JPH0254424B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a chromium oxide rod whose main composition is single-crystal chromium oxide and a method for producing the same. The present invention relates to providing a chromium oxide rod suitable as a thermal spraying material. [Prior Art] It has been known to use chromium oxide as a material for thermal spraying, but in all cases, a sintered product of chromium oxide 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 instantaneously melted for the purpose of imparting wear resistance, corrosion resistance, heat resistance, etc. to the surfaces of various metals, ceramics, etc. - A method of applying a thermal spray coating by spraying, such as plasma jet, is 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 can be smoothly supplied at a constant speed without clogging the thin tube from the powder supply device to the plasma gun nozzle during use. (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. In general, in order to satisfy these requirements, particularly (2) and (3) above, it is considered necessary that the particle shape of chromium oxide be as close to spherical as possible and that the particle size distribution be narrow. In particular, fine particles with a particle diameter of less than about 2 μm have a small inertia and are easily scattered and lost during injection. However, conventional chromium oxide for thermal spraying is mainly produced by a method of electromelting chromium oxide powder, pulverizing the resulting melt, and then sieving to recover the desired particle size. It is something that Therefore, a pulverization process becomes essential, which not only has the drawback that the yield of the desired particle size after classification is extremely low, but also that the resulting particles are in the form of angular, unstable pieces. It is polycrystalline, with irregular and rough fractured surfaces, and does not necessarily have sufficient fluidity as a powder.
Further, during thermal spraying, there were drawbacks such as easy scattering and a low 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. As a result of intensive research in view of the above-mentioned problems, the inventors of the present invention have found that by forming a rod shape using chromium oxide single crystal with coarse particle size as a raw material, there is no scattering during thermal spraying, and the thermal spraying yield can be improved. The present invention was completed based on the finding that a chromium oxide rod for thermal spraying can be obtained which can form a coating with good wear resistance and high temperature oxidation resistance. [Means for Solving the Problem] and [Operation] That is, the present invention provides a chromium oxide rod for thermal spraying, characterized in that it is mainly composed of single crystal chromium oxide having an average particle size in the range of 2 to 50 μm. It depends on the manufacturing method. A feature of the chromium oxide rod for thermal spraying according to the present invention is that it is composed of a coarse single crystal. Ordinary chromium oxide is used as an abrasive or pigment, but its average particle size is mainly
Although the particle size is in the range of 0.5 to 1.5 μm, the chromium oxide for thermal spraying which is the main composition in the present invention is composed of coarse single crystal particles with an average particle size in the range of 2 to 50 μm, preferably 5 to 50 μm. It is. The reason for this is that if it is less than 2 μm, it will easily evaporate at high temperatures;
This is because it basically lacks performance as a thermal spraying material, such as poor yield on the thermal spraying surface, and on the other hand,
This is because if the thickness exceeds 50 μm, it will be difficult to prepare the raw material, and it will also be difficult to dissolve, making it difficult to form a complete and uniform sprayed surface. Such coarse single-crystal chromium oxide can be obtained by heating and baking ordinary fine chromium oxide at 1200 to 1800°C for a relatively long time to grow particles. The chromium oxide rod for thermal spraying of the present invention is composed of the above-mentioned coarse single-crystal chromium oxide particles, which are bonded to each other by a binder and a sintering agent, but are substantially independent single particles. It has become something that has been done. In other words, it can be said that the chromium oxide rod maintains almost the same particle size and external shape of the main raw material chromium oxide single crystal. Further, the amount of single crystal chromium oxide contained in the chromium oxide rod for thermal spraying of the present invention is 70 to 98% by weight,
Preferably it is 80 to 98% by weight; if it is less than 70% by weight, the original effects of chromium oxide thermal spraying, such as wear resistance and high temperature oxidation resistance, will be impaired, and if it exceeds 98% by weight, the fired product will be mechanically damaged. It lacks strength and is extremely brittle, making it unpractical and undesirable. As described above, since the chromium oxide rod for thermal spraying according to the present invention is composed of coarse single crystals, when put into a plasma gun, these constituent particles take advantage of the characteristics of the coarse single crystal rod, and
It reaches the target substrate with a large inertial force, resulting in a good chromium oxide film with low scattering, loss, etc., and a high yield. Therefore, such a chromium oxide rod for thermal spraying has unprecedented desirable properties. The method for producing chromium oxide rods for thermal spraying in the present invention is not particularly different from the method for producing general rod-shaped products, but its distinctive feature is that it starts from coarse single-crystal chromium oxide particles with an average particle size of 2 to 50 μm. It is in the raw material. That is, in the case of dense fired products manufactured through the steps of kneading, shaping, drying, and firing raw materials, fine particles with an adjusted particle size distribution are generally used as raw materials, but the present invention is characterized by: Substantially independent coarse single particles obtained by firing a mixture of coarse chromium oxide, which originally has no sintering properties, and a suitable sintering agent and binder, molded into a rod shape. The present invention relates to a method of manufacturing a chromium oxide rod for thermal spraying, which is mainly composed of chromium oxide rod. The binder used in the present invention is one that imparts plasticity to the raw material, shape retention to the molded product, and increases the mechanical strength of the molded product when molding chromium oxide into a rod shape. Generally well-known methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, starch, polyvinyl ether, polyvinyl alcohol, polyethylene oxide, acrylic acid polymer, polyacrylamide, gelatin, etc., if they volatilize during baking, Both can be used. In addition, other binders include silica sol, alumina sol, and the like. There is no particular restriction on the amount added, and the amount may be determined based on workability and economic efficiency. For example, 5 parts by weight for 100 parts by weight of raw material single crystal chromium oxide.
Although it is preferably less than parts by weight, it does not necessarily have to be within that range. Next, as the sintering agent used in the present invention, since chromium oxide itself does not have sintering properties,
This is to retain chromium oxide, which is the main composition of the rod obtained by drying and firing the compact, and to impart mechanical strength to the rod itself. In the present invention, the addition of an appropriate sintering agent is is necessary. Examples of the sintering agent in the present invention include clay (Kibushi, Frogme clay, etc.), aluminum silicate, alumina, etc., but the type thereof is not particularly limited. In addition, the amount added is 2
~30% by weight, preferably 2-20% by weight is suitable. The reason for this is that as the amount of sintering agent contained in the chromium oxide rod for thermal spraying increases, the amount of single crystal chromium oxide decreases, which is the opposite of the reason for limiting the content of single crystal chromium oxide. The method of adding a binder, sintering agent, etc. to the raw material single crystal chromium oxide is to roughly mix it using a conventional mixing device, then adjust the humidity, and then knead it using a twin-screw kneader, etc. This is done by Molding into a rod shape is carried out using a vacuum extrusion molding machine, but any method is not particularly critical as long as the desired shape can be obtained. After drying the molded product, it is fired in an electric furnace, gas kiln, etc. After preliminary aging at approximately 400℃,
Calcination is performed at ~1800℃. If the firing temperature is less than 1000°C, the rod will not develop strength, and if it exceeds 1800°C, the constituent particles will become finer due to evaporation and condensation of chromium oxide, making it impossible to obtain the desired rod. In most cases, the temperature range is preferably from 1200 to 1700°C. Further, the optimum firing temperature may be determined depending on the type of sintering agent. The chromium rod for thermal spraying obtained by the manufacturing method of the present invention is mainly composed of coarse chromium oxide, which does not sinter to form a bond between particles, and substantially maintains its particle characteristics as it is. Ru. The size of the rod can be designed according to the mechanism and structure of the thermal spraying machine used, but usually the rod has a diameter of 2 to 10 mmφ and a length of 2 to 10 mm.
Cylindrical rods between 30 and 100 cm are generally preferred. The obtained chromium oxide rod is used as a thermal spraying material in the same way as powdered chromium oxide, but it is superior to powdered thermal spraying in terms of thermal spraying yield and working environment. [Example] The present invention will be explained in more detail with reference to Examples below. Example 1 1 Preparation of chromium oxide rod for thermal spraying Finely powdered chromium oxide with an average particle size in the range of 0.5 to 1.5 μm was placed in an alumina crucible and heated to 1500°C.
When sintering was carried out in an electric furnace at a high temperature under normal atmosphere, chromium oxide with an average particle size of 30 μm was obtained. To 100 parts by weight of chromium oxide obtained above, 3 parts by weight of carboxymethyl cellulose as a binder and 10 parts by weight of Kibushi clay as a sintering agent were blended,
After adding 9 parts by weight of water, the mixture was thoroughly kneaded. After aging overnight, 6.2mm in a vacuum extrusion molding machine.
A chromium oxide rod of 6.2 mmφ x 600 mm was formed using a φ die, dried at 110°C, and then fired in an electric furnace according to the following firing pattern. Room temperature to 400°C 3°C/min. 400°C Hold for 2 hours 400°C to predetermined temperature 5°C/min. Predetermined temperature held for 2 hours Natural cooling The results are shown in Table 1 below.

[Table] 2 Thermal Spraying Test The chromium oxide rod obtained by firing sample No. 6 in Table 1 at 1600°C was thermally sprayed using a plasma gun. As a result, compared to powder spraying, there was less scattering and loss of chromium oxide, improving the spraying yield and significantly improving the spraying work environment. Moreover, the obtained thermal sprayed coating was in a good condition comparable to that of powder sprayed coating. Further, when similar thermal spraying tests were conducted using chromium oxide rods of Sample Nos. 3, 4, 5, and 7, the same results as Sample No. 6 were obtained. [Effects of the Invention] As explained above, according to the chromium oxide rod for thermal spraying and the manufacturing method of the present invention, there is no scattering during thermal spraying, the thermal spraying yield is high, and the rod has excellent wear resistance.
An excellent effect can be obtained in that a thermal spray coating with excellent high-temperature oxidation resistance can be formed in a favorable working environment.

Claims (1)

[Scope of Claims] 1. A chromium oxide rod for thermal spraying, characterized in that its main composition is single-crystal chromium oxide having an average particle diameter in the range of 2 to 50 μm. 2. The chromium oxide rod for thermal spraying according to claim 1, containing 70 to 98% by weight of single crystal chromium oxide. 3. A chromium oxide rod for thermal spraying, which is characterized in that single-crystal chromium oxide particles having an average particle diameter of 2 to 50 μm are mixed with a sintering agent and a binder, and then the mixture is formed into a rod shape, and then heated and fired. Manufacturing method. 4. The method for producing a chromium oxide rod for thermal spraying according to claim 3, wherein the heating and firing temperature is in the range of 1000 to 1800°C.