Metal distortion with gas welding

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I am building a wrought iron railing out of mild steel tubing, using a oxy actl torch. Yes, I know arc, tig, mig would be better, but I don't have those.Each section has a 4-sided frame of 1 5/16" square tubing (065) which will then be filled with 5/8" square tubing pickets spaced about 4" apart. The longest section is 12 feet.I had no real problems welding up my frames, but I did notice that the rails had to be well supported or the whole thing would sag slightly when I welded the corners. I was able to straighten out the slight bends by jumping up and down on it a bit.The real problems started when I began adding the pickets. The top and bottom rails started showing some up and down curve every time I added a picket, so I decided to tack them all in place first using as little heat as possible.Even tacking them in added some distortion to the rails. I can live with it but I don't want it to get worse.I fully welded one short section and it is not acceptable. Too much wave in the rails.As far as I can tell, what is happening is as I weld a picket, it grows in length and actually dimples the wall of the rail being heated. When it cools down it the rails pull together, giving the roller-coaster look. How should I have built this railing, and is there any way to do the long section without ending up with a roller-coaster.
Reply:Hey TNS 1, howdyado? Heat distortion is most pronounced with torch welding, especially compared to other methods like arc welding. Even arc welding though will distort a gate, or fence section. I have not figured this one out either, but I would guess it entails the extensive use of jigs to clamp the whole assembly on a sturdy surface. All my projects of this nature so far have become warped. Unfortunately, I don't have the advantage of a great, big, layout table to prove or disprove my theory. Good luck.Anybody else got an edumacated idea? Last edited by tanglediver; 08-19-2010 at 12:32 AM.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:This is the biggest welding project I have attempted. I have no easy way to clamp this to anything, it is just too big. Even if it was clamped I wonder if it would solve the problem. There is a lot of force involved to cause that bending. For welding the frame I laid the rails on bricks out in the yard and used a level to make it as flat as possible. As I said, that part worked out OK. The pickets are so much smaller compared to the rails that I am surprised they are giving me grief.I was hoping there would be a smart method for the torch. One idea is to use a bigger tip and try to do just a little at a time. Another idea is to weld all the pickets to the bottom rail first without the top rail in place. That way the picket has nothing to push against and distort. That would not help with the top rail though. The last idea is to rent or borrow an arc welder. From what I have read about arc welding, the area you heat up is smaller and easier to contain. Also I believe it can be done quicker so the heat does not travel as far. Maybe someone will pipe in and let me know if this is correct.
Reply:you can't beat physics but you can try minimise the effects.try clamping 2 of the frames against each other with a small packer in the centre so that the bow runs the other way. this might help counter the pull of the weld. also make sure you stagger your welds so the heat gets applied at differing spots each time, and only lay down absolute minimum weld material you can get away with.you can use the oxy to straighten the job after its welded by applying heat to the opposite side of the joint. with any luck the shrinkage will pull it straight, and if not then add a little gentle persuasion with a good hammer while the job is hot. i always try to think of steel as a liquid material- it moves like taffe when its hot.hope this helps mate, good luck and apologies for the rambling....Last edited by stamp; 08-19-2010 at 06:09 AM.
Reply:Thanks, that does give me some things to try. I'll try working on the fully welded section first to see if I can straighten it outSince the main problem is the rails pulling together as the picket shrinks, I'll try heating the outside of the rail as you say. I am reluctant to take a hammer to it, but I do have a small hydralic jack I could place beside each picket. I'd prefer to avoid the distortion in the first place, but if I can find a good straightening method that does not take too long, that is almost as good.
Reply:move around, dont get any spot too hot...you could also try to put heat on the opposite side of the warp to pull itback..
Reply:In the future, use a jig.  Make sure all pickets fit properly and parts (rails) are securely held in place and supported. Properly fit mean no forced picket or no gaps between picket and rail.      Even if you build in "air" you could use some pipe clamps.
Reply:Properly fit mean no forced picket or no gaps between picket and rail.
Reply:OK, so I picked up one of those cheap 90A flux core wire welders. There is no heat problem now, but it produces the most butt ugly welds you have ever seen - spatter everywhere, slag and 'dog piles'.  I am no pro, but it seems to be a lot easier to shape a weld and create a fillet with a torch, plus you can actually see what you are doing. The wire welder seems able to create a strong weld, but there is no chance of a fillet, since it piles on way too much material. This just requires more time with the grinder than it took to create the weld. I keep wanting to turn the feed down more but it is already at minimum. I have tried changing the feed and current setting, but I don't see a lot of difference in weld quality.
Reply:Heat=Distortion.  Really no good way around it except planning for it, or repairing it with heat.  Even restrained joints will "spring" when released, or the weld will crack sometimes if the built up stress is excessive."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Those cheap HF machines can often be a PITA, especially if you don't know how to use it to begin with. Personally you would be better off with a mig with gas, as it's much easier to see what you are doing and it handles thinner materials better. Post up some picts of your welds and we might be able to make some suggestions.Even without seeing the picts I can probably make a few guesses at some of your problems. 1st it sound like you need more heat to get the toes to fill in more and smooth out the bead. Try setting the machine to a higher heat setting and doing the weld. Yes that may cause the heat distortion to raise it's ugly head again, but thats just the way it is. This is where sometimes a machine with infinite adjustments can help as opposed to tapped voltage settings. You get a bit more control. You should be able to turn the wire down to zero. If you can't, I'd chalk that up to the cheap design of that machine. Hate to say it, but you get what you pay for. As far as the slag and spatter, thats the down side to FC wire. I've never had much luck with small welds and slag. Usually it's tough to get the material hot enough for the slag to come off easily with stick. I have a gas mig, so I almost never run FC wire.Small pieces like the pickets can often be welded with "spot" welds rather than a more traditional type of bead. Set the gun where you want it and just make one puddle, then move to the 2nd side and make another. It's often how you see production fence done. The down side is that moisture can get in between thru the gaps.It's been years since I did much O/A welding, mostly brazing. I'd have probably tried to deal with the heat issues you had before the same way I'd do it with tig. Turn the heat down and go smaller. Try to run a smaller tip and make the puddle as small as possible. I assume it's mostly decorative fencing, so as long as the metal stays together, you really don't need strength..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Originally Posted by tns1OK, so I picked up one of those cheap 90A flux core wire welders. There is no heat problem now, but it produces the most butt ugly welds you have ever seen - spatter everywhere, slag and 'dog piles'.  I am no pro, but it seems to be a lot easier to shape a weld and create a fillet with a torch, plus you can actually see what you are doing. The wire welder seems able to create a strong weld, but there is no chance of a fillet, since it piles on way too much material. This just requires more time with the grinder than it took to create the weld. I keep wanting to turn the feed down more but it is already at minimum. I have tried changing the feed and current setting, but I don't see a lot of difference in weld quality.
Reply:I finished welding all the pickets. Once I found these key things it went very fast. 1) With this 16ga mild steel tubing, set power to low and feed ~52) clean the tip whenever it starts popping and you can't make a bead3) keep the ground a few inches from the weld - I moved it to each picket 4) always drag (lead) the weld. You can't see the bead while pushing My square pickets were all set with one edge pointing forward instead of presenting a flat face. I think this made it easier to weld all the forward edges on the front side and then all the rear edges on the back side. I used a wire wheel and angle grinder to clean up all the mess created by the first weld session before starting the second. I used up a whole roll of the Lincoln 211 0.030 wire and had to switch to the original HF wire for the last few welds. Surprise, surprise, it worked even better. It was much easier to start a bead, and clearly was a hotter weld. I did punch thru a couple of times, which never happened with the Lincoln wire.I did use the anti-spatter spray which helped some on cleanup, but I guess you just have to plan for a lot of grinding for those messy welds.
Reply:Yeah, flux core is a drag, see that's a pun, sort of a ... oh nevermind.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:All my welding is O/A, and I agree that the welds are a LOT prettier than what I have seen from the low end MIG setups.Pre-heating the rail before welding in the picket might help BUT the rails may deform from the preheat as well. The more uniform the heat the less non-uniform distortion - with the exception that latent stress from milling may release under heat (tough to anticipate that one).Spend as little time as possible on each weld.  A larger tip will heat things more quickly and reduce the HAZ - you just have to be careful with the distance from the work to avoid burn through.  Also consider less welding - one or two tacks will probably be sufficiently strong for the pickets.  If you doubt this use a piece of scrap rail and scrap picket material, hit it with one or two small welds and then try to destroy it.  I suspect that you will be surprised at how strong it will be (assuming you fuse the base metal).Hobart LX235Victor 250 Oxy-Acetylene Rig (welding and cutting)Bobcat 773F-350, 1999, 4x4, 16' 10K# trailerOutdoor Wood Burner - 10 cords/year