214 Modern Welding Copyright Goodheart-Willcox Co., Inc. Spatter occurs, the weld shows porosity, and the bead is discolored. Refer to Figure 8-35 for suggested gas fl ow rates for various metals and thicknesses. Shield- ing gas fl ow rates for FCAW–G are similar to those used for GMAW. Flow rates for shielding gas depend on the nozzle size and the distance the nozzle is from the weld area. Adjust the fl ow rate up or down to obtain a weld prop- erly protected by the shielding gas. Heavier shielding gases like CO2 and argon drop away from the weld area when welding is being performed out of position. Therefore, the gas fl ow rates must be increased for out-of-position welding. An increase of 10 cubic feet per hour–20 cubic feet per hour (5 liters per minute–10 liters per minute) is appropriate. 8.4.5 Selecting the Correct Gas Nozzles and Contact Tips The gas nozzle at the end of the GMAW or FCAW gun delivers the shielding gas to the weld area in a smooth, unrestricted fl ow. See Figure 8-36. The gas nozzle is usually made of copper, which is an excel- lent heat conductor. A copper nozzle resists melting when exposed to the heat generated in the welding operation. The same nozzles are used for FCAW–G and GMAW. The construction of the nozzle end of a GMAW gun is shown in Figure 8-37. Nozzles are available with different exit diameters. Welding gun manufacturers normally provide infor- mation on the correct nozzle for various applications. A general-purpose nozzle works well for most applications. Shielding Gas Flow Rates and Types of Gas Metal Thickness Shielding gas flow Shielding gas inches mm ft3/hr lpm Aluminum and aluminum alloys 1/16 1.6 25 12 Argon 1/8 3.2 35 16 1/4 6.3 35 16 3/8 9.6 40 19 3/4 19 90 42 75% He, 25% Ar Carbon and low-alloy steels 1/16 1.6 25 12 75% Ar, 25% CO2 for short circuiting transfer 98% Ar, 2% O2 for spray transfer 1/8 3.2 25 12 1/4 6.3 30 14 3/8 9.6 35 16 3/4 19 50 24 Stainless steels including nickel alloys 1/16 1.6 30 14 90% He, 7.5% Ar, 2.5% CO2 for short circuiting transfer 98% Ar, 2% O2 for spray transfer 1/8 3.2 30 14 1/4 6.3 35 16 3/8 9.6 35 16 1/2 12.7 40 19 Magnesium and magnesium alloys 1/16 1.6 50 24 Argon 1/8 3.2 50 24 Argon or 75% Ar, 25% He 1/4 6.3 60 28 3/8 9.6 60 28 Copper and copper alloys 1/8 3.2 25 12 Argon or 75% Ar, 25% He 1/4 6.3 35 16 3/8 9.6 40 19 Goodheart-Willcox Publisher Figure 8-35. Suggested shielding gas flow rates for GMAW and types of shielding gas to use for various base metals and thicknesses. Flow rates for FCAW steels and stainless steels are similar to those shown in this table.