THE THEORY OF GROWTH OF BLOW HOLES AND SHRINKAGE CAVITIES IN IRON CASTINGS AND ITS EVIDENCES

Abstract

Knowledge of the characteristics of the vapor tension of gas dissolved in the molten bath is primarily needed for dealing with the growth of blow holes and shrinkage cavities in cast iron. For instancerthe boiling condition of the molten bath develops in case the total vapor tension has excelled the total external pressure consisting of the atornospheric and liquid pressures.
In other words, blow holes appear in the molten bath, where
The vapor tension of the dissolved gas varys with the change of temperatures. Above all, the change at the instant of solidification is predominant. At first, P'CO causes segregations at the solidification stage and enhances the gas pressure, the increase of which is, however, checked by the coexistent Si at a certain pressure (Fig. 2.). Nextly P'N2 tends to increase with cooling of the molten pig, but on the contrary does not cause segregations at the solidification stage. Therefore it does not increase the vapour pressure in solidification. Thirdly segregations are most prominent in P'H2 and its vapour pressure remarkably increases with the process of solidification. Therefore, while the P'H2 at the ordinary melting stage is as low as below 0.05 atm, the pressure at the solidification stage becomes as high as 0.5 atm, causing the boiling of the molten pig (Fig. 7.). The author gives some interesting explanations by combining the characteristics of the abovementioned three kinds of vapor tensions with the gowth of blow holes and shrinkage cavities in cast iron.