Cooling system and cooling method of rolling steel

A cooling method that cools hot rolled long steel bar, using a cooling system that is provided with a cooling water supply nozzle that supplies cooling water into a chamber, a blow outlet that blows out a cooling medium that is produced by mixing compressed gas for cooling that is introduced through a gas inlet and the cooling water, and a plurality of chambers each having a nozzle plate that is provided at the blow outlet so as to face the rolled steel bar, and that has a plurality of nozzle holes for spraying the cooling medium that is produced by mixing the cooling water and the compressed gas for cooling, the cooling method comprising:

• rectifying the compressed gas for cooling that is introduced to the chamber through the gas inlet with a rectifying plate that is disposed between the gas inlet and the cooling water supply nozzle, so that the compressed gas for cooling that is introduced from the gas inlet disperses throughout an entire chamber, and so that a droplet flow rate distribution of the cooling medium that is sprayed toward the rolled steel bar from the nozzle plate becomes uniform along the longitudinal direction of the rolled steel bar;
• producing the cooling medium by mixing the cooling water that is supplied from the cooling water supply nozzle and the compressed air for cooling, wherein the compressed gas for cooling passes through a gap formed between the rectifying plate and inner walls of the chamber and disperses throughout the entire chamber;
• and
• spraying the cooling medium toward the surface of the rolled steel bar that is arranged along the blow outlet at a speed of 50 to 200 m/s through the plurality of nozzle holes of the nozzle plate, and uniformly cooling the entire length of the rolled steel bar.