[Leatherwelder]

when should you use electrode negative? I've been told it's when putting in a pipe root. What difference does it make? I'm new to welding so I'd appreciate all the info I can get.

[Artie F. Emm]

Welcome to the forum! There's a quick discussion of polarity and penetration here:
http://www.twi-global.com/technical-kno ... uld-i-use/

...but I can't answer the pipe welding question (sorry).

[Mike]

Welcome to the forum.

[gnabgib]

Overhead root run.

[castweldsolutions]

DC- will cause an electrode to have an increased deposition rate, and a decrease in penetration. The weld profile will be wide and shallow. DC- is great if you need to put a lot of filler passes down quickly.

DC+ will have less of a deposition rate, but an increase in penetration. The weld profile will be less as wide, but deeper.

Sometimes you need to run a certain type of current because the electrode will only work well in one current. 6010 for instance, is designed to run in DC+ only and doesn't work well in AC or DC-

Hope this helps

[Bill Beauregard]

With the flow of electrons goes the flow of heat. Straight polarity, or Electrode negative heats the electrode less. I'm no expert, but to me it seems logical to use it when less deposition is desirable as in thin sheet metal weld with 6013.

[Leatherwelder]

when should you use electrode negative? I've been told it's when putting in a pipe root. What difference does it make? I'm new to welding so I'd appreciate all the info I can get.

Thanks Guys for the info, much appreciated. Looking forward to chatting with all on the forum. :

[Bill Beauregard]

Welcome to the forum! There's a quick discussion of polarity and penetration here:
http://www.twi-global.com/technical-kno ... uld-i-use/

...but I can't answer the pipe welding question (sorry).

Your reference seems authoritative. Trouble is it spawns another Question; If DCEP melts a TIG tungsten, while DCEN preserves it all day, how does the opposite happen with stick? Inquiring minds want to know.

[castweldsolutions]

Welcome to the forum! There's a quick discussion of polarity and penetration here:
http://www.twi-global.com/technical-kno ... uld-i-use/

...but I can't answer the pipe welding question (sorry).

Your reference seems authoritative. Trouble is it spawns another Question; If DCEP melts a TIG tungsten, while DCEN preserves it all day, how does the opposite happen with stick? Inquiring minds want to know.

Artie, the article you posted from TWI's website states, "...With DC electrode positive (reverse) polarity, more heat is generated at the workpiece.....and DC electrode negative (straight) polarity generates more heat at the electrode...."

I don't mean to be so contradictory, and maybe I'm reading this wrong, but I believe this is totally incorrect. All of the books that I have read all state the same info, that 70% of the heat is focused at the electrode when in DC+ and 70% of the heat is focused at the workpiece when in DC-, and that this rule stays true whether you're tig welding or stick welding.

I was taught, and I believe this to be true, that though the majority of the heat is focused on the electrode at DC+, there is an increase in penetration because the electrode now acts, so to speak, like a hot knife through butter. This also explains why you cant tig weld in DC+, because the 70% of heat focused on the electrode is too much for the tungsten to handle, thus melting it away. Tig welding in DC- works best because only 30% of the heat is focused, which is enough to melt the base metal, but not melt the tungsten.

Bill, to answer your question, it's not so much the opposite happening, but rather, the SMAW electrode burning away is simply what it is designed to do. A SMAW electrode acts as both the conductor for the arc and the filler, where as the tungsten acts only as the conductor for the arc.

Hope this helps.

[Bill Beauregard]

Forgive me if I'm crediting the wrong person, or mis quoting their info. I've posed questions regarding this subject before. I think it was Minnesota Dave who brought the theory that EP or reverse polarity created something like a small explosion in the tip of the electrode, causing it to travel like a molten bullet to the joint. This seems logical to me, as I know that copper for example, expands to 60,000 times its volume when it vaporizes.

[Otto Nobedder]

The simplest explanation I can give is this:

DCEN preserves the tungsten in GTAW.

DCEP melts the electrode in SMAW/MMA

This is what's supposed to happen in each case.

Steve S

[Poland308]

This is the first time I've heard about running smaw on dcen. Can't imagine rod deposit is any good.

[MinnesotaDave]

Forgive me if I'm crediting the wrong person, or mis quoting their info. I've posed questions regarding this subject before. I think it was Minnesota Dave who brought the theory that EP or reverse polarity created something like a small explosion in the tip of the electrode, causing it to travel like a molten bullet to the joint. This seems logical to me, as I know that copper for example, expands to 60,000 times its volume when it vaporizes.

I believe you are right, I think I have posted this type of material at some point.
"there is a jet action and / or expansion of gases in the arc at the electrode tip. This expansion causes the molten metal to be propelled with great speed across the arc. The molten metal impacts the base metal with greater force. This heavy impact on the base metal helps to produce deep, penetrating welds." Modern Welding 1997 Althouse, Turnquist, Bowditch, and Bowditch."

DCEP jet action.GIF (21.24 KiB) Viewed 1101 times

[kermdawg]

Would be cool to get one of those high speed cameras like they have on myth busters and film each polarity at 40k frames per second or whatever speed they have


Edit- I love google https://m.youtube.com/watch?v=wHHS66be7Sg