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  1. #1
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    Default Narrower arc from blunt tungsten

    A fellow on Welding Web (I think he's in witness protection so I won't name him) posted a chart of tungsten shapes, and how they relate to arc width and penetration (or lack of it). The chart is without explanatory information. I don't know if AC, DC or if it matters.
    It shows that a very blunt grind produces a pinpoint arc, while a needle like grind produces a wide arc with little penetration. I've been grinding to a needle point trying to focus the arc. It seems that was the wrong thing to do.
    We have discussed why, My uninformed guess has to do with the surface current phenomenon and the fact that electrons seek to continue running straight. A current on a cylindrical object will be concentrated on the surface. This higher current will tend to steer the rest of the current. As the shoulder of the grind is farther away from the work piece arc will originate farther away, if from a long pointed tungsten. From a shorter point it will be easier for current to continue along its "current" path, ionizing, then arcing across the gap.

    I'm guessing here. Is there merit to my theory, or are other forces at play?

  2. #2
    Join Date
    Nov 2003
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    3,102

    Default

    would like to see the chart....

    it isn't the stuff from section 4 and 5 of this guide is it..??

    http://www.millerwelds.com/pdf/gtawbook.pdf

    .

    *******************************************
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  3. #3
    Join Date
    Dec 2007
    Location
    Oklahoma
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    Default

    Quote Originally Posted by Willie B View Post
    A fellow on Welding Web (I think he's in witness protection so I won't name him) posted a chart of tungsten shapes, and how they relate to arc width and penetration (or lack of it). The chart is without explanatory information. I don't know if AC, DC or if it matters.
    It shows that a very blunt grind produces a pinpoint arc, while a needle like grind produces a wide arc with little penetration. I've been grinding to a needle point trying to focus the arc. It seems that was the wrong thing to do.
    We have discussed why, My uninformed guess has to do with the surface current phenomenon and the fact that electrons seek to continue running straight. A current on a cylindrical object will be concentrated on the surface. This higher current will tend to steer the rest of the current. As the shoulder of the grind is farther away from the work piece arc will originate farther away, if from a long pointed tungsten. From a shorter point it will be easier for current to continue along its "current" path, ionizing, then arcing across the gap.

    I'm guessing here. Is there merit to my theory, or are other forces at play?
    Diamond Ground products shows the same information. I don't remember if they gave an explanation.

    Griff

  4. #4
    Join Date
    Dec 2008
    Location
    west central Florida
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    87

    Default

    AWS handbook has a similar chart showing this. Processes like orbital welding, the angle the tungsten is ground to is an important parameter in the process and must be kept the same for repeatability.

  5. #5
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    Default

    No, I tried to copy and paste, no such luck. It came with no text, a series of black and white photographs of arc shapes at 200 amps. Scale is not specified, it appears to be 1/8" tungsten. They show arc, and cut and etched weld. Using a large variety of incrementally long points including square cut. The trend shows deep penetration, and narrow arc, and bead from blunt ground tungsten, and wide arc, shallow penetration from long pointed tungsten.

    I've been grinding long points in an effort to narrow bead width in aluminum, envisioning it delivering a pinpoint arc that would minimize the size of the heat affected zone. If this new information is good, I can narrow the heat affected zone with a blunt "golf pencil point".

    In the photos arc appears to originate from the shoulder where the tungsten begins to narrow, flaring out from there. In the extremely blunt grinds or balled from cylinder, arc appears to blow straight off the end of the tungsten.
    Last edited by WillieB; 06-20-2014 at 05:45 AM.

  6. #6
    Join Date
    Aug 2009
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    140

    Default

    The explanation as I recall is that the electrons tend to be admitted from the tungsten at a 90 degree angle to the surface of the tungsten. They then are curved towards the weldment by the electric field. If the electrode is ground to a very narrow angle the electrons are emitted almost sideways and thus require more time and effort to be pulled to the weldment. This allows them to move further from the electrode and thus a wider arc. If the electrode is blunt, an unsharpened electrode being the extreme case, they are already "aimed" more towards the weldment and thus produce a narrower arc.

    Think of firing a shotgun at various angles from horizontal to vertical and envision where the pellets will land. Sort of the same concept.

    Ken

  7. #7
    Join Date
    Apr 2012
    Location
    Western Pa.
    Posts
    219

    Default Narrower arc from blunt tungsten

    Had small amount of steel Tig on Friday. Tried blunt tungsten as similar to what is du for Alm.
    Can't say as this small test that I agree.
    I've always sharpened to point for steel & just didn't seem as good with blunt style grind. My arc seemed wider & less penetration than with pencil sharp grind. But was small amount of welding so not fair test but not so sure I like it as well. Will try again next week.
    Greg

  8. #8
    Join Date
    Dec 2007
    Location
    PA
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    354

    Default

    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.
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  9. #9
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    Dec 2008
    Location
    west central Florida
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    Default Examples

    This is from the AWS Handbook, eighth edition
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  10. #10
    Join Date
    Nov 2003
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    3,102

    Smile

    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
    .

    *******************************************
    The more you know, The better you know, How little you know......

    “The bitterness of poor quality remains long after the sweetness of low price is forgotten”

    Buy the best tools you can afford.. Learn to use them to the best of your ability.. and take care of them...

    My Blue Stuff:
    Dynasty 350DX Tigrunner
    Dynasty 200DX
    Millermatic 350P w/25ft Alumapro & 30A
    Millermatic 200

    TONS of Non-Blue Equip, plus CNC Mill, Lathes & a Plasmacam..

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