Variable magnetic strength permanent magnetic drum

Claim 1

IN A PERMANENT MAGNET SEPARATOR COMPRISING A ROTATABLE MATERIAL CONVEYING DRUM, ANDA PERMANENT MAGNET ASSEMBLY WITH THE DRUM HAVING A PLURALITY OF POLE PIECES ADJACENT THE INTERIOR SURFACE OF THE DRUM AND HAVING PERMANENT MAGNETS EXTENDING BETWEEN THE POLE PIECES AND MAGNETIZED IN THE DIRECTION BETWEEN SAID POLE PIECES FOR ESTABLISHING A WORKING MAGNETIC FIELD AT THE EXTERIOR OF THE DRUM, THE IMPROVEMENT COMPRISING SHUNTING MEANS OF MAGNETIC MATERIAL WITHIN SAID DRUM AND DISPOSED AT LEAST PARTIALLY WITHIN THE CONFINES OF THE PERMANENT MAGNETS THEMSELVES IN THE REGION BETWEEN THE POLE PIECES WHICH REGION IS OFFSET FROM THE POLE PIECES IN THE DIRECTION OF MAGNETIZATION OF THE PERMANENT MAGNETS; AND MOVABLE RELATIVE TO SAID POLE PICES TO A PLURALITY OF SHUNTING POSITIONS PROVIDING SUCCESSIVELY GREATER VOLUMES OF MAGNETIC MATERIAL WITHIN THE CONFINES OF THE PERMANENT MAGNETS THEMSELVES IN SAID REGION BETWEEN THE POLE PIECES AT THE INTERIOR OF SAID PERMANENT MAGNET ASSEMBLY, AND MEANS FOR MOVING SAID SHUTING MEANS SELECTIVELY RELATIVE TO SAID POLE PIECES TO SAID SHUNTING POSITIONS TO CORRESPONDINGLY ADJUST THE STRENGTH OF THE WORKING MAGNETIC FIELD EXTERIOR TO SAID DRUM.