The mechanisms of axial transport of dry powders in continuous and batch ball mills have been investigated. In a batch ball mill the particles migrate toward the center of the mill and this motion is a function of ball filling, particle filling, mill speed, mill length, wall roughness, etc. The distribution of particles along the mill was observed to be similar for continuous ball mills at low flow rate to that in batch mills at the same operating and mill conditions. The diffusion coefficient in the batch ball mill was measured for different ball and particle filling and empirical equations were fitted to the experimental values. The steady-state particle filling along the batch and continuous ball mills was described by a diffusion/convection model. Comparison of the experimental results for particle filling along the mill with the prediction of the model indicate that the main mechanism of transport in batch continuous and batch ball mills is a random diffusion process with a systematic motion of particles away from the ends of the mill.
