1. Field of the Invention
The invention relates to a papermakers' fabric and more particularly to such a fabric free of edge curl while providing an excellent machine surface and an improved forming surface.
While the improved papermakers' fabric of the present invention could be advantageously used in the forming, transfer, press or drying sections of a papermaking machine, for purposes of an exemplary showing the fabric will be described in its application as a forming fabric.
2. Prior Art
Several well known types of papermaking machines utilize a forming fabric comprising a fabric of interwoven warp and filling yarns formed into an endless belt. A layer of wet pulp is deposited on the forming side of the papermakers' fabric and water is withdrawn from the pulp through the fabric by vacuum means or the like located on the machine side of the fabric.
Such papermakers' fabrics can be manufactured in two basic ways. First, they can be flat woven by a flat weaving process with their ends joined by any one of a number of well-known methods to form an endless belt. Alternatively, they can be woven directly in the form of a continuous belt by means of an endless weaving process. Both methods are well known in the art. In a flat woven papermakers' fabric, the warp yarns extend in the machine direction and the filling yarns extend in the cross-machine direction. In a papermakers' fabric having been woven in an endless fashion, the warp yarns extend in the cross-machine direction and the filling yarns extend in the machine direction. As used herein the terms "machine direction" and "cross-machine direction" refer respectively to a direction equivalent to the direction of travel of the papermakers' fabric on the papermaking machine and a direction transverse this direction of travel.
In the usual practice, papermakers' fabrics are manufactured utilizing weave patterns such as the 1/2 twill, 2/1 twill, 2/3 twill, 3/2 twill, 1/4 twill, 4/1 twill, 1/5 twill, 5/1 twill and variations thereof such as the sateens. These most commonly used weave patterns have one characteristic in common. They are all unbalanced weaves yielding two-sided fabrics; one side being warp faced and the other side being filling faced. This characteristic leads to an imbalance of forces within the fabric structure, together with the different conditions which obtain at the edges of the papermakers' fabric when used on a papermaking machine (such differences including less lubrication by water, less vacuum being applied, etc.) result in a tendency of the papermakers' fabric to curl at its longitudinal edges. This tendency to curl results both in running problems and wear problems.