Performance of Flow and Heat Transfer in a Hot-Dip Round Coreless Galvanizing Bath
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nized (HDG) steel is widely used to manufacture automobile and high-grade household appliances because of its sufficient corrosion resistance, weldability, and formability. In HDG process, steel strips of various widths and thicknesses are introduced into a liquid zinc bath at line speeds ranging from 1.0 to 3.0 m/s. The steel strips are continuously coated by rapid immersion in a zinc alloy bath at around 733 K (460 °C).[1] Forming the inhibition layer is a rapid process (0.10 to 0.25 seconds) and requires a uniform supply of Al at the strip entry within the snout,[2] and fluid dynamics affects the thickness of the inhibition layer.[3] The operating parameters, such as strip speed, strip and bath temperature and steel strip dissolution bath configuration, placement, as well as bath chemistry, can influence the characteristics of the fields of flow, molten zinc temperature in the bath[4] and, then, can influence the final coating thickness, the snaky coating,[5] and dross pick-up on steel strip.[6] Hence, the flow field and turbulence in the bath are important in QIANG YUE, CHENGBO ZHANG, LI ZHOU, HUI KONG, and JIA WANG are with the School of Metallurgy Engineering, Anhui University of Technology, Ma’anshan, 243002, China. Contact e-mail: [email protected] YONG XU is with the Cold Rolling Plant, Shanghai Meishan Iron & Steel Co., Ltd, Nanjing, 210039, China. Manuscript submitted April 3, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
analyzing the quality of inhibition layer. The effect of various operating parameters must be quantified to elucidate the system and optimize process control parameters. The results could be used to determine the mechanism underlying the association of molten zinc flow patterns and temperature fluctuations in the bath with dross formation and strip surface quality. Molten zinc flow and heat transfer in a HDG pot primarily affect the success of steel sheet production and minimization of dross formation in the HDG process.[7] Physical and numerical models are used to explore flow inside the bath, simulate the process, and optimize process parameters. Molten zinc flow in HDG bath can be investigated using cold models at a reduced scale. Lo[8] modeled zinc flow in a continuous galvanizing bath through a water-tank simulation. The flow pattern was visualized by a laser sheet flow visualization technique in cold models. The velocity components are measured by laser Doppler velocimetry[9] or particle image velocimetry.[10,11] Kurobe[12] investigated the dispersion of melted ingots in a continuous HDG plating bath by using a transparent cold model vessel at a reduced scale of one-tenth. CaCO3 particles, with a mean diameter of 0.001 m, and 5.0 mass pct KCl aqueous solution were used as tracers in eye inspection and analysis using an electrical conductivity sensor and a laser beam sensor. Li investigated the distribution and accumulations of bottom dross in a HDG bath by water model experiments.[13] However, water modeling simulation does not
consider inductors, but uses a motor to drive three different steel strip s
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