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Tool Talk Discussion Forum

Welding DC+ vs DC- vs AC ... please explain !

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Alberta Mike

08-24-2006 15:16:07
64.42.242.2



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Picked up a nice stick welder here at an auction sale last weekend for my son who lives out of town. It is a Lincoln AC/DC and I notice that the DC option has two choices, DC+ or DC-. Can someone explain for me:

1. What is the difference between arc welding with AC and welding with DC? And when would you use one or the other?

2. What is the difference between arc welding with DC+ and welding with DC-? And when would you use one or the other?

Thanks for the information.

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Craig in MO

08-26-2006 05:16:18
71.1.103.201



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Alberta Mike, 08-24-2006 15:16:07  
MSB
DC current flows negative to positive
Craig



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george md

08-26-2006 21:59:03
12.191.226.107



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Craig in MO, 08-26-2006 05:16:18  
Craig,

back in my days in college in electrical
engineering , electron flow was from neg to pos,
and current flow was from pos to neg . In radio tubes the cathode is the emmiter and the plate is the collector , the plate is pos charged
and hence the electron flow from neg to pos . But
all electrical theory is based on the fact that
current flows from pos to neg . Seems like the electrical world is about as organized as a soup sandwich . Maybe it has changed since I got my degree in the early 60's .

george

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T_Bone

08-25-2006 15:37:33
4.240.90.119



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Alberta Mike, 08-24-2006 15:16:07  
Hi Mike,

Great info has already been posted on the subject so I'll take the discussion in a different direction.

Welding is a process of heating the base metal to where it can accept drolets of molten metal from the electrode to join metal.

AC, DCEN and DCEP are used to control those droplets of molten metal.

The flow of electrons in DC welding circuits is from negitive to positive and is called straight polarity.

When we reverse the welding leads then electron flow is from positive to negitive also called reverse polarity.

When AC current is used for welding, you get a base metal cleaning action that cleans on the alternating phase of the current, anotherwords the current cylces up and down thru the frequency and the base metal is cleaned and filler metal is deposited in both directions. This works well in the flat position and when the base metal hasn't been prep'd as it should be and where the molten droplets has a chance too fast freeze to the base metal.

When DCEN is used for welding the most of the cleaning action stops as far as the frequency is concerned as DC current only flows along the surface of a line and doesn't alternate thru the base metal like the AC current did.

Since electron flow is from negitive to positive then the molten droplets flow too the base metal from the electrode causing a very fast deposit of the droplets. The slang term is known as fast freeze between weldors. If the droplets fast freeze to the base metal then the base metal is cooler while welding thus is a good choice for sheet metal welding or filling poor joint fit up.

When DCEP is used for welding electron flow is from base metal to the electrode and most of the heat build up is on the base metal. What this does is allows for greater molten puddle control for the weldor when using the correct electrodes. Transfer of the molten droplets is slightly slower than using DCEN or AC.

This will cover the basics of some of the differences but in reality there's alot more to using AC, DCEN or DCEP than what's been written here, so I will add too this at a latter time.

T_Bone

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Rick Castle

03-03-2007 18:22:18
74.195.203.104



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to T_Bone, 08-25-2006 15:37:33  
So when I use 6010 i need to have my electode holder pluged into the positive and the ground in the negative right. I was tols that it was supose to be the oppisite which makes no sense. Rick



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Ryan - WI

08-24-2006 19:28:32
66.114.188.110



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Alberta Mike, 08-24-2006 15:16:07  
Mike, the way that I explain it to my high school welding students is this.

DC- Deep penetration, short surface
DC+ Shallow penetration, tall surface

AC is in the middle.

DC is used when you want the weld to go deep into a material (like thick plate) or float on the surface (like sheet metal)



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Craig in MO

08-24-2006 19:21:50
71.1.103.201



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Alberta Mike, 08-24-2006 15:16:07  
I have heard that DC is better for vertical and overhead welding. Is that true. All I have done is AC with my Lincoln 225 and I try to do all my welding horizontally.



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Stan in Oly, WA

08-24-2006 18:11:52
208.64.241.151



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Alberta Mike, 08-24-2006 15:16:07  
Hi Mike,

One way to look at the polarity issue is by the welding rods that are available to you. 6010 runs DC+ only. 6011, which is similar to 6010 (forceful arc, deep penetration, light slag) runs best on AC, but runs all right DC+. 6012 runs best DC-, not good at all DC+. 7018 runs DC+ up to about 300 amps, better on AC above that. 6013 runs well either AC or DC+ for general welding, but was developed for high speed sheet metal work on DC-. And so forth.

The trouble with that approach is that it goes at the issue backward. What's important is matching the electrode (rod) to the job first, then running it on its best polarity after that. You would rarely match the polarity to the job first, and the rod to the polarity second---with two main exceptions: If you are having a problem with arc blow (the arc wanders off course because of the magnetic field caused by the location of the ground, or some other magnetic field disturbance) which you can't resolve by moving the ground clamp, you can turn to AC, which is not subject to arc blow. The other situation where polarity would be a primary consideration is when you know you need more of the heat in the work than in the rod. DC- provides 2/3 of the heat to the work, DC+ provides 2/3 of the heat to the electrode, and AC is 50/50. 6012 and 6013 electrodes were both originally developed for high speed sheet metal work on DC-, so that would be an example of a time to choose that polarity. I don't do much sheet metal work with stick, high speed or any other way, so I couldn't say. I do know that 6012 running DC- is unusually good at filling gaps in bad fitups, but 6010 is good for that too, and there's not as much slag to entrap with 6010.

DC is generally considered to strike an arc easier and stay lit better than AC, but if any electrode strikes easier or stays lit better than 6013 running AC (or DC, to be fair) I haven't run across it.

There are some real differences between the three polarities in stick welding, but they're not so profound that an inexperienced operator would even necessarily notice them. If your son gets to the point where he can tell just when to use one polarity rather than another, or even just how high to set the current, before he's burned ten thousand sticks, then he's got a real gift and maybe he should look into something that pays better.

All the best, Stan

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Tim B from MA

08-25-2006 08:03:36
68.162.218.211



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Stan in Oly, WA, 08-24-2006 18:11:52  
Stan,

If you haven't already, you should write a book. Maybe you should get together with T-Bond and do it!

As always with these welding questions, great answer. Thanks for taking the time.



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Tim B from MA

08-25-2006 08:57:53
68.162.218.211



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Tim B from MA, 08-25-2006 08:03:36  
oops, T-Bond ?? I think that is James' brother.

I meant T-Bone.



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Stan in Oly, WA

08-25-2006 22:38:14
208.64.241.151



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Tim B from MA, 08-25-2006 08:57:53  
Hi Tim, my new favorite guy,

You're very kind.

T_Bone has actually done extensive writing on welding, soldering, and various related metal working subjects. The archives of this forum contain hundreds of his postings, and at least several dozen of them are extensive explanations of difficult processes. His writing is always lucid, always entertaining, always highly informative. Of the postings from this forum which I've cut and pasted into a Good Information file in Word, somewhere between 20% and 25% are his.

I'm trying to gain some momentum as a metal sculptor. My medium is steel and my preferred process is stick. I've been trying for several years to develop a method where instead of welding together component pieces that have been shaped and worked by other processes, I use the electrode itself to shape and texture, as well as to join, undifferentiated small pieces of steel, and an oxy/acetylene cutting torch as a stone carver would use a chisel, to remove material. Well, as I said, it's an ongoing process, and not easy for a guy with a short attention span.

Thanks again, Stan

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msb

08-24-2006 19:34:44
74.133.28.248



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Stan in Oly, WA, 08-24-2006 18:11:52  
Easiest way to understanding it is the current flow in an AC welder goes bach and forth from the electrode to the parent metal usually at 60 cycles per second.
DC + curent flows in only one direction(which way,I forget).DC- current also flows in only one direction and opposite of the DC+ that I can't remember.One way concentrates(DC_ I believe) the heat on the electrode.
The other polarity position(DC +, I believe) concentrates the heat on the parent metal.That position is best if you want deep penetration.---The opposite is good for thin metal where burn through is a problem like sheet metal.

The AC welder is a compromise between a DC welder and is much less expensive to manufacture. All have their place though.

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Cliff (VA)

08-24-2006 17:53:16
209.3.199.213



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 Re: Welding DC+ vs DC- vs AC ... please explain ! in reply to Alberta Mike, 08-24-2006 15:16:07  
There are lots of professional welders on this site. I am NOT one of them. But to give you a quick answer, as I understand it typically AC makes it easier to strike an arc than DC. Some rods work better with AC or DC, they are usually marked that way. DC allows you to put more heat either into the work or into the rod based on the polarity.

HTH

Cliff (VA)



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