Method and apparatus for controlling a grinding mill

Claim 1

IN A CLOSED-CIRCUIT WET-GRINDING PROCESS IN WHICH NEW SOLIDS AND WATER COMPONENTS FEED TO A GRINDING MILL, A PULP COMPOSED OF SOLIDS AND WATER GOES FROM THE MILL TO A HYDRAULIC CLASSIFIER, AN OVERFLOW PRODUCT IS RECOVERED FROM THE CLASSIFIER, AND AN UNDERFLOW PRODUCT COMPOSED OF SOLIDS AND WATER RETURNS FROM THE CLASSIFIER TO THE MILL FOR FURTHER GRINDING OF THE SOLIDS COMPONENT THEREOF, A CONTROL METHOD COMPRISING DETERMINING INDIVIDUALLY THE QUANTITIES OF THE RETURNING SOLIDS AND WATER COMPONENTS OF THE UNDERFLOW PRODUCT BEFORE IT REACHES THE MILL, SETTING THE TOTAL QUANTITY OF SOLIDS AND THE SOLIDS-TO-WATER RATIO DESIRED IN THE MILL, DEVELOPING A SIGNAL PROPORTIONATE TO THE DIFFERENCE BETWEEN THE QUANTITY OF RETURNING SOLIDS AND THE SETTING FOR TOTAL SOLIDS, DEVELOPING ANOTHER SIGNAL PROPORTIONATE TO THE DIFFERENCE BETWEEN THE QUANTITY OF RETURNING WATER AND THE DESIRED QUANTITY DETERMINED BY THE RATIO SETTING, AND ADJUSTING THE QUANTITIES OF NEW SOLIDS AND WATER COMPONENTS FEEDING TO THE MILL IN ACCORDANCE WITH SAID SIGNALS TO MAINTAIN BOTH THE TOTAL QUANTITY OF SOLIDS ENTERING THE MILL AND THE SOLIDS-TO-WATER RATIO IN THE MILL SUBSTANTIALLY CONSTANT AS LONG AS THE SETTINGS REMAIN UNCHANGED BEFORE ACTUAL CHANGES TAKE PLACE IN THE LOAD INSIDE THE MILL.