Anodizing tank cathodes gassing

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Posted by David A. Kraft, VP, Anacote Corp (68.161.193.179) on April 09, 2008 at 07:08:08:

We are having an issue in 1 of our 2 anodizing tanks.

I know you like lots of details, so here goes:

We run 2 anodizing tanks – they are both approximately 1100 gallons.

In one of the tanks, our Tank #7, we are seeing gassing at the aluminum cathodes, indicative of attack. These tanks are approximately 10 years old & this is a new issue. It happened a few months ago & we ended up neutralizing & dumping the tank & remaking the solution & the problem went away – now, a few months later, it is back again.

We have checked for stray current & found none.
We have analyzed for chromates & nitrates in the bath & found none.

These are high volume production tanks. Operating parameters:
- aluminum @ 6-8 g/l (controlled with Ecotec APU unit)
- sulfuric @ 220 g/l – we know this is a little high, BUT, we have reason for running at this level & have done so for 30+ years.

When we transferred the problem tank to another tank for neutralization, before dumping, we inserted a cathode & still observed the problem.

Both anodize tanks are the same, except, the problem tank has a MAE, proprietary additive, for higher temp hardcoating. We have been using this additive for 20+ years.

Before I go & dump the tank again, anyone have any ideas?

Thanks

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: We are having an issue in 1 of our 2 anodizing tanks. : I know you like lots of details, so here goes: : We run 2 anodizing tanks – they are both approximately 1100 gallons. : In one of the tanks, our Tank #7, we are seeing gassing at the aluminum cathodes, indicative of attack. These tanks are approximately 10 years old & this is a new issue. It happened a few months ago & we ended up neutralizing & dumping the tank & remaking the solution & the problem went away – now, a few months later, it is back again. : We have checked for stray current & found none. : We have analyzed for chromates & nitrates in the bath & found none. : These are high volume production tanks. Operating parameters: : - aluminum @ 6-8 g/l (controlled with Ecotec APU unit) : - sulfuric @ 220 g/l – we know this is a little high, BUT, we have reason for running at this level & have done so for 30+ years. : When we transferred the problem tank to another tank for neutralization, before dumping, we inserted a cathode & still observed the problem. : Both anodize tanks are the same, except, the problem tank has a MAE, proprietary additive, for higher temp hardcoating. We have been using this additive for 20+ years. : Before I go & dump the tank again, anyone have any ideas? : Thanks

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