JP4051551B2 - Hydrodynamic bearing - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hydrodynamic bearing, and more particularly, to a hydrodynamic bearing suitable for use in a portion where corrosion resistance is required, including for a hard disk drive.
[0002]
[Prior art]
In recent years, hydrodynamic bearings have been widely used as bearings used in devices that require high speed and high precision rotation. In general, a hydrodynamic bearing injects a working fluid such as lubricating oil between a shaft and a bearing, and forms a fine dynamic pressure groove in one of the shaft and the bearing. The pressure of the working fluid is increased by the generated pumping action or the like, and the shaft is supported by the pressure so as to be relatively rotatable with substantially no contact with the bearing (see, for example, Patent Document 1).
[0003]
As an application suitable for using such a dynamic pressure bearing, a dynamic pressure bearing in a hard disk drive is known. The dynamic pressure bearing in this application usually employs a structure in which a dynamic pressure generating groove such as a herringbone pattern is formed on the inner peripheral surface of the sleeve and a shaft is passed through the groove. The hydrodynamic bearing used in this hard disk drive device is required to be particularly easy to process, sliding characteristics, wear resistance and corrosion resistance. In order to meet such demands, a conventional hydrodynamic bearing for a hard disk drive device has a structure in which, for example, a Cu-Zn-based copper alloy such as brass is used as a base material and a coating layer is formed on the surface thereof by hard Ni plating. Things are used.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-223214
By the way, in recent years, dynamic pressure bearings are required to have high machining accuracy, including the inner diameter dimensional accuracy (clearance with respect to the shaft), as the speed is increased and minimized, and when Ni plating is applied to the surface as described above, The problem that the product yield is deteriorated due to the variation in the thickness of the plating layer has been pointed out.
[0006]
[Problems to be solved by the invention]
Therefore, it has come to the coating-less is considered, conventionally, in the copper alloy that is used in the dynamic pressure bearing, as with existing copper alloy, the Pb and Bi to improve its free-cutting First, it contains a low-melting-point soft metal component that is supersaturated and easily precipitates and disperses. For this reason, it has been pointed out that the low melting point metal such as Pb or Bi that has been deposited and dispersed dissolves in the working fluid of the hydrodynamic bearing, causes the working fluid to deteriorate, and leads to poor lubrication. Moreover, it cannot be said that copper alloys such as brass themselves satisfy the requirements for wear resistance and corrosion resistance.
[0007]
The present invention has been made in order to cope with the above-described problems, and provides required performance such as corrosion resistance and wear resistance in applications such as a hard disk drive device without applying a coating such as Ni plating, which is likely to cause defects. An object of the present invention is to provide a hydrodynamic bearing that can be satisfied and can exhibit stable performance over a long period of time with a high production yield.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the hydrodynamic bearing of the present invention is melted in a mold, and the shaft is inserted in a relatively rotatable manner while maintaining a non-contact state through a lubricant as a working fluid. in substantially cylindrical pressure bearing forming the inner peripheral surface dynamic pressure generating grooves of the sleeve, the sleeve, the copper (Cu) and zinc (Zn) because Do that α brass, a silicon (Si) 2 In order to prevent deterioration of the working fluid due to dissolution of bismuth (Bi) and lead (Pb) in the working fluid, lead ( It is characterized by being made of a copper alloy having a content of Pb) of 0.1% by weight or less (claim 1).
[0009]
Here in the present invention, the copper alloy of the sleeve may be employed a hard phase consisting of the compounds of Brass and silicon a structure in which are mixed in a matrix (claim 2) suitably.
[0010]
The present invention uses a copper alloy that can obtain free-cutting properties without including a low melting point soft metal component that precipitates and disperses due to supersaturation such as Pb and Bi, and can obtain wear resistance and corrosion resistance in a boundary lubrication state. , Trying to achieve the intended purpose.
[0011]
That is, in the hydrodynamic bearing of the present invention, compounds having different cooling rates are formed into a matrix by the compound ratios of copper, zinc and silicon in the copper alloy, thereby forming a hard phase and a soft phase. As a result, free machinability, wear resistance and corrosion resistance are obtained.
[0012]
The condition that the free-cutting property is good is that the cutting waste generated at the time of cutting is not continuous and long, and it is divided shortly even at the time of steady cutting, but the copper alloy used in the hydrodynamic bearing of the present invention Is a state in which a hard phase composed of a compound of copper, zinc and silicon and a soft phase of α brass are mixed, so even if it does not contain a low-melting-point soft metal component that is supersaturated and precipitates and disperses, Does not become continuous, is appropriately divided and becomes short, and good free machinability is obtained.
[0013]
In addition, since a hard phase and a soft phase are mixed due to the copper compound, the amount of wear is reduced in the boundary lubrication state of the hydrodynamic bearing even if the surface is not coated with other metals such as Ni, which is good. Abrasion resistance can be obtained and corrosion resistance can be secured.
[0014]
The hydrodynamic bearing of the present invention operates with a low melting point soft metal as in the case of using a copper alloy in which Pb or Bi is added to conventional brass or the like, without coating the surface with hard Ni plating or the like. It will not dissolve in the fluid and cause deterioration. Therefore, according to the present invention, it is possible to obtain a hydrodynamic bearing capable of maintaining high performance over a long period of time without causing a decrease in yield due to variations in the thickness of the coating layer such as Ni plating.
[0015]
As a copper alloy used in the hydrodynamic bearing of the present invention, Cu ₄ ZnSi and Cu ₈ Zn ₂ Si become a hard phase, and these are mixed in a matrix in the soft phase of α brass, so that good free machinability and resistance to resistance are obtained. Abrasion can be obtained, and an alloy having excellent corrosion resistance can be obtained.
[0016]
About the content rate of each component in the copper alloy used for the hydrodynamic bearing of the present invention, it is essential that the hard phase and the soft phase due to the difference in the compounding ratio are mixed in the matrix structure of the alloy. The soft phase may contain silicon.
[0017]
If the content of the metal component of the present invention is such that Zn is in the range of 5 to 35% by weight and Si is in the range of 2.0 to 7% by weight, the hard phase of the aforementioned Cu ₄ ZnSi and Cu ₈ Zn ₂ Si is used. Are formed at an effective rate. In addition, although it is preferable not to contain about lead, since it inevitably elutes from a metal mold | die etc. during melting, what is necessary is just to stay within the solid solution limit of Cu-Zn-Si at least. The content is preferably about 0.1% by weight or less.
[0018]
Furthermore, in the present invention, if the Si content is 2.0% by weight or more, as shown in FIG. 2, the corrosion resistance and the reduction of the wear amount as a copper alloy are particularly good. On the other hand, when the Si content is 7% by weight or more, the copper alloy itself becomes too hard and the workability is deteriorated. FIG. 2 shows the reduction in oxidation resistance and wear amount according to each content of Si, with the oxidation resistance and wear amount of a Cu—Zn alloy not containing Si being 100. The smaller the value, the better the oxidation resistance and wear reduction effect. Here, the oxidation resistance is a numerical value of the degree to which the sleeve surface changes to black due to oxidation.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view of an essential part of an embodiment of the present invention.
[0020]
The dynamic pressure bearing 3 includes a sleeve 1 and a shaft 2, and a dynamic pressure generating groove 1 a having a herringbone pattern, for example, is formed on the inner peripheral surface of the sleeve 1. A shaft 2 is rotatably inserted into 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. .
[0021]
In the above configuration, when the shaft 2 and the sleeve 1 rotate relative to each other, a high pressure is generated in the working fluid by the pumping action or the like of the dynamic pressure generating groove 1a, so that the shaft 2 and the sleeve 1 are kept in a non-contact state. Can rotate.
[0022]
The material of the sleeve 1, with respect to brass ing from Cu and Zn, is obtained by addition of Si, supersaturated low melting soft metal component to be deposited distributed in such Pb and Bi does not contain. In the copper alloy forming such a sleeve 1, the cooling caused by the mixed state of Cu ₄ ZnSi and Cu ₈ Zn ₂ Si in the matrix structure, that is, both are compound of copper and the compounding ratio is different. Due to the difference in speed, a hard phase and a soft phase are mixed. The sleeve 1 has no coating on its surface.
[0023]
An example of the processing method of the sleeve of the hydrodynamic bearing of this invention is shown.
After the copper alloy is melted and alloyed, it is extruded into a rod shape, and the material molded into the rod shape is tempered at about 400 ° C. After tempering, the material is cut 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 particle size of the hard phase is reduced by rolling.
[0024]
The material of the shaft 2 is not particularly limited, but stainless steel (austenite or martensite), high carbon steel, or other various alloys can be used.
[0025]
According to the sleeve 1 of the above 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 that is the material thereof, it is rich in free-cutting properties. Therefore, high-precision machining is easy, and at the same time, wear can be suppressed even in the boundary lubrication state, and the low-melting point soft metal does not dissolve in the working fluid such as a lubricant, and the corrosion resistance and resistance. Excellent wear resistance and stable performance over a long period of time. In addition, since the surface is not coated with Ni plating or the like, there is no risk of a decrease in manufacturing yield due to variations in the coating thickness.
[0026]
【The invention's effect】
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, in which a hard phase and a soft phase are mixed due to a difference in the mixing ratio of the copper compound. So, without applying a coating such as hard Ni plating on the surface of the existing copper alloy as before, it has excellent wear resistance and corrosion resistance, and can maintain stable performance for a long time without deteriorating the working fluid. Thus, a hydrodynamic bearing suitable for use in a radial bearing of a hard disk drive or the like can be obtained. Moreover, since it is rich in free-cutting properties and is not plated on the surface, it can be manufactured relatively easily and a high yield can be achieved.
[Brief description of the 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 changes in characteristics due to the addition of silicon to brass in the present invention.
[Explanation of symbols]
1 Sleeve 1a Dynamic pressure generating groove 2 Shaft 3 Dynamic pressure bearing

Claims (2)

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 relatively rotatable while being kept in a non-contact state through a lubricant that is melted by a mold and working fluid. In the hydrodynamic bearing
The sleeve, copper (Cu) and zinc (Zn) because Do that α brass, a silicon (Si) containing 2.0 to 7 wt%,
In order to prevent deterioration of the working fluid due to dissolution of bismuth (Bi) and lead (Pb) in the working fluid, bismuth (Bi) is not contained and the content of lead (Pb) is 0.1. A hydrodynamic bearing characterized by comprising a copper alloy having a weight percent or less.   2. The hydrodynamic bearing according to claim 1, wherein the copper alloy of the sleeve includes a hard phase composed of a compound of brass and silicon mixed in a matrix.

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