Extrudate Characteristics Produced from High Density Screw-Type Extruder Machine

Abstract

Etrudate characteristics of briquettes produced and effects of extrusion factors using an existing screw extruder have been investigated. The feedstock material used in the test is sawdust collected from sawmills around Ibadan metropolis. Particle distribution analysis of materials collected showed that the size varies between 6-8 mm with 10-20% powdery component (< 4 mesh) which is known to give better products. Samples of briquettes produced were used for physical characterization. Physical characteristic studies on samples indicate briquette length (>300mm), dimensionally stable with no significant change in dimension during and after production. Performance tests carried out on machine revealed three (3) critical factors that significantly affect extrusion process; 1) Pre-densification within the extruder barrel results in high pressure requirement to push material through the die ring 2) Due to high pressure requirements as a result of early densification, there is a loss of power along power transmission line 3) Short material dwell time within the die results in weak products. Notable conditions of briquette during extrusion include; 1) extrudate surface cracks, 2) shooting (sudden explosion within the extruder barrel) leading to forceful ejection of materials from the machine and 3) extrudate bowing (warping) attributable to 1) non uniform extrudate thickness, 2) surface quality of the inner race of die ring, 3) loose inter-particle networking and binding properties of material– a condition not favourable to briquette formation, 4) localized heating within the extruder as a result of moisture differentials.