The flow of powder into simple and stepped dies

An experimental study of die filling into constrained cavities of simple and complex geometries is presented. A model shoe system for the study of powder flow in air and vacuum has been developed. Transparent dies and shoes have been used, which allow the flow and rearrangement of the powder to be observed using a high-speed video system. Both qualitative and quantitative estimations of the influence of powder characteristics and shoe kinematics on the die filling process have been made. Measurements of filling rate and filling ratio for various shoe and die geometries are presented. The influence of airflow is revealed by comparison of experiments conducted in air and in vacuum. Possible positive and negative contributions of the entrained air during die filling have been addressed. Results are presented in the context of the Beverloo equation, which was originally developed to characterize hopper flow. The concept of a critical velocity is introduced, below which complete filling of a standard die is achieved. This provides a measure of the flowability of a powder and can be used to gauge the influence of airflow and pressure on the filling process. (C) 2003 Elsevier B.V. All rights reserved.