DETECTING NON-SYMMETRICAL NOZZLE WEAR IN A PLASMA ARC TORCH

摘要

A method and apparatus for detecting non-axisymmetric wear (i.e. grooving 22) of the orifice (12) of the nozzle (13) of a plasma arc torch (1) involves placement of a probe adjacent a plasma jet (21) that emerges from the nozzle (13) such that a number of electrically isolated elements (23) of the probe surround the jet (21) and measuring a voltage drop across an electrode (11) of the torch (1) and each probe element (23) to detect whether there is any deflection of the plasma jet (21). The presence of a groove (22) causes the jet (21) to deflect and is indicated by an increased voltage at the probe elements (23) towards which the jet is deflected and a decreased voltage at the opposite elements. The probe may be formed by segmenting a shield (17) of the torch. Alternatively, the voltage across an electrode (11) of a plasma torch (1) and an external electrode (30) that provides a sloping surface (31) to which the plasma arc jet attaches may be monitored while relatively rotating the torch (1) and the external electrode (30) to detect changes in length of the arc, any such change indicating that the nozzle of the torch is grooved. The degree of wear of a nozzle (i.e. size of a groove) is determinable by comparing the size of a measured voltage variation with a reference voltage representative of an ungrooved nozzle.