Cool Water

He’s a devil not a man,
and he spreads the burning sand with water.
Cool, clear water.
“Cool Water” recorded by Sons of the Pioneers (and many others)
Songwriter Bob Nolan

Got my anodizing process restarted after the move to New Mexico. This involved adding some plumbing to a garage utility sink for the cooling water loop.

One of the desired conditions for sulfuric acid anodizing is a bath temperature of 20C (68F). The DC supply is injecting power into the bath and the production of aluminum oxide is exothermic, so the bath is likely to rise in temperature during the 1 hour process time. If I would make a bath of 1 gallon or more volume, the bulk of the acid/water solution would limit the temperature rise. But I use only 1 quart of solution, making forced cooling necessary. My blog post of 22 Aug 2012 details the water cooled cathode.

In Lovells MI, my well water came out of the ground at 4 to 12 deg C year around (pump setting 50 ft, water table 1 ft). Overcooling was quite possible, so I had to supply the cooling water intermittantly while watching a thermometer. Probably made an on/off cycle every 5 minutes. Running the process took constant attention.

Here in NM we have been having warm weather for the season, 75F for several days. I am on city water, and the houses here are built on a slab. I do not know the building practices, but it seems that there is not much insulation between the cold water pipes and the concrete. When I first open a cold tap, the water may run at 24C for a while, gradually dropping to 18C. So there is not much temperature difference available for cooling. With a steady flow through the tubes, I could only keep the bath temperature down to 23C. Having more tubing in the cooling loop would probably allow lower temperature.

As for the resulting anodize layer, I cannot observe that it is adversely affected by the slightly higher temperature. And, I spend much less time watching the thermometer.

Another process consideration is that here at 5800 ft elevation, water boils at about 200F. So sealing the anodize layer has to be done at the lower temperature. My data sources say that anything above 170F should be OK, see blog post of 3 March 2012.

Update 23 May 2017: Resolution is to put a submersible aquarium pump, frozen blue ice packs and water into a small insulated container. Use the pump to run a closed cooling loop. With cooling water at 14C, I was able to maintain cell at 20C. I did stabilize the cell solution near 20C before starting.



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1 Response to Cool Water

  1. Pingback: Anodizing Temperature Control | North Branch Reels

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