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getting "stains" on my cast aluminum during polishing. What the world is it?

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  • getting "stains" on my cast aluminum during polishing. What the world is it?

    this one has me perplexed- lol. i take my time to get a good sanding job... i always start polishing with, at least as far as i can tell, a very smooth level surface.

    So after a couple seconds on the buff...i stop and wipe off...and i always end up with what looks like deep "stains" in the metal. I dont think i'm over heating the metal....i dont use much pressure?

    one time i tried some heavier "cutting" on those areas and it did basically get rid of them. but then as i progressed in polishing ....i ended up opening up small pits, etc. and ended up with a "bumpy" surface.

    Ugh....

    i use to work with a lot of mild carbon steel...hot rolled as it's called. many times as a coil was unwound....moisture in the laps would make light stains on the surface. That's what these sorta look like.

    i can't figure out if i'm doing something wrong, or if it's just how cast aluminum is?

  • #2
    Re: getting "stains" on my cast aluminum during polishing. What the world is it?

    A picture would help,i have seen stains on some cast aluminium that looks like if diferent type of material used in that casting would not mix properly but not all castings do that.

    as far as the opening up of small pits that is usually caused by removing too much material from the casting surface.
    http://www.peintureenpoudrepb.com
    http://www.polissagepb.com
    http://www.powdercoatpb.com
    baz

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    • #3
      Re: getting "stains" on my cast aluminum during polishing. What the world is it?

      baz---- yeah, thats what i figured. i took off too much material. lemme see if i can get a good pic of it and upload.

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      • #4
        Re: getting "stains" on my cast aluminum during polishing. What the world is it?

        Click image for larger version

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        maybe you can see the brownish stain? here's the strange thing....i re-sanded. then switched up my 'technique' and it was gone. 'course not sure if it was from sanding or buffing. i buffed in two opposite directions..and moved my work pc. much slower. maybe thats better. not sure!

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        • #5
          Re: getting "stains" on my cast aluminum during polishing. What the world is it?

          The surface seems very bumpy in the pic. I believe the pits are valleys and the brown is overheated raised up metal. I have polished cast aluminum (not exactly fun) and block sanded it to 1200 grit then started in with the buffs...

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