Authors researched into the effect of the elements in the pig iron on the graphite nodulization in the structure of the cast iron treated magnesium, and the following results were obtained.
  (1) Sn, Sb, As or Pb is a subversive element and then pig iron should be used with knowledge of safe limits on these elements.
  (2) Additional magnesium must be added to irons of higher sulfur content, and increasing amounts of sulfur in the pig iron decrease the reproductivity of nodular cast iron.
  (3) Si, Mn, P, Cu, Ni, Cr, V, Mo, W, Co, Al, Ti or B being contained below some contents in the pig iron, effects little on the graphite nodulization.

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  Several physical and chemical properties of the cast iron obtained from special pig iron (Electric furnace melted pig iron or reproduced pig iron by cupola furnace melting) melts by cupola furnace melting were compared with that of the ordinary cast iron made with blast furnace pig iron. The testings and experiments were carried out with respect to followings : Mechanical strength, micro-structure, draw and shrinkage, fluidability and hardness number etc.
  The experiments described in this paper have confirmed that no apparent difference were observed between the special pig iron of this type and ordinary pig iron, but the former showed rather more superiorities. (N. T.)

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  The vapour occured in mold, usually develops gas pressure in its inner layer of mold. Whether this vapour pressure will be large or small, is mainly dependent upon the permeability of mold if moisture content is constant. The fact that this pressure constitutes the back pressure into the facing parts, gives the various effects on the surface of castings.
  The experimental results obtained are as follows.
 1) If the voids between sand grains which have a close relation to permeability, appear at the surface area of mold, it follows that the larger the permeability is, the rougher the casting surface becomes.
 2) The balancing condition between the pressure of molten metal against the mold surface and the back pressure against the molten metal surface, gives remarkable influences upon the surface of castings.
 3) The balancing condition of pressure is so much related to the kind of casting metal, pouring head and pouring method that the control of mold permeability should be decided by each casting method.
 4) Due to the existence of abnormal voids at the surface of mold, the control of back pressure is subjected to be difficult. The mold surface should be normal.
 5) If the back pressure due to backing sand is high and the permeability of facing sand is good, the vapour occured blows up into the molten metal coming in contact with the mold surface. In case of poor permeability of facing sand, the sand grains are forced into the casting surface or the mold being partially cracked, vapour blows up there.
 6) In a comparatively low back pressure, a good surface finish is obtained. In a excessive low pressure, molten metal penetrates into the fine voids of mold surface, resulting in a poor surface finish.
 7) Facing sand should be as fine as possible and permeable backing sand should be used to obtain a good surface finish. (Oct. 30, 1950)

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