In cupola melting, the effects of blast volume and melting temperature to the shrinkage cavities were studied, and the following results were obtained.
  (1) Shrinkage cavities are caused by the oxidation largely. Therefore in low blast volume a sound casting is obtained.
  (2) Near the standard blast volume, shrinkage cavity begins to occur, but its degree is affected by melting temperature.
  (3) In high melting temperature about 1450°C, inner shrinkage cavity is smaller than in medium melting temperature about 1400°C. Therefore the high temperature melting is necessary to obtain a sound casting.
  (4) Outside shrinkage cavity occurs reversely. That is, in high melting temperature it is larger than in medium melting temperature.
  (5) In low melting temperature the bad result is obtained in every blast volume.

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  The relationship between mold surface, casting surface and the voids owing to sand particles was investigated. Further more, the relation between moldability, mold surface and casting surface was studied.
  The results of these experiments are as follows ;
  1) Both in mold surface and casting surface, is concluded R=cs or R=cs+b. In other words, the surface roughness of mold or casting is proportional to the grain size of molding sand.
      where : R=Surface roughness of mold or casting.
                   S=Grain size.     c, b=Coefficient.
  2) Sc=K·Sm+b₂ is concluded. In another expression, the surface roughness of casting is proportional to that of mold.
      where : Sc=Surface roughness of casting.
                   Sm=Surface roughness of mold.
                   k, b₂=Coefficient.
  3) Moldability affects considerablly the surface roughness of casting. In the case of poor moldability, the voids which are not proportional to the grain size of molding sand, occur so abnormally that the molten metal intrudes there, resulting in “penetration” of casting.

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  The auther reported in the before number (No. 8, Vol. 21) that the sulphur in the cast iron can be determind by measuring density of its sulphur print, and introduced the new type mean densitometer for this purpose. In this number he reported the practical result of this method at the foundry during one year. This result shows that the new method is serviceable. This method can not be applied for much content of sulphur, because the reflecting density of photographic paper does not increase lineally, according as increase of sulphur. The density of print is nearly saturated from 0.3% to 0.5% of sulphur. The influence to varies the density of print is studied, and the condition of printing is decided. The density of print is little affected by the other elements in the commercial cast iron, for instance P, Ni, Cr, Al, Mn and Cu. When (C+Si)<5%, the density is a little more increase than soft common cast iron.
  In this case, K=0.196. When Magnesium is added to molten cast iron for nodular graphite, this method is not serviceable as common cast iron, especially high content of sulphur.

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