Abstract:
Traditional methods of grading potato tubers require high man-hour, cause fatigue to workers and has low output. Hence, engine driven machine capable of grading potato tubers into different size classes was designed, manufactured, tested and evaluated. The prototype grader consisted of frame, feeding table, grading cylinder, catchment tray, shaft, pulleys and belt and transportation wheels. Tubers of Gudene potato variety widely grown in Ethiopia were used in the performance evaluation. Physical attributes such as major, intermediate and minor diameters, density and repose angle were studied. The experimental design used was laid in split- split- plots where grading cylinder speeds (10, 15, 20 rpm) were main plots, angle of inclinations (5, 10, and 15°) were sub-plots and feeding rates (20, 30, 40 Kg.min-1) were sub-sub-plots with three replications. Performance evaluation of the prototype machine was carried out in terms of grading capacity, grading system efficiency, mechanical damage and fuel consumption. The results indicated that grading capacity and fuel consumption of the grader increased with increasing cylinder speed and feed rate while percentage mechanical damage and grading system efficiency decreased with increasing angle of inclination. The maximum grading system efficiency of 97.57 and 97.67% was observed, when the machine was operated at speed of 15rpm, angle of inclination of 5° and feed rate of 20 and 30 Kg.min-1, respectively. At this optimum condition, the grading capacity, mechanical damage and fuel consumption were 1800.75 and 2000.46 Kg.hr-1, 3.22 and 3.56% and 1.89 and 2.84 ml.Kg-1, respectively. From the performance indices of the potato grading machine, it can be concluded that the performance of the prototype machine is very much acceptable with high prospect for extending the technology for small and medium scale farmers.
