If moulding sands were rammed uneven at edges and corners in moulds, it would apt to induce penetrations of the molten steel and cause pinholes in the castings. It was observed especially in monlds prepared by moulding machines. In this experiment, the effects of several kinds of starch binders on the contraction of moulding sands were investigated, chiefly, then the effects of bentonites, moisture contents, grain distributions and shapes of grains were studied.
  The results obtained are as follows :
  (1) It showed better flowability in the sand of single grain distribution than that of mixed, and rounded sand did also in comparison with subangular one.
  (2) Addition of bentonites to 6% moistened sand gained good flowabilities in such sequence as Yamagata, Niigata and Gumma products.
  (3) As a result of measuring several factors which influenced on a_N value (flowability prescrihed by NIK) the increase of bentonite contents aggravated especially in the case of dextrine added sands, the increase of moisture contents aggravated except in the sand of dextrine added. And the increase of secondary binders made a little worse in β starch and dextrine added sand, but improved a little in α starch added sands. Although the value of a_N expresses the natural flowability, it is doubtful that a_N expresses the rammability and the uniformity in the sand moulds by moulding machines.
  (4) In the sand mould by moulding machines it seems that the ratio of compressive strength of the practical mould to the green compressive strength (MC/GC) has inverse interrelation to the height of specimens which rammed at one time with 2kgs weight.
  (5) The relation of a_N and MC/GC to the rammability and the unifomity of the mould hardness in the mould by moulding machine was investigated and tendency of proportional relation was observed.
  (6) It was proved by several experiments that the sands of moderate flowabilities were more practical, because the sands of excellent flowabilities often caused the difficulties in drawing the patterns.

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  Studies on pin holes caused by moulds have been reported by many investigators. But, quantitative evaluation of pin holes, effects of vent holes in the moulds and the experimental relations between the drying depth in the moulds and the casting thicknesses have been remained uncleared up to the present. So, the author has investigated on the pin holes caused by the moulds applying simple plate-like specimens.
  The results obtained were as follows ;
  (1) The numbers of pin holes appearing on some cut surfaces of the specimens were counted to estimate the intensity of pin holes. This seemed to be more reliable than any other method tried before.
  (2) The shapes of the pin holes were related to the drying degree of the mould surface ; pipy shape by green sand mould and conical type by drying mould. These should be investigated and discussed refering to the velocity of the heat absorption on the mould surface and gas pressure.
  (3) The intensity of pin holes was related strongly to the drying degree of mould. The pin hole was not occurred in the casting if the mould was dried perfectly.
  (4) The maximum point of pin hole intensity was appeared at the casting of 36mm thickness in the present investigation.
  (5) Technical trials of setting vent holes in the moulds to improve the pearmiability of the mould seemed to be useless by the results of this investigation.

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  “Kamaishi” pig iron and electrolytic iron were melted in a Tammann furnace or in a criptol furnace to obtain molten cast iron having the analysis of around 3 per cent C, and 1.5 per cent Si. The samples for hydrogen analysis were taken from the melt at various melting conditions, and hydrogen was determined by the vacuum extraction method at 1000°C. The results are concluded as follows.
  (1) Even though the pig iron and the electrolytic iron originally contained much hydrogen, this hydrogen was evolved on melting, and the hydrogen content of the melt reduced to a certain value depending on the melting conditions.
  (2) In the Tammann furnace, the hydrogen content of the melt was found to be reversibly correlated to its temperature.
  (3) In the criptol furnace, the hydogen content of the melt increased with increasing humidity of the air, even when the observed hydrogen content was higher than the calculated values.
  (4) The hydrogen content of the melt was reduced by covering its surface with gaseous argon. The outside of the crucible was also needed to be covered with gaseous argon in order to get lower hydrogen content.
  (5) The hydrogen content of the melt was reduced by blowing gaseous oxygen on the surface of the melt or by the addition of millscale on the surface at higher temperature (over 1400°C).

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  Water glasses of high viscosity are very unfavourable for the use of gas moulding process from the view points of reactivity of the binders with CO₂ gas, the mould strength and the easiness of mulling and stripping.
  While, those of low viscosity remain much water content in the mould, being harmfull to the casting metals.
  The author has studied the methods of determining the optimum viscosity by experimental works.

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  Physical properties of bentonites at room temperature used for green sand moulds and skin dry moulds for steel castings were described.
  The results are summarized as follows.
  (1) Suitability of testing methods applicable to bentonite for mould, particularly of the penetration test, the liquid limit test and the swelling test, were comparatively examined.
  (2) The physical properties of bentonite-water mixtures were found to be under an extensive influence of the inherent characteristics of the bentonite, but not influenced by the so-called fineness.
  (3) The physical properties of bentonite-water mixture with a water-to-bentanite ratio as low as normally employed for actual mould sands, the testing method for which is rather difficult to conduct, were found to be satisfactorily deductable from testing results on mixtures with high water-to-bentonite ratio, which are for readily obtainable by such testing method, the liquid limit test or swelling test.

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