# Pebble Mill Design Calculations – HOW TO

Pebble Mill: Rod Mill Pebble Mill Circuit

The calculation for determining grinding power for Pebble milling (secondary autogenous) can be the same as for ball milling from rod mill product size to the desired specified size, neglecting the diameter efficiency factor if less than 1.0.

5.47 x 1.102 x 1.341 x 500 = 4039 HP

To this add the power required to wear the pebbles down to rod mill product size (pebble mill feed size).

F = 70,000 micrometers.

P = 1,200 micrometers.

Wi = 13.2

W = 10 x 13.2/√1,200 – 10 x 13.2/√70,000 = 3.31 kwh/s. ton

The inefficiency factor to allow for the inefficient use of power in wearing down from pebble size to rod mill product size is 2.0.

3.31 x 2.0 x 1.102 x 1.341 x 30/500 x 500 = 294 HP

4039 + 294 = 4333 HP

Select two 2200 HP pebble mills. For specific sizing refer to mill manufacturers for recommendations as they have proprietary equations for calculating mill power draw taking into account the various ore media and pulp factors involved.