Operating instructions

31BOC Smootharc Advance II MIG 250C Operating manual
9.2 Inductance
Inductance is dened as the rise in current 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 ow 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 o󹟽 the wire violently. This rapid melt ings 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
tted 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 e󹟽ects:
→ reduced spatter
→ heat control
→ has no e󹟽ect 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)
9.3 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/
she has to hold the trigger down for long periods of time and may cause
discomfort. This is can be similar to repetitive strain injury (RSI) that has
become a very popular topic for compensation by o󹟾ce 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 rst depressing it and 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. (Remember, 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 nished 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 and aluminium.