Impax IM-MMA140, Instruction Manual, Page: 17 / 24

16
OPERATION
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.
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. Under these conditions and in
original packaging, electrode storage time is
practically unlimited. It should be noted that
electrodes are now available in hermetically
sealed packs which obviate the need for drying.
However, if necessary, any unused electrodes
must be redried according to manufacturer's
instructions.
Drying of Electrodes
Drying is usually carried out following the
manufacturer's recommendations and
requirements will be determined by the type of
electrode.
IMPORTANT – Thermostatic Protection
(Duty Cycle)
This product has a rated duty cycle of 40%. The
percentage represents the welding time in a 10
minute period for example 40% means that the
welding time is 4 minutes with a rest time of 6
minutes in a ten minute period although the
actual duty cycle will depend on the amperage
used. If the Welding Power Supply is used for
longer than the duty cycle or if you are welding
using large welding rods you may experience a
temporary current shut off. This is to protect the
transformer inside the Welding Power Supply
from overheating.