7.10 Wire Feeders Used with GMAW/FCAW
The wire electrode used in gas metal arc welding comes in large coils (spools) or drums. These wire coils or drums contain hundreds or even thousands of feet (meters) of wire.
Small coils of wire are mounted on free-turning axles near the wire feed mechanism. If the larger drums of wire are used, the drum is placed near the wire feeder. The wire is smoothly drawn from either the coil or drum.
Wire feeders consist of a coil-mounting device, a set of drive wheels for the wire (which are commonly referred to as drive rolls), and an adjustable, constant-speed motor to turn the wire drive wheels. Figure 7-38 shows a wire feeder with the drive wheels outside the wire feed control unit. Both drive wheels have gear teeth on the outside circumference. The driven wheel moves the second wheel by means of the gear teeth. One of the wheels is driven by an adjustable dc type constant-speed motor. The tension on the wire passing between these wheels is adjusted by turning a tensioning device that moves the wheels closer together or farther apart.
Sometimes, wire feeders are contained inside the GMAW machine. Figure 7-33 shows such a machine. Other welding outfits have the wire feeder separate from the welding machine. See Figure 7-39.
An inch switch or a jog switch on the wire drive control panel is used to rotate the drive motor slowly. Occasionally, it is necessary to change wire reels, replace parts, or clear a problem in the wire drive unit. To reinstall the electrode wire through the cable liner and contact tube, the wire must be moved ahead slowly. The wire is moved slowly so that it does not bend or kink within the electrode cable. Note the wire jog switch in Figure 7-38.
The shielding gas hose may have air in it before its first use after a long shutdown period. To clear or purge the hose and gun, the shielding gas is turned on for a short period prior to welding. A purge switch on the wire feeder or power supply may be provided for this purpose. When the purge switch is pressed, shielding gas will flow. The flow will continue until the purge switch is released.