Like I said in my first little post , religion , politics and I guess you
could add motor oil to the list of a million things that are debatable , I
will still stick with the NASA report and a little common sense , the last
engine mount that I TIG welded was brought up to cherry red , both to do a
little alignment adjusting and to help level out some of the built up strain
from the initial TIG welding , my wife has a diamond ring that is very hard
but not very ductile , I really don't like the idea of having an EAA Biplane
engine mount turned into a diamond , not very flexible , even 1020 can
develop hardness after welding , raise the carbon to 30/100 of 1% and things
really get hard , go to 4140 and you are headed back to the diamond ring
state again .
Best To All
Phil Lohiser
"Stuart & Kathryn Fields" wrote in message
.. .
Phil: The stress relieving that you described: of slowly raising the
temperature to1020 Deg. F and holding it for 3hrs then dropping at a
certain rate is certainly different than heating to cherry with an OA in
less than a minute and then letting it cool in less than a couple of
minutes. The guy I referenced in an earlier posting was responsible for
the TIG welding of 1800 Aerostar engine mounts that did not crack and had
no post weld heat treatment. That, while anecdotal and not a report of a
truly scientific examination of the weld joints using metallurgical
techniques, does carry some weight with me. Not to mention his survey of
a group of airframe manufacturers which included Piper and Mooney that
were surprisingly, using MIG with no pre or post heating. An awful lot of
successful experience of welded joints without OA "Stress Relieving".
BTW my Baby Belle gets trailered to a bunch of events every year and has
in excess of 125,000 trailer miles over roads that have set ELTs off and I
have never found a crack in any of the welded joints and this includes a
17' tail boom that has a bunch of welded cluster joints and is not
supported anywhere but at the front end by 4-5/16 bolts in double shear.
My ship is one of at least 5 with high trailer miles and I've yet to hear
of a cracked weld joint. This is an accumulation of about 15years
experience with these ships.
I note however that these joints were designed with amateur builders in
mind and the frame and joints are not designed close to the ragged edge
but have a sufficient margin to allow for less than expert welders. E.g.
the tail boom is of 0.049 wall tubing where similar tubing on the Bell 47
is as small as 0.025. There are a lot of contributing factors to a
successful TIG welded joint.
I know of no metallurgical research or experiments that prove the very
quick and uncontrolled OA "Stress Relieving" is an effective useful tool
in producing a successful TIG welded joint. In fact my limited research
into the metallurgical reports found reports of decreased tensile strength
in the material as the result of Post Weld Heat Treatment. I know that
this is an area of strong opinions and I'm sure that I will be digging
into the metallurgy of welded joint more as I feel like I've just barely
got my nose into an area that is much more complex than I thought.

Stu
"Phil" wrote in message
...
NASA published an advisory many years ago that was reprinted in Sport
Aviation , I don't have the article at my fingertips , as I remember ,
NASA stated that any 4130 weld assembly that was TIG welded and used on
Aircraft should be post heated via Oxy/Acet , anyone who has ever done
any welding and especially ARC welding must know and has experienced the
tension that has built up after the weld has cooled , just a pinch of
common sense would tell you that this tension load will be there for the
life of the weldment , to raise the temp. of a given cluster up to a
point that allows that cluster to seek it's sweet spot without that
locked in tension and possible premature failure would only make common
sense , NASA is far from perfect but they were on the money with this
advisory .
I don't know how many people that write books on welding have actually
worked on the floor with real airplanes and have actually welded on
commercial airplanes , I have seen many lineal inches of Oxy/Acet weld
laid down and never saw a crack or fracture of that weld that occurred on
the floor even before an assembly was painted , I have seen many TIG
welded assemblies that would crack shortly after welding and again before
they saw paint , if you have an engine mount that needs a small amount of
machining and the machinist is damaging high speed steel end mills with
hardened 4130 , this has to be very telling , it's been a few years since
I worked for a Jet engine repair station , as I recall , all welded parts
were placed in a oven and slowly raised to about 1020 Deg. F. and held at
that temp. for 3 hrs. and then the temp. was dropped at a certain rate
for several hours , they didn't do this for there own pleasure , this was
FAA mandated .
Best
Phil Lohiser
"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