Electrode with emissive element having conductive portions
First Claim
1. An emissive element for supporting an electric arc in a plasma arc torch using an oxygen gas to create the plasma, said element comprising:
- a body having a front face for supporting the electric arc, said front face being defined by at least two distinct components formed from different materials, said materials comprising;
an emissive material having a low work function for readily emitting electrons in support of the arc and being reactive with the oxygen plasma gas to form an oxide during an operation of the torch, said oxide forming an electrically resistive layer on the front face of the body upon cooling subsequent to the operation of the torch; and
a conductive metal material having an electrical conductivity greater than the oxide layer for supporting the arc during the initiation of a subsequent torch operation at least until the oxide reaches an operating temperature, the conductive material being disposed on the front face of the body in a predetermined pattern defining a path from a periphery of the front face toward a central region thereof.
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Accused Products
Abstract
The invention relates to an emissive element for supporting an electric arc in a plasma arc torch using an oxygen gas to create the plasma. The element includes a body having a front face for supporting the electric arc which is defined by at least two distinct components formed from different materials. The first component is an emissive material having a low work function for readily emitting electrons in support of the arc and being reactive with the oxygen plasma gas to form an oxide during an operation of the torch. The oxide forms an electrically resistive layer on the front face of the body upon cooling subsequent to the operation of the torch. Hafnium is a preferred material for the first component. The second component comprises a conductive material having an electrical conductivity greater than the oxide layer for supporting the arc during the initiation of a subsequent torch operation at least until the oxide reaches an operating temperature. Silver and copper are preferred materials for the second component. The conductive material provides a conductive path which allows the arc to be supported thereon until the oxide layer reaches an operating temperature, thereby preventing thermal cracking and removal of the oxide layer. Accordingly, electrode start erosion is reduced.
59 Citations
26 Claims
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1. An emissive element for supporting an electric arc in a plasma arc torch using an oxygen gas to create the plasma, said element comprising:
a body having a front face for supporting the electric arc, said front face being defined by at least two distinct components formed from different materials, said materials comprising; an emissive material having a low work function for readily emitting electrons in support of the arc and being reactive with the oxygen plasma gas to form an oxide during an operation of the torch, said oxide forming an electrically resistive layer on the front face of the body upon cooling subsequent to the operation of the torch; and a conductive metal material having an electrical conductivity greater than the oxide layer for supporting the arc during the initiation of a subsequent torch operation at least until the oxide reaches an operating temperature, the conductive material being disposed on the front face of the body in a predetermined pattern defining a path from a periphery of the front face toward a central region thereof. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An emissive element for supporting an electric arc in a plasma arc torch, said element comprising:
an elongate body having a front face for supporting the electric arc, said body comprising; a plurality of emissive filaments extending through the elongate body which define an array of adjacent emissive portions with interstices therebetween at the front face of the body, said filaments being formed of an emissive material having a low work function for readily emitting electrons in support of the arc; and an electrically conductive material filling the interstices between the adjacent emissive filaments at the front face of the elongate body. - View Dependent Claims (15, 16, 17, 18, 19)
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20. An electrode for supporting an electric arc in a plasma arc torch, said electrode comprising:
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a metallic holder having a front face and a receptacle formed in the front face; and an emissive element mounted in the receptacle of the holder and having a front face substantially coplanar with the front face of the holder for supporting the electric arc, said front face of the emissive element being defined by at least two distinct components formed from different materials, said materials comprising; an emissive material having a low work function for readily emitting electrons in support of the arc; and an electrically conductive metal material adjacent to said emissive material, the conductive material being disposed on the front face of the emissive element in a predetermined pattern defining a path from a periphery of the front face of the emissive element toward a central region thereof. - View Dependent Claims (21, 22, 23, 24, 25)
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26. A method of operating a plasma arc torch using an oxygen gas to create the plasma, said method comprising the steps of:
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supplying an oxygen gas adjacent to an emissive element having a front face and being formed of two materials comprising an emissive material and a conductive material, the conductive material being disposed on the front face in a predetermined pattern defining a path from a periphery of the front face toward a central region thereof; applying an electric potential to the emissive element such that an electrical arc is supported by the emissive material which is formed of a material having a relatively low work function; oxidizing a portion of the emissive material adjacent to the arc; disconnecting the electrical potential such that the arc is extinguished and the oxidized portion of the emissive material is allowed to cool and thereby form an electrically resistive oxide layer; and reapplying the electric potential to the emissive element and initiating an electric arc which is at least initially supported by the conductive material until the oxide layer reaches an operating temperature.
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Specification