JP2001090727A - Dynamic pressure bearing device and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dynamic pressure bearing and a method of its manufacture formed with no nitride layer in the inside of a tap hole or a hole in a shaft inside, to be difficult of generation of rust, and improve workability, to be capable of extending a tool life. SOLUTION: In a dynamic pressure bearing device, having relatively rotated shaft 1 and sleeve 3 to constitute a dynamic pressure bearing part between an external peripheral surface of the shaft 1 and an internal peripheral surface of the sleeve 3 to relatively rotate the shaft 1 and the sleeve 3 by dynamic pressure action of this dynamic pressure bearing part, the shaft 1 is applied with nitride treatment in the total peripheral surface, one end face removes a nitride layer 12 by the nitride treatment, and this end face is formed with a tap hole 15 without applying the nitride treatment extended in an axial center direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic bearing device applicable to, for example, a motor for a hard disk drive and a method for manufacturing the same.

[0002]

2. Description of the Related Art A dynamic pressure bearing device comprising a shaft and a sleeve which rotate relative to each other and having a dynamic pressure generating groove formed in at least one of an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve is provided. Once the relative rotation starts at high speed, dynamic pressure is generated by the dynamic pressure generating groove, and the rotor rotates with high rigidity and high core runout accuracy. For example, if this is used as a bearing device of a motor for a hard disk drive, a high recording density is obtained. Can be obtained.

[0003] In such a dynamic pressure bearing, there has conventionally been a sleeve made of a copper alloy having good workability.
In this case, it is ideal to eliminate the difference in thermal expansion between the copper alloy sleeve and the shaft to reduce the change in the gap due to the temperature change. Therefore, a hydrodynamic bearing having a shaft having both a linear expansion coefficient equivalent to that of a copper alloy sleeve and a hardness capable of minimizing abrasive wear has been desired.

As a hydrodynamic bearing device satisfying such conditions, as described in JP-A-10-89345, a sleeve is made of a copper alloy, a shaft is made of austenitic stainless steel, and nitriding is performed on a surface layer of the shaft. 2. Description of the Related Art A hydrodynamic bearing whose surface hardness is increased by performing a treatment is known. However, nitriding is a process that replaces the passivation film consisting of a chromium layer of stainless steel with iron nitride.Therefore, when nitriding is performed, the corrosion resistance inherent in stainless steel is significantly reduced, and the problem of easy rusting occurs. there were.

In particular, many shafts are provided with a tapped hole which is a non-through hole for fixing a motor, and the tap hole easily accumulates moisture. If the water enters the valleys and valleys of the tap hole from the outside, it is likely to remain inside the tap hole, and it is difficult to clean dirt once attached. The inside of the hole is very susceptible to rust. Therefore, if nitriding is performed after tap hole processing, rust is easily generated inside the hole, and in actual mass production of dynamic pressure bearings,
The problem of frequent rust defects is likely to occur.

On the other hand, in order to prevent the generation of rust, it is conceivable that the tap holes are formed after the nitriding treatment. However, tools such as drills and taps for machining the hardened nitride layer on the surface after the nitriding treatment are considered. However, there is a problem that the tool is severely worn and the tool life is significantly shortened.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and a nitride layer is not formed in a tap hole or a hole inside a shaft.
An object of the present invention is to provide a dynamic pressure bearing which hardly generates rust, has good workability, and can prolong a tool life, and a method of manufacturing the same.

[0008]

According to the first aspect of the present invention,
A shaft and a sleeve that rotate relatively, a dynamic pressure bearing portion is formed between an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve, and the shaft and the sleeve are separated by a dynamic pressure action by the dynamic pressure bearing portion. In the hydrodynamic bearing device that performs relative rotation, the shaft is subjected to nitriding on the entire peripheral surface, the one end face is subjected to the nitriding treatment by the nitriding treatment, and the end face is subjected to the nitriding treatment extending in the axial direction. It is characterized in that a tap hole not formed is formed.

According to a second aspect of the present invention, in the dynamic pressure bearing device of the first aspect, a through hole is formed in the shaft in a radial direction of the shaft, and the inside of the through hole is subjected to nitriding treatment. It is characterized by having been done.

According to a third aspect of the present invention, in the dynamic bearing device according to the second aspect, the through hole is a hole for circulating a lubricating fluid.

According to a fourth aspect of the present invention, there is provided the dynamic pressure bearing device according to the first aspect, wherein the dynamic pressure bearing device is applied to a hard disk drive motor. A screw is attached.

According to a fifth aspect of the present invention, there is provided a shaft and a sleeve which rotate relative to each other, and a dynamic pressure bearing is formed between an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve. In the method for manufacturing a dynamic pressure bearing device in which the shaft and the sleeve are relatively rotated by a dynamic pressure action, the shaft is subjected to a nitriding treatment on the entire peripheral surface, and then the at least one end surface of the shaft is subjected to the nitriding treatment. The formed nitride layer is removed, and a tap hole extending in the axial direction is formed on the end face from which the nitride layer has been removed.

According to a sixth aspect of the present invention, in the method of manufacturing a dynamic bearing device according to the fifth aspect, a nitriding treatment is performed after forming a through-hole extending in a radial direction or an axial direction of the shaft. It is characterized by.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a dynamic pressure bearing device and a method of manufacturing the same according to the present invention will be described with reference to the drawings. The dynamic pressure bearing device according to the present invention has a feature particularly in the shaft of the dynamic pressure bearing, and is applicable to the motors shown in FIGS. 1 to 3 described below. FIG.
FIG. 1 shows an example of a shaft rotation type disk drive motor to which the dynamic bearing device according to the present invention can be applied. FIG.
As shown in the figure, a cylindrical boss 9 with a flange is fixed to the hole formed in the center portion of the base 10 by press-fitting, and the lower half of the sleeve 3 is fixed to the inner peripheral side of the boss 9 by press-fitting. I have. A boss 9 is provided on the outer peripheral side of the sleeve 3.
Above, a stator core 5 composed of a laminated core is fitted and fixed to the sleeve 3 by an appropriate means such as adhesion. The stator core 5 has an appropriate number of salient poles radially,
A drive coil 4 is wound around each salient pole.

The sleeve 3 is a cylindrical member, and the shaft 1 is inserted on the inner peripheral side. On the outer peripheral side of the lower end of the shaft 1,
A ring-shaped thrust plate 7 is fixed by press fitting or the like. The thrust plate 7 is fitted at appropriate intervals in a concave portion formed at the lower end of the sleeve 3, and forms a thrust bearing between the sleeve 3 and the counter plate 8. At the lower end of the sleeve 3, a recess having a diameter larger than the recess into which the thrust plate 7 is fitted is formed. A counter plate 8 is fitted into this recess, and is fixed to the sleeve 3 by bonding or other appropriate means. I have.

A radial dynamic pressure bearing is constituted by the sleeve 3 and the shaft 1. A minute gap is formed between the outer peripheral surface of the shaft 1 and the inner peripheral surface of the sleeve 3, and the outer peripheral surface of the shaft 1 is A radial dynamic pressure generating groove is formed on at least one of the inner peripheral surfaces of the inner circumferential surface 3, and a dynamic pressure generating oil is interposed in a formation portion of the dynamic pressure generating groove to form a radial dynamic pressure bearing.

The upper end of the shaft 1 is integrally formed with a rotor case 2. The rotor case 2 also serves as a motor housing and a disk holding hub, has a cup-shaped shape, and covers the stator of the motor having the stator core 5 and the drive coil 4. A short cylindrical drive magnet 6 is fixed to the inner peripheral surface of the inner wall of the body 22 of the rotor case 2. Drive magnet 6
In the figure, N poles and S poles are alternately magnetized in the circumferential direction.

The shaft 1 has a tapped hole 15 formed by a central axis from the upper end. The rotor case portion 2 has a flange 21, and the hard disk and the spacer fitted on the outer periphery of the body portion 22 of the rotor case portion 2 are placed on the flange to regulate the position. A disk mounting screw (not shown) is screwed into the tap hole 15 and a clamper (not shown) is mounted. The hard disk and the spacer are suppressed by the clamper, whereby the hard disk is mounted on the rotor case portion 2.

The rotational position of the drive magnet 6 is detected by a magnetic sensor, and power supply to each drive coil is suppressed in accordance with the detection signal, thereby providing a magnetic attraction between the salient poles of the stator core 5 and the drive magnet 6. A repulsive force is generated and the drive magnet 6 is urged in the circumferential direction, and the rotor of the motor including the shaft 1, the rotor case 2, and the thrust plate 7 is driven to rotate.

Due to the rotational force of the shaft 1, a dynamic pressure is generated by a dynamic pressure bearing device comprising a dynamic pressure generating groove formed on at least one of the outer peripheral surface and the inner peripheral surface of the sleeve 3 and oil interposed therebetween. Then, the shaft 1 rotates without contacting the inner peripheral surface of the sleeve 3. Further, a dynamic pressure is generated in a thrust dynamic pressure bearing portion formed between opposing surfaces of the thrust plate 7 and the counter plate 8, and the shaft 1 is moved to the counter plate 8.
Rotate while floating from.

Incidentally, in the shaft-rotating disk drive motor shown in FIG. 1, in order to fix the disk to the rotor case portion 2, the clamp member is fixed with a screw using a tap hole 15 provided in the shaft 1. It has become.

FIG. 2 shows another example of a double-shaft fixed disk drive motor to which the dynamic bearing device according to the present invention can be applied. The description of the same components as those in FIG. 1 is omitted. In the shaft 1, a through hole 16 extending in the radial direction of the shaft is formed. The lubricating oil is held only in the sleeve 3, a communication hole 17 is provided in the center of the shaft 1 as an air vent hole, and the intermediate concave portion of the radial bearing communicates with the outside air via a through hole 16. ing.
A frame mounting screw (not shown) is mounted in the tap hole 15.

FIG. 3 shows still another example of a shaft rotation type disk drive motor to which the dynamic pressure bearing device according to the present invention can be applied. A through hole 16 extending in the radial direction of the shaft is formed in the shaft 1, and a circulation hole 18 communicating with the through hole 16 is formed at the center of the shaft 1 from the end face of the shaft 1 on the counter plate 8 side. The lubricating oil is filled in the sleeve 3, and the inside of the sleeve 3, which constitutes a radial bearing and a thrust bearing, the through hole 16 and the circulation hole 18 are provided.
It circulates inside.

In the dynamic pressure bearings used in various motors as described above, it is necessary to eliminate the difference in thermal expansion between the sleeve and the shaft, and to reduce the change in the gap due to the temperature change. As a material satisfying such conditions, phosphor bronze is used as the material of the sleeve, and SUS is used as the material of the shaft.
303 is used. Here, the SUS used for the shaft
Since the hardness of 303 cannot be increased by quenching and tempering, it is necessary to perform a nitriding treatment to harden the shaft surface in order to prevent scratches and abrasive (scratch) wear in the working process. is there.

In the following, a description will be given of a shaft machining process that can be used in the dynamic bearing device according to the present invention. FIG.
(A) shows, as a typical example, a round bar 11 having a diameter of, for example, about 5 mm for processing as a shaft. First, a nitriding process is performed on the entire circumference of the round bar 11 before performing the tap hole processing (FIG. 4B). Next, as shown in FIG. 4C, one end face 13 of the round bar whose entire circumference is nitrided is cut or ground to remove the nitride layer 12 on the surface of this end face portion. As described above, since the nitride layer 12 is removed from the end face 13 where the tap hole processing is performed, when a screw hole or the like is formed from the end face 13, workability is good and tool life can be extended.

Next, as shown in FIG.
A tap hole 15 extending in the axial direction from the end face 13 from which the nitride layer 12 has been removed is formed. Finally, as shown in FIG. 4 (e), the nitride layer 1
The surface is finished by centerless polishing except a part of 5.

According to the dynamic pressure bearing using the shaft manufactured by such a method, since the nitride layer is formed on the outer periphery of the shaft, it is possible to prevent scratches and secure the wear resistance. On the other hand, since no nitride layer is formed inside the tap hole, rust can be prevented from being generated. Further, since no nitride layer is formed on the surface on which the tap hole processing or the hole processing is performed, the workability is good and the tool life can be extended.

As shown in FIG. 2 or FIG. 3, when a shaft having a through hole extending in the radial direction of the shaft is used to circulate the lubricating fluid, FIGS. 4 (a) and 4 ( b)
A step of providing a through-hole may be added during the step, and the nitriding treatment may be performed after the through-hole is formed. Unlike the tap holes described above, the through holes are not bag-shaped but penetrated, so it is difficult for water to accumulate inside the holes, and it is easy to clean dirt,
This is because even if the through holes are nitrided, the problem of rust generation is small.

When the dynamic pressure bearing according to the present invention is used in a shaft rotating type motor, a disc mounting screw is attached to a tap hole provided in the shaft. Screws for frame attachment are attached to the holes.

[0030]

According to the first aspect of the present invention, there is provided a shaft and a sleeve which rotate relative to each other, and a dynamic pressure bearing portion is formed between an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve. In a dynamic pressure bearing device in which the shaft and the sleeve are relatively rotated by a dynamic pressure action by a dynamic pressure bearing portion, the shaft is subjected to a nitriding treatment on an entire peripheral surface, and a nitride layer is removed from one end surface by the nitriding treatment. Since the end face is formed with a non-nitrided tap hole extending in the axial direction, the end face on which the tap hole processing is performed is not formed with a nitride layer. Life can be extended. In addition, since no nitride layer is formed inside the tap hole, no rust is generated inside the tap hole. Further, since the nitride layer is formed on the outer periphery of the shaft, it is possible to prevent the occurrence of scratches and sufficiently secure the wear resistance.

According to the second or third aspect of the present invention, in the dynamic pressure bearing device according to the first aspect, the shaft is formed with a through hole extending in a radial direction of the shaft. Since it is used for circulating a lubricating fluid and the inside of the hole is subjected to nitriding treatment, sufficient hardness can be ensured for the through-hole in which water removal or cleaning is easy.

According to a fourth aspect of the present invention, in the dynamic bearing device according to the first aspect, the dynamic bearing device is applied to a motor for driving a hard disk, and the tap hole has a disk mounting screw or a screw. Since the frame mounting screw is attached, when using such a dynamic pressure bearing for a hard disk drive motor, attach the disk mounting screw to the tap hole provided on the shaft, and when using the shaft fixed type motor, use the tap. A frame mounting screw can be attached to the hole.

According to the fifth aspect of the present invention, there is provided a shaft and a sleeve which rotate relative to each other, and a dynamic pressure bearing is formed between an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve. In a method of manufacturing a dynamic bearing device in which the shaft and the sleeve are relatively rotated by a dynamic pressure action of a bearing portion, the shaft is subjected to a nitriding treatment on an entire circumferential surface, and then the nitriding of at least one end surface of the shaft is performed. Removing the nitrided layer formed by the treatment,
Since a tap hole extending in the axial direction is formed on the end face from which the nitride layer has been removed, since the nitride face is not formed on the end face where the tap hole processing is performed, the workability is good and the tool life can be extended. it can. In addition, since no nitride layer is formed inside the tap hole, no rust is generated inside the tap hole. Further, since the nitride layer is formed on the outer periphery of the shaft, it is possible to prevent the occurrence of scratches and sufficiently secure the wear resistance.

According to a sixth aspect of the present invention, in the method of manufacturing a dynamic pressure bearing device according to the fifth aspect, after the through-hole extending in the radial direction or the axial direction of the shaft is formed in the shaft, nitriding is performed. As a result, sufficient hardness can be ensured for the through-holes from which moisture can be easily removed and easily cleaned.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a motor that can use a dynamic bearing device according to the present invention.

FIG. 2 is a sectional view showing another example of the motor.

FIG. 3 is a sectional view showing still another example of the motor.

FIG. 4 is a process chart showing an example of a manufacturing procedure of a shaft that can be used in the dynamic pressure bearing device according to the present invention.

[Explanation of symbols]

 1 shaft 3 sleeve 13 shaft end surface 12 nitride layer 15 tapped hole

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuya Togawa 5329 Shimosuwa-machi, Suwa-gun, Nagano Prefecture Inside Sankyo Seiki Seisakusho Co., Ltd. (72) Teruo Kohata 4487-8 Kamimizo, Sagamihara-shi, Kanagawa Sanwa Seiko Co., Ltd. F term (reference) 3J011 AA04 AA20 BA02 BA08 CA02 CA05 DA02 MA23 QA04 RA03 5H607 AA00 BB01 BB14 BB17 BB25 CC01 DD03 EE10 GG12 GG15 GG25 KK00

Claims (6)

[Claims] 1. A dynamic pressure bearing portion is provided between an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve, wherein the dynamic pressure bearing portion is provided between the outer peripheral surface of the shaft and the inner peripheral surface of the sleeve. In a hydrodynamic bearing device for relatively rotating a shaft and a sleeve, the shaft is subjected to nitriding on the entire peripheral surface, and one end surface is free of a nitride layer formed by the nitriding treatment. A hydrodynamic bearing device, wherein an extended tap hole that is not subjected to the nitriding treatment is formed. 2. The dynamic pressure bearing according to claim 1, wherein a through hole extending in a radial direction of the shaft is formed in the shaft, and the inside of the through hole is subjected to a nitriding treatment. apparatus. 3. The hydrodynamic bearing device according to claim 2, wherein the through hole is a hole for circulating a lubricating fluid. 4. The dynamic pressure bearing device according to claim 1, wherein the dynamic pressure bearing device is applied to a hard disk drive motor, and a disk mounting screw or a frame mounting screw is mounted in the tapped hole. Pressure bearing device. 5. A dynamic pressure bearing part is provided between an outer peripheral surface of the shaft and an inner peripheral surface of the sleeve, the shaft comprising a relatively rotating shaft and a sleeve. In a method of manufacturing a hydrodynamic bearing device for relatively rotating a shaft and a sleeve, the shaft is subjected to a nitriding process on an entire peripheral surface, and then a nitriding layer formed by the nitriding process on at least one end surface of the shaft. A method for manufacturing a hydrodynamic bearing device, characterized in that a tap hole extending in the axial direction is formed on the end face from which the nitride layer has been removed. 6. The method for manufacturing a hydrodynamic bearing device according to claim 5, wherein a nitriding treatment is performed after forming a through hole extending in a radial direction or an axial direction of the shaft in the shaft.