Structure of a Vertical Sand-Roller Rice Mill

　　Vertical sand‑roller rice mills are primarily used for processing grains such as corn, millet, and sorghum in northern China. They are widely employed in small and medium‑sized grain processing plants and rural communities, producing corn grits that are round, smooth, and resemble pebbles, with an excellent texture when cooked.

　　

　　I. Structure of the Vertical Sand-Roller Rice Mill

　　

　　1. Feeding section: feed hopper and feed gate.

　　

　　2. The whitening section comprises the grain‑feeding chute, sand rollers, bran sieve, rice‑discharge chute, adjustment handwheel, cutting blade, discharge gate, and rice‑discharge nozzle, among other components. 3. The bran‑removal section consists of a pulley, fan, bran separator, airflow‑adjustment plate, and bran‑discharge outlet. The efficiency of bran removal is controlled by adjusting the airflow. The vertical sand‑roller rice mill is a high‑speed, gentle‑grinding model. Its roller surface linear velocity typically ranges from 10 to 15 m/s, and the average pressure exerted on the material remains below 5 kPa. During operation, raw grain enters the grinding chamber via the hopper; under the high‑speed abrasive action of the rotating rollers, the outer husk is stripped away while further whitening takes place. The ground grains are then discharged from the machine through the rice‑discharge nozzle. During the whitening process, some of the husks and bran residues are expelled through screening holes around the whitening chamber, while the remainder is carried away by the airflow as the grains exit the chamber. Both streams of bran are conveyed out of the machine together by the fan.

　　

　　The milling chamber operates at low pressure, resulting in less broken rice; however, the grain’s husks and bran are abraded unevenly. Depending on the specific requirements, it may be necessary to screen the milled product and subject the larger grains to a second or third whitening pass until the desired quality is achieved.

　　

　　The efficiency of grain whitening is determined by the interplay of the stopper blade, the grain‑feeding wings, the inlet gate, the clearance within the whitening chamber, and the machine’s operating speed. Specific procedures should be adjusted according to the moisture content of the raw grain and the desired level of whitening, with the number of processing passes selected accordingly.