WEB-FORMING SECTION OF A PAPER MACHINE

摘要

A web-forming section of a paper machine includes a lower wire loop having a wire run which constitutes a lower wire of the web-forming section and which forms a single-wire initial portion of a dewatering zone of the web-forming section, and an upper wire unit having an upper wire loop which together with a run of the lower wire forms a two-wire dewatering zone constituted by a joint run of the upper and lower wires within which dewatering takes place substantially through the upper wire, wherein a first open faced forming roll is situated within the upper wire loop so that the two-wire dewatering zone begins and curves upwardly in the region of the first forming roll, a forming shoe within the lower wire loop having a curved deck whose center of curvature is ed on the side of the lower wire loop and which guides the joint run of the upper and lower wires, a second forming roll situated within the lower wire loop after the forming shoe and which guides the joint run of the upper and lower wires over a downwardly curved sector thereof. Initial dewatering occurs in the single-wire initial portion of the dewatering zone to an appropriate extent through the lower wire. In the two-wire dewatering zone within the range of the first and second forming rolls and the forming shoe situated therebetween, dewatering occurs first within the sector of the first open forming roll in two directions through both the upper and lower wires whereupon within the region of the forming shoe, the dewatering takes place primarily upwardly through the upper wire and thereupon the dewatering pressure is further increased within the range of the second forming roll with dewatering taking place substantially through the upper wire.