Impax IM-TIG200 Instruction Manual page 26

MMA OPERATION
Cellulosic electrodes contain a high proportion
of cellulose in the coating and are characterised
by a deeply penetrating arc and a rapid burn-off
rate giving high welding speeds. Weld deposit
can be coarse and with fluid slag, deslagging
can be difficult. These electrodes are easy to
use in any position and are noted for their use in
the stovepipe (vertical down position) welding
technique.
Features:
• • Deep penetration in all positions
• Suitability for vertical down welding
• Reasonably good mechanical properties
• High level of hydrogen generated - risk of
cracking in the heat affected zone
Rutile Electrodes contain a high proportion of
titanium oxide (rutile) in the coating. Titanium
oxide promotes easy arc ignition, smooth arc
operation and low spatter. These electrodes are
general purpose electrodes with good welding
properties. They can be used with AC and DC
power sources and in all positions. The
electrodes are especially suitable for welding
fillet joints in the horizontal/vertical position.
Features:
• Moderate weld metal mechanical properties
• Good bead profile produced through the
viscous slag
• Positional welding possible with a fluid slag
(containing fluoride)
• Easily removable slag
Basic electrodes contain a high proportion of
calcium carbonate (limestone) and calcium
fluoride (fluorspar) in the coating. This makes
their slag coating more fluid than rutile coatings
- this is also fast-freezing which assists welding
in the vertical and overhead position. These
electrodes are used for welding medium and
heavy section fabrications where higher weld
quality, good mechanical properties and
resistance to cracking (due to high restraint) are
required.
Features:
• Low hydrogen weld metal
• Requires high welding currents/speeds
• Poor bead profile (convex and coarse surface
profile)
• Slag removal difficult
Iron powder electrodes contain an addition of
metal powder to the flux coating to increase the
maximum permissible welding current level.
Thus, for a given electrode size, the metal
deposition rate and efficiency (percentage of the
metal deposited) are increased compared with
an electrode containing no iron powder in the
coating. The slag is normally easily removed.
Iron powder electrodes are mainly used in the
flat and horizontal/vertical positions to take
advantage of the higher deposition rates.
Efficiencies as high as 130 to 140% can be
achieved for rutile and basic electrodes without
marked deterioration of the arcing
characteristics but the arc tends to be less
forceful which reduces bead penetration.
Care of Electrodes
The quality of weld relies upon consistent
performance of the electrode. The flux coating
should not be chipped, cracked or, more
importantly, allowed to become damp.
Drying of Electrodes
Drying is usually carried out following the
manufacturer's recommendations and
requirements will be determined by the type of
electrode.
Storage
Electrodes should always be kept in a dry and
well-ventilated store. It is good practice to stack
packets of electrodes on wooden pallets or
racks well clear of the floor. Also, all unused
electrodes which are to be returned should be
stored so they are not exposed to damp
conditions to regain moisture. Good storage
conditions are 100°C above external air
temperature. As the storage conditions are to
prevent moisture from condensing on the
electrodes, the electrode stores should be dry
rather that warm.
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