JPH0675858B2 - Method of manufacturing ceramic sphere - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for manufacturing a ceramic sphere used for a ball bearing or the like.

[Technical background of the invention and its problems]

Balls such as ball bearings are required to have excellent mechanical properties such as wear resistance, and therefore attention is paid to the use of ceramics as the material thereof. Such ceramic spheres have been conventionally manufactured by (a) rolling granulation method, (b) stirring granulation method, (c) mechanical pressing method, (d) isostatic pressing method, (e) dango dime method and the like.

In the rolling granulation method (a) or the stirring granulation method (b), while rolling or stirring the ceramic powder, additives such as water, an organic solvent, a binder and other plasticizers are added, It is formed into a spherical shape. However, with these methods, the density tends to be non-uniform in the sphere, and it is difficult to improve wear resistance.

The mechanical pressing method of (c) is essentially unsuitable for forming spheres because the pressing direction is one direction, and is applied only to cylindrical or straw-shaped formed bodies.
There is also a problem that the density becomes non-uniform in the molded body.

The isostatic method (d) is an effective method for molding spherical molded bodies with a uniform density. However, since it takes time to fill the spherical mold with the ceramic powder, the productivity is low.

The dango dime method of (e) has been conventionally used for clay-containing ceramics, but has not yet been established as a method for forming fine ceramics.

[Object of the Invention]

The present invention has been made in consideration of the above circumstances, and an object thereof is to provide a method capable of producing a ceramic sphere having a uniform density at a low cost without lowering the productivity.

[Outline of Invention]

The method for producing a ceramic sphere of the present invention comprises a step of rolling or stirring ceramic powder, a liquid and a binder to form a sphere, a step of drying the sphere, and a step of maintaining a dry state on the surface of the sphere. A step of forming a protective film of
The method is characterized by comprising a step of performing pressure molding by an isostatic press and a step of firing the obtained molded body.

According to such a method, the mass productivity of the rolling granulation method or the stirring granulation method can be utilized, and by using the isostatic method, it is possible to obtain a ceramic sphere having a high uniformity of the molding density. As a result, ceramic spheres having excellent wear resistance can be obtained at low cost.

Example of Invention

 Examples of the present invention will be described below.

Example 1 First, 100 parts by weight of yttria partially stabilized zirconia powder having a specific surface area of 5 m ² / g and 5% aqueous solution of polyvinyl alcohol 3
After premixing with 0 part by weight, three types of spheres having diameters of 2.5 mm, 6.3 mm and 12.5 mm were granulated using a rolling granulator. Next, the spheres are dried to reduce the residual water content in the spheres to zero.
Adjusted to 5%. Next, use commercially available rubber paste with kerosene 3
A double diluted product was prepared and tumbled and dried while spraying on the sphere to form a rubber film of about 0.1 mm on the surface of the sphere.

Then, each of the obtained spheres was divided into two groups, and one group (Example) was pressurized with a pressure of 2 ton / cm ² using a wet isostatic press. By this molding, the diameter of the sphere is 2 mm and 5 m
It was compressed to about m and 10 mm. The other group (Comparative Example) was not pressed by the isostatic press.

Then, put each sphere in an alumina bowl, in air,
Baking was performed at 1500 ° C. for 2 hours. As a result, the diameters of the spheres of the examples were 1.4 mm, 3.6 mm and 7.1 mm, respectively. Also, the diameters of the spheres of the comparative examples are 1.6 mm, 3.9 mm and 7.8 m, respectively.
It became m.

The zirconia spheres obtained as described above were placed in a polybin and subjected to skid for a whole day and night to smooth the surface. Then, it was put into a pot mill, the relationship between time and wear rate was investigated, and a wear resistance test was conducted. The results are shown in the figure.

As is clear from the figure, when comparing the zirconia spheres obtained by the method of the example with the zirconia spheres of the comparative example that were rolling only and were not pressurized by the isostatic press, the comparative examples were the same time. Has a much higher wear rate. It is considered that this is because the density of the spheres was non-uniform because the method of the comparative example did not apply pressure by the isostatic press.

Further, in the conventional isostatic press method in order to produce 100 kg of sintered zirconia spheres having a diameter of 7.8 mm, labor of 10.25 hours was required, whereas in the method of the present invention, labor of only 1.5 hours was required, We were able to greatly improve productivity.

Example 2 First, 100 parts by weight of alumina powder having a specific surface area of 25 m ² / g and a purity of 99.99% was put into a tumbling granulator and, while rotating, 0.5
A solution prepared by dissolving 50 parts by weight of magnesium sulfate in 50 parts by weight of a 10% aqueous solution of polyethylene oxide is sprayed, and the diameter is
Granulated into 8 mm spheres. Next, this sphere was dried to remove water. Then, prepare a solution of polyvinyl butyral dissolved in methyl ethyl ketone, tumbling dry while spraying on the sphere, about 0.05 mm on the surface of the sphere.
Of polyvinyl butyral film was formed.

Then, the spheres were placed in a bag made of a 20 mesh net and pressed with an isostatic press at a pressure of 1.5 ton / cm ² . This pressure resulted in a sphere diameter of 5.5 mm. Subsequently, for comparison, this sphere and a sphere that was not pressed by an isostatic press were placed in an alumina bowl and baked in air at 1450 ° C. for 2 hours to obtain an alumina sphere.

The density of the obtained alumina spheres was 3.95 g / cm ³ , and the Vickers hardness was 1600 kgf / mm ² at a load of 5 kg. on the other hand,
The density of the spheres fired without isostatic pressing is 3.58 g / cm ³ , and the Vickers hardness is 5 kg load.
It was 1080 kgf / mm ² .

Next, these two types of alumina spheres were polished to a diameter of 4 mm, 10 thrust bearings each were fitted, and a rolling durability test was conducted at a contact stress of 200 kgf / mm ² and 600 rpm. As a result, in the spheres which were not subjected to the eye static pressing, the surface was cracked after 26 hours, whereas the alumina spheres obtained by the method of the present invention were
No change was observed after 100 hours.

In the above examples, the case of producing spheres of zirconia and alumina was described, but the method of the present invention is not limited to this, non-oxides such as silicon nitride and silicon carbide, or composites such as mullite, spinel and cordierite. Needless to say, the same applies to oxides.

Regarding the combination of the ceramic powder and the liquid used for rolling granulation, for example, when a water-resistant ceramic powder such as β-alumina or magnesia is used, an organic solvent such as acetone or toluene may be used. The agent may be used according to it.

〔The invention's effect〕

As described in detail above, according to the present invention, it is possible to manufacture a ceramic sphere having high productivity and high density uniformity,
As a result, it is possible to produce a ceramic bearing or the like having good wear resistance and long life at low cost, which is a remarkable effect.

[Brief description of drawings]

The figure is a diagram showing the relationship between time and wear rate in a wear resistance test of zirconia spheres produced by the method of the example of the present invention and the method of the comparative example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuo Nomura 87-1573, Tokai, Onuma, Togane-shi, Chiba, Toshiba Ceramics Co., Ltd. Togane Plant (56) References Japanese Patent Publication Sho 55-16044 (JP, B2)

Claims (2)

[Claims] 1. A step of rolling or stirring ceramic powder, a liquid and a binder to form a sphere, a step of drying the sphere, and a protective film for maintaining a dry state on the surface of the sphere. And a step of press-molding by an isostatic press, and a step of firing the obtained molded body. 2. A method of adding a liquid and a binder while rolling or stirring ceramic powder, or adding a binder solution to ceramic powder in advance and then rolling or stirring. 2. The method for producing a ceramic sphere according to item 1 above.