What would I gain or lose on 75/25 vs CO2 on a mig

The connectors are not a big deal. any welding shop "should" have them. I am planning on building a large wrought iron fence with concertina wire atop it around my new shop too and CO2 seems reasonable for this project. So you have answered one aspect of my question I failed to pose. (Thanks) I have a CO2 regulator from a soda machine, I assume it should work fine, I need to dig it up or just replace it so I don't blow my solenoid. The remainder of the question still piques my interest and you say the cost was 3-1 CO2 vs. 75/25 that in itself makes having a large cylinder well merited I think as long as it will not destroy my gear or welds. Is there a difference in flowmeters and regulators for CO2 vs. mixed gasses, I never tinkered with the aspect.
Still seeking the answers and thanks Steve,
Rob
Fraser Competition Engines Chicago, IL.

This is not a technical answer, so don't take it that way.
I used to do wrought iron. (actually ornamental metal consisting of square tubing)
I used straight CO2. I asked about the 75/25, and was told that it would weld hotter because of less cooling from less CO2, and that the bead would be flatter and better in appearance.
They were 100% right on all accounts. But for almost triple the cost, I never used more than that one bottle.
Fast forward to present: Now I use only 75/25 because it is what was suggested. Maybe straight CO2 would work. There is a bit of a difference in the connectors, and don't know if a 75/25 regulator would need the flat faced CO2 connector or not. No big deal and not expensive.
I would just say to analyze what you are doing, and if the specs call for it, use mix. If not, CO2 does just fine. Usually, there is someone where you buy your gas or supplies that knows all the numbers and can give you a technical answer.
Steve

IIRC, and that would be a first, a CO2 regulator is a little different. I know that the little CO2 regulators were pretty cheap, looking like an air gauge rather than a regulator. IIRC, the high side on a CO2 tank is nowhere near the 1800-2000# of a 75/25 mix tank. The CO2 regs don't handle a lot of flow. When it does, as in continuous welding, it freezes up like a popsicle. I have had them freeze on me. I am not sure if the actual guts are different, or just the fittings so it will mate to a CO2 tank.
My new Lincoln came with a 75/25 mix regulator, and I didn't want to go changing it.
Will someone who knows such things please chime in?
Steve

CO2 bottles do get to 2000+/- psi range. CO2 in my experence will cool down to about 1200 psi during heavy use, in cooler weather, but seldom drop any farther than that, until empty. Remember CO2 is liquid inside a full bottle, and pressure remains fairly stable until all the liquid is gone.
I use the same regulators on CO2, on Argon, and Argon/mix. They are the inexpensive "Magnum" Lincoln regulators with the standard high-pressure gage that reads up to 4000 psi. One came with my MIG and I picked up the other two at the welding supply store. As far as I know they will all fit any bottle. I also have one of the high dollar, ($200+ 1994 price) high pressure (6000 psi +) regulators that I used to use on liquid nitrogen bottles. The bottles with regulators set on the back of the welding cart and the gas hose gets changed between the MIG/TIG. I don't use a flow meter with CO2. Never had it freeze up, but then I haven't built any battleships or aircraft carriers with it either

Must be you get different CO2 than I do, mine tops out at about 500 psi.
Anyway.. Flowmeters commonly have more than one scale on the glass as different gasses will displace the ball differently at the same flow. Regardless of that, the only flow that's useful is what's required to shield the puddle.. so the flowmeter isn't all that necessary.
You will have no problem with CO2 in non-critical applications, I'd not hesitate to use it for cages and such. I use it exclusively in my MIG, if I need something different I either stick or TIG it.
I don't know any reason why a soft-drink fountain regulator won't work, unless it won't flow enough.. Try it, if you're happy then it works. If it freezes, put a heat lamp on it.
John

You will get better penetration with CO2, which is an advantage because MIG in short circuit mode is prone to problems with lack of fusion to start with. You will have more spatter (read cleanup) and a slightly less stable arc. You may need to use a wire with more deoxidizers than when welding with 75/25.

Carbon dioxide is a more active gas and will give you more penetration with the same settings on your machine. With an adapter you can run any old flowmeter. As one person mentioned at long flow times the regulator will ice up so hanging a trouble light on it will give it enough heat. Proper carbon dioxide regulators have an electric heater built into them. I have seen conventional regulators frozen solid and were damaged as a result. I am talking about caked ice covering the regulator and suddenly you lose your gas... a relatively extreme case.. You will get more spatter with carbon dioxide. The strength of weld does change slightly between mix and non mix. The literature I have read often would caution that using a mix over pure carbon dioxide will increase ultimate tensile strength and yield but at the cost of ductility and low temp impact strength. This is not important for fencing. Randy

For what its worth...as a dauber..I also changed to CO2, and dont regret it. I still keep a tank of 75/25 on hand if I need a pretty weld. I tend to weld rusty scrap iron into Stuff with an old DanMig wire machine. There is indeed more splatter and sometimes the arc tends to have something of a mind of its own..the 75/25 had a far more pleasant Frying Bacon noise when running...but the cost savings is something I found most important, after good strong welds with good penetration of course.
I changed over to CO2, useing the same regulator and the same flow gage, (changed to the co2 scale) and the tank feels just about as heavy as it did when I got it. By now Id be on the second tank of 75/25 at at least 3x the cost.
Shrug.. take it for what its worth.
Gunner
"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.
Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

Following on from Randy everything I have read so far is correct, but here are few of important facts:- 1. Co2 exists as a liquid in the cylinder rather than a compressed gas and there is more gas in an Co2 cylinder as opposed to a mixed gas cylinder. In the UK our normal argon mix cylinders hold 11Cu/mtr of gas and a Co2 cylider holds 19cu/mtr. 2. The Co2 vapour in a Co2 bottle is contaminated with water ( this is partially why you get snow when you open the cylinder valve without the reg). When we used to use Co2 we would use a liquid withdrawal cylinder which has a dip tube ( the same as a Co2 fire extinguisher) and a heater between the reg and cylider was essential. This not only stopped the reg from freezing but also vapourised the Co2 from liquid to gas. If you were only doing a small amount I would just use a vapour withdrawal cylinder.
3. Co2 is good in dip transfer (short circuit) but will not spray i e above about 200 amps. If you want a low cost gas for heavy welding above 1/4" use Co2 and E71T1 flux cored wire, it is fantastic for high speed welding in the flat or vertical up.
Regards
Finbarr (Lancashire UK)

Whoops, my bad. Looked it up- at 80F, 970psi. Can't imagine how I was so far off, but I was.. So I either only look at the guage when I'm turning the valve off (cold tank) or I'm full of shit;-), 'bout even odds there..
John