JPH11280767A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the excellent rolling service life, and maintain density small by forming at least either of a bearing ring and a rolling body out of ceramics having the composition by adding zirconia by a specific quantity to alumina. SOLUTION: When zirconia is added to alumina as ceramics used for either of a bearing ring and a rolling body, a grain boundary of alumina is strengthened, strength is increased, and the rolling service life is also lengthened. It is necessary to add zirconia by at least 5 wt.% or more therefor. However, since the rolling service life is shortened when an adding quantity of zirconia too much, it is necessary to set a zirconia adding quantity not more than 50 wt.%. When the adding quantity of zirconia is not more than 50 wt.%, density of zirconia-added alumina can be maintained small as illustrated to thereby restrain an increase in a rolling body load by centrifugal force generated when the rolling body rotates at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing, and more particularly to a rolling bearing in which at least one of a race and a rolling element is made of ceramics.

[0002]

2. Description of the Related Art Ceramic rolling bearings have a lower density than iron in water and corrosive atmospheres utilizing the corrosion resistance of ceramics, at high temperatures utilizing heat resistance, and in strong magnetic fields utilizing non-magnetic characteristics. It is used in fields such as machine tools and HDDs that take advantage of this fact. In addition, these ceramic rolling bearings have excellent characteristics such as corrosion resistance, high rigidity, high speed, insulation, and non-magnetism compared to steel rolling bearings. Expansion is expected. Ceramics used for this rolling bearing include silicon nitride, zirconia, alumina, and silicon carbide.

[0003]

Among the ceramics used in the above-mentioned rolling bearings, silicon nitride is generally used because it has the longest rolling life and is most suitable as a material for rolling bearings. Is done. However, the high cost is preventing the use of silicon nitride from expanding. Zirconia has a large density of 6 g / cc, so its use is limited. This is because, as the density increases, the rolling element load due to centrifugal force generated when the rolling element rotates at high speed increases.

On the other hand, alumina is the cheapest in terms of price and its density is not so high. However, alumina has a problem that it is difficult to use as a bearing because it has low strength, short life, low fracture toughness and poor surface roughness after processing.

An object of the present invention is to provide an inexpensive ceramic rolling bearing having excellent rolling life, low density and low cost.

[0006]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that by adding a predetermined amount of zirconia to alumina, a ceramic rolling bearing having high strength, low density, low cost and long life can be obtained. It was found that it could be obtained.

Therefore, a rolling bearing according to the present invention is characterized in that in a rolling bearing having a race and a rolling element, at least one of the race and the rolling element is made of alumina and 5 watts of zirconia.
It is made of ceramics with a composition of at least t% and not more than 50 wt%.

When zirconia is added to alumina, the grain boundaries of alumina are strengthened, the strength of alumina is increased, and the rolling life is extended. In order to increase the strength of alumina, it is necessary to add at least 5 wt% of zirconia. However, if the added amount of zirconia is too large, the rolling life is rather shortened. For this reason, the amount of zirconia added needs to be 50 wt% or less.

If the amount of zirconia added is 50 wt% or less, the density of alumina to which zirconia is added is also 5%.
g / cc or less. Therefore, it is possible to suppress an increase in the rolling element load due to the centrifugal force generated when the rolling element is rotating at a high speed. In particular, a gyro-slip occurs in a bearing having a contact angle such as an angular ball bearing. If such a low-density material is used for the rolling element, the gyro-slip can be suppressed to a small value.

As described above, zirconia is contained in an amount of 5 wt% or more and
By setting the content to not more than wt%, the rolling life can be extended, the density can be kept small, and it can be manufactured at low cost because it is based on low-cost alumina.

[0011] In addition, when only alumina is used, the fracture toughness value is low, and when polishing is performed, the processing is performed while crushing, so the surface roughness of the finished surface is not good. However, by adding zirconia having high fracture toughness, the surface is processed by ductile grinding, so that the roughness of the processed surface is improved and the workability is improved.

[0012]

Embodiments of the present invention will be described below.

(1) Method for producing a sintered body and its characteristics A mixture of Al ₂ O ₃ (alumina) raw material powder and ZrO ₂ (zirconia) powder added at a weight ratio of 15%, 50% and 80% is uniformly prepared. After mixing, molding and sintering were performed. Sintering was performed in the atmosphere at a sintering temperature of 1600 to 1700 ° C. The resulting sintered body is a ball of size 3/8 ",
The ball surface was finished with submicron diamond abrasive grains.

For comparison, 100% Al ₂ O ₃ balls and 100% ZrO ₂ balls without the addition of ZrO ₂ powder were produced in the same manner.

15 wt% of ZrO ₂ in Al ₂ O ₃ , 50
Table 1 shows the properties (density, fracture toughness, hardness, and thermal conductivity) of the ceramic when wt% and 80 wt% were added.
For comparison, 100% of Al ₂ O _{3 and} 100% of ZrO ₂
Table 1 also shows the characteristics.

[0016]

[Table 1]

From the results shown in Table 1, it was found that the density and the fracture toughness increased as the amount of ZrO ₂ added increased. This is considered to be because ZrO ₂ has a higher density and a higher fracture toughness value than Al ₂ O ₃ .

When the amount of ZrO ₂ added was changed, the density of Al ₂ O ₃ added with ZrO ₂ changed as shown in FIG.

Further, the hardness and the thermal conductivity decreased as the amount of ZrO ₂ added increased. A higher hardness is advantageous for increasing the rolling life, but any hardness is sufficiently higher than the hardness HV800 of the bearing steel, so that there is no particular problem. Regarding the thermal conductivity, the thermal conductivity of Al ₂ O ₃ is large, but ZrO
₂ has low thermal conductivity. Although the bearing generates heat during use, the higher the thermal conductivity is, the better the cooling performance is without increasing the temperature inside the bearing. Therefore, the addition amount of ZrO ₂ should not be too large.

(2) Ball crushing strength and life test Next, the Al manufactured as described above was used._TwoO_Three100% ball
And Al_TwoO_ThreeTo ZrO_Two15 wt%, 50 wt%,
When the surface roughness of each ball to which 80wt% is added is measured,
In both cases, a crushing strength test and a rolling life test were performed.
In addition, Al_TwoO _ThreeTo ZrO_Two50 wt%, 80 wt%
Measurement of surface roughness and rolling life of the added ball
Only tests were performed.

The crushing strength test is carried out by stacking two balls 1 and 1 as shown in FIG. 2 and applying a load while increasing the load until the ball 1 breaks, and obtaining the load when the ball 1 breaks. Done.

In the rolling life test, as shown in FIG. 3, a driving force is transmitted from a pulley 18 to a shaft 15 via a coupling 17 to provide a support bearing (model number 6312) 14 for supporting the shaft 15 and the test bearing 4. Load spring 16
The test was performed until the ball 1 was broken while applying a constant load through the ball. The support bearing 14 and the test bearing 4 are respectively composed of balls 11, 1; inner rings 12, 2;
It consists of three and three. Table 2 shows the conditions of the rolling life test.

Table 3 shows the results of the measurements of the surface roughness, crushing value and rolling life.

[0024]

[Table 2]

[0025]

[Table 3]

According to the results shown in Table 3, in the case of the ball 1 of 100% Al ₂ O ₃ , the surface was separated from the surface of the ball 1 in a very short time, and the operation was stopped. On the other hand, ZrO ₂
In the case where the addition amount of Al is increased to 15 wt% and 50 wt%, the life tends to be longer than in the case of the ball 1 of 100% Al ₂ O ₃ , and the broken form of the ball 1 is a normal bearing. It turned out that it was the same peeling as. But,
When the amount of ZrO ₂ added was increased to 80 wt%, the life tended to be shortened. From this, Zr
It has been found that the added amount of O ₂ needs to be 50 wt% or less.

If the amount of ZrO ₂ added to Al ₂ O ₃ is set to 50 wt% or less, the density of Al ₂ O ₃ to which ZrO ₂ is added can be reduced to 5 g / cc or less from the results shown in FIG. Recognize.

In the case of a ball 1 made of 100% Al ₂ O ₃ ,
The fracture toughness value of Al ₂ O ₃ was small, and the surface roughness was as large as Ra 0.082 μm for processing while crushing the processed surface. However, 15wt the fracture toughness is greater ZrO ₂
% And 50 wt%, the processed surface tended to be smooth, and it was found that the effect of smoothing the processed surface was saturated at 50 wt% or more.

Further, crushing value becomes intensity 17.02kN by adding ZrO ₂ 15wt%, Al ₂
O ₃ as compared to 100% of the intensity 8.67kN was found to increase significantly.

In the above embodiment, the case where Al ₂ O ₃ added with ZrO ₂ is used for the ball of the bearing has been described, but the inner ring or the outer ring may be made of such ceramics.

In the above embodiment, the case where a ball is used as a rolling element has been described. However, the present invention is not limited to this, and the present invention can be widely applied to rolling bearings in general.

The embodiment disclosed this time is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0033]

As described above, in the rolling bearing of the present invention, at least one of the race and the rolling element is made of a ceramic having a composition in which zirconia is added to alumina in an amount of 5 wt% to 50 wt%. An inexpensive ceramic rolling bearing having excellent rolling life, low density and low cost can be obtained.

[Brief description of the drawings]

1 is a graph showing changes in Al ₂ O ₃ of density ZrO ₂ is added when changing the addition amount of ZrO _2.

FIG. 2 is a diagram showing how a crushing strength of a ball is measured.

FIG. 3 is a diagram showing a configuration of a rolling life test measuring instrument.

Claims (1)

[Claims] 1. A rolling bearing having a bearing ring and a rolling element, wherein at least one of the bearing ring and the rolling element is made of a ceramic having a composition in which zirconia is added to alumina in an amount of 5 wt% to 50 wt%. bearing.