Electrodes type for Shielded Metal Arc Welding
(81 votes)The electrodes used in the SMAW process have many different compositions of core wire and a wide variety of fluxcoveringtypes and weights. Standard electrodes diameters of the core wire range from 1.6 to 8 mm ( 116to 516in.).Electrode length usually ranges from 230 to 455 mm (9 to 18 in.); the shorter lengths are associated with the smallerdiameterelectrodes. A bare, uncoated end of the electrode (the grip end) is provided for making electrical contact in theelectrode holder.
The coating on the electrode has numerous functions. It provides:·
- GAS (NORMALLY, CARBON DIOXIDE), FROM THE DECOMPOSITION OF CERTAINCOATING INGREDIENTS TO SHIELD THE ARC AND WELD ZONE FROM THEATMOSPHERE·
- DEOXIDIZERS, FOR SCAVENGING AND PURIFYING THE DEPOSITED WELD METAL·
- SLAG FORMERS, TO PROTECT THE DEPOSITED WELD METAL FROM ATMOSPHERICOXIDATION AND TO HELP SHAPE THE WELD BEAD·
- IONIZING ELEMENTS, TO MAKE THE ARC MORE STABLE AND TO OPERATE WITHALTERNATING CURRENT·
- ALLOYING ELEMENTS, TO PROVIDE SPECIAL CHARACTERISTICS TO THE WELDDEPOSIT·
- IRON POWDER, IN CERTAIN ELECTRODES, TO INCREASE PRODUCTIVITY FOR WELDINGFERROUS METALS
The American Welding Society (AWS) has established a system for identifying and classifying the different types ofwelding electrodes. All SMAW electrodes have the prefix letter E to indicate welding electrode. The symbols that followthe prefix are based on criteria that best describe the welding capabilities of the electrode metal. These criteria includechemical composition of the deposited weld metal, weld-metal mechanical properties, certain process parameters, orcombinations of all factors.
Mild and Low-Alloy Steel-Covered Electrodes. The prefix used to identify these electrodes is followed by a numberseries that indicates minimum strength level, position capability, and type of covering and welding current. Table 2explains how the number series is used in AWS A5.1, the specification for carbon steel electrodes for shielded metal arcwelding and AWS A5.5, the specification for low-alloy steel electrodes. The first two digits after the E in the E6010electrode designate a tensile strength of at least 430 MPa (62 ksi) for the deposited metal in the as-welded condition. Thethird digit indicates the position in which satisfactory welds can be made with the electrode. Thus, the 1 in E6010, forexample, means that the electrode is satisfactory for use in all positions (flat, vertical, horizontal, and overhead). The 2 inE6020 indicates that the electrode is suitable for the flat position and horizontal fillets. The last digit or last two digits,taken together, indicate the applicable current type to be used and the type of covering on the electrode.
Stainless Steel Covered Electrodes. The three-digit number that follows the prefix E indicates the chemicalcomposition. In addition, letters or numbers can be used to indicate composition modifications or position usability. Thespecification AWS A5.4 identifies and classifies covered corrosion-resisting chromium and chromium-nickel steelwelding electrodes.
Nickel and Copper Alloys. The designations for nonferrous product classifications, such as nickel and nickel alloys inAWS A5.11 and copper and copper alloys in AWS A5.6, follow the prefix with a list of chemical element abbreviationsthat are significant in identifying product composition, such as ENiCu, ENiCrFe, ECuSi, and ECuNi.
Surfacing Welding Electrodes. The designations for these products are contained in specifications AWS A5.13 andA5.21. They are very similar to the system used to identify nonferrous electrodes.Aluminum and Aluminum Alloys. The specification for aluminum and aluminum alloy arc welding electrodes, AWSA5.3, uses the E prefix to indicate a covered electrode, followed by a series of numbers that identify the chemicalcomposition that is equivalent to Aluminum Association alloy designations (for example, E1100, E3003, and E4043).
Suffix symbols are used in various classifications. The AWS A5.5 specification for low-alloy filler metals uses suffixessuch as -A1, -B2, -B2L, and -C1 to indicate chemical compositions. the weld deposit chemicalcomposition associated with a number of suffixes found on low-alloy electrodes. The classifications for nonferrousproducts in the AWS A5.6 specification for copper alloys and in the AWS A5.11 specification for nickel alloys list aletter or number suffix that indicates position in a series of similar alloy groupings.
A similar suffix pattern is also used inthe AWS A5.13 and AWS A5.21 specifications for surfacing welding electrodes. Covered stainless steel electrodesemploy a number, -15 or -16, as a suffix to identify usability. The -15 suffix indicates that the Electrode is designed forall-position operation using DCEP electrical current. The -16 suffix indicates all-position operation with either ac orDCEP.
