Bill: I recently did an article for our Experimental Helo magazine and did
some research on PWHT and found things like a minimum of 2hrs required @ 300
degrees C to adequately stress relieve a weld. All of the reports that I
read didn't think that the few tens of seconds of OA heating as a post weld
technique for stress relief was very effective. If you Google stress
relief of welded joints you will get a surprise. There has been a large
amount of testing and review of both pre-heat and post weld heat treatment
done on various materials complete with microscopic examination of the
affected areas. Further, Richard Finch, an EAA tech counselor and one time
head of Aerostar aircraft welding department said that 1800 Aerostar engine
mounts were all TIG welded without pre or post heat treatment. Records show
no cracking, while Fairchild Swearingen's Metroliners all had cracking
problems with TIG welded engine mounts that were both pre and post weld
heat treated. He did mention, however that the Metroliner mounts were TIG
welded with the copper coated welding rod common to OA welding. I know what
the "old timers" say about this but there doesn't seem to be much scientific
data to support the "old tried and true" method.

stu fields
Experimental Helo magazine.
"Bill Daniels" bildan@comcast-dot-net wrote in message
. ..
I'm 100% confident that I can use O/A to produce a clean, void free weld
in 4130 that is stronger than the surrounding metal. I can also do that
with TIG but I'm not as sure that the join is completely stress free. The
extreme heat from TIG is concentrated in a tiny area whereas the O/A torch
has heated the surrounding metal and effectively relieved the stresses.

That said, if I could afford TIG, that's what I would use. If stress
build-up bothered me, I could always stress releive by reheating and slow
cooling the weld with the old O/A torch.

Bill Daniels


"Phil" wrote in message
...
Have been doing A/C welding of 4130 for 30 yrs. both as an EAA Amateur
and for A/C manufacturing company under Mil. Spec. Cert. ,almost all A/C
welding was done with Oxy./Acet. until the 1960's , at that time it was
found that one could speed up production with TIG welding and the supply
of skilled Oxy./Acet. welders was drying up , I understand that the MIG
process has been approved for some time , a real shame that Oxy. has
slowly been eliminated from the A/C manufacturing , won't go into the HAZ
, Thermal Shock and loss of ductility thing as it is like religion and
politics , it always starts a fight , for all around reliability with
respect to welding 4130 , I would place Oxy./Acet. at the top of my list
and TIG and MIG as second and last , Spirit Of St. Louis was Gas welded
as was all of those old J3's , T Craft's .
Happy New Year
Phil Lohiser
EAA 1273
"wright1902glider" wrote in message
...
While browsing a bit more of that "good 'ole internet wizdom", I ran
accross this page:

http://www.ihpva.org/com/PracticalIn...materials.html

Its a human-powered vehicle website, but on this page, the author
seems to think that 4130 cro-mo steel can't be welded with an oxy-
acetylene torch. Does this sound right? It was always my belief that
we've been OA welding airplanes out of the stuff for decades. Who is
wrong on this point?

Harry "I'm still stuck in the wood-age" Frey