Polymer extrusion, an important polymer processing technique, is a continuous process, during which material property, machine variables and process variables interact with each other in determining the final product quality. Control of key process variables such as melt pressure and barrel temperatures with high precision is essential to achieve a good product quality in extrusion process.

In this thesis, an overall control system is proposed for the extrusion process with two independent control loops, a single-input-single-output (SISO) control loop for the melt pressure at die output and a multi-input-multi-output (MIMO) control loop for the barrel temperatures. The dynamics of the melt pressure and barrel temperatures are analyzed before the controller construction. It is f...[ Read more ]

Polymer extrusion, an important polymer processing technique, is a continuous process, during which material property, machine variables and process variables interact with each other in determining the final product quality. Control of key process variables such as melt pressure and barrel temperatures with high precision is essential to achieve a good product quality in extrusion process.

In this thesis, an overall control system is proposed for the extrusion process with two independent control loops, a single-input-single-output (SISO) control loop for the melt pressure at die output and a multi-input-multi-output (MIMO) control loop for the barrel temperatures. The dynamics of the melt pressure and barrel temperatures are analyzed before the controller construction. It is found that the melt pressure dynamics is nonlinear and time-varying while the extruder barrel temperatures are of nonlinear, slow response characteristics with different zones highly coupled. Advanced control algorithms are adopted in this project to control these key variables. Experimental results demonstrate that fast response, near-zero overshoot and precise tracking performance could be achieved through the proposed control strategies. The robustness of the control system is also verified by investigating the variations of operation conditions with respects to different materials and set-points.

The benefits of the proposed controllers can be reflected by product quality, which can be indicated by the product diameter variation. Comparing with commercial controller, the reduction of process variables variation brings significant improvement on product quality. The robustness and effectiveness of the proposed controllers are reflected under different operation conditions and materials as well.