気孔生成の機構

概要

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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 φ 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.
社団法人溶接学会の論文
1981-09-05