Previous in Forum: What Would Happen If One Jet Engine Failed   Next in Forum: Engine KW VS Generator KW Output
Close
Close
Close
12 comments
Guru

Join Date: Jul 2008
Posts: 1566
Good Answers: 139

Another Welding Gas Question

07/05/2010 11:37 PM

Our small prototype shop just started using 75% helium, 25% argon for TIG on aluminum and found that the gas mixture was too hot. They were using 100% argon but switched due to the cost. They plan to switch to 25% helium, 75% argon next time to have a cooler mixture.

In the past I Googled gas mixtures and found many sites that stated that "X" was hotter than "Y". I never found a good reason why.

Third on my list is that the gas mix controls how much of a high intensity, small scale greenhouse effect the gas provides.

Second on my list is the ability of the gas to ionize influences how much current flows through the arc and therefore how much energy is dissipated in the puddle.

The top of my list is "I don't really understand what is going on".

Anyone out there know why the various pure or mixed argon, CO2, helium, etc. gasses are hotter or colder than the other ones? Also, how well will the "TIG on aluminum" results match up with "TIG on stainless steel" or "MIG on mild steel"?

Thanks,

Bruce

This question was inspired by the CO2 question at http://cr4.globalspec.com/thread/56797/CO2.

__________________
Few things limit our potential as much as knowing answers and setting aside questions.
Register to Reply
Pathfinder Tags: Welding welding gas
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Jul 2008
Posts: 1566
Good Answers: 139
#1

Re: Another Welding Gas Question

07/06/2010 4:03 PM

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.

__________________
Few things limit our potential as much as knowing answers and setting aside questions.
Register to Reply
Guru
Hobbies - RC Aircraft - New Member

Join Date: Aug 2007
Posts: 851
Good Answers: 9
#2

Re: Another Welding Gas Question

07/06/2010 10:55 PM

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

Register to Reply
Anonymous Poster
#3

Re: Another Welding Gas Question

07/06/2010 11:04 PM

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.

Register to Reply Score 1 for Good Answer
Guru

Join Date: Jul 2008
Posts: 1566
Good Answers: 139
#4
In reply to #3

Re: Another Welding Gas Question

07/06/2010 11:10 PM

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

__________________
Few things limit our potential as much as knowing answers and setting aside questions.
Register to Reply
4
Power-User

Join Date: Nov 2006
Location: Chennai - India.
Posts: 273
Good Answers: 18
#5
In reply to #4

Re: Another Welding Gas Question

07/07/2010 3:20 PM

Argon and Helium are monatomic gasses, but helium is one tenth as light in weight as compared to argon. Argon density is 1.3 times that of air and ten times that of helium.

Compared to argon shielding, which forms a effective and a blanket over the welding area, helium requires two to thee times more flow rates and this increases the cost of shielding for helium.

But, one important factor for helium is it gives higher arc voltages for a given arc length and welding currents compared to argon, which means that, the helium arc is hotter than the argon arc. Helium is therefore preferred over argon for welding thicker materials and those having high thermal conductivity such as copper and aluminum and high speed mechanised welding.

For thinner materials like 10 to 15 mm and in the current rages up to 150 amps, argon has a pronounced edge over helium and give better control during welding.

As helium gives higher arc voltage and higher heat input, this can be a disadvantage for pure helium as form a wider bead and with a shallow penetration compared to argon or CO2 - which gives maximum depth of penetration among all the gases used in welding.

This is why mixture gases with 50-75% helium is used to balance between characteristics of argon and helium desired.

Another advantage for argon is its good arc stability on AC and DC and good cleaning with AC. Helium give better arc stability with DC but poor arc stability and cleaning action with AC. That is why argon is preferred for AC welding of Aluminum and Magnesium than helium for TIG welding of Al.

Pure nitrogen mixed with argon is used for copper as it gives greater heat input like helium and very inexpensive.

Again, pure argon, pure helium or argon-helium mixture my cause lot of spatter , undercuts at edges. to overcome the problem, small additions of oxygen or CO2 is in the volumes of 1-5%O2 or 3- 10 % of CO2 are added. This mixture (incl. pulsed DC Techniques) gives promotes good side wetting for the bead and eliminates undercuts. But to avoid porosity, occurring due to O2, deoxidisers like Mn,Al, Ti,Zr and Si are added in the filler metals.

Carbon di-oxide is widely used for welding of mild steel as it is inexpensive, gives sound weld deposits, deeper penetration compared to argon and helium and adequate mechanical properties at high welding speed.

CO2 has higher hot-cracking resistance compared to SAW, SMAW and TIG processes. It also improves weld metal ductility and toughness, CO2 with Argon is well suitable in spay arc type welding used in MAG/CO2 process. This mixture also give higher Tensile & yield strength compared to welding with pure CO2 gas.

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.

To conclude,

Argon or He as a mixed gas is used for welding non ferrous metals,

Argon(+) 1 to 2% O2 for Austenitic and Ferritic steels in down hand spray transfer,

Argon(+) 20% CO2 for Ferritic steels for all position welding,

Argon(+) 15% CO2 (+)5% O2 for Austenitic and Ferritic steels - all positions and

CO2 for Ferritic steels in all position welding and like wise.

Trust above details gives a fair picture of gases used in welding of various metals and processes.

Sridhar,

__________________
What we have done for ourselves alone dies with us: while what we have done for other and the society remains and is immortal.
Register to Reply Good Answer (Score 4)
Power-User

Join Date: Nov 2006
Location: Chennai - India.
Posts: 273
Good Answers: 18
#6
In reply to #5

Re: Another Welding Gas Question

07/07/2010 3:28 PM

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.

__________________
What we have done for ourselves alone dies with us: while what we have done for other and the society remains and is immortal.
Register to Reply
Associate

Join Date: Jun 2008
Location: India,Pune
Posts: 46
Good Answers: 1
#8
In reply to #5

Re: Another Welding Gas Question

07/11/2010 8:00 AM

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

__________________
if you are a managment professional or youth who wants to start business contact for free help for your project including financial assistance through NGO in and around Pune India
Register to Reply
Power-User

Join Date: Nov 2006
Location: Chennai - India.
Posts: 273
Good Answers: 18
#9
In reply to #8

Re: Another Welding Gas Question

07/11/2010 1:06 PM

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.

__________________
What we have done for ourselves alone dies with us: while what we have done for other and the society remains and is immortal.
Register to Reply
Guru
Hobbies - DIY Welding - pipewelder

Join Date: Apr 2007
Location: North Georgia, USA
Posts: 671
Good Answers: 33
#7

Re: Another Welding Gas Question

07/07/2010 4:03 PM

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.

__________________
pipewelder
Register to Reply
Guru

Join Date: Jul 2008
Posts: 1566
Good Answers: 139
#10

Re: Another Welding Gas Question

07/12/2010 10:45 PM

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

Thank you,
Bruce

__________________
Few things limit our potential as much as knowing answers and setting aside questions.
Register to Reply
Anonymous Poster
#11

Re: Another Welding Gas Question

07/13/2010 4:00 AM

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

Register to Reply Score 1 for Good Answer
Guru

Join Date: Jul 2008
Posts: 1566
Good Answers: 139
#12
In reply to #11

Re: Another Welding Gas Question

07/15/2010 6:08 AM

Thank you. More great and useful comments.

Bruce

__________________
Few things limit our potential as much as knowing answers and setting aside questions.
Register to Reply
Register to Reply 12 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Anonymous Poster (2); BruceFlorida (4); kirannawathe (1); NSS (1); pipewelder (1); SRIDHAR (3)

Previous in Forum: What Would Happen If One Jet Engine Failed   Next in Forum: Engine KW VS Generator KW Output

Advertisement