Abstract: In a slag crushing device according to the present invention, a cylindrical body having a slag insertion port in its one end and a discharge port in the other end is rotatably provided around a shaft center so inclined that the position of the discharge port is below the position of the slag insertion port. At least one crushing annular body having a smaller radius than that of the cylindrical body and idled parallel with the shaft center of the cylindrical body is arranged inside of the above cylindrical body. This crushing annular body is guided by a guide frame provided on the inner periphery of the cylindrical body. The guide frame is provided with apertures for introducing slag into the crushing annular body and apertures for discharging the slag crushed.

Abstract: A melting and holding furnace comprising a preheating and melting chamber defining a preheating tower section in an upper position and a melting section in a lower position, a holding chamber communicating with the melting chamber, and a well communicating with the holding chamber. A melting burner is provided for jetting out flames obliquely downwardly into the melting section.

Abstract: A melting and holding furnace comprising a melting chamber, a well, and a holding chamber disposed between the melting chamber and the well. The holding chamber includes a plurality of submerged banks projecting from its bottom and extending transversely of a line linking the melting chamber and the well.