Autogenous comminution of hard magnetic materials - by exposure to time-varying electromagnetic fields

摘要

(A) Autogenous comminution of hard magnetic materials is carried out using direct electromechanical energy conversion by means of varying electromagnetic fields acting on the materials. The materials are stochastically magnetised, independently of geometrically preferred directions, as a random flow in a separate magnetising device; and then fill an annular chamber (1) surrounded by two constantly spaced, opposed closed and pref. rotationally symmetrical excitation systems (6,7) generating time-varying electromagnetic fields which circulate in the same direction and which pass in one direction through the electromagnetically active work space of the chamber (1). The materials are moved apparently chaotically along different endless paths in the work space by the electromagnetic fields; and a gaseous or liq. carrier stream (10) is injected to discharge the comminuted magnetic materials as a two-phase mixt. (11) from the chamber (1). USE/ADVANTAGE - The process is used esp. for fine and ultra-fine comminution of pelletised and pre-sintered hexaferrites. It produces magnetic powder or suspensions with high purity and narrow particle size distribution in a single treatment unit at low energy cost (one-half to one-tenth of the energy costs of prior art processes).