Abstract
Molds with exothermic self-hardening sand bound by sodium silicate have a tendency to cause the movement of mold wall and induce casting defects such as external and internal shrinkage. In order to eliminate these defects, it is very inportant to control the return sand and the quantity of sodium-silicate, and to adopt a method for treating the return sand. Pouring of the molten iron into a heavy section casting is liable to cause the movement of mold wall because of a large quantity of heat transfer and the exertion of pressure on the surface of the mold. In this report the following problems are investigated (1) The quantity of sodium-silicate (2) The quantity of residual sodium-silicate round the return sand grains. (3) The degree of sand grain bonding. (4) The characteristics of sand against temperature. (5) The degree of ramming of mold. The results obtained are as follows. (1) Adding a large quantity of sodium-silicate and using the sand over the bench life tends to cause the movement of mold-wall. (2) Mold with sand of smaller thermal expansion tends to cause more casting defects. (3) Mold with larger amount of sand with residual sodium-silicate tends to cause more casting defects. (4) When using sand with good flow, the degree of ramming does not affect so much the formation of casting defects.
