PURPOSE: To continuously and uniformly produce a molten iron subjected to graphite spheroidizing treatment by feeding under pressurizing and adding graphite spheroidizer into a tundish at the time of shifting molten iron in a molten iron vessel into molten iron basin part through the tundish.
CONSTITUTION: The tundish body 1 is demarcated into a molten iron receiving chamber 2, sealed graphite spheroidizing treatment chamber 3, killing chamber 4 and pouring chamber 5 with partition walls 7, 8, 9 and at lower end parts of the partition walls 7, 8, 9, communicating holes 10, 11, 12 (10 is larger than 11) are formed. By this constitution, the molten iron A is poured into the molten iron receiving chamber 2 from the molten iron vessel 18 and at the time of reaching to the prescribed level of molten iron in the tundish body 1, the graphite spheroidizer is injected into the molten iron A from an injection lance 6 and made uniform in the killing chamber 4, and the generated dross is floated up and separated, thus the molten iron A is allowed to flow into the pouring chamber 5. In the pouring chamber 5, by pulling up a stopper 21, a pouring hole 14 is opened and the molten iron A is poured into a molten iron basin part 20 in a strip-continuous casting machine 19 through a pouring nozzle 15. By this method, the graphite spheroidizing treatment is continuously and uniformly executed to the molten iron A to obtain ductile cast iron, etc., having good quality.