To add to the pilot arc video:
-There are pilot arc torches that use high voltage / high frequency to ionize the plasma gas (air) and there are pilot arc torches that use the blowback starting method to ionize the air. Both types will fire a non transferred pilot arc in the air.
- Many plasma systems allow the use of a selector switch to determine if the pilot arc is allowed to refire when cutting expanded metal as shown in the video. This is a key feature that dramatically improves nozzle life when cutting on normal plate, yet allows for the pilot arc to rmain on when cutting expanded metal or wire grating.
-More advanced plasma systems also have circuitry know as the pilot arc controller.....a separate IGBT controlled circuit that reduces current flow through the nozzle when in the expanded metal cutting mode....again a feature that increases consumable life. This circuit rapidly drops the amperage (in a few miliseconds) to a level that is less damaging to the consumables....then when the metal reappears...just as quickly ramps back up to cutting amperage.
The primary function of the pilot arc is to maintain ionization between the torch electrode (negative) and nozzle (positive when the arc is not cutting metal), secondarily, it allows the torch to transfer to the positive plate from a much higher distance in mechanized cutting applications....allowing for more room so the molten metal pierce blowback does not damage the torch consumables, and third, the pilot arc allows for much better transfer on painted, coated, or dirty, rusty plates being cut.
Since the pilot arc is a plasma arc between the electrode and the nozzle...the heat load of this arc stays in the torch, with most of it transferring to the nozzle. It is important that the pilot are on time remain at a minimum, and that a pilot arc controller circuit that reacts quickly is part of the design, thereby improving consumable life and reducing the cost per foot of cut.
Jim Colt
