The hardening reaction between water glass and dicalcium silicate (abbreviated as C₂S) is utilized in the self-hardening mold. However, the mechanism involved in the hardening reaction and the strengthening of the mold by the above reaction have not yet been elucidated.
  In order to find them out, the main products of the hardening reaction was analyzed from observations with a polarized microscope together with values from X-ray diffraction and refraction index measurement. The main product was found to be an amorphous material which is very similar to silica gel. This is considered to produced by the coagulation of Ca⁺⁺ ion liberated from C₂S in the water glass and the ion exchange reaction between Ca⁺⁺ ion and Na⁺⁺ ion contained in the water glass.
  Subsequently, the reason for the strengthening of this mold was studied by measureing the strength of the test piece placed in a vapor saturated atomosphere. From this experiment, it was surmised that the strengthening of the mold was due to the formation of a silica-like gel and the removal of the water from the water glass which retains the C₂S unreacted.

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  Because of the presence of graphite, the stress-strain properties of gray cast irons usually differ in compression and in tension. So, it can be considered that the neutral axis of a beam made of gray cast iron shifts toward the compression side under bending load. But the behaviors have not been made clear enough. Our experiments have been conducted to learn about the behaviors and the differences between the stress that occurs in a real beam and the stress that is calculated on the assumption of an ideal elastic material.
  The results may be summarized as follows ;
  (1) Even under a great bending load, the distribution of the strains in the beams made of gray cast irons display linearity.
  (2) Up to a certain stress, stress-strain diagrams in tension and in compression of cast iron tend to exhibit the same straight line and show the same elastic behaviors. In this case, no movement of the neutral axis is recognized. But on increasing the load, the neutral axis of the beam shifts towards the compression side. A beam of high tensile strength usually needs high bending load to move the neutral axis but even then the amount of its movement and its increasing rate are small.
  (3) Under a low bending load, the stress distributions of beams show straight lines and they are in approximate agreement with the stress assuming an ideal elastic material. But on increasing the load, the stress distributions gradually show a curved pattern. The stress which occurs in the compression side surface approximately agrees with the stress that is calculated by assuming an ideal elastic material but the stress which occurs in the tension side surface becomes less than that. Nodular graphite cast isons do not show much differences between the stresses in the compression side and in the tension side.
  (4) The fracture by bending load of a beam of gray cast iron occurs when the stress in the tension side surface comes close to the tensile strength of the beam material.

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  This paper is a report on the results of viscosity measurement of molten cast iron by a rotation viscometer with an internal rotor.
  Experimental procedures were as follows : An alumina crucible was set in a siliconit furnace and heated to a fixed temperature after which a molten iron was poured in the crucible. The furnace was then thrust up and the internal rotor was immersed in the molten iron coaxially with the center line of the crucible. Then the internal rotor was rotated. The internal rotor was made of electrode graphite and heated preliminarily with a heating element. Viscosity torque arising from the rotation of the internal rotor was converted into an electric quantity from which the coefficient of viscosity was obtained.
  The diameter of the internal rotor was 30 mm and the length of its immersed part was 60 mm. The internal diameter of the alumina crucible was 45 mm. The internal diameter of the alumina crucible was 45 mm. The speed of rotation of the internal rotor was 15.7rpm.
  Since a laminar flow was necessary for viscosity measurement with the rotation viscometer, the rotor had to be rotated slowly. Therefore, the viscosity torque was very weak and hard to detect. This viscosity torque was detected as the increase in the load current of the DC shunt motor which rotated the internal rotor. A feedback compensator of a field control system which made the revolution rate uniform was used to raise the sensitivity of measurement. The above revolution rate of 15.7 rpm was the limit, i.e., it was the minimum revolution rate.
  Even with such a high sensitivity measurement, the flow was a little out of the laminar state in low viscosity areas. Hence viscosities in these areas seemed to be measured as a little lower than true values. It was believed, however, that the laminar flow was kept in high viscosity areas and reliable values could be obtained.
  Chemical composition of cast iron used for the viscosity measurement were: 3.26%C, 1.36%Si, 0.46%Mn, 0.072%P, 0.085%S. This iron was melted in a graphite crucible using a kryptol furnace under the following three melting conditions, and effects that these melting conditions had upon viscosity were investigated:
  1) Normal melting: Iron was melted at 1,480°C.
  2) Oxidized melting: 1%Fe₃O₄ was added after normal melting.
  3) Inoculation: 0.5%Ca-Si was added after normal melting.
  It was clarified from results obtained that the viscosity of molten cast iron changed remarkably with melting conditions as summarized in the follwing :
  1) The viscosity of oxidized iron was the highest. It rose rapidly especially at low temperatures and reached, for instance, 25 cp at 1,225°C.
  2) The viscosity of inoculated iron was 3.0-4.3 cp at 1,300-1,250°C which was the same as in normally melted iron and its rising gradient at low temperatures was the most gentle, being only 7.5 cp at 1,225°C.
  3) The viscosity of normally melted iron was 9.4-11.0 cp at 1,225-1,220°C.

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