JP2002188638A - Dynamic pressure bearing and spindle motor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dynamic pressure bearing and a spindle motor which are free from the seizure and abrasion deterioration for a long period. SOLUTION: A shaft member 3 and a sleeve member 4 placed opposite to the shaft member 3 with a slight clearance are provided. The sleeve member 4 and the shaft member 3 are mutually rotatable. In the dynamic bearing in which stainless steel is used as a base material for either of the sleeve member 4 or the shaft member 3, and in which Cu-based material is employed as a base material for the other member, Si of 1-2 wt.% is contained as the Cu-based material. Respective metal elements of Mn, Al, Fe and Ni are contained. In the light of the improvement of durability of the dynamic pressure bearing, Mn of 2.5-5.0 wt.% content is preferable. As to the other metal elements, Al of 4-7.5 wt.%, Fe of 3-3.5 wt.% and Ni of 2-3 wt.% contents are preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic pressure bearing and a spindle motor using the same, and more particularly to a dynamic pressure bearing excellent in seizure resistance and durability and a spindle motor using the same.

[0002]

2. Description of the Related Art Magnetic disk devices such as hard disk drives (HDDs) and high-capacity floppy disk drives (FDDs) have been significantly increased in capacity and miniaturization year by year. It is required to have a long life, quietness, and excellent runout accuracy. Therefore, a dynamic pressure bearing of a type that rotates around a shaft through a gas or a liquid without using a ball as a bearing structure of a spindle motor has been developed. The structure of the dynamic pressure bearing mainly includes a shaft (shaft) member having a thrust plate, and a sleeve member disposed to face the shaft member with a small gap. In the dynamic pressure bearing, fluid is usually interposed between the shaft member and the sleeve member during the rotation of the spindle motor, but this does not mean that contact does not occur between the shaft member and the sleeve member. In particular, when the spindle motor starts and stops, contact between the shaft member and the sleeve member tends to occur. Therefore, it is important to secure the seizure resistance and wear resistance of the bearing member used as the characteristic of the bearing member used here. In addition, it is also important to secure mechanical strength and hardness for supporting the rotating part.

[0003] As a material used for such a shaft member and a sleeve member, a steel material, particularly a stainless steel, is widely used in view of versatility, low cost, and workability. However, when stainless steel is used for both the shaft member and the sleeve member, when the shaft member and the sleeve member come into contact, the temperature at the contact portion rapidly increases,
The metal of both members melts and seizure occurs. Therefore, conventionally, in order to prevent such seizure, different materials have been used for the shaft member and the sleeve member, that is, materials having different hardness have been used. Specifically, a combination using stainless steel for one side and using a Cu-based material for the other side has been generally used.

[0004]

However, according to such a combination of stainless steel and Cu-based material, although the seizure is suppressed to some extent, the combination of stainless steel and C
Since the hardness difference between the u-based materials is too large, there is a new problem that the Cu-based materials are worn unilaterally and lack durability.

The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a dynamic pressure bearing and a spindle motor which do not cause seizure and do not deteriorate for a long period of time. .

[0006]

According to a first aspect of the present invention, there is provided a hydrodynamic bearing comprising a shaft member and a sleeve member opposed to the shaft member with a small gap therebetween. And the shaft member are rotatable with each other, and stainless steel is used as one base material of the sleeve member and the shaft member, and Si is 1 to 1 as the other base material.
It was configured to use a Cu-based material containing 2% by weight and further containing each metal element of Mn, Al, Fe, and Ni.

Here, from the viewpoint of further improving the durability of the dynamic pressure bearing, the content of Mn is preferably in the range of 2.5 to 5% by weight. Other metal element contents: Al: 4 to
7.5% by weight, Fe: 3 to 3.5% by weight, Ni: 2 to 3
Each range of weight percent is preferred.

Further, from the viewpoint of further increasing the hardness of the stainless steel to further improve the seizure resistance, the stainless steel is desirably heat-treated. Here, nitriding treatment is preferable as the heat treatment.

According to another aspect of the present invention, there is provided a spindle motor including any one of the dynamic pressure bearings described above.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present inventors have proposed a stainless steel-C
As a result of intensive studies on whether durability can be improved while maintaining excellent seizure resistance in a u-type material dynamic pressure bearing, it has been found that a specific amount of Si should be contained in a Cu-type material. The present invention has been made.

According to the experiments by the present inventors, surprising results were obtained that the wear resistance was improved by increasing the particle size of the intermetallic compound of Si formed on the Cu base material in the Cu-based material. The cause of this has not been clearly elucidated so far, but the fact that a Si intermetallic compound which has grown significantly in the Cu base material and has a higher hardness than Cu, specifically, Mn ₅ Si ₃ is present in a dispersed state. It is speculated that the hardness of the Cu-based material partially increases due to this, and as a result, the wear resistance is improved.

FIG. 1 is a schematic view of an SEM photograph of a Cu-based material. FIGS. 1A to 1C show aluminum bronze (AIBC).
2C), high-strength brass (HBSC-4E), a Cu-based material used in the present invention. Si content is 0.07,
0.09, 1.39% by weight. As the Si content increases from (a) to (c) in the same figure, the particle size of the Si intermetallic compound 1 in the Cu base material 2 increases. In addition,
Here, the Si intermetallic compound 1 is specifically Mn ₅ Si ₃ . Then, when an abrasion test described below was performed on these Cu-based materials, 120, 80, 30 (× 10
⁻³ mm ³ ), indicating that the larger the Si content, the smaller the abrasion loss. The hardness Hv25 measured at the same time is 2
80, 283, 283 and the difference in Si content did not have an advantage. By including a specific amount of Si in the Cu material as described above, it is possible to improve the wear resistance while maintaining the same hardness as that of the conventional Cu material, that is, while maintaining the seizure resistance.

The amount of Si contained in the Cu-based material is 1
It is important that it is in the range of ~ 2% by weight. If the Si content is less than 1% by weight, the particle size of the formed intermetallic compound is small, and sufficient abrasion resistance cannot be obtained. On the other hand, if the Si content exceeds 2% by weight, the generated intermetallic compound becomes too large and the material itself becomes brittle. A more preferred Si content is in the range of 1.3 to 2.0% by weight.

The Cu-based material used in the present invention further contains Mn, Al, Fe and Ni metal elements. First, Mn produces an intermetallic compound with Si, and has an effect of improving wear resistance. The content of Mn is not particularly limited, but if it is less than 2.5% by weight, the particle size of the produced intermetallic compound may not be sufficiently large, and the abrasion resistance may not be improved. On the other hand, if the content exceeds 5% by weight, the amount of intermetallic compound generated becomes too large, and the ductility of the material may be reduced. Therefore, the content of Mn is 2.5 to 5
A range of weight% is preferred.

Al has the effect of increasing the hardness of the Cu-based material. If the Al content is less than 4% by weight, the above effect cannot be sufficiently obtained. On the other hand, if the Al content exceeds 7.5% by weight, the intermetallic compound may be miniaturized and wear resistance may be reduced. For this reason, the Al content is preferably in the range of 4 to 7.5% by weight.

Fe also has the effect of increasing the hardness of the Cu-based material. If the Fe content is less than 3% by weight, such an effect may not be sufficiently obtained, while the content is 3.
If it exceeds 5% by weight, the material may be brittle. For this reason, the Fe content is preferably in the range of 3 to 3.5% by weight.

Ni has the effect of improving the corrosion resistance and strength of the Cu-based material. If the Ni content is less than 2% by weight, such an effect may not be obtained. On the other hand, if the content exceeds 3% by weight, the ductility of the material may be reduced. Therefore, the Ni content is 2-3.
A range of weight% is preferred.

If necessary, the Cu-based material used in the present invention may contain a conventionally known metal element as long as the effects of the present invention are not impaired.

The stainless steel used in the present invention is not particularly limited. For example, conventionally known SUS303, SUS304Se, SU
Austenitic stainless steel such as S304Pb, SUS416,
Martensitic stainless steel such as SUS420F and SUS420Pb, and ferritic stainless steel such as SUS430F can be suitably used. Of course, stainless steel that can be used in the present invention is not limited to these.

In the stainless steel used in the present invention,
Heat treatment may be performed to increase the surface hardness. Examples of such heat treatment include general vacuum quenching and carburizing and quenching, as well as carbonitriding, sulphonitriding and nitriding. Among these heat treatments, the nitriding treatment is particularly desirable because the types of stainless steel that can be treated are wide and a very high surface hardness of Hv 1,000 or more can be obtained. Here, as the nitriding treatment, conventionally known treatment methods such as liquid nitriding represented by salt bath nitriding, gas nitriding, and ion nitriding can be used.

However, the nitriding treatment can provide a surface hardness as high as Hv1,000 or more as compared with ordinary vacuum quenching and carburizing quenching, but the material expands due to the nitriding treatment to increase its size, and the compound layer is hardened. Since the surface is roughened due to the formation of undulations, irregularities are generated. Therefore, in actual use, the outermost surface layer usually needs to be polished and removed. In order to avoid such surface polishing and removal after the nitriding treatment, it is recommended that the layer formed by the nitriding treatment has a thickness of 10 μm or less. A more preferred layer thickness is 5 μm or less. The thickness of the nitrided layer can be controlled mainly by the processing time.

FIG. 2 is a sectional view showing an embodiment of the dynamic pressure bearing of the present invention. The sleeve 2, which is a sleeve member,
It is provided around the shaft 1 which is a part of the shaft member, with a small gap (clearance) therebetween. The lubricating fluid 3 is held in the clearance. The sleeve 2
Herringbone or spiral dynamic pressure generating grooves (not shown) are formed. In such a dynamic pressure bearing, when the shaft 1 or the sleeve 2 rotates, the lubricating fluid 3 held in the clearance between the sleeve 2 and the shaft 1 is moved along the groove pattern of the dynamic pressure generating groove (not shown). When pressed, a local high pressure portion is generated in the lubricating fluid 3,
The load in the radial direction and the thrust direction of the sleeve 2 is supported.

In the dynamic pressure bearing of FIG. 2, the dynamic pressure generating groove is formed on the sleeve 2 side, but the dynamic pressure generating groove may be formed on the shaft 1 as a matter of course. Further, the dynamic pressure bearing of FIG. 2 is a fluid dynamic pressure bearing using a lubricating fluid, but the dynamic pressure bearing of the present invention may be an air dynamic pressure bearing not using a lubricating fluid.

The lubricating fluid that can be used in the present invention is not particularly limited, and conventionally known lubricating fluids can be used. Examples thereof include polyol ester oil, diester oil, poly-α-olefin oil, mineral oil, and fluorine oil. Can be

Next, the spindle motor of the present invention will be described. A major feature of the spindle motor of the present invention is that the spindle motor includes the above-described dynamic pressure bearing. Hereinafter, further description will be made with reference to the drawings. FIG. 3 is a sectional view showing an embodiment of a spindle motor provided with the dynamic pressure bearing of the present invention. The bracket 11 has a base 111 provided at the center.
And a peripheral wall 112 provided in an outer peripheral direction of the base 111.
And a flange 113 further extending outward from the peripheral wall 112, and these are formed integrally and coaxially.

An annular projection 114 is formed at the center of the base 111, and a fixed sleeve (sleeve member) 2 is fitted and fixed thereto by, for example, press fitting. A through hole 121 is formed in the center of the fixed sleeve 2 in the axial direction, and a thrust groove 122 opened in the axial direction downward is formed in the lower end thereof.

The shaft (shaft member) 1 includes a shaft portion 131,
Thrust plate 132 formed at the lower end of shaft 131
Consists of A DLC film (not shown) is formed on the surface. The shaft portion 131 and the thrust plate 132 of the shaft 1 are inserted into the through hole 121 and the thrust groove portion 122 of the fixed sleeve 2 via a certain gap,
The counter plate 14 is mounted so as to cover the outside of the thrust plate 132.

The upper end of the shaft 1 is fitted and fixed in a hole 151 formed in the center of the upper surface of the substantially cylindrical rotor hub 15. On the inner peripheral surface of the rotor hub 15, a rotor magnet 16 that is multipolarly magnetized in the circumferential direction is disposed over the entire circumference. A radially inward portion of the rotor magnet 16 has an annular projection 11 formed on a base 111 of the bracket 11 so as to face the rotor magnet 16.
4. The fixation between the stator 17 and the annular projection 114 may be performed by press-fitting, or by fixing with an adhesive.

A flange 154 is provided on the lower side of the outer periphery of the rotor hub 15.
Is formed, and a hard disk is mounted therein. Specifically, after being positioned by the outer peripheral portion 152 of the rotor hub 15 and a plurality of hard disks are mounted on the flange portion 154, the hard disks are screwed into the holes 153 by a clamp member or the like. It is held and fixed.

The shaft 131 of the shaft 1 and the fixed sleeve 2
And a small gap is formed between the thrust plate 132 and the thrust groove 122 to hold the lubricating fluid 3. And the upper part of the inner peripheral surface of the fixed sleeve 2
Herringbone-shaped dynamic pressure generating grooves 123a and 123b that generate dynamic pressure in the lubricating fluid as the shaft 1 rotates are formed in the lower lubricating fluid holding portion. The dynamic pressure generating grooves 123a and 123b are connected to the shaft 1 when the motor rotates.
A supporting force is generated that keeps the radial direction. Also, on the upper surface of the thrust plate 132 and the upper surface of the counter plate 14, a herringbone-shaped dynamic pressure generating groove 133, 1 for generating a dynamic pressure in the lubricating fluid as the shaft 1 rotates.
41 are formed. These dynamic pressure generating grooves 133, 141
Generates a supporting force for holding the shaft 1 in the axial direction when the motor rotates.

[0031]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the following examples do not limit the present invention.
Any design change within a range that can conform to the spirit of the preceding and following statements is included in the technical scope of the present invention.

(Abrasion Resistance Test) A steel ball made of SUS304 was placed on a flat Cu-based material (Nos. 1 to 7) having the composition shown in Table 1 and reciprocated under the following conditions. A dynamic test was performed, and the wear amount of the material after the test was measured. Material No. With respect to 1, 3, 4, and 7, the amount of material transferred to steel balls and the hardness Hv25 were also measured. The results are shown in Table 2. The amount of wear is calculated by measuring the depth and width of wear with a surface roughness meter and calculating the volume. The amount of transfer is determined by measuring the amount of Cu transferred to the steel ball by EDX (energy dispersive X-ray analyzer:
Cu by Energy Dispersive X-ray micro analyzer)
It is determined from the peak intensity.

Load on steel ball: 200 g Sliding speed: 20 mm / sec Test time: 1 hr Test temperature: 20 ° C. Presence or absence of lubricant: None

[0034]

[Table 1]

[0035]

[Table 2]

As is apparent from Table 2, the conventional Cu-based material No. In the case of 1-4, the wear amount is 80 × 10 ⁻³ mm ³
On the other hand, No. satisfying the conditions of the Cu-based material defined in the present invention. In the case of 5 to 7 Cu-based materials, the wear amount was remarkably small at 60, 50, 30 (× 10 ⁻³ mm ³ ). In addition, No. 1 was measured on behalf of the Cu-based material specified in the present invention. With the Cu-based material of No. 7, the amount of Cu transferred to the steel balls was 8 (unit: COUNT), which was much smaller than that of the conventional Cu-based material. On the other hand, the hardness Hv is 283, which is
It was almost equivalent to the base material. Thus, the Cu-based material specified in the present invention exhibited excellent wear resistance while maintaining the same hardness as the conventional one.

[0037]

According to the dynamic pressure bearing of the present invention, stainless steel is used as one base material of the sleeve member and the shaft member, and the other base material contains 1 to 2% by weight of Si.
Since a Cu-based material containing each metal element of n, Al, Fe, and Ni is used, excellent abrasion resistance can be obtained while maintaining the same seizure resistance as before.

When the Mn content is in the range of 2.5 to 5% by weight, the durability of the dynamic pressure bearing can be further improved. The content of the metal element is set to Al: 4 to 7.
When the respective ranges are 5 wt%, Fe: 3 to 3.5 wt%, and Ni: 2 to 3 wt%, the durability of the dynamic pressure bearing can be further improved.

When a heat-treated stainless steel is used, the hardness of the stainless steel can be further increased, and the seizure resistance can be further improved.

Further, the spindle motor of the present invention is provided with the above-mentioned dynamic pressure bearing, so that it can be used for a long period of time without causing seizure or deterioration.

[Brief description of the drawings]

FIG. 1 is a simulated view of an SEM photograph showing the size of a Si intermetallic compound.

FIG. 2 is a view showing one embodiment of the dynamic pressure bearing of the present invention.

FIG. 3 is a diagram showing one embodiment of a spindle motor of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Intermetallic compound 2 Substrate (Cu) 3 Shaft (shaft member) 4 Sleeve (sleeve member) 5 Lubricating fluid

Continued on the front page F term (reference) 3J011 BA02 CA02 CA05 KA02 QA04 QA17 SB02 SB03 SB04 SB12 SB15 SB20 5H607 AA00 BB01 BB09 BB14 BB17 BB25 CC01 DD16 GG01 GG02 GG09 GG12 GG14 GG15 KK10

Claims (6)

[Claims] A shaft member, and a sleeve member opposed to the shaft member with a minute gap therebetween, wherein the sleeve member and the shaft member are mutually rotatable,
In a dynamic pressure bearing in which stainless steel is used as one base material of the sleeve member and the shaft member, and a Cu-based material is used as the other base material, the Cu-based material contains 1 to 2% by weight of Si. And a dynamic pressure bearing containing metal elements of Mn, Al, Fe and Ni. 2. The dynamic pressure bearing according to claim 1, wherein the content of Mn is in the range of 2.5 to 5% by weight. 3. The content of each metal element is from Al: 4 to
7.5% by weight, Fe: 3 to 3.5% by weight, Ni: 2 to 3
3. The dynamic pressure bearing according to claim 1, wherein the content is% by weight. 4. 4. The dynamic pressure bearing according to claim 1, wherein said stainless steel is heat-treated. 5. The dynamic pressure bearing according to claim 4, wherein said heat treatment is a nitriding treatment. 6. A spindle motor comprising the dynamic pressure bearing according to claim 1.