Electrode component thermal bonding

Abstract

An electrode for supporting an arc in a plasma arc torch is provided and includes an emissive element for supporting the arc, which may be formed of hafnium; a relatively non-emissive member comprising a first metal including silver, which is positioned to circumscribe a front surface of the emissive element; and a metallic holder for holding the non-emissive member. The holder is in one embodiment made of a copper alloy including a major portion of copper and a minor portion of another metal, such as nickel. After assembly, the electrode is subjected to a heat treatment that causes a thermal bonding between the relatively non-emissive member and the metallic holder, which, during subsequent operation of the electrode, provides good thermal conduction away from the emissive element and improves the consumable life of the electrode. Advantageously, during the heating step, the nickel attenuates the eutectic reaction between the copper and the silver that would otherwise occur and allows bonding over a wide range of temperatures and heating cycle durations. In addition, the temperature at which bonding occurs between the non-emissive member and the holder is also raised. As a result, if desired, a thermal bond can also be formed between the hafnium emissive element and the non-emissive member during the same heating cycle, thus further promoting thermal conductivity of the electrode. In alternative embodiments, other metals and other configurations, such as the use of an intervening plating, powder or sleeve are used to raise, and provide a greater range for, the temperatures over which bonding occurs between the non-emissive element and the holder.