Design and construction of a motorised sorghum threshing and winnowing machine.

Abstract

Sorghum is the third most important cereal crop grown in Uganda after maize and finger millet occupying 285,000ha of arable land (http://teca.fao.org). It is widely grown in various districts in Uganda including: Karamoja, Kigezi, kapchorwa on medium (2-6ha by 12% population) and large (more than 6ha 3% population) scale and on small scale (less than by 85% population) in other parts of the country (Chris Balya, 2000). Kapchorwa, Karamoja and Kigezi districts are considered to be the major producers of sorghum in Uganda and produce the best quality sorghum mainly referred to as Epuriput which yields 2500. 3000kg/ha under good management and 1250-2000kg/ha at farmer level (http://teca.fao.org). Harvesting is carried out by cutting the heads with knives. The harvested crop is transported to the farmer's home and spread on the ground to dry. When the drying is complete, threshing by beating the crop with sticks is done to remove the grain from the plant. This is followed by winnowing to remove chuff and bagging in plastic bags. The above processes are accompanied by high quantitative and qualitative losses, are highly tedious, labor intensive, time consuming and also pause health hazards to the personnel involved. Threshing only takes place either when needed for domestic consumption or when a market has been identified. There are a number of sorghum threshing machines on the; market which are manual, automatic; and tractor operated but Some of these are slow, expensive in terms of replacing the constantly breaking belts for tractor operated thresher, the initial cost of the tractor is also high which cannot be afforded by most people in Uganda. The thresher was designed and constructed by first sizing of the components through analysis of forces acting on the components, material Selection, fabricated and assembled. The selected materials were those which would withstand the applied forces in order to avoid failure of the components during operation of the sorghum thresher. The threshing capacity of the prototype was 108kg/h and an avenge threshing efficiency of 58%, average cleaning capacity of 85%, and a percentage loss of 27% obtained by carrying out three tests at fated engine speeds of 4000rp.m,3800rpm and 3600-rpm of a 5HP engine using a constant feed rate of 165kg/h. The prototype has limitations of immobility, threshing efficiencies, threshing and cleaning losses. The prototype costed at 1820000 UGX compared to 4500000UGX of Tonnet Agro Engineering. Company, Economic analysis of prototype was carried out using the benefit cost method to determine its viability. The benefit-cost ratio was 1.19 since it was greater than I project was viable.