JPH05135896A - Induction plasma torch - Google Patents

Abstract

PURPOSE:To execute homogeneous thermal spraying without external influence by generating horizontally balanced plasma flame in melting and thermally spraying powder on an induction plasma torch. CONSTITUTION:A carrier gas introduction tube 4 made of a boron nitride sintered body, an intermediate tube 3, an outer tube 2, and a cooling tube 13 are successively and concentrically engaged with and threadably attached to a cylindrical support 1 in which multistage-concentrical inserting holes 1a-1e, and 1j, 1k made by a boron nitride sintered body as a raw material are formed in the cylindrical support.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an induction plasma torch which is capable of efficiently heating powder of ceramics, metal or the like in an inductively coupled plasma, melting and injecting the powder, and which is mainly used for thermal spraying.

[0002]

2. Description of the Related Art Heretofore, as an induction plasma torch, a torch having a water-cooled induction coil provided in a triple structure of an outer tube made of transparent quartz, an intermediate tube, and a carrier gas introducing tube is often used. Originally, in order to form a satisfactory molten coating on an object to be sprayed using an induction plasma torch, it is necessary to generate a plasma flame in a perfectly balanced manner on the left and right to completely melt the supplied powder. In order to do this, it is necessary for the tubes to be perfectly concentric in the torch configuration.

However, a quartz outer tube, an intermediate tube,
It is said that it is very difficult to construct a completely concentric torch by using each carrier gas introduction pipe.

In view of such circumstances, the present inventors have proposed a completely concentric induction plasma torch using a sintered body of boron nitride as a raw material. That is, a carrier gas introduction pipe, an intermediate pipe and an outer pipe made of a boron nitride sintered body are sequentially fitted into a cylindrical support made of a sintered boron nitride body and having a multi-stage concentric insertion hole formed therein. An induction plasma torch having a structure in which a gas supply tube for introducing gas in a tangential direction to the tubes is fitted and screwed to the tips of the intermediate tube and the outer tube in the support.

The structure of this torch will be described with reference to the longitudinal sectional view of FIG. 2. In the figure, reference numeral 1 is a cylindrical support obtained by processing a boron nitride sintered body. Inside this support 1 is 1
Multi-stage insertion holes a to 1e are concentrically provided by repeatedly drilling and threading the support 1 with a lathe or the like, and the carrier gas introduction pipe 4 and the intermediate pipe 3 are provided in these insertion holes. The outer tube 2 is fixed by fitting screws.

To form the insertion hole for the cylindrical support 1, first, the insertion hole 1a for inserting and inserting the carrier gas introduction pipe 4 is formed through the support 1, and then the intermediate pipe 3 is formed. The insertion hole 1b is formed concentrically with the insertion hole 1a at a position approximately in the middle of the support 1, and then the insertion hole 1c of the outer tube 2 is formed. Next, the intermediate pipe 3 is placed above the insertion hole 1b for supporting the intermediate pipe 3.
An insertion hole 1d having the same diameter as or slightly smaller than the inner diameter of the outer tube 2 is formed, and an insertion hole 1e having the same diameter as or slightly smaller than the inner diameter of the outer tube 2 is formed above the outer tube 2 supporting insertion hole 1c.

In this way, concentric circles 1a to 1 are formed inside.
On the cylindrical support 1 made of boron nitride sintered body on which e is formed,
Similarly, in order to attach the outer tube 2, the intermediate tube 3, the carrier gas introduction tube 4, the plasma gas supply tube 5, and the sheath gas supply tube 6 which are each formed in a cylindrical shape using a boron nitride sintered body, first, in the insertion hole 1a. The carrier gas introducing pipe 4 is penetrated from below and screwed and fixed with a screw 9. Thereafter, similarly, the intermediate tube 3 is screwed into the insertion hole 1b and the outer tube 2 is sequentially screwed into the insertion hole 1c, and then the plasma gas supply pipe 5 and the sheath gas introduction pipe 6 are tangentially connected to the insertion holes 1d and 1e, respectively. Screw part 1 provided on
f Insert into 1g and screw. A small gap of about 1 mm is provided between the inner peripheral surface of the outer tube 2 and the outer peripheral surface of the intermediate tube 3 in order to increase the speed of the supplied gas and enhance the cooling efficiency.

Using an induction plasma torch which is concentrically formed using the boron nitride sintered body in this way, a plasma of argon gas or the like is provided between the plasma gas supply pipe 5 and the carrier gas introduction pipe 4 and the intermediate pipe 3. 5 gas
The sheath gas such as argon gas is supplied from the sheath gas supply passage 6 between the intermediate pipe 3 and the outer pipe 2 at 20 liters / min. 1g of 100μm powder
5kW, 13.5 for induction coil 11 in the state of supplying / min.
When a high frequency of 6 MHz is applied, a well-balanced normal plasma flame 12 is generated, the powder is melted, and a film is formed on the sprayed object 10.

[0009]

However, even if the molten powder is sprayed by the induction plasma torch manufactured by using the boron nitride sintered body as a raw material to have a completely concentric structure as described above, the induction coil 11 is required.
If the distance L ₃ from the lower end of the outer tube to the lower end of the outer tube 2 is too short, the powder is melted by the plasma flame, the cooling solidification and the oxidation reaction by the low temperature air from the outside of the plasma torch occur at the time of the thermal spraying, and the thermal spraying to the sprayed object 10 is performed. May cause defects.

Further, if the distance L ₁ from the lower end of the induction coil 11 provided on the outer circumference of the outer tube 2 to the object to be sprayed 10 is short, the powder is not sufficiently melted by the plasma flame and the thermal spraying failure is caused. Occurs. For example, when alumina was used as the powder and was sprayed under the above conditions, the gray color of γ-alumina was exhibited, and only a black striped coating was obtained around the periphery.

As a measure for preventing such thermal spray failure, it is conceivable to lengthen the outer pipe (that is, lengthen the distance L ₃ from the lower end of the induction coil 11 to the lower end of the outer pipe 2). If 2 is too long, the sheath gas and the plasma gas are mixed at the lower end of the torch, the outer tube is not sufficiently cooled by the sheath gas, and the outer tube is overheated, which is not preferable. In particular, when the distance L ₃ is 20 mm or more, overheating of the outer tube becomes severe, so that oxygen outside the outer tube and boron nitride, which is the material of the outer tube, combine to start sublimation, and as a result, the outer tube This causes the problem that it will start to collapse from the outer wall and eventually the outer tube will be punctured.

[0012]

The present invention has been studied to solve various problems in the induction plasma torch described above, and as a result, a cooling pipe for cooling the outer pipe from the outer wall surface with a cooling gas is provided around the outer pipe. It has been found that if a plasma torch with a four-layer structure is provided on the outer tube, even if the outer tube is lengthened, overheating of the outer tube is prevented and normal thermal spraying is always possible. ..

That is, the present invention comprises a boron nitride sintered body, a cylindrical support having a multi-stage concentric circular insertion hole formed therein, a carrier gas introducing tube made of a boron nitride sintered body, an intermediate tube, and an outer side. A pipe and a cooling pipe were fitted and screwed in order, and a gas supply pipe for introducing gas in a tangential direction to the pipe was fitted and screwed to the tips of the intermediate pipe, the outer pipe and the cooling pipe in the support. (EN) An induction plasma torch having a four-layer structure in which the lower ends of the outer pipe and the cooling pipe are separated from the lower end of the induction coil provided on the outer periphery of the cooling pipe by 20 mm or more.

[0014]

According to the present invention, a cooling tube is provided around the outer tube to form a plasma torch having a four-layer structure of a carrier gas introduction tube, an intermediate tube, an outer tube and a cooling tube, so that the outer tube is protected during thermal spraying. When the outer tube is made long by supplying cooling gas from the outer wall surface, that is, when the distance L ₃ from the lower end of the induction coil to the lower ends of the outer tube and the cooling tube is 20 mm or more. However, normal plasma spraying can be performed without causing a situation of spraying failure.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to FIG. Note that, in FIG. 1, the portions denoted by the same reference numerals as those in FIG. 2 have the same operations as described in the section of the related art with reference to FIG.

In FIG. 1, 13 is a cooling pipe provided around the outer pipe 2. The cooling pipe 13 is made of sintered boron nitride, has a cylindrical shape, and has substantially the same length as the outer pipe 2. A screw having a small pitch is threaded on the outer circumference of the outer end of the outer pipe of the support 1. The screw holes 1a and the screw holes 1j formed concentrically at the positions are screwed and fixed to the screw holes 1j by screws 14 having a small pitch cut at the tips of the screw holes 1j.

Reference numeral 15 is a supply pipe for cooling gas supplied between the cooling pipe 13 and the outer pipe 2 to cool the outer pipe 2. The supply pipe 15 is provided in the cooling pipe 13 supporting insertion hole 1j. It is screwed in the tangential direction to an insertion hole 1k formed above with the same or slightly smaller inner diameter as the cooling pipe 13. 1m
Is a screw with a small pitch cut in the insertion hole 1k for this screwing.

In order to form the above-mentioned insertion holes 1j and 1k in the support body, the insertion hole 1j may be formed after the formation of the insertion hole 1c for inserting the outer tube 2 into the support hole. The formation may be performed after forming the insertion hole 1e.

The induction plasma torch of the present invention thus obtained comprises a cooling pipe 13, an outer pipe 2, and an intermediate pipe 3.
And each of the carrier gas introducing pipes 4 are manufactured from a boron nitride sintered body, and these are concentrically provided in the respective insertion holes formed inside the cylindrical support 1 made of the boron nitride sintered body,
And by making the outer tube and cooling tube long enough,
Plasma gas such as argon gas is supplied from the plasma gas supply pipe 5 between the carrier gas introduction pipe 4 and the intermediate pipe 3 at a rate of 5 liters / minute, and from the sheath gas supply pipe 6 between the intermediate pipe 3 and the outer pipe 2. 20 sheath gas such as argon gas
In liters / minute and from cooling gas supply pipe 15 to cooling pipe 1
Cooling gas such as argon gas is supplied to 3 at a rate of 20 liters / minute, and 1 g / g of alumina powder having a particle size of 5 to 50 μm is supplied together with the carrier gas from the carrier gas introduction pipe 4.
5 kW for induction coil, 13.5
When a high frequency of 6 MHz is applied, a well-balanced normal plasma flame 12 is generated, the alumina powder is completely melted, and the thermal sprayed material 10 has uniform thermal conductivity, excellent insulation, and resistance to heat. A film with high voltage could be formed.

In the above, the outer pipe 2 and the cooling pipe 13
Is the distance L from the lower ends of the induction coils 11 to their lower ends.
_{When 3} is 30 mm and the distance L ₁ from the lower end of the induction coil 11 to the sprayed object 10 is 75 mm, a uniform white alumina film is formed on the sprayed object, and L ₁ is 55 mm. In that case, an alumina film which was gray but had no stripe pattern was formed.

According to the present invention, as described above, even if the distance L ₃ from the lower end of the induction coil to the lower end of the outer tube is set to be 20 mm or more (preferably 20 to 40 mm) and a region where the sheath gas and the plasma gas are mixed is generated, Since the outer tube is sufficiently cooled by the cooling gas from its outer wall surface, there is no fear of being overheated. Therefore, there is no possibility that the boron nitride forming the outer tube is sublimated by being combined with external oxygen and the outer tube is damaged.

[0022]

As described above, the induction plasma torch of the present invention is constructed by concentrically fitting and screwing all the members using a boron nitride sintered body, and has a cooling pipe around the outer pipe. Since it has a four-layer structure,
It is possible to generate a well-balanced plasma flame on the left and right at the time of use, and by disposing the cooling pipe, it is possible to lengthen the outer pipe and efficiently perform melting and spraying of the powder.

Further, since all the members can be obtained by cutting the boron nitride sintered body, it is possible to easily manufacture a large amount of members having the same size. Furthermore, each member is formed by a cylindrical support body. Since the fitting holes are concentrically fitted and screwed to each other, there is a great effect that the designing and manufacturing can be performed with high accuracy. Even if a force is applied to the induction plasma torch from the outside and the cooling pipe, the outer pipe, etc. are damaged, the screws are cut, so that the replacement is easy.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of an induction plasma torch according to the present invention.

FIG. 2 is a vertical sectional view of a conventional induction plasma torch.

[Explanation of symbols]

 1 Cylindrical support 1a Insertion hole 1b Insertion hole 1c Insertion hole 1j Insertion hole 2 Outer pipe 3 Intermediate pipe 4 Carrier gas introduction pipe 9 Screw 11 Induction coil 12 Plasma flame 13 Cooling pipe 14 Screw

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Emilio Fujiwara 2-14-3 Awaji, Higashiyodogawa-ku, Osaka-shi, Osaka Prefecture Sansha Electric Manufacturing Co., Ltd. (72) Hiroyasu Murata 2-chome, Awaji, Higashi-yodogawa-ku, Osaka Sanwa Denki Seisakusho Co., Ltd. (72) Hidehisa Tachibana 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City, Osaka Prefecture Sansha Denki Seisakusho Co., Ltd.

Claims (2)

[Claims] 1. A carrier gas introduction pipe, an intermediate pipe, an outer pipe, and a cooling pipe made of a boron nitride sintered body, which are formed on a cylindrical support made of a sintered boron nitride body and having a multi-stage concentric insertion hole formed therein. The pipes are fitted and screwed in order, and a gas supply pipe for introducing gas in a tangential direction to the pipes is fitted and screwed to the tips of the intermediate pipe, the outer pipe, and the cooling pipe in the support body. 4-layer induction plasma torch. 2. The induction plasma torch having a four-layer structure according to claim 1, wherein the positions of the lower ends of the outer pipe and the cooling pipe are separated from the lower end of the induction coil provided on the outer periphery of the cooling pipe by 20 mm or more.