Patent ID: 8529998

Claim:
A method for manufacturing a molten metal plated steel strip, comprising: jetting a gas from a gas wiping nozzle onto a surface of a steel strip continuously drawn up from a molten metal plating bath to control an amount of plating on the surface of the steel strip; wherein the gas wiping nozzle comprises a primary nozzle portion and at least one secondary nozzle portion provided at least one of above and below the primary nozzle portion; wherein the secondary nozzle portion jets the gas in a direction tilted from a direction in which the primary nozzle portion jets the gas so that a gas jet from the secondary nozzle portion meets a gas jet from the primary nozzle portion; wherein the secondary nozzle portion jets the gas at a lower flow rate than the primary nozzle portion; wherein the gas wiping nozzle is positioned with respect to the steel strip such that a lower surface of a tip of the gas wiping nozzle forms an angle of 60° to 72° with respect to the steel strip; wherein the tip of the gas wiping nozzle has a longitudinal section having an outer angle of 60° or less; wherein the primary nozzle portion includes a first nozzle member, and the secondary nozzle portion is defined by the first nozzle member and a second nozzle member disposed outside the first nozzle member, and wherein an end of the second nozzle member defining a gas jetting port of the secondary nozzle portion has a thickness of 2 mm or less; wherein a sum of a thickness of an end of the first nozzle member defining a gas jetting port of the primary nozzle portion, a slit width of the gas jetting port of the secondary nozzle portion, and a thickness of the end of a second nozzle member defining the gas jetting port of the secondary nozzle portion is 4 mm or less at at least one of the upper side and the lower side of the gas wiping nozzle; wherein the gas jetting port of the secondary nozzle portion is displaced in a direction extending away from the steel strip by at least 20 mm and at most 100 mm from the gas jetting port of the primary nozzle portion; and wherein the secondary nozzle portion jets the gas so that a flow rate of the gas jet from the secondary nozzle portion is 20 m/s to 150 m/s at a confluence with the gas jet from the primary nozzle portion.