Design and construction of a motorized bean thresher-cum winnower.

Abstract

Cotton bean (Phaseolus vulgaris) is. a short season crop with most varieties maturing in a range of 2-4months from emergency to physiological maturity and it's the most important legume in Uganda followed by ground nuts. Their importance is centered on the quantities of Carbohydrates, proteins: vitamins, fats, folic acid; minerals contained in their cotyledons, making it competing favorably as an energy source with root and tuber crops. They ate also non-meat source of iron and relatively inexpensive compared to meat. 26% of the post -harvest losses are. due to bean threshing and this is because 46% of farmers’ still use the traditional methods of threshing and most of them use manual winnowing methods. This results into the. production of low quality beans that fetch low prices, reduces the output, highly tedious, labor intensive and exposes farmers to ill health resulting from inhalation of dust. Therefore, the aim of this project was to design, construct, test and carry out economic evaluation of bean thresher-cum winnower for medium scale farmers. This would improve their production and productivity of high quality beans. The design of the various machine parts was carried out by analysing forces acting on them which led us to selection of proper materials to withstand the forces to avoid failure. Stainless steels of various grades were the main materials recommended to be used because they ate food grade, strong and durable. Engineering drawings of the various components were drawn before the various components were constructed and then machine parts fabricated. A fully functional prototype resulted after all the above operations yielded results of optimum machine performance. at a feed rate of 0.06Kg/s with a threshing and cleaning efficiency of 79.9 % and 57.8% respectively. Seed damages of 8.3%. and machine output of l0lkg/hr of bean seeds. However, it was found out that the threshing and cleaning efficiencies decreased with increase in feed rate from 79.9% to 78.6% and 57.8% to 56.5% respectively; Mechanical seed damages also decreased with Increase in feeding rate from 8.3 to 7.5%. The Cleaning efficiency was low because the testing of the prototype was. done using beans of small properties compared to design specifications. This Was due to the difficulty to get beans of large sizes (NABE4, K132, NABE3) yet the concave sieve hole diameter was big. This therefore, compromised the blower efficiency because it could allow heavy chaffs to pass through the sieve which the blower can't handle. In order to maximize the cleaning efficiency of the blower, sieve hole diameter should be reduced and conclusions. be drawn appropriately. The machine has a total. cost of 2,536,650 UGX which includes all the taxes, cost of material, machinery and hired labour to construct the machine plus overhead costs.