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Re: Degassing Alluminium

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  • Lyle
    You don t need any borax to pour good sound aluminum castings. and really don t need to degas either if everything else is done correctly which is why I asked
    Message 1 of 8 , Jun 5, 2007
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      You don't need any borax to pour good sound aluminum castings. and
      really don't need to degas either if everything else is done
      correctly which is why I asked the question "why?"
      I only use my vacumn table for pouring stuff into rubber molds and
      the occasional jewelery.
      LL

      --- In hobbicast@yahoogroups.com, "Jack" <jacktarr68@...> wrote:
      >
      > MUCH SIMPLER if you just stir in some borax when you skim, then
      pour.
      > Most of my castings are machined before use...the ONLY times I have
      > found voids is when I was out of borax and poured anyway.
      >
      > You need a good size vac pump to be of any use otherwise too slow.
      > High temp vac chambers are a very neat way of relieving a
      foundryman
      > of a good chunk of his available credit.
      > Jack
      >
      >
      >
      >
      > --- In hobbicast@yahoogroups.com, "Lyle" <creepinogie@> wrote:
      > >
      > > Jax makes a nice table top vacumn caster. the other half of it
      > > doubles as a vacumn table for pouring plastic into rubber molds.
      So
      > > your idea is feasible but I need to ask why do you need it for
      > > aluminum? Are you making jewelery?
      > > LL
      > >
      > > --- In hobbicast@yahoogroups.com, "Andrew Mawson" <andrew@>
      wrote:
      > > >
      > > > --- In hobbicast@yahoogroups.com, "Mark Stacey" <pav@> wrote:
      > > > >
      > > > > I was wondering if hobby casting vacuum degassing is
      feasible.
      > > Place
      > > > > the crucible in a vacuum chamber, apply vacuum, release and
      > pour?
      > > What
      > > > > time is required to degas say a pint of molten alloy? Any
      one
      > > tried
      > > > > this for themselves and seen an improvement in casting
      quality?
      > > Google
      > > > > doesn't bring up any helpful links that give details on time
      > etc.
      > > > >
      > > > > Thanks to all those health and safety wonks who want to point
      > out
      > > how
      > > > > hot the metal is, I'll cook the vacuum pump, yada, yada,
      yada,
      > > DON'T!
      > > > > I just want to know if it's feasible. If no one knows I'll
      have
      > > at it
      > > > > and report back in a year or to based on my current
      completion
      > of
      > > > > project rate.
      > > > > Cheers
      > > > > Mark Stacey
      > > > >
      > > >
      > > > Mark,
      > > >
      > > > I'm sure it's possible, but I'm not sure it's the way to go !
      > > > Temperature control of the cooling melt is going to be a
      problem.
      > > >
      > > > Fed up plunging purple tablets and choking on chlorine fumes, I
      > > took to
      > > > bubble degassing using argon in a home made probe. Probe was a
      > > length
      > > > of 15mm stainless steel tube crimped flat at one end with a
      > series
      > > or
      > > > radial 1mm holes drilled just behind the crimp, and a 15mm
      lever
      > > valve
      > > > at the other. I use the argon cylinder and regulator from my
      TIG
      > > welder
      > > > and open the lever valve until bubbles emerge - do it for 15
      > > seconds
      > > > then withdraw the probe and pour the melt. Works a treat. It's
      a
      > > > physical process, not chemical, any inert gas will do. I used
      to
      > > use
      > > > dry nitrogen until I got the TIG
      > > >
      > > > AWEM
      > > >
      > >
      >
    • Mark Stacey
      Thanks for the information. This was pretty much what I thought my experiment would be like apart from fitting a big vacuum reservoir be linked in and out of
      Message 2 of 8 , Jun 6, 2007
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        Thanks for the information. This was pretty much what I thought my
        experiment would be like apart from fitting a big vacuum reservoir be
        linked in and out of the system. Just need to find the time now.
        Cheers
        Mark Stacey

        --- In hobbicast@yahoogroups.com, "Chris Horne" <chris@...> wrote:
        >
        > --- In hobbicast@yahoogroups.com, "Mark Stacey" <pav@> wrote:
        > >
        > > I was wondering if hobby casting vacuum degassing is feasible. Place
        > > the crucible in a vacuum chamber, apply vacuum, release and pour? What
        > > time is required to degas say a pint of molten alloy? Any one tried
        > > this for themselves and seen an improvement in casting quality? Google
        > > doesn't bring up any helpful links that give details on time etc.
        > >
        > > Thanks to all those health and safety wonks who want to point out how
        > > hot the metal is, I'll cook the vacuum pump, yada, yada, yada, DON'T!
        > > I just want to know if it's feasible. If no one knows I'll have at it
        > > and report back in a year or to based on my current completion of
        > > project rate.
        > > Cheers
        > > Mark Stacey
        > >
        >
        > I had a go at it once, (and only once) and I wouldn't call my
        > experiment a success, but it wasn't a failure either...
        >
        > The only way to be sure would be a microscopic examination, but I
        > didn't take it that far.
        >
        > Briefly, I used an Edwards single stage High vacuum pump which was the
        > pump on my home built vacuum former before I bought a better machine.
        >
        > I had a No16 crucible nearly full of molten Al
        > I stood it in a propane tank that had had the top cut off, (and ground
        > flat, first with an angle grinder, then upside down on a linisher)
        >
        > The vacuum pump was connected via a flexi hose to a 1/4 steel plate
        > which acted as the lid to the tank.
        >
        > The vacuum seal was a ring of old rubber sheeting, stuck on with
        > double sided tape.
        >
        > To guard against splashing of the metal, I laid a thin steel cover
        > over the crucible before laying the lid on and holding down to make
        > the seal before the vacuum took over.
        >
        >
        > The main problem was not being able to see what was going on inside,
        > If you try this, arrange to have a window of oven glass or similar to
        > look through.. the window doesn't need to be very big, maybe a couple
        > of inches..
        >
        > Anhywhichhow.. I had no idea of the temperature of the melt as I
        > couldn't work out how to dip my pyrometer for a short spell, I didn't
        > want to leave it in the melt for too long.. in case it cooled and
        > cracked the crucible...
        >
        > So I released the vacuum after a couple of minutes
        >
        > There was no appreciable difference between the castings produced this
        > way than those done with pool shock chlorine... except less smell,
        > more fuss, and more handling of the crucible.
        >
        > I haven't tried since.. my experiments have leaned more toward
        > permanent molds and vacuum assist, a much better use of the pump IMHO
        >
        > Chris
        >
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