JP2002242942A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing that is easily manufactured, and is long service life, even if the rolling bearing is used under environment that water is mixed into lubricant, under high-vibration accompanied by high speed rotations and under heavy-load. SOLUTION: A ball bearing 1 has an outer ring 2, an inner ring 3, and a plurality of balls 4 disposed to be capable of rolling between the outer ring 2 and inner ring 3. In the ball bearing 1, oxide films 2a, 3a containing Se are formed on raceway surfaces of the outer ring 2 and inner ring 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing used for various machines such as a machine tool used in automobiles, electricity, information, construction, agriculture, steel, and other industrial fields.
In particular, in the environment where there is a risk that water may be mixed into the rolling bearings for engine accessories (such as rolling bearings used in alternators, electromagnetic clutches, intermediate pulleys, car air compressors, water pumps, etc.) and the lubricant inside the bearings. Rolling bearings suitably used in (for example, transmissions for automobiles, bearings for hub units and engine accessories, guide roll bearings and backup roll bearings for steel, bearings for railway vehicles, bearings for construction machinery, bearings for agricultural machinery, Papermaking machine dryer roll bearings).

[0002]

2. Description of the Related Art Generally, the life of a rolling bearing tends to be extremely reduced when moisture is mixed in a lubricant. For example, when 6% of water is mixed into a lubricant in a rolling bearing, it is reported that the rolling life of the rolling bearing is reduced from a fraction to a twentieth of that of a lubricant before mixing. ("Rolling fatigue at surface origin and internal origin", NSKBearing Journal, No. 636, pp. 1-10, 1977, Furumura, Shirota, Hirakawa).

[0003] In a rolling bearing used in an environment where water is present and comes into contact with the water, there is a great risk that water will enter the inside of the bearing. For example, in a vehicle wheel bearing, moisture is likely to be mixed into a lubricant inside the bearing under the influence of muddy water and rainwater on a road surface. Also, cooling water and rolling water are likely to be mixed into the lubricant in guide roll bearings of continuous casting equipment for steel materials and backup roll bearings of rolling mills. Further, it is said that since a paper roll dryer roll bearing is used in a process of drying wet paper containing water, water vapor is likely to be mixed into the bearing.

[0004] In such a rolling bearing, although the amount of water mixed into the internal lubricant is only about 100 ppm, it is reported that the life is reduced by 32 to 48% (Effects of Water and Oxygen During Rolling). Con
tact Lubrication, Wear, 12 (1968), pp. 331-342, P. Schatz
berg and IMFelsen). The reason why such a phenomenon occurs is that the mixed water is chemically decomposed to generate hydrogen ions, and the hydrogen ions are adsorbed on the rolling surface of the rolling bearing and become hydrogen atoms to form a high strain field (maximum shear stress position). In the vicinity), and the stress corrosion cracking type may be broken.

[0005] Therefore, in order to prevent the life of the rolling bearing used in an environment in which it comes into contact with water as described above, measures are taken to prevent water from entering the inside of the rolling bearing (such as a contact rubber seal). Sealing device etc.). On the other hand, in recent years, as automobiles have become smaller and lighter, engine accessories have also been required to be smaller and lighter, and also to have higher performance and higher output. Then,
During operation of the engine, for example, a high vibration and a high load (about 4 to 20 G by gravitational acceleration) due to high-speed rotation act on the alternator bearing through the belt. This causes early peeling of the bearing and shortens the life of the bearing.

[0006] Such early peeling phenomenon is caused by the fact that a few% of water contained in the lubricant (for example, about 0.1% of water may be contained in grease) is high. vibration,
It is considered that the stress corrosion cracking type is generated due to cracking in the same manner as in the case of the above-mentioned rolling bearing in which water is mixed in the inside, by chemically decomposing under high load to generate hydrogen ions.

[0007] Condensation can be considered as a source of moisture in the bearing. For example, bearings for engine accessories are often used in a high-temperature state, and are cooled to the atmospheric temperature after the operation is stopped. Therefore, moisture in the air existing in a small space inside the bearing may condense. A measure to prevent early peeling under high vibration and high load due to such high speed rotation is described in "SAE Technical Paper: SAE9.
50944 (Date February 27-March 2, 1995
1) to 14), the fatigue mechanism of alternator bearings and the change of grease from E grease to M grease, which has a high damper effect, to absorb high vibration and high load with M grease A technique for preventing early peeling by doing so is disclosed.

[0008] Japanese Patent Application Laid-Open Nos. 2-190615 and 6-43349 disclose, in a bearing used under a high vibration and a high load associated with the high speed rotation described above, the decomposition of a lubricant. Describes that hydrogen is generated, and the generated hydrogen atoms penetrate into the steel, thereby causing cracks at an early stage. In the above two publications, as a countermeasure against such early peeling, the bearing rolling surface has a thickness of 0.1 mm.
A method has been disclosed in which an oxide film having a thickness of about 2.5 μm is formed to suppress intrusion of hydrogen from a bearing rolling surface.

[0009]

However, with respect to a rolling bearing in which measures are taken to prevent water from entering the inside, for example, a contact rubber seal mounted on a chock outside the bearing and a contact rubber seal built in the bearing are used. It is thought that the water concentration in the lubricant can be suppressed to less than about 10% when water is used in combination, but it is impossible to completely prevent water from entering the lubricant.

[0010] Further, with respect to the bearings disclosed in JP-A-2-190615 and JP-A-6-43349, a process of forming a triiron tetroxide film by immersing a bearing ring in a caustic soda aqueous solution heated to a low temperature ( (Which is generally called black dyeing), which has a problem that the production is troublesome. Also, nitric acid (or a solution of nitric acid diluted with alcohol such as ethanol), hydrochloric acid,
An oxide film can also be formed in an oxidizing aqueous solution such as sulfuric acid by a process of corroding the bearing rolling surface to a degree that causes coloration. However, this process has problems in terms of equipment and processing time.

The thickness of the oxide film is at most 2.5 μm.
When the bearing load is large, the roughness of the bearing rolling surface is likely to deteriorate, and as a result, problems such as increased vibration may occur. As a means for forming an oxide film on the bearing rolling surface, there is a method other than the above-described method in which the bearing is heated at a high temperature in the atmosphere. However, when the bearing is heated in the atmosphere without controlling the temperature, oxidation is strongly caused and a scale (black scale) having a thickness of several μm is generated on the surface of the bearing. When scale occurs, metal loss occurs due to the unevenness,
There is a risk of starting points such as pits. Also, if the bearing is left in the atmosphere, the moisture in the air may react with the surface of the steel to cause atmospheric corrosion.

Accordingly, the present invention solves such problems of the conventional rolling bearing, and is used in an environment where water is mixed in a lubricant, or under high vibration and high load due to high speed rotation. Another object of the present invention is to provide a rolling bearing which has a long life and is easy to manufacture.

[0013]

In order to solve the above problems, the present invention has the following arrangement. That is, a rolling bearing according to the present invention is a rolling bearing including an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring, wherein a raceway surface of the inner ring is provided. At least one of the raceway surface of the outer ring and the rolling surface of the rolling element
Finally, an oxide film containing selenium is provided.

With such a configuration, hydrogen atoms generated by the decomposition of water mixed in the lubricant and the decomposition of the lubricant itself can enter the steel constituting the rolling bearing from the bearing rolling surface. Since the suppression is suppressed, the early peeling due to the generation of hydrogen is prevented, and the rolling bearing has a long life. Preferably, the content of selenium (Se) in the oxide film is 5 wt% or more. When the content of Se is less than 5 wt%, the bond between the raceway surface or the rolling surface and the oxide film is weakened, and the strength of the oxide film is reduced. As a result, the life of the rolling bearing becomes insufficient. In order to further increase the strength of the oxide film, the content of Se is more preferably 10 wt% or more.

On the other hand, if the content of Se is too large, the surface roughness of the oxide film deteriorates.
More preferably, it is at most t%. From the above,
The content of Se is preferably 5 wt% or more,
More preferably, it is 0 to 35 wt% or less. Also,
The thickness of the oxide film is preferably from 10 to 2000 nm. If it is less than 10 nm, the strength of the oxide film is insufficient, and if it is more than 2000 nm, the surface roughness of the oxide film deteriorates, so that the life is insufficient. In order to make these inconveniences less likely to occur, the thickness of the oxide film is more preferably 100 to 1000 nm.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a rolling bearing according to the present invention will be described in detail with reference to the drawings. [First Embodiment] FIG. 1 is a partial sectional view showing the configuration of a ball bearing which is a first embodiment of the rolling bearing of the present invention.

The ball bearing 1 includes an outer ring 2 (fixed wheel), an inner ring 3 (rotating wheel), a plurality of balls 4 rotatably disposed between the outer ring 2 and the inner ring 3, and not shown. Cage and outer ring 2
And a lubricant (not shown) such as grease filled in a space formed between the inner ring 3 and the inner ring 3. The raceways of the outer ring 2 and the inner ring 3 are provided with oxide films 2a and 3a containing Se. This oxide film 2
The content of Se in a, 3a is 5 wt% or more, and the thickness of oxide films 2a, 3a is 10 to 2000 nm.

Next, a method of manufacturing such a ball bearing 1 will be described. The outer ring 2, the inner ring 3, and the balls 4 are made of bearing steel (SUJ2), and are subjected to ordinary heat treatment (830 to 85).
After quenching at 0 ° C and oil cooling, tempering at 180 to 240 ° C) was used. The surface hardness of the outer ring 2, the inner ring 3, and the ball 4 is HRC 57 to 63, the amount of retained austenite is 0 to 20%, and the surface roughness Ra of the outer ring 2 and the inner ring 3 is Ra.
Is 0.01 to 0.03 μm, and the surface roughness Ra of the ball 4 is 0.1 to 0.03 μm.
003 to 0.010 μm.

After the outer ring 2 and the inner ring 3 are subjected to ordinary grinding (polishing) (or super-finishing may be performed after the grinding, if desired), the raceway surfaces of the outer ring 2 and the inner ring 3 are formed. Oxide films 2a and 3 containing Se at room temperature
a was provided. Thereafter, grease was sealed inside the ball bearing to manufacture the ball bearing 1. It is needless to say that the rolling surface of the ball 4 may be provided with an oxide film containing Se.

FIG. 2 shows a method and processing conditions for forming the oxide films 2a and 3a. This oxide film forming treatment does not require any thermal treatment such as heating, and all steps from the degreasing step to the drying step can be performed at room temperature. However,
In the drying step, drying while heating is preferable because it has the effect of shortening the time required for drying. For example, warm air drying using a dryer or the like is effective.

Since all the steps can be performed at room temperature, the process of forming an oxide film can be performed very easily as compared with the above-mentioned prior art (such as a method using an aqueous solution of caustic soda or an oxidized aqueous solution). . Further, as another prior art, Japanese Patent Application Laid-Open No. 2-190615 discloses a method of forming an oxide film on a bearing rolling surface by subjecting a bearing in which grease is sealed to heat treatment at 200 ° C. or lower in the atmosphere. It has been disclosed. However, the present invention does not perform any thermal treatment such as heating on the bearing before sealing the grease, forms an oxide film containing Se on the bearing rolling surface at room temperature, and then seals the grease. Therefore, it is significantly different from the above-mentioned conventional technology.

The oxidation treatment step of the oxide film formation treatment is performed by using Se.
This is performed by immersing the rolling bearing at room temperature in an oxidation treatment solution containing Se is one of the Group VIB elements and combines with many metals and non-metals like oxygen. Selenium oxide (SeO ₂ ) is used as an oxidizing agent or an oxidation catalyst (“Chemical Dictionary”, Tokyo Chemical Dojin, 1989.1).
0.20). Therefore, if the steel is treated with the oxidation treatment solution containing Se, in addition to the bond between Se and Fe, strong F
It is considered that the oxide film of e can be sufficiently formed even at room temperature. A commercially available solvent such as Black First (manufactured by Kozai Co., Ltd.) can be used as the solvent for the oxidizing solution.

Next, the results of two types of life tests performed on various deep groove ball bearings having substantially the same configuration as the above-described ball bearing 1 will be described with reference to Tables 1 and 2 and the graphs of FIGS. explain.

[0024]

[Table 1]

[0025]

[Table 2]

On the other hand, in the life test, the use of tap water at 5 wt%
Lubricating oil mixed (turbine VG6 manufactured by Nisseki Mitsubishi Corporation)
This is a life test under lubrication according to 8) (hereinafter referred to as a life test under water mixing). In the test bearing, 19 types having oxide films having different Se contents and thicknesses (Examples 1 to 5) were used.
13, comparative examples 1 to 6) deep groove ball bearing (JIS nominal number 6)
206), a life test was performed using a test machine as shown in FIG. That is, while rotating the test bearing,
The vibration sensor detects the vibration of the test bearing.

The test load Fr was 8800 N and the number of revolutions was 39.
The test was terminated when the rotation time was set to 00 rpm and the vibration value became 5 times the initial vibration value as the life. However, when the initial vibration value was not five times after 100 hours, the test was terminated. And the flaking (the presence or absence of peeling) of the track surface was confirmed. In addition, a life test was performed for each of ten types of bearings, and the average time was shown in the table as the life.

The other life test is a rapid acceleration / deceleration test in which the number of revolutions is switched every predetermined time (for example, every 9 seconds) (9000 rpm and 18000 rpm) assuming use in engine accessories (hereinafter, rapid acceleration / deceleration). Life test).
This test is similar to that described in JP-A-9-89724. The test bearings include 19 types (Examples 14 to 26, Comparative Examples 7 to 12) of deep groove ball bearings (JIS call number 630) having oxide films having different Se contents and thicknesses.
Using 3), a life test was performed using a testing machine as shown in FIG. That is, the test bearing is rotated while water circulated by the pump is injected into the test bearing, and vibration of the test bearing is detected by a vibration sensor.

The load condition is set as P (load load) / C (dynamic load rating) = 0.10, E grease is used as the sealed grease, and the life is determined when the vibration value becomes five times the initial vibration value. The test has been completed. However, when the initial vibration value was not five times after 1500 hours, the test was terminated. And the flaking of the raceway surface
It was confirmed. In addition, a life test was performed for each of ten types of bearings, and the average time was shown in the table as the life.

The ball bearings of Comparative Examples 1 and 7 had no oxide film, and were manufactured by enclosing grease in a polished state. Comparative Examples 2 to 4
Although the ball bearings of Nos. 8 and 10 have an oxide film containing Se, the content and thickness of Se are out of the scope of the present invention. Further, the ball bearings of Comparative Examples 5 and 11 were provided with an oxide film by heating to a high temperature in the atmosphere (at 280 ° C. for 20 minutes). Further, the ball bearings of Comparative Examples 6 and 12 were manufactured by immersing a bearing ring in a heated aqueous solution of caustic soda to form a triiron tetroxide film (blackening treatment), and then sealing the grease to produce a bearing. It is.

In all Examples and Comparative Examples, steel balls made of SUJ2 subjected to ordinary quenching and tempering were used for the rolling elements. The results of the above life test are summarized in Tables 1 and 2, and graphs of the life are shown in FIGS. FIGS. 3 and 4 are graphs showing the results of the life test under water mixed in Table 1, and FIGS. 5 and 6 are graphs of the results of the rapid acceleration / deceleration life test in Table 2. In the graphs of FIGS. 3 to 6, the results of the examples are indicated by “●”, and the results of the comparative examples are indicated by “○”. In addition, the numerical value of the column of "peeling" in Tables 1 and 2 is the number of bearings in which the peeling occurred among the ten test bearings.

As can be seen from Tables 1 and 2 and FIGS.
Those having an oxide film containing Se (Examples 1 to 1)
3, 14 to 26) had good results of the life test. This is because the oxide film prevents the hydrogen generated due to the decomposition of water in the lubricating oil from entering the steel,
It is considered that cutting was suppressed early. On the other hand, in Comparative Examples 1 and 7, since almost no oxide film was present, all of the ten test bearings suffered early peeling due to the generation of hydrogen. In Comparative Examples 2, 3 and 8, 9, the same oxide film forming treatment as that of the example was performed. However, in Comparative Examples 2, 8, the content of Se in the oxide film was small.
In Comparative Examples 3 and 9, the Se content was 5% or more, but the life of the oxide film was short because the thickness of the oxide film was insufficient (less than 10 nm). Further, in Comparative Examples 4 and 10, the oxidation treatment time was too long, and the thickness of the oxide film was too large, causing surface roughness and shortening the life.

Further, in Comparative Examples 5 and 11, in which the oxide film was formed by being left in the air at a high temperature, the hardness of the bearing was reduced due to the high temperature treatment, and the thickness of the oxide film was reduced. It was too large, the oxide film was scaled and brittle, and many pits were generated on the surface. further,
Comparative Examples 6 and 12 were subjected to a general black dyeing treatment and the thickness of the oxide film was appropriate, but the surface was severely roughened due to the corrosion treatment at a high temperature, and the vibration increased during the life test, resulting in rotation. It stopped and the life was short.

From the above results, it was found that the content of Se in the oxide film is preferably 5% or more, more preferably 10 to 35%. The thickness of the oxide film is 10 to 2
It turned out that 000 nm is preferable and 100-1000 nm is more preferable. As the material of the bearing of each embodiment, a bearing steel having a normal austenite and a residual austenite amount of the bearing of 0 to 20% was used. However, case hardened steel and carburizing and carbonitriding thereof were performed. Or an induction hardened steel can be used, and a bearing having the same excellent life as described above can be obtained.

[Second Embodiment] Next, a needle roller bearing which is a second embodiment of the rolling bearing of the present invention will be described. 2. Description of the Related Art Conventionally, rolling bearings have been used for a rotating portion that transmits power of an automobile transmission, but needle roller type bearings are often used from the viewpoint of load capacity and space. Particularly in engine pedals and automatic transmissions, needle roller bearings including radial type and thrust type are often used.

On the other hand, since the lubrication path to the bearing is complicated in the automatic transmission due to its structure, the lubricant may not be sufficiently supplied in many cases, and the automatic transmission is often used under severe lubrication conditions. For this reason, it is known that the oil film formation on the rolling contact portion of the bearing becomes insufficient, and peeling damage and sliding wear occur on the raceway surface, and defects such as peeling and abnormal vibration occur early. 10-259
541).

In addition, the use conditions are becoming more severe due to the demand for higher temperature and higher speed. In transmissions and the like, there is a phenomenon that peeling occurs with a structural change different from conventional peeling. ing. In needle roller bearings, Cr, M
The addition of elements such as o and V that improve wear resistance (Japanese Patent Laid-Open No. 10-259541) and the carburizing or carbonitriding of the rolling elements and the inner and outer rings increase the hardness and compressive residual stress of the bearing surface. And adjusting the surface roughness of the rolling elements and the inner and outer races (Japanese Patent Laid-Open Nos. 2-168021 and 3-117724) to prevent peeling damage and sliding wear, and provide a long service life. It has been reported that.

However, such a method hardly considers the peeling accompanied by the structural change as described above. Then, when the present inventors investigated the needle roller bearing in which flaking occurred, they found a bearing in which flaking occurred with a structural change in addition to the peeling damage. The following are conceivable causes of such a phenomenon. In the case of a needle roller bearing, since the load acting on the rolling elements is large, the rolling elements are caused to spin. It is presumed that due to the rotation slip, the lubricant was decomposed to generate hydrogen atoms, or the water mixed in the lubricant was decomposed to generate hydrogen atoms, thereby causing peeling with a structural change.

As a countermeasure against the above-mentioned early peeling, in a ball bearing lubricated with a lubricant (grease or the like), an oxide film having a thickness of 0.1 to 2.5 μm is formed on the raceway surface. There is the above-mentioned prior art in which the intrusion of hydrogen from the raceway surface is suppressed by the method described in Japanese Patent Laid-Open No. 2-19061.
5, Heikai 6-043349). However, the above-described conventional technology is a technology applied to a ball bearing, and in a needle roller bearing in which a larger sliding occurs between a rolling element and a fixed ring, an oxide film on the surface is peeled off and the surface becomes longer. Life may not be reached.

The above-mentioned prior art also has the above-described problems in the section of the problem to be solved by the invention. Further, the means for forming an oxide film on the bearing rolling surface other than the above-described prior art also has the above-described problems in the section of the problem to be solved by the invention. Then, when the same oxide film as that of the first embodiment was applied to the surfaces of the races and rolling elements of the needle roller bearing, the needle roller bearing showed an excellent life.

That is, the needle roller bearing of this embodiment is
In a needle roller bearing including an inner ring, an outer ring, and a plurality of rolling elements rotatably disposed between the inner ring and the outer ring, a raceway surface of the inner ring, a raceway surface of the outer ring, And an oxide film containing selenium is provided on at least one of the rolling surfaces of the rolling element.

With this configuration, the hydrogen atoms generated by the decomposition of the lubricant caused by the sliding of the rolling elements and the hydrogen atoms generated by the decomposition of the moisture mixed in the lubricant are caused by the raceway and the rolling rings. The penetration of the inside of the moving body is suppressed by the oxide film. In this case, early peeling due to the generation of hydrogen is prevented well, and the needle roller bearing has a long life.

In such a needle roller bearing, the content of Se in the oxide film is preferably at least 5 wt%. When the content of Se is less than 5 wt%, the bond between the raceway surface or the rolling surface and the oxide film is weakened, and the strength of the oxide film is reduced. As a result, the life of the needle roller bearing becomes insufficient. In order to improve the strength of the oxide film, the content of Se should be 10 wt%.
More preferably, it is the above.

If the content of Se is too large, the surface roughness of the oxide film is deteriorated.
More preferably, it is at most t%. From the above,
The content of Se is preferably 5 wt% or more,
More preferably, it is 0 to 35 wt% or less. Also,
The thickness of the oxide film is preferably from 10 to 2000 nm. If it is less than 10 nm, the strength of the oxide film is insufficient, and if it is more than 2000 nm, the surface roughness of the oxide film deteriorates, so that the life is insufficient. In order to make these inconveniences less likely to occur, the thickness of the oxide film is more preferably 100 to 1000 nm.

The method of manufacturing such a needle roller bearing (such as an oxide film forming process) is the same as in the first embodiment, and a description thereof will be omitted. Next, the results of life tests performed on radial needle roller bearings and thrust needle roller bearings provided with an oxide film containing Se will be described with reference to Tables 3 and 4 and the graphs in FIGS.

[0046]

[Table 3]

[0047]

[Table 4]

For each of the radial needle roller bearing and the thrust needle roller bearing, 19 types having 13 different oxide films having different Se contents and thicknesses (Example 13 and Comparative Example 6)
Test bearings were prepared. In addition, the comparative example 13 of Tables 3 and 4,
The needle roller bearing No. 19 does not have an oxide film, and is manufactured by enclosing grease in a state after polishing. Further, although the needle roller bearings of Comparative Examples 14 to 16 and 20 to 22 have an oxide film containing Se, the content and the thickness of Se are out of the range of the present invention. Further, the needle roller bearings of Comparative Examples 17 and 23 were provided with an oxide film by heating to a high temperature in the atmosphere (at 280 ° C. for 20 minutes). Further, in the needle roller bearings of Comparative Examples 18 and 24, the bearing rings were immersed in a heated caustic soda aqueous solution to form a triiron tetroxide film (black dyeing treatment), and thereafter grease was sealed therein to manufacture the bearings. It was done.

In all Examples and Comparative Examples, SUJ2 needle rollers which had been subjected to ordinary quenching and tempering were used as rolling elements. A life test was performed on these test bearings using a conventional life tester. That is, the vibration of the test bearing was detected by the vibration sensor while rotating the test bearing, and the test was terminated when the vibration value became five times the initial vibration value as the life. However, when the initial vibration value did not become 5 times after 500 hours, the test was terminated. And the flaking (the presence or absence of peeling) of the track surface was confirmed. In addition, life tests were performed on ten bearings of each type, and the average time was shown in Tables 3 and 4.

The conditions of the life test of the radial needle roller bearing and the thrust needle roller bearing are as follows. In addition,
Assuming the actual use of needle roller bearings, the lubricating oil used for both bearings is gear oil (Castrol Synth manufactured by Castrol, Inc.) dedicated to automatic transmissions.
TEC ATF), and the lubricating oil was used after mixing 5 wt% of water.

[Life Test Conditions of Radial Needle Roller Bearings] Bearing name: NA5902 Test load: 2500 N Rotational speed: 6800 rpm Lubrication temperature: 100 ° C. [Life test conditions of thrust needle roller bearings] Bearing name: FTNA-3047 Test load: 2500 N Rotational speed: 6800 rpm Lubrication temperature: 100 ° C. The results of the above life tests are summarized in Tables 3 and 4, and graphs of life are shown in FIGS. 9 and 10 are graphs of the life test results of the radial needle roller bearings in Table 3, and FIGS. 11 and 12 are graphs of the life test results of the thrust needle roller bearings of Table 4. is there. In the graphs of FIGS. 9 to 12, the results of the examples are indicated by “●”, and the results of the comparative examples are indicated by “○”. In addition, the numerical value of the column of "stripping" in Tables 3 and 4 is the number of bearings which caused flaking out of the ten test bearings.

As can be seen from Tables 3 and 4 and FIGS. 9 to 12, those having an oxide film containing Se (Example 27)
To 39, 40 to 52), the results of the life test were good. This is presumably because the oxide film suppresses the intrusion of hydrogen generated due to the decomposition of water in the lubricating oil into the steel, and thus the peeling was suppressed at an early stage. On the other hand, in Comparative Examples 13 and 19, almost no oxide film was present, and all of the ten test bearings suffered early peeling due to the generation of hydrogen. Comparative Examples 14 and 15 and 20 and 21 were subjected to the same oxide film forming treatment as in the Examples, but Comparative Examples 14 and 20 had a small content of Se in the oxide films. , 21 have a Se content of 5% or more, but the oxide film thickness is insufficient (10 n
m), resulting in a short life. Furthermore, in Comparative Examples 16 and 22, the oxidation treatment time was too long, and the thickness of the oxide film was too large, causing surface roughness and shortening the life.

Further, in Comparative Examples 17 and 23, in which the oxide film was formed by being left in the air at a high temperature, the hardness of the bearing decreased due to the high temperature treatment, and the thickness of the oxide film was reduced. It was too large, the oxide film was scaled and brittle, and many pits were generated on the surface. Further, Comparative Examples 18 and 24 were subjected to a general black dyeing treatment, and the thickness of the oxide film was appropriate, but the surface was severely roughened due to the corrosion treatment at a high temperature, and the vibration increased during the life test. The rotation stopped and the life was shortened.

From the above results, it was found that the content of Se in the oxide film is preferably 5% or more, more preferably 10 to 35%. The thickness of the oxide film is 10 to 2
It turned out that 000 nm is preferable and 100-1000 nm is more preferable. As the material of the bearing of each embodiment, a bearing steel having a normal austenite and a residual austenite amount of the bearing of 0 to 20% was used. However, case hardened steel and carburizing and carbonitriding thereof were performed. Or an induction hardened steel can be used, and a bearing having the same excellent life as described above can be obtained.

The first and second embodiments described above are examples of the present invention, and the present invention is not limited to both embodiments. For example, the type of lubricant used is not limited to those used in both embodiments, and ordinary lubricants commonly used for rolling bearings can be used. Further, in the present embodiment, the ball bearing and the needle roller bearing have been described as examples of the rolling bearing. However, the rolling bearing of the present invention can be applied to other various ball bearings and roller bearings. It is.

[0056]

As described above, the rolling bearing of the present invention has the following features.
Since the raceway surface and rolling surface have an oxide film containing Se, it has a long life even when used in an environment where water is mixed into the lubricant or under high vibration and high load due to high speed rotation. so,
Easy to manufacture.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a structure of a ball bearing which is an embodiment of a rolling bearing of the present invention.

FIG. 2 is a process chart showing a method and processing conditions for forming an oxide film.

FIG. 3 is a graph showing the correlation between the Se content of the oxide film and the life in the life test under water mixing of the bearing of the first embodiment.

FIG. 4 is a graph showing the correlation between the thickness of the oxide film and the life in the life test under water mixing of the bearing of the first embodiment.

FIG. 5 is a graph showing the correlation between the Se content of the oxide film and the life in a rapid acceleration / deceleration life test of the bearing of the first embodiment.

FIG. 6 is a graph showing the correlation between the thickness of the oxide film and the life in a rapid acceleration / deceleration life test of the bearing of the first embodiment.

FIG. 7 is a schematic view showing the structure of a tester used for a life test under water mixing.

FIG. 8 is a schematic diagram showing a structure of a test machine used for a rapid acceleration / deceleration life test.

FIG. 9 is a graph showing the correlation between the Se content of the oxide film and the life in a life test of the radial needle roller bearing of the second embodiment.

FIG. 10 is a graph showing a correlation between an oxide film thickness and a life in a life test of the radial needle roller bearing of the second embodiment.

FIG. 11 is a graph showing the correlation between the Se content of the oxide film and the life in a life test of the thrust needle roller bearing of the second embodiment.

FIG. 12 is a graph showing the correlation between the thickness of the oxide film and the life in the life test of the thrust needle roller bearing of the second embodiment.

[Explanation of symbols]

 1 Deep Groove Ball Bearing 2 Outer Ring 2a Oxide Film 3 Inner Ring 3a Oxide Film 4 Ball

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shinji Fujita 1-5-150 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J101 AA02 AA14 AA42 AA52 AA62 BA10 BA53 BA54 BA55 BA70 DA05 EA80 FA08 FA31 GA11 GA21 GA28

Claims (1)

[Claims] 1. A rolling bearing comprising an inner ring, an outer ring, and a plurality of rolling elements rotatably arranged between the inner ring and the outer ring, wherein a raceway surface of the inner ring and the outer ring A rolling bearing, wherein an oxide film containing selenium is provided on at least one of a raceway surface and a rolling surface of the rolling element.