Sorting fibers in a suspension uses a wet sieve action with short fibers passing through the sieve for outer paper/cardboard layers and longer fibers in a fraction over the sieve for the inner layer

摘要

To separate a fiber suspension (S) into fiber fractions, where the suspension is composed of chemically broken down cellulose fibers and mechanically broken down wood fibers, it is given a wet sieve processing where one fraction (A) passes through the sieve and another fraction (R) travels over the sieve. The sieve openings are set to give a mean flow speed through it of at least 2 m/sec. The mean flow speed through the sieve is pref. at least 3 m/sec. The sieve openings are slits, with a clear width (w) of max. 0.5 mm or max. 0.2 mm. The fraction which passes through the sieve contains the chemically processed cellulose fibers and short wood fibers from the mechanical processing, and the overflow fraction contains long fibers. The wet sieve separation action is within a pressure suspension sorting appts., with a cylinder sieve. When the fiber suspension is used for the prodn. of paper or cardboard, the fraction (A) passing through the sieve is used for the outer layers and the overflow fraction (R) forms the inner layer.