--Sometimes, just at the end of a bead I'm doing in tig, after I
shut off the power, the bead ends with this thing shaped like a volcano;
i.e. one burst bubble or some such I guess. Going back and trying to fill it
can sometimes be difficult; i.e. I think I've got it, then I turn off the
power and the damned flaw is back! Can someone describe what's going on?
EXACTLY the same problem I have with some 3/16 x 1" strap Ive been
using for this and that.
Once you have moved on up the weld line..you look back to see this
bubble form, pop and leave a crater.
Hope someone comes up with an answer.
"I think this is because of your belief in biological Marxism.
As a genetic communist you feel that noticing behavioural
patterns relating to race would cause a conflict with your belief
in biological Marxism." Big Pete, famous Usenet Racist
I've had this too a couple of times but I could get rid of it by
adjusting downslope to a bit longer.
Not an expert though, just someone who's teaching himself to TIG; with
the help of this group.
I have had problems with that in the past. I think that a combination of:
getting stuff really clean.
throttling back on the heat as the end approaches
holding the torch over the weld puddle until it stops glowing or
the postflow switches off solved it.
I am a LONG way from being an expert at this, but when I asked how to solve
this problem of the local folks who are really good at welding, they
suggested that at the end of the bead I throttle down the voltage and run
the torch backward over the bead I've completed for a "dab" or so. This
seems to have helped the end of my beads look a little cleaner, and
minimized the "cratering".
Ernie will probably chime in and tell me this is the wrong thing to do (and
then I will adopt his suggestion, of course), but FWIW this has helped me.
Sounds like Hydrogen to me.
Hydrogen is fully soluble in the liquid steel in the weld pool, but as it
freezes the hydrogen is expelled, hence your 'volcano'.
Hydrogen is not present in your material or filler rod, but may be being
generated by decomposition of grease, oil, or water on the job. (or any
organic material for that matter!)
Try thoroughly cleaning the metal to be joine and mak sure there's no
condensation on it by warming it.
Your gas shield is going away before the metal is solidified and the
molten metal is oxidizing to form a crater.
When this happens resist the urge to just weld over it.
It is better to grind out the crater with a die grinder, then weld it
Otherwise you are just stirring the oxides right back into the weld
I'm really really sure this isn't the case for steel. I studied
hydrogen in steel welds for my Doctoral research. Is so for Al
apparently - hydrogen in melt causes blowholes. But steel - really
strong convincing evidence says no, hydrogen does not get rejected out
on solidification. So immune is steel to this fault that you can use
cellulosics (xx10's), which deliberately give sky-high hydrogen levels
to make the arc fierce - narrow, stiff and penetrative (and get shield
without much slag). There is no way that TIG even running across
slatherings of grease like for a pure joke could come within a tenth
(???) of the hydrogen level cellulosics give.
[reasoning -- cellulose resists breakdown 'til the last second, then
shoots down between the steel core wire and the flux covering into the
arc - it is very difficult to jack up the hydrogen level in the arc so
high without this "injection mechanism"]
I'd ask our keen student of welding aobut slope-down, with view to
explanation beng a "shrinkage pipe" to start with.