Flow field analysis inside a molten Zn pot of the continuous hot-dip galvanizing process

Abstract

The flow field inside a molten zinc pot of the continuous hot-dip galvanizing process of steel strips was investigated experimentally. A 1/5-scale transparent water model with induction heaters, scrapers, and baffles was used in this study. Instantaneous velocity fields were measured using a single-frame PIV velocity field measurement technique with varying the strip velocity Vs, flow rate 0 of the induction heater, scraper location, and baffle type, The general flow pattern inside the strip region is hardly influenced by the strip speed V., flow rate Q, and the scraper location around the stabilizing roll. When the induction heater is not operated, a pair of vortices is formed in the inner part of the strip: a clockwise rotating flow at the entrance region and a counter-clockwise rotating flow at the exit region. In the exit region outside of the strip, the flow detached from the stabilizing roll divides into two parts: a counter-clockwise rotating flow in the upper region and a clockwise rotating flow in the lower region. For the cases of no scrapper and scrapper, detached from the stabilizing roll, the flow separates from the moving strip and ascends to the free surface. As the flow rate of the induction heater increases, the ascending flow is weakened and the counter-clockwise rotating flow in the upper area of the outside region becomes tranquil. This indicates that the flow in the upper area of the exit region is greatly influenced by the operation of the induction heater. When a scraper is attached onto the stabilizing roll, the separated flow from the strip is guided downward and the up-rising flow around the stabilizing roll becomes slow and tranquil. By attaching baffles near the moving strip in addition to the stabilizing rolls, the flow entrainment into the corner region between the strip and the stabilizing roll is greatly reduced. These flow control devices should be helpful in reducing top drosses in the zinc plating process.