What causes this? MIG issue

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Attachment 862611Sorry if it's already a subject somewhere but u don't know what to call it to search under.When I make tack welds, very rarely but sometimes I let off the trigger and a little spike/blob forms out of nowhere on my tack.I couldn't replicate it it I wanted to and it just melts off when I weld over it usually but what's the deal here? All I can think is my amps are too low or something?The picture shown was a tack on 1/8" wall, hobart 210mvp, C25 at 13cfh.www.FirehouseFabricators.comZachLincoln 210mpLincoln SW200Hypertherm Powermax 45xp2x4 CNC Plasma Table.
Reply:Seems like a gas issue because of the unshielded corner. Try wrapping your gloved hand around the nozzle when tacking and see if it helps.
Reply:Originally Posted by M J DSeems like a gas issue because of the unshielded corner. Try wrapping your gloved hand around the nozzle when tacking and see if it helps.
Reply:'Gassing out". Gasses from pollutants in the joint/material coming up through the molten weld pool. Little volcano there."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:This usually happens as a result of dirty material.  Could be due to impurities/rust in the metal itself or pulled from inside the tubing if it wasn't cleaned/ground to bare metal.If you ground it out and re-tacked, it likely wouldn't have happened again at that spot.MM200 w/Spoolmatic 1Syncrowave 180SDBobcat 225G Plus - LP/NGMUTT Suitcase WirefeederWC-1S/Spoolmatic 1HF-251D-1PakMaster 100XL '68 Red Face Code #6633 projectStar Jet 21-110Save Second Base!
Reply:Interesting. Thanks for the help.Does anyone really clean out the inside of tubing especially small 1" tubing for mig welding?www.FirehouseFabricators.comZachLincoln 210mpLincoln SW200Hypertherm Powermax 45xp2x4 CNC Plasma Table.
Reply:I at least remove any burr from the inside If I cut it with my abrasive chop saw.  It it is real crusty I might run a file in there a few times.  If you grind out the "volcano" there is a pretty good chance that it will weld OK after grinding it out.
Reply:Yep! Dirty material! I get those occasionally too.
Reply:No doubt dirty material. I have a 55 gallon drum for some steel storage and made a divider to separate the steel. I used 3/8'' zinc plated all thread rod and where the coating was heavy it did the same thing. Where it was all weathered it was fine.
Reply:If you are getting it on the first tack only, and not subsequent tacks, purge the gun before you start.Turn down the wire and pull the trigger for a few seconds, trim the wire, turn it back and go.Mine will do that if the gun has set for a while.  The gun line fills up with air.
Reply:I sometime see this when welding TIG if I simply cut power to the torch.  Molten metal literally "grow" from base metal and reach up and try to the touch the tip of the tungsten rod.  If I make a fast lateral movement, it will sometime turn and try to the follow the tip.  Of course, it couldn't get very far since it cold off quickly.  .