Apparatus for forming nitrogen cloud to produce hot-dip coated steel sheet with excelent surface quality and method for producing zinc-aluminium hot-dip coate

Provided is an apparatus, which is provided between the surface of a plating bath for hot-dip plating and air knife equipment for controlling the thickness of plating metal attached to the surface of a strip, so as to form a nitrogen cloud (curtain) along the periphery of the strip rising from the plating bath. The apparatus of the present invention: has a semicylinder-shaped body spaced at a predetermined distance from the surface of the plating bath and of which the bottom surface is opened so as to face the surface of the plating bath; has a slit, through which the strip passes, formed on the upper surface of the body; has a lower gas exhaust part formed along the periphery of the lower end portion of the body, and spraying nitrogen gas toward the surface of the plating bath so as to block external air; includes inner gas exhaust parts arranged at both sides of the strip so as to face each other, while traversing the bottom surface of the body in the width direction of the strip, so as to spray the nitrogen gas toward the strip; and has a plurality of spray nozzles, formed at the inner side of the body, for spraying the nitrogen gas toward the strip.