Investigation of the performance 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 (LFC) 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 investigation 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 a vented EPS-bead-canister condition using a 1.90-cm (3/4-in.)-diameter fill hose increases 51 pct 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 3-second fill time increased 28 pct, from a 276 kPa fill pressure to a 552 kPa fill pressure. It was also discovered that the air flow rate under a pressurized EPS-bead-canister condition is not a strong function of fill pressure, but instead strongly depends on the EPS bead canister pressure. The average EPS bead-mass per cycle for a pressurized canister and a 1.90-cm-diameter fill hose increased 45 pct from 55.22 g for a 28 kPa EPS bead canister pressure to 80.21 g for an 83 kPa EPS bead canister pressure at a fill pressure of 276 kPa. 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 1.90-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-in.)-diameter fill hose showed similar behavior to those for a 1.90-cm-diameter fill hose. Four correlations are proposed to predict the dimensionless bead-mass per cycle from either the dimensionless fill or canister pressure and the dimensionless fill time.