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A7 TIG Orbital System 150
© Kemppi Oy 2016
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OPERA
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3.5.2 Shielding and backing gas
Select proper shield gas/gas mix for optimum results.
100% argon is normally used for TIG welding. In certain
cases, you can benefit from using a mixed gas, such as 95%
argon, 5% hydrogen. This mixed gas gives better control of
the weld puddle and lower heat input. Adding hydrogen
or helium increases the arc voltage and creates a "stiffer",
more focused arc column.
Industrial grade inert gas is sufficient for most stainless
steel welds. Use a higher purity grade for high quality
welds on easily oxidizable alloys.
The purpose of purging is to replace unwanted air and
other vapor contaminants from the root pass by a gas
that prevents oxidation during welding. Oxidation can
produce a variety of problems, such as root oxidation
(sugar), incomplete fusion, porosity and changes in weld
chemistry, which can affect weld mechanical and corrosion
resistance properties adversely.
Use purging when welding stainless steel, nickel alloys,
and most nonferrous base metals. Argon is commonly
used.
The “chamber” created around the tube joint by the
installation of the weld head is flooded with inert gas
that both protects the weld puddle from oxidation and
the tungsten electrode. The gas hose material used
in the weld heads is specifically designed to prevent
atmospheric moisture from contaminating the shielding
gas by permeation.
The gas regulator/flow meter should be set for 4
bar (60 PSI) and a suitable flow rate. Recommended gas
flow rate is 3 to 5 l/min for backing gas and 5-10 l/min
for shielding gas. Set pre-purge time so that backing gas
volume is about 10 times the volume to be put inside the
tube.
You can apply separate backing gas for root
protection. When using backing gas, also use dual flow-
meter regulator that allows having two independently
regulated (shielding and backing gas) circuits from one gas
bottle.
3.6 Instructions for welding
Use the following 5-step procedure to start welding:
1. Select and install suitable collets.
2. Mount weld head around the tube.
3. Pre-purge the tube ID with shielding gas.
4. Select the program you want to use.
5. Start welding by pressing the Start button.