The effects of mill speed, filling and pulp rheology on the dynamic behaviour of the load in a rotary grinding mill

Abstract

The effects of mill filling, rotational speed, and pulp conditions on the dynamics of the load within a wet-grinding mill are examined using measurements of torque and load position. The test equipment provided an accurate torque measurement, the toe and shoulder position of the load were measured using a conductivity probe mounted in the mill shell. The rheology of particulate pulps is examined at various solids concentrations and the static angle of repose of the load is given for a number of pulp conditions. All the variables tested influence the load position, and hence the torque, with filling and speed having the greatest effects. The variables have interactive effects on both the torque and load position. Increasing mill speed and filling both cause an increase in torque to a maximum value, further increases in speed or filling cause a torque reduction. The effects of the variables on power and slip are shown. The position of the load toe is influenced only by the filling, up to ·speeds of approximately 80 percent critical, whereas all the variables cause the load shoulder to rise as their magnitudes are increased. The dynamic motion of the load is examined by defining four areas where specific motion exists; a preliminary definition of these areas is proposed which is based on observation of cinematographic film and measured load positions. A comparison of power predicted by published equations and measured power is made, and a modified equation is proposed which can predict power for speeds up to 95 percent of critical.