12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

The surface quality of galvanized steel sheets is considerably influenced by intermetallic dross particles, which inevitably form during operation. η-phase Fe2Al5 top dross and δ-phase FeZn7 bottom dross particles have been reported to be entrapped into the coating causing functional and optical defects. Moreover, particles are frequently mentioned to adhere to the stationary and the moving bath equipment. Particularly, dross particles which are adhered to sink and stabilizer rolls can cause imprints on the surface of the steel strip. Furthermore, the cleaning of the rolls is related to down times of the mill. An efficient management of dross particle dynamics is thus a key criterion for running galvanizing mills.
CFD-DPM models give a comprehensive insight into the dynamics of dross particles and their tendency to come in contact with relevant surfaces. Buoyancy and settling effects of dross particles, which lead to the accumulation of top and bottom dross in regions of the galvanizing bath are predicted with the model. A special focus is put on a sub-model investigation of the surrounding of the sink roll. Factors of influence on the dross dynamics and accumulation such as particle type, particle size, wall roughness and line speed are elucidated with the DPM model. In addition, a new approach in modelling dross based on scalar transport equations is presented, which enables the inclusion of the thermodynamics and the reaction kinetics of dross formation.