Development of computer control strategies for plastic extruders

Abstract

The basic idea of automatic control of extrusion machinery is considered. Dynamic interaction among process variables is discussed and it is suggested that a practical form of control might involve steady‐state control of screw and barrel temperature coupled with dynamic control of screw speed. Several alternative forms of control strategy are examined and it is suggested that for higher forms of control, a computer is required together with an accurate process model relating control and controlled variables. With such a strategy, polymer temperature and pressure at the die would be controlled by continuous variations in screw speed coupled with infrequent control of die resistance to counter long term drift and to facilitate pressure and temperature change matching. Methods for developing process models are considered including those for adaptive/predictive control strategies using time‐series techniques and some experimental results are given. The basic form of a computer control system is outlined and the areas where further research is required are indicated.