JP2001280345A - Ball bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a high level of the quality of a ball as much as possible and improve the rotating performance in a ball bearing having a ceramic ball. SOLUTION: The quality of the ceramic ball 13 is determined that the diameter irregularity is 0.016 μm or less, the sphericity is 0.06 μm or less, the surface roughness by center line average roughness Ra is 0.08 μm or less, and the size variation per unit container of a diameter of a lot is 0.10 μm or less. As the quality of the balls 13 to be incorporated into the ball bearing 10 can be unified at a high level, and the individual difference is remarkably reduced, the non- synchronous rotary run-out (NRRO) and the vibration can be remarkably reduced in comparison with a conventional ball bearing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ball bearing having a ceramic ball.

[0002]

2. Description of the Related Art Conventionally, ball bearings using ceramic balls have been known. In recent years, for example, a spindle shaft of a hard disk drive, a video tape recorder (VT),
R) Ball bearings used for supporting parts such as cylinder head motor shaft or polygon scanner motor shaft
Extremely high rotation performance is required.

[0003]

The ceramic balls used in the above-mentioned ball bearings are not specified by Japanese Industrial Standards or the like, and are generally operated in accordance with those specified for steel balls.

However, steel balls for ball bearings (J
Even if a ceramic ball that satisfies the highest grade of G3 specified in IS B 1501) is used, at the present time, a non-synchronous rotational runout (NR) is not possible.
RO) is poor, and sufficient rotational performance cannot be satisfied. This is because the provisions of the ball in the current Japanese Industrial Standards described above are not sufficient to be applied to ceramic balls because of the relationship stipulated on the assumption that the material is steel.

In view of such circumstances, an object of the present invention is to provide a ball bearing having a ceramic ball with a ball quality as high as possible and to further improve the rotational performance.

[0006]

The first ball bearing according to the present invention comprises:
A ball made of ceramics having a diameter of 0.06 μm or less and a sphericity of 0.06 μm.
μm or less, surface roughness is 0.008 as center line average roughness Ra
μm or less, and the difference between the lot diameters is set to 0.10 μm or less.

A second ball bearing according to the present invention is characterized in that, in the above-mentioned first structure, the ball is made of a silicon nitride ceramic which has been subjected to isotropic pressure sintering (HIP).

[0008] A third ball bearing of the present invention is characterized in that, in the above-mentioned first configuration, the ball is made of a zirconia-based ceramic subjected to isotropic pressure sintering (HIP).

In short, in the present invention, the quality of all balls incorporated in a ball bearing is made uniform at a high level by specifying the quality of ceramic balls more precisely than the G3 grade of JIS B 1501. .

[0010]

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

FIG. 1 to FIG. 4 show an embodiment of the present invention. 1 is a longitudinal sectional view showing an upper half of a ball bearing, FIG. 2 is a longitudinal sectional view of an HDD device to which the ball bearing of FIG. 1 is used, FIG. 3 is a schematic configuration diagram of an NRRO test apparatus, and FIG.
FIG. 4 is an explanatory diagram showing a form of vibration measurement.

First, the HDD device shown in FIG. 2 will be briefly described. In the drawing, 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, and 4 denotes a rotor hub. Reference numeral 5 denotes a rotor fixed to the inner circumference of the rotor 3, and an information recording medium 5 such as a magnetic disk or an optical disk disposed on the outer circumference of the rotor hub 3.

Next, the ball bearing 10 will be described with reference to FIG. In the illustrated example, a deep groove ball bearing is shown as the ball bearing 10. The ball bearing 10 includes an inner ring 11, an outer ring 1
2, a plurality of balls 13 and a retainer 14 are provided, and the lubricant is sealed by the seals 15, 15.

The inner and outer rings 11, 12 are formed of a metal material such as bearing steel or stainless steel as required. Ball 13
Is formed of silicon nitride ceramics or zirconia ceramics.

Here, as for the quality of the ceramic ball 13, the diameter difference is 0.06 μm or less, and the sphericity is 0.1 mm.
06 μm or less, the surface roughness is 0.0
It is characterized in that the difference between the diameters is set to 08 μm or less and the difference between lot diameters is set to 0.10 μm or less.

Next, a method of manufacturing the ceramic ball 13 will be described. First, silicon nitride powder or zirconia powder, or a sintering aid suitable for them, for example, is crushed to an average particle size of 1.0 μm or less and mixed, and a solvent is added thereto and kneaded to obtain an average particle size of 60 to Granulate to 130 μm. The outer shape is adjusted by a die press using the granulated powder. After degreased, the compact is sintered under normal pressure and further subjected to isotropic pressure sintering (HIP).

In the above-described isotropic pressure sintering, in the case of silicon nitride, the temperature is set to about 1700 ° C. in a nitrogen gas atmosphere,
Performed at pressures below ２０００2000 atmospheres. Thereafter, the sintered body is finished into a sphere by machining. In machining, usually 4-6
In the process, the abrasive stone is sequentially used with a fine particle size, and is finally finished using a diamond powder having a particle size of 0.1 to 0.2 μm. As a result, the accuracy of the ball 13 becomes submicron, and the ball 13 is finished to a mirror surface.

As for the ball bearing 10 using the ceramic ball 13 manufactured in the above-described embodiment, the non-rotational run-out (NRRO) and the vibration were examined, and will be described.

Here, three types of samples, two types of the present invention made of zirconia-based ceramics and one type of conventional product, were prepared. The ball bearing used for the test has a nominal number of 695.

The quality of the ceramic balls 13 of the first invention is 0.06 μm in diameter and 0.06 μm in sphericity.
μm, surface roughness is 0.008μ in center line average roughness Ra
m, and the difference between the lot diameters is set to 0.10 μm.

The quality of the ceramic balls 13 of the second invention is 0.04 μm in diameter and 0.04 μm in sphericity.
μm, surface roughness is 0.004μ in center line average roughness Ra
m, and the difference between the lot diameters is set to 0.06 μm.

In the conventional product, the quality of the ceramic ball 13 is equivalent to the grade G3 in JIS B1501, that is, the diameter difference is 0.08 μm and the sphericity is 0.0
8 μm, surface roughness 0.012 μm as center line average roughness Ra
m, the difference between the diameters of the lots is set to 0.13 μm.

The NRRO test apparatus shown in FIG. 3 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 radial run-out 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 asynchronous rotational run-out (NRRO) amount.

As a result of the asynchronous rotational runout (NRRO) measurement, assuming that the conventional product is “1”, the second invention product is “0.4” and the first invention product is “0.5”. All of the invention products were greatly reduced to about 1/2 of the conventional products.

Further, regarding the vibration measurement of the ball bearing 10,
As shown in FIG. 4, 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 mounted on the spindle shaft 32 in a horizontal posture.

As a result of the vibration measurement, if the conventional product is “1”, the second invention product is “0.4”, and the first invention product is “0.4”.
The value of the invention product was "0.5", and the value of each of the invention products was greatly reduced to about 1/2 of the conventional product.

As described above, the ceramic ball 1
The quality of all the balls 13 incorporated in the ball bearing 10 is made uniform at a high level and the individual difference is drastically reduced by defining the quality of the ball 3 more precisely than the G3 grade of JIS B 1501. Runout (NRRO)
And vibration can be made much smaller than conventional products, and it can be particularly suitable for a device that requires high-precision rotation performance.

By the way, regardless of the zirconia-based ceramic or the silicon nitride-based ceramic, the above-mentioned isotropic pressure sintering (HIP) is always applied to the ceramic ball 13 in order to improve the load resistance. Is preferred. This is because the load resistance of the ball 13 is inferior when only normal pressure sintering is performed. This is supported by the following durability test.

The durability test apparatus shown in FIG. 5 was used. The durability test apparatus shown in the figure comprises a rotating shaft 41 and a receiving member 4.
2, a grooved thrust trace 43 and a sample flat plate 44 are arranged, and a plurality of (three) steel balls 45 are interposed between the thrust trace 43 and the sample flat plate 44.
The steel balls 45 have a diameter of ／ ″, and the PCD of each steel ball 45 is 38.5 mm.
, The receiving member 42 is pressed against the rotating shaft 41.

In this durability test, the product of the present invention (the first
Invention product) and a comparison product. The product of the present invention was formed by isostatic pressing sintering of zirconia ceramics on a sample plate 44, while the comparative product was sintered under normal pressure without isostatic pressing of zirconia ceramics. It is formed by only the binding process, and other conditions are the same as those of the product of the present invention.

As conditions, lubrication using spindle oil is used, the rotation speed of the rotating shaft 41 is set to 1200 rpm, and the load is increased stepwise. The load is increased every 1.08 × 10 ⁷ repetitions of the load.

As a result, as shown in FIG. 6, in the case of the comparative product, the load per ball is 500 N and the surface pressure is 3.9 GP.
Although damage occurred at a, the product of the present invention suffered damage at a load of 1310 N per ball and a surface pressure of 5.3 GPa.

For reference, in the case of silicon nitride ceramics formed by isotropic pressure sintering, damage occurs even when the load per ball is increased to 1310 N and the surface pressure is increased to 5.9 GPa. Without, continue normal operation.

Incidentally, in the case of silicon carbide ceramics, the load per ball is 261 N and the surface pressure is 3.6 GP.
In the case of alumina ceramics, the load per ball is 65.3N and the contact pressure is 2.2G.
Since damage occurred at Pa, it can be said that the use of the balls 13 with silicon carbide-based ceramics and alumina-based ceramics is limited to those under low load conditions.

In producing the ceramic balls 13 based on the above test results, isotropic pressure sintering (HIP) is applied to both zirconia-based ceramics and silicon nitride-based ceramics. Manufacturing is preferable in terms of increasing load resistance. However, when the ball 13 is made of zirconia-based ceramic, its linear expansion coefficient is close to that of steel, so that when the inner and outer rings 11 and 12 are formed of different materials such as steel, the range of variation of the bearing temperature is limited. This is advantageous in that the gap variation inside the bearing can be suppressed in a situation where the size becomes large.

[0037]

According to the first to third aspects of the present invention, the quality of a ball to be incorporated in a ball bearing is made uniform at a high level by specifying the quality of a ceramic ball more precisely than the G3 grade of JIS B1501. Since the individual difference has been drastically reduced, the asynchronous rotational runout (NRRO) and vibration can be significantly reduced as compared with conventional products, making it particularly suitable for devices requiring high-precision rotational performance. it can.

According to the second and third aspects of the present invention, since the load resistance of the ceramic ball can be increased, it can greatly contribute to the improvement of the durability of the ball bearing.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an upper half of a ball bearing according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of an HDD device to which the ball bearing of FIG. 1 is used;

FIG. 3 is a schematic configuration diagram of an NRRO test apparatus.

FIG. 4 is a longitudinal side view of an explanatory view showing a form of vibration measurement.

FIG. 5 is a schematic configuration diagram of a durability test apparatus.

FIG. 6 is a table showing the results of a durability test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Ball bearing 11 Inner ring 12 Outer ring 13 Ball 14 Cage

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 3J101 AA02 AA32 AA42 AA54 AA62 BA02 BA10 DA20 EA41 EA42 EA44 FA01 FA31 GA24 GA53 5H605 AA05 BB05 BB14 BB19 CC04 DD09 EB04 EB10 GG21

Claims (3)

[Claims] 1. A ball bearing using a ceramic ball, wherein the ball has a diameter difference of 0.06 μm or less,
A ball bearing having a sphericity of 0.06 μm or less, a surface roughness of 0.008 μm or less in center line average roughness Ra, and a difference between lot diameters of 0.10 μm or less. . 2. The ball bearing according to claim 1, wherein said ball is made of silicon nitride ceramics subjected to isotropic pressure sintering (HIP). 3. The ball bearing according to claim 1, wherein the ball is made of a zirconia-based ceramic subjected to isotropic pressure sintering (HIP).