Fading anodizing color

[Dan Orcutt]

I'm not sure if this is the best place to put this, but here goes:

I am anodizing rediguns, which are from cast (356 T) alluminum. I then laser engrave (+/- 40 watt ) the customer's logo onto the parts. In the past we had no fading (anodizing color) issues. We either had color or not. (Due to a poor rack)

Recently our initially decent colors have faded after a day or two, in some instances to almost no color at all. These would be indoors, no moisture, etc.

I changed the anodizing bath, tried to clean up the dyes, built a new rack (titanium) to get a better electrical contact, and still am having issues.

Note: These parts are taking color in about a minute, as opposed to 10 minutes in the dye.

Anybody seen similar or ideas on where to fix the problem?

[Kev Williams]

I was speaking to a customer the other day, he makes aluminum intake manifolds, and he told me
they won't even try anodizing cast aluminum because half the time it doesn't work

I machine and etch more anodized aluminum than just about anything, but I wish I knew more
about the anodizing process...

(for that matter, I wish some of the anodizing shops knew more about the process!)

[Mike Null]

+1 on that! It seems to be more of an art than a science.

[Mike Cowlishaw]

The key is likely the prep - what are you doing to them when you start the process? I'm going to guess you are doing soft ano? I have a LOT of the stuff I make hard ano'd. The guy at the ano house, tells me the key is always the preparation. Castings often require some special prep to be successful......
(unfortunately my favorite place for 35 years is going out of business next week, due to a lot of zeal from the .gov people - but that's another topic)

[Dan Orcutt]

Yes, cast is tricky. Our process' worked for a year plus, then..........

I've tried to go back to the originals, but I am missing something. The color has to be being absorbed into the part, or so it seems. It doesn't seem reasonable to be evaporating.

[Dan Hintz]

You have to be absolutely sure cast parts are clean of all processing chemicals, because cast has an easier time holding onto them. If not cleaned properly, not only will your item fail to anodize properly, but you'll also contaminate each bath it goes into, hosing any further processing of parts.

Have you changed dyes? If not, fading color generally means the color has not really taken hold and/or you're not getting a good seal after dyeing. Make sure your anodized layer is thick enough... do you have the equipment to measure the thickness? If not, send a set of sample pieces out... one from an old (but good) batch, one freshly anodized but likely to fade, and one that has faded already.

[dave standing]

You need to ensure that you have an anodised film thickness of 25 microns. Anything less and you won't get enough dye in the honeycomb to have any chance of sealing it in. The sealing process is to boil the parts in distilled water for at least 15 minutes. This hydrates the aluminium oxide at the surface end of the cells, under a microscope it looks like the end of a shotgun cartride. This locks the dye in and gives you lightfastness.

[Mike Null]

I agree with Dan. Every time I've had quality issues it has been because the processor allowed his process to become contaminated. The first thing that happened was that the parts were not cleaned. You wouldn't believe the junk this anodizer was producing and shipping. My customer finally switched to powder coat.

[Kev Williams]

This is one of my favorites- can someone explain this to me so I can explain it to the plating shop?
$1400 worth of aluminum that I fab into operator control panels for multi-million $ equipment came back like this-
and not the first time...

rainbow.jpg

[Dan Hintz]

This is one of my favorites- can someone explain this to me so I can explain it to the plating shop?
$1400 worth of aluminum that I fab into operator control panels for multi-million $ equipment came back like this-
and not the first time...

rainbow.jpg

Light interference rings... bad distribution of current over the plate (likely provided by a point source, not a mesh). Note how the layers add up to a single point in the middle.

[Neil Pabia]

This is one of my favorites- can someone explain this to me so I can explain it to the plating shop?
$1400 worth of aluminum that I fab into operator control panels for multi-million $ equipment came back like this-
and not the first time...

rainbow.jpg

I'd bet some hippy will pay big bucks for that...lol