Chapter 8 Gas Metal and Flux Cored Arc Welding 217 Copyright Goodheart-Willcox Co., Inc. Another way to adjust the electrode extension is with a longer or shorter gas nozzle. A shorter nozzle can be used with short circuiting transfer and a longer nozzle with spray transfer. Flux cored electrodes must be heated to a higher temperature than solid electrodes to vaporize some of the fl ux and create a shielding atmosphere around the weld. A welding gun for FCAW–S can use an exten- sion to guide the wire. The extension does not conduct current from the gun to the electrode. The current is passed to the electrode by the contact tip. Beyond the contact tip, the extension guides the wire, in some cases for a few inches. The extension allows for a very long electrode extension and allows the fl ux cored wire to preheat. Contact tips wear and must be changed regu- larly. Eight hours of continuous welding with a steel electrode can excessively wear a contact tip. Regular replacement of the contact tip ensures a continuous, good electrical contact with the welding wire. Examine the contact tip occasionally. If the round hole is becoming elongated or if the arc appears to be fl uctuating while welding, it is time to replace the tip. A fl uctuating arc may be due to a worn contact tip that does not make consistent contact with the electrode. A pair of welding pliers (welpers), are used to remove and install the nozzle, contact tip, and adapter. The tool is a combination of wire cutters and needle-nose pliers. The back sides of the needle-nose pliers are used to remove spatter from the inside of a nozzle. Warning Always ensure a contact tip is sufficiently cool before at- tempting to replace it. Removing a hot contact tip can burn your fingers and damage the threads in the adapter. During arc welding, the inside and outside of the nozzle and the outside of the contact tip can become covered with solidifi ed spatter. Spatter builds up inside the nozzle and blocks the fl ow of shielding gas or causes the shielding gas fl ow to become turbulent. The lack of shielding gas, reduced shielding gas, or gas turbulence can cause weld contamination. Use the welpers to clean spatter from inside the nozzle as needed to maintain a good fl ow of shielding gas. Spat- ter can be kept from sticking by spraying or dipping the nozzle in anti stick compound. 8.4.6 Selecting and Installing a Liner The welding wire travels from the wire feeder to the welding gun in a cable. A conduit (liner) installed inside the cable protects the cable from the continu- ous wear of the welding wire. The liner also prevents the welding wire from getting tangled or stuck while traveling through the cable. There are two types of liners. One is a hardened steel wire wound in a tight coil to form a tube. This wound steel liner is used for welding hard materials like steel and stainless steel. See Figure 8-41. The second type of liner is made of Tefl on®, a type of plastic. It is much softer than the wound steel liner material. Tefl on® liners are used for welding softer materials, especially aluminum wires. Long contact tip Nozzle Short contact tip Visible extension Electrode extension Electrode extension Goodheart-Willcox Publisher Figure 8-40. The length of the contact tip and the amount of electrode extension affects the amount of heating that the welding wire receives. The heating takes place in the length of welding wire that extends from the contact tip. With a long contact tip, there is less extension and thus, less heating. Trigger switch connection Coiled wire liner Combination gun cable Goodheart-Willcox Publisher Figure 8-41. A coiled wire liner may be used in a GMAW cable to guide the welding wire. The wire liner sticking out of this welding gun cable is replaced when worn.