Patent ID: 6228221
Filing Date: 2001-05-08
Classification: D21F,F26B

Abstract:
A process of dewatering a fibrous web in a dewatering press including a counterpart face, a shoe press unit having a revolving flexible press belt and at least one press shoe such that the at least one press shoe is arranged to press the flexible press belt against the counterpart face, at least one nip formed by the flexible press belt being pressed against the counterpart face and having a length extending in a web travel direction and being at least substantially similar to a length of the at least one press shoe in the web travel direction, and a device that guides the fibrous web and at least one dewatering belt being guided through the extended nip, the process comprising:pressing the fibrous web within the extended nip;determining a dwell time of the pressing of the fibrous web within the extended nip, wherein the dwell time is less than approximately 12 ms; andmaintaining the determined dwell time, wherein the determining of the dwell time comprises:establishing a minimum pressure in accordance with the formula:P.sub.min =(T.sub.abs.times.100).sup.3 N/m.sup.2, wherein P.sub.min represents the minimum pressure, and T.sub.abs represents the absolute dry content of the fibrous web at an inlet of the extended nip;determining a length of the extended nip in accordance with a total length of one of a portion of and a plurality of portions of the extended nip in which a pressure greater than the minimum pressure is exerted;determining a speed of the fibrous web through the extended nip; andcalculating the dwell time from the determined length of the extended nip divided by the determined speed of the fibrous web.