Combination rod and ball grinding mill

Claim 1

A GRINDING MILL COMPRISING: A CASING SUPPORTED FOR ROTATION ABOUT A CENTRAL AXIS; INLET MEANS CONNECTED TO ONE END OF SAID CASING FOR DELIVERING MATERIALS TO BE GROUND TO THE INTERIOR OF SAID CASING AND DISCHARGE MEANS CONNECTED TO OTHER END OF SAID CASING; A PERFORATED BULKHEAD WITHIN SAID CASING INTERMEDIATE THE ENDS THEREOF AND TRANSVERSE THERETO; A CHARGE OF FINE GRINDING MEDIA WITHIN SAID CASING ON THE SIDE OF SAID BULKHEAD FACING SAID DISCHARGE MEANS; A CHARGE OF COARSE GRINDING MEDIA WITHIN SAID CASING ON THE SIDE OF SAID BULKHEAD FACING SAID INLET MEANS; AN ANNULAR WALL WITHIN SAID CASING AND TRANSVERSE THERETO, SAID ANNULAR WALL BEING AXIALLY SPACED AWAY FROM THE SIDE OF SAID PERFORATED BULKHEAD FACING SAID INLET MEANS, SAID WALL AND SAID BULKHEAD DEFINING THEREBETWEEN AN INTERMEDIATE CHAMBER BETWEEN AN INLET END CHAMBER AND A DISCHARGE END CHAMBER WITHIN SAID CASING, SAID FINE GRINDING MEDIA BEING CONFINED TO SAID DISCHARGE END CHAMBER BY SAID BULKHEAD AND SAID COARSE GRINDING MEDIA BEING CONFINED TO SAID FEED END PORTION BY SAID ANNULAR WALL WHICH PROVIDES A BARRIER THERETO, SAID ANNULAR WALL ALSO DEFINING A CENTRAL OPENING FOR COARSE GROUND MATERIAL AND PIECES OF BROKEN COARSE GRINDING MEDIA TO FLOW FROM SAID INLET END CHAMBER INTO SAID INTERMEDIATE CHAMBER WITH THE COARSE GROUND MATERIAL FLOWING FROM SAID INTERMEDIATE CHAMBER INTO SAID DISCHARGE END CHAMBER THROUGH SAID PERFORATED BULKHEAD FOR FURTHER GRINDING BY SAID FINE GRINDING MEDIA BUT SAID PIECES OF BROKEN COARSE GRINDING MEDIA BEING TRAPPED WITHIN SAID INTERMEDIATE CHAMBER.