Quantitative investigation of powder flow during die filling using positron emission particle tracking

The flow behaviour of powders during die filling was investigated using the positron emission particle tracking (PEPT) technique, from which quantitative information on the flow of individual particles was obtained. Two grades of spherical microcrystalline cellulose powders with different particle sizes were used as the model powder systems. It is shown that the trajectories of tracked particles at different initial positions are consistent with the overall flow patterns observed using a high-speed video system and linear kinematics (i.e. displacement and velocity) of the tracked particles in the moving direction of the feed shoe correspond very well with the specified shoe motion. Furthermore, a close examination of the vertical velocity component (i.e. in the gravitational direction) of the tracked particles that were deposited into the die reveals that for the system with large particles, the particles flow into the die at a higher falling velocity, compared to the system with small particles. This is primarily due to the effect of the presence of air in the die, which can significantly inhibit the flow of small particles, while its effect on the flow of large particles is small.