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Splotchy anodize or dye result

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  • neilfj
    replied
    Glad to help.

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  • seanc
    replied
    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:



    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!

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  • M_D
    replied
    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.

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  • Sid03
    replied
    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?

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  • M_D
    replied
    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.

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  • Sid03
    replied
    related to part of this post....

    Caswells desmut will also de-oxidize, correct?

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  • Fibergeek
    replied
    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.

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  • M_D
    replied
    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.

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  • sccc
    replied
    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!

    Leave a comment:


  • Fibergeek
    replied
    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.

    Leave a comment:


  • M_D
    replied
    The temperature very possibly was a factor, as the other guys have said. We have got some very nice results at 80-82º, but it is on the edge and if other parameters are off much failure is likely. The light spots on your part may because the electrolyte (acid) began to damage the areas anodized surface, it rarely would be even over the entire surface. Have you tried to wipe the streaks and spots off? Sometimes you get residues on the finished part that wipe right off, or at least with a little effort come off. It is important to rinse thoroughly and especially when using hot solutions you need to get the parts out and into a rinse tank in the least amount of time possible.

    In our operation, the parts are pre-cleaned as needed to remove all visible contamination, and then cleaned in a final hot solution. Hand scrubbing with brushes and detergent such as Dawn dish soap in water as hot as is comfortable to work in, with rubber gloves, is effective also.

    Getting the parts clean, in other words free of all oil, grease wax and etc., so water will sheet, might be only half of the required preparation, depending whether there is native aluminum oxide present. Aluminum oxidizes readily so unless the oxide has recently been removed somehow there is going to be some amount present, and it is next to impossible to tell by looking at the parts how much or how thick the oxide is. The oxide retards the formation of a good anodized coating, and if the oxide varies in thickness, you will get an uneven color, with the light areas showing where the heavier native oxide was. Parts that have an even oxide coating may turn out with an even appearance, but it is harder to get the colors deep. We do a lot of fresh and fully machined parts (the entire surface is machined), in which case we do not have to de-oxidize them, and they come out looking bright and shiny. So in addition to cleaning the parts of oil and etc., for best results the oxide has to be remove so all that is left is clean bare aluminum.

    The oxide can be removed in various ways. The Caswell stripper, or a mixture of sodium hydroxide and water, will remove the oxide, and etch the part to some degree. You have to experiment to get the right mix ratio to suit as it affects the final look. A weaker mixture (say a few teaspoons to ¼ cup per gallon) takes longer, 10-20 minutes depending on temperature and will leave a flat surface (low gloss), and a strong (12-16 ounces lye per gallon, use with caution) will tend to do the job in 10-60 seconds and leave a brighter surface. But once it starts to bubble hard, if left in longer it will dull and flatten the surface also. If the part gets a light film of smut on it from the lye, it should be sufficiently de-oxidized. The smut can be easily removed with the Caswell desmut solution.

    As far as 100% surface coverage it is true that it can’t be done. Most commercial anodizing is done with titanium racks. Depending on the parts size and what it require to fully secure it on the rack, a couple of small sharp contacts may be all it takes, but there will be at least at least a couple of little pinpoints that aren’t anodized.

    Fibergeek, this is a photo of some of the parts I used the CD Welder on that I told you about, I have higher resolution copies if they would do you any good.

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  • M_D
    replied
    ..

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  • Fibergeek
    replied
    I would suggest using some hardware store aluminum barstock, say 0.25" x 1" or similar. This is practically guaranteed to be 6061 or 6063, the most common alloys in use, and has excellent anodizing characteristics.

    Like you said, anodize is an insulator. This means that it is physically impossible to have "100%" coverage. You aren't looking close enough. The pros have gotten real good at hiding the connection point(s).

    Connection resistance obeys Ohm's Law exactly, 1 ohm of connection resistance will drop 1 Volt for each Amp applied, exactly.

    You should add some old fashioned vigorous scrubbing to your cleaning process, you'll find that it works wonders. Perhaps M_D or Easttex can make some specific recommendations, since these guys (among others here) are anodizing for commercial purposes.

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  • sccc
    replied
    fibergeek, thanks for the comments!

    As I’ve replied to neilfj, I will better control the parameters next time and post new pictures of the results.

    The test pieces I’m using are cut from an old 1/8” plate which I’ve had for a number of years, not recently machined at all. After polishing it with the “wadding” polish, I had sprayed & rubbed it off w/simple green, rinsed it and left it to soak in hot SP degreaser for 15 minutes. Since it passed the water break test, I presumed it was good to go. But perhaps not? Will SP degreaser not get at embedded polishing compounds? What's better to use?

    Notably, the reverse side was only brushed and blasted, so there was no polishing compound/chemical there, yet it shows the streaked finish. A different effect than the polished side though.

    Whatever I’ve done wrong will hopefully be resolved w/tighter temp & rinse control next time.

    Regarding my DMM resolution, you are right. I have my decimal point off by one. My bad, I should have checked the numbers more carefully before posting. The resolution is 0.1 ohm, and I use that AFTER taking test lead resistance out of the equation.

    With test leads clipped together, the meter reads steady 0.9 ohm. With the leads about 1 cm. apart, w/in the connection area, the meter fluctuates between 0.9 and 1.0 ohm. With leads about 3 cm. apart, on either side of the connector area, the meter fluctuates between 1.0 & 1.1 ohm. So I had presumed this is the natural resistance of the aluminum. Is it possible that even this low a resistance is interfering w/anodize current flow?

    With one test lead on the anodized area, continuity goes open circuit, so I know I’ve got SOME degree of growth there. I don’t have any means of actually measuring thickness, but I’ll try a crude scratch test later, and see how hard it is to break through.

    As a trivia after thought, I wonder how the “big boys” do their anodizing to get 100% coverage. Until I started to learn about anodizing, I never knew that it was an insulator. But I’ve got a few pieces in my scrap pile that are 100% covered. These are some @ 1/16” plates, 3x10”, some dyed red, some black, which I picked up from an aerospace surplus place, just for possible project use. They appear to have been from a production test, since they are stamped w/alloy identification, e.g.. 7075-T6 & 6061-T6. I just took a closer look at them, and there is nowhere that I can find any spot where a mechanical or electrical connection was made. Even the edges appear 100% anodized. Is this possible? How’d they do that?

    Thanks for your help!

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  • sccc
    replied
    neilfj, thanks again.

    Regarding temperature, I've been working from Caswells plating instructions. For the earlier, non-LCD, method they list a range of 65-80º, w/72º being optimal, so I fudged a bit and figured 82º would still give reasonable results. In the LCD specific instructions, they only mention the 70-72º optimal temp., but I presumed the range would be appropriate to both methods. Is the temp that much more critical w/LCD?

    I had also assumed that one could manipulate one or more the variables to compensate for others that were not w/in range. e.g., if the temp were higher than desired (softer, open pores), you could run at a higher current (harder, closer pores), and the 2 results effectively cancel each another.

    I've also realized I have a natural chiller. Over night temps still drop to 55º here in the northwest, so I'll just set the bucket outside one night, and run the test in the early morning after (the obvious is always the last thing you think about!).

    Regarding the connection, I think you've misinterpreted the photos, and I could have explained it better. If you look at photo 4, right side, the 1cm.sq. area centered on the hole is the only connection spot. As you can see, this area is clearly delineated by the dye. Electrolyte did creep up the sides, but the connection point itself shows no anodize growth, still has 100% continuity, (w/in 0.1 ohm, see my next response to fibergeek), and absorbed no dye whatsoever. The aluminum connector itself shows similar characteristics. The exposed surface did get some wetting by electrolyte, and did take some dye, but the mating surface is clean w/ full continuity. So I have to presume the connection was good. I'll try something different next time.

    I used the 4.5 amp/sq.ft. because it is recommend as the best compromise between hardness and dye absorption. Caswells recommended range is 3-6 amps, with the lower giving softer, open pores, w/more dye absorption, while the higher current gives the harder surface at the expense of dye absorption. I might have to try a higher current density as you suggest.

    re: the unknown alloy: isn't that always the case w/hobbyists? The "real life" parts that I plan to anodize are of unknown alloy, and since the manufacturer has been defunct for 40-50 years, there's no way to find out. I just have to wing it here, and try to get an acceptable test finish and see how it works, then try the real piece. The "real" piece(s) are of cast alloy tho, so I need to find something similar to test with first.

    Thanks for your help.

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