Letter 21047

Treating galvanized steel sheets to avoid white rust [India] 

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Hello,

Can anybody help in finding solution for treatment of galvanized steel sheets against white corrosion. The sheets are exposed to very humid conditions. I am looking for a treatment which can give prolonged protection without paints. Any suggestion is highly appriciated.

Thanking you,

Ramchander Gegula
- Hyderabad, Andhrapradesh, India

You are already chromating these galvanized sheets?

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

Hi,

Hope you have chromate treatment facilities there in your process. Keep chromate solution temperature above 80 degree centrigade to dry up the sheet after chromate treatment, next you can use hot air to dry up the swheet after treatment. Corrugate the sheets as soon as possible in the humid condition.Arrange cross ventilation during stroage--if necessary use padastal fan at the stroage area.Last of all if the condition does not improve your last resort would be to use oil in the corrugation machine(through special arrangement), which may help you to beat white rust formatiom.

Regards,

Mahbub Hossain
M/S POWER TRADE BUILDING SYSTEM LTD - Dhaka, Bangladesh

Chromating unit is surely a good solution to prevent Galvanised sheet from white rust formation.But chromic acid is another factor which can arise problem of pollution.
Please suggest whether this problem can be minimised by using chemical coaters?If yes,can coating by chemical coater avoid the use of cleaning section in Color coating line?
Please explain the merits and demerits of this alternative.

tks,

Sunil Chauhan
- Indore, M.P, India

During a panel discussion at Sur/Fin 2006 in Milwaukee, one of the participants claimed that the new TCP hexavalent-free chromate conversion coatings developed for aluminum work well on galvanized materials as well. I would suggest that you contact one of the four licensees for further discussion. They are Henkel, Luster-On, Metalast, and Surtec.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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