Patent Grant
7059357
The present invention relates generally to papermaking, and relates more specifically to multilayer 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.
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 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, stability and life potential. 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. No. 5,437,315 to Ward and U.S. Pat. No. 5,967,195 to Ward. Warp-stitched multilayer fabrics are known in the art. Examples of such fabrics are shown in U.S. Pat. No. 5,152,326 to Vohringer, U.S. Pat. No. 6,202,705 B1 to Johnson and PCT Patent No. WO 02/00996 A1.
The present invention relates to warp-stitched multilayer papermaker's fabrics that employ weave patterns which can provide one or more of the following advantages: good drainage, increased join strength, reduced weaving time, increased weft yarn counts on the papermaking surface (and hence improved fiber support) and increased fabric modulus. The fabrics of the present invention are particularly useful as papermaker's forming fabrics, although the teachings of the present invention may also be advantageous in certain felt and dryer applications.
Certain embodiments of the present invention are directed to warp-stitched triple layer papermaker's fabrics. In one such embodiment, the warp-stitched triple layer fabric has a set of top warp yarns woven from a first warp beam that are interwoven with a set of top weft yarns, and a set of bottom warp yarns woven from a second warp beam that are interwoven with a set of bottom weft yarns. The fabric further includes a set of stitching warp yarns woven from a third warp beam that interweave with at least some of the top weft yarns and with at least some of the bottom weft yarns to bind the top fabric layer and the bottom fabric layer together. The stitching warp yarns may be woven as stitching warp yarn pairs such that at locations in the fabric where the first of the two stitching warp yarns in the pair weaves in the top fabric layer, the second yarn in the pair drops below the top fabric layer so that together the two stitching warp yarns in each pair complete the weave in the top fabric layer.
In another embodiment of the present invention, the warp-stitched fabric is a multilayer papermaker's fabric that has a set of bottom warp yarns, a set of bottom weft yarns, a set of top weft yarns and a set of warp stitching yarn pairs. The bottom warp yarns are interwoven with the bottom weft yarns. The stitching warp yarns interweave with both the bottom weft yarns and the top weft yarns, and are woven such that at locations where the first of the stitching warp yarns in a pair weaves in the top fabric layer, the second stitching warp yarn in the pair drops below the top fabric layer to interweave with one or more bottom weft yarns to bind the top fabric layer and the bottom fabric layer together. In this embodiment, for each stitching warp yarn pair, the first stitching warp yarn of the stitching warp yarn pair may weave on a first side of one of the bottom warp yarns while the second stitching warp yarn of each stitching yarn pair may weave on the other side of that bottom warp yarn. The fabrics of this embodiment may further include a set of top warp yarns that interweave with the top weft yarns in the top fabric layer.
In additional aspects of the present invention, the papermaker's fabric may include stitching yarn pairs that are substantially stacked above a bottom warp yarn. The stitching warp yarns and/or the top warp yarns may have a smaller diameter than the bottom warp yarns. The top weft yarns may have a smaller diameter than the bottom weft yarns. The papermaking surface may be woven in a plain weave pattern. The machine side surface may be woven such that in each repeat unit of the fabric, each stitching warp yarn passes below the same bottom warp yarn as does the bottom warp yarn directly adjacent to it. The stitching warp yarn may also be woven so that it couples with the bottom warp yarn at locations where the yarns pass below the bottom weft yarns so as to form side-by-side machine-side warp direction knuckles. At least some of the top weft yarns that the stitching warp yarns pass over immediately before dropping down below the top fabric layer may have a larger diameter and/or a higher modulus than the remainder of the top weft yarns. Additionally, in embodiments which include pairs of stitching warp yarns, the two yarns in each pair may cross over different numbers of top weft yarns in each repeat of the fabric. The two yarns in each stitching warp yarn pair may also tend to gravitate toward each other.
Additional aspects of the present invention includes methods of manufacturing warp-stitched triple layer fabrics and methods of using the triple layer papermaker's fabric described herein for making paper.
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 “true” warp-stitched triple layer papermaker's fabrics in that they include a set of warp yarns and a set of weft yarns that only weave in the top layer of the fabric, as well as a set of warp yarns and a set of weft yarns that only weave in the bottom fabric layer. These fabrics also include stitching warp yarns that weave in both the top fabric layer and the bottom fabric layer to bind the layers together. In certain embodiments of the present invention, the stitching warp yarns are provided as pairs of two stitching yarns that together replace the equivalent of a single warp yarn 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 yarn in the pair weaves below the papermaking surface. Throughout the fabric, the yarns in each pair trade these positions. At least one of the yarns 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 yarn pairs are referred to as “stitching warp yarn pairs.”
In certain embodiments of the invention, the “true” warp-stitched triple layer papermaker's fabrics are woven from three separate warp beams. As will be appreciated by those of skill in the art, in manufacturing papermaker's fabrics using a flat weaving process, the warp yarns are fed into the loom off of one or more warp yarn beams (or “warp beams”) and the weft yarns or “picks” are “thrown” one-by-one by the loom so that they pass in the desired over/under pattern with respect to the warp yarns to weave the fabric. The tension on the yarns in each warp beam may be independently controlled, and the types of yarns provided on each beam (e.g., yarn size, modulus, filament type, etc.) may be varied. By weaving the warp-stitched fabrics of the present invention off of three separate warp beams, at least two distinct advantages may accrue.
First, by using three separate warp beams, it is possible to vary the size and/or type of yarn used for (1) the top warp yarns, (2) the bottom warp yarns and (3) the stitching warp yarns. This may be advantageous because the requirements for yarns that weave in the top layer versus the bottom layer versus both layers may differ. By way of example, in many applications, it may be desirable to use larger, sturdier warp yarns in the bottom fabric layer to provide good stretch resistance and stability. In contrast, finely woven warp yarns are often preferred on the papermaking surface as such yarns may facilitate providing a highly uniform surface that exhibits good drainage while providing a high degree of fiber support. The stitching warp yarns may have their own unique requirements. Through the use of three separate warp beams, the fabric designer can optimize the type and sizes of yarns used for the yarns that weave in different parts of the fabric. Second, the use of a separate warp beam for the top, bottom and stitching warp yarns also allows for independent tension control on each type of warp yarn. This tension control may also be used to increase the uniformity of the papermaking surface as variations in tension may impact the degree of the crimp that each type of yarn exhibits on the papermaking surface.
Pursuant to another aspect of the present invention, multilayer warp-stitched papermaker's fabrics are provided which include stitching warp yarn pairs that are substantially stacked above a bottom warp yarn. This aspect of the present invention is best explained with reference to
As shown in
As discussed above, each of the stitching warp yarn pairs 20, 25; 21, 26 are “substantially stacked” over a bottom warp yarn (yarns 51 and 53). By “substantially stacked” it is meant that the stitching warp yarns that comprise each pair, at least in locations where they weave in the papermaking surface, are generally located above a bottom warp yarn as opposed to being located in the open area falling between two adjacent bottom warp yarns. By weaving the fabric to include such stacked stitching yarn pairs it may be possible to improve the straight-through drainage of the fabric. It will be understood, however, that the stitching warp yarns that comprise the stitching warp yarn pair will not be stacked over the bottom warp yarn at all locations. This can best be seen in
Pursuant to another aspect of the present invention, the fabric may include stitching warp yarn pairs which are woven so that the two yarns in each such pair interlace with the bottom weft yarns on opposite sides of a bottom warp yarn. This feature of the present invention is illustrated, for example, in
An embodiment of the warp-stitched triple layer fabrics of the present invention is illustrated in
As seen in
As shown in
Referring now to
As shown in
As noted above, in the fabric depicted in
As shown in
As shown in
In the embodiment of the present invention depicted in
As can also be seen in
The coupling arrangement that occurs between the bottom warp yarns 151, 153, 155, 157 and the stitching warp yarns 120–127 may have several beneficial effects in certain fabrics. First, in many fabrics the bottom warp yarns 150–157 will be woven using larger, sturdier yarns than the yarns used for the top warp yarns 110–113 or the stitching warp yarns 120–127, since smaller diameter yarns are usually selected for yarns that weave on the papermaking surface. Thus, by having the stitching warp yarns 120–127 couple with a bottom warp yarn 151, 153, 155, 157 at locations where the stitching warp yarns 120–127 form a knuckle on the machine side surface, the stitching warp yarns are partially protected from wear by the larger bottom warp yarns that they couple with. This may advantageously extend the life of the fabric, as a potential failure point for a multilayer fabric is wear of the stitching yarns that come in contact with the papermaking machine. Additionally, having two warp yarns coupled at the locations where the warp yarns pass below the bottom weft yarns to form a knuckle on the machine side surface potentially acts to increase the upward force on the bottom weft yarn at that location. This increased upward force helps to “bury” the warp yarn knuckle on the machine side surface up into the bottom fabric layer 104, which further may help to reduce the machine-induced wear on the bottom warp yarns 151, 153, 155, 157 and the stitching warp yarns 120–127.
Another fabric 200 constructed according to the teachings of the present invention is illustrated in
As seen in
As shown in
Referring now to
As shown best in
As noted above, in the fabric depicted in
As shown in
As shown in
Another fabric 300 constructed according to the teachings of the present invention is illustrated in
As seen in
As shown in
Referring now to
As noted above, in the fabric depicted in
As shown in
As shown in
The principles of the present invention can be extended to a variety of different types of fabrics. For instance, the principles may be employed in fabrics woven on different numbers of harnesses, as shown by the exemplary 20 and 25 harness embodiment fabrics that are pictured and described above. The principles may also be employed with fabrics having various top to bottom weft yarn ratios. Various of the principles may also be employed on any multilayer fabrics, and not just the “true” triple layer fabrics depicted in
As noted above, certain embodiments of the present invention are directed to “true” triple layer fabrics—meaning triple layer fabrics that include (1) a set of warp yarns and a set of weft yarns that each weave exclusively in a top fabric layer, (2) a set of warp yarns and a set of weft yarns that each weave exclusively in a bottom fabric layer and (3) stitching warp yarns that stitch the top and bottom fabric layers together. Pursuant to the teachings of the present invention, it will be appreciated that the warp-stitched true triple layer fabrics may have improved stacking, increased permeability and higher fiber support as compared to double layer fabrics. Additionally, by using stitching warp yarn pairs that complete the weave in the papermaking surface, it is possible to bind the fabric together at numerous locations, thereby providing a very stable fabric that is resistant to interlayer wear.
Pursuant to another aspect of the present invention, the yarns comprising each stitching warp yarn pair may interlace with the top fabric layer an unequal number of times in each repeat of the fabric. For example, as shown best in
Pursuant to another aspect of the present invention, the stitching warp yarns in each stitching warp yarn pair may be woven so that they tend to gravitate toward each other in the weave. This may be accomplished by having the weft yarns exert forces on each stitching warp yarn that urge the stitching warp yarn in the direction of the other yarn in each stitching warp yarn pair. These forces may facilitate substantially stacking the stitching warp yarns above a bottom warp yarn (except near the points where the stitching warp yarns interlace with the bottom weft yarns) so as to provide for improved straight-through drainage in the fabric.
As noted above, in certain embodiments of the present invention, the warp yarns are woven from three separate warp beams and at least two different sizes of warp yarns may be used. This may provide several potential benefits. For example, in many conventional weft-stitched triple layer fabrics, the weft stitching yarns contribute very little to the strength of the join of the fabric (i.e., where the two ends of a flat woven fabric are connected to form the endless belt) as compared to the top weft yarns and the bottom weft yarns. In warp-stitched fabrics such as the fabrics of the present invention, no weft stitching yarns are provided so that all of the weft yarns contribute more significantly to the strength of the join. Thus, the fabrics of the present invention may have improved join strength as compared to more conventional triple layer fabrics. Additionally, the fabrics of the present invention may exhibit increased fabric modulus (i.e., the fabric is less prone to stretching and elongation). This feature results from the fact that warp-stitched multilayer fabrics that include paired stitching warp yarn pairs tend to have a higher warp yarn count as compared to conventional weft-stitched multilayer fabrics. The fabrics of the present invention also will tend to have reduced weaving time (as the stitching yarn pairs are implemented as warp yarns, thus reducing the number of required weft yarns). Additionally, implementing the stitching yarn pairs as warp yarns helps to reduce the crowding of yarns in the fabric in the weft direction, thus allowing for a higher weft yarn count on the papermaking surface per inch, which can improve the level of fiber support provided.
Those of skill in the art will appreciate that numerous modifications can be made to the above described fabrics. By way of example, the yarns that form each stitching warp yarn pair can be woven in a wide variety of different weave patterns to complete any given weave pattern in the top fabric layer. Thus, for example, in the fabric depicted in
Those of skill in the art will likewise appreciate that the stitching warp yarn pairs need not be included between every adjacent pair of top warp yarns. Instead, a stitching warp yarn pair may be provided after every second, third, fourth or fifth top warp yarn. Additionally, the top warp yarns themselves could be replaced by stitching warp yarn pairs in certain embodiments of the present invention. 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 warp yarns 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 inter-layer wear problems.
Yet another modification is to vary the positions of the stitching warp yarns that form each stitching warp yarn pair. For instance, the fabric 100 depicted in
Pursuant to another aspect of the present invention, the size and or stiffness of selected of the top weft yarns may be varied to improve fabric performance. As illustrated best in
The use of larger diameter and/or higher modulus top weft yarns may also improve the uniformity of the papermaking surface at the transition points themselves. If such yarns are not used, the papermaking surface knuckle formed by the top weft yarn directly over the transition point may be lower than the remainder of the knuckles formed by the top weft yarns because the stitching warp yarns at that location pass down at a steeper angle and hence provide less support to the top weft yarn. By using larger diameter or higher modulus yarns on the top weft yarn positions that straddle the transition point it is possible to raise the height of the top weft yarn that passes over the transition point at the transition point location.
Notably, in the bottom fabric layers 104, 204, 304 of fabrics 100, 200, 300, respectively, the set of bottom warp yarns and the set of bottom weft yarns form a machine-side surface having only “single float” warp knuckles. By a “single float” machine-side warp knuckle it is meant that when the bottom fabric layer is viewed from the top, no warp yarn passes under more than one consecutive weft yarn (such that the warp yarn 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 primarily or exclusively of machine side “single float” warp knuckles.
The fabrics pictured and otherwise described and claimed herein may be employed in a variety of applications, including fine paper grades, tissue paper, brown paper and newsprint, but is especially beneficial for fine paper, newsprint and brown paper applications.
The configurations of the individual yarns utilized in the fabrics of the present invention can vary, depending upon the desired properties of the final papermakers' fabric. For example, the yarns may be multifilament yarns, monofilament yarns, twisted multifilament or monofilament yarns, spun yarns, or any combination thereof. Also, the materials comprising yarns employed in the fabric of the present invention may be those commonly used in papermakers' fabric. For example, the yarns may be formed of polypropylene, polyester, nylon, or the like. The skilled artisan should select a yarn material according to the particular application of the final fabric.
Regarding yarn dimensions, the particular size of the yarns is typically governed by the mesh of the papermaking surface. In a typical embodiment of the triple layer fabrics disclosed herein, preferably the diameter of the top weft yarns, the top warp yarns and the stitching warp yarns is between about 0.10 and 0.22 mm, the diameter of the bottom warp yarns is between about 0.14 and 0.27 mm, and the diameter of the bottom weft yarns is between about 0.18 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 weft yarns, the top warp yarns and the stitching warp yarns have diameters of about 0.13 mm, and the diameter of the bottom warp yarns is about 0.17 mm. In this embodiment the diameter of the bottom weft yarns is between about 0.33 and 0.36 mm. The total top finished end count on this fabric is 34 ends per centimeter. Fabrics employing these yarn sizes may be implemented with polyester yarns or with a combination of polyester and nylon yarns.
The fabrics of the present invention have been described herein are flat woven fabrics and hence the warp yarns for these fabrics run in the machine direction (a direction aligned with the direction of travel of the papermakers' fabric on the papermaking machine) when the fabric is used on a papermaking machine and the weft yarns for these fabrics run in the cross machine direction (a direction parallel to the fabric surface and traverse to the direction of travel) when the fabric is used on a papermaking machine. However, those of skill in the art will appreciate that the fabrics of the present invention could also be woven using an endless weaving process. If such endless weaving were used, the warp yarns would run in the cross machine direction and the weft yarns would run in the machine direction when the fabric was used on a papermaking machine.
Pursuant to another aspect of the present invention, methods of making triple layer papermaker's fabrics are provided. Pursuant to these methods, the fabrics are woven using three separate warp beams. Warp yarns that weave exclusively in the top fabric layer are provided off of the first warp beam. Warp yarns that weave exclusively in the bottom fabric layer are woven off of the second warp beam. Warp yarns that weave in both the top and bottom fabric layers are woven off of the third beam. The warp yarns on the second beam preferably have a larger diameter than the warp yarns woven off the first beam. Additionally, the warp yarns woven off the third beam may differ from the warp yarns woven off both the first and second warp beams, e.g., they might have a lower modulus of elasticity.
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.
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| Number | Date | Country | |
|---|---|---|---|
| 20040182465 A1 | Sep 2004 | US |
