Determination of rational values of inclination angles of straw walker sections

Abstract

Crop yield has been harvested by combine harvesters where threshed grain has been separated from straw by the straw walkers or rotary straw separators. The conventional combine harvesters consist of four, five, six or eight straw walkers with stepped surface. The number of steps, their height and the inclination angle of straw walkers sections (screens) are differed in the straw walkers of various producers. In this study the impact of the inclination angle of the sections of straw walker on grain separation through the straw layer has been tested. About 20 % of the grains threshed and unseparated through the concave of the threshing device have still remained trapped in the straw layer fed on the straw walkers. It has been defined that the greatest number of grains has been separated through the straw layer when it fell from the first section of straw walkers onto the second one. The optimum value of Froude-number of four straw walkers was 2.58 (the rotational speed of the crankshafts was 215 min"1). The rational inclination angle of the first straw walkers section was 22°, the second one was 10°, and the third one was 18°, when the straw feed rate on the straw walkers was 2.08 kg (s-m)"1. The intensity of grain separation can be controlled using the rotational speed of the crankshafts or the inclination angle of the straw walker sections.