Mixing gases

[FarmBoy9205]

I need help with 2 questions.
1. Is there any type of mixer available so I can buy just co2 and argon and mix the gases at final use to produce a c25 or c10?
2. For Tiging Stainless is straight Argon used or another gas?

Thanks
Jim

[GilaSlim]

1. http://store.cyberweld.com/smithgasmixers.html

2. Straight Argon

[Rocky D]

Here's the source...as you can see there are more than one flavor of mixer to be had.
http://www.smithequipment.com/products/pdfpages/page60.pdf

[calweld]

Keep an eye on Ebay ..... I picked up a nice Smith, two-gas mixer, for about a tenth of the new cost, last year.

[FarmBoy9205]

Thanks I appreciate the help. Also would it work to make your own mixing valve by bring the c02 and argon gas in at 180 degrees from each other and 90 degrees from output side, using a piece of heavy walled drilled pipe? The mixing percentages could be adjusted based of input cfm's. Do you think this will work?

[SundownIII]

Farmboy,

NO.

[nhamilto40]

To understand what will work you need to understand how your equipment actually works.

The common "flowmeter" used in welding is actually a regulator/flow meter/needle valve combination.

Here is how it works:

1. The regulator regulates the bottle pressure to a preset pressure (commonly 100 psi).

2. The flow meter measures the flow from the regulator to the needle valve.

3. The needle valve is used to adjust the gas flow to the desired rate (cfm).

So if you combine the outputs of two "flowmeters" you will get the result you are looking for when your mig gas solenoid is open. Your problem will happen when your gas solenoid is closed. In this case your gas hose will be filled with a gas mixture determined by the preset pressures of the regulator stage your "flowmeters". If for example you use identical "flowmeters" where each regulator is preset to 100 psi you will get a 50/50 mix of argon/carbon dioxide until your mig hose is cleared.

Another possible problem is the precision of your carbon dioxide flowmeter. Assuming a 20 cfm total flow rate it will need to be precise enough to set a 4 cfm flow for c25, a 1.8 flow for c10 or a 0.4 flow for c2 etc.

[Dmaxer1]

To understand what will work you need to understand how your equipment actually works.

The common "flowmeter" used in welding is actually a regulator/flow meter/needle valve combination.

Here is how it works:

1. The regulator regulates the bottle pressure to a preset pressure (commonly 100 psi).

2. The flow meter measures the flow from the regulator to the needle valve.

3. The needle valve is used to adjust the gas flow to the desired rate (cfm).

So if you combine the outputs of two "flowmeters" you will get the result you are looking for when your mig gas solenoid is open. Your problem will happen when your gas solenoid is closed. In this case your gas hose will be filled with a gas mixture determined by the preset pressures of the regulator stage your "flowmeters". If for example you use identical "flowmeters" where each regulator is preset to 100 psi you will get a 50/50 mix of argon/carbon dioxide until your mig hose is cleared.

Another possible problem is the precision of your carbon dioxide flowmeter. Assuming a 20 cfm total flow rate it will need to be precise enough to set a 4 cfm flow for c25, a 1.8 flow for c10 or a 0.4 flow for c2 etc.

That's the most convincing explanation I've heard to-date of the shortcomings of mixing gases without a dedicated gas mixer. It sounds like once the weldor releases the trigger (assuming identical flowmeters), the buildup to 50/50 will commence in the hose immediately downstream from the mixing point. If, as I have done with good apparent results, the weldor is mixing C-25 with straight argon to achieve C-8, the effects will be less noticeable when the arc is re-initiated. On the other hand, I've looked at the flowmeters when welding stops and they appear to drop to zero flow immediately. How is it then that mixing to a 50/50 ratio continues in the hose?

If it occurs as you say, does the 50/50 mix permeate quickly all the way to the nozzle? Perhaps just purging the lines for a few seconds (I have a gas purge switch on my wirefeeder) will restore the correct mix.:)

[Roger]

Shielding gas flow meters are calibrated in units of CFH not CFM.
Victor welding flow meters are now calibrated for 25PSIG/1.7 BAR or 80PSIG/5.4BAR supply pressure. BAR is metric atmosphere pressure unit (1 BAR = 14.5 PSI). USA ATM atmosphere pressure unit is 14.7 PSI.

Calculate internal hose volume in cubic inches from regulator flow meter to welder. 3/16 inch hose 10 feet long (120 inches). It is 13.25 cubic inches (CI).

With 25 psi supply to flow meter.
(1.7 BAR + 1) X internal volume of hose = gas volume in hose at 25 PSI.
1.7+1 = 2.7 X 13.25 = 35.8 cubic inches gas in hose.

1 cubic foot = 1728 cubic inches
20CFH = 34560 cubic inches hour or 576 cubic inches minute or 9.6 cubic inches second.

Lower flowmeter regulated input pressure reduces flow surge when shielding gas solenoid valve opens. Not really wasted gas as preflow timers and/or flow surge are needed to get good shielding at weld start.

[usmcpop]

Gases are also mixed by filling a tank based on partial pressure:

http://www.baue.org/library/highpressure_mixing.php

Here's how it's done for diving gasses:

http://www.s297830378.onlinehome.us/usn/Chap16.pdf

[Roger]

Gases are also mixed by filling a tank based on partial pressure:

http://www.baue.org/library/highpressure_mixing.php

Here's how it's done for diving gasses:

http://www.s297830378.onlinehome.us/usn/Chap16.pdf

Been there, did, taught and photographed it. Surface supplied mix gas and saturation diving. Breathing gas mixture's percentage is critical but always have O2 analyzers to catch problems and lots well trained experienced people and approved procedures with check lists. Stuff happens but practiced emergency procedures should contain problems with divers trained to work under pressure.

[Rocky D]

Roger, in your line of work, did that include US Navy Seals?

[SundownIII]

Rocky,

My guess is that it did not. The comments about "surface supplied" and saturation dives does not go hand in hand with Special Ops diving. It would suggest to me that maybe he was involved in oil rig work.

Mixed gas and rebreathers are more common terms.

Military diving has been an area where they were really in the forefront. Even 20 years ago, when I was doing that type work, we were using equipment that didn't become available to the civilian dive community for at least 10 more years.

[Roger]

Some Seals were in surface supplied diving classes I took or taught. I did free ascent training at BUDS Coronado facility. I sometimes provided non combat photo support of seals, shooting training or public relations still photos & movies. During my time had to have seal training to go with teams in combat.

Worked for diving warrant officer that was UDT trained and LT. Thornton.

http://www.navyseals.com/michael-e-thornton

http://www.navyseals.com/?q=thomas-r-norris

Big change now is EOD and SEALS have their own rating not just NEC/MOS
Makes sense as they always worked in their own commands.

[FarmBoy9205]

That's the most convincing explanation I've heard to-date of the shortcomings of mixing gases without a dedicated gas mixer. It sounds like once the weldor releases the trigger (assuming identical flowmeters), the buildup to 50/50 will commence in the hose immediately downstream from the mixing point. If, as I have done with good apparent results, the weldor is mixing C-25 with straight argon to achieve C-8, the effects will be less noticeable when the arc is re-initiated. On the other hand, I've looked at the flowmeters when welding stops and they appear to drop to zero flow immediately. How is it then that mixing to a 50/50 ratio continues in the hose?

If it occurs as you say, does the 50/50 mix permeate quickly all the way to the nozzle? Perhaps just purging the lines for a few seconds (I have a gas purge switch on my wirefeeder) will restore the correct mix.:)

Thanks for all the information. I can see to do this right I need a commercial mixer or buy the gas premixed.