Design, fabrication and performance evaluation of a small drum type potato grader

Abstract

Abstract

Grading potatoes by size is an important operation for preparing tubers for seed and for commercial purposes. If potatoes were sold after grading, this would be beneficial to both producers and consumers. Since mechanical graders are not locally available, potatoes are graded, when necessary, by hand. This is a time consuming, costly, and inefficient method. This work concerns the development of a potato-grading machine for small-scale farmers. The grader consisted of a hopper, grading unit, prime mover and catchment tray fitted on a frame. The grader was made of locally available materials to keep the cost low. The grading unit was made up of plastic oil container, hopper and catchment tray made up of mild steel sheet and the frame was made up of mild steel angle bar. A 0.75 hp, single phase electric motor was used as a prime mover with a gear box (30:1) for reducing the rpm. Machine parameters for the evaluation included the speed of the grading unit (RPM) and inclination of the grading unit. These were tested on potato tubers taking note their influence on grading system efficiency, capacity, damaged tubers and power consumption as independent variables. Data were analyzed and the results indicated that optimum set-up of the grader was at 6 RPM speed of the grading unit, inclination of 3⁰giving a system efficiency of 91.57 %, capacity 420.10 kghr^-1, damaged tubers of 1.17 % and low power consumption of 9.30 W-hr. The cost of the grader was estimated to be Tk45,000.00 with a break-even quantity of 50 tons of tubers in one year.