New DC electromagnetic wiping system for hot‐dip coating

Abstract

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.

Citation

Dumont, M., Ernst, R., Fautrelle, Y., Grenier, B., Hardy, J.J. and Anderhuber, M. (2011), "New DC electromagnetic wiping system for hot‐dip coating", COMPEL - The international journal for computation and mathematics in electrical and electronic engineering, Vol. 30 No. 5, pp. 1663-1671. https://doi.org/10.1108/03321641111152810