Plasma burner and method of operation

• US 4,580,031 A
• Filed: 07/31/1984
• Issued: 04/01/1986
• Est. Priority Date: 08/10/1983
• Status: Expired due to Term

• Current Assignee: Fried. Krupp Gesellschaft mit beschrankter Haftung
• Original Assignee: Fried. Krupp Gesellschaft mit beschrankter Haftung
• Inventors: Tomalla, Gebhard, Bebber, Hans J., Rossner, Heinrich-Otto
• Primary Examiner(s): PASCHALL, MARK H
• Application Number:
  US06/636,411
• Time in Patent Office: 609 Days
• Field of Search: 219/121 PM, 219/121 PP, 219/121 PQ, 219/121 PR, 219/75, 219/76.16, 313/231.31-231.51, 315/111.21, 315/111.31
• US Class Current: 219/121.59
• CPC Class Codes: H05H 1/34 Details, e.g. electrodes, nozzles
• CPC Class Codes: H05H 1/3478 Geometrical details

Abstract

Plasma burner having a frontal face from which a plasma jet is to be projected, for producing a long initial firing arc, having first and second concentrically arranged electrodes extending perpendicularly to the frontal face, and a nozzle surrounding the electrodes, the first electrode being centrally arranged to constitute an auxiliary electrode and having a cylindrical main portion, an electrode tip at its front end and a conically tapered portion located between the main portion and the electrode tip and tapering toward the electrode tip, the second electrode being annular and surrounding the first electrode to constitute a nozzle electrode, and having a central channel composed, successively, in the direction toward the frontal face, of a first cylindrical section, a conically tapered section and a second cylindrical section smaller in diameter than the first cylindrical section, the central channel and the first electrode together forming an annular channel. The diameter of the first cylindrical section is 1.2 to 2.5 times the diameter of the cylindrical portion. The tapered portion and the tapered section each have a cone angle of 20° to 80°. The distance between the electrode tip and the plane of the transition between the conically tapered section and the second cylindrical section of the central channel, taken with reference to the direction in which the conically tapered portion tapers is such that the ratio of that distance to the diameter of the second cylindrical section is between -1 and +2.

Claims

1. Plasma burner for producing an elongated initial firing arc, said buner having a frontal face from which a plasma jet is to be projected, said burner comprising first and second concentrically arranged electrodes having a common axis which extends perpendicularly to said frontal face, and a nozzle surrounding said electrodes, said first electrode being centrally arranged in said burner to constitute an auxiliary electrode and having a cylindrical main portion and an electrode tip at the end of said first electrode which is directed toward said frontal face, said first electrode further having a concially tapered portion loacated between said main portion and said electrode tip and tapering toward said electrode tip, said second electrode being annular and surrounding said first electrode to constitute a nozzle electrode, and being formed to have a central channel composed, successively, in the direction toward said frontal face, of a first cylindrical section, a conically tapered section and a second cylindrical section smaller in diameter than said first cylindrical section, said conically tapered section of said central channel meeting said second cylindrical section of said central channel at a transition plane, and said central channel and said first electrode together forming an annular channel, wherein:

the diameter of said first cylindrical section of said cental channel is 1.2 to 2.5 times the diameter of said cylindrical portion of said first electrode;

said tapered portion of said first electrode and said tapered section of said central channel have a cone angle of 20°

to 80°

; and

the transition plane between said conically tapered section and said second cylindrical section of said central channel is perpendicular to the common axis of said electrodes, and said first electrode is positioned so that said electrode tip is located on said common axis within a linerar region having first and second end boundaries, the first end boundary being spaced from said transition plane in the direction toward said frontal face and having a distance from said transition plane which is equal to the diameter of said second cylindrical section of said central channel, and the second end boundary being spaced from said transition plane in the direction away from said frontal face and having a distance from said transition plane which is equal to twice the diameter of said second cylindrical section of said central channel.

2. Plasma burner as defined in claim 1 wherein said central channel is further composed of a third cylindrical section following said second cylindrical section in the direction toward said frontal face and having a diameter which is larger than, and up to three times larger than, the diameter of said second cylindrical section.

3. Plasma burner as defined in claim 2 wherein the ratio of the length of said second cylindrical section, along the axis of said electrodes, to the diameter of said second cylindrical section is between 0.2 and 3.

4. Plasma burner as defined in claim 3 wherein the ratio of the length to the diameter of said second cylindrical section is between 1 and 1.5.

5. Plasma burner as defined in claim 3 wherein the ratio of the diameter of said first cylindrical section to the diameter of said main portion of said first electrode is between 1.5 and 2.

6. Plasma burner as defined in claim 5 wherein the ratio of the diameter of said first cylindrical section to the diameter of said main portion of said first electrode is substantially 1.7.

7. Plasma burner as defined in claim 2 wherein said first electrode further has a second conically tapered portion located between said first-recited conically tapered portion and having a cone angle which is larger than that of said first-recited conically tapered portion and is between 40°

and 80°

.

8. Plasma burner as defined in claim 2 wherein the cone angle of said tapered section of said central channel is between 30°

and 60°

.

9. Plasma burner as defined in claim 8 wherein the cone angle of said tapered section of said central channel is substantially 40°

.

10. Plasma burner as defined in claim 2 wherein the ratio of the diameter of said third cylindrical section to the diameter of said second cylindrical section is between 1 and 1.5.

11. Plasma burner as defined in claim 10 wherein the ratio of the diameter of said third cylindrical section to the diameter of said second cylindrical section is substantially 1.25.

12. Plasma burner as defined in claim 2 wherein the ratio of the distance bewteen said electrode tip and said plane to the diameter of said second cylindrical section is between 0 and +1.

13. Plasma burner as defined in claim 2 wherein the cross section of said annular channel decreases uniformly in the direction toward said frontal face of said plasma burner.

14. Plasma burner as defined in claim 2 wherein said nozzle is radially spaced from said second electrode to form therewith an annular nozzle channel, and further comprising an electrically insulating lining carried by said nozzle within said nozzle channel.

15. Method of operating a plasma burner for producing an elongated initial firing arc, said burner having a frontal face from which a plasma jet is to be prjected, said burner comprising first and second concentrically arranged electrodes having a common axis which extends perpendicularly to said frontal face, and a nozzle surrounding said electrodes, said first electrode being centrally arranged in said burner to constitute an auxiliary electrode and having a cylindrical main portion and an electrode tip at the end of said first electrode which is directed toward said frontal face, said first electrode further having a concially tapered portion located between said main portion and said electrode tip and tapering toward said electrode tip, said second electrode being annular and surrounding said first electrode to constitute a nozzle electrode, and being formed to have a central channel composed, successively, in the direction toward said frontal face, of a first cylindrical section, a conically tapered section and a second cylindrical section smaller in diameter than said first cylindrical section, said conically tapered section of said central channel meeting said second cylindrical section of said central channel at a transition plane, and said central channel and said first electrode together forming an annular channel, wherein:

the diameter of said first cylindrical section of said central channel is 1.2 to 2.5 times the diameter of said cylindrical portion of said first electrode;

said tapered portion of said first electrode and said tapered section of said central channel have a cone angle of 20°

to 80°

; and

the transition plane between said concially tapered section and said second cylindrical section of said central channel is perpendicular to the common axis of said electrodes, and said first electrode is positioned so that said electrode tip is located on said common axis within a linear region having a first and second end boundaries, the first end boundary being spaced from said transition plane in the direction toward said frontal face and having a distance from said transition plane which is equal to the diameter of said second cylindrical section of said central channel, and the second end boundary being spaced from said transition plane in the direction away from said frontal face and having a distance from said transition plane which is equal to twice the diameter of said second cylindrical section of said central channel, wherein said central channel is further composed of a third cylindrical section following said second cylindrical section in the direction toward said frontal face and having a diameter which is larger than, and up to three times larger than, the diameter of said second cylindrical section, said method comprising creating an electric current between said first and second electrodes while causing a plasma-forming gas to flow through said central channel to form an initial firing arc which is projected from said frontal face of said burner, said step of causing being carried out by supplying gas to said central channel in a manner such that the Reynolds number of gas flow in at least a portion of said channel has a value of between 10 and 2300.

16. Method as defined in claim 15 wherein said Reynolds number has a value of between 10 and 100.

17. Method of operating a plasma burner for producing an elongated initial firing arc, said burner having a frontal face from which a plasma jet is to be projected, said burner comprising first and second concentrically arranged electrodes having a common axis which extends perpendicularly to said frontal face, and a nozzle surrounding said electrodes, said first electrode being centrally arranged in said burner to constitute an auxiliary electrode and having a cylindrical main portion and an electrode tip at the end of said first electrode which is directed toward said frontal face, said first electrode further having a conically tapered portion located between said main portion and said electrode tip and tapering toward said electrode tip, said second electrode being annular and surrounding said first electrode to constitute a nozzle electrode, and being formed to have a central channel composed, successively, in the direction toward said frontal face, of a first cylindrical section, a conically tapered section and a second cylindrical section smaller in diameter than said first cylindrical section, said conically tapered section of said central channel meeting said second cylindrical section of said central channel at a transition plane, and said central channel and said first electrode together forming an annular channel, wherein:

the diameter of said first cylindrical section of said central channel is 1.2 to 2.5 times the diameter of said cylindrical portion of said first electrode;

said tapered portion of said first electrode and said tapered section of said central channel have a cone angle of 20°

to 80°

; and

the transition plane between said conically tapered section and said second cylindrical section of said central channel is perpendicular to the common axis of said electrodes, and said first electrode is positioned so that said electrode tip is located on said common axis within a linear region having first and second end boundaries, the first end boundary being spaced from said transition plane in the direction toward said frontal face and having a distance from said transition plane which is equal to the diameter of said second cylindrical section of said central channel, and the second end boundary being spaced from said transition plane in the direction away from said frontal face and having a distance from said transition plane which is equal to twice the diameter of said second cylindrical section of said central channel, wherein said central channel is further composed of a third cylindrical section following said second cylindrical section in the direction toward said frontal face and having a diameter which is larger than, and up to threee times larger than, the diameter of said second cylindrical section, said method comprising causing a plasma-forming gas to flow through said central channel, and supplying, from a single current source, an alternating current to said burner to create, with the gas, an initial firing arc, and a primary arc-forming current to said burner to create a primary arc.