CO2/Argon mixing

[poseidon2]

Can any of you gas experts please help? I need some info on mixing my own shielding gas! I'm in the diving industry and have access to free Argon and Oxygen and high pressure cylinders. A friend of mine has a fire protection company with loads of CO2. SO...... The question is this:- CO2 is filled by weight Argon is filled by pressure so what weight of CO2 would I put in a cylinder before I top it off with Argon. I may be having a flight of fancy so it may not be that easy

 

[Wozzaaah]

Errr...wouldn't it all depend on what size cylinder you were going to use?
Ideally, you'd do it properly and SAFELY and have two separate cylinders, one filled with argon and one with CO2 and use a gas mixer setup to blend the two en-route to the machine.
Safer still, why don't you just use pure CO2 and be done with it, especially as you have a ready supply of it?

I'm suspecting this thread will go the way of other similar ones and attract all manner of stupid suggestions so don't be at all surprised if it gets closed or deleted.

 

[poseidon2]

Err... No, it wouldnt depend on cylinder size IF you are blending by pressure. 50% of a 50ltr 200bar cylinder is 100bar & 50% of a 25ltr 200bar cylinder is still 100bar. But CO2 is in kg's so that is my problem, mixing measurements. Please bear in mind I'm a skinflint, I got the MIG for nowt so obviously I want the gas for nowt too

 

[Wozzaaah]

You asked

what weight of CO2 would I put in a cylinder before I top it off with Argon.

that would be dependent on the cylinder size wouldn't it?

 

[rikrobson]

there are different ratios in the mix gas availability, 5% for light/thin steel and 20% co2 is also common, so I'd guess thjat it would not be that critical if there was at lease some co2 in the argon, or just use co2

 

[shenion]

You would fill the CO2 by pressure as it remains a gas.

For a normal 75/25 mix, fill to 25% pressure using CO2, then rest with argon. CO2 is usually 900 PSI or so as a liquid. So unless your are filling at over 3600PSI, then the partial pressure of CO2 will always be less than the liquid pressure.

 

[Hitch]

And then ideally, theres an addition of Oxygen to add to the mixture aswell....

 

[poseidon2]

Yes but what pressure does say 10kg of CO2 equate to in say a 10ltr cylinder? I know what I can do.....experiment!!!!!!!!!!!!!

 

[poseidon2]

Scrub that, thanks SHENION

 

[voipio]

It's worth bearing in mind the temperature range that the mixed gas cylinder is expected to operate under. The CO2 will liquify, changing it's ratio in the mix, if it's partial pressure exceeds around 20Bar at -19degC, 40Bar at around 6degC, and 60Bar at 22degC.

 

[voipio]

10kg of CO2 amounts to about 5090 litres at standard temp and pressure. In a 10litre cylinder that would represent a fill pressure of 501Bar! Clearly the majority of the 10kg of CO2 would be in the liquid state and, since 10kg of liquid CO2 would actually take up around 13 litres, it wouldn't fit into a 10litre cylinder anyway!