Nippon Steel Corporation

Tadashige Namba

Norichika Nagira

Hiroshi Ikegami

Kozaburo Ichida

Katsuhiko Yui

Yasuo Misawa

Takeo Dazai

Yoshio Saitoh

Mineo Murata

The present invention relates to a method for cooling a steel strip in a continuous-annealing furnace. Conventionally, the steel strip is cooled by a water medium and, thus, oxidation is inevitable. Recently developed roll cooling methods can prevent oxidation but are disadvantageous in that the steel strip (1) is nonuniformly cooled as seen in its short width direction. The present invention attains uniform cooling by means of feedback-feedforward control, in which the blowing width of the gas-jet cooler (21, 53) is controlled by detecting the sheet temperature distribution with thermometers (24, 55, 60).

Method for cooling a steel strip in a continuous annealing furnace

In a cooling zone of a continuous annealing line engineered to continuously process longitudinally travelling steel strip, the strip is first slowly cooled to a desired temperature at a rate of not higher than 20.degree. C./sec. by means of a jet stream of cooling gas ejected against the surface of the strip and subsequently quenched to a desired temperature at a rate of not lower than 70.degree. C./sec. Thinner strip is quenched by high-speed gas-jet cooling that is effected by ejecting a jet stream of cooling gas against its surface, while heavier strip is quenched by bringing it into contact with the perimeter of cooling rolls cooled by a coolant. Namely, quenching is achieved either by high-speed gas-jet cooling or roll cooling depending on the thickness of the strip being processed. A cooling apparatus for implementing the cooling method described above comprises a high-speed gas-jet cooling zone where the strip is cooled by means of a jet stream of cooling gas ejected against its surface and a roll cooling zone following the high-speed gas-jet cooling zone where the strip is brought into direct contact with a plurality of cooling rolls. Means to exert longitudinal tension on the strip travelling through the roll cooling zone are provided at the entry and exit ends thereof.

Method and apparatus for cooling steel strip

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Kitakyushu, Japan

Tadashige Namba