Abstract. A milling chamber consisting of a rice sieve and a rotating roller plays critical roles in modulating the milling performance of rice grains.
However, the mechanism of how the geometries of the rice sieve and rotating roller affect the particle collisions and the interaction time
remains not fully understood. Our experimental results show that the milling
degree and rate of broken rice of the octagonal rice sieve are largest among the hexagonal sieve, octagonal sieve, and circular sieve. Through
the discrete element method, we illustrate that the peak milling degree at the octagonal sieve is attributed to the competition between the
decreasing force and increasing milling time with the increase in edges. In addition, the geometries of the convex ribs of the rotating roller are
investigated to optimize the structure of the milling chamber. In the
left-hand spiral or right-hand spiral of the convex ribs, the rice particles
are accumulated in the inlet or outlet regions, respectively, which leads to
an uneven milling degree in the axial direction. The uniformity of a milling process can be promoted by increasing the number of convex ribs, which will
reduce the milling degree on the other hand.