24
Selection of the Correct Polarity on the Power
Source
Many power sources are fitted with an optional
reverse polarity dinse connector.
To achieve the optimum welding it is important
to adhere to the consumable manufacturer's
instruction to select the polarity.
As a general rule all solid and metal cored wires
are welded on electrode positive. (Work return
lead fitted to the negative connector.)
Some grades of self shielded flux cored wires
(i.e. E71T-11, E71T-GS etc) needs to be welded on
electrode negative. (Work return lead fitted to the
positive connector.)
Selection of the Correct Shielding Gas
The selection of the shielding gas has a direct
influence on the appearance and quality of
the weldbead.
The thickness of the material to be welded will
determine the type of shielding gas that has to
be selected. As a general rule the thicker the
material (C-Mn and Alloy steels) are the higher the
percentage of CO
2
in the shielding gas mixture.
Different grades of shielding are required for
materials such as stainless steel, aluminium
and copper.
The following table gives an indication of the
most common shielding gases used for Carbon
Manganese and alloy steel.
Material thickness
Recommended
shielding gas
1–8 mm
Argoshield Light
5–12 mm
Argoshield Universal
>12 mm
Argoshield Heavy
6.6 4T/2T Trigger Latch Selection
On all MIG machines there is no current or wire
feed until the trigger on the torch is depressed. If a
welder is doing a lot of welding then he has to hold
the trigger down for long periods of time and may
cause discomfort. This is can be similar to repetitive
strain injury (RSI) that has become a very popular
topic for compensation by office workers.
On all machines a special function called 2T and
4T is available. Also referred to as trigger latching,
this special feature allows the operator to relax the
trigger after first depressing it, the gas shielding to
start before the welding commences. This feature
is of particular importance as it ensures that the
weld will have adequate gas shielding to eliminate
the risk of oxidisation (contaminants) causing a
defective weld. (Remember, a defective weld may
not be detected by a visual inspection.)
The 2T/4T function also allows for the shielding gas
to continue after the weld has finished and cooled.
This eliminates the risk of oxidation while the
weld is still in its molten state. This is particularly
important when welding stainless steel materials.
Summary of Contents for BOC RAPTOR 160 MIG
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