Date of Award

12-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Polymer Engineering

Major Professor

Roberto Benson, Dayakar Penumadu

Committee Members

Joseph E. Spruiell, Kevin M.Kit, Bin Hu

Abstract

Lost Foam Casting (LFC) is a metal casting technology that facilitates fabrication of near-net shape metal castings using expanded polystyrene (EPS) foam patterns that are coated with refractory slurry and is effective for producing aluminum or iron castings of complicated geometry. However, the LFC process can produce considerable amount of scrap due to casting defects. Removing the EPS thermal decomposition products through the ceramic coating ahead of the advancing metal front during the liquid metal pour is a key factor in obtaining a defect free casting. Developing a fundamental understanding of foam degradation mechanism is essential in improving LFC process.

Modeling of the LFC process till date has completely neglected the effect of styrene on the overall thermal degradation of EPS foam. The dissolution effect of styrene is investigated by presenting the thermodynamic principles of polymer solution theory along with experiments to verify its impact on polystyrene degradation. By subjecting EPS Foam samples directly either to thermal radiation or to styrene vapor, it is demonstrated that styrene’s solubility of polystyrene significantly alters the degradation mechanism of EPS foam in LFC process and thus can control the metal fill process leading to reduction of defects in castings.

LFC process uses expanded polystyrene foam patterns in which isomers of pentane are used as blowing agents to achieve the expansion. In order to expand polystyrene, steam is used as a heat source and the expansion process takes place via conduction of heat from the surface of unexpanded polystyrene beads into the bulk. Pentane isomers are volatile organic compounds and green house gases that are either liberated directly into the atmosphere or combusted using expensive setup. The environmental impact of the current process using pentane as an expansion agent has been considered and a new method for manufacturing of EPS foam has been developed with benign expansion agent. Laboratory experiments are demonstrated where PS pellets are successfully expanded into foam. Novel heating technology using microwave radiation is proposed and implemented in order to achieve efficient volumetric heating for the manufacturing of foam with target density.

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