Opinions on DCEP / DCEN

[Bill Edwards]

I agree, something has varied - probably travel speed, and possibly without the welder realising he's doing it.

I had wanted to settle this by doing the same (etching them) but lack spare time as it's not really something you can ever do with just one piece, unless you had a robot operating the rod.

 

[AdrianH]

I would expect from comments and reading a lower cap height with DCEN, all others variables kept the same, all seem to point to less burn off, not what we've seen in the pic.

Adrian

 

[Richard.]

I would expect from comments and reading a lower cap height with DCEN, all others variables kept the same, all seem to point to less burn off, not what we've seen in the pic.

Adrian

Why a lower cap on dcen?

 

[AdrianH]

If you have a WPS then follow it
Otherwise as Al says DCEP gives penetration (more "heat" to the rod about 2/3, compared with 1/3 to the workpiece)
DCEN is the opposite - 1/3 to the electrode, 2/3 to the work piece and then some snipped

You have all been saying that with DCEP you get more heat in the rod, and on that I will not disagree, so, to me, for a fixed travel rate, i.e moving along the workforce I would expect more rod to be burned off and deposited then with DCEN. So a fixed travel rate of 10 inch per minute for argument may well burn off a full rod on DCEP, but as above at the same travel rate I would still expect rod left with DCEN. travel rate being different to feed rate as in how much rod is used per inch.

Just pinching Dimitri's picture a second, you can not get more into the parent metal, that is already full!, you can cause mixing in there but more metal can not fit in there so more burn off means more metal on top.


This is all how I see it in my mind of course and you are free to disagree.

I have been wondering about one of the rod holders that you set off burning then leave and it burns it self down to the end, sort of automatic feed under it's own weight.

These would provide the same amount of metal per inch, in my mind if used of DCEP or DCEN as the rod has to burn off for the feed to progress. so forget the amount of fill or metal on top would they show differences in penetration into the workpiece or would that not have enough fixed rates, Amps being the same?

Adrian

 

[Dimitri De Spiegeleer]

It's true that the travel speed is very welder-dependent, but the different burn characteristic (DCEN vs. DCEP) also accounts for a part of the difference.
Either way, travel speed has an almost negligible influence on the penetration depth. Should I have welded a bit faster, I doubt there would've been a noticeable difference in penetration depth.

This is nice, I feel again some testing coming up...
I will update this thread when I've got the results.

 

[Richard.]

DCEN is a lower penetrating polarity. It is used for that reason in a lot of applications. Many hard facing rods and wires are run in dcen for overlay because penetration isn't the ultimate goal here and with such consumables minimum dilution with the parent material is required so as not to effect the consumable properties such as hardness for example.
If your overlaying a plate with a hard consumable you don't want too much of the soft steel in the composition there for running in neg polarity helps with this because it pens and dilutes less. You do get more cap height also with dcen because rather than penetrating deep it does tend to more sit on the top. Argue all you want with which polarity penetrates deepest but argue with the guys that use it day in day out in the field for the said reasons why above. I don't know the exact complications regarding atoms and all that but I believe Al covered that well.

 

[wheresmejumper]

The best pipe welder ive seen on here,flange jockey,claimed he ran dcen (albeit with 6013) because it gave more penetration .
He was wrong of course,but the moral is just weld the bloody thing!!you don't need to really know the ins and outs

 

[AdrianH]

Well OK Richard, I did not want to go into Hardfacing rods as that is not the argument, as different rods for different tasks have different electrode coverings. So different characteristics.

For example Cell rods produce Hydrogen, requires a higher arc voltage to get the same current. Same current but higher voltage means more heat input and hence more pen for them.

Hard facing rods, you say are all DCEN. Well?

I have just checked 4 spec sheets and these are saying DCEP, DC reverse (Which is DCEP) or AC use. These are, just from 4 sites that list Hardfacing rods and are not giving me the safety data sheets as opposed to current and voltages. I have not missed out any that said DCEN, so I am sure you will find some.

Here we are:-


I do not want this to turn into a slanging match, but neither do I want because it is!

Adrian

 

[Richard.]

I did not say ALL hard facing rods were dcen. I used that as an example to show you why a lot of them are used in dcen. It was very relavent and you've simply used the whole "every rod is different" card but missed the point by a mile. The difference in the rods wasn't relievent it was the point as to why they are used in dcen which is because it offers less penetration and dilution. Adrian your the only person contesting this fact and your theory's that you've pulled out of books and the Internet are not helping you as your arguing a proven fact. I wasn't using hard facing as to argue about charactoristics I was using it as a reason why they are used often in en polarity. It's the same with hard facing wires too. Yes the process is different but the reason behind the polarity is very relevant to this pointless argument. Less dilution less penetration more cap height.
FYI. DC reverse is reverse or negative polarity.

 

[AdrianH]

I did not say ALL hard facing rods were dcen. I used that as an example to show you why a lot of them are used in dcen.

OK I will agree you did not say all, you said many. Just that the ones I found say DC+ or DCEP or AC. And if this is what the manufacturer says then I would expect that to be the procedure and that running DCEN would not be procedural, even Nikko and UTP are DCEP.

I could not find the use sheets for Murex or ESAB, plenty of HSDS but very few that specify what polarity. What you are actually saying is for less mixing run them DCEN.

DC reverse I have always believed to be DCEP as DCEN is straight polarity?

BUT ANYWAY, do not fear, I think I have found something where I can follow the guys words as to why, as you all say DCEP gives deeper Pen, so pinching these words direct from the web page written by a guy called Northwelder, at the time in Calgary, here goes:-
---------------------------------------------
"This is my attempt at explaining
" Why does SMAW have greater penetration with EP vs GTAW having greater penetration with EN ?"
(without much reference to particle physics,since I obviously don't know enough!).

First, I think most would agree that a major factor. in achieving penetration, is the heat transmitted to the weld puddle, by various means, through the arc, in both processes. This is called thermal efficiency.

In GTAW, the most heat energy is transferred to the weld puddle in EN, making this polarity more thermally efficient. When the polarity is switched to EP, then the major part of the heat energy is focused on the electrode, and this makes the weld puddle cooler and less penetrating than on EP, or less thermally efficient. Also heat energy is dissipated through the electrode into the shielding gas and electrode holder.

In SMAW, the most heat energy is transmitted to the weld puddle in EP, because most heat is concentrated on the electrode, as in GTAW, but since the electrode is being consumed, much of this energy is transferred directly back to the weld pool with the molten metal, making the weld pool hotter. In SMAW - EN, the weld pool is cooler since less heat being on the electrode also means less molten metal being transferred to the weld pool, and therefore, EN is less thermally efficient and penetrating.

This is also compounded with other factors in SMAW, such as the fact that the plasma column is directed and focused by the coating crater, (coating melting slower than the core metal) in a way similar to a hose nozzle. This is not as efficient in GTAW, which has a sort of pear-shaped column that is controlled mainly by the shape of the electrode. (In some automated GTAW processes, greater plasma control is achieved with a magnetic field). Another factor influencing thermal efficiency in GTAW EN and EP is that the weld pool is cooled by the feeding of the filler rod, and the flow of shielding gas. In SMAW, the slag cover slows the weld pool cooling and increases penetration well. THis is all coupled with the fact that, according to EsabU, there are 9 different purposes for the flux in SMAW, and many hundreds of ingredients which could affect penetration.

Given the above, you might expect SMAW to have greater thermal efficiency than GTAW, and in fact, it does."

-----------------------------------
Now, I understand that and can see the mechanism behind it . Thank god you all say.

So thank you for bearing with me, Richard go have a nice cuppa and cool down.

Adrian

 

[Richard.]

OK I will agree you did not say all, you said many. Just that the ones I found say DC+ or DCEP or AC. And if this is what the manufacturer says then I would expect that to be the procedure and that running DCEN would not be procedural, even Nikko and UTP are DCEP.

I could not find the use sheets for Murex or ESAB, plenty of HSDS but very few that specify what polarity. What you are actually saying is for less mixing run them DCEN.

DC reverse I have always believed to be DCEP as DCEN is straight polarity?

BUT ANYWAY, do not fear, I think I have found something where I can follow the guys words as to why, as you all say DCEP gives deeper Pen, so pinching these words direct from the web page written by a guy called Northwelder, at the time in Calgary, here goes:-
---------------------------------------------
"This is my attempt at explaining
" Why does SMAW have greater penetration with EP vs GTAW having greater penetration with EN ?"
(without much reference to particle physics,since I obviously don't know enough!).

First, I think most would agree that a major factor. in achieving penetration, is the heat transmitted to the weld puddle, by various means, through the arc, in both processes. This is called thermal efficiency.

In GTAW, the most heat energy is transferred to the weld puddle in EN, making this polarity more thermally efficient. When the polarity is switched to EP, then the major part of the heat energy is focused on the electrode, and this makes the weld puddle cooler and less penetrating than on EP, or less thermally efficient. Also heat energy is dissipated through the electrode into the shielding gas and electrode holder.

In SMAW, the most heat energy is transmitted to the weld puddle in EP, because most heat is concentrated on the electrode, as in GTAW, but since the electrode is being consumed, much of this energy is transferred directly back to the weld pool with the molten metal, making the weld pool hotter. In SMAW - EN, the weld pool is cooler since less heat being on the electrode also means less molten metal being transferred to the weld pool, and therefore, EN is less thermally efficient and penetrating.

This is also compounded with other factors in SMAW, such as the fact that the plasma column is directed and focused by the coating crater, (coating melting slower than the core metal) in a way similar to a hose nozzle. This is not as efficient in GTAW, which has a sort of pear-shaped column that is controlled mainly by the shape of the electrode. (In some automated GTAW processes, greater plasma control is achieved with a magnetic field). Another factor influencing thermal efficiency in GTAW EN and EP is that the weld pool is cooled by the feeding of the filler rod, and the flow of shielding gas. In SMAW, the slag cover slows the weld pool cooling and increases penetration well. THis is all coupled with the fact that, according to EsabU, there are 9 different purposes for the flux in SMAW, and many hundreds of ingredients which could affect penetration.

Given the above, you might expect SMAW to have greater thermal efficiency than GTAW, and in fact, it does."

-----------------------------------
Now, I understand that and can see the mechanism behind it . Thank god you all say.

So thank you for bearing with me, Richard go have a nice cuppa and cool down.

Adrian

I'm very cool cheers
I'm very glad you've found a reading that computes. I can guarantee that if Al hadn't posted after mine agreeing with me you wouldn't of dropped this in to say "oh yes I get it now" you would of continued to argue with every word I said. That's fine because I would of got board of listening to your book passages and new findings and probably ignored the thread which I should of done 3 pages ago tbh. I thought you were doing a course on mma welding???? Seriously the best advice I can offer you is pick up the bloody torch and get some metal put down. You'll learn a 100x more doing that than you will hunting through links for big welding words

 

[AdrianH]

Al's post had nothing to do with it Richard, just posting in the thread keeps me going off looking for explanations that I could understand, the post I found was from 2014 answering a question same as mine posted in 2004. So the answers do need some digging out.

Please do not forget, I am a hobby welder, so not had the written procedures put in front of me to follow until it becomes second nature and I do not question it. I do not do hard facing, use different types of rods, etc. My experience is just 6013 rods ESAB and Murex and some practical training from another member on here to techniques to which I am very grateful for. I just like to know why you all say what you do and not just accept because that is the way it is without understanding it, and as mentioned before I find some posts contradict each other.

The welding course has completed, I will have the cert come Easter time and it still means nothing. When it comes to asking how the arc works in the evening classes the theoretical handouts are just not there. I can post on here the written information I got on the course mostly H&S. My understanding has come from the Internet and mainly my books, why would I not believe them.


Apologies to Farside once again.

Adrian

 

[TechnicAl]

Oi vai............