Screw extrusion is widely used in industry today, but little is known about the design and operation of this type of equipment outside of the polymer industry. With the advent of high performance, high value ceramic materials, it has become important to understand how to produce product consistently and economically. A mathematical model has been devised for a flooded screw that brings together paste rheology and a model of screw extrusion developed from methods with frictional solids flow. The resulting model defines the paste using parameters derived from experiments with an instrumented ram extruder. The governing equations are applicable to the flow in a single screw extruder channel of any cross-section. Experiments have been performed both with and without flow on a 20mm diameter laboratory extruder using a set of screws of varying angle and depth together with pastes of various rheologies. Pressure measurements from experiments without flow could show a marked offset from predictions with screws of low helix angles, although the effects of changing the screw speed universally yielded good agreement. It is hypothesised that this pressure offset was due to a localised enhancement of the static shear stress value at the rapidly moving barrel surface. This enhancement was possibly caused by either pressure or localised changes in the rheology in this high shear region. If the static shear stress parameter is adjusted in the model then the predictions show universally good agreement with these experiments. Experiments with flow also showed general consistency with predictions made by the model, as did experiments carried out on a 3" diameter industrial machine The interpretation of the performance of a fully flooded screw with flow was complicated by the interaction of the screw and the die Future work should centre upon the effects at the barrel surface and the improvements of both pressure and rheology measurement. An attempt should also be made to extend the model to describe flow situations of greater complexity, taking account of converging channels and leakage around the flights. The flow of pastes in twin screw extruders should also be addressed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:633072 |
| Date | January 1993 |
| Creators | Burbidge, Adam Stewart |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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