TIG: Argon, Helium, and CO2...?

Date 09-25-2002 15:11

Question about gases here. I understand that you normally use 100% argon with TIG. I've also seen that folks will sometimes use 100% helium with TIG to improve penetration. Helium transfers more heat than argon (right?), so that makes sense.

I've also read that you don't use CO2 with TIG because CO2 transfers too much heat and melts the tungsten electrode. I'm just curious, but couldn't you use a mixture of Argon and CO2 to get the same heat transfer that you get with Helium? The most common complaint about Helium is that it's expensive, so wouldn't this give you the same heat transfer at a cheaper price? Or is there other properties which helium has but Argon+CO2 does not have that make helium's use necessary?

Thx,
Dave

By GRoberts (***)

Date 09-25-2002 18:24

The problem with CO2 ,or O2 for that matter, is that it reacts with the electrode, and oxidizes (contaminates) it. It isn't really a problem with the temperature of the electrode gettting too hot.

By DaveSisk (**)

Date 09-26-2002 14:06

Oh, I get it. The CO2 decomposes into it's base elements when energy is added, so it's actually an issue of how well it shields rather than it's heat transfer with TIG considered. Given this, why isn't CO2 a big issue with MIG welding?

Thx,
Dave

By GRoberts (***)

Date 09-26-2002 14:47

Yes, the issue with CO2 is how well it shields, but we're only talking about the electrode, not the weld pool. The Oxygen provided in the arc from CO2 or O2 in the sheilding when GMA welding is absorbed by the weld pool, and the metal being transferred to the weld pool, but they are not exposed to the arc for that long, so it is not enough oxygen to cause porosity when welding (unless you use too much O2, and then porosity will form). When you are GTA welding, the oxygen instead reacts with the electrode which is exposed to the oxygen for a large amount of time, and gets contaminated. The main difference though, is the electrode with GMAW is supposed to melt, while you try to avoid that with GTAW.

By DaveSisk (**)

Date 09-26-2002 19:09

Thanks for the explanation!

Dave

By Rod MI

Date 09-26-2002 05:55

Hi DaveSisk I'm not a welder but I've tried to weld with AR/Co2 mix and it will not work with TIG I get porosity blow holes and the tungsten melts sow I'm going to try Argon this weekend I'm shire it will work on AL you just get black sooty craters when trying to weld

By pipewelder_1999 (****)

Date 09-26-2002 21:37

Don't feel bad. I was testing three pipe/tube welders that were all brothers from the same state/town that indicated to me they were the best in (state unnamed) and I left them to prep/bevel their coupons. I came back about an hour later and they still hadn't tacked up the coupons. They explained that the contractor had cheap junk for tig rigs and back in (state unnamed) they had the good stuff. I grinned and left to give them another chance to discover their error (since they were the best, I hated to run em off ). Even more tig rigs were piled on the table when I got back.

I then explained what the big silver section painted on the top of the "argon" bottle meant and also the fact that "75/25 ARCo2" on the sticker was another fine way to identify what type of gas. I think they had also changed the gas bottle once.

They were very skilled from what I remember so it can happen to anybody.

Have a nice day

Gerald Austin

By autoweld (*)

Date 09-27-2002 13:09

You can also purchase differant blends of AR/HEL thats works very well when looking to increase penetration and improving travel speeds on stainless steels and Aluminum. The two gases work very well together with Argon helping with the arc starting and shielding and the Helium with the increased heat transfer. I hope this helps you out and if you need more info let me know. I work with shielding gases everyday for one of the large gas porducers.