JPS63101519A - Rolling body made of ceramics - Google Patents

Abstract

PURPOSE:To posess uniform pressure strength, by a method wherein a rolling body made of ceramics forms crystal texture of silicon nitride material having no orientation property, and isotropy is substantially provided. CONSTITUTION:Based on 100 wt pts silicon nitride powder, approximate 5 wt pts yttrium oxide, approximate 4 wt pts aluminium oxide, and approximate 3 wt pts aluminum nitirde are added for enough crashing and mixing. Approxi mate 5 wt pts organix binder and a proper amount of a solvent are added in the mixture powder for kneading, and the mixture is granulated so that a granular powder grain is average-sized to be approximate 70mum in diameter. By using the granular powder, atmospheric sintering is effected, and isotropic pressurizing sintering processing is applied. Thus, the formed rolling body sub stantially has isotropy, and provides uniform pressure strength.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a ceramic rolling element, and more particularly to a ceramic rolling element that has excellent pressure resistance and less variation in life.

(Prior art) In recent years, attempts have been made to use ceramic members such as silicon nitride sintered bodies, which have excellent heat resistance and wear resistance, are lightweight and have high rigidity, as materials for balls and rollers that are the rolling elements of bearings. Therefore, it is expected to be used as a member for bearings, especially those used under high temperatures.

Ceramic members for such bearings include:
Since the normal pressureless sintering method has large internal pores and lacks pressure resistance, those formed by hot pressing are used.

(Problem to be Solved by the Invention) However, even in rolling elements made of Ceramic 8 made by the hot pressing method, internal bores of 5 to 8 μm are scattered, and in general, the fracture strength of ceramics increases as internal defects such as bores become larger. It is still insufficient, as it is said that the hobto press method weakens the material.Furthermore, the hobto press method is uniaxially pressurized, and the resulting sintered compact has orientation, and therefore has anisotropy in mechanical properties. It has the disadvantage of being brittle against loads from any direction, and has the problem of large variations in service life.

In addition, in order to form rolling elements, such as balls, by the hot press method, the shape of the molded object by the pot press method is limited to a simple shape, so it is first formed into a flat plate shape, then cut into rod shapes, and then After being processed into a round bar, each ball is processed into an approximate shape and then finished into the final shape by barrel polishing. As described above, the formation of rolling elements from ceramic sintered bodies by the hot pressing method has the problem of high processing costs and poor productivity.

Therefore, there has been a strong desire for a ceramic rolling element produced by pressureless sintering that can be formed into a shape that approximates the final shape, has low processing costs, and has a compressive strength equal to or greater than that produced by hot pressing.

The present invention was made to solve these conventional problems, and has almost uniform pressure resistance against loads from any direction, less variation in life, and lower processing costs. The purpose is to provide a ceramic rolling element.

(Means for Solving the Problems) The ceramic rolling element of the present invention is characterized by having an internal pore size of 3 μm or less and being made of a gay nitride material whose crystal structure has no orientation.

That is, the ceramic rolling element of the present invention is obtained by controlling each manufacturing condition in a combination of pressureless sintering and isostatic pressure sintering (HIP) among the manufacturing processes of ceramic sintered bodies, For example, it can be manufactured as follows.

First, an appropriate amount of sintering aid is added to silicon nitride powder, mixed and pulverized, and then granulated by, for example, a spray dryer method. The particle size of this granulated powder is preferably in the range of 50 to 100 μm; if it exceeds 100 μm, internal voids will become large after sintering, and if it is smaller than 50 μm, no further effect will be obtained.

Next, it is molded into a shape that approximates the final shape of the rolling element by a mold press method, a rubber press method, or the like. After degreasing, this molded body is sintered under normal pressure, and then subjected to isostatic pressure sintering treatment in an inert gas atmosphere, for example, a nitrogen gas atmosphere, and the treated body is finished into a final shape by processing such as barrel polishing. Here, as for the temperature conditions for isotropic pressure sintering treatment, the higher the temperature, the smaller the internal voids will be. However, if the temperature is too high, a heterogeneous layer may be formed on the surface layer, reducing the pressure resistance, and if the temperature is too low, this effect will be reduced. Since this is insufficient, a range of 1500°C to 1800°C is preferred.

The pressure is 10 to 2000 kO/c, preferably 3
The range is 00 to 1000k (1/cze).

(Function) In the ceramic rolling element of the present invention, the internal pore size is 3 μm or less, so it has excellent pressure resistance, and since pressureless sintering is used, the obtained sintered body does not have orientation. Therefore, it has substantially isotropy, and exhibits almost uniform compressive strength in any direction.

Note that isotropy here means that the strength against external pressure does not differ depending on the direction.

(Example) Next, examples of the present invention will be described.

Example 1 First, 5 parts by weight of yttrium oxide, 4 parts by weight of aluminum oxide, and 3 parts by weight of aluminum nitride as sintering aids were added to 100 parts by weight of silicon nitride (Si3N4) powder, and the average particle size was Thoroughly pulverize and mix with a ball mill so that the particle size is 1.0 μm or less. 5 parts by weight of an organic binder and an appropriate amount of solvent are added and kneaded to this mixed powder, and the average granulated powder particle size is approximately 70 μm using a spray dryer method. It was granulated so that

Next, using this granulated powder, a press pressure of 1000kp/cd was applied.
It was molded into the shape shown in drawing (a) using a mold press.

After degreasing this molded body, approximately 180
Normal pressure sintering was performed at 0°C for 14 hours, and then nitrogen gas was sintered for 10 hours.
Isostatic pressure sintering treatment was performed under the conditions of 00k (1/aj), approximately 1700° C., and 140 minutes.

This silicon nitride sintered body was barrel polished to a diameter of 10 nm.
A ball for a bearing was formed.

Examples 2 to 4 Using the same silicon nitride powder as in Example 1, ceramic balls were formed under the same conditions as in Example 1 except for the manufacturing conditions shown in the table. Note that the shape of the molded product when using a dry rubber press is shown in drawing (b).

Comparative Example Also, for comparison with the present invention, a conventional hot press method was used with a press pressure of about 1000! 7/aa, temperature approximately 1800
A flat silicon nitride sintered body was molded under conditions of 0.degree.

When the interiors of the ceramic balls of Examples 1 to 4 and Comparative Examples thus obtained were examined by non-destructive testing, the ceramic balls of Examples 1 to 4 all had several 2-3 μm bores inside. For just existing. hand,
The ceramic ball of the comparative example had bores of 3 to 8 μm scattered both on the surface and inside.

Further, using the ceramic balls of Examples 1 to 4 and Comparative Example, a crushing test and a rolling fatigue test were conducted in the following manner. The results of each test are shown in the table.

(Crushing test) According to JIS-8-1501, the crushing strength was measured using an Instron universal testing machine at a crosshead speed of 5 mm/min, and is shown as the maximum contact pressure.

(Rolling fatigue test) Three ceramic balls were rotated on a 5IJJ board using a thrust type bearing testing machine, and the test was conducted at 100 klJ for the first 200 hours and at 250 kl for the 200th hour onward.
The test was conducted by applying a load of 100 g.

(Blank below) [Effects of the Invention] As explained above, according to the present invention, a substantially isotropic silicon nitride sintered body with an internal pore size of 3 μm or less is used. Ceramic rolling elements can be obtained that have excellent pressure resistance that is almost equal to that of the ceramics, and have a long life and little variation.

Furthermore, compared to the conventional hot press method, since pressureless sintering is used, the shape of the molded body can be approximated to the final shape, so processing costs can be reduced.

[Brief explanation of the drawing]

Drawing (a) shows the shape of a molded body formed by die pressing according to an embodiment of the present invention, and (b) shows the shape of a molded body formed by dry rubber pressing.

Claims (4)

[Claims] (1) A ceramic rolling element characterized by being made of a silicon nitride material with an internal pore size of 3 μm or less and a substantially isotropic grain boundary structure. (2) The ceramic rolling element according to claim 1, wherein the silicon nitride material is obtained by isostatically sintering a pressureless sintered body. (3) The ceramic rolling element according to claim 2, wherein the pressureless sintered body is formed using silicon nitride granulated powder having an average particle size of 50 to 100 μm. (4) Isostatic pressure sintering in an inert gas atmosphere at 150
The ceramic rolling element according to claim 2, which is coated at 0 to 1800°C and 10 to 2000 kg/cm^2.