Gas wiping nozzle and methods for manufacturing hot-dip metal-coated steel strip and gas wiping nozzle

A gas wiping nozzle that is configured to blow gas to a steel strip pulled up from a molten metal bath to adjust a coating weight of a molten metal on a surface of the steel strip, wherein:

• at least a surface of the gas wiping nozzle is made of a ceramic, and an arithmetic mean roughness Ra and a peak count PPI, which are measures of surface roughness, of the gas wiping nozzle satisfy Formula (1)
• PPI
• >
• c
• ⁢
• 1
• ×
• Ra
• +
• c
• ⁢
• 2
• (
• 1
• )
• PPI:
• peak count (number of peaks per inch)
• Ra:
• arithmetic mean roughness [μm]
• c1 and c2:
• determined constants for each ceramic used in a surface of the gas wiping nozzle, a surface roughness of the gas wiping nozzle satisfies Formula (2)
• cos
• ⁢
• θ
• w
• =
• r
• *
• cos
• ⁢
• θ
• e
• (
• 2
• )
• θw:
• apparent contact angle on a rough surface
• θe:
• contact angle of a liquid droplet on a smooth surface
• r:
• area ratio of the rough surface to the smooth surface (r≥1). the ceramic is SiAlON or alumina. when the ceramic is SiAlON, c1 is-35 and c2 is 100, and when the ceramic is alumina, c1 is-28 and c2 is 170.