Major Problem welding hot roll steel with mill scale

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I have been welding hot roll steel for years and never had this problem. I am getting major porosity and bubbling while welding this corner. My press brake vendor totally screwed up the size of the notch so I now have to fill this gap. The gap is a pain in the *** but not a problem. The problem I dont think is related to the gap I am having to fill. I could be wrong but I have filled some major gaps before both with and without the use of a copper backer.I am getting major porosity. I have thoroughly cleaned the tip of the MIG gun. I am getting none of this problem when I immediately go weld mild steel tubing. Only when welding this hot roll.I am even prepping the outside and inside of the joint. I am using a dremel on the inside and, granted, only stripping away about .25" of mill scale on the inside. I have a ton of these pans to weld up. Any ideas? Can there be a problem at the steel mill with content of the metal? I am cleaning the metal with water, Dawn soap and acetone.Thanks, joelsee picsyou can see the bubbling start in this very first weld
Reply:Are you getting a heavy gas surge upon starting? You might have your gas flow to high. Putting a gas dam around your corner to hold the gas may help also. Is that block alum? Why such a big gap? A bend relief would have helped tighten that joint if the corners were notched less.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Looks like you are trying to fill the gap in one pass..What I would do is do each end one pass at a time until they meet in the middle.Trying that big of a gap never works out correctly with one big "Blob" pass in the middle......zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Jimmy_popThis is an unhandy fill condition.Down-hand [on a broad joints] behaves this way - essentially there isn't enough parent metal to chill the puddle.Consider these options.First: .024 wire and situate the corner straight-up so the joint is flat.Turn your heat down a smidge.  Start at the flange corners, and run a wash-pass inboard to the top.Second:  Same position but run two passes horizontally, again starting at the flange corner and run inboard to the top.Pause momentarily between passes for chill.Third:Experiment with three passes - left, right and center.Running, out-board-in, provides a heat-sink for the thermal gradient, and: two passes will result in greater fill depth at the apex of the corner.If ultiple passes proves better fill, tilting a little off straight-up mayprovide a better shoulder for each pass.Opus.Last edited by OPUS FERRO; 09-10-2014 at 02:11 PM.Reason: Door #3 . . .
Reply:Just guessing but is it possible that it has something to do with the expanding air between the puddle and the backing plate? The orientation could then play a role as well. If the plate was upside down and you were welding from the bottom and up you couldn't trap any air.The reason I was thinking along these lines is that the weld looks kinda similar to when you're welding something that is closed from all sides. Then the hot air can't excape and wants to bubble out through your puddle.
Reply:Had this myself, agree with zapster in building up sides.
Reply:Get yourself a piece of aluminum angle like 3x3x3-8 inch and clamp it on the outside or the inside depending on which surface needs to be flush. 2 or 3 smaller beads would be better than 1. If you don't cover the backside you will keep getting porosity and inclusion with that big of a gap.
Reply:I really really do appreciate the thoughts you guys shared. I will re-read and look at each of them again tomorrow and I try again to weld these corners. I did adjust gas higher and lower. Since the metal is 12ga., I did try welded squarely on the side edge thinking I would build up the left and right until they met in the middle. The instant I started to weld on the open edge of the open corner, it would instantly bubble up. As a test, I did a spot weld on the mill scale out in the open, flat area and there was no problem. it welded like normal. Something about welding in or anywhere near that open joint it does not like.Tomorrow I am going to source some stainless steel 3/8 x 1" set screws and use those as a filler/backing plates. It wont really matter that the set screws will get welded into these parts.I did successfully weld the corner closed without any problem with the TIG and silicone bronze. The just takes forever. I did vertical down starting in the center of the top and worked the 1/16" SiBr rod left and right and weaved the gap closed. It felt like it welded fine. I built it up so that I could flap disc the corner smooth. Looked ok. I wasn't really trying to make the weld look good since I was not confident it was going to work.
Reply:Have you tried using a piece of say 1/2 copper pipe to back the weld? I'm guessing you are getting venturi effect O2 drawn in as the gas blows through that gap. Sent from my HTCONE using TapatalkUsing Tapatalk
Reply:Yeah, the first photo shows a copper backer in place and the bubbling starts immediately.
Reply:Sorry, I completely missed it.  Does it act better if you approach from one side to the corner?Sent from my HTCONE using TapatalkUsing Tapatalk