GB2073998A

GB2073998A - A process of producing a homogeneous, radially confined plasma stream and a burner for carrying out the process

Info

Publication number: GB2073998A
Application number: GB8011491A
Authority: GB
Original assignee: Vysoka Skola Chemicko Technologicka V Praze
Current assignee: Vysoka Skola Chemicko Technologicka V Praze
Priority date: 1980-04-08
Filing date: 1980-04-08
Publication date: 1981-10-21
Also published as: GB2073998B

Abstract

A liquid stabilized plasma arc burner comprises an arc chamber (2), a rod-shaped cathode (5) extending into the arc chamber, a nozzle (9) having a circular hole (10) therethrough and arranged in a wall of the arc chamber, and a rotational anode (12) arranged down-stream of the nozzle. The anode (12) has an axis of rotation which makes with the axis of the circular hole (10) in the nozzle (9), or with the plane containing the latter axis and the nearest point of the anode, an angle between 0 DEG and 20 DEG . The smallest distance of the peripheral surface of the anode (12), located in the vicinity of the circular hole (10) of the nozzle (9), from the axis of the circular hole (10) in the nozzle (9) is equal to or larger than the radius of the circular hole (10) in the nozzle (9) and smaller than the radius of the front surface of the rod-shaped cathode (5). In the process the plasma stream is stabilized by a vortex of liquid injected tangentially (8) into at least one of the spaces between the orifice plates (7) or the orifice plates (7) and the nozzle (9) and, after leaving the nozzle (9), is bent to the peripheral surface of the anode (12). <IMAGE>

Description

SPECIFICATION A process of producing a homogeneous, radially confined plasma stream and a burner for carrying out the process The invention relates to a process of radial stabilization and homogenization of a plasma stream and to a liquid stabilized arc burner (torch) for carrying out this process.

With known plasma burners great attention is usually paid to accurate guidance of the arc in a channel between a cathode and an anode, especially with the help of a vortex of stabilization liquid. In the space behind the anode however certain discontinuities and axial displacements of the plasma stream from the ideal path given by outlet nozzle axis take place. These deviations which negatively influence industrial usage of plasma burners, especially accurate cutting or shearing of material, are, if the negative effects of surrounding media are disregarded, caused by shifting of the arc on the effective internal area of the ring anode employed. In order to direct the plasma stream in a desired way it is under effect of an additional magnetic field produced usually by a coil in concentric arrangement around the nozzle outlet.The use of this process however complicates considerably the whole process of plasma generation and directing of the plasma stream is strongly dependent on the intensity of the magnetic field of the coil used which is, in addition, exposed to high temperatures. As far as the burner (torch) is concerned usually a rod-shaped electrode, often made of graphite, is used which extends with its active part into the arc chamber discharging into the nozzle which simultaneously forms a ring anode.

This arrangement has however certain disadvantages, especially as regards limited service life of the ring anode, necessity of its intensive cooling and with it connected limitation of the achievable burner output while simultaneously keeping acceptable operation time without the necessity of large repairs.

Arc stabilization is also a problem.

One of the known and usually used ways of reducing these disadvantages are various modifications of the channel between the arc chamber and the nozzle by using throttle orifice plates and especially tangential arrangement of the liquid inlet resulting in a protective vortex. Also this embodiment has disadvantages known to men skilled in the art.

The invention provides a process of radial stabilization and homogenization of a plasma stream with concentration of charged particles between 2 x 1024 and 3 x 1022 and with temperatures between 15000 "K and 60 000 "K, in a plasma burner wherein the arc formed between the front surface of a rod-shaped cathode arranged in the arc chamber of the burner and an anode arranged outside the arc chamber passes through at least two orifice plates, is stabilized by a vortex of a liquid injected tangentially into at least one of the spaces between the orifices plates or between the orifice plates and the nozzle, passes through a nozzle hole and, after leaving the nozzle, is bent in one direction to the peripheral surface of the anode lying outside the main outlet plasma stream from the nozzle.

The invention also provides a liquid stabilized plasma arc burner comprising an arc chamber, a rod-shaped cathode extending into the arc chamber, a nozzle having a circular hole therethrough and arranged in a wall of the arc chamber, and a rotational anode arranged downstream of the nozzle, wherein the above is situated outside the arc chamber and is formed as a body of rotation the axis of rotation of which makes with the axis of the circular hole in the nozzle, or with the plane containing the latter axis and the nearest point of the anode, an angle between 0 and 20 and the smallest distance of the peripheral surface of the anode, located in the vicinity of the circular hole of the nozzle, from the axis of the circular hole in the nozzle is equal to or larger than the radius of the circular hole in the nozzle and smaller than the radius of the front surface of the rod-shaped cathode.

Preferably the peripheral surface of the anode is turned away from the nozzle and either cylindrical or conical.

The anode may be mounted with respect to the burner body with the possibility of displacement around the axis given by adjustment mechanism or by interconnected holders connected with the burner body and with the body of a drive of the rotational anode.

In a further preferred embodiment the point of the anode which is nearest to the axis of the circular hole in the nozzle is with respect to a vertical plane containing the axis of the circular hole displaced against the direction of rotation of the anode.

A substantial improvement of homogeneity and accurate radial confinement of the plasma stream is attained by the arrangement of the active anode surface rotating at a constant rotational frequency outside of the main plasma stream and by the stated size of the nozzle, anode and cathode. High output and a long serve life of the burner are also obtained by the other mentioned measures which contribute to the accuracy of the arc path, increase the arc stability and increase also the service life of the individual thermally most stressed parts particularly of the rotational anode with internal liquid cooling.

One embodiment of a liquid stabilized arc plasma burner according to the invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, where Figure lisa side elevation of the burner with the arc chamber in section, and Figure 2 is a front elevation of the burner from the anode and nozzle side.

As can be seen in Figure 1 the burner comprises a body 1 including an arc chamber2 delimited by an internal shell 3 between which and the body 1 of the burner is a space 4for the circulation a cooling medium, for example water. A rod-shaped cathode 5 sealed with packing 6 extends into the arc chamber 2. Co-axially with the cathode 5 are arranged orifice plates 7 of the stabilising channel in between which lead tangential inlets 8 of stabilization liquid, for example of ionized water. In the front side of the burner body 1 there is arranged a nozzle 9 provided with a circular hole 10 in the vicinity of which there is situated the peripheral surface 11 of a rotational anode 12 arranged in the body 13 of the drive attached by an adjustment mechanism 14to the body I of the burner.The adjustment mechanism 14 is preferably so adapted that the body 13 with the rotational anode 12 during compensation of wear in the course of its motion to the hole 10 of the nozzle 9 is simultaneously inclined to this hole and thus rectifies the asymmetric wear of the surface 11. The corresponding joint can be situated both in the adjustment mechanism 14 and on holders fixed to the two connected parts and defining a suitable radius of the anode 12 displacement. Rotational anode 12 is shown in a position in which its axis 02 is parallel to the axis ol of the circular hole 10 in the nozzle 9 and it is so arranged that its peripheral surface 11 is in the vicinity of the circular hole 10 in the nozzle 9 at a distance larger than the radius of this hole but smaller than the radius of the cathode 5.

The rod-shaped cathode 5 has a planar front surface 15 arranged in this case perpendicularly to the axis o1 of the circular hole 10 in the nozzle 9. The cathode 5 is mounted in a feeding device 16. In addition to showing the mutual arrangement of the circular hole 10 in the nozzle 9 and of the rotational anode 12 Figure 2 shows also an inlet 17 for additional pulverized or liquid material. The axis 2 of the rotational anode 12 is in this case skew to the axis ol of the circular hole 10 in the nozzle 9. In Figure 1 there is by a dashed line illustrated also displace mentofthefrontsurface 15 of the cathode 5 and conical shape of the peripheral surface 11 of the rotational anode 12 diverging away from the nozzle 9. Also an arrangement of the rotational anode 12 and of the nozzle 9 may be used where the axes o and o2are parallel or concurrent. In orderto maintain the stability of the arc the angle between these axes should be relatively small and should not exceed 20 .

Claims

1. A process of radial stabilization and homogenization of a plasma stream with concentration of charged particles between 2 x 1024and3 x 1022 and with temperatures between 15 000"K and 60 000 K, in a plasma burner wherein the arc formed between the front surface of a rod-shaped cathode arranged in the arc chamber of the burner and an anode arranged outside the arc chamber passes through at least two orifice plates, is stabilized by a vortex of a liquid injected tangentially into at least one of the spaces between the orifice plates or between the orifice plates and the nozzle, passes through a nozzle hole and, after leaving the nozzle, is bent in one direction to the peripheral surface of the anode lying outside the main outlet plasma stream from the nozzle.

2. A process of radial stabilization and homogenization of a plasma stream in a plasma burner substantially as herein described with reference to the accompanying drawings.

3. A liquid stabilized plasma arc burner comprising an arc chamber, a rod-shaped cathode extending into the arc chamber, a nozzle having a circular hole therethrough and arranged in a wall of the arc chamber, and a rotational anode arranged downstream of the nozzle, wherein the anode is situated outside the arc chamber and is formed as a body of rotation the axis of rotation of which makes with the axis of the circular hole in the nozzle, or with the plane containing the latter axis and the nearest point of the anode, an angle between 0 and 20 and the smallest distance of the peripheral surface of the anode, located in the vicinity of the circular hole of the nozzle, from the axis of the circular hole in the nozzle is equal to or larger than the radius of the circular hole in the nozzle and smaller than the radius of the front surface of the rod-shaped cathode.

4. A plasma burner according to Claim 3 wherein the peripheral surface of the anode is turned away from the nozzle.

5. A plasma burner according to Claim 3 or 4 wherein the peripheral surface of the anode is cylindrical.

6. A plasma burner according to Claim 3 or 4 wherein the peripheral surface of the anode is conical.

7. A plasma burner according to any one of Claims 3 to 6 wherein the anode is mounted with respect to the burner body with the possibility of displacement around the axis given by adjustment mechanism or by interconnected holders connected with the burner body and with the body of a drive of the rotational anode.

8. A plasma burner according to any one of Claims 3 to 7 wherein the point of the anode which is nearest to the axis of the circular hole in the nozzle is with respect to a vertical plane containing the axis of the circular hole displaced against the direction of rotation of the anode.

9. A liquid stabilized plasma burner constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in the accompanying drawings.