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camdigger 07-30-2022 12:15 PM

Flame straightening
 
This is one of the best presentations I've seen on the how's and whys of flame straightening. Most interesting to me is a brief reference to applying it to Aluminum sheet metal

A few years ago, there was a collision with a steel framed overpass bridge near here. They brought in a specialized crew and straightened out most of the damage while only shutting down one lane of the 4 lane underneath and one on the 2 lane road on top. Took nearly a month, but they got it all done in situ.

https://youtu.be/IxzV9VeUpLY

Whitetrash 07-30-2022 02:27 PM

When I was at the fab shop we built a custom size I-Beam for a steel mill crane run. The top and bottom flanges were bowed and had to be straightened before they could tacked up and welded. Two of the Old Hands worked with one of the big rosebuds with the head the size of a popcan and a stringline brought them into spec. It was pretty cool to watch.

Lowe.Buuck 08-02-2022 02:37 AM

I got interested in this topic a few years back. Not a lot of information online about the specifics.

The "Bible" on the topic is Flame Straightening Technology for Welders by John P. Stewart. 106 pages describing 36 processes with illustrations.

Welding Fabrication & Repair by Frank M. Marlow, P.E. has some information and illustrations on Flame Straightening in Chapter 4, Bending & Straightening.

Fundamentals of Flame Straightening (32 pages) is available as a PDF from Linde and BOC.

Removal of Out-Of-Plane Distortion in Mild Steel Panels Using Flame Heating by Larry Lee Janca at MIT. 164 page PDF.

One important thing to note is it takes a lot of heat. If you plan on using a large OA rosebud make sure you pay attention to the acetylene withdraw rate on your tank. You can only remove 1/7 of the tank volume per hour. If you withdraw more than that you will also remove some of the acetone from the tank.

I have a 150,000 btu OA rosebud. On a 150 cuft tank you can only use it 9 minutes per hour.

You may want to look at rosebud tips designed for oxy-propane. The tanks only contain propane and the only limitation is the rate that liquid propane converts to vapor. You need one 100# tank per 100,000 btu of torch capacity. Small BBQ tanks don't provide enough space for the liquid propane to convert to vapor fast enough to supply large rosebud tips.

You can plumb multiple propane together to supply larger tips.


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