Abstract: Apparatus for screening papermaking stock comprises two annular flat screening plates arranged in parallel spaced relation to form a screening chamber therebetween which is bounded on its outer periphery by a cylindrical wall, and wherein a rotor includes vane portions which extend into this screening chamber to agitate the stock so that particles of sufficiently small size can pass through the screening plates into annular compartments outside the screening plates from which they flow into a peripheral chamber having an outlet port. The screening chamber includes an annular space which is surrounded by the accepts chamber and is radially beyond the vane portions of the rotor wherein reject material collects for discharge through an outlet tube which extends through the accepts chamber to the outside of the apparatus.

Abstract: In screening apparatus for paper making fiber incorporating a cylindrical screen member provided with cylindrical screening perforations, each of the perforations is characterized by a concentric frustoconical inlet end portion having a maximum diameter at the inlet surface of the screening member which is substantially greater than the portion of the perforation of minimum diameter, the maximum diameter of these inlet end portions being such that adjacent such portions closely approach or intersect each other to define multiple ridges on the surface of the inlet side of the screening member.

Abstract: In screening apparatus for paper making stock including a housing, a cylindrical perforated screen member separating the interior of the housing into a supply chamber and an accepts chamber on the inside and outside respectively of the screen member, an inlet port for supplying stock to one end of the supply chamber, an outlet port from the accepts chamber, a reject port from the supply chamber, and a rotor mounted for rotation within the screen member, the rotor is characterized by comprising a substantially circular disk which is of a thickness constituting a very minor fraction of the axial length of the screen member and has vanes mounted on its outer periphery which extend lengthwise of the screen member for rotation with the disk in the annular space between the periphery of the disk and the inner surface of the screen member.