JP2003254331A - Dynamic pressure bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic pressure bearing for satisfying requested performance such as corrosion resistance and abrasion resistance of a hard disk driving device without performing coating such as Ni plating to be cause of a failure and for showing stabilized performance for a long time with a high manufacturing yield. <P>SOLUTION: A sleeve 1 is formed from a copper alloy obtained by containing silicon (Si) in α brass mainly composed of copper (Cu) and zinc (Zn) without containing a low-melting-point soft metal component, and a hard phase composed of a compound of brass and silicon and a soft phase composed of α brass is mixed for existence in the matrix condition. Scraping property, abrasion resistance and corrosion resistance are thereby improved to eliminate coating such as Ni plating. Since a low-melting-point soft metal component is not contained, deterioration of the operating fluid is prevented. <P>COPYRIGHT: (C)2003,JPO

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 more particularly to a dynamic pressure bearing suitable for use in hard disk drive devices and other parts requiring corrosion resistance.

[0002]

2. Description of the Related Art In recent years, a dynamic pressure bearing has been widely used as a bearing used in a device required to rotate at high speed and with high precision. Generally, a hydrodynamic bearing is configured such that a working fluid such as lubricating oil is injected between the shaft and the bearing, and a fine hydrodynamic groove is formed on one of the shaft and the bearing so that the shaft and the bearing rotate relative to each other. The pressure of the working fluid is increased by the generated pumping action or the like, and the pressure rotatably supports the shaft relative to the bearing in a substantially non-contact manner (for example,
See Patent Document 1).

A dynamic pressure bearing in a hard disk drive is known as an application suitable for using such a dynamic pressure bearing. In the dynamic pressure bearing for this application,
Usually, a dynamic pressure generating groove such as a herringbone pattern is formed on the inner peripheral surface of the sleeve, and the shaft is penetrated through the groove. The dynamic pressure bearing used in this hard disk drive is required to have especially easy workability, sliding characteristics, wear resistance and corrosion resistance. In order to meet such a demand, a conventional dynamic pressure bearing for a hard disk drive uses, for example, a Cu—Zn-based copper alloy such as brass as a base material,
A structure having a coating layer formed by hard Ni plating on its surface is used.

[0004]

[Patent Document 1] Japanese Patent Laid-Open No. 11-223214

By the way, in recent years, the dynamic pressure bearing is required to have a high machining accuracy such as the inner diameter dimensional accuracy (clearance with respect to the shaft) along with the speeding up and miniaturization.
When Ni plating is applied to the surface as described above, it has been pointed out that the product yield is deteriorated due to the variation in the thickness of the plating layer.

[0006]

Therefore, although coatingless has been studied, the copper alloy conventionally used for the dynamic pressure bearing has the same free-cutting property as the existing copper alloy. In order to improve the temperature, Pb and Bi are included, and a low melting point soft metal component that is easily saturated and easily deposited and dispersed is contained. Therefore, it has been pointed out that the low melting point metal such as Pb or Bi that has been precipitated and dispersed dissolves in the working fluid of the dynamic pressure bearing and causes deterioration of the working fluid, resulting in poor lubrication. Moreover, it cannot be said that the copper alloy such as brass itself satisfies the requirements for wear resistance and corrosion resistance.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to improve corrosion resistance and wear resistance in applications such as a hard disk drive without applying a coating such as Ni plating which is likely to cause defects. It is an object of the present invention to provide a dynamic pressure bearing that can satisfy the required performance and can exhibit stable performance over a long period of time with a high manufacturing yield.

[0008]

In order to achieve the above object, the dynamic pressure bearing of the present invention has an inner peripheral surface of a substantially cylindrical sleeve in which a shaft is relatively rotatably inserted through a working fluid. In a dynamic pressure bearing in which a dynamic pressure generating groove is formed, the sleeve contains 0.5 to 7% by weight of silicon (Si) in α brass containing copper (Cu) and zinc (Zn) as main components. It is characterized by being composed of a copper alloy containing no low melting point soft metal component (Claim 1).

In the present invention, the sleeve copper alloy has a silicon (Si) content of 2.0 to 7% by weight.
In addition, it is possible to preferably employ a configuration in which a hard phase composed of a compound of brass and silicon is mixed in a matrix (claim 2).

The present invention provides a copper alloy which is free of low-melting-point soft metal components such as Pb and Bi that precipitate and disperse due to supersaturation, and which has free-cutting properties and wear resistance and corrosion resistance in a boundary lubrication state. By using it, it is intended to achieve the intended purpose.

That is, in the dynamic pressure bearing of the present invention,
Compounds with different cooling rates are matrixed due to the different compounding ratios of copper, zinc and silicon compounds in the copper alloy, and by forming a hard phase and a soft phase,
It has free-cutting property, wear resistance and corrosion resistance.

The condition that the free-cutting property is good is that the cutting chips produced during cutting do not become continuous and long and are cut into short pieces even during constant cutting, but with the dynamic pressure bearing of the present invention, The copper alloy used is a state in which a hard phase made of a compound of copper, zinc and silicon, and a soft phase of α brass are mixed, so that it does not contain a low melting point soft metal component that is supersaturated and precipitates and disperses. Cutting debris does not become continuous,
It is appropriately divided into short pieces, and good free-cutting properties are obtained.

Further, since the hard phase and the soft phase of the copper compound are mixed, the wear amount is reduced in the boundary lubrication state of the dynamic pressure bearing even if the surface is not coated with other metal such as Ni. In addition, good wear resistance can be obtained and corrosion resistance can be secured.

Further, the dynamic pressure bearing of the present invention does not have to be coated with hard Ni plating or the like on its surface,
Unlike the conventional case where a copper alloy in which Pb or Bi is added to brass is used, the low melting point soft metal does not melt into the working fluid and cause deterioration. Therefore, according to the present invention, it is possible to obtain a dynamic pressure bearing capable of maintaining high performance for a long period of time without causing a decrease in yield due to variations in the thickness of a coating layer such as Ni plating.

As the copper alloy used in the dynamic pressure bearing of the present invention, Cu ₄ ZnSi and Cu ₈ Zn ₂ Si form a hard phase, and these are mixed in the soft phase of α-brass in a matrix form, so that a good free cutting is achieved. And corrosion resistance can be obtained, and the alloy can also have excellent corrosion resistance.

With respect to the content of each component in the copper alloy used for the dynamic pressure bearing of the present invention, the point is that the matrix structure of the alloy is a copper compound in which a hard phase and a soft phase are mixed due to the difference in the compounding ratio. The soft phase may contain silicon.

In the content ratio of the metal component of the present invention, if the Zn content is in the range of 5 to 35% by weight and the Si content is in the range of 0.5 to 7% by weight, the aforementioned Cu ₄ ZnSi and Cu ₈ Zn _{2 are} added.
A hard phase of Si is formed at an effective rate. Although it is preferable not to contain lead, it is inevitably eluted from the mold or the like during melting, so at least Cu-Zn-
It should be kept within the solid solution limit of Si. The content is preferably about 0.1% by weight or less.

Further, in the present invention, when the Si content is 2.0% by weight or more, as shown in FIG. 2, particularly, the corrosion resistance as a copper alloy and the reduction of the wear amount are improved. Further, if the Si content is 7% by weight or more, the copper alloy itself becomes too hard and the workability deteriorates. This FIG. 2 shows the oxidation resistance and the wear amount decrease according to each content ratio of Si with the oxidation resistance and the wear amount of the Cu-Zn alloy not containing Si as 100, and the numerical value on the vertical axis. The smaller the value, the better the oxidation resistance and the effect of reducing the wear amount. Here, the oxidation resistance is a numerical value of the degree to which the surface of the sleeve changes to black due to oxidation.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an essential part of an embodiment of the present invention.

The dynamic pressure bearing 3 comprises a sleeve 1 and a shaft 2,
On the inner peripheral surface of the sleeve 1, for example, a dynamic pressure generating groove 1a having a herringbone pattern is formed. A shaft 2 is rotatably inserted inside the sleeve 1. The outer peripheral surface of the shaft 2 facing the dynamic pressure generating groove 1a is a uniform cylindrical surface, and a working fluid (not shown) such as a lubricant is filled between the sleeve 1 and the shaft 2. .

In the above structure, when the shaft 2 and the sleeve 1 rotate relative to each other, a high pressure is generated in the working fluid due to the pumping action of the dynamic pressure generating groove 1a, etc.
The sleeve 1 can relatively rotate while maintaining a non-contact state.

The material of the sleeve 1 is brass having Cu and Zn as main components, to which Si is added, and does not contain a low melting point soft metal component such as Pb or Bi that is supersaturated and precipitates and disperses. . In the copper alloy forming such a sleeve 1, Cu ₄ ZnSi and Cu _{8 are} contained in the matrix structure.
A state in which Zn ₂ Si is mixed, that is, a state in which a hard phase and a soft phase are mixed due to a difference in cooling rate caused by a difference in the compounding ratio of copper compounds. The surface of the sleeve 1 is not coated at all.

An example of the method for processing the sleeve of the dynamic pressure bearing of the present invention will be shown. After melting and alloying the copper alloy, it is extruded into a rod shape, and the rod-shaped material is tempered at about 400 ° C. After tempering, it is rolled into a predetermined cross-sectional shape to obtain a cutting material. A sleeve is manufactured by cutting this cutting material. Here, the hard phase is uniformly dispersed by tempering the copper alloy, and the grain size of the hard phase is reduced by rolling.

The material of the shaft 2 is not particularly limited, but stainless steel (austenitic or martensitic), high carbon steel, or other various alloys can be used.

According to the sleeve 1 of the above-described embodiment of the present invention, since the hard phase and the soft phase made of the copper alloy are mixed in the matrix structure of the copper alloy, which is the material thereof, the free cutting property is improved. Due to its richness, high precision machining is easy and at the same time,
Wear can be suppressed even in the boundary lubrication state, and low melting point soft metal does not start to dissolve in the working fluid such as lubricant, excellent corrosion resistance and wear resistance, and stable performance over a long period of time can do. Moreover, since the surface is not coated with Ni plating or the like, there is no fear that the manufacturing yield will decrease due to the variation in the coating thickness.

[0026]

As described above, according to the present invention, the material of the sleeve in which the dynamic pressure generating groove is formed is a copper alloy, and the hard phase and the soft phase are different due to the difference in the mixing ratio of the copper compound. Since they are mixed alloys, they do not have to be coated with hard Ni plating on the surface of existing copper alloys as in the past, have excellent wear resistance and corrosion resistance, and have stable performance for a long time without degrading the working fluid. A dynamic pressure bearing that can be maintained and is suitable for use as a radial bearing of a hard disk drive is obtained. Moreover, since it is rich in free-cutting property and the surface is not plated, it is relatively easy to manufacture and a high yield can be achieved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an essential part of an embodiment of the present invention.

FIG. 2 is a graph showing a characteristic change due to addition of silicon to brass in the present invention.

[Explanation of symbols]

1 sleeve 1a Dynamic pressure generating groove 2 axes 3 Dynamic bearing

Claims (2)

[Claims] 1. A dynamic pressure bearing in which a dynamic pressure generating groove is formed on the inner peripheral surface of a substantially cylindrical sleeve into which a shaft is inserted so as to be rotatable relative to a working fluid, and the sleeve is made of copper (Cu). And a zinc (Zn) -based α brass containing 0.5 to 7% by weight of silicon (Si) and a copper alloy containing no low melting point soft metal component. . 2. The copper alloy of the sleeve is silicon (S
The hydrodynamic bearing according to claim 1, wherein the content of i) is 2.0 to 7% by weight, and a hard phase composed of a compound of brass and silicon is mixed in a matrix.