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Newbie needs help with black dye and glossy finish

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  • Newbie needs help with black dye and glossy finish

    Here at my company we have been anodizing some small aluminum parts black. The turnout has been great, they are very black. Although I would like to match some other work that I had seen at a machine shop in town. All of their pieces have a glossy finish to them. Since you can still see the tooling marks on their pieces ( by the way it is 6061) I figured that it wasn't polishing before the anodizing. I have run my pieces with and without tooling marks (I am using drain cleaner to remove them) and all of my pieces are flat black. I am using caswells kit and was wondering if someone knows the secret to the closs finsh. Thank You. Shaw Aero Instruments.

  • #2
    might want to look at the polishing section on that

    but the bets work i've done to remove tooling is to purposely leave a good bit of metal on the part when tooling it, then use a belt sander to smooth it out by hand, this will take some mass off of the part so don't make it to perfect tolerances then try to take off tooling marks,

    touch up with fine grit sand paper and hit it with a polishing wheel and compound


    • #3
      I don't have the time at the moment, but I can tell you what I know latter.


      • #4
        Polishing the parts before anodizing will result in glossy finishes. With anodizing, it's wusiwug (what u see is what u get).
        Using drain cleaner to remove tooling marks will greatly add to the flat look you are experiencing. I suggest sanding the parts with 320 wet-or-dry aluminum oxide sandpaper, then polish with black compound on a sisal wheel, folloowed by tan compound on a spiral sewn cotton wheel (no need to go finer than that... the acid will remove a high gloss anyway).
        I do things.


        • #5
          Here are a few things I have found in regard to the subject, that work for us. First, it is correct that what you see as far as surface texture before anodizing is about what you will see after anodizing. It definitely won’t get any better, but will be dulled some, although the dulling can be kept to a minimum.

          If the surfaces are very nice and shiny as machined, then you should be able to get a quite shiny, almost polished finish, only with the tool marks. You need to degrease and clean without dulling the surface, which means either cleaning by hand or using a heated cleaner. Some cleaners, such as the SP cleaner Caswell sells do a good job heated, but once beyond 150º F will readily dull the surface, sometimes before fully cleaning the part. So, staying around 140º will help, as will pre-cleaning all visible traces of cutting oils in hot soapy water.

          Also, in many instances an etching step, usually involving an alkali such as lye or sodium hydroxide, is employed. This will dull the surface even more than the heated cleaner. I have found no need for this step on parts that retain the as machined finish. Our parts have almost a mirror finish as machined, and once fully cleaned in a manner to retain maximum gloss, anodize to a glossy finish. If the parts were older, or perhaps in a humid environment, there could eventually be an oxide formed on them that would inhibit a high quality anodized coating. If this were to happen, using a bright dip may be needed for best results (see next paragraph).

          If you need further enhancement on fresh parts (or to de-oxidize old parts without dulling the surface), either polishing the part or bright dipping it will increase the gloss. Bright dipping is not easily done safely (from both a health and environmental perspective) in a small shop due to the type of acid used and the temperature involved. Also, if the parts aren’t fully machined, some of the un-machined surfaces may not take the dye as well and will not be very glossy. It would depend on how much native oxide was on the un-machined areas, and that can vary a lot. The deepest and darkest black color on parts I have either seen or done were either as machined surfaces, bright dipped, or polished.

          The longer the parts are anodized the more they tend to loose their glossiness. Also, if your operation is not quite right yet, and you get excessive dissolution, the gloss will go away and the surface will look like chalky paint to one degree or another. So a thinner coating that dyes well may be best, depending on the look you are shooting for. A thinner coating looks somewhat metallic. If the coating is done under good conditions and built up thicker, it still will retain most of the gloss, but look more like a polished lacquer where there is not much if any metallic look left.

          Hopefully these points will help you achieve your goal.


          • #6

            Thanks, All of this info is very helpful. I will begin experimenting with all your suggestions asap.