218 Modern Welding Copyright Goodheart-Willcox Co., Inc. Do not run hard welding wire like steel through a Tefl on® liner because the hard welding wire will wear through the liner and then wear through the cable. Soft electrodes should not be run through a steel liner. Fine particles will be scraped from the electrode and plug the liner, preventing proper feeding of the weld- ing wire. Fine metal fi lings can accumulate in a coiled liner. It is a good idea to blow compressed air through this type of liner occasionally to remove these very fi ne particles. Remove the adapter from the welding gun when the liner is being blown out. Warning When blowing out a liner, always point its open end toward the floor or a trash can. Never allow the open end to point toward yourself or any other person. Occasionally, liners become worn or clogged with fi ne metal particles. Also, if the liner gets kinked, the welding wire will not feed smoothly. The liner must be replaced when this happens. Liners were traditionally installed from the wire feeder side of the cable. Some new liners are installed from the gun end, which is faster. Using a front end installed liner reduces the time to change the liner, which improves effi ciency. To replace a liner installed from the wire feeder side of the cable, disconnect the gun cable from the wire feeder. Remove the nozzle, contact tip, adapter, and any setscrews used to keep the liner in place. Then, remove the liner from the gun and cable. Install the new liner by pushing it fi rmly until it bottoms out against the cable. Secure the liner in place, if necessary on your gun. Most liners are made slightly long and must be trimmed to a specifi c length. Each manufacturer supplies instructions for this pro- cess. The liner is cut long because when the adapter is installed, it compresses the liner slightly. This pre- vents any gaps or kinking of the liner. Attach the adapter. Attach the cable to the wire feeder, then feed the wire through the cable and liner to the gun. Install the contact tip and fi nally the nozzle. To replace a liner that installs from the gun end of the cable, remove the nozzle, contact tip, and adapter. Remove the old liner and install a new one. Follow the manufacturer’s directions and cut the liner to specifi ed length. Reinstall the adapter, which com- presses the liner. Feed the electrode wire from the wire feeder to the gun. Reinstall the contact tip and nozzle. 8.4.7 Selecting the Correct GMAW or FCAW Welding Wire The welding wire used must match, or be compatible with, the base metal being welded. When you are fol- lowing a welding procedure specifi cation, the type of electrode to be used is specifi ed in the WPS. For weld- ing in construction or manufacturing, the type of elec- trode and diameter will be specifi ed. Follow all speci- fi cations when selecting the proper welding wire. When not welding to a specifi cation, the welder should determine the type of base metal being welded. Determine if GMAW or FCAW will be used. Select an appropriate welding wire type according to the infor- mation and charts provided in Chapter 7, Gas Metal and Flux Cored Arc Welding Equipment and Supplies. You can use electrode manufacturers’ websites to determine what electrode to use for a welding task. Small-diameter wire usually costs more than large- diameter wire. The rate at which fi ller metal is deposited with small-diameter wire makes up for its added cost. Because of the small diameter and the high currents gen- erally used in GMAW and FCAW, small-diameter weld- ing wire is melted more rapidly than large-diameter wire. Small-diameter wire is thus deposited at a much higher rate. Once the correct welding wire is selected, it should be loaded in the wire feeder. The correct-size and correct-type drive rolls must be used in the wire feeder. The correct size contact tip must be installed into the welding gun. The wire should be fed through the electrode cable using the inch switch until about 2″ to 3″ (50 mm to 75 mm) of wire extends beyond the nozzle. Cut the welding wire so its extension is correct for the type of welding being done. 8.5 Preparing Metal for Welding Proper preparation of the base metal and proper preparation of the welding joint are key to producing a quality weld. Take the time to prepare a good joint fi t-up and your welds will be of a higher quality. Many weld specifi cations do not specify clean- ing. This does not mean welding can be done on con- taminated and oxidized surfaces. Contaminants and oxides can be trapped in the weld bead and produce a poor quality weld. The weld joint should be clean and without oxidation. Repair welding may be required on used, worn, and oxidized metal. Even in these situations, the base metal should be cleaned as well as possible to prepare the metal for welding.