CHARACTERIZATION AND COMPARISON OF STRESS HISTORY IN VARIOUS SIZED TWIN- SCREW EXTRUDERS USING RESIDENCE-STRESS DISTRIBUTIONS
Pappas, William Lawrence
Bigio, David I
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Extrusion is used in production across a broad spectrum of industries, including piping and tubing, food, plastics and pharmaceutical. Because some applications involve stress-sensitive ingredients, it is important to be able to predict the amount of stress exerted on the material. Unfortunately, characterization of the stress magnitudes within a twin-screw extruder is extremely difficult due to its complexity. This thesis presents an approach to characterizing the stress history through the use of residence-stress distributions. Stress beads are used to determine the percentage of polymer that is exposed to a particular magnitude of stress at each location along the residence distribution. A comparison of various mixing geometries on three different sized extruders is performed for a wide range of operating conditions. An extensive DOE analysis of the results yields characteristic equations that are capable of predicting the amount of stress bead breakup for any given operating parameters.