JP2595365B2 - Thermal plasma jet generator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to electrical insulation, thermal insulation, abrasion, corrosion resistance, and the like, and generation of a thermal plasma jet when a functional film is formed by plasma spraying or thermal plasma CVD. The present invention relates to a method and an apparatus.

Conventional technology Conventionally, thermal spraying technology has been used for a long time, for example, as wear resistance, insulating film, etc., and is broadly classified into gas thermal spraying using combustion gas as its melting means and electric thermal spraying using electric energy as its melting energy. Further, arc spraying, plasma spraying, and the like are generally used in electric spraying. In recent years, the plasma spraying method has recently attracted attention due to the quality of a sprayed coating. FIG. 7 shows a conventional example of a plasma spraying apparatus. A DC arc 4 is generated between the water-cooled cathode 1 and the water-cooled anode 2 by the power supply 3, and the plasma working gas 5 supplied from the rear is heated by the arc 4 and ejected from the nozzle 7 as ultra-high temperature plasma 6. The thermal spray material is a powder, which is placed on a carrier gas 8, blown into a plasma jet, melted by heating, accelerated, and made to collide with the surface of the substrate 9 at a high speed to form a film. At this time, the working gas is often argon or nitrogen, or helium or hydrogen is often added to these gases.

Problems to be Solved by the Invention Conventionally, in such a plasma spraying torch, the cathode 1 and the anode 2 are coaxial as shown in FIG.
The maximum area is about 2 to 3 cm depending on the output. Particularly, when a large-sized substrate such as an electronic display is used to form a coating by thermal spraying or thermal plasma CVD, the distance between the torch and the substrate 9 is reduced. To make it bigger and get more area,
As shown in FIG. 8, it is necessary to form the film forming region 12 while traversing the substrate 10 or the torch 11. When the distance between the substrate 9 and the torch is increased, the collision speed of the molten particles reaching the substrate 9 is slowed down. Therefore, the thermal sprayed coating is a coating having many pores and a highly uneven surface. Further, the method of traversing the substrate 10 or the torch 11 as shown in FIG. 8 has drawbacks such as uneven film thickness in the direction of movement in the Y-axis direction 13 in FIG. In addition, it has disadvantages such as a long time required for film formation and poor mass productivity.

An object of the present invention is to provide a method and apparatus for generating a thermal plasma jet capable of forming a plasma sprayed coating or a thermal plasma CVD coating on a large active area in view of the problems of the prior art.

Means for Solving the Problems The present invention has an endless end face having a flat shape opposed in the depth direction, a cathode and an anode for generating an arc, and an electrode surface opposed to the cathode and the anode. An excitation coil for generating a magnetic field having the same polarity to rotate the arc on the endless end face, a supply path for supplying a plasma working gas between the cathode and the anode end face, and a supply path for supplying powder or gas into the plasma A thermal plasma jet generator comprising: a mouth; and a direct current power supply for applying a direct current to the cathode and the anode.

In the present invention, an arc is generated between the endless end faces of the cathode and the anode, and the arc is circulated on both endless end faces by a magnetic field having the same polarity at the end faces generated by the exciting coils provided on both electrodes, thereby forming an arc. The generation area is formed into a long linear or slit shape, a plasma working gas is supplied to the arc generation area to obtain high-temperature thermal plasma, and powder or gas is supplied to the high-temperature thermal plasma, and the plasma flow to the substrate is formed into a sheet. This makes it possible to perform film formation by thermal spraying or CVD over a large area.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration diagram of a thermal plasma jet generator according to a first embodiment of the present invention. Reference numeral 14 denotes a plasma working gas, and reference numeral 15 denotes an introduction path of the gas, and a cathode 16 and an anode 17 are opposed to each other at a lower portion thereof with a predetermined distance therebetween. The cathode 16 and the anode 17 have an endless structure that is flat in the depth direction of FIG. 1, as shown in the sectional view taken along the line AA of FIG. Excitation coils 18 and 19 for generating a magnetic field in the electrodes are provided around the ends of the electrodes 16 and 17. Further, a jet port 20 for thermal plasma is provided below the flat electrodes 16 and 17, and a powder as a spray material is placed on a carrier gas 21 on a side surface thereof, or a gas as a CVD raw material is applied to the plasma gas. Supply port 23 for feeding into 22
Is provided. A direct current is applied to both electrodes 16 and 17 by a power supply 24. As shown in the AA cross-sectional view of FIG. 2, both electrodes 16 and 17 have endless end faces. FIG. 3 is a perspective view of the apparatus shown in FIG. 1, wherein the flat electrodes 16 'and 17' extend in the longitudinal direction, and the length is at least larger than the diameter of the current plasma spraying torch outlet. The region 25 formed between the opposing electrodes 16 ′ and 17 ′ has a shape closer to a slit.

The operation of the thermal plasma jet generator of this embodiment configured as described above will be described below.

First, an arc is generated in the gap between the electrodes by a separate pulse current generator or the like between the cathode 16 and the anode 17, and then the power supply 24
Thus, a high current is applied at a low voltage to keep the arc 26 stable. After that, the excitation coil 18 provided on the cathode 16 and the anode 17,
19 is energized to generate a magnetic field at each electrode. At this time, when the magnetic field is excited so as to have the same polarity at the electrode end faces,
At the end face, the magnetic flux is directed to the outside of the electrode, and at that time, a driving force is applied to the arc 26 according to the so-called Fleming's left rule based on the direction of the arc current and the direction of the magnetic field, and the arc 26 circulates at high speed around both endless electrode end faces. It becomes 27.
At this time, the orbital moving speed of the arc is represented by the following equation, and is proportional to the product of the magnetic flux density, the arc current, and the arc length.

F∝B × I × L F: Driving force B: Magnetic flux density I: Arc current L: Arc length To increase the arc moving speed from the above formula, arc current,
Although the arc length can be increased, in the present invention, it is better to increase the magnetic flux density in order to make the arc generating space slit-shaped as low as possible.

The area formed by the opposing electrodes generated in this way
Introducing path of upper plasma working gas 14 into 25 arc regions
Supplied by 15. At this time, as the plasma working gas, argon, nitrogen, hydrogen, helium and the like can be considered. arc
The plasma working gas supplied to the inside 26 is heated to a high temperature to be in a plasma state, and at the same time, the current density and the energy density are increased by the thermal pinch effect to become ultra-high-temperature thermal plasma 22 and ejected from the ejection port 20 at a high speed.

At this time, in the case of thermal spraying, when a thermal spray material such as metal or ceramic is supplied into the thermal plasma from the powder or gas supply port 23 provided at the lower portion of the jet port 20, they are heated and melted, and the high speed of the plasma jet is achieved. It rides and hits the substrate to be flattened to form a desired film. Further, in the case of thermal plasma CVD, by supplying a source gas into the thermal plasma from the supply port 23, CVD utilizing a non-equilibrium process in a high temperature state of the thermal plasma becomes possible. Regardless of thermal spraying or CVD, according to the present invention, since the arc 26 is moving around the flat endless electrode end face, the electrode 26
Although there is a slight temporal temperature distribution in the longitudinal direction of 16 and 17, it is considered that there is almost no effect on plasma generation etc. due to the high arc circulation speed, and the arc generation area
Since the slit 25 is formed, the plasma density in that region can be increased.

As described above, according to the thermal plasma jet generator of the present invention, the thermal plasma jet 22 has a so-called sheet shape or a shape close to a linear shape as shown in FIG.
It is possible to form a film with a width corresponding to the width of the substrate.Thus, it is possible to form a film over the entire width of the substrate with utmost traversing the substrate or torch. The velocity distribution and temperature distribution of the particles in the radial direction of the torch can be reduced, and a film can be formed that has a characteristic that film thickness unevenness hardly occurs during film formation. In this embodiment, the supply of the powder or the gas is performed from the lower part of the electrode. However, the configuration may be such that the arc 26 is ejected from the upper part of the space of the arc generating region 25.

FIG. 4 is a block diagram of the thermal plasma jet generator showing the relation.

In the figure, reference numeral 28 denotes a passage for introducing a plasma working gas 29, inside which a cathode 30 having an open end face is provided.
An excitation coil 31 for generating a magnetic field is provided around the periphery.
An anode 32 whose end face is located on the outer periphery of the cathode 30 is provided, and the anode 32 is provided with an excitation coil 33 for generating a magnetic field. Further, a jet port 34 of a thermal plasma jet is provided below the anode 32. Further, a powder or gas supply port 35 is provided at the center of the cathode 31, and the supply port 35 has an ejection hole 36 so as to eject in the outer peripheral direction. FIG. 5 is a cross-sectional arrow diagram along BB in FIG. In the case of FIG. 5, the cathode 30 'and the anode 32' are annular. In the electrodes 30 and 32, as shown in FIG. 6 (a sectional view taken along the line BB in FIG. 4), the cathode 30 "and the anode 32" may be elliptical or flat. 5 and 6, the cathode 31 and the anode 32 are coaxially arranged.

Next, the operation of the related thermal plasma jet generator configured as described above will be described.

Basically the same as the first embodiment, the cathode 30 and the anode
Air gap between electrodes by pulse current generator etc. installed separately between 32
An arc 38 is generated in 37, and then a high current is applied at a low voltage to keep the arc 38 stable. Then cathode 30 and anode
The excitation coils 31 and 33 provided in 32 are energized to generate a magnetic field in each electrode. At this time, when the magnetic field is excited to have the same polarity at the electrode end face, the magnetic flux is directed outward from the electrode at the end face. As a result, the arc 38 orbits both electrode end faces at high speed.

The upper plasma working gas 29 is supplied from the introduction path 28 to the arc 38 generated in this manner. At this time, as the plasma working gas, argon, nitrogen, hydrogen, helium and the like can be considered. Plasma working gas supplied in arc 38
29 is heated to a high temperature to be in a plasma state, and at the same time, the current density and the energy density increase due to the thermal pinch effect and become ultra-high temperature thermal plasma, which is ejected from the ejection port 34 at a high speed. At this time, a powder or gas supply port provided at the center of the cathode 31
From 35, when thermal spraying materials such as metal and ceramic are supplied into the thermal plasma in the thermal spraying field, they are heated and melted, collide with the substrate at the high speed of the plasma jet, and the flattened desired coating is formed. To form. Further, in the case of thermal plasma CVD, by supplying a raw material gas into the thermal plasma from the supply port 35, CVD utilizing a non-equilibrium process in a high temperature state of thermal plasma becomes possible. Further, since the ejection holes 36 are provided so as to eject the powder or gas to be supplied outward from the center at this time, the powder or gas is uniformly supplied to the ultra-high temperature region of the arc generation region, and the heat melting or reaction is performed. Be uniformed. Further, according to the present invention, the distance between the arc generating point and the substrate is always constant. Further, in order to form a film on the substrate by thermal spraying or CVD, the diameter of the rings 30 'and 32' may be increased, or the cathode 30 "and the anode 30" may be formed as in the first embodiment.
This is possible by flattening the 32 ″ shape and has the same effect.

Effect of the Invention As described above, according to the present invention, a plasma sprayed film or a thermal plasma CVD film having a very uniform heat melting or reaction can be formed in a large area, and an apparatus having extremely high productivity is provided. The practical effect is great.

[Brief description of the drawings]

1 is a sectional view showing a thermal plasma jet generator according to one embodiment of the present invention, FIG. 2 is a sectional view taken along line AA of FIG. 1, FIG. 3 is a perspective view showing the same embodiment, FIG. FIG. 5 is a cross-sectional view showing a related thermal plasma jet generator, FIG. 5 is a cross-sectional view showing a first shape of a BB cross section in FIG. 4, and FIG.
FIG. 7 is a cross-sectional view showing a second shape of the BB cross section in FIG. 4, FIG. 7 is a cross-sectional view showing a conventional thermal plasma jet generator, and FIG. 8 is a film formation using the conventional thermal plasma jet apparatus. It is a perspective view which shows a method. 14 …… Plasma working gas, 16 …… Cathode, 17 …… Anode, 18
... exciting coil, 19 ... exciting coil, 22 ... thermal plasma jet, 27, 38 ... arc, 23 ... powder, gas supply port.

Claims (1)

(57) [Claims] 1. A magnetic field having an endless end face having a flat shape facing in a depth direction and having a cathode and an anode for generating an arc, and having the same polarity on an opposite electrode surface to the cathode and the anode. An excitation coil that causes the arc to circulate on the endless end face, a supply path for supplying a plasma working gas between the cathode and the anode end face, a supply port for supplying powder or gas into plasma, the cathode and A thermal plasma jet generator, comprising: a direct current power supply for applying a direct current to an anode.