Model and strategies for computer control of a twin-screw extruder

The dynamics of twin-screw extrusion of corn meal was studied. Second-order transfer functions with numerator dynamics were used to model the dynamic responses of process variables to step changes in extruder operating parameters. Step changes in screw speed, feed rate and barrel temperature set-point caused inverse responses in die pressure and motor torque. Overshoot responses were found for die pressure and motor torque to step changes in feed moisture. Product temperature always displayed an over-damped second-order response for step changes of all extruder operating parameters. These models were validated and the implications of using these models for computer control of a twin-screw extruder were discussed.