Tweco 300 MST Arcmaster - Manual (Page 30)

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3.04.03 HOT START
This parameter operates in STICK mode and improves the start characteristics for stick electrodes. e.g.
low hydrogen electrodes. It sets the peak start current on top of the WELD current.
e.g. HOT START current = 150 amps when Weld Current = 100 amps & HOT START = 50A
3.04.04 WELD (A)
This parameter sets the STICK & Lift TIG weld current.
3.04.05 ARC CONTROL
This parameter operates in STICK mode only and is used to adjust percentage increase in welding
current and is proportional to arc length (arc voltage). This control provides an adjustable amount of
arc control (or dig). This feature can be particularly beneficial in providing the operator with the ability
to compensate for variability in joint fit up in certain situations with particular electrodes, e.g. cellulose
and hydrogen controlled electrodes. In all welding processes, the amount of penetration obtained is
dependent on the welding current; ie the greater the penetration, the greater the current.
Arc Force Position Current Increase when Arc
Voltage is less than 18V
Effect on Welding Performance
Minimum (0) 0A Soft arc, Low spatter, Low
penetration
Medium (20%) 32A Normal arc, Improved fusion
characteristics,
Normal penetration
Maximum (100%) 160A Hard arc, Deep penetration
Table 5 – Weld Parameter Descriptions
In general, having the ARC CONTROL set at 100% (maximum) allows greater penetration control
to be achieved. With the ARC CONTROL set at 0% (minimum) the Power Source has a constant
current characteristic. In other words, varying the arc length does not significantly affect the
welding current. When the ARC CONTROL set to 100%, it is possible to control the welding
current by varying the arc length. This is very useful for controlling penetration on root runs and
side wall wash on vertical up fillet welds.
i) Root runs
During root runs the weld pool forms a “keyhole” shape. If too much weld current is
used, the hole blows out and the weld collapses. If too little weld current is used, the
hole closes up and penetration is lost. The size of the hole also determines the arc
length; i.e. as the hole gets bigger, the arc gets longer.
If arc force is used, the increase in the arc length causes the weld current to decrease
until the hole starts to close up but if the hole closes up to much then the arc length
decreases which causes the weld current to increase. Too little or too much arc force
makes this process unstable. The operator must adjust the arc force until a happy
medium is reached.