2010 Volume 82 Issue 2 Pages 92-96
Several frozen molds were produced from various types of sand, and the effects of sand characteristics such as material, grain size, and grain shape on the cooling behavior of lead-free bismuth bronze cast into the frozen maids were examined. Basically, the frozen mold enabled lead-free bismuth bronze to provide faster cooling rates compared with conventional green sand molds. In addition, the cooling potential of frozen mold was improved by the following sand particle properties; higher thermal conductivity, greater grain size, and spherical shapeness. Based on the above results, a heat transfer model in the frozen mold was developed. In the frozen mold, ice near the mold surface contacting molten metal thaws immediately, and changes to vapor just after pouring which then blows out from the mold removing the heat from the casting. Finally, the casting is cooled down through the heat transfer between sand particles when water disappears in the mold. This model suggests that it is important for the frozen mold to have good air permeability to enhance its ability as a cold source. A finer structure was successfully produced in the lead-free bismuth bronze casting by using a frozen mold consisting of coarse spherical alumina grain, which provides the fastest cooling rate to castings.
