JP2000297819A - Bearings using ceramic coated balls - Google Patents

Abstract

(57) [Problem] To provide a ball bearing which can simultaneously prevent both fretting wear and preload loss. A ball of a ball bearing is formed of a metal material having substantially the same linear expansion coefficient as the race of the ball bearing, and a ceramic coated ball is formed by coating the ball surface with a ceramic material. Even if there is a temperature difference between the time of assembling the bearing and the time of use, the raceway and the ball expand or contract in the same manner, so that preload loss or excessive preload can be prevented as with a ceramic ball. In addition, since the ball and the bearing ring are in contact with each other via the ceramic layer, high rotational performance and high acoustic performance that can prevent filleting wear can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing using a ceramic coated ball, and more particularly, to forming a hard ceramic film on the surface to enhance filleting resistance, and also to prevent a phenomenon of preload loss due to a temperature change. The present invention relates to a bearing suitable for an HDD spindle motor device or the like using a rolling element made possible.

[0002]

2. Description of the Related Art For example, as a bearing for an HDD device, a small angular ball bearing is frequently used in a spindle motor shown in FIG. 5 and a swing arm motor shown in FIG. The former ball bearing 1 includes a cup-shaped flange 2 on which a magnetic disk (not shown) is mounted, and a shaft 4 erected on a base 3.
The motor M is used to smoothly rotate around the motor, and particularly high rotational and acoustic performance is required. In the latter ball bearing 1 for a swing arm, the swing arm 7 for positioning the head 6 by accessing the effective area of the magnetic disk D is smoothly moved around a shaft 9 erected on a base 8 by a motor. Used to swing drive. Preload is applied to these ball bearings 1 at room temperature in order to increase the shaft support rigidity. However, in the case of a motor of an HDD device, downsizing is required, so that a constant-pressure preload method requiring a space cannot be adopted. Therefore, the inner rings 1n of the two ball bearings are mounted on the shafts 4 and 9 and the outer ring 1g is mounted on the inner peripheral surface of the flange 2 or the sleeve 10 as an object to be rotated by an adhesive, respectively, in a state where a load is applied from above and preloaded. A fixed position preloading method is adopted.

In the ball bearing 1 of the HDD device, fretting wear (fine motion wear) occurs due to minute vibration of the rotating portion (2, 10) in the rotation direction during transportation of the device, which adversely affects acoustic performance and vibration performance. Easy to receive. This fretting wear occurs on the ball B of the bearing 1. Therefore, as a countermeasure against fretting wear, use of a ceramic material for the ball B of the bearing has begun to be performed. This is because the surface properties, hardness, mechanical strength, chemical stability, wear coefficient and the like of ceramics are superior to steel materials such as bearing steel.

[0004]

However, even though the ceramic balls have excellent surface characteristics, they have a 70% smaller linear expansion coefficient and a 50% lower elastic modulus than steel balls.
%large. For this reason, in the case of a fixed-position preloading system such as a ball bearing for a motor of an HDD device, when the temperature increases during use of the device, a change in the maximum contact stress between the ball and its rolling surface increases, and the bearing increases. The rigidity (preload) is greatly reduced, and in extreme cases, there is a possibility that so-called preload loss occurs in which the preload becomes zero during use.

Hereinafter, the possibility of occurrence of the preload loss will be examined. For the elastic deformation and stress of the contact portion where the ball and the rolling surface are in rolling contact, Hertz's elastic contact theory can be applied. Generally, as shown in FIG. 7 (a), when two objects I and II, which are elastic bodies having a smooth surface, come into contact with each other, a main surface which is orthogonal to each other in a plane of symmetry near the contact point. Curvature surfaces 1 and 2 exist. Then, as shown in FIG. 7 (b), the main curvature radii r _I1 and r _I2 in the cross section of the main curvature surfaces 1 and 2, respectively, and the main curvature surface 1
And 2 have principal radii of curvature r _II1 and r _{II 2} respectively. These principal radii of curvature r _I1 , r _I2 , r _II1 , r
_The principal curvatures, which are reciprocals of _II2 (each principal curvature radius is positive for a convex surface and distinguished by a negative sign for a concave surface) are ρ _I1 , ρ _I2 , ρ _II1 , and ρ _II2 , respectively.

[0006] In this contact portion, a contact ellipse A having two radii of a length orthogonal to each other (a major radius a and a minor radius b) is formed. Now, the maximum contact stress acting on the center of the contact ellipse A due to the vertical load Q applied to the contact ellipse A is σ _max ,
Assuming that the amount of approach between the two elastic bodies I and II due to the load Q is δ, σ
_max and δ are given by the following equations, respectively.

[0007]

(Equation 1)

Therefore, the ball B and the rolling groove of the outer ring 1g and the inner ring 1 in the angular ball bearing 1 as shown in FIG.
Consider applying to contact with n rolling grooves. Now, the ball B is made of ceramic, and the outer ring 1g and the inner ring 1n are made of steel.
The ceramic material has a longitudinal modulus of elasticity E _I = 3.20 × 10 ⁴ kg / mm ² Poisson's ratio m _I = 10 / 2.7 Linear expansion coefficient A _I = 3.2 × 10 ⁻⁶ / ° C. Thermal conductivity B _I = 10.8 w / m, k steel longitudinal elastic modulus ^{_{E II = 2.12 × 10 4 kg}} / mm 2 Poisson's ratio m _II = 10/3 linear expansion coefficient ^{_{A II = 11.8 × 10 -6 /}} ℃ thermal conductivity B _II = 76 w / m, with k Therefore, the maximum contact stress σ for ceramic balls
_{The maximum} and the approach amount δ are σ _max = 210 × (1 / μν) ₃ √ ｛(Σρ) ² Q｝ (1) δ = (1.13 / 10 ³ ) (2K / πμ) ₃ √ ｛ΣρQ ² ｝ (2) μν, 2K / πμ is a function of ρ.

In FIG. 8, the diameter of the ball B is d, and the outer ring 1 g
Groove curvature radius r _o of the groove curved in cross section including the bearing axis of the raceway groove, the radius of curvature of the groove curved in a cross section perpendicular to the bearing axis and R _O, also in a cross section including the bearing axis of the raceway groove of the inner ring 1n Assuming that the radius of curvature of the curved surface is r _i , and the radius of curvature of the groove curved surface in a cross section orthogonal to the axis l is R _i ,
The principal curvature sum Σρ = ρ _I1 + ρ _I2 + ρ _II1 + ρ _II2 is represented by the following equation.

For the inner ring and the ball, Σρ = 4 / d + (1 / R _i ) − (1 / r _i ) (3) For the outer ring and the ball, Σρ = 4 / d + (1 / R _o ) − (1 / r _o ) (4) and the auxiliary variable cos τ = | (ρ _I1 −ρ _I2 ) + (ρ _II1 −
ρ _II2) | / Σρ in the case of the inner ring and the ball _{cosτ = {(1 / r i} ) + (1 / R i)} / Σρ ... (5) If the outer ring and the ball _{cosτ = {(1 / r o} ) − (1 / R _o )｝ / Σρ (6)

[0011] k than the spring constant k = dQ / dδ = 1 / {(1.13 / 10 3) (2K / πμ)} · 3/2 · 3 √ (Q / Σρ) (7) Here, ball bearings for HDD Name B5-39 (inner diameter 5
Numerical calculations are performed on the assumption that a ball having a diameter of 2 mm (mm, outer diameter 13 mm, width 3 mm) is made of ceramics.

Ball diameter d = 2.0 mm r _i = 1.07 mm (average), r _o = 1.07 mm
(Average) R _i = 3.5 mm, R _o = 5.50 mm + δ _s = 5.
508 mm where clearance δ _s = 16 μm (average) By applying these values to equations (3) to (6), Σρ, co
Table 1 shows the results of calculating sτ and obtaining μ, ν, μν, and 2K / πμ.

[0013]

[Table 1]

From equations (1), (2) and (7),
When the maximum contact stress σ _max and the approach amount (deformation amount) δ of each of the inner and outer rings are calculated, This relationship of kα ₃ √Qασ _maxi from the equation (8) is satisfied.

Next, the case where the ball is made of steel and the outer ring and the inner ring are also made of steel will be described. In the case of a steel ball, the maximum contact stress σ _max and the approach amount δ are σ _max = 187 × (1 / μν ) ₃ √ ｛(Σρ) ² Q｝ δ = (1.28 / 10 ³ ) (2K / πμ) ₃ √ ｛ΣρQ ² ｝. Therefore, when comparing the same maximum contact stress σ and proximity amount [delta] _c 'corundum load Q of relative _maxi' 'the load Q and proximity amount [delta] _c of the ceramic balls, Here, δ _c = δ _i + δ _o .

The load Q 'and the approach amount δ' for a steel ball are
It can be seen that in each case, it is 1.4 times that of ceramic balls.
The values of σ _maxi are 20, 40, 60, 80, 100, 12
FIG. 9 plots the result of calculating the load-approach amount between the ceramic ball and the steel ball with 0,140 kg / mm ² . Generally, the magnitude of the bearing preload σ _max is 100k
g / mm ² , and the elastic deformation amount (approach amount) δ _c of the contact point of the ceramic ball at that time is δ _c = 0.522 from FIG.
μm, which is a considerably small value.

Hereinafter, the effect of the temperature difference on the bearing preload will be described.
A comparison is made between the case of ceramic balls and the case of steel balls.
The difference ΔA of the coefficient of linear expansion between the steel material and the ceramic material is ΔA = 11.8 × 10 ⁻⁶ / ° C (steel) −3.2 × 10 ⁻⁶ / ° C (° C) =
8.6 × 10 ^-6 / ℃ The contact rigidity between the ball and the inner ring raceway surface is the maximum contact stress σ _maxi
When the amount of elastic deformation δ _c at the contact point is 0.2 μm or less, the value of the contact stiffness rapidly decreases. Therefore, now, the difference Δδ _c between the steel and ceramics in the amount of elastic deformation (approach) is 0.
The value of the temperature change ΔT corresponding to 2 μm is calculated as the ball diameter d = 2 mm
Calculating for the case where ΔT = Δδ _c /ΔA·Diameter=0.2/(8.6×10 ⁻⁶ × 2 ×
10 ³ ) = 11.6 (℃). Therefore, the above general σ _max = 100k
g / mm ² elastic deformation amount of ceramic ball δ _c =
A value of 0.522 μm (see FIG. 2) corresponds to a temperature difference of 30.3 ° C. That is, when the temperature difference between the preload setting and the use of the bearing reaches 30.3 ° C., the preload disappears, and σ _maxi = 0, so that the preload release phenomenon occurs.

In the combination of ceramic balls and steel inner and outer rings, only the ball diameter d changes due to the temperature difference ΔT. The change amount Δd is as follows: Δd = ΔA × ΔT × d = 8.6 × 10 ⁻⁶ × ΔT × d (10) For example, when d = 2 mm, the maximum contact stress σ _maxi = 100 kg
/ Mm ² , the elastic deformation amount δ _c of the ceramic ball at this time is δ _c = 0.52 μm. (A) When the assembling temperature is 20 ° C. and the operating temperature is 80 ° C., Δ
T = 60 ° C, Δd = 8.6 × 10 ^-6 × 60 × 2.0 × 10 ³ μm = -1.032 μ
m The preload loss condition is a dimensional difference Δ = δ _c + Δd <0. In this case, the preload is released.

(B) Assembling temperature 60 ° C., operating temperature 80
° C, ΔT = 20 ° C, Δd = 8.6 × 10 ^-6 × 20 × 2.0 × 10 ³ μm = -0.344 μ
There will be a dimensional difference of m. In this case, Δ = 0.18 μm
Therefore, the preload does not come off. However, from FIG. 9, since the maximum contact stress σ _{maxi max} 60 kg / mm ² when the amount of elastic deformation δ _c = 0.18 μm of the ceramic ball is, the rigidity is the rigidity value when the initial σ _max = 100 kg / mm ^2. 40%
This means that it has decreased.

(C) When the temperature at the time of assembling is lowered to 60 ° C. and the temperature at the time of transportation is lowered to 20 to 0 ° C., the temperature change ΔT
= −40 ° C. to −60 ° C. and Δd = 0.69 to 1.0 μm, so that Δ = δ _c + Δd = 1.21 to 1.52 μm, and the preload increases. Maximum contact stress σ _{maxi for} Δ = δ _c
Try to find. From the equation (8), the elastic deformation amount δ _c of the ceramic ball is δ _c = δ _i + δ _o = (8.05 × 10 ⁻⁴ + 8.43 × 10 ⁻⁴ ) ₃ √Q ² = 16.48 × 10 ⁻⁴ Q ^{2 / 3} Thus _{^{Q 1/3 = √ (δ c ·}} 10 4 /16.48) = 24.633√δ c than similarly ^{_{(8), σ maxi = 1.78 × 10 2}} 3 √Q = 1.78 × 10 2 × 24.633√δ c = 43.85 × 10 ² √δ _c (11) That is, when δ _c = 1.21 × 10 ^-3 mm, σ _maxi = 152.5 kg / mm ^{2 When} δ _c = 1.52 × 10 ^-3 mm, σ _maxi = 171 kg / mm ² _Yes , for σ _maxi = 100 kg / mm ² , if the temperature is lower than during assembly, the preload increases and the contact pressure increases.

As is clear from the above calculation, the difference in the coefficient of linear expansion α between the ceramics and the steel causes an increase or decrease in the preload. When the bearing operating temperature rises above the assembling temperature, the preload drops, and when it falls, the preload increases. . When the bearing rigidity changes in this way, for example, the natural frequency of the HDD spindle motor changes, and a specific frequency vibration generated by a combination of the number of peaks of the geometric error components of the ball of the ball bearing and the inner and outer ring rolling surfaces. , The possibility of vibration resonance increases. In addition, considering the temporal change from the start of rotation to the temperature stabilization, resonance will inevitably appear.

Accordingly, the present invention has been made in view of such conventional problems, and has as its object to provide a ball bearing which can simultaneously prevent both fretting wear and preload loss. .

[0023]

To achieve the above object, according to the present invention, a ball of a ball bearing is made of a metal material having substantially the same linear expansion coefficient as the race of the ball bearing. It is characterized in that the surface of a metal ball is coated with a ceramic material. Since the surface of the ball of the ball bearing of the present invention is coated with a ceramic material,
It has excellent surface hardness, mechanical strength, and chemical stability, and has the same fretting resistance as ceramic balls. Moreover, since the ball body is made of metal such as steel, it has the same linear expansion coefficient as the inner and outer rings. In addition, the maximum stress change in the contact portion does not occur with respect to the temperature rise of the entire bearing. Therefore, even if the temperature rises during use,
Phenomena such as a decrease in bearing rigidity and loss of preload do not occur.

In addition, it is advantageous for a transient phenomenon of a temperature change because the ceramic ball has a smaller longitudinal elastic modulus and a higher thermal conductivity than a ceramic ball.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 As a first embodiment of the present invention, a surface-coated sphere (ball) having a diameter of 2 mm used as a rolling element of a ball bearing (B5-39) for HDD will be described.

An outline of the film forming process is as follows. The surface of a steel ball having a diameter of 2 mm, which was polished after heat treatment and had an accuracy just before final finishing, was coated with TiN by PVD.
At a predetermined processing temperature. Thereafter, quenching and tempering are performed in a vacuum furnace to recover the hardness decrease due to the coating temperature.

Next, a coating film thickness of 0.2 to
By performing diamond wrap processing until the thickness becomes 2.5 μm, heat treatment deformation is removed, and surface roughness, waviness, roundness, and dimensional accuracy are adjusted to predetermined accuracy. The above-mentioned steps (1) to (4) are for high-temperature film formation in which steel balls of a workpiece are PVD-treated at a temperature appropriately selected within a relatively high temperature range of 200 to 600 ° C. in order to increase the film strength. In order to reduce the cost by omitting the process, the steel ball of the work is subjected to PVD processing at a low temperature of 160 ° C., and the subsequent heat treatment is omitted before proceeding to the direct process.

In the first embodiment, a low-temperature PVD process at 160 ° C. was performed. (1) Example of PVD Processing Step An HCD type PVD apparatus as shown in FIG. 1 is used. The upper lid 1 of the apparatus is opened, and a large number of steel balls W, which are works, are arranged in the chamber 2. (A) The inside of the chamber is evacuated to a high vacuum (10 ^-10 to 1)
0 ^-13 Torr).

(B) Ti, which is a metal base material 3 for film formation, is mounted in the crucible 4. (C) The metal base material 3 for film formation is heated and melted by the electron beam gun 5 and evaporated. (D) The reaction gas N ₂ is introduced into the chamber 2 together with the carrier gas Ar, and the inside of the chamber is set to 10 ⁻³ to 10 ⁻⁴ Torr.
Adjust to r.

(E) Glow discharge is performed between the plasma electron gun 6 and the metal base material 3 for film formation to ionize Ti to form a plasma state, thereby forming a TiN film on the surface of the work W. The reaction at this time is 2Ti + N ₂ → 2TiN (When TiC is formed, C ₂ H is used instead of N _2.
2 can be introduced to make 2Ti + C ₂ H ₂ → 2TiC + H ₂ . (F) At this time, a potential difference of several hundreds to several thousand volts is selected between the workpiece W and the metal base material 3 for film formation.

The film thickness is determined in advance by the film forming speed (approximately
0 μm / hr) is correctly obtained and controlled by time.
In the example of the first embodiment, it was 0.5 to 1 μm / hr. It is desirable that the work W is preheated to 100 ° C. or higher in advance. In this embodiment, the temperature of the work W at the time of PVD film formation is selected to be 160 ° C.
It can be selected as appropriate at a processing temperature of ° C. As described above, low-temperature film formation is desirable when cost is to be reduced by omitting steps, and high-temperature film formation is desirable when it is desired to increase film strength. (2) Fretting evaluation test Through the above low temperature PVD process, a 2.5 μm thick T
A 2 mm diameter surface-coated sphere formed on an iN coating is diamond-wrapped to a film thickness of 2.0 μm, and a ball bearing (B5- 39) were assembled. Using this as a test body, a fretting durability test was performed using a test apparatus shown in FIG.

In FIG. 2, reference numeral 10 denotes an axial biasing means comprising a washer and a preload spring, which is fixed to the shaft 11.
The shaft 11 is fixed by a rotation stopper 12. A housing 16 whose lower part is supported by a support bearing 14 is connected to an AC servomotor 17 and is driven to swing and rotate at a set angle and number of times. Reference numeral 20 denotes four test bearings.
The above-mentioned surface-coated sphere is incorporated. In each test bearing 20, the outer ring 20-1 is fitted to the inner diameter of the housing 16 and the inner ring 20-2 is passed through the shaft 11, and
The sleeves 21A and 21B, which are separate from the sleeve 1, are alternately mounted on each other. The shaft and the inner ring do not rotate, and the housing and the outer ring are rotatably supported. The sleeves 21A and 21B are pressed in the axial direction by the disc spring 22 of the axial biasing means 10, and a preload (Fa) is applied to the inner ring 20-2, the outer ring 20-1, and the rolling element 20A of the test bearing 20.

The test conditions were set as follows. Test bearing: B5-39 Frequency: 27 Hz Swing angle: 2 ° Load Fa: 14.7 N Swing frequency: 1 × 10 ⁵ times Grease amount: 12 mg (NS7) After the test under the above conditions, 4 The test bearing 20 was taken out, its average bearing acoustic value was determined, and the value was arranged in relation to the coating thickness of the surface-coated sphere as the rolling element 20A. (3) Evaluation result of fretting FIG. 3 shows the acoustic performance db before the fretting test.
4 shows the relationship between the thickness (based on a microphone sound pressure gauge) and the coating thickness.

FIG. 4 shows the acoustic performance d after the fretting test.
The relation between b and the coating thickness is shown. 3 and 4, the acoustic performance on the vertical axis is represented by a ratio where the sound pressure (db) of the test bearing (B5-39) having a coating thickness of 2.0 μm before the test is set to 1.0. As shown in FIG. 3, when the completed film thickness after diamond wrapping is less than 0.2 μm, the film becomes uneven and unevenness occurs, and the surface roughness, roundness, and dimensional accuracy are insufficient. The performance varies and the value is poor. In addition, although the relationship between the film thickness and the cost has a positive proportional correlation with the time, the proportional relationship is broken from around a film thickness of more than 2.5 μm, and the deposition rate is slightly reduced. , Rising costs. From this, it can be said that the coating thickness of the surface-coated sphere completed as a rolling element is preferably in the range of 0.2 to 2.5 μm from the viewpoint of acoustic performance and cost.

In the PVD process in the fretting evaluation test, when a high-temperature film-forming step at a processing temperature of 400 ° C. is selected, it is considered that the TiN film formed on the sphere surface after the vacuum quenching and tempering is considered to be a thermal crack. It was confirmed that some cracks occurred. From this point as well, it is necessary to keep the film thickness to 2.5 μm or less.
In addition, from the viewpoint of acoustic performance, as is apparent from FIG. 3, stable performance is obtained when the film thickness is 0.2 μm or more, and it can be said that the lower limit is desirably 0.2 μm.

FIG. 4 shows the relationship between the acoustic performance db and the film thickness after the fretting test. Regarding the acoustic characteristics after the rocking test, remarkable acoustic degradation is observed when the film thickness of the completed sphere is less than 0.2 μm. Also,
If the film thickness exceeds 2.5 μm, a part of the coating is peeled off and fatigued, and the acoustic performance is deteriorated due to the deterioration of the coating.
Therefore, as in the case of FIG.
It can be seen that the range of 2.5 μm is excellent in fretting resistance. Embodiment 2: As a second embodiment of the present invention, a case where a TiN film is formed by performing PVD processing at 400 ° C. on a surface of a steel ball having a diameter of 2 mm used for a rolling element of an HDD ball bearing (B5-39). Will be described.

In the PVD processing step of this example, a 2.5 μm-thick TiN coating was formed using the HCD type PVD apparatus shown in FIG. 1 under the same conditions as in Embodiment 1 except for the processing temperature. Was. The steel ball that has been subjected to PVD processing at a high temperature of 400 ° C. is heated at a temperature higher than the tempering temperature at the time of quenching and tempering in the previous process, and the hardness decreases. Then, heating is performed at 830 ° C. for 30 minutes in a vacuum furnace, and thereafter, quenching and tempering are performed to obtain a base material hardness HRC of 60 to 63.
Thus, the decrease in hardness due to the coating temperature was recovered. Then, the surface roughness, roundness, dimensional accuracy and the like were adjusted to predetermined accuracy by diamond wrapping until the coating film thickness became 2.0 μm.

In this embodiment, although the deformation of the test sphere after the heat treatment is large, the processing cost is increased.
Since the adhesion between the coating material and the surface of the test sphere is higher than in the case of the treatment temperature of 160 ° C. (Embodiment 1), it is advantageous in terms of acoustic life under severe use conditions. FIG. 4 shows that in the range of the coating thickness of 0.2 to 2.5 μm, the high-temperature PVD treatment at 400 ° C. (marked by ○) was lower than the low-temperature PVD treatment at 160 ° C. (marked with ○). It shows that there is little variation and that it is also excellent in sound degradation.

In each of the above embodiments, the TiN film is described as the hard film.
AlN, TiAlN, ZrN, HfN, CrN, TiC
The present invention can be similarly applied to N, WC, diamond, Al ₂ O ₃ coating and the like. Although the case where the hard coating is formed by the PVD method has been described, the CVD method is similarly effective as these film forming methods.

The base material of the surface-coated sphere is made of various cemented carbides having secondary hardening ability, high-speed steel such as SKH, special steel for wear-resistant and non-deformable such as SKD, and SUS.
In the case of martensitic stainless steel such as 440C, the hardness does not decrease even in the high-temperature treatment at the time of film formation, so that the quenching and tempering treatment at the time of film formation can be omitted. Also,
By setting the accuracy of the sphere before the PVD process to be high, the diamond wrapping process after the film formation can be omitted.

Also, instead of diamond wrap, B
Abrasive grains such as N and SiC can also be used. Also,
Also the ball diameter becomes smaller, for example, even when compared with the d = 1/16 inches (1.588 1.20 mm) as 2mm ball, the ball diameter ratio 0.794 times, [delta] _c is because 0.809 times, the maximum contact stress (preload change ) Are almost the same value.

As described above, in particular, the rolling element of the spindle rolling bearing or the swing arm bearing of the HDD device which requires the anti-fretting performance has a thickness of 0.2 to 2.5 μm.
By forming the hard coating of m by the PVD method or the CVD method, it is possible to improve the acoustic characteristics of the bearing and to provide a rolling bearing that satisfies low-cost requirements.

[0043]

As described above, according to the first aspect of the present invention, a hard coating is formed on the surface of a sphere in a thickness of 0.2 to 2.5 μm.
To provide a surface-coated sphere having excellent fretting resistance at low cost. According to the second aspect of the present invention, it is possible to provide a low-cost bearing device having a long life and good acoustic characteristics using the surface-coated sphere of the first aspect as a rolling element.

[Brief description of the drawings]

FIG. 1 is a schematic view of an HCD type PVD apparatus.

FIG. 2 is a schematic diagram of a fretting evaluation test apparatus.

FIG. 3 is a diagram showing a relationship between a spherical coating film thickness, acoustic performance before a fretting test, and manufacturing cost.

FIG. 4 is a diagram showing a relationship between a sphere coating film thickness and acoustic performance after a fretting test for each PVD processing temperature.

FIG. 5 is a sectional view of an HDD spindle motor.

FIG. 6 is a partially cutaway perspective view of the HDD swing arm motor.

FIGS. 7A and 7B are diagrams illustrating a main curvature surface and a main curvature radius of a point contact portion between two curved surfaces, where FIG. 7A is a perspective view and FIG. 7B is a cross-sectional view.

FIG. 8 is a partial sectional view of an angular contact ball bearing.

9 is a diagram showing the correlation between the calculated value and the maximum contact stress sigma _maxi load Q- approaching amount [delta] _c in the ceramic ball and steel ball.

[Explanation of symbols]

 1 Ball bearing 1n Inner ring 1g Outer ring B Ball

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Arifori Horie 1-5-50 Kugenuma Shinmei, Fujisawa-shi, Kanagawa F-term in NSK Ltd. (reference) 3J101 AA02 AA42 AA54 AA62 BA10 DA03 DA05 DA11 EA02 EA05 EA06 EA41 EA42 EA43 EA44 EA78 FA01 FA15 FA35 FA60 GA53 5D109 BB04 BB13 BB16 BB21 BB27 5H605 AA00 AA05 BB05 CC04 DD05 EA19 EB04 EB10 FF00 FF10 GG10

Claims (1)

[Claims] 1. A ceramic coated ball, wherein the ball of the ball bearing is formed by coating a ceramic material on the surface of a metal ball made of a metal material having substantially the same linear expansion coefficient as the race of the ball bearing. Bearing used.