1974 Volume 60 Issue 1 Pages 96-103
A study has been carried out on the dross formation in continuous galvanizing in relation to the aluminiumcontent in the bath.
Iron and aluminium concentrations in drosses formed in conventional galvanizing lines are determined.In the laboratory, Zn alloys containing 0.22% Pb, 0.13-4.60% Al and 0.066-0.24% Fe are molten ingraphite crucibles and held at 465°C for 40hrs before cooling. Using the sectioned ingots, spectroscopic analysisof the portions free from dross and quantitative microscopy analysis of dross compounds are performed:
On the basis of these results, the amount of dross and that of aluminium consumed in the dross formationreaction in conventional processes are estimated. Conclusions derived are as follows:
Drosses contain two compounds, namely δ and Fe2Al5.
When the aluminium content in the bath is in the range of 0.09-0.14%, δ and Fe2Al5 can coexist. Inthis case the higher the aluminium content, the lower the fraction of δ-compound. When the aluminiumcontent is higher than 0.15% the δ-compound can not be found.
The amount of the bottom dross is estimated to decrease rapidly with increasing the aluminium contentin the bath up to 0.14% and becomes negligible above 0.15% Al. The amount of the top dross, however, increasesrapidly with increasing the aluminium content up to 0.14% and decreases gradually above 0.15% Al.
The amount of aluminium consumed in the dross formation reaction is estimated proportional to the amount of iron dissolved from sheets.