According to the previous studies made by the authors, it has been ascertained that the contents of SiO₂, as an inclusion, increased when the molten cast iron was oxidized and that its increment was remarkably great when the melt was oxidized at the temperature below 1400°C. And also, it was known qualitatively that the possibility of the occurrence of shrinkage cavities became greater as the SiO₂ content increased. The authors have affirmed quantitatively that in many cases the melting conditions in which the melt was oxidized, coincided with the conditions, that lead to occur shrinkage cavities, and examining the phenomena of structural abnormality due to suspending silica, further investigations are carried out so as to study the causes of the formation of shrinkage cavities in the oxidizing melting.
  The results obtained by this experiment are as follows :
 (1) In the low temperature oxidizing melting which leads increment of suspending silica, the possibility of the occurrence of shrinkage cavities becomes greater, but contrary to this, in the case of high temperature oxdizing melting in which the suspending silica does not introduce the possibility, it is lessen and this results in sound castings.
 (2) Shrinkage cavities occur with few exceptions in case of the low temperature and almost non-oxidizing melting, and any connections can be seen between the possibility of the occurrence of shrinkage cavities and suspending silica. However, sound castings can be produced even in the non-oxidizing condition if the melting temperature increased.
 (3) The shrinkage cavities appeared in the oxidizing melting differ its shape in accordance with the degree of oxidation and, in the intense oxidizing condition, the internal shrinkage becomes smaller and smaller till it turns into external shrinkage. However, the total volume of internal and external shrinkages increase as the rate of oxidation intensified.
 (4) The causes of the formation of internal shrinkage will have some relations to the structural abnormality which is led by suspending silica in the melt : the precipitation temperature of primary crystal increases and the eutectic temperature is super-cooled, then the zone of solidification becomes wide, consequently the feeding of metals through dendritic primary crystal into the center of the crystal is interrupted.
 (5) The causes of the formation of external shrinkage are thought that the suspending silica segregates in the center part of the casting and this segregation hasten the completion of solidification and thus the suction of shells into the inner parts becomes great.

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  The auther operated a cupola with varing the amount of coke and air volume and has made some investigations on the Jungbluth's curve. The other operating conditions except air volume and amount of coke were kept constant in this experiment. The results obtained are as follows :
  (1) Some relations are observed between tapping temperature and carbon content in molten metal.
  (2) The melting rates are always constant when tapping temperature shows maximum value in either the case which is operated with constant air volume and various coke ratio or the case in which the coke ratio is constant and only the air volume is varied.

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  The flows of metal in cylindrical and in rack gear type castings were investigated for aluminium by the same method as stated in previous reports.
  In cylinder castings, gating systems of top, bottom, step, pencil and ring were applied respectively and it was found that the attitude of metal flows in gates and cylinders and the time to be taken to fill up the casting.
  For the rack gear type casting, it was found that there occurred an eddy flow in every tooth of the gear when the mould was set horizontally, but the metal flowed less disturbed in an inclined one.

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  In recent years, green sand molds have been used widely for the production of steel castings and this might be due to its reduction of labors and expenditures. In our workshop, the study has been carried out on this subject since 1951 and has achieved notable results in the use of green molds and cores.
  This study only refers to the very limited defects which we usually face with in the operation. But still these seem very important problems in practice.
  The main factors which thought to cause penetration are pouring temperature, molten metal pressure, size of sand grain, moisture content in molds, mold hardness and so on. It might be very effective to use silica-flour to prevent penetration.

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