Design of single screw extruder for homogenizing bulk solids

Abstract

The research was conducted to design a single screw extruder from locally available materials for the mixing and homogenization of bulk solids, such as the composites of cassava and yam starch-glycerol with nanoparticles. The design was made by computing the hopper outlet size, shaft diameter, screw geometry, barrel volume and the capacity of the conveyor, empirically. The stresses in the conical section of the hopper were also evaluated to assess its load requirement, thus avoiding any problem associated with the flow of materials through the hopper opening. The extruder was dynamically simulated to assess its throughput at the feeding, compression and metering zones. This was done by investigating the dynamic effect of the time of operation, with respect to the linear displacement, velocity and power, from the practical motion of the moving auger by Computational Fluid Dynamics method. The results showed that the vertical pressure acting downwards and the shear stress within the section were 37.02 and 6.44 kPa. The shaft diameter and screw geometry, which includes screw pitch and angle, were 20 and 56 mm, and 16.54o. The capacity of the extrusion conveyor and its power requirement were respectively, 18.46 tons/hour and 2.04 kW. The maximum linear displacement and velocity occur at the compression zone at every 3.03 rev/sec, which cause the bulk solid materials to melt, and are pushed by the resulting pressure into the metering zone. The relationship between the linear displacement and the time of operation obeys the power law. Consequently, a 5 hp electric motor was selected to power the single crew extruder.