JPH08167497A - Plasma spraying torch - Google Patents

Abstract

PURPOSE: To provide stabilized plasma, uniformized heating and accelerating of particles, and high quality sprayed coating formed with less energy used, by supplying spray powder longitudinally from a base part of a plasma jet passage in a positive electrode. CONSTITUTION: Cooling water is passed through cooling water passages 10, 12 in order to cool a positive electrode 1 and a negative electrode 5, while Ar or the like is passed, via a mixing passage 7 for spray powder and a working gaseous medium, from a hole formed in the negative electrode 5 to a plasma chamber 'a'. Spark discharge is generated between the two electrodes 1, 5, by applying a positive voltage and a negative voltage to the positive electrode 1 and the negative electrode 5 respectively from a direct current power source and also by applying a high-frequency voltage between the positive electrode 1 and the negative electrode 5. Owing to this spark discharge, plasma is generated between the positive electrode 1 and the negative electrode 5, and a plasma jet of high temperature and high speed bursts out of a plasma-jet nozzle 'b'. After the plasma has become stable, spray powder is supplied from a spray-powder supply passage 8 to the plasma generating chamber. Because the powder is supplied in the same direction as the bursting direction of the plasma jet, heating and accelerating of particles are uniformized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma spraying torch for efficiently heating a sprayed powder.

[0002]

2. Description of the Related Art A plasma spraying torch for generating a jet of plasma generated by passing a current between an anode and a cathode and supplying a sprayed powder to the jet to form a sprayed coating on the surface of a workpiece. As a conventional one, the one shown in the vertical sectional view of FIG. 2 is known.
That is, in FIG. 2, a plasma jet passage 23 having an enlarged diameter is opened on the axis of the copper anode 21, and an insulator 24 having a hole is formed on the base side of the anode 21.
Are fixed coaxially. A cathode current introducing portion 26 having a tungsten cathode 25 attached to the tip thereof is inserted into the hole of the insulator 24, and the cathode 25 is arranged in the base end portion (plasma generating chamber a) of the anode 21.

The insulator 24 is provided with a working gas supply passage 27 so that its tip communicates with the base of the plasma jet passage 23. On the other hand, near the tip of the anode 21, the tip has a plasma jet passage 23. A sprayed powder supply passage 28 is provided near the outlet (spout b) of the nozzle so as to pass therethrough at a substantially right angle. Further, a cooling water passage 29 is provided in the anode 21, and a cooling water inlet portion thereof is formed in the anode current introducing portion 30. The cathode current introducing portion 26 also has a cooling water passage communicating with the cooling water passage 29 of the anode 21. A passage 31 is provided.

In performing plasma spraying with such a plasma spraying torch, first, the anode 21 and the cathode 2
In order to cool 5, the cooling water is passed through the cooling water passages 29 and 31, and the working gas is supplied from the working gas supply passage 27 to the plasma generation chamber 22 such as Ar gas, He gas, N ₂ gas, or a mixed gas thereof. Shed. Next, a positive voltage is applied to the anode 21 from the DC power source and a negative voltage is applied to the cathode 25, and then a high frequency voltage is applied from the high frequency power source between the anode 21 and the cathode 25 to cause spark discharge between the electrodes 21 and 25. generate.

Due to this spark discharge, plasma is generated between the anode 21 and the cathode 25 due to the voltage applied from the DC power source previously applied, the plasma generating chamber a is filled with high temperature plasma, and the plasma jet nozzle It is ejected from b as a high-temperature and high-speed plasma jet. At this time, the current is gradually increased to stabilize the plasma jet, and then the spray powder is supplied from the spray powder supply passage 28 to the plasma generation chamber a near the plasma jet nozzle b. The particles of the thermal spray powder supplied to the plasma jet are heated and accelerated, and are jetted together with the high-temperature and high-speed plasma jet.

However, in such a plasma spraying torch, the supply of the sprayed powder is near the plasma jet nozzle b and is substantially orthogonal to the jetting direction, so that the particles of the sprayed powder supplied are heated. In addition to being inefficient, the particles are not uniformly heated and accelerated, and there are many particles with low energy because of insufficient heating and acceleration in the plasma jet. , The strength and adhesion are reduced.

When forming a mixed film of metal and ceramic, the metal, ceramics and the like are formed in the spray powder supply passage 28 in the same manner as described above.
Two types of ceramic thermal spray powder are supplied. Since the supplied two kinds of sprayed powders of metal and ceramic have different densities, particle sizes and melting points, if the sprayed powders are supplied near the plasma jet nozzles b and substantially orthogonal to the jetting direction. , The temperature rise and acceleration of each particle becomes more uneven,
Therefore, the mixing ratio of the mixed sprayed coating becomes unstable, and the compactness, strength and adhesion are lowered.

[0008]

The above-mentioned conventional ones have the problems that the efficiency of heating the particles of the sprayed powder is poor and that the particles are not uniformly heated and accelerated.

The present invention has a technical object to solve these problems.

[0010]

The present invention employs the following means to solve the above-mentioned problems.

That is, as a plasma spray torch, the base end has a plasma jet passage having an enlarged diameter and an anode having a cooling water passage around it, and the diameter of the base end of the plasma jet passage is almost the same. An insulator having a hole of a diameter and an ambient gas passage that conducts to the tip of the hole and the tip of which is coaxially coupled to the base end of the anode, and a working gas / sprayed powder mixing passage that is coaxial with the insulator. A cathode base having a cooling water channel in the periphery and a front part coaxially inserted in close proximity to the surrounding gas passage of the insulator, and a base end coaxially coupled to the tip of the cathode base, and a plasma jet flow channel with an outer diameter of the anode And a cylindrical cathode having a diameter smaller than the diameter of the base of the.

[0012]

In the present invention, when a voltage is applied between the cathode stand and the anode, and the working gas is sent from the working gas / sprayed powder mixing passage, the space between the anode and the cathode (a plasma jet passage portion having a large diameter of the anode). Plasma is generated at. At this time, when the plasma stabilizing gas is supplied from the surrounding gas passage, the plasma becomes stable. Then, when a mixture of the working gas and the sprayed powder is sent from the working gas / sprayed powder mixing path, these are supplied into the plasma from the tip of the cathode, where the sprayed powder is rapidly heated to a high temperature and high speed. It is ejected together with the plasma jet from the plasma jet and the flow path outlet.

In this way, stable plasma is obtained, and the sprayed powder is supplied to the plasma in the axial direction from the tip of the cathode, that is, the base of the plasma jet flow path of the anode, so that the plasma is efficiently and uniformly heated. To be done.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIG. The anode 1 has a cylindrical shape made of copper and coaxially has a plasma jet channel 3 having a diameter whose base end portion is enlarged (plasma generation chamber a). A cooling water passage 10 is provided around this, and there are radial inlets and outlets on the outer side surface, which also serve as the anode current introducing portion 11.

The insulator 4 has a cylindrical shape having the same diameter as the anode 1, and has a hole c having a diameter substantially the same as the diameter of the base end portion of the plasma jet passage 3 of the anode 1. In addition, a peripheral gas passage 9 is provided at the tip end portion so that the tip end portion is oriented radially and communicates with the hole c.
The insulator 4 has its tip coaxially coupled to the base end of the anode 1.

The cathode base 6 has a stepped cylindrical shape with the tip having the same diameter as the hole c and the base having a large diameter. The tip is coaxially squeezed to open the tip, and the base is closed. A powder mixing path 7 is provided. A spiral groove d is cut on the inner surface of the mixing passage 7. Further, a working gas passage 13 and a sprayed powder passage 14 are provided which are connected to the base end of the mixing passage 7.

A cooling water passage 12 is provided around the mixing passage 7, an inlet and an outlet in the radial direction are arranged on the side surface of the base portion, and also serves as the cathode current introducing portion 15.

The front part of the cathode stand 6 is closely inserted into the hole c from the base end part of the insulator 4 until its tip reaches near the surrounding gas passage 9.

A base end of a cylindrical tungsten cathode 5 having a diameter smaller than that of the base of the plasma jet passage 3 is coaxially attached to the tip of the cathode base 6.

When performing plasma spraying with such a plasma spraying torch, first, in order to cool the anode 1 and the cathode 5, cooling water is caused to flow through the cooling water passages 10 and 12, and the working gas / sprayed powder mixing passage 7 is provided. Through the hole (working gas and sprayed powder supply passage 8) of the cathode 5 into the plasma generating chamber a, working gas is flowed at a flow rate of, for example, Ar gas of about 25 l / min. Next, a positive voltage is applied to the anode 1 from the DC power source and a negative voltage is applied to the cathode 5, and then a high frequency voltage is applied between the anode 1 and the cathode 5 from the high frequency power source to generate a spark discharge between the electrodes 1 and 5. Generate.

Due to this spark discharge, plasma is generated between the anode 1 and the cathode 5 by the voltage applied from the DC power source previously applied, the plasma generating chamber a is filled with high temperature plasma, and the plasma jet nozzle It is ejected from b as a high-temperature and high-speed plasma jet. At this time, the current is gradually increased to, for example, about 700 A, and then, for example, about 1.5 l / min of N ₂ gas is flown from the surrounding gas passage 9, the current and voltage are about 700 A and about 38 V, and the plasma jet is generated. Stabilize.

After the plasma jet is stabilized, the sprayed powder, for example, Al having a particle size distribution of about 10 to 40 μm is fed from the working gas / sprayed powder supply passage 8 to the plasma generating chamber a through the working gas / sprayed powder mixing passage 7. ₂ O ₃ powder is supplied at a flow rate of about 20 g / min using Ar gas at about 5 l / min as a carrier gas. The particles of the thermal spray powder supplied to the plasma are rapidly heated and accelerated, and are ejected together with a high-temperature and high-speed plasma jet. At this time, the thermal spray powder supplied to the plasma is supplied in the same direction as the jet direction of the plasma jet, so that the heating and acceleration of the particles are uniform, and a high quality thermal spray coating having sufficient compactness, strength and adhesion. Is formed. Further, the sprayed powder is swirled by the spiral groove d along the working gas in the working gas / sprayed powder mixing path 7 to be provided with straightness and supplied to the center of the plasma, so that the heating efficiency is good. Further, the H ₂ gas supplied from the surrounding gas passage 9 forms an arc point at a portion where the distance between the anode 1 and the cathode 5 is large and stabilizes the plasma, and the cathode 5 is cooled by the H ₂ gas to extend its life. Become. The H ₂ gas causes the sprayed powder to move to the center of the plasma.
It is possible to prevent the sprayed powder from adhering to the inner peripheral surface of the anode 1 and obstructing the flow of the plasma jet.

In forming a mixed coating of metal and ceramic, the two kinds of spray powder are swirled together with the working gas in the working gas / spraying powder mixing passage 7 to be uniformly mixed and given a straight traveling property to form plasma. 2 because it is supplied to the center
The heating and acceleration of the seed particles become uniform, and a high quality sprayed coating having a stable mixing ratio, sufficient compactness, strength and adhesion is formed.

[0024]

According to the present invention as described above,
A stable plasma is obtained, and since the sprayed powder is supplied to the plasma in the axial direction from the tip of the cathode, that is, the base of the plasma jet flow path of the anode, it is heated efficiently and uniformly. Therefore, a high quality sprayed coating can be formed with energy saving, heating and acceleration of particles can be made uniform, plasma generation can be stabilized, and a high quality sprayed coating can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an embodiment of the present invention.

FIG. 2 is a vertical sectional view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anode 3 Plasma jet flow path 4 Insulator 5 Cathode 6 Cathode stand 7 Working gas / spraying powder mixing path 8 Working gas and spraying powder supply path 9 Surrounding gas path 10 Cooling water path 11 Anode current introducing part 12 Cooling water Passage 13 Working gas passage 14 Sprayed powder passage 15 Cathode current introduction part

Claims (1)

[Claims] 1. A base end portion has an enlarged diameter plasma jet flow passage and an anode having a cooling water passage around the plasma jet flow passage, and a hole having a diameter substantially equal to the diameter of the base end portion of the plasma jet flow passage. Along with an insulator having a peripheral gas passage that conducts to the tip of the same hole and the tip being coaxially coupled to the base end of the anode, a working gas / sprayed powder mixing passage is coaxially provided, and a cooling water passage is provided around it. A cathode base whose front end is coaxially and closely inserted to the vicinity of the surrounding gas passage of the insulator, and a base end of which is coaxially coupled to the tip of the cathode base and whose outer diameter is larger than the base diameter of the plasma jet passage of the anode. A plasma spray torch, comprising a small cylindrical cathode.