Metal finishing Q&As since 1989

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Salt Spray Headache is back

2007

Hi Everyone,

I thought my salt spray headache was gone but it is back again.
From my letter 45725 Ken you mention that no sanding is best or lightly with 1200 grit.
How about just bare.
We went another 3 months with no problems.
I was wondering if perhaps they are receiving too much chem film. They are coming out nice and gold.
I looked back at some panels dated 2 years ago and they appear to be hardly chem filmed. I was not here at that time and can only visual speculate that perhaps they were not dipped for the same amount of time.
I check my tanks on a weekly basis and have found no problems.
I hope someone can help.

Thanks,

Micheline Forth
finishing company - Rincon, GA, USA

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First of two simultaneous responses --

Have you tried a different source for your test panels? I have seen a marked difference in the quality of our 2024-T3 panels between suppliers.

Also, are you monitoring such things as fluoride ion activity and hex/tri-chrome ratios in your conversion bath? These can be useful indicators of the actual bath health. Drying temp and gel-set times can also affect salt spray performance. We've noticed very poor corrosion resistance at dryer temps >140F and coating/salt spray layover times >96 hours @ 70F.

Terry Lycans
- Dayton, Ohio, USA
2007

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Second of two simultaneous responses -- 2007

'Too much chem film' probably isn't the problem, as long it isn't powdery. Verify good adhesion by gently rubbing with a white cotton cloth or some rubber eraser.

Some 'usual suspects' where a good process has gone bad are:
1) Old test panels. Get new ones (with peel-off protective plastic film), and
2) Old deox/desmut solution. Iron build up and leaves a thin immersion plating on aluminum. Try using 20 vol% nitric acid.

See also Letters #3335 and 13479 (among many others on this subject).

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.