JPH0660385B2 - Method of manufacturing chromium oxide rod for thermal spraying - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a chromium oxide rod, and more specifically, it will be used for a thermal spray coating for surface modification of metals, ceramics and the like. The present invention relates to providing a chromium oxide rod suitable as a material for use.

<Prior Art> It has been conventionally known to use chromium oxide as a material for thermal spraying, but in all cases, a sintered product was crushed and its particle size was adjusted.

<Problems to be solved by the invention> Recently, various high-performance thermal spray materials are instantaneously melted for the purpose of imparting wear resistance, corrosion resistance, heat resistance, etc. to the surface of various metals and ceramics. A method of applying a thermal spray coating by spraying, for example, a plasma jet is adopted, but chromium oxide is also used as one of the thermal spray materials for imparting wear resistance and high temperature oxidation resistance.

It is said that it is important to satisfy the following requirements as a chromium oxide for thermal spraying used for such a purpose.

(1) A chromium oxide film with desired performance can be obtained on the surface of the base material (2) Good fluidity as a powder, without blocking the thin tube from the powder supply device to the plasma gun nozzle during use, It can be supplied smoothly at a constant speed.

(3) The ratio of the chromium oxide powder that is thrown into the plasma gas during thermal spraying to reach the surface of the target substrate without scattering and loss and effectively form a film, that is, the yield of thermal spraying is high. .

In general, in order to satisfy these requirements, especially (2) and (3) above, it is considered necessary that the particle shape of chromium oxide is as close to spherical as possible and that the particle size distribution is narrow. Especially, fine particles having a particle size of about 5 μm or less have a small inertia and are easily scattered and lost during injection.

However, since conventional chromium oxide for thermal spraying is produced by a method of pulverizing an electromelt obtained after electromelting a powder of chromium oxide and further sieving to recover a desired particle size portion. The pulverization process is indispensable, and therefore, not only the defect that the yield of the desired particle size portion after classification becomes very poor, but the particle state of the obtained one is angular irregular-shaped fragmental polycrystal, The surface has an irregular and rough crushed surface, and the fluidity as a powder is not always sufficient, and there are drawbacks such that it is easily scattered during thermal spraying and the yield of thermal spraying is likely to decrease. In addition, the work environment is deteriorated due to the scattering of chromium oxide and the like, which is also a very serious drawback.

The present inventor, as a result of earnest research in view of the above problems,
A chromium oxide rod having a peculiar property composed of coarse single crystal chromium oxide as a main composition, which is obtained by subjecting a chromium oxide fine powder having a particle diameter of 2 μm or less as a raw material to a heat treatment in the presence of a grain growth promoter, is obtained. The present invention has been completed by finding out that it is possible.

<Means for Solving Problems> and <Action> A sintering agent and a grain growth promoter for the powder are mixed with a main material of chromium oxide powder having an average particle diameter of 2 μm or less, and then the mixture is rod-shaped. The present invention relates to a method for producing a chromium oxide rod for thermal spraying, which is characterized in that after being molded into a sheet, it is heated and fired.

Ordinary chromium oxide is used as an abrasive and a pigment, but its average particle diameter is in the range of 0.5 to 1.5 μm. Such fine powder chromium oxide is a powder, a rod or a thermal spray material. Is unsuitable as Chromium oxide suitable for the material is composed of coarse particles having an average particle diameter of at least 2 μm or more, and preferably in the range of 5 to 50 μm. The reason for this is that if it is less than 2 μm, it is likely to evaporate at a high temperature and the yield on the sprayed surface is poor, so that it basically lacks in performance as a spraying material. This is because it is difficult to melt, and a perfect and uniform sprayed surface tends not to be formed.

However, the present invention is characterized by producing a chromium oxide rod for thermal spraying using the usual fine chromium oxide as a raw material as described above.

That is, according to the present invention, as described above, finely powdered chromium oxide is used as a main material, and a mixture thereof with a sintering agent and a grain growth promoter as necessary starting materials is kneaded, molded, dried and fired.

Therefore, when the fine chrome oxide is used as a raw material to form a rod-shaped sintered body, it is possible to form a rod of coarse chrome oxide as a result by accommodating grain growth.
It is possible to use the raw material of fine powder chromium oxide.

Next, as the sintering agent, since the chromium oxide powder as described above does not have sinterability by itself, it is used to impart mechanical strength to a molded rod or a fired product containing this as a main material.

As the sintering agent, for example, clay (Kibushi, frog clay, etc.),
Aluminum silicate, alumina, etc. are not particularly limited in kind. Further, the addition amount is 2 to 30 wt% with respect to 100 parts by weight of the raw material chromium oxide, and preferably 2 to 20%.
wt% is suitable. If the amount of the sintering agent added is less than 2 wt%, the calcined product will have insufficient mechanical strength and will be very brittle and will not withstand practical use. If it is more than 30 wt%, the original effect of chromium oxide spraying will be the abrasion resistance. , High temperature oxidation resistance, etc. are impaired.

Further, in the present invention, the average particle size of the main raw material is 2 μm.
Since fine chromium oxide of m or less is used, it is necessary to add a grain growth promoter that promotes grain growth of chromium oxide particles during heating and firing.

Examples of such grain growth promoters include titanium oxide, alkali metal salts, alkali metals, silicates, and alkaline earth metal salts, but the kind thereof is not particularly limited.

The addition amount of these is 0.5 to 15 wt%, preferably 1 to 10 wt% with respect to 100 parts by weight of the raw material chromium oxide. If the grain growth accelerator is less than 1 wt%, chromium oxide will not grow to a grain size of 5 μm or more, which will not only reduce the yield at the time of thermal spraying, but also will not provide stable thermal spraying performance. On the other hand, if the content is 15 wt% or more, the wall of the firing furnace is attacked or the spraying effect of the chromium oxide rod, which is a fired product, is impaired, which is unsuitable.

In the present invention, rods are molded and fired from the above raw materials, but an initial binder is required in order to have the strength of the rod molded body that is usually obtained in the molding step.

As the initial binder used in the present invention, when forming chromium oxide into a rod shape, it imparts plasticity, formability and shape maintainability to the raw material mixture, and increases the mechanical strength of the formed product, For example, specifically well-known methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, starch, polyvinyl ether, polyvinyl alcohol,
Any polyethylene oxide, acrylic acid-based polymer, polyacrylamide, gelatin, etc. that can be exhibited by firing can be used. Further, the addition amount is not particularly limited with respect to 100 parts by weight of the raw material chromium oxide, and the amount may be determined depending on workability and economy.

The method of adding an initial binder, a binder such as a sintering agent, and a grain growth promoter to the raw material chromium oxide is to roughly mix the mixture with a conventional mixing device, and then to adjust the humidity and use a biaxial kneader or the like. It is carried out by kneading.

A vacuum extrusion molding machine is used to form rods,
Any means can be used as long as the desired shape can be obtained.

After drying the molded product, it is fired in an electric furnace, a gas kiln or the like, but the method for producing the chromium oxide rod for thermal spraying in the present invention is
There is no particular difference from the manufacturing method for general rod-shaped products.

The feature is that the average particle size is 2 μm.
The following fine powder chromium oxide particles are used as a starting material, and the chromium oxide fine powder is sintered simultaneously with coarse single crystallization without damaging the rod shape during the heating step.

That is, in general, in the case of a dense fired product produced in the steps of kneading, molding, drying and firing the raw materials, fine particles having a adjusted particle size distribution are used as the raw material, but in the present invention, it is originally sintered. The fine chromium oxide particles grow into coarse single crystals by firing a rod-shaped mixture of an appropriate sintering agent and a grain growth promoter added to non-crystalline chromium oxide. Sintering is also performed in parallel, and as a result, a suitable chromium oxide rod for thermal spraying, which is equal to or more than the rod, can be manufactured using coarse grain chromium oxide as a raw material.

As the firing conditions, a debinding agent is performed at about 400 ° C., and then firing is performed at 1200 to 1800 ° C. When the firing temperature is 1200 ° C. or lower, not only the rod does not exhibit strength, but also the grain growth of chromium oxide is not sufficiently performed, and a desired chromium oxide rod for thermal spraying having a particle diameter of 5 μm or more cannot be obtained. Also, if the temperature exceeds 1800 ° C, the constituent particles become finer due to evaporation and condensation of chromium oxide,
I can't get the target rod. In many cases,
The range of 1300 to 1800 ° C. is preferable, but the optimum firing temperature must be determined according to the types of the sinter and the grain growth promoter.

Thus, the obtained chrome oxide rod for thermal spraying of the present invention is composed of substantially independent single particles although the above-mentioned coarse particles are bonded to each other by a binder. .

That is, it can be said that the fine powder of the main raw material chromium oxide grows during heating and firing, and as a result, the rod becomes composed of coarse single-crystal chromium oxide.

Thus, when the chromium oxide rod for thermal spraying according to the present invention is made up of a coarse single crystal having an average particle size of 5 to 50 μm, when it is introduced into the plasma gas, these constituent particles take advantage of this feature and have a large inertia. It reaches the target substrate by force, and it is possible to obtain a good chromium oxide film with less yield and less scattering.

Therefore, such a thermal spraying rod has preferable properties not heretofore available.

Example 1 With 100 parts of raw material having a fine-particle unoxidized chromium in the range of 0.2 to 2 μm of average particle size as a main material and having a raw material compounding ratio as shown in Table-1, 3 parts of methyl cellulose and a small amount of water After kneading with and molding into a rod shape with a molding machine,
A rod (4.8 mmφ × 600 mmL) was manufactured by firing in an electric furnace at a predetermined strength for 2 hours each.

The grain growth of chromium oxide in each obtained rod was observed with a microscope, and the anti-sedimentation strength of the rod was measured at two fulcrum distances of 5
The load was applied to the midpoint of 9 mm and the hardness was measured with a wooden hardness meter. The results are summarized in Table 2.

Example 2 A chromium oxide rod obtained by firing under the conditions of ⊚ in Example 1 was subjected to thermal spraying using a plasma gun. Compared with powder spraying, there was less dispersion of chromium oxide, loss, etc., and the spraying yield was improved, and the spraying work environment was also greatly improved.

Further, it was in a good condition as good as that of the thermal spray coating powder obtained by this method.

<Effects of the Invention> According to the method of the present invention, ordinary fine powder chromium oxide is directly used as a raw material without preparing coarse-grained chromium oxide as the chromium oxide for thermal spraying by another method, and chromium oxide for thermal spraying is used. The rod can be manufactured industrially advantageously.

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Claims (3)

[Claims] 1. A main material of a chromium oxide powder having an average particle diameter of 2 μm or less, a sintering agent and a grain growth promoter of the powder are mixed, and then the mixture is formed into a rod shape, followed by heat firing treatment. A method for producing a chromium oxide rod for thermal spraying, which comprises: 2. A method for producing a chromium oxide rod for thermal spraying according to claim 1, wherein the grain growth promoter is at least one or two selected from titanium oxide, alkali metal salts and alkaline earth metal salts. Law. 3. The method for producing a chromium oxide rod for thermal spraying according to claim 1, wherein the heating and firing temperature is in the range of 1200 to 1800 ° C.