question about mig welding fault .. why it happens

admin

hey i recently been using the mig welder on small square tubingwhen i finish the weld, the metal is red hot but sometimes when i finished welding, it appears that something grows out of the red hot area, like a little worm coming out or  somethingIm pretty sure it some sort of porosity, is it possible its cause by a lack of gas at that particular spot?Can anyone tell me why this happens?Thank you in advance
Reply:I think it is trapped gas coming out while the weld is cooling...BobBob WrightSalem, Ohio  Birthplace of the Silver & Deming Drillhttp://groups.yahoo.com/group/southbend10k/http://groups.yahoo.com/group/sawking/1999 Miller MM185 w/ Miller 185 Spoolmate spoolgun
Reply:ah i can see how this could be the caseis it because theres to much gas volume coming out or welding to quickly?the mig welder i use is hooked up to an outside source with no control over pressure output
Reply:Its from no gas. When you release the trigger, the electricity and the cover gas stop flowing. The weld puddle, while still red hot, is exposed to oxygen in the air. This oxidizes the puddle, resulting in a slag spot. If your machine had a post flow setting for the gas, this wouldnt happen. Try reversing back onto your weld just a bit and it will help...
Reply:It'll do that when you're closing up tubing too. Lots of quick heat, the air inside expands and vents out.
Reply:I just welded up a 1" alum cube for fun. But when I 'sealed' the chamber, it blew out on my tungsten. I thought that something as small as 1 cubic inch would have reached it's max expansion before I got to the last sealing. It didn't. Drill a hole somewhere else to let the pressure out.Last edited by Craig in Denver; 07-26-2008 at 01:05 AM.9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:I have heard both explanations before,  I was told to hesitate before pulling the gun away from the weld.  If you are welding new tubing there is oil inside, hence what Sandy said.Give more detail about your weld, are you sealing it up.
Reply:Originally Posted by Craig in DenverI just welded up a 1" alum cube for fun. But when I 'sealed' the chamber, it blew out on my tungsten. I thought that something as small as 1 cubic inch would have reached it's max expansion before I got to the last sealing. It didn't. Drill a hole somewhere else to let the pressure out.
Reply:well .. my employer isnt concerned about quality, its more about production (which i total disagree with) but i was told i was to slow doing quality , so i said ok and just throw it on there like every one else nowneedless to say, i wont be there long. i dont want to obtain these bad habitsand i was just wondering for my own knowledge why this happens, Thanks for all the posts
Reply:TEK:Since I'd like to show it off to the buddies, I'll try to patch the 'blow hole' now that it's cooled (and the tungsten is reground ).9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:Sandy is correct.  Seen this a hundred times.  JGSMAW,GMAW,FCAW,GTAW,SAW,PAC/PAW/OFCand Shielding Gases.  There all here. :