Analyze this(not a movie review).......

[M_D]

I have noticed that running past PAR usually makes dying easier. I have done a few parts lately that were run past PAR at equilibrium for 10-20 minutes and dyed solid black in 2-3 minutes. Blue hasn't been a problem, I have found if the blue doesn't take then it is a bad anodize job. Red seems to dye best if run past PAR. I have anodized to PAR, and the red wouldn't get dark, so I have pulled parts back out of the dye, rinsed and anodized more. Sometimes, just a few more minutes in the anodizing tank makes a big difference, and the red dye takes.

My red PH is high too, 7-8. I noticed when I mix a new batch of red, it will not work as well untill it ages a day or so. I have read that distilled water will drop in PH as it is exposed to air, because it absorbs CO2 which is acidic. The red dye concentrate seems to be fairly high on the PH scale.

[Sid03]

I think caswell should mix up some of their red dye and see what it measures new. Id be surprised if it is in the range that their dye supplier states it should be.


Today I ano'd another part to test things out again.....see if it would still work as it did yesterday. I ran a larger piece, and ran into something strange. After anodizing the part was very dark. Instead of a yellowish tinit, it was almost grey/black. I actually had to go get a camera to take a couple pics! Any ideas why something would get so dark? IT's suppose to be the same series of aluminum as I have been using also. It's dark enough that just sealing and having it look silver would be totally out of the question. Any ideas?

It's late, but if I did the math right PAR turned out to be 4.29ohms.

[NeoMoses]

Sid, I believe you calculated PAR correctly. The high value of PAR indicates a very thick anodized layer. This sounds like a higher current density than 4.5 A/ft^2 was achieved. I have achieved finishes like that when I was going for higher current density anodizes. I usually don't see a dark gray layer formed until my current density is over 15 A/ft^2 or so... I'm not sure exactly why your part reacted as it did.

By chance, was your part bead blasted? I notice that my bead blasted finishes always appear more gray than a gloss finish.

Please post your pictures, I'd be interested to see them. I'll post some of my pictures later on today.

[Sid03]

no, it was machine finished. It was either 6061 or MIGHT have been cast then machined. Would cast aluminum react like that? How can I post pics? Thanks

[NeoMoses]

Most cast alloys that I have anodized have turned very dark gray. The only color that takes well is black.

[NeoMoses]

Here's the picture that Sid sent me.

[Fibergeek]

Agitation promotes an even coating, the lack of it shouldn't prevent any coating or by itself make the coating thin.

Be careful about creating two variables in your experiments. Attack one variable at a time, you will make things harder to figure out if several things are allowed to change in the same experiment.

Different alloys or even small differences in prep. can cause the raw anodize to have different shades, so does current density.

Your description "scratches easily" is disquieting. although anodize doesn't achieve full hardness until it dries out completely, it shouldn't scratch easily. What do you mean by "easily". Coatings grown at way too low a current density (under 2A/sq.ft.) do this. Can you reproduce a good electrical connection? Unless you are using a real CC mode power source (the current is held constant, regardless of resistance and voltage) you will be at the mercy of any connection resistance. CC can compensate for this, up to its max voltage capability. This is called "voltage compliance". However; even with CC, the coating resistance (PAR) you calculate from current and voltage figures will be wrong if the connection resistance is high, or even worse, changing as you anodize. Anodizing beyond PAR may help this situation, but it doesn't fix the actual problem. Problems like this will return unexpectedly and will haunt you. Please take connections seriously.

BTW, the same evil effects occur with the "old method" no one was aware of it because they weren't trying to measure anything. Bad results were blamed on the aluminum alloy type, chemical reactions, etc. You still hear that alloys like 7075 are hard to anodize, no they aren't.

We've had some posts here lately describing the pains and expense pros endure to get good connections (racking) ever wonder why?

[Sid03]

Fibergeek- You dont think the lower piece in that picture looks VERY dark?The piece above it is what it started out looking like. I think it may have been cast aluminum. I will run some stuff that i KNOW is 6061 and see if everything turns out good again