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Thread: Porosity, Why?

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  1. #1
    Join Date
    Oct 2007
    Location
    W. KY
    Posts
    28

    Default Porosity, Why?

    I ran out of gas for my mig so I thought it would be a good time to learn some on tig. The photo shows my problem, porosity. The metal was clean of all mill scale, the cuts were with a band saw and there was no oil on it. I thought maybe I had the flow rate to low on the argon, it was at 20 cfm so I upped it to 30 cfm, no help. The tungeston was 2% thoriated, i made sure not to dip it. I did notice that the tip was yellow after I would weld.

    Any ideas? Thanks, Justin
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  2. #2
    Join Date
    Dec 2007
    Location
    alabama
    Posts
    745

    Default

    First question what size cup?
    2nd, any air circulating around you?
    2, XMT's 350 cc/cv
    1, XMT 350 vs
    1, TRAILBLAZER 302
    1, MILLER DVI
    1, PASSPORT PLUS
    1, DYNASTY 200 DX
    1, MAXSTAR 150 STL
    1, HOBART CHAMP
    1, HF-251 BOX
    1, S-74d
    1, S-75DXA
    2, 12-RC SUITCASES
    2, 30 A spoolguns

  3. #3
    Join Date
    Oct 2007
    Location
    W. KY
    Posts
    28

    Default

    Not sure of the cup size, I'd guess about 5/8" or 1/2". There was no air movement at all, it seems that all of them start out fine but about half way through the porosity starts. The welds are in a non critical area, they're ugly know buy I have to learn sometime.

    Thanks, Justin

  4. #4
    Join Date
    May 2008
    Location
    Troy, MI
    Posts
    323

    Default

    I see a black halo around the porosity. Is it possible that your tungsten dabbed (or touched) the weld puddle?

    I also see some mill scale on the parent metal. Try grinding off the mill scale and rust. This can also cause porosity.

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  5. #5
    Join Date
    Dec 2007
    Location
    alabama
    Posts
    745

    Default

    Using a gas lens ?
    2, XMT's 350 cc/cv
    1, XMT 350 vs
    1, TRAILBLAZER 302
    1, MILLER DVI
    1, PASSPORT PLUS
    1, DYNASTY 200 DX
    1, MAXSTAR 150 STL
    1, HOBART CHAMP
    1, HF-251 BOX
    1, S-74d
    1, S-75DXA
    2, 12-RC SUITCASES
    2, 30 A spoolguns

  6. #6
    Join Date
    Aug 2006
    Location
    Melbourne, Australia
    Posts
    107

    Default

    In my opinion the most likely culprit would be gas coverage. Outside corner welding like you have there is often the joint that will show up gas coverage problems. The problem lies in that the gas from the torch tends to slide straight past the weld joint as it is the path of least resistance, this can then draw air along with it as in fact you now have a low pressure area.
    The common mistake is to increase gas flow but this simply increases the speed of gas slipping past the weld joint which in turn is an even greater low pressure area drawing in more air.
    Gas lenses slow down the gas flow giving a much more even gas coverage and I love them to bits. If you don't have any gas lenses try decreasing your gas flow out the torch and shorten the amount of tungsten stickout.
    This technique has worked well for me in the past but now I use gas lenses exclusively (except for Magnesium welding ) and the problem doesn't crop up like it used to.
    Regards Andrew from Oz.
    We are tig welders, gravity doesn't worry us.

    Miller Dynasty 350 Tig.
    OTC AVP300 AC/DC 300 amp hybrid wave Tig. (now retired)
    Kemppi MLS 2300 230amp AC/DC Tig for home with all the bells and whistles.

  7. #7
    Join Date
    Mar 2008
    Location
    Anchorage AK
    Posts
    344

    Default

    Quote Originally Posted by justinp61 View Post
    The tungeston was 2% thoriated, i made sure not to dip it. I did notice that the tip was yellow after I would weld.

    Any ideas? Thanks, Justin


    Yellow tip males me think you had the tungsten sticking out too far.

  8. #8
    Join Date
    Oct 2007
    Location
    W. KY
    Posts
    28

    Default

    The rods are 706s and the torch has a regular cup on it. On the tungeston stick out, it's 3/16" to 1/4". I'll try the lower flow rate and see what happens. I had the same problem with the weld on a 1/2" shaft with a 3/8" thick flat washer welded to it for a slide hammer I'm building. I'm going to figure this thing out if it's the last thing I do, in the mean time, Monday I'll get my mig bottle filled.

    Thanks Guys, Justin

  9. #9
    Join Date
    Dec 2007
    Location
    alabama
    Posts
    745

    Default

    Use a bigger cup and make sure you keep the cup pointed directly down over the weld with just a slight angle towards the direction of travel.
    2, XMT's 350 cc/cv
    1, XMT 350 vs
    1, TRAILBLAZER 302
    1, MILLER DVI
    1, PASSPORT PLUS
    1, DYNASTY 200 DX
    1, MAXSTAR 150 STL
    1, HOBART CHAMP
    1, HF-251 BOX
    1, S-74d
    1, S-75DXA
    2, 12-RC SUITCASES
    2, 30 A spoolguns

  10. #10
    Join Date
    Oct 2007
    Location
    W. KY
    Posts
    28

    Default

    What size cup would you recommend? I have to go to town Monday to get my bottle filled anyway so i might as well pick one up.


    Thanks, Justin

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