When welding with GTAW, you have to make a couple of choices; weld with direct current, either straight polarity (EN), or reverse polarity (EP), if not direct current, then alternating current.
Direct current, electrode positive (straight polarity) can be used to weld most metals and EWTh-X, EWCe, or EWLa are the electrode types most often selected. Good arc efficiency is achieved with about 70% of the energy transferred into the weld.
Alternating current typically utilizes EWP or EWZr. Both pure tungsten and zirconiated tungsten will form a hemispherical end or a balled end if the electrode diameter is matched with the proper amperage range. The energy transfer is only about 50% into the weld, however you have the benefit of cathodic cleaning of the base metal with AC.
As stated by Lawrence, EWTh-X will form little nodules at the business end when welding with AC. The arc is unstable and the tungsten spits, sputters, and in general give a rather unpleasant welding experience.
Pure tungsten tends to contaminate easily and it doesn't carry the amperage the EWZr will. So the tungsten with the brown paint strip is usually preferred by all but the company "bean counters" when welding with AC.
Your choice of AC or DC is highly dependent on the metals being welded. Aluminum usually is welded with AC, argon shielding gas for thickness up to about 1/2 inch, argon helium mixes for thicker sections, and EWZr electrodes (with a balled end) for better current capacity and resistance to contamination. That's not to say you can't use DCEN, but the shielding gas of choice is usually helium, the electrode is usually EWTh-2 (with a tapered end), and there is no cathodic cleaning as is the case with alternating current. Thus, it is very important to clean the material just before assembly and welding if you elect to weld aluminum with DCEN.
Other threads have addressed the pros and cons of EWTh-X, versus EWLa and EWCe-X.
I hope Lawrence and I have answered your question.
Best regards - Al
Lawrence & Al: I recall the nodules [I guess] or at least the arc wandering, but I probably dipped the electrode and contaminated it too. I have a box of 1/16" Zr as well as the usual red & green, I will try them the next time they are appropriate. I only recently made the leap into the 1980's with the purchase of a Syncrowave 300 to replace My old 360 A/BP, I don't see an inverter in My future. Thanks for the explanations.
Hey Expertfab
When you get to those pearly gates... Don't worry about making a case for yourself..
Ephesians 1:4
According as he hath chosen us in him before the foundation of the world,
that we should be holy and without blame before him in love.
The "perfect candidate" has already done what is necesary :)
The theme continues:
Timothy 1:9
"Who hath saved us, and called us with an holy calling,
not according to our works, but according to his own purpose and grace,
which was given us in Christ Jesus before the world began"
HAIL the lawrence!!!!!!!!!!!!!!
I have been making XRAY quality welds with 2% for YEARSSSSSSSSSSSSSS yep I agree its not the best but you kno what..... it will shoot fine even on a $175,000 turbine. Lawrence I REALLY LIKE YOUR quotes.....I will see your there my friend and you can show me all I did not know.
Best Regards
Tommy