A stir casting system for drawdown of light particles in manufacturing of metal matrix composites

An extensive set of experiments was carried out to examine the effects of impeller types, impeller locations (submergence), solid volume fraction, and baffle configuration on the drawdown efficiency. Flow simulations in a turbulent regime were also performed to investigate the flow patterns, spatial homogeneity (using the mean age distribution), and particle drawdown mechanisms (using a particle level simulation with the discrete phase model). A combination of two casting impellers (a helical impeller near the top and a radial one near the bottom) with two half-baffles was determined to be the optimal configuration for complete drawdown with enhanced particle distribution, while avoiding air entrainment and lowering the impeller speed. Hydrodynamic mechanisms leading to superior drawdown and dispersion performance of the optimal design are discussed with the formation of free surface swirling, turbulence strength, roles of half baffles and helical/radial impellers on the flow and particle motions.