A simple calculation for residency time of grinding balls inside grinding mills

The residency time of grinding balls inside grinding mills has been calculated in the present work assuming an abrasive wear mechanism without breakage. From the ratio of total weight of balls in the mill to the daily addition weight of balls, the ratio of the grate openings size of the mill to the original ball size, and the rotation rate of the mill, the residency time of grinding balls can be determined numerically. The influence of these parameters on residency time was studied in detail. The existence of grate openings was shown to reduce the residency time significantly. The calculated results were fairly consistent with two experimental observations in both mills with and without exit grates.