Nozzle shield for a plasma arc torch

Claim 1

In a plasma arch torch for cutting and piercing a metal workpiece having a body, an electrode mounted within the body, a nozzle with an outlet orifice mounted on the body at one end thereof, means for introducing a primary gas flow passing through the body, between the electrode and the nozzle, and exiting through the nozzle outlet orifice, and means for directing an electrical current between said electrode and said nozzle to produce a plasma arc exiting the torch through said nozzle orifice, and impinging on said workpiece where it liquifies and splatters the molten metal, the improvement comprising, an electrically conductive shield mounted on said torch body, said shield generally surrounding said nozzle in a spaced relationship and having an exit orifice aligned with said nozzle orifice, said exit orifice being sufficiently large that it does not interfere with said arc, but being sufficiently small that substantially all of the splattered molten metal strikes the shield without reaching said nozzle and other components of said torch, means for insulating said shield electrically from said body to prevent double arcing, said shield being electrically floating, and means for producing a secondary gas glow through said body, said secondary gas flow passing through the space between said nozzle and said shield at a rate sufficient to cool the shield and a first portion of said secondary gas flow exiting said space through at least one bleed port formed in said shield and a second portion exiting through said shield exit orifice, said second portion being of a velocity that it stabilizes the plasma produced by said primary gas flow exiting said torch at said nozzle orifice and said shield exit orifice.