Another Welding Gas Question

Posted after 11:30 PM and sometime before 6 AM I was already off the front page. Next time I'll post as "Guest" and make it sound like a homework question. That way it will spend more time on the front page and I'll get a better chance of a response.

I would try to wean yourself off HE as soon as you can. The price for one isn't all that cheap any more and may soo skyrocket to u heard heights.

Helium Shortage Story

Joe

Hi Bruce...While I am no expert, TIG welding of Aluminium should be done with pure Argon. The addition of Helium, as you say will raise the heat of the arc which is proportionate to the percentage of Helium used. Helium is usually one of the more expensive gases. The reason why Argon is cooler is because it has a lower arc voltage. Nitrogen gives the highest heat output but does not give a good surface finish. May I recommend "The Science & Practice of Welding" by A. C Davies which is regarded by some as the "Welding Bible"

I hope this is of some help.

Thank you. I'll look for the book. I don't know why they switched from pure Argon.

You may have given me part of the answer to my initial question. If different gases have different "arc voltages" than that would affect the amount of current flow and therefore the amount of heat.

Thank you,
Bruce

One small correction pl.

The only limitation is, the arc is harsh and with high spatter level compared to other gasses. As carbon in CO₂ gas induces corrosion in Stainless Steels, a mixture of 90% He(+) 7.5% He (+) 2,5% CO₂ is used at times for SS welding (or) 70% He (+) 25% Ar (+) 5% CO₂ is used for low alloy steels.------

should be read as 90% He(+) 7.5% Ar (+) 2.5% CO₂

Thanks,

Sridhar.

Sir,

a very good answer. I remembered the school days and teachers.

Thanks a lot

While welding aluminium tanks I had used CO2 for purging and commercial grade Ar.

Even reduced flow of Ar by 10 % gave acceptable good welds.

However no lab studies are conducted. Invite your expert comments

kiran

Thanks for your comments Kiran. What ever the knowledge I gathered is just off loaded to other friends.

Towards using CO2 and Argon as purging gas, I have my own doubts as the very purpose of purging is avoid oxidation at the root side. CO₂ decomposes to carbon monoxide and oxygen at arc temperatures, producing an oxidizing effect approximately equal to that obtained by the use of an inert gas with 8-10% of O₂ and this will produce more porosity on the root side.

In spite of using CO₂ gas you have not come across the said defects means, the Al could be an alloy of Mn or Mg and filler wire are added with Mn & Si. Since they are all heavy di-oxidizers, oxidation or porosity would not have formed on the weld or you would not have checked with radiography.

Further, if the media used for your tank are of corrosive nature, the effect will be felt immediately.

Considering all above, you can avoid CO₂ gas and use only argon for purging even though it is of a commercial grade.

Sridhar.

I would suggest that you stay with argon. I have never used anything other than pure argon for any type TIG welding and pure argon is cheaper than mixed gas where I live($13.25 for a large bottle of argon). I have read that some companies are experimenting with mixed gas for certain specialty types of TIG welding but in the 30 years I have welded I have never actually ran across anyone using a mixed gas with TIG welding.

I think the addition of Helium gas does cause the weld arc and puddle to be hotter and penetrate deeper if you are TIG welding on thicker sections it could help. You can go to the AWS web site and get recommended amounts for the different gas mixtures.

I do use mixed gases like tri mix for stainless and 75%argon/ 25% Co2 for carbon steel MIG welding. With MIG, mixing Co2 with argon tends to clean the base metal better than argon alone and causes the arc and puddle to be hotter than using pure argon as well. Using pure Co2 with MIG on the other hand creates a ton of spatter that sticks to the weld and base metal.

Thank you Sridhar, Pipewelder and others. I left town for a few days and came back to some very helpful responses.

Thank you,
Bruce

BruceFlorida:

...Greetings from a fellow Floridian.

Members have provided some in depth responses to the main thrust of your questioning. Those responses are good, so there is no need to rehash that info. There may be some value in broadening the discussion some.

As some previous comments note; He/Ar mixtures require a higher flow rate compared to pure Ar AND He is typically more expensive than Ar. Obviously, savings will not be found in the analysis of dollar cost of shielding gas expended per hour of welding.

In some situations, using He/Ar mixtures does provide the opportunity for reducing expenses. He/Ar mixtures (being 'hotter') can allow greater welding speeds, higher deposition rates, and increased penetration in comparison to welding using pure Ar. This can translate to fewer passes, shorter weld time required per piece, less total shielding gas consumed and less distortion and internal stress (and less work post-welding to deal with distortion/stress).... but only if the process is optimized for the change in shielding gas.

The chance of realizing cost savings by switching from Ar to He/Ar probably depends significantly upon the preparations and process changes made in conjunction with switching. If the welders are not increasing the pass rate, then switching to a more expensive gas mixture will certainly not save money.

In a small prototype shop, it will be harder to realize savings from switching to He/Ar mixture than it would be in a large job shop or production facility. Typically, in a small prototype shop, a small portion of time is spent actually laying down beads and a large portion of time is spent, understanding and communicating specifics of the work piece, adjusting equipment, doing fit-up, and finding solutions to unforeseen obstacles. The opposite would be typically the case in a large job shop or production facility. The benefit of higher welding speeds favors a boring repetitive process.

What other cost savings approaches has your shop considered?

-- Are workpieces being welded in essentially draft free areas? Baffles and curtains to limit drafts can allow for reduced shielding gas flow and better weld quality. Often a welders desire to have a fan blowing directly on them created sufficient drafts on the workpiece as to require excessive rates of shielding gas. This sometimes is the result of a mistaken belief that this keeps them from breathing the fumes, but in fact, the fumes are often entrained in the recirculating fan current, leading to certain exposure. If the concern is heat, it would be wise to device another way for the welder to stay cool. A large AC bill may be much cheaper than a large shielding gas bill.

-- How is the shielding gas being delivered. Shielding gas rates can often be reduced with the use of appropriate cones and gas lenses. In my experience, large gas lenses, when used in draft free environments can provide extremely low flow rates. I suspect this is due to the minimal amount of turbulence and lack of significant entrained air that might otherwise disturb the blanked to shielding gas.

-- Have you delved into waveform much? Waveform shaping for AC welding and the use of a pulser for DC welding can facilitate large improvements in penetration, minimizing distortion, and increasing pass rates.

With a little more knowledge of the specific type of prototyping in which your shop is involved, it would be easier to talk about things that would be more applicable to your situation.

BBB

Thank you. More great and useful comments.

Bruce