Interaction between viscous fluids and media balls in wet ball milling

Abstract

An experimental study was conducted on the interaction between a viscous fluid and solid spheres in a ball mill to elucidate and optimize the slurry preparation process for ceramics. In ceramic manufacturing, the grinding and mixing of raw materials are critical because they form the most upstream process and directly influence product quality. However, this process significantly relies on empirical rules and the tacit knowledge of engineers, and a detailed understanding—particularly through slurry-mixing visualization and optimization—remaining largely unexplored. Slurry-mixing conditions in a ball mill were replicated using a 90 wt% glycerin solution as a Newtonian fluid and a 0.92 wt% carboxy methyl cellulose aqueous solution as a non-Newtonian fluid, which are transparent fluids with viscosities similar to that of actual slurry, enabling visualization of the mixing process. The effects of the number of balls in the rotating cylindrical vessel and the rotational speed of the vessel on the mixing process were visualized. The results showed that oscillation and falling of media balls became more pronounced at rotation speeds between 65 and 85 rpm, enhancing the mixing efficiency. The ball-filling ratio, J, significantly influenced mixing: J = 0.2 induced frequent sliding and falling of balls, leading to effective energy transfer, whereas J = 0.3 suppressed dynamic motion. In addition, the effects of the viscous fluid and solid spheres on mixing dynamics were analyzed in detail using particle image velocimetry. The findings of this study are expected to provide practical guidance on the optimization of ball mill operations.