Converting Boric-Sulfuric Anodizing Bath To sulfuric Anodize

A. If it were me, I'd trash the bath and start anew. I'm not very familiar with Boric acid anodizing, and the film properties it produces, especially when it comes to dyeing parts. You weren't too specific on the type of film properties you are trying to achieve by converting to sulfuric. I'm also assuming that you want to be able to repeat quality results -- how could you ever do that if you're basically starting off with an unknown from the get-go?

A. You need to discard that solution and start over. Since the bath is relatively dilute, you really aren't throwing away many dollars by discarding the bath or spending many dollars to waste treat it. So, don't feel too bad about getting rid of it.

A. I've dealt with glycol in anodizing baths two or three times. In my experience the glycol was always visible, so there was little doubt that I had a leak in a cooling coil. Thankfully, the acid never entered into the cooling system, it was always coolant that leaked into the acid. In any case, it is easy to remove the glycol with activated carbon. I used a portable filtration system that included the pump, hoses, and a filter chamber that was capable of accepting bulk granulated active carbon. I filtered the bath for a weekend through the system, replaced the cooling coil and then was back in business.

A. Yes Eric, there is a test for potential glycol in your tank. Have the bath analyzed for TOC. I would send two samples, one baseline created with sulfuric acid/water and additive, if you use one...and the other should come straight from your tank. Compare the results. If you see a significant difference, than there's a good chance you have a leak.

Most labs can do this very quickly.

The other thing I do on a frequent basis is to monitor the pH of my glycol on a bi-weekly basis. If you see it start to drop..you have a potential issue. My glycol solution generally starts off with a pH of around 8, so it doesn't take much of a leak for it to start to drop. Anything below a pH of 4, and you'll have to worry about potentially damaging your chiller.

Another little tip would be to add some phenolphthalein ⇦ this on eBay & Amazon [affil links] to your glycol solution (my glycol solution holding/recirculation tank is clear poly-pro, and it's easy to see). If the pink/purple color goes away quickly over a few days then you know you're having a significant pH drop.

A. Yes, it appears you have two problems...the same ones I've experienced previously, which has lead us to put in the aforementioned PM's to catch something like this at the early stage. Sounds like Jon got lucky, and didn't suck and appreciable amount of acid into his cooling media.

I honestly can't say what the negatives would be to having glycol in your bath, as soon as we caught the issue, we changed out both the anodizing tank, and the glycol solution (I simply can't take risks when it comes to the quality of the product I produce....nor could I afford the downtime because my chiller was damaged). I would think that it may potentially cause quality issues with dyed work, as the glycol may not be completely rinsed off prior to dyeing, but I'm not sure.

I think Jon's suggestion of filtering the anodizing bath through a carbon filter is a good one (If I understood your post correctly, it sounds as if you added activated carbon granules to the bath sample...I think you were confused, as John suggested to FILTER the bath through a carbon filtration process, not add activated granular carbon to the solution), if you don't want to discard the bath. Then re-analyze to check the effectiveness of the filtering. To my knowledge, little if any research has been done to determine an acceptable level of T.O.C. in the anodizing solution.

If I were you, I would replace my glycol solution..you're getting dangerously close to causing potential damage to your chiller barrel. At the very least, shut that particular bath down until the exchanger leak is repaired..or you'll obviously continue to drop your glycol pH.

Another little tip: Have a drain valve installed in your cooling media supply/return line. It makes the checking of the pH of the glycol much more convenient. :)

A. Alrighty, I definitely misunderstood what you posted when you posted your methodology. Although, it's is my understanding that one should first run their bath through a 20 µm (variable, depending on the flow rates you want to achieve, and the particle size you want to remove) filter, followed by filter chamber containing activated carbon (as Jon suggested) for best results. I've never tried this filtration process, perhaps Jon could elaborate. I'd like to learn more in case this situation happens again (which, inevitability, it will).

FYI, when we thought potentially had a heat exchanger leak (after noticing a pH drop in the glycol solution), and checked our baths for T.O.C. , the level on one bath was over 1800 ppm. The other bath was less than 100 ppm. At this point, if I recall correctly, the pH of my glycol was similar to yours (less than 5)

We tore apart the heat exchanger of the bath with the significant TOC level, and looked very closely at every one of the individual plates...we found just one plate (I think there's around 20-25 plates in each of my heat exchangers) with a hole, that couldn't have been bigger than a pin head. Hard to say how long the leak was there. I had previously been checking the pH of my glycol once every 2 months...but after learning this lesson, we went to a bi-weekly check.

Alrighty then. Sorry for the delay in the response.
A) glycol contaminated soln @ 150 TOC
B) carbon treated soln 0 TOC
C) baseline solution 0 TOC.
I measured turbidity with a refractometer on the above sol'ns and determined values for purified sol'ns. The carbon filtration went quite smoothly, I used an empty filter chamber in which I placed an anode bag loaded with granular activated carbon. This chamber was repiped from the existing filter pump, in that the existing pump pumped through to the carbon chamber, and repiped to the poly pro chamber to filter carbon dust. The repiping was done with a series of true union valves to run both chambers simultaneously, or filters alone. This way you can change out the carbon anytime, without any down time. I now use this set-up for all my sol'ns. I believe the refractometer proved sol'n clarity, as TOC values were verified. I have more queries and will post them on a new thread, but I wished to have kept this one going.
Happy electrolyzing.
Regards,