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billfunk29 04-18-2016 01:13 PM

Flame straightening
 
I stumbled across this document for flame straightening metal. Mostly aimed at thicker sections, but does a good job covering basic thermal behavior of metal. Good advise for any car guys narrowing rear axles.
https://www.boconline.co.uk/internet...410_113398.pdf

JimRussell 04-18-2016 01:23 PM

Quote:

Good advise for any car guys narrowing rear axles.
Hi Bill,

It works great aligning wheeling machine frames too.

Gojeep 04-20-2016 06:49 AM

I used these techniques when straightening my frame after fully boxing it and repairs on the Willys.

weldtoride 04-21-2016 07:37 PM

Similar article from our old uncle:

http://www.fhwa.dot.gov/bridge/steel/02.cfm

excerpt for those not wanting to read a lot:

2.3.1 Vee Heat

The vee heat is the most fundamental pattern used to straighten strong axis (category S) bends in steel plate elements. As seen in Figure 6, a typical vee heat starts with a very small spot heat applied at the apex of the vee–shaped area using an oxy–fuel torch. When the desired temperature is reached (usually around 650°C or 1200°F for mild carbon steel), the torch is advanced progressively in a serpentine motion toward the base of the vee. This motion is efficient for progressively heating the vee from top to bottom. The plate will initially move upward (Figure 6a) as a result of longitudinal expansion of material above the neutral axis producing negative bending. The cool material adjacent to the heated area resists the normal thermal expansion of the steel in the longitudinal direction. As a result, the heated material will tend to expand, or upset, to a greater extent through the thickness of the plate, resulting in plastic flow.
At the completion of the heat, the entire heated area is at a high and relatively uniform temperature. At this point the plate has moved downward (Figure 6b) due to longitudinal expansion of material below the neutral axis producing positive bending. As the steel cools, the material contracts longitudinally to a greater degree than the expansion during heating. Thus, a net contraction occurs. The net upsetting is proportional to the width across the vee, so the amount of upsetting increases from top to bottom of the vee.
http://www.fhwa.dot.gov/bridge/steel/images/fig6.gif
Figure 6. Stages of movement during vee heat.
This variation produces a closure of the vee. Bending is produced in an initially straight member, or straightening occurs (if the plate is bent in the opposite direction to that of the straightening movement, Figure 6c). For many applications, it is most efficient to utilize a vee that extends over the full depth of the plate element but, partial depth vees may be applicable in certain situations. When using partial depth vees, the open end should extend to the edge of the element. The vee depth is varied by placing the apex at a partial depth location. The most typical partial depth vees are the three–quarter and half depth. Applications for partial depth vees will be discussed in later sections.

SWT Racing 05-02-2016 07:27 PM

1 Attachment(s)
I have done this on ERW and DOM tubing structures a number of times. I tried it with limited success a while back on my planishing hammer frame, but I couldn't get it hot enough with MAPP gas. I'll have to bring our small oxy/acetylene rig home to finish it.

Attachment 37349

dwmh 05-03-2016 03:01 PM

Great article Bill, well explained.

Regards
Dave


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