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Science Forum Index » Engineering - Joining (Welding) Forum » TIG inert gas question CO2
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| Harald Noack |
 Posted: Tue Jan 23, 2007 1:32 pm |
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Hello!
Does anybody know why NO CO2-inert-gas is used in TIG-welding ? (only
He,Ar,..)
Thanks!
Harald Noack |
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| MES |
| Posted: Tue Jan 23, 2007 1:39 pm |
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Because CO2 is an active gas that is known to increase penetration in a
weld.
"Harald Noack" <noack@sbox.tugraz.at> wrote in message
news:ep5c99$os2$1@skirner.kfunigraz.ac.at...
Quote: Hello!
Does anybody know why NO CO2-inert-gas is used in TIG-welding ? (only
He,Ar,..)
Thanks!
Harald Noack
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| Richard Smith |
| Posted: Thu Jan 25, 2007 5:35 pm |
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"Ipeak" <pgtaw@hotmail.com> writes:
Quote: CO2 is an active gas, not inert. CO2 breaks down in the arc and will
oxidize the tungsten electrode and the weld. Not sure why its not an
issue with short arc MIG where 100% CO2 can be used, assume that short
arc is cold enough process and deoxidizers in wire electrode are
sufficient to keep weld clean.
Hi
As Ipeak says, CO2 in your shielding gas when TIG'ing would rip your
tungsten to pieces. The tungsten is non-consumable and any CO2 in
your gas it is consumed!
In MIG, as the wire is fast fed and consumable, reactions of the wire
in the gas don't matter from the point of view of running an arc.
TIG using inert gas -- unlike all other welding processes(?), TIG is
penetrative even when running with pure inert gas. Dunno why - any
expert say why this is?
So for special metals (Ni, Ti, S'less) needing a pure inert shield you
can TIG weld and you get the deep narrow penetrative welds you would
certainly be looking for.
MIG is inherently unpenetrative. Active gases (notably CO2) increase
pen. How do you get away with using CO2 (oxidising) for general
fabrication? - because there is going to be oxidation going on...
Well, the oxide of iron has a lower melting point than iron itself.
Steel holds that characteristic until you start getting up to
higher-alloy and stainless steels. So the oxides forming float out on
top of the weld pool. So, to put it simply, you get away with it...
A few dexidisers as part of the consumable wire composition and you
suffer no detriment whatsoever.
Now, you can't "get away with it", using CO2, if the oxide of the
metal has a higher melting point that the metal - which is the case
for most other metals.
Well know example:
m.pt of Al metal - ~600degC
m.pt. of Al2O3 (alumina) - ~2000degC
But because iron is this exception, it is v.cheap to extract. So
there is a lot of steel about... Which is what you end up welding
most of the time. Which is why you meet a lot of Ar/CO2.
OK?
Rich. S. |
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| Kryptoknight |
| Posted: Sun Jan 28, 2007 11:35 am |
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the "O" in co2 is the problem element.you can use "mag" (metal active gas)
CO2 with tig, just not on metals that required inert gas, like stainless and
aluminum, etc.
"Harald Noack" <noack@sbox.tugraz.at> wrote in message
news:ep5c99$os2$1@skirner.kfunigraz.ac.at...
Quote: Hello!
Does anybody know why NO CO2-inert-gas is used in TIG-welding ? (only
He,Ar,..)
Thanks!
Harald Noack
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