(54i) Segregation during Die Filling with Air-Sensitive Powders
Die filling is a typical process step in the manufacturing of a wide range of particulate products (e.g. pharmaceutical tablets, catalyst pellets and powder metallurgical components) in various industries. Segregation of powder mixtures during die filling can have a detrimental effect on the quality of the end product. In this study, segregation tendency of powder mixtures with air-sensitive components during die filling was explored, for which binary mixtures of two powders with either different particle sizes or true densities were considered. A model die filling system with a segmented shoe and die was developed and used to quantitatively examine segregation during die filling. The results indicated that, during die filling, depending on the shoe speed, different segregation mechanisms effected, ranging from the percolation segregation mechanism often occurring in hoppers to the fluidization (air-current) segregation mechanism. The latter prevails when fine or light particles are involved, especially when the die filling process is primarily dominated by bulk flow.