JPS63319252A - Production of chromium oxide rod for thermal spraying - Google Patents

Abstract

PURPOSE:To produce the titled rod having a high yield of thermal spraying by molding a mixture of Cr2O3 powder with a sintering agent and a grain growth accelerator to the shape of a rod, heating and calcining the molded body. CONSTITUTION:100pts.wt. Cr2O3 powder of <=2mum average particle size is mixed with 2-30wt.% sintering agent such as clay, 0.5-15wt.% grain growth accelerator for the Cr2O3 powder such as TiO2 and a prebonding agent such as methylcellulose. The mixture is molded to the shape of a rod and the molded body is dried, freed of the prebonding agent by heating to about 400 deg.C and calcining at 1,200-1,800 deg.C.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for producing a chromium oxide rod, and more specifically, to a method for producing a chromium oxide rod, and more specifically, a method for producing a chromium oxide rod by thermal spraying used in a thermal spray coating for surface modification of metals, ceramics, etc. The present invention relates to providing a chromium oxide rod suitable as a material for use in industrial applications.

<Prior Art> Conventionally, the use of chromium oxide as a material for thermal spraying has been known, but in both cases the sintered product has been pulverized and the particle size has been adjusted before use.

<Problems to be solved by the invention> Recently, various high-performance thermal spray materials have been instantly melted for the purpose of imparting wear resistance, corrosion resistance, heat resistance, etc. to the surfaces of various metals, ceramics, etc.・Methods of applying thermal spray coatings by spraying, such as plasma jets, are used, and chromium oxide is also used as one of the thermal spraying materials to impart wear resistance and high-temperature oxidation resistance. .

It is said that it is important for thermal spray chromium oxide used for such purposes to satisfy the following requirements.

(1) A chromium oxide film with the desired performance can be obtained on the surface of the base material. (2) It has good fluidity as a powder and does not block the thin tube from the powder supply device to the plasma gun nozzle during use. Must be able to be supplied smoothly at a constant speed.

(3) Of the chromium oxide powder added to the plasma gas during thermal spraying, the proportion that reaches the surface of the target substrate without scattering or loss and effectively forming a film, that is, the yield of thermal spraying is high. .

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

However, conventional chromium oxide for thermal spraying is manufactured by a method of electrolyzing chromium oxide powder, pulverizing the resulting melt, and then sieving to recover the desired particle size. However, the pulverization step becomes essential, and the disadvantage is that the yield of the desired particle size after classification is extremely poor, and the resulting particles are all angular, irregularly shaped fragments. The crystals have irregular and rough fractured surfaces, do not necessarily have sufficient fluidity as a powder, and have drawbacks such as being easily scattered during thermal spraying and easily reducing the yield of thermal spraying. In addition, the deterioration of the working environment due to scattering of chromium oxide, etc. was also a very large drawback.

The inventor of the present invention has conducted intensive research in view of the above problems, and as a result,
Using fine chromium oxide powder with a particle size of 2 μm or less as a raw material, heat treatment in the coexistence of a grain growth promoter yields a chromium oxide rod with unique properties consisting mainly of coarse single-crystal chromium oxide that turns blue. The present invention was completed after discovering that

<Means for solving the problem> and effects> A sintering agent and a grain growth promoter for the powder are mixed into the main material of chromium oxide powder with an average particle size of 2 μTrL or less, and then the mixture is shaped into a rod. The present invention relates to a method for producing a chromium oxide rod for thermal spraying, which is characterized in that the rod is formed into a chromium oxide rod and then heated and fired.

Normally, chromium oxide is used as an abrasive and a pigment, but its average particle size is in the range of 0.5 to 1.5 μm, and such fine powder chromium oxide can be used as a thermal spray material, whether it is powder or rod. It is inappropriate as such. Chromium oxide suitable for this material consists of coarse particles with an average particle size of at least 2 μm or more, preferably in the range of 5 to 50 μm. The reason for this is that if the thickness is less than 2 μm, it will evaporate at high temperatures and the yield on the sprayed surface will be poor, resulting in a basic lack of performance as a thermal spray material.On the other hand, if it is 50 μm, it will be difficult in terms of rod manufacturing conditions and during thermal spraying. This is because it is difficult to dissolve and tends to prevent a complete and uniform sprayed surface from being formed.

However, the present invention is characterized in that a chromium oxide rod for thermal spraying is manufactured using the above-mentioned ordinary finely powdered chromium oxide as a raw material.

That is, the present invention uses finely powdered chromium oxide as a main material as described above, and mixes this with a sintering agent and a structural length accelerator as necessary starting materials, and then kneads the mixture.
Manufactured by molding, drying and firing processes.

Therefore, when making a rod-shaped sintered body from fine chromium oxide as a raw material, by allowing grain growth to occur, it is possible to form a rod of coarse chromium oxide as a result.
This enables the use of finely powdered chromium oxide as a raw material.

Next, as a sintering agent, since the above-mentioned chromium oxide powder itself does not have sinterability, it is used to impart mechanical strength to molded rods and fired products made of the chromium oxide powder as a main material. .

Examples of the sintering agent include clay (Honbushi, Frogme clay, etc.),
Examples include aluminum silicate, alumina, etc., but the type is not particularly limited.

The amount added is 2 parts by weight per 100 parts by weight of raw material chromium oxide.
~3Qwt%, preferably 2~20wt% is appropriate.

If the amount of sintering agent added is less than 2wt%, the fired product will lack mechanical strength and will be extremely brittle and cannot be put to practical use. If it is more than 3Qwt%, the friction resistance purity, which is the original effect of chromium oxide thermal spraying, will be reduced. , high-temperature oxidation resistance, etc. are impaired.

Furthermore, in the present invention, the average particle system is 2μ as the main raw material.
Since fine chromium oxide with a size of less than m is used, it is necessary to add a grain growth promoter to promote grain growth of chromium oxide particles during heating and firing.

Such grain growth promoters include, for example, titanium oxide, alkali metal salts, alkali metal silicates, alkaline earth metal salts, etc., but the type thereof is not particularly limited.

The appropriate amount of these additives to be added is 0.5 to 15 wt%, preferably 1 to 10 wt%, based on 100 parts by weight of raw material chromium oxide. If the grain growth promoter is less than 1 wt %, chromium oxide grains will not grow to a size of 5 μm or more, which not only lowers the yield during thermal spraying but also makes it impossible to obtain stable thermal spraying performance. Moreover, if it exceeds 15 wt%, it is unsuitable because it corrodes the walls of the firing furnace or the solvent effect of the chromium oxide rod, which is the fired product, is impaired.

In the present invention, the above-mentioned raw materials are molded into a rod and fired, but an initial binder is required in order to provide the strength of the rod formed body obtained in a normal molding process.

As the initial binder used in the present invention, when molding chromium oxide into a rod shape, it imparts plasticity, moldability, and shape maintainability to the raw material mixture, and increases the mechanical strength of the molded product. For example, the commonly known methylcellulose, ethylcellulose, carboxymethylcellulose, ethylcellulose, starch, polyvinyl ether,
Polyvinyl alcohol, polyethylene oxide, acrylic acid polymers, polyacrylamide, gelatin, etc. can all be used as long as they exhibit their properties during baking.Additionally, the amount to be added is particularly limited to 100 parts by weight of raw chromium oxide. There is no limit, and the amount can be determined based on work efficiency and economy.

The method of adding initial binder, binder such as sintering agent, and grain growth promoter to the raw material chromium oxide is to roughly mix it using a conventional general mixing device, then adjust the humidity and mix it with a two-shaft mixer, etc. This is done by kneading using.

Forming into a rod shape is done using a vacuum extrusion molding machine.
Any method may be used as long as the desired shape can be obtained.

After drying the molded product, it is fired in an electric furnace, gas kiln, etc., but the method of manufacturing the chromium oxide rod for thermal spraying in the present invention is as follows:
In particular, there is no difference from the manufacturing method for general rod-shaped products.

However, its characteristic feature is that the average particle diameter is 2 μm.
Using the following fine powdered chromium oxide particles as a starting material, the fine chromium oxide powder is sintered at the same time as coarse single crystallization without damaging the rod shape during the heating process.

That is, in the case of dense fired products manufactured through the process of kneading, molding, drying, and firing of raw materials, fine particles with adjusted particle size distribution are generally used as raw materials, but in the present invention, originally sintered By firing a mixture of inert fine chromium oxide and a suitable adhesive and grain growth promoter, molded into a rod shape, fine chromium oxide grains grow and become coarse single crystals, and on the other hand, Grain boundary sintering is also performed in parallel, and as a result, a chromium oxide rod suitable for thermal spraying that is equivalent to or better than the rod can be manufactured using coarse-grained chromium oxide as a raw material.

As for the firing conditions, after debinding is performed at about 400°C, - firing is performed at 1200 to 1800°C. If the firing temperature is below 1200°C, not only will the rod not have sufficient strength, but the chromium oxide grains will not grow sufficiently.
It is not possible to obtain a chromium oxide rod for thermal spraying having a desired particle size of 5 μm or more. Furthermore, if the temperature exceeds 1800°C, the constituent particles become finer due to evaporation and condensation of chromium oxide, making it impossible to obtain the desired rod. In most cases, a range of 1,300 to 1,800°C is preferred, but the optimum firing temperature must be determined depending on the type of sintering agent and grain growth promoter.

Thus, the obtained chromium oxide rod for thermal spraying of the present invention is composed of substantially independent single particles, although each of the coarse particles as described above are mutually bonded by a binder. .

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

As described above, since the chromium oxide rod for thermal spraying according to the present invention is composed of coarse single crystals with an average particle size of 5 to 50 um, when it is introduced into plasma gas, these constituent particles take advantage of this characteristic to exert a large inertia. It reaches the target substrate with force, and produces a good chromium oxide film with little scattering, loss, etc., and a high yield.

Therefore, such a rod for thermal spraying has desirable properties not found in the past.

Example 1 A small amount of 3 parts of methylcellulose was added to 100 parts of a raw material made of finely powdered chromium oxide with an average particle size in the range of 0.2 to 2μ milk, with the raw material blending ratio as shown in Table 1. The mixture was kneaded with water, molded into a rod shape using a molding machine, and fired at a predetermined strength in an electric furnace to produce a rod (4.8 parts mmφX600rRaL).

The grain growth of chromium oxide in each rod obtained was observed with a microscope, and the bending strength of the rod was measured by measuring the two supporting distances RI.
A load was applied to the midpoint of 159 tpun, and the hardness was measured using a Suisan type hardness tester. The results are summarized in Table 2.

Table 1 Note 1 The marks at the top of each column of the table indicate the coating and grain growth observed under a microscope, expressed in 4 stages x 2 Grain growth deficiency Δ: Slightly insufficient grain growth ○: Grain growth is good (average particle diameter = 7μm) 02 Grain growth is very good (average particle size: 30μ77L) Note 2 The numbers at the bottom of each column in the table represent the bending strength Kt.

Example 2 A chromium oxide rod obtained by firing under the conditions marked with ◎ in Example 1 was thermally sprayed using a plasma gun. Compared to powder spraying, there is less scattering and loss of chromium oxide, improving the spraying yield and greatly improving the spraying work environment.

Moreover, the condition was comparable to that of the thermal sprayed powder coating coated by water droplets.

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

Claims (3)

[Claims] (1) Mixing a sintering agent and a grain growth promoter for the powder with the main material of chromium oxide powder with an average particle size of 2 μm or less, then forming the mixture into a rod shape, and then heating and firing the mixture. A method for manufacturing a chromium oxide rod for thermal spraying, characterized by: (2) The 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. (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.