Rumor concerning roll cage....is it true?

[JackD]

Both torch welding and brazing were common.
Both methods produce roughly the same effect on the parent metal but brazing spread the load at the joint better.

[sockjohn]

In Europe it is common practice to braze weld their equivalent to 4130.
Often overlooked, even with a beautiful laid down TIG weld on 4130 is the backside of the material .
If it is exposed to oxygen in the back and not the protective cloud of the appropriate weld gas or flux, it will oxidize and cut the joint strength substantially.
The gusset ruling in SCTA was as the result of a cage that was replaced on the shoulder hoop of a 4130 car and it punched through the top rail when the car went on it's top and the entire assembly came off intact.   

My understanding from the tube and fabric homebuilt aircraft guys is that both TIG and gas welding of 4130 are acceptable, and if done properly are about equivalent strength. 
In Europe all aircraft must be welded by a certified welder, home built or not.

They recommend purging the inside of the tube with argon for both, and use a slightly feathered flame to reduce oxidation with the torch.

Please use due diligence as I am relying on memory from stuff I've read on homebuilt aircraft websites, but they are a pretty good source of welding info.

[LittleLiner]

Something to ponder  . . Keep this in mind while considering FAA standards as applied to racecars.   . . . . Aircraft built with tube airframes use materials that are as light as possible and strong enough as welded to stay together and NOT crash.  Racecars are (hopefully) built from materials that are strong enough and welded together to stay together when they DO crash.   

My car (if it ever gets done) will have a cage using 1 and 3/4 DOM with .134 wall even though our class allows smaller and thinner tubing.  If we ever go to larger displacement the car will still be legal.  If we convert it to dragracing it will pass NHRA tech. 

If you can't fit both the cage made with 1 and 3/4 inch tubing and your driver in a car, then I suggest you get a bigger car or a smaller driver.

[bak189]

Hey, this I understand....."braze welding"  being from the "old country"  I have been using it for over 55 years....over the years there as been a lot of improvement in this type of welding.  One being the in-line feeding of flux to the weld....this makes for a clean and strong weld.  Brazing rods are now on the market with super high tensile
strength....most of this stuff is only on the market in Europe.....they still use braze welding to large extend on racing equipment........it works great with 4130.....Yes, we do use TIG on some suspension pieces, but the main chassis are braze
welded.  The big trick is heat control....this comes only with experience and time...................................

[maguromic]

Littleliner well said!  The rule book just lists minimums and should be used as a guideline.  Why would you want to skimp on safety?  If you feel you need bigger tubing then put it in!  But keep the rumors out.

[Carl Johansson]

As I recall -  and I'm certainly no expert -  the 4130 welding issue is gas escape from inside the tube.  Apparently if you want to use  4130 you have to drill a gas escape hole within a few inches of where you will be welding.

way beyond my understanding -  but thats what the smart guys with experience tried to explain to me!

carl Johansson

[JackD]

The vent hole can be any distance from the weld as long as it relieves the pressure of the hot expanding gases inside the material.

[bak189]

Yep, you need a vent hole.......The "experts" will tell you that if you use braze welding on 4130
it will crack next to the weld, this is where heat control is so very important.  We have fabricated
M/C frames for various roadracing bikes using 1.25 Dia. tubing of .039 wall thickness and brazed them, with no problems.  However, if you were to throw it down the road, with only .039 wall you will need a new frame from us. One interesting sideline regarding 4130....next time you fly in a European build Airbus......the 4130 sold in Europe
if bend  90 degrees on a 4 inch radius....lay it on the bench and come back the next day you will find small hair-line cracks on the outside of the bend.......not so with U.S  4130.  I know this is somewhat getting away from  roll-bars, for this, forgive me.

[sockjohn]

Y  We have fabricated
M/C frames for various roadracing bikes using 1.25 Dia. tubing of .039 wall thickness and brazed them, with no problems.  However, if you were to throw it down the road, with only .039 wall you will need a new frame from us.

I think I've ridden mountain bikes with tubing that thick, at least at the weld!  (Most bikes use butted tubing to save weight)

Really thin steel tubing runs into issues with denting, especially on anything that might get dropped to the ground.  This is part of the reason bikes use Aluminum with such good success.

Back to the topic at hand, littleliners post is worth rereading, oversize is a good thing!  Especially if you might bump up the engine later and go faster.

[Rick Byrnes]

Actually, you can tig weld 4130 and other "exotic" alloys, but you must heat treat, (normalize) after welding.  I have done this, and it is not extremely difficult.  My front axles are all 4130, but normalized and then heat treated to a specific hardness by a professional.  Then tested for cracks.

We can do the normalizing of welded joints in our own shops.  Proper heat is all that is required, and there are crayons that are temp indicating for the right temperatures.

4130 is stronger, more resistant to bending, and just as long lasting in the type of structure we build.  Particularly if we still use the heavy wall thickness like I have.
My belief is that my chassis in 4130 will protect me better than the same deal in DOM.

Rick

[GeneF]

As a welder-fabricator for the past 30+ yrs. and involved in racing for even longer, I've gained some knowledge in the field of welding tubular structures of various materials. I won't get into the do's and dont's of welding c/m but would would suggest to those interested to go to the Lincoln Electric web site and do a search in their Knowledge page as there is some good info on welding thin wall (1/8" or less) c/m- filler rod, preheat, post heat, purging etc.
 
Having said that, I don't see a viable reason to use c/m in LSR  applications as low weight is generally not a high priority as in drag/oval racing. One thing I would like to mention is that there is various types of c/m. The only type that is acceptable to use in a structural (frame/roll cage) application is that in the "normalized" condition. This is a process that restores the "elasticity" back into to the steel after the initial processing. This will always be marked as "condition n" on the tube or plate. Any other c/m not marked that way will be very brittle.

 Back in the early-mid 70s there was a situation where non-normalized c/m was being sold to sprint car builders, in the Penn. area, as condition n. Whether intentional or by accident it resulted in some injuries and (I could be wrong on this) the death of sprint car driver Toby Tobias. I do remember a pic in Stock Car Racing magazine of a sprint car left with 4 jagged posts sticking up from the top frame rail after a flip, due to this.

[Dean Los Angeles]

4130 DOM has a tensile strength of 100,000 psi. The tensile strength of silver braze alloys is 40,000-70,000 psi. Seems like a poor choice to me.

TIG WELD 4130!
The Lincoln Electric Company, Welding Services. June 2000

Yes, you can TIG weld 4130 tubing up to .120" wall thickness easily with the techniques and procedures described in this bulletin. Answered are the top ten most frequently asked questions about TIG welding 4130 Chrome-Moly. These attached procedures apply to typical sporting applications such as experimental airplanes, racing car frames, roll cages, go-carts, bicycles, and motorcycle frames. The suitability of these techniques and procedures must be evaluated for your specific application.

Q. Can I weld 4130 using the TIG process?
A. Yes, 4130 Chrome-Moly has been TIG welded in the aerospace and aircraft industries for years. As with all welding, proper procedures and techniques must be followed.

Q. Do I need to pre-heat?
A. Thin wall tubing (< 0.120" wall) applications do not typically require the normal 300?F to 400?F pre-heat to obtain acceptable results. However, tubing should be at room temperature (70?F) or above before welding.

Q. What filler material do I use?
A. Although there are several good filler materials, ER80S-D2, is one you should consider. This filler material is capable of producing welds that approximate the strength of 4130. ER-70S-2 is an acceptable alternative to ER80S-D2, as is ER70S-6, although the weld strength will be slightly lower.

Q. When I use ER70S-2 filler material, do I give up strength for elongation?
A. Yes. The filler material, when diluted with the parent material, will typically undermatch the 4130. However, with the proper joint design (such as cluster or gusset, for example), the cross-sectional area and linear inches of weld can compensate for the reduced weld deposit strength.

Q. Why is 4130 filler metal not recommended?
A. 4130 filler typically is used for applications where the weld will be heat treated. Due to its higher hardness and reduced elongation, it is not recommended for sporting applications such as experimental airplanes, race car frames, roll cages, etc.

Q. Can I weld 4130 using any other filler metals?
A. Some fabricators prefer to use austenitic stainless steel fillers to weld 4130 tubing. This is acceptable provided 310 or 312 stainless steel fillers are used. Other stainless steel fillers can cause cracking. Stainless filler material is typically more expensive.

Q. Do I need to heat treat (stress relieve) 4130 after welding?
A. Thin wall tubing normally does not require stress relief. For parts thicker than .120", stress-relieving is recommended and 1,100?F is the optimum temperature for tubing applications. An Oxy/Acetylene torch with neutral flame can be used. It should be oscillated to avoid hot spots.

Q. Do I have to pre-clean 4130 material?
A. Remove surface scale and oils with mild abrasives and acetone. Wipe to remove all oils and lubricants. All burrs should be removed with a hand scraper or de-burring tool. Better welding results with clean materials.

Q. Do I need to back-purge 4130 material?
A. Backpurging is not normally necessary, although some fabricators do. It will not hurt the weld and may improve the root pass of some welds.

Q. Should I quench the metal after I finish welding?
A. ABSOLUTELY NOT! Rapid quenching of the metal will create problems such as cracking and lamellar tearing. Always allow the weld to slow cool.

[hitz]

One thing that helps tig and acetylene welds from getting brittle is to wrap them with asbestos cloth (or more properly now) header wrap immediately after welding. A simple test is to file a weld after it has cooled to room temperature.
Someone else has mentioned on this site that HREW A513 (hot roll electric weld) tubing doesn't weld as well as DOM A513 and I couldn't agree more. Even after cleaning  the HREW out side with wire wheels and the inside with soap, water and a bottle brush it still contaminates tig and acetylene welds. Stick weld (7018) will work in this case very well as the flux carries the impurities to the top and is disposed of when the flux is cleaned off. This doesn't work well on the clusters though because it is hard to chip well. Old guys don't weld as good as they used to. 

  Harv

[bak189]

WRONG.....regarding tensile strength of braze welding alloy filler rod......the new alloys in both here and Europe are as high as 95.000 PSI......some of the better rods in the U.S. are
MG130 and Eutectic 16.............the 90.000 PSI and up rods come out of Germany........using  gas fluxing (which adds liquid flux through the acetylene line) also adds to the strength of the weld.

[JackD]

4130 DOM has a tensile strength of 100,000 psi. The tensile strength of silver braze alloys is 40,000-70,000 psi. Seems like a poor choice to me.

It is kinda like comparing the weight of 10 apples and 10 oranges.
While the tensile strength varies, so does the area covered at the joint.

"Day is sum purrty charp cookiys out dare."