Argon Regulator question

A sort of shelf life as the two gasses will seperate after time with the Ar gass settleing to the bottom of the cylinder where the dip tube picks up the Ar gass first. The gasses themselfs do not change and will last for ever.

I thought I'd cut a fat hog and buy one tri-mix cylinder for all my use and after 10yrs or so I used the Ar gass leaving behind some Co2 and He which didn't work well as a cover gass, (out of correct volume).

That's why I suggested 100% Ar gass as a one only gass to keep around.

T_Bone

Actually, no. Since all three materials are gases, even at 2000 PSI, they should fully diffuse and intermix with each other within the cylinder. That's what gases do. There should not be any "settling" or separation of the components within the tank. This would be violation of the second law of thermodynamics.

This is a good thing -- otherwise all the CO2 and argon in the atmosphere would settle to the earth's surface, leaving us to suffocate.

There is a secondary effect that may explain T_Bone's empirical observation. The rubber hose connecting the tank to the MIG machine establishes a diffusion membrane. The more energetic (lighter) gas molecules are more likely to diffuse across this membrane than the heavier ones. Over time, this will allow the gas mixture to change its composition. This is most pronounced with the helium (just look at how fast an He filled toy balloon goes flat). But over enough years, the AR will difuse through the hose faster than the CO2, leaving the mixture relatively richer in CO2 than it started. This is not a violation of the second law because the tank + hose does not form a closed system. (The enrichment effect can be reduced by keeping the tank valve closed except when using the machine.)

Gas diffusion is a known method for separating two materials close to each other in density. Just ask the Iranians and North Koreans...

Ever notice how methane and radon gas sink, and helium or hydrogen ballons rise? ;-)

The second law of thermodynamics states:

"heat flows from a higher temperature source to a lower temperature source"

The settling of the gas would not occur in the open atmoshere but would occur with-in a vaccum or pressure vessel. If the gases wouldn't seperate then we wouldn't have the refrigeration effect than makes some of our refrigeration equipment work.

Example:
The typical RV refrigerator uses this therory. Here we combine hydrogen gas and ammonia gas and heat that solution and drive off the hydrogen gas thus leaving behind the ammonia gas to cause the refrigerating effect then condense the gases to recombine the gases to once again restart the refrigeration cycle.

In the above example we did not violate the 2nd law of thermodynamics to seperate or recombine the gases but used this Law to obtain the refrigerating effect.

This gas seperation effect can best best explained by Dalton's Law that states:

"The total pressure of a confined mixture of gases is the sum of the pressure of each of the gases in the mixture"

The law further states:

" That each gas behaves as if it occupies the space alone"

Moisture content of each gas would also have a effect on the seperation/combining process.

One should never leave any gas cylinder valve open for storage. This is for safety as well for gas leakage.

T_Bone

You'll need a flowmeter. A flowmeter measures cylider pressure (in psi) as well regulates flow (in cfh) for cover gas. A good enclosed shop setting is 25cfh. Outside welding may require 35cfh. A good flowmeter will measure several different gasses and is well worth the small extra cost.

Use a 1/4" x 25ft rubber hose rated for all welding gasses.

Mix gas always runs about 30% more in cost than a pure gas. Here 100%Ar is $65/200cft, 75Ar/25Co2 is $85/200cft, 100%Co2 $45.

Cylinder cost was $125 for a owner cylinder. $5.25/mth on rental cylinders with a $75? deposit. A 200cft cylinder is a good all around cylinder size. Smaller cylinders the gas cost is about triple the cost. Only buy cylinders from long established gas supply companys.

If your considering ever getting into Tig welding then buy one cylinder of gas, 100%Ar, as it can be used for all common welding processes and metals. A typical home shop doesn't need several cylinders of gas when your typical useage is under 200cft/yr.

If your welding nothing but Mig on Fe, then get 100% Co2 as it will weld just fine.

If you going to weld exhaust pipe, use .023 wire with a #7 cup. Innershield (fluxcored) wire doesn't work well for this application. Neither will stick welding.

Nothing wrong with innersheild welding process. Like any welding process it takes time to learn to use the process and the little tricks that help and a welding machine with a 60% to 100% duty cycle to be cost effective.

Here are some of my past thoughts on flowmeters:

There's several items that control how much cover gas flow is required while Mig or Tig welding. Lets start off with how a typical flow meter/gauge works.

Gauges:

There are two basic types of gauges:

1) flow meter:
A flow meter has two gauges on the manifold assymble:

a) The high pressure gauge that reads tank pressure contents in PSI.

b) The "caliberated" gas flow meter that controls cover gas flow measured in cubic feet hour (CFH).

There are two basic typical flow meter configurations, square vertical dial, and round vertical dial. Both use a center steel ball to denote gas flow.

Each side of one type of a typical "caliberated" square vertical flow meter is marked with a Argon flow scale, a Helium flow scale, a Carbon dioxide scale, and a Nitrogen scale. Why?

Each cover gas has a different weight thus will flow more or less CFH when comparred another gas. This is why I used the term "calibrated" flow meter as it accurately reads and measures other types of gases. This will become useful when using a welding process that requires different types of a mixed cover gas, like Mig welding Aluminum.

You can buy a premix gas cylinder (higher gas cost) that "maybe" be exactly what is required or mix your own gas with seperate pure gas cylinders (lower cost) that will always be what is required.

One flow meter also can accurate measure 4 different types of gas and once again at a lower cost.

The round verticle dial is read from the "calibrated" center dial and typicaly covers several different types of gases.

This type of flow meter typicaly measures 5 to 200 CFH depending on the type of gas being metered.

2) Round flow gauge:
A typical round flow gauge has two gauges on a manifold assymble, however there are one gauge round flow gauges:

a) The high pressure gauge that reads tank pressure contents in PSI.

b) The "caliberated" gas flow meter gauge that controls cover gas flow measured in cubic feet hour (CFH).

c) A one gauge round flow gauge only measures cover gas flow and not cylinder contents.

This type of flow gauge is not as accurate as a flow meter and usually only measures one type of gas. I do have one dual round flow gauge that measures Argon and Carbon dioxide. This dual gauge is marked with AR numbers on the out side scale and the Co2 numbers on the inside scale.

This type of gauge typicaly measures 0 to 30CFH.

What controls how much cover gas flow is needed?

When you do not get porosity with-in the weldment while welding!

What normally happens while with low cover gas flow, is tiny gas bubbles form on the face of the weld from the oxygen thats allowed to enter the weld zone, called porosity. As the cover gas decreases the porosity travels deep with-in the molten puddle to the root of the weld. When this happens then the weld needs removed and rewelded. Notice as your grinding out the porosity filled weld of just how deep the porosity can penetrate.

While welding carbon steel, you will notice the arc sputter then porosity form on the weld face then porosity proceeds thru out the weldment.

While welding SS, you will notice alot of carbon forming on the weld face. As the cover gas decreases, porosity once agains forms on the face first then proceeds thru out the weldment.

While welding Aluminum, the enitre weld will have porosity thru out almost 100% of the time.

The torch cup size determines how the cover gas is spread over the weld. A #10 cup will spread a wider gas flow area than a #7 cup. How far the cup is held above the molten puddle at a given gas flow will determine adaquote gas coverage.

A gas flow of 15CFH maybe adaquote gas coverage with a #10 cup while at a 1/4" arc length at 140amps, inside a shop but not outside.

As the welding amperage increase so does cover gas flow rate as the heat pushs the cover gas away from the molten puddle. While 15cfh maybe adaquote at 150amps, 30cfh maybe needed at 225amps and 45cfh at 275amps.

Hand and body positon around the torch will greatly influance gas flow rate needed.

Welding inside with no external air current decreases gas flow rate.

Clean weld joint preperation will take less cover gas than a dirty joint.

AR or Co2 uses less cover gas than a HE mixed cover gas.

A v-groove joint will take less cover gas than a butt weld joint.

A weld joint using a chill bar or backing bar will use less cover gas than a open root weld.

T_Bone

The manual that came with your MIG welder should detail the type of regulator you need. You also should determine from the manual if you also need a flowmeter or whether the welder has a built-in fixed orifice such that you only need to provide a fixed inlet pressure such as 30 or 50 psig or something similar. A two stage regulator is nothing more than two single stage regulators in series. The first one is non-adjustable from cylinder pressure to some intermediate pressure while the second, adjustable one, one reduces from that intermediate pressure to the usage pressure. The two stage unit requires less adjustment to maintain a constant usage pressure as the cylinder pressure drops. Many of the smaller mig units come with fixed regulators (no adjustment) and fixed orifices for a relatively constant gas flow as the cylinder pressure drops. It's not that critical that the pressure be held absolutely constant in such an application. The flow rate is typically 20-30 cubic feet per hour. Unless you are into the larger nozzle sizes you are not likley to need any more than that nor are you likely to need an adjustable regulator. Again, your specific welder instructions should guide you to the correct equipment.

As JL indicated, if you are welding carbon steel, a better choice for a shielding gas would be a 75%/25% argon/CO2 mix. That gas is also sometimes referred to as C-25. The straight argon would be more appropriate for aluminum. Argon is relatively expensive. I have one of the large bottles that I haven't filled in over 5 years but as I remember a refill was about $75 back then. I also can't remember what my 75/25 cost since it's been over 5 years for that also. The small bottles would obviously be less expensive and more portable but would not last as long. I believe straight CO2 is also used for steel MIG since it is cheaper than the C-25. I have never used it so I can't comment.

It depends on what you bought the welder for. My MIG is a 150 amp Lincoln and I run 0.023 dia solid wire with C-25 for everything less than about 10 gauge. If you are going to be doing predominantly sheet metal (even exhaust tubing), I think you would do best to go with 0.023 solid wire and gas shielding using C-25 rather than getting into flux core. It will depend on whether your machine needs any optional parts to even feed flux core. It may also depend on what kind of range your machine has for adjusting the wire feed rate. Your instruction manual should tell you all about that.

Rod