Title of Invention

AHOLLOW ANODE PLASMA TORCH

Abstract

A hollow anode plasma torch comprising: a twin electrode configuration consisting of a tubular anode; a rod shaped cathode; means for holding the anode and cathode in position with respect to melt surface; a platform for mounting the said anode and said cathode in position; means for lifting the platform; means for supplying and controlling the power to the twin electrode configuration; a short fuse wire provided between the said anode and cathode shortening the electrodes by means of high frequency short technique; means for data acquisition of current and voltage supply; a magnetic field provided around the anode and cathode for rotation, stabilization and impedance control of the arc; wherein one end of the anode is used for introducing the gas and material while the other end of the anode, participates in the arc.

Full Text

FORM - 2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION Section 10 AHOLLOW ANODE PLASMA TORCH" INSTITUTE FOR PLASMA RESEARCH, of Bhat Village, Gandhinagar 3 82424, Gujarat, India; The following specification (particularly) describes the nature of this invention and the manner in which it is to be performed:- The present invention relates to the hollow anode plasma torch for producing large volume thermal plasma for material processing. De-concentrated or large volume plasma has better heat transfer efficiency to surrounding gasses resulting in increased throughput. Thus, techniques to reduce large volume thermal plasma is thrust area in the thermal plasma processing. Conventionally, in-flight plasma torch, gas heater plasma torch and the like have been developed to produce large volume hot plasma. Concentrated plasma source exhibit high viscosity and the material ( in powder form) introduction into the viscous zone posses serious problem. Sumary of the Invention The thermal plasma source of the subject invention produces large area (de-concentrated) plasma column obtained with hollow vertical anode and solid or hollow inclined cathode. Both the electrodes used in the subject application are cylindrical in shape and are continuously fed to operate the source without interruption. The anode and the cathode arcs faces the melt separately. The coupling zone of the arcs is connected by diffused plasma column over the melt. The anode arc column diameter can be increased to some extent with increasing the inner diameter of anode. The angle of inclination between the electrodes does not severely affect the performance of the arc, hence minimizes the geometrical effects. The object of the present invention is to develop a hollow anode plasma torch which produces large volume of thermal plasma. It is another object of the present invention to develop a plasma torch which can trap material in the plasma. In a still another object of the present invention to develop a plasma torch which produces plasma without interruption. In the still another object of the present invention to develop a plasma torch which reduces the uneven erosion of the anode. To overcome the drawback involved in the existing methods, the subject invention deals with the technique to produce large area plasma column into which the material (in powder form) can be trapped by thermal gradient force present in the plasma, thus facilitating the introduction of material. According to the present invention there is provided a hollow anode plasma torch comprising: a twin electrode configuration consisting of a tubular anode; a rod shaped cathode; means for holding the anode and cathode in position with respect to melt surface; a platform for mounting the said anode and said cathode in position; means for lifting the platform; means for supplying and controlling the power to the twin electrode configuration; a short fuse wire provided between the said anode and cathode shortening the electrodes by means of high frequency short technique; means for data acquisition of current and voltage supply; a magnetic field provided around the anode and cathode for rotation, stabilization and impetance control of the arc; wherein one end of the anode is used for introducing the gas and material while the other end of the anode, participates in the arc. The subject application may better be understood with reference to the accompanying drawings, which are for illustrative purposes and the same should be construed to restrict the scope of the application. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 relates to diagnostic setup used in the present torch development; Figure 2 relates to the electrode arrangement and arc structures of Twin electrode assembly torch; Figure 3 relates to hollow vertical anode and inclined cathode Torch plasma source; Figure 4 relates to gas shroud arrangement used to stabilize hollow vertical anode and inclined cathode Torch; Figure 5 relates to hollow vertical anode and inclined cathode Torch with graphite cathode replaced by water-cooled tungsten torch; 6 Figure*relates to various electrode arrangements to produce hollow anode plasma torches; Figure 7 relates to plasma torch utilizing magnetic field for increasing arc impedance and arc rotation; Figure 8 relates to co-axial plasma torch employing the hollow anode and receded cathode. Accordingly the present invention relates to a hollow anode plasma torch comprising: a twin electrode configuration consisting of a tubular anode; a rod shaped cathode; means for holding the anode and cathode in position a platform for mounting the said anode and said cathode in position; means for lifting the platform; means for supplying and controlling the power to the twin electrode configuration; means for initiating the arc; means for data acquisition of current and voltage supply; wherein one end of the anode is used for introducing the gas and material while the other end of the anode. DESCRIPTION OF THE INVENTION Electrode assembly of the subject invention consists of tubular anode and rod shaped cathode. The said electrodes are held in position by bushes also used for electrical connection. The anode (a) and the cathode(c) are mounted on the platform, which is be lifted by rack and pinion arrangement. The angle of inclination between the said electrodes are adjusted by the movement of the bushes. The angle of inclination between anode and the cathode is more than 45°. Gas and material (in powder form ) is introduced from the one end of the said anode and the other end of the said end participates in the arc. The said gases are selected from the group consisting of argon, hydrogen, oxygen, air and the like or the mixture thereof. The arc is initiated by shorting both electrodes using fuse wire, the fuse wire initiation can be replaced by high frequency spark technique. These methods of arc initiation are well known in the art. The spark then triggers the arc discharge and the material supply will (e) be activated to sustain the arc. The arc voltage and current are measured using digital volt (f) and current meter (g) respectively. The instantaneous current and voltage readings are recorded on to a computer (d) using data acquisition card (ADC card.) Material to be melted or fused (b) or kept below the electrodes. The said plasma arc is produced between the twin electrodes assembly torch (TEA) inclined to each other (included angle is around 45° ) as shown in figure 2. It is clear from the figure 2 At low included angles i.e. Plasma arc produced by (HVAICT) hollow vertical anode and inclined cathode torch as shown in figure 3. Plasma arc has two columns connected by a diffuse column. The said anode arc root anchors on to the periphery of the pipe. Thus the intensity of the visible light emission also peaks periphery resulting in temperature profile (assumed to vary in similar way as visible light from the arc at anode) peaking at periphery of the tube. This hollow temperature profile (gradient towards the center) exerts thermophoretic forces on the particles directed towards the center. Fth=a2 The particles introduced through the center of the anode column get trapped due to thermophoretic forces and melts. Blowing the air through anode increases the heat transfer to gas and it also helps in stabilizing the plasma. Stable operation of the arc needs the melt surface to be at 5 to 6 cm beneath electrodes. However, it does not depend on the the material property thus making torch suitable for ceramic material processing. The voltage-current (V-l) characteristics of (averaged over long duration) of TEA and HVAICT are given in table 1 below. The electrical characteristics of both TEA and HVAICT nearly remain same. Experiment were carried to investigate the dependence of the arc V-l characterstics with the angle of inclination. The results of the study indicate the angle of inclination does not effect on the performance of the torch. Simultaneous rotational and axial feeding may further improve the stabilization. Table 1 Arc Current (Amps) Twin Electrodes Arc voltage (volts) TEA Hollow Vertical Anode and Inclined Cathode Torch (HVAICT Arc Voltage) Volts 70 103 104 80 110 95 100 97 117 120 127 117 150 128 126 The results of the study indicates that the angle of inclination does not affect critically on the performance of the torch. Simultaneous rotation and axial feeding improves the stabilization, the increase in arc current consequently increase the tearing force on anode and cathode arcs jets thus restores large volume arc mode operation. During such operation, the anode arc root localizes at extreme radial location for longer time, causing non-uniform anode surface erosion. Ocassionally the HVAICT runs short arc mode. Constricted single arc column connecting directly anode and cathode with high audible noise are the features of short arc mode. During the short arc mode operation the arc voltage falls by few tens of volts. Increasing the arc current (few tens of amperes) can restore large volume mode of operation. A shroud (h) is used for covering the cathode (see figure 5) for preventing arc running into short arc mode. Blowing gas through it further decreases the possibility of short arc mode occurrence. Mechanically rotating the anode or magnetically rotating the anode arc root reduces the non-uniform erosion. The arc fills entire anode inner diameter and arc column appears like cylindrical pipe. As shown in figure 5, the cathode is provided with gas shroud to increase the stabilization of the arc. The gas shroud helps in localizing the cathode root and reduces the voltage excursions. Further, it also prevents the short the short arc mode operation. Here, the graphite cathode is replaced by water-cooled tungsten rod. The cathode arc column of water cooled tungsten appears much more extended than the one where graphite is used. The structure of anode column and electrical characteristics remains unchanged. Extension of twin electrode assembly to multiple electrode operation is shown in figure 7, where the anode may either be single or multiple electrodes. The stability and the erosion rate of electrodes is reduced by magnetically rotating the arc as shown in figure 8. There is another configuration of exploiting the hollow anode. Here, the cathode surrounds the anode but the cathode tip is slightly receded. The magnetic filed is used to rotate both anode and cathode arc roots. Further, it also helps in stabilization by providing conducting path along the field lines. In order to increase the arc column diameter at anode side, anode with larger inner diameter is used resulting in a marginal arc voltage enhancement due to increased arc length. To increase the diameter of the arc the diameter of WE CLAIM: 1. A hollow anode plasma torch comprising: a twin electrode configuration consisting of a tubular anode; a rod shaped cathode; means for holding the anode and cathode in position with respect to melt surface; a platform for mounting the said anode and said cathode in position; means for lifting the platform; means for supplying and controlling the power to the twin electrode configuration; a short fuse wire provided between the said anode and cathode shortening the electrodes by means of high frequency short technique; means for data acquisition of current and voltage supply; a magnetic field provided around the anode and cathode for rotation, stabilization and impedance control of the arc; wherein one end of the anode is used for introducing the gas and material while the other end of the anode, participates in the arc. 2. A hollow anode plasma torch as claimed in claim 1 wherein the means for lifting the platform are rack and pinion arrangement. 3. A hollow anode plasma torch as claimed in claim 1 wherein the means for holding the anode and cathode in position are copper bushes provided on the platform adjusting the indination between anode and cathode between 45-60°C. 4. A hollow anode plasma torch as claimed in claim 1 wherein the gas and material are introduced from one end of the said anode, producing arc at the other end of the anode. 5. A hollow anode plasma torch as claimed in claim 1 wherein the said gases are selected from the group consisting of argon, hydrogen, oxygen, air or the mixtures thereof. 6. A hollow anode plasma torch as claimed in claim 1 wherein the anode is made up of graphite. 7. A hollow anode plasma torch as claimed in claim 1 wherein the said electrodes are flared or conocal shaped electrodes for tailoring plane. 8. A hollow anode plasma torch as claimed in claim 1 wherein a shroud is provided surrounding the said cathode through which gas is injected for stabilization of the arc. 9. A hollow anode plasma torch substantially as hereinbefore described with reference to accompanying drawings. Dated this 24th day of April, 2001.

Documents:

404-mum-2001-cancelled pages(25-02-2005).pdf

404-mum-2001-claims(granted)-(25-02-2005).doc

404-mum-2001-claims(granted)-(25-02-2005).pdf

404-mum-2001-correspondence(ipo)-(03-01-2006).pdf

404-mum-2001-drawing(26-07-2002).pdf

404-mum-2001-form 1(24-02-2005).pdf

404-mum-2001-form 1(26-07-2002).pdf

404-mum-2001-form 1(27-04-2001).pdf

404-mum-2001-form 1(28-06-2001).pdf

404-mum-2001-form 19(01-01-2004).pdf

404-mum-2001-form 2(granted)-(25-02-2005).doc

404-mum-2001-form 2(granted)-(25-02-2005).pdf

404-mum-2001-form 26(28-06-2001).pdf

404-mum-2001-form 3(27-04-2001).pdf

404-mum-2001-form 4(29-07-2002).pdf

404-mum-2001-form 5(25-07-2002).pdf

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