Continuous annealing device and continuous hot-dip galvanising device for steel strip

A steel strip continuous annealing device that has a vertical annealing furnace in which a heating zone, a soaking zone, and a cooling zone are arranged in the stated order, and anneals a steel strip passing through the zones in the order while being conveyed in a vertical direction in the vertical annealing furnace, comprising:

• a first throat extending in a lateral direction and provided between the heating zone and the soaking zone;
• a second throat extending in the lateral direction and provided between the soaking zone and the cooling zone;
• an atmosphere separation portion including at least one of a partition plate, a seal roll, a damper, and a gas separation device forming an air curtain;
• a gas delivery port for introducing gas into the vertical annealing furnace;
• and
• a gas discharge port for discharging gas from the vertical annealing furnace,
• wherein the heating zone, the soaking zone, and the cooling zone communicate through the first throat and the second throat,
• the atmosphere separation portion is provided in each of the first throat and the second throat to separate an atmosphere in the heating zone from an atmosphere in the soaking zone and to separate an atmosphere in the soaking zone from an atmosphere in the cooling zone,
• the gas delivery port and the gas discharge port are provided in each of the heating zone, the soaking zone, and the cooling zone,
• one of the gas delivery port and the gas discharge port is positioned in an upper part and the other one of the gas delivery port and the gas discharge port is positioned in a lower part in each of the zones,
• the steel strip continuous annealing device is configured to be switchable between a first mode and a second mode,
• in the first mode the gas delivery port and the gas discharge port provided in each of the heating zone, the soaking zone, and the cooling zone are opened so as to switch the atmosphere in each of the zones, and
• in the second mode the gas delivery port provided in each of the zones is opened and the gas discharge port in each of the zones is closed for operation, and wherein
• the steel strip continuous annealing device is switched to the first mode when a dew point inside the vertical annealing furnace reaches a threshold temperature, and to the second mode when the dew point inside the vertical annealing furnace is below the threshold temperature.