JPH0639681B2 - Chromia-alumina rod for thermal spraying and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention relates to a chromia-alumina rod containing coarse particles of a chromia-alumina-based oxide solid solution as a main composition and a method for producing the same. The present invention relates to providing a chromia-alumina rod suitable as a thermal spray material used for a thermal spray coating for surface modification of metals, ceramics and the like.

<Prior art> Recently, various high-performance ceramic rod materials for thermal spraying are instantaneously melted and jetted for the purpose of imparting wear resistance, corrosion resistance, heat resistance, etc. to the surface of various metals and ceramics. A so-called ceramic rod thermal spraying process is used.

As the ceramic rod material for thermal spraying, chromia, alumina, zirconia, zircon, etc. are used, and they are properly used according to their applications due to their chemical and physical characteristics.

For example, although chromia has excellent wear resistance, the present inventor has succeeded in developing a chrome oxide rod for thermal spraying which makes use of its characteristics, and has already applied for a patent (Japanese Patent Application No. 62-153457).
No. 62-52870).

<Problems to be solved by the invention> However, the thermal spray coating by the chromia rod has excellent heat resistance and acid resistance, and since it exhibits a black color, it is also excellent in radiant heat transfer,
Since the thermal spray coating is dense, it has the drawback of being vulnerable to heat shock. On the other hand, the thermal spray coating of alumina rod is heat resistant,
Although it has excellent acid resistance, it has high reflectance due to its white film, and its radiant heat transfer is less than 20% of that of chromia.

In other words, there has been a demand for commercialization of a chromia-alumina rod having both advantages.

Therefore, as a result of intensive research, the present inventor found that solid solution particles of a chromia-alumina-based oxide having an average particle size in a specific range are suitable as a thermal spray material for surface modification of metals, ceramics and the like. The present invention has been obtained.

<Means for Solving the Problems> That is, the present invention relates to a chromia-alumina rod for thermal spraying, which has a coarse particle of a chromia-alumina-based oxide solid solution as a main composition, and an average particle diameter thereof in the range of 2 to 70 μm, and its production. Pertaining to the law.

The method of producing the rod is characterized in that coarse particles of a chromia-alumina-based oxide solid solution having an average particle diameter in the range of 2 to 70 μm are mixed with a sintering agent and a binder, and then the mixture is formed into a rod shape. It is to be fired after being molded into.

<Operation> The present invention will be described in detail below.

In the present invention, the solid solution particles of the chromia-alumina-based oxide constituted as the main composition have an average particle size of 2 to 70 μm.
It is preferably composed of coarse particles in the range of 10 to 70 μm. The reason 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 lacks the basic performance as a sprayed material. On the other hand, if it exceeds 70 μm, the solubility at the time of spraying becomes poor, This is because it tends to be difficult to form a complete and uniform spray-coated surface.

Thus, the thermal spraying rod according to the present invention is characterized in that the solid solution particles of the chromia-alumina-based oxide are composed of coarse and substantially primary particles from the viewpoint of the thermal spray density and the uniformity of the thermal spray coating. To do.

Here, the chromia-alumina-based oxide solid solution particles are substitution type solid solutions in which the chromium atoms of the chromia crystal lattice are replaced with aluminum atoms, or the aluminum atoms of the alumina crystal lattice are replaced with chromium atoms. This can be confirmed from the relationship between the shift of the powder X-ray diffraction line and the chemical analysis value.

The solid solution rate should be set according to the purpose of use of the thermal spray rod, and is not particularly limited, but in many cases chromia is about 10 to
It is in the range of 90% by weight, preferably 20-80% by weight.

Next, a rod mainly composed of coarse particles of such a chromia-alumina-based oxide solid solution means chromia-
The amount of coarse particles of alumina-based oxide solid solution is
It is 70 to 98 wt%, preferably 80 to 98 wt%, which is the main component.

Therefore, the other component composition is a sintering agent or other auxiliary agent for maintaining the molding strength of the rod, and contains, for example, clay. The reason for setting such a composition ratio is that if it is less than 70 wt%, the original effects of thermal spraying, such as wear resistance and high-temperature acid resistance, are impaired, and if it exceeds 98 wt%, the mechanical strength of the fired rod is insufficient. It becomes very brittle and is not suitable for practical use, which is not preferable.

The size of the rod varies depending on the type of thermal spraying machine, the type of thermal spraying material, the purpose of thermal spraying, etc., but in most cases, a cylindrical rod with a length of 2 to 10 mmφ and a length of 30 to 100 cm is used as described below. It is common. However, it is not limited to this for the above reason.

Next, a method for manufacturing the chromia-alumina rod for thermal spraying of the present invention will be described.

The method for producing a chromia-alumina rod for thermal spraying according to the present invention is not different from the method for producing a general rod product, but one of the features is that a general ceramic molded product is finely fired because it is densely fired. In contrast to using the raw material, the starting material is a solid solution of coarse particles of chromia-alumina-based oxide having an average particle diameter of 2 to 70 μm.

The term "coarse particles" as used herein refers to substantially independent and coarse single particles, and the particle size means a value obtained by a particle size distribution measurement method by a laser diffraction method. Such a solid solution of coarse primary particles is, for example, an acid is added to alumina hydrate containing a chromium salt, and the mixture is calcined at a temperature of 400 ° C., then leached with water, then dried, and then 1400. It can be produced by firing at a temperature of ℃ or higher. Since such solid solution particles have a high refractory temperature and are coarse primary particles, they lack inter-particle sinterability and moldability by themselves, and therefore, in producing a rod having this as a main composition, a binder is used. Or need a sintering agent.

The binder used in the present invention, when forming the coarse particles of the chromia-alumina-based oxide solid solution into a rod shape, imparts plasticity to the raw material, shape-retaining property to the molded product, and improves the mechanical strength of the molded product. For example, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, hydroxymethyl cellulose, starch, polyvinyl ether, polyvinyl alcohol, polyethylene oxide, acrylic acid-based polymer, polyacrylamide, gelatin will volatilize during firing. Anything can be used. Other binders include silica sol and alumina sol. The addition amount of these binders is not particularly limited, and the amount may be determined depending on workability, economy, etc., for example, with respect to the coarse particles of the raw material chromia-alumina-based oxide solid solution, 5 wt% or less is preferable, but especially It is not limited.

Next, as the sintering agent, to hold coarse particles of the chromia-alumina-based oxide solid solution, and to impart mechanical strength to the rod itself by sintering between the particles,
If necessary, it is a substance that promotes moldability together with the above-mentioned binder, and examples thereof include clays such as kibushi clay and frog eye clay, and aluminosilicates.

The amount of the sintering agent added is appropriately 2 to 30% by weight, preferably 2 to 20% by weight, based on the chromia-alumina rod for thermal spraying. The reason is that if it is less than 2 wt%, the mechanical strength of the fired product is insufficient, it is extremely brittle and it cannot withstand practical use, and if it exceeds 30 wt%, wear resistance which is the original effect of the chromia-alumina rod, This is because high temperature acid resistance and the like are impaired.

The method of adding the binder and the sintering agent to the coarse particles of the chromia-alumina-based oxide solid solution as the raw material is as follows. It is performed by kneading using a machine or the like.

The rod-shaped molding is performed using a high-pressure type vacuum extrusion molding machine, but any means can be used as long as it is a method capable of obtaining a desired shape.

That is, the size of the rod may be molded by using a die corresponding to the mechanism of the thermal spraying machine used, the structure, etc., but usually a cylindrical rod having a diameter of 2 to 10 mmφ and a length of 30 to 100 cm is used. It is common.

After the molded product is dried, it is fired in an electric furnace, a gas kiln or the like, but in the present invention, pre-firing is preferably performed at around 400 ° C.

The reason for this is that pre-firing is desirable for main firing by decomposing and removing the binder added to the coarse particles of the chromia-alumina-based oxide solid solution and removing water.

Next, main firing is carried out.The firing conditions may be determined as the optimum firing temperature according to the workability such as the type of the sintering agent, the addition amount, etc. and the rod solubility during thermal spraying. It is preferable to carry out the firing. The reason is that the firing temperature is
Below 1000 ℃, rod strength is low and not practical,
This is because if the temperature exceeds ℃, the strength becomes unnecessarily high, the solubility of the rod at the time of thermal spraying decreases, and the firing energy is wasted.

The chromia-alumina rod for thermal spraying obtained by the production method of the present invention is composed mainly of solid solution particles of coarse chromia-alumina-based oxide whose particle characteristics are substantially maintained as they are.

Therefore, it is very excellent in terms of thermal spray yield and working environment as compared with the powder thermal spray material.

The present invention will be specifically described below with reference to examples.

<Examples> (1) Preparation of solid solution of chromia-alumina-based oxide H ₂ O 58.3%, Cr ₂ O ₃ 10.3%, Al ₂ O ₃ 1
13.8 kg of sulfuric acid having a concentration of 98 wt% was gradually added to 100 kg of alumina hydrate containing 8.4% of 3.0% Na 2 O (all wt%), mixed well, dried at 110 ° C. for 6 hours and pulverized. Next, after firing in an electric furnace at 800 ° C. for 30 minutes, it was naturally cooled. Then, the soluble salts are removed by leaching with water and dried to obtain 23 kg of a solid solution of powdery chromia-alumina-based oxide.
Obtained.

Solid solution of the above powdery chromia-alumina oxide 20 kg
Was placed in an alumina container and baked at 1800 ° C. for 5 hours in an electric furnace. 100 parts of water was added to this fired product, and after crushing, it was separated by filtration and dried to obtain solid solution particles of the raw material chromia-alumina oxide. The solid solution particles of the raw material chromia-alumina-based oxide have an average particle diameter of 25 μm, an angle of repose of 34 degrees, and Cr ₂ O.
_{It was 3} 44.0 wt% and Al ₂ O ₃ 55.7 wt%, and was coarse particles of chromia-alumina-based oxide of black and polyhedron which was black with a slight green color.

The particle size distribution is measured by the laser diffraction method (measured by SK-LASER MICRON SIZER PRO-9000 manufactured by Seishin Enterprise Co., Ltd.)
I asked for. Further, it was confirmed by X-ray diffraction that chromia-alumina was a complete solid solution.

(2) Preparation of chromia-alumina rod for thermal spraying Raw material chromia obtained in (1) Chromia-to 10.0 kg of solid solution particles of alumina oxide, 0.3 kL of methyl cellulose as a binder
g, 2.0 kg of kibushi clay as a sintering agent was roughly mixed by a V-type mixer, 1.2 kg of water was added and sufficiently mixed, and then kneaded using a biaxial kneader. After aging overnight,
With a vacuum extrusion molding machine, using a 4.7 mmφ die, length 600
A chromia-alumina rod of mm was molded, dried at 105 ° C., and then fired in the following firing pattern in an electric furnace.

Room temperature to 400 ° C. 10 ° C./min 400 ° C. 1 hour hold 400 ° C. to predetermined firing temperature 5 ° C./min predetermined firing temperature 3 hours hold Natural cooling results are shown in Table 1.

(3) Thermal spray test Test method The chromia-alumina rods of Samples 3, 4, 5, 6 and 7 in Table 1 were subjected to a thermal spray test on a test iron plate using a ceramic rod thermal spraying apparatus under the following conditions.

Thermal spraying conditions: Acetylene gas pressure 1.2 kg / cm ² Oxygen pressure 3.8 kg / cm ² Air pressure 5.8 kg / cm ² Rod feed rate 100 mm / min As a comparative example, powdered chromia-alumina powder powder flame sprayer was used under the following conditions. And a thermal spray test was conducted in the same manner.

Thermal spraying conditions: acetylene gas pressure 0.85 kg / cm ² oxygen pressure 3.5 kg / cm ² air pressure 4.0 kg / cm ² powder feeding rate 1.2 kg / hr Evaluation results Table 2 shows the results of the above thermal spraying tests.

As a result, the workability such as scattering, the appearance, and the like were favorable, and the yield was good, as compared with general powder thermal spraying.

<Effects of the Invention> As described above, according to the chromia-alumina rod for thermal spraying and the method for producing the same of the present invention, during thermal spraying, no scattering occurs, the thermal spray yield is good, and the wear resistance and high temperature acid resistance are high. An excellent effect that a superior thermal spray coating can be formed under a good working environment is obtained.

Claims (5)

[Claims] 1. A chromia-alumina rod for thermal spraying, which comprises coarse particles of a chromia-alumina oxide solid solution having an average particle diameter in the range of 2 to 70 μm as a main composition. 2. A chromia-alumina rod for thermal spraying according to claim 1, wherein the coarse particles of the chromia-alumina oxide solid solution are contained in the rod in an amount of 70 to 98 wt%. 3. The coarse particles of the solid solution have a chromia of 10 to 90.
The chromia-alumina rod for thermal spraying according to claim 1, wherein the chromia-alumina rod is contained in an amount of wt%. 4. Coarse particles of a chromia-alumina-based oxide solid solution having an average particle diameter in the range of 2 to 70 μm are mixed with a sintering agent and a binder, and then the mixture is molded into a rod shape. Method for producing chromia-alumina rod for thermal spraying characterized by firing treatment 5. The method for producing a chromia-alumina rod for thermal spraying according to claim 4, wherein the firing temperature is 1000 to 1800 ° C.