This investigation was carried out to clarify (1) why metals cool slower in vacuum sealed molds than in green sand mold or self-hardening sand mold, (2) the effect of various degrees of vacuum sealing and grain size of mold sand on the rate of heat transfer. Binder and water were added to the molding sand and N-process molds were also used to compare with the vacuum sealed molds.
  The rate of heat transfer in the vacuum sealed mold is smaller than that in the N-Process mold. The rate of heat transfer decreases by reducing the grain size of molding sand and increasing the degree of vacuum sealing. When there is a binder in a mold, the rate of heat transfer increases. Moisture in the mold has only a slight effect on the rate of heat transfer. It was assumed that the absence of a binder and the presence of rarefied air caused the metal to cool slowly in the vacuum sealed mold.