Amount of Aluminium Addition Required in Continuous Galvanizing Baths

Abstract

As the aluminium in galvanizing bath is consumed through the reaction of dross and the alloy-layer formation, it is usually difficult to keep the aluminium content in the bath at a predetermined value. On the basis of our recent results, the aluminium content in tailored zinc required to keep the aluminium content in the bath at a desired level has been calculated.
The aluminium content in tailored zinc (y_T) can be expreessd as the sum of the aluminium concentration in liquid zinc (y) and the amount of aluminium consumed, in concentration, through dross and alloy- layer formations:
y_T=y+(aΔW₁+bΔW₂)·200/w
where w is coating weight of sheet, and ΔW₁ and ΔW₂ are iron dissolved and iron in alloy layer, respectively.
Under conditions of sheet temperature of 470°C, line speed of 100m/min and coating weight of 305g/m²-sheet, the aluminium content in tailored zinc is estimated to be 0.31% to maintain the bath at 0.14% Al. When the coating weight is in the range of 305±60g/m², to increase the aluminium content in the bath by 0.01% the aluminium content in tailored zinc should be increased by 0.05-0.08% under the operational condition of 0.10-014% Al in the bath.