Abstract

S. V. Irtwange

Based on the results of measurements of moisture content of grains, cowpea grain and pod sizes, grain-pod ratio, angle of friction of grains and some information from literature, a motorized cowpea thresher using a star-shaped beater to which beater belts were attached was designed and locally built. Five varieties of cowpea, K59, Ife-Brown, IT84E- 124, Ife-Bimpe and TVX 715 which are fairly representative of the most popular varieties in Nigeria were selected for the measurement of design parameters. The statistical design used in studying the effect of variety on length, width, thickness, equivalent diameter, sphericity, pod weight and grain-pod ratio with 30 replications, moisture content with 3 replications and angle of friction with 5 replications was complete randomized design (CRD). The moisture content for the grain varieties ranged from 11.06 to 12.02% w.b while the size and shape measurement parameters namely; length, width, thickness, equivalent diameter and sphericity ranged from 8.22 to 10mm, 6.04 to 6.83 mm, 4.36 to 5.38 mm, 6.00 to 7.09 mm and 0.71 to 0.79 respectively for grains. For the pods, the length, width and thickness ranged from 124.78 to 194.93 mm, 7.28 to 9.15 mm and 5.27 to 7.86 mm respectively. The pod weight and grain- pod ratios ranged from 1.96 to 3.39 and 0.75 to 0.86 respectively for all the varieties tested while the angle of friction of grains on mild steel ranged from 23.6o to 26.6o . The results of the study as indicated by analysis of variance (ANOVA) show that there is highly significant effect (P 0.01) of variety on all the grains and pods measurement parameters except angle of friction where non -significance was observed. Skewness and kurtosis analysis indicates that the frequency distribution curves for grains and pods measurement parameters generally approximated those of the normal distribution. Based on the optimum machine parameters, the machine throughput was determined to be 101.19, 110.86, 74.33, 75.81 and 102.09 kg grains/hour for K59, Ife-Brown, IT84E-124, Ife-Bimpe and TVX 715 respectively. Preliminary performance evaluation tests carried out on the fabricated thresher using IT84E-124 as the test material at recommended beater and fan speeds of 500 rpm and 1400 rpm respectively indicated average threshing efficiency of 96.29%, percentage damage of 3.55% and percentage threshed and undamaged grains of 92.74%. A cleaning efficiency and loss of 95.60 and 3.71% respectively was observed indicating that with the use of a star-shaped beater, drudgery and cost can be reduced to a minimum and yet achieving good quality products.