JPH01319297A - Method and apparatus for high speed and temperature-controlled plasma display - Google Patents

Abstract

PURPOSE: To prolong the life of an anode region in the vicinity of the periphery of a nozzle outlet by providing a discontinuous portion on the surface of a place along a nozzle bore having a sufficient size on the upstream side of a nozzle outlet orifice. CONSTITUTION: A bore 57 spreading exists on the outlet end portion 52a of a nozzle anode 52, the spreading bore 57 forms a radial direction shoulder portion, and a peripheral shelf 58, constituting an effective path, an anode ring 59 is arranged apart by a certain distance from the outlet end portion 52a of the anode nozzle 52. Vortex-like gas flow 53 revolving in the periphery of a cathode electrode 32 passes in the cone-like decreasing region 35 of a nozzle path 54 formed by an anode bore 51, centers an arc column 55 along the bore 51, and passes a downstream point 56 exceeding a nozzle outlet. Thereby, the life of a peripheral anode region of the outlet of the outlet nozzle of a plasma torch can be prolonged.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for plasma arc spraying at considerably higher currents and voltages than conventional plasma spray systems, and in particular to a method and apparatus for plasma arc spraying at substantially higher currents and voltages than conventional plasma spray systems. Concerning a system for extending the life of the surrounding anode region.

[Prior Art and Problem to be Solved by the Invention] In all current plasma spray systems using electric power injection, the arc column itself or the ionized plume of the arc is exposed to very high temperatures. The device is configured to be used as a heat source. This fact is of great importance in Mizude's pending U.S. Patent Application No. 024,485, filed March 11, 1987, in which the arc column is It also extends far beyond the nozzle exit. According to FIG. 1 of the drawings, a conventional plasma spray torch 10' is shown, in which water cooling means have been intentionally removed from the drawing for the sake of simplicity. The cylindrical, cup-shaped electrically insulating body piece 10 supports the cathode electrode 12 coaxially, and at the end of the body piece 10 opposite to the end that supports the cathode electrode 12, the cathode electrode 12 supports the cathode electrode 12 coaxially. It projects towards, but is spaced from, a second body piece 11 which closes the open end of the shaped body piece 10 . The second body piece 11 is provided with an axial bore lla defining the plasma spray torch nozzle passage 9. By connecting a potential difference between the cathode electrode 12 and the second body piece 11 acting as an anode, an arc 17 is formed. The arc 17 passes from the electrode 12 to the inner wall of the nozzle passage 9. The length of this arc 17 is determined by the flow of plasma-forming gas, indicated by arrow G, through the gas supply tube 15 and into the annular manifold 24 around the cathode electrode 12.
Stretched. The tube 15 connects to the body piece through a matched radius hole 15a in the side of the cylindrical body piece.

A transverse partition 13 of insulating material, such as the transverse partition of the body piece 10 , supports the electrode 12 . The partition 13 is provided with a plurality of small-diameter passages 23 that reach the nozzle passage 9 so that flow occurs around the tapered tip 12a of the cathode electrode 12. As indicated by arrow P, the powder to be atomized passes into the arc heating gas at a point beyond the anode foot 18 of the arc 17. The powder is directed through the tube 16 and flows into a passage 16' aligned with the protection tube 1.6 and opening into the bore 11a;
This is to ensure that the powder flow is as centered as possible along the hot gas jet 25 exiting the end of the nozzle 9.

A very bright conical arc region extends a short distance beyond the exit of the nozzle 9, with this region constituting a distinct spread of ionized gas species. A large heat transfer coefficient occurs within the conical region 19. As can be appreciated, gas heating is applied to the flow of particles P across the ionized region 19 within the hot gas jet 25. Additionally, the particles develop a high velocity (but less than the speed of sound) in the jet 25 such that they impinge on the surface of the workpiece 22 and form a coating 21 on the surface of the workpiece. By way of example, a conventional plasma spray torch 10' is provided with a flow of 100 SCFH of nitrogen gas using a 5/16 inch nozzle passage 9 bore diameter, and the torch is provided with an operating current of 750 amps and 80 volts. arc voltage is given. The ionized area or region 19 extends approximately 1/3 the end 9a of the nozzle.
Observed to exceed an inch. The overall power level achieved is 60KW. The combined cathode and anode losses are approximately 30 volts with a net heating capacity (I2R heating of gas) of 37.5 KW. Assuming that the further heating loss is 20% of the cooling water, the gas heating will be a statistical 30KW. The enthalpy increase of the plasma gas in such a conventional system under the conventional operating parameters described above is approximately 14.5008 tu
/ Bond.

In all current plasma devices using the so-called low voltage arc (approximately 80 volts), the device operates as shown in FIG. High heating areas are very beneficial when the material to be sprayed is heat insensitive. However, for materials that can be thermally damaged, such plasma systems are not suitable for materials that can be thermally damaged. ;421, could not match the quality of the "D-Gun" or Applicants' prior fast combustion systems.

In a conventional plasma torch, the powder is shaped like cone 1 in Figure 1.
9 and passing through the cone 19 relied on almost instantaneous particle heating. Many of these particles (particularly the smaller sizes) are actually sufficiently fused and perhaps even vaporized.

Heat sensitive materials such as tungsten carbide (WC) are decarbonized to form undesirable W2. Furthermore,
The molten particles can be significantly oxidized.

The "D" gun 1 and apparatus of U.S. Pat. Rather than being melted, the powder particles are thermally softened and therefore retain their chemical composition and are only slightly oxidized even when sprayed onto workpieces held in the open atmosphere.

FIG. 2 shows applicant's pending U.S. application Section 024.48.
5 is a longitudinal cross-sectional view of an improved non-displacement plasma arc torch with an enlarged arc due to the main part of No. 5; FIG. 2nd a
The figure shows the nozzle bore 31 of the plasma arc torch in Figure 2.
FIG. 3 is an enlarged longitudinal cross-sectional view of the outlet end of FIG. With reference to Figure 2.2a, the improved plasma spray torch is designated by the number 1
A cylindrical electrically insulating body piece 30, designated 0 and similar to the body piece 10' in the prior art plasma torch of FIG. 1, is used. The body piece 30 is closed by a second cylindrical body piece 31, and the opposite end of the body piece 10 includes a transverse end wall 30a that coaxially connects the cathode electrode 32. The cathode electrode 32 is supported by the main body piece 30 and protrudes through an annular chamber 41 inside the main body piece 30 .

The legs 32a of the cathode electrode 32 are connected to the torch nozzle passage 34.
It projects into a conical reduction area 35 of the bore 31a forming a . The flow of plasma gas with high vortex strength produces an enlarged ionized arc column region achieved by tangentially arranging the gas supply pipe or tube 26 with respect to the annular chamber 41 surrounding the cathode electrode 32, as indicated by the arrows. The gas flow, designated C, enters the chamber 41 tangentially through the passage 33 and exits through the conical reduction region 35 leading to the bore 31a, as clearly shown in FIG. be. In this way, the conical reduction region 35 smoothly passes the vortex flow into the reduced diameter nozzle passage 34. The principle of conservation of angular momentum gives rise to greater vortex strength due to the reduction of the outer boundary diameter of the gas flow. The small diameter core of the vortex is located on the wall of the passageway 34 (bore 31a
) indicates a low gas pressure with respect to the gas pressure of the gas layer close to ).

An enlarged arc column 37 results with the arc column positioned to pass well past the outlet 34a of the nozzle 34 through the low pressure core. Due to physical phenomena not fully understood by Applicants, a decrease in the diameter of the nozzle 34 and/or an increase in the arc current creates a greater critical pressure drop in the passage through the nozzle 34 to the atmosphere, resulting in a subsonic So as to eliminate the vagaries of arc anode spots related to their counterparts. Due to supersonic flow,
The anode area is more enlarged and extends over the inner wall of the nozzle 34 near the nozzle outlet 34a and over a thin peripheral radius area of the body piece 31 surrounding the nozzle outlet 34a. The enlarged arc 37 (ionized region) is of reduced diameter compared to the ionized region 19 of the prior art torch of FIG. Nozzle outlet 34
The length of the arc extending beyond a is also increased considerably over the length of ionized region 19 of the prior art device of FIG. For example, torch 1 in Fig. 2゜2a
0 works well using nitrogen 12O8CFH under an applied voltage of 200 volts across the gap between cathode electrode 32 and anode 31 at a current of 400 amperes. In such an example, the nozzle diameter is 3/16
inch and at operating parameters, the ionized area extends 1-1/4 inch beyond the nozzle exit 34a, and the net gas enthalpy (20% after cooling loss)
is 27,000 Btu/bond, approximately twice that of the prior art device of FIG.

FIG. 2a shows an enlarged arc 42 in an enlarged view,
The anode foot 36 of the arc 42 remains at the exit of the nozzle 34 and the interaction of intense anode heating in the presence of readily available atmospheric oxygen causes the cavity 39 to erode into the nozzle 31. . Formation of the cavity 39 requires several hours of operation, and as the cavity corrodes deeper into the nozzle, the corrosion rate becomes smaller. This reduction is probably due to the presence of a gas that prohibits oxygen from flowing into the cavity. In any case, cavities are best removed invisible.

Accordingly, it is an object of the present invention to utilize pending U.S. Application No. 024.
The object of the present invention is to provide a method and apparatus for extending the life of the surrounding anode region at the exit of the exit nozzle of a plasma torch of the type described in No. 485.

[Means and actions for solving problems]

The present invention is an improvement in plasma arc torches,
The plasma arc torch has a cylindrical casing defining a chamber, the casing including a bore defining an axially extending anode nozzle passageway, a first conductive end wall defining an anode electrode, and a second conductive end wall defining an anode electrode. It has an opposite end wall. A cathode electrode is mounted coaxially within the opposite end wall of the cylindrical casing and a first
and is electrically insulated from the first end wall and terminating before the first end wall. At the end facing the cathode electrode, the anode nozzle passage bulges outward and expands into a conical shape. Means are provided for directing a plasma generating pressurized gas into the chamber formed by the cylindrical casing, the cathode electrode, and the end walls. A potential difference is created between the cathode electrode and a first end wall forming the anode nozzle, creating a plasma arc flame that typically exits the anode nozzle passageway, with a surrounding metal ring surrounding the nozzle exit orifice. This is the condition in which the anode foot is normally configured.

The modification is at a discontinuity in the surface at a location along the nozzle bore sufficiently upstream of the nozzle exit orifice and of sufficient size to allow the arc to pass to the anode wall near the discontinuity, thus allowing the downstream Establishing an arc column with an ionized region of give.

Preferably, the plasma-generating gas is fed tangentially into the end of the chamber remote from the anode nozzle passage, and the gas is
A condition that establishes a vortex flow indicating a low-pressure core extending through the nozzle passage, the core establishing a small diameter arc column extending partially through the nozzle passage, and a vortex flow of gas along the anode bore wall. The boundary layer provides a path for the arc to strike the anode nozzle passage wall immediately at or just downstream of the disturbed area provided by the discontinuity in the nozzle passage wall surface. The surface discontinuity is formed by a flared bore extending axially inwardly from the nozzle outlet along a portion of the nozzle axis and forming a radial shoulder with the main bore of the rear nozzle. Good too. Instead, a shallow annular groove machined into the anode nozzle bore of sufficient depth and width functions to form a surface discontinuity. The anode nozzle passage has a reduced diameter nozzle bore over a short axial region upstream of the nozzle outlet, the reduced diameter nozzle bore forming a radial shoulder with the nozzle bore facing upstream of the nozzle outlet; Surface discontinuities may also be provided. Preferably, means are provided for directing the material to be atomized into the high velocity hot gas flow downstream of the arc column and into the downstream ionized region, so as to eliminate excessive heating of the particles atomized by the torch. I have to. Furthermore, a reduced diameter nozzle bore region is arranged between the end of the arc column and/or the associated downstream ionized region and the means for guiding the material to be atomized, the reduced diameter nozzle bore region , which forms the nozzle throat of an enlarged nozzle that functions to produce a supersonic jet stream at the nozzle exit.

〔Example〕

Referring to FIG. 3, a plasma spray torch of the non-expanding arc type is designated 10' and is similar in many respects, if not identical, to the plasma spray torch shown in FIG. Elements common to the plasma spray torch shown in FIG. 2 use the same numerals. Therefore, the cylindrical electrically insulating body piece 30 is coupled to the body piece 31' and closes the end of the annular chamber 41 to the tapered tip 32a of the cathode electrode 32, and in this position,
The cathode electrode tip or foot 32a forms a conical reduced area 35 of the bore 31' forming the torch nozzle passageway 54.
protrude inward. The body piece 31' is shown with a nozzle passage 54, which is considerably longer than the nozzle passage 34 of Applicant's previous apparatus of FIG. A feature of the embodiment of the invention of FIG. 3 is the presence of a flared bore 57 at the outlet end 52a of the nozzle anode 52, which flared bore 57 defines a radial shoulder defining an effective channel. That is, a peripheral shelf 58 is formed and the anode ring 5 is placed at a distance from the outlet end 52a of the anode nozzle 52.
I try to place 9. Similar to Applicant's prior device of FIG. 2, the basic elements of the plasma torch are constituted by a cathode electrode aligned with the nozzle bore 51. As shown in FIG.

A swirling gas flow 5 swirling around the cathode electrode 32
3 is a nozzle passage 5 formed by an anode bore 51;
4 into the conical decreasing region 35 of 4, thereby centering the arc column 55 along the bore 51 to pass beyond the nozzle exit to some downstream point indicated at 56.

The radial shoulder or peripheral shelf 58 formed by bore 51 and flared bore 57 is of relatively small width;
There are axial locations within the nozzle 52 that cannot be reached due to diffusion of atmospheric oxygen. Applicants have determined that a flared bore diameter approximately 1/10 greater than the nozzle bore diameter 51 is sufficient to position the anode ring 59 as desired.
Established.

Typical high voltage operation is 3-3/4 from the cathode tip.
The anode ring 59 is placed in an inch, where the main nozzle bore 51 is 5-1/16 inches and the flared bore 57 is 11/32 inches. In a typical plasma arc torch, the gas G swirling through chamber 41 was nitrogen at an operating voltage of 400 volts for the torch.

By increasing the axial depth of the bore 57, which extends from the outlet end 52a of the anode nozzle 52 to the location shown in dashed plane A, the voltage can be further reduced by increasing the axial depth of the bore 57 to an effective 5/16 inch of a 1 inch bore. At the end, the voltage is reduced to 100 volts.

Applicants have found it very surprising that providing such a small surface area shelf or radial shoulder 58 provides sufficient control over the arc length characteristics. This allows the unique plasma spray device 10' to operate effectively.

Applicant's conclusion is that the disturbance of the peripheral (boundary layer) flow along the anode wall (bore 51, widened bore 57)
The anode ring 5 provides a path for the arc to pass directly to the wall in the disturbed region or just downstream of the disturbed region.
form 9.

In a slight modification of the embodiment of FIG. 3, for an arc torch shown in essentially the same configuration as the embodiment of FIG. 3, instead of a flared bore 57, the torch of FIG. The anode wall has a shallow annular groove 60 machined into the bore 5 which is the same size as the anode wall of the embodiment of FIG.
1.

Reference to FIG. 3b shows another modification of the embodiment of FIG. 3.

In this case, the nozzle anode 52' is provided with a bore 51 similar to that in FIG. 3, but at the nozzle outlet end 52'.
At a, a slight annular projection with a reduced diameter bore 74 is provided, which reduced diameter bore 7.4 has a shoulder 75, which shoulder 75 faces upstream. ,
A discontinuity in the surface of the nozzle bore is provided at a point along the bore upstream of the nozzle outlet 52'a. Also, in the downstream ionized region the arc column 55 is retained entirely within the enlarged anode bore, thus extending the lifetime of the surrounding anode region near the nozzle exit of the plasma torch, while improving arc length characteristics. Gives you plenty of control.

Alternatively, in FIG. 3C, a thin, radially inwardly projecting ring 76 may be machined into the anode inner wall, provided that the surface discontinuities are within the chamber 41. located at a desired axial position along the uniform swirling gas flow that begins and passes through the nozzle bore 51;
The arc should be of sufficient size to pass through the anode 52'' at the desired axial location.

The new plasma mode of operation is such that the powder is directed into the arc column 37 of Applicant's prior FIG. 2 apparatus or the ionized conical region 19 of a prior art FIG. 1 plasma arc torch. Similarly, ffl (jt) is a device that can be guided by the high-velocity gas flow downstream of the arc column 55.

FIG. 4 is a longitudinal cross-sectional view of a non-transfer plasma arc torch 10'' according to another variation of Applicant's embodiment of FIG. , the cup-shaped body 30 coaxially mounts an anode nozzle 61 downstream of the cathode electrode foot 32a, which is preferable to the leading arrow labeled "powder" than is currently possible using more conventional plasma devices. The relatively high exit jet velocity in the embodiment of FIG. The cathode electrode 32 can also be used to accelerate the velocity of the anode nozzle or anode piece 6.
An anode nozzle passage 74 formed by a bore 74 of 1
axially aligned. The gas vortex flows around the periphery of the cathode electrode 32 and into the annular chamber 41.
Established as in the device shown. In this case, the enlarged bore 6 for the radial shoulder or anode shelf 66
5, an anode ring 62 accompanies the terminal end of the arc column 64 downstream. Furthermore, the reduced cross-sectional area of the throat 6
7 is provided to maintain the upstream gas pressure at the desired elevated pressure.

The diverging enlarged nozzle 68 forms a supersonic jet stream 71 characterized by an impact diamond 72 . Powder is directed into the expanded gas stream by passing the powder through radial tubes 69 and diagonal holes 70 so that the powder material enters the ultrasonic jet 71 . It is important to note that the powder particles 73 follow only the thermally sensitive gas, perhaps only a small percentage of the separated gas forming a supersonic jet stream. Ionized species are not present in sufficient numbers to sustain arc action, ie, to form the glowing cone normally associated with pressure. The ionized regions are 20, . Flows more fully developed by embodiments of the present invention are perhaps half where temperatures in the range of 1,000°F can be reached. Radiation risks are essentially eliminated, especially in the ultraviolet range. However, the temperature of the injection is well above the temperature of the injection available in internal combustion systems. Therefore, the entrained particle 7
3 is rapidly brought to melting temperature before being deposited 21 on a substrate, such as substrate 22 in FIG. Impact the particles 73 on the substrate 22' or other piece to be coated by adjusting the relationship between gas enthalpy, injection velocity, and the distance the particles exist before impacting the substrate in the path of the supersonic jet 71. It is possible to make it into a thermally softened state. In the embodiments shown in Figures 3 and 4, the positive and negative electrical connections are
From a power source (or not shown) to the cathode electrode 32 on both sides and to the anode electrode 52 in FIG. 3 and anode electrode 61 in FIG. 4, respectively.

Although the present invention has been shown and described in detail with reference to illustrative embodiments, it is understood that various modifications may be made in form and detail without departing from the spirit and scope of the invention. will be understood by those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a conventional plasma spray torch used for spray coating a substrate; FIG. 2 is a longitudinal cross-sectional view of the non-transitional plasma arc torch of pending U.S. patent application Ser. No. 024.485; FIG. 2a is an enlarged longitudinal cross-sectional view of the exit end of the plasma arc torch nozzle of FIG. 2; FIG. Figures 3a, 3b and 3c, longitudinal cross-sectional views of the nozzle exit section of a non-transferred plasma arc torch including a flared bore therein and forming a preferred embodiment of the present invention, illustrate another embodiment of the present invention. FIG. 3 is a cross-sectional view of a modified nozzle exit section for the non-transitional plasma arc torch forming the non-transitional plasma arc torch of FIG. 3; FIG. The enlarged nozzle downstream of the enlarged bore is shown in FIG. FIG. 3 is a diagram showing that powder is thermally softened. 10', 10'''...Plasma spray torch 30・
...Electrical insulation body piece 31'...Body piece, 32...Cathode electrode 41...Chamber 51...Nozzle bore 57...Enlarged bore 58...Radial shoulder 59...Anode Ring 60...Annular groove 61...Anode nozzle 62...Anode ring 65...Enlarged bore 66...Radial shoulder 67...Throat 68...Enlarged nozzle 69...Tube 70...Diagonal hole 74...Bore of reduced diameter 75...Shoulder 76...Ring

Claims (1)

Claims: 1. A first conductive end wall that is a cylindrical casing defining a chamber and that includes an enlarged longitudinal nozzle bore that defines an axially extending anode nozzle passageway and that defines an anode electrode. and a second opposite end wall, wherein the cathode electrode is coaxially mounted within the opposite end wall of the cylindrical casing and the cathode electrode is mounted coaxially within the opposite end wall of the cylindrical casing. the anode nozzle passage is electrically insulated from the first end wall and terminates in front of the first end wall, the anode nozzle passageway projecting outwardly and conically widening at the end facing the cathode electrode; a conical casing; means for guiding plasma to generate pressurized gas in a chamber formed by the cylindrical casing, the cathode electrode, and both end walls; and the cathode electrode and the anode nozzle. creating a potential difference between a first end wall and a first end wall of the anode nozzle passage, causing a plasma arc flame typically exiting the anode nozzle passageway, with the anode foot typically defined by a peripheral metal ring surrounding the nozzle exit orifice. a surface discontinuity at a location along a nozzle bore of sufficient size and sufficiently upstream of a nozzle exit orifice to cause the arc to strike an anode nozzle passageway wall near the discontinuity; so that in the downstream ionized region,
Establishing an arc column that is entirely retained within the enlarged longitudinal nozzle bore, thus extending the lifetime of the surrounding anode region near the exit of the plasma torch nozzle, while providing sufficient control over the arc length characteristics A plasma arc torch including a surface discontinuity such that the means for directing the plasma to produce a pressurized gas in the chamber tangentially directs the gas into an end of the chamber remote from the anode nozzle passageway. means for supplying the gas to establish a vortex flow of gas indicative of a low pressure core extending through the anode nozzle passageway, said core being in a position to establish a small diameter arc column extending partially through said nozzle passageway; , the boundary layer of the gas vortex along the anode nozzle passage wall is such that the arc passes through the anode nozzle passage wall immediately at or just downstream of the disturbed area provided by the discontinuity in the nozzle passage wall surface. A plasma arc torch comprising a gas supply means adapted to provide a path such as: A plasma arc torch characterized in that it includes means for directing the material to be atomized into the hot gas stream and the downstream ionized region, thereby eliminating excessive heating of the particles atomized by the torch. . 2. A flared bore extends axially inwardly from the nozzle outlet along a portion of the nozzle axis and forms a radial shoulder with the main bore of the anode nozzle, the radial shoulder extending from the discontinuity. 2. The plasma arc torch according to claim 1, wherein the plasma arc torch is in a state such that it constitutes a plasma arc torch. 3. The plasma arc torch of claim 2, wherein the flared bore has a diameter that exceeds the diameter of the nozzle bore by less than 25%. 4. The flared bore has a diameter that exceeds the diameter of the nozzle bore by less than 40%, and the axial position of the radial shoulder is predetermined for the arc between the cathode electrode and the anode electrode at the radial shoulder. 3. The plasma arc torch of claim 2, wherein the plasma arc torch is selected to provide a desired arc voltage. 5. A shallow annular groove is machined into the anode nozzle bore of sufficient depth and width to form a discontinuity in said surface at an axial location sufficiently upstream of the anode nozzle passageway exit to form a discontinuity within the anode nozzle bore. 2. The plasma arc torch of claim 1, wherein said plasma arc torch is adapted to ensure arc passage to the anode wall. 6. said anode nozzle passage has a reduced diameter nozzle bore forming a radial shoulder over a short axial region upstream of the nozzle outlet, said nozzle bore facing upstream of the nozzle outlet and discontinuing said surface; 2. The plasma arc torch according to claim 1, wherein the plasma arc torch is in a state of forming a part of the plasma arc torch. 7. The plasma arc torch of claim 1, wherein the anode nozzle bore has a radially inwardly projecting ring defining a discontinuity in the surface upstream of the nozzle exit over a short axial length. 8. between the end of the arc column and/or the associated downstream ionized region and the means for directing the material to be atomized, a reduced diameter nozzle bore region, the reduced diameter nozzle bore region 2. The plasma arc torch of claim 1, further comprising a nozzle float of an enlarged nozzle which is operative to produce a supersonic jet stream at the nozzle outlet. 9. a cylindrical casing and a first electrically conductive end wall including an enlarged longitudinal nozzle bore forming an axially extending anode nozzle passageway and forming an anode electrode;
a second opposite end wall, the cathode electrode being coaxially mounted within the opposite end wall of the cylindrical casing and having a cathode electrode electrically connected from the first end wall. insulated and terminating before the first end wall, the anode nozzle passageway projecting outwardly at the end facing the cathode electrode and carrying a conically expanding plasma arc torch. The method of operation includes the steps of creating a plasma that creates a pressurized gas in the chamber and creating a potential difference between the cathode electrode and the anode nozzle to create a plasma arc flame normally exiting the anode nozzle passageway. A method of operating a plasma arc torch comprising: providing a discontinuity at a point along a lengthwise nozzle bore of sufficient size sufficiently upstream of the nozzle exit orifice, the arc proximate the discontinuity; into the anode nozzle passage wall, thus establishing an arc column in the downstream ionized region that is all retained within the enlarged longitudinal nozzle bore, and therefore near the anode nozzle exit. directing the particles to be atomized at a location within the plasma arc flame downstream of the arc column; The downstream ionized region is in the region of the plasma arc flame in the form of a high velocity hot gas flow exhibiting non-ionization, and the particles are
is accelerated to a significant velocity to impact the surface of the workpiece to be coated, thereby
A method of operating a plasma arc torch comprising: removing excessive heating of particles prior to impact. 10. The method of claim 9, wherein the location of the surface discontinuity is selected to select a predetermined desired arc voltage between the anode and cathode. 11. producing said high-velocity hot gas flow exhibiting non-ionization and of reduced diameter downstream of the end of the arc column and/or associated ionized region and upstream of the injection point of the particles to be atomized; and extending the hot gas flow into a flared nozzle bore section downstream of said reduced diameter nozzle bore region forming a nozzle throat and an end of the flared longitudinal nozzle bore. 11. The method of claim 10, including the step of generating a supersonic jet stream exiting from the jet stream. 12. a cylindrical casing and a first conductive end wall including an enlarged longitudinal nozzle bore forming an axially extending anode nozzle passageway and forming an anode electrode; and a second opposite end; a cathode electrode is coaxially mounted within the opposite end wall of the cylindrical casing and is electrically insulated from the first end wall; 1, the anode nozzle passageway terminates at the end facing the cathode electrode,
A method of operating an outwardly projecting, conical plasma arc torch in which a plasma is generated in the chamber to generate a pressurized gas and a potential difference is created between the cathode electrode and the anode nozzle; A method of operating a plasma arc torch comprising the step of producing a plasma arc flame normally exiting from said anode nozzle passageway, said method comprising: producing a plasma arc flame generally extending from said anode nozzle passageway, the plasma arc torch having a plasma arc flame of sufficient size at a point along a flared longitudinal nozzle bore sufficiently upstream of said nozzle exit orifice; of arc passes into the anode nozzle passage, thus establishing an arc column in the downstream ionized region that is all retained within the enlarged longitudinal nozzle bore, and therefore near the anode nozzle exit. and directing particles to be atomized at a location within the plasma arc flame downstream of the arc column, while providing sufficient control over the arc length characteristics. , the downstream ionized region is in the region of the plasma arc flame in the form of a high velocity hot gas flow exhibiting non-ionization, and the particles are
is accelerated to a significant velocity to impinge on the surface of the workpiece to be coated, thereby
A method of operating a plasma arc torch comprising: removing excessive heating of particles prior to impact.