Grinding plant

A grinding plant for autogeneous or semiautogeneous grinding of material in at least two separate grinding mills in a primary grinding step and a secondary grinding step which works with material obtained from the primary grinding step, the grinding chamber of the primary mill having a first and a second outlet means, the first outlet means including a group of openings for discharge from said grinding chamber relatively finely ground material which is to be ground in the secondary mill, the second outlet means having at least one opening to discharge from said grinding chamber material containing relatively coarse pieces to be used as grinding media in the secondary mill;

• the plant further including means connected between said mills for passing to the secondary mill at least all of the material removed from the primary mill which has not been ground to the desired final size, means for controlling during the grinding operation the discharge of material from the primary mill via the second outlet means so that the secondary mill will operate with a preselected quantity of grinding media, the grinding chamber of the secondary mill having an outlet means including a number of openings with a smallest cross-section which is at least substantially equal to the smallest cross-section of the openings in said first outlet means of the primary mill, and a classifying means arranged to receive the material from the secondary mill and to separate said material into a finely ground product and an intermediary material requiring further grinding, and means for continuously returning said intermediary material to the primary and secondary mills in such adjustable proportions between the amounts of material returned to the primary and secondary mills that the driving means of the primary mill operates with a preselected power consumption.