JPH10102228A - Thermal spraying method by magnetic field controlled plasma - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a injected thermal spraying material to stick to the surface of a substrate at a high yield by directly controlling a plasma jet and thereby changing the shape of the plasma jet in accordance with the flow of spray particles. SOLUTION: While an operating container gas is fed to a plasma torch 26 at the inside of a vacuum container, d.c. under high voltage is applied to the space between an anode 31 and a cathode 32 to generate arc discharge, and the operating gas 45 is ionized and is jetted as a plasma jet 52 from a nozzle 34. A powdery thermal spraying material is fed therein from a feed port 38 and is metled under heating to form into the flow of spray particles, which is stuck to solidify to the surface of a substrate 48 to form coating 51. At this time, a d.c. under certain voltage is applied to an electromagnetic coil 25 in the direction clockwise from the view in the direction of the plasma jet 52 to generate the stationary magnetic field, and the magnetic field is operated to the plasma jet 52. In this way, the particles can be cramped to the magnetic field, so that the plasma jet having a shape in accordance with the coordination of the magnetic field can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal spraying method using a magnetic field control plasma.

[0002]

2. Description of the Related Art A conventionally known plasma spraying method is performed by using a plasma torch as schematically shown in FIG. In this plasma torch 1, a conical cathode 3 is provided at the center of a base 2, and a cylindrical anode 5 is attached around the cathode 3 via an annular insulator 4 attached to the base 2. I have. A cooling chamber 6 is provided inside the anode 5, and a cooling water inlet 7 is provided in the cooling chamber 6. The cooling chamber 6 communicates with the cooling water discharge port 9 through the communication hole 8 of the insulator 4 and the inside of the base 2.

[0003] A working gas inlet 10 is provided in the insulator 4, and a sprayed material supply cylinder 12 is provided in the outlet of the anode 5, that is, in front of the nozzle 11.

The inert gas is supplied from the working gas inlet 10 and an arc discharge is generated by applying a high voltage between the electrodes 5 and 3, and the inert gas is supplied to the arc column 13. Contact and ionize. The ionized plasma is ejected from the nozzle 11 and becomes a plasma jet 14.

[0005] A powdered thermal spray material 15 is injected into the above-mentioned plasma jet 14 from a feed cylinder 12 by a feed gas. The thermal spray material 15 is heated and melted by the plasma jet 14 and accelerated, and is sprayed as a flow of thermal spray particles on the surface of the substrate 16 to be thermal sprayed. The thermal spray particles solidify while deforming flat and form a coating 1 on the surface of the substrate 16 to be thermal sprayed.
7 is formed.

As shown in the figure, there are an external feeding method in which the sprayed material 15 is fed from outside the nozzle 11 and an internal feeding method in which the sprayed material 15 is fed from inside the nozzle 11. Further, in order to prevent the reaction between the atmospheric gas and the spray particles and to reduce the porosity of the coating, the above-mentioned plasma torch 11 and the substrate 16 to be sprayed are used.
Is placed in a vacuum vessel and sprayed in a low-pressure atmosphere.
The so-called reduced pressure spraying (LPPS) is also conventionally known.

[0007]

In order to efficiently form a film on the surface of a substrate to be sprayed by plasma spraying as described above, the injected sprayed material is deposited on the surface of the substrate at a good yield, preferably the whole amount. There is a need.

However, in the conventional method, the injected thermal spray material jumps out of the plasma jet due to the injection condition of the thermal spray material or the influence of a shock wave generated in the plasma and flows along the outer periphery of the plasma jet, causing a stall. There was a problem that the yield of film formation did not increase due to insufficient heat melting.

In order to solve the above problems, it is necessary to change the heat input and the shape of the plasma jet by controlling the shape of the torch, the torch voltage, the torch current, the type of working gas, the gas flow rate, the atmospheric pressure and the like. Therefore, there is only a method of indirect control, and there is a problem that control is complicated.

Accordingly, a first object of the present invention is to directly control the plasma jet to change the shape of the plasma jet in accordance with the flow of the spray particles, thereby improving the spray efficiency.

Further, in the above-mentioned low-pressure spraying method, since the plasma jet is jetted into a low-pressure atmosphere, there is a problem that the temperature of the plasma decreases due to adiabatic expansion, and the heating efficiency of the sprayed material decreases. Therefore, a second object of the present invention is to improve the heating efficiency of a thermal spray material by performing reheating of plasma, in addition to the first object.

Further, when aiming at complete melting of the sprayed material, it is necessary to increase the capacity of the plasma torch. In this case, since the torch current is limited by the allowable current density of the electrode, it is necessary to increase the torch voltage. Therefore, a third object of the present invention is to increase the torch voltage in addition to the first object, thereby increasing the capacity of the plasma torch.

[0013]

In order to achieve the first object, the present invention provides a method for feeding a thermal spray material in powder form to a plasma jet generated by a plasma torch, and using the plasma jet to spray the thermal spray material. Is heated and melted and accelerated to form a flow of spray particles, and in a method of forming a film by plasma spraying in which this is sprayed onto the surface of the substrate to be sprayed to form a film, the flow is disposed coaxially around the outer periphery of the plasma torch. A magnetic field is applied to the plasma jet by an electromagnetic coil, and the plasma jet is controlled so that the flow of the spray particles is taken into the plasma jet according to the magnetic field arrangement of the magnetic field.

In order to achieve the second object, the above-mentioned magnetic field is made to work constantly or is made to change with time, so that the plasma generated by the plasma torch is reheated. I did it.

In order to achieve the third object, the magnetic field is also applied to an arc column generated between the anode and the cathode of the plasma torch to increase the torch voltage, thereby increasing the plasma torch. Output was increased.

[0016]

FIG. 1 shows a plasma spraying apparatus. The plasma spraying in this case is based on a reduced pressure spraying method. In the above-described apparatus, a vacuum vessel 21 is installed on a footrest 20, and a base 23 is supported by adjusting legs 22 inside the vacuum vessel 21. A winding frame 24 having a center hole in the horizontal direction is installed on the base 23, and an electromagnetic coil 25 is wound around the winding frame 24.

A plasma torch 2 is provided in the center hole of the winding frame 24.
6 is fixed coaxially. The above plasma torch 26
As shown in FIG. 2, a conductor inner cylinder 29 is inserted and integrated into a conductor outer cylinder 27 via a cylindrical insulator 28, and the outer cylinder 27 and the tip of the insulator 28 A cylindrical anode 31 is attached, and an insulator 28 and an inner cylinder 29 are provided.
A bullet-shaped cathode 32 is attached to the tip of the. The front end of the cathode 32 faces the rear end of the center hole 33 of the anode 31 with a required discharge gap. A nozzle 34 having a tapered opening 30 coaxial with the center hole 33 is attached to the tip of the anode 31.

A working gas supply port 3 is provided at the end of the outer cylinder 27.
5 is provided, and a feed port 35 is provided between the outer peripheral surface of the insulator 28 and the inner peripheral surface of the outer cylinder 27.
Is in communication with The tip of the feed passage 36 is connected to the cathode 3
Around 2, it reaches an annular nozzle member 37 interposed between the anode 31 and the cathode 32, and is opened to the center hole 33 of the anode 31 via the outer periphery of the cathode 32.

The above-mentioned anode 31 is provided with a feed port 38 for sprayed material in the radial direction (internal feed system). The feed port 38 is opened to the inner peripheral surface of the center hole 33.

A cooling water passage 39 is provided inside the anode 31, and is provided by being folded back in an annular cooling water passage 40 between the anode 31 and the nozzle 34. Cooling water passage 3
The inlet side of 9 communicates with a supply passage 41 provided inside the inner cylinder 29 and the insulator 28, and the outlet side communicates with a cooling water discharge passage 42 provided inside the outer cylinder 27. Is done.

The outer cylinder 27 and the inner cylinder 29 are connected to an external DC power supply 43, and the electromagnetic coil 25 is also connected to another external DC power supply 44. The working gas 45 and the cooling water are also supplied from outside.

The nozzle 3 of the plasma torch 26 having the above configuration
1, a six-axis articulated robot 47 is installed on the base 23 as shown in FIG. 1, and the robot 47 grasps the substrate 48 to be sprayed. At a predetermined position in front of the

In FIG. 1, reference numeral 49 denotes a vacuum exhaust port, and reference numeral 50 denotes a viewing window.

In the above apparatus, the substrate 4 to be sprayed is
8, a film 51 is formed by exhausting air in a vacuum vessel 21 from a vacuum exhaust port 49 using a vacuum pump to reduce the pressure inside the vacuum vessel 21 and supply a working gas 45 to the anode 31 and the cathode 32. During this time, an arc discharge is generated by applying a high DC voltage. The working gas 45 is ionized by contacting the arc column, and is ejected from the nozzle 34 as a plasma jet 52.

On the other hand, a powdery spray material is supplied into the above-mentioned plasma jet 52 from a spray material supply port 38.
The thermal spray material is injected into the plasma jet 52 and heated and melted to form a stream of thermal spray particles, which adhere to the surface of the substrate 48 in a planar manner and solidify to form a film 51.

In the plasma spraying as described above, a constant voltage direct current is applied to the electromagnetic coil 25 in the clockwise direction as viewed in the direction of the plasma jet 52 to generate a stationary magnetic field.
The magnetic field acts on the plasma jet 52. Then, the charged particles of electrons and ions in the plasma have a radius (Rama radius) corresponding to the plasma temperature and the magnetic flux density of the magnetic field.
Makes a spiral motion around the magnetic field lines, and does not move in the vertical direction of the magnetic field due to the magnetic field lines unless it collides with other particles. Therefore, the particles can be constrained by the magnetic field by making the radius of the Rama smaller than the mean free path indicating the degree of collision with other particles. as a result,
A plasma jet of a shape corresponding to the magnetic field configuration can be formed,
At the same time, the flow of the plasma jet can be controlled in the direction of the line of magnetic force.

In this case, depending on the arrangement of the electromagnetic coil 25 as described above and the direction of the current flowing therethrough, the plasma jet 52 can be deformed in a divergent shape (see FIG. 3A), or FIGS. As shown in (c), the second electromagnetic coil 2 is provided at a predetermined interval in front of the electromagnetic coil 25.
5 'is arranged, and a current in the opposite direction to the above-mentioned electromagnetic coil 25 is passed (in the case of FIG. 5B) or a current in the same direction is passed (in the case of FIG. 10C) to change the magnetic field configuration. , The plasma jet 52 depending on the respective magnetic field configuration
Can be changed.

On the other hand, the thermal spray material is heated and melted by the plasma jet 52 and accelerated. However, the flow of the thermal spray particles cannot be controlled by the magnetic field. For this reason, some of the spray particles may jump out of the plasma jet 52, but by selecting the arrangement of the electromagnetic coils 25 and 25 'having a magnetic field configuration that encompasses the entire flow of the spray particles, most of the spray particles Into the plasma jet 52. For this reason,
The film 51 can be formed more efficiently than conventional plasma spraying without applying a magnetic field.

As described above, when a stationary or time-varying magnetic field is applied to the plasma jet 52, the shape of the plasma jet 54 can be directly controlled. In the case of a steady magnetic field, the plasma jet 52 is used. Speed u
Traverses the magnetic field of the magnetic flux density B in the radial direction in the radial direction, a circumferential electromotive force u × B is generated, and a current is generated. In the case of a time-varying magnetic field, the electromotive force (-r
/ 2 × dBz / dt, where r is a distance in the radial direction from the plasma center axis, and dBz / dt is a change rate of the magnetic flux density Bz in the center axis direction at a position of the distance r.

When these currents flow into the plasma having electric resistance, Joule heating occurs, and the temperature of the electrons in the plasma rises. At the same time, collision with particles in other plasma becomes active, and ions and ions are generated. Excitation and ionization of neutral particles are promoted, and the whole plasma is reheated.

As described above, in the vacuum spraying method, the temperature of the plasma jet 52 injected into the vacuum vessel 21 decreases due to adiabatic expansion. However, the interaction with the magnetic field as described above reheats the entire plasma. By doing
The temperature drop due to adiabatic expansion can be compensated. As a result, it is possible to eliminate insufficient melting of the thermal spray material.

Further, the above-mentioned magnetic field acts on the plasma jet 52, but also acts on the arc column generated between the anode 31 and the cathode 32 at the same time. Since the magnetic force due to the magnetic field acts in the direction of the central axis of the arc column, the arc column contracts,
Reduce cross-sectional area (pinch effect of magnetic field). For this reason,
The potential gradient of the arc column increases and the torch voltage increases. As a result, the output of the plasma torch 26 can be increased without increasing the torch current, and the sprayed particles can be completely melted.

(Test Example 1) Using the apparatus described in the above embodiment, a film formation test was performed under the following specifications and conditions. Cathode (tungsten) φ8 mm Anode (copper) Inner diameter φ8 mm to φ12 mm Torch current 600 A Container pressure 13 kPa Electromagnetic coil Inner diameter 70 mm, length 157 mm, 1000 turns Maximum magnetic field density B = 0.84 T Magnetic field arrangement Applicable coil center axis 3 (a) Spreading type Working gas Argon (Other helium, nitrogen, and hydrogen can be used.) Gas flow rate 60 l / min Thermal spray material NiCrALY powder Feed rate 20 g / min Base material Light blasted Steel (SS400) 150 mm x 150 mm x 3.2 mm Spray distance 150 mm Spray time 30 seconds.

(Results of Test Example 1) (1) In order to know the effect of the magnetic field on the shape of the coating, the maximum magnetic field density B on the center axis of the electromagnetic coil is B = 0, B =
0.3T and B = 0.6T were changed.

FIGS. 4A to 4C show the shape of the film, and the intersection of the vertical line L and the horizontal line H indicates the center axis of the torch. From this result, it can be seen that the area of the film increases after the application of the magnetic field (B = 0.3T 0.6T) as compared to the case before the application of the magnetic field (B = 0). FIG.
(A) shows the film thickness distribution in the vertical line L direction, and FIG. 5 (b) shows the film thickness distribution in the horizontal line H direction.

In FIG. 5A, the thickness of the coating in the direction of the vertical line L shows a peak near the central axis and at a position 30 mm below the vertical line L passing through the central axis before the application of the magnetic field, and below the central axis. The part shows a larger value. However, after the application of the magnetic field, the peak of the film thickness moves to the center axis of the torch.

Therefore, before the application of the magnetic field, the flow of the plasma jet is slightly shifted to the central axis direction and the central axis due to the effect of the gas supplied from the upper part of the vertical line passing through the central axis. Although the direction is downward, the plasma moves along the magnetic field that spreads radially from the central axis after the application of the magnetic field, so that the flow of the plasma jet is also controlled only in the central axis direction.

As described above, by controlling the plasma jet by the magnetic field and widening the plasma jet,
The flow of the thermal spray particles is taken into the flow of the plasma, and an efficient film formation can be performed.

(2) When the output of the plasma torch is increased by increasing the plasma torch voltage due to the pinch effect of the magnetic field, the heat input from the plasma torch to the plasma jet also increases, and the thermal efficiency of the torch also increases. FIG. 6 shows current-voltage characteristics of the plasma torch at magnetic flux densities B = 0 and B = 0.6T. Before the application of the magnetic field, the torch voltage increases with an increase in the torch current. Even after the application of the magnetic field, the torch voltage similarly increases with an increase in the torch current, and shows a larger value as the magnetic flux density increases.

Test Example 2 The effect of heating by a magnetic field was examined under the following specifications and conditions. Cathode (tungsten) φ8 mm Anode Inner diameter φ6 mm to φ10 mm Torch current 300 A to 500 A Container pressure 2700 Pa Electromagnetic coil Inner diameter 103 mm, length 60 mm, 8 turns The coil current is pulse-shaped with a maximum value of IC _max = 24 kA in 3.5 ms after application. .

At this time, the maximum magnetic flux density B = 0. 84T Magnetic field configuration The configuration shown in FIG. 3 (c) Working gas argon.

(Results of Test Example 2) (1) FIG. 7 shows the central axis distribution of the emission intensity of the visible light of the plasma jet (proportional to the temperature and density of the plasma). After applying a magnetic field (IC _max = 24 kA), τ = 3.5 ms
I = 4 without applying a magnetic field that produces the same torch output as
50A is also shown. In the central axis distribution of the emission intensity before applying a magnetic field of I = 300 A, 40 mm, 65 mm
The light emission in the vicinity becomes strong, and a large shock wave is generated.
In the case of I = 450 A, similarly, a large collision wave is generated and the output is increased, but the emission intensity in the flow direction is almost the same. However, the emission intensity after application of a magnetic field of I = 300 A is about twice as high as that before the application of the magnetic field, and the distribution gradually decreases in the flow direction.
Heated uniformly in the flow direction.

[0043]

As described above, according to the present invention, the flow direction and spread shape of the plasma jet are controlled by selecting the magnetic field configuration so as to follow the flow of the thermal spray particles and take in the flow. Therefore, there is an effect that a film can be formed with good yield.

The above-mentioned magnetic field simultaneously serves to reheat the plasma jet and increase the capacity of the plasma torch, and also has the effect of promoting the melting of the thermal spray material.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an apparatus according to an embodiment.

FIG. 2 is an enlarged sectional view of a plasma torch part according to the first embodiment;

FIGS. 3A to 3C are conceptual diagrams showing a relationship between a magnetic field configuration and a shape of a plasma jet.

FIGS. 4A to 4C are front views of a film shape.

FIG. 5 (a) A vertical thickness distribution diagram of a coating (b) A horizontal thickness distribution diagram of a coating

FIG. 6 is a diagram showing a current-voltage characteristic of a plasma torch.

FIG. 7 is an emission intensity distribution diagram of a plasma jet.

FIG. 8 is a conceptual diagram of a conventional plasma torch.

[Explanation of symbols]

 Reference Signs List 20 leg stand 21 vacuum vessel 22 adjusting leg 23 base 24 winding frame 25, 25 'electromagnetic coil 26 plasma torch 27 outer cylinder 28 insulator 29 inner cylinder 30 opening 31 anode 32 cathode 33 center hole 34 nozzle 35 working gas supply port 36 Supply passage 37 Nozzle member 38 Supply port 39 Cooling water passage 40 Annular cooling water passage 41 Cooling water supply passage 42 Cooling water discharge passage 43 DC power supply 44 DC power supply 45 Working gas 46 Cooling water 47 Robot 48 Sprayed substrate 49 Decompression Exhaust port 50 Viewing window 51 Coating 52 Plasma jet

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akira Omori 7-1-8 Doimachi, Amagasaki City Inside Kinki High Energy Processing Technology Research Institute (72) Inventor Noritaka Eguchi 7-1 Doimachi, Amagasaki City Address 8 Kinki High Energy Processing Technology Laboratory

Claims (3)

[Claims] 1. A powdery thermal spray material is fed to a plasma jet generated by a plasma torch, and the thermal spray material is heated and melted by the plasma jet and accelerated to form a flow of thermal spray particles. In the plasma spraying method in which a film is formed by spraying the surface of the material, a magnetic field is applied to the plasma jet by an electromagnetic coil installed coaxially on the outer periphery of the plasma torch, and the flow of the spray particles according to the magnetic field configuration of the magnetic field. Spraying by a magnetic field control plasma, wherein the plasma jet is controlled so as to be taken into the plasma jet. 2. The method according to claim 1, wherein the plasma generated by the plasma torch is reheated by operating the magnetic field constantly or by changing the magnetic field over time. Spraying method using magnetic field controlled plasma. 3. The plasma torch according to claim 1, wherein the magnetic field also acts on an arc column generated between the anode and the cathode of the plasma torch, thereby increasing the torch voltage and thereby increasing the output of the plasma torch. 3. A thermal spraying method using the magnetic field controlled plasma according to 1 or 2.