A movable string sieve - analysis of seed screening

The conditions of seed movement in a string sieve set into reciprocating motion have been formulated for cereal, vetch, pea, lupine and faba bean seeds. In the analyzed string sieve, seed movement was determined by a combination of the following parameters: angular velocity of the crank, crank radius, seed size, seed’s coefficient of external friction, string diameter and angle of inclination of the separator screen. A string sieve for cleaning and sorting most farm-produced seeds was analyzed. The width of the separating groove was set at 1 mm at the beginning of the screen and 11 mm at the end of the screen, and the strings had the diameter of 4 mm. Our results indicate that seeds cannot be effectively graded in the modeled string sieve. The angular velocity of the crank exceeds the velocity which is applied to power conventional separator buckets, and it could damage the separator. A reduction in the angular velocity of the crank to the recommended level caused seeds to become jammed directly before the screening site. The above problem can be solved by propelling seeds into motion with the use of special sweeping brushes.