Design, fabrication and testing of a millet thresher

Abstract

A thresher was developed for threshing, separating, and cleaning millet seeds. The major components of the machine include threshing, separation and cleaning units. The threshing operation is achieved by rotational motion of a cylinder fitted with beater pegs above a stationary grid which results in the removal of the seeds from the panicles and their separation from the bulk of the straw. After being beating out, the grains fall through a concave grid into the cleaning unit which consists of two sieves that undergo reciprocating motion. Whilst the grains are moving over these sieves, a constant blast of air is being sent through them which blow out materials that are lighter than the grain. The machine was designed to be powered by a 5 hp electric motor. It was tested to thresh, separate and clean the millet seeds. The results showed that the machine had the highest threshing and cleaning efficiencies of 63.2 and 62.7%, respectively, when pearl millet panicles were processed at 13% moisture content and at an 800 rpm threshing cylinder speed. The lowest threshing and cleaning efficiencies of 40.68 and 50%, respectively, were obtained when the pearl millet panicle was processed at 17% moisture content and a 600 rpm threshing cylinder speed, and at 17% moisture content and 700 rpm. Thus, the optimum operating parameters of the machine were 13% moisture content (wet basis) of pearl millet panicles and 800 rpm threshing drum speed. The successful development of this machine is expected to reduce drudgery associated with the traditional method of threshing millet and therefore increase productivity of farmers.