Web-forming section of a paper machine intended for modernization of a fourdrinier wire

Claim 1

In a web-forming section of a paper machine, such as modernization of a fourdrinier-wire part, comprising a fourdrinier wire loop having a wire run constituting a lower wire of said web-forming section and a single-wire, substantially horizontal initial portion of a dewatering zone of the web-forming section within which web-forming stock is dewatered through the lower wire by draining means, said web-forming section further comprising an upper wire unit including a looped upper wire guided by guide and web-forming rolls, said upper wire together with a run of said lower wire forming a two-wire dewatering zone within which dewatering takes place substantially through the upper wire, the improvement comprising a combination of the following components arranged so as to be jointly operative as follows: a first forming roll having an open face situated inside the upper wire loop, said two-wire dewatering zone beginning in the region of said first forming roll where said two-wire dewatering zone is curved upwardly over a sector of said first forming roll, and wherein a horizontal plane tangent to the lower part of said first forming roll is substantially coplanar with the plane of said lower wire and the open face of said first forming roll has an open area which is at least 50% of the entire area of said roll; a forming shoe within the two-wire dewatering zone situated within the fourdrinier wire loop after said first open forming roll in the direction of web travel, said forming shoe being provided with a curved deck which contacts the lower wire, said deck being curved downwardly over a certain angle and wherein said deck has an upper face which is located above the plane of said lower wire; a reversing roll situated inside the upper wire loop after said forming shoe in the direction of web travel and guiding a joint run of the upper and lower wires over an upwardly curved sector of said reversing roll until said joint run substantially coincides with the plane of said lower fourdrinier wire; a second reversing roll situated within the upper wire loop for separating the upper wire from the lower wire before the upper wire reaches said second reversing roll; and wherein said forming and reversing rolls and forming shoe situated therebetween are situated with respect to each other such that after the initial dewatering occurs in the single-wire initial portion of the dewatering zone to an appropriate extent through the lower wire, dewatering takes place within the two-wire dewatering zone, first within said sector of said first open forming roll in two directions through both said upper and lower wires, whereupon within the region of said forming shoe, the dewatering takes place primarily upwardly through the upper wire, and wherein lowermost points of said first forming roll, said first reversing roll, and said second reversing roll are all disposed at substantially the same level.