MESSER SolidWELD MIG 250GS Guide D'utilisation page 13

Selection of the Correct Power Source
Power sources for MIG welding is selected on a number of
different criteria, including:
1
Maximum output of the machine
2
Duty cycle
3
Output control (voltage selection, wire feed speed control)
4
Portability
The following table gives an indication of the operating amperage
for different size wires.
Wire Size Amperage Range (A)
0.8 mm 60–180
0.9 mm 70–250
1.0 mm 90–280
1.2 mm 120–340
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) need 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 in the shielding gas mixture.
2
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 Ferroline C15
5–12 mm Ferroline X2 C12
>12 mm Ferroline He20 C12
More detailed selection charts, including recommendations
for welding parameters (voltage, amperage, electrical stickout,
travelspeed and gasflow rate) can be found in the following pages.
MIG 250GS Operating manual 013