A friend is a metal shop teacher in a local high school.
He has an older Hobart TIG welder and he tells me that his tungsten
electrodes seem to lose their points much too fast.
What are some possible causes for this assuming that the current is
not set too high and that he's using the proper shielding gas?
What is the proper polarity as defined by electrode positve or
negative rather than stating forward or reverse polarity?
This may be his problem. How can he determine it for sure?
What helped me learn it FINALLY was USNavy, except substitute SSN. Straight
Stinger Negative. That leaves only one other one, so that has to be
If the rod is positive, +, more heat will be on it. If rod is negative, -,
less heat will be on the rod. Reverse symbol + has two reversed legs to
make the + sign. Straight just has one straight leg to make the - sign.
Make the piece you want the hottest to be the +.
That took me a long time to grasp.
That's why AWS has long recommended that the terms straight and reverse
polarity be replaced with DCEN and DCEP (Electrode Positive or Negative).
I like to think of the direction of electron flow through the arc, from
negative to positive, just like in a Cathode Ray Tube (CRT) where the
negative electrons go from the cathode (electron gun) to the anode
(screen) - just in case you forget that the cathode is negative anode
positive. The energy of the electrons is deposited entirely in the
positive side of the arc (while conducted and radiated heat travels in
all directions), putting the most heat in the positive side. For a high
penetration rod like 6011 the use of DCEN makes the electrons hit the
puddle for a hotter and deeper puddle, for a fill electrode like 7018
DCEP will melt more electrode with less heat input to the workpiece. (In
electron beam welding *all* of the heat is deposited by the electrons,
since there is no arc to radiate and conduct - a DCEN process where the E
is an Electron gun.)
Obviously the goal of TIG welding is to melt the workpiece not the
electrode, so DCEN is used (ignoring all variants of AC). Electrode tip
life is also affected by:
Tip angle, where a sharp angle like 60 degrees total across the section
of the tip will result in a hotter and shorter lived tip than a 90 or 120
degree tip. I consider 90 degrees as "standard", rarely use 60 (good for
brazing small parts) and move toward 120 for current over 150 amps or
so. (tip angle also affects arc size and shape, with a 60 degree tip
producing the broadest least concentrated arc and the 120 degree tip
producing the smallest most concentrated arc - consider that the
electrons tend to leave the electrode surface straight out perpendicular
to the surface. so one must make a trade off between tip life and arc
Tip flat, the size of the flat disk ground square across the end where
the sharp point was, typically around 5 or 10 percent the diameter of the
electrode. You can TIG with a sharp point (no flat), but, unless you are
using a very low current like under 10 amps (where the sharp point is
best) then the sharp tip will quickly melt back a bit, to about where the
flat should have been. The ground flat at the end electrode works better
than the melted back electrode because a ground surface with lots of
grooves and sharp edges on a microscopic scale emits electrons better
than a smooth melted surface. Higher current needs a larger flat.
(The tip cone and flat are normally symmetrical about the center of the
electrode but can be ground canted to one side where limited access makes
it desirable to direct the arc a bit to the side.)
Electrode size, too small an electrode will guarantee short tip life.
Lincoln used to have some pretty good books on the subject, probably
still does, recommended highly.
eng> > > He isn't running reverse polarity is he ?
In TIG Electrode Negative covers everything except Aluminum and
Aluminum and Magnesium use AC.
Electrode Positive can be used to get a nicer ball on your tungsten
before AC welding aluminum.
You can TIG weld aluminum using DC Electrode Positive, but your
tungsten will get hammered hard.
The limiting factor is that the tungsten has to be at least as think as
Other things that can cause the tungsten to erode are contaminated gas,
a leak in the gas fittings somewhere can taint your argon with air,
running the high freq. continuously in DC (should be start only),using
the wrong type of tungsten for your polarity, and using an undersized
tungsten for the job.