Use of 100% CO2

Date 10-04-2005 14:21

I'm not certain as to what that will cause using the CO2 that you described, because I've not tried it. We also use 100% CO2 with our FCAW machines.
But the problem I would have to get around using it here in our shop would be conforming to AWS D1.1:2004 Paragraph 5.3.1.3 which states that ..."the gas or gas mixture used for shielding "shall be" of a welding grade and have a dew point of -40F or lower". We have to submit certs of conformance on our wire and gas. So we need the documentation to support that the gas is of a welding grade and has a dew point of -40F or lower.

Maybe other forum users have used it on non-coded work and someone can attest to welding with the grade used in the fountain drinks.
John Wright

By Lawrence (*****)

Date 10-04-2005 15:20

I can see how this thread is gonna play out already..

"Tastes Great"

"Less Filling"

"The Champange of Shield Gasses"

http://www.wittemann.com/techdocs/food_grade_co2.pdf

What else can one say about carbon dioxide?

It's Sublime :)

By swnorris (****)

Date 10-04-2005 16:59

Excellent point John!! There are at least two different grades of CO2 available. Food grade, which is used in soda machines and such, and commercial grade, which is used in welding applications. I'm thinking the only difference between these two grades of CO2 is that the bottle that it comes in. I mean, C02 is CO2, right? Both the food grade and the commercial grade gases are 99.97% CO2. The food grade bottles are internally glass coated, whereas the industrial cylinders are straight steel. The reason that there is a difference, is that the food systems have the possibility of back flowing into the bottle when the gas runs out. If the bottle was a standard industrial bottle, the system would have the possibility of becoming contaminated with rust from the inside of the bottle. CO2 disolved in liquid from beverages is quite acidic and rusts the
inside of gas cylinders.

By ziggy

Date 10-04-2005 22:18

Not knowing the process or code that labtechy is speaking of, but GMAW run with 100% CO2 will typically make the process GMAW-S which is not prequalified in D1.1. Just a thought.

By mdhaynes Date 02-23-2008 01:46

Just thought I would throw this in the mix. There is also a Medical grade. The primary difference between the two products is the product traceability from manufacture to point of use with USP (medical) product. Medical product must come from a plant registered with the FDA. The plant must validate their equipment and process to ensure the plant operates as designed and reliably produces product to specification. These plants must also follow all applicable Current Good Manufacturing Practices (CGMPs) as published in parts 210 and 211 of CFR 21. These are the same rules drug companies follow. Due to the costs of the validation only a few plants across the country are registered and all USP grade product must come from these plants. Medical grade CO2 must be 99% pure which the lowest purity grade of CO2. While not as pure as food or beverage grade, the medical product does have a pedigree that the food and beverage grade may not have. Medical grade product may only be sold to licensed practitioners as it is classified as a prescription drug.

With the implementation of appropriate record keeping and product testing, similar traceability is possible for industrial and food and beverage grade CO2. Almost all product sold as industrial is produced to and also sold as food grade product. more detail in the CGA Pamphlet G6.2 "Commodity Specification for Carbon Dioxide" from the CGA.
Mark

By billvanderhoof (****)

Date 10-05-2005 02:50

We use straight CO2 gmaw on mild steel. You can't get into spray transfer. You get a little more spatter. It steals a little carbon from the puddle (probably C + CO2 -> 2CO) so a little CO is being created. I suspect that it's temperature is still high enough when it finds some oxygen that it burns. The result of the loss of carbon is that the deposited metal is a little weaker than if another shield gas was used. It's liquid in the cylinder so a lot fits in and that makes it way cheaper.
Bill

By CHGuilford (****)

Date 10-05-2005 16:39

Actually, the way I understood the shielding gas reaction was that the CO2 breaks into C + 2O in the arc zone; that some of the C + O reacts with the welding puddle and most of the remaining C + O quickly recombines into CO at elevated temperatures. Within a short time and distance the CO gains another O and becomes CO2.
The materials used in the filler metals are selected to tie up the unwanted compounds.
I might not have that exactlyright , just relaying what I was told some years ago.
Chet

By billvanderhoof (****)

Date 10-06-2005 06:45

OK sold, At those temperatures the CO2 would surely at least partially dissociate. The atomic oxygen would then easily grab the carbon. Same end result though.
Bill

By labtechy (*)

Date 10-05-2005 14:09

Interesting discussion guys! Thanks. The welder in question was welding a homemade trailer to be pulled on the road.
Getting back to the quality of the gases and what the manufacturer does with them... That's another story. I called the company about the food grade CO2 .. Guy kinda mumbled on the phone. When I asked about the welding grades, he asked if I needed certs, costs more because of the traceability and verification of equipment.
Do you see a loss of strength using 100% CO2? I would really like to test a few 505's in the lab to verify this myself. I suspected there would be a reaction with the gas since CO2 is not considered inert.
Another interesting note here is the CO2 welding tanks(steel) come with roughly 1600 psi in them and are inspected regularly (yearly). The tanks from the soda business are loaded to 2500 PSI. After looking at the tanks, I couldn't see any regular inspection marks on them.

By billvanderhoof (****)

Date 10-06-2005 07:45

Some loss of strength but since you are welding 60000 psi material with 70000 psi wire usually not enough to render the weld weaker than the mild steel.

At room temperature CO2 will be in the cylinder as liquid and gas. The equilibrium pressure at this temperature is about 800 psi. If you draw off some of the gas causing a momentary drop in pressure some of the liquid will boil until the pressure returns to 800 psi. If you pump in more gas causing a momentary rise in pressure some of the gas will condense into liquid until again the pressure is 800 psi. At higher temperatures the equilibrium pressure will also be higher. At about 80 degrees F and 1010 psi the critical point is reached. Above this temperature the liquid phase cannot exist and the CO2 behaves as a gas. Above the critical point you could pressurize to 1600 or 2500 psi. As soon as the temperature fell to room temp the gas would condense and the pressure would fall to 800. One would limit the mass of CO2 in the cylinder to that which would result in a safe pressure at the highest expected temperature.
Bill

By labtechy (*)

Date 10-07-2005 12:04

Thanks Bill,
I just saw a manufacturers specs on their mig wire weld strengths with different gases. You are correct. The tensile strengths comparing mixed gases versus 100% CO2 were negligible (about 2800 psi). I tend to view manufacturers specs as being on the high side too.
Appreciate all who posted here. I won't confse the poor guy who asked me. I'll just tell him keep doing what you are doing.
Thanks

By 357max

Date 10-09-2005 00:36

100% CO2 provides a more aggressive, digging short circuit metal transfer arc on hot rolled steel. You will need about 3 volts more than the argon/co2 blends when short circuiting. About 20-21 volts when welding. If you have a 150 amp arc; that translates into 450 watts more energy. You don't have to grind off the mill scale that is present on hot rolled. Though it is better if you do. If you have a machine with meters and an inductance control it is really quite easy to set a minimum spatter weld condition. Set the wire feed speed for 120-150 amps, set the voltage for 20-21 and start the inductance at 0 and increase to the point where spatter is minimum.