The reverse happens if the arc is lengthened during welding. The wire feeding mechanism automatically drives the electrode wire from the wire spool to the welding gun and arc at a uniform rate. The speed of the wire feeding mechanism is adjustable, so that the wire-feed speed can be set to equal the melting rate. If the unit is to be used with a constant-current voltage power source, the drive unit speed is varied automatically by an electronic control device. The function of the welding gun is to deliver the wire, shielding gas, and welding current to the arc area.
Guns are either the push or pull type.
The pull gun has drive rolls that pull the welding wire from the wire feeder, and the push gun has the wire pushed to it by drive rolls in the wire feeder itself. Both guns have a trigger switch that controls the wire feed and arc as well as the shielding gas. When the trigger is released, the wire feed, arc, and shielding gas stop immediately. With some equipment, a timer is included to permit the shielding gas to flow for a predetermined time to protect the weld until it solidifies. Guns are available with a straight or curved nozzle.