Page 224 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 209

Electrode extension, also known as stickout, is the distance from the
contact tip to the end of the electrode. It applies only to the wire-feed
processes. As the electrode extension is increased in a constant-voltage
system, the electrical resistance of the electrode increases, causing
2
the electrode to be heated. This is known as resistance heating or I R
heating. As the amount of heating increases, the arc energy required
to melt the electrode decreases. Longer electrode extensions may be
employed to gain higher deposition rates at a given amperage. When
the electrode extension is increased without any change in wire-feed
speed, the amperage will decrease. This results in less penetration
and less admixture. With the increase in electric stickout, it is com-
mon to increase the machine voltage setting to compensate for the
greater voltage drop across the electrode.
In constant-voltage systems, it is possible to simultaneously
increase the electric stickout and wire-feed speed in a balanced man-
ner so that the current remains constant. When this is done, higher
deposition rates are attained. Other welding variables such as voltage
and travel speed must be adjusted to maintain a stable arc and to
ensure quality welding. The ESO variable should always be within
the range recommended by the manufacturer.
Electrode diameter means larger electrodes can carry higher weld-
ing currents. For a fixed amperage, however, smaller electrodes result
in higher deposition rates. This is because of the effect on current
density discussed in the following.
Polarity is a definition of the direction of current flow. Positive
polarity (reverse) is achieved when the electrode lead is connected to
the positive terminal of the direct-current (dc) power supply. The
work lead is connected to the negative terminal. Negative polarity
(straight) occurs when the electrode is connected to the negative ter-
minal and the work lead to the positive terminal. Alternating current
(ac) is not a polarity, but a current type. With ac, the electrode is
alternately positive and negative. Submerged arc is the only process
that commonly uses either electrode positive or electrode negative
polarity for the same type of electrode. AC may also be used. For a
fixed wire-feed speed, a submerged arc electrode will require more
amperage on positive polarity than on negative. For a fixed amper-
age, it is possible to utilize higher wire-feed speeds and deposition
rates with negative polarity than with positive. AC exhibits a mix of
both positive and negative polarity characteristics.
The magnetic field that surrounds any dc conductor can cause
a phenomenon known as arc blow, where the arc is physically deflected
by the field. The strength of the magnetic field is proportional
to the square of the current value, so this is a more significant potential

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