200 Modern Welding Copyright Goodheart-Willcox Co., Inc. 8.2.3 Spray Transfer Spray transfer gas metal arc welding requires current and voltage settings higher than those required for globular transfer. Spray transfer occurs when very fi ne droplets of metal form at the tip of the welding wire. The droplets travel at a high rate of speed directly through the arc stream to the weld pool. See Figure 8-6. Spray transfer takes place only when the shielding gas contains a high percentage of argon. To weld non- ferrous metals and alloys, use 100% argon shielding gas. A shielding gas mixture containing at least 80% argon is required for spray transfer on carbon or low- alloy steels or stainless steels. Before spray transfer can occur, the welding machine’s current setting must be set high enough. The current must be above the transition current, which is the current required for the transfer method to change from globular to spray transfer. The transition current varies with the electrode diameter, the composition of the electrode, and the length of electrode extension (the amount that the end of the welding wire sticks out beyond the end of the contact tip). The transition current increases as the electrode diameter increases and decreases as the electrode extends farther from the contact tip. The transition current is higher for steel than aluminum. Until the transition current is exceeded, the metal transfers as large globules. Above the transition cur- rent level, the pinch force becomes great enough to squeeze the metal off the tip of the electrode as fi ne droplets. See Figure 8-7 for transition current levels for various electrode materials and wire diameters. Metal droplets Stage 2 Wire necks down Shielding gas envelope Arc Stage 1 Goodheart-Willcox Publisher Figure 8-6. Spray transfer method. The droplets are concentrated in the center of the arc. Spray transfer occurs only when a high percentage of argon gas is used. Spray Transfer Transition Currents Wire material Wire electrode diameter Shielding gas Minimum spray arc current, A inches mm Carbon steel Carbon steel Carbon steel Carbon steel Stainless steel Stainless steel Stainless steel Aluminum Aluminum Aluminum Deoxidized copper Deoxidized copper Deoxidized copper Silicon bronze Silicon bronze Silicon bronze 0.030 0.035 0.045 0.062 0.035 0.045 0.062 0.030 0.045 0.062 0.035 0.045 0.062 0.035 0.045 0.062 0.8 0.9 1.2 1.6 0.9 1.2 1.6 0.8 1.2 1.6 0.9 1.2 1.6 0.9 1.2 1.6 98% argon-2% oxygen 98% argon-2% oxygen 98% argon-2% oxygen 98% argon-2% oxygen 99% argon-1% oxygen 99% argon-1% oxygen 99% argon-1% oxygen argon argon argon argon argon argon argon argon argon 150 165 220 275 170 225 285 95 135 180 180 210 310 165 205 270 Note: Spray transfer will only occur when a high percentage of argon is used. Reproduced with permission of the American Welding Society, Miami, FL Figure 8-7. Spray transfer transition currents. The Welding Handbook, 9th Edition, Volume 2, Table 4.1, Globular to Spray Transition Currents.