What Happened?

[mti11988]

Well, I still have one plate that doesn't want to anodize. I am just about to put it through a 3rd time!! I am thinking I have some bad material or something. It is supposed to be 6061 T6 but I have no certification. When the finished part is placed next to other 6061 T6 parts I have done they look like ****. Like a burnt grey or something. Looks almost like old, corroded aluminum wheels that have been outside too long. They go in clean but come out looking like ****. Although they get harder and harder to clean up each time. Strip, Sand, Scotch Brite this time. The other parts look real nice.
As far as voltage goes it seems like I do have low voltages. Lower than I figured I would have. The voltage has never really been high on any of that parts I have done so far (not that I recall anyway).
Acid ratios are based on the kit I purchased. 1 Gallon of NAPA Battery Acid mixed with 3 gallons of water. I have a total of 3 gallons of battery acid mixed with 9 gallons of water for a total 12 gallon mix.
Baffled.

[sswee]

The burnt Gray sounds like smut. Are you using DeOx/DeSmut? The only parts I have had do just what you describe have been cast. I haven't run into plate or bar stock material that did it yet. What current density are you running?

[mti11988]

OK, you are way over my head on this. Today is made sure and dip the part in the desmut before going to the anodize tank so hopefully that will take care of any desmut issues. The manual says that desmut usually isn't necessary unless you use certain grades and 6061 T6 isn't one of those. But I did use the desmut today.
Current Desnity = ??
I bought the Cawsell Kit and I am following the rules in their manual. I think maybe 4.5 is the answer but I am not sure. I shoot for 4.5 amps per square foot. My voltage is much lower than what you or others are running but I don't see any real control over that with my setup. I must run the current correct I think. Voltage is what it is, right? Currently, I am running 16 amps through my system. The voltage drop from the rack to the cathode is about 5 volts. 2 volts (1.9) are being dropped across the resistor. So Total voltage is still only about 7 volts. This is different from the other day and I really don't know why. Same part, same setup, same everything except desmut.
I will know how this turns out in about an hour and a half.
Bill

[sswee]

The DeOx/DeSmut does more than desmut parts. On 6061-T6 where smut is not a problem, there are still natural oxides that form on the aluminum if it sits around for a time. The desmut removes these. If I have a part that is run and does not anodize, I strip/etch with sodium hydroxide long enough to remove any partial coating and desmut for 2 to 5 minutes. Unless you are after a high shine on the part, it should be ready to reanodize after this process.

Current Density or CD is the current run through the part per square foot to anodize. You use it on the 720 rule. You probably just haven't heard the term.

The voltage is governed by Ohm's law. The low voltage means there is little resistance against the current going through the circuit. It indicates how the circuit is. Low voltage can indicate connection problems, tank or part temp is high, acid concentration is high in electrolyte, or you may not be running the amperage through the part that you think you are.

If you have trouble again on the part. You may try running a higher CD of 6A per square foot one time. If for some reason you are not getting the current you think you are, it should show a potential problem by the changes it produces.

Steve

[mti11988]

Interesting. I found an ammeter with 0.5 amp resolution / accuracy for $90 from a supplier that someone here mentioned. I think I will be purchasing it today as I want to KNOW what current is going through the system.
Also, I just put a very small part in the tank that should require 1 amp at 4.5 CD. Circuit showed about the same 5 volts across the part when I set it up. I cranked it up to where I now indicate 1.5 amps amd the voltage across the part is about 9 volts. Much more activity in the tank. I can tell you this. My voltages do NOT match the voltages in the 720 rule calculator. Something must be wrong.
Oh, I also cleaned the Cathode Plates but it didn't seem to make any measurable difference in the Current / Voltage.

[sswee]

The voltage figured in the 720 rule calculator is just an approximate under ideal conditions. There are too many variables to get the caculated voltage all the time. I have had runs hit on it but for the most part are +-2V to +-4V. Everything has an effect on it. I let my tank evaporate down a couple of inches and it made a big difference on the voltage. I've seen tank temp change the voltage as much as +-4V.

What type of tank agitation are you using? If there is no agitation through aeration or a pump to circulate the electrolyte, the part temp and the electrolyte around the part goes up decreasing the voltage.

Where are you checking the voltage on the circuit?

How did the part do when you raised the CD up?

Steve

[mti11988]

I used an aquarium filter supplied with the Anodize Kit for agitation.
I check the voltage with a digital voltmeter. Cen Tech Brand.
The part leveled out at 1.3 amps which is correct per the 720 rule calculator. I also had about 11.6 volts through the part when I checked it again. The part came out real good this time, of course it is a small part and those have always been working to some degree or other.

I really hate to bother you further with this but now I have a question about color. I am doing clear anodize and the part looks duller than we we get them commercially done. They also have a slight green tint to them. The sealer from Caswell is green. Does this have anything to do with it?

[sswee]

No bother at all. I haven't had any discoloration due to the sealer. If I run to 1 mil coating it gives a yellowish coloring from the thickness of the coating. It could look like a green tint in the right light. You might try going to a .5 mil coating. It should take care of the color problem and help with the dullness. You might check with the commercial shop to see what thickness they anodize to. Anything else don't hesitate to ask. SS

Just a thought. If the small parts do good and problems arise with the larger parts, how close is the part to the cathode on the larger parts?

[mti11988]

About 6 inches away whenI run the plate. My cooler is about 12.5 - 13" wide on the inside and the plate is 1/2" thick. I get closer with the small parts acually. I do not go below 3 inches.
Thanks

[sswee]

The larger SA in the tank will have an effect on the voltage and the proximity to the cathode. Always thinking about the problems that don't find a definite answer. SS