HELIUM INFUSION IN SAND MOLDS: MEASUREMENT ANALYSIS OF HEAT TRANSFER PROPERTIES MECHANISMS

Conventional sand casting is an important manufacturing process that is marred by low solidification rates due to inferior heat transfer properties of the mold material that in turn result into inferior microstructure and mechanical properties of the cast part. This paper reports an increase in heat transfer properties of porous silica sand mold material by helium infusion. Heat transfer properties investigated in helium environment include apparent thermal conductivity and heat diffusivity. Apparent thermal conductivity in both air and helium environments is measured using ASTM E1225 (standard test method for thermal conductivity of solids using guarded comparative longitudinal heat flow technique) at a low temperature range (25°C to 125°C) to safeguard mold integrity and to prevent binder gases’ influence on measurements. Value of heat diffusivity is then mathematically deduced at 100°C for simulating the effect of helium presence. Further, a hypothesis is postulated herein for heat transfer mechanism in the porous silica sand mold wherein a case of operationally feasible “continued flow helium infusion” in the sand casting process is mathematically investigated via Biot number analysis. Results show that helium infusion increases the heat transfer properties of porous silica sand mold; the value of apparent thermal conductivity of sand mold specimen is found to be increased ~89% at 25°C and ~99% at 125°C with helium inside the pores as compared to the baseline (without helium) whereas heat diffusivity is shown to increase ~94% at 100°C in comparison to baseline (without helium). The results of experiments are validated at significance level of 0.05 via analysis of variance “ANOVA”. Biot number analysis carried out at two hypothetical flow rates of 1 L/min and 4 L/min supports the postulated hypothesis and establish the role of helium flow rate as a new process parameter in helium administered sand casting process.