Nodular graphite cast iron adding magnesium element, especially the structure in increasing magnesium addition or cooling speed and varying the heat treatment have been studied.
  The Results obtained are as following : —
  1) Addition of magnesium has the effect of stabilizing carbide.
  2) Adding pure magneisium about 0.65% gives us the nodular graphite cast iron having good ductility in the case of its thickness is 5mm or more. Under 3mm thickness, however, the structure shows the white cast iron.
  3) Magnesium element plays the role of stabilizer preventing the crystalization of graphite to some extent.
  4) In these kinds of nodular graphite cast irons kish graphite grows the shape of a mono-crystal or its resemble.
  5) The decomposing condition of pearlite in the annealing at the temperature 700°C is the same as in the case of ordinary grey cast iron.
  6) Magneaium addition produces the free cementite having the tendency of decompose easily.

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  Studing on sand particles of casting sand led us to the conclusions as following :
  1) In the case of equal size of sand grain, the strength of a sand mold rises in inverse proportion to square of the mean diameter of sand grain.
  2) The permeability of sand mold increases proportional to the mean diameter of sand grain.
  3) The roughness of casting surface influenced proportionaly by the space size between each sand grain which measured by applying the surface tention test using mercury to this. (N. T.)

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  This paper is the results of an investigation of surface quality of castings produced in the mold made of silica sand containing clay and graphite. The outline is as follows :
  Group 1－Single grain containing scaly graphite. The mold containing more scaly graphite produced fine surface of castings in case of coarse sand.
  Group 2－Single grain containing granular graphite. The granular graphite usually produced fine surface of castings in case of fine sand.
  Group 3－Compound grain. A. F. A. fineness number is an important function for surface roughness of castings.
  Group 4－Kinds of graphite. The scaly graphite produced better surface than the granular graphite.
  Group 5－Considerations. If the amount of graphite plus clay is below 23 per cent, it will be R=CS. But above 25 per cent, it will be R=CS+b.

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