JP2003232367A - Roller bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To intend to enhance further reliability by broadly extending lifetime of a bearing. <P>SOLUTION: In a roller bearing in which a plurality of rolling bodies are interposed to make it possible to roll in circumferential direction between an outer race and an inner race, at least one of the outer and inner races and the rolled bodies comprise a bearing steel in which presumed value in magnitude of interface of a system of a maximum oxidate is less than 5 μm in presumed area 30,000 mm<SP>2</SP>according to statistical method of polar regions. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to, for example, an aircraft,
The present invention relates to rolling bearings used for automobiles, steel, etc., and particularly to rolling bearings that require reliability of bearing life.

[0002]

2. Description of the Related Art Conventionally, oxide-based non-metallic inclusions contained in bearing steel have been one of the substances that have a great influence on the rolling life of bearings. Al ₂ O ₃ , CaO, SiO _{2 and the} like are well known as the oxide-based non-metallic inclusions, but among them, particularly hard Al ₂ O as an oxide-based inclusion that governs the rolling bearing life. ₃ and the like, is large in size, as a large number, the life of the bearing is possible is already known to fall extremely.

[0003] Conventionally, in order to improve the reliability of rolling life of bearings and to extend the life of the bearings, the purpose is to reduce the amount of oxygen in the steel (deoxidation) in the steelmaking process, and to achieve high deoxidizing ability, Al This is due to the fact that deoxidation treatment was performed alone or by adding both Al and Si, but in the end it may remain in the steel without being completely removed by refining during the steelmaking process. Probably the cause.

Further, in Japanese Patent Laid-Open No. 11-193855, a toroidal continuously variable transmission is used in a polar statistical method (Keiki Murakami, "Effects of Metal Fatigue Minute Defects and Inclusions", Yokendo 1993.
The first method issued March 8, 2013, pp. 233-261) is used to disclose a method for reliably guaranteeing the service life.

[0005]

[Problems to be Solved by the Invention] Conventional Al alone or Al
In the bearing steel deoxidized by the addition of both Si and Si, the residual non-metallic inclusions are dominated by the oxide-based non-metallic inclusions of Al ₂ O ₃ . The average size of this inclusion is about 5 μm, but the maximum size exceeds 10 μm,
Further, cluster-shaped inclusions in which the inclusions are densely packed in the flow direction may remain. For this reason, the rolling life of a bearing incorporating a bearing part manufactured using this steel is low, but a short-life product occurs, which is not yet sufficient from the point of view of the reliability of the rolling life of the bearing. There is a problem.

Further, in Japanese Unexamined Patent Publication No. 11-193855, the present invention is applied not to the bearing but to the transmission, and the maximum inclusion estimated value is 50 μm or less. Therefore, even if it is applied to the bearing, the life is surely secured. It is difficult to guarantee, and it is difficult to further improve reliability. The present invention has been made in order to eliminate such inconvenience, and an object thereof is to provide a rolling bearing capable of significantly extending the life of the bearing and further improving the reliability. To do.

[0007]

In order to achieve the above object, the invention according to claim 1 is a rolling bearing in which a plurality of rolling elements are interposed between an outer ring and an inner ring so as to be rollable in the circumferential direction. At least one of the outer ring, the inner ring, and the rolling element has an estimated area of 30,000 m by the polar statistical method.
The estimated value of the maximum oxide inclusion size is 5 at m ² .
It is characterized in that it is made of bearing steel having a thickness of not more than μm.

According to the above means, Al existing on the rolling surface is
_Since it is presumed that the size of very hard oxide inclusions such as ₂ O ₃ is small, it is possible to reduce the number of short-life products that occur infrequently and improve the reliability. In this case, it is preferable to use bearing steel having an Al content of 0.005% by weight or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the present invention will be described below with reference to the drawings. Figure 1 shows the square root of the maximum inclusion area A (maximum inclusion size) and -log-log (T-1
/ T), FIG. 2 is a schematic diagram of the thrust type life test, FIG. 3 is a graph showing the relationship between the Al content in steel and the L ₁₀ life ratio, and FIG. 4 is the maximum inclusion estimation. Dimensions and L ₁₀
5 is a graph showing the relationship with the life ratio, FIG. 5 is a graph showing the relationship between the square root of the maximum inclusion area A (maximum inclusion size) and the field of view area, and FIG. 6 is the square root of the maximum inclusion area A ( It is a graph showing the relationship between the maximum inclusion size) and the number of measurements.

In the rolling bearing of this embodiment, at least one of the outer ring, the inner ring and the rolling element has an estimated value of the maximum oxide inclusion size of 5 μm or less when the area estimated by the polar statistical method is 30,000 mm ² . It consists of a certain bearing steel. The details will be described below. First, Examples 1 to 10 shown in Table 1 in which various amounts of Al are contained on the basis of medium carbon steel and high chromium carbon steel, and other chemical components (C, Cr, Si, O) are also changed. 16 types of steel materials of Comparative Examples 1 to 6 were obtained.

[0011]

[Table 1]

Next, the cross-sectional area of each steel material of about 100 mm ²
Microscopic observation in a total area of about 500 mm ² .
Maximum non-metallic inclusions (Al ₂ O
₃ , CaO, SiO ₂ etc.) were measured. Table 2 shows the results of estimating the size of the largest inclusion that was not directly recognized by the extreme value statistical method from the measured size of the largest inclusion in the entire field of view and the size of the largest inclusion visually recognized in each field of view. Shown in.

[0013]

[Table 2]

The size of the largest non-metallic inclusion here means the maximum length in the case of a linear defect, and the maximum diameter in the case of a granular defect. Regarding the specific example of the method for measuring the maximum inclusion size by the extreme value statistical method, the above-mentioned Comparative Example 3 (JIS SUJ
2) will be described. First, the area of each field of view is fixed to 50
And 0 mm ^2, the area A of the maximum inclusion is visible in the visual field was measured, from which the largest inclusion size (= {square root} A
_max ) and use this as the measured value.

Then, the maximum inclusion size visually recognized in each visual field is plotted on the abscissa and -log-log (T-1 / T) is plotted on the ordinate, and the relationship between the two is plotted. As shown in FIG. The relationship between the probability and the maximum inclusion size becomes a straight line. The value of T here is T = {(S + S ₀ ) /
S ₀ }, where S is the estimated area and S ₀ is the measured area.

[0016] This time, the S and 30,000 mm ^2, next to T = 61 is T asked to S ₀ as 500 mm ² from the above equation, the vertical axis (-log-log (T-1 / T)) = 5.
7, the straight line (horizontal broken line) in FIG. 1 can be drawn. And
A perpendicular line (vertical dashed line) is drawn from the intersection with the straight line, and the value at the point that reaches the horizontal axis is estimated to be the maximum size of the inclusion that was not visually recognized. In this case, it becomes 13.4 μm.

The details of the extreme value statistical method are described in Takanori Murakami, "Effects of Metal Fatigue Minute Defects and Inclusions" (Yokodo 1993).
Issued on March 8, 1st edition), especially pages 88-99, 112-
P. 125, pp. 233-258. Also, this time, the 100 mm ² 5 places a viewing area S _0, a total of 500 mm ^2, the estimation area S by Polar statistical method was 30,000 mm ^2, the body and 6 of JP-A-11-193855 and JP-7 This is because, as disclosed, the variation in the estimated value of the maximum inclusion is reduced to differentiate the materials and obtain a more reliable value.

That is, the visual field area S _{0 is set} to 30 in the plane to be inspected.
And an area having a 0 mm ² or more size, the measurement of the square root √Amax area as the size of the largest inclusion in the field area having the 300 mm ² or more size, etc. optical microscope, does not overlap the inspection portion Repeat 5 times or more. The reason why the visual field area is set to 300 mm ² or more is as follows.

FIG. 5 (Japanese Patent Laid-Open No. 11-193855)
As shown in FIG. 6), the same material has the area S₀Strange
The square root of the area of the largest inclusion √Amax
Product S ₀According to the results of several estimations in
Product S₀Is 300 mm²If less than,
There is a large variation in the value of √Amax obtained by
Area S₀Is 300 mm²In the case above, √Ama
It is clear that the variation in the value of x is small.
It was

Therefore, the area S ₀ is 300 mm ²
It is desirable to set it as above. In FIG. 5, the above-mentioned √Amax is estimated three times using two kinds of test pieces having different melting conditions and processes, and both test pieces B and G in the figure are SCr420 steels. . The reason why the number of times of measurement is 5 or more is as follows.

As shown in FIG. 6 (corresponding to FIG. 7 of Japanese Patent Application Laid-Open No. 11-193855), the number of times of measurement is changed, and the square root √Amax of the area of the maximum inclusion is calculated several times in one measurement of the same material. According to the estimated results, when the number of measurements is less than 5, there is a large variation in the value of √Amax obtained by the extreme value statistical method, and when the number of measurements is 5 or more, the value of √Amax is It became clear that the dispersion of the values was small. For this reason, it is desirable that the number of measurements be 5 or more. In FIG. 6, using the same test pieces B and G as in FIG. 5, the estimation of √Amax is performed three times.

If the above-mentioned estimated area S is set to a value that is too small, the difference in size of the maximum inclusions between the materials becomes small, making it difficult to differentiate between the materials. If the value is set to a large value, the size of the maximum inclusion becomes large, which is far from the reality, so S =
It is desirable to set it to 30,000 mm ² or more. Next, a disk-shaped life test piece (outer diameter: 60 mm, thickness: 6 mm, surface roughness: using each of the steel materials of Examples 1 to 10 and Comparative Examples 1 to 6).
Ra of 0.008 to 0.01 μm) was manufactured for each of 10 sheets, and a life test was performed by a thrust type durability life tester. In the production of the test piece, steel having a C (carbon) content of 0.8% by weight or less was carburized to have a surface C% of about 1.0% by weight.

As shown in FIG. 2, the thrust type durability life tester uses a plate-shaped test piece with balls (steel balls: steel balls) as rolling elements.
SUJ2) is placed and the ball is rotated under the condition that the thrust load is applied. The test conditions are shown below. Surface pressure: 5500 MPa Rotational speed: 1000 min ⁻¹ Lubricating oil: Turbine oil # 68 Test temperature: 80 ° C. The life test was performed 10 times for each of the steel materials of Examples 1-10 and Comparative Examples 1-6, and the Weibull The total rotation time from the short life side to the peeling of 10% of the test pieces was obtained from the distribution function, and this was taken as the life. And
When the L ₁₀ life of Comparative Example 3 was set to 1, the L ₁₀ life ratio was obtained. The results are also shown in Table 2. In addition, the Al of each steel material is shown in FIG.
The relationship between the content and the L ₁₀ life ratio is shown.

As is clear from Table 2 and FIG. 3, Examples 1 to 10 in which the maximum inclusion size is 5 μm or less and the Al content is 0.005 wt% or less are about 10% less than the reference Comparative Example 3. 6 times or more of the long life result was shown, whereas in Comparative Examples 1 to 6 in which the maximum inclusion size exceeded 5 μm, the life extension could not be expected. It is considered that in Comparative Example 1, the carbon content in the steel was large and the carbides in the steel were large, which was the starting point and showed a short life.

Comparative Example 2 showed a short life as a result of large amounts of C 2 and Cr, large amounts of Al ₂ O ₃ due to large amounts of oxygen and Al present in the steel in addition to large carbides. It is estimated that Comparative Example 4 is also presumed to have a short life as a result of the large amount of Al ₂ O ₃ formed due to the large amount of oxygen and Al existing in the steel.

Comparative Example 5 has a low C weight% and is not carburized.
Time consuming, costly and non-conforming, and its lifespan
The value did not reach the example. In addition, FIG.
Maximum estimated inclusion size and L of Examples 1 to 10 and Comparative Examples 1 to 6
_TenIt is the figure which plotted the relationship with a life ratio. Clear from the figure
As you can see, when the maximum inclusion size is 5 μm or less, L_Tenlifespan
You can see that is improving. Also, preferably 3 μm or more
L below_TenLess variation in lifespan and more reliable
It

[0027]

As is apparent from the above description, according to the present invention, since the bearing life can be greatly extended, it is possible to provide a rolling bearing which can further improve reliability. You can

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a square root of a maximum inclusion area A (maximum inclusion size) and −log−log (T−1 / T).

FIG. 2 is a schematic view of a thrust type life tester.

FIG. 3 is a graph showing the relationship between the Al content in steel and the L ₁₀ life ratio.

FIG. 4 is a graph showing the relationship between the estimated maximum inclusion size and the L ₁₀ life ratio.

FIG. 5 is a graph showing the relationship between the square root of the area A of the largest inclusion (the size of the largest inclusion) and the visual field area.

FIG. 6 is a graph showing the relationship between the square root of the area A of maximum inclusions (maximum inclusion size) and the number of measurements.

Claims (2)

[Claims] 1. In a rolling bearing in which a plurality of rolling elements are interposed between an outer ring and an inner ring so as to be able to roll in the circumferential direction, at least one of the outer ring, the inner ring and the rolling element is polar statistics. A rolling bearing comprising a bearing steel having an estimated size of maximum oxide inclusions of 5 μm or less in an area estimated by the method of 30000 mm ² . 2. The rolling bearing according to claim 1, wherein a bearing steel having an Al content of 0.005% by weight or less is used.