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Control Panel of Raptor 250R MIG
Voltage meter
9 Power indicator light
1 2T/4T button
2 Process selection switch
Current meter/
Wire speed meter
3 Inductance Knob
4 Wire speed/Arc current knob
5 Voltage Knob
5.2 Inductance
Inductance is defined as the rise in current temperature to above
normal, in any electrical circuit that results in the melting of the
wire at some point. Consider dip transfer (short¬circuiting arc) in
action. Before the wire strikes the work-piece, there is no flow of
current and the OCV has maximum value. When the wire strikes
the work-piece it creates what is known as a "dead short". This
short-circuit causes the current to rise rapidly and burn off the wire
violently. This rapid melt flings about metal globules as it takes
place. These globules settle on the work-piece and welding torch in
the form of "spatter".
To control the rise rate of short-circuiting current, a choke (or
inductor) is fitted in series with the welding power cable. This
inductor "chokes" the rate of rise of current and ensures a smooth
arc condition.
Inductance controls the rate of rise of short-circuiting current. It
becomes evident that inductance must be a function of time and
current, since it controls the time taken for the current to rise to
the pre-set value. Hence an increase in inductance results in less
frequent short-circuiting. Fewer short-circuits imply that the arc
is present for a longer duration of time. Increased "arc-on" time
means increased heat.
Therefore, on a heavier plate where more heat is required to
ensure good fusion, more inductance would contribute immensely.
Conversely on thinner sections less inductance would lead to a
decrease in "arc-on" time, and consequently a "cooler" arc which
enables thin materials to be welded with ease.
Summarising, inductance has the following effects:
reduced spatter
•
heat control
•
has no effect when spray-arc welding, because there is no more
•
change in current, the inductance coil plays no further part.
A certain amount of inductance with spray-transfer will provide
softer starts (the initial short-circuit)
BOC RAPTOR 200C & 250R MIG Operating manual
Control panel of wire feeder
17 Wire inch button
15 Wire speed
adjustment
18 Voltage adjustment
5.3 Synergic Control (One Knob Control)
In synergic control the machine will automatically select the
voltage and wire feed speed to be in balance depending on the
curve that has been selected for that application. For example,
if the voltage is changed the wire speed will be automatically
adjusted for the selected voltage.
Most power sources will allow fine adjustment for individual
welding preferences.
5.4 4T/2T Trigger Latch Selection
On all MIG machines there is no current or wire feed until the
trigger on the torch is depressed. If a welder is doing a lot of
welding then he has to hold the trigger down for long periods of
time and may cause discomfort. This can be similar to repetitive
strain injury (RSI) that has become a very popular topic for
compensation by office workers.
On all machines a special function called 2T and 4T is available.
Also referred to as trigger latching, this special feature allows
the operator to relax the trigger after first depressing it, the gas
shielding to start before the welding commences. This feature
is of particular importance as it ensures that the weld will have
adequate gas shielding to eliminate the risk of oxidisation
(contaminants) causing a defective weld. A defective weld may not
be detected by a visual inspection.
The 2T/4T function also allows for the shielding gas to continue
after the weld has finished and cooled. This eliminates the risk
of oxidation while the weld is still in its molten state. This is
particularly important when welding stainless steel materials.
15
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