48 thereof the edge of the blade over which the material falls to the next blade substantially corresponds to the thread of the apparatus in accordance with the prior art blades 44 are mounted on the shaft in such a way that the average inclination thereof to the plane parallel to the shaft 28 is about 60 u00b0 75 u00b0 blades 44 may be mounted on the shaft 28 either according to the fig3 wherein the end view of the feed screw resembles for example a three leaf clover in other words significant gaps 50 remain between blades 44 through which openings a portion of the material may fall even past the next blade the blades may also be arranged in such a way that the leading edge 52 of each blade is located under the trailing edge 48 of the preceding blade so that the pulp particle falls directly onto the next blade it is a feature of the construction and position of blades 44 that the pitch of the blade is considerably higher compared with the thread in accordance with prior art so that the kinetic speed of the material in the axial direction at the blade is higher the blades 44 are also positioned in relation to each other in such a way that the trailing.