DESIGN, FABRICATION AND PERFORMANCE EVALUATION OF A SMALL DRUM TYPE POTATO GRADER

Abstract

Grading potatoes by size is an important operation for preparing tubers for seed and for commercial purposes. Potatoes are sold in the market without grading in Bangladesh. If potatoes were sold after grading, this would be beneficial to both producers and consumers. Since mechanical graders are not available, potatoes are graded, when necessary, by hand. This is a time consuming, costly, and inefficient method. In view of this fact, the present work was undertaken to design, fabricate and evaluate the performance of a small drum type potato grader for village level operations that will provide a practical means of grading marketable potato tubers by size. The grader consists 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 0.75hp, 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 30 giving a system efficiency of 88.40%, capacity 280.90 kghr-1 , less damaged tubers of 2.22% and low power consumption of 13.95 W-hr. The cost of the grader was estimated to be Tk45,000.00 with a break-even quantity of 63 tons of tubers in one year. Further improvement, of the device could be done to reduce the percentage of damaged tubers and cost effectivity together with ease of loading and operation of the machine.