Metal finishing Q&As since 1989
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Solution volume growth problem in hard anodize tank due to high humidity
May 3, 2011
Hello,
I have an issue with my hard anodize tank, because the low temperature of the tank and the high humidity in the air, the volume of the tank increases every day and the concentration of the acid decreases. Any suggestion to prevent this?
regards
manufacture engineer - Chihuahua, Mexico
May 3, 2011
Hi, Yohands. I find it hard to believe that high humidity is the cause of significant solution growth in a cold tank. I think a leaking cooling coil is more likely if the tank is water cooled. Why do you believe the high humidity to be the cause?
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
First of two simultaneous responses -- May 4, 2011
Agreed Ted, I couldn't imagine humidity being a cause for a tank volume to increase. Especially when you factor in drag-out. If it's a traditional hardcoat tank (no additive) being chilled to 30-32° f, then I also can't imagine only water being used as the chilling medium, as it would surely freeze (I keep my glycol based medium around 20° f.)
If you're using glycol as a chilling medium, have a sample of your anodizing bath analyzed for TOC. That will tell you if you have a coolant pipe leak..or, you can also just check the pH of your cooling medium..if its low (below 5) then you definitely have an issue, as you're potentially sucking in corrosive solution to your chiller.
Marc Green
anodizer - Boise, Idaho
This is typical, I see it all the time in Florida and have heard of it before in Mexico. You just have to keep titrating, dipping out, and adding back, save the dip out in a drum outside, let it evaporate and use to add the strengthened solution back in. The water will evaporate, the H2SO4 will concentrate as the water goes back into the air.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Second of two simultaneous responses -- May 4, 2011
Well, I stand corrected then. Honestly, I can't imagine humidity significantly raising the level of solution in tanks, especially, as I said before when drag-out is factored in. All the more reason to love the nice, dry climate of Idaho, I suppose :)
Marc Green
anodizer - Boise, Idaho
First of three simultaneous responses -- May 5, 2011
I second Robert Probert. It's typical, but it should be manageable.
Jon Barrows, MSF, EHSSC
GOAD Company
Independence, Missouri
Second of three simultaneous responses -- May 5, 2011
I have to agree with Robert, I see it all the time here in the UK. It is especially true if you are running a high sulfuric concentration solution (we operate at about 400 g/l) as the sulfuric affinity for water is so voracious it will pull any moisture around it into the solution.
And only to repeat what has already been stated the only way is to bucket out the excess and keep re-adding the sulfuric to maintain the concentration.
Aerospace - Yeovil, Somerset, UK
Third of three simultaneous responses -- May 6, 2011
First of two simultaneous responses -- May 6, 2011
Hello,
I know the problem is humidity because in the dry season we don't have that problem, and when we do, we check the concentration daily, drain the excess of solution and add more acid to reach the concentration again, but I asked to see if somebody have a solution, probably we can install a cover over the tank, to close it when the tank is not in use.
regards
- Chihuahua, Mexico
Wow, I had no idea. I'm curious, those of you that live in high humidity climates...how much does the level of your tank increase on a daily basis?
Marc Green
anodizer - Boise, Idaho
Second of two simultaneous responses -- May 6, 2011
I never had an issue with this on the east coast FL, till I moved to the southwest, Tucson. Every monsoon season we would have to decant
Ken
- Daytona Beach Florida US
First of four simultaneous responses -- May 9, 2011
If you are using air agitation, you are pumping a lot of moist air thru a chilled solution. A perfect dehumidifier.
Chris Jurey, Past-President IHAALuke Engineering & Mfg. Co. Inc.
Wadsworth, Ohio
Second of four simultaneous responses -- May 9, 2011
Like I said above, dip it out, set the drum out in the sun, I have been to Chihuahua where it is very hot, let the water evaporate, pore the concentrated solution back into the tank. Or, as my client in North Carolina does, since the Type II is used more and dragged out more, he just bails the hardcoat over into the Type II.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
Third of four simultaneous responses -- May 9, 2011
Hi Marc,
The UK isn't as bad as some places, but we spend most of our summer with humidity around the 60% RH mark. We run a 2000 litre hard anodising tank and even with drag out as a consideration we still have to bucket out about twice a week, about 5 gallons a time, so a good estimate for the particular process we run (which is a very high sulfuric content at 400 g/l) is about 10 gallons a week (40-50 litres a week), I guess in more humid areas the bail out rate will be considerably higher.
Aerospace - Yeovil, Somerset, UK
Fourth of four simultaneous responses -- May 10, 2011
Today I serviced one of my clients for the 225th bi-weekly time, and his hardcoat tank, 32 °F, was up 4 inches higher than two weeks ago, we had to decant and send to waste treatment.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
May 10, 2011
May 11, 2011
Thanks, Robert. I learned something from this thread that I obviously didn't know.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 18, 2011
May I suggest to Mr. Chris to use a dehumidifier for your agitation air and PP floating balls.
Good luck
Khair Shishani
aircraft maintenance - Al Ain, UAE
July 8, 2011
Interesting Discussion.Experienced it myself too.
1 Air Agitation can also bring in water into the solution as others have mentioned earlier.frequent compressed air tank draining is a must.dehumidifier is also recommended.
2 Look for uninsulated (usually PU insulation ) small lengths of exposed piping that brings the chilled water into the solution, over the tank, - that can have ice formation which can later on melt when the anodising process is stopped for any reason.This can add substantial water to the tank.Remedy: do not leave any uninsulated pipe lengths over the tank.
- Belgaum, Karnataka, India
July 12, 2011
Ravi,
is a good observation the ice in the pipelines, we have some over the tank, from the chiller, I'll insulate it.
also we are going to try the floating balls recommended by Cair.
thanks to all for your advice.
- Mexico
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