A complete SMAW station, Figure 5-6, includes
the SMAW outfit plus the following:
• Ventilation.
• Welding table.
• Welding booth with an opaque (solid) or filtered
transparent plastic screen.
• Covered electrodes.
• Chipping hammer and wire brush.
Arc Welding Machine
Arc welding machines produce either a constant
current (CC) or a constant voltage (CV). Manual
welding processes, such as SMAW, require a constant
current (CC) welding machine. If a CC welding
machine is not used, large changes in current occur
whenever a welder changes the arc length slightly.
Since it is impossible to manually maintain a constant
arc length without any variation, a CC welding
machine is used.
CC welding machines are also called droopers or
droop curve machines. This name is derived from the
voltage versus amperage curve produced by the
machines. Figure 5-7 shows the curve shape for a CC
welding machine.
Examine Figure 5-7 closely. An increase from 20
volts to 25 volts is a 25% increase in voltage. This
change in voltage results in an increase in current
from 125 amps to 130 amps, only a 4% increase. If the
welder varies the arc length, it causes a change in volt-
age. However, the amperage changes very little with
a CC welding machine. Although the current varies
slightly, these welding machines are considered con-
stant current. Both ac and dc welding machines are
available as constant current machines.
Selecting an Arc Welding Machine
Ac welding machines meet most welding require-
ments. They are easy to use and generally cost less
than comparable dc welding machines. Therefore,
they are widely used on the farm and in the home
shop. See Figure 5-8.
Because the polarity can be changed, dc welding
machines are more versatile than ac machines. The
ability to change the polarity allows the welder to
make out-of-position welds and to weld thin metal
more easily. It also allows the welder to vary the heat
applied to the metal. DCEP provides deep penetration
for welds on thick metal; DCEN deposits filler metal
faster. DCEN is used more easily on thin metal.
Some arc welding machines are combination
ac/dc machines. These machines can be used as ac
welding machines and then can easily be switched to
Welding Technology Fundamentals 54
Figure 5-6. This is a well-equipped shielded metal arc welding
station.
Volts
80
70
60
50
40
30
20
10
0
0 25 50 75 100 125 150 175 200
Amperes
Figure 5-7. A volt-amp diagram for a constant current
machine. The constant current (CC) welding machine is called
a drooper because of this curve. A 25% change in voltage
results in only a 4% change in amperage. The current change
is so slight that the current is considered constant.