(PDF) Correlations for the grindability of the ball mill as a measure ...
Critical Speed: If the peripheral speed of the mill is very high, it begins to act like a centrifuge and the balls do not fall back, but stay on the perimeter of the mill and that point is called the "Critical Speed" (nc).This phenomenon is called centrifuging. Ball mills usually operate at 65% to 75% of the critical speed.