Gases - Selco Unistep 3500 Instrucciones De Uso

SELECTION GUIDE OF WELDING PARAMETERS WITH REFERENCE TO THE MOST TYPICAL APPLICATIONS AND MOST
COMMONLY USED WIRES.
Wire diameter - weight per metre
Voltage
arc (v)
Low penetration for thin
16 - 22
SHORT - ARC
Automatic fillet welding
24 - 28
GLOBULAR-ARC
(transition area)
Low penetration with
adjustment to 200 A
30 - 45
SPRAY - ARC

6.1.3 Gases

MIG-MAG welding is defined mainly by the type of gas used: inert for MIG welding (Metal Inert Gas), active for MAG welding
(Metal Active Gas).
Carbon dioxide (CO 2 )
Using CO 2 as a shielding gas, high penetrations and low operating cost are obtained with high feeding speed and good mechanical
properties. On the other hand, the use of this gas creates considerable problems with the final chemical composition of the joints
as there is a loss of easily oxidisable elements with simultaneous enrichment of carbon in the weld pool.
Welding with pure CO 2 also creates other types of problems such as excessive spatter and the formation of carbon monoxide porosity.
Argon
This inert gas is used pure in the welding of light alloys whereas, in chrome-nickel stainless steel welding, it is preferable using argon
with the addition of oxygen and CO 2 in a percentage of 2% as this contributes to the stability of the arc and improves the form of
the bead.
Helium
This gas is used as an alternative to argon and permits greater penetration (on thick material) and faster wire feeding.
Argon-Helium mixture
Provides a more stable arc than pure helium, and greater penetration and travel speed than argon.
Argon-CO 2 and Argon-CO 2 -Oxygen mixture
These mixtures are used in the welding of ferrous materials especially in SHORT-ARC operating mode as they improve the specific
heat contribution. They can also be used in SPRAY-ARC. Normally the mixture contains a percentage of CO 2 ranging from 8% to
20% and O 2 around 5%.
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0,8 mm 1,0-1,2 mm
Good penetration and
materials melting control
60 - 160 A 100 - 175 A
Automatic welding
with high voltage
150 - 250 A 200 - 300 A
Automatic welding
with multiple runs
150 - 250 A
200 - 350 A
1,6 mm 2,4 mm
Good flat and vertical
melting
120 - 180 A 150 - 200 A
Automatic welding
downwards
250 - 350 A 300 - 400 A
Good penetration Good penetration, high
downwards deposit on thick materials
300 - 500 A 500 - 750 A
Not used
Not used