Composite electrode for a plasma arc torch

Abstract

A plasma arc torch that includes a torch body having a nozzle mounted relative to a composite electrode in the body to define a plasma chamber. The torch body includes a plasma flow path for directing a plasma gas to the plasma chamber in which a plasma arc is formed. The nozzle includes a hollow, body portion and a substantially solid, head portion defining an exit orifice. The composite electrode can be made of a metallic material (e.g., silver) with high thermal conductivity in the forward portion electrode body adjacent the emitting surface, and the aft portion of the electrode body is made of a second low cost, metallic material with good thermal and electrical conductivity. This composite electrode configuration produces an electrode with reduced electrode wear or pitting comparable to a silver electrode, for a price comparable to that of a copper electrode.

We claim: 
     
       1. A composite electrode for use in a plasma arc torch comprising:
 a body defining a bore and a cooling area which receives a liquid coolant, the body comprising a forward portion defining a bottom wall and a forward portion side wall, an aft portion defining an aft portion side wall, the bottom wall, the forward portion side wall and the aft portion side wall defining the cooling area, and a forged direct weld joint of forged quality;
 the forward portion of the body comprising a first material with a heat transfer property, the forward portion including a first mating surface; 
 the aft portion of the body comprising a second material different from the first material, the a heat transfer property of the second material is different than the heat transfer property of the first material, the aft portion including a second mating surface; and 
 the forged direct weld joint is formed between the forward and aft portions along the first and second mating surfaces and between the forward portion side wall and the aft portion side wall without introduction of an additional material to provide, thereby providing direct metallurgical coupling between the first material and the second material along the forged direct weld joint to define the cooling area having a bottom wall surface area formed of the first material, a forward portion side wall surface area formed of the first material, and an aft portion side wall surface area formed of the second material, the forged direct weld joint being leak-proof; and 
 
 an emissive element disposed within the bore and in thermal contact with the forward portion. 
 
     
     
       2. The composite electrode of  claim 1 , wherein the first material has high thermal conductivity. 
     
     
       3. The composite electrode of  claim 1 , wherein the first material has thermal conductivity greater than about 400 Watts/m/deg-K. 
     
     
       4. The composite electrode of  claim 1 , wherein the first material has high thermal diffusivity. 
     
     
       5. The composite electrode of  claim 1 , wherein the first material has thermal diffusivity greater than about 0.1 m 2 /sec. 
     
     
       6. The composite electrode of  claim 1 , wherein the first material has thermal diffusivity greater than about 0.17 m 2 /sec. 
     
     
       7. The composite electrode of  claim 1 , wherein the first material comprises silver or an alloy thereof. 
     
     
       8. The composite electrode of  claim 1 , wherein the second material comprises aluminum, brass, copper, or an alloy thereof. 
     
     
       9. The composite electrode of  claim 1 , wherein the emissive element comprises hafnium, zirconium, tungsten, thorium, lanthanum, strontium, or alloys thereof. 
     
     
       10. A composite electrode for use in a plasma arc torch comprising:
 a body defining a bore and a cooling area which receives a coolant, the body comprising a forward port ion, an aft port ion, and a forged weld joint;
 the forward port ion of the body comprising a first material with a heat transfer property, the forward portion including a first mating surface; 
 the aft port ion of the body comprising a second material different from the first material, the heat transfer property of the second material is different than the heat transfer property of the first material, the aft portion including a second mating surface; and 
 the forged weld joint disposed between the forward and aft portions along the first and second mating surfaces to provide direct metallurgical coupling along the forged weld joint, the forged weld joint having a bend test strength and a tensile test strength equal to that of the first material; and 
   an emissive element disposed within the bore and in thermal contact with the forward portion.   
     
     
       11. The composite electrode of  claim 10 , wherein the first material has high thermal conductivity. 
     
     
       12. The composite electrode of  claim 10 , wherein the first material has thermal conductivity greater than about 400 Watts/m/deg-K. 
     
     
       13. The composite electrode of  claim 10 , wherein the first material has high thermal diffusivity. 
     
     
       14. The composite electrode of  claim 10 , wherein the first material has thermal diffusivity greater than about 0.1 m 2 /sec. 
     
     
       15. The composite electrode of  claim 10 , wherein the first material has thermal diffusivity greater than about 0.17 m 2 /sec. 
     
     
       16. The composite electrode of  claim 10 , wherein the first material comprises silver or an alloy thereof. 
     
     
       17. The composite electrode of  claim 10 , wherein the second material comprises aluminum, brass, copper, or an alloy thereof. 
     
     
       18. The composite electrode of  claim 10 , wherein the emissive element comprises hafnium, zirconium, tungsten, thorium, lanthanum, strontium, or alloys thereof. 
     
     
       19. A method of forming an electrode for a plasma arc torch, the method comprising:
 utilizing a combination of physical force and acceleration and deceleration ofdirect welding a forward portion comprising a first metallic material with a heat transfer property andto an aft portion comprising a second metallic material with thea heat transfer property of the second metallic material being different than the heat transfer property of the first metallic material to form an electrode body includingcomprising the forward portion defining a bottom wall and a forward portion side wall, the aft portion defining an aft portion side wall, where the bottom wall, the forward portion side wall and the aft portion side wall define a cooling area, and a hermetic joint formed between the forward portion side wall and the aft portion side wall providing direct metallurgical coupling between the forward and aft port ionsportions along the hermetic joint, the direct metallurgical coupling defining the cooling area having a bottom wall surface area formed of the first metallic material, a forward portion side wall surface area formed of the first metallic material, and an aft portion side wall surface area formed of the second metallic material; and 
 forming a bore within the forward port ion to surround at least a port ion of an emissive insert; and 
 inserting the an emissive insert into the bore forward portion to provide thermal contact between the emissive insert and the forward portion. 
 
     
     
       20. The method of  claim 19 , wherein the first material has thermal conductivity greater than about 400 Watts/m/deg-K. 
     
     
       21. The method of  claim 19 , wherein the first material has high thermal diffusivity. 
     
     
       22. The method of  claim 19 , wherein the first material has thermal diffusivity greater than about 0.1 m 2 /sec. 
     
     
       23. The method of  claim 19 , wherein the first material has thermal diffusivity greater than about 0.17 m 2 /sec. 
     
     
       24. The method of  claim 19 , wherein the first material comprises silver or an alloy thereof. 
     
     
       25. The method of  claim 19 , wherein the second material comprises aluminum, brass, copper, or an alloy thereof. 
     
     
       26. The method of  claim 19 , wherein the emissive element comprises hafnium, zirconium, tungsten, thorium, lanthanum, strontium, or alloys thereof. 
     
     
       27. The method of  claim 19 , wherein the physical force is a frictional force or a forge force. 
     
     
       28. The method of  claim 19 , further comprising the step of applying electricity in combination with the physical force to create a leak-proof joint without the introduction of an additional material. 
     
     
       29. A composite electrode for use in a plasma arc torch, the composite electrode manufactured by a method comprising:
 providing an aft portion of an electrode body comprising a first metallic material and having a first mating surface;   providing a forward portion of the electrode body comprising a second metallic material and having a second mating surface configured to join with the first mating surface, wherein the first and second metallic materials have a heat transfer property, the value of the heat transfer property for the second metallic material being greater than that of the first metallic material; and   directly welding the first and the second mating surfaces to form a joint, wherein directly welding is a process selected from the group consisting of friction welding, inertia friction welding, direct drive friction welding, CD percussive welding, percussive welding, ultrasonic welding and explosion welding.   
     
     
       30. The method of  claim 29 , wherein the joint between the first and second mating surfaces forms a hermetic seal.