BOC Smootharc MMA 130, Руководство по эксплуатации

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Lift Arc™
During this method of arc initiation, the
tungsten is actually touching the workpiece.
This occurs at very low amperage that is only
sufficient to pre-heat, not melt the tungsten.
As the tungsten is moved off the plate, the arc
is established. With this method, there is little
chance of tungsten inclusion occurring.
3.3 Process Variables
DCEN
When direct-current electrode-negative
(straight polarity) is used:
• Electrons strike the part being welded at a
high speed.
• Intense heat on the base metal is produced.
• The base metal melts very quickly.
• 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.
Use of DCEN
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.
DCEN - Narrow bead - Deep penetration
Nozzle
Ions Electrons
DCEP
The DCEP (reverse polarity) are different from
the DCEN in following ways:
• High heat is produced on the electrode rather
on the base metal.
• The heat melts the tungsten electrode tip.
• 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.
Use of DCEP
• 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).
DCEP - Wide bead - Shallow penetration
Nozzle
Ions Electrons