ano fading....

[Sid03]

Did some parts a couple months ago. Parts are half red and half orange. The orange seems fine(although may be harder to notice since its a liter color) but the red is fading. Actually, it seems to rub off. If you rub it a bit with your finger, you will get a small amount of pinkish/red on your finger.

....bad sealant?

[Fibergeek]

No, dissolution problem. You anodized it too long, or at too high an electrolyte temp.,or at too low a current density, or some combination of these. This is the "chalky residue" I posted to you about previously.

[M_D]

I think it is dissolution also. I have had it happen. Once or twice was because the parts were accidently left in the anodizing tank too long. Another time was when we changed the electrolyte, which threw our normal time data off. And I have seen it when the temperature got too high as well.

The parts might look super when first dyed, but when they are sealed and or dryed, the truth comes out. It doen't seem to affect the part evenly, so some areas may look "ok", while others are not ok.

[Sid03]

im not sure about that. Im very familiar with the chalky residue.......and this doesnt have it. The finish was a nice deep red........even, with no residue on the surface.

Its been a couple months, and after the part being handled regularly you can just now see spots of the red fading to silver.

The parts looked absolutely fine after sealing and drying. Had a nice shiny red finish. You sure what you mentioned is correct? In fact....I have some of teh same parts laying around that DID have the chalky finish problem I discussed before and they are yet to fade clean to silver......and have been used much more then the red parts.

[M_D]

I do know there are various degrees of dissolution. When it is barely noticable you can leave scratch marks in the anodized finish with a course nylon brush, but it won't necessarily rub off, at least not right away. Then there is the extreme where the anodized layer basically falls off.

I guess I couldn't swear that is your problem, but it sounds like it to me.

[neilfj]

Its more a matter of where the cell walls have broken off that affects what symptom you see. Dissolution thins the walls of the anodized cells, eventually eating them away almost completely. If the dissolution is stopped before the cell is completely eaten away, the thin walls will remain, which are easy to fracture and break. On a dyed piece, the closer the break is to the metal substrate, the more of a whitish appearance they take. Since the dye doesn't penetrate the entire depth of the cell, a good portion beneath the dye is still clear. When the cell breaks low, this clear part of the cell shatters and cracks, giving what appears to be a whitish powder. (kind of like salt crystals..salt looks white, until you look at it with a microscope where you see the crystals are clear).

If the cell shatters higher up, there is a higher the percentage of the dye that is present and a lower percentage of the clear cell wall. This will give the powder a color similar to the dye being used.

What appears to have happened in your case is that the tops of the cells, including the sealing plug, have broken off, giving you the colored powder. What remains is a small portion of the clear cell wall, through which you will be able to see the silver of the aluminum metal.

Just a guess without being able to examine the part, but it seems to fit.

[Sid03]

my point is...there is no powder or chalky residue. When the parts were finished, they looked fine. The color is simply fading............mostly rubbing off in areas where the parts are handled often.

[Fibergeek]

Yes.
Like Neilfj said; The top most parts of the pore structure have broken off, taking most or some of the sealant with it. With no sealing the dye will "fade" (actually its coming out). If you soak these parts in alcohol (any kind) or even water, does the dye come out? If any does, you lost your seal.

[Sid03]

so, just for the record...........using sealant thats outdated 3 months and using it below temp COULDNT cause what i mentioned?

[Fibergeek]

Outdated sealant? You didn't mention that. Could that be the cause? I don't know, maybe. I still think dissolution is more likely.