Method for resisting formation of undulations in a fiber/water mixture during forming of a paper web in a paper-making machine

DETAILED DESCRIPTION The object of the present invention is to provide a novel method and arrangement with which the above-described detrimental undulation phenomena of a fiber/ water mixture occurring on a forming wire can be minimized, if not prevented.
For achieving this aim, and other aims which will become apparent later on, this invention is mainly characterized in that undulations in the fiber/water mixture supplied onto the wire through a lip slice aperture of a headbox of a paper-making machine are minimized, if not prevented, by establishing above the forming wire an air curtain extending over the entire width thereof, the air mass directly above and upon the wire in the region of said air curtain being set in motion in the same direction along which the wire travels at a web velocity, and at an air velocity which substantially equals the web velocity.
The arrangement comprises a blow box extending over the whole breadth of the wire and forming an air channel through which the fiber/water mixture passes in contact with the moving air curtain.
The blow box is connected with feed conduits for feeding blow air into the air channel.
The blow box is provided with a plurality of nozzles transverse to the traveling or advancement direction of the wire.
The nozzles are successively arranged along the advancement direction.
Jets of air are blown through the nozzles into the air channel formed between the blow box and the wire to form the moving air curtain which moves along the traveling direction of the wire at a velocity substantially the same as the speed with which the wire moves.
The moving air curtain blankets the fiber/water mixture, and the tendency of undulations to form is minimized due to the small, if not negligible, differential velocity between the air velocity of the moving air curtain and the web velocity of the fiber/water mixture.
The present invention may be performed on Fourdrinier wire sections, that is, on planar wire sections, or on so-called hybrid wire sections, said last-mentioned having a single wire at an initial part of the forming zone or station, on which the web has time to acquire a certain degree of couching before moving on to a twin-wire forming zone, where dewatering is effected through two opposed wires