Prepping aluminum and copper for paint
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  1. #1
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    Default Prepping aluminum and copper for paint

    I'm thinking about using white vinegar to pickle the surfaces before using a two part industrial primer.
    What other choice is there?

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    Quote Originally Posted by rons View Post
    I'm thinking about using white vinegar to pickle the surfaces before using a two part industrial primer.
    What other choice is there?
    That is interesting, for aluminum you buy an etching primer that is made for it. Dont know about copper alloys. It will be interesting to see what people have to say.

    Charles

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    Thanks Charles.

    Maybe a weak solution of pool acid in water. Or a weak solution of paint stripper.
    The copper will be heating up and then cooling down as part of an air compressor condenser coil.

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    Would the paint not insulate the copper if you are using it to cool the compressed air?

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    Quote Originally Posted by CBlair View Post
    Dont know about copper alloys. It will be interesting to see what people have to say.

    Charles
    Is a layer of tarnish better for adhesion or a bare clean shiny surface?

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    Alumaprep for aluminum. Then prime and paint.

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    Quote Originally Posted by DavidScott View Post
    Would the paint not insulate the copper if you are using it to cool the compressed air?
    To prevent the copper from corroding on the outside surface and turning to a washed out muddy looking brown color it is worth the small sacrifice in efficiency.

    Analogy would be giving a dog a little bit of vanilla ice cream sacrificing a little bit of health for a lot of happiness.

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    Here is a quote from a forum;
    I am actually an AC product manager for a large OEM, so I can be of some use on this question.
    Being an AC geek, it kills me to think of painting a beautiful aluminum HX. That being said, here are a few options:
    1. HVAC houses sell "coil cleaners" that are typically foaming alkalines or acids. Using one of these on your HX could leave it very shiny and sexy looking indeed. You would want to remove the condenser first to avoid etching other things. (BTW: Don't ever let your HVAC repairman use one of these on your home system if it is made of copper tubing and aluminum fins. It will accelerate galvanic corrosion.)
    2. In FLA there are several coil coating businesses that can give you several choices of coatings and colors. Truthfully, if the coil is all aluminum microchannel it doesn't need coating for anti-corrosion. You could get a very sexy gold color that would stand up to "beauty shop toxicity" but it will cost a few hundy. For DIY or turnkey, try Blygold Florida - Blygold
    3. Paint the darn thing. If you do paint it, expect degraded performance. Best case scenario is a 5% loss of capacity at 90F. That's if you can control your paint thickness to < 0.5 mils or so. If you hand spray the coil with off-the-shelf paint, expect to see way less cooling at high ambients and reduced compressor life.

    Can I Paint My A/C Condensor? [Archive] - MX-5 Miata Forum

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    The link has a comment relating to black body radiation for improving performance.

    Thanks guys for giving me a pause on the paint idea. My compressor came with the inter-cooler painted.
    I'm thinking about stripping the paint and just leaving it.

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    For aluminium, I have used etching primer in spray can for years (available in car painting shops). With good results, both for epoxy and single component paints.

    For copper - if You want to have really good results, then there is a whole industry where copper is painted all day all night - printed circuit boards (PCB) ! And the temperatures etc in PCB world are quite harsh.
    How its done ?

    2 possibilities

    1) we use following process.
    a) cleaning (degreasing) with peroxide solution - removes all stains and fingerprints
    b) structural etching whish leaves pocket with negative walls (imagine a cave). Solution of acids and inhibitors (ant-acid basically)
    c) anti tarnish coating, which oxidizes the surface with strong and thin oxide layer

    And then, the 2 component paint adhises like hell, it withstand molten lead and all the hells imaginable.

    Other process which is used and which is much better alternative for home shop - degrease and roughen with sandblast.
    And You could use PCB paints, these are quite cheap and available and you can paint directly to copper. They need 1 hour at 150 deg Celsius for curing or maybe 8 hours at 120 deg.

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    I once had an iron Sportster with some borken fins ... cut pieces of copper to fit the broken areas, brazed them in, bead blasted then black wrinkle and baked in the oven for an hour at 300.

    Saw the bike several years later, still looked good, you couldn't see the repair at all.

    You might be overthinking this, you can always do a quick sand then hit it with a little more rattle-can if it gets too shabby

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    I can do bead blast but the object is too large and heavy for a blast cabinet. Would have to drape some plastic and then go from there. But not today.

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    Quote Originally Posted by rons View Post
    To prevent the copper from corroding on the outside surface and turning to a washed out muddy looking brown color it is worth the small sacrifice in efficiency.

    Analogy would be giving a dog a little bit of vanilla ice cream sacrificing a little bit of health for a lot of happiness.
    No problem, just brush their teeth when you're done. Done it many times, often after a trip to the vet as there was a Ben and Jerry's nearby.


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