Axial feed plasma spraying device

A spray coating apparatus includes a cathode and an anode nozzle to form a pair. A front end of the anode nozzle is provided with three or more plasma jet jetting holes, and a spray material jetting hole is disposed at the center of an area surrounded by the plasma jet jetting holes. The spray material jetted through the jetting hole is fed into the center axis of a complex plasma arc or a complex plasma jet. The spray material jetted through the spray material jetting hole is melted at high thermal efficiency, to thereby enhance yield of coating film. Reflection of the spray material by the outer periphery of plasma flame, penetration of the spray material through plasma flame, and scattering of the spray material caused by reflection or penetration, due to the differences in particle diameter, mass, etc. of the spray material is prevented.

BACKGROUND OF THE INVENTION

The present invention relates to an axial feed plasma spraying apparatus.

In conventional plasma spraying apparatuses, a spray material is typically fed into a plasma arc or a plasma jet generated in front of the nozzles, in a direction orthogonal to the plasma (i.e., via an external feeding method). In the feeding method, when the spray material has a small particle size and a small mass, the plasma arc or plasma jet repels the material before the material reaches the center of the plasma. When the spray material has a large particle size and a large mass, the material penetrates the plasma arc or plasma jet. In both cases, the yield of spray coating from the used spray material is problematically poor.

In recent years, demand has arisen for plasma spraying of a suspension material containing sub-micron particles or nano particles, or a liquid material of an organometallic compound. When the aforementioned external feeding method is employed, the yield of spray coating is considerably poor, impeding the use of these materials as spray materials, which is also problematic.

In order to enhance the density and adhesion of spray coating film, the speed of the spray material particles jetted by a plasma spray apparatus must be elevated. However, when the conventional external feeding method is employed, with increasing speed, the plasma arc or plasma jet repels an increased number of spray material particles before the material reaches the center of the plasma. Thus, the conventional feeding method is not suited for high-speed feeding.

One known method for solving the above problems is an axial feed plasma spraying apparatus, which is adapted to feed a spray material into a plasma generation chamber in a nozzle, and jetting of the molten spray material together with a plasma jet through a plasma jet jetting hole (see, for example, Patent Documents 1 and 2).

According to the methods disclosed in Japanese Patent Application Laid-Open (kokai) No. 2002-231498 and Japanese Patent Application Laid-Open (kokai) No. 2010-043341, the spray material is melted in a plasma generation chamber disposed in a nozzle. Therefore, the molten spray material is deposited on the inner wall of the plasma generation chamber, on the tips of the electrodes, or in the plasma jet jetting hole, thereby impeding stable and continuous operation. In addition, the products obtained by such a plasma spraying apparatus sometimes bear non-uniform deposits of such material.

Another problem is considerable wear of a nozzle, which is caused by jetting of a spray material through the nozzle at ultra-high speed, increasing wear of the jetting hole.

Also, the plasma generation chamber remains at high pressure because of the plasma gas fed into the chamber. Thus, when a spray material is fed into the plasma generation chamber, a spray material feeder receives back pressure. This imposes a particular pressure-resistant design on the material feeder.

Japanese Patent Application Laid-Open (kokai) No. Hei 7-034216 discloses a plasma spraying apparatus having a plurality of divided plasma jet jetting holes, which are disposed in parallel, so as to increase the area of the formed coating film. This plasma spraying apparatus also has the same problems as described in relation to the aforementioned known axial feed plasma spraying apparatuses.

Japanese Patent No. 4449645, Japanese Patent Application Laid-Open (kokai) No. Sho 60-129156, and Japanese Patent Publication (kokoku) No. Hei 4-055748 disclose plasma spraying apparatuses each having 2 to 4 cathodes and 2 to 4 counter anode nozzles in which plasma flames (also called plasma jets) provided through the anode nozzles are converged.

However, the plasma spraying apparatuses disclosed in this art still have a problem of considerably low yield of spray coating. The problem is caused by poor contact of the converged plasma flame with the sprayed material due to non-uniform damage of cathode nozzles and anode nozzles occurring during the course of spraying operation and due to lack of flow rate uniformity of working gases. This results in insufficient heat exchange and scattering of the spray material to undesired sections of the apparatuses.

Also, since a plurality of cathodes and anode nozzles are cooled, the apparatuses must be provided with a complex cooling path, leading to considerable energy loss of cooling water. In addition, maintenance of such cooling systems is very cumbersome and requires a long period of time.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention is to prevent deposition or adhesion of a molten spray material on or to the inner wall of a plasma generation chamber, an electrode, and a plasma jet jetting hole. Another object of the invention is to melt the spray material jetted through the spray material jetting hole at high thermal efficiency, to thereby enhance yield of coating film. Still another object of the invention is to prevent reflection of the spray material by the outer periphery of plasma flame, penetration of the spray material through plasma flame, and scattering of the spray material caused by reflection or penetration, due to the differences in particle diameter, mass, etc. of the spray material.

The present invention provides a plasma torch comprising a cathode, an anode nozzle, plasma gas feeding means, and spray material feeding means, characterized in that the cathode and the anode nozzle form a pair; that the anode nozzle is provided with three or more plasma jet jetting holes which are disposed at specific intervals along a circle centered at the center axis of the nozzle, so as to split a flow of plasma jet or plasma arc; and that a spray material jetting hole is disposed at the front end of the anode nozzle to be located at the center of an area surrounded by the plasma jet jetting holes.

In an embodiment of the present invention, the plasma jet jetting holes are slanted such that flows of plasma jet or plasma arc jetted through the plasma jet jetting holes intersect one another at an intersection point on the center axis of the nozzle in front of the nozzle.

In another embodiment of the present invention, the plasma jet jetting holes are disposed in parallel or generally in parallel to the center axis, such that flows of plasma jet jetted through the plasma jet jetting holes do not intersect at a point on the center axis of the anode nozzle, before the plasma jet or plasma arc reaches a coating substrate.

In another embodiment of the present invention, the plasma generation chamber of the plasma torch is segmented into a front chamber and a rear chamber, each of which is provided with plasma gas feeding means. In another embodiment of the present invention, the plasma gas feeding means is disposed in a tangential direction with respect to the plasma generation chamber, so as to generate a swirl (i.e., helical) flow of the plasma gas fed through the plasma gas feeding means.

In another embodiment of the present invention, a sub plasma torch is disposed in front of the anode nozzle such that the center axis of the sub plasma torch intersects the center axis of the main torch. In another embodiment of the present invention, the sub plasma torch is disposed such that flows of sub plasma jet or sub plasma arc intersect one another at an intersection point of the flow of plasma jet or plasma arc provided by the main torch or at a point in the vicinity of the intersection point.

In another embodiment of the present invention, a plurality of sub plasma torches are provided. In another embodiment of the present invention, the number of the sub plasma torches is identical to that of the plasma jet jetting holes of the main torch. In another embodiment of the present invention, three plasma jet jetting holes are employed, and three sub plasma torches are provided. In another embodiment of the present invention, each flow of plasma arc jetted through each of the plasma jet jetting holes is joined to form a hairpin curved arc respectively with a flow of sub plasma arc achieved by one of the sub plasma torches, which is in the closest vicinity, and flows of hairpin curved arc are independent from one another without intersecting.

In another embodiment of the present invention, the center axis of the sub plasma torch is orthogonal to the center axis of the main plasma jet, or slanted, toward the rear direction, with respect to the center axis of the main plasma jet. In another embodiment of the present invention, an ultra-high-speed nozzle is attached to the front end of the anode nozzle. In another embodiment of the present invention, the spray material feeding means is provided with a plurality of spray material feeding holes. In another embodiment of the present invention, the polarity of the cathode and that of anode are inverted.

The effects of the present invention are as follows.

According to the present invention, a spray material is not directly fed into a plasma generation chamber, but is fed (jetted) to the center of plasma jet or plasma arc in front of the front end of the nozzle. Thus, the molten spray material is not deposited on the interior of the plasma generation chamber, an electrode, and a plasma jet jetting hole. As a result, stable, continuous plasma spraying can be attained, and the products obtained by such a plasma spraying apparatus do not bear such spit-like deposits. In addition, since the plasma generation chamber has no spray material jetting hole, no back pressure is applied to a spray material feeder. Thus, no particular pressure-resistant design is needed for the material feeder, and the service life of the nozzle can be prolonged.

According to the present invention, the plasma jet jetting holes are slanted such that flows of plasma jet or plasma arc intersect one another at an intersection point in front of the nozzle. Thus, the spray material jetted through the spray material jetting hole can be uniformly heated and melted in plasma jet or plasma arc, realizing plasma spraying at high thermal efficiency and high product yield.

According to the present invention, the spray material is fed into the axial center high-temperature space of plasma jet or plasma arc. Thus, there can be prevented reflection of the spray material by the outer periphery of plasma flame, penetration of the spray material through plasma flame, and scattering of the spray material caused by reflection or penetration, due to the differences in particle diameter, mass, etc. of the spray material. As a result, granulation or classification may be omitted in the spray material production step, and thereby a low cost spray material can be used. In addition, not only powdery spray material but also liquid spray material may be used, if required.

According to the present invention, the plasma jet jetting holes are disposed in parallel or generally in parallel to the center axis such that flows of plasma jet jetted through the plasma jet jetting holes do not intersect at a point on the center axis of the anode nozzle, before the plasma jet reaches a coating substrate. Thus, flows of the plasma jet jetted through the plasma jet jetting holes form a cylindrical shape flow targeting the substrate. As a result, the spray material jetted through the spray material jetting hole does not come into direct contact with the plasma jet immediately after jetting of the material, and can flow to the substrate while the material is surrounded by the divided plasma jet flows to minimize contact with air.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1shows embodiment 1 of the present invention, which is a spraying apparatus called “one-stage-type single torch.” InFIG. 1, reference numeral1denotes a torch, serving as the axial feed plasma spraying apparatus of the present invention. The torch1has a pair of cathode and anode nozzle; i.e., a cathode8and an anode nozzle (anode)2. The cathode8is formed in the rear part of the torch1, and the anode nozzle2is formed in the front part thereof.

A front end3of the anode nozzle2is provided with three plasma jet jetting holes4which are disposed at specific intervals along a circle centered at the center axis of the nozzle. The plasma jet jetting holes4are angled such that flows of plasma jet12jetted through the plasma jet jetting holes4intersect one another at an intersection point P on the axis passing the center of the circle.

Reference numeral5denotes a spray material jetting hole which is disposed at the center of the circle on which the plasma jet jetting holes4are disposed. A spray material is fed to the spray material jetting hole5via a spray material feeding hole6connected to a spray material feeder (not illustrated).

Reference numeral7denotes a plasma generation chamber which is provided in the anode nozzle2and to the rear of the plasma jet jetting holes4. The cathode8is disposed at the axial center of the plasma generation chamber7. When a power switch13is closed, a high current/low voltage is applied from a power source10to the anode nozzle2and the cathode8, whereby a plasma arc11is generated in front of the cathode8. The plasma arc11is branched into said plurality of plasma jet jetting holes4, and jetted through jetting holes4, to thereby form flows of plasma jet12, which intersect at the intersection point P in front of the jetting holes4.

Reference numeral9denotes plasma gas feeding means for feeding a plasma gas (e.g., an inert gas) into the plasma generation chamber7. In Embodiment 1, jetting holes9aare disposed in a tangential direction with respect to the plasma generation chamber7, so as to generate a swirl flow in the plasma generation chamber7, to stabilize the plasma arc11. Reference numeral15denotes an insulation spacer, and33indicates the jetting direction of the molten spray material.

In Embodiment 1, three plasma jet jetting holes4having the same size are provided. However, the number of the jetting holes is not particularly limited to 3, and a number of 3 to 8 is preferred for practical use. The inclination angle of any of the jetting holes4is determined in accordance with the position of P in front of the front end of the nozzle3. In Embodiment 1, the three jetting holes4are disposed along a circle at uniform intervals. However, the intervals may be appropriately modified in accordance with needs.

InFIG. 2, members having the same structure and functions as those of the members shown inFIG. 1are denoted by the same reference numerals, and overlapping descriptions will be omitted. As shown inFIG. 2, in Embodiment 2, a plasma generation chamber7provided in the anode nozzle2and is segmented into a rear chamber7aand a front chamber7b, except for the axial center portion of the chamber7. Each of the chambers7a,7bis provided with plasma gas feeding means; i.e., jetting holes9a,9b. A cathode8is attached to the rear chamber7a.

Since the plasma generation chamber7is segmented into the rear chamber7aand the front chamber7bin Embodiment 2, the output of plasma arc11can be enhanced, and inexpensive compressed air, nitrogen, or the like can be used as a plasma gas to be fed to the front chamber7b. In Embodiment 2, the anode nozzle2consists of a nozzle portion2aof the rear chamber7aand a nozzle portion2bof the front chamber7b. Switches13aand13bselectively couple the power supply10between the anode sections2aand2band the cathode8.

InFIG. 3, members having the same structure and functions as those of the members shown inFIG. 1are denoted by the same reference numerals, and overlapping descriptions will be omitted. As shown inFIG. 3, Embodiment 3 is a complex torch comprising the torch1as described in Embodiment 1, and a sub plasma torch51disposed in front of the torch1, such that the flow of sub plasma jet62, in the direction orthogonal to the main plasma jet flow, intermingles with the main plasma jet12aat the intersection point P (hereinafter, the sub plasma torch may be referred to simply as “sub torch”). A nozzle64of the sub torch51serves as a cathode, and a sub torch electrode56serves as an anode. Through provision of the sub torch51, a complex plasma arc31can be formed, at the intersection point P or a point in front of P. The Complex plasma arc31includes the main plasma arc11aprovided by the main plasma torch1a(hereinafter may be referred to simply as “main torch”) and a sub plasma arc61provided by sub torch51.

In Embodiment 3, the sub torch51is disposed so as to be orthogonal to the intersection point P. However, the sub torch51may be slightly slanted toward the rear direction. Most preferably, the sub plasma arc61jetted through the sub torch51intermingles with the main plasma arc11aat the intersection point P, but the intermingle point may be slightly shifted to the left or right of point P as viewed inFIG. 3.

The sub torch51has no spray material feeding means and has only one sub plasma jet jetting hole54at the axial center.

By means of the complex torch, the sub plasma arc61formed by the sub torch51is added to the main plasma arc11aformed in front of the anode nozzle2of the main torch1a, to thereby form the complex plasma arc31. In this case, since a spray material can be directly fed to the axial center of the complex plasma arc31, the material remains at the center of the plasma arc31for a longer period of time, thereby elevating melting performance.

InFIG. 3showing Embodiment 3, reference numerals13b,13cdenote switches coupling power supply10ato anodes2and56. Reference numeral32is a complex plasma jet, reference numeral50is a sub power source coupled by switches53between anode56and cathode64of sub torch51. Reference numeral57is a plasma generation chamber, while reference numeral59is a plasma gas feeding means, and reference numeral65is an insulation spacer.

InFIG. 4, members having the same structure and functions as those of the members shown inFIGS. 1 to 3are denoted by the same reference numerals, and overlapping descriptions will be omitted. Embodiment 4 is a complex torch having the two-stage-type single torch described in Embodiment 2 in combination with the sub torch51described in Embodiment 3, for attaining the surprising and unexpected synergistic effects obtained from utilizing Embodiments 2 and 3.

OPERATION EXAMPLES

Operation Examples of the aforementioned Embodiments 1 to 4 are as follows.

(1) Operation Example of Embodiment 1

Spray coating film: ceramic spray coating film

(2) Operation Example of Embodiment 2

Spray coating film: ceramic spray coating film

(3) Operation Example of Embodiment 3

Spray coating film: ceramic spray coating film

(4) Operation Example of Embodiment 4

Spray coating film: ceramic spray coating film

Embodiment 5 is a complex torch similar to that of Embodiment 4 having one sub torch51, but the complex torch of Embodiment 5 has three sub torches51, arranged as shown inFIGS. 5 to 8. Embodiment 5 contemplates a linear and stable flow of plasma arc or plasma jet. InFIGS. 5 to 8, members having the same structure and functions as those of the members shown inFIG. 4are denoted by the same reference numerals, and overlapping detailed descriptions will be omitted. InFIGS. 5, 10A, 10B, and 10Ceach denote a transistor power source, and S1, S2, and S3each denote a switch.

The complex torch of Embodiment 5 has an anode nozzle2bprovided with three plasma jet jetting holes4in a circumferential direction with uniform intervals. The number of the jetting holes4(FIG. 6) and the interval between the holes may be appropriately modified in accordance with needs.

As shown inFIG. 8, each jetting hole4is slanted by an angle θ with respect to the center axis2C of the anode nozzle2. The inclination angle θ is appropriately modified in accordance with needs, and is adjusted to, for example, from about 4° to about 6°. The jetting hole4consists of an inlet4aof an inverted frustum shape, and a straight tube outlet4bconnected to the inlet4a. The main plasma arc11aand the main plasma jet12acan readily enter the jetting hole4. The spray material jetting hole5is provided with one spray material feeding hole6(FIG. 5). However, a plurality of feeding holes6may be provided in accordance with needs. In one possible mode, a pair of feeding holes6are centro-symmetrically disposed, and different spray materials may be fed through the respective feeding holes6, followed by mixing the materials.

As shown inFIG. 7, the main torch1ais provided with a plurality of jetting holes9a. Each jetting hole is disposed in a tangential direction with respect to the plasma generation chamber7a. Therefore, the plasma gas G fed through one jetting hole9ais guided along the inner wall of the plasma generation chamber7ain a direction denoted by arrows A9, to thereby form a swirl flow. In a similar manner, the plasma gas fed through another jetting hole9binto the plasma generation chamber7bforms a swirl flow. The swirl flow is divided into respective plasma jet jetting holes4. In each jetting hole4, the plasma gas flows with a swirling action and is jetted to the intersection point P (FIGS. 5 and 8).

Sub plasma torches51are provided three in number, that number corresponding to the number of the plasma jet jetting holes4of the main plasma torch1a. The sub torches51are disposed in a circumferential direction with respect to the center axis of the main torch at uniform intervals, as seen inFIG. 6, such that the center axis of the main torch1aintersects the center axis of each sub torch51. Each sub torch51generates a sub plasma arc61by closing the switches53a,53b, or53c(on state). The sub plasma arc61is joined to form arc of a hairpin shape (so-called hairpin arc) with a flow of the plasma arc11aof the main torch1apresent at the closest vicinity of each sub plasma torch. As a result, a conduction path is formed from the tip of the cathode8of the main torch1ato the anode tip of a sub torch electrode56of the sub torch51. The switches53a,53b, and53care opened after the formation of the hairpin arc (off state).

The spray material fed through the spray material feeding hole6is jetted through the spray material jetting hole5to the aforementioned intersection point P. While the material is melted at high temperature, it flows while being surrounded by flows of the main plasma jet12a(FIG. 5). The particles of the molten spray material; i.e., melt particles, collide with a substrate (coating substrate)80, to thereby form a spray coating film70. In this case, since three flows of the hairpin arc are converged at the intersection point P, the complex plasma arc31or the complex plasma jet32can be more stabilized, as compared with the case where one sub torch is employed (Embodiment 4).

Embodiment 6 is shown inFIGS. 9 and 10. InFIGS. 9 and 10, members having the same structure and functions as those of the members shown inFIG. 2are denoted by the same reference numerals, and overlapping detailed descriptions will be omitted.

This embodiment is a single torch similar to that of Embodiment 2 (FIG. 2), but the plasma jet jetting holes4are disposed in parallel or generally in parallel (slightly slanted) to the center axis, as shown inFIGS. 9, 10. Embodiment 6 contemplates prevention of intermingling the flows of plasma jet12A jetted through the plasma jet jetting holes4A at an intersection point on the center axis2C of the anode nozzles2a,2bof the torch1, before the plasma jet12A reaches a coating substrate80. The center axis (center axis line)2C of the anode nozzles2a,2bcoincides with the center axis (center axis line) of the main torch1a.

As shown inFIG. 10, six plasma jet jetting holes4A are disposed (on an imaginary circle) in a circular pattern at specific equal angular intervals so as to surround the spray material jetting hole5. The number and intervals of disposition of the jetting holes4A may be appropriately chosen in accordance with needs. For example, 4 jetting holes4A with uniform intervals may be employed.

The aforementioned plasma jet jetting holes4A are disposed in parallel to the center axis2C of the anode nozzles2a,2b. However, the holes are not necessarily disposed in parallel, and may be disposed generally in parallel. Specifically, the jetting holes4A are disposed with a small inclination angle such that flows of plasma jet12A jetted through the jetting holes4A do not intersect at a point on the center axis2C of the anode nozzles2a,2b, before the plasma jet12A reaches a coating substrate80. Such a small inclination angle is, for example, +2° to −2°, so that the plasma jetting holes4A are disposed generally in parallel to the center axis2C of the anode nozzles2a,2b.

In Embodiment 6, the spray material jetted through the spray material jetting hole5is melted by the plasma jet12A, and the formed melt particles collide with the substrate80, to thereby form a spray coating film70. In Embodiment 6, the spray material jetting hole5is disposed at the center of an imaginary circle (center axis) on which the plasma jet jetting holes4are present, and the plasma jet jetting holes4A are disposed on the circle at specific intervals. Thus, flows of the plasma jet12A jetted through the plasma jet jetting holes4A form a cylindrical shape flow targeting the substrate80.

The spray material jetted through the spray material jetting hole5goes straight to the substrate80, while being surrounded by the cylindrical plasma jet. Thus, the spray material does not come into direct contact with the plasma jet immediately after jetting of the material, and can flow to the substrate while the material is surrounded by flows of the divided plasma jet12A, to thereby minimize contact with air. As a result, a spray coating film of interest can be formed, even when there is used a spray material which melts with low heat due to low melting point or a small particle size. A spray coating film of interest can be formed, even when a spray material which is deteriorated in function by oxidation or transformation, due to high heat for melting, or which sublimates, and otherwise would fail to form a spray-coating film.

Embodiment 7 is shown inFIGS. 11 and 12. InFIGS. 11 and 12, members having the same structure and functions as those of the members shown inFIGS. 5 to 10are denoted by the same reference numerals, and overlapping detailed descriptions will be omitted.

This embodiment is a complex torch similar to that of Embodiment 5 (FIGS. 5 to 8), but the plasma jet jetting holes are disposed in parallel or generally in parallel (slightly slanted) to the center axis, as shown inFIGS. 11, 12(similar to Embodiment 6 (FIGS. 9, 10)). Embodiment 7 contemplates prevention of intermingling the flows of plasma arc11aor plasma jet12ajetted through the plasma jet jetting holes4A at an intersection point on the center axis2C of the anode nozzles2a,2bof the torch1a, before the plasma arc11aand plasma jet12reaches a coating substrate80.

As shown inFIG. 12, three plasma jet jetting holes4A of the main torch1aare provided at uniform intervals in a circumferential direction with respect to the center axis of the main torch. These jetting holes4A are formed in the same manner as employed in Embodiment 6. Sub plasma torches51are provided three in number, that number corresponds to the number of the letting holes4A of the main plasma torch1a.

In Embodiment 7, flows of sub plasma arc61provided by the sub torches51are joined to the main plasma arc11ajetted through the plasma jet jetting holes4A at the closest vicinity of the sub torches, to form a hairpin arc. As a result, a conduction path is formed from the tip of the cathode8of the main torch1ato the anode tip of a sub torch electrode56of each sub torch51.

In this way, three hairpin arc flows are individually generated so that the flows of main plasma arc11ajetted through the plasma jet jetting holes4A do not intersect one another. Also, flows of plasma jet12ajetted through the jetting holes4A do not intersect one another before the plasma jet collides with a coating substrate80.

In Embodiment 7, the spray material fed through the spray material feeding hole6does not enter directly to the main plasma jet12aor the main plasma arc11a. In addition, contact of the spray material with air is inhibited, since the material is surrounded by the space defined by the main plasma jet12aand the main plasma arc11a. By virtue of the characteristic features, the same effects as those of Embodiment 6 can be attained.

Embodiment 8 is shown inFIG. 13. InFIG. 13, members having the same structure and functions as those of the members shown inFIG. 4are denoted by the same reference numerals, and overlapping detailed descriptions will be omitted. In this embodiment, a complex torch similar to that of Embodiment 4 (FIG. 4), but the sub torch51torch is slanted toward the rear direction, with respect to the center axis of the main plasma jet, as shown inFIG. 13. Embodiment 8 contemplates a linear and stable flow of plasma arc or plasma jet.

In Embodiment 8, the sub torch51is slanted in the rear direction with respect to the intersection point P. That is, the sub torch51is slanted in such a direction that the sub torch electrode56is apart from the main torch1a. The inclination angle; i.e., the angle between the center axis of the main torch1aand the center axis of the sub torch51, is 45°. The inclination angle may be appropriately modified and is selected from a range, for example, of from about 35° to about 55°. Needless to say, this feature of Embodiment 8 may be applied to Embodiment 3 (FIG. 3) and other embodiments.

Embodiment 9 is a single torch similar to that of Embodiment 2, but an ultra-high-speed nozzle90is attached to the front end3of the anode nozzle2, as shown inFIG. 14. Embodiment 9 contemplates production of ultra-high-speed plasma jet. InFIG. 14, members having the same structure and functions as those of the members shown inFIG. 2are denoted by the same reference numerals, and overlapping detailed descriptions will be omitted.

The ultra-high-speed nozzle90of Embodiment 9 consists of an upstream funnel-like section93, which opens and widens radially toward the inlet of a drawn section91; and an downstream funnel-like section95, which opens and widens radially toward the outlet of the drawn section91. The upstream funnel-like section93has a length in the axial direction almost the same as that of the downstream funnel-like section95. The opening size of the downstream funnel-like section95is greater. InFIG. 14, reference numeral W denotes a cooling medium supplied to a cooling section, and12S denotes a supersonic plasma jet.

In Embodiment 9, the plasma jet12jetted through the plasma jet jetting holes4is transferred to the upstream funnel-like section93and narrowed in the drawn section91. When the narrowed plasma jet12is released to the downstream funnel-like section95, whereby the plasma jet rapidly expands, thereby generating an ultrasonic speed plasma jet12S. As a result, the flying speed of the particles of the molten spray material can elevated to a supersonic speed; for example, a speed 3 to 5 times the speed of sound. Thus, a high-performance spray coating film having higher density and high adhesion can be formed.

Needless to say, the high-speed nozzle of Embodiment 9 may also be employed in Embodiment 1 and other embodiments.

The present invention is not limited to the aforementioned Embodiments, and the following embodiments also fall within the scope of the present invention.

(1) The polarity of the cathode and that of the anode employed in each of the single torches and complex torches of the above Embodiments may be inverted. Specifically, the polarity of the cathode8and that of the anode nozzle2of the single torch, the cathode8and that of the anode nozzle2of the main torch of the complex torch, or the sub torch electrode56and the nozzle64of the sub torch may be inverted, respectively.

(2) In the above Embodiments, three plasma jet jetting holes4are provided on the front end3of the anode nozzle2of the above Embodiments such that the three holes are disposed on a single imaginary circle at specific intervals. Alternatively, a plurality of plasma jet jetting holes4may be provided such that the holes are disposed at specific intervals on a plurality of (two or more) concentric imaginary circles present at specific intervals. Through employment of the alternative feature, plasma flame assumes a ring-like form, and air entering into the plasma flame can be prevented. In the above case, the jetting holes4are arranged in a houndstooth pattern. However, the disposition pattern may be appropriately modified in accordance with needs.

The present invention is widely employed in industry, particularly in surface modification treatment. The present invention is applicable to a variety of uses such as liquid crystal/semiconductor producing parts, electrostatic chucks, printing film rollers, aircraft turbine blades, jigs for firing, a power generation element for solar cells, fuel cell electrolytes, as examples.

DESCRIPTION OF REFERENCE NUMERALS

It will become apparent to those skilled in the art that various modifications to the preferred embodiment of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.