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COPYRIGHT 2000 THE ESAB GROUP, INC. LESSON
III 3.1 Development of Covered Electrodes
During the 1890's, arc welding was accomplished with bare metal electrodes. The welds produced were
porous and brittle because the molten weld puddle absorbed larg quantities of oxygen and nitrogen
from the atmosphere. Operators noticed that a rusty rod produced a better weld than a shiny clean rod.
Observations also showed than an improved weld could be made by wrapping the rod in newspaper or by
welding adjacent to a pine board placed close to and parallel with the weld being made. In these cases,
some degree of shielding the arc form the atmosphere was being accomplished. These early observations
led to the development of the coated electrode.
3.1.0.1 Around 1920, the A.O. Smith Corporation developed an electrode spirally wrapped with paper,
soaked in sodium silicate, and then baked. This was the first of the cellulosic type electrodes.
It produced an effective gas shield in the area and greatly improved the ductility of the weld metal.
3.1.0.2 Because of the method used to manufacture these paper covered electrodes, it was difficult
to effectively add other ingredients to the coating. In 1924, the A.O. Smith Corporation began work
on coatings that could be extruded over the core wire. This method allowed the addition of other
flux ingredients to furhter improve or modify the weld metal and by 1927, these electrodes were
being produced commercially.
3.1.0.3 Since 1927, many improvements have been made and many different types of electrodes have
been developed and produced. Through variations in the formulations of the covering and the amount
of covering on the mild steel core wire, many different classifications of electrodes are produced today.
3.2 Manufacturing Covered Electrodes
Mild steel covered electrodes, also commonly called coated electrodes, consist of only two major elements;
the core wire or rod and the flux covering. The core wire is usually low carbon steel.
It must contain only small amounts of aluminum and copper, and the sulfur and phosphorous levels
must be kept very low since they can cause undesirable brittleness in the weld metal. The raw material
for the core wire is hot-rolled rod (commonly called "hot rod"). It is
