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#11
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Welding question -
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 |
#12
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Welding question -
This question , about welding with O,A is right . or should I say the
answer . I have noticed while welding I tend to use just a little richer Acetylene. mixture to keep from oxidizing the weld . the bubbles and so on and even cracking is the result of my running too much oxygen .Too much heat will also do the same thing. now what I mean by that is too big a flame for the job.. This usually happens when I try and weld a thick piece to a thin piece , seems one tends to get too much heat ( the thin ) and pop and bubble and crack . I also have found , for myself of course , that welding with a 4130 rod to 4130 frame I will get cracks in the weld , and even on the sides .. seems to me that as the metal cools it draws up and that's when I get the cracks . Going back over my weld with the torch before it get too cold sometimes helps . but I have found that using a soft metal rod works best on a hard metal weld . Using a coat hanger wire once to patch a frame was proof enough for me. I started buying soft metal rods to weld 4130 and 4140 .. But I am not a tickler for exact and perfect welding . An aircraft bolt is soft and will stretch allot before it breaks as compared to a grade 8 hardened bolt . It's just I was reading and learning from all of you and I remembered from my experiences .I pray I did not over step my bounds here . Thanks for allowing me to butt in . wesmarso "Chuck Harris" wrote in message ... Orval Fairbairn wrote: In article .com, "Mike" wrote: 'regular' welding rod? What's that? Not a 4130 rod for welding 4130? - Mike Nope 4130 rod for welding 4130 will require heat treat, or it will be brittle and crack. Use standard, off-the-shelf welding rod from your local welding supplier. Oh, I forgot to mention, the welded material gets just as hot as the weld, so if you have cracking problems that require heat treatment, you are going to have problems regardless of the rod you use. Most of the time, cracking problems are hydrogen embrittlement, and are prevented by using a low hydrogen rod, such as the 7018,8018,9018... series of rods. -Chuck |
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