Welding chomoly tubing

[candgp]

What type rod do you use when welding chomoly tubing?

[martymayes]

What type rod do you use when welding chomoly tubing?

For Oxy/Acy and TIG on new metal, ER70S-2

If you are doing a repair and the metal may be rusty or have other impurities, ER70S-6

[candgp]

Thank you, this is for a repair and will be a big help.

[Aaron Novak]

For Oxy/Acy and TIG on new metal, ER70S-2

If you are doing a repair and the metal may be rusty or have other impurities, ER70S-6

Actually I would NOT suggest ER series fillers for OA welding. Many of the alloying elements in the ER fillers are un-needed in the OA process and just lead to excess sparking etc.

RG-45,60 or 65 are suggested to be based on joint configuration, material thicknesses and heat treatment if the OA process is used. ER70 series are suggested for the TIG process.

[Bugs66]

RG-45 for sure. Don't waste your time with electric rod for O/A. Been there done that.

[prasmussen]

Hey, what keeps us from brazing things together with one of the high strength brazing alloys? Race car person said braze joints were more flexible and resistant to cracking. And those joints have to be lot easier to get right. Tack-weld the frame together then braze over that for the best of both? Just a thought. Guess that's why Young Eagles run away when I offer them a ride?

[Mike Switzer]

I don't know of any sanctioning body that allows brazed joints on a race car chassis.

[Aaron Novak]

Mike,
Indeed in europe filelt brazed chassis components are not uncommon for race vehicles. However.....it is more difficult to produce an acceptable fillet braze than fillet weld. Fitment is also more critical with a braze. In the racing world it is done mainly for ease of field repair. If you are building an experimental you are free to use bubblegum if you wish, but somehow I dont see the thrill in bucking engineering and time tested methods when there is no performance gain. If you want to be a "cowboy" and do things "different" for the sake of being cheap or eccentric....please dont fly over my house.

[Mike Switzer]

Mike,
Indeed in europe filelt brazed chassis components are not uncommon for race vehicles.

Interesting. I will re-phrase my statement to say i don't know of any sanctioning body in this country that would allow it. :)

Personally, if I have to fire up the torch anyway I would rather weld it.


I think the last time i brazed anything was several years ago when I needed to weld a piece of 1/8" pipe to a radiator cap so i could pressurize a block to find a crack. I melted down one cap so i ended up brazing it, (it only had to hold 16psi)

[prasmussen]

Mike,
If you want to be a "cowboy" and do things "different" for the sake of being cheap or eccentric....please dont fly over my house.

Easy son, those of us from Montana are rather fond of our cowboy heritage.

[Aaron Novak]

No insult intended:
For future reference, when I use the term "cowboy" , I am using in in the context of vernacular common to people working in engineering fields.

Definition: People or Persons who defy common practice, engineering data and historical data when designing or fabricating something, due to sheer laziness or some strange desire to fight a perceived "establishment". Typically persons in this category have an inability to fill out paperwork, and suffer from extreme cases of selective hearing ( especially in the presence of field experts ). The decisions made by such persons mentioned above as "cowboys" are referred to as being "shot from the hip".

No implied connection is made to the above mentioned "cowboys" of the engineering vernacular set, and of persons who live, or have lived in what is generally thought of as the "western" half of the USA from the middle 1800's to the 1960's, working cattle, getting saddle sores and allowing John Wayne to earn a sizeable fortune.

[prasmussen]

Nice man. Gotta love him. He built on his full-scale, slightly banana-shaped warbird replica for at least 14 years. Everyone stood around hoping for the best but frankly expecting disaster when he taxied it for the first time. We all agreed it must be wind shear that caused it to crab sideways down the taxiway. Lost track of him. Really hope all turned out well. But that brings up a third category beside the cheap and the cowboys: the enthusiastically inept.


Although the chances of those intrepid aviators hurting anyone but themselves (and I sincerely certainly hope not) is slight, your point about over-flight is well taken. The real danger, in my opinion though, is that if the builder/pilot community does not educate/advise and prevent the somewhat predictable results from these mostly well-meaning groups of fellow aviators, the regulatory structure of homebuilding will become unmanageable for everyone.


That's away from welding tubing though......


Here's what I have been thinking:




Charts I've gotten from the forums/workshops at AirVenture indicate some new brazing alloys are as “strong” as welds.

If heat is the enemy of steel, wouldn't it be better to look in the direction of the lowest temperature process?


Maybe lower temperature oxy-hydrogen welding could be used to produce cleaner welds and shops (who wears a mask after all?).

I've worked with silicone bronze enough to know that alloy can be bent many more times than steel before cracking.

If the Eurozone uses brazing for a quick fix on racing cars, wouldn't it make easier relocating parts as I “refine” my aircraft design?



Problem is my ignorance of a way to test my joints to see if the idea is really worth pursuing.



Q: What is the tensile strength of brazed joints
A: It all depends
No manufacturer lists the tensile strength of their brazing alloys. This is not to make life difficult for the ultimate consumer. It's because people tend to place to much emphasis on any number that might be published. Design engineers sometimes base designs on a number that's not appropriate for the ultimate use.
In fact, the strength of a brazed joint depends more on the design and the brazing procedure then on the filler metal used.
Furthermore, tensile strength numbers apply to material in the wrought state. When the filler metal is used in brazing, it is effectively recast. Recast metal has different properties from the wrought metal.
Empirical testing of various brazed joints has shown that the PSI of the alloy does not correlate directly to the strength of the tested joint. We know some of the factors that influence this process. For example, if the alloy is overheated, the lower melting elements are burned off to a higher degree. This effectively changes the composition of the deposited metal. Thus our advice is to encourage customers to do their own testing of the brazed joint.

But there are some rules of thumb:
If customers insist on a certain PSI number, we suggest a number ranging from 60,000-70,000 PSI when tested in the wrought state.

Another rough guideline is that joints properly brazed with silver alloys have a shear strength that exceeds three times the shear strength of the thinner, joined metal.



Any thoughts? BTW no offense taken.

[Mike Switzer]

I've worked with silicone bronze enough to know that alloy can be bent many more times than steel before cracking.

Sort of correct, but... For steel to bend you must exceed the yield strength. If you do not exceed the yield strength it will not bend, and therefore will not fatigue. Engineers design steel structures so that the structural members and the welds will not exceed the yield strength, which for the 4130 currently available for homebuilding is 70 - 75,000 psi depending on size & wall thickness. The yield strength of the hardest commonly available hard commercial bronze is approx 55,000 psi.

A properly designed steel structure with properly designed welds will not bend at all and should last forever.

[Aaron Novak]

I guess I dont see what is to gain by brazing your structure? You cant improve upon something that does not fail, and there would be no weight savings or fatigue life gain. Is ability an issue? Because I will tell you this, if you cant weld, you cant braze. Oxyhydrogen is unsuitable for steel welding. Who says heat is the enemy of steel? If you want to design a brazed structure ( lug or fillet ), and develop the process, do the research and testing, then by all mean go for it. But for all the work involved....Im struggling to see the gain????

[prasmussen]

No, I chose to gas weld my SA-3A which is on the gear. Just wondering about stuff. Guess the gain is that we have given candgp something to think about.

These forums are such a great idea!

[candgp]

No, I chose to gas weld my SA-3A which is on the gear. Just wondering about stuff. Guess the gain is that we have given candgp something to think about.

These forums are such a great idea!

Thanks to all who have replied to my question, it has been helpful and informative.

[dgapilot]

Thanks to all who have replied to my question, it has been helpful and informative.
I've seen 4130 that's been brazed and it looks ugly. It cracks on the underside. Go try it on some plate and see what happens. Mild steel can be brazed without any problems, but I would caution you against doing it on 4130.

[prasmussen]

Interesting. Any idea what's happening chemically to the metal that causes it to crack?

[dgapilot]

Not sure, I was going to replace some mild steel pars with 4130. They had brazed fittings, so I brazed the new ones and got ugly cracks. I also saw some samples from someone else that does welded repairs all the time. Same type cracks with his samples..

[prasmussen]

Cracks on the back side only? I have gotten the steel too hot and had it try to do a half braze and half weld where I can see it on the metal surface. That is truly ugly. Don't know what the alloy of brass and steel is called but it is a disaster when it happens because it is brittle junk and has to be ground down to bare steel before starting over. Can't weld it, can't braze it, just have to play it again Sam. Anyone a metalurgist?

[Aaron Novak]

4130 should have no issues with brazing. If you are having issues, it is purely from the technique, process and skill of the person doing the work. Overheating is the usual culprit.

[58boner]

Do think there are some applications on steel fuselages where brazing would be just fine. Those long brackets for attaching skins, to avoid bending the longerons from heat, etc.

[eiclan]

Gday to continue this thread,Can I tack weld the frame with the mig? The wire is the er70s and is this compatible with the mild steel filler rod used with the oxy?

[pacerpilot]

You can tack with Mig. Be careful not to make the tack too big because you'll need to go over it during the final welding.

[pacerpilot]

I was reading this thread and am intrigued by the suggestion/interest of/in brazing an airframe. I have to wonder why? Brazing is an unproven process for airframes. Also, in my experience it has been a more difficult process to produce. I've found it much easier to control heat affected areas, filet size and, all other aspects of a weld joint versus a brazed joint. Torch rigs and No. 7 rod are cheap. I'd stick with what we've been flying on for 100 years. I do like brazing for repairing cracks in castings such as boat exhausts, blocks, etc. Anyway, just my opinion and experience.

[Aaron Novak]

I was reading this thread and am intrigued by the suggestion/interest of/in brazing an airframe. I have to wonder why? Brazing is an unproven process for airframes. Also, in my experience it has been a more difficult process to produce. I've found it much easier to control heat affected areas, filet size and, all other aspects of a weld joint versus a brazed joint. Torch rigs and No. 7 rod are cheap. I'd stick with what we've been flying on for 100 years. I do like brazing for repairing cracks in castings such as boat exhausts, blocks, etc. Anyway, just my opinion and experience.

I aggree 100%. However I do have to argue with you on a point of brazing not being "proven". Back in the WW1 timeframe you do see brazed structures in airframes. Typically they used "lugs" common to bicycle manufacturing at the time. The Wrights used braze welding on the 1903 and later flyers (bicycle guys ya know). The extensive use of brazing vs. welding in the pre 1925 period seems to have been directly related to the steel manufactures ability to control some of the alloying elements in their tubing and sheet....mainly sulphur. Once the root cause of welding failures was found to be in the steel itself, the manufacturers changed the steel to be applicable to welding....and welding thus took off ( no pun intended ). Back to the present though.....cant beat RG-45 and a nice safe, sound and comfortable system of welding.

[prasmussen]

Aaron's advice is spot on; RG-45 is likebutter. You'll love it! It's worth asking and paying extra for. AndI've found it will flow into a make-your-mother-proud fillet ifre-heated with a slightly carburizing torch flame. Anybody know ifsuch a re-heat significantly affects the strength of the weld? Surelydon't want a weld to become brittle and the additional carbon has tobe changing the character of the metal in some way.


For what it's worth, although I'llcontinue to experiment with ways brazing might make building quicker,easier or better, I have found a couple of problems with the process.It's the flux. The MSDS brings up some significant issues for asmall space with less than industrial ventilation. And, after thebraze has cooled, the flux must be completely removed or the residual acidswill cause corrosion. Corrosion is bad.