Dye not absorbing... with pictures!

[Chevalier]

I have taken a few pics of what i have been anodizing and hope someone can shed a little light on my problem!
Pic 1

http://homepage.eircom.net/~chev2010/2004_0218_164738AA.JPG

I ramped the voltage from 0-18 over 2-3 min and left in a 10% bath for 60 min. The part has a yellow tint, won't take any dye(cold or warm), but does seem to have a anodic layer(can be scraped off).

Pic 2

http://homepage.eircom.net/~chev2010/2004_0218_164806AA.JPG

Connection out of the acid to be sure it won't fail!, no dye absorbed, there is a anodic layer that can be scraped off. Done using LCD in a 5% bath, final voltage 10.8V @ 4.5asf.

Pic 3

http://homepage.eircom.net/~chev2010/2004_0218_164818AA.JPG

Connection out of the acid to be sure it won't fail!, no dye absorbed, there is a anodic layer that can be scraped off with a bit of effort! I ramped the voltage 0-18 over two min, 60 min in the 10% bath.

Pic 4

http://homepage.eircom.net/~chev2010/2004_0218_164844AA.JPG

This is what is really bugging me! the parts seen(except the failed one seen earlier) were done using a cheap battery charger when i first tried anodizing things! using an old cloth dye that I found in a cupboard.

I bought some new dye thinking that was the problem, but it doesn't work on these parts either! When anodizing the parts, the room temp was about 6-10 celsius(42-50F). The original parts that did take dye look great!

Any ideas? / anything I didn't mention?
Thanks

[neilfj]

First, are you using Caswell's Dye?
Was the temp of the dye 'room temp' also?
What was the temp of the anodizing tank electrolyte?

I had trouble dyeing at lower temps and found that using the dye at 130-140F solved the problem.

I also also found that the electrolyte at 70-75F improved dye absorption.

If your electrolyte and dye temps are indeed 'room temp', I'd give it another try at the higher temps.

[NeoMoses]

Take a look at the graph in this thread: http://www.caswellplating.com/bbs/vi...765&highlight=

That is 12 A/ft^2 constant current anodizing in a 1:1 acid:water electrolyte. If you'll notice, the peak voltage is about 15 volts, and doesn't get near that until about 15 minutes into anodizing. Ramping from 0-18 volts in 2-3 minutes is sure to give you a higher current density in the beginning than you are expecting. 18 volts in general sounds a bit high for a 10% acid bath. Try ramping from 0-13 volts in about 5-10 minutes in the same acid bath, also anodizing for 60 minutes. I'd like to see how that turns out.

What type of power supply do you have?

[Chevalier]

Thanks for the suggestions. When I was trying to dye the parts, I put them in the dye when the dye was at room temp. seeing that this didn't work, I slowly heated the dye with the part still in it, but this didn't do anything!
Neomoses: I'll give 13V a shot and let you know how it goes. I just got a lab supply that does 0-18V and 0-10 Amps.

Thanks

[Fibergeek]

Ramping up the voltage in order to keep the current at the desired level mimics the operation of a current source. But you have to monitor the current to do it correctly. If you have a lab power supply, use it in constant current mode. It will ramp the voltage automatically and correctly, you don't have to do anything.

In another attempt to dispell the oldest anodizing old wive's tale:

Many believe (including a suprising number of anodizing professionals) that anodizing in Voltage Mode; ramping up the voltage at startup, forgives the requirement to know the surface area of the work. If you don't know the surface area it is impossible to know the current density. This is Ohm's Law; being a real physical law, it cannot be defeated, if you try to beat it you will be its victim every time. It will only be a matter of degree.
Many pros rely on doing a batch of anodizing of more or less the same size, so that the surface area is (more or less) the same. They have learned by experience that this batch size will have (more or less) a given current density for a given voltage. Also by experience, the particular voltage ramp applied will (more or less) mimic the correct V vs. I curve (Ohm's Law). In cases where these assumptions fall apart, and poor results are obtained, it is blamed on chemistry, alloy composition, etc..
This practice has its origin in the primitive power supplies that were available in anodizing's "stone age", CC mode wasn't practical on a large scale. This is no longer the case due to the advances in industrial electronics over the past 50 years, but old habits die hard.

[Chevalier]

Well, I tried another part, and it still doesn't work(using CC)! So the next thing that I think can be improved on is heating my acid bath. I'm thinking of buying a fish tank heater(the glass bar type-because they are cheap and the one I am looking at is adjustable from 60-90F). The only problem I can think of is keeping the acid bath mixed so heat won't build up in one spot, I've seen Neomoses system(very nice) but was thinking an air system would be easier to rig up and try, the only problem with the air system is the forming of acid mist(big problem?) and would it actually spread the heat from the heater around the tank?
The air temp. around here is about 41F, so the bath would be way below 72F!!!

Thanks for any input.
Robert

[Fibergeek]

If your ambient air temperature is around 41 deg. F. your electrolyte temp. will be close to it, and way too cold. By all means warm up your electrolyte to 70 -75 deg. F.

If you review NeoMoses' and Neilfj's agitation system threads again; and price out the parts, I think you'll find an aquarium "jet pump" agitation system is as simple and cheap as a suitable aeration system. I doubt that agitation or aeration will make any thermal problems for you on this scale.

[NeoMoses]

ahh, you're not running at room temps! Yes, that is definately a factor in dyeing. I can see differences in color from 68F to 72F. You need to get that tank temperature up to at least 65F to anodize, 70-72 would be ideal.

[M_D]

I looked at the pictures, and in the first one I noticed the pits and the distinct color patterns. It appears the part may be burned (pits and dark uneven color) from too much power and/or time. Your tank temp may be too cold, but with enough excess power I think you can still burn it. I suppose what I see as pits may be simply nicks or other surface imperfections that were present before. If that is the color obtained straight out of the anodizing tank, and it wasn?t burnt, then it may not be cleaned well enough of oxide and other surface contaminants.