BOC Smootharc TIG 185 DC Manuel d'utilisation - Page 5
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BOC Smootharc TIG 185 Operating Manual
2.3 Process variables
Process variable
Explanation
DCEN
When direct-current electrode-
Narrow bead,
negative (straight polarity) is used:
deep penetration
•
Electrons strike the part being welded
at a high speed
Nozzle
•
Intense heat on the base metal is
produced
•
The base metal melts very quickly
Ions
Electrons
•
Ions from the inert gas are directed
towards the negative electrode at a
relatively slow rate
•
Direct current with straight polarity
does not require post-weld cleaning
to remove metal oxides
DCEP
The DCEP (reverse polarity)
Wide bead,
are different from the DCEN in
shallow penetration
following ways:
•
High heat is produced on the
Nozzle
electrode rather on the base metal
•
The heat melts the tungsten
electrode tip
Ions
Electrons
•
The base metal remains relatively
cool compared to sing straight
polarity
•
Relatively shallow penetration is
obtained
•
An electrode whose diameter is
too large will reduce visibility and
increase arc instability
Usage
For a given diameter of tungsten
electrode, higher amperage can be
used with straight polarity. Straight
polarity is used mainly for welding:
•
Carbon steels
•
Stainless steels
•
Copper alloys
The increased amperage provides:
•
Deeper penetration
•
Increased welding speed
•
A narrower, deeper, weld bead
•
Intense heat means a larger diameter
of electrode must be used with DCEP
•
Maximum welding amperage should
be relatively low (approximately six
times lower than with DCEN)
2.4 Shielding gas selection
Material
Shielding gas
Brass
Argon
Cobalt-based alloys
Argon
Copper-nickel (Monel)
Argon
Deoxised copper
Helium
Helium(75%)/
Argon(25%)
Nickel alloys (Inconel)
Argon
Helium
Steel
Argon
Helium
Magnesium alloys
Argon
Stainless steel
Argon
Helium
Titanium
Argon
Helium
BOC Smootharc TIG 185 Operating Manual
Benefits
Stable arc
Low fume
Stable and easy to control arc
Stable and easy to control arc
Can be used for copper-nickel to steel
Increased heat input
Stable arc
Good penetration
Stable arc
Lower penetration
Stable arc
Manual operation
High speed automated welding
Stable arc
Good penetration
High speed automatic welding
Deeper penetration
Small concentrated HAZ
Used with continuous high frequency AC
Good arc stability
Good cleaning action
Good penetration
Good arc stability
Deeper penetration
Stable arc
High speed welding
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