PROCESS VARIABLES OF INSTANT GRANULATOR AND SPHERONISER .3. SHAPE AND SHAPE DISTRIBUTIONS OF PELLETS

The complete 2(6) study design was used to investigate the influence of the process variables of a continuously working granulator, and a spheroniser on the shape and shape distributions of pellets. Shape parameters were derived from size parameters measured by image analysis. Of seven shape parameters suggested, roundness and elongation most effectively distinguished pellets from each other. For a homogeneous pellet batch, 200 pellets need to be measured, but in the case of a heterogeneous batch, even up to 800 measurements were required to achieve reliable and reproducible results. The most important process variables affecting the shape of pellets were the size of the granule outlet in the granulator, the speed of the friction plate and the residence time: rounder pellets could be produced using larger granule outlet, faster speed of the friction plate and longer residence time.