Types of electrode
- MX Chanal
- May 19, 2018
- 6 min read
The Types of Electrodes
The Types of Electrodes
Bare Electrodes
Bare welding electrodes are made of wire compositions required for specific applications. These electrodes have no coatings other than those required in wire drawing. These wire drawing coatings have some slight stabilizing effect on the arc but are otherwise of no consequence. Bare electrodes are used for welding manganese steel and other purposes where a coated electrode is not required or is undesirable.
Light Coated Electrodes
Light coated welding 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 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.
Shielded Arc or Heavy Coated Electrodes
Shielded arc or heavy coated welding 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. See figure 5-31 below.
Functions of Shielded Arc or Heavy Coated Electrodes
These welding 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.
They reduce impurities such as oxides, sulfur, and phosphorus so that these impurities will not impair the weld deposit.
They provide substances to the arc which increase its stability. This eliminates wide fluctuations in the voltage so that the arc can be maintained without excessive spattering.
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.
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.
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.
Tungsten Electrodes
No consumable welding electrodes for gas tungsten-arc (TIG) welding are of three types: pure tungsten, tungsten containing 1 or 2 percent thorium, and tungsten containing 0.3 to 0.5 percent zirconium.
Tungsten electrodes can be identified as to type by painted end marks as follows.
Green -- pure tungsten.
Yellow -- 1 percent thorium.
Red -- 2 percent thorium.
Brown -- 0.3 to 0.5 percent zirconium.
Pure tungsten (99. 5 percent tungsten) electrodes are generally used on less critical welding operations than the tungsten’s which are alloyed. This type of electrode has a relatively low current-carrying capacity and a low resistance to contamination.
Throated tungsten electrodes (1 or 2 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 welding electrodes containing 0.3 to 0.5 percent zirconium generally fall between pure tungsten electrodes and throated 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 (see figure 5-33). 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 of the arc is standard practice. Maintenance of electrode shape and the reduction of tungsten inclusions in the weld can best be accomplished by superimposing a high-frequency current on the regular welding current. Tungsten electrodes alloyed with thorium and zirconium retain their shape longer when touch-starting is used.
The welding 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. (3.2 mm) might be used for butt joints in light gage material, while an extension of approximately 1/4 to 1/2 in. (6.4 to 12.7 mm) might be necessary on some fillet welds. The tungsten electrode of torch should be inclined slightly and the filler metal added carefully to avoid contact with the tungsten. This will prevent contamination of the electrode. If contamination does occur, the electrode must be removed, reground, and replaced in the torch.
Direct Current Arc Welding Electrodes
The manufacturer’s recommendations should be followed when a specific type of welding 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 suited, corrections for poor fit-ups, and other specific conditions.
In most cases, straight polarity electrodes will provide less penetration than reverse polarity electrodes, and for this reason will permit greater welding speed. 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. 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.
Carbon Electrodes
The American Welding Society does not provide specification for carbon welding 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.
Stick Electrodes
Stick welding electrodes vary by:
size: common sizes are 1⁄16, 5⁄64, 3⁄32 (most common), 1⁄8, 3⁄16, 7⁄32, 1⁄4, and 5⁄16 inch. Core wire used with electrodes needs to be narrower than the materials that are welded.
material: stick welding electrodes come in cast iron, high carbon steel, mild steel, iron-free (nonferrous) and special alloys.)
strength: referred to as tensile strength. Each weld needs to be stronger than the metal being welded. This means that the materials in the electrode need to be stronger as well.
welding position (horizontal, flat etc): different electrodes are used for each welding position.
iron powder mix (up to 60% in flux): iron powder in the flux increases the amount of molten metal available for the weld (heat turns powder into steel).
soft arc designation: for thinner metals or for metals that don't have a perfect fit or gap.
SMAW Welding Electrode Diagram
As described above there are many kinds of electrodes. Heretare the most popular stick welding (SMAW) electrodes:
E6013 and E6012: For thin metals and joints that do not easily fit together.
E6011: Good for working on surfaces that are oily, rusted or has dirt. Versatile in that it works with DC or AC polarity. Creates little slag, another big plus. Note that this electrode should not be placed into an electrode oven.
E6010: Similar to the E6011 but only works with direct current (DC). Note that this electrode should not be placed into an electrode oven.
E76018 and E7016: Manufactured with iron powder in the flux. Creates strong welds, but has a puddle that might present some control issues for beginners. Collage Saved
Comments