Lincoln Electric INVERTEC IM904 - Manual (Page 17)

B-5 OPERATION B-5
INVERTEC STT II (CE)
WELDING PARAMETERS AND GUIDE-
LINES
The INVERTEC STT II (CE) is neither a constant cur-
rent (CC) nor a constant voltage (CV) power source.
In general, wire diameter will be increased one size
compared to conventional (CV) power sources. The
larger the wire diameter the higher the deposition rate
(Up to 1/16
” ). Wire sizes below .035 ” are unnecessary
for most applications. The INVERTEC STT II (CE) is a
current controlled machine which is capable of chang-
ing the electrode current quickly in order to respond to
the instantaneous requirements of the arc and opti-
mize performance. By sensing changes in welding
current, and hence the electrode state, the power
source will supply varying output currents to minimize
spatter. The Peak and Background currents are two
such current outputs that can be adjusted.
Wire Feed Speed controls the deposition rate. Peak
Current controls the Arc Length. Background Current
controls the Bead Contour. And Tailout increases
Power in the Arc.
PEAK CURRENT
The Peak Current control acts similar to an
“ arc pinch ”
control. Peak current serves to establish the arc
length and promote good fusion. Higher peak current
levels will cause the arc to broaden momentarily while
increasing the arc length. If set too high, globular type
transfer will occur. Setting this level to low will cause
instability and wire stubbing. In practice, this current
level should be adjusted for minimum spatter and
puddle agitation.
Adjust Arc Length with Peak Current
Note: In 100% CO
2
shielding gas applications the
peak current level should be set greater than in a cor-
responding application using a gas blend with a high
percentage of Argon. Longer initial arc lengths with
100% CO2 are required to reduce spatter.
BACKGROUND CURRENT
The Background Current provides the control for the
overall heat input to the weld. Adjusting this level too
high will cause a large droplet to form and globular
type transfer to occur resulting in increased spatter.
Adjusting this level to low will cause wire stubbing and
also poor wetting of the weld metal. This is similar to
a low voltage setting on a standard CV machine
Adjust Bead Shape using Background Current
Note: Background Current levels for applications using
100% CO
2
is less than similar procedures involving
gas blends with high percentages of Argon. This is a
result of the greater heat generated in the 100% CO
2
arc. (100% CO
2
is 35 volts/cm and 100% Argon is 20
volts/cm. 75% Argon, 25% CO
2
is about 24 volts/cm.
Contact Tip to Work Distance
HOT START
The Hot Start control can be set to enhance establish-
ing the arc and provide the capability of increasing the
heat at the start of the weld to compensate for a cold
work piece. Hot start adjusts the time that additional
current is applied during the starting of the arc. Refer
to
“ Operational Features and Controls ” in this section
for a description of this control.
TAILOUT
The tail out provides additional heat without the molten
droplet becoming too large. Increase as necessary to
add
“ Heat ” to the arc without increasing arc length.
(This will allow for faster travel speeds and produce
improved wetting). As tailout is increased, the peal
and/or background current is usually reduced.
WELDING ARC PERFORMANCE
For optimum spatter reduction, the arc should be con-
centrated on the puddle.