Abstract: The present invention relates to a method for comminuting a coarse lump mineral material in an autogenous grinding system, in which feed to the grinder is divided into a coarse fraction and a fine fraction. The coarse fraction is coarser than the inflection point on the coarse side of the knee of the particle size distribution curve of the charge of said autogenous grinder; the fine fraction is substantially all finer than the point of intersection between two tangents drawn between the adjacent inflection points on either side of the knee of the particle size distribution curve of the charge. The ratio between the amounts of fractions is determined on the basis of achieving a given charge quantity for a particular, selected set point power value for the mill in question, and determined with respect to a selected degree of grinding. Grinding efficiency is greatly increased by selecting feed sizes in accordance with the present invention.

Abstract: A drum mill intended for autogenous or semi-autogenous wet-grinding processes has a screening wall, which is arranged adjacent an end wall provided with a hollow material-discharge trunnion and which separates said end wall from the grinding space, whereat said screening wall has at least one first group of relatively small grate openings through which fine material ground in the mill constantly leaves the grinding space and departs through the discharge trunnion, and at least one second group of relatively large openings through which mixed material, comprising both fine and coarse material, can leave the grinding space. This second group of openings communicates with an individual material outlet via a switching means by which the material mixture passing through said second group of openings can be prevented from leaving the mill.