The process in the PS apparatus consists of four stages: Mixing is the first technological operation affecting the granulate quality. The uniformity of mixing depends on the aerodynamic mode of the apparatus, the ratio of components in the mixture, the shape and density of particles. At the stage of adding granulating liquid there is clumping of particles of granulated mass due to the bonding forces of both the liquid itself and the solution formed by wetting the surface layer of the processed material with this liquid. At the drying stage, the lumps turn into solid agglomerates, partially destroyed by friction between themselves and with the walls of the apparatus. The process of granulation in fluidized bed occurs simultaneously with drying of the resulting granules with hot air. The finished granulate is dried to the optimum moisture content. Powdering of the dried granulate takes place in the same apparatus. The obtained dried granules may have a rough surface, which makes it difficult to pour them out of the feed hopper into the matrix of the tablet machine in the process of tabletting.

In addition, the granules may stick to the die and punches of the tablet press, which can cause both weight disturbances and some defects in the tablets. To avoid these undesirable phenomena, the operation of “powdering” the granulate is resorted to. This operation is carried out by free application of finely ground substances to the surface of the granules in a periodic mode. By powdering, sliding and loosening agents are introduced into the tablet mass. Formation and growth of granules in the fluidized bed occurs due to two physical processes: wetting clumping and sticking with subsequent agglomeration. The quality of granules and their fractional composition depend on many factors determining the course of the granulation process, the main ones being the velocity of the liquefying gas, the composition and feed rate of the granulating liquid, and the temperature in the bed. There are two hypotheses about the mechanism of granule formation in fluidized bed: granulation centers in fine powder are droplets of granulating liquid; granulation centers are particles of a certain size introduced into the disperse composition of the powder.