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Title: Chemical and physical constitution of the bath during galvannealing to galvanising transition
Author: Jestin, N.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 2003
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The ZODIAC (Zinc and Other Developments in Alloy Coatings) line is targeted mainly at the automotive sector. The continuous hot dip galvanising line is currently using a single pot practice for the production of both galvannealed (GA) and galvanised (GI) coatings. During the GA campaign, as iron dissolves from the strip, the presence of an increasing quantity of iron in the molten bath results eventually in the precipitation of bottom dross particles. These particles may become trapped within the coating and cause pimple defects during the forming operation. The accumulation of bottom dross particles in the galvanising bath affects the operating efficiency of the production line. To bring these bottom dross particles to the bath surface, the bath aluminium level is increased. This allows the transformation of bottom dross into top dross particles and the production of GI coatings. Top dross particles rise to the bath surface where they are removed, by the operators, in the skimmings. Three major trials have been conducted on the ZODIAC line to investigate the chemical and physical constitution of the galvanising spelter during the GA to GI transition. The results reveal interesting information on the constitution of the galvanising spelter during the transition, particularly with respect to bath chemistry (total and effective Al as well as total and soluble Fe levels), dross characterisation of the bath (types and sizes of particles), skimmings characterisation (Al and Fe levels) and coating characterisation (Al and Fe levels). Numerical regression analyses have allowed the determination of the way in which operating and metallurgical parameters affect the compositions of the coating during production runs. The results of mass balance calculations reveal the distributions of the Al and Zn, resulting from the bath additions, during the transition. Investigations have been conducted to try to determine the influence of the way in which the Al alloying additions is made (e.g. by jumbo or brightener bars additions, location of additions) on dross formation and dross transformation behaviour.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Eng.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available