Heat and moisture transfer in sand molds containing water
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I.
INTRODUCTION
M O S T shaped castings, especially in cast iron and steel, are produced in green sand molds and CO2 molds which contain water. The behavior of water in a sand mold is very complicated because heat flow includes vaporization and condensation of moisture, and these phenomena have not been well understood. However, the gas vapor transformed from water in a sand mold is considered to be one of the major causes of casting defects, such as blow holes. 1-4 Furthermore, heat flow in a sand mold determines the solidification rate, and a knowledge of heat transfer in sand molds is necessary for control of solidification. Thus, an analysis of heat and moisture transfer in a sand mold containing water is important, both for control of solidification and prevention of casting defects. Paschkis, 5 Saito, et al. ,~ Katashima and Matsuura, 7 Fukusako, et al. ,~ and Kubo, et al. 9 reported on heat transfer analyses in green sand molds which contain several percent water. However, the transfer of moisture was not analyzed in these papers. The authors made assumptions, such as formation of a transportation zone, but did not analyze moisture transfer itself. Although Cappy, et al. 10 reported on a mathematical simulation of heat and moisture transfer in a green sand mold, the method employed is not adequately described, and the agreement between calculation and experiment is limited. On the other hand, Eckert and Pfender, 11and Couvillion 12 analyzed heat and moisture transfer in soil. Analyses on the drying process of porous material containing liquid are also reported by Crank 13 and Whitaker.14 However, these papers treat conditions of small temperature differences at low temperatures, and assume equilibrium among porous materials, liquid and gas, i.e., assuming that the temperatures of the porous materials, liquid and gas are equal, and that the gas is at the saturation pressure at the given temperature. However, in metal casting, temperature differences in the sand mold are large and range from several degrees Kelvin to more than one thousand degrees Kelvin, and the vapor moves through the sand mold under nonequilibrium conditions. Consequently, none of the previous analyses can be applied to sand molds. It is the purpose of this paper to present a new model to express heat and moisture transfer in sand molds containing water. KIMIO KUBO, formerly Visiting Assistant Research Scientist at the University of Michigan on leave from Osaka University, Osaka, Japan, is Research Engineer, Hitachi Research Laboratory, Japan. ROBERT D. PEHLKE is Professor, Department of Materials and Metallurgical Engineering, University of Michigan. Ann Arbor, MI 48109-2136. Manuscript submitted May 20, 1985. METALLURGICALTRANSACTIONS B
II. M O D E L I N G AND NUMERICAL CALCULATION A. Basic Equations Schematic distributions of temperature and moisture content in a sand mold containing water are shown in Figure 1.15'16'17 In a sand mold containing water into which metal is poured, water near the metal-mold interface vaporizes and the ev
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