Patent ID: 7150808

Claim:
An apparatus for forming a paper or cardboard web from a fibrous suspension, said apparatus comprising: a twin wire section consisting of a first wire loop formed by a first wire (v 1 ), a second wire loop formed by a second wire (v 2 ), and at least one headbox, from which headbox the fibrous suspension is fed into a space between the first and the second wire loops, said first wire loop being provided with a dewatering box ( 1 ) placed above the first wire and arranged to drain water from the fibrous suspension between the first and the second wire loops via a bottom ( 11 ) of the dewatering box and through the first wire, said apparatus further comprising: two successive dewatering zones (L 0 , L 1 –Li) provided in an area of the dewatering box, wherein a direction of web movement in the first dewatering zone is away from the dewatering box, and runs of each first wire loop are substantially straight, while in the second dewatering zone a direction of web movement is towards the dewatering box and water drainage from the fibrous suspension is arranged to take place substantially in a direction towards the dewatering box, wherein the bottom of the dewatering box includes parts formed as strips in a second dewatering zone, and wherein to achieve effective water drainage in the second dewatering zone, the bottom ( 11 ) of the dewatering box is formed as straight like portions (L 1 –Li) and edges (P 1 –Pi) between them, over which the web between the two wires moves, the edges (P 1 –Pi) between the straight portions (L 1 –Li) cause wire tension for producing pressure pulses for increasing dewatering efficiency.