I was told today by some guys on the job that on straight polarity all the heat is concentrated on the electrode and reverse polarity all the heat was in the metal. I softly stated my case because i was taought it was the other way around and this is why they ball tungsten on reverse polarity. I also was toolin through Lincoln Electrics website looking for some info about A/C polarity to do a paper on it for school and saw that they also say that all the heat is on the electrode in straight polarity and reverse polarity all the heat in on the work piece. So am i crazy or what please help me!!! And witch way does electricity flow, from + to - or - to + or does it not matter or have a starting point? Also On the A/C sign wave does it go to + first or - first? Appreciate any help you all can give me thanx R.C
GTAW:
DC- = arc energy is concentrated in the BM
DC+ = arc energy is concentrated in the electrode
- to +
With the current technology, an AC sinewave can be modified to initiate at either polarity. It is still - to +.
This may be the subject of debate, nor does it apply to all arc welding processes.
There may be great misconception on how the heat flows in a welding arc.
There are two theroys to consider.
One, conventional theroy, states that electricitry flows from positive to negative. In many non-welding cases, this may be true.
In welding, however, we are concerned with electron theroy. Electrons are really the heating part of an electrical arc. They do run in reverse of conventional electrical theroy.
If you have a tig machine, this is easy to prove.
Set a 1/16 tungsten at straight polarity (tungsten is negative) and 125 amps or more is easily handled.
Set the same tungsten at reverse polarity, and it will have trouble handling 15-20 amps or less.
That said, it is easy to see that the heat is moving from the tungsten to the work on straight polarity and from the work to the tungsten on reverse polarity.
At least, this is how it was explained when I was at Miller Electric Servivce School a few years back.
Email me directly if you have any questions.
Good Luck-brad
Thanx guys i had a feeling i was right just didn't want to step on any toes becuase i'm new. Just going to let it go. Thanx again
Hi R.C.
Arc theory is rather a complicated subject (to me at any rate) and it is not as easy to just say that in one polarity this happens and in another polarity the opposite happens. This is so because there are other variables such as the type of electrode, flux and gas.
In general however, the big difference lies with the electrode. In the case of the non-consumable electrodes (Tungsten in other words) we have what is known as a cold emmitter. In the case of cold emmitters, the most heat lies on the positive side of the arc. In other words, when welding GTAW with DCEN, then the most heat is going into the base metal.
In the case with consumable electrodes, we have what is known as a hot emmitter. In the case with hot emmitters, the opposite is true. Thus, when welding SMAW or GMAW with DCEP, the most heat is going into the base metal.
With what process were the steam fitters welding? If you tell us that, then we can quickly establish who was right regarding the specific instance.
Just to address your question about which way round current flows. Here it depends on your definition. In the early days of electricity, it was "randomly" decided that a current flow will be defined as moving from a positive pole to a negative pole. Many books still use this notation and is then generally called a "current flow".
Now we know that electrons flow from a negative pole to a positive pole. We therefore have a notation stating that "electron flow" is from negative to positive. All this makes for great confusion, as I am sure you have seen.
Hope this helps
Regards
Niekie Jooste
They were doing the SMAW process. They said put it over to straight polarity where all the heat is on the electrode and i thought that was wrong. I was taught and have seen in welding textbooks 2/3rd's heat on workpiece on straight polarity and rest on electrode and 2/3rd's heat on electorde on reverse ploarity and the rest on workpiece.
I can not vouch for the sources that you used, I can only go with what I learned during my welding engineering course. We worked from the AWS handbook.
If the steam fitters were using the SMAW process, then I must agree with them that the most heat would be on the electrode when welding with DCEN. (streight polarity) I am not sure why they would want to do this, because it will result in less penetration and possibly overheat the electrode. (Unless it is designed for use in DCEN)
Also, if the people that you were talking to were experienced welders, they would not need a text book to tell them where the most heat lies when welding in different polarities. They would no doubt have welded in different polarities many times, which would have given them an appreciation of where the heat lies, without any text book theory. While there are many misconceptions amoungst welders regarding the properties of welds etc, it is my experience that when it comes to the actual deposition and welding technique, they have a good idea of what is going on.
Hope this helps
Regards
Niekie Jooste
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