JPH10193U - Ball bearings for hard disk drive spindle motors - Google Patents

Abstract

(57) [Summary] [Purpose] Improvement of rotation accuracy / acoustic characteristics and corrosion resistance [Construction] The shaft portion 1 constituting the inner raceway surface 1a and the outer ring 5 constituting the outer raceway surface 5a have a chromium content of 9 to 10. 14
% Of martensitic stainless steel, and the ball 3 is formed of bearing steel. The chromium content of 9 to 14% is set from the viewpoint of improving the rotational accuracy and acoustic characteristics while ensuring the corrosion resistance required for the bearing unit for the spindle motor.

Description

[Detailed description of the invention]

[0001]

[Industrial applications]

 The present invention relates to a ball bearing for rotatably supporting a disk spindle in a spindle motor of a hard disk drive (HDD).

[0002]

[Prior art]

 In a hard disk drive (HDD), a disk spindle on which a magnetic disk is mounted rotates at a constant speed, and a magnetic head mounted on the tip of a plate bar called an access arm moves above or below the magnetic disk. Then, information is written to a predetermined position on the magnetic disk, and information is read from a predetermined position on the magnetic disk. The rotation of the disk spindle is performed by a motor section mainly including a stator and a rotor, and the rotation of the disk spindle is supported by a ball bearing fixed between the housing and a fixed shaft.

[0003] The above-described ball bearings for spindle motors require high rotational accuracy in order to prevent the magnetic disk from oscillating with respect to the magnetic head. At the same time, corrosion resistance and low outgassing are required. With regard to rotational accuracy, with the recent increase in disk capacity, non-repetitive accuracy has been particularly required to be improved. (Non-repetitive accuracy refers to the continuous tracking of the rotation When the trajectories are superimposed on each other, the width of the trajectory thus created is referred to as the width). A general requirement for non-repetitive runout accuracy is 0.2 μm or less in both the radial and axial directions. A typical required noise value is 40 dBA (temporal sound) in the state of the spindle motor. Corrosion resistance is required because bearings are often delivered to users without external rust prevention treatment, and are often used. Due to the inability to perform the work of bonding and fixing to parts, and the possibility of functional failure such as head crash due to outgas generated from the bearing.) This is because rust may occur on the bearing when used in actual equipment.

[0004] By the way, bearings are generally formed of bearing steel. If corrosion resistance is particularly required, the bearing is formed of a corrosion-resistant material such as martensitic stainless steel. However, this corrosion-resistant material is a steel containing carbon and chromium, and since there are many giant carbides generated by the eutectic of carbon and chromium, the workability is poor and the corrosion resistance of the ball is low. It is difficult to ensure accuracy (sphericity, surface roughness, ball diameter). Therefore, it is known that the non-repeatability and acoustic characteristics of bearings using this corrosion resistant material are considerably inferior to those of bearings using general bearing steel.

[0005] Conventionally, bearing forming materials that are required to simultaneously have rotation accuracy, low noise, and corrosion resistance are as follows by comparing the required degrees of contradictory characteristics of rotation accuracy, low noise, and corrosion resistance as follows. Often decided.

(1) Bearing steel is used when the requirements for rotational accuracy and low noise are particularly severe and the corrosion resistance can be neglected to some extent.

(2) Stainless steel is used particularly when the requirements for corrosion resistance are severe.

[0008] (3) When both the requirements of rotation accuracy, low noise, and corrosion resistance are severe, use bearing steel (parts other than the raceway surface) plated with corrosion resistance.

[0009]

[Problems to be solved by the invention]

 In the case of ball bearings for spindle motors of hard disk drives, high corrosion resistance is not required, but the problem of rust cannot be ignored, so the above configuration (1) cannot be adopted, and the required values of rotational accuracy and acoustic characteristics are severe. Therefore, the above configuration (2) cannot be adopted. On the other hand, according to the above configuration (3), rotation accuracy, low noise and corrosion resistance can be satisfied at the same time, but extra steps are required for plating, and it is difficult to perform bearing processing after plating. It is. Therefore, there is a problem in cost performance.

An object of the present invention is to secure the required rotational accuracy, low noise, and corrosion resistance required for the above-described ball bearing for a spindle motor while considering cost.

[0011]

[Means for Solving the Problems]

 The present invention relates to a hard disk drive in which a member constituting an inner raceway surface and a member constituting an outer raceway surface are formed of martensitic stainless steel, and a plurality of balls interposed between the inner and outer raceways are formed of bearing steel. To provide ball bearings for spindle motors.

The present invention also provides a shaft portion having two rows of inner raceways formed on the outer peripheral surface, a pair of outer races having outer raceways formed opposite to the two rows of inner raceways, respectively, It has a plurality of balls arranged between the inner raceway surface and the outer raceway surface of each outer ring, and a preload applying means for applying a preload by elastically pressing a pair of outer races in opposite axial directions. A ball bearing unit for a spindle motor of a hard disk drive, wherein a shaft portion and a pair of outer rings are formed of martensitic stainless steel, and a plurality of balls are formed of bearing steel.

As the martensitic stainless steel, a martensitic stainless steel having a chromium content of 9 to 14% can be used.

[0014]

[Action]

 The rotational accuracy and acoustic characteristics of ball bearings are related to the accuracy of the raceway surface (roundness, surface roughness) and the accuracy of the ball (sphericity, surface roughness, dimensional differences between balls). The effect of ball accuracy is great. Therefore, by forming the ball from bearing steel and ensuring its accuracy, the rotation accuracy and acoustic characteristics required for the spindle motor ball bearing can be ensured. At the same time, by forming the members constituting the inner and outer raceways from martensite stainless steel, required corrosion resistance can be secured. Even if giant carbide remains on the inner and outer raceway surfaces, there is no giant carbide in the ball, so there is no contact between the ball and raceway surface by the giant carbide, and the rotation accuracy and sound The effect on the characteristics is reduced. On the other hand, the corrosion resistance of the ball is ensured by a lubricant such as grease inside the bearing, so that there is no concern that the corrosion resistance is reduced by forming the ball with bearing steel.

In order to further improve the rotational accuracy and acoustic characteristics, it is effective to reduce the giant carbide remaining on the inner and outer raceway surfaces, and for that purpose, the chromium content of the members constituting them is effective. Need to be reduced. The corrosion resistance required for spindle motor ball bearings is sufficient to replace the external rust prevention treatment applied to bearings for general use, and high corrosion resistance is required, such as bearings used in corrosive atmospheres. It is not done. On the other hand, if the chromium content is too reduced, the problem of rusting occurs. The inner and outer raceways are made of martensitic stainless steel with a chromium content sufficient to provide the required corrosion resistance even in an environment such as dew condensation in the atmosphere. It is possible to achieve a balance between the rotational accuracy and acoustic characteristics required for the ball bearing for use and the corrosion resistance, and the chromium content is in the range of 9 to 14%.

[0016]

【Example】

 Hereinafter, embodiments of the present invention will be described.

FIG. 1 shows the present invention applied to a bearing unit for a spindle motor of a hard disk drive (HDD). This bearing unit includes a shaft portion 1 having two rows of inner raceway surfaces 1a formed on the outer peripheral surface, and a pair of outer races 5 having outer raceway surfaces 5a formed opposite to the two rows of inner raceway surfaces 1a. A plurality of balls 3 arranged between each inner raceway surface 1a and the outer raceway surface 5a of each outer ring 5, a cage 4 for holding the balls 3 at equal circumferential intervals, It comprises a non-contact seal 6 mounted on the opposite end, and a coil spring 16 mounted between a pair of outer rings 5 via a spring seat 15. The pair of outer rings 5 are pressed in opposite axial directions by a coil spring 16, whereby a preload is applied to the bearing. In addition, grease is sealed in the bearing, and sealed by the non-contact seal 6.

A pair of the outer races 5 forming the inner raceway surface 1a and the outer raceway 5a forming the outer raceway surface 5a are formed of a martensitic stainless steel having a chromium content of 9 to 14%. Made of steel. The chromium content of 9 to 14% is set from the viewpoint of improving the rotational accuracy and acoustic characteristics while securing the corrosion resistance required for the bearing unit for the spindle motor. That is, when the chromium content is 14% or more, the corrosion resistance is improved, but the rotation accuracy and acoustic characteristics are reduced. Conversely, if the chromium content is 9% or less, the rotational accuracy and acoustic characteristics are improved, but the required corrosion resistance cannot be obtained. Therefore, as a chromium content within the above range, sufficient corrosion resistance can be obtained even in an environment such as dew condensation in the atmosphere, and high rotational accuracy and low noise required for a spindle motor bearing unit can be secured. The value was selected.

FIG. 2 shows a result of noise measurement performed on a deep groove ball bearing in which the inner ring and the outer ring are formed of martensitic stainless steel and the balls are formed of bearing steel. In this figure, diagram 1 is the above bearing having a chromium content of 10%, diagram 2 is the above bearing having a chromium content of 13%, diagram 3 is a bearing and wire using only bearing steel (SUJ2). FIG. 4 shows the noise measurement results for a bearing in which the inner and outer rings and the balls are formed of SUS440C (chromium content: 16 to 18%) of martensitic stainless steel. As is clear from the measurement results, the ball bearing according to the present invention has good acoustic characteristics.

[0020]

[Effect of the invention]

 As described above, in the present invention, in the ball bearing for a spindle motor of a hard disk drive, the members constituting the inner and outer raceways are formed of martensitic stainless steel to secure the corrosion resistance of the bearing, Is made of bearing steel to ensure the accuracy of the ball and to prevent contact between giant carbides at the contact point between the ball and the raceway. Therefore, according to the present invention, it is possible to secure the rotation accuracy, acoustic characteristics and corrosion resistance required for a ball bearing for a spindle motor of a hard disk drive, and to reduce costs as compared with a configuration in which corrosion-resistant plating is performed. it can.

Further, by using a martensitic stainless steel having a chromium content of 9 to 14%, a configuration more suitable for the required values of rotational accuracy, acoustic characteristics, and corrosion resistance of a ball bearing for a spindle motor of a hard disk drive. It can be.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention.

FIG. 2 is a diagram showing noise measurement results.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Shaft part 1a Inner raceway surface 3 Ball 5 Outer ring 5a Outer raceway surface

Claims (4)

[Utility model registration claims] 1. A ball bearing for a spindle motor of a hard disk drive in which a magnetic disk is mounted and a disk spindle rotatably driven by a motor unit is rotatably supported, wherein members constituting inner and outer raceways are martensitic stainless steel. A ball bearing for a spindle motor of a hard disk drive, wherein a plurality of balls formed of steel and interposed between the inner and outer raceways are formed of bearing steel. 2. The ball bearing for a spindle motor of a hard disk drive according to claim 1, wherein said martensitic stainless steel has a chromium content of 9 to 14%. 3. A shaft portion having two rows of inner raceway surfaces formed on an outer peripheral surface, a pair of outer races having outer raceway surfaces opposed to the two rows of inner raceway surfaces, and each of the inner raceways. A plurality of balls disposed between the outer raceway and the outer raceway surface of each of the outer races; and a preload applying means for elastically pressing the pair of outer races in opposite axial directions to apply a preload. A ball bearing unit for a spindle motor of a hard disk drive, wherein the shaft portion and the pair of outer rings are formed of martensitic stainless steel, and the plurality of balls are formed of bearing steel. 4. The ball bearing unit for a spindle motor of a hard disk drive according to claim 3, wherein the martensitic stainless steel has a chromium content of 9 to 14%.