Physical and Chemical Analysis of the Thermal Degradation Products of Expanded Polystyrene Patterns with Short Thermal Exposures

摘要

Folds are a type of defect in aluminum structures that is common and unique to lost foam castings. The results from previous studies indicated that the early interaction between expanded polystyrene (EPS) thermal degradation products and the ceramic coating has the highest influence on fold defect formation in lost foam aluminum casting. In this study, we designed an experiment (the drop-through experiment) to simulate this early, transient state. The goals of this study are to investigate the thermal degradation kinetics of EPS at the metal front and the thermal degraded material partitioning at the metal front. Three types of EPS (Beads "A", Beads "B", and Beads "C") combined with two types of coatings (Coating "I" and Coating "ii") were evaluated with the drop-through experiment. The data obtained from this study included the chemical and physical properties of EPS thermal degradation products in the kinetic zone (short thermal history) of the metal front. The main conclusions we drew from this study are: (1) the majority of the EPS thermal degradation products at the molten metal front were liquid polystyrene and were mostly recovered from the coating (2) the bromine additive in the polystyrene matrix releases free bromine radicals that cleave the polymer into smaller chains in the temperature range of 650 deg C-800 deg C. This information will contribute to a better understanding of fold defects in lost foam castings and the identification of additives and other process changes that will reduce or eliminate fold defects.