Vacuum-spraying grinder

A vacuum-spraying grinder in which material to be ground is sprayed by centrifugal force on to an impact surface, said grinder comprising:

• a fixed chamber;
• means connected to said chamber for connection to suction means so that the chamber is under suction pressure;
• a target mounted in said chamber comprising a ring having an impact surface directed inwardly of said chamber, said impact surface having a vertical axis of symmetry of revolution;
• a rotor located at least partially in said chamber and defining a vertical axis of rotation coincident with said axis of symmetry of revolution of said impact surface of said target, said rotor comprising an upper part in the form of a horizontal disc defining radial channels which communicate with a central orifice provided in the upper part of said disc, and a lower part in the form of a vertical shaft for the support and drive of said rotor, said disc being located at the level of said target and inside the space defined by said impact surface thereof;
• means for feeding material to be ground to said central orifice of said disc and permitting continuous feeding of said grinder;
• means for removing ground material from the lower end of said vacuum chamber;
• and
• means for supporting, driving and guiding said shaft of said rotor comprising:
• at least one active radial magnetic bearing comprising a stator surrounding said shaft over a part of the height thereof, and a rotor carried by said shaft in spaced relation with said stator;
• an active axial magnetic stop comprising a movable part carried on said shaft and a fixed part located in spaced relation opposite said movable part of said stop;
• radial and axial position detector means for detecting the radial and axial positions of said shaft, said detector means being connected to circuit means for controlling the energization of said stator of said magnetic bearing and said magnetic stop in accordance with output signals from said detector means to compensate any unsymmetrical wear of said rotor by shifting of the rotor within the space between the stator and rotor of the radial magnetic bearing;
• an electric motor comprising a stator surrounding said shaft over a part of the height thereof and a rotor mounted on said shaft in spaced relation with said stator;
• and
• ball bearing means, mounted around said shaft and on which said shaft rests when it is not in operation.