Welding mistake - Fixable?

I tigged a long 6"x.250" square tube to the center of a 1/2" x 18" square plate yesterday. With our welder maxed at 300A we were able to
achieve good penetration (tested first on a scrap piece) and a nice weld. The problem is, because I was rushing (and because I'm stupid) I didn't tack or clamp down the 1/2" plate. The edges curled slightly and now I'm wondering if there is an easy way to bend the plate flat again (I'd prefer to not have to start over). I do have a 40 ton shop press available as well as a torch. I am concerned about any bending operation with affecting the integrity of the weld, although the portion of the plate that curled is beyond where the tube is centered on.
Any suggestions?
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snipped-for-privacy@signaturefactory.com wrote:

How is this 18" square plate going to be used? Does it get fastened to something? If it were e.g. going to be welded to the deck of a ship, you could simply push it flat all around with hydraulics and weld it down. If it were going to be bolted to a wooden floor, you could make up some kind of jig with a lump in the middle and use bolts all around the edges to pull it down, effecting a straightening bend.
GWE
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Grant Erwin wrote:

It will be fastened to a concrete floor. I didn't feel that the concrete anchors (sleeve type 5/8" in diameter) had sufficient strength to bend the plate down. Do you think they would?
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wrote:

run into this often building pipe supports.What we do is not straighten the plate.go ahead and place the 4 anchors,then put a nut on each one.Then place the plate on top of these nuts and place another nut on top.by adjusting these nuts you can get the square tubing to be plumb.If you do not want the gap underneath open,go get some grout at the supply store(home depot,etc) and push the grout under the base plate.
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Sounds like you have classic heat shrinkage on the welds. Are there distinct bend lines at the welds? Apply red heat to the back side of the welds along with some clamps and strong backs to bend it back into shape.
snipped-for-privacy@signaturefactory.com wrote:

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RoyJ wrote:

Yes when we measured the bend is defintely occuring right around the welds. I guess we should have preheated the plate.
Apply red heat to the back side of the

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snipped-for-privacy@signaturefactory.com wrote:

I wouldn't have preheated; I would have preloaded using hydraulics. I'm not sure, how, but imagine if the plate were set on a 1/2" thick slice of the tube you were going to weld it to, directly where the tube will be welded but on the other side, the whole thing on a very heavy plate, and heavy C clamps pulling the edges down everywhere, which would tend to force the middle up. Then put your tube in the middle of the top side, weld it up, and release everything - the plate will be flat if you do everything right and if I'm not completely mistaken.
I'm not sure what preheating would have done for you. How would that have controlled distortion?
Grant
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On Tue, 10 Oct 2006 12:21:03 -0700, Grant Erwin

Last time I did something like this..I put a chunk of 3/16 plate directly under the weld line and pulled all 4 corners down a smidge, then welded it. It stayed.. mostly..flat. Beat the shit out of the first attempt which curled like a potato chip.
Gunner
"A prudent man foresees the difficulties ahead and prepares for them; the simpleton goes blindly on and suffers the consequences." - Proverbs 22:3
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Preheat wouldn't have done any good. The problem is that you added a lot of heat to one side, the weld area shrunk as it cooled. You may be able to compensate somewhat by heating the opposite side and shinking that but the mass of your weld won't allow it to go back to the original flatness without some added force.
snipped-for-privacy@signaturefactory.com wrote:

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Actually I was thinking that preheat would reduce the cooling rate and hence reduce the shrinkage stress across the weld.
RoyJ wrote:

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Just an idea: Suppose you Vee out a square on the side opposite the weld, and then weld it up.
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This sort of thing happens all the time at our shop, If we need to take out the distortion we usualy use a press if the piece can be put into the press. As long as you don't overbend the piece and your weld is completely fused to both the tube and plate then I wouldn't worry about the breaking the weld. Or you could do what we call flame straightening!. That is simply using a torch to bend it straight again, simply put "If it was straight before you put in all the heat to distort it, then use heat to straighten it"
If my mental picture is what you are discribing then you could just run a torch along the axis of the weld just outside of the weld on the opposite side of the plate ie: run the heat on the backside of the plate. We use this technique all the time to straighten parts that have distorted due to welding.
I have also used a torch to straighten beams and tubes that came from the supplier bent and twisted.
One other thing I just thought of is a usefull tool for flame straightening is a compressed air blower connected to a hose that sucks from a pail of water so you get a spray of air and water to cool the spot that you just heated. Works great on mild steel, however can cause problems on medium or high carbon steel.
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