tig welding

[akbushpilot2006]

I need help
I have been tig welding 4130 tubing together for a few weeks I have been getting better at it I have read everything I can find you tubed everything seems pretty simple just takes lots of practice. I have noticed that in a few places on the frame I will start welding everything thing seems normal then the puddle explodes!! It only happens when I am welding 4130 to the old tubing mild steel I think. I have not had this problem everywhere just certain area in the frame been really pissing me off about wore out a grinding wheel grinding tungstens any ideas thanks for any thought

[dave powelson]

Contamination outside or especially inside the tubes.
Oil, moisture, paint the biggest offenders.
Swab the tube insides and LOOK inside them as well.
The old tubes need to be cleaned, solvent wipe
and wire brush any old fillets and dress them up with
burr after solvent wiping and solvent brushing and drying.

Old air frame tubing will often be have linseed oil put into
the tube section, via a small hole towards the top or upper end,
which is then welded shut--this is done after the tube connection
joints are finished. One can carefully drill out the hole seal weld,
using this as a vent, then with low, low heat (propane torch) play
this around to cook out the linseed oil.

Propane works well to get low heat burnoff of paint, on the frame repairs.
Silicone gooped (for corrosion protection) on tail draggin' dusters in
the tube joints at the tail wheel, gets burned off this way for repair or
inspection....then re-gooped with silicone.

Chrome-moly that's been hit-can also have little, fractured chunks
come spitting out from the parent damaged tube; which is a clue as
to just how much unseen stress/damage remains in that poor tube.

[wkdivr]

One of the things that happen, is you have a gas buildup in the tube, and it blows out at the end. When joining tubes together, you need to drill a small hole to vent the heated gas in the tube.

[shovelon]

One of the things that happen, is you have a gas buildup in the tube, and it blows out at the end. When joining tubes together, you need to drill a small hole to vent the heated gas in the tube.

Yep, absence of vents is 99% of the bubbling problem on 4130.

[Oscar]

what size vent? 1/16" good enough? 1/8"?

[wkdivr]

I wouldn't go any bigger then 1/8th. Hell, 1/16th would probably be ok. Try to locate the vent holes where they won't be seen, and don't weaken the tube.

[akbushpilot2006]

Contamination outside or especially inside the tubes.
Oil, moisture, paint the biggest offenders.
Swab the tube insides and LOOK inside them as well.
The old tubes need to be cleaned, solvent wipe
and wire brush any old fillets and dress them up with
burr after solvent wiping and solvent brushing and drying.

Old air frame tubing will often be have linseed oil put into
the tube section, via a small hole towards the top or upper end,
which is then welded shut--this is done after the tube connection
joints are finished. One can carefully drill out the hole seal weld,
using this as a vent, then with low, low heat (propane torch) play
this around to cook out the linseed oil.

Propane works well to get low heat burnoff of paint, on the frame repairs.
Silicone gooped (for corrosion protection) on tail draggin' dusters in
the tube joints at the tail wheel, gets burned off this way for repair or
inspection....then re-gooped with silicone.

Chrome-moly that's been hit-can also have little, fractured chunks
come spitting out from the parent damaged tube; which is a clue as
to just how much unseen stress/damage remains in that poor tube.

Thanks for the insight