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inconsistent coloration in zinc phosphatizing

November 10, 2011

That's my pleasure to table my questions in front of you.

We are coupling manufactures in India having a broad business.

We are processing our M.S. as well as CI Material in Zinc Phosphating. But M.S. material is showing different shades which causes bad appearance.
We are not having any chemical properties check point to detect material for various grades of M.S. Some material show dark grey while other parts of same couplings show black / heavy rough phosphating.

We require all material with uniform shade.

We are maintaining TOTAL ACID 42-46 ml.

Mainly we prefer amorphous type black phosphating shade.

Also due to atmospheric phenomenon, material starts to rust early; to clear such rust & patch marks of rust we require some solutions.


November 24, 2011

Zinc phosphating is very sensitive to how active the surface is to the etching effects of the phosphoric acid.

My current employer uses zinc phosphate as one of the optional treatments for hot dip galvanized and electro-galvanized. These are very similar subsrtates varying mainly in thickness of the zinc coating. The hot dip galvanized coating takes the zinc phosphate as a grey coating while the electro-galvanized is a black coating.

One of our customers, a manufacturer of high end roofing, has us produce a zinc phosphated substrate with a clear coat on top as one of his products. This puts us in the position of trying to colour control zinc phosphate, not easy.

Ronald Zeeman
Coil Coating - Brampton, Ontario, Canada
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