LCD anodize of a large piece?

[scocklin]

I have been trying to determine if it would be possible for me to strip off an old anodized layer, clean de-smut and re-anodize and dye a piece of aluminum 43 feet long and approximately 7 inches in diameter.

The first thing that comes to mind is what type of container do you anodize something as large as this in, I’m thinking 12” diameter SCH 40 PVC pipe. Five 10 foot lengths should do it but I have calculated the liquid volume and came up with 58.7 gallons per 10 foot length of or about 294 gallons for 50 feet.

The square footage of the piece of aluminum being anodized is about 160 square feet. If I where to try to anodize this as a whole using 6 amps per square foot I would need a industrial grade anodizing power supply that could put out at least 964 amps, and a 3 phase 480V line to hook it up to.

So my questions are this:

Can I anodize sections of the aluminum tube separately; I was thinking I would need to build a cathode configuration using two separate sections of aluminum sheet. I would use a 100 amp power supply. The cathodes would be able to anodize 16.6 square feet at a time using 6 A/SF. I would physically move the cathodes down the length of aluminum tubing making one move every 60, 90 or 120 minutes depending the coating thickness I’m going for. I think I would have to make my cathodes 4.3 feet in length each and in order to anodize the entire 43 foot piece I would have to move it 10 times.

Or if I purchased a 250 amp power supply could I double my cathode length and do it in 4 moves.

Can I use one container for the whole process? I realize I would have to flush the container with fresh water after each step. The critical step would be the rinse between the sulfuric acid electrolyte and dye. Or would I be safer with two containers, one for the electrolyte only and the other for stripping, cleaning, de-smutting and dyeing.

I realize this would be an extremely expensive process to put together. I’m just in the “what if, can I do it” phase right now.

[Fibergeek]

It sounds like you are proposing anodizing a sailboat mast, quite a project.

Some basics:

1. Moving the cathode(s) won't work too well if you want a reasonably uniform anodic coating along the entire length; it may be possible to take some advantage of an applied cathode shadow to avoid over- anodizing the earlier sections, but I've never heard of this being done.

2. Research the cost of a 100 or 250 amp rectifier, for this cost alone it would probably be cheaper contracting a commercial anodizing shop to do this for you, it will probably be cheaper. There are several in Baltimore.

3. You will require quite a lot of electrolyte, sealant, and dye. Do you want this much on your (residential) property? How will you dispose of it when you are finished? Will your local govt. allow it?

Question: If this is a mast, considering the size, are they actually anodized? If not, how are new ones finished?

[scocklin]

Thanks Fibergeek, I have been thinking about this as a small business. I don’t believe there are many if any companies that re-anodize sailboat mast. Most boat owners resort to a coat or two of paint once the anodized layer wares off or is damaged. Most mast are anodized new at the factory, either silver or black. I wouldn’t do this at my home and yes the large amount of chemicals would reclassify me as a large scale operation way above the horizon and well insight of EPA radar.

However if moving the cathode is not a practical solution then I should probably go back to the drawing board. Again thanks for your help.