JP2000120695A - Dynamic pressure bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the cost and enhance the reliability of a shaft, sleeve, etc., as component parts of a dynamic pressure bearing device. SOLUTION: A dynamic pressure bearing device is equipped with a shaft 101 capable of being fixed at two ends, a sleeve 102 installed rotatably on the shaft 101 with a gap reserved in between, lubricating oil 111 to fill the gap, and a dynamic pressure groove 105 formed in at least either of the shaft 101 and sleeve 102 confronting each other with the gap interposed. The shaft 101 and sleeve 102 are made from steel material subjected to a grinding process, and their surfaces are covered with nickel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dynamic bearing device. More specifically, the present invention relates to a surface treatment technique and a surface processing technique for a shaft and a sleeve incorporated in a dynamic pressure bearing device.

[0002]

2. Description of the Related Art FIG. 5 is a schematic sectional view showing an example of a conventional hydrodynamic bearing device. This dynamic pressure bearing basically includes a shaft 101, a sleeve 102, and a thrust plate 103. The shaft 101 can be fixed by screw holes 110 formed at both ends, and has a so-called both-ends support structure. The thrust plate 103 is fixed around the shaft 101. The sleeve 102 stores the shaft 101 and the thrust plate 103 therein through a gap, and is capable of rotating by itself. The gap is filled with the lubricating oil 111. An axial dynamic pressure groove 105 is formed on the outer peripheral surface of the shaft 101, and a radial dynamic pressure groove 104 is formed on the upper and lower surfaces of the thrust plate 103. The dynamic pressure bearing having such a configuration includes a shaft 101 and a sleeve 102 which are relatively rotatably arranged.
Lubricating oil (bearing fluid) 111 is injected into the space between the shaft 101 and the bearing 101, and a dynamic pressure is generated in the bearing fluid by the pumping action of the dynamic pressure groove 105 provided in at least one of the shaft 101 and the sleeve 102. The shaft 101 and the sleeve 102 are supported so as to be relatively rotatable by the dynamic pressure. In particular, both-end fixed type fluid bearings are mechanically stable, and are therefore applied to high-speed and precise spindle motors. However, since the upper and lower ends of the liquid lubricating film (lubricating oil) of the fixed-end fluid bearing are open, the force supporting the lubricating oil is mainly the surface tension at the upper and lower open ends, sliding friction force and internal dynamic pressure. It is. Therefore, it is necessary to employ some kind of lubricating oil leakage prevention structure. For example, various measures have been taken such as forming an air pocket in a gap into which the lubricating oil is injected to increase the surface tension and reduce the weight of the lubricating oil.

FIG. 6 is a schematic view showing another example of a conventional hydrodynamic bearing device. Parts corresponding to those of the prior art shown in FIG. 5 are denoted by corresponding reference numerals to facilitate understanding. ing.
In this conventional example, one end of the bearing is closed to realize a structure (single bag structure) in which lubricating oil does not leak. However, in this single-bag structure, the screw hole 110 can be necessarily provided only on the open end side of the shaft 101, and it is not a fixed type at both ends.

[0004]

[0005] Since a fluid dynamic pressure bearing with fixed ends requires high shaft rigidity and high machining precision, parts such as shafts and sleeves are made by cutting stainless steel. General. Rolling or etching has been used as a method of forming a dynamic pressure groove on stainless steel. The rolling method is a method in which a groove pattern is pressed and transferred to the surface of stainless steel. Etching is a method in which a mask is formed on the surface of stainless steel using photolithography, and the surface of the stainless steel is chemically etched through the mask. However, in these methods, the stainless steel itself, which is a material, is expensive and difficult to groove, so that an inexpensive bearing device cannot be provided.

FIG. 7 shows an example of a dynamic pressure groove pattern formed on the surface of stainless steel. The dynamic pressure groove 105 can be formed by etching, rolling or laser processing as described above.

FIG. 8A schematically shows a cross-sectional shape of a dynamic pressure groove 105 formed by etching. In the etching method, a portion where the resist is not applied is etched to form the dynamic pressure groove 105. However, there is a problem that the inner wall near the opening of the dynamic pressure groove 105 is eroded. (B) schematically shows the cross-sectional shape of the dynamic pressure groove 105 formed by rolling. Rolling is to form the dynamic pressure groove 105 by plastically deforming the stainless steel material itself. However, since burrs and sagging are generated in the opening of the dynamic pressure groove 105, secondary processing for removing these is necessary.
(C) shows the cross-sectional shape of the dynamic pressure groove 105 formed by laser processing. In the laser processing, a ceramic film is formed on the surface of the material in advance, and the ceramic film is irradiated with a laser beam and selectively removed to form a dynamic pressure groove 105. However, laser processing is complicated and expensive. In addition, there is an inconvenience that a bulge occurs in the opening of the dynamic pressure groove 105.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems of the prior art, the following measures have been taken. That is, the dynamic pressure bearing device according to the present invention has, as a basic configuration, a shaft that can be fixed at both ends, a sleeve rotatably mounted around the shaft through a gap, and a fluid filled in the gap. And a dynamic pressure groove formed in at least one of the shaft and the sleeve facing each other via the gap. As a characteristic feature, at least one of the shaft and the sleeve is formed by coating a surface of a steel material subjected to grinding with nickel. Preferably, the nickel is formed on a surface of a steel material by a plating method. In one embodiment, the surface of the steel material is entirely coated with nickel and then selectively removed to provide a dynamic pressure groove. Alternatively, a dynamic pressure groove may be provided by selectively coating the surface of a steel material with nickel (electroforming).

According to the present invention, steel is used as a material of a shaft and a sleeve constituting a dynamic pressure bearing device of a fixed type at both ends. Iron and steel, particularly free-cutting steel, can be easily processed in the order of μm. Further, in the present invention, the surface of a steel material is plated with nickel. Nickel plating can prevent precipitation of impurity elements such as S and P in the free-cutting steel on the surface. At the same time, nickel plating can be formed with high processing accuracy. Using this nickel plating, it is possible to form a dynamic pressure groove on the surface of the shaft or sleeve.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a spindle motor incorporating a dynamic pressure bearing device according to the present invention. As shown, the spindle motor has a shaft 101 implanted in the center of a base plate 129. Screw holes 110 are formed at both ends of the shaft 101, so that both ends of the spindle motor can be fixed. The upper end of the shaft 101 has a plate 12
3 is attached. A holder 121 is arranged on the base plate 129 so as to surround the shaft 101. A core 124 and a coil 1 are provided on the outer peripheral surface of the holder 121.
25 are mounted. Base plate 129, shaft 101, plate 123, holder 1 described above
21, the core 124 and the coil 125 are on the stator side of the spindle motor. Shaft 101 and holder 121
The sleeve 102 is inserted between them. Sleeve 10
A thrust plate 103 is attached to a lower end of the second plate 2. A hub 122 is integrally formed on the upper end of the sleeve 102. The magnet 12 is provided on the inner peripheral surface of the hub 122.
6 is attached. Sleeve 10 described above
2. The thrust plate 103, the hub 122 and the magnet 126 are on the rotor side of the spindle motor.
The spindle motor having such a configuration is the base plate 1
The 29 side is a closed end, and the plate 123 side is an open end. Therefore, the spindle motor has a single-bag structure while having a structure of supporting both ends, has excellent mechanical operation stability, and has no leakage of lubricating oil.
The lubricating oil 111 is injected into a gap between the shaft 101 and the sleeve 102 and a gap between the sleeve 102 and the holder 121. In addition, axial dynamic pressure grooves 1 are formed on the inner peripheral surface of the sleeve 102 and the inner peripheral surface of the holder 121.
05 is formed. Further, radial dynamic pressure grooves 104 are formed on the upper and lower surfaces of the thrust plate 103.

A feature of the present invention is that the shaft 101
And at least one of the sleeves 102 is formed by coating a surface of a steel material which has been subjected to a grinding process with nickel. Nickel is formed on the surface of a steel material by a plating method. Iron and steel materials, particularly free-cutting steel, can be easily processed in the order of μm. Further, nickel plating can prevent precipitation of impurity elements such as S and P in free-cutting steel on the surface. By using free-cutting steel instead of conventional stainless steel, a shaft or sleeve can be produced with high processing accuracy. Precipitation of impurity elements can also be suppressed. As a result, the spindle motor according to the present invention has high reliability and is suitable for applications such as hard disk drives. In particular, since free-cutting steel is used instead of expensive stainless steel, it is possible to contribute to a reduction in parts cost.

The nickel plating not only suppresses the precipitation of impurities but also forms a dynamic pressure groove by processing the surface thereof. This is shown in FIG. A nickel coating 150 is formed on the surface of a steel material 100 used as a material for a shaft or a sleeve. The dynamic pressure groove 105 can be formed by patterning the nickel coating 150. At this time, the thickness of the nickel coating 150 is about 5 to 20 μm. Etching and electroforming are mentioned as a patterning method of the nickel film 150. In the etching, after the nickel coating 150 is formed on the entire surface of the steel material 100, the nickel coating 150 is selectively removed through a mask to remove the dynamic pressure grooves 1.
05 is formed. In the electroforming method, a negative resist is first formed on the surface of the steel material 100, and the nickel film 150 is selectively plated on the surface of the steel material 100 via the resist. Thereafter, if the unnecessary resist is removed, the dynamic pressure groove 105 can be formed.

A specific example of the above-described electroforming method will be described with reference to FIG. As shown in (A), after the surface of the steel material 100 is degreased, a resist R for preventing plating adhesion having a film thickness corresponding to the depth of the dynamic pressure groove is formed on a portion where the dynamic pressure groove is to be formed. Print. Next, as shown in (B), the printed resist R is baked and solidified, and then subjected to ordinary cleaning and surface activation treatment in order, followed by hard electroless plating with abrasion resistance to a predetermined thickness. Is formed. Thereafter, as shown in FIG. 3C, the resist R is removed after successive washing and drying, and the dynamic pressure groove 105 is removed.
To form

More specifically, a free-cutting steel is ground to prepare a shaft, which is degreased with an alkaline solution, and then a resist is printed with a film thickness of 5 μm or more on a portion to be a dynamic pressure groove. As the resist, an epoxy-based ink or a ceramic ink is preferable as a result of taking into account printability, acid resistance, alkali resistance, adhesion to steel materials, and ease of removal after plating. Next, the printed resist is baked (at 150 ° C. for 20 minutes), solidified, washed successively with alkali, and subjected to a surface activation treatment with hydrochloric acid, and then subjected to nickel-phosphorus alloy (pH 4.5, 90 ° C.). Abrasive hard electroless plating is performed for 20 minutes and the thickness is 5 μm (± 0.5 μm).
m) was formed. The dynamic pressure grooves may be formed by performing electrolytic plating instead of the wear-resistant hard electroless plating.

Instead of using a resist, a dynamic pressure groove may be formed by performing nickel electroforming using a mask that can be handled alone. This example is shown in FIG. (A) shows a mask M used for forming a thrust dynamic pressure groove in a thrust plate. (B) schematically shows a method of forming a thrust dynamic pressure groove in the thrust plate 103 using the mask shown in (A). As shown in the figure, a mask M shown in (A) is attached to the upper and lower surfaces of the thrust plate 103 in close contact, and is immersed in a nickel plating tank 200 to perform nickel plating of a desired thickness. (C) shows a cylindrical mask M used to form a dynamic pressure groove on the inner peripheral surface of the sleeve or the outer peripheral surface of the shaft. As shown in (D), when forming an axial dynamic pressure groove on the inner peripheral surface of the sleeve 102, the cylindrical mask M is attached to the sleeve 102.
Immersed in the nickel plating tank 200. When a dynamic pressure groove is formed on the outer peripheral surface of the shaft 101, the shaft 101 may be immersed in the nickel plating tank 200 with the shaft 101 inserted inside the cylindrical mask M as shown in FIG.

[0015]

As described above, according to the present invention,
Shafts and sleeves, which are components of the hydrodynamic bearing device, are formed by coating a surface of a ground steel material with nickel. The use of steel materials typified by free-cutting steel in place of conventional stainless steel makes it possible to create shafts and sleeves with high machining accuracy, and at the same time reduces the precipitation of impurity elements from steel materials by applying nickel plating it can. The use of nickel coating for forming the dynamic pressure grooves also leads to an improvement in processing accuracy. Specifically, unlike the conventional etching method, there is no erosion of the inner wall near the opening of the dynamic pressure groove. Also, unlike the conventional rolling method, no burr or dripping occurs at the opening of the dynamic pressure groove. Compared with the conventional laser beam method, the number of processes is reduced, mass production is possible, and cost is reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a spindle motor incorporating a dynamic bearing device according to the present invention.

FIG. 2 is a schematic view showing a characteristic portion of the present invention.

FIG. 3 is a process chart showing a method of forming a dynamic pressure groove using an electroforming method.

FIG. 4 is a schematic view showing a method of forming a dynamic pressure groove using an electroforming method.

FIG. 5 is a cross-sectional view illustrating an example of a conventional hydrodynamic bearing device.

FIG. 6 is a cross-sectional view showing another example of the conventional hydrodynamic bearing device.

FIG. 7 is a plan view showing an example of a pattern of a dynamic pressure groove.

FIG. 8 is a cross-sectional view showing a defect of a dynamic pressure groove formed by a conventional method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 100 ... Steel material 101 ... Shaft 102 ... Sleeve 103 ... Thrust plate 104 ... Thrust dynamic pressure groove 105 ... Axial dynamic pressure groove 111 ... Lubricating oil 150 ... Nickel coating

Continuing from the front page (72) Inventor Isamu Takehara 1-8-8 Nakase, Mihama-ku, Chiba City, Chiba Prefecture Inside Seiko Instruments Inc. (72) Inventor Ryoji Yoneyama 1-8-8 Nakase, Mihama-ku, Chiba City, Chiba Prefecture Seiko Instruments Inc. Inside the company (72) Inventor Takafumi Suzuki 1-8-8 Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. (72) Inventor Toshiharu Smaller 1-8-1, Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. (72) Inventor Tadao Iwaki 1-8-1, Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. (72) Inventor Naoki Kawawada 1-8-8, Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. ( 72) Inventor Atsushi Ota 1-8-8 Nakase, Mihama-ku, Chiba-shi, Chiba Seiko Instruments Inc. (72) Inventor Koji Nitori Chiba 1-8-8 Nakase, Mihama-ku, Chiba F-term (reference) in Seiko Instruments Inc. 3J011 AA04 BA02 BA08 CA02 DA02 QA03 SB15 4K024 AA03 AB01 AB08 BA02 BB05 FA05 FA15 GA16 5H607 BB01 BB02 CC01 DD03 GG12 JJ00 KK00

Claims (4)

[Claims] 1. A shaft that can be fixed at both ends, a sleeve rotatably mounted around the shaft through a gap, a fluid filled in the gap, and a shaft and a sleeve facing each other through the gap. A dynamic pressure bearing device provided with a dynamic pressure groove formed on at least one of the shafts, wherein at least one of the shaft and the sleeve is formed by coating a surface of a steel material subjected to a grinding process with nickel. Dynamic bearing device. 2. The dynamic pressure bearing device according to claim 1, wherein said nickel is formed on a surface of a steel material by a plating method. 3. The dynamic pressure bearing device according to claim 1, wherein the surface of the steel material is entirely coated with nickel and then selectively removed to form a dynamic pressure groove. 4. The dynamic pressure bearing device according to claim 1, wherein the surface of the steel material is selectively coated with nickel to form a dynamic pressure groove.