Splotchy anodize or dye result

[Fibergeek]

Thanks for the cleaning advise M_D.

Could you post the low resolution picture (conserving Caswell's BW) in the Sput Welder thread? Please add also any observations and/or comments you may have on it.

[sccc]

Gentlemen:

Sorry my reply is delayed, but other priorities intervened. Thanks to everyone, for all your advice.

I've run another test (photos here), and as usual, Murphy was there. The finish came out blemish free this time, but now the color is off. Two steps forward, one back!

I changed my procedures to comply with everyones recommendations. The piece was kept thoroughly wet at all times. Electrolyte temp was 72º at the start, and had risen to 75-76º at the end. Voltage ramped up as expected, rather quickly at first, continually slowing over time. It peaked at 11.2v this time, at about 70-72 minutes, and began slowly dropping. At 75 minutes voltage was down to 11.0v, so I figured PAR had been reached, and pulled the part out.

As you can see from the photos, the blemish problem is gone, but the dye didn't take nearly as well as the first attempt. So I'm guessing the temperature difference caused this. Since I prefer the deeper color of the first test, next time I'll drop the current to try and get the deeper color back.

M_D, what a great looking piece of fabrication! What color blue did you use on those parts? That’s just about the color I’m chasing after.

Thanks everyone!

[M_D]

sccc, it sounds like you made some progress. Also, thanks for the compliment on the parts in my photo. I believe that blue is called Electric Blue. We can get anything from a light tint to a very deep, dark, and rich blue with it, somewhat like the darker shaded areas look like in the photo.

Let me give you a few hints on color depth. First off, when you change one thing, like the current density, you usually need to at least change the anodize time, unless you were just out of the ballpark beforehand and need to bring one factor in line. If you lower the amperage, you would need to increase the time to keep it relatively even with what you just did. To make it darker, you may or may not need to increase the anodize (or dye time if it was short before) time even more. There is a saying that you can't change anything, without changing everything. That is, every change will affect the whole deal. You might even try anodizing at the same current, and increase the time another 10 minutes, or increase the current and anodize for the same time.

Different acid concentrations in the electrolyte, electrolyte temperature, and current density affect the pore structure. Generally, to an extent, the thicker anodized coating gives a deeper color potential. There is a maximum point though; I think fibergeek reported it is like 6 or 7 tenths thick. If you have the proper balance of acid concentration, temperature, and current density, you can juggle the anodize times and extend them further than you have done, without running into trouble. Some pore structures take and hold the dye better, or simply give a different look. For example, you can put a thick coating on and dye it a deep color, with the results looking a lot like a paint or powder coating. With a few little changes and a thinner anodize coat, you can get the same deep color, but with more of a metallic look.

I know it might sound over whelming, but the bottom line is there is quite a bit of latitude when anodizing, and experimentation and practice will help you to learn the boundaries and effects of certain parameters. Once you find a sort of happy medium where the parts turn out relatively consistent, then you can start adjusting the parameters and seeing where they take you. One thing I will say is this, consistent preparation and control of the variables is a must. Otherwise, you may have either an exceptionally good or bad result, and blame or credit the wrong thing, which can lead you astray. Once you get lost, you need a baseline to go back to. I think that is one of the best things about the LCD formula, if it is followed faithfully you will get good results. If not, there was something out of tolerance to find and adjust.

[Fibergeek]

Wernick, Pinner, and Sheasby in The Surface Treatment and Finishing of Aluminum and its Alloys report on testing for dye penetration in an anodized layer. The bottom line is that dye (any dye) won't penetrate any further than 0.7 mils (0.0007") regardless of what you do. For dyeing purposes, there is no point in an anodize layer thicker than 0.7 mils.

[Sid03]

related to part of this post....

Caswells desmut will also de-oxidize, correct?

[M_D]

Based on my testing it doesn't do that well for de-oxidizing, but if the parts are left in for hours it will eventually. There are other chemicals used as well as stripper or sodium hydroxide, but we use the sodium hydroxide on parts that we feel need to de-oxidized. Various alloys act differently, but ones like 2011 and 6061 will quickly have a smut layer form from the sodium hydroxide action. We leave them in until a light layer is formed, the time will depend much on concentration and temperature. It seems like a fairly strong solution with a short (30-120 seconds) imersion time works best overall for us, as compared to a weak solution and longer time.


Curiously, some alloys like 6063 (and 1000 series if I remember correctly) are much slower to form a smut layer and resists the normal dulling from the lye. We de-oxidize 6063 in the sodium hydroxide bath according to the 6061 times. The finished results and consistency are much better on parts that are totally de-oxidized.

We did get 5 gallons of Caswell's de-smutting concentrate, and do use it for that purpose and it works very well for that.

[Sid03]

so say I strip the ano off some parts.....let them dry, then polish. Say the parts then sit a couple days, or even weeks before ano. Your saying they can oxidize and the desmut/deoxidizer that caswells carries simply wont remove it?

[M_D]

We have anodized fully machined parts that are several weeks old (even a few months, actually), and they come out perfect without a seperate de-oxidizing step. So, unless there is something about the buffing process that causes parts to oxidize quicker than normal, I would guess the parts should anodize ok even after a fews weeks time goes by.

On the other hand we have parts that are vibratory tumbled, and they need to be de-oxidized because of that. Even if the parts are freshly machined, de-oxidized in sodium hydroxide, and tumbled for 10 minutes, they still need to go through the de-oxidizing step again before tumbling.

[seanc]

Gentlemen:

I began this thread under the login “sccc”, but that was a temporary login because my regular one wasn’t working, and I couldn’t get it reset due to ISP problems. That’s fixed now, so all my future posts will be from “seanc”.

I’ve run 2 more anodize tests, and now know the source of my original problem (I think), and can now get great results! See:

http://www.hogheaven.com/hobby/plati...fourthtry.html

neilfj, you had my problem properly identified first time. Keeping the part wetted at all times!

In my 3rd test, everything was going well until the after the part was sealed. In my haste to get it out of the hot sealant into the rinse tub, I dropped the part. By the time I could grab it back up, it had mostly dried. Doesn’t take long when the part is at 210º or so! If I’d have been thinking right, I should have put it back in the hot sealant, but I didn’t. I rinsed it, and the finish is horrible, as the photo shows. This might be salvaged by polishing, but I haven’t tried yet. Just wanted to get the photos first.

So on my 4th test, I did 2 things differently. 1) reduced dye temp to 120º (a recommendation I saw elsewhere), and 2) left the part in the sealant, and cooled the sealant by dropping the tank into a larger bucket of cold water. When the sealant was down to 90-95º, I pulled and rinsed it. It came out great! I plan to cool the sealant this way from now on.

So I think I’ve got this figured out, and my next run will be on the real parts.

Thanks everyone!

[neilfj]

Glad to help.