MIG welding issue

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Hey guys for the past week or so i have had an ongoing problem with one of our welders. Basically about 1/2" past the weld pool a air bubble forms. We thought air was contaminating the weld, as one of the O rings were missing on the tip, but it wasn't the issue. Basically it happens usually when welding a corner, and running down, happens rarely but very frustratingwelder is a WIA 335Have a look at the pics any thoughts?cheers Attached Images
Reply:Change your head diffuser and nozzle for starters.
Reply:already done.
Reply:Take a picture of your gun with the nozzle off if you can and send.  Also, what gas are you using?  How much pressure?
Reply:http://www.millerwelds.com/resources...tips/MIG_tips/ This site has good information on discontinuities.
Reply:Scattered porosity, but almost all of it is along the centerline of the weld; the last place to freeze in the puddle.....Gas covereage in corner fillets is usually pretty good.  The base metal helps confine the shielding gas to the region around the weld.What kind of surface prep are you doing before welding?  Seems like you might have just enough contamination or scale to overcome the deoxidizers in the weld filler metal.  Or some kind of residue that is occasionally sufficient to cause some porosity.Check your gun cable and gas connections once more.  Intermittent porosity like you're showing could be an intermittent air leak...Something that only happens when the gun is pulled or twisted into a sharp angle.What's your gas type and flow rate?  Too high a flow rate could be causing turbulence and this can suck a little bit of air into the shielding gass pool.  If you're just on the edge, this could come and go, or show as a small bit of porosity here and there.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Had the same problem a while back turned out to be the wire I was using....had rust spots on it and maybe something else also.... changed the wire and all was great.....HF wire jezzzz not say all of it is bad but the roll I had was................BrandonLincoln Tombstone 225 A/C Steel StickerOld Victor O2/Acetylene setupMiller Syncrowave 250 Tig/PC-300 PulserMiller Millermatic 212 Mig HTP Invertatig 201 Giant Teck D50 Plasma cutterLots of HF grinders
Reply:Originally Posted by A_DAB_will_doScattered porosity, but almost all of it is along the centerline of the weld; the last place to freeze in the puddle.....Gas covereage in corner fillets is usually pretty good.  The base metal helps confine the shielding gas to the region around the weld.What kind of surface prep are you doing before welding?  Seems like you might have just enough contamination or scale to overcome the deoxidizers in the weld filler metal.  Or some kind of residue that is occasionally sufficient to cause some porosity.Check your gun cable and gas connections once more.  Intermittent porosity like you're showing could be an intermittent air leak...Something that only happens when the gun is pulled or twisted into a sharp angle.What's your gas type and flow rate?  Too high a flow rate could be causing turbulence and this can suck a little bit of air into the shielding gass pool.  If you're just on the edge, this could come and go, or show as a small bit of porosity here and there.
Reply:Unless it is an optical illusion the pics look like you are running a wide bead with no fill in the middle where it belongs.