ABSTRACT
The study was conducted to investigate some physical properties of soybean at three moisture levels (10, 12 and 14%) and also to modify an existing soyabean thresher developed by Amadu, (2012) which has a low output capacity (25.5 kg/hr) and a major problem of chocking during threshing operations. The average length, width and thickness of soybean grains ranged from 6.57 to 6.75 mm, 5.54 to 5.66 mm and 4.54 to 4.66 mm respectively as the moisture content increased from 10.0 to 14.0 % (db), respectively. The geometric mean diameter increased from 5.42 to 5.53 mm. The one thousand grain mass increased from 103.55 to 108.97 g and the sphericity increased from 0.8332 to 0.8417 with the increase in moisture content from 10.0 to 14.0 % (db). The bulk density decreased from 749.7 to 643.4 kg m-3, whereas the true density decreased from 1251 to 1121.12 kg m-3. While porosity increased from 40.07% to 42.60 % with the increase in moisture content from 10.0 to 14.0 % (db). The angle of repose increased linearly from 26.55 to 31.02 degrees with the increase in moisture content. The static coefficient of friction increased for both surfaces, namely, glass (0.54 to 0.58) and wood (0.71 to 0.79). The performance of the modified machine was evaluated using TGX 1448-2E soyabean variety as the test crop. The results were analysed statistically using a completely randomized design (CRD). Least significant difference (LSD) was used to assess the effect of parameter level. The optimum performance of the developed thresher was obtained at a speed of 700 rpm at a feed rate level of 4 kg/min and a concave clearance of 13 mm. The threshing efficiency, cleaning efficiency, scatter loss, grain damage and the output capacity were found to be 99.97, 97.64, 0.86, 1.0 % and 86.96 kg/hr respectively. The analysis of variance carried out showed that all the independable variables - cylinder speed, feed rate, and concave clearance have a significant effects on the dependable variables - Threshing efficiency, cleaning efficiency, scatter loss, mechanical grain damage and throughput capacity. In comparison between the existing machine and the modified one using student t-test, the results indicated that the modified machine is better in terms of threshing efficiency, cleaning efficiency, scatter loss and output capacity but were found to be statistically similar in terms of mechanical grain damage.