JP2564193Y2 - Ball bearings for spindle motors of information equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball bearing for rotatably supporting a spindle in a spindle motor of an information device such as a hard disk drive (HDD). 2. Description of the Related Art For example, a hard disk drive (HD)
D), the disk spindle on which the magnetic disk is mounted is rotated at a constant rotation speed, and the magnetic head mounted on the tip of a plate bar called an access arm moves above or below the magnetic disk, and a predetermined amount of the magnetic disk is moved. This is for writing information at a position or reading information from a predetermined position on a 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. The above-described ball bearings for spindle motors require high rotational accuracy in order to prevent the positional deviation of the magnetic disk with respect to the magnetic head, and also require acoustic characteristics to be stricter than general-purpose bearings. It has the characteristic that corrosion resistance and low outgassing properties are required. Regarding rotation accuracy, with the recent increase in disk capacity,
In particular, there is a need for improved non-repeatability (non-repeatability refers to the trajectory created when the trajectory of the repetitive runout of a rotating body is continuously superimposed in synchronization with the rotation. Width.) A general required value of the non-repetitive shake 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 used. (If external rust prevention oil is applied to the bearings, the Due to the inability to perform the work of bonding and fixing to the parts, and the possibility of functional failure such as head crash due to outgas generated from the bearings.) This is because there is a possibility that rust may be generated on the bearing when used in such a case. [0003] By the way, bearings are generally formed of bearing steel, but when corrosion resistance is particularly required, they are formed using a corrosion resistant material such as martensitic stainless steel. However, this corrosion-resistant material is steel containing carbon and chromium, and since there are many giant carbides generated by eutectic of carbon and chromium, the workability is poor, and the precision of the ball (particularly sphericity) , Surface roughness and ball diameter) are difficult to secure. Therefore, it is known that the non-repeatability and acoustic characteristics of a bearing using this corrosion resistant material are considerably inferior to those of a bearing using general bearing steel. [0004] Conventionally, a bearing forming material which is required to simultaneously have rotation accuracy, low noise and corrosion resistance is determined as follows by comparing the required degrees of contradictory characteristics such as rotation accuracy, low noise and corrosion resistance. It was often done. (1) Use bearing steel when the requirements for rotational accuracy and low noise are particularly severe and the corrosion resistance can be neglected to some extent. (2) Use stainless steel especially when corrosion resistance is severely required. (3) If the requirements for rotational accuracy, low noise, and corrosion resistance are both severe, use bearing steel (parts other than the raceway surface) plated with corrosion resistance. [0005] In the case of a ball bearing for a spindle motor, although high corrosion resistance is not required, the problem of rust cannot be neglected, so that the configuration of the above (1) cannot be adopted. Since the required values of accuracy and acoustic characteristics are strict, the configuration of (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 bearing processing after plating is difficult. is there. Therefore, there is a problem in cost performance. An object of the present invention is to ensure the rotation accuracy, low noise, and corrosion resistance required for the above-described spindle motor ball bearing while considering cost. According to the present invention, a member constituting an inner raceway surface and a member constituting an outer raceway surface are formed of martensitic stainless steel having a chromium content of 9 to 14%. -To provide a ball bearing for a spindle motor in which a plurality of balls interposed between outer raceway surfaces are formed of bearing steel. The rotation accuracy and acoustic characteristics of the ball bearing include the accuracy of the raceway surface (roundness, surface roughness) and the accuracy of the ball (sphericity,
Surface roughness, dimensional difference between balls) and the like, and the influence of the accuracy of the balls is particularly large. Therefore, by forming the ball from bearing steel and ensuring its accuracy, it is possible to ensure the rotational accuracy and acoustic characteristics required for the spindle motor ball bearing. At the same time, by forming the members constituting the inner and outer raceways from martensitic 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 giant carbides at the contact point between the ball and the raceway surface. The effect is reduced. On the other hand, the corrosion resistance of the ball is ensured by a lubricant such as grease inside the bearing. Therefore, there is no fear that the corrosion resistance is reduced by forming the ball with bearing steel. [0008] In order to further improve the rotational accuracy and acoustic characteristics, it is effective to reduce giant carbides remaining on the inner and outer raceways, and for that purpose, the chromium content of the members constituting them is reduced. Need to reduce. Corrosion resistance required for ball bearings for spindle motors 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. Therefore, by forming the members constituting the inner and outer raceway surfaces with martensitic stainless steel having a chromium content sufficient to obtain the required corrosion resistance even in environments such as condensation in the atmosphere,
It is possible to achieve harmony between the rotation accuracy and acoustic characteristics required for the spindle motor ball bearing and the corrosion resistance, and the chromium content is in the range of 9 to 14%. An embodiment of the present invention will be described below. FIG. 1 shows the present invention applied to a bearing unit for a spindle motor of a hard disk drive (HDD). The 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 opposed to the two rows of inner raceway surfaces 1a, respectively. A plurality of balls 3 arranged between each inner raceway surface 1a and the outer raceway surface 5a of each outer ring 5; a retainer 4 for holding the balls 3 at equal circumferential intervals; A non-contact seal 6 is provided at the end, and a coil spring 16 is provided between the pair of outer rings 5 via a spring seat 15. The pair of outer races 5 are pressed in opposite directions in the axial direction by the 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. The shaft portion 1 forming the inner raceway surface 1a and the pair of outer rings 5 forming the outer raceway surface 5a are formed of martensitic stainless steel having a chromium content of 9 to 14%, and the ball 3 is formed of bearing steel. Is formed. 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. That is, when the chromium content is 14% or more, the corrosion resistance is improved, but the rotation accuracy and the acoustic characteristics are reduced. Conversely, if the chromium content is 9% or less, the rotation 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. still,
In the same figure, diagram 1 is the above bearing with a chromium content of 10%, diagram 2 is the above bearing with a chromium content of 13%, diagram 3 is a bearing using only bearing steel (SUJ2), diagram 4 Is made of martensitic stainless steel SUS4
The noise measurement result about the bearing formed by 40C (chromium content 16-18%) is shown. As is clear from the measurement results, the ball bearing according to the present invention exhibits good acoustic characteristics. As described above, according to the present invention, in a ball bearing for a spindle motor of an information device, the members constituting the inner and outer raceways are made of a martensitic stainless steel having a chromium content of 9 to 14%. By forming the ball from steel, at the same time as ensuring the corrosion resistance of the bearing,
The precision of the ball was ensured, and the contact between the giant carbides at the contact portion between the ball and the raceway surface was prevented. Therefore, according to the present invention, it is possible to ensure the rotation accuracy, acoustic characteristics, and corrosion resistance required of the ball bearing for the spindle motor, and to reduce the cost as compared with a configuration in which corrosion-resistant plating is performed. In particular, by using a martensitic stainless steel having a chromium content of 9 to 14%, it is possible to achieve a configuration more suitable for the required characteristic values of rotation accuracy, acoustic characteristics, and corrosion resistance of a ball bearing for a spindle motor.

[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] 1 Shaft 1a Inner raceway 3 balls 5 Outer ring 5a Outer raceway

Claims (1)

(57) [Registration of utility model registration] (1) In a ball bearing for a spindle motor of an information equipment for rotatably supporting a spindle rotatably driven by a motor part, members constituting inner and outer raceways are provided. Chromium content 9-14
A ball bearing for a spindle motor of an information device, wherein a plurality of balls formed between the inner and outer raceways are formed of bearing steel.