PLASMA TORCH ELECTRODE WITH IMPROVED INSERT CONFIGURATIONS

• US 20070125755A1
• Filed: 08/30/2006
• Published: 06/07/2007
• Est. Priority Date: 09/07/2005
• Status: Active Grant

• Current Assignee: Hypertherm Incorporated
• Original Assignee: Hypertherm Incorporated
• Inventors: Cook, David, Mather, Jonathan, Sobr, John, Bouthillier, David, Eickhoff, Stephen
• Granted Patent: US 8,101,882 B2
• Time in Patent Office: Days
• US Class Current: 219/121.520
• CPC Class Codes: H05H 1/34 Details, e.g. electrodes, nozzles
• CPC Class Codes: H05H 1/3442 Cathodes with inserted tip

Abstract

An improved electrode for use in a plasma arc torch. The electrode includes an electrode body, a bore defined by and disposed in the electrode body, and an insert disposed in the bore. The insert and/or the bore of the electrode are configured to improve retention of the insert in the electrode, thereby extending electrode life. The invention also includes a method for forming the electrode. The method includes a step of positioning an insert into a bore of an electrode such that an exterior gap is established that is greater than a second gap.

Claims

1. An electrode for a plasma arc torch, the electrode comprising:

an electrode body formed of a high thermal conductivity material, the electrode body including a first end and a second end defining a longitudinal axis;

a bore defined by and disposed in the first end of the electrode body, the bore including a first portion, a second portion, and a third portion, the first portion including an outer open end of the bore, the third portion including an inner open end of the bore, the second portion of the bore defining at least a first and a second dimension each transverse to the longitudinal axis, the second dimension being closer to the third portion of the bore than the first dimension; and

an insert formed of a high thermionic emissivity material disposed in the bore, the insert including a first portion, a second portion, and a third portion, the first portion including an exterior end disposed near the outer open end of the bore, the third portion including an end disposed near the inner open end of the bore, the insert defining at least a first and a second dimension each transverse to the longitudinal axis, the second dimension being closer to the third portion of the insert than the first dimension;

wherein the electrode fulfils one or both of;

(a) the second dimension of the bore is greater than the first dimension of the bore, and

(b) the second dimension of the insert is greater than the first dimension of the insert.

3. The electrode of claim 1 or claim 2, wherein the electrode further comprises a sleeve disposed between the insert and the bore.

4. The electrode of any one of claims 1 to 3, wherein the second dimension corresponds to an annular notch.

2. An electrode for a plasma arc torch, the electrode comprising:

an electrode body formed of a high thermal conductivity material, the electrode body including a first end and a second end defining a longitudinal axis;

a bore defined by and disposed in the first end of the electrode body, the bore including a closed end and an open end, the bore defining at least a first and a second dimension each transverse to the longitudinal axis, the second dimension being closer to the closed end of the bore than the first dimension; and

an insert formed of a high thermionic emissivity material disposed in the bore, the insert including an exterior end disposed near the open end of the bore and a contact end disposed near the closed end of the bore, the insert defining at least a first and a second dimension each transverse to the longitudinal axis, the second dimension being closer to the closed end of the bore than the first dimension;

wherein the electrode fulfils one or both of

(a) the second dimension of the bore is greater than the first dimension of the bore, and

(b) the second dimension of the insert is greater than the first dimension of the insert.

5. An electrode for a plasma arc torch, the electrode comprising:

an electrode body formed of a high thermal conductivity material, the electrode body including a first end and a second end defining a longitudinal axis;

a bore defined by and disposed in the first end of the electrode body, the bore including a first end and a second end, the first end of the bore including an open end of the bore; and

an insert formed of a high thermionic emissivity material and disposed in the bore, the insert having a longitudinal length and including;

a first end portion including an exterior end surface disposed near the open end of the bore, a longitudinal length of the first end portion being no more than about 10% of the longitudinal length of the insert;

a second end portion, a longitudinal length of the second end portion being no more than about 20% of the longitudinal length of the insert;

a first portion between the first and the second end portions, the first portion defining a first dimension transverse to the longitudinal axis, the first portion including a first exterior surface;

a second portion between the first and the second end portions, the second portion defining a second dimension transverse to the longitudinal axis and including a second exterior surface, wherein the first dimension is greater than the second dimension; and

wherein a first angle of a tangent to the first exterior surface with respect to the longitudinal axis and a second angle of a tangent to the second exterior surface with respect to the longitudinal axis differ by at least 3 degrees.

6. The electrode of claim 5, wherein the longitudinal length of the first end portion is no more than about 2% of the longitudinal length of the insert.

7. The electrode of claim 5 or claim 6, wherein the longitudinal length of the second end portion is no more than about 10% of the longitudinal length of the insert.

8. The electrode of any one of claims 5 to 7, wherein the high thermionic emissivity material of the insert is hafnium or zirconium, or tungsten, or thorium or lanthanum or strontium or alloys thereof.

9. The electrode of any one of claims 5 to 8, wherein the high thermal conductivity material of the electrode body is copper or a copper alloy.

10. An electrode for a plasma arc torch, the electrode comprising:

an electrode body formed of a high thermal conductivity material, the electrode body including a first end and a second end defining a longitudinal axis;

a bore defined by and disposed in the first end of the electrode body, the bore including an open end and a closed end; and

an insert formed of a high thermionic emissivity material disposed in the bore, the insert comprising;

a first exterior surface exerting a first force against a first surface of the bore; and

a second exterior surface exerting a second force against a second surface of the bore, the second force being greater than the first force, and the second surface of the bore being longitudinally closer to the closed end of the bore than the first surface of the bore.

11. The electrode of claim 10, wherein the high thermionic emissivity material of the insert is hafnium or zirconium.

12. The electrode of claim 10 or claim 11, wherein the high thermal conductivity material of the electrode body is copper or a copper alloy.

13. The electrode of any one of claims 10 to 12, wherein the electrode further comprises a sleeve disposed between the insert and the electrode body.

14. The electrode of claim 13, wherein the sleeve is silver.

20. The electrode of any one of claims 5 to 19, wherein a central portion of the bore comprises at least two substantially cylindrical portions.

21. The electrode of any one of claims 5 to 20, wherein a central body portion of the insert comprises at least two substantially cylindrical portions.

22. The electrode of any one of claims 5 to 21, wherein at least one of a central portion of the bore and a central body portion of the insert is substantially cylindrical.

23. The electrode of any one of claims 5 to 22, wherein the bore comprises an annular extension.

24. The electrode of any one of claims 5 to 23, wherein the insert comprises a flared head.

15. An electrode for a plasma arc torch, the electrode comprising:

an electrode body formed of a high thermal conductivity material, the electrode body including a first end and a second end defining a longitudinal axis;

a bore defined by and disposed in the first end of the electrode body, the bore including a first portion, a second portion, and a third portion, the first portion defining an outer open end of the bore, the third portion defining an inner open end of the bore; and

an insert formed of a high thermionic emissivity material disposed in the bore, the insert comprising;

a first exterior surface exerting a first force against a first surface of the second portion of the bore; and

a second exterior surface exerting a second force against a second surface of the second portion of the bore, the second force being greater than the first force, and the second surface of the bore being longitudinally closer to the third portion of the bore than the first surface of the bore.

16. The electrode of claim 15, wherein the high thermionic emissivity material of the insert is hafnium or zirconium.

17. The electrode of claim 15 or claim 16, wherein the high thermal conductivity material of the electrode body is copper or a copper alloy.

18. The electrode of any one of claims 15 to 17, wherein the electrode further comprises a sleeve disposed between the insert and the electrode body.

19. The electrode of claim 18, wherein the sleeve is silver.

25. An electrode for a plasma arc torch, the electrode comprising:

an electrode body formed of a high thermal conductivity material, the electrode body including a first end and a second end defining a longitudinal axis;

a bore defined by and disposed in the first end of the electrode body, the bore including an open end and a closed end;

a projection disposed on a surface of the bore, the surface of the bore located away from the open end; and

an insert formed of a high thermionic emissivity material disposed in the bore, a contact surface of the insert surrounding at least a portion of the projection to secure the insert in the bore.

26. The electrode of claim 25, wherein the projection is disposed at or near the closed end of the bore, the projection extending partially towards the open end.

27. The electrode of claim 25 or claim 26, wherein the projection comprises barbs, grooves, or notches.

28. The electrode of any one of claims 25 to 27, wherein the projection is not integrally formed with the electrode body or the insert.

29. The electrode of any one of claims 25 to 28, wherein the projection is substantially symmetrical about the longitudinal axis.

30. The electrode of any one of claims 25 to 29, wherein the contact surface is a contact end of the insert.

31. A method for fabricating an electrode having an emissive insert for use in plasma arc torches, the method comprising the steps of:

forming an electrode body of a high thermal conductivity material, the electrode body including a first end and a second end defining a longitudinal axis;

forming a bore in the first end, the bore including a first portion and a second portion;

positioning an insert formed of a high thermionic emissivity material in the bore, the insert including a contact end and an exterior end;

aligning the contact end of the insert with the second portion of the bore and the exterior end with the first portion of the bore, such that a first gap is established between a first exterior surface of the insert and the first portion, and a second gap is established between a second exterior surface of the insert and the second portion of the bore, such that the first gap is substantially greater than the second gap; and

applying a force at the exterior end of the insert to secure the insert in the bore.

32. The method of claim 31, wherein the bore further comprises a third portion defining a second open end of the bore, the second portion of the bore located between the first and third portions of the bore.

33. The method of claim 31, wherein the second portion of the bore defines a closed end of the bore.

34. The method of any one of claim 31 to 33, wherein the first gap is nearer the open end of the bore than the second gap.

35. The method of any one of claim 31 to 33, wherein the first gap is nearer the closed end/second portion of the bore than the second gap.

36. The method of any one of claim 31 to 35, wherein the applied force is a longitudinal force applied at the exterior end of the insert that reduces the gap.

37. The method of any one of claim 31 to 35, wherein the applied force is a compressive force that compresses the open end of the bore about the insert.

38. The method of any one of claim 31 to 37, further comprising the step of positioning a sleeve formed of a second material in the bore before the force is applied, and the first gap is disposed between a surface of the sleeve and the first exterior surface of the insert.

39. A plasma arc torch comprising:

a torch body;

a nozzle within the torch body;

a shield disposed adjacent the nozzle, the shield protecting the nozzle from workpiece splatter;

an electrode mounted relative to the nozzle in the torch body to define a plasma chamber, the electrode comprising an electrode body formed of a high thermal conductivity material, the electrode body including a first end and a second end defining a longitudinal axis;

a bore defined by and disposed in the first end of the electrode body, the bore including a closed end and an open end, the bore defining at least a first and a second dimension each transverse to the longitudinal axis, the second dimension being closer to the closed end of the bore than the first dimension; and

an insert formed of a high thermionic emissivity material disposed in the bore, the insert including an exterior end disposed near the open end of the bore and a contact end disposed near the closed end of the bore, the insert defining at least a first and a second dimension each transverse to the longitudinal axis, the second dimension being closer to the closed end of the bore than the first dimension;

wherein at least one of

the second dimension of the bore is greater than the first dimension of the bore, or

the second dimension of the insert is greater than the first dimension of the insert.