using aluminum as a cathode

[scocklin]

I have some professional aluminum light stands that I want to re anodize and dye. I have broken down the stands into their individual parts. They run between ½ to 1 inch in diameter and about 32 inches long. I purchased a 6 inch diameter 10 foot section of PVC pipe and cut it down into 3 foot sections. I will use two of the sections as a stripping and cleaning tank and the third as my anodizing tank. I also have a 3 foot section of 4 inch diameter PVC capped that I will use as my dye tank.

I have caped off the bottoms and cleaned them out. I purchased some roofing aluminum and scrubbed it with steel wool. I tested it with an ohm meter and it ohms out completely on one side. I want to use the aluminum as a cathode in the anodizing tank but have always used lead cathodes. What can I expect to be different now that I am using aluminum as a cathode?

[sswee]

Shouldn't notice any difference as long as you have any coating that was on the alum. off. Is the SA of the alum. the same or larger than your part? Let us know how it goes.

[scocklin]

The surface area is close to the entire diameter of the 6 inch diameter tube. Two aluminum sheets fit perfectly inside the tube circling completely around and over lapping each other without needing to be physically attached to the tube surface.

My biggest worry is not knowing if I did in-fact completely remove all of the plastic coating from the aluminum. I put 30 volts through the aluminum and used a voltmeter to complete the circuit checking for continuity at various points on the surface. It read 30 volts through out the entire surface. I’m worried about possibly not removing all of the plastic coating and contaminating the acid bath. Do you know if the plastic used to coat the aluminum could possibly contaminate the bath?

[Fibergeek]

I found out the hard way about the plastic on Al roof flashing, it will leave a sticky plastic goop floating in the tank after a few hours. I had to use a belt sander to get all of the plastic off of the flashing. Actually, soaking it (expendable) sulfuric acid might be a good way to get it off.

The effect of aluminum cathodes vs. lead will be slightly less voltage required for a given current density. Your anodizing process remains the same.

How will you provide agitation?

[scocklin]

I could go two ways, one with air or I could use a circulation pump I purchased, I would welcome any suggestions.

Thanks for the heads up on the plastic. I have a large 2 handled orbital vacuum sander that I use on my boat. I’ll try it with some 60 grit paper on the flashing to make sure all of the plastic is off.

[Fibergeek]

I'd use a finer grit, maybe 150 to 220.

Because of the unique shape of your "tank" (very deep for its diameter) air bubbles might be easier, bubbling up from the bottom all the way to the top. The plating guys have been experimenting with large bubbles, roughly 1/4" spherical (rather than small) it seems to work better. To do this you need very low PSI, but a large volume of air.

[scocklin]

I'll give it a try; I've got about 20 stands that break down to 6 tubes each. As I said before the tubes are 1/2 inch to 1 inch in diameter. The tank is 6 inches in diameter and 3 feet long. I know about the 3 inch spacing between pieces and the cathode but I'd like to get at least 2 parts in the tank at a time. Can this be done?

[Fibergeek]

I don't know.

Actually I would be happier if the tank were larger, but I'm not sure just where the limits are. I've never dealt with a shape of tank like this before. The problem you MIGHT encounter would be inconsistant coating thickness.

Believe it or not, if you experience a problem you MIGHT do better with a cathode that does not cover the entire the whole internal circumference. Maybe an Al bar running the entire depth, with LESS than the surface area of the work. I know this sounds weird. Lines of force (what they call it in electroplating) MAY dominate due to the shape.

[scocklin]

I could not go into a larger tank mainly due to size and the amount of chemicals needed. My work area is shrinking as I get more into this hobby. The tank is tall so I'm going to try several pieces at a time at various depths. The use of aluminum bars sounds like a good idea. Would two or three bars running the length of the tank spaced evenly around the tank work?

[Fibergeek]

I'm talking about 1 bar, with maybe 1/3 the SA of the work. I know this goes against what you have learned dealing with more conventional shapes.

In any event, Scocklin is treading on new ground with this project. I'm sure I'm not alone in being very interested in how it turns out.

Please Steve, document everything carefully. A project like this has the potential to payback our investment in you (the time) in spades.