連続溶融めっきのガスワイピング時におけるエッジスプラッシュの発生機構およびその抑制法

抄録

An experimental investigation was performed on splashing from thestrip edge in the gas wiping process for continuous hot-dip coating. Critical linespeeds and critical nozzle pressures for the beginning of splashing are measured byuse of a cold model under different gas wiping conditions. Though splashingbecomes violent with increase in the line speed and the nozzle pressure, theintroduction of offset and/or downward wiping reduces splashing. The critical linespeed at the same nozzle pressure increases with nozzle-strip distance and decreaseswith nozzle slit gap, so that placing the narrow slit nozzle close to the strip andlow pressure wiping is effective to prevent splashing. The mechanism of splashingfrom the strip edge is clarified by the force balance of lift caused by gas flow andsurface tension acting on a convex portion of the liquid film surface. A linearcorrelation on the log-log scale was found between critical Weber number for thebeginning of splashing and the product of liquid film thickness ratio and flow downliquid film Reynolds number.