Shielding gas

[Garreth]

At work we TIG weld mild steel, aluminium and some stainless.

We are currently using BOC Pureshield Argon.

Whilst looking through the BOC catalogue I noticed that they say Alushield Light (70% Argon / 30% Helium) can be used for TIG on mild steel and aluminium plus stainless. The thickness range for mild steel and ally is thicker than with Pureshield Argon. I assume this is because the Helium gives a hotter arc ? The catalogue claims a flatter weld profile and faster travel speeds so that would make sense.

We are due a bottle change and I was wondering what peoples thoughts were on swapping to Alushield light ? This is for TIG only we use Argoshield universal on the MIG.

Cheers !

Garreth

 

[^neo^]

Lube up before you do, it's friggin pricey!

 

[Garreth]

They're paying not me

We don't use much - if its better I'll get them to change.

Cheers !

Garreth

 

[hotrodder]

I assume this is because the Helium gives a hotter arc ?

Yeah, helium increases the arc voltage (ionisation potentials or something complicated). It's very nice on thicker sections of ally (when someone else is paying) even if the welder is powerful enough that you don't need it. Never used it on carbon or stainless but i'm thinking it won't offer that much other than more expense and might be a PITA on thin sections i.e. i wouldn't consider it a total replacement for pureshield

 

[Omniata]

You'll need a higher flow rate as well with Helium being lighter than air...

If you were to use pure Helium you need nearly twice the flow rate, at nearly three times the price it has to be worth it...


Add to that, Helium supplies are diminishing so costs are going up even more...
It's extracted from oil from the oil wells, not from air, so you'll appreciate that it's value is related to oil...

 

[backpurge]

You'll need a higher flow rate as well with Helium being lighter than air...

You dont need a higher flow rate, in fact, if you are using gauges that are calibrated for Argon you set your flow slightly lower.

If you normally use Argon at 10 ltr/min and you swap to Alushield Universal you want to set your flow to around 8.5 ltr/min to give the same flow (it's all to do with the molecular size of the gas)

 

[Omniata]

You dont need a higher flow rate, in fact, if you are using gauges that are calibrated for Argon you set your flow slightly lower.

If you normally use Argon at 10 ltr/min and you swap to Alushield Universal you want to set your flow to around 8.5 ltr/min to give the same flow (it's all to do with the molecular size of the gas)

I was referring to the required flow and pure Helium, not what gauges he was using or mixed gas ...

It still stands from the older tech manuals, and some modern, that you need double the physical flow on account that it's lighter than air, as it doesn't cover the weld pool by flowing down over it but instead flows up and away, also the extra gas is required due to the ionisation effect that is more prevalent with Helium than Argon...

If you use a lower flow with Argon gauges, etc, that's fine and is a good point to note