This work has analyzed wave instabilities on steel strip in coating process. The aim of this study is to compare the results obtained by a small perturbations method with an experimental approach. Linear and tow dimensional Instabilities equations have been derived by small perturbations method and solved through numerical simulations. The investigation emphasizes the effect of controlling wiping parameters, the pressure gradient and tributions induced by the jet on the molten layer thickness. The local tability analysis has been shown that disturbances grow strongly in the rea close to the gas knives, before passing them. After passing the gas knives, the pressure gradient and surface shear stress stabilizes the flow. Far from the gas knives, where stabilizer effects are negligible, the flow is weakly unstable caused by gravity. Based on this theory, growth rate, wave speed, wave number and multiple waves’ length of instabilities have been studied. For an experimental approach, longest wave length has been calculated about 39 cm with Fast Fourier Transform method on certain galvanized strip thickness. This wave length has been situated in week instability region. Good agreement has been found between numerical solution and experimental work. Numerical results show that effect of edge build up instabilities lead to increase instability growth rate and amplification function on plate width. These instabilities are produced with jets on plate edges. Comparison between experimental results indicates that molten layer thickness increasing leads to decreasing in dominant wave length. In according to numerical results, instability amplification function increasing happened in smaller wave length. In conclusion, when coating thickness increases, wave instabilities will be larger.
