My first attempt:

[Indy]

I just finished my first batch with the LCD kit and while it wasn't perfect I was quite impressed with the results. One piece turned out pretty good but the others were mixed. I did five pieces in all and they included three different shapes.

• One piece didn’t take the dye at all (I was using orange) but it seemed pretty clear to me that the problem was with the connection for the piece
• The other three that didn’t turn out perfectly had a different issue. They seemed to take the dye pretty evenly and looked fine when I removed them from the sealant. After I removed them I let they air dry for a few minutes after which I started handling the pieces. Some of the layers started to rub off. The part was still orange just lighter in the places where the layer came off.

Here is a summary of what took place:

Surface area: 12 sq in.
Amperage: 0.25 amps
Peak Voltage: 7.50 volts (I never did reach this)
I was using the Caswell 3 amp rectifier

Voltage at start: 6.2 volts
After 15 minutes: 6.0 volts
At the end: 5.8 volts

The voltage never did climb, only declined gradually.

Ambient temperature: 67 degrees, temperature of anodizing tank should have been about 70 degrees as I was using the supplied heater

The time the parts spent in the anodizing tank was 144 minutes, as noted by the 720 calculator.

The parts spent 15 minutes in the dye and 15 minutes in the sealant. The sealant temperature was about 190-200 degrees but not at boiling. I am sure the dye temperature was quite high (about 150 degrees) but don’t know for certain how hot.

I forgot to do spray the parts with WD-40 immediately after removing them from the sealant tank and rinsing them. I also ended up handling the parts before I sprayed them.

The connections to the parts that did take the dye seemed good as the points where the aluminum wire was touching the parts didn’t take any of the dye.

I don’t know if handling the parts so soon after sealing them was an issue and after doing some research on the forum I noted that the problems I had may have been related to following:

• Not keeping the parts wet at all times
• Perhaps the parts spent too much time in the anodizing tank (I was using a 3:1 ratio to battery acid)

Can someone help me nail down a definitive problem? Thanks!

[Fibergeek]

• The other three that didn’t turn out perfectly had a different issue. They seemed to take the dye pretty evenly and looked fine when I removed them from the sealant. After I removed them I let they air dry for a few minutes after which I started handling the pieces. Some of the layers started to rub off. The part was still orange just lighter in the places where the layer came off.

This is the classical symptom of an excessive dissolution problem.

Excessive dissolution occurs in all degrees of severity; from a little surface powder that is easily wiped off and causes no other trouble, to outright failure.
It occurs when the rate of anodize formation is not fast enough to stay well ahead of the destructive dissolving (dissolution) of the anodic layer formed by the acid content of the electrolyte. If you are anodizing in CC mode you will see the voltage slowly go down over time, when it should be going up.

Anodic growth is controlled by current density and time, both increase it.

Dissolution is controlled by electrolyte temperature, acid concentration, and time, all of these increase it.

In your case; assuming the numbers you provided are correct, the main suspects are incomplete native oxide removal from the work, and lack of adaquate electrolyte agitation.

Any presence of native oxide retards or even prevents anodic coating formation, unfortunately it does little if anything to slow dissolution. Removing the oxide chemically is not as easy as it would seem, experienced anodizers work out their own procedure for removal and test it throughly, you can't be casual about this. For now, sand your work VERY THROUGHLY, and then clean it.

Agitation is commonly overlooked by beginners; the reasoning is that you are anodizing such a small piece in gallons of electrolyte, how can it have a temperature issue? In some cases you can't even measure any temperature increase in the electrolyte. Where the temperature counts is in the pores, not in the tank. Dissolution occurs in the pores, eating at them from the inside out. Agitation or aeration, or even stirring the electrolyte is the only way to get fresh (cooler) electrolyte into or close to the pores, where it counts.

In my setup (5 gallons of electrolyte) I use a 1/4 HP mechanical chiller, with digital temperature control, driven by a 420 GPH acid rated pump. This recirculates all of my electrolyte every 43 seconds, literally a "tempest in a teapot".
You don't actually need this much for LCD, but I've been fooling around with hardcoat (Type III) anodizing, where this level is mandatory. In practice; as long as all of the electrolyte stays in the tank, you can't have too much agitation, this applies to all anodizing.

BTW, I never put WD-40, oil, grease, wax, or anything else on the finished work, it simply doesn't need it to be the correct color or shade. This means I have dissolution firmly under control.

[M_D]

I don't have time for a comprehensive reply, but I'll point out some basics here. First, if you have an actual 12 square inches (.084 square feet) and used .25 amps I feel you are on the low side for current density. For instance, 5 amps current density would be .417 amps.

Second, you almost certainly anodized for too long. You have to under stand that although the 720 rule tells how long to anodize with a given current density to acheive a .001" layer, you don't usually need or want that thick of a layer. It is harder to get that much thickness without failure, especially in the beginning stages of experience. You might try 5-6 amps for 80-90 minutes, and see what that does for you.

While being exact is good, there is some latitude for average decrotive anodizing, so when parts fail it is likely that something is substantially out of order and you didn't just miss by a minute or 5% on the current.

Having the one connection fail may have even helped the remaining parts, as more current would have flowed through them.

Anodizing at a little higher rate of current density and for fewer minutes should help to straighten things out. You may have other issues also, but these two stand out.

Once the parts are sealed, handling them gently should not cause catastrophic defects.

[Indy]

I am using a 3 amp Caswell rectifier>>>

so I don't think I can get up to 5-6 amps. But I assume that I just need to up the current that I am running through the parts...and perhaps dilute the electrolyte? I will start with a higher current and less time and see what happens this weekend once my Ti clips arrive.

[Indy]

Ok...nevermind about that 5-6 amp comment

I just realized what you were saying...increase the amperage to 5-6 amps to sq ft.

Thanks!

[M_D]

Your problem sounds like dislution to me too. Yes, I meant 5-6 amps per square foot. And like fibergeek said, you need to have clean parts. I can't say conclusively, but I believe the real low current density might be a bit more sensitive to native oxide. But either way, it is one of several variables to control in order to be consistent.

Hopefuly your next parts turn out better for you.

[Indy]

Thanks to both you!

I will let everyone know how I get on.

[Fibergeek]

To explain what M_D is saying:

M_D is suggesting an entirely valid approach to fixing a dissolution problem, increase the current density so that the anodize layer forms faster. Increasing the CD has no effect on dissolution rate other than the increased power dissipation will raise the temperature thus increasing the dissolution rate, this too can be minimized by some agitation. This works more often than not and is easy to do.

I happen to know for a fact (and have data to support) that even on 2xxx series alloys (traditionally more prone to dissolution problems) LCD anodizing at 3 ASF will work fine, PROVIDED some sort of agitation is used. The downside to 3 ASF is that it is slow. It is included in the LCD range for those who are "power supply challenged", the reasoning being that slow is still better than not at all.

At least get a big wooden or plastic spoon and slowly stir the electrolyte for 15 seconds or so every five minutes while you are anodizing. You will be surprised at the improvement. Any and all anodization methods require agitation for good results, this is hardly unique to LCD.

[Indy]

Thanks again guys>>>

this time the results were excellent! I increased the ASF and did some manual stirring, as well as cleaning the parts off with some scotchbrite beforehand and I am very happy with the results.

Two questions if I may...

* What does it take to get to the peak voltage of 12.50 volts that I calculated? I only reached a peak of 8.6 volts. Is it just the connection?

* I was anodizing 6061 aluminum. Will there be a big difference if I begin working with 1050 aluminum?

[Fibergeek]

* What does it take to get to the peak voltage of 12.50 volts that I calculated? I only reached a peak of 8.6 volts. Is it just the connection?

* I was anodizing 6061 aluminum. Will there be a big difference if I begin working with 1050 aluminum?

Yes the connection to the work (anode) can do this, the voltage being off by that much is quite allot. If your PS REALLY IS operating in CC mode, a bad connection will make the voltage look too high, not too low. You know that you are operating in CC mode because the amperage shown on the meter stays at the value you set throughout the entire anodization, right?

The other thing that can do it is that your surface area calculation is wrong, thus the actual CD is less than you think it is. For this symptom, the calculated surface area is too small. Check your math.

The voltages will be a bit lower (10-15%) for 1xxx series alloys compared to 6xxx series, because 1xxx is closer to pure aluminum, and thus is more conductive.

[Indy]

Yes I am using a rectifier>>>

and the amps are staying constant. So the most likely culprit is that my surface area calculation is wrong? Could the low voltage also be because I am using an aligator clip to connect the tank bar to the positive lead?

[Fibergeek]

No.
Since you are sure that you are operating in CC mode, any bad connection will result in the voltage being too high. It doesn't matter where the connection is, they all count.

I use alligator clips too for connections that are not in the electrolyte.

[Indy]

I am an idiot



found the source of the surface area miscalculation. Thanks again Fibergeek!