Shape separation is used to handle impurities that are similar in size to grain particles but different in shape. Typical equipment includes spiral separators, drum separators, and perforated disc separators. Spiral separators have no moving parts and rely on centrifugal force from the inner and outer spiral surfaces to separate spherical seed-like impurities. Drum separators use a horizontal rotating drum with perforations on its inner surface to separate spherical and short particle impurities. Perforated disc separators use a cast iron disc with numerous perforations as it rotates, carrying short particles into a collection trough.
Separation based on airflow characteristics utilizes the difference in suspension velocity between grain and impurities in the airflow. Circulating air separators can be used to remove light impurities from grains. Grain enters the airflow through a hopper and falls to the bottom for discharge, while impurities are carried by the airflow to a dust collection chamber for settling. Mobile air separators are used for cleaning grains before storage or for cleaning raw materials in grain and oil processing enterprises. They can change the sieve mesh according to the size of corn, soybeans, and wheat particles for seed selection and grading. The equipment consists of a working section and a frame support section. The working section includes a hopper, screen cylinder, movable baffle, fan, dust collector, and auger. The frame support section includes the frame and wheels. The working process is as follows: grain first passes through the screen cylinder for initial cleaning to remove large and light impurities. Then, as it passes through the movable baffle, light impurities and dust in the grain are sucked out by the airflow into the deceleration chamber. Light impurities fall and are discharged by the auger, while dust falls into the dust collection box via the dust collector. Small impurities pass through the screen and are discharged, and clean grain is discharged from the clean grain outlet. The equipment has a processing capacity of 50-80 tons/hour, a power fan of 7.5kW, and overall dimensions of 5000mm × 1950mm × 4200mm. During use and maintenance, the equipment does not need cleaning and should be placed in a well-ventilated and dry place. If the auger becomes clogged, open the bottom cover to remove light impurities. The dust collection box should be cleaned regularly. If any abnormal noise is detected, stop the machine immediately for inspection. Adjust the counterweights according to the grain feeding situation. No human contact is allowed with any rotating parts before the machine is stopped.
Separation based on friction and impact resistance is used to separate impurities with poor friction and impact resistance. For example, a wheat thresher uses a rotor equipped with striking plates rotating inside a perforated cylindrical sieve, causing the wheat grains to be impacted and rubbed, thus removing adhering impurities. A awn remover has a similar structure but different operating parameters and is used to remove the awns from rice and barnyard grass. The working component of an impact suction fan is a high-speed rotating pin disc; the grain is discharged after impurities are separated by impact and friction.