Paper web drying and polishing stations moistens the web surface by pressure forces at the end of or after the drying station before it passes through the roller press gaps of the calender to set the web moisture content

摘要

To dry and polish the surface of a fiber web (1), especially of paper, the web is passed through a drying section round a number of drying cylinders (2) and through a calender with a number of web polishing roller press gaps (3). Before the web (1) passes through the calender assembly, it is moistened through the action of pressure forces. The moisture is pressed into the fiber web (1) and/or drawn through the web by an underpressure on the opposite side of the web. The final moistening action is at the last one-third of the drying station, or between the drying and calender stations. The intensity of the moistening action is set in zones across the web (1) width, preferably according to the lateral moisture profile content measurements of the web after wetting. The web travels through the drying and calender stations at a speed of -1200 m/min. and preferably -1500 m/min. The quotient of the web length between the final moistening point and the first calender roller press gap, divided by the web movement speed, equals at least 1 sec. The web is heated in the calender, and the roller press action on it is controlled in zones across the web width. The web (1) is cooled before wetting. The web (1) follows a short free and unsupported path between a number of wetting points and/or after moistening and before polishing, with an adjustable difference speed between the web supports (4) flanking the short path. An Independent claim is included for a web processing assembly, where the web (1) passes over a suction roller (5) while hot steam is applied to the web as it passes round the suction zone. Preferred Features: The web (1) passes over a cylinder (2') with a damp mantle surface, and is pressed by a blanket (6) against the mantle surface, as it moves round the roller. The moisture is sprayed on the cylinder (2') and/or spread by a scraper rod or applied by a transfer roller and/or sprayed with steam. After transferring moisture to the web (1), the free edge surfaces of the cylinder (2') are scraped and/or treated with suction. Before wetting, the web (1) passes over at least one cooling cylinder (2), in contact with the web (1) on the side which is to be wetted. After moistening, the blanket (6) is separated from the web (1), to allow the web (1) to move along a short path, with free and unsupported travel, and the web support (4) at the end of the free path has a separate drive. Preferably both surfaces of the web (1) are moistened in succession. On leaving the drying station, the web (1) moves along a serpentine path round a number of guide rollers (7) before it reaches the calender. The calender is composed of at least three polishing rollers (8) which, in pairs, form press roller gaps (3). At least one polishing roller (8) is heated and at least one polishing roller (8) has a controlled bending action. Only one side of the web (1) is in contact with the heated cylinders (2), using the side which is to be moistened, or both sides are to be moistened and are in contact with the heated cylinders.