Patent ID: 9702020
Date: 2017-07-11
CPC Classifications: C21D,C23C,F27B,F27D

Claim:
1. A continuous annealing furnace for a steel strip comprising a heating zone, a soaking zone and a cooling zone disposed in this order and configured to transport the steel strip in upward and/or downward directions, a joint connecting the soaking zone and the cooling zone being disposed at an upper portion of the furnace, the heating zone and the soaking zone having no partition wall therebetween, the furnace being a vertical annealing furnace and being configured such that an atmosphere gas is supplied from outside the furnace into the furnace, the gas in the furnace is discharged through a steel strip inlet at a lower portion of the heating zone while part of the gas in the furnace is suctioned and introduced into a refiner equipped with an oxygen removal device and a dehumidifier to lower the dew point by the removal of oxygen and water in the gas, the refiner being disposed outside the furnace, and the gas with the lowered dew point is returned into the furnace, the furnace having gas suction openings disposed in a lower portion of the joint between the soaking zone and the cooling zone and at least one of in the heating zone and the soaking zone, the heating zone being free from any gas suction openings in a region extending 6 m in a vertical direction and 3 m in a furnace length direction both from the steel strip inlet at a lower portion of the heating zone, the furnace having gas ejection openings disposed in a region in the joint between the soaking zone and the cooling zone, the region being located above a pass line in the joint, and in a region in the heating zone, the region being located above a position 2 m below the center of upper hearth rolls in the vertical direction.