Plasma arc torch and nozzle assembly

In combination, a plasma torch having a nonconsumable electrode adapted to be connected in circuit with a power supply and workpiece for establishing a transferred plasma arc between the nonconsumable electrode and the workpiece through a nozzle assembly arranged beneath said electrode relative to said workpiece and means for passing a swirling flow of gas around said arc and through said nozzle assembly thereby forming a constricted plasma arc of high current density;

• said nozzle assembly comprising:
• a first arc constricting passageway having a longitudinal axis in alignment with the longitudinal axis of said nonconsumable electrode;
• a second arc constricting passageway in coaxial alignment with said first arc constricting passageway, said second arc constricting passageway having an essentially constant diameter throughout its length;
• a water chamber separating said first and second arc constricting passageways;
• and
• means for introducing a jet of liquid into said water chamber for enveloping said swirling gas and arc within said second arc constricting passageway;
• wherein said first and second arc constricting passageways are each of a predetermined length in a predetermined relationship to one another and to the length of the water chamber separating said passageways defined as follows:
• L.sub.1 =K (L.sub.2 +Wg)
• where K is a multiplying constant which must be greater than one and less than about four, and wherein
• L.sub.1 is equal to the length of said first arc constricting passageway;
• L.sub.2 is equal to the length of said second arc constricting passageway;
• and
• Wg is equal to the length of said water chamber separating said first and second passageways.