Narrower arc from blunt tungsten

[WillieB]

I thought so.

[OscarJr]

If I could sneak into that physics course, or spend my life savings to have that knowledge, I'd do it. Otherwise, if you would be willing to enlighten me, I'd be richer for the knowledge. Others would benefit or at least be entertained.

Simple. Calculate the actual skin depth for tungsten for a given AC frequency:



omega = 2π*f = 2π*100Hz (for example).
sigma= 1.79E(7) Siemens/m
mu= 4πE(-7)*(1+6.8E(-5)) = 1.2567E(-6)

Crunch the #s, and

delta=0.0563 meters @ 100Hz.

The radius of a 1/8" tungsten is 0.0015875 m for comparison. At 100Hz as an example, the effective skin depth is ~35x the radius of a 1/8" tungsten to put it in perspective.

Due to the nature of the sigma function, this means that for a 1/8" tungsten you'd have to raise the AC frequency > 5,500Hz for the skin depth to just barely begin to decrease smaller than the radius of the entire electrode (< 0.0625"). In other words, for 1/8" tungsten at any AC frequency less than ~5.5 kHz, the entire cross-sectional area is "consumed" for current transfer.

Different conductors will have different values for mu and sigma, therefore this is only for tungsten and the numbers here cannot be extrapolated for any other conductor because the delta function is non-linear.

[WillieB]

If I could sneak into that physics course, or spend my life savings to have that knowledge, I'd do it. Otherwise, if you would be willing to enlighten me, I'd be richer for the knowledge. Others would benefit or at least be entertained.

[OscarJr]

Sorry about that! Sometimes I don't talk pretty much too good Engrish.
As for skin effect, Nicola Tesla would disagree with your statement were he here.

No he wouldn't. Look up the formula (or approximation thereof) and plug in the values for tungsten's conductivity and permeability. Then try varying angular frequencies and you will see for yourself. This is covered in any undergraduate physics course on introduction to electromagnetic field theory.

[WillieB]

I tried it last night with aluminum, 1/4" x 2" crossed flat against flat overlap and 1/4 to 16 gauge 6061, 200 amp 200 HZ 80% EN 4043 3/16 3/16 blunt ground tungsten tapering with pedal as it heated up. I found it worked as well as long pointed, or better. I didn't find it necessary to stop to adjust stick out as the tungsten shrunk away. Thoriated, 2% lanthanated, and ceriated performed pretty similar until I ran out of argon. That does not work well!

[H80N]

Can I hijack my own thread? Define chopper technology. I mistakenly it seems guessed it was the way a syncrowave made square wave AC. People corrected me on that.

Willie...

You were right... Square Wave machines use SCR's... Silicon Controlled Rectifiers... and they are commonly referred to as "Choppers"...

those chopper circuits were used to control current and AC balance in the Syncrowave welders...
it was a huge technological leap at the time...

[WillieB]

You mean "hypothesis".

But anyways, no need to test anything. The test results are on the Miller diagram. Also "surface current", or "skin effect" as it is called, only really applies to AC electricity, well above the 100kHz range. For DC welding, and for all practical AC welding, current will travel well into the interior of the conductor (tungsten).

Sorry about that! Sometimes I don't talk pretty much too good Engrish.
As for skin effect, Nicola Tesla would disagree with your statement were he here.

[WillieB]

Can I hijack my own thread? Define chopper technology. I mistakenly it seems guessed it was the way a syncrowave made square wave AC. People corrected me on that.

[H80N]

Do not see a reference to type of machine... it will make a difference if applied to an inverter with multiple waveforms and adjustable frequency...like a Dynasty..
I have a feeling this is for a Mag Amplifier or chopper supply..

[OscarJr]

Oscar,
It wasn't you who posted and I saw, but it is the item I spoke of. I've been away, haven't tried testing the theory. Anything that will help to put the heat in the joint, instead of out in the field should make for a straighter finished piece.

You mean "hypothesis".

But anyways, no need to test anything. The test results are on the Miller diagram. Also "surface current", or "skin effect" as it is called, only really applies to AC electricity, well above the 100kHz range. For DC welding, and for all practical AC welding, current will travel well into the interior of the conductor (tungsten).

[WillieB]

Oscar,
It wasn't you who posted and I saw, but it is the item I spoke of. I've been away, haven't tried testing the theory. Anything that will help to put the heat in the joint, instead of out in the field should make for a straighter finished piece.

[OscarJr]

me?

Not sure if you mean me, but I was one of the first to reference those pictures from the Miller handbooks, and from ArcZone, and another from Google Images.









Now that I think about it, it couldn't have been me since I'm in no way in witness protection, LOL. But I do know that once I posted those pictures, others started saving them and posting them up once the same topic was brought up again.

[H80N]

I have settled on running 2% Lanthanated with a pointed or just slightly blunted tip on my Dynasties... and adjusting arc width on AC Aluminum by the frequency... higher freq.. narrower the bead...

here is an interesting video from Jody.... maybe a little off topic but interesting and related..

http://www.youtube.com/watch?v=bpanERwagaU

[Ltbadd]

Examples

This is from the AWS Handbook, eighth edition

[Burnt hands]

These pages from Tig Handbook may help.

I use a sharp point and 200 Hz, advanced squarewave, 75% balance when I tig aluminum and find it works to give me a tighter, narrower arc.

Also have been playing with pulsing on DC and have found that I get a more focused arc at 2000 pps than without pulsing.