Figure 7-7.Electrode covering and gaseous shield that protects
weld metal from the atmosphere.
In general, all electrodes are classified into five
1. Mild steel
2. High-carbon steel
3. Special alloy steel
4. Cast iron
The widest range of arc welding is done with electrodes
in the mild steel group.
Electrodes are manufactured for use in specific
positions and for many different types of metal. They
also are specially designed to use with ac or dc welding
machines. Some manufacturers electrodes work iden-
tically on either ac or dc, while others are best suited for
flat-position welding. Another type is made primarily
for vertical and overhead welding, and some can be used
in any position. As you can see, electrode selection
depends on many variables.
Types of Electrodes
Electrodes are classified as either bare or shielded.
The original bare electrodes were exactly as their name
impliedbare. Today, they have a light covering, but
even with this improvement they are rarely used because
of their limitations. They are difficult to weld with,
produce brittle welds, and have low strength. Just about
all welding is done with shielded electrodes.
The shielded electrode has a heavy coating of sev-
eral chemicals, such as cellulose, titania sodium, low-
hydrogen sodium, or iron powder. Each of the chemicals
in the coating serves a particular function in the welding
process. In general, their main purposes are to induce
easier arc starting, stabilize the arc, improve weld
appearance and penetration, reduce spatter, and protect
Figure 7-8.Explanation of AWS classification numbers.
the molten metal from oxidation or contamination by the
As molten metal is deposited in the welding process,
it attracts oxygen and nitrogen. Since the arc stream
takes place in the atmosphere, oxidation occurs while
the metal passes from the electrode to the work. When
this happens, the strength and ductility of the weld are
reduced as well as the resistance to corrosion. The
coating on the electrode prevents oxidation from taking
place. As the electrode melts, the heavy coating releases
an inert gas around the molten metal that excludes the
atmosphere from the weld (fig. 7-7).
The burning residue of the coating forms a slag over
the deposited metal that slows down the cooling rate and
produces a more ductile weld. Some coatings include
powdered iron that is converted to steel by the intense
heat of the arc as it flows into the weld deposit.
Electrodes are often referred to by a manufacturers
trade name. The American Welding Society (AWS) and
the American Society foresting and Materials (ASTM)
have set up certain requirements for electrodes to assure
some degree of uniformity in manufacturing electrodes.
Thus different manufacturers electrodes that are within
the classification established by the AWS and ASTM
should have the same welding characteristics. (See
In this classification, each type of electrode is
assigned a specific symbol, such as E-6010, E-7010, and
E-8010. The prefix E identifies the electrode for