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Tuesday, January 20, 2015

Anodizing - part 3

Tying up a few loose ends

Being able to control the water temperature at will in the test bucket has been a satisfying success. It came however with strings attached, since I have had to manually stir the water in order to mix the cold lower layers, with the hot top layers.

I was a little surprised at the magnitude of this temperature extremes, reaching at times over 100℉ (38℃), and have been thinking about ways to overcome such temperature distribution ever since.

First though, I needed to address the temporary R&D nature of the heating assembly, by finalizing the design, and securing its components in an appropriate enclosure.

8" x 8" x 4" ( 20 x 20 x 10 cm) plastic junction box

Cutting the tabs off the electric outlets

installing two 240v outlets

PID getting wired

PID enclosure update

Back to the temperature issue... I have decided to go with an air injection setup, where PVC pipes would create an air distribution manifold capable of delivering pressurized air (2 psi) to the bottom of the bucket. I decided to call this a “bubbler” for lack of a more descriptive name. 

Anyway, the air coming out of the holes in the manifold should in theory provide enough water agitation to equalize the temperature. If this were to work, it would eliminate the need to reach in the acid with some device to stir it, and prevent it from dripping all over, as I reach in and out of the bucket.

Full of good ideas, I headed to Lowes to pick up some supplies, and begun assembling the “proof of concept” bubbler number one.

Air manifold prototype

Drilling 1/16" (1.6 mm) holes in the PVC pipes

Testing of the design in the water bucket proved very successful, with water temperatures consistently uniform throughout the entire range necessary for anodizing.

Testing the bubbler in water

The bubbler is agitating the water thoroughly.

Much improved temperature distribution

Bucket bubbler testing

I designed the bubblers to remain in their respective buckets at all times, including storage, in order to prevent accidental spills. The quick disconnect fitting at the top of the PVC manifold is still a few inches above the level of the acid at the 4 gallons mark, but low enough that the Gamma Seal lids can still close, and seal the buckets with their dangerous contents.

One of the unexpected issues that was highlighted in the test was that of the hose weight. The hose is so heavy that it tilted the bubbler over, if not restrained.

To counter that, I put together more PVC tubes in the form of an upside down U, with a quick disconnect on one side, a swivel connector on the other, and a 0-20 psi regulator in the middle.

Low pressure regulator with swivel connector

Small PVC stub is helping to stabilize the manifold

Swivel quick disconnect allows the air hose to lay naturally

This redesign completely addressed the previous shortcoming, so I happily moved on to reproducing the bubbler five more times, one for each bucket.

"I'm starting to detect a pattern here!"

Bubblers permanently installed in each bucket

Brass fitting above the acid, but below the level of the lid.

One last small modification I made was to the “fishing pole” parts holder design. I dropped the center section about a half inch (1.2 cm) to make some room over the top for a lid. 

A quick revision to the part holder

It looks like an apocalyptic steel scorpion from Terminator 15

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