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Racking Material Question. 6063 vs Ti.

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  • Racking Material Question. 6063 vs Ti.

    Hi All. I have a small 5 gallon type 2 anodizing line running in my home shop, Just a proof of concept and practice at this point before I ramp up to a full sized system to bring anodizing in house at our main shop. My question for now is regarding racking material.
    I have tons of architectural 6063 extruded aluminum I can use to make custom racks, and from my research it seems there are several benefits to Al racking. More conductive, less heat and cheaper. Drawbacks; They don't last as long, you have to strip before every use. And that kinda brings me to my questions.

    1) If I strip the anodize layer from the rack before use, then I would also need to take the rack's surface area into consideration for my 720 rule calculations, right? I mean, it's going to anodize just like the parts on the rack.
    2) Assuming the above is true, how is it that for titanium racks you don't need to consider the rack's surface area for 720 rule calculations? Does the titanium anodize so little that it's negligible?
    3) Why do I have to strip the entire aluminum rack before use? Can't I just anodize the whole rack, then only strip/scrape off the areas where I need contact with the work piece? That way I get the benefit of aluminum's better conductivity and lower cost, and the anodic layer will insulate the rest of the rack. I suppose the question is how long an anodized rack would last. The acid will eventually eat away at the anodic layer(right??).
    4) What about titanium clad aluminum? Anyone have experience with it? And to that point, what else can I cover aluminum racks with to improve performance and lifespan? I remember reading about aluminum racks for sale that had some special cladding or treatment.. can't seem to find it again.

    I know it's allot of questions but they're all around the same problem. My actual issue is that I have so much 6063 laying around that it would be a shame to spend a ton of money on Titanium racks when we can make our own. And I will kinda sorta be limited with my rectifier size and feel I can push more material through with Aluminum racks than Ti and create less heat.

    Thank you in advance for any advise.

  • #2
    if you dont strip your entire piece of aluminum, it will contaminate and ruin your anodizing solution when you drop the anodized aluminum into the anodizing tank.<br />
    <br />
    using titanium racks now will save you money later. they will "anodize" but when you anodize titanium the color of the rack changes color by the amount of currant that is applied. this doesnt effect the rack. you wont have to worry about stripped the layer of anodizing bc essentially, you cant.

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    • #3
      Using Aluminum Racks will eventually contaminate the bath with excess of Aluminum, Your much better off to use Titanium Racking.
      --
      Jason Vanderbroek
      315 946 1213 x116
      www.caswellplating.com

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      • #4
        Go ahead and use your aluminum racks. Dissolved aluminum is inevitable regardless, aluminum cathodes or the very parts you are anodizing will release aluminum into the tank at the start of each run anyway.

        1) If I strip the anodize layer from the rack before use, then I would also need to take the rack's surface area into consideration for my 720 rule calculations, right? I mean, it's going to anodize just like the parts on the rack.
        If you are using the 720 rule then you will need to account for it.

        2) Assuming the above is true, how is it that for titanium racks you don't need to consider the rack's surface area for 720 rule calculations? Does the titanium anodize so little that it's negligible?
        Ti may draw less current but you still need to account for it.

        3) Why do I have to strip the entire aluminum rack before use? Can't I just anodize the whole rack, then only strip/scrape off the areas where I need contact with the work piece? That way I get the benefit of aluminum's better conductivity and lower cost, and the anodic layer will insulate the rest of the rack. I suppose the question is how long an anodized rack would last. The acid will eventually eat away at the anodic layer(right??).
        You can do just as you mentioned with stripping only the bottom section of the racks after each use too. Regarding rack life, disolution isn't a concern IMO if they are thick enough they will last you a very long time depending on how many runs you plan to do per week.

        If anodizing is going to be added to your shop as you mention then dealing with DA is just part of the process. Whether you choose to learn how to do your own tank titratation or it or send it out, monitoring and maintaining DA and Acid Depletion is just part of the game.

        4) What about titanium clad aluminum? Anyone have experience with it? And to that point, what else can I cover aluminum racks with to improve performance and lifespan? I remember reading about aluminum racks for sale that had some special cladding or treatment.. can't seem to find it again.
        I can't answer this question, no experience with the material.

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        • #5
          My take...

          1. Yes include all AL racking in the area calculations. Another thing with AL racking is make sure the rack alloy is compatible with the part's alloy. If you anodizing 2024 AL parts with 6061 AL racks you will be disappointed with the results as the two alloys anodize at very different rates.

          2. If you use TI racks you would not include the racking material in the area calculations. Stripped TI will stop drawing appreciable current after about 30-40 seconds at a given voltage.

          3. If you don't strip the AL racks between each use, you cannot know how much current goes into the rack and how much goes into the part and therefore you can't accurately predict your coating thickness. This would be like anodizing a part with 0.5 mil on it together with a stripped part. Both parts will grow oxide, but it's unpredictable. If you strip each time, you always start from a known condition and have a better chance of achieving your desired results.

          4. Since the only part of the rack that would anodize is the exposed surface, treat TI clad AL racks the same as you would TI racks. Insofar as the process is concerned, the bath never makes contact with the AL inside the clad racks so it is irrelevant.




          Last edited by KevinB; 12-05-2018, 09:21 AM.
          Process control doesn't give you good quality, it gives you consistent quality.
          Good quality comes from consistently doing the right things.

          Process control systems for Anodizers
          If a post helps you out LIKE the post
          I'm not an Amateur Metal Finisher. I've just been around the industry for a dozen years or so helping and consulting when and where I can.

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