Cooling apparatus for a hot rolled steel strip and methods for cooling a hot rolled steel strip

A method for cooling a hot rolled steel strip comprising introducing a hot rolled steel strip into a cooling apparatus comprising:

• a top surface cooling means provided above a hot rolled steel strip which is transferred with transfer rollers after a hot rolling to cool the top surface of the hot rolled steel strip;
• and
• a bottom surface cooling means provided below the hot rolled steel strip to cool the bottom surface of the hot rolled steel strip,
• each of the top surface cooling means and the bottom surface cooling means comprising:
• a protective member disposed close to the surface of the hot rolled steel strip, having at least one cooling water passage hole;
• at least one cooling water header opposing the hot rolled steel sheet separated by the protective member;
• and
• a plurality of cooling water jetting nozzles protruding from the at least one cooling water header for jetting cooling water approximately vertically toward the surface of the hot rolled steel strip through the at least one cooling water passage hole, said cooling water jetting nozzles having tips, wherein the tips of the cooling water jetting nozzles are disposed farther from the hot rolled steel strip than the surface, opposing the hot rolled steel strip, of the protective member;
• the at least one cooling water passage hole disposed in the protective member is slit shaped;
• and
• the longitudinal direction of the slit shaped at least one cooling water passage hole inclines in the horizontal plane with respect to the transferring direction of the hot rolled steel strip;
• whereby cooling water is jetted from the plurality of cooling water jetting nozzles through the slit shaped at least one cooling water passage hole.

A method for cooling a hot rolled steel strip comprising introducing a hot rolled steel strip into a cooling apparatus comprising:

• a top surface cooling means provided above a hot rolled steel strip which is transferred with transfer rollers after a hot rolling to cool the top surface of the hot rolled steel strip;
• and
• a bottom surface cooling means provided below the hot rolled steel strip to cool the bottom surface of the hot rolled steel strip,
• each of the top surface cooling means and the bottom surface cooling means comprising:
• a protective member disposed close to the surface of the hot rolled steel strip, having at least one cooling water passage hole;
• at least one cooling water header opposing the hot rolled steel sheet separated by the protective member;
• and
• a plurality of cooling water jetting nozzles protruding from the at least one cooling water header for jetting cooling water approximately vertically toward the surface of the hot rolled steel strip through the at least one cooling water passage hole, said cooling water jetting nozzles having tips, wherein the tips of the cooling water jetting nozzles are disposed farther from the hot rolled steel strip than the surface, opposing the hot rolled steel strip, of the protective member, and the distance from the tips of the cooling water jetting nozzles to the surface of the steel strip is determined to secure an impinging velocity in view of the flow of the cooling water after cooling.