Abstract
In order to clarify the hulling characteristics of impellers, the motion of a rough rice grain fed on the rotating blade was analyzed theoretically and some hulling tests were carried out.
The main results were as follows:
1. The experimental values of velocity and angle of grains ejected from the impeller with the blade C, which had the smallest curvature, agreed well with the calculated results. With the blade A and the B, however, the both results did not agree well, especially of the discharge, angle, because of the effect of air flow.
2. The coefficient of dynamic friction between grains and blades was 0.55 approximately and about 90 percent of the static friction. These values varied a little with the load and the direction of grain's motion.
3. Moving on the rotating blade, the grain receives Coriolis force and centrifugal one. At 1500rpm, the calculated resultant force on a grain was more than 140g with the blade B which had the greatest curvature, and about 60g and 30g with the blade A and the C, respectively.
4. Some of the rough rice grains moved on the blade were hulled, and its hulled ratio increased with the load.
From the above mentions, it was considered that some grains were hulled by the frictional force on the blade A and B, as grains passed through the impeller.
5. In the normal use, the static air pressure inside the impeller was lower about 10cm Aq than the atmospheric one. Provably, such a negative pressure could scarcely affect the hulling action of grains.
The grain-blade impact at the inlet-end of the impeller seemed to be one of another hulling factors.
