EN SMAW vs EP SMAW

Date 05-20-2016 14:30

Hi all, the question im going to ask is im sure have been asked many times before. I have read couple of the older discussions regarding the subject topic but things have not been cleared to me. I would like to ask it once again and hope that experts will share their valuable experience and knowledge. Here is a question.
I read in one of the older discussions regarding why in SMAW EP penetrates more and in GTAW EN penetrates more. The concept of current density was brought into discussion which is defined as amperage/ cross sectional area of electrode. It was discussed that for the same amperage, current density in GTAW is higher for EN at a given amperage and it was compared to the same amperage SMAW EP and it was claimed to less current dennsity in case of SMAW EP.
If we take this concept of current density and apply it to SMAW only and then check what would be the current density at given amperage in both SMAW EP and SMAW EN what would be the result? I recently had a training of welding, a teacher told me that current carrying capacity is maximum in case of DCEN so at given amperage you can use smaller diamter of electrode, applying this concept to current density it is clear that DCEN would have higher current density than EP. But books says EP SMAW penetrates more than EN SMAW. EN SMAW gives higher higher deposition rate instead. Lots of confusion.
Thank you all in advance who will take time in responding to this basic question.

By kcd616

Date 05-20-2016 15:38 Edited 05-21-2016 02:37

ok
my first thoughts
DCEP is mostly xxx10 cellousic rod or lo hy xxx18 or xxx28
DCEN is mostly jet rod xxx24 or xxx14
which explains penetration and deposition
GTAW DCEP is mostly used on aluminum and for the cleaning action (Lawrence is best at this)
hope this helps
and not to many people tell me I am wrong and stupid :red:

sincerely,
Kent

By waqasmalik (**)

Date 05-20-2016 17:20

Thank you for ur response sir. Lets suppose we are considering specific case of SMAW of 6013.

By kcd616

Date 05-20-2016 18:03

6013?????
used that in the early 1970's
for sheet metal
then moved to GMAW
maybe someone uses in field now for sheet metal
but highly doubt it ( I would use 7014)
and if it is for sheet metal run DCEN
sincerely,
Kent

By Lawrence (*****)

Date 05-20-2016 18:49

Others have spoken in detail in archived posts about the current density issue so I'm going to leave that alone.

I think the important thing to know when dealing with E6013 is how it performs, unless this is just to satisfy your scientific curiosity.

E6013 is designed to work with EN, EP and AC current... very versatile. However it has limited applicability in structural code work due to it's fluxing system and non-low-hydrogen designation.

EP produces the deeper penetrating welds comparatively.

EN produces the shallowest penetration and is used primarily on sheet, think base metal, vertical down or in specific instances when penetration needs to be *minimized*

AC produces something in-between as far as penetration goes.

Overall this makes E6013 desirable in areas or conditions when motor generators only produce AC, or for buzz boxes, home use and light agricultural repairs.

EN vs EP current densities, direction of current flow and deposition rates are all very interesting to talk about, and I look forward to the responses of the guys with deeper electrical backgrounds... But maybe you just want advice about how to best use the E6013 or if it is advisable to use it at all.

By waqasmalik (**)

Date 05-21-2016 01:18

AWS handbook eighth edition volume 1, Welding technology. Chapter 2,physics of welding,page 46. It states that
" The areas over which the current flows into arc terminals(anode and cathode spots) has a strong effects on the arc configuration and on the flow of heat energy into these terminals. The current density at the workpiece terminal is of utmost importance to the size and shape of fusion zone and to the depth of fusion in a welded joint".
My question is why EP SMAW penetrates more than EN SMAW while EP SMAW has less current density?
Its not specific 6013 case, it can be any SMAW electrode which can be operated on DC + and DC-, just to draw comparison of penetration.

By 357max

Date 05-21-2016 01:47

Two fundamentals of electric arc welding - Electricity (Welding Theory) travels from the negative terminal to the positive. The DCEP Arc Plasma (Ionized gases) travels from Positive to the negative terminal. The ionized gases are created by the flux decomposing into a gas that then becomes ionized/plasma in the heat of the arc. Different electrode types have different fluxes producing different amounts of ionized/plasma; such as 6010/6011 versus the 6013 or 7014. The SMAW electrode has less mass than the base metal and therefore greater heat from the current flow through the electrode. That arc plasma energy is concentrated by the electrodes flux crucible/cup and is driven/pushed into the negative terminal base metal therefore provides the deeper penetration.
Welding with DCEN the electricity travels from the electrode to the base metal (greater mass) and the Plasma (Ionized gases) travels from the positive base metal to the negative electrode. Now the concentration of arc plasma and resistance of a small diameter electrical conductor focused on the electrode melts the electrode faster therefore producing shallow penetration and higher deposition rates.
Using a constant ampere/current arc welding machine and comparing GTAW versus SMAW note the arc voltage for a 150 ampere arc with each process. The GTAW arc will have ~~12 to 16 volts with argon shielding and the Tungsten electrode does not consume in the arc. SMAW electrodes are consumed in the arc and its 150 ampere arc will produce 25 to 40 volts. Volts X Amperes is watts per second. Voltage produces pressure to move the 150 amperes/current across the arc.

By kcd616

Date 05-21-2016 02:40

Max,
Thank you
great stuff
and very informative
sincerely
Kent

By 357max

Date 05-21-2016 01:21

E6013 was used and is being used to weld 4130 Chromium Molybdenum Low Alloy Steel tubing for aircraft frames with DCEN. If welding less than one inch thickness carbon steel and above the freezing temperature of water welding with DCEP will produce very sound welds. And yes it welds quite nicely with AC with a compromise in penetration characteristics shallow versus deeper as provided with DCEN or DCEP.
WW II GI welders claim WWII was won with OAW RG 45 & E6013. Quite a statement for a buzz box and a farmers rod.

By Lawrence (*****)

Date 05-21-2016 02:06

Great posts Max!

Thanks

By kcd616

Date 05-22-2016 09:37

Max
btw I was taught by guys who worked in the shipyards
during WW1 and WW2 I am so old (some think I worked on the jobs :eek:

)
but to the point they used 6010
the rod I learned on
just my experience
sincerely,
Kent

By waqasmalik (**)

Date 05-22-2016 11:21 Edited 05-22-2016 11:28

Per AWS 5.1, dia 3.2mm E6013 has useful current carrying range is 80-130. I assume its at DCEP because its not mentioned there. What would be the current carrying range on DCEN under similar conditions for a same diamtre electrode? More or less.

By 357max

Date 05-22-2016 15:25

The E6013 could be welded with 80-130 amps with AC DCEP or DCEN. Amperage has the most affect on weld penetration. DCEP will produce the deepest penetration at those amperages. DCEN will have the least penetration at those amperages and AC will be about midpoint on the penetration characteristics.

By waqasmalik (**)

Date 05-22-2016 16:47

Thank you for responding sir, but dont you think that DCEN will have more current carrying capacity compared to DCEP? Electrons being the greatest source of heat are moving away from electrode which is cathode in DCEN, so we can increase the current to higher than 130 without danger of resistance heating causing chipping of flux and spattering.

By waqasmalik (**)

Date 05-22-2016 17:20

I read in AWS handbook as mentioned already that current density at workpiece terminal is of utmost importance to the size and shape of fusion zone and to the depth of fusion in welded joint. So from this i think that depth of fusion aka penetration has most to do with current density. Im trying to understand and discuss this concept in both EP and EN for SMAW. This is just to satisfy my scientific curiosity otherwise i know which polarity is most favorable for which electrode, process or situation.

The concept i have about GTAW current density is explained below. Please correct me if im wrong.

GTAW

DCEP: Least penetration and wide weld bead. For a given amperage you need larger diamter tungsten electrode so current density is less.120 amps will need 6mm diamter of tungsten electrode with argon shielding. Area over which heat flows into the workpiece is more, arc is less constricted which gives less penetration.

DCEN: Max penetration and narrow weld bead. For a given amperage u can use smaller diamter compartively. For 120 amps you can use 1.8 mm diamtre tungsten electrode if it is EWcr, EWth or EWLa and 2.4mm diamtre if it is EW or EWZr. In any case, area over which heat flows into the workpiece is less compared to DCEP so arc is constricted and current density is high which results in higher penetration.

Can the same concept of current density be applied to SMAW to understand the effect of it on penetration in relation to polarity.

Thank you all

By kcd616

Date 05-23-2016 02:51

this is a Kent thought process
GTAW is all to itself (PAW maybe similar) tell me how wrong I am Lawrence :red:

GTAW run A/C for aluminum and magnesium
DCEN for everything else
SMAW IMHO only done maybe anymore in field work
GMAW, FCAW are how you make $$$$$$$$$$$$$$$
and those 2 run DCEN,
unless your welding foil, then I heard run A/C (never done it)
but those machines cost real $$$$$$$$$$$
same as PAW aka plasma arc welding (never ran a PAW, so no opinion)
sincerely,
Kent

By Northweldor (***)

Date 05-25-2016 21:55 Edited 05-25-2016 22:09

"...Can the same concept of current density be applied to SMAW to understand the effect of it on penetration in relation to polarity."

In answer to your question, I think the answer is no. There are too many other variables (besides current density) operating to increase or decrease penetration in the SMAW process. As I have said in earlier posts, I think thermal efficiency is the best explanation.

The following article gives some idea of the complication of comparing between processses

http://www.lincolnelectric.com/en-ca/support/process-and-theory/Pages/variables-weld-penetration.aspx