Gas Mixture for GMAW?

Date 06-03-2010 03:19

I would be hard convinced to buy into a 3 part mixture for steel work. I've used stargon before, not much to say, but using CO2 AND O2 is kind of pointless. CO2 disassociates into O2 and free carbon in the arc anyways.

for general all around GMAW a two part gas is just fine 85-15 and 90-10 are becoming quit popular. Anything over 18% CO2 prevents you from going into spray mode (easily) so in industry 75-25 has fallen out of practice. For home hobbyist use and small machines the higher arc energy of CO2 mixtures means that it has more penetrating power for little 110 machines.

100% CO2 has fallen nearly completely out of favor for everyone but hobbyists who use it cause it's dirt cheap. Too much spatter and too erratic of an arc to make sense for commercial work anymore.

By js55

Date 06-03-2010 11:25

Metarinka,
While I would agree that tri mix is overkill for carbon steel I would disagree with the CO2 argument. It hasn't fallen out of favor (even saying fallen out of favor is a bit of an exaggeration IMO) so much because of spatter problems which can be easily controlled with minimal training and understanding (we ran miles and miles and miles and miles of S-6 with 100% CO2 with nary a spatter problem at one facility I worked for) but because of aggressive marketing from gas sellars wanting to sell the more expensive argon mixes(even these ridiculous proprietaries as you well indicated), a little bit because of impact properties, and also with people wanting to get multiple transfer modes from a single gas, again as you indicated.
The 90/10's and 80/20's have been used and pushed by the Europeans for decades while the Japanese have preferred CO2 since argon is so unbelievably expensive there.
100% CO2 has distinct disadvantages, but advantages as well, such as a wider penetration pattern for fillet welds, less expense for bulk systems eliminating the need to additional storage tanks and/or mixers, though I am not fond of the condensate issues with CO bulk.

By Lawrence (*****)

Date 06-08-2010 15:45

Tri-mix gas is a sales rip-off scam for 99% of what is out there.

For short circuit GMAW on plain carbon steel CO2 100% or any two part gas will do the trick just fine.

There are a few exceptions for very thin mateiral, C02 will be slightly deeper penetrating than both 90/10 or 75/25.

If your parameters are set properly you can make spatter free welds with any of these (parameters for Co2 100% will be tighter)

90/10 is my choice for a single bottle situation because it will spray and short circuit... Unlike 75/25

By warmka weld (*)

Date 06-10-2010 23:27

Not to high-jack thread,but why are mixed gasses with higher argon levels so touchy? Been trying some 90/10 lately and just the slightest bit of mill scale, or nozzle dip, etc and i get porosity like crazy. maybe its just me if so what am i doing wrong? thanks

By jwright650 (*****)

Date 06-11-2010 12:47

I have a case of that this morning for some reason with 90/10 & MCAW(Lincoln Metalshield MC-706)...still investigating...it's very intermittant at the moment so I'm having a hard time nailing down the source of contamination. I have it happening at the fillet welds on the Base Plate on some columns. Steel is clean, fitup is tight, tip and nozzel clean, gas is flowing around 30-32CFH, no breezes.

By 803056

Date 06-13-2010 21:49

The flow rate looks to be on the low side for GMAW John.

Best regards - Al

By jwright650 (*****)

Date 06-14-2010 11:26

Thanks Al...I'll look at that again. Our Lincoln rep is coming this Wed to investigate as well. It might just be this one roll of wire, I dunno yet. We only had two rolls of it, and the first roll did fine and this second roll was spuratically troubled with porosity. Kind of wierd, the passes were either fine or full of holes...no inbetween. You could lay a fillet down really pretty and immediately as you pull the trigger on the next pass the holes would start popping up, then the very next pass might be completely fine. We were under the gun production wise, so that roll came off and FCAW went back on and no more troubles...so I think I can rule out the equipment(hoses, whip, nozzel, etc) as being the culprit.

By CHGuilford (****)

Date 06-15-2010 16:38

John,
How long are the welds? How much time is "immediately"? How long is the hose between your regulator and the wire feeder?

Al mentioned that your flow rate sounds low - at first I thought "Yeah, but not too bad". However, we used to have problems from surges in the gas flow. It would start off way too high, so guys turned down the regulator. Then longer runs of weld would have porosity.

The reason: Starting in a kind of backwards order, gas flows past the flow meter at a fixed rate, through the hose to the business end of the torch. Stop the gun, the gas solenoid closes and flow stops to the gun. However, the outflow side of the flow meter is at a lower pressure than the inflow side, so gas still flows until pressure on both sides equalize. Basically, the hose is inflating like a balloon. Pull the trigger again, solenoid opens,...and the "balloon" deflates without the flow being regulated (flow meter is upstream, mounted on the column). This doesn't last long but it is noticeable and can cause problems if you don't compensate for it. The usual fix is to turn down the flow rate, which didn't really cause the surge but it seems like the right thing to do. So on short welds you're OK but longer welds may not have eonugh gas.
Watch the regulator on the wall when someone welds. You will probably see the ball rise slowly, although the welder may tell you the surge is pretty strong. Then you see the ball drop slowly after the solenoid closes.
FCAW is more tolerant of this because it has "extra" shielding material.

If this is what's happening, you could try mounting a flowmeter on the wire feeder (inline types work OK but check the actual flow rather than trus the markings). That would help even out flow rates.

By jwright650 (*****)

Date 06-15-2010 17:07

Thanks Chet...The run of hose from the flow meter to the machine is about 15ft or so and then another 15ft of whip to get to the biziness end. I'll check the flow rate a little closer while welding to see what happens to the little floating ball.

Frets me when we have troubles and everybody scrambles to remove everything in place and put back the FCAW before I really get a chance to dig very deep into the problems.....production manager doesn't like to see people gathered around a machine asking questions, he wants to see nothing but elbows and whatever...LOL

The welds were "all around" fillet welds at the base plate of some W12x49's. Not long fillets by any stretch, especially on the inside of flanges(from the web out to the toes). I first thought we had too much flow and was creating some turbulance up inside the column, when placing those welds, but it didn't matter if he was welding up in the corner or out on the outside face of the flanges.

Initially I wrote some welding procedures to cover the GMAW, and then gave the welder a qualification test and all seemed to be fine. Welder was tickled at how quickly he could fill up that coupon. The bends came out great, nothing but clean material deposited.

Rolled through that first roll of wire and no hiccups, all seemed to be fine. This welder using 1/16" MCAW was finishing ahead of his partner on the same table using 3/32" FCAW and then sitting back smoking a ciggy watching his buddy walk back over to the wall and pull out the air hose and go back over all over his welds to chip the slag. He would rub it in every chance he got about how much quicker the MCAW wire was...but after that second roll of wire was put on, something happened....

By 52757

Date 06-15-2010 20:33

John, keep us informed. I have the same intermittent problem occuring with a 92\8 gas mix using a Lincoln L-56. Have had the reps in, kind of driving everybody nuts trying to figure it out.

By js55

Date 06-16-2010 11:06

John,
Does the porosity sit on the surface for the most part or run deep?
Is it cluster or individual?
Is it rounded, elongated, at an angle to the surface or perpendicular?
When you switched wires was it the same lot or different lot?

By jwright650 (*****)

Date 06-16-2010 11:16

Jeff,
It is swiss cheese....a glob of swiss cheese. You don't have to go far with the fillet weld before you realize it isn't wetting in good, just globbing up....raise your shield and behold the mess....I don't have the package(the box or spool) for the first roll, so I'm not sure. Lincoln guy and my maintenance guy had already opened the box and put the roll on while I was looking for a cylinder cart to haul the gas bottle on.

We have only had two 50# rolls of this and the 2nd roll is now sitting in my office with 2/3rds of the roll still on the spool.

By js55

Date 06-16-2010 13:03

John,
I don't think its the gas.
Without a breeze it is unusual for gas to cause intermitent severe cluster porosity, and is certainly less prone to happen with high Ar mixes with its density as opposed to say high He mixes
If you had a small leak in the system it is also unusual for it to be severe cluster porosity.
Something extreme is happening fast and then going away.
It sounds more like gaps in the metal core. Which would explain why one coil is doing it and the other isn't.
I've never experienced it with MC myself but I sure have with FC. And whereas FC has deoxidizers in the core and MC doesn't (other than Mn and Si in the metal) it could still cause a turbulence or shortage of filler metal deoxidizers such as Mn and Si.
The other thing is, when I have had it with FC I ran off about 50 to 100 feet of wire and it disappeared.

By jwright650 (*****)

Date 06-16-2010 16:13 Edited 06-16-2010 16:17

UPDATE:
I personnally welded for several hours with this wire along with my Lincoln rep.......I tried to create the same mess, and with Lincoln's help, never could get the issue to raise it's head...rust, millscale, and cutting oil.....even with the gas flow down to about 20cfh.....BTW, which was where I found the regulator setting when I hooked the bottle back up(I don't know if my maintenance guy had fumbly fingers when he removed the regulator, or if the welder had it set that low)....but I welded open root beveled plates 18" long with about a 1/8" gap...no porosity. I welded over orange rust...no porosity. I welded over millscale on plate...not a pin hole one. Never wiped off the cutting fluid, just started welding...no porosity. So...after several hours of welding, I have yet to re-create the same kind of mess.

By js55

Date 06-16-2010 16:18

If my assessment is correct you may have gone past the core gaps.
This would be consistent with my running 50 to 100 feet of wire before welding again and the problem being gone.

By jwright650 (*****)

Date 06-16-2010 16:21

I'm keeping that roll on that machine until it is gone(unless told to do otherwise). If it comes back I will check things out again.

A while back, I had a roll of FCAW(not Lincoln, another brand that we used to use) just like you described...we even cut open the wire and could see that there where gaps in the core materials. Welding supply house swapped it out with no questions.

By CHGuilford (****)

Date 06-16-2010 16:26

John, What you described sounds like you are losing the shielding gas flow intermittently but nearly completely when it happens.

I'm sure you know all this:
I would check the system A to Z. Got the right gas hooked up? Could the supplier have mis-labeled the bottle?
Connections tight?
Flow meter working properly? If hooked to a bottle is it freezing up?
Lines pinched somewhere - maybe when the feeder is in a certain position, or a line against a corner? Clogged with dust/debris? Water in the line?
Solenoid working right - staying open as long as it should? Erratic electrical connection?

A roll from another lot may solve the problem.

And a last possibility - does someone not want it to work right? Or maybe a joke has gone too far?

By jwright650 (*****)

Date 06-16-2010 17:01

At lunch, I grabbed a short piece of beam that was cut off with a Oxy/fuel torch and thrown in the scrap bin....I centered the ragged cut up on a piece of plate and welded along that ragged cut with the slag and crap still on it....not even that would produce a single pore of porosity. I just knew that would do it.

By CHGuilford (****)

Date 06-17-2010 16:10

Sounds like the "can-do" attitude becomes "can't, don't" by the time it makes its way to that "welding machine". That's the hardest part of the system to fix.

By jwright650 (*****)

Date 06-17-2010 16:33

Sounds like you have run across that attitude before in your travels. Yup, hard to fix that part. I'll give it some more time.

By jwright650 (*****)

Date 07-01-2010 12:04

Al,
I received a new batch of wire and I think you nailed it..."so far" I haven't experienced any further bouts with porosity<fingers crossed>....increased the flow rates up higher than what I was used to. When all else fails, read in the instructions...well, the data sheet for the MC wire says flow rates need to be between 40 and 60cfh. This pegs my flowmeter, but at least I'm getting enough shielding now.

By 803056

Date 07-01-2010 14:21

Good to know. Thanks for the follow-up. I'm happy to hear the porosity issues are diminished because I'm sure it will not go away completely. Someone will sneeze, forget to remove the cutting fluid, etc. and "pop" there it is again!

Best regards - Al

By jwright650 (*****)

Date 07-01-2010 14:30

I think it's funny....the welder who was calling the wire junk, saying not to ever put that stuff on his machine again....is over there right now welding channel splices with a 7018. I grabbed two pieces of the same channel out of the scrap bin with cutting fluids still on them and spliced both of them together with that junk wire while I was watching him cuss because he blew a hole through the 3/16" web. I just smiled and grabbed another couple of pieces and spliced them while he was flipping that piece over to gouge back out the spot where he was dabbing in material to fill the hole.

Some guys just love to take the tough route. Lead them to water, but you can't make them drink.

By 803056

Date 07-01-2010 15:59

I depend on fellas like that. The thicker the skull and more stubborn they are, the more money I make.

Best regards - Al

By jwright650 (*****)

Date 07-01-2010 17:20

Even funnier still, he's still over there welding channel as I type, meanwhile, I've welded up all of the connections on 3 beams plus all of the bent plate full length on the top flanges of those beams, 1/4" fillets both sides - 2@12, then seal welded for galvanizing and he still isn't finished monkey'ing around with those silly little C6 channels. People are starting to notice and comment about how quick this wire lays it down, and how nice it looks(which is making it hard to walk around with this swollen head and fit through my office door).....LOL

By commonarc (**)

Date 06-14-2010 21:11

How does the wire look? Any rust or contamination on the roll of wire? I once saw a guy working on the bench using WD40 and he sprayed it on an exposed roll of wire by accident. Nothing but porosity once the WD40 got into the liner.