In batch granulation of powdered superphosphate, the mean granule size is directly proportional to the amount of water present during granulation, an optimum water content being found for which the proportion of granules falling within a specified size range (e.g., 1–4 mm.) is at a maximum. This optimum proportion of water is lowered by increasing the temperature of granulation.
A radioactive tracer technique has shown that the rate of granulation of the small particles in the powder is greater than that of the large particles.
The rate of granulation in rotary granulators is directly proportional to the peripheral speed of the granulator. A pan granulator gives a more closely sized product than a drum.