Abstract:
A single screw fish feed extruder have been developed using locally sourced materials as a means of encouraging effective fish feed production in Nigeria. It has been evaluated for performance in terms of the system and product parameters. It provides a test rig which will be useful in further research and training. The developed machine comprises of the feeding unit, the compression unit and the die unit. The machine was driven by a 4kW electric motor coupled to a gear reduction box. Experiments were carried out between August, 2012 and February, 2013 at the Agricultural Engineering workshop of the Federal University of Technology, Akure. The effect of some parameters such as; screw speeds (100 rpm, 150 rpm, and 200 rpm), moisture content of ration (20 %, 25 %, 30 % and 35 %), and die diameters (3 mm, 5 mm, 9 mm) on specific mechanical energy requirements, expansion ratio, bulk density and pelleting efficiency were determined.
Results showed that increasing the screw speed from 100 rpm to 150 rpm tend to increase in extrusion capacity and extrusion efficiency from 8.43 g/min to 9.13 g/min and 63.25 % to 68.50 % respectively. And decrease in bulk density from 1.05 g/cm3 to 0.94 g/cm3; decrease in specific mechanical energy from 24.70 kJ/kg to 22.30 kJ/kg. By increasing the die diameter from 3 mm to 5 mm, the specific mechanical energy tends to reduce from 28.44 kJ/kg to 26.46 kJ/kg, reduce bulk density from 1.05 g/cm3 to 0.97 g/cm3. And increase extrusion efficiency from 63.25 % to 68.00 %. Results also showed that increase in moisture content from 20 % to 25 % tend to reduce the specific mechanical energy from 28.44 kJ/kg to 24.99 kJ/kg, reduce bulk density from 1.05 g/cm3 to 1.01 g/cm3. And increase the extrusion efficiency from 63.25 % to 72 %.
The maximum extrusion capacity of 10.73 g/min with maximum efficiency of 80.50 % was obtained at the speed of 150 rpm, material moisture content of 25 % and die diameter of 5 mm producing extrudates with bulk density of 0.73 g/cm3.
