Effect on tungsten electrode without shielding gas 1

[waqasmalik]

Hi all, i work for a company which is involved in welding of aluminium using TIG with Argon as a shielding gas. Square wave AC TIG welding plant is used. Today i asked the welder to disconnect the shielding gas and then try to generate an arc, he did so but the tungsten electrode started changing its colour to blackish.

What i thought was that in the absence of shielding gas, only the air in the gap between the tip and work piece is ionized hence producing oxygen and nitrogen ions but because the shielding gas is not there so oxygen oxidize the tungsten electrode. Am i right in my claim?

 

[Tmoose]

What was the intent of doing that test?

 

[DeleteriousPhases]

Yes, it oxidized immediately, and should have generated a lot of heat. Any air contaminants would have ionized, and it would cycle 50% negative and positive rapidly back and forth. We observe that many gtaw machines have a post flow option to allow the electrode to cool below reaction temperature and prevent unintentional contamination.

Trying to quantify what's on the electrode will take more than a random guess. But the majority will be oxides of some type for sure.

 

[waqasmalik]

The intent was just learning from whatever the outcome is

 

[racookpe1978]

Keep the burned electrode (the combination of no cooling gas and lots of oxygen and nitrogen at 2500 degrees tungstunned it right proper, didn't it?) as an reminder to buy "welding grade" Argon (or Helium) for your TIG rigs.

 

[berkshire]

waqasmalic,
Well it looks like you just discovered why the shielding gas is there in the first place. The high frequency tracer will sometimes generate an arc with no gas that will not affect the electrode. However as soon as full current passes through that arc, and the electrode heats up Oxidization is immediate and inevitable. It is important to note that any shielding gas that contains oxygen in any form will have that oxygen dis-associated by the arc , with bad results to the Tungsten. A shop mistake that fortunately is not too common is putting a Mig mix of 2% oxygen/98% argon onto a Tig supply . It can drive a welder nuts for a few minutes, before he goes to find out what his helper has done.
B.E.

You are judged not by what you know, but by what you can do.

 

[DeleteriousPhases]

to add to berkshire's statement when thinking of dissociation, due to the shielding gas being transparent and using a bare filler rod, it doesn't disperse radiant energy as with flux covered electrodes, and it can break down cleaners and solvents readily. one such reaction occurs readily with chlorinated solvents, cleaners and brake fluid which all decompose into poisonous phosgene gas when exposed to the radiant UV energy from welding. a real safety concern if you're using chemical cleaners on your aluminium parts.

 

[DeleteriousPhases]

a simple link from a safety website in western canada explains it pretty well. Certain you can find others.

Link

 

[ornerynorsk]

That is also the proper procedure should you ever wish to ruin a set of collets, or melt down the torch.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.