Pulverizing and particle-size classifying apparatus

A ball mill provided with balls inside said mill and adapted for the milling of material to produce a pulverized product, and having electromagnets as means for generating magnetic force acting on said balls, comprising:

• a horizontally oriented rotary mill casing of a given longitudinal length and of cylindrical shape, and having two end heads and adapted to rotate in a direction of rotation,
• said mill casing being supported on and driven by two hollow shafts extending horizontally and in opposite directions along a center line of the mill casing, one shaft extending from one end head, and the other shaft extending from the second end head, one shaft being for admission of material to be pulverized in the mill, and the other shaft being for removal of resulting pulverized product from the mill in a gas-borne state;
• a cylindrical stationary electromagnet-supporting casing concentric with and external to said rotary mill casing, the circumference of said stationary casing being scaled in degrees in the direction of rotation of said mill casing, with the point of 0.degree. being at the highest point of said stationary casing , only two zones of electromagnets being supported at an inner side of said stationary casing, said zones extending along the total overall longitudinal length of said mill-casing, one zone being from approximately 135.degree. to 180.degree. and the other zone being from approximately 225.degree. to 360.degree. in circumference;
• each zone comprising a plurality of identically constructed electromagnets, each electromagnet being solidly mounted on and secured to the inner surface of said stationary casing with each of their magnetic pole axes being aligned perpendicularly to said center line of said mill casing and with a uniform running clearance provided between each electromagnet and said mill casing, the electromagnets being equally spaced apart and located at and distributed throughout said two zones so that longitudinal rows and circumferential rows of the electromagnets are formed in said two zones, and said electromagnets consisting of three electrical groups, the first group consisting of electromagnets distributed on one longitudinal row at approximately 225.degree., the second group consisting on one-half of the electromagnets that are not part of said first group, and the third group consisting of one-half of the electromagnets that are not part of said first group and are not said second group, said electromagnets of said second and third groups being arranged in a staggered manner so that an electromagnet of the second group is circumferentially immediately and longitudinally immediately adjacent to an electromagnet of the third group to form a zig zag arrangement, and means for energizing the electromagnets so that when any one electromagnet of said second and third groups is energized, the electromagnets of said second and third groups immediately next to it in circumferential and longitudinal directions are de-energized;
• and a network of electrical circuits which control the electromagnets, said network consisting of three circuit groups corresponding to said three electromagnet groups, the first circuit group serving the first electromagnet group to keep this group suitably energized at all times, and the second and third circuit groups serving each of said second and third electromagnet groups to alternately and cyclically energize said second and third electromagnet groups.