Two-Phase Flow Characterization of an Expandable Polystyrene Injector for Use in the Lost Foam Casting Process

Abstract

A significant portion of casting defects in the Lost Foam Casting process can be traced back to a lack of consistency in the Expandable Polystyrene (EPS) foam pattern. The present study focuses on determining the cause of EPS foam pattern irregularities through the characterization of the two-phase flow of an EPS bead injector. The process variables studied during this experiment include fill time, fill pressure, EPS bead canister pressure, and fill hose diameter. It was found that the air flow rate under vented EPS bead canister condition using a 1.9 cm (3/4 inch) diameter fill hose increases 33% from a 276 kPa (40 psig) fill pressure to a 552 kPa (80 psig) fill pressure, and the EPS bead mass per cycle for a three second fill time increased 28% from a 276 kPa fill pressure to a 552 kPa fill pressure. The average EPS bead mass per cycle for a pressurized canister and a 1.9 cm diameter fill hose increased 71% from 55.22 grams for a 28 kPa EPS bead canister pressure to 80.21 grams for a 83 kPa EPS bead canister pressure at a fill pressure of 276 kPa. It was also discovered that the air flow rate under pressurized EPS bead canister condition is not a strong function of fill pressure but instead strongly depends on EPS bead canister pressure. The EPS bead mass per cycle for a 1.27 cm diameter fill hose exhibited a lower EPS bead mass per cycle than that for a 1.9 cm diameter fill hose for both the vented and pressurized canister conditions; however, the air flow rates and tip pressures observed for a 1.27 cm (1/2 inch) diameter fill hose showed similar behavior to those for a 1.9 cm diameter fill hose.