Abstract: A plasma torch used for heating a molten steel has an outer cylinder is provided. The torch includes a double tube, the bottom of which is blocked annularly. The torch also includes a bottomed cylindrical anode electrode that is installed within the outer cylinder with a gap existing between the anode electrode and the inside of the double tube. The plasma torch is provided such that pure copper is not used as a material for the anode electrode, the material has a softening point exceeding 150° C., and the ratio of an electric conductivity D of the anode electrode 28 to an electric conductivity N of the outer cylinder satisfies the formula: 0.2≦D/N<1.0. The plasma torch prevents the melting loss and wear of the anode electrode caused by the splashes and the heat produced in the anode electrode, suppresses generation of a side arc, shows an extended life, and stabilizes the casting operation and improves the quality of the slab.

Abstract: A plasma torch 20a used for heating a molten steel has an outer cylinder 26 composed of a double tube 21, the bottom of which is blocked annularly, and a bottomed cylindrical anode electrode 28 that is installed within the outer cylinder 26 with a gap existing between the anode electrode 28 and the inside of the double tube 21, the plasma torch being characterized in that pure copper is not used as a material for the anode electrode 28, the material has a softening point exceeding 150° C., and the ratio of an electric conductivity D of the anode electrode 28 to an electric conductivity N of the outer cylinder 26 satisfies the formula: 0.2≦D/N<1.0. The plasma torch prevents the melting loss and wear of the anode electrode caused by the splashes and the heat produced in the anode electrode, suppresses generation of a side arc, shows an extended life, and stabilizes the casting operation and improves the quality of the slab.