Casting method and casting apparatus for DC casting

A method for casting longitudinal cast products including casting longitudinal cast products in a semi-continuous manner using a DC casting apparatus having a mold, wherein the mold has top and bottom openings and partially solidifies molten metal that enters into the mold via the top opening and outputs the cast product via the bottom opening, recording a thermal image of the cast product output via the bottom opening, determining at least three non-overlapping temperature ranges comprising a first, second and third, determining a peak temperature in the thermal image; comparing the peak temperature with the at least three temperature ranges; and performing operations depending on where the peak temperature falls within the at least three temperature ranges.