Dynamic response of a twin-screw lab-size extruder to changes in operating variables

Abstract

Dynamic responses of a twin-screw extruder were studied. Die pressure and motor torque responses were obtained by introducing step changes in feed rate, screw speed, and screw speed-feed rate simultaneously by using a laboratory size torque rheometer/twin-screw extruder combination. Differences in step-up and step-down cases were examined. Experimental results showed that the step inputs in the screw speed and feed rate resulted in a range of dynamic responses of die pressure and motor torque. Die pressure and motor torque always responded in the same manner. The response of die pressure and motor torque was modeled by a first-order transfer function for step changes in the feed rate. The same dynamic responses to step changes in screw speed and screw speed-feed rate simultaneously were modeled by an inverse response. The use of process gains in the system was discussed. ©1996 Academic Press Limited.