On Sun, 21 May 2006 10:39:03 -0400, Chuck Harris wrote:

Mike Anderson wrote:

The desire to use TIG with a higher end rod and post heat treat is the
best but the question is answered correctly for a repair in structural
aircraft members where heat treatment is not possible would be with an
ER70 rod and OA welding. It was only a few years ago that the FAA
even addressed TIG in the AC43.13.

Mike

Here is what Linde says in the "The Oxy-Acetylene Handbook", p233:

Talking of 4130 "chrome moly steel:

"One of the more familiar applications of this material is in structural
tubing for aircraft. In such structures the light gage base material is
welded using a slightly excess acetylene flame and the normal steel welding
technique. Although the strength of the weld metal in such a weld is
lower per unit area than that of the base metal, the weld is made to develop
the desired strength by increasing the normal reinforcement considerably.
By following such a procedure, this "Chrome-Moly" base metal can be successfully
welded. On the other hand, if a S.A.E. X-4130 rod were used in welding
such structures or if an attempt were made to follow a similar procedure
in X-4130 plate material 1/2 or 3/4 in. thick, the weld would not be at all
successful."

They then direct us on to Chapter 22 to discuss the correct welding technique
for 4130. There, they spell out in depth the problems with welding an air
hardening steel, such as 4130. They mention that most of these problems can
be handled by preheating welding areas to relieve hidden stresses, and using
a low carbon steel rod, similar to Norway iron. They specify Oxweld No. 7 as
being the desired rod for tubing of less than 0.1" thickness. They then go
on to say that for tubing greater than 0.1" thickness, you will need a stronger
steel in your rod, and suggest Oxweld No. 1 with a recommendation of heat treatment.
For more rigorous applications, they then recommend Oxweld No. 32 with a
requirement of heat treatment.

Going into Linde's appendixes, finds that the Oxweld No. 7 rod isn't even a
steel rod, but rather a pure iron rod with a 45KPSI tensile strength. The No. 1
rod is a High Test Steel (low carbon steel), and the No. 32 is Chrome Moly Steel
(eg. 4130).

The ER70 mig wire is a 70KPSI tensile strength mild steel. It is the same filler
steel as any of the E70xx rods.

Linde's book would be a very good place to go if one wanted to learn how to
properly OA weld 4130.

-Chuck


O.K., you are correct.

I agree that learning the proper method of joining any material you work
with is important and I haven't any idea what FSDO he will try to use or
who will be signing the log book or the 337 if it turns into that big a
job.

It was foolish to answer without enough information....

Who is going to sign the work off?

There is where the answer should be sought.

Mike