Process and apparatus for producing a fibrous material web

Abstract

Process and apparatus for producing a fibrous material web from a fibrous material suspension. The process includes conveying the fibrous material suspension between two endless, continuously revolving porous belts positioned to form a twin wire zone, removing a part of the suspension fluid through the porous belts so that the fibrous material web begins forming between the belts, guiding the two endless belts and the material web being formed therebetween through uniform pressure drainage elements, and removing additional suspension fluid with the uniform pressure drainage elements. The process further includes supplying an additive though at least one of the belts to the forming fibrous material web in a vicinity of the uniform pressure drainage, and one of controlling and regulating the supply of the additive to provide a particular ratio between quality levels of a top side of the forming web and a web underside of the forming web. The apparatus includes two endless, continuously revolving belts positioned to form a twin wire zone. The twin wire zone includes an inlet adapted to receive a suspension flow and the belts are porous so as to enable flow of suspension fluid therethrough. Uniform pressure drainage elements are positioned such that the belts, with the fibrous material therebetween, are guided through, and in contact with, the uniform pressure drainage elements. The uniform pressure drainage elements include a portion supporting the belts having at least one of a perforated and recessed surface adapted for receiving suspension fluid, so that drainage occurs through an essentially pulsation-free drainage pressure. A supply device for an additive can be coupled to at least one of the uniform pressure drainage elements, and a control or regulation device is provided to vary at least one of a volume flow and a pressure of the additive to be supplied.