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Old 04-19-2017, 11:05 PM
Metal1 Metal1 is offline
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Default 4130 welding

Should a certain filler be used to keep the strength intact at the joints on moly? I've seen people welding moly cages in with regular -6, -3 rod and it just seems like to it would defeat the purpose of the moly itself. Shouldn't NHRA test this?
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Old 04-19-2017, 11:13 PM
mastuart mastuart is offline
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I believe they use that rod because the average guy will have better luck using it. Some of the 4130 get mixed in with it when welding. You don't want brittle joints. After welding the joint should be annealed. I THINK IT IS THE PREFERED ROD TO USE UNLESS THE WELDMENT IS GOING TO BE HEAT TREATED.
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Last edited by mastuart; 04-19-2017 at 11:17 PM.
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Old 04-20-2017, 12:43 AM
crystallographic crystallographic is offline
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Quote:
Originally Posted by Metal1 View Post
Should a certain filler be used to keep the strength intact at the joints on moly? I've seen people welding moly cages in with regular -6, -3 rod and it just seems like to it would defeat the purpose of the moly itself. Shouldn't NHRA test this?
Believe me, NHRA has done comprehensive tests on the "4130 welding topic" for cages, chassis and safety equipment, over the years.

And so has the FAA, by the way.

There have been many welding text books written which include the "4130 topic" and the basic rule is this:

If you are going to heat treat the finished welded part, then you weld your 4130 with 4130 rod.

If you are not going to heat treat the finished part/assembly, then you weld it with mild steel - e.g. ER70S6, 3, 2 or ER70D2, or RG45, or RG60, etc etc.

Remember that countless numbers of airplane frames (airframes) were gas welded and TIG welded 4130 for the last 75 years, using mild steel fillers.

NHRA specifies that all roll cages shall be 4130 of such and such wall thickness and welded with mild steel, using TIG - and there shall be a hole drilled in such and such location to verify wall thickness of the tubing. And the weld beads shall not be less than such and such width, so the the weld penetration should be sufficient for this assembly.

Anyway, that is the general idea of what you are dealing with .....
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Old 04-20-2017, 06:02 AM
dschumann dschumann is offline
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An' don't grind your welds on tubing.

Majority of the strength is in the fillet.
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Old 04-20-2017, 08:07 AM
billfunk29 billfunk29 is offline
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Default cage tubing

I tried some Docol R8. Strong, but weld friendly.
http://www.aedmotorsport.com/catalog.../docol-tube-r8

Nice stuff. I won't be going back to ChroMo.
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Old 04-20-2017, 11:01 AM
crystallographic crystallographic is offline
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I tried some Docol R8. Strong, but weld friendly.
http://www.aedmotorsport.com/catalog.../docol-tube-r8

Nice stuff. I won't be going back to ChroMo.
Overseas sourcing tolerance and quality problems persist, with CroMo.
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