Textiles: weaving – Fabrics – Drier felts
Reexamination Certificate
2000-08-23
2001-08-21
Falik, Andy (Department: 3765)
Textiles: weaving
Fabrics
Drier felts
C162S903000, C442S207000
Reexamination Certificate
active
06276402
ABSTRACT:
BACKGROUND
The present invention relates to papermakers fabrics and, in particular, fabrics intended to facilitate the initial formation of an aqueous paper web in the manufacture of paper.
Papermaking machines generally are comprised of three sections: forming, press, and drying. Papermakers fabrics are employed to transport a continuous paper sheet through the papermaking equipment as it is being manufactured. The direction of travel of the fabric on the papermaking equipment is commonly referred to as the machine direction. The requirements and desirable characteristics of papermakers fabrics vary in accordance with the particular section of the machine where the respective fabrics are utilized.
In particular, in the forming section of papermaking equipment, forming fabrics are utilized to initially create an aqueous paper sheet or web from a pulp slurry. Typically, the pulp slurry is deposited on the top or paper carrying side of the moving forming fabric which transports the slurry over suction boxes or other means to form the paper web. The surface characteristics and drainage characteristics of the forming fabric play an important role in the initial formation of the aqueous paper web.
Multilayer forming fabrics are known in the art. For example, U.S. Pat. No. 5,025,839 discloses a dual layer forming fabric for use in the papermaking process which includes single system of zig zagging machine direction (MD) yarns which interweave with two layers of cross machine direction (CMD) yarns.
U.S. Pat. Nos. 5,013,330; 4,515,853; and 3,885,603 disclose forming and other types of papermakers fabrics having distinct top and bottom interwoven fabric layers which are interconnected by binding or stitching yarns. Such fabrics are generally known as “triple layer” fabrics, the “third” layer being the layer of binding or stitching yarns which interconnects the upper yarn system with the lower yarn system.
Early triple layer fabrics utilized different size machine direction (MD) yarns in the upper and lower fabric layers; the upper MD yarns being roughly one half the diameter than the lower MD yarns with twice as many upper MD yarns than lower MD yarns. Common weave patterns for the bottom or machine side layer were plain weave and 1:3 broken twill.
One of the problems with such triple layer fabrics was the relatively high caliper of the fabric. The high caliper allowed water drained from the aqueous paper web to be carried inside the fabric and caused problems of rewetting of the sheet during forming. Another draw back was that the bottom MD yarns tended to arrange themselves between the top layer MD yarns restricting straight through drainage and the ability to easily clean the fabrics. Also if the bottom MD yarns were not evenly spaced and correctly positioned they could cause “shadow marking” in the paper web formed on the fabric. Non-uniform spacing caused non-uniform drainage which attributed to undesired marking.
To decrease the caliper of triple layer fabrics, the same size MD yarns began to be used in both the top and bottom layers of such fabrics. A draw back to this construction was that in order to maintain the fine mesh top layer, much smaller lower MD yarns were employed which required comparably smaller lower CMD yarns which tended to shorten fabric life. To permit the use of larger CMD bottom yarns for better wear, it was possible to weave the lower MD yarns in pairs which, however, resulted in the reduction of straight through drainage in the fabric since the paired lower MD yarns would block the spaces between the upper MD yarns. It would be desirable to provide a triple layer fabric which permits the use of uniformly sized upper and lower MD yarns in conjunction with larger lower CMD yarns without substantially impairing straight through drainage of the fabric.
SUMMARY
A “triple layer” fabric is provided having upper and lower systems of interwoven yarns interconnected into an integral fabric by a system of stitching yarns. Preferably, the fabric is a forming fabric having upper and lower layers of uniformly sized machine direction (MD) yarns. Upper and lower layer cross machine direction (CMD) yarns weave, respectively, with the upper and lower MD yarns to define the upper and lower yarn systems. A stitching layer of CMD yarns binds the upper and lower yarn system together.
The lower layer CMD yarns are preferably larger in diameter than the MD yarns, the upper layer CMD yarns and the stitching yarns. The lower layer CMD yarns weave in a repeat pattern with respect to the lower layer MD yarns such that the lower layer CMD yarns weave in a repeat defined by floats under groups of at least three lower MD yarns and over pairs of adjacent lower MD yarns. Each lower layer MD yarn is in at least two different pairs relative to at least two different lower layer CMD yarns within the repeat which maintains a substantial degree of stacking of the lower layer MD yarns below respective upper layer MD yarns.
The weave repeat is also selected such that the stitching yarns are woven so as to be recessed within the fabric away from the surfaces defined by the interweaving of the upper MD and CMD yarns and the lower MD and CMID yarns, respectively.
In an alternative embodiment, the stitching yarns are incorporated into the upper layer of the fabric where selected upper layer MD yarns interweave with one or more layer CMD yarns in manner such that the interweavings are recessed from the bottom surface of the fabric. Preferably, less than half of the upper layer MD yarns are selected for the additional stitching function.
Other objects and advantages of the present invention will become apparent from the following description of a presently preferred embodiment.
REFERENCES:
patent: 5169709 (1992-12-01), Fleischer
patent: 5641001 (1997-06-01), Wilson
patent: 5826627 (1998-10-01), Seabrook et al.
patent: 5937914 (1999-08-01), Wilson
patent: 5944062 (1999-08-01), Gampe
patent: 5975148 (1999-11-01), Lee
AstenJohnson, Inc.
Falik Andy
Volpe & Koenig P.C.
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