To prevent the heat of an exhaust gas from being lost, and improve the pre-heating efficiency of scrap by a method wherein a shaft of a double structure, which constitutes the pre-heating device, is cooled by spraying in response to the temperature of an internal plate.
A shaft 21 has a double structure of a cylindrical external plate 21a and an internal plate 21b, and in a hollow part between them, a cooling water supply pipe 71 is inserted. When the external plate 21a and the internal plate 21b are constituted of mild steel, a solenoid valve 91 is opened by a signal transmitted from an operation device 111 when a temperature detected by a temperature detector 101 tries to become higher than 350°C, and cooling water is sprayed from a nozzle 71a, and the internal plate 21b is cooled. On the contrary, when the temperature detected by the temperature detector 101 is descending lower than 300°C, the solenoid valve 91 is closed by the signal transmitted from the operation device 111, and the spraying of the cooling water from the nozzle 71a is stopped.
NIWA YUKIO
KATO MASASHI
