A Ball Mill Critical Speed (actually ball, rod, AG or SAG) is the speed at which the centrifugal forces equal gravitational forces at the mill shell's inside surface and …

Mill Critical Speed Determination. ... This mill would need to spin at RPM to be at critical speed. Result #2: This mill's measured RPM is % of critical speed. ... the formula used for Critical Speed is: N c =76.6(D-0.5) where, N c is the critical speed,in revolutions per minute, D is the mill effective inside diameter, in feet.