PROCESS VARIABLES OF INSTANT GRANULATOR AND SPHERONISER .2. SIZE AND SIZE DISTRIBUTIONS OF PELLETS

The size and size distributions of pellets produced by continuous granulation and extrusion/spheronisation were evaluated. The effect of six process variables on two levels was studied. Pellet size was determined by image analysis, but also manually from enlarged photographs. The amount of pellets needed to give a reliable and representative mean size value was studied. For heterogeneous batches an appropriate number of pellets to be measured would be 800, while in the case of a homogeneous batch 200 pellets might be enough. The effect of size of the granule outlet of the instant granulator and speed of the spheroniser friction plate was most significant on all size parameters - when a larger granule outlet (consequently lighter kneading during granulation), and a higher speed of the friction plate were used, pellets were smaller, and the distributions were narrower. A greater load of spheroniser and a longer residence time in the spheroniser reduced the size of pellets.