Sand mold bonded with sodium silicate and dicalcium silicate has more merits than CO₂ sand mold. The demerit of CO₂ sand mold is that the mold bonded with sodiumsilicate has a difficulty in collapsibility because of its too high residual strength after heating at high temperatures. Generally speaking, the collapsibility of the mold can be improved by using such sodium silicate as having high mol-ratio or adding organic compounds to the sand. Then, a study has been made in order to clarify how the collapsibility of dicalcium silicate sand mold is influenced by such factors as the mol-ratio and specific gravity of sodium silicate solution. Further, the influence of the addition of alkali earth oxides and carbon aceous compounds having a tendency to thermal decomposition on the collapsibility of the mold has been made with the cases of castings having various thicknesses. The experimental results were:
  1) The collapsibility of mold was dependent upon the residual strength of the mold. However, this could not be applied to the case of heavy castings in which fusion took place.
  2) The higher the strength at room temperature, the higher the strength of the mold at high temperatures. Hence, to obtain the best collapsibility it was preferable to reduce the strength of the mold to the lowest limit of strength at which molding could be performed, namely to the extent of 10 to 15kg/cm²
  3) The less the amount of sodium silicate addition, the lower the residual strength.
  4) The residual strength of mold was reduced by increasing the mol-ratio and decreasing the concentration of the sodium silicate solution.
  5) The residual strength could be reduced by adding bentonite or carbon aceous compounds.
  6) Addition of magnesium oxide had favourable effect upon the reduction of the residual strength and collapsibility at comparatively lower temperature range from 100 to 400°C. However, no improvement could be realized at higher temperature from 800 to 1,000°C.
  7) The favourable influence of magnesium oxide addition was more remarkable at temperatures of wider range in case carbon aceous compounds were added. The most favourable contents of magnesium oxide and carbon aceous compounds were 0.5 and 1.0% respectively.

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  The penetration of wash into sand mold is an important characteristic of the mold wash which is effective upon eliminating errosion scabs or penetration of molten metal in casting. To measure the degree of the penetration of mold wash the authors designed a method in which mold wash of carbon and clay was made to penetrate into a transparent bed consisting of round glass grains whose grain size ranged from 50 to 90 meshes. For preparing mold wash coke, earth graphite and flake graphite were used as carbon material and kaolin and bentonite as clay material. The experimental results were as follows:
  1) The method of measuring the penetration of mold wash by using the transparent cylinder containing round glass grains proved to be sufficiently useful.
  2) The depth and rate of penetration and separation of water from the penetrated wash were easily measured from outside. In this case, there was found a close corelationship between the penetration of wash into the glass grain bed and that of wash into ordinary sand mold.
  3) The degree of penetration was inversely proportional to the viscosity of wash which was varied by the water content of the wash.
  4) The degree of penetration was varied with the ingredients of wash. Particularly, it was noticed that only in case earth graphite (natural amorphous graphite) was used, penetration was promoted by increasing the content of clay added to the graphite wash.

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  The strength of sand mold bonded with water glass was increased by dehydrating the mold. The sand mold was made by mixing pure silica sand with water glass. The dehydration of the sand mold was accomplished to an extent of 80% under reduced pressure, while it was dehydrated to around 60% in an atmosphere of 51% in humidity. In the latter case, the compression strength of the mold was about 40 kg/cm² when the amount of water glass added 5%. It was increased with increasing the amount of addition, molar ratio, and specific gravity of water glass to be added to the sand.

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  Refractory coating of metal mold has to be adhesive to the mold surface, low thermal conductivity and thermally stable. Oxide film formed on metal mold is effective upon improving the adhesion of refractory coating to the mold surface. Also addition of oxidizing agents to coating material results in improving the adhesive property of the coating as well as the colloidal condition of the material. Phospheric acid is preferred to be used as a bonding agent. The insulating property of coating is improved by:
  1) Using insulate refractory containing fine flour.
  2) Making porous coating.
  3) Making stable coating of less thermal shrinkage.

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  Bishop-Pellini curve is modified for calculating the riser dimensions of steel castings when the shape factor is small. The relation is given by :
    V_r/V_c=5/(L+W)⁄(T)
  where V_r is the volume of riser,
    V_c is the volume of castings,
    L, W, and T are the length width, and thickness of the castings respectively.
  Rewriting this, the following formula is obtained.
    [Written in non-displayable characters.]
  where D is the diameter of the riser,
    H is the height of the riser,
    k is the ratio of H to D.
  By using this formula, authors made a slide rule. It is useful for calculating the diameter and height of riser when the length, width and thickness of castings are given.

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