ABSTRACT
When a rotational rheometer containing powder is started. the steady-state torque is not achieved immediately. as is illustrated in Fig. 14.7. Several rotations of the rotor are required before the torque becomes constant. As might be expected. the steady-state torque increases significantly and linearly with the normal
load applied to the surface of the powder. The initial density of of the granular material also has a strong influence on the startup torque of a rheometer. as shown in Fig. 14.8. Loosely packed powders tend to have a monotonically increasing torque as the number of revolutions increases. Consolidated powders, produced by tapping or vibrating the powders to increase the density of packing, produce a maximum in the torque which can be considerably greater than the steady-state torque.
