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Galvanizing is powdering off of part




Sir, We are in to business of wire mesh crates. we stack the material in our godwan. After a period of time if we touch the crates the galvanizing comes off in powder form. what is the soiution to avoid this situation?

RAJENDRA PAWAR
Material stacked in my godwan - Mumbai, Maharastra, India
April 3, 2008



Hi, Rajendra. Sorry, I don't know what you mean by "godwan". The galvanizing apparently was not done properly. There is no fixing it to my knowledge, only redoing it.

Regards,

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 3, 2008



First of three simultaneous responses --

Perhaps Rajendra is describing "white rust" which is a subject well covered in this forum. Search the archives.

Bill Reynolds
Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.

April 4, 2008



Second of three simultaneous responses -- April 4, 2008

Galvanizing is a SACRIFICIAL coating.

It protects by being corroded preferentially. In preference to the steel its protecting.

Corrosion of the galvanizing (desirable) forms mainly zinc carbonates and oxides. These are often in the form of white powdery solid that comes off.

What you describe sounds normal, though you have given no idea about the extent, rate, amount, and timescale.
You should expect to see some white powder. If you don't then either:
* it isn't a corrosive place you have the item, or
* its not galvanizing you've got.

geoff_crowley
Geoff Crowley
Crithwood Ltd.
Westfield, Scotland, UK
crithwood logo



Third of three simultaneous responses -- April 6, 2008

Sir:

Under google, "india 'godwan'" the first two were:
"warehouse/Godwan."

You likely have a "white rust" problem which can be searched on this web site.

Regards,

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



First of two simultaneous responses --

Actually he is telling about White Rust. It generally created by Oxidation of Zinc. It should be prevented by using 1% dichromate solution but it also depend where is his Warehouse situated. If it is near by Sea or coastal region then corrosion is more than far from Sea.

Rakesh Singh
- Noida, U.P., India
April 8, 2008



Second of two simultaneous responses -- April 8, 2008

Sir:
As possible solutions to your problem, if you could answer the following questions it would be useful:

1)What is the aluminum content of the zinc?
2)What is the conductivity of your quench water? (Is it cloudy with sludge?) Do you have hex chrome in your quench?
3)What is the chemistry of your zinc? (e.g. zinc content, especially tin.)
4)Do you operate a "wet" kettle (with black bubbly top flux)? Or are you operating a "dry" kettle (bare zinc)?
5)In storage do you separate your product or is it stacked tightly together?

Regards,

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



April 9, 2008

Sir:
1% hexchrome is far too concentrated for a quench. With proper pH and other additives, the proper concentration is between about 100ppm and 1,000ppm hexchrome (e.g. 0.01% to 0.1% hexchrome). 1% hexchrome that gets hot is bad for the workers health.
Regards,

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