PURPOSE: To obtain billets of a square shape having no surface flaws from ingots of a trapesoidal section by providing camber-preventing guides in the inlet and outlet of the 1st pass formed of a flat roll pair and selecting the roll diameters of the respective passes according to the sizes of rolled materials.
CONSTITUTION: In the stage of rolling a billet of a square section from an ingot of a trapezoidal section produced by continuous casting, the 1st pass is so formed as to decrease the two parallel side lengths of the ingot with a pair of flat rolls 13. Guiding rolls 12 are provided on the inlet and outlet side of the 1st pass and while the upward camber of a material 10 to be rolled is suppressed, the material is rolled in such a way that the rate of reduction in the length of the long sides attains ≥30%. In the rear stage, the material is subjected to the rolling that accompanies shaping in the plural passes of roll pairs having calibers. The material is rolled by selecting the diameters of the rolling rolls in the respective passes in such a way that the ratio Ld/Hm between the average value Hm of the height size on the inlet side and outlet side of the passes and the projected size Ld of the contact area of the rolls and the material 10 in the rolling direction attains ≥0.5.
NOGUCHI YUKIO
SONE HIDEKI
KUWAHATA TSUNEO
