Flame bending ss questions

JimMoser · Oct 24, 2018

I am trying to straighten out these hand rails that I didn't build , initially I was going to shorten the two center stanchions but thought I would try flame bending as they looked to have too much sheer in them , first one turned out perfect after two attempts at spot heating the reverse way I wanted it to bend but the second one is stubborn. Still trying to get one end down 1/2 inch. Is it better to just put a few heat spots at a time or is heating the whole distance a better or worse technique. I wish I had an 8 ft. Welding table to clamp it to and then use a porta power but thought I would try the heat technique but I don't have much experiance heating . 1 1/2 inch schedule 40 ss pipe. Appreciate any suggestions.

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adama · Oct 24, 2018

Have you got anything you can clamp it too, hell even a decent ratchet strap? Putting some pull in the way you want it to go will help it move a fair bit more. Gotta make sure your getting the spots hot enough too, you need to get it so it expands, then gets soft nough that it relaxes the push, then and only then as it cools will it pull back tighter and straighten.

You seam to just be spot heating the top, for that, i would go further around the sides a bit, say a hot spot covering the top 1/4 of the tubes dia in that pic,

Rob F. · Oct 24, 2018

What to they bolt down to when installed? If concrete the last 1/2" will suck down with the bolts.
As adama said, you can use a ratchet strap (2" wide) or come along to help pull into shape. Put as tall a spacer on the center feet and go over these with strap and attach at each end to pull them into straight. Try not to heat the same place twice.

Ken hosford · Oct 24, 2018

If it bolting to concrete it should be straightened , 2 chains, bottle jack and beam . your bend is the welds at the tee shrinking . So put bottle jack at the tee and restrain a couple of feet apart . if no beam got a fork lift ? it"s fork may be enough .

Jim Moser · Oct 25, 2018

I got it , thanks Adama, I did use a pipe clamp and a little more heat around the perimeter. I originally tried to use a come along but it just bent the legs in , so had to straighten them back. these are bolted into bulwarks on a crab boat , They would pull down fine but the owner is a little finicky so just obliging. I guess the reason for the post was just what the best practice is ? Seems like spot heating is preferred to heating over a long distance on the pipe, Just curious about the reasoning ?

Bondo · Oct 26, 2018

So I read this an hour ago, and I just realised that the original bow is the wrong direction if the weld caused the curve. Adama is right about how much heat, but I'm just confused on how they were bowed.

I have a heavy w12x 26 beam left over from a job 20'long and I use that to help straighten things. Use 2 heavy ratchet straps and a bottle jack or porta power to push.

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adama · Oct 26, 2018

No the issue is not spot or localised area heating, issue on stainless is you don't want it to get that hot and cold too many times as the grain growth will make it lose a lot of its corrosion resistance and can taken to extreams make it even brittle too.

The whole goal with heat straightening is to make that localized spot swell yet constrain it with the cold steel around it so it has to swell, not just expand, then and only then will it shrink smaller once it cools back down.

Jim Moser · Oct 26, 2018

yes Bondo, the curve is oppisate to Normal distortion, usually get a bump around the stancion bird mouth, I usually restrain it with a clamp setup while welding to keep it straight. The picture shows it just after heating it so it bent farther but came back close to desired shape. just one end was stubborn and the bar clamp solved that. Don't think I would like to do this with polished SS but this is just workboat pipe railing.

gary-sc · Oct 26, 2018

Jim, I didn't see the original post was from you. I'm around the corner from you on 17th ave, if you need to bring it in any closer you can borrow my welding table, clamps and 20 ton enerpac setup.

On flame straightening, heating a smaller area works best for me. I find cooling the heated area down fast with a spray bottle with water in it helps to get more movement. I don't use an OA setup for heat source, actually TIG is my preferred heat source because I can keep the heat focused.

adama · Oct 26, 2018

gary-sc said:
I don't use an OA setup for heat source, actually TIG is my preferred heat source because I can keep the heat focused.

For the odd stainless i have done i did the same, keeping the argon flowing and the largest gas lens i had worked pretty dang good on the polished 304 tube too, good enough simple polishing paste brought it back to beutiful! Normally though when im applying heat to straight it has always been big ugly steel sections.

Illinoyance · Oct 26, 2018

I see the spots you heated. Heating to the left of the upright with the clamp on it may have compounded the problem. Try additional heating close to the upright with the clamp on it, but to the right side. Heat the top 90* of the pipe to red heat and allow it to cool. If that has not moved it enough move to the right a couple inches and repeat. If necessary move right a couple inches and heat again. The most effective spot to heat is in the 6 to 8" adjacent to the post with a clamp on it. Heating to the left of that post will also tend to bring the far right post up to the board you have clamped there.

Just realized there were two ends that need to be straightened. Repeat the same thing next to the post nearest the far end.

Bondo · Oct 26, 2018

I straighten shafts using tig all the time. I use my air compressor to help control the move as the closer the shaft gets to straight, the more and colder air I put on it to cool it down.

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Jim Moser · Oct 26, 2018

Thanks for the offer Gary , Got it close enough though and it was a good learning experiance watching the metal move.

PlasmaOnTheBrain · Oct 26, 2018

When you guys use Tig to heat straighten, are you forming a puddle or just striking an arc and holding at 5-10 amps and moving around before the metal melts? Never tried it my self, kinda curious how it works.

I've straightened 3/8" stainless plates with oxy/fuel before, tried to keep from getting much above a dull red (in darker/shadowed areas) to avoid any issues. Keeping the "other" side of the heat cold helped, as did having a bunch of weight on the part in the direction it needed to go.

adama · Oct 27, 2018

^ Balled tungsten from alu welding, then as many amps as you can get with out forming a puddle, kinda everything you can do to not get penetration. As a rule i do it with the pedal and find you have to back off as you get near red heat, you need to practice on some scrap.

Have also used the tig as a heat source when setting riveting, also when upsetting ends on smaller rods, with the tig you make damn near a molten ball on a 10mm rod in seconds, then hammer it into a form - dolly fast, it goes very very fast and productively.

gary-sc · Oct 27, 2018

adama said:
^
Have also used the tig as a heat source when setting riveting, also when upsetting ends on smaller rods, with the tig you make damn near a molten ball on a 10mm rod in seconds, then hammer it into a form - dolly fast, it goes very very fast and productively.

Never thought of using tig as a mini forge, thanks Adama I will definitely use that one.

I don't heat anywhere near to molten with heat straightening. not sure of the amps because I usually just set for 25 and use the pedal to control heat, but I don't think I've ever gone anywhere near full pedal. Next time I do it i'll get one of my guys to watch what the actual amps are.

Bondo · Oct 27, 2018

Flame straightening is just like welding, practice, practice, practice.

When I straighten shafts, if I'm doing a non critical shaft, instead of getting red hot to pull a lot, I will add filler wire and that will pull 3x more then just heat alone ever could. This helps from adding too much heat. Then just grind off. If it's critical, you can only make the smallest of small puddles, but it's better to have control over small heats then a large overall heat at times.

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PlasmaOnTheBrain · Nov 3, 2018

adama said:
^ Balled tungsten from alu welding, then as many amps as you can get with out forming a puddle, kinda everything you can do to not get penetration. As a rule i do it with the pedal and find you have to back off as you get near red heat, you need to practice on some scrap.

What polarity are you running that on? I could see cases for all 3, AC being the hardest to justify.

adama · Nov 4, 2018

Just std steel welding settings, theres no point with AC or reverse as your then just dumping more the heat in the tig torch. You want the heat flow to go to the work still to make it hot, i just find the natural wander of a balled tungsten reduces the molten spot risk - helps disperse the heat.

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