A METHOD OF INVESTIGATING ROD MOTION IN A LABORATORY ROD MILL

The work reported here measured the position of a rod in a laboratory mill at 1/25 second time intervals using an active light source in the rod and a video camera. The detailed picture of the charge movement w hich was obtained was used to calculate mill power using rod lift and torque arm models. Theoretical analysis showed that the presence of sl ip does not change the mill power because the lower power required for lift in the presence of slip is counter-balanced by the extra power r equired to overcome friction. Power predicted from a simple slip surfa ce treatment is not correct because media emerging through the slip su rface has to rise further to over-ride media emerging lower in the sur face. The powers calculated from the lift model and the torque arm mod el (assuming all rods contribute to torque) were almost identical, but did not predict the correct variation in power with mill rotational s peed. It was concluded that a valid fundamentally based prediction of mill power is still not available.