Study on Gas Wiping Mechanism for Continuous Galvanizing Line

Abstract

The relations between coating weight and control factors are investigated quantitatively in order to clear the mechanism of the gas wiping process. A fundamental equation model proposed from an analysis of the results is as follows :
W=K₀P^-K₁D^K₂V^K₃ exp(K₄/V)
where,
W : coating weight (g/m²·both sides)
P: gas pressure at nozzle header (kg/cm²·G)
D : distance between nozzles (mm)
V : line speed (m/min)
Although coefficients vary with the working conditions, this equation gives coating weight in the range of 7% standard deviation of error for our commercial line (K₀=0.45, K₁=0.63, K₂=0.88, K₃=0.50, K₄=8.3).
Important factors for efficiency are the gas itself and the slit gap of nozzle. For minimization of the friction loss at nozzle, the selection of low viscous gas and relative large slit gap are effective.