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 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 cooling apparatus for cooling a metallic material has at least one cooling beam with a plurality of coolant application elements for applying the metallic material with a coolant. Each coolant application element has an outlet opening with a cross-sectional area for discharging the coolant. In order to be able to adapt such known cooling apparatuses even more precisely to different temperature distributions across the width of the metallic material to be cooled the density of the cross-sectional areas of the outlet openings of the coolant application elements in the width direction y of the cooling beam be distributed or dimensioned according to the amount of the slope of the distribution of the temperature T(y) of the metallic material across its width before the inlet under the cooling beam.

A cooling apparatus for cooling a metallic material has at least one cooling beam with a plurality of coolant application elements for applying the metallic material with a coolant. Each coolant application element has an outlet opening with a cross-sectional area for discharging the coolant. In order to be able to adapt such known cooling apparatuses even more precisely to different temperature distributions across the width of the metallic material to be cooled the density of the cross-sectional areas of the outlet openings of the coolant application elements in the width direction y of the cooling beam be distributed or dimensioned according to the amount of the slope of the distribution of the temperature T(y) of the metallic material across its width before the inlet under the cooling beam.

A rolling mill control system and method includes use of sensors located between rolling mill stands to directly measure metal sheet or plate flatness, thickness profile, position, and the camber of the rolls in the mill. A feedback loop control system adjusts or adapts rolling mill control mechanisms to control the rolling process.

A rolling mill control system and method includes use of sensors located between rolling mill stands to directly measure metal sheet or plate flatness, thickness profile, position, and the camber of the rolls in the mill. A feedback loop control system adjusts or adapts rolling mill control mechanisms to control the rolling process.

A production equipment line for a hot-rolled steel strip comprises a rough rolling mill group comprised of plural rough rolling mills for hot rolling a material which is heated up to a predetermined temperature to a finish rolling start sheet thickness and a finish rolling mill group comprised of plural finish rolling mills for controlled-rolling the material to a final sheet thickness, wherein at least one of the plural rough rolling mills is a reversible rolling mill. The production equipment line for a hot-rolled steel strip is provided with a slow cooling apparatus for slowly cooling the material at a water volume density of less than 1000 L/min.Math.m.sup.2 and a rapid cooling apparatus which is arranged next to the slow cooling apparatus and rapidly cools the material after the slow-cooling at a water volume density of not less than 1000 L/min.Math.m.sup.2.

A production equipment line for a hot-rolled steel strip comprises a rough rolling mill group comprised of plural rough rolling mills for hot rolling a material which is heated up to a predetermined temperature to a finish rolling start sheet thickness and a finish rolling mill group comprised of plural finish rolling mills for controlled-rolling the material to a final sheet thickness, wherein at least one of the plural rough rolling mills is a reversible rolling mill. The production equipment line for a hot-rolled steel strip is provided with a slow cooling apparatus for slowly cooling the material at a water volume density of less than 1000 L/min.Math.m.sup.2 and a rapid cooling apparatus which is arranged next to the slow cooling apparatus and rapidly cools the material after the slow-cooling at a water volume density of not less than 1000 L/min.Math.m.sup.2.

A straightening system is provided to perform straightening in conformity with a shape pattern of a the material. The straightening system includes a cooling device configured to spray a cooling fluid in a predetermined pattern with respect to a plurality of regions of the material, divided in a width direction, to cool the material that is heated in a heating furnace and then passes through a rolling mill. The straightening system also includes a straightening device configured to straighten the material passed through the cooling device. The straightening system further includes a flatness measuring system configured to measure flatness of the material passed through the cooling device and a controller configured to receive data of the flatness of the material from the flatness measuring system and to control the cooling device in response to the data to enhance the flatness of the material.

A straightening system is provided to perform straightening in conformity with a shape pattern of a the material. The straightening system includes a cooling device configured to spray a cooling fluid in a predetermined pattern with respect to a plurality of regions of the material, divided in a width direction, to cool the material that is heated in a heating furnace and then passes through a rolling mill. The straightening system also includes a straightening device configured to straighten the material passed through the cooling device. The straightening system further includes a flatness measuring system configured to measure flatness of the material passed through the cooling device and a controller configured to receive data of the flatness of the material from the flatness measuring system and to control the cooling device in response to the data to enhance the flatness of the material.