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Thread: Degassing confusion

  1. #31
    Senior Member
    Join Date
    Aug 2012
    Hinchinbrook QLD
    I just use dry chlorine for degassing my ally melts. About a teaspoon for 6-800 ml of liquid. On my last melt I had a much larger volume of liquid ally, about double, so I roughly doubled the dry chlorine too. But the resulting casting was much better in terms of porosity. So if I double the volume of metal and double the volume of CL why is the net result different? Have I not been using enough CL to start with? Is there a minimum amount of CL required to get the chemical reaction needed? If i went 4X with the ally could I stay with 2X the CL and still get a good product?

    Cheers Phil

  2. #32
    Senior Member Robert's Avatar
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    Sep 2008
    Charlotte, Nascarolina
    My guess is that you just had less gas in that batch. If you keep you atmosphere oxidizing you may not need to degas at all. I don't degas and I have had very few porosity issues.
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  3. #33
    I've been reducing my aluminium scrap to ingots for later use.
    I faced a couple of the muffin tin ingots in the lathe and the resulting surface had black inclusions.
    When I polished the face it showed up even more very very small black spots.
    Would this be the hydrogen porosity everyone is talking about?
    The melts weren't de-gassed or fluxed.

  4. #34
    Iirc hydrogen porosity leads to voids (think like foam) instead of inclusions. Do you use a charcoal furnace? Maybe the inclusions are bits of carbon?

  5. #35
    any easy way to get the carbon out? i have some doing the same when machined.

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