Machinery's Handbook, 31st Edition
Flux-Cored Arc Welding 1591 Shielding Gases and FCAW Electrodes.— The E70T-X flux-cored electrodes that are recommended for flat and horizontal welds use CO 2 gas shielding. Because of new OSHA welding smoke restrictions, manufacturers of FCAW electrodes now provide E70T-X consumable electrodes that can be used with less reactive argon + CO 2 mixtures to reduce smoke levels. The fast-freezing slag, all-position, E71T-1 flux-cored electrodes can use either CO 2 or argon + 15 to 25 percent CO 2 mixtures for welding carbon, low-alloy, or stainless steels. The argon + CO 2 mixture is often selected because it provides the highest energy from a reactive gas mixture with a compatible voltage range. Instead of CO 2 , welders often prefer the arc characteristics, lower smoke levels, and lower voltage requirements of the argon + CO 2 mixtures for all-position welding. How ever, if lower reactive argon mixtures such as argon + oxygen, or argon with less than 13 percent CO 2 , are used, the weld voltage requirements and the arc plasma energy are reduced, adding to the possibility of changing the mechanical properties significantly, increasing the porosity, and raising the potential for forming worm tracks. Shielded Metal Arc Welding With the shielded metal arc welding (SMAW) process, commonly known as stick weld ing, it is most important to select an electrode that is suited to the application. For weld- ing austenitic stainless or high-alloy steels, the electrode is first selected to match the mechanical and chemical requirements of the metal to be welded. Secondary require- ments such as the welding position, penetration potential, deposition capabilities, and ease of slag removal are then considered. Many electrodes for SMAW welding of low- to medium-carbon steels have unique characteristics making them the most suitable and cost-effective for a specific welding application. In interpreting the ANSI/AWS Standard specification code for SMAW electrodes shown in Table 10, for example, E60XX, the E stands for a low-carbon steel, metal arc welding electrode. The next two digits, such as 60 or 70, indicate the approximate tensile strength of the weld deposit in thousands of psi. Of the last two digits, the next (second to last) number indicates the positions in which the electrode can be used: 1 = indicates the electrode is suitable for use in flat, horizontal, vertical, and overhead positions; 2 = the electrode can be used in the flat position for all welding types, and in the horizontal position for fillet welds only; 4 = the electrode is suitable for use in the flat, horizontal, vertical-down, and overhead positions. Note that number “3” is no longer used as a position designation. The final digit, combined with the above, indicates the type of flux coating, as shown in Table 10. Table 10. Significance of Digits, ANSI/AWS A5.18-1979 Third and Fourth Digits Flux Type and Characteristics, SMAW Electrodes 10 High-cellulose coating bonded with sodium silicate. Deep penetration, energetic spray-type arc. All-positional, DCEP a only 11 Similar to 10 but bonded with potassium silicate to permit use with AC or DCEP 12 High-rutile coating, bonded with sodium silicate. Quiet arc, medium penetration, all-positional, AC or DCEN 13 Similar to 12 but bonded with sodium silicate and with easily ionized materials added. Gives steady arc on low voltage. All-positional, AC or DCEN 14 Similar to 12 with addition of medium amount of iron powder. All-positional, AC or DC 15 Lime-fluoride coating (basic low-hydrogen) bonded with sodium silicate. All-positional. For welding high-tensile steels. DCEP only
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