The transitional torque characteristics of a particle bed have been measured by using a rotary shear tester which is basically a Couette type rheometer. The torque measured on the rotor shaft under constant operating conditions showed the maximum value to be at the initial period. It then decreased exponentially with changes in the packed state of the particle bed around the shearing surface during rotation. The magnitude of the decay coefficient k of the torque indicated some of the dynamic physical properties of the solid particles, such as flowability and surface condition. It was found that the conical rotor was suitable for the more sensitive and accurate measurement of the change in the torque. A dimensionless parameter k/N_R, where N_R is the rotor speed, was introduced and compared with the other flowability indices. It was experimentally shown that this parameter was more sensitive in detecting slight changes in the physical properties of the particles during mixing and coating operations. The coating processes in two different types of mixers and the coating state of the binary mixture were evaluated based on this parameter.

^† This report was originally printed in J. Soc. Powder Technology, Japan, 24(7), 462-468 (1987) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Powder Technology, Japan.