A device for sieving foreign bodies out of a material stream, wherein the device comprises a roller sieve comprising a plurality of rollers disposed in parallel to one another and discs disposed on the plurality of rollers such that they are perpendicular to the axial extension of the rollers, wherein the discs of adjacent rollers are engaged so as form slot areas between the discs and the adjacent rollers, and the discs comprise impulse discs for disaggregating a material stream disposed on the roller sieve, and conveyor discs for conveying the material stream in a transport direction and through the slot area. A corresponding process and an apparatus or system for the production of composite boards with such a device.