WELDING OPERATIONS I - OD1651 - LESSON 1/TASK 1
arc blow (an unstable arc condition) that is particularly harmful
when welding in corners or restricted places and when high
currents, as required in thick sections, are used. Arc blow, in
these cases, causes blowholes and slag inclusions in the weld as
well as a lack of fusion.
(2) Alternating current is used in atomic hydrogen welding, and
in those carbon-arc processes that require the use of two carbon
electrodes, in order that a uniform rate of welding and electrode
consumption may be accomplished. In carbon-arc processes, where
one carbon electrode is used, straight polarity with direct
current is recommended because the electrode is thus consumed at
a slower rate.
i.
Electrode Defects and their Effects.
(1) If certain elements, or their oxides, are present in
electrode coatings, they will materially effect the stability of
the arc.
If these impurities are present in considerable
quantities of light or heavy coatings, the electrodes will not be
able to compensate for defects in the wire. In bare electrodes,
because there is almost no coating on the wire, the composition
and uniformity of the wire is an important factor in the control
of arc stability.
Impurities in the wire can cause the arc to
become unstable.
(2) Aluminum or aluminum oxide, even when present in quantities
not exceeding 0.01 percent, will cause the arc to become
unstable.
Silicon, silicon dioxide, and iron sulfate also tend
to make the arc unstable.
But, iron oxide, manganese oxide,
calcium oxide, and iron sulfide tend to stabilize the arc.
(3) When phosphorous or sulfur are present in excess of 0.04
percent, they will impair the weld metal because they are
transferred from the electrode to the molten metal. Phosphorous
causes grain growth, brittleness, and "cold shortness" (brittle
when below red heat) in the weld, and these defects increase in
magnitude as the carbon content of the steel increases.
Sulfur
acts as a slag, breaks up the soundness of the weld metal, and
causes "hot shortness" (brittle when above red heat). Sulfur is
particularly harmful to bare, low-carbon steel electrodes with a
low manganese
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