Multi-stage jet mill

Claim 1

A multi-stage jet mill comprising at least two relatively thin cylindrical milling chambers, each comprising spaced opposed front and rear walls held in spaced parallel relationship by a circumferential wall including an annular manifold, the front wall of each chamber having an inlet for material to be milled, the inlet of the first of two successive milling chambers being coaxial with the axis of the mill, and the rear wall of each chamber having an outlet arranged centrally thereof for discharging the milled material from the respective chambers, a plurality of jet nozzles arranged circumferentially in the circumferential wall of each chamber in communication with its respective manifold, means to supply pressurized gas to said manifolds for introducing pressurized gas by way of said jet nozzles into each milling chamber adjacent the periphery thereof, said jet nozzle axes arranged tangentially with respect to a concentric circle inwardly of the circumferential wall of its respective chamber so as to set up a circular movement of the material being milled within each milling chamber, the material discharge outlet of the first of two succesSive milling chambers comprising concentrically arranged inner and outer discharge openings coaxial with the axis of said mill for classifying the material discharged from said first chamber the said inner discharge opening of said first milling chamber outlet being constructed and arranged to discharge a relatively finely ground portion of the milled material from said first milling chamber directly out of said multi-stage mill, and the said outer discharge opening of said first milling chamber outlet being constructed and arranged to discharge a relatively coarse portion of the milled material from said first milling chamber into the next succeeding milling chamber of said mill.