Problems of powder flow in tabletting processes

Summary The flow of non-compacted granules in the tablet machine hopper is discussed with relevance to the unit dose of drug, which is required to be dispensed. The various factors used to describe powder flow such as angle of repose, interparticulate cohesion and friction, flow through apertures, bulk density and die fillability are considered. The effects of humidity and of addition of fines or lubricants and the use of commercially available apparatus for induced die feeding are included.During compression powder flows to form a dense compact. Theories of this densification and the effects of entrapped air and die wall friction during the compression and ejection of the tablets are examined.An attempt is made to correlate non-uniformity in the final tablet with problems of powder flow.Paper presented at a meeting of the British Society of Rheology, University of Nottingham, April 6–8, 1965.