New DC electromagnetic wiping system for hot-dip coating

Purpose - The purpose of this paper is to study an electromagnetic (EM) wiping process based on the EM brake (EMB) principle for hot-dip galvanizing lines. This EMB system must act complementary to a classical air wiping system for higher drag out velocities for which the only air wiping system is no more sufficient.Design methodology approach - At first, the basic phenomena of the braking of a liquid driven by an upcoming strip thanks to a DC magnetic field are analyzed with a simplified analytical model. This model shows the influence of different relevant parameters such as the magnetic field intensity or the strip upcoming velocity. Then, a 2D numeric finite elements model coupling the EMs, the fluid mechanics and a deformed mesh technique is set up and shows clearly the braking effect on the liquid zinc. At last, some first results of a 3D extension of the former 2D model are shown, mainly concerning the end effects on the edge of the strip. This EM wipe effect has been experimentally demonstrated in a prototype hot-dip galvanizing line.Findings - The paper shows the possibility of controlling the thickness of a liquid zinc layer thanks to a DC magnetic field produced by high-intensity permanent magnets.Originality value - Such an innovative way of wiping liquid zinc thanks to a DC magnetic field is able to wipe liquid zinc excess and control the liquid layer thickness with a low electric losses level. This is a major advantage compared with other known wiping techniques such as high-frequency pin-shaped inductors which may imply an overheating of the liquid zinc.