Polarity

admin

I have a Millermatic Challenger 172. I recently tried some flux core, then changed back to solid with 75/25. I welded up a fence panel out of 16 gauge square tube, everything seemed to go well, the welds are good and strong, no burn throughs. Then I noticed the welder was still on straight polarity from the flux core, I had forgotton to reverse the polarity!But like I said my welds are strong and penetration looks good. The only thing I noticed as I was welding was that it was just about impossible to burn through. I thought it was because I was getting better, but now it tells me there must be less penetration with straight polarity on solid wire.So should I grind it all off and start over? Are there ever times when using straight polarity on solid wire with gas is desireable?
Reply:Straight polarity, direct current electrode negaitve (DCEN), can be used for solid wire MIG in an application such as surface cladding of stainless steel over carbon steel where it is important to limit penetration and dilution of the weld for metallurgical reasons.  I know this is true for pulsed MIG which I have seen run just fine, I do not have first hand experience with conventional MIG on DCEN.  It sounds like it ran well for you.
Reply:I guess if you turned it up far enough maybe you got enough penetration/fusion for the welds to hold.  I would weld up a similar joint to the ones  you did on the job on some scrap material leftover from the job and do a destructive test and see what happens.  If the destructive test results seem strong enough for a fence to hold up, then no problem.  If not, well then I guess you have a very big, unfortunate mess on your hands...MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:I’ve forgotten to change polarity with flux core and the bead was a mess, porous, cold and lumpy.
Reply:Originally Posted by DesertRider33I guess if you turned it up far enough maybe you got enough penetration/fusion for the welds to hold.  I would weld up a similar joint to the ones  you did on the job on some scrap material leftover from the job and do a destructive test and see what happens.  If the destructive test results seem strong enough for a fence to hold up, then no problem.  If not, well then I guess you have a very big, unfortunate mess on your hands...