208 Modern Welding Copyright Goodheart-Willcox Co., Inc. To correct the cause of a bird’s nest, use the cor- rect contact tip-to-work distance, which is explained later in the chapter, or adjust the settings on the weld- ing machine or wire feeder. If this does not solve the problem, determine if there is a misalignment of the guide tubes and rolls or if there is a blockage in the cable or liner. To load a spool of welding wire, remove the spool retainer and the empty spool. Place the new spool onto the hub on the wire feeder. Install the retaining device that holds the spool to the hub. This is usually a threaded fastener. Some retainers are spring-loaded and can be used to adjust the turning resistance of the spool. The resistance should be set low enough that the spool turns easily when the wire is pulled, but just high enough that the spool does not turn freely by itself if the wire is not being pulled. Wire feeder rolls have one or two grooves cut in them. Select and install rolls that have the same groove diameter as the diameter of the welding wire being used. Remember to change the wire feeder rolls if the elec- trode diameter or type changes. V-groove rolls are used with solid electrodes and small diameter metal cored wires. Knurled rolls are used for fl ux cored electrode wires and larger diameter metal cored wires. U-groove rolls are used with softer wires, like aluminum. The fi nal adjustment is to apply the proper force from the rolls to the electrode. Adjustment is made using a spring-loaded knob. Tighten the knob to apply only enough force to drive the wire without slippage. Too much force on the rolls and wire may cause the solid wire to fl atten, especially if the wire is alumi- num. The application of too much force may crush fl ux cored electrodes. If the wire is damaged, it does not feed through the wire cable and torch properly. If not enough force is applied to the wire, the rolls slip and do not drive the wire consistently. See Figure 8-27C. Once these adjustments have been made, the wire feeder is ready to feed wire continuously. Only the wire feed speed needs to be adjusted to meet the require- ments for each welding job. Adjust the wire feed speed to obtain the amperage and transfer method desired. Wire feeders often include an inch switch or jog switch, which is used to feed wire to the gun at a rela- tively slow speed to prevent kinking the wire. Feeders also have a purge switch. When the purge switch is pressed, shielding gas fl ows. It continues to fl ow until the purge switch is released. This feature purges air from the shielding gas lines prior to welding, without wasting welding wire. 8.4.3 Gases and Gas Mixtures for GMAW and FCAW–G The gases used in shielding gas mixtures for GMAW are argon (Ar), carbon dioxide (CO 2 ), oxygen (O 2 ), helium (He), and in some cases, nitrogen (N2). Figure 8-29 lists shielding gas selections for GMAW on a number of metals. Gases used for FCAW–G of carbon, low-alloy steel, and stainless steel include carbon dioxide (CO 2 ) and an Ar-CO2 mixture. Procedure Removing a Bird’s Nest To eliminate the bird’s nest and continue welding, perform the following steps: 1. Turn off the power source and the wire feeder. 2. Open the housing to expose the wire feeder mechanism and raise the upper pressure roll(s). 3. Cut the bird’s nest wire at the inlet wire guide and the outlet wire guide. Refer to Figure 8-28. This eliminates the bird’s nest. 4. Remove the welding wire from the cable assembly going to the welding gun. This removes wire from the cable. 5. Feed new wire into the cable assembly and lower the upper pressure roll(s). 6. Make any necessary adjustment to roll pressure and alignment. 7. Feed the welding wire to the gun by pulling the trigger on the gun, or by pressing the inch or jog switch. Inlet wire guide Outlet wire guide Goodheart-Willcox Publisher Figure 8-28. Removing a bird’s nest by cutting the welding wire behind the inlet wire guide and before the outlet wire guide.
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