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"Hard coat anodizing tank level rises each morning"


We do type III anodizing. I am observing increase in level of sulfuric acid bath. Is it due to the condensation from the atmosphere? if yes, how do I avoid it? We maintain temperature at about 35 F at night time.We need to remove this excess acid every day. Is there any solution?
Please help.

Shanti A. Raikar
anodizing shop - San Jose, California

I rather doubt if it is condensation, but if it is, simply cover the tank at night. visqueen and pvc pipe would do for a trial for under 10 bucks.

James Watts
- Navarre, Florida


A. Good day Shanti,

How are you cooling your acid?
Didn't you notice any loss of your cooling fluid?

Best of luck,

Hocine Djellab
- Verdun, Quebec, CANADA


A. I worked in a shop in San Jose for 15 years doing hard anodize (30 °F). We always accumulated condensation and periodically had to decant, probably every other month.

Willie Alexander
- Colorado Springs, Colorado

A. What you are experiencing is high humidity. The sulfuric hardcoat solution is hygroscopic. It will absorb water from the air, thus giving you the solution level rising. The only solution I can think of in your case is to condition the space to maintain a relative humidity that is low. Unfortunately this can be costly, so you may be left to only decant the solution as it rises.

Best of Luck

Ira Donovan, M.S.F.
Kansas City, Missouri

A. Yes condensation will surely increase the volume of water (only water). I have experienced that many times in Florida.
Obviously you are dipping out acid with the water, so be sure to titrate and add acid back each day so that you will get consistent repeatable pore size. Hey, this is a new idea on controlling the dissolved aluminum within limits.

And, OH, if it is not condensation, then there is a leak in the heat exchanger system.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina


A. You can check the chemical composition of the solution to see whether the acid concentration has decreased with the increasing solution level. If acid concentration is decreased then there is water added into the tank. The water may come from the condensation of air or a leakage from a pipe in the tank.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey

November 5, 2008

A. Dear Shanti
In my opinion you should check the following:
1- Any leaks from the water supply pipes ( valves).
2- Leakage from the drainage pipe. My be the water comes from another tank through the drainage valve of the tank.
3- Leakage from the cooling water to the acid solution in the heat exchanger.

Hasan Khader
- Rammallah , West Bank , Palestinian Territory

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