Plasma arc torches and methods of operating and testing the same

In a plasma torch comprising relatively displaceable electrode and nozzle means having first and second positions relative to one another in which said electrode respectively contacts said nozzle means and is spaced an operating distance from said nozzle means, said nozzle means providing a gas chamber having a plasma outlet opening, means for flowing gas into said chamber, and means for creating a starting arc by relatively displacing said electrode and nozzle means from said first toward said second position, the improvement comprising:

• a system for controlling said means for creating a starting arc including means for creating a voltage across said electrode and said nozzle means, detecting means for detecting a closed circuit condition when said electrode and nozzle means are in said first position, and enabling means for enabling said means for creating a starting arc only if said detecting means detects a closed circuit condition when said electrode and nozzle means are in said first position.

A method of testing a plasma torch prior to starting thereof, said torch comprising relatively displaceable electrode and nozzle members having first and second positions relative to one another in which said electrode respectively contacts said nozzle and is spaced an operating distance from said nozzle, said method comprising:

• applying a test voltage between said electrode and nozzle, sensing for a closed circuit condition when said electrode and nozzle are in said first position, and enabling creating a starting arc between said electrode and nozzle only when a closed circuit condition is sensed with said electrode and nozzle in said first position.

In a plasma torch comprising relatively displaceable electrode and nozzle means having first and second positions relative to one another in which said electrode respectively contacts said nozzle means and is spaced an operating distance from said nozzle means, said nozzle means providing a gas chamber having a plasma outlet opening, means for flowing arc gas into said chamber, means for flowing an arc current between said electrode and nozzle means, and means for relatively displacing said electrode and nozzle means between said first and second positions, whereby a starting arc is created as said electrode and nozzle means move from said first toward said second position, the improvement comprising:

• means for creating a first force for holding said electrode and nozzle means in said second position, and means for selectively creating a second force for overriding said first force and relatively displacing said electrode and nozzle means from said second position to said first position against said first force.