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4.0 Overview
Shielding gases for TIG welding are important for
keeping the arc stable and protecting the molten
weld metal from contamination during welding.
The major function of a shielding gas is to
surround the weld zone with a protective shroud
of non-reactive shielding medium. This removes
harmful elements from the atmosphere (oxygen,
nitrogen gas) which would give a poor quality
weld deposit if they contacted the molten metal.
The TIG process cannot use a shielding gas that
has an oxidising agent in it i.e. CO
2
or O
2
. This
is due to the reaction with tungsten and will
cause immediate particle disintegration of the
tungsten.
The gases that can be used are Argon by itself
or additions of helium. The use of helium has
the effect of increasing the heat in the arc, or
molten pool and therefore more penetration
and a molten pool that remains fluid for longer
periods of time and allows contaminants to
'boil' off before freezing. The recommended
flow rate is from 5 l/min to 10 l/min depending
on the amperage being used.
One of the major causes of contaminated
welds/tungstens is the operator removing or
turning off the gas flow before cooling past the
critical level has taken place. For example when
finishing a weld the torch should be held at
the end until the pool has cooled past the 'red'
stage. This is also the case for the tungsten, as it
will turn to a blue colour (oxide) if shielding is
removed prior to cooling.
4.1 General Instructions for
Pressure Regulators
Before mounting the regulator
1. Step aside and open the cylinder valve. This
is called "cracking the cylinder" and by doing
this you will release any dirt that may be
trapped in the valve of the bottle.
Regulator connection
1. Fit the regulator "bull-nose" into the cylinder
valve and tighten the nut (do not over
tighten)
2. Turn the regulator bonnet in an anti clockwise
rotation, so that there is no pressure on the
regulator diaphragm. This is the fully off/no
flow position.
3. Attach hose nut/nipple to the regulator outlet.
4. Connect the gas hose to the nipple with the
supplied hose clamp.
5. Connect the other end of the hose into the
machine wire feeder quick connection nipple.
Setting the regulator
1. Open the valve of bottle slowly
2. The high pressure gauge will show the
pressure in the bottle.
3. Open the regulator bonnet until the desired
pressure is achieved on the low pressure
gauge (12 to 20 L/min usually).
4. Pull the torch trigger to simulate a welding
condition, and readjust the regulator bonnet
to the desired pressure that will be required
while welding (it is normal for the gas
delivery gauge to drop back while in use due
to pressure drop when in the static position).
Close the valve of the cylinder after welding
has stopped. If the machine will be out of
use for a long period of time, you should
unscrew the regulator bonnet screw to act as a
secondary valve.
4. Shielding Gases
