Wolf, Greenfield & Sacks
Proceses 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, and 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. For venting, a vent tube and another solenoid valve are added to the torch. In the flow pattern switching mode, two independent gas supply lines with control valves feed separate sets of gas inlets to the plasma chamber, one set producing a swirling flow and the other set producing a radial then axial flow. 
Hypertherm, Inc.
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Lifeng Richard W. Nicholas A.
Luo Couch, Jr. Sanders