OK....just to clarify on the Plasma Pilot Arc question.
Early hand held plasma torches were designed with a high frequency assisted "scratch start".....these torches needed to get very close to the material...and in many cases had to touch the materials in order to create a current path that would get the plasma arc started. These systems were difficult to get the plasma arc started on rusty, painted or dirty material.....and once you did get the arc started the current would ramp up to cutting current quickly...not allowing the user to pull the torch back to the proper standoff. This would immediately damage the nozzle orifice and cause poor cut quality. Unfortunately...many people have tried older technology plasma cutters and cemented the image in their minds that they are difficult to get the arc started, and they are difficult to use...and they don't cut very well.
The next technology with plasma torches involved using a high frequency start torch that established an arc between the torch electrode and nozzle, using a high voltage or high frequency discharge to ionize the plasma gas, then th plasma gas would provide a path for the DC current...which would then create a high intensity "pilot arc" ...this is a DC, non transferred plasma arc that woula fire in the air.....and when brought close to a work grounded plate would allow for easy penetration of rust, dirt, paint etc. Pilot arc torches using this technology were much easier to use....especially on dirty plate. Unfortunately...this technology would take a toll on the plasma torch nozzle as well....as a pilot arc would maintain an arc from electrode to nozzle, this putting a larger heat load on the nozzle orifice causing rapid wear.
Fast forward to the '90's. In Hypertherm's plasma engineering labs in Hanover NH, USA, an engineer was trying to figure out a way to eliminate the high voltage , high frequencyy starting circuitry.....which would allow portable, new technology plasma systems to be lighter, smaller, lower cost. The Blowback start technology was developed and patented...this technology uses a moving electrode inside the torch that creates a short circuit spark as gas pressure pulls it away from the nozzle, ionizing the gas inside the torch without the use of high frequency. These blowback torches could develop and fire a pilot arc in air, and the new technology inverter power supply could keep the pilot current low (to extend nozzle life) and transfer to the plate through dirt, rust, etc. At about the same time, in the same labs...torch shield technology was developed (same engineer, Dr. Nicholas Sanders)...the blowback start technology and torch shield technology revolutionized hand held plasma cutters with longer consumable life, easier torch starting as well as dramatically better cut quality. These enhancements led the way to lighter, lower cost plasma cutting systems as well.
That's kind of the history of pilot arc starting in a plasma torch. Many manufacturers use similar technology today (expired patents) for blowback pilot arc starting.
Jim Colt
