gas mixtures

Hi, can anyone fill me in on why CO2 allows for deeper penetration into your
plate (normal mild steel) than a tri-mixture does, i.e. Tri-Mix (argon, CO2,
helium)? I know from experience that there is a considerable less amount of
spatter with the tri-mix, but was always unsure of the penetration reason.
this is just regular steel, and am using a GMAW machine. any info would be
appreciated. thx ;-)
Reply to
Bob
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CO2 is not inert, it is active, hence why it is sometimes refered to as MAG welding.
Reply to
Ernie Leimkuhler
I'm a Physicist type and this is my theory (concept).
He - light gas - throw it at something and it floats up. Ar - heavier gas but still goes up after a brush. It is 9x heavier after all. CO2 - Carbon and Oxygen - wow - throwing coal ? - bams into the metal. If the Carbon catches on fire the oxygen feeds it :-) A molecule not atoms.
(Actually the Carbon can't burn directly, but I understand the carbon is absorbed into the metal. Splitting of a molecule is not as bad as an atom... )
Martin
Reply to
Eastburn
Tri-mix is all inert, so all the heat is generated by the arc. Carbon dioxide is an active gas, under the heat of the arc it disassociates, and the atomic oxygen *very* actively reacts with the iron to generate more heat. (Mostly it reacts with the wire, and the iron oxide produced is mostly thrown off as spatter, so it doesn't corrupt the weld.)
Gary
Reply to
Gary Coffman
You don't list gas % but probably high Argon %. Argon readily ionizes creating low resistance arc. This letslower voltage setting used resuling in lower energy. Argon is also poor heat conductor but helium is great conductor.
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makes CO2 gas unique? The CO2 plasma provides unique "gas dissociation properties". In the MIG arc, the CO2 molecules break down from CO2 to CO - O2. When close to the cooler weld surface the C0 - O2 molecules form back to CO2. The dissociation adds energy to the weld.
The heat using 100% CO2 is so great it's easy to go from Short Circuit transfer to Globular transfer were the drops from the wire are 4 times wire diamiter. The drops are transfered under the influcle of gravity. Globular Transfer is only good for down hand position. If the voltage is too low when in Globular Transfer the arc length is too short letting the drop get too large and short to work then explode producing splatter. Upping Voltage will lengthen arc length and lessen splatter as large drop will sepperate from wire before it shorts. Too high voltage may cause lack of fusion and penetration because of too long arc. Can also get buried arc transfer using 100% CO2 but not Spray Transfer.
If the Argon in your mix is at least 80% with up to 20% CO2 and your welder will support about 24V to 30 V @ 200amp to 300 amp it can produce spray transfer mode. Minimum Volts and Amps required depend on wire diameter and gas mix. Can then get better penitration and metal transfer rate than using 100% CO2.
Reply to
R. Duncan
This thread may hold the answer to why I am having trouble with my new MIG welder (Lincoln 135--120 volt). I was doing fine using flux-core wire, and slowly learning to make a decent looking weld. I decided to try welding with gas shielding, and chose CO2, based on a number of people in the group--it's cheap and readily available.
I have not been able to make a weld. Using .025 wire, I can barely get an arc at my hottest setting, and the deposited metal is in beads, barely stuck to the surface. My impulse is to turn up the heat, but I'm using all I've got.
I have already discovered that I needed to reverse the polarity. I have purged a lot, and raised my gas pressure, to make sure I was getting enough. I can hear the CO2 and feel it blowing on my lip.
I am working in a sheltered, outdoor location, so breezes could be hurting me, but I have seen others weld outdoors with MIG. And, even if I wait for calm air, I don't do any better.
Does all this discussion about the dissociation of CO2 in the arc mean that it takes more voltage (current) to weld with it? Or am I doing something wrong that I don't recognize, due to being so low on the learning curve?
If I have to, I will just continue using flux-core, but I'd sure like to know what's going on.
Reply to
Leo Lichtman
arc at my hottest setting, and the deposited metal is in beads, barely stuck to the surface. My impulse is to turn up the heat, but I'm using all I've got. This thread may hold the answer to why I am having trouble with my new MIG
Reply to
Keith Marshall
If you can weld with fluxcore wire it should easly get an arc with solid wire. Open circuit voltage between work lead and electrode lead should be about 10 V DC on lowest Voltage switch position and about 27V on highest switch position.
Thie sounds like bad shielding gas. I'll bet if you try welding with no shielding gas it will weld the same. You can feel flow of gas from nozzle is why bad gas instead of no gas. What is your flow rate? It should be between 20 & 40 CFH with trigger pulled and gas flowing.
Could also be caused by air being sucked into shielding gas as it flows to Nozzle. Remove your mig gun cable from welder and check that the O-ring seal is there, in proper place, and O-ring doen't have a rough area cut out from inserting gun lead into welder with unlubricated O-ring. If no problems there then check for seal problems at gun end. If no problem there Then take your welder and shielding gas bottle to welding dealer that sold your CO2 and try another bottle of gas with your welder. If another gas bottle doesn't fix your problem. Then Lincoln dealer or repair shop should fix it. Any problems call Lincoln's number in manual. .
Reply to
R. Duncan
I'm not an expert but from experiance, you could have to much resistance or a bad connection. Make sure the metal is shiny under your work clamp, that you have the right tip, and that all the connections are tight inside your machine.
Of course that is just my guess :)
Justin
Reply to
Justin
I think Franks post is more likly hit the cause of your problem. Once when the .023 wire I was using ran out changed to real cheap harbor frieght .023 wire that really was .022. Really messed up my settings making cold welds but could make it work by changing settings. If you are still using .030 or .035 contact tip it would give your problem. Century contact tips from Sears will work if you can't find anyone else selling them on week end. Your drive roller should have a .025 groove and .035 groove. IF so just remove it and install so .025 groove is used.
If your gas was bad it would require more amps and higher volts to weld and the beads would be full of holes like swiss cheese. Once you get you welder working right with solid wire try it try welding without gas to see what it looks like.
Reply to
R. Duncan

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