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coating on brass

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  • coating on brass

    I have some brass that I've cut up for use in electrical contacts. It started life as a decorative piece for a kitchen or vanity, so it came with a coating of some sort that I didn't consider when I cut it up. It had a protective paper on one side which I peeled off, and this is the side that's coated. I apparently don't have a solvent that will eat it- tried acetone, toulene, lacquer thinner, etc.

    I tried burning it off, and it smells very much like epoxy when you burn that- and this experiment is over, I don't want that smell in my shop. It didn't actually burn off even with direct flame, but it did get a little weaker. It still took some effort to sand it away.

    So far, sanding it off is working the best, but that's labor intensive and my fingers are already tired. There's a very slight curl to these strips, a consequence of using the shear, so scraping isn't working well either. Any ideas?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Probably a 2K urethane clear coat like you use on a car. Tough as nails

    Bead blast it..

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    • #3
      Yes, I think it is a urethane, not an epoxy- the smell is similar but not quite the same.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        Hmm- I just remembered the Cole Parmer chemical compatibility chart, so I looked up polyurethane and sulfuric acid. It said 'severe effect', so - having some muriatic acid on hand I just dumped the load of strips into a container and poured some acid in. We'll see how that goes.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          Well I got my answer- muriatic acid is eating it right up! At first it didn't seem to be doing anything, so I left it for a while, then gave it a good cold water rinse so I could handle the pieces to check them out. Of course I dumped the whole lot into the relatively small container, so the acid couldn't get to all the surfaces that well. Now I have a larger container and have the pieces spread out, so it should complete the process. But the results on a few of the pieces were great- I could just push the coating away with my thumbnail. No effect on the brass that I can see, but I don't think I'd leave it too long anyway.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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          • #6
            Originally posted by darryl View Post
            ... muriatic acid ... No effect on the brass that I can see, but I don't think I'd leave it too long anyway.
            Brass is copper and zinc, and muriatic acid loves zinc. So I would expect the surface zinc to be dissolved, leaving a more copper (redder) appearance. I think the "not too long" is a good approach.

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            • #7
              Much better than using acid, which likely had little if any effect on the actual coating, would have been paint remover, Tal-Strip or similar. Automotive type stripper would likely have melted that stuff right off, at least it has for me for removing coatings on decorative aluminum, etc, but acid very likely only attacked the underlying metal which caused the coating to be released. I suppose the coating is off now BUT what did it do to the metal? As someone else pointed out it likely dissolved the Zinc, or most of it, to a certain depth (that may not be a problem??) but for sure the surface of the brass has undergone some changes due to the contact with the strong acid.

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              • #8
                There was some slight discoloration, but very little. As I suggested I didn't leave it in the bath too long, probably 15 minutes or so. The 'treatment' didn't dissolve the coating, it left me with strings of it in the acid bath. There was little to no requirement to 'peel' anything afterwards, just a few passes with a thumbnail to push it away. Yes I did wash it all with plenty of water before sticking my hands in it, and I also used a generous amount of baking soda in the last wash as a neutralizer.

                For a reference I have the first few strips that I used elbow grease on to remove the coating- these never saw the acid. I can't tell any difference in the coloration between them, nor can I feel any lost of strength in a flex test. For my application, if the surface has lost part of its zinc that's fine since its an electrical contact anyway and if there's a higher concentration of copper on the surface that's good.
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  Originally posted by radkins View Post
                  . . . very likely only attacked the underlying metal. . .
                  How do you suppose it got to the underlying metal? Had to get through the coating first!
                  Southwest Utah

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                  • #10
                    It started from the edges of the strips. It appears to me that the surface of the coating tried to stay intact while the edges curled up, drawing the acid in under it.

                    I just checked a few more of these brass strips for conductivity. Before any further steel wool or sandpaper treatment, a light touch with a probe shows continuity over the whole surface. The coating is truly gone.
                    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                    • #11
                      Originally posted by chipmaker4130 View Post
                      How do you suppose it got to the underlying metal? Had to get through the coating first!
                      Not at all, it simply went under the coating and dissolved the metal at the point of adhesion, acid will not do anything much to a plastic type coating.

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                      • #12
                        Originally posted by darryl View Post
                        It started from the edges of the strips. It appears to me that the surface of the coating tried to stay intact while the edges curled up, drawing the acid in under it.

                        I just checked a few more of these brass strips for conductivity. Before any further steel wool or sandpaper treatment, a light touch with a probe shows continuity over the whole surface. The coating is truly gone.

                        As is any oxidation or any other surface contaminate, although the oxidation will eventually return, so it could be that the acid left you with an even better surface.

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