PERFORMANCE EVALUATION AND OPTIMIZATION OF HAMMER MILL USING RESPONSE SURFACE METHODOLOGY

Abstract

Milling operation is one of the mostly used size reduction technique in several household and food processing industries. In this study, the performance of a hammer mill that was fabricated in the Department of Agricultural and Environmental Engineering Workshop was evaluated and the optimal performance conditions were determined. The evaluation was carried out with maize sample of a known weight with a specified moisture content (4 – 16% wet basis) was introduce at a constant feed rate (180 – 60 kg/h) through the hopper to the hammer mill operated at constant machine speed (1200 – 3000 rpm). The weight of the milled product and the time taken to complete the operation was recorded for further calculation. For product characterization, the milled products were characterized using a mechanical sieve shaker (LAARMANN, LMSM – 75/200) with a Tyler sieve set ranging between (0.125 – 4mm). The result shows that the milling efficiency, milling capacity and material loss of the hammer mill ranges from 60.76% - 94.85%, 16.95 kg/h - 106.93 kg/h, and 5.5% - 39.24% respectively for both varieties of maize and the increase in the machine speed, feed rate and decrease in moisture content significantly (P < 0.05) increases the quantity of milled product and the rate at which the product was milled with reduced quantity of product loss. For the product development and characterization, five product with distinct size was obtained in the range of 0.125 mm – 2.00 mm sieve size and the particle mean diameter, particle size deviation and fineness modulus ranges from 0.27 mm - 0.59 mm, 0.35 - 0.14 and 3.8 - 1.6 for both varieties of maize (Danny middle resistance yellow maize, DMRSTYM and Danny middle resistance white maize, DMRSTWM) and the increase in the speed of the hammer mill and decrease in moisture content of the grain significantly (P < 0.05) decreases the particle diameter, particle size deviation and fineness modulus of the milled product for both varieties of maize whilst, the effect of feed rate on the characteristics of the milled product is not significant at P < 0.05. for both varieties of maize. For the multi-variable regression analysis, the accuracy of the models with factor interaction was higher than the accuracy of the model with no factor interaction which indicate that the interaction between the crop and the machine parameter also contribute to the variation in the performance of the hammer mill. for optimization of the performance (Using response surface methodology (RSM) approach) the obtained optimum machine performance values for DMRSTWM variety were 92.98%, 94.77 kg/h, and 7.03% for the milling efficiency, milling capacity and material loss respectively with optimum milled product characteristics values of 0.28 mm, 0.20 and 2.80 for particle mean diameter, particle size deviation and fineness modulus of the milled product respectively with 0.966 desirability value. The obtained optimum machine performance values for DMRSTYM variety were 96.66%, 106.93 kg/h, and 3.34% for the milling efficiency, milling capacity and material loss respectively with optimum milled product characteristics values of 0.30 mm, 0.19 and 2.95 for particle mean diameter, particle size deviation and fineness modulus of the milled product respectively with 0.780desirability value. The best crop and machine parameter for the optimum performance of the hammer mill were 4%, 180 kg/h and 2964.21 rpm for grain moisture content, feed rate and machine speed respectively (DMRSTWM variety) and 4.01%, 179.99 kg/h 2999.99 rpm for grain moisture content, feed rate and machine speed respectively (DMRSTYM variety) and this could be implement in both small and large scale feed and food processing industries.