JP2002327751A - Rolling bearing and spindle motor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling bearing using the rolling bearing capable of controlling destruction of devices caused by an electrical charge of static electricity by means of a rolling body having the designated value of electric resistance and the designated coefficient of thermal expansion and also controlling a rotating runout caused by the difference of thermal expansion during high speed rotation, and also to provide a spindle motor using the bearing. SOLUTION: In the rolling bearing in which all of rolling bodies are made of ceramics, the rolling bodies are composed of one or more of silicon nitride rolling bodies and zirconia rolling bodies. The value of electric resistance of at least one kind of the rolling bodies is 10<2> to 10<7> Ω.cm. The number of the silicon nitride rolling bodies is 50% or more of all the rolling bodies, and the diameter of the silicon nitride rolling bodies is 0.03 to 0.3 μm larger than the diameter of the zirconia rolling bodies.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rolling bearing and a spindle motor using the same, and more particularly to a rolling bearing excellent in charge suppression and rotational stability at high speed, and a spindle motor using the same.

[0002]

2. Description of the Related Art In recent years, hard disk drives (HD)
D) and other magnetic recording devices, optical disk devices or DVDs,
The development of mobile products and various game machines has been remarkable. Usually, these various disk drives are made to function by rotating a rotation shaft at high speed by a rotation drive device such as a spindle motor.

Conventionally, metal such as bearing steel has been used for a bearing (bearing) member for supporting such a rotating shaft, particularly for a bearing ball. However, since metals such as bearing steel do not have sufficient wear resistance, in fields where high-speed rotation of 5,000 rpm or more is required, for example, in the above-mentioned electronic equipment, etc., there is a large variation in life and a reliable rotation. The drive could not be provided.

[0004] In order to solve such problems, it has recently been attempted to use silicon nitride for bearing balls. Silicon nitride has excellent abrasion resistance because of its excellent sliding properties among ceramics.
It has been confirmed that a reliable rotation drive can be provided even at high speed rotation.

[0005]

However, since the bearing balls made of silicon nitride are electrically insulating, static electricity generated when rotating at a high speed is rotated by a rotating shaft made of a metal member such as bearing steel. In addition, there have been problems in that static electricity is not satisfactorily dissipated in a ball receiving portion (a component of a bearing member other than a so-called bearing ball).

If the static electricity is not sufficiently dissipated and charged more than necessary, an adverse effect is exerted on an electronic device, for example, a recording medium using a magnetic signal such as a hard disk drive. The phenomenon that the equipment itself was destroyed occurred.

Further, since the silicon nitride bearing ball has a coefficient of thermal expansion of one-third or less of that of metal, the expansion due to heat generated at the time of high-speed rotation is extremely small. It has been found that problems such as inconsistency with the thermal expansion of the manufactured rotating shaft portion and ball receiving portion (so-called components of the bearing member other than the bearing ball) occur.

As described above, when the thermal expansion of each part does not match, rotational vibration (asynchronous vibration) and the like occur, and as a result, phenomena such as hindering stable operation of electronic devices such as hard disks have occurred.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems. By providing a rolling element having a predetermined electric resistance value and a thermal expansion coefficient, it is possible to prevent the breakdown of equipment due to electrostatic charging. An object of the present invention is to provide a rolling bearing in which rotation is suppressed and rotational runout due to a difference in thermal expansion during high-speed rotation is suppressed, and a spindle motor using the same.

[0010]

According to the present invention, there is provided a rolling bearing comprising:
In a rolling bearing in which all of the rolling elements are ceramics, the rolling elements include at least one or more silicon nitride rolling elements and zirconia rolling elements, and at least one of the silicon nitride rolling elements and the zirconia rolling elements has an electrical resistance value of at least one. 10 ² to 10 ⁷ Ω · cm.

[0011] The rolling bearing of the present invention comprises at least one or more silicon nitride rolling elements and zirconia rolling elements,
In addition, at least one of the silicon nitride rolling element and the zirconia rolling element has an electric resistance of 10 ² to 10 ⁷ Ω ·
When the diameter is set to cm, the thermal expansion of the rolling element and the components holding the rolling element can be matched, the rotation at high speed can be stabilized, and further, the electrification can be prevented and the device can be prevented from being damaged.

It is preferable that at least one of the silicon nitride rolling element and the zirconia rolling element contains 10 to 40% by mass of a carbide and has an electric resistance of 10 ² to 10 ⁷ Ω · cm. Examples of the carbide include Si, T
It is preferable to use carbide of at least one element selected from i, Nb, Hf, W, Mo, Ta, Cr, Zr, Mn and B.

The number of silicon nitride rolling elements is at least 50% of the total number of rolling elements, the diameter thereof is larger than the diameter of zirconia rolling elements by 0.03-0.3 μm, and the zirconia rolling elements are adjacent to each other. Preferably, they are arranged so as not to match.

The number of silicon nitride rolling elements is set to 50, which is the total number of rolling elements.
% Or more, it is possible to suppress the abrasion of the rolling element when rotating at a high speed, and to prevent the device from being damaged. Further, by making the diameter of the silicon nitride rolling element larger than the diameter of the zirconia rolling element by 0.03 to 0.3 μm,
Rotation stability when rotated at high speed can be improved. In addition, the rotation can be further stabilized by preventing the silicon nitride rolling elements and the zirconia rolling elements having different wear resistance and thermal expansion from being adjacent to each other.

It is preferable to keep the number of silicon nitride rolling elements disposed between the zirconia rolling elements constant, so that the rotation can be stabilized.

The rolling bearing of the present invention can be used for equipment for rotating a rotating shaft by a rotary drive device, and is preferably used for a bearing portion such as a spindle motor.

A spindle motor according to the present invention includes the above-described rolling bearing. The spindle motor of the present invention has excellent stability at high speed rotation, and its bearing portion is hardly charged. Therefore, the spindle motor is particularly suitable for electronic devices that require high speed rotation and are easily affected by charging. For example, it is effective to use the spindle motor of the present invention in an electronic device such as a hard disk drive that requires high-speed rotation and is easily affected by charging because it uses a magnetic signal. As other electronic devices, the present invention is also suitable for optical disk devices, magneto-optical disk devices, and the like.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partially cutaway front view of the rolling bearing of the present invention.

The rolling bearing 1 of the present invention comprises an inner ring 2 and an outer ring 3 disposed outside the inner ring 2, and a spherical silicon nitride rolling element 4 and a zirconia rolling element 5 disposed between the inner ring 2 and the outer ring 3. Become. The electrical resistance value of at least one of these rolling elements is 10 ² to 10 ⁷ Ω · cm.
It is.

Since the silicon nitride rolling element is excellent in abrasion resistance, by using it for a rolling bearing, the life of the rolling bearing can be extended. However, parts other than the rolling elements, for example, the inner ring 2 and the outer ring 3 are made of a metal material such as bearing steel, whereas the thermal expansion coefficient of the silicon nitride rolling elements is one third or less of the thermal expansion coefficient of the metal. Therefore, when all the rolling elements are made of silicon nitride rolling elements, a rolling runout or the like occurs in the rolling bearing due to a difference in their thermal expansion coefficients due to heat generated during high-speed rotation.

For example, grooves for guiding the rolling elements 4 and 5 are formed on the outer periphery of the inner race 2 and the inner periphery of the outer race 3.
When the rolling element is a silicon nitride rolling element, when the bearing generates heat, the curvature of the groove and the curvature of the surface of the rolling element are different from each other, so that a rotational runout or the like occurs.

On the other hand, the thermal expansion coefficient of the zirconia rolling element is closer to the thermal expansion coefficient of bearing steel and the like than the thermal expansion coefficient of the silicon nitride rolling element. In the present invention, by providing at least one or more zirconia rolling elements, it is possible to suppress the occurrence of rotational runout or the like due to the above-described reasons. In other words, it can be said that the rolling bearing of the present invention is particularly effective for parts other than the rolling elements, for example, those in which the inner ring and the outer ring are made of a metal material.

Further, by setting the electrical resistance of at least one of the silicon nitride rolling element and the zirconia rolling element to 10 ² to 10 ⁷ Ω · cm, for example, static electricity generated in the outer ring 3 can be reduced. The static electricity can be dissipated to the inner ring 2 through the moving body and further discharged through a portion electrically connected to the inner ring 2.

The reason why the electric resistance value is set to 10 ² to 10 ⁷ Ω · cm is that when the electric resistance value is less than 10 ² Ω · cm, various additives are added. This is because the electrical resistance value is 10
If it exceeds ⁷ Ω · cm, the generated static electricity cannot be diffused through these rolling elements.

In the rolling bearing of the present invention, as the number of zirconia rolling elements increases, the occurrence of rotational runout and the like can be suppressed. However, the wear resistance of zirconia rolling elements is inferior to the wear resistance of silicon nitride rolling elements. Therefore, when the number of zirconia rolling elements is increased, wear due to high-speed rotation proceeds. Therefore, in the present invention, it is preferable that the number of silicon nitride rolling elements be 50% or more of the total number of rolling elements.

Further, since the thermal expansion coefficient of the silicon nitride rolling element and the thermal expansion coefficient of the zirconia rolling element are different, the thermal expansion coefficient is smaller than that of the zirconia rolling element in consideration of the rotational stability of the bearing at the time of heat generation. It is preferable that the diameter of the silicon nitride rolling element be larger than the diameter of the zirconia rolling element by 0.03 to 0.3 μm. Spindle motors provided in recent electronic devices have a rotation speed of 5000 rpm, and a rotation speed of 100 rpm.
The rotation speed tends to be higher than 00 rpm, and it is important to take measures against abrasion resistance and rotation runout at high rotation speed.

The diameters of the silicon nitride rolling element and the zirconia rolling element are determined, for example, as follows. First, three arbitrary diameters are measured for each rolling element, an average value is calculated from the measured values of the diameters, and this is defined as the diameter of the rolling element. If there is only one rolling element of the same type,
This is the diameter of a rolling element of that type. When there are a plurality of rolling elements of the same type, the diameters of the rolling elements of the same type among the diameters of the rolling elements previously determined are averaged to obtain the diameter of the rolling elements of that type.

It is preferable that at least one of the silicon nitride rolling element and the zirconia rolling element contains 10 to 40% by mass of a carbide and has an electric resistance value of 10 ² to 10 ⁷ Ω · cm. The carbide to be contained preferably has an average particle size of 2 μm or less. The electric resistance value can be adjusted by containing a carbide. If the content of the carbide is less than 10% by mass, a desired electrical resistance value cannot be obtained, so that the rolling bearing may be charged. When the content exceeds 40% by mass, abrasion resistance,
Since the strength, fracture toughness, etc. decrease, problems such as unstable rotation of the rolling bearing and shortened service life occur. The preferable content of the carbide is 15 to 30% by mass.

The mass% is adjusted by the amount of carbide added when producing a silicon nitride or zirconia rolling element. The method for measuring the carbide content in the finished rolling element after sintering is as follows. Burning infrared absorption method and EP
It is also possible to measure the carbon content of the carbide (and / or the metal component constituting the carbide) by MA or the like and calculate from the obtained numerical values.

The electric resistance value of the rolling element in the present invention basically indicates a volume resistance value.
The measurement is performed using an apparatus as shown in FIG. As the electrodes 6 and 7 for measuring the electric resistance, those having an opening 8 at the center corresponding to the diameter of the rolling element to be measured are used. A rolling element 9 such as the silicon nitride rolling element 4 or the zirconia rolling element 5 is sandwiched between such measurement electrodes 6 and 7. Rolling element 9
Is adjusted by the spring 10 or the like. Then, the electric resistance value of the rolling element 9 is measured by the tester 11 connected to the measurement electrodes 6 and 7, and this is set as the electric resistance value in the present invention. In the figure, reference numeral 12 denotes an insulator.

As the carbide, for example, Si, Ti,
Examples include carbides of at least one element selected from Nb, Hf, W, Mo, Ta, Cr, Zr, Mn, and B.

The Young's modulus of the silicon nitride rolling element and the zirconia rolling element used in the rolling bearing of the present invention is 200 G
The strength is preferably Pa or more, the strength is 300 MPa or more, and the Vickers hardness is 1000 or more.

For example, the Young's modulus of these rolling elements is set to 20
By setting the pressure to 0 GPa or more, the workability is improved and a rolling element having a high sphericity can be formed, and vibration and noise during high-speed rotation can be reduced. Therefore, even when the electronic device itself shakes (can be carried around) like a portable electronic device, stable high rotation can be maintained for a long period of time.

Next, another embodiment of the rolling bearing of the present invention will be described. FIG. 3 shows that the silicon nitride rolling elements 4
FIG. 5 is a partially cutaway front view showing a rolling bearing in a case where two zirconia rolling elements 5 are used and arranged so that the zirconia rolling elements 5 are located symmetrically with respect to the center.

When a plurality of zirconia rolling elements 5 are used, it is preferable that the zirconia rolling elements 5 are not adjacent to each other. Since the zirconia rolling elements 5 are more likely to wear than the silicon nitride rolling elements 4, when used for a long period of time, the zirconia rolling elements 5 that are easily worn and the silicon nitride rolling elements 4 that are hard to wear may have a difference in size. There is. For this reason, if the zirconia rolling elements 5 are placed next to each other, problems such as unstable rotation and vibration may occur.

When a plurality of zirconia rolling elements 5 are used, it is preferable to arrange the silicon nitride rolling elements 4 and the zirconia rolling elements 5 so as to have an equal ratio. That is, it is preferable that the silicon nitride rolling elements 4 arranged between the zirconia rolling elements 5 are arranged so that the number thereof is constant.

For example, as shown in FIG. 3, when two zirconia rolling elements 5 are used and 14 silicon nitride rolling elements 4 are used, one zirconia rolling element 5 is arranged and then the silicon nitride rolling elements 4 Is preferably arranged so that seven are continuously arranged. By using the zirconia rolling element 5 which is easy to wear and the silicon nitride rolling element 4 which is hard to wear, it is possible to maintain a stable rotation even when the size has been changed by using for a long time. It is possible to do.

Although the case where the silicon nitride rolling element and the zirconia rolling element are spherical has been described above, the present invention is sufficiently effective also when a cylindrical rolling element or the like is used.

Next, a case where the rolling bearing of the present invention is applied to a spindle motor will be described. FIG. 4 is a cross-sectional view showing a spindle motor having the rolling bearing 1 of the present invention.

The fixed shaft 14 erected on the motor base 13 is connected to the hub 1 via a pair of upper and lower rolling bearings 1a and 1b.
5 is rotatably mounted. On this hub 15, a disk 16 which is a rotating body is mounted. Motor base 1
A stator 17 having a coil is fixed to an outer peripheral portion of the hub 3, while a rotor magnet 18 facing the stator 17 with a gap therebetween is fixed to an inner diameter surface of the hub 15. The inner ring 2 is attached to the fixed shaft 14 and the outer ring 3 is attached to the hub 15 with an adhesive.

Here, the rolling bearings 1a and 1b are provided with a silicon nitride rolling element 4 and a zirconia rolling element 5. In the rolling bearings 1a and 1b, at least 50% of the total number of the rolling elements is provided with the silicon nitride rolling elements 4, and the diameter thereof is set to be larger than the diameter of the zirconia rolling elements 5 by 0.03 μm to 0.3 μm. Preferably, the zirconia rolling elements 5 are arranged so as not to be adjacent to each other.

By applying the rolling bearing of the present invention to a spindle motor, it becomes possible to rotate the spindle motor stably at high speed and to suppress the influence of static electricity generated by the rotation. .

Such a spindle motor can be used for various kinds of equipment, and it is particularly effective to use it for electronic equipment which is easily affected by charging. Specifically, rotate at high speed like a hard disk drive,
It is effective to use a recording medium having a recording medium using a magnetic signal which is easily affected by charging.

[0044]

Embodiments of the present invention will be described below with reference to embodiments. (Examples 1 to 7 and Comparative Examples 1 to 3) When the rolling bearing of the present invention was used for the bearing portion of the spindle motor, the vibration and the electrostatic breakdown of the spindle motor were evaluated.

Used for bearing part of spindle motor
The number of rolling elements was set to 10 in each of Examples and Comparative Examples. Departure
In the illustrated embodiment, the zirconia rolling element and the silicon nitride
Examples 1 to 3 have one or more element rolling elements.
In Example 4, it is assumed that only the silicon carbide rolling element has conductivity.
-6 have conductivity only in the zirconia rolling element,
In Example 7, both the silicon nitride rolling element and the zirconia rolling element were used.
Has conductivity. In this specification,
Having conductivity means having an electric resistance value of 10²-10 ⁷Ω ・ c
m, the diameter of each rolling element is 2 mm
Unified. Also, the inner ring of any rolling bearing
The outer ring was made of bearing steel SUJ2.

Comparative Example 1 was made of only a zirconia rolling element having no conductivity, and Comparative Example 2 was made of a silicon nitride rolling element and a zirconia rolling element, both of which had no conductivity. Example 3 was made of only a conductive silicon nitride rolling element.

The vibration of the spindle motor is measured by measuring the sound intensity with a microphone (pickup sensor) when the outer ring is operated at a rotation speed of 7000 rpm for 10,000 hours continuously and the sensor output exceeds 30 dB. Was determined to be vibration “present”, and the case of 30 dB or less was determined to be vibration “absent”.

Regarding electrostatic breakdown, a spindle motor is incorporated in a hard disk drive and the rotation speed is reduced to 70%.
After 100 hours of continuous operation at 00 rpm, check if the hard disk drive operates normally for 100 units. Indicated as "Yes".
Table 1 shows the results.

[Table 1]

As can be seen from Table 1, when the rolling bearing of the present invention was used, the vibration was suppressed to a low level in any case, and no electrostatic breakdown occurred.

On the other hand, in Comparative Example 1 in which all the rolling elements were zirconia rolling elements having no conductivity, although the generation of vibration was suppressed to a low level, it was recognized that electrostatic breakdown occurred. . In Comparative Example 2 using a zirconia rolling element and a silicon nitride rolling element having no conductivity, generation of vibration was suppressed to a low level, but it was recognized that electrostatic breakdown occurred. In Comparative Example 3 using only a silicon nitride rolling element having no conductivity, although there was no electrostatic breakdown,
It was observed that the occurrence of vibration increased.

The reason why such a result was obtained in Comparative Example 3 was that the rolling element was affected by thermal expansion due to frictional heat when rotating at high speed, and in particular, was composed only of the silicon nitride rolling element. In this case, it can be said that the thermal expansion coefficient of the silicon nitride rolling element is significantly different from the thermal expansion coefficients of the outer ring and the inner ring portion, so that the silicon nitride rolling element is more affected by the thermal expansion.

From the above results, the rolling bearing of the present invention
It is considered to be effective when applied to a part where heat generation is severe, for example, a part that rotates at high speed. Therefore, the performance of these devices can be improved by applying them to devices that need to suppress static electricity and need to rotate at high speed, for example, spindle motors such as hard disks.

(Embodiments 8-12, Comparative Example 4) In the case where the rolling bearing of the present invention is used for the bearing portion of the spindle motor, the vibration of the spindle motor when the dimensions of the zirconia rolling element and the silicon nitride rolling element are changed. Was examined.

In Examples 8 to 12, eight silicon nitride rolling elements (with conductivity) and two zirconia rolling elements (no conductivity) were used, and the diameter of the zirconia rolling element was subtracted from the diameter of the silicon nitride rolling element. The dimensional difference was set to be in the range of 0 to 5 μm. For comparison, two silicon nitride rolling elements (with conductivity) and two zirconia rolling elements (without conductivity) were used.
The zirconia rolling element was used to produce a die having a dimensional difference of −0.3 μm (the zirconia rolling element was larger) obtained by subtracting the diameter of the zirconia rolling element from the diameter of the silicon nitride rolling element. did.

The vibration of the spindle motor was measured by a microphone (pickup sensor) when the outer ring side was operated at a rotation speed of 10,000 rpm for 10,000 hours continuously.
The intensity of the sound was measured in the following manner. When the sensor output exceeded 30 dB, the vibration was "present", and when the sensor output was 30 dB or less, the vibration was "absent". Table 2 shows the results.

[Table 2]

As can be seen from Table 2, when the rolling bearing of the present invention was used, the vibration was kept low in each case. Although not shown in the table, the dimensional difference is 0.0
In Examples 9 to 11 in the range of 3 to 0.3 μm, it was recognized that the vibration was particularly suppressed to a low level.
This is to increase the diameter of the silicon nitride rolling element in advance in consideration of the small thermal expansion of the silicon nitride rolling element, and to match the thermal expansion of the zirconia rolling element due to heat generated when the silicon nitride rolling element is rotated at a high speed of 10,000 rpm or more. It seems that it was possible.

In each of Example 8 having substantially no dimensional difference and Example 12 having a large dimensional difference, it was concluded that the vibration was "somewhat". This is because the rotation speed is 7000 rpm
It is considered that, when the rotation speed is about 10,000 m, a small dimensional difference has no effect, but when a high-speed rotation of 10,000 rpm or more is performed, the influence appears. Note that the notation of “somewhat” is different from the notation of “yes” because the time during which the sound becomes 30 dB or more is delayed by 2000 hours or more.

On the other hand, in the case where the zirconia rolling element is larger or the number of zirconia rolling elements is larger as in Comparative Example 4, when the rotation speed is higher than 10000 rpm, the influence on the vibration appears. It was confirmed that it would come.

[0059]

According to the rolling bearing of the present invention, at least one of the rolling bearings is made of ceramics.
At least one of the silicon nitride rolling element and the zirconia rolling element has an electrical resistance of 10 ² to 10 ⁷ Ω · c.
By setting m, rotation deflection and electrification at the time of high-speed rotation can be suppressed, and damage to equipment using the same can be suppressed.

[Brief description of the drawings]

FIG. 1 is a partially cutaway front view showing an example of a rolling bearing of the present invention.

FIG. 2 is a schematic diagram showing a means for measuring an electric resistance value of a rolling element.

FIG. 3 is a partially cutaway front view showing another example of the rolling bearing of the present invention.

FIG. 4 is a sectional view showing a spindle motor to which the rolling bearing of the present invention is applied.

[Explanation of symbols]

 1 rolling bearing 4 silicon nitride rolling element 5 zirconia rolling element

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // G11B 19/20 C04B 35/58 102Y (72) Inventor Kazuhiro Shinozawa 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Address Toshiba Yokohama Office F-term (reference) AA37 AA38 BA12 BA18 BA20 CA07 5D109 BB08 BB13 BB16 BB21 BB22 BB31 5H605 AA12 CC04 EB10 FF10

Claims (9)

[Claims] 1. A rolling bearing in which all rolling elements are made of ceramic, wherein the rolling elements comprise at least one or more silicon nitride rolling elements and zirconia rolling elements, and at least one of the silicon nitride rolling elements and zirconia rolling elements. A rolling bearing having an electrical resistance value of 10 ² to 10 ⁷ Ω · cm. 2. The method according to claim 1, wherein at least one of the silicon nitride rolling element and the zirconia rolling element contains 10 to 40% by mass of a carbide, and has an electric resistance of 10 ² to 10 ⁷ Ω · cm. Item 7. The rolling bearing according to item 1. 3. The method according to claim 1, wherein the carbide is Si, Ti, Nb, Hf,
The rolling bearing according to claim 2, wherein the rolling bearing is a carbide of at least one element selected from W, Mo, Ta, Cr, Zr, Mn, and B. 4. The number of said silicon nitride rolling elements is at least 50% of the total number of rolling elements, the diameter thereof is larger than the diameter of said zirconia rolling elements by 0.03 to 0.3 μm, and said zirconia rolling elements are The rolling bearing according to any one of claims 1 to 3, wherein the rolling bearings are arranged so as not to be adjacent to each other. 5. The rolling bearing according to claim 1, wherein the number of silicon nitride rolling elements disposed between the zirconia rolling elements is constant. 6. The rolling bearing according to claim 1, wherein the rolling bearing is used for a bearing portion of a spindle motor. 7. A spindle motor comprising the rolling bearing according to claim 1. Description: 8. The spindle motor according to claim 7, wherein the spindle motor is used for an electronic device. 9. The spindle motor according to claim 8, wherein the electronic device is a hard disk drive.