Wolf, Greenfield & Sacks
Process and apparatus for reducing electrode wear in a plasma arc torch
 A process and apparatus for reducing wear of an electrode in a plasma arc torch involves altering the gas flow in a plasma chamber surrounding the electrode immediately before and continuing after cutting of the current that sustains the arc. The altering includes closing off the gas flow upstream of the chamber, switching from a swirling flow to a radial/axial flow through the plasma chamber, reducing the arc current level in conjunction with either of the above, the venting the plasma chamber to rapidly change the gas flow and pressure in the chamber. The interval is sufficient to reduce electrode wear, but short enough that the arc remains stabilized until cut-off. In the flow stop mode, a solenoid valve is placed on an inlet tube for the plasma gas. Flow altering also occurs on start up. A gas preflow is established prior to pilot arc ignition. On transfer, the flow increases to its full operating value in conjunction with an increase in the arc current. The preflow can be axial, or partially axial. Also, the type or composition of the gas used in the preflow and in the operating flow can change during the start up from a less reactive to more reactive gas. 
Hypertherm, Inc.
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Nicholas A. Lifeng Richard W.
Sanders Luo Couch, Jr.