Metal finishing Q&As since 1989

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Anodizing a barrel

Hello I have a aluminum barrel, which also has exhaust holes in it, but I want to anodize it. I know that you can anodize but have a question on how to do it. I know that there is a way where you can shove a wire in one of the holes and anodize it in 1 pass, but I want the whole thing anodized. I know that you can do a double dip with half and half, but the anodize doesn't conduct electricity, so how would you do it.

Mark Matheson
anodizing - Vancouver, Washington, USA
2007

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Not sure if I really understand what you are asking, but yes, there is always a spot, a rack mark, where there is no anodizing. So if you are dipping half at a time, you will need to mask or do something to allow an un-anodized spot for contact so you can anodize the other half.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

So do you know how the manufacturers do a complete anodize? if they use the same process, how would they do it without any bare surfaces? Because I saw some anodized pieces that have no bare spots.

Mase Mufoa
- Portland, Oregon
2007

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First of three simultaneous responses --

With proper racks and racking the parts on areas that are no visually prominent, the mark is very small- sometimes less than a pinhead, so are not readily visible.

James Watts
- Navarre, Florida
2007

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Second of three simultaneous responses --

If they've been anodized, then they will have some bare spots where contact was made. Anodizers make them as small as possible, and try to put them in areas where they are not easily seen, but a close look will find them.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
2007

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Third of three simultaneous responses --

There is no way around not having a bare spot in the anodic coating, as anodizing is an electrochemical process, and electrical contact must be made. At the point of contact, no coating will form. If there is a threaded hole, that would serve the purpose of contact. The contact point need not be very big, and may be hard to see..or perhaps it's been "touched up" with some kind of marker, maybe its on the internal surface of the barrel, I don't know for sure...but I guarantee you its there.

Marc Green
anodizer - Boise, Idaho
2007

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As Ted noted, their is always a contact mark. The anodize is non-conductive, there is no other way to do it. You may not ordinarily notice this because the contact marks can be very small - and there are different ways to color the bare metal to make it less visibly apparent - but they are there.

Jim Gorsich
Compton, California, USA
2007