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Aluminum anodizing using sodium bisulfate solution contaminated

Discussion in 'METAL FINISHING, CUTTING & WORKING' started by eac67gt, Apr 15, 2013.

  1. eac67gt

    eac67gt United States Moderator Staff Member H-M Supporter-Premium

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    I have been using sodium bisulfate solution for anodizing with great results for a while now. The other day I repainted the light post in front of my house. The ornament on top was black like everything else and I wanted to see if I could anodize it like I did the decrotive balls on the ends of the ladder rail in posting http://www.hobby-machinist.com/showthread.php/14708-Another-anodizing-project . I stripped the paint off the piece and it definitely appeared to be aluminum. I cleaned it up good and polished it for anodizing. I went through all the processes that I normally do for anodizing. The whole time handling this it appeared to be aluminum What aluminum alloy is hard to say. When I put it in the anodizing tank it reacted just like the other aluminum I have anodized. It appeared to get a layer to it similar to the other parts I have done. Then I tried to dye it. It would not take the dye. I figured it was not a good alloy to anodize so I sprayed it gold and put it on the lamp post light.

    The tank solution was performing perfectly good the day before I tried this anodizing of the ornament. Now the solution will not successfully anodize my parts I have been anodizing. What happened to the solution? Did the metal the light ornament was made of contaminate the solution? I will have to refill the tank and start over to get my process back where it was. :bawling::dunno:

    Ed
     
  2. Walt

    Walt United States Active User Active Member

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    Hi Ed,

    I have no experience with anodizing, but some training as a chemist. The first thing I would look at is the pH of the solution. How do you normally determine when the acid capacity of the solution is exhausted?

    Walt
     
  3. eac67gt

    eac67gt United States Moderator Staff Member H-M Supporter-Premium

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    Hi Walt,
    Honestly this is all fairly new to me in the last 5 months. I have only been checking it with the hygrometer I use for the car battery. It gives me a specific gravity in the good range of a car battery. I know that sounds crazy I guess but it is all I have for now. I bought more chemical last night and distilled water and am going to refill the tank. It is only about 2.5 gallons so it is no big deal. I am still trying to understand all the ins and outs of this process.

    Have a great day!
    Ed
     
  4. Walt

    Walt United States Active User Active Member

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    Hi Ed,

    I certainly don't know the specifics of anodizing well enough to state definitively that what you are doing is wrong.

    But, I do know the main activity of the sodium bisulfate is due to it's weak acidity. That gets used up. My guess is that the specific gravity isn't going to work to keep track. A really inexpensive way to test for acidity is phenolphthalein.

    http://en.wikipedia.org/wiki/Phenolphthalein

    I'm not certain this test is sensitive enough for your need, but it's pretty cheap. I'll see if I can find a source for you.

    http://www.sciencecompany.com/Phenolphthalein-30ml-1-oz-P6364.aspx

    Is $3.50 plus shipping cheap enough for an evaluation?

    Edit/ I found a source for pH paper.

    http://www.carolina.com/ph-test-pap...rips-ph-00-to-60-pack-100/894727.pr?question=

    This isn't quite as cheap as the phenolphthalein solution, but will give you a more exact indication of the acidity of your solution. According to Wikipedia, the pKa for sodium bisulfate is 1.99. If memory serves, this should be the approximate pH you will see in a fresh solution. When the pH goes much higher than this, guessing about pH 2.5-3, the solution will be close to exhausted. I'll dig around more to confirm this. In any case, what you will be looking for is to take an initial reading. This should shift very slowly toward bigger numbers as the acid capacity is used up. At that point it will suddenly head toward pH 7, or neutral.

    Or you can just throw out the solution when it stops working!
    /Edit

    Walt
     
    Last edited: Apr 16, 2013
  5. eac67gt

    eac67gt United States Moderator Staff Member H-M Supporter-Premium

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    Thanks for the input. What I did was refilled the tank for now. I also ordered a digital ph meter that has a range of 0 to 14 with 0.1 resolution. It comes with case adjusting screw and buffer solution for calibration. Matching colors on a piece of paper is not one of my good points so I went digital. I think it will work good enough for my needs. What do you think. http://www.amazon.com/gp/product/B007Z4EYI8/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1

    It makes total sense in what you said about the ph rising as I use it. We have run a lot of parts through the one mix. The same parts I have been trying to get through in this batch were drawing twice the current in the old solution than in the new solution. This also made the tank heat up which is not good for anodizing.

    Well my alarm just went off telling me the batch in the new solution is ready to be checked. Hopefully this is all the problem was because things were going really good until now. The sad thing is in multiple tries of anodizing the same laser host I have destroyed some of the parts. Luckily I have another to replace it.

    Thanks again and have a great day!

    Ed
     
  6. outsider347

    outsider347 United States Active User Active Member

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    Ed
    I d like to give anodizing a try on some parts for a 911 I.m restoring

    where did you find the info to get started?
    Caswell?

    thanks for your response

    ed
     
  7. eac67gt

    eac67gt United States Moderator Staff Member H-M Supporter-Premium

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    To be honest if you are restoring a 911 I don't know if I would do anodizing if you never have done it before. There is a learning curve to it. The anodizing I do is using sodium bisulfate which is swimming pool ph negative. The pros and other hobbyist use sulfuric acid. Caswells is one place to get what you need if you are going to go sulfuric acid. I have had good results with what I am using but recently learned I need to keep a closer watch on the ph level. The issues I was having had to do with the ph level getting to high.

    See some of the links, if you already haven't, that are in this posting http://www.hobby-machinist.com/show...d-On-Anodizing-Aluminum-Info-Websites-Methods .
    Hopefully it will shed light on all the ins and outs of anodizing when you read these pages the links lead too.

    I want to mention when a part is anodized and it does not suit or has issues you can strip the anodizing off and reanodize. The problem you can get though is lose of material you are anodizing. The removal process uses caustic materials which will eat the aluminum away if you are not careful. This is why I warn against doing your 911. If the 911 is important to you and you want it anodized I would have it professionally done. Cost I have no idea.

    Ed
     
  8. Tom Griffin

    Tom Griffin United States Active User Active Member

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    Ok, I give up...what's a 911?
     
  9. eac67gt

    eac67gt United States Moderator Staff Member H-M Supporter-Premium

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    You know I am not really sure. After I thought about it maybe it is a Porsche 911. At first when I replied I thought it was a 1911. My brain don't work right. :nuts:

    Never the less if he is restoring something I would be leery about anodizing if you never did it before.
     
  10. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    I didn't know you could anodize an entire Porsche!
     
  11. PurpLev

    PurpLev United States Active User Active Member

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    well, the good news about this, is that for fairly cheap you are back in business, just a slight detour.
     
  12. Tom Griffin

    Tom Griffin United States Active User Active Member

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    Hmmm, a vintage 1911 has no aluminum parts, so it must be a Porsche. :thumbsup:

    Tom
     
  13. eac67gt

    eac67gt United States Moderator Staff Member H-M Supporter-Premium

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    Yep for $7 at Lowes I got more ph neg and refilled the tank. The solution was not contaminated just weak. I now have a digital ph meter and can keep an eye on it and just add more ph neg when needed. I wish I would have saved some of the old solution before I dumped it so I could have checked it with the ph meter just to see how high the ph had gotten. The new mix works just as good as it did when I first started about 6 months ago. When thing I did see that slowly probably degraded the solution was I would leave the cathode in the tank for extended periods of time and crystals would grow on it. There was one point I probably took a cup of crystals out after leaving the cathode in for 2 weeks. Now when I am done I take the cathode out every time.

    Hey Tony you can anodize an entire Porsche if the tank is big enough. :rofl::rofl::rofl::rofl:


    Ed
     
    Last edited: Apr 23, 2013
  14. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    Depends on the finish you want. Chemical stripping tends to leave a rough surface when I've had it done, even professionally, so if I wanted a smooth, consistent surface, I'd spend some time carefully removing it with abrasives, then polishing it as needed. The key is to make the finish prior to anodize match the desired end result. Shiny will be high gloss, something like glass bead will be matte. Most trim anodizing I've seen is not glossy, so I believe I'd go with a low pressure walnut blast or similar. If not done right, chemical stripping can leave pits that are impossible to hide.
     
  15. outsider347

    outsider347 United States Active User Active Member

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    Yep
    1979 Porsche 911
    The window frames are anodized black, but the PO allowed them to rattle in the doors resulting in the need of a re do

    would it be best to chemically strip the old anodize off, or sand it?
    Maybe best to then have the ano re applied by a pro
    what do you think?
    tks

    - - - Updated - - -
     
    Last edited: Apr 23, 2013
  16. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    Am I seeing things, or did I post an answer before you posted the question? That's the way it displays for me.
     
  17. eac67gt

    eac67gt United States Moderator Staff Member H-M Supporter-Premium

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    Are you seeing things or aren't you. Is the south pole really the bottom of the planet or the top. :headscratch:

    Yep that is the way I am seeing it Tony. First time I saw that.

    You are right on the money though Tony. I would not use a chemical means to try and strip the old anodizing off. If over applied it does pit the metal and there is a general loss of metal also. In a trim piece I don't think thinning of the metal is something you really want to chance.

    Maybe you should have it priced with a professional anodizer to have the old stripped/blasted off and re-anodized and then go from there. The anodizing itself you are probably going to want a pro to do anyway because based on what a lot of trim pieces are in size it would be costly for you to set up a tank big enough to do the pieces in.

    If you do the stripping yourself as Tony said it is best to use the walnut blasting to do least amount of damage.

    Ed
     
  18. motoseeya

    motoseeya Iron Registered Member

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    A lot of lamps for outside are not aluminum they are some kind of like pot metal I can't for the life of me pull the name out right now. I think my hard drive is just getting old. I will think of it
    in a day or too. motoseeya
     

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