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Thread: Heating 4130

  1. #1
    jimboflying's Avatar
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    Heating 4130

    If you heat 4130 with a torch to bend it and then let it air cool to room temperatures do the mechanical properties change?

  2. #2

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    My understanding is that if you do not use an oxidizing flame, or a carburizing flame, and you allow it to cool evenly without stress, it will have the same properties as it had before. Of course, as long as it was not previously heat treated..
    May you always choose the time and place you land..

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    Timely question for me to. I'm about to bend the tabs on the rudder horn for my rudder and I was thinking of using the torch to heat the bend line. When you say neither oxidizing or carburizing flame you mean to use a "regular welding flame. Correct? I know I should know this stuff but i don't remember for sure.

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    That's how I have always understood it. It's probably time for one of the seasoned welder guys to chime in.
    May you always choose the time and place you land..

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    Gordon Misch's Avatar
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    The tubing we use is "condition N", normalized. That means it is air-cooled, not oven-cooled (annealed) or quenched. So yes, perfectly ok to heat with a torch and allow to air cool.

    Q, a carburizing flame has a secondary feathery flame that extends beyond the principal flame cone. It can add carbon to a molten puddle, changing the alloy some. A neutral flame has just enough oxygen to eliminate the feather, and is the highest temperature mixture. An oxidizing flame has more oxygen than neutral. The flame cone will be a little bit brighter (lighter?) blue, will be shorter, and a little noisier. The excess oxygen can oxidize (burn) the steel. A neutral or very slightly carburizing flame is what you want.
    Gordon

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    mike mcs repair's Avatar
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    practice first some....

    do not let it cool quickly in air or it WILL crack....

    kinda play flame over it to slow the cooling, or cover with some sort of insulation....

  7. #7

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    Heat to a dull red color, no more if you can avoid it. As Mike says, let it air cool SLOWLY. Someone opening a door close twhere you are working can cause enough air movement to "shock cool" the work peice. I keep a bat of pink insulation handy to drape over the work as soon as Im done to help control the cooling rate.

  8. #8
    Marty57's Avatar
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    As I welded my fuselage, I learned a lot about welding and flames. I like to have a small secondary flame just past the bluer flame, just a hint more oxygen. Too much oxygen and you will see the metal sparkle just a bit (like a 4th of July sparkler) and that is never good and changes the structure of the 4130 some. My experience has been that without a small secondary feather from oxygen when welding you will get some un-burned acetylene and than POP and sparks and molten metal goes flying not fun! There is an art to it. When heating for a bend you are not heating to melting, just a dull red usually will do so no worry either way. I was taught to only weld in a closed room with no breeze at all and back the flame away slowly to cool slowly. A few times I have heard it go "tink" when cooled too slow and than upon inspection there is a crack. Bend away !!!!!

    Marty57
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    This is why I have not finish welded anything I have made. Only tack welds on everything. The first pieces I built were all 6 tail feather pieces. I had read the old WWII aircraft welding book and learned about following the grain and someone showed me how to set up for a neutral flame and that is all I have ever done. I noticed the popping occasionally Marty mentioned but so far no cracking and I always worked outside to prevent any fire hazard. Now I am glad I didn't finish weld any parts or I would have had cracking as Mike pointed out. I think I will either hire a good tig welder or trade work for the finish welds. On the next project if one comes up I will go to welding school first. Thanks again Gordon, mike, Marty, wronghand and SuperClub! This site still amazes me. It would not have been possible to get anywhere as far as I've gone without the advice on here.

  10. #10
    fobjob's Avatar
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    As I understand it, 4130 is quite ductile when cold, but is brittle when hot. Beware of the formation of microcracks when subjecting it to force when hot....

  11. #11
    mike mcs repair's Avatar
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    Quote Originally Posted by qsmx440 View Post
    ... Now I am glad I didn't finish weld any parts or I would have had cracking as Mike pointed out...
    thats not what i meant, the original post is about BENDING tubing once heated.... NOT welding... weld away!!!

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    The instructions with the Pitts Special plans state "bend 4130 sheet cold...do not heat!" Curtis Pitts was the man!

  13. #13
    fobjob's Avatar
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    Then there is the issue of TIG having been a no-no on 4130 at one time because of the formation of microcracks on the edge of the heat zone due to thermal stress on hot 4130. I take it some preheat is required/recommended before touching it with TIG to prevent this?"

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    How much of a bend are you putting in the tube?? What thickness??. If putting the tube through a lot of bend. Go get some play sand a plug one end, pore in tube to top ,plug with cork, heat up tube and bend it. The tube will not collapse on you, depending on how much bend you want. 4130 N comes heat treat to a certain Rockwell Hardness. Any time you heat this it will change the hardness. If you want to soften the tube or Anneal it, heat up and let it cool to touch. for drilling. You can test this out on some extra tubes. BearHawk uses 4130N with mild steel filler rod. It will not crack out on you like it would with 4130 filler rod. 4130 filler rod in places, ONLY if you plan to heat relieve the area.

  15. #15

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    Jimbo, If there is a Welder supply near you. I know Lincoln has a truck with all there machines on it. and they go to different places demoing. If you are part of the EAA they might come to one of your local meetings. The big EAA flyin coming up at the end of July in Wisconson, has Miller and Lincoln there and you can learn to weld Aluminium, steel with tig, mig or tourch demo,s

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