JPH04280954A - Method and apparatus for plasma thermal spraying and thermal sprayed film obtained with this method - Google Patents

Abstract

PURPOSE:To improve closeness, stickness and uniformity of a thermal sprayed film on the surface of a base material by arranging an atomizer closed to the outlet of a plasma torch in a plasma thermal spraying apparatus. CONSTITUTION:Directing toward the passage 11 of plasma flame 10 in a plasma thermal spraying apparatus, one or more of two fluids-nozzles 12 which supply water and air are set crossing each other and by supplying plasma gas from a gas inlet 1a of the plasma torch 1, high temp. gas of 1000 deg.C is generated and a thermal spraying material of metal or ceramic, etc., is supplied to this high temp. gas from a material-supplying nozzle 1c to form a large quantity of drips 6. Atomized water drips from the two-fluids nozzle 12 are collided against the plasma flame 10 and the excess part at the tip part of the plasma flame 10 is separated and the plasma flame is collided against a base material 14 without lowering speed and temp. of the drips 6 to form the fine thermal spraying film 15 having uniform thickness is formed with excellent adhesive strength.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a plasma spraying method and apparatus for obtaining a sprayed coating that requires high functionality such as wear resistance, corrosion resistance, or ceramic solid electrolyte, and a sprayed coating obtained by the method. .

0002

2. Description of the Related Art As shown in FIG. 5, a conventional invention of this type supplies thermal spraying material 26 in the form of powder to a portion of a plasma torch 21 near an anode 23 through a material supply nozzle 25 to form high-temperature fine droplets. 27, this is transported and accelerated by the plasma flame 24 ejected from the outlet 28 of the plasma torch 21, and the droplets 27 are made to collide with the base material 29 disposed at the front of the plasma flame 24, so that the droplets 27 are deposited on the surface of the base material. A sprayed film 30 of the sprayed material is formed.

At this time, the plasma flame 24 attracts the surrounding air 31 in the space from the outlet of the plasma torch 21 to the base material, and the plasma flame 24 expands into the shape shown in the figure, and the droplets in it are expanded. The thermal history of the droplet 27 varies widely depending on its path, and the speed at which the droplet collides with the base material 29 decreases, which impairs the uniformity of the sprayed film 30 formed on the surface of the base material 29. Decrease its density.

In order to improve this problem, as shown in FIG. 6, the length from the tip 32 of the cathode 22 of the plasma torch 21 to the anode point 33 of the anode 23 is made longer than that in FIG. At the same time, an annular gas passage 35 is provided outside the plasma gas passage 34 around the cathode 22 concentrically therewith, and a passage 37 in the tangential direction is formed in the annular wall 36 between the two gas passages 34 and 35. , the plasma gas 39 introduced from the plasma gas inlet 38 is swirled in the plasma gas passage 34 around the cathode 22 and flows toward the outlet 28, and this gas is generated between the cathode tip 32 and the anode point 33. There are plasma spray devices that use a long arc 20 to heat the plasma flame sufficiently to form an elongated plasma flame 24 and improve the focusing and stability of the beam of droplets 27 contained therein.

However, if the length L6 of the plasma flame 24 is made sufficiently longer than L5 in this manner, when droplets of thermal spray material collide with the base material 29, the plasma flame conveying them also collides with the base material. As a result, the base material 29 may be overheated by the plasma flame, and the material of the base material 29 may be damaged.

In order to prevent the base material from being damaged by the elongated plasma flame 24, the base material 29 is placed far away from the outlet 28 of the plasma torch 21 in the plasma flame 24, and the plasma flame 24 is connected to the plasma torch. It is conceivable to cool down the temperature of the droplet 27 with air between the outlet 28 and the base material 29, but this would reduce the speed of the droplet 27 when it collides with the base material, and also cause the droplet 27 to Decreases the density and adhesion of the sprayed film formed by cooling. That is, preventing damage to the base material and improving the performance of the sprayed film require contradictory conditions regarding the magnitudes of the distances L5 and L6, and it is difficult to achieve both.

Therefore, as shown in FIG.
Some of the co-inventors of this application invented a plasma separation device 42 of a type that crosses the
(Refer to No. 78) There is a method in which the distance L8 between the outlet 28 of the plasma torch and the base material 29 is made shorter than the conventional one to prevent the base material 29 from being damaged by the heat of the plasma flame 24. As the capacity increases, plasma separation becomes difficult, and if a large amount of gas flow 41 is ejected, the flow direction of the plasma flame 24 becomes unstable, and the performance of the sprayed film formed on the surface of the base material 29 deteriorates. , problems such as burning out of the base material 29 occur.

When the plasma spraying apparatus shown in FIG. 8 is operated properly with a small capacity, the plasma torch 21 shown in FIGS. 5, 6, and 7 is composed of one torch. is the main torch 21a and some sub-torches 2
1b.

The cathode 22 of the main torch 21a and each sub-torch 2
Power sources 43 and 44 are connected between the anode electrode 23b of 1b and an arc 20 is generated between the tips of both electrodes 22 and 23b, thereby heating the plasma gas flowing therethrough,
This forms a plasma flame 24.

Further, a plurality of nozzles 42 for ejecting a gas flow 41 are provided around the exit of the plasma torch 21, and the gas flow ejected from the nozzles 42 intersects with the plasma flame 24 to cool the plasma. After separation, the remaining droplets 27 collide with the base material 29 to form a sprayed film 30.

[0011]

[Problems to be Solved by the Invention] An object of the present invention is to reduce the distance between the material feed position of the plasma torch and the base material even if the distance between the material feeding position of the plasma torch and the base material is further shortened than when using the plasma separation device using the gas flow. The aim is to further improve the quality of the sprayed film, such as its density, while also preventing damage to the sprayed film.

Another object of the present invention is to further increase the velocity of the plasma flame ejected from the outlet of the plasma torch when it impinges on the base material, compared to that achieved by the gas flow.

Another object of the present invention is to solve problems such as deterioration in the performance of sprayed films due to generation of fumes in ordinary plasma spraying.

[0014]

[Means for Solving the Problems] The present invention includes disposing at least one atomizer around a plasma flame generation area near the exit of a plasma torch, and making the ejection direction of the atomizer intersect with the ejection direction of the plasma flame, Separate the plasma from the plasma flame,
The present invention relates to a plasma spraying method and apparatus for colliding droplets of sprayed material remaining at that time with the surface of a base material to form a sprayed film thereon, and a sprayed film obtained by this spraying method.

[0015]

[Operation] The plasma flame near the exit of the plasma torch is mixed with the spray ejected from the atomizer installed around that part, and the part near the outer periphery of the plasma flame is efficiently heated by the spray and the heat of vaporization of the liquid. The plasma is separated from the plasma flame by cooling the plasma to a temperature of 100°C to extinguish the plasma.

[0016] Furthermore, the velocity of the droplets colliding with the base material placed immediately after the intersection point of the plasma flame and the spray can be reduced without reducing the velocity near the exit of the plasma torch, and the sprayed material at the exit can be reduced. To make a droplet collide with a base material in a state where the temperature of the droplet is maintained at a high temperature without substantially lowering it and in a state without fumes.

Furthermore, when the liquid being sprayed vaporizes, it instantaneously expands violently and is ejected in the flow direction of the plasma flame, accelerating the droplets and causing them to collide with the base material at the same flow rate.

[0018]

[Embodiment] An embodiment of the present invention will be explained based on the attached drawings.The axial direction of the cathode 2 of the main torch 1 and the axial direction of the anode 4 of one or more sub-torches 3 are provided so as to intersect with each other. , the voltages of the power supplies 16 and 17 are applied between the cathode 2 and the outer cylinder of the main torch by closing a starting switch (not shown) to start the main torch. Then, a starting arc (not shown) is formed, which heats the main plasma gas, which becomes a plasma flame and is emitted from the tip of the main outer cylinder toward the outside of the torch. Next, a starting switch (not shown) is closed between the anode 4 and the outer cylinder of the sub-torch 43, a voltage is applied, and a sub-torch starting arc (not shown) is generated, and the tip of the outer cylinder of the sub-torch is emitted. Plasma spews out from the exit. In this way, both plasmas having conductivity cross each other, and a conductive path is formed by the plasma gas from the tip of the cathode 2 to the tip of the anode 4. In this state, turn off both start switches,
A voltage is applied between the electrodes 2 and 4 by power sources 16 and 17 to form a steady hairpin arc 5 from the cathode 2 to the anode 4.

Oxygen, air, argon, or nitrogen gas-based plasma gas is supplied from the gas inlet 1a of the main torch 1 through the swirl flow generator 18 to generate a high-temperature gas of 10,000° C. or more. A thermal spray material such as metal or ceramic is supplied into the high-temperature gas from the material supply nozzle 1c to instantaneously form countless droplets 6.

Toward the passage 11 of the plasma flame 10 near the outlet 8 of the jacket 7 of the plasma flame 10,
One or more two-fluid nozzles 12 of an atomizer that supply water 12a and air 12b are arranged so as to intersect with each other, and the spray of water droplets from the two-fluid nozzles 12 is applied to the plasma flame 10. The excess portion is separated and the droplet 6 is made to collide with the base material 14 without reducing its speed and temperature to form a sprayed film 15 of uniform thickness.

Further, in this embodiment, two nozzles 12 are used.
Although a fluid nozzle was used, a one-fluid nozzle could be used. Further, the shape of the spray may be any shape such as a cone or a fan shape, if necessary. Water is suitable as the liquid to be sprayed, considering its latent heat of evaporation, ease of handling, and no release of harmful substances, but other fluids may be used as necessary.

Furthermore, in the above embodiment, when the plasma flame 10 is operated at 100 kW without water spraying, the length of the plasma flame 10 extends 150 mm forward from the outlet 8 of the plasma generator, as shown by the chain line 10a in FIG. During this period, the temperature of the plasma flame 10a is 20
00° to 3000° C., and if the base material 14 is placed during thermal spraying, cracks will occur in the base material 14 and the sprayed film 15, making the sprayed film 15 unusable.

In order to prevent cracks from occurring, it is necessary to move the base material 14 away from the position indicated by the chain line 14a. In this way, high-performance thermal spraying can be achieved by lowering the speed and temperature of the droplets. Unable to obtain membrane.

Next, in this embodiment, when water is sprayed by the atomizer, the plasma flame 10 becomes as shown in FIGS. 3 and 4.
It is cut to form a conical shape as shown by the solid line 10b. This conical plasma flame 10 acts as a tunnel-like jacket that minimizes the cooling of the droplets 6 of molten spray material, reducing the excess heat load on the base material 14 and the spray coating 15 from the water sprayed by the atomizer. It is possible to remove the heat of vaporization in advance and prevent the adverse effects of the heat load.

[0025] Also, along with the explosive expansion of water at this time,
The gas is rapidly injected along with the plasma gas, accelerating the droplets 6, thereby forming a dense sprayed film.

Next, an experimental example based on this embodiment is as follows. Air pressure 3kg from atomizer nozzle 12
Water with a maximum water jetting amount of 200 cc/min at f/cm2 is jetted 15 mm downstream from the outlet 8 of the plasma flame 10, and the porous ceramic base material 10 is jetted from the outlet 8 of the torch.
When the temperature was measured at a spraying distance of 40 mm by attaching a CA thermocouple to the base material while spraying, the temperature of the base material 14 was 250 to 300°C. This temperature is a temperature at which the base material 14 can sufficiently withstand heat.

[0027] Furthermore, the nitrogen gas permeability, which indicates the density of the YSZ sprayed film sprayed by this method, was 7 x 10-7 cm.
4/gs, and this density is 10 times that of the YSZ sprayed film obtained by conventional atmospheric pressure plasma spraying, and this value is higher than that of the YSZ sprayed film obtained by the reduced pressure plasma spraying method, which requires advanced equipment. This corresponds to the denseness of the membrane.

Furthermore, Cr2O3 (10-44μm) used as a wear-resistant film by the method of this example
When thermal spraying was carried out, Cr2O3 easily sublimed and a large amount of fume was generated in normal thermal spraying, which not only spoiled the appearance of the product but also became incorporated into the sprayed film and significantly reduced the performance of the sprayed film. However, according to the present invention, there is no fume generation, so extremely high performance Cr2
It became possible to form a sprayed film of O3.

Although the present invention has been described above based on the embodiments shown in the accompanying drawings, the present invention is not limited to these embodiments, and may be implemented with partial changes and additions within the gist of the present invention. It is possible to do so.

For example, the position of the two-fluid nozzle 12 of the atomizer is set as shown in FIG.
Although it is preferable that it be inside the mantle 7 as shown in FIG. 7, it may be outside if the purpose is to separate the plasma flame.

When the present invention is carried out using a torch such as that shown in FIGS. 7 and 6, the material nozzle 26 and By installing the atomizer nozzle 12 between the base materials 29, a plasma separation effect can be obtained.

Furthermore, the inner surfaces of the main torch and the sub-torch can be made into a double structure, and water or the like can be circulated inside to cool each torch.

[0033]

As described above, the present invention prevents the base material from being damaged by the high heat of the plasma flame, and can provide a sprayed film with high performance in terms of density, adhesion, and uniformity. Furthermore, the performance of the sprayed film is not degraded by fumes generated during plasma spraying.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing an example of a plasma spraying method, an apparatus therefor, and a sprayed film using the method of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG. 1;

FIG. 3 is a schematic diagram of main parts of the embodiment of FIG. 1;

FIG. 4 is a right side view of FIG. 3;

FIG. 5 is a longitudinal cross-sectional view of the prior art.

FIG. 6 is a longitudinal cross-sectional view of another prior art.

FIG. 7 is a sectional view taken along line VIII-VIII in FIG. 7;

FIG. 8 is a longitudinal cross-sectional view of still another conventional technique.

9 is a sectional view taken along line VIII-VIII in FIG. 8; FIG.

[Explanation of symbols]

1 Plasma torch 1a Gas inlet 1c Material supply nozzle 2 Cathode 3 Deputy torch 4 Anode 5 Arc 6 Droplets 7. Cloak 8 Exit 10 Plasma flame 11 Passage 12 Two-fluid nozzle 14 Base material 15　Thermal spray coating

Claims (3)

[Claims] 1. A plasma spraying method characterized by causing spray from an atomizer to cross toward a plasma flame near the exit of a plasma torch. 2. A plasma spraying apparatus characterized in that an atomizer nozzle is disposed toward and intersects with the path of the plasma flame near the exit of the plasma torch. 3. Thermal spraying is obtained by causing spray from an atomizer to cross toward a plasma flame near the exit of a plasma torch, and forming the spray on a base material located downstream of the crossing portion of the plasma flame. film