Reheating welds fix things?

[cycsf]

I am wondering if I can reheat welds to have it realign itself, it is for a small scale bridge designed by students to bring into competition. The welds were kind of touched up with a tig, and the results were not good, so members of the bridge have shifted and caused the connections to not fit right, so I am wondering if there is a way to reheat the welds to have everything sit back in place, like to have something support the middle of the bridge while the reheating of the welds are done, probably with several torches to have the the entire section of members to be heated at the same time.

Thanks, hope to get some opinions

[Dualie]

Pictures of the conditions were dealing with would help.

[cycsf]

unfortunately a picture can not be posted due to competition, its an under truss bridge, each section has 2 set of webbing XX imagine that the connections is at the middle of the x's and the top and bottom is the deck and under truss. each section has two connections to it. so at the current state now, the connections don't line up well without using some force to push it in place, their about 1/8inch to 1/4 inch off, so I am wondering if reheating welds is even possible to fix it.

[stamp]

wouldn't it be easier to weld some temporary supports to hold it all in place, then gouge or grind out the welds, realign the job and reweld the whole thing?

[cycsf]

sounds like a plan, probably should have used that from the start, wonder if there is anything else easier/quicker?

[4on12]

More information is needed to give an accurate solution.
What material are you working with? 1-1/2" X 1-1/2" X 1/8" angle iron will require a different approach than would 2"X2"X.095 wall tube. Aluminum, stainless steel, mild steel?
How long is the material that you are using?
With mild steel you can heat the side opposite the weld to relieve some of the stress that causes the metal to "pull". This can be tricky though. It can be easy to get to much movement and end up with a bigger mess than when you started.
If you have some left over material, mock up a test weld joint and try heating the back side of the welds to see what happens.
Stainless steel and aluminum are not as forgiving as mild steel when it comes to flame straightening.
If you have access to a good hydraulic jack or a porta-power type jacking system you can force the parts beyond what you need and then let them spring back. An example would be if you need 20" and you have 19-1/2", force it to 20-1/2" then let it CAREFULLY relax and see what you have. If you still have 19-1/2" then force it to 21" and see what you have. Keep spreading and checking until it relaxes back to 20".
Good luck and keep us posted.






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[Rhyno]

Originally Posted by cycsf

I am wondering if I can reheat welds to have it realign itself, it is for a small scale bridge designed by students to bring into competition. The welds were kind of touched up with a tig, and the results were not good, so members of the bridge have shifted and caused the connections to not fit right, so I am wondering if there is a way to reheat the welds to have everything sit back in place, like to have something support the middle of the bridge while the reheating of the welds are done, probably with several torches to have the the entire section of members to be heated at the same time.

Thanks, hope to get some opinions

It sounds like you are asking for POST Weld Stress Relieving/Heat treatment. Depending on where you live, that service should be available. Unfortunately, I don't comfortably, understand the technical moves for the process. I don't know how to tell you to do it, or the recipe.

-Rhyno

[weldbead]

sounds like you wanna sofeten it up, push it back where it belongs, and nail it? it probably will move all over hell and get worse rather than better.\good luck to you.

[weldgault]

It will be better to start over. I have heard of to many failures in trying to do what you are trying to do. JG

[farmersamm]

FORGET ABOUT THE WELDS

You have now entered the wonderful world of flame straightening/heat shrinking.

Get a book on it, or look it up on the web. Fascinating stuff

You CANNOT weld without being conversant in heat shrinking, believe me

You create distortion with heat, and you fix the distortion with heat

[tanglediver]

Call for artillery support!!

[Crawford]

Originally Posted by farmersamm

FORGET ABOUT THE WELDS

You have now entered the wonderful world of flame straightening/heat shrinking.

Get a book on it, or look it up on the web. Fascinating stuff

You CANNOT weld without being conversant in heat shrinking, believe me

You create distortion with heat, and you fix the distortion with heat

any book the holy bible of them all? or is one just as good as another, i would love to learn as my classes i don't believe are covering that topic.

[Metarinka]

http://www.google.com/search?hl=en&c...:1&sa=N&tab=wp

start looking around there's books and information bulletins on it. I don't have access to my resources but I used to have about a 2 hour class that i taught my welders/fabricators on how to flame shrink and straighten properly. It's powerful but I prefer to weld it right the first time so you don't have that problem.

[Crawford]

Originally Posted by Metarinka

http://www.google.com/search?hl=en&c...:1&sa=N&tab=wp

start looking around there's books and information bulletins on it. I don't have access to my resources but I used to have about a 2 hour class that i taught my welders/fabricators on how to flame shrink and straighten properly. It's powerful but I prefer to weld it right the first time so you don't have that problem.

good to know either way if someone comes to pay you to fix another persons mistakes! thanks for the link.

[mjhughes]

Wood doesn't deform with heat. Might be able to clamp to a nice thick piece of maple while you heat it up and draw it straight with clamps. As far as the ensuing fire goes, I've found it best to call 911 ahead of time for prompt service.

[farmersamm]

Lincoln's Procedure Handbook of Arc Welding has a chapter devoted to heat distortion, ways to alleviate it, and heat shrinking to cure it. It's all in the Bible

[Baila La Pinza]

Your best bet would be to go to a local fab shop and offer one of the experienced guys a drink to heat treat it for you, he/she'll probably be able to fix it for you in about 10 minutes with the gas axe, where as, if you don't know what you're doing you'll end up in a worse situation than before.