Factors of Operation Affecting Performance of a Short Axial-flow Soybean Threshing Unit

This study aimed at investigating the operational factors that affect the performance of a short axial-flow soybean unit. The result would be applied in developing a soybean combine harvester to be installed with a small tractor. The axial-flow soybean threshing unit is composed of a rotor of 0.48 mm diameter and 0.70 m length, peg tooth clearance (PC) of 41.4 mm, concave clearance (CC) of 20 mm, and guide vane inclination (GI) of 80 degrees. The investigated factors included grain moisture content (MC), rotor speed (RS), and feed rate (FR). The split-plot experiment was planned by setting the main plots of soybean moisture contents at three levels, i.e., 14.94, 23.55 and 36.04% wb and the sub-plot of 3 x 3 factorial RCBD treatment: the rotor speed as the first factor having 3 levels, i.e., 7.54, 10.01 and 12.56 m/s; and the feed rate as the second factor with 3 levels, i.e., 100, 150 and 200 kg/h. The experiment demonstrated that the MC and the RS significantly affected the threshing efficiency, unthreshed loss, separating loss, total loss, and percentage of breakage. The FR was found to significantly affect threshing efficiency and percentage of breakage but not on unthreshed loss, separating loss and total loss. The short axial-flow soybean threshing unit is recommended for soybean moisture content of not over 16% wb and rotor speeds between 10 to 12 m/s, while feed rates should not exceed 150 kg/h.