Metal finishing Q&As since 1989

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Zinc phos for hot dipped galvanized?

We have been forced to change our powder coater due to a bankrupcy. They offered us quality coating of our hot dipped galvanized hinges and latch parts for years. Adhesion was excellent. They used a 7 stage zinc phos wash. Is a zinc phos the best for coating hot dipped galvanized product, as we are having little success with companies that use a iron phos wash?

Thank you for your help.

Geoff Faulkner
hardware - Port Huron, Michigan
2004

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First of two simultaneous responses --

My experience was that it is a little hard to tell when you have a good phosphate coating on galvanize. My nickel says that zinc phosphate is significantly superior to iron phosphate if really good adhesion is required. For minimal work, iron will normally work. Talk to both of the two major phosphate solution mfgr's. I think that a calcium modified one will give better adhesion as it has finer and dense crystal formation. The big boys will have better opinions. This is just a question to ask them.

James Watts
- Navarre, Florida
2004

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Second of two simultaneous responses --

Yes, zinc phosphating is the cadillac of treatment systems.

Ronald Zeeman
Coil coating - Brampton, ON, Canada
2004