EFFECT OF EXTRUSION CONDITIONS ON THE PERFORMANCE OF A SINGLE SCREW FLOATING FISH FEED EXTRUDER

Abstract

The need to enhance the quality of fish feed produced in Nigeria was the major consideration of this project. The machine is an already existing one at the engineering workshop of the department of Agricultural and environmental engineering of the Federal University of Technology, Akure. Raw fish feed material used were locally sourced from fish feed producers in Akure. The performance of the extruder was evaluated by studying the response of the extrudates under varying extrusion conditions (number of cutting blade, cutter speed, die sizes and moisture content) using the evaluation parameters (extrusion efficiency, extrusion capacity, material retained, expansion ratio, feed temperature and feed floatability). The experiment was conducted using a factorial design comprising of four levels of number of cutting blade, three levels of cutter speed, three levels of die sizes. Two independent variable levels which were the moisture content and screw speed were pre-selected based on the results of the preliminary tests. The effects of extrusion conditions on the evaluation parameters of the extrudates and the optimized condition were studied through resulting graphs obtained using Microsoft Excel 2010 and Response Surface Optimization Tool. Analysis of variance (ANOVA) was employed to determine the significance of the effect of the factors on the evaluated parameters using Microsoft excel. The results revealed that; extrusion efficiency was at its maximum value at 97.28 and at its minimum value at 70.83%, the degree of variation in the extrusion efficiency highly depends on the variation of the die size and moisture content. The die size has great effect on the extrusion capacity. The degree of variation in the material retained highly depends on the variation of the die size and moisture content followed by the number of blade and the cutter speed has the least influence on the amount of extrudate produce with respect to the feed input. Expansion ratio of the fish feed extrudate highly depends on the variation of the die size, number of blade and cutter speed. The highest feed temperature was obtained when the machine was operated at 122 rpm cutter speed, 4 mm die size, 40 % moisture content and 4 cutter blades while the lowest temperature was recorded when the machine was operated at 256 rpm cutter speed, 8mm die size, 40 % moisture content and 1 cutter blade. The machine recorded its maximum value 78.7 % of floatability when it was operated at 198 rpm cutter speed, 6mm die size, 30 % moisture content and 4 cutter blades. It can be concluded that different parameters involved in the extrusion process are important and interrelated. The optimum evaluation parameters were obtained for the process conditions when Number of blades, Cutter blade speed, Die size, and Moisture content were 3, 179 rpm, 8 mm and 32.43 % respective