Multi-ply forming fabric providing varying widths of machine direction drainage channels

Claim 1

A forming fabric for use at the wet end of a paper making machine to receive wet pulp and form the same into a consolidated web by affording discharge of the free water content of the wet pulp, comprising a multi-ply fabric having a width in the cross direction (CD) corresponding to the width of the paper making machine and a length in the machine direction (MD) in the form of a continuous loop corresponding to the length of the path of travel of the fabric through the paper machine, the uppermost ply of said multi-ply fabric comprising a self-sustaining weave construction having monofilament warp filaments of a given diameter interwoven with shute filaments in a selected weave pattern, the lowermost ply of said multi-ply fabric comprising a series of warp filaments and shute filaments interwoven with said warp filaments to produce a self-sustaining fabric construction which is characterized by a high degree of porosity, and integrated binder filaments interconnecting the upper and lower plies, and being interwoven with the upper and lower plies, said upper ply providing on the paper side of the wire an array of elongated CD knuckles spanning multiple MD filaments in a diagonal line pattern, all of said MD filaments in said self-sustaining weave of the upper ply when viewed from the top providing a drainage channel between each two adjacent MD filaments, said MD filaments being disposed in groups providing wide drainage channels between groups and at least one narrow channel between the filaments in each group, said MD filaments in the lower ply interwoven with CD filaments to provide on the machine side an array of CD knuckles transverse to the channels provided between the group of MD filaments in the upper ply.