An investigation of powder production by dry grinding in tumbling media mills

Fine powder production in tumbling media mills was investigated in laboratory, pilot, and production scale experiments using quartz feed. Steel balls, ceramic balls, ceramic cylinders, and flint pebbles were compared as grinding media for grinding efficiency and economic value. A method for joining the sieve and sedimentation particle size analyses was developed. The wear of various grinding media was analyzed via laboratory, pilot and production scale tests. The wear pattern of non-spherical media was determined. The grinding mill power requirements for different shape and density media were studied. These power measurements were correlated with the production scale power consumption, and they were compared with the existing predictive equations. The bulk properties of fine powders in a full scale production environment were measured.; The breakage kinetics were evaluated using the population balance method. The parameter values of the specific rates of breakage and primary breakage distribution functions of the same feed material obtained with the steel balls, ceramic balls, ceramic cylinders, and flint pebbles in the laboratory batch tests were the same with the exception of the breakage rate constant. The breakage rate constant varied with the media density, but this variation was not linear. The power consumption, however, was found to vary linearly with the media density.; The freshly generated fine quartz powder in an industrial grinding environment was observed to be very fluidlike. This property appeared to correlate with the powder temperature and the surface properties of the fine particles as they were generated. Due to this fluidlike property, fine quartz powders flowed readily through the mill without overfilling. This property created an exit classification effect in the mill and also influenced the residence time distribution. When these two effects were accounted for, the experimental product size distributions obtained in the pilot and plant scale tests were accurately simulated using the information from the laboratory scale tests. The scale-up of the production rates from the laboratory results were found to be a problem.