Abstract
This paper presents a new computational framework to investigate the driving force for the formation of intermetallic dross particles in the zinc bath and dross build-up on the bath hardware. This is a major problem in continuous hot-dip galvanizing lines. The Computational Fluid Dynamics (CFD) model calculates the turbulent thermo-chemical flow conditions within the liquid melt. A detailed modeling of the steel strip–liquid interface enhances this approach, by means of a conjugated heat transfer calculation and a spatially resolved, temperature- and concentration-dependent iron dissolution and aluminum uptake. The heart of the computational framework is a thermodynamic model, which assesses the driving force for the formation or dissolution of dross particles in the bath and dross build-up on stationary and rotating equipment. The simulation results are validated with temperature and species depth profile measurements. The applicability of the CFD model is shown by investigating the locally resolved aluminum uptake and iron dissolution at the steel-strip surface, and the multi-physics conditions in the region near the roll. The novel approach of evaluating the thermodynamic driving force enables the assessment of the formation of dross build-up at the roll surface.
Highlights
HOT-DIP galvanizing process is the main metallurgical process for continuous zinc coating of a steel strip, wherein the steel is immersed into a molten zinc alloy operated at temperatures in the range of 450 °C to 480 °C
This section illustrates the capability of the proposed model. It is subdivided into two parts: Firstly, the results of the spatially resolved iron dissolution and aluminum uptake at the steel-strip interface are presented, and secondly, the thermodynamic assessment of the driving force for dross formation in the bath and the dross build-up formation on the bath hardware are shown
When the immersing steel strip has a different temperature than the zinc bath, two effects can be observed
Summary
HOT-DIP galvanizing process is the main metallurgical process for continuous zinc coating of a steel strip, wherein the steel is immersed into a molten zinc alloy operated at temperatures in the range of 450 °C to 480 °C. State-of-the-art studies have tried with varying complexity (and focus) to simulate the concentration and temperature distribution in the bath and near the steel strip: Model-based 1D approaches have been applied to assess the temperature distribution in the steel strip, the iron dissolution at the solid-liquid interface, as well as the aluminum uptake in the coating layer.[10,11,12,13] It was shown that the local temperature and concentration gradients significantly influence the dissolution of iron and the uptake of aluminum These approaches are fast and robust, but lack a detailed resolution of the temperature and species distribution within the entire zinc bath. This enables the different operating conditions and their effect on the dross build-up to be evaluated
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