Abstract

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VISUALISATION OF DROSS MOVEMENT DURING GALVANIZING OF STEEL

B.N.ROY, CHANDRA KAMAL GUPTA


Large amount of waste material is observed near the surface of the bath in the form of Dross during the study of continuous galvanizing line. This waste material,Dross, is the by-product of the galvanizing process which consists of loose iron particles (iron salts) that have reacted with zinc in the galvanizing kettle. Dross is formed due to reaction between aluminium, iron and zinc in the zinc bath. This Dross causes defect on the coated product which results in reduced quality of the product. No efficient method, however, has been developed till date. For the development of an efficient method of removing the dross, it is important to elucidate the motions of the top and bottom dross in a real hot dip plating bath. The combined phenomena of aluminium, strip temperature and iron dissolution were simulated in order to predict and to better understand the generation and movement of inter metallic dross particles within certain regions of a typical galvanizing bath. Temperature and aluminium concentration can be correlated with the solubility limits of aluminium and iron in the zinc bath to determine the amount of precipitated aluminium in the form of Fe2Al5Znxdross. A numerical analysis was done to simulate the velocity and temperature fields in an industrial galvanizing bath for the continuous coating of steel strip. The information worked out in this paper is of major significance in the prediction of the formation of dross particles, which can cause defects on the coated product. Mathematical model is developed and parameters are optimized with the help of simulation technique. Also the dross formation is reduced and the process parameters are improved. The simulations allow visualization of regions of varying velocity and temperature fields and clearly illustrate the mixed and stagnant zones for different operating conditions