Device for separating impurities from fibrous material

The assembly to clean a suspension of impurities, especially a bio-mass or with a fiber content and particularly of used paper material, has a sieve body (1) with a sieve mantle (1.1) of rotation symmetry. The assembly to clean a suspension of impurities, especially a bio-mass or with a fiber content and particularly of used paper material, has a sieve body (1) with a sieve mantle (1.1) of rotation symmetry. The sieve has side walls (1.2,1.3) with an inflow (1.3.1) at one side and an outflow (1.2.1) at the other side. The sieve body has a rotor (2), shrouded by the sieve mantle (1.1), with a rotor shaft (2.1) and a number of rotor blades (2.2), with a drive (5) for the rotor shaft (2). At least some of the rotor blades (2.2) have at least two longitudinal sections (2.2.1,2.2.2) with a design and array to act on the material with axial parallelism and opposing impelling forces. The sieve (1) is shrouded by a mantle (3) which forms a ring gap (4) between it and the sieve mantle (1.1). The ring gap (4) forms a sediment channel at its lower zone, where sediment is extracted by a screw conveyor. The drive (5) is reversible. The axis of the rotor shaft (2.1) is pitched at an angle to the horizontal. The sieve mantle (1.1) has zones without perforations.