JPH0135724B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing polycrystalline alumina sintered bodies having micropores, such as bearings, micro-orifices, and micro-nozzles. Conventionally, for example, in manufacturing bearings, the following method has been adopted. First, synthetic ruby and sapphire raw materials are single-crystalized by the Bernoulli method or the like. Next, this single crystal is cut and the outer diameter is shaped. Furthermore, holes are formed in this molded body by laser processing, diamond processing, or the like. After this, it is polished and finished to make the bearing. Although these processes have been highly automated through the development of specialized machines, the large number of steps involved and complexity has led to a rise in production costs. Therefore, a method of manufacturing the bearing using a conventional general ceramic manufacturing process may be considered. First, the particle size of synthetic ruby and sapphire raw materials is adjusted and granulated to obtain starting materials. Next, Figure 1 a~
The starting material is press-molded using the mold shown in c to form a molded article having micropores. That is, after inserting the lower punch 2 from the lower part of the die 1 and protruding the pin 4 from the hole 3 of the lower punch, the area surrounded by the die 1 and the lower punch 2 is filled with the starting material 5 (the first Figure a). Subsequently, the upper punch 7 and the lower punch 2, each having a pin insertion hole 6 penetrated through the center corresponding to the pin 4, are pressurized to press-form the starting material 5 (as shown in FIG. 1B). Continuing,
The upper punch 7 is raised, and the lower punch 2 is also raised to place the molded product 9 having micro holes 8 into the die 1.
Lift it up and take it out (as shown in Figure 1c). Thereafter, the molded body is fired to produce a bearing. However, conventional manufacturing methods have the following problems. First, it is difficult to make ultra-fine pins with a diameter of 50 to 400 μm. Furthermore, since uneven stress is applied to the pins during press molding, the pins are subject to severe wear and may even break. Additionally, it is difficult to fabricate equipment for attaching the fine pins, and the pins are difficult to hold. Therefore, it has not been possible to obtain a polycrystalline alumina sintered body having micropores using conventional methods. The present invention was made to eliminate the above drawbacks, and by improving the mold used during molding, it has the same appearance and performance as synthetic ruby and sapphire, and has micropores of 50 to 400 μm. The object of the present invention is to provide a method for producing a polycrystalline alumina sintered body having the following properties. The present invention will be explained in detail below. First, high-purity alumina powder, such as alumina for synthetic ruby and alumina for synthetic sapphire, is calcined in air to alphanize the crystal phase and improve powder formability, sinterability, etc.
Stabilize the shrinkage rate. In particular, in order to improve moldability, unless calcination is performed to remove crystallization water and reduce the specific surface area, lamination and mold adhesion will occur, and the frictional resistance with the mold will be large, making molding impossible. Next, the secondary particles generated by calcining are wet-pulverized using a pot mill to reduce the particle size to 0.3 to 2.3μ.
Adjust to m. The reason for limiting the particle size of the alumina powder is that if the particle size of the alumina powder is less than 0.3 μm, lamination and mold adhesion will occur, resulting in poor formability; This is because the sintered body deteriorates and the alumina powder does not become porcelain. In addition, when adjusting the particle size, Cr ₂ O ₃ , NiO,
A color tone adjusting agent such as MnO may be mixed. Next,
High-purity alumina powder whose particle size has been adjusted so that it can be press-molded is mixed with a binder using a high-purity alumina milking drum, and then granulated through a nylon mesh. At this time, a crystal growth inhibitor such as MgO may be added if necessary. Thereafter, the moisture content and particle size are adjusted to improve the fluidity of the granulated powder and prevent metal adhesion, and lubricating oil is added to the powder to prepare it as a starting material. Next, the starting material is press-molded using, for example, the molds shown in FIGS. 2a and 2c. That is, after inserting the lower punch 2 having the pin insertion hole 3 through the center from the lower part of the die 1, the starting material 5 is filled in the area surrounded by the die 1 and the lower punch 2 (see Fig. 2). a) As shown). Subsequently, the upper punch 11 with the pin part 10 for hole forming integrated into the lower part is lowered, and the pin part 10 is fitted into the insertion hole 3 of the lower punch 2, and the lower punch 2, the pin part 10 and the upper punch 11
The starting material 5 is press-molded (as shown in FIG. 2b). Subsequently, the upper punch 10 is raised and the lower punch 2 is raised to lift the molded body 9 having the micropores 8 onto the die 1 and take it out (as shown in FIG. 2c). Note that this mold may be made up of multiple units. After the above steps, the molded body is fired to obtain a polycrystalline alumina sintered body. Prior to this firing, in order to volatilize the binder, the molded body may be calcined at a temperature lower than that during firing. Therefore, according to the present invention, by integrating the pin part with the upper punch, it becomes easy to manufacture a mold having a diameter of 50 to 400 μm, and wear of the pin part is reduced, which is not necessary in the past. A hot pin attachment device is no longer required. Therefore, by using the above mold and adjusting the particle shape, polycrystals having micropores can be produced without deteriorating formability such as lamination and mold adhesion, and deteriorating sinterability. It became possible to obtain an alumina sintered body. Examples of the present invention will be shown below. Example 1 The high-purity alumina powder used as a raw material was synthetic ruby alumina [trade name manufactured by Baikovsky Co., Ltd.].
JOBKS−23; Al ₂ O ₃ 99.99% product, Cr ₂ O ₃ 4% content,
γ-Al ₂ O ₃ + α-Al ₂ O ₃ phase (abbreviated as FR in Table 1 below)] and alumina for synthetic sapphire [trade name BKS-28 manufactured by Baikovsky; Al ₂ O ₃ 99.99
% product, γ-Al ₂ O ₃ + α-Al ₂ O ₃ phase (FW in Table 1)
)] was used. Next, each raw material alumina powder was calcined in air. Table 1 shows the state of the alumina crystal phase determined by X-ray diffraction of each alumina powder after calcination. Next, the secondary particles generated by calcining are made of high purity alumina porcelain (99.5% Al ₂ O ₃ ).
The powder was wet-pulverized using a pot mill consisting of a pot and a ball to adjust the particle size, and then heated and dried to prepare a crushed powder having an average particle size shown in Table 1. Next, add a 3.5% solution of polyvinyl alcohol to the above crushed powder and add 33% Vol% of polyvinyl alcohol and MgO to _MgSO4 .
After adding 1.84 wt% in the form of 7H ₂ O, it was mixed in a high-purity alumina porcelain milker and granulated through a nylon mesh (#60). After this, in order to improve the fluidity of the granulated powder and prevent it from adhering to the mold, add 1 to 30% of the water.
The particle size was adjusted to 2%, the particle size was adjusted to 80 to 325 mesh, and 1 to 2% of lubricating oil was added to prepare the starting material. Next, after inserting the lower punch 2 with the pin insertion hole 3 through the center from the lower part of the die 1, the starting material 5 is inserted into the area surrounded by the die 1 and the lower punch 2.
(as shown in Figure 2a). Next, at the bottom
The upper punch 11 integrated with the pin part 10 for hole forming having a diameter of 110 μm is lowered to remove the pin part 1.
0 was fitted into the insertion hole 3 of the lower punch 2, a molding pressure of 1 t/cm ² was applied to the lower punch 2, the pin portion 10 and the upper punch 11, and the starting material 5 was press-molded (as shown in Figure 2b). . Subsequently, the upper punch 10 was raised, and the lower punch 2 was also raised to lift the molded product 9 having micropores 8 onto the die 1 and take it out (as shown in FIG. 2c). For molding at this time, we calculated the dimensions by multiplying the predetermined shrinkage rate, made a mold with 7 cavities, and used an automatic cam press to create a mold with 150 to 300 cavities.
The molding speed was 1/min. Regarding the molded body obtained by press molding,
As for its moldability, experiments were conducted regarding lamination, mold adhesion, and mold wear. Regarding lamination, experiments were conducted using a mold with a molding pressure of 1 t/cm ² and an upper punch pin diameter of 20 μm. Regarding mold adhesion, an experiment was conducted using the same mold as above. Regarding mold wear, a mold with an upper punch pin diameter of 110 μm was used, and the number of shots was measured when the pin diameter reached 95 μm, the lower limit of product tolerance, due to wear. The above experimental results are shown in Table 1 below. Next, the above molded body was heated to 950°C in air,
Temporary firing was performed. Finally, the bearing was fired by heating to 1800° C. in a hydrogen stream to produce a bearing made of a polycrystalline alumina sintered body as shown in FIG. The sintered body of the obtained bearing was examined by die check, and the results are also listed in Table 1 below. Additionally, the dimensions of the above bearing were measured. The locations where the dimensions were measured are shown in Figure 3, and the measurement results are shown in Table 2 below.

[Table] * Blaine air permeation method average particle diameter. Measurement after secondary particle disintegration As is clear from Table 1 above, Figures 2 a to c
Even when molded with a mold improved by
When using finer starting materials (No. in Table 1)
1 to 4), lamination and mold adhesion are significant, and the frictional resistance with the mold is large, making molding impossible. Furthermore, when starting materials having a coarser particle size than the average particle size range of the present invention are used (Nos. 13 and 14), lamination does not occur during molding, but sinterability deteriorates.
Even if the molded body is fired, it will not become porcelain. On the other hand,
Methods of the present invention (Nos. 5 to 12) using a starting material consisting of crushed powder with an average particle size in the range of 0.3 to 2.3 μm
This shows that it is possible to obtain a bearing made of a polycrystalline alumina sintered body that not only does not cause lamination during molding but also has good porcelain structure after firing. Note that the specific gravity and Vickers hardness are equivalent to synthetic ruby and the like.

[Table] As is clear from Table 2, the variation in dimensions was small and a substantially uniform bearing material could be obtained. In addition, the polishing allowance for final finishing can be appropriately taken. Example 2 The same high-purity alumina powder as in Example 1 was used as a raw material for both alumina for synthetic ruby and alumina for synthetic sapphire. Next, each raw material alumina was heated to 1250°C in air to form secondary particles. Next, the secondary particles were wet-pulverized in a pot mill, and at the same time, both raw materials alumina were mixed in an appropriate ratio to adjust the color tone. The mixing ratio and particle size are shown in Table 3 below. Hereinafter, each step of granulation, press molding, and firing was performed under the same conditions as in Example 1. The color tone of the bearing manufactured through the above process is shown in the third table below.
Shown in the table.

[Table] As is clear from Table 3, the color tone of the bearing manufactured by the manufacturing method according to the present invention can be freely changed by changing the blending ratio of raw material alumina. Further, the appearance and characteristics of the bearing are equivalent to synthetic ruby or synthetic sapphire. Note that the shape of the polycrystalline alumina sintered body having micropores produced by the method of the present invention is not limited to that shown in FIG. 3, but can be changed to the shape shown in FIGS. Polycrystalline alumina sintered bodies having micropores of various shapes as shown can be obtained. As described in detail above, according to the present invention, molding is performed using a mold consisting of a starting material made of alumina powder whose particle size has been adjusted and an upper punch integrated with a hole-forming pin, and then firing. Therefore, various effects listed below can be exhibited. (1) Bearings with micropores can be created without the complicated process of cutting and drilling single crystals.
Micro orifices, micro nozzles, etc. can be molded in a single process called press molding.
For this reason, polishing processing becomes easy, processing costs can be reduced, and it is also advantageous in terms of equipment and yield. (2) Conventional ceramic manufacturing technology is applied, so by using an automatic press, 1 to 2
Mass production of 10,000 pieces/hour press is possible.
Products become cheaper. (3) By changing the mold, products with various sizes and shapes can be manufactured, and the needs of a wide variety of products can be met relatively easily. Moreover, since the mold structure is simple, it is possible to reduce the cost of the mold and to limit the time required for replacing the mold. (4) Even though it is a sintered body, it can maintain the same performance and quality as a single crystal product, and when incorporated as a bearing in a watch or other various instruments, it can fully meet the purpose of use. be. (5) By changing the sintering temperature, it is possible to manufacture products with varying crystal grain sizes, which can be used for various purposes. (6) By adding a color tone adjusting agent such as Cr ₂ O ₃ to the raw material alumina powder at different mixing ratios, the color tone can be freely changed and the product value can be improved.

[Brief explanation of drawings]

Figures 1 a to c are sectional views showing a press forming process according to the prior art, Figures 2 a to c are sectional views showing a press forming process according to the present invention, and Figure 3 is a bearing manufactured by the method of the present invention. and FIGS. 4 to 7 are cross-sectional views showing other polycrystalline alumina sintered bodies having micropores manufactured by the method of the present invention. 1...Die, 2...Lower punch, 3...Bottom punch hole, 4...Pin, 5...Starting material, 6...Upper punch hole, 7...Upper punch, 8...Minute hole, 9
... Molded object, 10 ... Pin portion, 11 ... Upper punch.

Claims (1)

[Claims] 1 The particle size of high-purity alumina powder is 0.3 to 2.3 μm.
The starting material is granulated and press-molded using a mold that integrates a hole-forming pin and an upper punch to form a molded body with micropores, followed by firing. 1. A method for producing a polycrystalline alumina sintered body having micropores.