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Galvanized steel sheets are darkening (both galvanized plain and galvanized skinpass)





January 4, 2009

Q. Hello,
I AM WORKING IN IN QUALITY.
RECENTLY WE ARE FACING A PROBLEM OF DARKENING OF GALVANIZED SHEET.
KINDLY PROVIDE ME THE DATA FOR THE SAME WITH REFERENCE TO CAUSE & REMEDIES & RE-OCCURRENCE FOR THE SAME DEFECT. THIS DEFECT IS APPEARING IN BOTH GALVANIZING PLAIN AS WELL AS IN GALVANIZED SKINPASS.
KINDLY DO THE NEEDFUL AS SOON AS POSSIBLE.
I WILL BE HIGHLY OBLIGED.
THANKS
REGARDS,

AJAY MOHAN
ASST MANAGER - NAGPUR, MAHRASTRA & INDIA



January 11, 2009

A. Sir:

Perhaps the steel is too high in silicon, phosphorus, or aluminum and reacting to form zinc/iron alloy fully to surface. Perhaps your chromate quench is wrong in pH, or contaminated causing darkening of product.

I do not know what skin-pass means.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA



January 14, 2009

A. Dear Mr.Mohan,

As per my information galvanizing material (Zinc) is not having shining appearance so for that in the process of galvanizing Aluminium is used. The problem of darkness in the galvanized sheet after some time is the "excessiveness of the aluminium" used during production.

Amit Sharma
- New Delhi




July 5, 2012

Q. What are the most probable causes for the darkening of a galvanized iron sheet? The coating on the sheet is mostly Zinc with trace amount of Aluminum. This darkening occurs throughout the sheet which seemed like it's still part of the coating. Could Aluminum have influence on this darkening effect? Or are there any other factors that could have caused this darkening on the sheet?

Ruthy Abac
- Philippines


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