Mixing your own welding gasses questions

Try asking on the welding NG. sci.engr.joining.welding They may be able to help you better.

John

Hi Eric

You don't need a mixing chamber , just a "Y" connector with back-check valves on both sides. The gasses will mix on their own in the hose.

You will need a kind of fancy regulator for your CO2. The liquid CO2 will freeze your regulator so you have to get either the kind with the heat fins or the kind with a little electric heater inside.

We had both types as SSCC until we retired all of our CO2 bottles. The entire welding industry has gone to mixed gas for wire feed so CO2 is a bit of a dinosaur.

For hobby work it can be OK, just messier. To mix your won you have to have the back-check valves or you can contaminate one gas bottle with the other gas.

Even here in the winter time, burning .035 wire, Ive never had a CO2 regulator freeze up, and Ive pushed em hard doing corral fencing out of sucker rod and old oil field pipe. Maybe with a bigger wire and more gas it would/could happen, but most of us cheap ass guys here in the erl patch use CO2 for rough work and I dont recall anyone mentioning freeze up.

As Ernie says..CO2 is a fair amount messier than C25 and the bead doesnt look as pretty..but it works fine for utility welding and is way way cheaper than mix. I save my (3) 135cf tanks of C25 for stuff that needs to be pretty, like window bars or gates, and burn Co2 for just about everything else. Co2 tends to splatter a smidge more than C25, so I simply spray my work piece with anti splatter spray (bought a case of 12 large cans on ebay for $10 including shpping) and go for the gusto.

Straight Co2 is hotter than C25 and a fair amount hotter than straight argon, ..so with a bity buzzbox mig..it helps, helps me anyways.

The regulators for CO2 are simply the cheap CO2 regulators one finds on Ebay for $20. You may have to change the input or output connectors..but thats cheap.

I was getting 5-7 tanks of C25, at about $23 each, to one $12 tank of Co2. Significant savings if you are doing utility work.

Shrug..YMMV and Ernie is the expert..Im only a dauber.

Gunner

"If thy pride is sorely vexed when others disparage your offering, be as lamb's wool is to cold rain and the Gore-tex of Odin's raiment is to gullshit in the gale, for thy angst shall vex them not at all. Yea, they shall scorn thee all the more. Rejoice in sharing what you have to share without expectation of adoration, knowing that sharing your treasure does not diminish your treasure but enriches it."

- Onni 1:33

You don't need a mixer, just two regulators and flowmeters. The percentage mixture will be be in cubic volume units rather than weight units. I don't know how welders specify gas mixtures, whether it is by weight or volume. If the mixture needs to be made by weight, then you need to check the molecular weight of Argon vs. the molecular weight of CO2. CO2 weighs 12 (C) + 15.9*2 (O2) = 43.8 while the monatomic Argon is 39.9, so the difference is probably within the accuracy of the flowmeters. So, set the Argon for 3 times the flow of the CO2, and you should be set.

As for regulator freezing, just get the gas delivery bottles rather than the siphon-tube bottles at the gas supplier, and you should never have a problem. The liquid in the bottle should evaporate PLENTY fast for TIG/MIG shielding applications with no trouble.

Don't even THINK of trying to mix gas in a bottle. A dual flowmeter setup is so simple to construct, that unless you need to crawl through the pipes in a ship with the welder on your back, there's no point in doing it that way.

Jon

Interesting thread. As I've got the CO2 bottle on the MIG and Argon on the TIG, I'd like to try this also. My CO2 regulator has the little ball flow meter, this gives an idea of flow rate. Are you saying just get one of these for the argon and tie together? Sounds too simple to be true. As you start/stop constantly when welding I think it would be difficult at best to not have the % of gasses constantly changing on you.

A variation of Ernie's suggeston occurs to me. Get an old 100 lb. propane bottle (free). Fill to a certain pressure with gas CO2, slow enough to not freeze up. Then connect to the argon and fill to higher pressure. I don't know the max. pressure on the argon regulator but its prettty low. You might have to repeat the procedure too often when welding.

If someone (Eric?) does this with good success, I'd sure like to hear about it.

Thanks Ernie. I hadn't even thought about the special reg. It'll have to be cheap enough for the whole thing to work. Eric

Thanks Gunner and Jon for your helpful replies. I believe that the gas ratio is based on volume, which makes things easy. But I'll call first. I didn't know that there were liquid and gas delivering CO2 bottles but it makes sense. Karl, I think that with the pressure set the same for both gasses the flow meters would work fine for delivering the proper ratio. I don't see how the mix would change when the flow was stopped and started. If both flow meters dump into a manifold, and it is the output from the manifold that is valved with the solenoid on the welder, it seems that the gas delivery would remain constant. I'm surprised you don't have a flow meter on your argon bottle. How do you know the flow? I personally can't tell from the sound if the gas flow rate is excessive. I can tell when it's too low by welding though. Eric

Maybe I was an engineer for too long. But it will be impossible to set both regulators to exactly the same pressure and get 3X the flow out of one (75:25 = 3:1). When you stop welding, the higher pressure one will continue to fill the line with a shot of pure gas. A large manifold would help but you'll still have this problem.

Karl

It would be good to have adjustable pressure regulators, so that they could be set to the same pressure. Our shop at work does exactly that, although they have fancy glass flowmeters that are about 8" tall, not the cheap plastic ones 2" tall that are part of the fixed-pressure regulator.

I believe a lot of shops that do a mix of different welding tasks and materials use such a scheme.

Jon

Agreed, the regulators can never be set EXACTLY the same. But, a small difference in pressure will only cause a small error in mixture. If one regulator is set for 15 PSI (gauge) and the other for 14 PSI, then the error will only be 1 part out of ~30 (absolute pressure in line). Check valves might be necessary if the regulators are the self-relieving type. If you use modest pressures and a small needle valve for each gas, instead of a wide-open orifice and a regulator set for infinitesimally above atmospheric pressure, this should just not be a problem. Those fixed-pressure regulator-flowmeter setups might be set for quite different pressures, so adjustable regulators seem a good idea.

Jon

Greetings Karl, I'm NOT an engineer so it's easy for me to be wrong on things like this. This is how I mentally pictured the setup: Imagine a pipe closed at one end with two smaller pipes leading into it. One pipe's cross sectional area is 3 times the other pipe. Both pipes are much smaller than the pipe they empty into. When the large pipe is capped at both ends (solenoid valve closed) the pressure seen at each smaller pipe is the same. When the large pipe is open the smaller pipes flow freely. I have looked inside my flow meters and the orifice that the gas flows through is quite small compared to the diameter of the gas hose that leads to the torch. This is where I came up with the pipe visual. Back to your argument now. I hadn't really thought about how the higher pressure gas would force itself into the lower pressure region inside the lower pressure regulator. You are correct of course. It's so easy with thought experiments to imagine ideal conditions which don't exist. So as Ernie said, you must use back flow preventers to prevent contaminting the lower pressure cylinder. Since this type of gas mixing is being done it must work well enough to be practical. I still have a question though. How do you know how much argon you are using without a flow gauge? Eric

I, of course, have no clue. I set the TIG pressure regulator so it worked maybe ten years ago, haven't touched it sence. I buy about 1 to 1 1/2 tanks a year so i haven't looked to find a way to save on argon.

Please let me know if you find a mixing method that works well. I'd like to try something other than pure argon or pure CO2 on the MIG.

Karl

Based on my experience so far I think that the check valves are needed and should be close to the wire feeder. One thing that I've not seen anybody mention is the need for a restriction right at the wire feeder. I've been refining my setup to try and get it to work right and so far I'm not totally happy with it. It's fine once you start welding but the start still isn't right. I started out with my flow meters on the tanks and a 50' hose to my wire feed unit. This proved very unsatisfactory in that I got a big burst of gas when I pulled the trigger due to the storage capacity of the long hose. I've changed that to where my flow meters are on the cart for my wire feeder and the regulators on the bottles. This is working better but I still get a short burst of gas. I've not got around to putting the check valves on and I believe they may help a little but I also plan on putting a needle valve on the inlet of the wire feeder so that I can stop the sudden burst of gas I get when I pull the trigger.

The system I've seen has needle valves on the flowmeters. I don't believe our shop has check valves, either. The mixing manifold feeds into the single solenoid gas valve in the welder. I've been refining my setup to try and get it to work right

Yes, I agree that the long hose between regulators and gas valve is not good. If nothing else, it wastes gas every time the valve opens, and Helium and Argon are not cheap. I get the same thing on my TIG machine, but the hose between regulator and valve is about 6', so I live with it.

Jon

Why not just get a tank of C25??

Gunner

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Well, you sure aren't spending gobs on argon so it must be set correctly. And I will let you know if I decide to use a manifold. Eric