Cooking Up A Batch Of Homebrew Welding Gas

A weld bead laid down with homemade CO2

You know the feeling — you’re making good progress on a weekend project, you’re really in the groove, things are going right. Right up until you run out of That One Thing™ that you can’t do without, the only store that sells it is closed, and you get a sudden case of whiplash as your progress hits a virtual brick wall.

Of course, every challenge holds the opportunity to hack your way around it, which is how [Lucas] ended up building this carbon dioxide generator. The “IG” in MIG welding stands for the “inert gas” that floods the weld pool and keeps the melted metal — the “M” in MIG — from rapidly oxidizing and ruining the weld. Welders often use either straight CO2 or a mix of CO2 and argon as a MIG shielding gas, which they normally get from a commercial gas supplier, generally on non-weekend days.

[Lucas] turned to grade-school chemistry for his CO2 generator, using the vigorous reaction of baking soda and vinegar to produce the gas. Version one was sketchy as all get-out; the second iteration still had some sketch factor thanks to the use of ABS pipe, but the inclusion of a relief valve should prevent the worst from happening. After some fiddling with how to get the reagents together in a controlled fashion, [Lucas] was able to generate enough CO2 to put down a decent bead — a short one, to be sure, but the video below shows that it worked.

Could this be scaled up to something for practical use? Probably not. But it’s cool to see what’s possible, and something to file away for a rainy day. And maybe [Lucas] can use this method to produce CO2 for his homemade laser tube. But again, probably not.

30 thoughts on “Cooking Up A Batch Of Homebrew Welding Gas

  1. I liked most of this. It’s important for kids to learn to imagineer, and test ideas. I was immediately put off a bit that he did not initially add baking soda to, say, 8oz of vinegar, repeatedly, and watch for no more bubbles to determine ratios, but began playing with no idea. When he finally did so, he went to the internet. :>( The kids should have been shown the math a bit more. A 3rd grader can follow, if not do, a 6th grader’s project like this, and 6th grade is an adequate level to demo strate everything here, properly.

    Side note; Old fire extinguishers used this method. The baking soda was held in a basket above the fluid. Inverting the unit did the mix. In their case, only enough pressure to force the vinegar-water mix out was required. That CO2 did this was a very small plus for these extinguishers.

    I offer an A, B, or C, depending on which elementary grade of students he was trying to reach. But, I liked it, within those limits. 5 points for demonstrating the welding application. 3 for originality. 2, as fun factor.

  2. Pedant point: The “IG” stands for inert gas. CO2 is an ACTIVE gas. This is why the process is formally known ad GMAW, for gas metal arc welding.

    A key element of a good gas is purity. This includes dry to parts per million or better, and no other hydrogen producing contaminants to a couple parts per million or better. This setup really won’t achieve either. If I was doing bodywork and not worried about a perfect weld? This would be ok. Any structural weld? No.

    “Could this be scaled up to something for practical use?” No. Not without much more trouble than it is worth. The acid carryover alone is enough to be a problem.

    1. ^ this, a lot of amateur welders here use “pub gas” – raw CO2 for fizzy drinks – because it’s cheaper than proper Argon/CO2 mix (Argoshield), but there’s a very good reason the professionals and industry use proper welding gas and not the cheaper CO2.

      Also, as a friend put it, Argoshield seems to magically make you a better welder if you’ve started with CO2.

      1. I repaired damaged dumpsters for a local trash collection company to pay for college, the way it was explained to me by one of the old full timers was it depends on the item being fabricated, CO2 (C100) is has increased weld penetration as compared to Argon/CO2(C25) mixes and creates a lot of splatter but also “cleans” the paint and rust off metal better. so it’s typically used on industrial equipment and items that don’t have to be pretty, like dumpsters.

        C25 creates much nicer looking weld with significantly less splatter with less penetration which is compensated for by using higher voltage. I’d reckon the increase in cost is offset by the lower amount of man hours to clean up the spatter.

        1. There are other differences, including weld metal hardness and ductility, wet in, Appearance is a factor, but not the prime factor in most cases. CO2 is really only included in gases for steel. Other materials, aluminum for example, can not be welded with CO2 at any level.

          A lot of metal is put in with straight CO2. Impure CO2, in particular with acid or water contamination, is not suitable for welding. Gas for beverages may, or may not, be suitable, depending on the source. Gas for paintball guns, ditto. But I wouldn’t take the chance. There isn’t a real purity standard, as long as it isn’t toxic.

          Oxygen is funny the same way. Medical O2 is generally not suitable for oxy-acetylene work, for example. It may be as low as 95%, with N2 and H2O making the difference,

          The argon at lower percentage smooths the arc, reduced spatter, and can reduce hardness. At higher levels, it allows the transition to transfer modes other than short-arc. Lower levers allow globular transfer, and higher levels alloy spray, which allows VERY high deposition rates with ductile deposits and little cleanup.

  3. Okay so the youtube embed must have changed, because before I used to be able to touch and scroll on my mobile without the video automatically loading and playing, and now it’s like a landmine waiting to go off.

    Is this a real thing or am I just turning into an old man? If it is real, did someone make this choice actively or is it an emergent property of whatever garbage update we’re victim of lately?

        1. I have never in my life seen dry ice with my own eyes, so YMMV. Yeah, I could order some, but not on weekend, and I would have to drive over one hour to nearest big city.

          Dry ice in grocery stores? Forget it.

          1. Where do you live that grocery stores don’t carry dry ice? Have you ever asked?

            Right now there are 3 grocery stores in my area and I’ve bought dry ice at each in the past. I’ve lived in some small towns in the past but if there is a chain grocery store in town guaranteed they have dry ice in a little freezer up front by checkout.

        2. The first time I saw a dry ice cooler in a grocery store around here I was intrigued — never saw one when I lived back east, but in Idaho, dry ice is a big seller with hunters and others. I wanted to take a peek in the cooler, just to see how the dry ice was packaged — blocks? pellets? So I lifted the lid of the cooler, and saw nothing but fog. I put my head a little closer, blew the fog away, and was rewarded with a big blast of CO2. Stupid move — felt awful the rest of the day. Lesson learned.

  4. My projects are always running into the “ain’t got one of them handy” blockade. Sometimes the store is closed and it is a frustrating chance to develop and learn patience. Sometimes it is quicker (and maybe more fun) to make one on the lathe rather than drive to the store. A whole spectrum of decisions in this arena.

    I just acquired a truckload of boxes full of circuit boards and dumped them in the yard (for now). It is the Arizona desert here, and a little rain won’t hurt them for the most part. I don’t know how I lived without them. It seems like every other day I am going out to the pile and rummaging for a part.

  5. On-demand flow-regulated CO2 generation was solved a century ago or more, with the Kipp’s Apparatus; Think of marble chips in one side of an oversized U-tube, with gas take-off above. If gas demand falls, gas pressure pushes the acid below the chips, with the excess backing up in the other U-tube arm. The glass ones we used in the chemistry lab was fancier in architecture, but worked the same. Not good for pressurising, though.

    A bag or two of garden lime (CaCO3) would drop the price of half the ingredients, and agricultural vinegar has already been suggested. Builder’s lime is no good, whether unslaked (CaO) or slaked (Ca(OH)2), there’s no CO2 to be had. It’s not just a base which is needed, but a carbonate.

    1. For myself I can dig chalk out of my garden, which supplies the calcium carbonate for free. Crush it down for quicker reaction.
      I suppose at a pinch just raid the pantry for some malt vinegar.

      Agreed what was said above about using CO2 for welding in the first place, but it would suffice for welding where absolute strength isn’t critical

  6. My first thought on “homebrew welding gas” was making acetylene, and how to do so without explosions. A scrapyard where I used to get welding tanks refilled used a quite large and very antique acetylene generator to refill those tanks on site, I assume it took some quite special compressor or other equipment to get it into the tanks at high pressure, dissolved in acetone. Oxygen and other gasses were brought in from a gas supplier.

    A retro tech article on acetylene generators and how a gas that likes to KABOOM when squeezed to 15 PSI or higher is put into tanks at much higher pressure would be a nice one to see on HaD.

    1. Was also my thought.
      I think the key to safely fill the C2H2 into tanks is to do it slow, so it has time to dissolve into the acetone without too much pressure.
      I once saw i picture of a device to transfer C2H2 from one tank to another. This was a quite thin – nearly capillary – tube. The explanation was, that this prevents (or only lowers the danger?) of explosive decomposition.

    2. Ask any one who a ship builder about gasses it will scare the shit out of you gassed and oxy create a very bad situation if not ventilated well we use meters with horns not powered by any spark devices or it’s lights out for you and the guy’s you share your life with with including your wife and kids and dogs amen brother it will kill you watch your back

  7. I’ve been using an old medical oxygen tank (good to 3k psi) and a couple pounds of dry ice to weld forever. Even out in the shop in the middle of an Arizona summer I’ve never seen over 2k psi in the tank and ambient has to be over 150°.

    You do have to change out the teflon washer and the O rings on the regulator a bit more frequently. Even with that I’ve saved myself a couple thousand bucks over the last few years. Dry ice is like $3 a lb at Fry’s not a 1/4 mile from my house.

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