Electrode for plasma arc torch and method of fabrication

• US 6,177,647 B1
• Filed: 04/29/1999
• Issued: 01/23/2001
• Est. Priority Date: 04/29/1999
• Status: Active Grant

• Current Assignee: Thermacut, S.R.O. (IBG Industrie-Beteiligungs GmbH & Co. KG)
• Original Assignee: Tatras Inc.
• Inventors: Zapletal, Jiri
• Primary Examiner(s): Walberg, Teresa
• Assistant Examiner(s): VAN, QUANG T
• Application Number:
  US09/301,630
• Time in Patent Office: 635 Days
• Field of Search: 219/121.52, 219/121.51, 219/121.59, 219/121.36, 219/146.21, 219/119, 219/121.48, 219/121.5, 313/631, 313/627
• US Class Current: 219/121.52
• CPC Class Codes: H05H 1/34 Details, e.g. electrodes, nozzles
• CPC Class Codes: H05H 1/3442 Cathodes with inserted tip
• CPC Class Codes: H05H 1/3478 Geometrical details

Abstract

An electrode for plasma arc torches has a tip body having a tip cavity with a cavity sidewall. An emissive insert having an insert sidewall resides in the tip cavity. A noble metal foil is interposed between the insert sidewall and the cavity sidewall. To fabricate the electrode, a tip body blank is provided, and a tip cavity having a cavity sidewall is formed therein. An emissive insert having an insert sidewall and being loosely insertable into the tip cavity is provided. The insert sidewall is provided with a textured surface with protuberances. A noble metal foil is selected, having an insert-contacting surface and a cavity-contacting surface. The emissive insert and the noble metal foil are placed into the tip cavity of the tip body blank, arranged such that the insert-contacting surface of the foil faces the insert sidewall of the emissive insert, while the cavity-contacting surface of the foil faces the cavity sidewall. After the emissive insert and the foil have been placed in the tip cavity, the tip body blank is placed into a die and radially deformed to compress the tip body blank and force the metal foil to conform to the textured surface of the insert sidewall. The deformed tip body blank is then machined to a final electrode configuration.

Claims

1. An electrode for use in plasma arc torches, the electrode comprising:

a tip body fabricated from copper or a copper alloy, said tip body having a central axis and a free terminating surface substantially normal to said central axis;

a tip cavity having a cavity sidewall, said tip cavity residing in said tip body and extending to said free terminating surface;

an emissive insert having an insert sidewall which is textured to provide a textured surface, said insert sidewall being substantially symmetrical about said central axis of said tip body and said emissive insert forming part of said free terminating surface when said emissive insert is positioned in said tip cavity;

a foil of a noble metal interposed between said cavity sidewall and said insert sidewall, said foil having an insert-contacting surface, which is in interlocking, engaging contact with said textured surface of said insert sidewall, and a cavity-contacting surface, which is substantially parallel to said insert-contacting surface so as to be in interlocking, engaging contact with said cavity sidewall, said insert-contacting surface and said cavity-contacting surface being separated by a thickness T of less than about 0.01 inches.

2. The electrode of claim 1 wherein said thickness T is between about 0.002 and 0.006 inches.

3. The electrode of claim 2 wherein said foil is silver.

4. The electrode of claim 3 wherein said silver has a purity of at least about 99.93%.

5. The electrode of claim 4 wherein said textured surface is provided by scoring the surface to form a series of grooves.

6. The electrode of claim 4 wherein said textured surface is formed by etching to form a mottled surface.

7. The electrode of claim 1 wherein said textured surface increases the surface area of said insert sidewall by at least about 30%.

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

providing a copper tip blank, the tip blank having a central axis and a free terminating surface substantially normal to the central axis;

boring a tip cavity in the free terminating surface of the tip blank, the tip cavity having a cavity sidewall symmetrically disposed about the central axis of the tip blank;

providing the emissive insert, the emissive insert having an insert sidewall symmetrically disposed about an insert axis, the emissive insert being configured so as to be loosely insertable into the tip cavity and, when so inserted, positioned such that the insert axis is substantially coincident with the central axis of the tip blank;

texturing the insert sidewall;

providing a noble metal foil having an insert-contacting surface and a cavity-contacting surface separated by a thickness which allows the foil to be interposed between the insert sidewall and the cavity sidewall;

positioning the emissive insert and the foil into the tip cavity, the foil being interposed between the insert sidewall and the cavity sidewall with the insert-contacting surface of the foil facing the insert sidewall of the emissive insert, and the cavity-contacting surface of the foil facing the cavity sidewall of the tip blank;

deforming the tip blank sufficiently to assure interlocking engaging contact of the insert-contacting surface of the foil with the textured insert sidewall of the emissive insert, and of the cavity-contacting surface of the foil with the cavity sidewall of the tip blank,

whereby the insert-contacting surface of the foil becomes mechanically interlocked with the textured insert sidewall of the emissive insert, and the cavity-contacting surface of the foil becomes mechanically interlocked with the cavity sidewall; and

machining the tip blank to form the electrode tip.

9. The method of claim 8 wherein the emissive insert has a diameter of greater than about 0.06 inches, further wherein said step of positioning the emissive insert and the foil into the tip cavity further comprises:

wrapping the insert-engaging surface of the foil around the insert sidewall to provide a foil-wrapped insert; and

positioning the foil-wrapped insert into the tip cavity.

10. The method of claim 9 where the foil is chosen to be silver having a purity of at least 99.3% silver by weight, and further wherein said step of texturing the insert sidewall further comprises:

passing the emissive insert through a die configured to provide longitudinal grooves.

11. The method of claim 9 where the foil is chosen to be silver having a purity of at least 99.3% silver by weight, and further wherein said step of texturing the insert sidewall further comprises:

etching the insert sidewall to provide a mottled surface of the insert sidewall.

12. The method of claim 8 wherein the emissive insert has a diameter of less than about 0.06 inches, further wherein said step of positioning the emissive insert and the foil into the tip cavity further comprises:

rolling the foil with the cavity-contacting surface facing outwards to a diameter less than that of the tip cavity;

inserting the rolled foil into the tip cavity and allowing the foil to expand such that the cavity-engaging surface of the foil resides against the cavity sidewall; and

positioning the emissive insert into the tip cavity such that the foil is interposed between the insert sidewall and the cavity sidewall.

13. The method of claim 12 where the foil is chosen to be silver having a purity of at least 99.3% silver by weight, and further wherein said step of texturing the insert sidewall further comprises:

passing the emissive insert through a die configured to provide longitudinal grooves.

14. The method of claim 12 where the foil is chosen to be silver having a purity of at least 99.3% silver by weight, and further wherein said step of texturing the insert sidewall further comprises:

etching the insert sidewall to provide a mottled surface of the insert sidewall.

15. The method of claim 8 wherein said step of texturing the insert sidewall increases the surface area of the insert sidewall by at least about 30%.