Patent Application
20080289716
1. Field of the Invention
The present invention relates to belts, and, more particularly, to belts used in the paper machinery field.
2. Description of the Related Art
It has been found in the paper machinery art that it is possible to create a “press nip” by wrapping fabrics around a roll at high contact angles with a wet paper sheet between the fabrics. By applying high tensile load to the outer fabric, compressive forces are transmitted to the sheet and force water into the inner fabric. The advantage of this method verses a normal roll press is that the pressing zone and dwell time can be very large and the compressive force on the paper relatively low so that sheet bulk is not minimized by undue compression.
The outer fabric in this arrangement, in addition to experiencing high tensile loads, must have sufficiently high permeability on the range of 100 to 600 CFM (cubic feet/min) to permit air passage through the fabric to help dry the sheet, and in some cases permit evaporation of water from the sheet.
While this approach is effective in drying the paper, the tensile demand on the outer fabric is extremely high. The running tension is in the range of 15 to 80 kN/m. These loads are far higher than those for normal textile fabrics which may cause the outer fabric to stretch and narrow excessively and any joints or seams to fail prematurely. One approach to eliminate this problem has been to incorporate steel belts which withstand the tension. However, they are too heavy and can be dangerous if they fail in operation. In addition to that, they may not have sufficient permeability to achieve the proper drying function of the paper.
Therefore a need exists for a fabric in such an environment that can operate under consistently high tension without significant change in dimensions (creep) and also without joints and/or connections that can cause failure.
The invention, in one form, is directed to an endless fabric belt subjected to a substantial running tension. The belt has one of a flat or endless woven fabric formed from at least one MD (machine direction) strand approaching zero creep at high tensile loads. An at least one CMD (cross machine direction) strand is interwoven with the MD strand. The MD strand has first and second ends spliced to one another to form an endless belt, the splice forming a significant linear MD overlap with each other.
The invention, in another form, is directed to a method of forming an endless fabric belt subjected to a substantial running tension. The method includes the steps of interweaving an at least one MD (machine direction) strand with at least one CMD (cross machine direction) strand to form a fabric. At least the MD strand is formed from material approaching zero creep at high tensile loads and has first and second ends. The first and second ends of the MD strand are spliced to one another with a significant linear MD overlap to form an endless belt.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one embodiment of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner.
The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description is taken with the drawings making apparent to those skilled in the art how the forms of the present invention may be embodied in practice.
Referring now to the drawings,
There is a significant increase in dryness with the belt press 18. The belt 32 should be capable of sustaining an increase in belt tension of up to approximately 80 KN/m without being destroyed and without destroying web quality. There is roughly about a 2% more dryness in the web W for each tension increase of 20 KN/m. Conventional synthetic belts may not achieve a desired tensile force of less than approximately 45 KN/m and the belt may stretch too much during running on the machine.
In accordance with the present invention, the belt illustrated in
The MD yarn 34 may be looped to form the endless belt 32 by being interwoven with CMD yarn 40. Alternatively a plurality of MD yarns 34 may be interwoven with a plurality of CMD yarns 40 to form a flat woven belt joined at the ends of MD yarns 34 to form an endless belt.
The MD yarns 34 may be combined with standard polymer yarns to control cost of the belt or they may be twisted or spliced into a composite yarn.
The resultant structure enables operation of a press fabric that is able to withstand the ultra high tensile loads up to 50 kilo Newton per meter and approach zero or creep. Furthermore, the yarns provide adequate porosity at least above 100 cfm to enable efficient drying of the fabric so pressed between the outer fabric 32 and the inner fabric 7.
While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
