JPH0741931A - Plsma thermal spraying device - Google Patents

Abstract

PURPOSE:To prevent the damage of electrodes and to manage the quality of a thermally sprayed film on a solid base to be the finest state to all times by providing the inside wall surface of a nozzle part for injecting a plasma jet with an attachable and detachable cover consisting of an arc resistant material. CONSTITUTION:This plasma thermal spraying device is formed out of electrode pair 20, 22 for generating the plasma 31, a power source connected thereto, a gas spraying section, a powder charging section 14A for charging raw material powder to the plasma jet 4 and a nozzle section 24. A working gs is blown to the plasma 31 in the gas blowing section to form the plasma jet 4. The molten raw material powder molten by plasma heat is ejected together with the plasma jet 4 from the nozzle section 24. The inside wall surface of the nozzle section 24 is provided with a cover consisting of the arc resistant material. This cover consists of a sleeve 30 which is attachably and detachably fitted to the nozzle part 24 and has an electrical conductivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for spraying powder melted on the surface of a solid substrate to form a film.

[0002]

2. Description of the Related Art A plasma spraying apparatus heats and melts powdery ceramics, or a spraying material such as metal or plastic with plasma to form liquid fine particles. It is for colliding (spraying) and forming a film on the solid substrate. By coating with a solid material, ring resistance, wear resistance, electrical insulation, etc. are improved.

FIG. 3 is a system diagram showing the structure of a conventional plasma spraying apparatus. A plasma torch 1 ejects a plasma jet 4 containing liquid fine particles toward the surface of a solid substrate 2 on which a film is to be formed. Wirings 13A and 1 are connected to the anode terminal 20A and the cathode terminal 22A of the plasma torch 1.
The power supply 18 is electrically connected via 3B. The power source 18 includes a DC power source 18A and a high frequency power source 18B. In addition, the gas spraying unit 15 is connected to the gas cylinder 9 through the pipe 12A.
It is connected to the gas supply port 15A of the plasma torch 1 through a pipe. Further, the powder feeding unit 14 is configured to change the raw material powder 5
Is connected to the powder supply port 14A of the plasma torch 1 through a pipe 12B. A gas cylinder 8 is connected to the pipe 12B. FIG. 4 is a sectional view showing the configuration of the plasma torch 1 of FIG. The plasma torch 1 is provided with a cathode 22 having a cathode terminal 22A at the center of its axis. The positive electrode 20 is arranged on the outer periphery of the negative electrode 22 via an insulator 21. The positive electrode 20 includes an anode terminal 20A and a nozzle portion 24.
Is formed. As described above, the plasma torch 1 is provided with the gas supply port 15A, and the working gas 10 is blown onto the tip portion 22B of the negative electrode 22. Further, the plasma torch 1 is provided with a powder supply port 14A,
The raw material powder 5 is put into the plasma jet 4.

In FIG. 4, a voltage is applied between the positive electrode 20 and the negative electrode 22 to generate a plasma arc at the tip 22B of the negative electrode 22. A working gas 10, for example, argon gas is blown to this plasma arc, and a plasma jet 4 is ejected in the direction of arrow 25. At that time, the raw material powder 5 is introduced into the plasma jet 4, and the raw material powder 5
Is melted by plasma heat and becomes liquid particles. The plasma jet 4 is ejected from the nozzle 24 together with the liquid particles.

Returning to FIG. 3, the high frequency power source 18B is for an arc trigger for causing the direct current from the direct current power source 18A to flow between the electrodes of the plasma torch 1. High frequency power supply 18
By B, a high voltage is superposed between the electrodes to once cause dielectric breakdown between the electrodes. Since a dielectric breakdown between the electrodes makes them conductive, a large current of tens of volts or thousands of amperes flows between the electrodes even if the voltage of the DC power supply 18A is low, and high-temperature plasma is generated. The gas cylinder 9 is filled with a working gas 10. The gas cylinder 8 is filled with a carrier gas 6, for example, argon gas. The carrier gas 6 is for sending the raw material powder 5 to the powder supply port 14 </ b> A by its wind pressure and for introducing it into the plasma jet 4.

In FIG. 3, a solid body 2 is arranged to face a plasma torch 1 with a gap length G therebetween. The plasma jet 4 spreads in the radial direction as it progresses along the gap length G, and forms a circular film 17 having a diameter D in the range on the surface of the solid body 2. When alumina Al ₂ O ₃ powder having a melting temperature of 2300 ° K is used as the raw material powder 5,
A tens of thousands K plasma jet 4 is generated by a direct current of several thousand amperes to spray alumina powder. For example, if the gap length G is set to 10 cm, a circular ceramic film 17 having a diameter D of about 10 cm can be formed on the surface of the solid substrate 2. After forming the film 17, the peripheral shape of the film 17 is finished into a desired shape by edging.

[0007]

However, the conventional device as described above has a problem that the positive electrode is damaged by the heat of the plasma jet. Since the positive electrode serves both as an energization and a container surrounding the negative electrode, copper C _U is generally used because of both conductivity and workability. However, since the melting point of copper is as low as 1358 ° K, the inner wall surface of the nozzle portion of the positive electrode was damaged by the heat each time a plasma jet of tens of thousands of degrees was blown. When plasma spraying was performed many times, the nozzle portion was deformed, and it was necessary to replace the entire positive electrode. It is conceivable to form the entire positive electrode with an arc-resistant material having a high melting point, but this material is not practical because it is expensive and does not necessarily have good workability.

An object of the present invention is to prevent the positive electrode from being damaged by plasma spraying.

[0009]

In order to achieve the above object, according to the present invention, an electrode pair for generating plasma, a power source connected in parallel to the electrode pair, and a working gas for plasma are provided. A nozzle unit comprising a gas spraying unit for forming a spraying plasma jet, a powder charging unit for charging raw material powder into the plasma jet, and a nozzle unit for injecting the raw material powder melted by plasma heat together with the plasma jet. A cover made of an arc resistant material is provided on the inner wall surface of the above, and in such a structure, the cover is detachable from the nozzle portion. Further, in the above structure, the cover is made of a sleeve having conductivity and is fitted to the nozzle portion, or the cover is an insulating sleeve and the end of the sleeve on the plasma ignition side. And a conductive ring provided on the nozzle, and is fitted into the nozzle portion.

[0010]

By providing a cover made of an arc resistant material on the inner wall surface of the nozzle portion, the arc resistant material protects the plasma electrode even if the plasma jet passes, so that the positive electrode is not damaged at all. Since the arc resistant material is limited only to the nozzle part, the problems of material price and workability are solved.

In such a structure, by making the cover removable from the nozzle portion, even if the cover is damaged by the heat of the plasma jet, it is sufficient to replace the cover with a new one. The injection hole can always be kept in a constant shape. Further, since the cover is made of a conductive sleeve and fitted in the nozzle portion, the inner wall surface of the nozzle portion can be covered with the arc resistant material.

Further, the cover is composed of an insulating sleeve and a conductive ring on the side of the plasma firing, and by fitting the cover to the nozzle portion, the conductive ring becomes the positive electrode side of the plasma. To form. On the other hand, the price of the cover can be reduced by providing the insulating sleeve.

[0013]

EXAMPLES The present invention will be described below based on examples.
FIG. 1 is a cross-sectional view of essential parts showing the structure of a plasma spraying apparatus according to an embodiment of the present invention. The conductive sleeve 30 made of an arc resistant material is used for the nozzle portion 24 of the plasma torch 1.
Is attached to the positive electrode 20 so that it can be detachably attached via the bolt 32.
Is attached to. The powder supply port 14A is also opened in the sleeve 30. Others are the same as the conventional configuration of FIG. The same parts are designated by the same reference numerals, and detailed description thereof is omitted.

In FIG. 1, the sleeve 30 is a nozzle portion 2.
Play the role of 4. That is, the positive electrode 20 and the negative electrode 2
The foot on the positive electrode 20 side of the plasma arc 31 that occurs first between the two is on the left inner surface of the sleeve 30, and is formed after that. The sleeve 30 also protects the nozzle 24 against the plasma jet 4. Sleeve 3
Examples of the conductive arc-resistant material forming 0 include tungsten W (melting point 3660 ° K), tantalum T
a (melting point 3250 ° K), titanium carbide TiC (3400-
3500 ° K.) and has a melting point much higher than that of copper. Therefore, even if the plasma jet 4 touches the sleeve 30, the damage is hardly generated. Even if the sleeve 30 is damaged by a number of times of thermal spraying, if the sleeve 30 is replaced with a new one, the injection hole of the nozzle portion 24 can always be kept in a constant shape. As a result, the quality of the film formed on the solid body can be controlled to the optimum state at all times.

FIG. 2 is a cross-sectional view of essential parts showing the structure of a plasma spraying apparatus according to another embodiment of the present invention. A conductive ring 35 is joined to the left end of the insulating sleeve 33. The insulating sleeve 33 and the conductive ring 35 are joined to a mounting member 34 and fixed to the positive electrode 20 via a bolt 32. Others are the same as the configuration of FIG.

In FIG. 2, both the insulating sleeve 33 and the conductive ring 35 are made of an arc resistant material and serve as a cover for the nozzle portion 24. That is, the foot of the plasma arc 31 generated first on the positive electrode 20 side is
On the conductive ring 34, an insulating sleeve 33 protects the nozzle part 24 against the plasma jet 4 which is subsequently formed. The material of the insulating sleeve 33 is, for example, alumina Al ₂ O ₃ (melting point 2300 °).
K), zirconia ZrO ₂ (melting point 2950 ° K), etc., and have a melting point much higher than that of copper. The mounting member 34 does not have to be in direct contact with the plasma jet 4 and therefore need not be an arc resistant material. Insulating sleeve 33
The material is generally less than an order of magnitude less expensive than the conductive arc resistant sleeve material in FIG. for that reason,
FIG. 2 shows a structure in which the cost of the nozzle portion 24 is greatly reduced.

[0017]

EFFECTS OF THE INVENTION By providing a cover made of an arc resistant material on the inner wall surface of the nozzle portion, for example, in the form of a sleeve, the positive electrode is never damaged and the equipment cost for plasma spraying is greatly reduced. Was done. In such a structure, by making the cover removable from the nozzle part, the injection hole of the nozzle part can be always kept constant, and the quality of the film formed on the solid body can be always controlled to the best condition. .

In this structure, since the cover is partially made of an insulating sleeve, the cover cost is reduced and the equipment cost for plasma spraying is further reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing the configuration of a plasma spraying apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of essential parts showing the configuration of a plasma spraying apparatus according to another embodiment of the present invention.

FIG. 3 is a system diagram showing the configuration of a conventional plasma spraying device.

4 is a cross-sectional view showing the configuration of the plasma torch of FIG.

[Explanation of symbols]

1: plasma torch, 4: plasma jet, 20: positive electrode, 22: negative electrode, 24: nozzle part, 14: powder supply port, 32: bolt, 31: plasma arc, 30: conductive sleeve, 33: insulation Sleeve, 34: fittings, 35: conductive ring,

Claims (4)

[Claims] 1. A pair of electrodes for generating plasma, a power source connected in parallel to the pair of electrodes, a gas spraying unit for spraying a working gas onto the plasma to form a plasma jet, and a raw material powder charged into the plasma jet. In the case where the inner wall surface of the nozzle portion is provided with a cover made of an arc-resistant material, the inner wall surface of the nozzle portion is provided with a powder charging portion and a nozzle portion for injecting the raw material powder melted by plasma heat together with the plasma jet. Characteristic plasma spraying equipment. 2. The plasma spraying apparatus according to claim 1, wherein the cover is detachable from the nozzle portion. 3. The plasma spraying apparatus according to claim 1 or 2, wherein the cover is made of a conductive sleeve and is fitted in the nozzle portion. 4. The nozzle according to claim 1 or 2, wherein the cover is made of an insulating sleeve and a conductive ring provided at an end of the sleeve on the plasma ignition side, and is fitted to the nozzle portion. A plasma spraying device characterized by being combined.