Impax IM-TIG200 Instruction Manual page 37

TIG OPERATION
Welding Polarity
DC Electrode Negative Polarity (Direct
Current Straight Polarity)
While Welding, there is a continuous flow of
electrons from the electrode to the workpiece.
This is the most used polarity, ensuring limited
wear of the electrode, since the majority of the
heat concentrates on the anode (workpiece).
Narrow and deep welds are obtained with high
travel speeds. Most materials, with the
exception of aluminum and magnesium, are
welded with this polarity (Fig.31).
Fig 31
DC Electrode Positive Polarity. (Direct
Current Reverse Polarity)
In this case, there is a continuous flow of
electrons from the workpiece to the electrode.
The reverse polarity is used for welding alloys
covered with a layer of refractory oxide.
With this polarity the electrode functions as
anode and is subjected to a high degree of heat;
the workpiece is bombarded by positive ions
sent from the electrode which break the surface
oxide.
In Electrode Positive Polarity, high currents
cannot be used, since they would cause an
excessive wear of the electrode.
Steel TIG Welding
The TIG process is very effective for welding
both carbon steel and alloy steel, especially in
applications requiring precision results. DC
Electrode Negative Polarity is required. Since
this process does not include the removal of
impurities, proper cleaning and preparation of
the edges is required.
Filler material: The filler rods must deposit welds
with mechanical characteristics appropriate for
the application.
Copper TIG Welding
Since the TIG welding is a process characterized
by high heat concentration, it is particularly
suitable for welding materials with high thermal
conductivity, like copper. As with steel, the DC
Electrode Negative Polarity is employed, with
argon as protective gas. Considering the fluidity
of molten copper, the use of backup support
may prove useful.
Filler material: In order to avoid the oxidation of
the molten material, filler materials containing
phosphorus, silicon or other deoxidating
materials are typically used. The mechanical
properties can also be improved through the use
of silver.
IMPORTANT – Thermostatic Protection
(Duty Cycle)
The TIG operation has a rated duty cycle of
20%. The percentage represents the welding
time in a 10 minute period for example 20%
means that the welding time is 2 minutes with a
rest time of 8 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.
The thicker the material being welded, the
greater the current required, therefore, the hotter
the machine will become and the quicker it will
cut out. When the windings reach performance
temperature the cut out switch will operate
illuminating the indicator lamp on the front
panel. After a few minutes the cut out switch will
reset and the welder will be ready for use.
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