WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 1
(a) The cellulose-coated types are composed of soluble cotton
or other forms of cellulose with a small amount of potassium,
sodium, or titanium and, in some cases, other minerals.
coating provides protection to the molten or solidifying metal by
developing a gaseous zone around the arc and a slag deposit over
(b) The mineral coatings consist of sodium silicate, metallic
oxides, clay, and other inorganic substances or combinations
With the mineral-coated electrode, protection to the
molten or solidifying metal is provided only by a slag deposit.
(c) The combination of a mineral and cellulose coating is
composed of various quantities of the substances previously
described for each of these coatings.
These coatings provide
various protection effects to the arc, and to the molten or
solidifying metal, depending on the type of base metal being
e. Functions of Electrode Coatings. Some of the more important
functions of the coatings on the shielded-arc or heavy-coated arc
electrodes are described in the following subparagraphs.
(1) The coatings produce a reducing or nonoxidizing atmosphere
in the arc by oxygen and nitrogen from the air.
coating, the oxygen would readily combine with the molten metal,
remove alloying elements from the metal, and cause porosity and
(2) The coatings reduce impurities such as oxides, sulfur, and
phosphorous so that these impurities will not impair the weld
(3) They provide substance to the arc, which tend to increase
its stability, so that the arc can be maintained without
(4) Coatings reduce the attractive force between the molten
metal and the end of the electrode, and reduce the surface
tension of the molten metal. Vaporized and melted coatings cause