Bottom block for D.C. casting of aluminum rolling ingots

In a vertical DC casting apparatus for the casting of large rectangular-shaped aluminum rolling ingots conprising a DC casting mold and a bottom block, wherein the bottom block is adapted to be inserted into the mold before casting to thereby seal the discharge end of the mold and wherein the bottom block is adapted to be withdrawn from the mold during casting and thereby allow the solidifying ingot to emerge from the discharge end of the mold where coolant is applied onto the surfaces of the ingot, the improvement comprising a bottom block of generally rectangular horizontal cross section having generally pyramid-shaped projections at each corner on the top of the bottom block which extend laterally along the edges of the bottom block a distance from the corner of not more than one-third of the bottom block length and width respectively, for reducing the solidification rate at the corners of the solidifying ingot during the initial part of casting by preventing the application of coolant onto the corners of the ingot when the ingot initially emerges from the discharge end of the mold.