Machinery's Handbook, 31st Edition
1586 Flux-Cored Arc Welding deposition rates and allows use of the highest penetrating current without concern for ex- cessive heat-related problems during welding. When used in the optimum current range, the deposited filler metal matches the required amount of filler metal for the specific size of the weld, determined by the plate thickness. The following suggestions and recommendations are made for FCAW welding of car bon, low-alloy, and stainless steels having flat surfaces. For vertical up welds on steels of thicknesses from 1 ∕ 8 to 3 ∕ 16 in. (3.2 to 4.8 mm) and for vertical up welds on pipe in the thick ness range of 1 ∕ 4 to 1 ∕ 2 in. (6.4 to 13 mm), consider the 0.035-in. (1.0-mm) diameter E71T-1 electrode. For vertical up welds on steels in the range of 1 ∕ 4 to 3 ∕ 8 in. (6.4 to 9.6 mm) thick ness, consider the 0.045-in. (1.2-mm) diameter E71T-1 electrode or, in nonheat-sensitive applications, the 0.062-in. (1.6-mm) diameter E71T-1 electrode. For vertical up welds on steels of over 3 ∕ 8 in. (9.6 mm) thickness, consider the 0.062-in. (1.6-mm) diameter E71T-1 electrodes for optimum deposition rates. For flat and horizontal welds on steels of 3 ∕ 8 to 3 ∕ 4 in. (9.6 to 19 mm) thickness, consider the 1 ∕ 16 -in. (1.6-mm) diameter E70T-X electrodes. For flat and horizontal welds on steels over 3 ∕ 4 in. (19 mm) in thickness, consider the 3 ∕ 32 -in. (2.4-mm) E70T-X electrodes. FCAW Welding of Low-Carbon Steels.— Low-carbon steel is usually called carbon steel or mild steel. The most-used FCAW electrode for welding carbon steels in the flat or horizontal welding positions is the type E70T-1, which is suited to welding of reason- ably clean steel using single-pass or multi-pass welds. Type E70T-2 has added deoxidiz- ers and is suited to surfaces with mill scale or other contamination. This type is used when no more than two layers of weld are to be applied. Type E70T-5 is used for single- pass or multi-pass welds where superior impact properties or improved crack resistance are required. The E70T-X electrodes typically range in size from 0.045 to 3 ∕ 32 in. (1.2 to 2.4 mm) in diameter. Type E71T-1 all-position electrodes are available in diameters of 0.035 in. (1 mm) to 0.062 in. (1.6 mm). With the FCAW process, multi-pass welds are defined as a condition where three or more weld passes are placed on top of each other. Settings for Gas-Shielded, All-Position, FCAW Electrodes.— The optimum setting range (volts and amps) for vertical up welding with all-position FCAW electrodes is rather narrow. The welder usually obtains the greatest degree of weld puddle control at the rec ommended low to medium current settings. The electrode manufacturers’ recommended current range for an E71T-1 electrode of 0.045-in. (1.2-mm) diameter for vertical up weld ing may be approximately 130 to 250 amps. Using the 0.045-in. (1.2-mm) diameter elec trode at 250 amps for a vertical up weld in 1 ∕ 4 -in. (6.4-mm) thick steel, the welder may find that after 3 to 4 inches (75–100 mm) of weld, the weld heat built up in the steel being welded is sufficient to make the weld puddle fluidity increasingly difficult to control. Reducing the current to 160–220 amps will make it possible to maintain control over the weld puddle. A typical optimum setting for a vertical up weld with an E71T-1, 0.035-in. (1.2-mm) diameter, all-position electrode is as follows. First, set the wire feed rate. If the wire feeder maximum rate is 650 to 750 in/min (16.5–19.0 m/min), the setting mark on the adjustment knob should be set between the one and two o’clock positions on the dial to obtain a feed rate of 450 in/min (11 m/min). If the wire feeder has a digital readout, the rate setting should be the same. At the 450-in/min setting, the welding current with the 0.035-in. all- position electrode should be optimized at between 160 and 170 amps. The welding voltage should be set at 27 to 28 volts with the electrode tip just touching the weld. If there is a gap causing the weld puddle to become too fluid, the voltage should be lowered. If the elec trode runs into the weld, causing spatter, the voltage needs to be increased. With the above conditions, welding steel of 1 ∕ 8 to 1 ∕ 4 in. thickness will deposit 5 to 7 lb/h (2.2 to 3 kg/h). The 0.035-in. electrode is also ideal for welding steel pipe with wall thick nesses of less than 1 ∕ 2 in. (13 mm). The thickness of the pipe after bevelling controls the size of electrode to be used. The 0.035-in. (6.4-mm) electrode can produce a 1 ∕ 4 -in. (6.4-mm) vertical up fillet weld on such a pipe without weaving.
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