Subject: Heat warping (was: MIG, what is wrong?)

From: Michael Spencer <[email-masked]>
Date: Tue, 16 Apr 96 14:29:40 EDT

Joe McGlynn wrote:
> Just to stir up the pot, anybody have an idea why metal "warps" when
> you weld it?  My view is that localized heating of a part causes a
> couple of things to happen.  First the metal expands in that one area.
> The metal also gets "soft".  The outward expansion of the heated area
> presses against the cooler surrounding area and the softned metal
> actually "shrinks" in the heat affected zone

There's an old trick for straightening pipe. Heat the convex side of
the bend with a torch. The bend in the pipe gets *worse* because the
metal on that side expands. But, because the heated metal becomes
somewhat more malleable than the rest, the unheated remainder acts as
a press or clamp and compresses the heated metal. When the pipe cools,
it returns to a position straighter than before heating. Judicious
repititions of the process can get a pipe to as close to dead straight
as is usually required for such sections. The same trick works with
heavy solid sections too, but the greater heat sinking effect makes it
harder to control.

- Mike

-- 

Michael Spencer               (902) 543-8375
[email-masked]
URL: http://www.mit.edu:8001/people/mspencer/home.html
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From: [email-masked] (Gene Olson and Chris Wilson)
Date: Tue, 16 Apr 1996 14:48:17 -0400 (EDT)

My former assistant Rich Maslowski used to work in a trailer maint. depot.

He said they would use the contraction routine to recrown flatbeds. By
welding a bar down the bottom center of each I beam with a high heat
setting, the metal would first expand and upset itself while hot and then
(steel being much stronger in tension than compression) when it cooled it
would force a sow backed trailer back up into an arch which had the camber
to carry a load.

Gene

 The Studios of Gene Olson and Chris Wilson - Working in Metals, Stone,
Mixed Media
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