<< ...I beg to differ! People have built aircraft for decades using much
thinner tubing thicknesses than Rohn 25 or 45 have. Naturally, thin-walled
tubing is a bit more challenging to weld, but the tubing sides of 25 and 45
are plenty thick by comparison...Bill Coleman, AA4LR...>>
I changed the subject on this offshoot of tower repair thread for future
I think welding on galvanized metal releases some nasty, toxic, fumes, so
more precautions must be taken. Although it certainly is possible to weld to
thin sections, the following must be taken into account:
1) The heat from welding will be hot enough to change or completely destroy
the heat treatment of the metal. It may even take it as far as fully
annealing (essentially softening) the local metal adjacent to the weld.
Annealing will reduce a heat-treated metal's yield stress, while at the same
time, making it more ductile. That means if will fail with less load, but
tend to bend more and absorb energy before breaking.
2) Sometimes, it is possible to preserve some amount of heat treatment by
quenching the welded area with ice water immediately after welding, but the
results are quite variable. This is similar to the original hardening of the
metal. You can then scrape a bright patch on it (if it is steel) and
carefully re-heat the area *gently* with a torch and read the color change
on the metal to temper it. When a metal is fully hardened, it has great
yield strength bu is more brittle/less ductile. Tempering to various
temperatures (also called 'drawing') after hardening simply strikes a
balance betwwen the two conditions of hard/brittle and soft/ductile.
3) I don't know the extent of the heat tretment of the steel in Rohn towers.
We already know is that it is certainly ductile enough to absorb energy and
bend to some degree, thankfully for our friend with the damaged tower.
Welding on the section could possibly leave the welded area softer and more
ductile than the original condition if it is heat-treated.
4) I would not recomment welding on a section that is highly stressed unless
it was supported or unless the welding were carried out in carefully
controlled portions to prevent the entire section from becoming red hot and
soft at one time.
If anyone knows the actual heat treatment of Rohn's steel, please jump in
and help steer this thread. Perhaps it's on one of their drawings.
I used this effect recently to bend some aluminum rod in tight, 90 degree
bends for an antenna mount for my bicycle (good shop tip coming up).
How many of you have tried to bend aluminum, especially 6061-T6 (hardened)
only to have it crack? I heated the area I wanted to bend with a torch,
destroying the teat treatment in the bend area, and making the metal more
ductile. I made the bends (crack free), then reheated them and quenched them
with ice water.
So go forth and weld carefully!
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