Journal of Engineering Research and Reports

A kneader for a groundnut oil expeller, based on the screw press principle, was designed, constructed, and evaluated through performance testing. The design of the machine was done using standard engineering equations and the components of the machine include feeding inlet, kneader shaft, rotating paddles, screw-type blades housed in a semi-cylindrical chamber, kneading cylinder, transmission belt, frame stand, pulleys, electric motor and oil outlet. In operation, the rotating paddles rotate at moderate speed of 40 rpm to mash and squeeze the groundnut paste, rupture more oil cells within the groundnut particles and promote the aggregation of small oil droplets into larger ones, making oil release easier. During kneading, frictional heat slightly increases the paste temperature, which further lowers oil viscosity and promotes flow. After 20 minutes of the kneading operation, the processed paste was discharged into the pressing chamber (screw press) for oil extraction. The machine was evaluated using 5 kg of groundnut paste. During testing, the maximum oil yield of 70% and an efficiency of 81% were attained under moderate processing parameters specifically, a feed rate of 10 kg/h, a rotational speed of 66.26 rpm, and a temperature of 96.89°C. Under these favorable conditions, oil loss was minimized to 19%. However, when the feed rate was increased beyond optimal levels, extraction losses rose sharply, peaking at 72%. Although the machine achieved its highest throughput at 20 kg/h, this came at the expense of extraction efficiency, which declined due to the shorter residence time of the paste in the chamber. This machine is recommended for small and medium groundnut oil processors since it is affordable, durable and has a low operating cost.