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. A diagram of the transfer of metal across the arc of a bare electrode is shown in below figure.
Molten metal transfer with a bare electrode
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:
1. It dissolves or reduces impurities such as oxides, sulfur, and phosphorus.
2. 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.
3. It increases the arc stability by introducing materials readily ionized (i.e., changed into small particles with an electric charge) into the arc stream.
4. 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
* 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 below figure.
