Simulation of flow in a continuous galvanizing bath: Part I. Thermal effects of ingot addition
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6/1/04
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Simulation of Flow in a Continuous Galvanizing Bath: Part I. Thermal Effects of Ingot Addition F. AJERSCH, F. ILINCA, and J.-F. HÉTU A numerical analysis has been developed to simulate the velocity and temperature fields in an industrial galvanizing bath for the continuous coating of steel strip. Operating variables such as ingot addition, line speed, and inductor mixing were evaluated in order to determine their effect on the velocity and temperature distribution in the bath. The simulations were carried out using highperformance computational fluid-dynamics software developed at the Industrial Materials Institute of the National Research Council Canada (IMI-NRC) in solving the incompressible Navier–Stokes equations for steady-state and transient turbulent flow using the k- model. Cases with and without temperature-dependent density conditions were considered. It was found that the strip velocity does not alter the global flow pattern but modifies the velocities in the snout, near the strip, and near the sink and guide rolls. At a low inductor capacity, the effect of induced mixing is small but is considerably increased at the maximum inductor capacities used during ingot-melting periods. When considering the thermal effects, the flow is affected by variations in density especially near the inductors and the ingot, while little effect is observed near the sheet-and-roller region. Thermal effects are also amplified when the inductor operates at high capacity during ingot melting. The simulations allow visualization of regions of varying velocity and temperature fields and clearly illustrate the mixed and stagnant zones for different operating conditions.
I. INTRODUCTION
THE demand for coated steel products continues to expand beyond the traditional applications for auto bodies, household appliances, and structural components. Residential and industrial buildings are also finding galvanized construction materials to be easy to use and cost-effective. However, the most important product in market value is the hot-dipped galvanized or galvannealed sheet destined for auto body manufacture. Corrosion resistance, ready-to-paint surface quality, weldability, and formability are some of the key characteristics required. Recent developments include stronger and thinner steels (interstitial free, dual phase, and Transformation Induced Plasticity (TRIP)) with thinner coatings. The modern hot-dip galvanizing operation is a complex metallurgical process where steel strips of various widths and thicknesses are continuously coated by rapid immersion in a zinc alloy bath operating at temperatures normally between 450 °C and 480 °C. Cold-rolled strip is first degreased, cleaned, and then heated in a reducing atmosphere before being introduced into a liquid zinc bath at line speeds from 0.5 to 2.0 m/s. A main sink roll guides the strip to a depth of about 1 meter below the bath surface before exiting between two guide-stabilizer rolls. The aluminum contents in the bath vary generally from 0.10 to 0.30 w
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