ELIMINATION OF SHRINKAGE CAVITY IN CAST INGOTS

摘要

An exemplary embodiment provides a method of fully or partially eliminating a shrinkage cavity in a metal ingot cast by direct chill casting. The method involves casting a metal ingot by introducing molten metal into a direct chill casting mold from a spout to form an upright ingot having an upper surface at a predetermined height. Upon completion of the casting, the lower tip of the spout is preferably maintained below the upper surface in molten metal at or near a center of the upper surface of the ingot. The metal flow through the spout is terminated while maintaining sufficient heat in metal within and supplying the spout to keep the metal molten for subsequent delivery through the spout. A partial shrinkage cavity is allowed to form in the upper surface of the ingot as metal of the ingot shrinks and contracts. Preferably before the partial cavity exposes the lower tip of the spout, the partial shrinkage cavity is preferably over-filled with molten metal, while all or significant spillage of molten metal from the partial cavity is avoided, and then the flow of metal through the spout is terminated. The steps of allowing a partial shrinkage cavity to form in the upper surface and then preferably over-filling the partial shrinkage cavity with molten metal from the spout before the cavity exposes the lower tip is repeated, preferably until no further contraction of the metal of the ingot causes any part of the upper surface to contract below the predetermined height. The spout is then removed from contact with molten metal of the ingot and all parts of the ingot are allowed to cool to a temperature at which the metal is fully solid.