more penetration with flux-core mig?

By welder_guy2001 (***)

Date 07-23-2002 03:59

you have to drag the flux core wire....it doesn't do so well when pushed along like a gas mig. make sure you're on the right settings. and move slow. it should be just like welding w/ gas mig, only you move a little slower, and you always drag the gun. and the manual is right...you do get more penetration w/ flux core. my little mig machine will only weld 1/8" steel...maybe 3/16" on a good day...but convert it to flux core and it'll weld 3/8" steel. and yes, i have destructively tested my welds to ensure penetration. i was using .030 E71T-GS.

and if you're feeling daring and wanna try some vertical up (flux core only welds vertical up...not down) you have to angle the gun in the opposite direction as you do w/ mig. you shoot the wire straight into the plate...maybe even 5 degrees pointing downward depending on your style.

overhead runs pretty much the same as welding in the flat position.

also, since you're having problems w/ penetration...maybe you're moving too slow...if the arc rides up into the puddle too far you won't get the penetration you desire. you need the arc to be at the same level as the base metal, not up in the puddle, which is about 1/16" higher than the base metal. try moving a little faster and notice how the puddle fills in behind the arc. it usually looks like it's not going to fill in, but it does in the end, even if it is 1/4" behind the arc. if you end up w/ slag inclusions on the sides of the bead, or lack of fusion on the sides, then you know you're going too fast.

and try messing around w/ the easy joints first...a lap weld w/ 1/8" plate is the easiest for your size machine.

By overthehill (*)

Date 07-23-2002 04:31

Hey bzzzzzzz,

I'm a little baffled by those claims of penetration, too. First of all, there are two kinds of fluxcore. Gas shielded and self shielded. I assume your talking about self shielding (no gas required). This uses DC-. From what I understand about polarity, the base metal heats up quicker with electrode negative. This allows the filler wire to FUSE at a lower voltage. That's why it is typically used (with fluxcore) on the small wire feed machines. There is a difference between fusing and penetrating. Gas shielded fluxcore and GMAW(solid wire with a shielding gas) use DC+. The electrode (filler wire) gets hot, and the superheated filler metal is violently transfered across the arc stream providing penetration. I sure would like someone elses opinion on this, but it seems to me that the self shielded fluxcore fuses extremely well, but penetration (on butt joints) is only obtained with proper metal preparation.

By welder_guy2001 (***)

Date 07-23-2002 14:20

that's why they only use a stick welder, self-shielded flux core, gas-shielded flux core, or submerged arc welding on structural steel...never MIG because it doesn't penetrate enough. i also asked the same question about self-shielded flux core-- how does it penetrate more if it's DC-? my instructor told me it had to do w/ the current density in the wire. the current is more concentrated in flux core wire than in mig wire.

and like i told bzzzzzz...in my experience w/ my Hobart 135 (a 100 amp machine) MIG welding w/ it is a lot like glueing it together...flux core is where the strength is. i've done the destructive tests myself...i had good penetration on a fillet weld on 3/8" plate in the flat and vertical up positions. when my machine is set up for MIG, it doesn't even come close...1/8" is the limit then.

By bzzzzzzzzzz (**)

Date 07-23-2002 15:15

I gotta be doing something wrong technique-wise then. Which isn't that unlikely. Thanks for the posts.

By stich585 (*)

Date 07-24-2002 03:35

A F.C.A.W. bead is very strong. My question is what is the ambient temperture of your work piece before you weld it? If it is below I believe 50 degrees the base metal will have a tendency to crystalize becoming brittle. This will cause the edges of your weld to fail (It is the base metal failing not your weld). Look at your destruction test, what it looks like can tell us alot about what is wrong.

By welder_guy2001 (***)

Date 07-24-2002 04:31

it could also be the type of joint you're welding...if it's a butt joint, you can't do that w/ an open root w/ flux core...you need a backing plate.

By John T. (*)

Date 07-25-2002 04:28

We've been welding structural steel for the last ten years with GMAW

By welder_guy2001 (***)

Date 07-26-2002 04:34

let me rephrase that...GMAW is not allowed by the AWS Bridge code because it doesn't penetrate enough.

By DGXL

Date 07-26-2002 16:26

Not sure where this info is coming from regarding bridges and GMAW. FCAW, GMAW, SAW, ESW and EGW are code approved processes.
Ref: D1.5:2002, 1.3.1.

By rodney schumach Date 08-10-2002 03:46

buzzzzzz; I have just started working in a welding shop and trying to get my 6G,we use GMAW with a 75/25 mix and I go stright in with the nossle level to the work at one inch away @ 50 cfm of gas. The wire speed is at 70 on a Miller Vintage machine. I have been welding mostly 1/2" thick stuff and get great pentration and a supper strong weld. I also run vertical up that way,and just watch the puddle and move just fast enuff to maintain a 1/2 wide leg on the bead. I havent really noticed much differance by puhsing or pulling. I focus on my bead confirnation and move just fast enuff to maintain that. Goooooooood luck..I too need it.

By dee

Date 08-10-2002 13:37

I know less than many bona-fide experts that often make helpfull comments, they might be able to expand further, but I understand there is also an issue with arc density that effects penetration much the same as reducing the diameter of the wire.
Flux core is a hollow tubular electrode with much less conductive area (in cross-section) than a solid core of the same diameter. It allows more amps per square inch of actual wire section and thereby more heat... the inside of the tube with most of the volume is filled with a non conductive flux.

An additional amount of heat is gained in chemical energy with the use of CO2, if my understanding here is also correct. The CO2 releases energy as heat when the arc ionization energy causes a disassociation of atoms in its molecules... it breaks down into CO and releases energy gaining an even hotter arc area. The more CO2 in a gas mix the hotter the spark will be, also because the Ar is wery easy to ionize and get a spark to run through it will take/allow proportionally more energy, or "heat", to initiate an arc and filler transfer as the proportion of Ar is reduced in a typical mixed gas.

A reductiion in electrode diameter will I believe improve penetration. Among other things that the flux does to the radiation and convection of the weld heat and internal flow of the weld puddle molten metal by way of insulation in a flux-core wire weld, it also functionally reduces the diameter of the wire and increases the current density thereby improvig penetration.

I never use the stuff; other solutions to the penetration issue are more practical to my present controlled indoor application.

regards,
d

By overthehill (*)

Date 08-10-2002 15:39

Dee, I might be right or wrong here, so take it for what it's worth. First, I think Bzzzz is talking about self shielding flux core with that little machine. Gas sheilded flux core requires quite a bit more voltage than those little machines provide. I am not sure how the gasses produced by the buning flux effect the arc density, but the EN polarity does play a major role in the performance of the wire.

You are right about the CO2 and Argon. CO2 provides more arc energy that helps break up surface oxides and surface tension. Pure argon produces a narrow dense arc stream at lower voltages, with a secondary stream that has very little energy. In wire feed, the gases are blended to provide the amount of arc energy neccessary for the type of process, characteristics of the metal, and the job.

As far as the "reducing the diameter of the wire to increase current density", I'm not sure about that. With a Constant Voltage power source, the voltage is set and the power source provides the amperage (current) necessary to burn off the wire and maintain the arc. Reducing the diameter of the wire reduces the amperage required, and increasing the wire diameter, increases the amperage required. Other things that affect the amperage are wire extension and wire speed. The shielding gas also plays a role in the voltage/amperage necessary to provide a stable envirement for optimum metal transfer.

With self shielding flux core, I think the key is the electrode negative. With EN, the metal heats up quickly, allowing the molten puddle to spread and fuse. As far as penetration with EN goes, I disagree with all the manuals, text books, and welding instuctors. I'm not really that arrogant, but I do think that what is true in theory is not necessarily true in practice. To keep it simple, EN heats up the metal, which allows the puddle to fuse, but requires a faster travel speed to keep the filler metal in the puddle from overheating and becoming so fluid that you can't control it. The faster travel speed limits penetration. Anybody remember welding sheet metal with 6013 on DCSP (that's what DCEN was called in those days)?

By dee

Date 08-11-2002 22:45

Interesting! You gave me wellcome chance to think here, Overthehill.

I conceed that Buzz was talking about self shielding FC.

DCEN polarity does indeed play a significant role in the penetration feature but just how much might determined if Buzz were to change polarity with his present wire, no? I could be wrong and I am not saying that this is something I know as fact but it seems to be a means of eliminating a variable.

Relating to current density this is something I learned from more than one source which seems to make sense. Splitting hairs a little, I dont see flux gasses affecting current density, but they might have an effect on arc energy if they change the ability of the dielectric (air) in the arc area to ionize. (I believe air or shield gas could be properly described as a dielectric)...

...I understood that a CV power supply adjusts current according to it's slope, which the engineers control by means of adjusting reactance or resistance in the circuit, but which we might consider to essentially be constant for whatever electrode the operator selects because it is determined by the design of the power supply...

...The rate of wire feed is proportional to the amperage. The rate of feed will remain constant but the amperage fluctuates according to variablles such as stick out, etc. If we could hold these variables constant we would find, according to my understanding, whatever wire we installed would be subject to identical electrical parameters. Thinner wire should, then, be subjected to a greater current density under equal conditions... it does. Moreover, how does the feed rate for flux core compare to solid electrode of the same diameter? If the feed rate is higher, as I thought it is, the amperage is also, further raising the heat and current density. I could still be confused with GSFC; I dont use metal core either, and might be mixing my metalfores as it were. I may have been wiser to avoid comment from the start.

You might be correct to say current density does not affect penetration, I'm still thinking on that one. It seems to call for some presumptions that I'm not willing to accept as valid, but I can't refute the idea in all cases and somehow I think I could argue in favor of the point on semantics if nothing else.

Within the past 6 months or so the AWS Journal featured flux core and discussed the dynamics of the process. The flux also modifies the behavior of the molten puddle allowing more heat to conduct into the base metal, I think. If I am right I believe this was a trait of FC to which improved penetration was also attributed. I had little interest in FC wire and paid little attention to the articles, but they must be archived for reference.

It's nice to dust off the old grey-cells for a change. They needed airing out.

regards,
d

By overthehill (*)

Date 08-12-2002 04:21

Hey, thanks for the response Dee. My main interest (right now) is understanding polarity, but in welding, everything works together so much that you don't just get to discuss one thing. Most of what I know comes from watching the puddle, I've never been what you'd call a technical welder. Wire feed is changing that. There is a lot more to the technical side of wire feed, and to use it effectively, you have to understand it. Read all my statements as questions. I don't mind being wrong, Im just intersted in why I see this differently.

I don't think you can test the penetration characteristics of FC by changing the polarity. It was engineered to run on DCEN and it probably won't work at all any other way.

I seem to be having a problem with current density and arc energy. I have only ever heard these terms used to discribe the arc between the electrode and the work. Both are determined by the characteristics of the shielding gas, whether it's from burning flux, or an external gas source. Argon, for example, transfers current very well, producing a dense narrow arc stream. This results in a secondary arc stream with very little arc energy. That's why Ar rich gasses are not used with short circuit GMAW. There is not enough energy at the lower voltages to break up surface oxides. Even in spray mixes, O2 is sometimes added to kind of stir things back up. CO2 on the other hand, does not transfer current well. The current is less dense, causing a broader arc stream with more arc energy. It does require more voltage and works great, it just isn't any fun to weld with. I have never read or heard of the wire size effecting arc density. By the way, you guys talking about EN and tig aluminum. The spiked penetration characteristics you described are exactly like the characteristics of the arc stream with an Ar shielding gas.

As far a CV power sources, somewhere I was lead to beleive that the voltage is set and remains constant (not perfectly, but we'll let that slide for the sake of the discussion). The current (amperage) varies as is necessary to maintain the arc. This is hard for an old stick rod hand like me to comprehend, it's like everything is backwards. In wirefeed, reducing the wire size automatically reduces the amperage. You don't get more by going smaller, you get less. (Maybe more weld time with the low duty cyle machines, but not more heat). Also, increasing the wire extension reduces the amperage. The long wire stickout is preheated, reducing the amperage necessary to burn off the wire. This is pretty obvious if you do it during a weld. Increasing the wire speed increases the amperage, it takes more to burn it off and maintain the arc. For what it's worth, on 10ga, FC self shieding uses 18% less volts, with a 45% lower wire speed than solid wire with 75/25 (according to the chart on my MM250). The deposition rates of FC self shielding are no where near that of solid wire.

That brings us to polarity. I'm lost on that one. FC self shieling penetrating? I bought one of those little 110 machines to do some tack up on a job site (there wasn't any 220 available and I didn't want to string out 400' of leads). I played with it a little back at my shop. Cranked it up to maxeen and tuned the wire, then welded on some 16ga. Made a cute little weld, but penetrate? I didn't even come close to burning through. I just don't get why everybody says DCEN provides penetration. Kind of changing the subject, I sure don't see how the EP cycle in AC tig welding provides surface cleaning, either. Anybody kind enough to explain that to me?

By dee

Date 08-12-2002 19:07

Over,
For the moment I want to clear up a few misimpressions left over from my last post. Not to get me wrong, read in a note of humility. My process experience is limited, and I am no man of letters... so read that into all of the following:

It was my belief that changing a SOLID wire which was being run DCEP to DCEN would serve to establish a feel for the difference in affect between the two polarities... presuming a familiarity with at least one of them. I may have said something else or been unclear, which I didnt intend. As you say, there are interrelated variables, and I was trying rehtorrically to change just one to illustrate its effect which was brought to question.

CURRENT DENSITY can be verified through any convenient technical reference. I know of only one definition of the term and it is calculated by dividing the amps being used by the cross sectional area (square cm or square inches) of the electrode. Technically, for the purpose of understanding deeper physics, any other applications of the term would be misapplied... it's helpfull to be on the same sheet of musing.

I'm not sure "arc energy" is technically respected terminology, but we all understand it to be a sum total of variables that relate to what we might think of as BTUs and heat; unofficially I would suggest it holds a similarity to Watts or horsepower or any other measure of power. I would suggest the two are proportionally related but I cant go much further out than that. The shielding gas and other variables you mention may prompt a change in the amperage setting (wire feed speed) of your machine but turning that knob or changing the wire size is what changes the current density, not the atmosphere... I am thinking of the dynamics in that context.

I dont know that I mentioned "arc density"; I never intended to use the term and if I did I misspoke... apparently I did.

(I was surprised to read that Ar rich gasses cannot break up surface oxides; they dont dip well on clean steel any much better, and I have never been shown that Ar/O2 mix on steel provides anything I cannot get from Ar/CO2 except potential trouble)

I am a little confused about your paragraph opening with CV sources; I was under the impression typical GMAW power supplies were of the constant voltage type, and that a small arc voltage change (like from altering stick-out) yields a large change in welding current. Welding current, furthermore, is increased according to the wire feed setting; I am unaware of any significant effect the wire diameter would have on weld current. I am confident this is correct and should also turn up in some kind of reference; I think it might clear up a small point of misunderstanding and could be a help.

Your clarification on wire feed rates apparently stands me corrected and my inaccuracy puzzles me. I plead no contest to your reference. Somewhere, though, in an AWS forum discussion, mention was made that deposition rates (actually feed rates) were higher for FCAW than for solid, and that a complex array of transfer dynamics were involved within the arc of flux core wire... we may have been discussing GSFC?... did I misinterpret?... have I inhaled too many fumes?.. at this point I am convinced I should have kept quiet at the get-go.

Finally, at an intuitive level, we know that larger electrode diameter requires higher power parameters to work. I am not focusing on the depth or width of penetration profiles but the idea that penetration is penetration and fusion is fusion; beyond that depends on technique.
With a small, low power, SMAW power supply I was given a small diameter electrode to learn with. When I tried an electrode that was too large and had difficulty I could see it didnt work. I dont know what would have happened or how I would have gotten confused if I started with the larger one. Somewhere herein lies the phenomenon to support my statement. A mind greater than mine may frame it into words and distill it from the complication of comparing a CV source to a CC source. I cannot... in fact the "trueisms" I understood intuitively are becoming lost as I over think the subject. This sometimes indicates a fundamental error.
It would be great if a bona fide authority would help.

Regards
d

By dee

Date 08-13-2002 00:15

Overthehill-
I had a heck of a time posting this; I keep locking up with memory conflicts... and my computer's giving me trouble too :-)

More info is available on another site; I referred the question to Ed Craig he posted his answer today at www.weldreality.com

from home page go to "weld product questions"; it's the thumbs up/thumbs down icon to the left, and look for the topic posted today's date.
You may want to peruse the entire site and particularly the area on consumables/ gasses for other enlightenments.

It is a current density issue that relates to penetration

regards
d