Jet flow characteristics of 3-slot nozzle at gas wiping process in continuous galvanizing line

Abstract

This paper presents a study of the gas wiping process, which is used in coating processes to control the final coating weight applied on a substrate. The wiping process is one of the factors which limit the maximum line speed of continuous galvanizing lines (CGL). A multi-slot type wiping nozzle was proposed for improving coating weight controllability, and was investigated by numerical simulation in recent years. Here, the impinging jet characteristics of a 3-slot nozzle are investigated by experimental and numerical analysis, focusing on the jets mixing process and the impinging pressure distribution. The gas wiping capability is tested in wiping model experiments with a molten paraffin coating. It is confirmed that the impinging pressure distribution of a 3-slot nozzle with a lower auxiliary jet velocity is sharper than that of a single-slot nozzle, and this leads to a coating weight decrease. When the jet velocity of the auxiliary slots approaches that of the main slot jet, the width of the impinging pressure distribution spreads and the coating weight increases. The turbulent kinetic energy of flow field is changed by auxiliary jets velocity, and the energy distribution decide the width of mixed jet flow.