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When should I dump Iron Phosphate solution

(-----) January 30, 2008

In our powder coat line, for the pretreatment the parts are going through cleaners first then to Iron Phosphate and Sealant tank. My question is how we know when to dump Iron Phosphate tank. Our Iron Phosphate supplier suggested we dump it every three months (depending on production). Can anybody tell me what kind of test I have to do to identify that the Iron Phosphate solution is old technically and we have to renew it.
When the Iron Phosphate solution is old, there is a yellowish residue in the bottom of Iron Phosphate tank. What is this residue chemically? Is it worth it we get it out of system by any kind of filtration system? If so can we keep solution longer? Is that residue useful in any industry?


First of two simultaneous responses -- January 31, 2008

Dump and recharge the tank, put a steel sample panel through at a specified line speed, temp and chemical concentration. Have the coating weight checked. Use this as a baseline. Periodically rerun the test using the same parameters as the first test. When the coating weight on the sample starts to decrease, the chemicals are reaching their end-of-life.

Sheldon Taylor
Sheldon Taylor
supply chain electronics
Wake Forest, North Carolina


Second of two simultaneous responses -- January 31, 2008

I expect more from vendors. If that is the best that they can do, I would switch vendors the first time that it was convenient.
That said, it does not have an infinite life, but if you take care of it and always have material in the tank to keep your acid points in balance, analyze regularly, it will last a lot of parts and a fairly long time VS a poorly maintained tank.
I would check out the book section and pick one. Generally, the ASM books are good but expensive.
The MIL spec will also give some guidance on testing.

There have been a few very good articles on phosphating in Metal Finishing, Product Finishing and AESF and the follow on organization's monthly magazine.

James Watts
- Navarre, Florida

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