Abstract:
Favabean threshing, in Ethiopia at present, is predominantly done by employing animals to trample the
crop on the ground. Traditional methods of threshing favabean require high man-hours, cause fatigue to
workers, have low output, and reduce seed quality. In an effort to alleviate these problems, diesel engine driven favabean thresher was designed, fabricated, tested and evaluated. The performance evaluation of
the thresher was made in terms of threshing capacity, threshing efficiency, cleaning efficiency, mechanical
seed damage, and fuel consumption. The performance evaluation was carried out at three levels of
cylinder speeds (400, 450, and 500 rpm), concave clearances (25, 30 and 35 mm), and feed rates (8, 12
and 16 kg/min). The experimental design laid was a factorial, split–split plot design. The maximum
threshing capacity of 933.64 kg/hr was obtained at a cylinder speed of 500 rpm, concave clearance of 35
mm, and feeding rate of 16 kg/min. The threshing efficiency and percentage of un-threshed grain highly
depended on concave clearance rather than other factors. Maximum threshing efficiency of 96.67% was
achieved at a cylinder speed of 400 rpm and a concave clearance of 25 mm. Maximum cleaning efficiency
of 95.00% was achieved at a cylinder speed of 500 rpm and a concave clearance of 25 mm. Maximum
mechanical damage of 6.31% was recorded at a cylinder speed of 500 rpm, and a concave clearance of
25 mm, and a feeding rate of 16 kg/min.
