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Is a 3/32 Electrode the Holy Grail?

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Re: Is a 3/32 Electrode the Holy Grail?

Postby Arclight Ironworks » Fri Jan 12, 2018 8:16 am

entity-unknown wrote:....Recap: Are we saying a tungsten grind that matches a sharpened fine point pencil is bad for Al and instead I need a flattened end?...

For the majority of cases, you'll optimize the Tungsten's arc stability and cathodic penetration effects by properly preparing and profiling the included angle to subtend ~ 30-45-60deg. An an option, you may slightly blunt the Tungsten's tip. In most cases, blunting the tip prior to welding out Aluminum aids in combating disintegration at the tip that primarily results from evaporation at LTE (local thermal equalibirum) within the plasma column during electron/ionic transfer. Note that blunting, if used for aluminum, should be small/small unlike shown in the image. IMPO. Using a larger diameter Tungsten (ie. 1/8") with REMs (rare-earth metal oxides), the propensity for erosion of the Tungsten {thermionic cathode} is significantly diminished sans a blunt tip. Lastly, there are certain cases where we profile the tip with two separate included angles.

The image, captured from the body of literature, represent what we employ 90+ percent of the time for steel/stainless steel and aluminum. Again, with a smaller blunting (if used). We profile based on our application (i.e. joint geometry, position, etc), the type/thickness of the materials to be welded, and the filler selected.

You have to "test and learn" and determine what works for your welding style and your application.

Tungsten Profiles.png
Tungsten Profiles.png (194.4 KiB) Viewed 81 times

"For a cathode to support an arc, some process must exist which provides current continuity at the cathode-plasma boundary. To escape from the metal the electrons should either overcome an energy barrier that exists at the cathode-plasma boundary (work function) or tunnel through this barrier. The first process is thermionic electron emission. It requires a hot cathode temperature for a substantial number of electrons to be emitted. The second process, field electron emission, requires high electric fields at the cathode surface to make the barrier low and thin and thus intensify electron tunneling. In the considered type of arc, the intermediate case takes place: the cathode is hot and its work function is lowered by a strong electric field at the surface (the Schottky Effect). Both factors (hot cathode and high electric field) play important roles in the electron emission process in thermionic arcs. However,the electric field while being strong enough to reduce thework function is not strong enough to provide any substantial electron tunneling." (Valerian Nemchinsky, 2014).
Last edited by Arclight Ironworks on Fri Jan 12, 2018 8:23 am, edited 2 times in total.
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Re: Is a 3/32 Electrode the Holy Grail?

Postby entity-unknown » Fri Jan 12, 2018 8:20 am

So thinkin about this a bit more, I want to expand on my question... it really depends on the thickness and penetration. But for a poor man's example, I'd say a fine point for thick, deep penetration, and a fairly flat end for more fine work? Basically exactly opposite of what I'd expect from drawing with a pencil?

Edit 1: And I see ArcLight provided a very detailed explanation after I posted this :) Reading now.

Edit 2: So after reading the post, I think I actually comprehend what's going on. I'd say I'm a 30 to 45 degree'er usually :D I honestly have always approached this with the concept of drawing with a pencil but what I should be thinking of is how the surface of the tungsten tip aligns to the welding area.

So if you were all my professors (I pretend you are :) ) these are the three ?s I'd ask to confirm what I read from ArcLight above:
So the sharper the tip, the less parallel the tip surface where the electrons leave the electrode is to the welding area, then the result is a wider arc which would equate to more heat with less initial penetration, so more heat is required to weld? Kinda like having a really bad arc gap and/or torch angle?

Then without getting too deep into the angles, the more blunt tip will provide more focused arc/heat with deeper penetration per second with the ability to control arc width by controlling the angle of the tip i.e. sharper = wider ?

Lastly, a 90 degree torch angle is more important with a sharper tip than a blunt i.e. the blunt tip gives more room for torch angle with less negative impact to your weld in comparison ? Does this also give flexibility with arc gap?
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Re: Is a 3/32 Electrode the Holy Grail?

Postby mechanic416 » Sun Jan 14, 2018 12:02 pm

I use 3/32" most of the time as I am welding from 80 to 150 amps. I use red, blue and purple as I have found they all weld steel and aluminum about the same. I sharpen my 3/32 and 1/8 to what ever looks good. I do not sharpen my .020, .040 or 1/16 most of the time, depending on what I am welding.
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