Different power sources, however,
may have different slope (or incline)
for the volt/ampere curve, and
some machines are designed to
enable some adjustment of the
slope. Figure 4.4 shows that when
the volt-ampere curve is flatter,
there is a greater change in current
for a given change in voltage. The
adjustment of the slope of the
volt/ampere curve enables the
welder to maintain better control of
the weld pool and penetration in
certain situations such as out of
position welding (vertical or
overhead positions) or depositing a
root pass in a pipe over a varying
gap. For example, by adjusting the
volt/ampere curve to be flatter an
intentional increase in the arc
length by a welder pulling the
electrode away increases the arc
voltage and decreases the current
sufficiently to reduce penetration or
risk of burn-through.
Conversely, electrode sticking is
also prevented when the rod is in
near contact with the base metal
and the arc length, and therefore
voltage is reduced, causing the
current to increase sufficiently to
increase the burn off rate to
prevent sticking. With a pure
drooping (or vertical) volt/ampere
curve, there would be no change in the current due to change in voltage or arc length. The welder
would have no control over the electrode burn-off rate in this case.