Electrodes are a necessity in welding. Molten metal becomes brittle or has other negative qualities when exposed to air as it absorbs nitrogen and oxygen. Slag covers protect the molten metal during welding from the surrounding atmosphere. The slag cover is usually obtained from the coating of the electrode.
Electrode usability is determined by the coating’s composition. The composition of the deposited weld metal and the electrode specification also helps to determine usability. These are important factors to consider when using electrodes.
Electrode coatings are carefully formulated using principles of physics, metallurgy, and chemistry. The coating is very useful as it stabilizes the arc, protects the metal, and improves the weld. The coating improves the weld by minimizing spatter, providing a smooth weld surface that has even edges, making a welding arc that is stable, allowing penetration control, providing a strong and tough coating, easier removal of slag, and an improved deposition rate. All of these factors play an important part in quality welds.
Metal-arc electrodes are grouped as heavy coated or shielded arc electrodes and thinly coated or bare electrodes. In arc welding, covered electrodes are the most popular kind. What kind of electrode is used in a welding job is determined by the properties that are required. These properties are high tensile strength, ductility, corrosion resistance, the base metal, weld position, and the polarity and current required.
Electrodes that are used for welding low alloy and mild steels might have six to twelve ingredients in their coatings. These ingredients include cellulose that provides a gas shield and metal carbonates that will adjust the slag. Titanium dioxide is often included which helps to make slag that is quick freezing but highly fluid. Other ingredients may be ferromanganese, clays, gums, and calcium fluoride. The metals used could be nickel, chromium, or molybdenum and iron or manganese oxide is also often used.
Light coated electrodes are electrodes that have a light coating applied to the surface by brushing, spraying, dipping, washing, wiping, or tumbling. The arc steam’s characteristics are improved by the coatings. The coatings reduce or dissolve impurities, makes the molten metal flow and become more uniform, and increases the arc’s stability. Some light coatings will create a slag.
Shield arc or heavy coated electrodes have coatings that are applied by extrusion or dipping. There are three general kinds: mineral coatings, cellulose coatings, and a combination of the two. Cellulose coatings provide a gaseous zone around the arc and weld zone to protect it. Mineral coatings create a slag deposit. These kinds of electrodes are used for welding cast iron, steels, and hard surfacing. These coatings increase arc stability, produce a reducing gas shield that surrounds the arc, and reduce impurities that can impair the weld deposit. The electrodes form a slag that solidifies slowly, holds heat, and lets the underlying metal to solidify slowly. This lets impurities float to the surface.
Direct current electrodes are to be used with reverse polarity, straight polarity, or both. Nearly all can be used with alternating current. Reverse polarity usually provides more penetration than straight polarity. Alternating current electrodes are coated electrodes used with alternating or direct current. This type of electrode is preferred in restricted areas or with high currents that are required for thick sections. It is often used in atomic hydrogen welding.
Electrodes come in many varieties and the kind you choose will depend on the area you are working in, the job itself, and the metals that you are using. The wrong kind of electrode can ruin your weld and force you to start all over again. Using the proper one will enable you to work faster, smarter, and have welds that are strong and durable.
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