JPH05339699A - Plasma thermal spraying method - Google Patents

Abstract

PURPOSE:To form a densely thermally sprayed film by increasing the temp. of the liquid drops of a thermal spraying material coexisting in the plasma flame ejected from a plasma torch to a high temp. and increasing the flow velocity thereof. CONSTITUTION:Carbon dioxide, oxygen or air 6 is supplied to an arc 15 generated between cathode 3 and anode 4 of a double torch type plasma thermal spraying device to form the plasma flame 23 and the powdery thermal spraying material 20 is supplied to this plasma flame 23, by which this material is fluidized together with this plasma flame 23 and is melted therebetween. The temp. thereof is thus increased and the speed is increased to bring the melt thereof into collision against a base material 25 for thermal spraying.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a plasma spraying method for forming a sprayed film of metal, ceramics or the like on a surface of a general machine tool with high precision.

[0002]

2. Description of the Related Art In a conventional plasma spraying method, a direct current high voltage is applied between a cathode and an anode of a plasma torch to form an arc therebetween, and an arc is ejected from around the cathode toward an outlet of the plasma torch. The arc is joined with a plasma gas such as argon to form a plasma flame there, and a powdered thermal spray material such as tungsten is supplied into the plasma flame, and while moving along with the flow of the plasma flame. A method of forming a sprayed film on the surface of a spray base material such as the general mechanical instrument by melting the melted plasma gas with high heat into a droplet state.

In this thermal spraying method, argon gas is used as the plasma gas as described above in consideration of protection of the electrode of the plasma torch and easy availability.
Due to the characteristics of this gas, its mass and thermal conductivity are determined, so the momentum, which is the product of the flow velocity and mass in the plasma flame due to the aforementioned argon gas, and the high heat of the plasma in the plasma flame is transferred to the thermal spray material. There is naturally a limit to the amount of heat that can be used.

Therefore, the speed at which the spray material carried by the plasma flame collides with the base material and the temperature of the droplets are also determined by the nature of the argon gas, and the sprayed film formed by the deposition of droplets on the surface of the base material. It is difficult to improve the compactness of the product above a certain limit.

When carbon dioxide is used as the plasma gas,
Due to their properties, it can be expected that the plasma flame will be faster and the temperature will be higher, but it is easy to damage the electrode by accelerating oxidation.
Cannot be used for a long time.

When nitrogen is used, the electrode is less likely to be damaged for the above-mentioned reason, but the specific gravity of the gas is 0.967 at 1 atmospheric pressure and the thermal conductivity at 1000 ° C. is 7.4. Therefore, it is impossible to improve the compactness of the sprayed film to a much greater extent than when argon is used, as compared with the cases where the argon gases are 1.380 and 5.0, respectively.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a thermal spraying method for making the internal structure of the thermal spray coating on the surface of the base material denser than that obtained by the conventional thermal spraying method using a plasma torch. That is.

Another object is to extend the arc to obtain a high voltage and a low current, prevent the electrodes from being worn, and to withstand long-term use.

Another object is to increase the momentum of the plasma flame ejected from the plasma torch toward the base material to increase the flow velocity of the droplets of the spray material, and to reduce the amount of heat of the plasma in powder spraying. It is to achieve high temperature by conducting the material with high thermal conductivity.

[0010]

SUMMARY OF THE INVENTION The thermal spraying method of the present invention ejects a protective gas from around the cathode of a main plasma torch through its outlet to generate an arc between the cathode and the auxiliary plasma torch. That is, the carbon dioxide gas and the powder-form thermal spray material are supplied toward the cathode side in FIG.

[0011]

The protective gas is ejected from the periphery of the cathode of the main plasma torch toward the outlet, and the cathode is protected. A high-voltage DC power supply is connected between the cathode of the plasma torch and the anode of the sub-plasma torch, and an arc is provided between them. To occur.

Carbon dioxide having a relatively large specific gravity is supplied toward the cathode side of the arc to form a plasma flame flowing at a high speed, and a powdery spray material is supplied into the plasma flame to flow at a high speed. While flowing, the powder thermal spray material is melted by the heat of the plasma to form innumerable droplets.

The high-speed droplets thus formed are collided with the surface of the liquid spray base material at high speed to be deposited, and a sprayed film layer having a dense internal structure is formed thereon.

[0014]

1 and 2, a hairpin-shaped arc 17 is formed between a main torch 1 and a sub-torch 2 of a composite type plasma torch, and a plasma gas is formed on the main torch 1 as a plasma gas. This is a thermal spraying method in which carbon dioxide is supplied to form a plasma flame 21, and the thermal spray material 20 supplied into the plasma flame 21 is made into droplets and speeded up to collide with the thermal spray base material to form a coating 24. ..

The main torch 1 of the composite plasma apparatus concentrically surrounds the main cathode 4 with the main cathode 4 forming the emission port 4a and the main space 4b with an insulator 27, and the main plasma 4 is enclosed in the main outer jacket 4. As shown in FIG. 2, the inlet 5 is formed in a cutting line direction with respect to the periphery of the main cathode 3, and from this, argon gas is supplied as the primary plasma gas 6 to the main space 4b to narrow the outside of the main jacket 4. A second main mantle 31 forming the mouth 31a and an insulator 29 are concentrically surrounded by a second main space 31b.
A main second plasma gas inlet 32 is formed in the main second outer jacket 31 in a cutting line direction with respect to the periphery of the main outer jacket 4, and a carbon dioxide gas 33 is supplied as a secondary plasma gas into the second main space 31b from here. To do.

Further, the sub-torch 2 surrounds the sub-torch starting electrode 9, and a sub-first outer jacket 10 having an emission port 10a is attached by an insulator 28 so as to be concentric with the sub-torch starting electrode 9, and further. Argon gas is fed from the sub gas inlet 11 as the sub plasma gas 12.

Further, the sub second outer jacket 36 is attached by an insulator 30 so as to be concentric with the sub outer jacket 10, and an argon gas is supplied as a sub secondary plasma gas 38 through a sub second plasma gas inlet 37. Sent in.

The negative terminal of the main power source 7 is connected to the main cathode 3, and the positive terminals thereof have switching means 8 and 3, respectively.
It is connected to the main outer jacket 4 and the main second outer jacket 31 via 4.

The positive terminal of the sub power source 13 is connected to the positive terminal of the main power source 7 and the sub mantle 10 of the sub torch 2, and the negative terminal of the sub power source 13 is connected to the sub torch starting electrode 9 via the switch means 14. It is connected.

The torches shown in FIGS. 1 and 2 are activated in the following order. That is, the switch 8 is closed and the main power source 7 is used to discharge the main cathode 3 and the discharge port 4a of the main jacket 4.
The main starting arc 15 is first formed between the two, and the argon gas as the primary plasma gas 6 is heated by this, so that the conductive plasma emitted from the emission port 4a of the main outer jacket 4 is constricted in the second main outer jacket 31. It is discharged from the main torch 1 through the mouth 31a.

At this time, if the switch means 34 is closed and then the switch means 8 is opened, the main starting arc 15 is extinguished through the plasma which has already been formed, and at the same time the arc emitted from the tip of the main cathode 3 is removed. , The main second mantle start arc 35 is formed, whereby the argon gas supplied as the primary plasma 6 and the carbon dioxide gas supplied as the secondary plasma gas 33 are heated, and due to the characteristics of the carbon dioxide gas. The plasma flame 23 having both high density and high thermal conductivity is emitted to the outside of the main torch 1.

Next, the switch means 14 is closed and the sub power source 1
When a sub-starting arc 16 is formed between the sub-mantle 10 and the sub-torch starting electrode 9 by 3, the sub-plasma gas 12 is heated by this arc and the discharge port 10a of the sub-mantle 10 is formed.
The conductive plasma is further formed, and the conductive plasma is further emitted to the outside of the sub-torch 2 through the narrowed opening 36a at the tip of the sub-second outer jacket 36.

When these processes are completed, the main torch 1 and the sub torch 2 are installed so that their central axes intersect, so that the conductive plasma emitted from each of them forms a conductive path, At this stage, switch 3
When 4 and 14 are opened, a steady hairpin arc 17 is formed from the tip of the main cathode 3 toward the outer surface of the discharge port 10a of the sub-mantle 10 by the main power source 7, and the amount of gas fed into the main torch 1 at this time. By adjusting the amount of gas fed into the sub-torch 2 respectively, a plasma flame 23 is formed which is substantially concentric with the central axis of the main torch 1 as shown in FIG.

The coating material 20 fed toward the plasma flame 23 from the material feed pipe 19 is immediately heated to a high temperature by the plasma 18 having a high enthalpy at a high temperature and melted to form a droplet 21 of the molten coating material. As shown above, while entrained in the plasma flame 23 having high density and high thermal conductivity as described above, it advances toward the base material 25 without spreading much. In the meantime, the droplets are accelerated by the plasma gas having a large density and are heated to a high temperature by the large thermal conductivity. In this way, the plasma flame 23 containing the droplets 21 of the molten coating material is formed on the frame jacket 26,
Also, the plasma separation means 2 provided immediately before the base material 25
Due to 2, the plasma 18 alone is separated, and immediately after that, the molten droplets 21 of the high-temperature coating material collide with the base material at a high speed to form the coating 24 densely.

The plasma spraying method using the hybrid plasma torch shown in FIGS. 1 and 2 has been described above. However, the present invention is not limited to this, and the hybrid plasma torch shown in FIGS. It is also possible to carry out by using.

In FIG. 3, an insulator 27 having a main gas inlet 5 of the same diameter and the same diameter as the center axis of the main cathode 3, a main jacket 4 having a discharge port 4a, and a main second gas inlet 32 are shown. Second outer sheath 3 having an insulator 29 provided with a stenosis and a narrowed opening 31a
A main torch 1 is constituted by 1.

At this time, as shown in FIG. 4, the main plasma gas 6 or the main second gas 33 is first introduced into the gas annular chamber 48 from the main gas inlet 5 or the main second gas inlet 32. It is sent through one swirl flow forming hole 49 or a plurality of swirl flow forming holes 49 arranged in equal parts so as to swirl the inner wall 50 of the insulator 27 or the insulator 29 as shown by an arrow 51. It

Next, the sub-torch starting electrode 9 arranged so as to intersect with the central axis of the main torch 1 has the insulator 28 and the sub-first outer jacket 10 having the emission port 10a in order so as to be concentric.
An insulator 2 which is attached by an insulator 30 and a secondary second jacket 36, and which further has a swirling gas forming means 47 of FIG. 4 similar to the insulator 27 or the insulator 29 of the main torch 1.
The sub gas 12 is fed from the sub gas inlet 11 provided in the No. 8, and the sub second gas 38 is fed through the sub second gas inlet 37 provided in the insulator 30. There is.

The negative terminal of the main power supply 7 is the main cathode 3.
, And the positive terminals are connected to the main outer jacket 4 and the main second outer jacket 31 via the switch means 8 and 34, respectively, and these constitute the main torch 1 as a whole.

The positive terminal of the sub power source 13 is connected to the positive terminal of the main power source 7 and the sub mantle 10 of the sub torch 2, and the negative terminal of the sub power source 13 is connected to the sub torch starting electrode 9 via the switch means 14. They are connected, and these form the sub-torch 2 as a whole.

The torches shown in FIG. 3 are activated in the following order. That is, the switch 8 is closed, and the main power source 7 first forms the main starting arc 15 between the main cathode 3 and the emission port 4a of the main jacket 4, whereby the main plasma gas 6 is heated and the main jacket 4 of the main jacket 4 is heated. The conductive plasma is discharged from the main torch 1 from the discharge port 4a through the narrowed opening 31a of the main second outer jacket 31.

At this time, when the switch means 34 is closed and then the switch means 8 is opened, the main starting arc 15 is extinguished via the plasma 18 already formed, and at the same time, it is emitted from the tip of the main cathode 3. The arc forms a main second mantle activation arc 35, which heats the main plasma gas 6 and the main second gas 33, and the plasma flame 23 is emitted to the outside of the main torch 1.

Next, the switch means 14 is closed and the sub power source 1
When a sub-starting arc 16 is formed between the sub-mantle 10 and the sub-torch starting electrode 9 by 3, the sub-gas 12 is heated by this arc and a conductive plasma 18a is formed from the discharge port 10a of the sub-mantle 10. This further causes the conductive plasma 18a to be emitted to the outside of the sub torch 2 through the narrowed opening 36a at the tip of the sub second outer jacket 36.

When these processes are completed, the main torch 1 and the sub-torch 2 are installed so that their central axes intersect, as described above, so that the conductive plasmas 18 and 18a emitted from the respective torches 1 and 2 are generated. Form a conductive path.

At this stage, the switches 34 and 14 are
When is opened, a steady hairpin arc 17 is formed from the tip of the main cathode 3 toward the outer surface of the emission port 10a of the sub-mantle 10 by the main power supply 7.

At this time, by adjusting the amount of gas fed into the main torch 1 and the amount of gas fed into the auxiliary torch 2, respectively, as shown in FIG. A plasma flame 23 is formed which is substantially concentric with.

At this time, as shown in FIG. 1, the auxiliary torch 2
The tip of the sub-torch starting electrode 9 is located in front of the emission port 10a of the sub-first outer jacket 10 and the anode point is the inner wall of the emission port 10a. Since the auxiliary starting arc 16 is located near the exit surface of the discharge port 10a, the anode point of the sub-starting arc 16 is formed on the exit surface of the discharging port 10a of the sub-first outer jacket 10, and the sub-starting arc 16 of the sub-torch 2 moves. Compared to the one in Fig. 1 from the outlet,
The steady hairpin arc 17 can be easily formed.

Further, by providing means for supplying gas so as to form a strong swirling flow around the arc 18a of the auxiliary torch 2, the arc 18a is maintained at the axial center position of the torch 2 and is concentrically swirled. To form
The heat load exerted on the discharge port 10a of the sub-mantle 10 of the sub-torch 2 and the inner wall of the constriction port 36a of the sub-second mantle 36 is uniformly reduced, and is not locally damaged by the arc 18a. Stable operation is possible without it.

A plasma flame 23 is fed from the material feeding pipe 19 shown in FIG.
The coating material 20 fed toward the surface is immediately heated to a high temperature by the plasma 18 having a high enthalpy at a high temperature to be melted, and is entrained in the plasma flame 23 as shown in the molten coating material 21, but does not spread so much. Base material 25
Proceed toward.

Plasma flame 2 containing this molten coating material 21
3 is a plasma separating means 2 provided immediately before the base material 25.
Due to 2, the plasma 18 alone is separated, and the coating material 21 melted immediately thereafter collides with the base material 25 to form the coating 24.

At this time, by providing means for supplying gas so as to form a strong swirling flow around the arc column, the arc column is maintained at the axial center position of the torch and the swirling annular gas sheath is formed concentrically. In the turbulent flow range that could not be achieved by the conventional composite torch type plasma spraying device that forms the plasma flame 23, the plasma flame 23 is squeezed to a high density and can be sprayed in a stable and extended state. However, since the base material 25 is sprayed at a high speed, a high quality coating 24 can be obtained with high efficiency.

FIG. 5 shows a plurality of auxiliary torches 2 which are radially provided on the central axis of the main torch 1 at equal angular intervals in the embodiment of FIGS. 3 and 4, and are shown in FIG. Portions denoted by the same reference numerals as those in FIGS. 3 and 4 have the same names and functions.

Two examples of the case where CO ₂ is fed as the second plasma gas from the main second gas inlet 33 using the composite type plasma spraying apparatus shown in FIG. 5 are shown below.

First Example As an example of the plasma spraying method in which sufficient acceleration is required by heating the sprayed particles 21, a thermal spraying material 20 such as WC-12% Co which is likely to be thermally decomposed in the atmosphere / high temperature region, The thermal spraying was performed under the low enthalpy thermal spraying conditions shown in Table 1.

[0045]

[Table 1]

Further, as the material property, fine granulated powder of primary particles which is easily thermally decomposed in plasma was used. As a result, in the case where CO ₂ is used as the plasma gas 33, as compared with the case where the conventional nitrogen is used, the film 24 is formed as shown in Table 2.
The hardness was significantly improved, and the wear resistance was also extremely good from the results of the aggressive wear test according to JIS-H-8615 shown in FIG.

[0047]

[Table 2]

The high quality coating properties obtained by CO ₂ plasma spraying in this way are due to the sufficient acceleration of the spray particles 21. 7 and 8
And from the X-ray diffraction results of FIG. 9, CO with a high gas density
_{2. It} can also be seen from the fact that the decomposition of WC is suppressed in the order of air and nitrogen, that is, in the order of increasing gas velocity.

Second Example As an example of the plasma spraying method required to accelerate and heat the sprayed particles 21, a Cr ₂ O ₃ sprayed material was sprayed under the spraying conditions shown in Table 3.

[0050]

[Table 3]

As a result, in the case of using CO ₂ as the plasma gas 33, the hardness of the film is greatly improved as shown in Table 4 as compared with the case of using conventional oxygen, air or nitrogen. As for wear resistance, JIS-H- shown in FIG.
The result of the abrasive wear test according to 8615 was good.

[0052]

[Table 4]

As described above, high quality coating characteristics were obtained by CO ₂ plasma spraying because CO ₂ has a good heat transfer property in a high temperature range and a thermal pinch effect is promoted to increase heat concentration and thus thermal spraying. This is because the particles 21 are sufficiently heated and accelerated. The fact that the spray particles 21 are sufficiently heated means that the spray efficiency when CO ₂ is used as the plasma gas 33 under the spray conditions of Table 3 is about 50 as compared with the conventional one using oxygen, air or nitrogen. You can also see from the improvement.

[0054]

Since the present invention is as described above, it is possible to make the internal structure of the sprayed film formed on the surface of the base material denser than that of the conventional method.

Further, by extending the arc, a high voltage and a low current can be obtained, and it is possible to prevent the tip portion of the electrode from being worn and endure the use for the front period.

In particular, by supplying carbon dioxide gas to the main torch, the momentum of the plasma flame is increased by utilizing the characteristics of the gas, that is, the high density and the high thermal conductivity, and the droplets of the sprayed material are increased. It is possible to achieve both high speed of flow velocity and high heat quantity of plasma with high heat conductivity.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a plasma spraying method of the present invention.

FIG. 2 is a cross-sectional view taken along the line II-II in FIG.

FIG. 3 is a vertical cross-sectional view of another embodiment.

FIG. 4 is a sectional view taken along line IV-IV in FIG.

FIG. 5 is a vertical cross-sectional view of still another embodiment.

FIG. 6 is a diagram showing the results of an abrasive wear test of a WC-12% Co sprayed coating.

FIG. 7 is a diagram showing an X-ray diffraction result of a WC-12% Co sprayed coating.

FIG. 8 is another diagram showing an X-ray diffraction result of the WC-12% Co sprayed coating.

FIG. 9 is another diagram showing an X-ray diffraction result of the WC-12% Co sprayed coating.

FIG. 10 is a diagram showing the results of an abrasive wear test of a Cr ₂ O ₃ sprayed coating.

[Explanation of symbols]

 1 Main Torch 2 Sub Torch 3 Main Cathode 4 Main Outer Cap 4a Outlet 4b Main Space 5 Main Gas Inlet 6 Main Plasma Gas 7 Main Power Supply 8 Switch Means 9 Sub Torch Starter Electrode 10 Sub Outer 10a Outlet 11 Sub Gas Inlet 12 Sub-plasma gas 13 Sub-power supply 14 Switch means 15 Main starting arc 16 Sub-starting arc 17 Steady hairpin arc 18 Plasma 19 Material feed tube 20 Coating material 21 Molten coating material droplet 22 Plasma separation means 23 Plasma flame 24 Coating 25 Base material 26 Frame Outer 27 Insulator 28 Insulator 29 Insulator 30 Insulator 31 Main Second Outer Coat 32 Main Second Gas Inlet 33 Main Second Gas 34 Switch Means 35 Main Second Outer Start Arc 36 Sub Second Outer 37 37 Sub Second Second gas inlet 38 Secondary second gas 39 Swirling flow gas forming means 40 Gas annular chamber 41 Swirling Forming hole 42 inner wall 43 arrow

Claims (4)

[Claims] 1. A plasma spraying method, wherein carbon dioxide, oxygen or air is used as the plasma gas of the plasma spraying torch. 2. An arc is generated between the cathode of the main torch and the anode of the sub-torch of the composite plasma spray torch, carbon dioxide is supplied to the main torch as plasma gas, and the gas is directed outward from the outlet of the main torch. To eject the plasma flame concentrically with the central axis of the main torch, and to supply the plasma flame with a powdered spray material, which is melted by the plasma flame to raise the temperature and speed, and collides with the spray base material. A plasma spraying method comprising: 3. An arc is generated between the cathode of the main torch and the anode of the sub-torch of the composite plasma spray torch, oxygen is supplied as plasma gas to the main torch, and the central axis of the main torch is discharged from the outlet of the main torch. A plasma flame is ejected outward while swirling concentrically with the powder flame, and a powdered thermal spray material is supplied to the plasma flame. A plasma spraying method, characterized in that the plasma spraying method comprises: 4. An arc is generated between the cathode of the main torch and the anode of the auxiliary torch of the hybrid plasma spray torch, air is supplied as plasma gas to the main torch, and the central axis of the main torch is supplied from the outlet of the main torch. A plasma flame is ejected outward while swirling concentrically with the powder flame, and a powdered thermal spray material is supplied to the plasma flame. A plasma spraying method, characterized in that the plasma spraying method comprises: