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Thread: AC TIG question

  1. #1
    Join Date
    Feb 2006
    Location
    Lancaster,CA
    Posts
    54

    Default AC TIG question

    My question is when we weld on AC I notice a chaulk like dust all over the tig cup, is this normal or am I doing something wrong?
    We have a SYNC 250DX, running 1/8" pure tungsten, 100% Argon, 20 to 40 cfm trying different gas flow to see if it produce a ifferent outcome.

    Thanks
    Sal

  2. #2
    Join Date
    Sep 2008
    Location
    Omaha, NE
    Posts
    447

    Default

    I only get this when i run low on or out of gas. Make sure that your bottle is full, regulator set properly (between 13 and 20 cfh will sufice for most jobs) Also make sure your collet bodiy is in good shape and that none of the holes are obstructed.

    If all of these check out you might try using a gas lense to help with the flow. Now, on your welds on AC aluminum work you should see a white area around the bead, this is from the cleaning action that occurs when the arc is in it's positive state, the actual heat input is all done in the negative state, thus why DC TIG is mostly done on DCEN (the torch being in the negative state at all times) DCEP will still weld but with less penetration, and is good for really thin stuff ( i mean REALLY THIN)

    Try those and report back!
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  3. #3
    Join Date
    Feb 2006
    Location
    Lancaster,CA
    Posts
    54

    Default

    Turbo thanks for the tips. I checked the tank and it is more than half full, I tried a new collet body and new tungsten and cup, just trying to rule out any and possible problems. Yes I get the cleaning marks on outside of the bead. The weld bead looks good but still get the powder like on the cup. Could it be a bottle of bad gas causing it?
    Thanks Again
    sal

  4. #4
    Join Date
    Oct 2007
    Posts
    2,949

    Default TIG Polarity

    Quote Originally Posted by turboglenn View Post
    I only get this when i run low on or out of gas. Make sure that your bottle is full, regulator set properly (between 13 and 20 cfh will sufice for most jobs) Also make sure your collet bodiy is in good shape and that none of the holes are obstructed.

    If all of these check out you might try using a gas lense to help with the flow. Now, on your welds on AC aluminum work you should see a white area around the bead, this is from the cleaning action that occurs when the arc is in it's positive state, the actual heat input is all done in the negative state, thus why DC TIG is mostly done on DCEN (the torch being in the negative state at all times) DCEP will still weld but with less penetration, and is good for really thin stuff ( i mean REALLY THIN)

    Try those and report back!
    Turbo: TIG welding in DCEP (DCRP) will blow a hole in 1/8 mild steel! Where'd you ever here DC+ has "less penetration?" It's EXACTLY the opposite. DC- has less penetration. You'll burn tungstens up galore, and melt your work in DC+.

    AC has no polarity, because AC is current. It alternates, and that's where you get your "cleaning," and "penetration" values. DC Current travels in a straight line.

    Dave
    "Bonne journe'e mes amis"

  5. #5
    Join Date
    Feb 2007
    Location
    Spruce Grove, Alberta,Canada
    Posts
    583

    Default

    Quote Originally Posted by davedarragh View Post
    Turbo: TIG welding in DCEP (DCRP) will blow a hole in 1/8 mild steel! Where'd you ever here DC+ has "less penetration?" It's EXACTLY the opposite. DC- has less penetration. You'll burn tungstens up galore, and melt your work in DC+.

    AC has no polarity, because AC is current. It alternates, and that's where you get your "cleaning," and "penetration" values. DC Current travels in a straight line.

    Dave
    It does not have less penetration it will however produce a very narrow bead which put's all the heat in a narrow area. You will also have a very dirty weld. We used to weld very thin aluminum with DCEP with a miller aerowave was designed to weld aluminum that way with high freq ,which in my opinion was the best aluminum welding machine I 've ever used and miller stopped making it. You could run a bead on the edge of a 3/32 piece of aluminum, it was awesome.

  6. #6

    Default

    DC electrode POS will give less penetration AND burn up tungsten if not sized properly to handle the current flowing up to the tungsten.

    DC EN gives penetration to the work piece.

    This is why tuning up your balance on AC to a higher number (which is adding more electrode NEG) gives MORE penetration and less cleaning.

    Andy

  7. #7
    Join Date
    Oct 2007
    Posts
    2,949

    Default "The Positive About Negative"

    Quote Originally Posted by ASKANDY View Post
    DC electrode POS will give less penetration AND burn up tungsten if not sized properly to handle the current flowing up to the tungsten.

    DC EN gives penetration to the work piece.

    This is why tuning up your balance on AC to a higher number (which is adding more electrode NEG) gives MORE penetration and less cleaning.

    Andy
    Andy: You worded it correctly, I did not. In GTAW, when in DCEP mode, cleaning action takes place on the work surface by impact of gas ions. 70% of the heat is developed at the positive tungsten electrode, so in order to obtain the same heat on the work piece, the current must be increased by 2.3. This necessitates using an electrode 4 times the diameter normally used in DCEN. The impracticallity of this is obvious.

    DCEN put's 70% of the heat in the work, and although it provides little to no cleaning, used with ferrous metals, it isn't really an issue. Gas ions flow FROM the work TO the elecrode, and electrons flow FROM the electrode TO the work.

    I just know from machine setting errors (leaving it on DCEP), I've "blown" holes in 1/8" flat stock, and ruined a few tungstens.

    Thanks for clarifying this.

    Dave
    "Bonne journe'e mes amis"

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