I remember reading about an anodising touch-up pen somewhere. Not a metallic paint marker, but a pen which uses a chemical to form a coating similar to anodising. I want to touch-up a bit of silver anodised aluminium on one of my gear pullers, which unfortunately got rubbed on the edge.
Anyone know if such pens are available and if they're any good? Likely sources would be appreciated (particularly sources in the UK).
You're thinking alodine. Only in the last few years has alodine touch up pens made it into the market. Not cheap, either.
There are numbers that usually go with alodine, such as 600, 1200, etc, that are expressions of the acid content and conversion coating. Different kinds are for different applications. It's best for paint preparations, as it helps the primer stick, which helps the paint stick best. Not sure how well it will work for your application as it tends to change the color to a tan or golden color. It doesn't come in different colors, as that's not what it's for.
If you decide to get some, you must use it and store it according to the instructions. Vapors of alodine and many solvents like to blow up your storage containers, which is a bit of an understatement. I can't tell you how many haz mat cabinets I've seen with alodine labels all over it and one container inside, with the regular cabinet overflowing. It's obviously not for the casual user.
I played a bit with a solution that was supposed to be for touching up black anodyzing, made a worse mess than just painting the sucker, etched the surface to a nasty grey. Don't know of anything to touch up a clear coating except some sort of lacquer or powdercoating. If there WAS such a thing, they'd be using it as a dip bath instead of anodyzing the stuff, it's an expensive process. For touchup, I usually use a black permanent marker it's usually at least as durable as the old decorative anodyzing. Doesn't help your problem, might help somebody else. On a gear puller, who cares? It's not like it's on public display 24/7 and it's not like it's going to rust in that particular spot.
Yes, those alodine markers are what I was thinking of. But, whoa, they're expensive! Can they touch-up coloured anodising successfully?
As it happens, I solved the problem. I called the manufacturer to ask how much a replacement part would cost, and they said "No problem, we'll mail one to you free", which was a nice surprise. I guess the moral is to ask, and sometimes you get lucky.
That, and unlike anodize, it enhances electrical conductivity instead of insulating against it. So -- it is used as a protective finish in military aircraft (and simulators such as a previous employer used to make) where it is necessary to get a good ground connection when you attach parts together.
It is also called "Iridite" (probably a different brand of the same thing), and that is what they called it where I worked. I managed to sneak a couple of home projects through the vats when working graveyard shift. :-)
A pity -- it is a nice way to go in terms of a finish which will work with the need for electrical conductivity.
You are mistaken here. Alodine is an insulator. To get a good ground you need to wirebrush it off (usually done with a wire brush in a drill with a pin in the center to guide it). If you want to keep Alodine and not scrape it off for bonding purposes, you must specify a "class 3" Alodine finish- so thin that tightening a bolt will punch through the non conductive conversion coating layer. You can test this by taking a piece of alodined aluminum and placing a smooth piece of metal on it (so as to not scrape the Alodine layer), and measuring the resistance between them.
This is covered in section 18.104.22.168 of MIL-C-5541, which can be downloaded here:
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