Old dog just learned new trick so I thought I would pass it along. Newly hired panel man was replacing the rusted out fender bead on a 69 Camaro and he blew cool air on the opposite side he was welding on and ended up with no mess and no warping. I have held a sponge/rag soaked with water doing this but it is messy. Have also used air but would weld short bead and then blow with air on the newly welded bead area. His way is much faster and doesn't blow away the shielding gas. Now if I just FELT smarter.
Interesting new trick... I've always used the messy water-soaked rag method too. I had an uncle who worked for Allison engine company as a welder. They were having trouble getting super clean perfect welds on jet engine parts. They made a way to blow shield-gas in from both sides and stopped their problem. I think they were probably welding exotic metals, and the boss didn't want any of it going to the scrap-bin.
Using an internal backing gas when welding stainless and other non-carbon steels is pretty much S.O.P. when the design requires the internal weld to not be contaminated by atmosphere. But blowing shop air on the back side of a carbon steel panel is a new one on me too? Very interesting. Is your new panel guy using a tight weld prep joint and then using some type of backing purge tape to keep the air from blowing away the shielding gas? John
At the time Uncle Marvin described this to me I thought it was some new "cutting edge" procedure. It was back in the mid-1970s, I think, when he told me about it. Funny how I remember some things from long ago as clear as yesterday, but, forget things more recent.
John, When I watched him he was welding the inner fender back onto the outer so there was no gap to contend with. You are right, it would take a very tight gap or a lap weld to keep the shielding gas from blowing away.
" Smart " Well Evan ; You're smart enough to learn a thing from that kid who prolly dropped a ciggy butt on your lawn........ . FWIW , I learn from the kids all the time , they're more often right these days . Of course , whenever they find some really old sick puppy , they bring it to me for sorting out .
There are a number of manufacturers, such as Aquasol Fibak Fiberglass Weld Backing Tape If you do a Google search for weld backing tape you'll find lots of options. John
