Formation of bleed bands in D. C. cast billets of 99.9% aluminum_Q

Abstract

This study was made to investigate the formation of bleed bands in D. C. cast billets. the 99.9% aluminium billets, 13cm in diameter, were D. C. cast. By controlling casting conditions, billets with and without bleed bands were produced. Using thermocouples inserted in the mold wall, the temperature was recorded during D. C. casting. At the end of casting, a small amount of ¹⁹⁸Au was added to the molten metal and then sump contours were observed by means of macro-and micro-autoradiography. Distribution of impurities such as iron and silicon was determined by X-ray microanalysis.
The results obtained are summarized as follows:
(1) In the billets with bleed bands, the base of ingot shell was remelted and in an extreme case, molten metal exuded on to the ingot surface, as proposed by Siebel et al1).
(2) Remelting proceeded preferentially along grain boundaries where melting point was low due to segregation of iron.
(3) Bleed bands likely to be formed by the Collins' mechanism2). were not observed.
(4) By the remelting mechanism, the effects of the casting speed and the mold taper on bleed bands could be qualitatively explained.