I was getting ready to do some stick welding with 7018 rod, using my Maxstar 140 inverter, and did a little reading (in a Synchrowave 250 manual) to refresh my memory on polarity settings. The manual said that DCEN is by far the most common setting for most rods, so I thought I had my answer. I set the Maxstar for DCEN, switch to the right for stick welding, and ran a bead. The arc didn't seem as smooth as I remembered, so I got out the manual for the inverter. It said that 7018 should be run DCEP. Is this because it's an inverter machine. I seem to remember in my welding class always setting the big transformer machine to DCEN for 7018 rod, but maybe I'm mistaken. Thanks, Gary Hastings
7018 is DCEP unless designated as 7018AC. Or that is the way I have run it, but have never run it on an inverter. We'll hear from someone who knows soon.
I learned that positive + meant more penetration, and negative - meant less penetration. Helped me visualize whether the action was taking place on the plate or the rod. And then there's straight or reverse terminology. I remembered USNavy, and SSN, or Straight Stinger Negative, and that helped me remember that one. I struggled with both until my mind caught something that helped me remember them.
I've written this standard answer to this standard question
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[DCEP = Direct Current, Electrode Positive DCEN = Direct Current, Electrode Negative AC = Alternating Current (the electrons shunt back-and-forth)]
[+ve = Positive -ve = Negative]
The standard answer for Stick / SMA is - DCEP gives more penetration, DCEN gives less penetration.
DCEN is reckoned to give faster deposition, which kind of follows. That would mean DCEP -> fusion, DCEN -> rapid deposition.
Scientific digression:
Thinking about X-ray tubes and the like, you'd expect it to be the other way around - DCEN would give more fusion. But they do what they do with electrons in a vacuum, and it seems that by the time you've added flux systems and the like, that thinking no longer applies. For TIG yes. For Stick no. Stick does as it does and I'll tell you my observations.
My evidence 1
Working in a boatyard welding up boat superstructures out of plate about 5mm thick...
We had big AC welding machines on the quay. I got a separate Rectifier and we carried that out over the water and had that beside where we were working.
Changing Amps meant a long walk back over the decks of boats. So changing polarity to change penetration was of "special interest"(!!!). You could do that right alongside you, no walk, by swapping over the electrode-clamp-lead and return-clamp-lead on the Rectifier output posts.
Using Cellosics (6010's) it was absolutely obvious that DCEP gives more general fusion ("penetration") and DCEN gives less.
If fit-up was good, you could "keyhole" to get full-thickness fusion of a butt / seam weld between the edges of two plates on DCEP. Often working vertical down and still having heat to spare (even vert-down you sometimes had to "whip" the rod to throw away a bit of heat).
If fit-up was bad and you had to fill a gap, you switched to DCEN. Then you got more metal and less heat. So you could dance around filling up gaps while keeping the pool under control.
My evidence 2
So at welding school in the UK we are taught using only 6013 (Rutile). And I'm being taught vertical-up T-fillet 6mm plate - one root run w. 2.5mm dia 6013 and one weave-cap 3.2mm 6013 on-the-same-amps.
I'm analysing claims about fusion / penetration.
Current seems to be same DCEP and DCEN, on machine dial. So burn-time must be important for fusion / penetration. Obviously, if the Amps and Volts stay the same (I didn't measure these accurately though), the longer the burn-time to burn the length of the rod, the more heat to [amount of deposited metal and length of joint] there must be (if you run-out along the same length of joint).
So we need to time how long a rod takes to burn full-length to same stub-length DCEP and DCEN. Nice simple straight bead-on-plates on-the-flat will do nicely. What do we observe?
What do we observe?
Running DCEN, the Rutiles (6013's) gave exactly 60s of burn five times repeated.
Running DCEP the 5 Rutiles burned between 60s and 67s (times fairly well-spaced in that time interval). So those burn-times were "all over the place". Though on average longer.
So it does seem that on DCEP you burn for longer and that would give more fusion.
However, the 6013 rod is clearly unhappy on DCEP, with the uneven burn-rates. So I was convinced to run 6013's on DCEN. If you look at the Lincoln web site for say Omnia's that's what they say - you can run them on AC or on -ve, meaning DCEN.
Practically, with 6013's - on DCEN with a precise burn, you keep a very short arc-length as part of the technique, getting a smooth flat bead surface and accurate focus of the arc heat where you want it - which wins-out any day. Especially in vertical-up welding when you are not usually pushed for obtaining penetration.
For Cellulosics (6010's) and Basics (7016's and 7018's) it's DCEP. They love it, giving smooth burn and plenty of fusion.
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Extra note - never burned a 7014. But they are an iron-powder Rutile. So you can see what you'd expect thinking of what we know of 6013's.
I used to use 3/32" 6011 with stinger negative to weld thin wall ornamental metal in the field. It has the behavior you describe, and with a short arc, and accurate amperage settings, lets you stack small puddles to hold together the .065" thick metal, even allowing for butt welding of two pieces, a thing that I've won money on more than once from a fellow who swears it couldn't be done. And most of the literature I've seen for 6011 suggests AC or EP.
I think that the info about DCEN being the most common and preferred setting for most rods was my misinterpreting the manual. It must have been referring to TIG settings, not stick welding. I got the same result with 7018 on the Maxstar as I did with the Synchrowave. DCEP was much better. Gary Hastings
With most TIG, you want the heat on the plate. Imagine the electrons pouring off the tungsten, building velocity in the plasma, then slamming into the plate, generating heat. That's what DCEN does. This keeps your tungsten from over-heating and falling apart.
DCEP (aka DCRP for Direct Current-Rod Positive) is the opposite. The electrons jump from the plate, build velocity, and slam into the rod, causing it to melt faster. This gives higher deposition rates with slightly less penetration.
AC (of whatever waveform) will jump back and forth between those two extremes, which makes it excellent for rapidly oxidized metals like Aluminum. The DCEP portion of the cycle blasts the oxides off the plate, then the DCEN portion heats it up and makes the weld pool.
Simplistic, but that's how I manage to remember it.
I always get screwed up trying to remember which was which when it came to cathode / anode. As long as I remember that electrons are negative charge, and always wanna to hook up with a sexy positive atom, I'm happy.
Surely this is NOT the case for Stick? On DCEP penetration / fusion is *greater*.
This is counter-intuitive if you think of the "X-ray tube" and TIG case. There is the model of which way the electrons go and where they slam into their target - the positive pole. And that model, which works for X-ray tubes and TIG,
does not work for Stick *.
Something changes, maybe with the presence of the flux and all that? - and DCEP gives greater pen. with Stick / SMA.
Many sources consider DCRP to stand for DC Revese Polarity. Use whatever meaning works for you.
The
Try not to overthink the electrons, IMHO the real key is understanding where you need to apply heat.
When using the TIG (and OA) process you need to add heat to the work and to the filler metal which is often used to cool the puddle by dipping the cooler unmolten filler rod into the molten puddle and cooling the puddle by removing the heat required for melting the filler rod. IIRC, school physics refers to this as the required 'heat of fusion' which occurs whenever a substance changes state. IIRC with water this is 550 cal/gm, I do not recall what it is for steel. With TIG we want to limit the heat added to the tungsten electrode.
When stick welding we need to add additional heat to melt the consumable electrode as well as to melt the iron powder in the coating, most of the penetration of the base metal is achieved with joint design and bevelling.
For what it's worth - generator DC welding machine at work - tried running our 6013's on the Negative pole (DCEN) and observed that visibly they do run better that way.
Follows what the manufacturer says on the packet - AC or DCEN.
Reckon DCEP for Basic (7016 and 7018) and Cellulosic (6010) always works better for me - and follows what the manufacturer says on the packet for those rods.
Remember that some rods can have special and functional uses when used at non mfr. settings. The one that I have used a lot is 3/32" 6011 with stinger negative to field weld .065" tube. A case where you just want to put a "stack of dimes" on there to hold it together for a long time. Quite a little whippy fast motion in case you haven't tried it. But all other references suggest DCEP or AC.
It's tricky, fun, and doable. Get your amperage so it just burns, and whip in and out of the puddle. Staying still will just get you a hole. Keep a short arc to place the next puddle, but you can lengthen it a little to whip out and in just as soon as you get a puddle, whip out, let it cool for a minisecond, then whip back in and do the next one. I learned on a Miller Thunderbolt, then did it in the field with the 16hp Lincoln, can't remember the model number. One of the real small portables. Would hardly do a 1/8"
7018, but for 3/32" for small repairs and rolling on to an elevator to get to the top floors, it was the cats meow. Had AC, too to run grinders and drills. Drive it right up to the gate and fix it without having to stretch out long cables. Couple of hundred pounds with tools and all, I'd say.
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