BOC Smootharc Multi 180 - Inductance Control; Trigger Latch Selection (2 T;4 T)

29BOC Smootharc Multi 180/200 Operating manual
Inductance
Inductance in welding is the control of current surges during short
circuits. Consider dip transfer (short-circuiting arc) in action. The wire
touches the weld pool 50 to 150 times per second. 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 thicker material 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)
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 welder
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.
How to set 2T/4T and spot welding
Refer also to steps at the end of 6.2 MIG/MAG modes.
1. Press [2] main menu button.
2. Turn selection knob [4] and select Spot Timer function. Press knob [4]
to conrm.
3. Using knob [4] set spot timer at: 0 sec for 2T function; 0.1 sec for 4T
function; more than 0.1 sec for Spot Welding.