straighten a bent 3 1/2 tube
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  1. #1
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    Default straighten a bent 3 1/2 tube

    Years back I read an article on straightening bridge girder
    with just a torch. So I have this 3 1/2 dia 20 foot long tube in well drilling rig and looking for some old time knowledge on where to heat in relation to the Hi spot.
    If nothing else a couple of rosebuds and jacks will have to do.
    Thanks

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    How much is it bent?
    pics will help.
    When you heat steel up to a red the metal will expand, when it cools it will shrink, the key is it will shrink more than it expanded.
    So you want to heat the high side, just dont freak out when you see it getting worse as you heat it. Do not heat the same spot twice.

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    Search for the term flame straightening. The way it works is you use heat to expand an area of metal. The rest of the metal is cold, and prevents the heated metal from expanding. This essentially forces the heated metal to "upset". When the heated area then cools, the upset area is smaller than it was before heating.

    I'm guessing this tube is relatively flimsy (say, compared to solid). IME, flimsy pieces need an external strongback to get good results from flame straightening.

    More later if necessary.

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    I know a guy who works at Bath Iron Works, Bath Maine and that is his job. I forget what he's called but they straighten warped metal walls, door frames, floors, etc. after the welders are through. He said they use heat, water, and air to bring surfaces back true to hang doors and the like.
    BIW is a military ship yard.

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    Straighten girders and open sections ..yes.......straighten tube with heat shrinking? ....very careful or it will be worse,and no longer round either .Been there ,done that ,many times........I suggest tube be straightened with jacks ,strongbacks ,and fitted supports,to prevent crushing.

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    When I had bent core barrel tubes I took them to a heat treat shop that had a straightening press.

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    Stick welding can do the same job, faster, and can be more controllable. Weld an arc partway around the circumference of the tube on the long side and it will shrink as it cools. The more you weld and the hotter you weld, the longer your bead(more degrees of arc), the more rod you feed in, the more it will shrink. So start small and work up.

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    Quote Originally Posted by Mud View Post
    Stick welding can do the same job, faster, and can be more controllable. Weld an arc partway around the circumference of the tube on the long side and it will shrink as it cools. The more you weld and the hotter you weld, the longer your bead(more degrees of arc), the more rod you feed in, the more it will shrink. So start small and work up.
    Yes, and let it cool COMPLETELY before adding more rod as you get close to straight. Easy to think it is almost straight when slightly warm and after adding more weld it shrinks past straight. Then you are welding on the other side to bring it back.... Go slow and let cool.

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    I worked with a I beam straightener who would eyeball the beam than walk along with a huge torch ,. the method he said was to heat then cool slow to make the surface expand , and to cool quickly to make the surface contract so pull together.
    beams looked poor fresh from the steel mill abut after he made his walk they looked very straight.. as I remember some beams were 5 or 6 or six feet high.
    My job was drilling the sides at ends and the some times the tops at a bridge company in Gary.

    My buddy Ray had an uncle who was a ships straightener. He would go all around the world on one ship and then another with his torches. Ships having a fire would be all bent up.

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    The hot side is the short side. Which ever side you heat will get smaller dimensionaly than what it was before. Find the highest point and heat directly under it.
    The entire process works on metal expanding when its hot. If you can make one side of a 1/4" plate +400*F and the other side around 80-100*F, you are inducing some serious mechanical strain which can make Lots of things move. Be mindful of the grade of steel and it's prior heat treatment.

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    YouTube

    Keith has a few videos showing how he straightens bent shafts with a torch. He’s got it down to an art form. It works and is as described in some of the above replies. Heat high side and quickly cool cause that side to shrink. But...I’m guessing if you were to just heat th inner curved part and not quickly cool it....you get a similar result.
    I did it the other day on my drawbar which had a decent bend in it. End result is better and good enough until I get around to making a new drawbar.

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    Thanks for all the info.I have done heat and quench,cold straighten in a press. I even snapped a 10 inch shaft that wouldn't move.
    But the term upset is what I had not heard.
    So the rig is still drilling holes and haven't got to try to straighten yet.


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