How do I bend a 10 ton beam with heat? 3

[VelvetHammer]

We are building box beam overhead cranes and during the fab process weare getting a slight axial camber in the beam. The shop has been using heat to try and pull them straight, but with only limited success. Is there any information out there for a repeatable process for this?

 

[MikeHalloran]

Spend a day in the shop watching the actual fab.

You'll probably see a difference in how the older guys who build 'em straight in the first place do it.

Is there some pay incentive in place that would affect the fabricators' behavior? E.g. pay per inch of weld, and not, e.g. lower pay for crooked beams?




Mike Halloran
Pembroke Pines, FL, USA

 

[Bribyk]

They've already bent it one way with heat, from the weld process. They need to review their welding procedures. If they are fully welding the side pieces onto the first top or bottom flange, like |_|, it will cause the _ piece to curl upwards as the welds on top of it cool.

This camber may not be such a bad thing. Some semi-trailers are built with camber in them already.

 

[desertfox]

Hi Velvethammer

Have a look at this site it may help:-

http://www.lincolnelectric.com/knowledge/articles/content/distortion.asp

regards

desertfox

 

[berkshire]

VelvetHammer
This may sound elementary, If you are getting a known curve when the part is welded, pre-bend the part the opposite way on the assembly fixture,or welding bench before you start welding. Or if you are just fabbing on the shop floor, do it during the tack welding procedure.
B.E.

 

[VelvetHammer]

Hey guys, thanks for all the input. Let me explain my problem with a little more detail...

These box beams are typically 2ft wide, 4ft high, and about 100ft long. The web plates have a camber cut into them (about 1/8" per 10') for obvious strength reasons. We build them upside down on a jig that has the same camber. Top flange first, then stiffening baffles, then web (side plates), and finally the bottom flange. The pieces are pressed together and onto the jig with a very lage hydraulic press. The parts are all tack welded about every inch. The beam is then taken out of the jig and subarc welded (both sides simultaneously) in a perfectly flat position. One side takes about 1 hour...we then flip it over (another 10 -15 minutes) and do the same to the other side. About every 5 or 6 beams we get a camber perpendicular to the built in camber, sometimes it's only 5/8 of an inch but sometimes it's 2 inches or more!

We have allowed the beam to cool in a variety of positions, but haven't found a consistent solution yet. So, we have to use heat to manually distort the beam back as straight as possible...which is almost a guessing game because of the unknown internal stresses. We are working on the variables of the fab process, but in the mean time, I have a stack of bent 20,000 lb beams I need to straighten. Any ideas?

 

[Zapster]

Have you looked at, "Guide for Heat-Straightening of Damaged Steel Bridge Members"

http://www.fhwa.dot.gov/BRIDGE/steel/heat_guide.pdf

 

[unclesyd]

There are several ways to approach your problem. One is to hire a company that uses flame straightening as their business or hire a consultant who specializes in this area. If you have time there are several books on the subject. Here on the Gulf Coast I would look around the shipyards to find an expert in the art of flame bending.
Are there any other fabrication industries near you that might use flame bending like a trailer or bridge company. Most larger steel erection companies have one or two people that do flame straightening.

http://danrdaltoninc.com/index.html

http://www.flameoninc.com/

http://www.aisc.org/MSCTemplate.cfm...tomSource/Faq/SteelInterchange.cfm&FaqID=2024

http://www.intota.com/expert-consultant.asp?bioID=605050&perID=108390

 

[MikeHalloran]

The peening guns that you probably use for SAW slag removal can also be used to bend the beam... and are yet another item to look at in your root cause investigation.





Mike Halloran
Pembroke Pines, FL, USA

 

[VelvetHammer]

Wow! Thanks for all of the info...I now have a place to start. This will be a great help!

 

[chicopee]

If you have any contact with your state DOT people who are involved in federally funded bridge construction, talk to them abut where references may be available. One company in Ct. that I use to work for was involved in girder fabrication whereby one procedure was to instill cambers by flamme treatement using Chemolene torches. I was never involved in this procedure however there is published material that the company was following.

 

[Tmoose]

"The web plates have a camber cut into them for obvious strength reasons."

I think camber is cosmetic, so the beam is straight when loaded, not for strength.
Arches are strong only when the ends are restrained from scooting outward.

 

[chicopee]

Cutting a camber on a web plate is fine,however, with the flamme treatment there was an advantage but I don't remember what it was. As I said there is literature and technical papers available.

 

[tbuelna]

VelvetHammer,

If your fab process involves welding, the first thing you should do to guarantee repeatability is to create a weld schedule that defines a detailed, step-by-step procedure for welding. It should include joint prep, machine settings, tooling and fixturing, pre/post heating, filler wire, and sequence of welding.

The distortions in your beam are due to residual strains caused by uneven heating/cooling during welding. They can be minimized or controlled by using a defined welding process, or they can be relieved post-welding by a thermal or mechanical stress relief. The drawback of trying to straighten a weldment that has not been properly stress relieved is that the strains in the material produced by welding do tend to relieve themselves over time, especially with aluminum weldments.

If it is not practical to perform a thermal stress relief on your weldment, you might try something like vibratory stress relief:

http://www.meta-lax.com/Home/Technology/technology.html

Good luck.
Terry