Pub gas, myths and truths

[Nigelw]

Been looking at a bit of a debate from a while back, but I never actually got any sense of what if anything was wrong with using it for welding purposes?

I use neat CO2 "pub gas" if you like and have done for years as it is cheap and mostly readily available to me.

So whats the truth behind it all????

[nickwilliams]

For clagging lumps of mild together, it works, and its cheap, but there is better stuff out there if you want to pay for it.

For more rigorous applications, using the proper stuff makes the job quicker, tidier and stronger.

[o_teunico]

Thats really interesting for me, as I am now working as a Coke/beer delivery man and have access to cheap (36 Eur.=7kg) gas without paying for the can itself. I have been thinking on converting my FCAW "No gas MIG" to pub CO^2.

[Anderzander]

I was told that it just runs hotter....

[discomikey]

argon CO2 mix makes gorgeous welds quite easy,

dont get me wrong you can do gorgeous welds on a CO2 bottle it just seems to be easier to be as neat with the mix IMO

[Boris113]

I would describe my welding as functional at best so don't have enough experience to comment, but there is an interesting comparision here.

It seems that neat CO2 gives a less steady arc and increased spatter.

http://www.mig-welding.co.uk/welding-gas.htm

[Bowie69]

Argon/CO2 mix is sooo much better for the stuff we all do.

[Stevie D]

Argo shield / cougar or whatever the non boc / air products equivilent is defenatley better to work with and gives a cleaner weld with less splatter.

As linked above by Boris there's quite a few heated debates over on the mig welding forum and elsewhere on the merits of both.

Personally I use my pure c02 'motor factors supplied - cost £20 for the cyclinder years back' as a backup for when my 'borrowed' boc bottle is empty - like it is at the moment.

I couldn't justify the cost of a contract bottle of argon / co2 from the likes of boc or air products anymore - have done in the past. I know there are other legitamit or dodgy refil alternatives now, but few and far between on this little island. I've an agreement that works for me most of the time - subject to availability of an exchange bottle.

Steve

[Ratty43]

I thought true pub gas (as opposed to proper CO2 welding gas) was meant to be inferior due to having nitrogen and other contaminants in it. I'll stand by to be corrected on that. Argoshield certainly gives far neater welds.

Thanks to welding gases UK I'm getting a 9kg bottle of argoshield for £30 with a refundable deposit of £40 on the cylinder. Far better than rental from BOC as it'll take me a year or so to use that.

[Phil Hancock]

Where i used to work we had a chap come in to do some of the welding, he had his own landy business and did a lot of welding. He used pub gas compared to my welding with argoshield universal. His welds looked like they had been laid on top of the parent metal (rather than melted into) with a lot of spatter and mine had flowed into the parent metal with a lot less spatter.

As i understand it argo mixes are for light welding which covers chassis work and neat CO2 is for a lot heavier work.

[ballcock]

Boc are doing a deal with a volkzone forum for a argoshield bottle which seems to be reasonably good according to reports. I don't know if any one on the forum is on it to give more accurate info.

[simonr]

I agree it's easier to get a good looking weld with ArgoShield than CO2, but I don't think there is much scientific evidence to suggest that a CO2 weld is weaker. It is possible to get nice looking welds with CO2, but it's much harder!

CO2 cools the weld more than Argon mix - but if you've got the power, it's not really an issue.

Personally, I use BOC ArgoShield Universal.

Si

[Anderzander]

CO2 cools the weld more than Argon mix - but if you've got the power, it's not really an issue.

Si

That's confusing - as I've been told the opposite - that CO2 runs hotter :-/

[Phil Hancock]

That's confusing - as I've been told the opposite - that CO2 runs hotter :-/

Big mig sets running CO2 used to have a gas heater as at high flows it would presumably freeze just like a CO2 extinguisher does.

[De Ranged]

I was taught that the CO2 will make for a slightly stronger weld due to some of the carbon being taken from the shield gas and slightly deeper penetration, the weld will be less visually appealing being a tighter more upright bead and there is more weld splatter

I've never heard of pub gas before, to me I'd be concerned with the volume of other gases in the shield as this isnt industrial gas to set standards, its a food gas they are worried about other contaminates... my concern would not be Nitrogen it would be Oxygen and Hydrogen... one makes the weld porous the other makes the weld brittle and neither of these would be a concern in a food gas

I personally run argoshield less splatter and a flatter weld

to the above post the freezing of the reg is because of a change of pressure the reaction is endothermic.... the shielding of the weld is not a change of pressure so no reason for the gas to take heat out of the weld

to gain the slight advantage in penetration I would say that the CO2 is burning slightly hotter

[smallfry]

I understood that there is no real difference in the strength of the weld as such, but the cooling effect of CO2, which argon does not do, hinders the weld penetration. hence the higher weld bead.

Argon is also inert and non reactive, whereas CO2 is not inert and reacts to temperature by expansion, which is what causes the spatter.

Only real difference in practice is that Argon mixes give a neater weld. In ideal conditions that is, and that is only if you are any good at it, but if you are welding rusty metal outside on a windy day no one would ever know.

[JeffR]

Having used both, I have to admit that I get significantly neater weld with Argoshield, both indoors and outdoors.

[Peter M]

A brief description lifted from my notes at work.

For non-ferrous metals and their alloys (such as Al, Ni and Cu) an inert shielding gas must be used. This is usually either pure argon or an argon rich gas with a helium addition.

The use of a fully inert gas is the reason why the process is also called MIG welding (metal inert gas) and for precise use of terminology this name should only be used when referring to the welding of non-ferrous metals

The addition of some helium to argon gives a more uniform heat concentration within the arc plasma and this affects the shape of the weld bead profile

Argon-helium mixtures effectively give a hotter arc and so they are beneficial for welding thicker base materials those with higher thermal conductivity eg copper or aluminium.

For welding of steels – all grades, including stainless steels – there needs to be a controlled addition of oxygen or carbon dioxide in order to generate a stable arc and give good droplet wetting. Because these additions react with the molten metal they are referred to as active gases and hence the name MAG welding (metal active gas) is the technical term that is use when referring to the welding of steels.

The percentage of carbon dioxide (CO₂) or oxygen depends on the type of steel being welded and the mode of metal transfer being used – as indicated below: -

• 100%CO₂

For low carbon steel to give deeper penetration and faster welding this gas promotes globular droplet transfer and gives high levels of spatter and welding fume

• Argon + 15 to 25%CO₂

Widely used for carbon and some low alloy steels (and FCAW of stainless steels)

• Argon + 1 to 5%O₂

Widely used for stainless steels and some low alloy steels

Gas mixtures - helium in place of argon gives a hotter arc, more fluid weld pool and better weld profile. These quaternary mixtures permit higher welding speeds, but may not be suitable for thin sections.

1.1.1Stainless steels

Austenitic stainless steels are typically welded with argon-CO₂/O₂ mixtures for spray transfer, or argon-helium-CO₂ mixtures for all modes of transfer. The oxidising potential of the mixtures are kept to a minimum (2-2.5% maximum CO₂ content) in order to stabilise the arc, but with the minimum effect on corrosion performance. Because austenitic steels have a high thermal conductivity, the addition of helium helps to avoid lack of fusion defects and overcome the high heat dissipation into the material. Helium additions are up to 85%, compared with ~25% for mixtures used for carbon and low alloy steels. CO₂ -containing mixtures are sometimes avoided to eliminate potential carbon pick-up.

Active shielding gas mixtures for MAG welding of stainless steels

For martensitic and duplex stainless steels, specialist advice should be sought. Some Ar-He mixtures containing up to 2.5%N₂ are available for welding duplex stainless steels.

Light alloys, eg aluminium and magnesium, and copper and nickel and their alloys

Inert gases are used for light alloys and alloys that are sensitive to oxidation. Welding grade inert gases should be purchased rather than commercial purity to ensure good weld quality.

Argon:

Argon can be used for aluminium because there is sufficient surface oxide available to stabilise the arc. For materials that are sensitive to oxygen, such as titanium and nickel alloys, arc stability may be difficult to achieve with inert gases in some applications.

The density of argon is approximately 1.4 times that of air. Therefore, in the downhand position, the relatively heavy argon is very effective at displacing air. A disadvantage is that when working in confined spaces, there is a risk of argon building up to dangerous levels and asphyxiating the welder.

Argon-helium mixtures:

Argon is most commonly used for MIG welding of light alloys, but some advantage can be gained by the use of helium and argon/helium mixtures. Helium possesses a higher thermal conductivity than argon. The hotter weld pool produces improved penetration and/or an increase in welding speed. High helium contents give a deep broad penetration profile, but produce high spatter levels. With less than 80% argon, a true spray transfer is not possible. With globular-type transfer, the welder should use a 'buried' arc to minimise spatter. Arc stability can be problematic in helium and argon-helium mixtures, since helium raises the arc voltage, and therefore there is a larger change in arc voltage with respect to arc length. Helium mixtures require higher flow rates than argon shielding in order to provide the same gas protection.

There is a reduced risk of lack of fusion defects when using argon-helium mixtures, particularly on thick section aluminium. Ar-He gas mixtures will offset the high heat dissipation in material over about 3mm thickness.

A summary table of shielding gases and mixtures used for different base materials is given in Table 2.

SUMMARY

Metal

Shielding gas

Reaction behaviour

Characteristics

Carbon steel

Argon- CO₂

Slightly oxidising

Increasing CO₂ content gives hotter arc, improved arc stability, deeper penetration, transition from 'finger'-type to bowl-shaped penetration profile, more fluid weld pool giving flatter weld bead with good wetting, increased spatter levels, better toughness than CO₂. Min 80% argon for axial spray transfer. General-purpose mixture: argon-10-15% CO₂.

Argon-

O₂

Slightly oxidising

Stiffer arc than Ar- CO₂ mixtures, minimises undercutting, suited to spray transfer mode, lower penetration than Ar-CO₂ mixtures, 'finger'-type weld bead penetration at high current levels. General-purpose mixture: Argon-3% CO₂.

Argon-helium- CO₂

Slightly oxidising

Substitution of helium for argon gives hotter arc, higher arc voltage, more fluid weld pool, flatter bead profile, more bowl-shaped and deeper penetration profile and higher welding speeds, compared with Ar- CO₂ mixtures. High cost.

CO₂

Oxidising

Arc voltages 2-3V higher than Ar-CO₂ mixtures, best penetration, higher welding speeds, dip transfer or buried arc technique only, narrow working range, high spatter levels, low cost.

Stainless steels

He-Ar- CO₂

Slightly oxidising

Good arc stability with minimum effect on corrosion resistance (carbon pickup), higher helium contents designed for dip transfer, lower helium contents designed for pulse and spray transfer. General-purpose gas: Ar-40-60%He-2%CO₂.

Argon- O₂

Slightly oxidising

Spray transfer only, minimises undercutting on heavier sections, good bead profile.

Aluminium, copper, nickel, titanium alloys

Argon

Inert

Good arc stability, low spatter, and general-purpose gas. Titanium alloys require inert gas backing and trailing shields to prevent air contamination.

Argon-helium

Inert

Higher heat input offsets high heat dissipation on thick sections, lower risk of lack of fusion defects, higher spatter, higher cost than Argon.

Table 2 Shielding gas mixtures for MIG/MAG welding - summary

[Hybrid_From_Hell]

If you could a tad less vague that would be good .................

Seriously fab 1st post, don't you dare leave !

Nige

[CwazyWabbit]

Brilliant post Peter, that explains it all, nothing like some good solid facts.

Thank you for taking the time to type it up.

Welcome to the forum, you'll fit in well here!

[ballcock]

Excellent post should be in the tech archive. I wonder if he could manage an on-line welding course for all us amateurs.

[De Ranged]

Thank you for taking the time to type that lot out, Peter

[zim]

We use coogar 5 with the mig and argon with the tig. The latter being more expensive and finishing quicker ?

G

[Peter M]

I wonder if he could manage an on-line welding course for all us amateurs.

Please don't think i am a welder, far from it, i am a welding/NDE inspector and have this info on hand should i need it. Only happy to share it with you all.

[CwazyWabbit]

That's just as handy Peter, we'll all be sending you stuff to X-Ray for us There's no doubt quite a bit you could enlighten us with about poor welds.