shielding gas

[wrench3047]

the only school training i've had in welding was in high school. In my shop class all we learned was stick and o/a welding/cutting. In the course we didn't cover mig or tig so i'm curious all the purposes of shielding gases. I've picked up different gases and mixes will give hotter spark. I understand (shielding) gas keeps atmosphere off the weld/electrode. Really my question what does gas shield against.

[walker]

Oxidation of the weld puddle is my understanding. It helps control reactions with atmosphere.

[wrench3047]

What would happen if I took a tig torch and attempted to weld without any gas hooked up

[Compchassis]

It would pop, blow the end of the tungsten apart and the arc would wander all over the place.

[Paul Seaman]

In tig the gas also forms an ion trail for the arc to follow. In other words no it won't work.

[Mike W]

The inside of the cup will also have a nasty look to it. Opps, forgot to turn the gas on.

[aphexafx]

...and if you're approaching anything around 50% of your torch's rated capacity (Amps) you will quickly overheat it and ruin it. The gas removes heat from the cup and the tungsten. This, however, is just a side effect that is taken advantage of.

Like everyone else said, hot metal of any kind is very reactive with oxygen, so the gas envelopes the area with an inert gas that displaces the oxygen in the air.

[dyn88]

if you try to tig weld without gas the puddle will always contaminate and boil (its actuallt the metal burning like a piece of wood) of the surroundig oxygen, Mig would be much the same but you wont get much pennetration and the bead will not form. The sheilding gas in both these operations keeps the oxygen in the atmosphere out, like the slag in stick welding.

[wrench3047]

Got it. Ion trail, oxidizing, burning metal. Sounds like the start of a SciFi movie. Thanks

[dyn88]

lol.................

[hankj]

Wrench,

Besides the O2, nitrogen is also a bad guy in the atmosphere. Just like exposure to oxygen will create oxides, exposure to nitrogen creates nitrides. Both of these things get trapped in the weld. The resut is porosity and imbrittlement. Not a good thing for your trailer hitch!

Hank

[dyn88]

hmmm hey hank when I weld super thin materials I use nitrogen as a sheild and have no problems. It seems to work the opposite of helium. The nitrogen ions get excited at a much lower voltage than argon. Ive never had a problem, but also never weld anything thicker than .008 so may never see the draw backs to the "nitrides"

[hankj]

I based the statement on what I've read in industry publications and welding texts, rather than practical experience. Considering that the atmosphere is 78% Nitrogen, and the primary purpose of shielding gas (or flux, for that matter) is to exclude the atmosphere from the weld, it seemed natural to me to accept the statement as fact.

What process are you shielding with the N? You are certainly correct that the energy of ioniozation is less than He - about half, and it IS an inert gas, so given that data, I can't see why it wouldn't work, and since it's inert, why it would combine with anything to form compounds.

I'll bet bt the end of today, I'll know a lot more about it! Thanks for the brain teaser!

Hank

[hankj]

88,

Here's something to gnaw on. Hopefully, the Brethren will chime in - they usually do. I know we have a couple of CE's in the mebership...

Quoted from "Welding Skills", by Giachino/Weeks, 1985, page 239:

"Of all the elements in the air, nitrogen causes the most serious problems in welding steel materials. When iron is molten, it is able to take a relatively large amount of nitrogen into solution. At room temperatures, however, the solubility of nitrogen in iron is very low. Therefore, in cooling, the nitrogen precipitates, or comes out of the iron as nitrites (itaclics added). These nitrites cause a high yield and tensile strength, and increased hardness, but a pronounced decrease in the ductility and impact resistance of the steel materials. The loss of ductility often leads to cracking in and near the weld material. Since air contains approximately 78% nitrogen by volume, if the weld metal is not protected from the air during welding, very pronounced decreases in weld quality will occur.In excessive amounts, nitrogen can also lead to gross porosity in the weld deposit."

Typos are the responsibility of the poster!

Go figure!

Hank

[dyn88]

very interesting I use Ni when welding thin stainless and aluminum,sometimes copper-nickel. well have to see where this brijngs us