HK1172933B - Plasma spraying device - Google Patents

Description

Plasma spraying device

Technical Field

The present invention relates to a plasma spraying apparatus that transfers a plasma arc to a conductive wire to generate a plasma flame and sprays the plasma flame while forming the wire into a droplet.

Background

Fig. 7 is a sectional view schematically showing a conventional plasma spraying apparatus. As shown in fig. 7, a conventional plasma spraying apparatus 90 includes: a first gas nozzle 91 forming a first gas passage 91 a; a second gas nozzle 92 disposed outside the first gas nozzle 91 and forming a second gas passage 92 a; a cathode 93 disposed substantially on the central axis of the nozzle opening 91b of the first gas nozzle 91 and the nozzle opening 92a of the second gas nozzle 92; a power supply device 94; and a wire guide hole 95 for supplying a conductive wire W for thermal spraying in the vicinity of the nozzle opening 92a of the second gas nozzle 92.

The wire W is supplied obliquely forward from the wire guide hole 95 toward the central axis of the nozzle opening 92 a. Then, the first gas discharged from the first gas passage 91a is converted into plasma by an arc generated between the wire W indirectly connected to the anode side of the power supply device 94 through the second gas nozzle 92 and the cathode 93 connected to the cathode side of the power supply device 94, and is discharged as a droplet D from the wire W. The droplets D are further refined and accelerated by the second gas injected from the second gas passage 92a to the front of the second gas nozzle 92, and are injected onto the object T to be processed, thereby forming the sprayed coating S.

In such a conventional plasma spraying apparatus 90, an inert gas such as nitrogen or argon is used as the first gas, and a gas such as compressed air, nitrogen, or carbon dioxide is used as the second gas (see, for example, patent document 1). However, in actual use, nitrogen gas, carbon dioxide gas, or the like is used as the second gas, which increases the running cost, and therefore, compressed air at low cost is used. In the plasma spraying apparatus 90, since the first gas turned into plasma is surrounded by the compressed air as the second gas, the jet of the first gas turned into plasma can be made thin, and the first gas can be made high-speed.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 9-308970.

However, in the conventional plasma spraying apparatus 90, the droplets D of the molten wire W are further thinned by the injection of the second gas, and a sufficient velocity is imparted to each droplet D, so that the metal material in the sprayed coating S is disturbed from the outer peripheral portion of the plasma flame F by the rapid convergence of the compressed air as the second gas at the time of melting. Therefore, the surface of the particles that become the droplets D is oxidized, and the sprayed coating S contains an oxide of the metal material.

Disclosure of Invention

Accordingly, an object of the present invention is to provide a plasma spraying apparatus capable of forming a sprayed coating with a small amount of oxide by reducing oxidation of the particle surface which becomes a droplet.

The plasma spraying device of the invention comprises: a cathode; a first gas nozzle forming a first gas passage at an outer periphery of the cathode to cover a front end portion of the cathode; a second gas nozzle disposed outside the first gas nozzle to form a second gas passage; and a wire passage for supplying a wire for thermal spraying to the vicinity of the nozzle opening of the second gas nozzle, wherein the first gas injected from the first gas nozzle is turned into plasma by an arc generated between a tip of the wire supplied from the wire passage and a cathode to form a plasma flame injected from the first gas nozzle, the tip of the wire is turned into a droplet, and the droplet is injected onto the object to be processed by the plasma flame and the second gas injected from the second gas nozzle, the plasma spraying apparatus further comprising: and a third gas nozzle that forms a third gas passage for injecting a third gas for injecting a gas that receives heat of the plasma flame at an outer peripheral portion of the plasma flame and has a high temperature, between the first gas nozzle and the second gas nozzle.

According to the plasma spraying apparatus of the present invention, the gas jet having a high temperature is formed by receiving the heat of the plasma flame from the inside of the third gas flow jetted from the third gas passage disposed between the first gas passage and the second gas passage. By this high-temperature gas injection, disturbance generated from the outer peripheral portion of the plasma flame due to rapid convergence of the second gas injected to the outside is suppressed, and diffusion of the plasma flame is prevented, so that oxidation of the particle surface to become droplets is reduced.

Here, compressed air, carbon dioxide, or the like can be used as the third gas, but an inert gas such as argon or nitrogen is preferably used as the third gas. When the inert gas is used as the third gas, a disturbance generated from the outer peripheral portion of the plasma flame due to rapid convergence of the second gas is prevented, and a high-temperature inert gas jet receiving heat of the plasma flame is formed at the outer peripheral portion of the plasma flame. Thus, the particles of the droplets are atomized and accelerated by the high-temperature inert gas injection, and are protected from oxidation by the second gas.

In the plasma spraying apparatus of the present invention, even when compressed air is used as the first gas, a sprayed coating with little oxidation can be formed. When compressed air is used as the first gas, the first gas contains about 20% of oxygen, but in the state of being turned into a gas plasma, the effect of oxidizing the sprayed metal is said to be small, and therefore, even when compressed air is used as the first gas, the oxidation of the sprayed film should be reduced. However, in the conventional plasma spraying apparatus, when the plasma flame is disturbed due to the rapid convergence of the second gas, the oxidation of the droplets is excessively promoted, and therefore, when the compressed air is used as the first gas, the quality of the coating film is degraded. On the other hand, in the plasma spraying apparatus of the present invention, since the high-temperature gas spray receiving the heat of the plasma flame is formed by the third gas on the outer peripheral portion of the plasma flame, disturbance of the plasma flame due to rapid convergence of the second gas can be prevented, and thus a sprayed film with little oxidation can be formed even when compressed air is used as the first gas.

Effects of the invention

(1) By providing the third gas nozzle that forms the third gas passage for injecting the third gas for injecting the gas that becomes high temperature by receiving the heat of the plasma flame at the outer peripheral portion of the plasma flame, between the first gas nozzle and the second gas nozzle, the diffusion of the plasma flame is prevented, and the oxidation of the particle surface that becomes the molten droplet is reduced, so that it is possible to form the thermal spray coating with less oxide.

(2) In the case where the inert gas is used as the third gas, a high-temperature inert gas jet which receives heat of the plasma flame is formed on the outer peripheral portion of the plasma flame, and the particles of the molten droplets are atomized and accelerated by the high-temperature inert gas jet, so that the particles are further protected from oxidation by the second gas, and a sprayed coating with less oxide can be formed.

(3) Even when compressed air is used as the first gas, a high-temperature gas jet that receives heat of the plasma flame can be formed by the third gas on the outer periphery of the plasma flame, and disturbance of the plasma flame due to rapid convergence of the second gas can be prevented, so that it is possible to form a sprayed coating that is less oxidized.

Drawings

FIG. 1 is a schematic configuration diagram of a plasma spraying apparatus according to an embodiment of the present invention.

Fig. 2 is a longitudinal sectional view showing details of a main part of the plasma spraying torch of fig. 1.

Fig. 3 is a view from direction a of fig. 2.

Fig. 4 is an explanatory view of the operation of the plasma spraying torch of fig. 1.

Fig. 5 is an explanatory diagram showing a sectional shape of a wire passage and a direction of a force applied to a wire.

Fig. 6 is an explanatory view showing a natural potential measuring method.

Fig. 7 is a sectional view schematically showing a conventional plasma spraying apparatus.

Detailed Description

FIG. 1 is a schematic configuration diagram of a plasma spraying apparatus according to an embodiment of the present invention. Fig. 2 is a longitudinal sectional view showing details of a main part of the plasma torch of fig. 1. Fig. 3 is a view from direction a of fig. 2. Fig. 4 is an explanatory diagram of an operation of the plasma torch of fig. 1.

In fig. 1, a plasma spraying apparatus 1 according to an embodiment of the present invention includes: a plasma spraying torch 2 for spraying the molten metal wire W onto the object to be processed by plasma flame; a gas supply source 3 that supplies a first gas and a second gas to the plasma spraying torch 2; a power supply 4 for supplying operating power to the plasma spraying torch 2; a wire reel 5 around which a wire W is wound; a wire straightening machine 6 for straightening a winding defect of the wire W drawn from the wire reel 5; and a wire supply mechanism 7 for supplying a wire W from a wire transport tube 8 to the plasma spraying torch 2.

As shown in fig. 2, the plasma spraying torch 2 includes: a first gas nozzle 10 forming a first gas passage 11; a second gas nozzle 20 disposed outside the first gas nozzle 10 to form a second gas passage 21; a third gas nozzle 30 disposed between the first gas nozzle 10 and the second gas nozzle 20 to form a third gas passage 31; a cathode 40 disposed substantially on the central axis of the nozzle opening 12 of the first gas nozzle 10 and the nozzle opening 22 of the second gas nozzle 20; and a wire passage 50 for supplying the wire W for spraying to the vicinity of the nozzle opening 22 of the second gas nozzle 20.

The first gas nozzle 10 is formed to cover the tip end of the cathode 40, and a first gas passage 11 is formed on the outer periphery of the cathode 40. The first gas supplied to the first gas passage 11 is a gas for generating a plasma flame to form a droplet at the tip of the wire, and is an inert gas such as nitrogen or argon. Alternatively, it is also possible to use compressed air as the first gas. The first gas supplied from the first gas passage 11 is supplied while rotating around the outer periphery of the cathode 40, and is ejected from the nozzle opening 12 of the first gas nozzle 10 toward the front of the second gas nozzle 20.

The third gas nozzle 30 is formed to surround the outside of the first gas nozzle 10, and a third gas passage 31 is formed on the outer periphery of the first gas nozzle 10. The third gas is a gas for forming a gas jet having a high temperature by receiving heat of the plasma flame generated from the first gas at an outer peripheral portion of the plasma flame, and is a gas such as compressed air or carbon dioxide. The second gas nozzle 20 is formed to surround the outside of the third gas nozzle 30, and a second gas flow path 21 is formed on the outer periphery of the third gas nozzle 30. The second gas is a gas for spraying from the outside in a sharply converging manner to further narrow the droplet and spraying the droplet at a sufficient speed to the object to be processed, as compared with the spraying of the plasma flame formed with the first gas, and is a gas such as compressed air or carbon dioxide.

The first gas preferably has a flow rate in the range of 50 to 120[ L/min ] since the temperature, speed and generation voltage of the plasma flame are appropriately changed according to the change of the gas flow rate. When the flow rate of the first gas is less than 50[ L/min ], the speed of the plasma flame is reduced, and the quality of the sprayed coating is degraded. On the other hand, when the flow rate of the first gas exceeds 120[ L/min ], the plasma flame speed increases and the temperature decreases, so that the quality of the sprayed coating decreases.

The second gas is ejected from the outside in a sharply converging manner to further narrow the droplets and impart a sufficient velocity to the droplets, as opposed to the ejection of the plasma flame formed with the first gas as described above, and therefore the flow rate is preferably 250 to 500[ L/min ]. Further, when the flow rate of the second gas is less than 250[ L/min ], the droplet is not sufficiently thinned, and the effect of imparting a sufficient velocity to the droplet is weakened, so that the quality of the sprayed coating is degraded. On the other hand, when the flow rate of the second gas exceeds 500[ L/min ], the droplet is made too fine and the droplet is cooled too much, so that the quality of the sprayed coating is degraded.

The third gas is subjected to the heat of the plasma flame generated by the first gas at the outer peripheral portion thereof to form a high-temperature gas jet, and therefore, the third gas is preferably in the range of 20 to 50% of the flow rate of the first gas in terms of volume ratio, and in the range of 5 to 10% of the flow rate of the second gas in terms of volume ratio, because disturbance of the plasma flame and gas diffusion due to the second gas jet can be suppressed. In order to more effectively exhibit the effect of suppressing the disturbance of the plasma flame and the gas diffusion by the second gas injection, it is preferable that the flow rate of the third gas is changed in conjunction with the increase or decrease of the flow rate of the second gas, and that the flow rate of the third gas is decreased when the flow rate of the second gas is small and the flow rate of the third gas is increased when the flow rate of the second gas is large.

Further, when the flow rate of the third gas is less than 20% of the flow rate of the first gas or less than 5% of the flow rate of the second gas, the effect of suppressing disturbance of the plasma flame and gas diffusion by the injection of the third gas is reduced, and therefore, it is difficult to obtain the effect of improving the quality of the sprayed coating. On the other hand, when the flow rate of the third gas exceeds 50% of the flow rate of the first gas or exceeds 10% of the flow rate of the second gas, the jet of the third gas is strongly generated, so that the inner side thereof receives the heat of the plasma flame and the high-temperature gas jet is not sufficiently formed, and the effect of suppressing the disturbance of the plasma flame and the gas diffusion cannot be sufficiently exhibited, and it is difficult to obtain the effect of improving the quality of the sprayed coating.

The wire passage 50 is constituted by a first wire passage 51a having a wire outlet 51b formed in the vicinity of the nozzle opening 22 of the second gas nozzle 20, and a second wire passage 52a that supplies the wire W at a predetermined inclination angle θ with respect to the first wire passage 51 a. The wire passage 50 imparts a bend to the wire W in a range not exceeding the elastic limit by the first wire passage 51a and the second wire passage 52 a.

As shown in fig. 3, the first wire passage 51a has a substantially rectangular cross-sectional shape elongated in the extending direction of the plasma flame, and is formed linearly penetrating the first wire guide member 51 disposed outside the second gas nozzle 20. Similarly, the second wire passage 52a has a substantially rectangular cross-sectional shape elongated in the extending direction of the plasma flame, and is formed to linearly penetrate the second wire guide member 52 arranged at a position offset from the first wire passage 51 a.

The width a of the first wire passage 51a in the longitudinal direction is set to be larger than the diameter d of the wire W by 10% to 95%. The width b of the first wire passage 51a in the short-side direction is set to be larger than the diameter d of the wire W by 3% or more and less than 10%. In the present embodiment, the diameter d of the wire W is 1.6mm, the width a in the longitudinal direction is set to be about 0.2 to 1.5mm larger than the diameter d of the wire W, and the width b in the short direction is set to be about 0.05 to 0.15mm larger than the diameter d of the wire W. The same is true for the second wire passage 52 a.

The so-called substantially rectangular cross-sectional shapes of the first wire passage 51a and the second wire passage 52a include, in addition to the rectangular cross-sectional shape, a shape in which corners of the rectangular cross-sectional shape are subjected to processing such as C-chamfering or R-chamfering in a range not to reach the outer surface of the wire W. Therefore, in the present embodiment, the wire W is also subjected to a force in a direction perpendicular to both the plane in the longitudinal direction and the plane in the short direction in the first wire passage 51a and the second wire passage 52 a.

In addition, the inclination angle θ of the second wire passage 52a with respect to the first wire passage 51a is an angle formed by the center line of the first wire passage 51a and the center line of the second wire passage 52 a. In the present embodiment, the inclination angle θ is set to about 1 to 5 °. The second wire guide member 52 is provided at a position where the first wire passage 51a and the second wire passage 52a are arranged with the gap c therebetween. In the present embodiment, the clearance c is set to about 3 to 10 mm.

In this way, in the plasma spraying torch 2 of the present embodiment, the first wire passage 51a and the second wire passage 52a are arranged with the gap c therebetween, and the linear first wire passage 51a and the linear second wire passage 52a are used to form the curved wire passage 50 having a high fitting property, and the wire W is bent within a range not exceeding the elastic range. Further, the first wire passage 51a and the second wire passage 52a may be formed in a curved shape.

The anode side of the power source 4 is connected to the first wire guide member 51, and is indirectly connected to the wire W in the first wire passage 51a passing through the first wire guide member 51. On the other hand, the cathode side of the power source 4 is connected to the cathode 40. Further, the anode side of the power source 4 may be directly connected to the wire W.

In the plasma spraying apparatus 1 configured as described above, when the wire W wound around the wire reel 5 is fed to the plasma spraying torch 2 by the wire supply mechanism 7, a strong winding defect of the wire W is corrected by the wire corrector 6 and stretched into a gentle curve. Then, the wire W is supplied to the wire passage 50 through the wire conveying pipe 8. In the wire passage 50, the wire W is also forced in the first wire passage 51a and the second wire passage 52a only in the direction perpendicular to either the plane in the longitudinal direction or the plane in the short-side direction, and as shown in fig. 4, a bending is imparted to the extension direction of the plasma flame F within a range not exceeding the elastic limit.

Here, the first wire passage 51a and the second wire passage 52a have a substantially rectangular cross-sectional shape that is long in the extending direction of the plasma flame F, and therefore, the distortion defect may escape in the extending direction of the plasma flame F. In particular, in the present embodiment, the width b in the short side direction is set to be larger than the diameter d of the wire W only in the range of 3% or more and less than 10%, and therefore, the wire W does not escape in the direction perpendicular to the extending direction of the plasma flame F. Therefore, even if some displacement occurs in the tip portion of the wire W with respect to the extending direction of the plasma flame F, the displacement in the direction perpendicular to the extending direction of the plasma flame F can be prevented from being positioned on the axis of the plasma flame F.

Figure 5 shows the cross-sectional shape of the wire passage and the direction of the force to which the wire is subjected. In fig. 5, the substantially rectangular cross section a is a rectangular cross section, the corner of the rectangular cross section of the substantially rectangular cross section B is a shape that is chamfered by C within a range that does not touch the outer surface of the wire W, and the corner of the rectangular cross section of the substantially rectangular cross section C is a shape that is chamfered by R within a range that does not touch the outer surface of the wire W. In these substantially rectangular cross-sectional shapes, the wire W is subjected to only a force in a direction perpendicular to each plane, regardless of whether the wire W touches the plane in the longitudinal direction or the plane in the short-side direction.

Since the wire W cannot be completely straightened into a straight line shape even by the wire straightening mechanism 7, a distortion defect remains. Then, the wire conveying pipe 8 is changed in the curved shape into various states by the processing of the plasma spraying torch 2 at the time of the operation, and is not formed into a constant shape. Therefore, when the wire W having the distortion defect left therein is conveyed in the wire conveying pipe 8 having such an inconstant shape, a force of bending or twisting in accordance with the shape of the wire conveying pipe 8 acts on the wire W. The wire W is conveyed while being bent freely within the elastic limit in the same manner as a spring at a position where the direction of the force is stable, while being bent and advanced within the wire conveying pipe 8 by the force of the bending or twisting.

At this time, in the above-described substantially rectangular cross-sectional shape, when the wire W touches the plane in the short side direction, the wire W receives a force in a direction perpendicular to the plane in the short side direction, that is, in the extending direction of the plasma flame F (hereinafter referred to as "X direction"), and passes through the distortion defect in the extending direction of the plasma flame F. When a force in a direction perpendicular to the extending direction of the plasma flame F (hereinafter referred to as "Y direction") acts when only the short-side direction flat surface is contacted, the wire W freely moves by the gap of the width b in the short-side direction and contacts the long-side direction flat surface. In particular, when a twisting force is applied, the forces in the X direction and the Y direction are dispersed into forces in the short-side direction and the long-side direction, and the forces act in the direction perpendicular to the respective surfaces, and act to suppress twisting of the wire W, so that the position of the wire W is stabilized.

On the other hand, in the case of a circular cross section or an elliptical cross section, when the wire W touches a curved surface of the circular cross section or the elliptical cross section, the wire W can move freely along the curved surface only by a force in a direction perpendicular to the curved surface. In particular, when a twisting force is applied, the wire W freely rotates along a curved surface, and therefore twisting of the wire W is not suppressed. Therefore, the direction in which the wire W is subjected to force is uncertain, and the position of the wire W becomes uncertain.

In this way, in the plasma spraying apparatus 1 of the present embodiment, the tip portion of the wire W can stably supply the wire W toward the center portion of the plasma flame F. Then, the first gas discharged from the first gas passage 11 is converted into plasma by an arc generated between the wire W indirectly connected to the anode side of the power source 4 through the first wire guide member 51 and the cathode 40 connected to the cathode side of the power source 4, and is formed into a plasma flame F, so that the wire W is ejected as droplets D. The droplets D are further atomized by the second gas ejected from the second gas passage 21 to the front of the second gas nozzle 20, are further accelerated, and are ejected onto the object T to be processed, thereby forming the sprayed coating S.

At this time, in the plasma spraying apparatus 1 of the present embodiment, the heat of the plasma flame F is received from the inside of the third gas flow jetted from the third gas passage 31 disposed between the first gas passage 11 and the second gas passage 21, and the high-temperature gas jet G is formed. By this high-temperature gas jet G, disturbance generated from the outer peripheral portion of the plasma flame F due to rapid convergence of the second gas jetted to the outside thereof is suppressed, whereby gas diffusion of the plasma flame F can be prevented, and oxidation of the surface of the particles that have become the droplets D can be reduced. This makes it possible to form a sprayed coating S with little oxidation on the object T.

In this way, in the plasma spraying apparatus 1 of the present embodiment, since the high-temperature gas jet receiving the heat of the plasma flame F is formed by the third gas on the outer peripheral portion of the plasma flame F, disturbance of the plasma flame F due to rapid convergence of the second gas can be prevented, and it is possible to form the sprayed film S with less oxidation even in the case of using the compressed air as the first gas.

In addition, in the case where the inert gas, that is, nitrogen gas or argon gas, is used as the third gas, as described above, disturbance generated from the outer peripheral portion of the plasma flame F due to rapid convergence of the second gas is prevented, and a high-temperature inert gas jet receiving heat of the plasma flame F is formed at the outer peripheral portion of the plasma flame F. Thus, the particles of the droplet D are atomized and accelerated in a state where the composition of the particles is prevented from being changed by the high-temperature inert gas injection, and are protected from oxidation by the second gas. This makes it possible to form the sprayed coating 72 with further reduced oxidation.

In the present embodiment, both the first wire passage 51a and the second wire passage 52a are formed as passages having a substantially rectangular cross-sectional shape that is long in the extending direction of the plasma flame, but only either one of the passages may be formed as a passage having a substantially rectangular cross-sectional shape that is long in the extending direction of the plasma flame. In this case, the first wire passage or the second wire passage having a substantially rectangular cross-sectional shape elongated in the extending direction of the plasma flame allows the distortion defect of the wire W to escape in the extending direction of the plasma flame F, and the tip portion of the wire W can be supplied to the center portion of the plasma flame F.

[ examples ] A method for producing a compound

Comparative tests were performed in the case where compressed air and nitrogen as an inert gas were used as the third gas and in the case where the third gas was not used. In this example, an aluminum alloy was used as the thermal spray material, and the natural potential of the thermal spray coating was measured as an index of the oxidation degree of the thermal spray coating, and the effect of the third gas was confirmed. Further, as a method for reducing the running cost, a thermal spray coating was formed using inexpensive compressed air as all of the first gas, the second gas, and the third gas, and the natural potential of the thermal spray coating was measured to confirm the effect of the gas 3 times. Fig. 6 is an explanatory view showing a natural potential measuring method.

As shown in FIG. 6, the natural potential was measured by using a tester using a saturated KCl salt bridge, an atmosphere of 5 w% NaCl was formed on the sprayed coating surface of the test piece (test TP), and a saturated silver chloride electrode as a control electrode. In order to stabilize the measured value of the potential, the potential after 600 seconds from the start of measurement was used as the measured value. Table 1 shows a summary of the test results, and table 2 shows the results of measuring the natural potential of the coating under the conditions shown in table 1.

[ TABLE 1 ]

[ TABLE 2 ]

As shown in table 1, when the third gas was not used and when compressed air was used for the third gas, the potential of the third gas was lowered by about 60mV when compressed air was used for the third gas. In addition, in the case of using nitrogen as an inert gas for the third gas, a value of about 150mV lower was shown. Further, the value was reduced by about 50mV when inexpensive compressed air was used as the entire gas. Thus, the fact that the oxidation of the inside of the sprayed coating was small was confirmed by using the third gas.

Industrial applicability

The plasma spraying apparatus of the present invention is useful as an apparatus for forming a spraying coating for rust prevention on the surface of a steel structure.

Description of the reference numerals

1 plasma spraying device

2 plasma spraying torch

3 gas supply source

4 power supply

5 spool of wire

6 metal wire straightening machine

7 wire supply mechanism

10 first gas nozzle

11 first gas passage

12 nozzle orifice

20 second gas nozzle

21 second gas passage

22 nozzle orifice

30 third gas nozzle

31 third gas passage

40 cathode

50 wire via

51 first wire guide member

51a first wire path

52 second wire guide member

52a second wire path.

Claims (5)

1. A plasma spraying device is provided with: a cathode; a first gas nozzle which forms a first gas passage on the outer periphery of the cathode so as to cover the front end of the cathode; a second gas nozzle disposed outside the first gas nozzle to form a second gas passage; and a wire passage for supplying a wire for thermal spraying to the vicinity of the nozzle opening of the second gas nozzle, wherein a first gas injected from the first gas nozzle is turned into plasma by an arc generated between a tip of the wire supplied from the wire passage and the cathode to form a plasma flame injected from the first gas nozzle, the tip of the wire is turned into a droplet, and the droplet is injected onto an object to be processed by the plasma flame and a second gas injected from the second gas nozzle,

the plasma spraying device further includes: and a third gas nozzle that forms a third gas passage for injecting a third gas for injecting a gas that receives heat of the plasma flame at an outer peripheral portion of the plasma flame and becomes high temperature, between the first gas nozzle and the second gas nozzle.

2. The plasma spraying device as claimed in claim 1,

the flow rate of the third gas is 20 to 50% of the flow rate of the first gas and 5 to 10% of the flow rate of the second gas by volume ratio.

3. The plasma spraying device as claimed in claim 1 or 2,

the third gas is compressed air or carbon dioxide.

4. The plasma spraying device as claimed in claim 1 or 2,

the third gas is an inert gas.

5. The plasma spraying device as claimed in claim 1 or 2,

the first gas is compressed air.