Ultrafine grinding mill of which fed material flows down through an agitated bed composed of small grinding medium

An ultrafine dry grinding mill comprising:

• a vertically-arranged cylindrical housing for containing a bed of grinding medium comprising grinding elements of varying diameters, said housing having a top, a bottom, an inner surface, and a longitudinal central axis;
• a screen closing said bottom of said housing, said screen having a mesh size preventing the grinding medium from passing therethrough;
• a rotary shaft arranged on said central axis of said housing;
• a plurality of stages of agitating blades mounted on and extending radially outward from said rotary shaft for rotation in parallel planes and including an uppermost stage and a lowermost stage, each stage including a plurality of blades, said blades of at least one of said stages being vertically-oriented and said blades of at least one of said stages being inclined relative to said longitudinal central axis of said housing, each of said blades having a tip spaced from said inner surface of said housing to define a gap between said tip and said inner surface at room temperature, and said lowermost stage being spaced from said screen to define a gap between said lowermost stage and said screen at room temperature, said gap between each said tip and said inner surface at room temperature and said gap between said lowermost stage and said screen at room temperature both being not more than two-thirds the smallest diameter of the grinding medium at room temperature.