Variables that Make a Difference in Ball Mill Operation
Ball mill operation is anything but simple. In ball mills using dry solids, the primary independent variables include mill speed, mill diameter, media size, residence time and solids loading. Although, for most ball mill manufacturers, the mill diameter is already in place. Let’s take a close look at each of these variables. Mill Speed This variable can easily be adjusted using a variable frequency drive (VFD). To calculate the mill speed, you need to start by finding the critical speed. Critical Speed (CS) refers to the rate at the grinding media will spin against the walls of the cylinder. The formula for calculating the critical speed is given as CS= ½∏ √(g/(R-r) Where g= gravitational constant R= the inside diameter of the ball mill r= the diameter of a piece of the media This formula is further reduced to CS= 265.45/√(R-r) In dry mills, the CS range from 50% - 70%, usually between 60% - 65%. If the CS is less than 50%, the energy imparted to the fractured