Abstract
Nucleation and growth of a blow hole during the solidification of molten metal were discussed in the light of the newly proposed 'solidification theory' by the author.The results obtained were as follows:(1) The gas evolves through the protruding gas bubble surface, and its volumetric velocity per unit area w as compared with the solidification speed v determines the direction of growth of the blow hole inside wall. In the case of v/w=2, the resulting blow hole is cylindrical.(2) It was deduced that the nucleation of a gas bubble occurs in the solute enriched zone on the solidifying interface, and that the blow hole enlarges rapidly to the thickness of the zone and then grows according to v/w in the bulk molten metal.(3) Starting from the spherical bubble nucleus, various blow hole contours may be formed according to the variou values of v/w. In case that solidification angle ψ is smaller than liquid phase angle θ, the blow hole becomes a little shorter.(4) 'Bubbling type' blow hole contour was reproduced well by means of the new theory.(5) It was considered that the diameter of the cylindrical blow hole can not exceed a certain maximum value depending on the surface tension and density of the liquid concerned.
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