BOC Smootharc Multi 180 - Polarity and Shielding Gases; Shielding Gas Selection Guide

39BOC Smootharc Multi 180/200 Operating manual
Polarity
Many power sources are tted 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 tted to the negative connector).
Some grades of self shielded ux cored wires (i.e. E71T-11, E71T-GS etc)
needs to be welded on electrode negative. (Work return lead tted to
the positive connector.)
Shielding gases
The selection of the shielding gas has a direct inuence 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 CO₂ in
the shielding gas mixture.
Di󹟽erent 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
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
they have to hold the trigger down for long periods which may cause
discomfort. This is can be similar to repetitive strain injury (RSI).
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 rst 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 nished 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.