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Thread: Arc Blow

  1. #1
    Join Date
    Mar 2008
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    15

    Default Arc Blow

    I was working with a friend on 1" plate, 22 1/2 bevel, for a 45 joint, 3G vert up,1/4 gap, with 1/4 " backer strip, he has to use 115 to 130 amps DC+, with 7018 H4 rods. He runs in to arc blow frequently. We went to the lowest 115 amp setting, changed rod positioning, held tight to joint, wrapped cables to try offsetting magnetic field, reposition ground to begining, and end of joint, heavy tacks, and a couple other things. As is normal, it is normally just on the root, 2nd, and sometimes the 3rd pass, and in the upper 3rd of the plate. He been pointing rod up, about 20 to 30 degrees, but has also tried going straight in, when blow starts. All equipment connections good. I have tried things that helped me, but need other ideas. Thanks

  2. #2
    Join Date
    Jun 2008
    Location
    Florida
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    110

    Default

    Why does he have to use DC? Try AC.
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  3. #3
    Join Date
    Sep 2005
    Location
    16919 Pole Rd. Brethren, MI 49619
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    4,363

    Default

    First, why does he use DC? Because its what he is sposed to be using. Look at an SA200, stick pipe welding machine, no AC to be found on it. This is out of position work, DC is so far superior. Only time my shop machine has ever been set to AC is for some nickle.
    I have to agree with Ironhead, this isn't the kind of arc blow everyone reads about in threads which for the most part is very rare and minor, easily corrected with tacks. I would say rod angle issues too, also have had old rods burn off to the side

  4. #4
    Join Date
    Mar 2008
    Posts
    15

    Default follow uo

    He is practicing, as per the wps he has, and DC+ is the polarity. What angle, do think he should adjust to, once the arc blow starts to show up?

  5. #5
    Join Date
    Jan 2007
    Location
    Noth Dakota
    Posts
    505

    Default

    Ya could just stop welding. grind a tish and start back up.

  6. #6
    Join Date
    Jan 2007
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    Alberta Red Deer
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    373

    Default

    rod angle, old rods, clean rods, heat the plate, and maybe a little grinding are the only things i can think of to cure the problem that i know of. some times also i have found that when the cables are coiled around each other at all arc blow can happen but other than that i dont know.
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  7. #7
    Join Date
    Nov 2007
    Location
    Southern Louisiana
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    421

    Default arc blow

    For our discussion here arc blow is simply magnetism building up in the base metal and causing a reaction in the arc. Any electrical circuit will have some electromagnetic field build up. Historically we have wrapped the part a couple of times with the work lead to counter act the field, heating the part also works where it is ok to heat the metal that high, there is a point where the metal gets hot enough that it becomes no responsive to magnetism.

    Most often what I have found is that the cables are all coiled up, out on the job the cables are stretched out but just running practice beads isn't worth the effort to string out your cables and then pick them back up. Sometimes I have even found the cables coiled up and sitting on top of the welder or still hanging on a steel holder. Once you have a copper cable coiled up and them it has steel running through it you have a transformer. 25 or 30 feet of cable coiled up also provieds a great way to magnetize tools when there is current flowing.

    So if all else fails think of the basics of magnetism, the larger the coil the stronger the field, so stretch out the coil. Also remember to weld toward your work clamp.

    Another idea that I picked up from one of our foreign engineers Tiejin is to loop the cable and fold it back on itself. See the picture attached.
    Attached Images Attached Images

  8. #8
    Join Date
    Sep 2005
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    Default

    I dont think for practice the ultimate condition of the rods are of much importance, when we say old rods I for one am talking old where they been laying in the same place, maybe years? As for rod angle it is a natural tendency to increase it as one goes up, you twist your wrist up instead of moving your arm up perpendicular to the work. It takes discipline, 0 to 10 degrees at most, almost straight and square. I still tend to do it.

  9. #9
    Join Date
    Jan 2008
    Location
    VA
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    298

    Default

    No, that is what makes it alternate.

    Good thread, thanks.
    Weekend wannab racer with some welders.

  10. #10
    Join Date
    Nov 2007
    Location
    Southern Louisiana
    Posts
    421

    Default

    Quote Originally Posted by Iron Head View Post
    That is very interesting!


    But wouldn’t that slow down the current?
    only if you kink it like a garden hose

    The purpose is to control the inductance in the line, where the EMF is expanding and collapsing. Controlling the magetic field is going to be key to arc blow.

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