Inconsistent Coloring

[PrecisionPB]

Heres what we run:

*Hyui Yi (sp?) 20a Rectifier

*10 gauge copper wire for connections (save connections to part in tank, for which we use a small gauge TI wire)

*15 gallon anodizing bath, 3:1 acid/water ratio. Electrolyte kept at 72 F.

*Caswell provided dyes, mixed with 2 gallons of distilled water. Dyes kept at 140 F.

*Parts anodized for 90 minutes at 6A/Sqft.

*Surface area calculations estimated, due to the non-uniform nature of parts being done.

*Parts throughly degreased and deoxidized before anodizing.


We seem to have trouble getting a good color match, sometimes within the same batch. Shades different, but with a rich glossy finish that holds up to wear and tear. Whats up? Suggestions? Do you need more information to help me out?

Thanks!
Rick

[sswee]

Are all the parts the same grade of aluminum?
Do the parts have the same finish before anodizing?
Do you have any chalky residue on the parts after you finish?
Are you using the 720 rule for you calculations?
What does your voltage peak at and finish at?
How long in the dye bath?
What colors or all?

It is probably something simple. These questions just help see a better picture of the situation.

[PrecisionPB]

To the best of my knowledge, all parts are of the same grade of aluminum.

Yes, all parts possess the same finish before anodizing.

Yes, some parts will have a chalky finish after sealer, but typically not after dye. This is usually remedied with a small dose of oil on the part. Some parts also show small discolored areas, but this is a rarity, and seems to be remedied by good prep work.

No, I dont use the 720 rule, or at least not in its entirety. Mostly, because I am confused by some of the numbers needed to input in order to calculate correctly.

15 - 30 minutes in dye, depending on how quickly color "takes".

Black seems to be the only color that turns out great, nearly every time.

[sswee]

From what have you said, I don't see any one thing that stands out as a single cause. How do you attach your wire to the part? If you have problem parts in a batch, it would indicate a weak connection on the parts with problems. The chalky residue indicates the start of a dissolution problem. How is your tank agitation? You probably haven't noticed if the problem parts come from the same area of the tank. Possibly a dead area or just not as much circulation promoting dissolution. How many parts in a run? What numbers are causing confusion in the 720 rule? For a .5 mil coating you are over running the part by 30 min at 6 ASF. Also a cause for the chalky residue. Let me know what you think or find. SS

[acidrain]

You are using the exact same CD, ano time, acid ratio and temperature as I am.
I have great results after dialing in my prep process. Something I always do now is etch (red devil lye) and de-smut. This seems to help get the parts down to virgin aluminum for trouble free anodizing and dyeing. Here is my process:

Degrease in lacquer thinner, blow dry with compressed air.
Etch in 70F Red Devil lye in 3gal water for a few minutes (more to strip old ano from parts). Rinse with distilled water.
De-smut @ 110F for a few minutes until bright white, rinse with distilled water.
Repeat those steps if any discoloration remains.
Prepare finish... bead blast or polish.
Rack the parts.
Degrease in lacquer thinner, blow dry with compressed air.
Only handle parts with gloved hands from this step forward.
Clean with 140F SP degreaser, rinse withy distilled water, check with water break test.
Immediately anodize the parts.
Rinse with distilled water.
Dunk in distilled water/baking soda neutralizer tank.
Rinse with distilled water.
Dye parts in filtered 140F dye solution for 15min (or less if lighter color is desired).
Rinse with distilled water.
Seal with filtered 200F nickel acetate solution for 20min.
Rinse with distilled water as the parts come out of the sealer (don't let the sealer dry on the parts).
Finish the sealed ano with WD40 and wipe clean.

By chance are you anodizing paintball gun parts? Which parts give you the most problems? Are they repeatedly the same problems?

[PrecisionPB]

After figuring out the 720 calculator (duh, I CANT believe I didnt understand it before... brain fart or something) and adding the acidic neutralizer as suggested, I have had nothing but flaw free work in the last several batches.

Thanks guys, really appreciate it.

[sswee]

Glad to hear it. I have had the occassional brain fart a time or two. What do you think was the primary cause on the color problem? acid contamination or anodize time

[PrecisionPB]

Having had Fibergeek mow down my theory on surface area calculation, Im going to have to say it was the acid contamination.

I tell you one thing: I have done 4 batches of differing SA's since I posted this thread. Since then, I have added the neutralizer, and begun using the 720 calculator. Maybe its my new positive attitude, but flawless batches since.

[sswee]

Having something come out good does wonders for ones attitude. Now if I can stop dropping parts after polishing them to anodize, I'd be happy.