Schumacher 00-99-000985/1009 - Manuel (Page 15)

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During the welding, the work pieces will become hot and will tend to
expand. The expansion may cause the pieces to shift from the regular
position. If possible, the work pieces should be clamped into the position
they are to occupy when the welding is completed.
Selecting The Proper Electrode 4.3
The welding electrode is a rod, or wire, of electrically conductive metal,
coated with a layer of flux.
When welding, electrical current flows between the electrode (rod) and the
grounded metal work piece. The intense heat of the arc between the rod
and the grounded metal melts the wire and the flux.
The rod wire joins with the base metal in the work piece to form the weld
bead. The burning flux forms a gas shield around the arc and helps to
control the flow of the fusing metals that form the weld bead.
The type and thickness of the metal and the position of the work
piece determines the electrode type and the amount of heat needed
in the welding process. Heavier and thicker metals require more heat
(amperage).
There is no hard and fast rule that determines the exact rod or heat setting
required for every situation. To check the rod requirements for particular
applications, refer to the rod guide on your welder, and then experiment on
some scrap metal.