A piercing machine includes a plurality of skewed rolls, a plug, a mandrel bar and an outer surface cooling mechanism. The outer surface cooling mechanism is disposed around the mandrel bar at a position that is rearward of the plug, and with respect to an outer surface of a hollow shell advancing through a cooling zone which has a specific length in an axial direction of the mandrel bar and which is located rearward of the plug, as seen from an advancing direction of the hollow shell, the outer surface cooling mechanism ejects a cooling fluid toward an upper part of the outer surface, a lower part of the outer surface, a left part of the outer surface and a right part of the outer surface of the hollow shell to cool the hollow shell inside the cooling zone.

A hot and cold composite formed square and rectangular steel tube and a production method for the same are provided. The radius of an outer corner of the square and rectangular steel tube meets the following conditions: when t is less than or equal to 6 mm, R is greater than 0 and less than 2.0 t; when t is greater than 6 mm and less than or equal to 10 mm, R is greater than 0 and less than 2.5 t; when t is greater than 10 mm, R is greater than 0 and less than 3.0 t, wherein t is the wall thickness of a straight tube part of the square and rectangular steel tube; R is the radius of each of the outer corners of the four corners of the square and rectangular steel tube; and the wall thickness of each corner of the square and rectangular steel tube is between 1.0 t and 1.8 t.

A system for cooling rolling mill material is provided that includes a conveyor system that receives rolling mill material and passes the rolling mill material through one or more cooling regions. A cooling structure that operates uniformly across the central and edge regions of the conveyor system. The cooling structure uses a first jet of air for cooling the central portion of the rolling mill material. A nozzle deck is positioned on the edge regions of the conveyor system produces a second of jet of air for cooling the edge portions of the rolling mill. The nozzle deck includes one or more adjustable nozzle structures for controlling the air flow produced by the second jet of air by varying the size of their air passage regions.

An apparatus for cooling a steel sheet includes: an apparatus body provided spaced apart from a steel sheet in the conveying path of the steel sheet; and a cooling unit provided in the apparatus body to supply a cooling fluid. The apparatus body includes: a first edge body that faces a first edge portion extending a certain distance from one side end of the steel sheet toward the center of the steel sheet; and a second edge body that faces a second edge portion extending a certain distance from the other side end of the steel sheet toward the center of the steel sheet. The first and second edge bodies may have stepped cross-sections in a direction perpendicular to the conveying direction of the steel sheet.

A method of producing a steel material, wherein when a cooling apparatus having a plurality of cooling sections disposed side by side in a longitudinal direction of a steel material cools the steel material hot worked or cooled/reheated, the steel material is conveyed at a conveyance distance L.sub.o (m) satisfying Equation (1), in one direction along with the longitudinal direction of the steel material, in the cooling apparatus, wherein L.sub.o is defined as conveyance distance (m) of steel material, m is a natural number, and L.sub.h is defined as length (m) of cooling sections in longitudinal direction of steel material:

(m−0.20)×L.sub.h≤L.sub.o(m+0.20)×L.sub.h  (1).

A hot and cold composite formed square and rectangular steel tube and a production method for the same are provided. The radius of an outer corner of the square and rectangular steel tube meets the following conditions: when t is less than or equal to 6 mm, R is greater than 0 and less than 2.0 t; when t is greater than 6 mm and less than or equal to 10 mm, R is greater than 0 and less than 2.5 t; when t is greater than 10 mm, R is greater than 0 and less than 3.0 t, wherein t is the wall thickness of a straight tube part of the square and rectangular steel tube; R is the radius of each of the outer corners of the four corners of the square and rectangular steel tube; and the wall thickness of each corner of the square and rectangular steel tube is between 1.0 t and 1.8 t.

A piercing machine includes a plurality of skewed rolls, a plug, a mandrel bar and an outer surface cooling mechanism. The outer surface cooling mechanism is disposed around the mandrel bar at a position that is rearward of the plug, and with respect to an outer surface of a hollow shell advancing through a cooling zone which has a specific length in an axial direction of the mandrel bar and which is located rearward of the plug, as seen from an advancing direction of the hollow shell, the outer surface cooling mechanism ejects a cooling fluid toward an upper part of the outer surface, a lower part of the outer surface, a left part of the outer surface and a right part of the outer surface of the hollow shell to cool the hollow shell inside the cooling zone.

A system for cooling rolling mill material is provided that includes a conveyor system that receives rolling mill material and passes the rolling mill material through one or more cooling regions. A cooling structure that operates uniformly across the central and edge regions of the conveyor system. The cooling structure uses a first jet of air for cooling the central portion of the rolling mill material. A nozzle deck is positioned on the edge regions of the conveyor system produces a second of jet of air for cooling the edge portions of the rolling mill. The nozzle deck includes one or more adjustable nozzle structures for controlling the air flow produced by the second jet of air by varying the size of their air passage regions.

A system for cooling rolling mill material is provided that includes a conveyor system that receives rolling mill material and passes the rolling mill material through one or more cooling regions. A cooling structure that operates uniformly across the central and edge regions of the conveyor system. The cooling structure uses a first jet of air for cooling the central portion of the rolling mill material. A nozzle deck is positioned on the edge regions of the conveyor system produces a second of jet of air for cooling the edge portions of the rolling mill. The nozzle deck includes one or more adjustable nozzle structures for controlling the air flow produced by the second jet of air by varying the size of their air passage regions.

The present application relates to a heat treatment unit, in particular a cooling hood, including a chamber with an inlet opening through which a gaseous cooling medium can be fed to the chamber, and a slot-shaped outlet opening through which the gaseous cooling medium can be discharged faster. The chamber includes a central chamber segment and a first and a second outer chamber segment extending from the central chamber segment, and both outer chamber segments have a cross-section tapering proportionally towards their distal ends, and a device for the heat treatment of hot-rolled long steel products.