JP2002339976A - Roller bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roller bearing having metal components and capable of ensuring the performance as high as that of a ceramic roller bearing. SOLUTION: This roller bearing 10 comprises metal races 11 and 12, and a metal rolling body 13, and a layer 20 having the hardness >=1,200 in terms of Vickers hardness(Hv) by the gas nitrosulphurizing treatment is provided at least on a surface of the rolling body 13. By setting the surface hardness of at least the rolling body 13 as high as possible compared to that of general metal members, the wear resistance of the rolling body 13 is improved, and the fretting durability of the bearing is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a rolling bearing.

[0002]

2. Description of the Related Art Conventionally, for example, a spindle shaft of a hard disk drive (HDD) or a floppy disk drive (FDD), a video tape recorder (V
In the case of a support bearing such as a cylinder head motor shaft of TR) or a motor shaft of a polygon scanner, it is necessary that the rotational performance, the acoustic performance, the fretting durability performance, and the like be extremely high.

In a rolling bearing used for such an application, at least the rolling element is made of ceramics.
High-speed rotation performance and fretting durability superior to ball bearings using ordinary steel balls are obtained.

[0004]

The above-mentioned conventional rolling bearings exhibit excellent performance but are expensive. Instead, there is a demand for a high-performance yet inexpensive rolling bearing.

[0005] As such a rolling bearing, various methods have been proposed in which various hardening treatments are applied to a raceway and a rolling element while being composed of metal parts.

As the hardening treatment, there are a method of forming a hard film and a method of modifying the surface.

The former method of forming a film has disadvantages such as insufficient interfacial strength with a metal base material and easy occurrence of peeling and the like.

In the latter method of surface modification, induction hardening treatment or various nitriding treatments are performed. In any of the treatments, the surface of the metal base material has a Vickers hardness (Hv) of 900.
The above is considered. Moreover, in the induction quenching treatment, a distortion occurs on the metal surface after the treatment, so that it is necessary to perform a polishing treatment, which increases the processing cost and requires a thicker surface layer portion, so that the hardened treatment layer hardly remains. It is pointed out. For the same reason, when the nitriding temperature is high in the nitriding process, the deformation after the process is large, and the accuracy and various functions are disadvantageous.

In view of such circumstances, an object of the present invention is to ensure the performance of a rolling bearing on a par with ceramics while using metal components.

[0010]

According to the present invention, there is provided a rolling bearing comprising:
As described in claim 1, the bearing ring and the rolling element are made of metal, and a layer having a hardness of 1200 or more in Vickers hardness (Hv) is formed on at least the surface of the rolling element by gas sulfide nitriding treatment. It is characterized by being provided.

[0011] The above-mentioned gas sulphating and nitriding is performed by other nitriding,
For example, a hardened layer that is dense and has a sufficient thickness can be formed at a relatively low temperature as compared with a salt bath nitriding treatment. In addition, since the hardness of the rolling elements is set to a predetermined value or more, the wear resistance of the rolling elements is improved at a level comparable to that of a rolling bearing using a ceramic rolling element, and the fretting durability of the bearing is improved. improves. In addition, the manufacturing cost can be lower than that of a rolling bearing using a ceramic rolling element.

According to a second aspect of the present invention, there is provided a rolling bearing wherein the race and the rolling element are made of metal.
At least on the surface of the rolling element, a hardened layer having a Vickers hardness (Hv) of 1200 or more is provided, and the surface roughness of the rolling element is 0.001 μm or less in center line average roughness (Ra). I have.

In this configuration, since at least the roughness of the surface layer of the rolling element is set to a predetermined value or less, rolling of the rolling element becomes smooth, which is advantageous in suppressing vibration.

According to a third aspect of the present invention, in the rolling bearing according to the first or second aspect, the rolling element comprises:
It is a ball having a sphericity of 0.05 μm or less.

In this configuration, since the rolling element is a ball with high shape accuracy, the rolling becomes smooth, which is advantageous in suppressing vibration.

According to a fourth aspect of the present invention, there is provided a rolling bearing according to any one of the first to third aspects, wherein the hardened layer has a diameter of 0.1% or more of a rolling element. And

In this configuration, since at least the thickness of the surface layer of the rolling element is set to a predetermined value or more, it is possible to prevent the occurrence of adhesive wear which causes a decrease in fretting durability.

According to a fifth aspect of the present invention, there is provided a rolling bearing according to any one of the first to fourth aspects, wherein the rolling element is made of martensitic stainless steel.

With this configuration, even when the gas sulphidizing and nitriding treatment is performed, a decrease in the hardness of the base material made of martensitic stainless steel is suppressed, and a decrease in the life of the rolling bearing is suppressed.

According to a sixth aspect of the present invention, the rolling bearing according to any one of the first to fifth aspects is characterized in that the surface layer of the rolling element is subjected to a gas nitrocarburizing treatment and then polished. It is characterized by being a nitrided layer obtained.

According to this structure, the distortion of the rolling element surface and the deterioration of the surface roughness caused by the gas sulphating and nitriding treatment are corrected by the polishing finish of the rolling element surface.

According to a seventh aspect of the present invention, in the rolling bearing according to the sixth aspect, when the gas sulfide nitriding is performed, the rolling bearing is temporarily set to 1% or more of the diameter of the rolling element. In addition, the diameter is set to 0.1% or more of the diameter of the rolling element by performing the polishing and finishing treatment.

In the first place, in the gas nitrosulphurizing treatment, the higher the treatment temperature and the longer the treatment time, the greater the thickness of the obtained hardened layer, but the distortion and the surface roughness deteriorate due to the treatment. In addition, the removal allowance due to the polishing finish for correction shown in claim 6 increases. Therefore, in the above configuration, the thickness of the hardened layer and the final hardened layer in the gas oxynitriding process are defined, and the allowance for the polishing finish after the gas oxynitriding process can be made appropriate.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on embodiments shown in the drawings.

First, an HDD device to which the ball bearing of the present invention is used will be briefly described. FIG. 1 is a sectional view showing the HDD device.

In the figure, reference numeral 1 denotes a spindle shaft, 2 denotes a stator fixed at an intermediate position in the axial direction of the spindle shaft 1, 3 denotes a rotor hub rotatably supported on the spindle shaft 1 via a pair of ball bearings 10, 10, Reference numeral 4 denotes a rotor fixed to the inner periphery of the rotor hub 3, and reference numeral 5 denotes an information recording medium such as a magnetic disk or an optical disk disposed on the outer periphery of the rotor hub 3.

Next, a ball bearing according to an embodiment of the present invention will be described. FIG. 2 is a sectional view of the ball bearing.

The illustrated ball bearing 10 is a deep groove ball bearing and includes an inner ring 11, an outer ring 12, a plurality of balls 13 and a retainer 14. The ball bearing 10 has a configuration in which a lubricant is sealed by seals 15 and 15.

The inner / outer rings 11, 12 and the balls 13 are formed of a metal material such as bearing steel or stainless steel as required.

Here, regarding the quality of the ball 13, "J
It is preferable to define the density more precisely than the G3 grade in "IS B 1501". By the way, "JIS B
The G3 rating in “1501” is defined as 0.08
μm, the sphericity is 0.08 μm, the surface roughness is 0.012 μm in center line average roughness Ra, and the difference between lot diameters is 0.1 μm.
This means that each is set to 13 μm.

Specifically, in this embodiment, regarding the quality of the ball 13, the diameter variation is 0.05 μm or less, the sphericity is 0.05 μm or less, and the surface roughness is 0.001 μm or less in center line average roughness Ra. , The difference between the lot diameters is 0.01
Set to μm or less.

The base material of the ball 13 is, for example, a martensitic stainless steel such as JIS SUS440C, the outer shape of which is adjusted, and the surface is subjected to gas sulfide nitriding to obtain a Vickers hardness. (Hv) 1200 or more nitrided layers 17 are provided.

Hereinafter, the gas sulfide nitriding treatment will be described.

First, the ball 13 having an outer shape is set in a chamber having an airtight structure, and a required reaction gas is supplied in a vacuum state. The reaction gas is a mixture of a carburizing gas, a nitriding gas, and a sulfurizing gas, that is, CO2.
₂ + (NH ₃ + N ₂ ) + H ₂ S is used.

Here, the temperature in the chamber is 480 ° C. to 600 ° C.
For example, the temperature is set to 500 ° C., and the temperature is maintained for 1 hour to 10 hours, for example, 5 hours. Thereafter, cooling is performed by oil cooling or air cooling over a required time.

Thus, first of all, the reaction gas, especially H ₂ S
Removes an impurity factor such as an oxide film inevitably present on the surface of the ball 13 as the target product, thereby exposing the pure surface of the base material of the ball 13. Subsequently, N quickly and deeply penetrates and diffuses into the base material of the ball 13 to form the nitrided layer 17 having a Vickers hardness (Hv) of 1200 or more, for example, 30 to 50 μm. Note that the depth of the nitride layer 17 can be controlled by appropriately setting the processing temperature and the holding time.

The nitride layer 17 formed as described above
As shown in FIG. 3, in order from the outermost surface of the ball 13 toward the inside, the relatively soft sulfurized layer 17 mainly composed of FeS is used.
a, a layered structure including a super-hard and dense nitride compound layer 17b containing Fe _2-3 N as a main component and a relatively hard nitrided diffusion layer 17c in which N atoms are diffused into the base material of the ball 13;

Further, by performing the above-described gas sulphidizing and nitriding treatment, the oxide film inevitably existing on the surface of the ball 13 can be removed and the nitrided layer 17 can be formed.
The processing temperature can be made extremely low as compared with ordinary gas soft nitriding or salt bath nitriding, and the balls 13 are less likely to be distorted. By the way, the surface roughness of the nitride layer 17 is as follows:
It is worse than the surface roughness of the target product before it is formed,
This is caused by the compound layer formed on the surface with a thickness of about 1 μm, and can be easily corrected by a polishing treatment after the treatment. Further, when the cross section of the nitride layer 17 was observed with a metallographic microscope (model: Olympus PMG3, magnification 400 times), the average particle diameter was 1 μm or less, and it was dense and smooth. The hardness of this nitrided layer 17 is 1200 to 1500 (test load 25 gf) in Vickers hardness (Hv).

The thickness of the nitride layer 17 is set to 1% or more, preferably 1.5% or more of the diameter of the ball 13 at the time of performing the above-mentioned nitrosulphurizing treatment. By performing the finishing treatment, the diameter of the ball 13 is set to 0.1% or more, preferably 0.15%.

Next, the ball 1 manufactured as described above is used.
No. 3 was subjected to a fretting test and will be described.

The fretting test was carried out in such a manner that the bearing was evaluated for swing durability under the following conditions, the axial vibration value of the bearing before and after the test was measured, and the amount of increase was determined. As conditions, the swing angle is 2 degrees (outer ring), the cycle is 6 Hz, the bearing preload is 1.7 kgf, and the number of swings is 100,000.
The ball bearing used in the test has a nominal number of 695.
Four samples of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared as samples. A test was performed for each sample with a sample number of n = 3, and the amount of increase in the axial vibration value of the bearing before and after the test was determined.

In the first embodiment, the ball 13 is made of SUS440C, and a nitriding layer 17 of Hv1200 is provided on the surface of the ball 13 by the above-mentioned sulphonitriding process. Here, the thickness of the nitrided layer 17 is 3 μm, which is the rolling element diameter (Bd · 2 mm).
0.15% of The quality of the ball 13 is as follows: the diameter variation is 0.05 μm, the sphericity is 0.05 μm, the surface roughness is 0.001 μm in center line average roughness Ra, and the difference between lot diameters is 0.01 μm. You have set.

In the second embodiment, the ball 13 is made of SUS440C, and a nitriding layer 17 of Hv1200 is provided on the surface of the ball 13 by the above-mentioned sulphonitriding process. Example 1 shows the thickness of the nitrided layer 17.
3 μm. And the quality of ball 13 is JI
Equivalent to the G3 class in SB1501, that is, the diameter difference is 0.08 μm and the sphericity is 0.08 μm.
m, the surface roughness is 0.012 μm in center line average roughness Ra,
The difference between the lot diameters is set to 0.13 μm.

In Comparative Example 1, the ball 13 was made of SUS440C, and a nitriding layer 17 of Hv1000 was provided on the surface of the ball 13 by the above-mentioned sulphonitriding treatment. The thickness of the nitride layer 17 was 3 μm as in Examples 1 and 2. The quality of the ball 13 is set to be the same as that of the second embodiment.

In Comparative Example 2, the balls 13 were made of silicon nitride ceramics formed by isotropic pressure sintering (HIP). The quality of the ball 13 is set to be the same as that of the second embodiment.

The results of the fretting test are as shown in the following table. In Examples 1 and 2, excellent fretting durability was obtained which was superior to Comparative Example 1 and was equivalent to Comparative Example 2. Was confirmed.

Sample Fretting Test Results (Increase in Vibration Value Before and After Test, mG) Example 13.1.
Example 22.9 Comparative Example 1152.3 Comparative Example 23.
2 The thickness of the nitrided layer 17 is less than 0.1% of the rolling element diameter (here, 0.1% of Bd = 2 mm, ie, 2 μm).
m), excellent durability was not obtained in the fretting test.

Further, the asynchronous rotational runout (No.
n Repeatable Run Out (NRRO) and vibration were examined, and will be explained.

The samples used here are the same as those in Examples 1 and 2 described above.
, And Comparative Examples 1 and 2 will be used, and the description will be omitted.

The NRRO test apparatus shown in FIG. 4 is used. In the illustrated NRRO test apparatus, reference numeral 20 denotes a sample bearing, 21 denotes a spindle shaft, 22 denotes a servomotor, 23 denotes a rubber coupling, 24 denotes a frame, 25 denotes an anti-vibration rubber,
26 is an air bearing, 27 is a non-contact displacement sensor, 28
Is a signal processing device.

In this apparatus, the run-out in the radial direction of the spindle shaft 21 is measured, and the overlap width in a state where the run-out for each rotation is overlapped is defined as the NRRO amount.

As a result of the NRRO measurement, when Comparative Example 1 is “1”, Comparative Example 2 and Examples 1 and 2 are “about 0.1”. That is, Comparative Example 2 and Examples 1 and 2 were significantly reduced to about 1/10 of Comparative Example 1.

The vibration of the ball bearing 10 is measured as follows.
As shown in FIG. 5, the displacement physical quantity in the radial direction is measured by bringing the vibration pickup 31 into contact with the outer ring 12 of the ball bearing 10 attached to the spindle shaft 32 in a horizontal posture.

As a result of the vibration measurement, when Comparative Example 1 is "1", Comparative Example 2 and Examples 1 and 2 are "about 0.03". That is, Comparative Example 2 and Example 1,
Sample No. 2 was significantly reduced to about 1/30 of Comparative Example 1. Moreover, Examples 1 and 2 were almost equivalent to Comparative Example 2.

As described above, the surface of the ball 13 has Hv
If the nitrided layer 17 having a hardness of 1200 or more is provided, the wear resistance of the ball 13 is improved, and the fretting durability of the bearing can be improved to the same performance as when a ceramic ball is used. .

In addition, regarding the quality of the ball 13, "JIS"
If the quality of all the balls 13 to be incorporated in the ball bearing 10 is made uniform at a high level and the individual difference is drastically reduced by specifying the density more precisely than the G3 class of "B1501",
Asynchronous rotational runout (NRRO) and vibration can be significantly reduced. Such a ball bearing 10 can be suitably used for a device that requires particularly high-precision rotation performance.

Note that the present invention is not limited to the above-described embodiment, and various applications and modifications are conceivable. For example, in the above embodiment, a ball bearing has been exemplified, but a roller bearing is also included in the present invention.

[0058]

According to the first to seventh aspects of the present invention, the race of the rolling bearing and the rolling element are made of metal, and at least the rolling element is subjected to a gas nitrocarburizing treatment to set the surface hardness to a predetermined value or more. Therefore, the abrasion resistance and fretting durability are improved at a level comparable to that of a rolling bearing using a ceramic rolling element, and the rolling bearing can be provided at a lower cost than a rolling bearing using a ceramic rolling element.

In particular, in the second aspect of the invention, at least the roughness of the surface layer of the rolling element is set to a predetermined value or less, so that the rolling element can smoothly roll, which is advantageous in suppressing vibration.

According to the third aspect of the present invention, since the rolling element is a ball having a high shape accuracy, the rolling becomes smooth, which is advantageous in suppressing vibration, and particularly, a high-precision rotation performance is required. It can be suitably used for an apparatus.

According to the fourth aspect of the present invention, since at least the thickness of the surface layer of the rolling element is set to a predetermined value or more, it is possible to prevent the occurrence of adhesive wear which causes a decrease in fretting durability. .

According to the fifth aspect of the present invention, since the material of the rolling elements is martensitic stainless steel, a decrease in the hardness of the base material can be suppressed even when the gas sulfide nitriding treatment is performed.
The reduction in bearing life can be suppressed.

According to the sixth aspect of the present invention, since the deformation of the rolling element surface and the deterioration of the surface roughness caused by the gas sulphonitriding can be corrected by polishing, the asynchronous rotational runout (NRRO) and vibration can be reduced. It will be much smaller.

Further, in the invention of claim 7, since the thickness of the hardened layer at the time of the gas oxynitriding treatment and the finally required thickness of the hardened layer are specified, the allowance for the polishing finish after the gas oxynitriding is provided. Can be made appropriate. This leads to a reduction in the allowance in the polishing finish, which can contribute to a reduction in manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an HDD device as an example of using a ball bearing of the present invention.

FIG. 2 is a sectional view showing an upper half of a ball bearing according to an embodiment of the present invention.

FIG. 3 is an enlarged cross-sectional view of the surface of a ball provided with a nitrided layer by a nitrosulphurizing process.

FIG. 4 is a schematic configuration of an NRRO test apparatus.

FIG. 5 is an explanatory diagram showing a form of vibration measurement.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ball bearing 11 Inner ring 12 Outer ring 13 Ball 14 Cage 20 Nitride layer of ball

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3J101 AA03 AA32 AA42 AA62 BA02 BA10 DA02 DA11 EA03 EA06 FA44 GA53

Claims (7)

[Claims] 1. A rolling bearing in which a bearing ring and a rolling element are made of metal, wherein a layer having a hardness of 1200 or more in Vickers hardness (Hv) is provided on at least the surface of the rolling element by gas sulphonitriding. A rolling bearing characterized by being made. 2. A rolling bearing in which a bearing ring and a rolling element are made of metal, wherein at least a surface of the rolling element has a hardened layer having a Vickers hardness (Hv) of 1200 or more, and a surface roughness of the rolling element. However, the rolling bearing has a center line average roughness (Ra) of 0.001 μm or less. 3. The rolling bearing according to claim 1, wherein the rolling element is a ball having a sphericity of 0.05 μm or less. 4. The rolling bearing according to claim 1, wherein the hardened layer has a diameter of 0.1% or more of a rolling element. 5. The rolling bearing according to claim 1, wherein the rolling element is made of martensitic stainless steel. 6. The rolling bearing according to claim 1, wherein a surface layer of said rolling element is a nitrided layer obtained by subjecting to a gas sulphonitriding process and then polishing and finishing. Rolling bearing. 7. The rolling bearing according to claim 6, wherein the thickness of said nitrided layer is once set to 1% or more of a diameter of a rolling element at the time of performing said gas sulfide nitriding treatment. A rolling bearing characterized in that the diameter is set to 0.1% or more of a rolling element by performing a polishing finish treatment.