CO2 oxidising?

[monkeymark]

I'm new to this so go gently

I recently welded galv sheets together using a Clarke 90 with flux core wire.

Seemed pretty good to me apart from running out of wire.

A fellow employee who knew to our site came in and took the **** at the spatter. I mentioned it was done gasless so he said it would be crap.

Mentioned I could have used co2 when he replied that using co2 would oxidize the sheet and render the weld useless.

Thoughts please. He's a know it all but it's made me think.

 

[mike 109444]

I hope not cos I've been restoring my car using CO2 !
Recon he has it wrong. BOC do large cylinders of CO2 as well as the mixes So what does he think they are for?

 

[hotrodder]

Yes, CO2 has an oxidising effect as it's dissociated in the arc into CO + O2. He's talking utter rubbish though in that while straight CO2 isn't ideal CO2 is purposely added to MIG (strictly speaking MAG as CO2 is an active gas rather than inert) shielding gas mixes like argoshield because it adds energy to the arc amongst other things. Many mixes also contain a little O2 because small amounts help weld 'wetting' by lowering the surface tension of the weld pool http://www.boconline.co.uk/en/produ...es/shielding-gases/argoshield/argoshield.html

The welding wire contains deoxidisers which 'mop' up oxides both resulting from the shielding gas and rust/scale etc on the steel. Silicon is one several elements used for this that's often visible on the surface of the weld as 'silica islands'. While you were using gasless/self shielded flux core wire there are also gas shielded/dual shield wires that can be designed around 100% CO2 or argon/CO2 mixes... http://www.lincolnelectric.com/en-g...ons/Pages/shielded-flux-cored-electrodes.aspx
TIG never uses gases containing any CO2 because it instantly oxidises the tungsten, as a result mild steel TIG wire is generally alloyed slightly differently to MIG wire, explained in more depth here http://www.mig-welding.co.uk/forum/threads/best-selection-of-rods-for-a-workshop.22172/#post-243247

You know that galv fumes are pretty unhealthy right?