Sciencey tig shield questions.

[Maker]

I get the feeling only @hotrodder will know.

Does helium produce a "hotter" weld than argon because it has a higher ionisation energy?
Or is it because it has a higher electronegatavity? Or something else?

If it's related to electronegavity, would neon work as a shielding gas even hotter than helium?

What about other noble gasses, krypton, xenon or radon*? Supposing you could get your hands on a tank (I found datasheets for these (not radon of course) from Linde so it must be available), would they all produce a colder weld?

Or am I completely wrong and it's got nothing to do with ionisation energy or electronegativity?

*Theoretically, if we pretend it's stable and ignore the fact that it would decay into mostly lead within a week.

And on a similar note, would nitrogen work or will the temperature of the arc cause it to react? Would it work for back purging?

 

[eSCHEn]

Interesting question Maker.

 

[hotrodder]

Backpurge will know FAR more about this sort of thing than me, probably TechnicAl too

AIUI it's the ionisation potential of helium that makes it 'hotter' by raising the arc voltage. Dunno what the deal would be with the other noble gases, comparing their ionisation potentials to argon and helium would give a clue. Density alters things some too, i would've thought xenon and and the theoretical version of radon would be too heavy to be useful? And i'm guessing they're all more spendy than argon?
ETA, I'm guessing the arc would be a different colour too

AFAIK pure nitrogen would trash the tungsten/nitride it. Same deal with many other metals, nitrogen embrittlement of steels and Ti for example. It is used for purging some flavours of stainless. It encourages the formation of austenite so can be used to mess with weld chemistry a bit (duplex flavours) and save money if purging large volumes with the austenitics.

Hydrogen is sometimes added to both argon and nitrogen for welding and purging (respectively) stainless. It raises the arc voltage a bit for higher travel speeds and is also very good at scavenging any O2 local to the weld so improving shielding quality at the same time. Argon + a little hydrogen is also useful for inconels which tend to have a sluggish/scummy weldpool without it. IIRC usually around 1.5 - 5% is added for manual work, upto ~ 10 or 15% for automated but i might be making that up

http://www.boc-gas.com.au/internet.lg.lg.aus/en/images/BOC Purging while welding brochure351_68116.pdf goes into far more detail on purging with nitrogen, argon and hydrogen mixes

Somewhere on the forum is a thread where Backpurge talked about (and posted some vids) adding tiny amounts of O2 to argon to improve arc stability when welding ally

 

[Maker]

AIUI it's the ionisation potential of helium that makes it 'hotter' by raising the arc voltage.

All I could find for ionisation potential was was this graph.

Which would suggest that neon would be hotter than argon but cooler than helium and other gases would all be colder.
I also found this thread where they talk about the possibility of using neon.

 

[Maker]

(and extracted from liquid air...so horrifically expensive)

Argon, oxygen* and nitrogen* are also extracted from liquid air by fractional distillation. Neon is more expensive because it isn't as abundant and there is less demand.

Xenon wouldn't be a good choice..due to its use as a general anaesthetic

Xenon is even less abundant so is even more expensive.

*I think both can be extracted using a "molecular sieve" but to a lower purity so it isn't used industrially.

 

[Maker]

Backpurge , can you help?

 

[eSCHEn]

Backpurge , can you help?

Some good info in the repair thread backpurge has done Maker: http://www.mig-welding.co.uk/forum/threads/repair-to-a-vespa-engine-casing.56723/

 

[Maker]

Some good info in the repair thread backpurge has done Maker: http://www.mig-welding.co.uk/forum/threads/repair-to-a-vespa-engine-casing.56723/

It was reading that I remembered I wanted to tag him here.

 

[eSCHEn]

Poor bloke is not gonna get any peace from us lot lol.

for you backpurge

 

[backpurge]

Will get back when I sort out how to condense it into something that makes sense

 

[Maker]

Will get back when I sort out how to condense it into something that makes sense

Does it make sense yet?

 

[Appyasme]

Looks like the share index for Morrisons

 

[fixerupper]

Gosh ,there are some very clever folk on this forum ....jeff