This application is directed generally to papermaking, and more specifically to fabrics employed in papermaking.
In the conventional fourdrinier papermaking process, a water slurry, or suspension, of cellulosic fibers (known as the paper “stock”) is fed onto the top of the upper run of an endless belt of woven wire and/or synthetic material that travels between two or more rolls. The belt, often referred to as a “forming fabric,” provides a papermaking surface on the upper surface of its upper run that 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 enhanced by the presence of a “batt” layer of the press felt. The paper is then transferred to a dryer section for further moisture removal. After drying, the paper is ready for secondary processing and packaging.
As used herein, the terms machine direction (“MD”) and cross machine direction (“CMD”) refer, respectively, to a direction aligned with the direction of travel of the papermakers' fabric on the papermaking machine, and a direction parallel to the fabric surface and traverse to the direction of travel. Likewise, directional references to the vertical relationship of the yarns in the fabric (e.g., above, below, top, bottom, beneath, etc.) assume that the papermaking surface of the fabric is the top of the fabric and the machine side surface of the fabric is the bottom of the fabric.
Typically, papermaker's fabrics are manufactured as endless belts by one of two basic weaving techniques. In the first of these techniques, fabrics are flat woven by a flat weaving process, with their ends being joined to form an endless belt by any one of a number of well-known joining methods, such as dismantling and reweaving the ends together (commonly known as splicing), or sewing on a pin-seamable flap or a special foldback on each end, then reweaving these into pin-seamable loops. A number of auto-joining machines are now commercially available, which for certain fabrics may be used to automate at least part of the joining process. In a flat woven papermaker's fabric, the warp yarns extend in the machine direction and the filling yarns extend in the cross machine direction.
In the second basic weaving technique, fabrics are woven directly in the form of a continuous belt with an endless weaving process. In the endless weaving process, the warp yarns extend in the cross machine direction and the filling yarns extend in the machine direction. Both weaving methods described hereinabove are well known in the art, and the term “endless belt” as used herein refers to belts made by either method.
Effective sheet and fiber support are important considerations in papermaking, especially for the forming section of the papermaking machine, where the wet web is initially formed. Additionally, the forming fabrics should exhibit good stability when they are run at high speeds on the papermaking machines, and preferably are highly permeable to reduce the amount of water retained in the web when it is transferred to the press section of the paper machine. In both tissue and fine paper applications (i.e., paper for use in quality printing, carbonizing, cigarettes, electrical condensers, and like) the papermaking surface comprises a very finely woven or fine wire mesh structure. Typically, finely woven fabrics such as those used in fine paper and tissue applications include at least some relatively small diameter machine direction or cross machine direction yarns. Regrettably, however, such yarns tend to be delicate, leading to a short surface life for the fabric. Moreover, the use of smaller yarns can also adversely affect the mechanical stability of the fabric (especially in terms of skew resistance, narrowing propensity and stiffness), which may negatively impact both the service life and the performance of the fabric.
To combat these problems associated with fine weave fabrics, multi-layer forming fabrics have been developed with fine-mesh yarns on the paper forming surface to facilitate paper formation and coarser-mesh yarns on the machine contact side to provide strength and durability. For example, fabrics have been constructed which employ one set of machine direction yarns which interweave with two sets of cross machine direction yarns to form a fabric having a fine paper forming surface and a more durable machine side surface. These fabrics form part of a class of fabrics which are generally referred to as “double layer” fabrics. Similarly, fabrics have been constructed which include two sets of machine direction yarns and two sets of cross machine direction yarns that form a fine mesh paperside fabric layer and a separate, coarser machine side fabric layer. In these fabrics, which are part of a class of fabrics generally referred to as “triple layer” fabrics, the two fabric layers are typically bound together by separate stitching yarns. However, they may also be bound together using yarns from one or more of the sets of bottom and top cross machine direction and machine direction yarns. As double and triple layer fabrics include additional sets of yarn as compared to single layer fabrics, these fabrics typically have a higher “caliper” (i.e., they are thicker) than comparable single layer fabrics. An illustrative double layer fabric is shown in U.S. Pat. No. 4,423,755 to Thompson, and illustrative triple layer fabrics are shown in U.S. Pat. No. 4,501,303 to Osterberg, U.S. Pat. No. 5,152,326 to Vohringer, U.S. Pat. Nos. 5,437,315 and 5,967,195 to Ward, and U.S. Pat. No. 6,745,797 to Troughton.
U.S. Pat. No. 5,967,195 to Ward discloses a triple layer fabric in which pairs of stitching yarns extend in the cross machine direction and form part of the papermaking surface, in essence “completing the weave” of the papermaking surface, while also stitching with the bottom layer. The fabrics disclosed in Ward have the same number of top machine direction yarns and bottom machine direction yarns. Such fabrics have proven to provide an excellent papermaking surface (particularly due to the integration of the stitching yarns into the weave of the papermaking surface) and to combat inter-layer wear. U.S. Pat. No. 6,896,009 shows a similar concept with MD stitching yarns. However, in some applications (e.g., brown paper), high open area and fiber support may be desirable. Also, the improvement of other performance characteristics, such as wear resistance, may be desirable.
As a first aspect, embodiments of the present invention are directed to a papermaker's fabric, comprising: a set of top MD yarns; a set of bottom MD yarns; a set of top CMD yarns interwoven with the top MD yarns to form a top fabric layer; a set of bottom CMD yarns interwoven with the bottom MD yarns to form a bottom fabric layer; and a set of stitching yarns that interweave with the top and bottom fabric layers. The top MD yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units. Each of the bottom MD yarns forms a bottom MD float by passing under three or more consecutive bottom CMD yarns.
As a second aspect, embodiments of the present invention are directed to a papermaker's fabric, comprising: a set of top MD yarns; a set of bottom MD yarns; a set of CMD yarns interwoven with the top MD yarns to form a top fabric layer; and a set of CMD stitching yarn pairs that interweave with the top and bottom fabric layers. The top MD yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units. Each of the bottom MD yarns forms a bottom MD float by passing under three or more consecutive CMD stitching yarn pairs.
As a third aspect, embodiments of the present invention are directed to a papermaker's fabric, comprising: a set of MD stitching yarns, the stitching yarns being arranged in pairs; a set of bottom MD yarns; a set of top CMD yarns interwoven with the MD stitching yarns to form a top fabric layer; and a set of bottom CMD yarns interwoven with the bottom MD yarns to form a bottom fabric layer. The MD stitching yarns and the top CMD yarns are interwoven in a series of repeat units and the bottom MD yarns, the MD stitching yarns and the bottom CMD yarns are interwoven in a series of corresponding repeat units. The MD stitching yarns have a first diameter, the bottom MD yarns have a second diameter, and the first diameter is less than the second diameter.
The present invention will be described more particularly hereinafter with reference to the accompanying drawings. The invention is not intended to be limited to the illustrated embodiments; rather, these embodiments are intended to fully and completely disclose the invention to those skilled in this art. In the drawings, like numbers refer to like elements throughout. Thicknesses and dimensions of some components may be exaggerated for clarity.
Well-known functions or constructions may not be described in detail for brevity and/or clarity.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein the expression “and/or” includes any and all combinations of one or more of the associated listed items.
Although the figures below only show single repeat units of the fabrics illustrated therein, those of skill in the art will appreciate that in commercial applications the repeat units shown in the figures would be repeated many times, in both the machine and cross machine directions, to form a large fabric suitable for use on a papermaking machine.
Turning now to
As can be seen in
Turning now to
Referring again to
Notably, the MD stitching yarns 101-108 each stitch underneath the bottom CMD yarns in a location where they can be protected by two adjacent bottom MD yarn floats. For example, MD stitching yarns 101, 102 stitch below, respectively, bottom CMD yarns 151, 155. Adjacent bottom MD yarns 141, 144 pass below both of these bottom CMD yarns. As such, the bottom MD floats formed by the bottom MD yarns 141, 144 can protect the MD stitching yarns from wear, which can increase the life of the fabric 100.
In addition, it is believed that the presence of the long MD floats (i.e., floats that pass below three or more bottom MD yarns) may reduce drag of the fabric on the paper machine. In many embodiments, the bottom MD yarns comprise monofilament yarns, which tend to have considerable molecular alignment in the axial direction (induced during an extrusion process). In MD yarns, this alignment is substantially parallel with the machine direction. This molecular alignment may reduce drag of the fabric and the power requirement on the paper machine. The MD float and the molecular alignment within the floats may together reduce the wear rate of the fabric on the paper machine.
The materials for an exemplary embodiment of the fabric 100 are described in Table 1, with weaving and performance characteristics of the fabric shown in Table 2.
It can also be seen from Table 1 that, in some embodiments, the MD stitching yarns are of smaller diameter than the bottom MD yarns (a ratio of top MD yarn diameter to bottom MD yarn diameter of between about 0.4 and 0.7 is typical). The use of finer MD stitching yarns can improve the papermaking surface, whereas the use of larger bottom MD yarns can improve wear.
The concept can also be applied to fabrics that have CMD stitching. For example, turning now to
As seen in
Still referring to
Referring now to
For example, as shown in
In addition, each of the stitching yarns 221a-230b passes below one of the bottom MD yarns to form a bottom knuckle, with the bottom knuckles of the stitching yarns of a pair being separated by five bottom MD yarns. For example, and as shown in
Notably, the stitching points of the stitching yarns are located immediately adjacent the bottom knuckles formed by the bottom CMD yarns as they pass below a bottom MD yarn. For example, as best seen in
It can also be seen in
As another example of a CMD-stitched fabric, a repeat unit of another fabric, designated broadly at 300, is illustrated in
Looking first at
Turning now to
Referring now to
It should also be noted in
Another example of a fabric that is MD-stitched is shown in
As can be seen in
Referring now to
Turning now to
Referring again to
Also, each of the stitching locations is positioned under a bottom CMD yarn that the adjacent bottom MD yarns do not pass under. As such, the stitching locations can be protected as described above.
The form of the yarns utilized in fabrics of the present invention can vary, depending upon the desired properties of the final papermaker's fabric. For example, the yarns may be monofilament yarns, flattened monofilament yarns as described above, multifilament yarns, twisted multifilament or monofilament yarns, spun yarns, or any combination thereof. Also, the materials comprising yarns employed in the fabric of the present invention may be those commonly used in papermaker's fabric. For example, the yarns may be formed of polyester, polyamide (nylon), polypropylene, aramid, or the like. The skilled artisan should select a yarn material according to the particular application of the final fabric. In particular, round monofilament yarns formed of polyester or polyamide may be suitable, and, as noted, the use of monofilament yarns as bottom MD yarns may be particularly suitable.
Those skilled in this art will appreciate that yarns of different sizes may be employed in fabric embodiments of the present invention. As noted above, in embodiments that include both top and bottom MD yarns, the top MD yarns may be of a smaller diameter than the bottom MD yarns. For example, the top MD yarns, top CMD yarns, and stitching yarns may have a diameter of between about 0.10 and 0.20 mm, the bottom MD yarns may have a diameter of between about 0.15 and 0.25 mm, and the bottom CMD yarns may have a diameter of between about 0.20 and 0.30 mm. The mesh of fabrics according to embodiments of the present invention may also vary. For example, the mesh of the top surface may vary between about 20×30 to 30×50 (epcm to ppcm), and the total mesh may vary between about 60×45 to 90×75.
In addition, the numbers of different types of yarns relative to other types of yarns may vary. For example, in some of the embodiments shown, the ratio of top MD yarns to bottom MD yarns is 1:1; in others, the ratio of “effective” top MD yarns (i.e., the number of top MD yarns plus the number of MD stitching yarn pairs) to bottom MD yarns is 1:1 or 2:3, but other ratios may also be employed. In some embodiments, the number of top CMD yarns to bottom CMD yarns is 1:1; in others, the number of “effective” top CMD yarns (i.e., the number of top CMD yarns plus the number of CMD stitching yarn pairs) is 2:1; and in other embodiments, the ratio of top CMD yarns to bottom CMD yarns is 5:2; however, other ratios may also be employed.
Finally, although each of the embodiments include a plain weave top surface, other embodiments may include a top surface having a different weave pattern, including twill, satin, or the like. In addition, the long MD float bottom surfaces of the fabrics may take other weave patterns, including satin, twill or the like.
Pursuant to another aspect of the present invention, methods of making paper are provided. Pursuant to these methods, one of the exemplary papermaker's forming fabrics described herein is provided, and paper is then made by applying paper stock to the forming fabric and by then removing moisture from the paper stock. As the details of how the paper stock is applied to the forming fabric and how moisture is removed from the paper stock is well understood by those of skill in the art, additional details regarding this aspect of the present invention need not be provided herein.
The foregoing embodiments are illustrative of the present invention, and are not to be construed as limiting thereof. Although exemplary embodiments of this invention have been described, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the claims. The invention is defined by the following claims, with equivalents of the claims to be included therein.
This application is a divisional application of application Ser. No. 12/018,385, filed Jan. 23, 2008 now abandoned, the contents of which are hereby incorporated by reference as if recited in full herein.
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Number | Date | Country | |
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Child | 12708684 | US |