Design and Development of a Single Screw Fish Pellet Extruder

A single screw extruder used for fish pellet production was designed, developed and tested. The major components of the machine included the hopper, the conditioning chamber, the barrel that was a stationery pipe member housing and the screw with the die and die holder fitted at the extreme end of the barrel for the extrusion process. Various mechanisms such as the Archimedean screw characteristics, the horizontal ribbon mixing mechanism and belt drive system of power transmission were chosen to give the required motion. The axial compressive force acting on the screw, the circumferential force acting on the barrel and the longitudinal force acting on the die plate were 59.27 kN, 337.26 kN and 49.28 kN, respectively. The total power required to operate the single screw extruder was 2.01 kW: 539 W to operate the conditioning chamber and 1.48 kW to operate the screw in the barrel and extrude the pellets through the die. The designed parameters for the screw shaft were 30 mm, die thickness 10 mm and a barrel thickness of 5 mm. The machine was tested with compounded feed at two screw shaft speeds, 254 and 761 rpm at three moisture contents levels of 15, 20 and 25 % (w.b.). At 761 rpm a maximum output capacity of 64.07 kg/hr was obtained at 25 % (w.b.) moisture content. A maximum output of 63.63 kg/hr was obtained for 254 rpm at a moisture content of 25 % (w.b.). Minimum output capacities of 61.633 kg/h and 61.100 kg/hr at 761 rpm and 254 rpm, respectively, were obtained at 15 % (w.b.) moisture content.