Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Dry flux modification for coating quality improvement of silicon steels and reduction of zinc consumption in hot-dip galvanizing

Original research objectives:
The industrial problem to overcame in General Galvanising is relevant to an overall cost reduction of the process/product and quality improvement. Due to the great variety of steel parts coated by a hot-dip galvanizing plant a very interesting innovation is the set-up of a methodology for the production of good quality galvanized parts at competitive cost and with special attention to the environment.

Based on some preliminary results obtained with a modified aqueous flux solution, the goals of this project were:
- 20% reduction of the interface reactivity of so-called reactive steels in a molten zinc bath in order to achieve for these steels the same quality of non-reactive steels;

- 0.5-1% reduction of the Zn/steel ratio in the galvanising shop;

- 25% reduction of fumes emission in the galvanising shop;

- 25% reduction of top dross.

Project’s actual outcome in terms of technical achievements:
The study is directed toward the set-up of a new flux formula and to a better knowledge of the influence of the parameters for a process in which the new flux solution will be used.

It has been found in the 1st year of research that in batch hot-dip galvanizing the traditional flux solution containing Zn and Ammonium chlorides may be substituted by a new not-traditional pre-treatment of the steels, based on the chemical deposition of a thin Cu-layer by means of the cementation reaction. This new low-cost Cu-route allows the addition of Al in the range of 0.025-0.05 wt% to the molten Zn-bath and therefore the complete inhibition of the Fe-Zn reaction for the so-called reactive steels. Furthermore because of the metallic nature of the pre-treatment the complete elimination of fumes emission during galvanizing, has been achieved.

The process has been scaled-up at a pilot scale and promising results were confirmed by experiments run in the pilot plants placed in the galvanising shop of 3 partners.

- With the new coating process the coating thickness for steels, whose Si content is placed in the reactivity pick, is more than 30% inferior while is it is unchanged for not-reactive steels. This is very important because a generalised reduction extended to non-reactive steels might affect the minimum coating thickness prescribed by Norms.

- The coating reduction has a positive effect on the reduction of Zn consumption per ton of galvanised steel. Nevertheless it depends on the steel-mix processed in the galvanizing shop. A most accurate value must be calculated on a long lasting campaigns run at a demonstration plant scale.

- Fumes emission during hot-dip galvanising is nearly nil with the new flux formula.

- The reduction of top dross formation has been noted during pilot trials. Also in this case the accurate value will be calculated on a long lasting production campaign.

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Reported by

Dipartimento di Fisica e Ingegneria dei Materiali e del Territorio, Facolta d'Ingegneria, Universita Politecnica delle Marche
Via Brecce Bianche
60131 Ancona
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