Welding Electrodes: Coatings and Classifications

When molten metal is exposed to air, it absorbs oxygen and nitrogen, and becomes brittle or is otherwise adversely affected. A slag cover is needed to protect molten or solidifying weld metal from the atmosphere. This cover can be obtained from the electrode coating which protects the metal from damage, stabilizes the arc, and improves the weld. . The composition of the electrode coating determines its usability, as well as the composition of the deposited weld metal and the electrode specification.

Electrode Classification

The American Welding Society’s classification number series has been adopted by the welding industry. The electrode identification system for steel arc welding is set up as follows:

1. E indicates electrode for arc welding
2. The first two (or three) digits indicate tensile strength (the resistance of the material to forces trying to pull it apart) in thousands of pounds per square inch of the deposited metal.
3. The third (or fourth) digit indicates the position of the weld. 0 indicates the classification is not used; 1 is for all positions; 2 is for flat and horizontal positions only; 3 is for flat position only.
4. The fourth (or fifth) digit indicates the type of electrode coating and the type of power supply used; alternating or direct current, straight or reverse polarity.
5. The types of coating, welding current, and polarity position are designated by the fourth (or fifth) identifying digit of the electrode classification are listed in the table below
6. The number E601O indicates an arc welding electrode with a relieved tensile strength of 60,000 psi; is used in all positions; polarity direct current is required.

Covered Electrodes

The formulation of different electrodes and their coatings is based on well-established principles of metallurgy, chemistry, and physics.

The coating protects the metal from damage, stabilizes the arc, and improves the weld in other ways, which include:

1. Smooth weld metal surface with even edges
2. Minimum spatter adjacent to the weld
3. A stable welding arc
4. Penetration and arc control.
5. A strong, tough coating.
6. Easier slag removal
7. Improved deposition rate

Metal-arc electrodes may be grouped and classified as:

• Bare or thinly coated electrodes
• Shielded arc or heavy coated electrodes

The covered electrode is the most popular type of filler metal used in arc welding. The composition of the electrode covering determines:

• Electrode usability
• Deposited weld metal composition
• Electrode specification

The type of electrode used depends on the specific properties required in the weld deposited. These include:

• Corrosion resistance
• Ductility
• High tensile strength
• Type of base metal to be welded
• Weld position (flat, horizontal, vertical, or overhead)
• Type of polarity and current required

Covered Electrode Coatings

Electrode coatings for welding low and mild alloy steels may have from 6 to 12 ingredients, which include:

• Cellulose provides a gaseous shield with a reducing agent in which the gas shield surrounding the arc is produced by the disintegration of cellulose
• Metal carbonates to adjust the basicity of the slag and to provide a reducing atmosphere
• Titanium dioxide to help form a highly fluid, but quick-freezing slag and to provide ionization for the arc
• Ferromanganese and ferrosilicon to help deoxidize the molten weld metal and to supplement the manganese content and silicon content of the deposited weld metal
• Gums and Clays to provide elasticity for extruding the plastic coating material and to help provide strength to the coating
• Calcium fluoride provide shielding gas to protect the arc, adjust the basicity of the slag, and provide fluidity and solubility of the metal oxides
• Mineral silicates provide slag and give strength to the electrode covering
• Alloying metals including nickel, molybdenum, and chromium to provide alloy content to the deposited weld metal
• Iron or manganese oxide to adjust the fluidity and properties of the slag and to help stabilize the arc
• Iron powder to increase productivity by providing extra metal to be deposited in the weld

Principal Types of Electrode Coatings for Mild Steel

1. Cellulose-sodium (EXX10):  Electrodes of this type of cellulosic material in the form of wood flour or reprocessed low alloy electrodes have up to 30 percent paper. The gas shield contains carbon dioxide and hydrogen, which are reducing agents. These shielding gases tend to produce a digging arc that provides deep penetration. The weld deposit is somewhat rough, and the spatter is at a higher level than other electrodes. It does provide excellent mechanical properties, particularly after aging. This is one of the earliest types of electrodes developed and is widely used for cross-country pipelines using the downhill welding technique. It is normally used with direct current with the electrode positive (reverse polarity).
2. Cellulose-potassium (EXX11): This electrode is very similar to the cellulose-sodium electrode, except more potassium is used than sodium. This provides ionization of the arc and makes the electrode suitable for welding with alternating current. The arc action, the penetration, and the weld results are very similar. In both E6010 and E6011 electrodes, small amounts of iron powder may be added. This assists in arc stabilization and will slightly increase the deposition rate.
3. Rutile-sodium (EXX12): When rutile or titanium dioxide content is relatively high with respect to the other components, the electrode will be especially appealing to the welder. Electrodes with this coating have a quiet arc, an easily controlled slag, and a low level of spatter. The weld deposit will have a smooth surface and the penetration will be less than with the cellulose electrode. The weld metal properties will be slightly lower than the cellulosic types. This type of electrode provides a fairly high rate of deposition. It has a relatively low arc voltage and can be used with alternating current or with direct current with electrode negative (straight polarity).
4. Rutile-potassium (EXX13): This electrode coating is very similar to the rutile-sodium type, except that potassium is used to provide for arc ionization. This makes it more suitable for welding with alternating current. It can also be used with direct current with either polarity. It produces a very quiet, smooth-running arc.
5. Rutile-iron powder (EXXX4): This coating is very similar to the rutile coatings mentioned above, except that iron powder is added. If iron content is 25 to 40 percent, the electrode is EXX14. If iron content is 50 percent or more, the electrode is EXX24. With the lower percentage of iron powder, the electrode can be used in all positions. With the higher percentage of iron paler, it can only be used in with a flat position electrode or for making horizontal fillet welds. In both cases, the deposition rate is increased, based on the amount of iron powder in the coating.
6. Low hydrogen-sodium (EXXX5): Coatings that contain a high proportion of calcium carbonate or calcium fluoride are called low hydrogen, lime ferritic, or basic type electrodes. In this class of coating, cellulose, clays, asbestos, and other minerals that contain combined water are not used. This is to ensure the lowest possible hydrogen content in the arc atmosphere. These electrode coatings are baked at a higher temperature. The low hydrogen electrode family has superior weld metal properties. They provide the highest ductility of any of the deposits. These electrodes have a medium arc with medium or moderate penetration. They have a medium speed of deposition but require special welding techniques for best results. Low hydrogen electrodes must be stored under controlled conditions. This type is normally used with direct current with electrode positive (reverse polarity).
7. Low hydrogen-potassium (EXXX6): This type of coating is similar to the low hydrogen-sodium, except for the substitution of potassium for sodium to provide arc ionization. This electrode is used with alternating current and can be used with direct current, electrode positive (reverse polarity). The arc action is smoother, but the penetration of the two electrodes is similar.
8. Low hydrogen-potassium (EXXX6): The coatings in this class of electrodes are similar to the low-hydrogen type mentioned above. However, iron powder is added to the electrode, and if the content is higher than 35 to 40 percent, the electrode is classified as an EXX18.
9. Low hydrogen-iron powder (EXX28): This electrode is similar to the EXX18, but has 50 percent or more iron powder in the coating. It is usable only when welding in the flat position or for making horizontal fillet welds. The deposition rate is higher than EXX18. Low hydrogen coatings are used for all of the higher-alloy electrodes. By additions of specific metals in the coatings, these electrodes become the alloy types where suffix letters are used to indicate weld metal compositions. Electrodes for welding stainless steel are also the low-hydrogen type.
10. Iron oxide-sodium (EXX20): Coatings with high iron oxide content produce a weld deposit with a large amount of slag. This can be difficult to control. This coating type produces high-speed deposition and provides medium penetration with low spatter levels. The resulting weld has a very smooth finish. The electrode is usable only with flat position welding and for making horizontal fillet welds. The electrode can be used with alternating current or direct current with either polarity.
11. Iron-oxide-iron power (EXX27): This type of electrode is very similar to the iron oxide-sodium type, except it contains 50 percent or more iron power. The increased amount of iron power greatly increases the deposition rate. It may be used with an alternating direct current of either polarity.
12. There are many types of coatings other than those mentioned here, most of which are usually combinations of these types but for special applications such as hard surfacing, cast iron welding, and nonferrous metals.

Deposition Rates

The different types of electrodes have different deposition rates due to the composition of the coating. The electrodes containing iron powder in the coating have the highest deposition rates. In the United States, the percentage of iron power in a coating is in the 10 to 50 percent range. This is based on the amount of iron powder in the coating versus the coating weight.

These percentages are related to the requirements of the American Welding Society (AWS) specifications. The European method of specifying iron power is based on the weight of deposited weld metal versus the weight of the bare core wire consumed. This is shown as:

If the deposit weight were double the weight of the core wire, it would indicate a 200 percent deposition efficiency, even though the amount of the iron powder in the coating represented only half of the total deposit. The 30% iron power formula used in the United States would produce a 100% to 110% deposition efficiency using the European formula. The 50 percent iron power electrode figured on United States standards would produce efficiency of approximately 150% using the European formula.

Light Coated Electrodes

Light-coated electrodes have a definite composition. A light coating has been applied on the surface by washing, dipping, brushing, spraying, tumbling, or wiping. The coatings improve the characteristics of the arc stream. They are listed under the E45 series in the electrode identification system.

The coating generally serves the functions described below:

• It dissolves or reduces impurities such as oxides, sulfur, and phosphorus
• It changes the surface tension of the molten metal so that the globules of metal leaving the end of the electrode are smaller and more frequent. This helps make the flow of molten metal more uniform
• It increases the arc stability by introducing materials readily ionized (i.e., changed into small particles with an electric charge) into the arc stream

Some of the light coatings may produce a slag. The slag is quite thin and does not act in the same manner as the shielded arc electrode type slag.

Heavy Coated or Shielded Arc Electrodes

Heavy Coated or Shielded Arc Electrodes have a definite composition on which a coating has been applied by dipping or extrusion. The electrodes are manufactured in three general types: those with cellulose coatings; those with mineral coatings; and those whose coatings are combinations of mineral and cellulose. The cellulose coatings are composed of soluble cotton or other forms of cellulose with small amounts of potassium, sodium, or titanium, and in some cases added minerals. The mineral coatings consist of sodium silicate, metallic oxides clay, and other inorganic substances or combinations thereof. Cellulose-coated electrodes protect the molten metal with a gaseous zone around the arc as well as the weld zone. The mineral-coated electrode forms a slag deposit. The shielded arc or heavy coated electrodes are used for welding steels, cast iron, and hard surfacing.

Functions of Shielded Arc or Heavy Coated Electrodes

1. These electrodes produce a reducing gas shield around the arc. This prevents atmospheric oxygen or nitrogen from contaminating the weld metal. The oxygen readily combines with the molten metal, removing alloying elements and causing porosity. Nitrogen causes brittleness, low ductility, and in Some cases low strength and poor resistance to corrosion.
2. They reduce impurities such as oxides, sulfur, and phosphorus so that these impurities will not impair the weld deposit.
3. They provide substances to the arc which increases its stability. This eliminates wide fluctuations in the voltage so that the arc can be maintained without excessive spattering.
4. By reducing the attractive force between the molten metal and the end of the electrodes, or by reducing the surface tension of the molten metal, the vaporized and melted coating causes the molten metal at the end of the electrode to break up into fine, small particles.
5. The coatings contain silicates which will form a slag over the molten weld and base metal. Since the slag solidifies at a relatively slow rate, it holds the heat and allows the underlying metal to cool and solidify slowly. This slow solidification of the metal eliminates the entrapment of gases within the weld and permits solid impurities to float to the surface. Slow cooling also has an annealing effect on the weld deposit.
6. The physical characteristics of the weld deposit are modified by incorporating alloying materials in the electrode coating. The fluxing action of the slag will also produce weld metal of better quality and permit welding at higher speeds.

Direct Current Arc Welding Electrodes

The manufacturer’s recommendations should be followed when a specific type of electrode is being used. In general, direct current shielded arc electrodes are designed either for reverse polarity (electrode positive) or for straight polarity (electrode negative), or both. Many, but not all, of the direct current electrodes, can be used with alternating current. Direct current is preferred for many types of covered nonferrous, bare, and alloy steel electrodes. Recommendations from the manufacturer also include the type of base metal for which given electrodes are suitable, corrections for poor fit-ups, and other specific conditions.

In most cases, reverse polarity electrodes will provide more penetration than straight polarity electrodes. Good penetration can be obtained from either type with proper welding conditions and arc manipulation.

Alternating Current Arc Welding Electrodes

Coated electrodes which can be used with either direct or alternating current are available. Alternating current is more desirable while welding in restricted areas or when using the high currents required for thick sections because it reduces arc blow. Arc blow causes blowholes, slag inclusions, and lack of fusion in the weld.

Alternating current is used in atomic hydrogen welding and in those carbon arc processes that require the use of two carbon electrodes. It permits a uniform rate of welding and electrode consumption ion. In carbon-arc processes where one carbon electrode is used, direct current straight polarity is recommended, because the electrode will be consumed at a lower rate.

Effect of Electrode Defects

If certain elements or oxides are present in electrode coatings, the arc stability will be affected. In bare electrodes, the composition and uniformity of the wire is an important factor in the control of arc stability. Thin or heavy coatings on the electrodes will not completely remove the effects of defective wire.

Aluminum or aluminum oxide (even when present in quantities not exceeding 0.01 percent), silicon, silicon dioxide, and iron sulfate cause the arc to be unstable. Iron oxide, manganese oxide, calcium oxide, and iron sulfide tend to stabilize the arc.

When phosphorus or sulfur is present in the electrode in excess of 0.04 percent, they will impair the weld metal. They are transferred from the electrode to the molten metal with very little loss. Phosphorus causes grain growth, brittleness, and “cold shortness” (i.e., brittle when below red heat) in the weld. These defects increase in magnitude as the carbon content of the steel increases. The sulfur acts as a slag, breaks up the soundness of the weld metal, and causes “hot shortness” (i.e., brittle when above red heat). Sulfur is particularly harmful to bare low carbon steel electrodes with a low manganese content. Manganese promotes the formation of sound welds.

If the heat treatment given to the wire core of an electrode is not uniform, the electrode will produce welds inferior to those produced with an electrode of the same composition that has been properly heat treated.

Solid Electrode Wires

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 below.

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 the 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 steel, aluminum alloys, nickel alloys, magnesium alloys, titanium alloys, copper alloys, and other metals.

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.

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 whether an electrode or welding rod.

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 a 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

Submerged Arc Electrodes

The system for identifying solid bare carbon steel for the submerged arc is as follows:

1. The prefix letter E is used to indicate an electrode. This is followed by a letter that 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 the 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 the 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 the 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 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.

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.

Occasionally, on copper-plated solid wires, the copper may flake off in the continuously fed wire 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.

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).

The continuous electrode wire is available in many different packages. They range from extremely small spools that are used on spool guns, to 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.

Flux-Cored or Tubular Electrodes

The flux-cored arc welding process is made possible by the design of the electrode. This inside-outside electrode consists of a metal sheath surrounding a core of fluxing and alloying compounds. The compounds contained in the electrode perform essentially the same functions as the coating on a covered electrode, i.e., deoxidizers, slag formers, arc stabilizers, alloying elements, and may provide shielding gas. There are three reasons why cored wires are developed to supplement solid electrode wires of the same or similar analysis.

There is an economic advantage. Solid wires are drawn from steel billets of the specified analyses. These billets are not readily available and are expensive. A single billet might also provide more solid electrode wire than needed. In the case of cored wires, special alloying elements are introduced in the core material to provide the proper deposit analysis.

The tubular wire production method provides the versatility of composition and is not limited to the analysis of available steel billets.

Tubular electrode wires are easier for the welder to use than solid wires of the same deposit analysis, especially for welding pipe in the fixed position.

Flux-Cored Electrode Design is an advantage. The sheath or steel portion of the flux-cored wire comprises 75 to 90 percent of the weight of the electrode, and the core material represents 10 to 25 percent of the weight of the electrode.

For a covered electrode, the steel represents 75 percent of the weight and the flux 25 percent. This is shown in more detail below:

More flux is used on covered electrodes than in a flux-cored wire to do the same job. This is because the covered electrode coating contains binders to keep the coating intact and also contains agents to allow the coating to be extruded.

Shelf-Shielding Flux-Cored Electrodes

The self-shielding type flux-cored electrode wires include additional gas-forming elements in the core. These are necessary to prohibit the oxygen and nitrogen of the air from contacting the metal transferring across the arc and the molten weld puddle. Self-shielding electrodes also include extra deoxidizing and denigrating elements to compensate for oxygen and nitrogen which may contact the molten metal. Self-shielding electrodes are usually more voltage-sensitive and require electrical stick-out for smooth operation. The properties of the weld metal deposited by the self-shielding wires are sometimes inferior to those produced by the externally shielded electrode wires because of the extra amount of deoxidizers included. It is possible for these elements to build up in multipass welds, lower the ductility, and reduce the impact values of the deposit. Some codes prohibit the use of self-shielding wires on steels with yield strength exceeding 42,000 psi (289,590 kPa). Other codes prohibit the self-shielding wires from being used on dynamically loaded structures.

Metal Transfer

Metal transfer from consumable electrodes across an arc has been classified into three general modes. These are spray transfer, globular transfer, and short-circuiting transfer. The metal transfer of flux-cored electrodes resembles a fine globular transfer. On cored electrodes in a carbon dioxide shielding atmosphere, the molten droplets build up around the outer sheath of the electrode. The core material appears to transfer independently to the surface of the weld puddle. At low currents, the droplets tend to be larger than when the current density is increased. The transfer is more frequent with smaller drops when the current is increased. The larger droplets at the lower currents cause a certain amount of splashing action when they enter the weld puddle. This action decreases with the smaller droplet size. This explains why there is less visible spatter, the arc appears smoother to the welder, and the deposition efficiency is higher when the electrode is used at high current rather than at the low end of its current range.

Mild Steel Electrodes

Carbon steel electrodes are classified by the American Welding Society specification, “Carbon Steel Electrodes for Flux-cored-Arc Welding”. This specification includes electrodes having no appreciable alloy content for welding mild and low alloy steels. The system for identifying flux-cored electrodes follows the same pattern as electrodes for gas metal arc welding but is specific for tubular electrodes. For example, in E70T-1, the E indicates an electrode; 70 indicates the required minimum as-welded tensile strength in thousands of pounds per square inch (psi); T indicates tubular, fabricated, or flux-cored electrode; and 1 indicates the chemistry of the deposited weld metal, gas type, and usability factor.

Classification of Flux-Cored Electrodes

1. E60T-7 electrode classification: Electrodes of this classification are used without externally applied gas shielding and may be used for single-and multiple-pass applications in the flat and horizontal positions. Due to low penetration and to other properties, the weld deposits have a low sensitivity to cracking.
2. E60T-8 electrode classifications: Electrodes of this classification are used without externally applied gas shielding and may be used for single-and multiple-pass applications in the flat and horizontal positions. Due to low penetration and to other properties, the weld deposits have a low sensitivity to cracking.
3. E70T-1 electrode classification: Electrodes of this classification are designed to be used with carbon dioxide shielding gas for single-and multiple-pass welding in the flat position and for horizontal fillets. A quiet arc, high-deposition rate, low spatter loss, flat-to-slightly convex bead configuration, and easily controlled and removed slag are characteristics of this class.
4. E70T-2 electrode classification: Electrodes of this classification are used with carbon dioxide shielding gas and are designed primarily for single-pass welding in the flat position and for horizontal fillets. However, multiple-pass welds can be made when the weld beads are heavy and an appreciable amount of mixture of the base and filler metals occurs.
5. E70T-3 electrode classification: Electrodes of this classification are used without externally applied gas shielding and are intended primarily for depositing single-pass, high-speed welds in the flat and horizontal positions on light plate and gauge thickness base metals. They should not be used on heavy sections or for multiple-pass applications.
6. E70T-4 electrode classification: Electrodes of this classification are used without externally applied gas shielding and may be used for single-and multiple-pass applications in the flat and horizontal positions. Due to low penetration, and to other properties, the weld deposits have a low sensitivity to cracking.
7. E70T-5 electrode classification: This classification covers electrodes primarily designed for flat fillet or groove welds with or without externally applied shielding gas. Welds made using-carbon dioxide shielding gas have better quality than those made with no shielding gas. These electrodes have a globular transfer, low penetration, slightly convex bead configuration, and a thin, easily removed slag.
8. E70T-6 electrode classification: Electrodes of this classification are similar to those of the E70T-5 classification, but are designed for use without an externally applied shielding gas.
9. E70T-G electrode classification: This classification includes those composite electrodes that are not included in the preceding classes. They may be used with or without gas shielding and may be used for multiple-pass work or may be limited to single-pass applications. The E70T-G electrodes are not required to meet chemical, radiographic, bend test, or impact requirements; however, they are required to meet tension test requirements. Welding current type is not specified.

The flux-cored electrode wires are considered to be low hydrogen since the materials used in the core do not contain hydrogen. However, some of these materials are hydroscopic and thus tend to absorb moisture when exposed to a high-humidity atmosphere. Electrode wires are packaged in special containers to prevent this. These electrode wires must be stored in a dry room.

Stainless Steel Tubular Wires

Flux-cored tubular electrode wires are available which deposit stainless steel weld metal corresponding to the A.I.S.I. compositions. These electrodes are covered by the A.W.S specification, “Flux-Cored Corrosion Resisting Chromium and Chromium-Nickel Steel Electrodes.” These electrodes are identified by the prefix E followed by the standard A.I.S.I. code number. This is followed by the letter T indicating a tubular electrode. Following this and a dash are four-possible suffixes as follows:

1.  -1 indicates the use of C02 (carbon dioxide) gas for shielding and DCEP.
2.  -2 indicates the use of argon plus 2 percent oxygen for shielding and DCEP.
3. -3 indicates no external gas shielding and DCEP.
4. -G indicates that gas shielding and polarity are not specified.

Tubular or flux-cored electrode wires are also used for surfacing and submerged arc welding applications.

Weld Quality and Deposition Rates

The deposition rates for flux-cored electrodes are shown below. These curves show deposition rates when welding with mild and low-alloy steel using direct current electrode positive.

Two types of covered electrodes are shown for comparison. Deposition rates of the smaller size flux-cored wires exceed that of the covered electrodes. The metal utilization of the flux-cored electrode is higher. Flux-cored electrodes have a much broader current range than covered electrodes, which increases the flexibility of the process. The quality of the deposited weld metal produced by the flux-cored arc welding process depends primarily on the flux-cored electrode wire that is used. It can be expected that the deposited weld metal will match or exceed the properties shown for the electrode used. This assures the proper matching of base metal, flux-cored electrode type, and shielding gas. Quality depends on the efficiency of the gas shielding envelope, on the joint detail, on the cleanliness of the joint, and on the skill of the welder. The quality level of weld metal deposited by the self-shielding type electrode wires is usually lower than that produced by electrodes that utilize external gas shielding.

Shielded Metal Arc Welding Electrodes

Shielded Metal Ard Welding is one of the most popular welding processes in the world. Shielded metal arc welding processes use different types of polarity which is dependent on the electrode selected and the required weld properties.

When direct current is used with a negatively charged electrode (DCEN), heat accumulates in the electrode, increasing the rate of electrode melting rate and decreasing the weld depth. If you reverse the polarity, so that you have a positively charged electrode (DCEP), the workpiece becomes negatively charged, increasing the weld penetration.

Shielded Metal Arc Welding electrodes are coated metal in a flux mixture. To prevent weld contamination it gives off gas as it decomposes. It provides a slag layer to protect the weld surface and it also introduces a deoxidizer to purify the weld. This approach improves weld quality and provides alloying elements to improve weld quality. Electrodes influence properties such as

• Corrosion resistance
• Ductility
• Strength

Factors to consider when selecting an arc welding electrode includes:

• the type of metal
• Amount of material to be added
• Workpiece position
• Required weld properties

Basic Electrodes (Low Hydrogen Electrode)

These types use three elements in the electrode coating:

• Limestone (CaCo3)
• Fluorspar (CaF2)
• Clay Asbestos

Electrode Mechanical Properties

• Ductility
• Notch toughness

These types of electrodes also have high resistance to cold and hot cracking, a property helpful when welding high-strength steel.

E7018 Electrodes

These types of electrodes have medium arc penetration, smooth penetration and low spatter. The electrodes use DC or AC polarity. When the iron powder is added E7018 electrodes give better recovery and welding speed. They can be used for thick or medium base metals due to the high level of crack resistance. E7018 I also used when you need a specified level of Charpy V notch impact energy and welds that need to be tough.

E7016 Electrodes

These types of electrodes are low-hydrogen and chemically basic. They have easy-to-remove slag, are friable, heave, and have an arc that somewhat penetrates and convex a weld face. They have superior crack resistibility. The E7016 is used on mild steel, 490MPa high-strength steel, and thick base metals.

Cellulosic Electrodes

The Cellulosic Electrode has a 30% organic material covering consisting of wood flour, alpha flock, or cellulose. The electrode when used develops a plasma jet that provides excellent penetration. The welding position is wide-ranging and is considered to be all position when used with direct. current polarity.

The electrodes have a strong arc force and enable the welded metal to freeze quickly. This is due to the organic material and moisture content.

This type of electrode is a favorite for pipelines where the weld progression is vertically downward.

E6010 Electrodes

The E6010 Electrode is good for all welding positions and for low carbon steel because of its ability to provide deep penetration, low levels of slag, and welds that are high quality in environments where there is dirt, paint, oil, or rust.

The E6010 contains 50% titania as limonite or rutile. The electrodes provide good arc stability in low operating voltage and can be used with alternating current. Weld properties include:

• Radiographic soundness
• Good mechanical soundness
• High deposition rate
• Medium penetration
• Good appearance

Rutile electrodes can be a good slag former when you adjust the surface tension, viscosity, and amount of flux agent.

E6013 Electrodes

The E6013 is considered to be a superior all-around rutile electrode. It is relatively insensitive to surface impurities such as rust.

Weld deposits are smooth and provide good finish weld beads in all welding positions including vertical down. Slag is simple to remove. The arc is stable at low welding currents, making it perfect for welding sheet metal.

Stick Welding Electrodes

Out of Position Welding

When welding out of position with a stick electrode the molten metal can spill out of the joint. To address this problem, stick electrodes for out of position welding required the following considerations:

• Requires operator skill
• High Expense
• Better for down hand welding using high-deposition electrodes

High Deposition Welding

High deposition applications include groove, fillet, lap, and corner welds in 3/16″ and thicker plate welded with the work slightly downhill or level. In this case, use Jetweld electrodes which have high levels of iron powder in the coating which produces high deposit rates to fill joints in the shortest period of time.

Stainless Steel Electrodes

AC-DC (-16) titania coated electrodes are the most popular types of stainless steel electrodes. Their dual current usage allows for stocking of one type for all requirements. The coating results in low spatter, complete penetration, and a smooth stable arc length.

These electrodes can be used in all positions.

Non-Consumable Electrodes

Types of Non-consumable Electrodes

There are two types of non-consumable electrodes.

Carbone Electrode

The carbon electrode is a non-filler metal electrode used in arc welding or cutting, consisting of a carbon graphite rod that may or may not be coated with copper or other coatings. The second non-consumable electrode is the tungsten electrode, defined as a non-filler metal electrode used in arc welding or cutting, made principally o tungsten.

The American Welding Society does not provide specification for carbon electrodes but there is a military specification, no. MIL-E-17777C, entitled, “Electrodes Cutting and Welding Carbon-Graphite Uncoated and Copper Coated”. This specification provides a classification system based on three grades: plain, uncoated, and copper coated. It provides diameter information, length information, and requirements for size tolerances, quality assurance, sampling, and various tests. Applications include carbon arc welding, twin carbon arc welding, carbon-cutting, and air carbon arc cutting and gouging.

Tungsten Electrode

The tungsten electrode is defined as a non-filler metal electrode used in arc welding or cutting, made principally of tungsten.

Pure Tungsten Non-consumable Electrodes are used for GTAW (gas tungsten arc welding) and TIG (Tungsten Inert Gas) welding, and PAW (Plasma Arc Welding). Uses include:

• Orbital Pipe and Tube Welding
• Micro-Tig (Automatic/mechanized TIG Welding)
• Manual Arc Welding
• Micro-Plasma (Automatic/Mechanized Plasma Welding)

Tungsten welding transfers an electric arc from a tungsten electrode to a workpiece. The arc is created when high voltage breaks down and ionizes the shielding gas between the workpiece and electrode. Curren then moves from the electrode to the work to create an electric arc. The tungsten electrode is the terminal for the electric arc and fuse metal together with or without filler material.

The geometry of the Tungsten electrode will impact the arc shape and bead size/shape, weld penetration, and electrode point longevity. You also need to know the right electrode grinding procedure and equipment in order to make sure the electrode dimensions are correct for the job. Another variable is material selection.

Tungsten Electrodes are sold in a variety of arc lengths and electrode diameters. For current electrode, diameter ranges refer to Table A.2 of the AWS A5.12M/A5.12:2009 specification for Tungsten and Oxide Dispersed Tungsten Electrodes for Arc Welding and Cutting.

Each tungsten stick has a color code that indicates the type of material in the tungsten. Refer to Table 1 of AWS A5.12M/A5.12:2009 Specification for Tungsten and Oxide Dispersed Tungsten Electrodes for Arc Welding and Cutting. In the United States, the published standard for Tungsten is called ANSI/AWS 15.12.

To improve Tungsten performance welders use emission-enhancing oxides such as Lanthanum, Cerium, or Thorium.

Gas Types

Non-consumable tungsten electrodes for gas types:

• Pure tungsten
• Tungsten containing tungsten arc (TIG) welding is of four 1.0 percent thorium
• Tungsten contains 2.0 percent thorium
• Tungsten containing 0.3 to 0.5 percent zirconium.

They are also used for plasma-arc and atomic hydrogen arc welding.

Identification

Tungsten electrodes can be identified by painted end marks:

1. Green – pure tungsten
2. Yellow – 1.0 percent thorium
3. Red – 2.0 percent thorium
4. Brown – 0.3 to 0.5 percent zirconium

Uses of Tungsten Electrodes

Pure tungsten (99. 5 percent tungsten) electrodes are generally used on less critical welding operations than the tungstens which are alloyed. This type of electrode has a relatively low current carrying capacity and a low resistance to contamination.

Thoriated tungsten electrodes (1.0 or 2.0 percent thorium) are superior to pure tungsten electrodes because of their higher electron output, better arc starting and arc stability, high current-carrying capacity, longer life, and greater resistance to contamination.

Tungsten electrodes containing 0.3 to 0.5 percent zirconium generally fall between pure tungsten electrodes and thoriated tungsten electrodes in terms of performance. There is, however, some indication of better performance in certain types of welding using ac power.

Finer arc control can be obtained if the tungsten alloyed electrode is ground to a point (fig. 8-3). When electrodes are not grounded, they must be operated at= maximum current density to obtain reasonable arc stability. Tungsten electrode points are difficult to maintain if standard direct current equipment is used as a power source and touch–starting arc is standard practice. Maintenance of electrode shape and the reduction of tungsten inclusions in the weld can best be ground by superimposing a high-frequency current on the regular welding current.

Tungsten electrodes alloyed with thorium retain their shape longer when touch starting is used. Unless a high-frequency alternating current is available, touch starting must be used with thorium electrodes.

The electrode extension beyond the gas cup is determined by the type of joint being welded. For example, an extension beyond the gas cup of 1/8 in. (0.32 cm) might be used for butt joints in light gauge material, while an extension of approximately 1/4 to 1/2 in. (0.64 to 1.27 cm) might be necessary on some fillet welds. The tungsten electrode or torch should be inclined slightly and the filler metal added carefully to avoid contact with the tungsten to prevent contamination of the electrode. If contamination does occur, the electrode must be removed, reground, and replaced in the torch.

Backing Materials

Backing materials are being used more frequently for welding. Special tapes exist, some of which include small amounts of flux, which can be used for backing the roots of joints. There are also different composite backing materials, for one-side welding. Consumable rings are used for making butt welds in pipe and tubing. These are rings made of metal that are tack welded in the root of the weld joint and are fused into the joint by the gas tungsten arc. There are three basic types of rings called consumable inert rings which are available in different analyses of metal based on normal specifications.