Low Voltage

[Jim99]

Hi All,

I have anodized several small test pieces of 6061 1”dia. x 1 ½” long. They take color well and when passed through a rinse following dye bath (Caswell) very little dye leeches off into water. When placed in boiling water to seal very little dye leeches off into boiling water.

When I try a piece of 6061 about 6” dia. ¾” it takes dye well, but when placed in boiling water to seal some of the dye leeches off into the water, to the point that the water turns the color and there is dye residue in the bottom of the sealing bath.

When I anodize the piece I use a 34 volt x 20amp c/c – c/v power supply set to c/c. Following 720 formula for the 6” dia. piece I set the power supply at 2.6 amps. The volts start at about 8.8 and ramp up about .1 per 15 min. The volts never reach the voltage in the 720 formula. At 2 hours of anodize time the voltage is about 10 volts.

My question is why are the voltage numbers are so low.

Thanks, Jim

[cameraman]

I'm calculating your surface area to be 70.69 sq in. You didn't say what current density you're using - working backward from the 2.6 amps it looks like you're using 5.3 a/ft2?

Someone with more experience will probably have some better ideas, but it looks to me like you're not getting good agitation. You might also try lowering the CD to 4.5 to get a smaller pore size.

[rclint]

I have come to the point where I mainly steam seal everything. 90% of parts will seal perfect when dipped in boiling water, it's the 10% that leaches dye all the way from the pores that is the problem. Most of the dye leaching from whati have seen is from cast aluminum, still it seems to work better for me to just steam seal everything, and then spray it down with wd40 I think it was acidraing who gave me the idea on wd40, it works

Clint

[sswee]

Without all the details I have read between the lines a little. It appears to be a couple of things off not much but together enough to cause your problem. Anodize time is directly related to the CD run. If you ran the part for 2 hours, that was enough time for a 1 mil coating at 6 ASF. I also calculated 70.69" SA, which at 6 ASF gives an amp setting of 3A (2.95A). Did you not calculate the edge of the part? With a 2.6A setting your anodize time was in excess and caused dissolution.(larger pore size mainly in your case). As for your low voltage. What was the tank temp. and how was your agitation? The higher the tank temp and the lower the amount of agitation will lower the voltage needed to push the set amperage and cause dissolution. What was your peak voltage during the run? The peak voltage calculated in the 720 rule has many parameters influencing it. A higher tank temp or acid concentration(possibly from low tank level from evaporation) and miscalculated SA will all lower you peak voltage.
In general it sounds like the pore size is a little too large to hold the dye well. Let us know what you find out or if any of this was the problem.
SS

cameraman,
FYI - higher CD's and lower tank temps will give smaller pore sizes.
SS

[cameraman]

oops, thanks swee.
What CD & temp do you use, for example on 'rf putters in misc colors' (in gallery)? Would you use a different CD for a light color as opposed to a dark color?

[sswee]

I normally use 8ASF @ 60* for 1 mil. I don't change anything in regards to color.
SS

[Jim99]

Hi All,

Thanks for all your replies. Will try some small changes on the next piece I anodize.

Surface area was a guess as the part has complex shape. I used 60sq” as part size. Trying to figure out how to post picture, then surface area would be visible to all. I was trying for 6ASF and 1 mil thickness. Tank temp was 70° at start and 68° at finish (working outside and timed it for sunset in effort to control temp).

Agitation used filtered shop air to alum tubing coil with 1/16” holes, maybe too much, as part was swaying in tank.

The peak voltage 10.1 at two hours run time. Just set tank up, one part battery acid to one part distilled water; checked with battery hydrometer was 1100. Using 1/8” alum tig welding wire to hang piece.

I’m please with the color of first real piece, now will try 4.5ASF and shorter run time. My results have been rewarding for the little experience I have, maybe I’m worrying too much about voltage.

Thanks again, Jim

[Jim99]

Hi,

Posted two pictures, if you view you will see why surface area was a guess.

Jim

[sswee]

No problem with your tank temp. and the aggressive agitation doesn't hurt as long as it doesn't effect your hook-up. I can see the difficulty figuring the SA. The amount you were off was not critical. I don't know if I would drop the CD having trouble with pore size holding dye. The main problem is going to be the acid concentration. It's way to high for the current densities your running. It needs to be 1 part battery acid to 3 parts distilled water. Approx. 5% by volume. At the lower CD's, the higher acid concentration causes dissolution and the lower voltage readings.
SS

[Jim99]

Hi SS,

One of my problems is too much information from too many different sources. Reading too many articles before starting and adding information from one to another. Somewhere I read that someone was checking acid bath with battery hydrometer and setting acid concentration at 1100. Turns out to be about 1 – 1.

I though “Heck” I’ve got some battery acid, battery charger and battery hydrometer out in shop, I can try this. Got some Rite dye and tried it and got OK results.

That’s how I got going on a 1 -1 acid concentration. I have a small three gallon tank, so will be no big deal for me to reset acid concentration. Will end up with larger acid bath. That may be a plus. Kind of like horsepower If some is good, more is better and way too much is just right.

Thanks for the help. Jim