Chapter 6 Dry granulation

Abstract

In dry fluidized-bed granulation spherical granules of which strength is sufficient to handle outside of a fluidized bed can be obtained from fine cohesive powders of organic and inorganic materials. The granule size converges after a few hours of the granulation, with the overall time that is needed much shorter than that of tumbling granulation. The converged size and density of the granules increased with increasing fluidizing gas velocity. The granule size is decreased and the granule strength increased with increasingthe specific surface area of the primary particles. The specific surface area is more important than the size. The granules with narrow size distribution are obtained from the powders with narrow size distribution. The granules are obtained regardless of their contents from a mixture of powdersthat can be granulated individually and one of the powders can be coated on core granules of another. A simple scale-up procedure applies to PSG as long as the same fluidizing air velocity and bed height are successfully maintained in the range of column diameters from 100 to 500 mm. Pressure-swing granulation is one of the dry fluidized-bed granulation methods is employed to the production of hardmetal tools and is promising for granulation of DPI materials. For the wide spread use of dry granulation methods, surface modification of powders before granulation is encouraged.