4130

[Jonny Hotnuts]

The other day I purchased a 12' section of 4130n to practice welding. THe fact is that I was surprised it welded really nice (TIG using a Miller Dynasty with pulse capabilities). I had always been under the notion that 4130 required the hand of god to weld and was very problematic.

That being said I did NOT back purge the welds (.83 and tight fish). The joints looked really nice and didnt notice any real different from welding 1020 DOM.

My question is that should I back purge the welds just to be on the safe side AND do I have to anneal the welds directly after welding. Is it not kosher to weld the entire chassis and THEN use a rosebud to anneal the welds or should I do it when the HEA is still hot?

Thanks for any advice,


~JH

[johnneilson]

This subject has been discussed here before.


http://www.landracing.com/forum/index.php/topic,8446.0.html

IMHO, 4130 ranks #2 in ease of welding, 304/316 is #1.

What fill rod are you using? and what process?

John

[manta22]

JH;

All the theoretical stuff aside, my test of a new filler rod, type of weld, material, etc. is to weld two pieces of tubing together at 90 degrees, sort of "T" shaped. Then put it in a big bench vise and bash the heck out of it with a heavy hammer. If the tubing bends and folds up rather than breaking the welds, you're OK. One advantage of this "non-quantitive" test is that it tests the joint for shock loads rather than just static loads.

Regards, Neil   Tucson, AZ

[Briz]

4130 welds just as easily as mild steel. So you wasted some expensive material there!
General rule is that for wall thicknesses less than .120" no stress relieving is necessary.
Strictly speaking, A33 rods are the best match. But normal A15 will be fine for the thicknesses you're talking about.
Back purging really isn't necessary in most cases.

[Jonny Hotnuts]

Filler rod:

1/16"
Blue Demon ER70 S2

[Peter Jack]

That'll work just fine JH. It's what most of the fabricators use.

Pete

[Jonny Hotnuts]

So you wasted some expensive material there!

Not so bad, got a 12' section and used 1'. After the first weld it looked so nice I didnt have any reason to continue cutting the stuff up. Will beat the pizz out of it with a hammer to see how well it holds.

The money part that stings is that this will be #3 of the same chassis. 1st twisted up, 2nd opted for 4130 and not 1020 DOM.

THe fun thing is that I have already been able to use some of the tube for work related projects.
I had to build some tables to stack janitorial supplies on to keep them off the ground (compliance issue). Note the legs....1.5" .120 DOM and what was part a race car chassis.



~JH

[Rex Schimmer]

JHN,
I always like to get a pic of my favorite 4130 tube fab job when this discussion comes up. This is an off road truck that was built at the Herbst Brothers shop. The material is .125 wall 4130 tubing. Note the cleaning of the mill scale from the welded area, also the weld was done with the same rod as you are using except it is .045 dia. I normally used .060 rod for years and after reading about this truck fab I converted to .045 and do think my welds are better. 4130 welds so well because it has very low contamination because it is "aircraft specification".

JHN a question regarding your chassis, if it twisted using 1.5 mild steel, going to 4130 may help but I would really think you need to look at your chassis design more carefully.

Rex

[maguromic]

That's just Terrible, Herbst that is.    That chassis has to be one of the best fabrications I have ever seen.  Tony

[johnneilson]

That's just Terrible, Herbst that is.    That chassis has to be one of the best fabrications I have ever seen.  Tony

Not only the fab work, look at the machine work on the jig/fixture and the weld table?

No expense spared here.

[Rex Schimmer]

The tube ends on the truck project were first laid out in CAD then the dimensional information was given to their CNC, 5 axis laser cutter which then cut the tube end for the perfect fit. I want one for Christmas!!!!

Rex

[johnneilson]

My Son raced karts for years, the chassis mfgr in Italy had a machine that looked like an extruder.
It in fact was a bar feeder with a laser cutting tip and a tube bender.
The pc is fishmouthed, extended and then bent, extended bent again and the finish cut is a fishmouth.

We would spec chassis with different tubing to change the flex rate and stiffness.

I want one of those machines............

John

[38Chevy454]

JHN a question regarding your chassis, if it twisted using 1.5 mild steel, going to 4130 may help but I would really think you need to look at your chassis design more carefully.

That is a good point.  4130 has the same basic material stiffness as mild steel.  Known as elastic modulus (E is the designation), for all steels, heat treated or not, is about 30 x 10E6 psi.  Chassis stiffness is a function of the design, mainly tubing diameter and the amoutn of triangulation in the design.  4130 is higher strength, so it can use thinner wall, but overall stiffness is not changed.

[panic]

If you use the same OD and thinner wall for 4130 the stiffness goes down slightly.
.065" 4130 is only 81% as stiff as .083" mild in 1.500" OD.
I'm not really confident that the sizes specified by many sanctioning bodies are well conceived. Does anyone know of a rule that specifies minimum OD/wall vs. free (unsupported) span length?

[hotrod]

I don't know of a rule that specifies free span but another issue largely ignored is a rule that takes into consideration the vehicle weight. Most only vary the tube size according to speed potential for the class.

The one exception to that which I found when I was looking a couple years ago, is the Desert truck racing folks have different tube sizes based on the vehicle weight.

Larry