Page 72 - SSAB Welding Handbook Edition 2

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12.0 The use of shielding gas Welding handbook

Argon
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The addition of argon in the shielding gas promotes
the formation of the arc during welding. An electric
arc in the gap between the electrode and the work
piece can be established when the atoms are ionized
to ions and electrons, see fig. 12.5. Argon atoms are
ionized relatively easily. Consequently, argon Fig. 12.6: The penetration profile promoted by a shielding gas with
high argon content.
promotes easy arc striking.

Anode The negative effects from a relatively small and
narrow penetration profile include an increased risk
for lack of fusion in the joint as well as a somewhat
higher susceptibility towards porosity in the weld
metal.
Electron movement

Ion movement Carbon dioxide

The carbon dioxide in the Ar/CO shielding gas
2
mixtures stabilizes the arc.

The CO also contributes to a higher capacity of heat
2
Cathode transfer to the liquefied melt, which influences the
geometry of the weld metal. It helps to give the weld
Fig. 12.5: Movement of electrons and ions in an arc. In this case, the metal a relatively large and round shape which is
electrode has a positive polarity and the joint has a negative illustrated in fig. 12.7. The shape and size of the weld
polarity. The temperature in the arc reaches several thousand
degrees Celsius. metal provides further resistance to lack of fusion
and porosity in the weld metal.

Argon also enhances the formation of the spray arc
transfer. However, a 100% argon shielding gas would
lead to an unstable arc so the shielding gases need to
include another gas component that has the ability to
stabilize the arc.
Fig. 12.7: Penetration performance of a shielding gas consisting of
Argon promotes a narrow and intense arc that only CO .
2
produces a deep penetration profile in the center of
the weld metal, often called the argon finger, see
fig. 12.6. It lowers the heat transfer capacity in the CO is normally added in relatively small amounts
2
melt during welding; contributing to a narrower according to the proposals in table 12.1. If the CO
2
penetration profile for each weld pass. content in the shielding gas is too high, it will
obstruct the formation of spray arc welding. The
maximum CO content under which spray arc
2
welding is feasible in Ar/CO mixtures is
2
approximately ≤ 25%.

72 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.