figure 10, a stitching MD yam pair, such as for example, stitching MD yarn pair 420, 425, is provided between each pair of adjacent top MD yams (e.g., yams 410-411). Each stitching MD yarn pair (such as pair 420, 425) is woven such that while one of the yams of the pair (e.g., yam 420) weaves in the top fabric layer 402 to complete the weave pattern in the top fabric layer 402, the other of the stitching MD yams (e.g., yam 425) drops down into the bottom fabric layer 404 to bind the top fabric layer 402 and the bottom fabric layer 404 together. In this manner, the stitching MD yam pairs 420, 425; 421, 426; 422, 427; 423, 428; 424, 429 both complete the weave of the top layer fabric 402 and also serve to bind the top and bottom fabric layers 402, 404 together. As further shown in Figure 10, the yams comprising the set of top CMD yams 430-439 are interwoven with the set of top layer MD yams 410-414 and the stitching MD yam pairs 420, 425; 421, 426; 422, 427;

423, 428; 424, 429 in a plain weave pattern, meaning that each of the top CMD yams 430-439 alternatively pass below one, and then above the next, of the machine direction yams that at that point are weaving in the papermaking surface. Referring now to Figure 11, a repeat unit of the machine side surface of the bottom fabric layer 404 of the fabric 400 is shown. The repeat unit includes a set of bottom MD yams 450-454 which are interwoven with a set of bottom CMD yams 460-464. The repeat unit further includes the stitching MD yarn pairs 420, 425; 421, 426; 422, 427; 423, 428; 424, 429 which are described above. As shown in Figure 11, the bottom CMD yams 460-464 of fabric 400 may be constructed using relatively large diameter yams that are well suited to sustain the wear caused by papermaking machine during use of the fabric 400. As can also be seen in Figure 11, the weave pattern of fabric 400 provides relatively long cross machine direction "floats" on the machine side surface. Figures 12A-12D depict the individual machine direction yarn paths of representative machine direction yams in the fabric 400. Figure 12A depicts the machine direction yam paths for top MD yam 410. Top MD yams 411-414 are woven in identical weave patterns. As shown in Figure 12 A, each of these top MD yarns 410-414 are woven in over-one/under-one patterns with the top CMD yams 430-439 (and each top MD yam 410-414 passes over the exact same top CMD yams 430, 432, 434, 436, 438) and do not weave with any yams in the bottom fabric layer 404.

Figure 12B depicts the machine direction yarn path of bottom MD yam 450. As shown in Figure 12B, bottom MD yam 450 weaves with the bottom CMD yams 460-464 in an over-two/under-one/over-one/under-one pattern - i. e., it passes over bottom CMD yams 460-461, passes under bottom CMD yam 462, passes over bottom CMD yam 463 and passes under bottom CMD yarn 464 in each repeat of the fabric. The other bottom MD yams 451-454 follow a similar "over-two/under-one/over- one/under-one pattern" weave pattern, although the starting point for the pattern is offset by one bottom CMD yams 460-464 for each adjacent bottom MD yam 450- 454. Figure 12C depicts the machine direction yarn path of stitching MD yarn 420. As shown in Figure 12C, stitching MD yarn 420 is woven in an under-one/over-four pattern with respect to the bottom CMD yams 460-464, and is woven in a under- seven/over-one/under-one/over-one pattern with respect to the top CMD yams 430- 439. Stitching MD yams 421-424 follow the same patterns with respect to the bottom CMD yams 460-464 and the top CMD yams 430-439 as stitching MD yam 420, except that the starting point for the pattern is offset by one bottom CMD yarns 460- 464 (and hence two top CMD yams 430-439) for each adjacent stitching MD yam 420-424. Figure 12D depicts the machine direction yam path of stitching MD yam 425.

As shown in Figure 12D, stitching MD yarn 425 is woven in an over-four/under-one pattern with respect to the bottom CMD yams 460-464, and is woven in a under- one/over-one/under-five/over-one/under-one/over-one pattern with respect to the top CMD yams 430-439. Stitching MD yarns 426-429 follow the same patterns with respect to the top CMD yams 430-439 as stitching MD yam 425, except that the starting point for the pattern is offset by one bottom CMD yams 460-464 (and hence two top CMD yams 430-439) for each adjacent stitching MD yam 425-429. Another sixteen harness triple layer fabric embodiment of the present invention is illustrated in Figures 13-15D and is designated broadly therein at 500. The fabric 500 (one repeat unit of which is illustrated in Figures 13 and 14) includes four top MD yarns 501-504, sixteen top CMD yarns 511-526, four bottom MD yams 541-544, eight bottom CMD yams 551-558, and four pairs of MD stitching yarns 531a-534b. These yams are interwoven as described below.

The top layer of the fabric 500 is a plain weave surface formed by the interweaving of the top MD yams 501-504, the top CMD yams 511-526, and stitching portions of the stitching yams 531a-534b. As shown in Figure 15A, each top MD yarn 501-504 follows an "over 1/under 1" sequence in interweaving with the top CMD yarns 511-526. For example, top MD yam 501 passes over top CMD yarn 511, under top CMD yam 512, over top CMD yarn 513, and so on until it passes under top CMD yam 526. Each of the other top MD yams passes over and under the same top CMD yams. As is the case with the fabric 300 illustrated in Figure 7, the stitching yam pairs combine to act as a single yam in completing the plain weave pattern on the top surface of the fabric 500. Each of the stitching yams designated with an "a" passes over three top CMD yarns as part of the repeat unit, and each of the stitching yams designated with a "b" passes over five top CMD yarns as part of the repeat unit. For example, stitching yam 532b passes over top CMD yams 512, 514, 516, 518 and 520, and its paired stitching yam 532a passes over top CMD yams 522, 524 and 526.

Top MD yarns 501-504 are each separated from one another by a stitching yarn pair. For example, stitching yam pair 532a, 532b is positioned between top MD yarn 501, 502. Thus, as the top MD yams 501, 502 both pass over top CMD yam 511, the stitching yarn pair 532b passes under top CMD yam 511, as the top MD yams 501, 502b both pass under top CMD yarn 512, the stitching yarn 532b passes over top CMD yarn 512, and so on to form the plain weave top surface for the fabric 500. Each pair of stitching yarns is offset from its neighboring stitching yam pairs by four top CMD yams. This can be seen by examination of Figure 13, wherein stitching yarns 531a, 531b both pass below top CMD yam 525 as they travel between the top and bottom layers of the fabric 500. Moving up Figure 13 and to stitching yarns 532a₅ 532b, these yarns both pass below top CMD yam 521 (which is offset from top CMD yarn 525 by four top CMD yarns) as they travel between the top and bottom layers.

The bottom layer of the fabric 500 is illustrated in Figures 14 and 15A-15D. Each of the bottom MD yarns is positioned beneath a top MD yam, and each of the bottom CMD yams is positioned beneath a top CMD yam. Because there are eight bottom CMD yarns and sixteen top CMD yams, every other top CMD yarn (for example, top CMd yam 511) has no bottom CMD yarn beneath it. These relationships can be seen in Figures 15A-15D.

Referring still to Figure 14, each of the bottom MD yarns 541-544 interweaves with the bottom CMD yams 551-558 in an "over 2/under 1/over 1/under 1/over 2/under 1 " sequence within the repeat unit. For example, bottom MD yam 544 passes over bottom CMD yams 551, 552, under bottom CMD yam 553, over bottom CMD yam 554, under bottom CMD yam 555, over bottom CMD yams 556, 557 and under bottom CMD yam 558. Each bottom MD yam is offset from its neighboring bottom MD yams by two top bottom CMD yams. For example, bottom MD yam 542 forms its "over 1 " segment over bottom CMD yarn 558, while neighboring bottom MD yam 543 forms its "over 1 " segment over bottom CMD yam 556. Referring now to Figures 14, 15B and 15D, as described above, when a stitching yam of a pair is not interweaving with top CMD yams, it passes below the top CMD yams. In this embodiment, like the embodiment of Figures 4-6D, one of the stitching yams of each stitching yam pair does not interlace with a bottom CMD yarn, but instead floats above it. More specifically, each of the "a" stitching yams interlaces with a bottom CMD yam, while each of the "b" stitching yams does not. For example, as shown in Figures 14, 15B and 15D, stitching yarn 531a stitches below bottom CMD yam 556, but its paired stitching yarn 531b does not stitch with any of the bottom CMD yarns. The stitching locations for the "a" stitching yams are offset from one another by two bottom CMD yarns; for example, stitching yarn 531a stitches below bottom CMD yam 556, and stitching yam 532a stitches below bottom CMD yam 554.

In the illustrated embodiment, the stitches formed by the "a" stitching yams are positioned adjacent a bottom side knuckle formed by a neighboring MD yarn. As an example, stitching yarn 531a stitches under bottom CMD yarn 556. Neighboring bottom MD yam 541 also forms a bottom side knuckle below bottom CMD yam 556. In this configuration, the bottom side MD yarn knuckle can help to protect the stitching knuckle from wear caused by contact with a paper machine during use. It can also be seen that, for every other bottom CMD yam, the bottom MD yams forming knuckles below it are adjacent to one another. For example, adjacent bottom MD yams 541, 542 form knuckles below bottom CMD yarn 551, adjacent bottom MD yams 544, 541 form knuckles below bottom CMD yam 553, and so on for bottom CMD yams 555 and 557.

This sixteen harness embodiment may be less susceptible to diagonal marking than other fabrics, and in particular other MD-stitched fabrics. The potential improvement in diagonal marking performance may be attributed to multiple factors, including the absence of interweaving between the "b" stitching yams and the bottom CMD yams, and reduced crimping of the "a" yams. Figures 16 and 17 illustrate a twelve harness fabric 600 that represents embodiments of the present invention. A repeat unit of the fabric 600 includes three top MD yams 601-603, twelve top CMD yams 611-622, three bottom MD yarns 631- 633, three bottom CMD yarns 641-643, and three stitching yam pairs 651a, 651b- 653a, 653b. The weave pattern of these yams is discussed below.

Turning first to Figures 16 and 18A-D, each of the top MD yams 601-603 is interwoven with alternating top CMD yams 611-622 in an "over 1/under 1" sequence, with each top MD yarn 601-603 passing over the same top CMD yams. Thus, top MD yarn 601 passes over top CMD yam 611, under top CMD yam 612, over top CMD yam 613, and so on throughout the pattern.

Each of the stitching yarn pairs 651a, 651b-653a, 653b includes an "a" stitching yam that weaves with the top CMD yams 611-622 in an "over 1/under 1 " sequence with the exception of one segment that passes under three top CMD yarns. For example, stitching yarn 651a passes below top CMD yam 611, above top CMD yarn 612, below top CMD yarn 613, above top CMD yarn 614, below top CMD yams 615-617, above top CMD yam 618, below top CMD yarn 619, above top CMD yam 620, below top CMD yarn 621, and above top CMD yarn 622. The "b" stitching yam of each pair passes below all of the top CMD yams with the exception of the CMD yarn that defines the center of the three yarn segment of the paired "a" stitching yam. As an example, stitching yarn 651b passes above only top CMD yam 616, which is in the center of the three yam segment of stitching yarn 651a that passes below top CMD yams 615-617. In this manner, together stitching yams 651a, 651b effectively fonn a top CMD yam that has an "over 1/under 1" sequence. Because the top surface knuckles of the stitching yarn pairs are offset from the top knuckles of the top MD yarns by one top CMD yarn, the top MD yams and stitching yam pairs form a plain weave surface on the top surface of the fabric 600. It should be noted that the top surface knuckles formed by the "b" yams are offset from adjacent "b" yam top surface knuckles by four top CMD yams.

Turning now to Figure 17, which illustrates the bottom surface of the fabric 600, and to Figures 18A-18D, each of the bottom MD yams 631-636 interweaves with the bottom CMD yams 641-646 in an "over 1/under 5" sequence (it should be understood that "over" and "under" as used herein refer to a fabric in which the bottom surface illustrated in Figure 17 is facing downwardly). As an example, bottom MD yam 632 passes above bottom CMD yams 641-645, then below bottom CMD yam 646. Adjacent bottom MD yams are offset from one another by two bottom CMD yams; thus, bottom MD yam 632 passes below (therefore forming a bottom side knuckle under) bottom CMD yarn 644, which is offset from bottom CMD yarn 636 (which bottom MD yam 631 passes below) by two bottom CMD yams.

The "b" stitching yams also pass below one bottom CMD yam. More specifically, the "b" stitching yams pass below a bottom CMD yarn that is positioned directly below a top CMD yam that is offset from the top CMD yarn over which the "b" yam passes by five top CMD yams. As an example, stitching yam 651b passes above top CMD yarn 616 and below bottom CMD yarn 641, which is located beneath top CMD yarn 612. Adjacent "b" stitching yams are offset from each other by two bottom CMD yarns. Also, the bottom side knuckles formed by the "b" stitching yams are offset from one adjacent bottom MD yarn by one bottom CMD yarn and from the other adjacent bottom CMD yam by three bottom CMD yams.

Embodiments of twelve harness versions of fabrics of the present invention may have improved life and lower caliper than other similar fabrics.

Figures 19, 20 and 21A-D illustrate a 24 harness embodiment of the present invention, designated broadly at 700. A repeat unit of the fabric 700 includes six top MD yams 701-706, twelve top CMD yams 711-722, six bottom MD yarns 731-736, six bottom CMD yarns 741-746, and six stitching yarn pairs 751a, 751b-756a, 756b. These are interwoven as described below.

Turning first to Figures 19 and 21A-D, each of the top MD yams 701-706 is interwoven with alternating top CMD yams 711-722 in an "over 1/under 1 " sequence, with each top MD yarn 701-706 passing over the same top CMD yarns. Thus, top MD yam 701 passes over top CMD yam 701, under top CMD yam 702, over top CMD yam 703, and so on throughout the pattern.

The stitching yam pairs 751a, 751b-756a, 756b combine to act as a single yarn in completing the plain weave pattern on the top surface of the fabric 700. Each of the stitching yarns forms three top surface knuckles in passing over top CMD yams; together, they form six top surface knuckles that are formed over the top CMD yarns that are passed under by the top MD yams 701-706. For example, stitching yam 751a passes over top CMD yams 702, 704, 706 and stitching yam 751b passes over top CMD yams 708, 710, 712, thereby forming an entire "effective" top MD yarn. (Those stitching yarns designated with an "a" are woven immediately adjacent a top MD yarn to their left (from the vantage point of Figure 19), and those stitching yarns designated with a "b" are woven such that the other stitching yam of the pair is positioned between it and the top MD yam immediately adjacent on the left in Figure 19). Together the top MD yams 701-706, the top CMD yams 711-722 and these upper portions of the stitching yams 751a-756b form a plain weave surface on the top surface of the fabric 700. Turning now to Figure 20, which illustrates the bottom surface of the fabric

700, and to Figures 21A-D, each of the bottom MD yams 731-736 interweaves with the bottom CMD yarns 741-746 in an "over 2/under 1 " sequence (it should be understood that "over" and "under" as used herein refer to a fabric in which the bottom surface illustrated in Figure 20 is facing downwardly). For example, bottom MD yarn 732 weaves above bottom CMD yams 741, 742, below bottom CMD yam 743, above bottom CMD yams 744 and 745, and below bottom CMD yarn 746. Adjacent bottom MD yarns are offset from each other by one bottom CMD yarn.

Still referring to Figures 20 and 21A-D, the lower portions of each stitching yarn 751a-756b stitch below one bottom CMD yam, with the stitching locations of the stitching yams within a stitching yarn pair being offset by three bottom CMD yarns. This results in the lower portions of the stitching yams forming an "effective" bottom MD yam. For example, stitching yarns 751a, 751b stitch below, respectively, bottom CMD yams 745 and 742. Each of these stitching locations is immediately adjacent a bottom surface knuckle formed by one of the adjacent bottom MD yams. As a result, bottom side knuckle pairs are formed by one bottom MD yam and one stitching yarn. For example, both bottom MD yam 741 and stitching yam 752a form bottom surface knuckles below bottom CMD yam 746.

The stitching yams 751a-756b are woven as "reversed" MD yams in the illustrated embodiment, in that the knuckle positions for stitching yam pairs that form top surface knuckles over the same top CMD yams are reversed between the "a" yarns and the "b" yams. For example, stitching yarn 751b forms knuckles over top CMD yams 708, 7010, 712, and stitching yam 751a forms knuckles over top CMD yarns 702, 704, 706. The next pair of stitching yarns that forms knuckles over these same subsets of top CMD yams, namely stitching yams 754a, 754b, is reversed; e_^, it is the "b" yam (754b) that forms knuckles over top CMD yams 702, 704, 706 and it is the "a" yam (754a) that forms knuckles over top CMD yams 708, 710, 712. This configuration is optional (and not employing it would reduce the size of the repeat unit of the fabric to three top MD yams, three bottom MD yams, and three stitching yarn pairs), but has shown to improve marking performance in some embodiments of the fabric.

Figures 22, 23 and 24A-D illustrate a fabric 800 that demonstrates that fabrics can be MD stitched with stitching pairs that appear less frequently in the repeat unit than the fabrics discussed above. A repeat unit of the fabric 800 includes three top MD yams 801-803, twelve top CMD yams 811-822, three bottom MD yams 831-833, eight bottom CMD yams 841-848, and a stitching yam pair 851a, 851b. These yams are interwoven as described below. Turning first to Figures 22 and 24A-B, each of the top MD yams 801-803 is interwoven with the top CMD yams §11-822 in an "over 1/under 1" pattern. The top MD yam 803 is offset from the top MD yams 801 and 802 by one top CMD yam to form a plain weave pattern. This pattern is completed by the stitching yam pair 851a, 851b. Stitching yarn 851a follows an "over 1/under 1/over 1/under 3" sequence that is repeated twice in the repeat unit. More specifically, stitching yarn 851a passes over top CMD yams 813 and 815, then passes below top CMD yams 816-818 before passing above top CMD yarn 819 to recommence the sequence. Stitching yarn 851b passes over one top CMD yam (CMD yam 817) to complete the plain weave top surface. Turning now to Figures 23 and 24A-B, each bottom MD yarn 831-833 is located below a corresponding top MD yarn and interweaves in an "over 3/under 1" sequence with the bottom CMD yams 841-848. The stitching yarn 851b also stitches in an "over 3/under 1" sequence, but, as noted above, in its "over 3" segment the stitching yam 851b also passes over a top CMD yam. The bottom MD yarns 831-833 and the stitching yam 851b are offset from each other such that the knuckles in the bottom surface of the fabric 800 form a broken twill pattern. The fabric 800 may exhibit increased life over similar forming fabrics. In addition, the fabric 800 may be prone to less edge curl, and have lower void volume, than similar fabrics. It should be understood that, although the fabric 800 has a 3 : 1 ratio of top MD yams to stitching yam pairs, other ratios, (such as 2:1 or 3:2) may also be employed.

A further fabric embodiment, designated broadly at 900 in Figures 25, 26 and 27A-D, demonstrates that the MD stitching concept may be employed with triple layer fabrics that do not have plain weave surfaces. A repeat unit of the fabric 900 includes four top MD yarns 901-904, eight top CMD yams 911-918, two bottom MD yarns 921, 922, four bottom CMD yams 931-934, and two stitching yams 941, 942. These are interwoven as described below.

Turning first to Figure 25, which illustrates the top surface of the fabric 900, the top MD yams can be divided into two subsets: one that includes two top MD yarns 901, 903 that follow an "under 3/over 1" sequence with respect to the top CMD yarns 911-918; and one that includes two top MD yarns 902, 904 that follow an "under 7/over 1" sequence with respect to the top CMD yams 911-918. The remainder of the top surface of the fabric 900 is foπned by the stitching yarns 941, 942, each of which interweaves in an "over 1/under 7" sequence with the top CMD yarns 911-918. The top MD yarns 901, 903 of the first set are offset from one another by two top CMD yarns. Each of the knuckles fomied by the MD yarns 902, 904 of the second set is located on a diagonal line A defined between two of the knuckles of the top MD yams 901, 903. The knuckles formed by the stitching yams 941, 942 are positioned along an opposite diagonal line B formed between the same knuckle of the top MD yam 903 and the next adjacent knuckle of the top MD yam 901. The result is a general herringbone pattern of knuckles on the top surface of the fabric 900.

The bottom surface of the fabric 900 (see Figures 26 and 27A-D) is formed by the interweaving of the bottom MD yams 921, 922 with the bottom CMD yarns 931- 934 in an "over 3/under 1 " pattern, and by the stitching of the stitching yams 941, 942 in a similar "over 3/under 1 " pattern. The bottom surface knuckles formed by the bottom MD yams 921, 922 and the stitching yarns 941, 942 are offset from each other by one bottom CMD yarn such that the bottom MD knuckles form a relatively distinct diagonal on the bottom surface of the fabric 900.

The fabric 900, with its herringbone pattern on the top surface, may be particularly suitable for the formation of tissue paper. This fabric also helps to demonstrate that patterns other than the plain weave top surface of the other fabrics illustrated above may be suitable for use with the present invention.

The present invention is directed to "true" triple layer fabrics - meaning triple layer fabrics that include (1) a set of MD yams and a set of CMD yams that each weave exclusively in a top fabric layer and (2) a set of MD yams and a set of CMD yarns that each weave exclusively in a bottom fabric layer - that are stitched together by machine direction yams. Such machine direction yam stitched true triple layer fabrics may typically be manufactured less expensively than most high-performance cross machine direction yam triple layer fabrics while providing improved fiber support (with the plain weave top surface) compared to conventional double layer fabrics. Pursuant to the teachings of the present invention, it will be appreciated that the machine direction yarn stitched true triple layer fabrics may have improved stacking of the machine direction yams, increased permeability and higher void volumes as compared to double layer fabrics. Additionally, by using yarn pairs that complete the weave in the papermaking surface as the stitching yarns it is possible to bind the fabric together at numerous locations, thereby providing a very stable fabric that is not particularly susceptible to interlayer wear.

Each of the fabrics 100, 200, 300, 400, 500, 600, 700, 800, 900 depicted in the figures includes MD stitching yarn pairs in which the yams that comprise the pair interlace with the top fabric layer an unequal number of limes in each repeat of the fabric. For example, as shown best in Figures 3B and 3C, each stitching MD yam pair 120, 124; 121, 125; 122, 126; 123, 127 of fabric 100 include a stitching MD yam (e.g., yam 120) that interlaces with the top fabric layer 102 five time per repeat and a stitching MD yam (e.g., yarn 124) that interlaces with the top fabric layer 102 three times per repeat unit of the fabric. This "unequal interlacing" configuration may provide improved fabric uniformity - particularly on the top surface. As will be appreciated by those of skill in the art, when the fabric is woven off two warp beams, the crimp of the warp yarns woven off each beam will be different. Thus, by weaving the top MD yams off the same warp as the stitching MD yarns that interlace the greater number of times in the top fabric layer, it may be possible to provide for a more uniform papermaking surface.

Those of skill in the art will appreciate that numerous modifications can be made to the above described fabrics. By way of example, the stitching MD yarn pairs can have a wide variety of weave patterns in terms which they complete the weave of the top fabric layer. Thus, the number .of top MD yarns that each stitching MD yam passes over to complete the plain weave pattern on the papermaking surface may vary, as may the frequency with which the yams pass in and out of the top fabric layer. Additionally, a variety of different weave patterns may be employed in the top fabric layer, specifically including 1x2 twill, 2x2 twill, 1x3 twill and 1x4 twill papermaking surfaces, as well as various derivatives of the above-mentioned weave patterns, specifically including broken twill patterns such as those embodied in 4 or 5 harness satin single layer fabrics, which are known in the art as providing a good papermaking surface. Likewise, the frequency of the stitch points and/or the ratio of top-to-bottom machine direction and/or cross machine direction yams may be varied. Thus, the scope of the present invention should be construed based on the claims appended hereto, as opposed to the illustrative examples of the claimed fabrics which are provided herein to fully enable those of skill in the art to practice the claimed invention.

Another exemplary modification would be to alternate for each adjacent stitching MD yarn pair the warp beam from which the stitching MD yams are woven. For example, the fabric of Figures 1-3 could be modified so that stitching MD yams 120, 125, 122, 127 are woven off the same warp beam as top MD yams 110-113 and stitching MD yams 124, 121, 126, 123 are woven off the same warp beam as bottom MD yarns 150-153 to effect this modification. This reversal of the stitching yam positions may reduce any diagonal pattern in the fabric and hence improve fabric performance.

Those of skill in the art will likewise appreciate that the stitching MD yarn pairs need not be included between every adjacent pair of top MD yarns. Instead, a stitching MD yam pair may be provided after every second, third, fourth or fifth top MD yarn. Those of skill in the art will also appreciate that the frequency of interlacing can be varied from that shown in the fabrics pictured herein. However, the stitching MD yams should sufficiently bind the upper and lower fabric layers together to prevent excessive movement between the fabric layers, as such excessive movement could result in severe inter-layer wear problems. Yet another exemplary modification would be to shift the positions of the top fabric layer and the bottom fabric layer of the depicted embodiments (or other embodiments) relative to each other. For example, in the fabric 100 of Figures 1-3, the position of the top fabric layer 102 with respect to the bottom fabric layer 104 might be shifted by one top CMD yarn. Pursuant to another aspect of the present invention, the size and or stiffness of selected of the top CMD yarns may be varied to improve fabric performance. As illustrated best in Figure 1, the papermaking surface of certain fabrics made according to the present invention include "transition points" where one of the stitching MD yams in a stitching MD yam pair completes its run on the papermaking surface and dives down into the center of the fabric while the second yarn of the stitching MD yam pair emerges from the center of the fabric to start its run on the papermaking surface. An example of such a transition point is the point where stitching MD yams 120 and 124 pass under top CMD yam 140 in Figure 1. At these transition points the yarns of the stitching MD yarn pair enter or exit the fabric at a steeper angle as the yams dive down to, or emerge from, a portion of their ran where they weave with the bottom fabric layer 104. This steeper angle may decrease the crimp on the stitching MD yams at the position where they pass over the last top CMD yarn adjacent to the transition point - i.e., where stitching MD yam 120 passes over top CMD yam 139 and where stitching MD yarn 124 passes over top CMD yam 141 - as the stitching MD yam exerts sufficient force on the top CMD yarn to pull the top CMD yarn slightly farther into the middle of the fabric at this point. Pursuant to the teachings of the present invention, it will be understood that this reduction in the crimp of the stitching MD yam knuckles adjacent the transition points can be reduced or eliminated by using slightly larger diameter top CMD yarns for the top CMD yams that bracket each transition point. In the fabric of Figure 1, this would mean making top CMD yams 131, 133, 135, 137, 139, 141, 143, 145 slightly larger than top CMD yarns 130, 132, 134, 136, 138, 140, 142, 144. For example, if top CMD yams 130, 132, 134, 136, 138, 140, 142, 144 are 0.15 millimeters in diameter, then top CMD yams 131, 133, 135, 137, 139, 141, 143, 145 may be made 0.17 millimeters in diameter. Instead of modifying the diameter of top CMD yams 131, 133, 135, 137, 139, 141, 143, 145, one may alternatively use stiffer yams (i.e., yams having a higher elastic modulus, such as an elastic modulus that is 50% higher) that will more effectively resist the tendency to be pulled into the fabric adjacent the transition points.

The use of larger diameter and/or higher modulus top CMD yams may also improve uniformity of the papermaking surface at the transition points themselves. If such yams are not used, the papermaking surface knuckle formed by the top CMD yarn directly over the transition point may be lower than the remainder of the knuckles formed by the top CMD yams because the stitching MD yams at that location dive down at a steeper angle and hence provide less support to the top CMD yarn. By using larger diameter or higher modulus yarns on the top CMD yarn positions that straddle the transition point it is possible to raise the height of the top CMD yam that passes over the transition point at the transition point location.

Notably, in the bottom fabric layers 104, 204, 304, 404 of fabrics 100, 200, 300, 400, 500 respectively, the set of bottom MD yarns and the set of bottom CMD yarns form a machine-side surface having only "single float" machine direction knuckles. By a "single float" machine-side machine direction knuckle it is meant that when the bottom fabric layer is viewed from the top, no machine direction yarn passes under more than one consecutive cross machine direction yam (such that the MD yam is on the machine-side surface) before passing back to the top surface of the bottom fabric layer. In a preferred embodiment of the triple layer forming fabrics of the present invention, the bottom fabric layer is woven so as to have a machine side surface composed exclusively of machine side "single float" machine direction knuckles.

The fabrics pictured and otherwise described and claimed herein may be employed in a variety of applications, including forming fine paper grades, tissue paper, brown paper and newsprint, but is especially beneficial fo fine paper, newsprint and brown paper applications. The configurations of the individual yams 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 yams, monofilament yams, twisted multifilament or monofilament yams, spun yams, 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 polypropylene, polyester, nylon, or the like. The skilled artisan should select a yam material according to the particular application of the final fabric. Regarding yam dimensions, the particular size of the yams is typically governed by the mesh of the papermaking surface. In a typical embodiment of the triple layer fabrics disclosed herein, preferably the diameter of the top CMD yarns, and all of the MD yams is between about 0.10 and 0.20 mm, and the diameter of the bottom CMD yams is between about 0.22 and 0.50 mm. Those of skill in the art will appreciate that yarns having diameters outside the above ranges may be used in certain applications. In one embodiment of the present invention, the top CMD yarns and all of the MD yarns have diameters between about 0.15 and 0.17 mm, and the diameter of the bottom CMD yams is between about 0.25 and 0.40 mm to provide fabrics with a target top mesh of 75x75 yams per inch. Fabrics employing these yam sizes may be implemented with polyester yams or a combination of polyester and nylon yarns.

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 paperstock is well understood by those of skill in the art, additional details regarding this aspect of the present invention will not be provided herein.

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.

Claims

THAT WHICH IS CLAIMED:

1. A triple layer papermaker's forming fabric comprising: a set of top CMD yams; a set of top MD yarns interwoven exclusively with the top CMD yams to form at least part of a top fabric layer having a papermaking surface; a set of bottom CMD yarns; a set of bottom MD yams interwoven exclusively with the bottom CMD yarns to form at least part of a bottom fabric layer having a machine side surface; and a set of stitching MD yarn pairs, wherein at least one of the stitching MD yarns in each stitching MD yam pair weaves in both the top fabric layer and the bottom fabric layer and wherein the stitching MD yarns in each stitching MD yam pair are woven such that at locations where the first of the two stitching MD yams in each stitching MD yam pair weaves in the top fabric layer the second of the two stitching MD yams in the stitching MD yam pair drops below the top fabric layer so that togetlier the two stitching MD yarns in each stitchmg MD yarn pair complete the weave in the top fabric layer, and wherein at least some of the stitching MD yams in the stitching MD yam pairs bind the top fabric layer and the bottom fabric layer together.

2. The papermaker's forming fabric of Claim 1 , wherein a stitching MD yarn pair is provided adjacent each top MD yam.

3. The papermaker's fabric of Claim 1, wherein a stitching MD yam pair is provided on each side of each top MD yam.

4. The papermaker's forming fabric of Claim 3, wherein the top MD yarns, the top CMD yams, and the stitching MD yam pairs form a top fabric layer having a plain weave pattern.

5. The papermaker's forming fabric of Claim 1 , wherein in each repeat of the fabric each stitching MD yarn passes below the same bottom CMD yarn as does the bottom MD yam directly adjacent to it.

6. The papermaker's forming fabric of Claim 5, wherein each stitching

MD yarn couples with one of the bottom MD yams at locations where the stitching MD yarns pass below the bottom CMD yams so as to form side-by-side machine-side machine direction knuckles.

7. The papermaker's forming fabric of Claim 1 , wherein each bottom MD yarn passes below two non-adjacent bottom CMD yams in each repeat of the fabric.

8. The papermaker's forming fabric of Claim 1 , wherein no more than two machine-side machine direction knuckles are formed on any bottom CMD yam in a single repeat of the fabric.

9. The papermaker's forming fabric of Claim 8, wherein two directly adjacent machine-side machine direction knuckles are formed on each bottom CMD yarn in each repeat of the fabric.

10. The papermaker's forming fabric of Claim 1 , wherein at least some of the top CMD yams that the stitching MD yams of the stitching MD yarn pairs pass over immediately before dropping down into the bottom fabric layer have a larger diameter than the remainder of the top CMD yams.

11. The papermaker's forming fabric of Claim 1 , wherein at least some of the top CMD yams that the stitching MD yams of the stitching MD yarn pairs pass over immediately before dropping down into the bottom fabric layer have a higher modulus than the remainder of the top CMD yams.

12. The papermaker's forming fabric of Claim 1 , wherein all of the yams in the set of top MD yams weave over the same top CMD yarns.

13. The papermaker's forming fabric of Claim 12, wherein the top CMD yarns that the top MD yams pass over have a smaller diameter than the remainder of the top CMD yams.

14. The papermaker's forming fabric of Claim 12, wherein the top CMD yarns that the top MD yams pass over have a lower elastic modulus than the remainder of the top CMD yams.

15. The papermaker's forming fabric of Claim 1 , wherein the two stitching

MD yarns in each pair of stitching MD yarns interlace over different numbers of top CMD yarns in each repeat of the fabric.

16. The papermaker's forming fabric of Claim 1 , wherein each bottom MD yam couples with one of the stitching MD yarns from the stitching MD yam pairs at locations where the bottom MD yam passes below a bottom CMD yarn.

17. The papermaker's forming fabric of Claim 1 , wherein in each repeat of the fabric the first stitching MD yam in each stitching MD yam pair passes below the same bottom CMD yarn as does the bottom MD yam directly adjacent to the second stitching MD yam in each stitching MD yam pair and the second stitching MD yam in each stitching MD yarn pair passes below the same bottom CMD yam as does the bottom MD yam directly adjacent to the first stitching MD yam in each stitching MD yarn pair.

18. The papermaker's forming fabric of Claim 1 , wherein each stitching MD yam couples with a non-adjacent bottom MD yarn at locations where each stitching MD yarn passes below one of the bottom CMD yams.

19. The papermaker's forming fabric of Claim 1 , wherein the stitching

MD yarns in each stitching MD yam pair tend to gravitate toward each other when weaving in the bottom fabric layer.

20. A triple layer papermaker's forming fabric comprising: a top fabric layer comprising a set of top MD yams interwoven exclusively with a set of top CMD yams; a bottom fabric layer comprising a set of bottom MD yams interwoven exclusively with a set of bottom CMD yarns; a set of stitching MD yarn pairs interwoven with the set of top CMD yams to complete the weave in the top fabric layer, wherein at least one of the yams in each stitching MD yarn pair also interweaves with the set of bottom CMD yarns to bind the top fabric layer and the bottom fabric layer together; and wherein the stitching MD yams and the bottom MD yams form side-by-side machine-side machine direction knuckles.

21. The papermaker's fabric of Claim 20, wherein a stitching MD yam pair is provided on each side of each top MD yam.

22. The papermaker's forming fabric of Claim 20, wherein in each repeat of the fabric each stitching MD yam passes below the same bottom CMD yam as does the bottom MD yarn directly adjacent to it.

23. The papermaker's forming fabric of Claim 20, wherein each bottom

MD yam passes below two non-adjacent bottom CMD yarns in each repeat of the fabric.

24. The papermaker's fomiing fabric of Claim 20, wherein at least some of the top CMD yarns that the stitching MD yams of the stitching MD yarn pairs pass over immediately before dropping down into the bottom fabric layer have a larger diameter than the remainder of the top CMD ya s.

25. The papermaker's forming fabric of Claim 20, wherein at least some of the top CMD yams that the stitching MD yarns of the stitching MD yarn pairs pass over immediately before dropping down into the bottom fabric layer have a higher modulus than the remainder of the top CMD yarns.

26. The papermaker's forming fabric of Claim 20, wherein the two stitching MD yams in each pair of stitching MD yams cross over different numbers of top CMD yarns in each repeat of the fabric.

27. The papermaker's forming fabric of Claim 20, wherein in each repeat of the fabric the first stitching MD yam in each stitching MD yam pair passes below the same bottom CMD yam as does the bottom MD yarn directly adjacent to the second stitching MD yarn in each stitching MD yarn pair.

28. A triple layer papermaker's forming fabric comprising: a set of top CMD yams; a set of top MD yams interwoven exclusively with the top CMD yams to form at least part of a top fabric layer having a papermaking surface; a set of bottom CMD yarns; a set of bottom MD yams interwoven exclusively with the bottom CMD yams to form at least part of a bottom fabric layer having a machine side surface, the bottom MD yams forming machine side MD knuckles as they pass below respective bottom CMD yams; and a set of stitching MD yarn pairs, wherein at least one of the stitching MD ya s in each stitching MD yarn pair weaves in both the top fabric layer and the bottom fabric layer and wherein the stitching MD yams in each stitching MD yam pair are woven such that at locations where the first of the two stitching MD yarns in each stitching MD yam pair weaves in the top fabric layer the second of the two stitching MD yams in the stitching MD yam pair drops below the top fabric layer so that together the two stitching MD yarns in each stitching MD yarn pair complete the weave in the top fabric layer, and wherein at least some of the stitching MD yams in the stitching MD yam pairs bind the top fabric layer and the bottom fabric layer together.

29. The papermaker's fabric defined in Claim 28, wherein the fabric is woven on 12 harnesses, and wherein the bottom MD knuckles define a broken twill pattern.

30. The papermaker's fabric defined in Claim 19, wherein one stitching yarn of each pair forms a bottom MD stitching knuckle as it passes below a bottom CMD yam, and wherein each bottom MD knuckle is formed below a bottom CMD yarn adjacent a bottom MD stitching knuckle formed under the same bottom CMD yarn.

31. The papermaker's fabric defined in Claim 30, wherein the fabric is woven on 24 harnesses.

32. The papermaker's fabric defined in Claim 28, wherein the ratio of top MD yams to stitching yam pairs is 1:1.

33. The papermaker's fabric defined in Claim 28, wherein the ratio of op MD yams to stitching yam pairs is 3:1.

34. The papermaker's fabric defined in Claim 28, wherein the top MD yarns, top CMD yarns, and stitching yams are interwoven such that the papermaking surface has a herringbone pattern.

35. The papermaker's fabric defined in Claim 34, wherein the fabric is woven on 8 harnesses.