WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 1
that the opposite is true and the greater heat is produced on the
negative side.
Electrode coatings affect the heat conditions
differently, depending on their composition.
One type of heavy
coating may provide the most desirable heat balance with straight
polarity, while another type of coating on the same electrode may
provide a more desirable heat balance with reverse polarity.
(3) Reverse polarity is used in the welding of nonferrous
metals such as aluminum, bronze, monel, and nickel.
Reverse
polarity is also used with some types of electrodes for making
vertical and overhead welds.
(4) The proper polarity for a given electrode can be recognized
when attempting a weld by the sharp, cracking sound of the arc.
The wrong polarity will cause the arc to emit a hissing sound and
the welding bead will be difficult to control.
g.
Direct Current Arc-welding Electrodes.
(1) In general, direct current (dc), shielded-arc electrodes
are designed either for reverse polarity (electrode positive) or
for
straight
polarity
(electrode
negative)
and
are
not
interchangeable.
Many, but not all, of the direct current
electrodes, both reverse and straight polarity, also can be used
with alternating current.
Direct current is preferred for many
types of bare and covered nonferrous and alloy steel electrodes.
These electrodes are used when ferrous welds are to be made in
horizontal, vertical, or overhead positions.
Recommendations
from electrode manufacturers include the type of base metal for
which given electrodes are suitable.
(2) In most cases, straight polarity electrodes (electrode
negative) will provide less penetration than the reverse polarity
electrodes (electrode positive) and, for this reason, will permit
greater welding speed.
Good penetration can be obtained with
either type under proper welding conditions and arc manipulation.
h.
Alternating Current Arc-welding Electrodes.
(1) Coated electrodes that can be used with either direct or
alternating current are available.
Alternating current is more
desirable under certain operating conditions.
Alternating
current reduces
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