Textiles: weaving – Fabrics – Drier felts
Reexamination Certificate
2001-10-19
2004-03-30
Calvert, John J. (Department: 3765)
Textiles: weaving
Fabrics
Drier felts
C139S3830AA
Reexamination Certificate
active
06712100
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the papermaking arts. More specifically, the present invention is a papermaker's fabric of the on-machine-seamable variety, such as an on-machine-seamable press fabric for the press section of a paper machine.
2. Description of the Prior Art
During the papermaking process, a fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, on a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric during this process, leaving the fibrous web on the surface of the forming fabric.
The newly formed web proceeds from the forming section to a press section, which includes a series of press nips. The fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two press fabrics. In the press nips, the fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the fibers in the web to one another to turn the fibrous web into a sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the web.
The web finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The web, or newly formed paper sheet, itself is directed in a sinuous path sequentially around each in the series of drums by a dryer fabric, which holds the web closely against the surfaces of the drums. The heated drums reduce the water content of the web to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speed. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Referring, for the moment, specifically to press fabrics, it should be recalled that, at one time, press fabrics were supplied only in endless form. This is because a newly formed paper sheet is extremely susceptible to marking in the press nip by any nonuniformity in the press fabric or fabrics. An endless, seamless fabric, such as one produced by the process known as endless weaving, has a uniform structure in both its longitudinal (machine) and transverse (cross-machine) directions. A seam, such as a seam which may be used to close the press fabric into endless form during installation on a paper machine, represents a discontinuity in the uniform structure of the press fabric. The use of a seam, then, greatly increases the likelihood that the paper sheet will be marked in the press nip.
In brief, the seam region of any workable on-machine-seamable, or OMS®, press fabric must behave under load, that is, under compression in the press nip or nips, like the rest of the press fabric, and must have the same permeability to water and to air as the rest of the press fabric, in order to prevent the periodic marking of the paper product being manufactured by the seam region. OMS® is a registered trademark of Albany International Corp.
Despite the considerable technical obstacles presented by these requirements, it remained highly desirable to develop an on-machine-seamable press fabric, because of the comparative ease and safety with which it could be installed on the press section. Ultimately, these obstacles were overcome with the development of press fabrics having seams formed by providing seaming loops on the crosswise edges of the two ends of the fabric. The seaming loops themselves are formed by the machine-direction (MD) yarns of the fabric. A seam is formed by bringing the two ends of the press fabric together, by interdigitating the seaming loops at the two ends of the fabric, and by directing a so-called pin, or pintle, through the passage defined by the interdigitated seaming loops to lock the two ends of the fabric together. Needless to say, it is much easier and far less time-consuming to install an on-machine-seamable press fabric, than it is to install an endless press fabric, on a paper machine.
There are several methods for producing a press fabric that can be joined on the paper machine with such a seam. One method is to flat-weave the fabric, in which case the warp yarns are the machine-direction (MD) yarns of the press fabric. To form the seaming loops, the warp ends are woven some distance back into the fabric body in a direction parallel to the warp yarns. Another technique, far more preferable, is a modified form of endless weaving, which normally is used to produce an endless loop of fabric. In modified endless weaving, the weft, or filling, yarns are continuously woven back and forth across the loom, in each passage forming a loop on one of the edges of the fabric being woven by passing around a loop-forming pin. As the weft yarn, or filling yarn, which ultimately becomes the MD yarn in the press fabric, is continuous, the seaming loops obtained in this manner are stronger than any that can be produced by weaving the warp ends back into the ends of a flat-woven fabric. In still another method, a fabric is woven endless, and the endless loop of fabric thereby obtained is flattened and given the form of two fabric layers joined to one another at two widthwise ends of the flattened loop. One or more widthwise yarns are then removed from each of the two widthwise ends to produce a short gap defined by the freed, that is, the newly unwoven portions of, lengthwise yarns at each end. These unwoven portions of the lengthwise yarns are then used as seaming loops when the two widthwise ends are brought together as described above.
Alternate approaches toward manufacturing a laminated fabric like that made according to the preceding method are shown in two recently issued U.S. patents. In commonly assigned U.S. Pat. No. 5,732,749 to Fargeout, the teachings of which are incorporated herein by reference, a laminated integrally woven on-machine-seamable papermaker's fabric includes two single-layer woven fabric plies sharing a common machine-direction (MD) yarn. The common MD yarn, which is the weft yarn on the loom during the weaving of the fabric by a modified endless weaving technique, forms seaming loops which join the plies to one another at the ends thereof. During the weaving of the press fabric, solvent-removable binder yarns join the two plies, which are accordingly integrally woven. When the weaving is completed, the solvent-removable binder yarn are removed through dissolution with an appropriate solvent, separating the plies and yielding the laminated structure.
In commonly assigned U.S. Pat. No. 5,939,176, the teachings of which are incorporated herein by reference, an on-machine-seamable multiaxial press fabric for the press section of a paper machine is made from a base fabric layer assembled by spirally winding a fabric strip in a plurality of contiguous turns, each of which abuts against and is attached to those adjacent thereto. The resulting endless base fabric layer is flattened to produce first and second fabric plies joined to one another at folds along their widthwise edges. Crosswise yarns are removed from each turn of the fabric strip at the folds to produce seaming loops. The press fabric is joined into endless form during installation on a paper machine by directing a pintle through the passage formed by the interdigitation of the seaming loops.
Generally, the manufacture of an on-machine-seamable press fabric includes the attachment of a staple fiber batt to one or both sides thereof. The attachment may be effected by a process called needling (fiber locking) or hydroentangling, while the fabric is joined into endless form. Once the desired amount of staple fiber batt has been attached,
Elkins Phillip R.
Yook Steven S.
Albany International Corp.
Calvert John J.
Frommer & Lawrence & Haug LLP
Muromoto Jr. Robert H.
Santucci Ronald R.
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