Grain winnowing means the method which utilizes the suspension speed and the density difference between grains and impurities and separates impurities under the airflow effect. Grain processing always adopts winnowing to remove the light impurities in the unprocessed raw grains.

According to airflow direction that brings away impurities, grain winnowing can be divided into vertical airflow winnowing, horizontal airflow winnowing or incline airflow winnowing. According to the GRAIN WINNOWING equipment position in the aspirator, it can be divided into suction type winnowing and blowing type winnowing. Suction type winnowing equipment works under negative pressure condition and the dust is not easily to fly over. It has stable working efficiency. Therefore, we usually adopt vertical airflow winnowing.

Next, let's talk about grain winnowing working principle:
Material granules movement speed and direction in the airflow mainly depends on relations between airflow effort P and granules weight G.
When P＜G, material has accelerated movement downward;
When P＞G, material has accelerated movement upward;
When P=G, material stays in the suspension state. At this moment, the airflow movement speed is the suspension speed of the material.