PPC 6020-Gravimetric extrusion control

A description is given of a gravimetric extrusion control system which greatly reduces the amount of time that has to be spent in setting up and maintaining the desired end product of an extrusion line. The gravimetric system improves quality, conserves material, and maintains a record of each extruder's material usage for inventory. By detecting and compensating for deviation in the extruder's output per screw revolution, average layer thickness and average total thickness or average tube inside diameter can be established and maintained automatically by weight. Gear pumps can help reduce short-term fluctuations to the die due to a poor screw design or high regrind levels and should be used in conjunction with gravimetric systems in some cases. The gravimetric system by itself allows for a more direct and complete extrusion control as compared to the gear pump while providing acceptable output control where short-term fluctuation is not a problem. The gravimetric system controls to an average value, thereby having a limited effect on the material distribution across the die. Prepackaged gravimetric additive feeding systems are easily incorporated to provide complete assurance and control of the materials into each extruder.<>