a. Bare or solid wire electrodes are made of wire compositions required for specific applications, and have no coatings other than those required in wire drawing. These wire drawing coatings have a slight stabilizing effect on the arc, but are otherwise of no consequence. Bare electrodes are used for welding manganese steels and for other purposes where a covered electrode is not required or is undesirable. A sketch of the transfer of metal across the arc of a bare electrode is shown in figure 8-1.
b. Solid steel electrode wires may not be bare. Many have a very thin copper coating on the wire. The copper coating improves the current pickup between contact tip and the electrode, aids drawing, and helps prevent rusting of the wire when it is exposed to the atmosphere. Solid electrode wires are also made of various stainless steels, aluminum alloys, nickel alloys, magnesium alloys, titanium alloys, copper alloys, and other metals.
c. When the wire is cut and straightened, it is called a welding rod, which is a form of filler metal used for welding or brazing and does not conduct the electrical current. If the wire is used in the electrical circuit, it is called a welding electrode, and is defined as a component of the welding circuit through which current is conducted. A bare electrode is normally a wire; however, it can take other forms.
d. Several different systems are used to identify the classification of a particular electrode or welding rod. In all cases a prefix letter is used.
(1) Prefix R. Indicates a welding rod.(2) Prefix E. Indicates a welding electrode.
(3) Prefix RB. Indicates use as either a welding rod or for brazing filler metal.
(4) Prefix ER. Indicates wither an electrode or welding rod.
e. The system for identifying bare carbon steel electrodes and rods for gas shielded arc welding is as follows:
(1) ER indicates an electrode or welding rod.(2) 70 indicates the required minimum as-welded tensile strength in thousands of pounds per square inch (psi).
(3) S indicates solid electrode or rod.
(4) C indicates composite metal cored or stranded electrode or rod.
(5) 1 suffix number indicates a particular analysis and usability factor.
Table 8-1. Mild Steel Electrode Wire Composition for Submerged Arc Welding
f. Submerged Arc Electrodes. The system for identifying solid bare carbon steel for submerged arc is as follows:
(1) The prefix letter E is used to indicate an electrode. This is followed by a letter which indicates the level of manganese, i.e., L for low, M for medium, and H for high manganese. This is followed by a number which is the average amount of carbon in points or hundredths of a percent. The composition of some of these wires is almost identical with some of the wires in the gas metal arc welding specification.(2) The electrode wires used for submerged arc welding are given in American Welding Society specification, “Bare Mild Steel Electrodes and Fluxes for Submerged Arc Welding.” This specification provides both the wire composition and the weld deposit chemistry based on the flux used. The specification does give composition of the electrode wires. This information is given in table 8-1. When these electrodes are used with specific submerged arc fluxes and welded with proper procedures, the deposited weld metal will meet mechanical properties required by the specification.
(3) In the case of the filler reds used for oxyfuel gas welding, the prefix letter is R, followed by a G indicating that the rod is used expressly for gas welding. These letters are followed by two digits which will be 45, 60, or 65. These designate the approximate tensile strength in 1000 psi (6895 kPa).
(4) In the case of nonferrous filler metals, the prefix E, R, or RB is used, followed by the chemical symbol of the principal metals in the wire. The initials for one or two elements will follow. If there is more than one alloy containing the same elements, a suffix letter or number may be added.
(5) The American Welding Society’s specifications are most widely used for specifying bare welding rod and electrode wires. There are also military specifications such as the MIL-E or -R types and federal specifications, normally the QQ-R type and AMS specifications. The particular specification involved should be used for specifying filler metals.
g. The most important aspect of solid electrode wires and rods in their composition, which is given by the specification. The specifications provide the limits of composition for the different wires and mechanical property requirements.h. Occasionally, on copper-plated solid wires, the copper may flake off in the feed roll mechanism and create problems. It may plug liners, or contact tips. A light copper coating is desirable. The electrode wire surface should be reasonably free of dirt and drawing compounds. This can be checked by using a white cleaning tissue and pulling a length of wire through it. Too much dirt will clog the liners, reduce current pickup in the tip, and may create erratic welding operation.
i. Temper or strength of the wire can be checked in a testing machine. Wire of a higher strength will feed through guns and cables better. The minimum tensile strength recommended by the specification is 140,000 psi (965,300 kPa).
j. The continuous electrode wire is available in many different packages. They range from extremely small spools that are used on spool guns, through medium-size spools for fine-wire gas metal arc welding. Coils of electrode wire are available which can be placed on reels that are a part of the welding equipment. There are also extremely large reels weighing many hundreds of pounds. The electrode wire is also available in drums or payoff packs where the wire is laid in the round container and pulled from the container by an automatic wire feeder.