JP2008190572A - Manufacturing method of hydrodynamic bearing and motor using its hydrodynamic bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrodynamic bearing excellent in shock-durability and sliding performance. <P>SOLUTION: A motor attached in a hard disk drive comprises a hydrodynamic bearing 4 which has a shaft 41 and sleeve 42 in which the shaft 41 is inserted. The sliding performance of the hydrodynamic bearing 4 with excellent shock-durability can be improved in such a way that the sleeve 42 is formed by phosphor bronze, and that a plating layer 420 formed by electroless nickel plating is arranged on a surface of the sleeve 42 after processing surface treatment by wood bath. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a dynamic pressure bearing, a motor using the dynamic pressure bearing, and a method of manufacturing the dynamic pressure bearing.

  In recent years, dynamic pressure bearings have been widely used in computers or peripheral devices. Among them, in a hard disk drive, a hydrodynamic bearing is used for a slider portion of a magnetic head and a spindle motor that rotates the disk.

By the way, in a dynamic pressure bearing, in general, a bearing surface comes into direct contact when starting and stopping. For example, in a spindle motor, the shaft and the sleeve come into direct contact (that is, remain unlubricated) when starting and stopping, or when receiving a large impact from the outside. One method for reducing damage to the bearing surface due to this contact is to harden the bearing surface.
Patent Document 1 discloses a method in which the surface of a sleeve made of a copper alloy is covered with a hard electroless nickel plating layer and the shaft side is made of stainless steel. With this configuration, wear of the bearing surface can be suppressed.

US Pat. No. 5,998,898

  By the way, as a method of applying electroless nickel plating to a copper alloy, a pretreatment method using a Watt bath (mainly nickel sulfate, nickel chloride, boric acid) has been used. After nickel plating, electroless nickel plating was applied. By doing in this way, the adhesiveness of the nickel plating layer to a copper alloy can be improved. However, in the conventional nickel electroplating using a watt bath, the crystal at the time of film formation is large, so that a nickel lump (nodule) of several μm may be formed on the surface film obtained after plating. Thereafter, since electroless nickel plating was applied, nodules of electro nickel plating remained as they were after electroless nickel plating, forming a lump of hard nickel plating. For this reason, in a hydrodynamic bearing having a bearing gap of about several to 10 μm, a nickel lump of several μm causes troubles such as seizure of the bearing.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a hydrodynamic bearing that is excellent in impact resistance and sliding performance and is less likely to cause troubles such as seizure.

The invention according to claim 1 is a method of manufacturing a hydrodynamic bearing, comprising a first member and a second member made of a metal material having copper as a main constituent element. The method of manufacturing a hydrodynamic bearing, wherein the member and the second member are supported relative to each other by a dynamic pressure generated in a lubricating fluid interposed between surfaces facing each other. A step of preparing a material for the second member, and a smooth base treatment layer is formed on the prepared member in a wood bath that is an aqueous solution containing chloride containing nickel chloride as a main constituent component. A step of forming a plating layer by performing electroless nickel plating on the member on which the undertreatment layer is formed;
Is provided.

  The invention according to claim 2 is the method for manufacturing the hydrodynamic bearing according to claim 1, wherein hydrofluoric acid is applied to the material of the second member prior to the step of forming the undertreatment layer. And a step of pickling with an acid containing a fluoride such as sodium fluoride, potassium fluoride or calcium fluoride.

  A third aspect of the present invention is the method of manufacturing a hydrodynamic bearing according to any one of the first to second aspects, wherein a solution mainly composed of nickel chloride and hydrochloric acid is used in the wood bath.

  Invention of Claim 4 is a manufacturing method of the hydrodynamic bearing in any one of Claim 1 thru | or 3, Comprising: Said 2nd member removes the said pretreatment layer and the said plating layer. In addition, it is made of a copper alloy such as phosphor bronze or brass and a material mainly composed of copper.

  A fifth aspect of the present invention is the method of manufacturing a dynamic pressure bearing according to any one of the first to fourth aspects, wherein the first member is made of stainless steel.

  A sixth aspect of the present invention is the method of manufacturing a hydrodynamic bearing according to any one of the first to fifth aspects, wherein the first member is a shaft, and the second member is the shaft. The outer peripheral surface of the shaft and the inner peripheral surface of the sleeve are opposed to each other through a minute gap to constitute a radial dynamic pressure bearing portion.

  A seventh aspect of the present invention is an electric motor, the dynamic pressure bearing manufactured by the method of manufacturing a dynamic pressure bearing according to any one of the first to sixth aspects, and the first member And a drive device for rotating the device relative to the second member.

  In electroless nickel plating on a copper member, a wood bath capable of forming a smooth film different from the conventional pretreatment is used, and electroless nickel plating is performed thereon. The wood bath is a mixed aqueous solution of nickel chloride and hydrochloric acid, and has conventionally been effective for pretreatment of stainless steel members.

  When electroless nickel plating is applied to a copper member using a wood bath, nodules are drastically reduced. In normal applications, even if the nickel mass of only a few μm is reduced, the product characteristics are hardly affected, but there is an extremely important improvement effect for the member of the hydrodynamic bearing. By reducing the nodules, troubles such as seizure when the hydrodynamic bearing with electroless nickel plating slides can be drastically reduced.

  Therefore, according to the present invention, by applying electroless nickel plating, it is possible to obtain a highly reliable dynamic pressure bearing that imparts excellent impact resistance and durability to the dynamic pressure bearing and at the same time does not seize. I can do it.

  FIG. 1 is a longitudinal sectional view showing the configuration of a disk driving motor 1. The motor 1 has a rotor portion 2 that is a rotating body and a stator portion 3 that is a fixed body. The rotor portion 2 is rotatably supported with respect to the stator portion 3 by a dynamic pressure bearing 4 having a shaft 41 and a sleeve 42. Is done.

  The rotor portion 2 has a substantially bowl-shaped rotor body 21 that opens to the stator portion 3 side (lower side in FIG. 1), and is formed of stainless steel (for example, SUS303) at the center of the rotor body 21. The shaft 41 whose surface is nitrided is fixed so as to protrude to the opening side. On the outer peripheral surface of the rotor main body 21, an annular projection 211 is formed on the side of the stator 3, which spreads outward and then bends downward. The inner periphery of the annular projection 211 has a multipolar magnetized circle. An annular field magnet 22 is fixed.

  The stator portion 3 has a substantially disc-shaped base plate 31 that extends in a direction perpendicular to the central axis J 1 of the shaft 41, and a cylindrical portion 311 that protrudes upward is formed at the center of the base plate 31. A substantially cylindrical sleeve 42 that is formed of stainless steel (for example, trade name DHS-1) and into which the free end side of the shaft 41 is inserted is inserted into the cylindrical portion 311 and fixed. The sleeve 42 is formed of a copper alloy (for example, phosphor bronze C5191B) and has a plating layer on the surface. In addition, around the cylindrical portion 311, an armature 32 in which a plurality of salient poles provided on an annular core are wound is provided facing the central axis J <b> 1 side of the field magnet 22. The field magnet 22 and the armature 32 constitute a drive mechanism of the motor 1, and the current supplied by a current supply circuit (not shown) connected to the armature 32 is controlled, whereby the rotor portion 2 is connected to the shaft 41. A torque (rotational force) for rotating the stator portion 3 around the center is generated.

  A disc-shaped thrust plate 411 extending around the central axis J1 is formed at the end of the shaft 41 on the free end side. An annular notch 421 is formed on the free end side of the shaft 41 on the inner peripheral surface of the sleeve 42, and the thrust plate 411 is fitted into a disk-shaped space formed by the notch 421. Further, a counter plate 43 that closes the lower opening of the sleeve 42 is provided at the lower end of the sleeve 42, and the counter plate 43 faces the lower surface of the thrust plate 411.

  FIG. 2 is an enlarged view of the dynamic pressure bearing 4 of the motor 1, and shows only the right side from the central axis J1 in FIG. As shown in FIG. 2, an annular groove 412 is formed on the outer peripheral surface of the shaft 41, and lubricating oil is filled between the shaft 41 and the sleeve 42 above and below the annular groove 412. The radial bearing portions 61 and 62 are configured. In the radial bearing portions 61 and 62, a groove (for example, a herringbone groove) for generating fluid dynamic pressure is formed on the inner peripheral surface of the sleeve 42, and the shaft 41 is perpendicular to the central axis J1 when the motor 1 rotates. Supported in a radial direction. In the radial bearing portions 61 and 62, a fluid dynamic pressure generating groove is formed on at least one of the outer peripheral surface of the shaft 41 and the inner peripheral surface of the sleeve 42, so that the radial bearing utilizing the fluid dynamic pressure is used. The function as a bearing part is fulfilled.

  Lubricating oil is filled between the upper surface (annular surface) of the thrust plate 411 and the surface facing the lower side of the notch 421, and between the lower surface of the thrust plate 411 and the upper surface of the counter plate 43, respectively. Thrust bearing portions 63 and 64 are formed. In the thrust bearing portions 63 and 64, fluid dynamic pressure generating grooves (for example, pump-in spiral grooves) are formed on the upper and lower surfaces of the thrust plate 411, and the shaft 41 is rotated when the motor 1 rotates. It is supported in the central axis J1 direction (also called the axial direction). In the thrust bearing portions 63 and 64, as in the radial bearing portions 61 and 62, a thrust bearing portion using fluid dynamic pressure is formed by forming a fluid dynamic pressure generating groove on at least one of the opposing surfaces. The function is fulfilled.

  Further, as described above, the plating layer 420 is formed on the entire surface of the sleeve 42 under specific conditions in the manufacturing process described later.

  Next, the flow of the process for manufacturing the dynamic pressure bearing 4 of the motor 1 will be described. FIG. 3 is a diagram showing a flow of processes for manufacturing the dynamic pressure bearing 4. When the hydrodynamic bearing 4 is manufactured, first, a sleeve member formed of a copper alloy (that is, a member in which a plated layer 420 is formed on the surface in a process described later to become the sleeve 42), and a shaft member ( That is, the shaft 41) is produced by, for example, cutting (step S11). Subsequently, a pre-cleaning process for the purpose of surface degreasing and scale removal for the purpose of cutting oil removal is performed as necessary (step S12). Then, after cleaning the surface, it is immersed in an acid solution to which a fluorine compound is added to remove the surface smut and activate the surface (step S13). Here, by using an acid solution to which a fluorine compound is added, it is possible to suppress the formation of a new oxide film on the surface of the sleeve member made of a copper alloy. Thereafter, the sleeve member is subjected to strike plating in a wood bath (mainly nickel chloride and hydrochloric acid) to form a smooth underlayer (step S14). Here, by performing slick plating, it is possible to suppress the occurrence of protrusions of 0.5 μm or more during the formation of the electric nickel. When the strike plating is completed, the sleeve member is subjected to electroless nickel plating (in this case, nickel phosphorus electroless plating is used), and a plating layer is formed on the underlayer of the sleeve member (step S15). .

  Subsequently, a rust preventive treatment is performed to form a rust preventive film (step S16), and after cleaning, a precipitation hardening treatment is performed on the sleeve member to crystallize the amorphous plating layer. (Step S17). The shaft 41 is inserted into a sleeve 42 having a plated layer formed on the sleeve member, and the counter plate 43 is attached to one opening of the sleeve 42 to complete the hydrodynamic bearing 4 (step S18).

  Hereinafter, the step of strike plating the sleeve member in step S14 with a wood bath (mainly nickel chloride and hydrochloric acid) will be described in detail.

The composition and conditions of the wood bath are as follows.
_{NaCl 2 · 6H 2 O 150g /} L~300g / L
HCl 40-100cc / L
Current density 0.75 to 2.0 A / dm ²

  Next, FIG. 4 is a surface state diagram (× 1000) after electro nickel plating (step S14) of the sleeve 42 manufactured by the manufacturing process of FIG. 3 (hereinafter referred to as Example 1), and FIG. It is the surface state figure (x500) (henceforth Example 2) which gave electroless nickel plating after electro nickel plating. FIG. 6 shows the surface of the manufacturing process shown in FIG. 3 activated with an acid solution containing no fluorine compound in step S13, and the surface treatment in step S14 is carried out using a conventional watt bath (mainly nickel sulfate, nickel chloride, boric acid). 7 is a surface state diagram (× 1000) (hereinafter referred to as Comparative Example 1) after electro nickel plating of the sleeve 42 applied as a component, and FIG. 7 is a surface where electroless nickel plating is applied after electro nickel plating in FIG. A state diagram (× 500) (hereinafter referred to as Comparative Example 2) is shown.

  Comparing the examples with the comparative examples, it is shown that the nickel bulk precipitates are more drastically reduced and the plating layer surface is smoother in the examples of the present invention (Example 1 and Comparative Example 1). This removes the oxide film on the surface of the phosphor bronze in the base treatment in step S13 and step S14 in FIG. 3, and prevents the film from being formed again, thereby making the surface resistance of the phosphor bronze member uniform, resulting in plating. This shows that the subsequent surface smoothness can be improved, and the subsequent electroless nickel plating can further reduce the nickel lump and suppress the occurrence of protrusions due to the leveling effect (Example 2 and comparison). Example 2).

  As described above, the motor 1 shown in FIG. 2 includes the dynamic pressure bearing 4 having the shaft 41 and the sleeve 42. The sleeve 42 has the plated layer 420 on the surface, and the plated layer 420 is subjected to a ground treatment with a wood bath. After the application, a plating layer is formed by electroless nickel plating. The shaft is formed of a material different from that of the plated layer 420 of the 41 sleeve 42. As a result, the dynamic pressure bearing 4 having excellent impact resistance while suppressing the adhesion between the shaft 41 and the sleeve 42 is realized, and a large impact is given when the motor 1 rotates at high speed. Also, it is possible to prevent troubles in driving the motor 1. Further, the sliding performance of the dynamic pressure bearing 4 can be improved, and the reliability of the motor 1 can be improved. Further, by using such a motor 1, it is possible to improve the reliability of the hard disk drive device having high impact resistance.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made.

  The structure of the hydrodynamic bearing 4 in the above embodiment is merely an example, and may be appropriately changed depending on the application.

  In the dynamic pressure bearing 4, a plating layer formed by electroless nickel plating and subjected to precipitation hardening may be formed on the sleeve 42. In order to easily manufacture the hydrodynamic bearing 4, it is preferable that a plating layer or a nitride layer is formed on the shaft 41 having a simpler shape than the sleeve 42.

  In the above embodiment, the shaft 41 is fixed to the rotor portion 2 and rotates with respect to the sleeve 42. However, the sleeve 42 is fixed to the rotor portion 2 (or formed integrally) and rotates with respect to the shaft 41. May be.

  In the above embodiment, the sleeve 42 is formed of a copper alloy. However, in addition to a copper alloy made of phosphor bronze, a copper alloy such as brass may be used, and the sleeve 42 is made of a compound containing copper as a main component. May be.

  In addition to the hard disk drive, the motor 1 can be used, for example, in an apparatus that drives an optical disk, a magneto-optical disk, and other disk-shaped recording media.

It is a longitudinal cross-sectional view which shows the structure of a motor. It is a figure which expands and shows a bearing mechanism. It is a figure which shows the flow of the process of manufacturing a bearing mechanism. It is a surface state figure of the sleeve after electric nickel plating in an example. It is a surface state figure of the sleeve after electroless nickel plating in an example. It is a surface state figure of the sleeve after electric nickel plating in a comparative example. It is a surface state figure of the sleeve after electroless nickel plating in a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Motor 4 Dynamic pressure bearing 22 Field magnet 32 Armature 41 Shaft 42 Sleeve 420 Plating layer

Claims (7)

The first member and a second member made of a metal material having copper as a main constituent element, the first member and the second member being interposed between the surfaces facing each other. A method of manufacturing a hydrodynamic bearing, which is supported so as to be relatively movable or rotatable by dynamic pressure generated in a lubricating fluid,
Preparing a material for the second member;
For the prepared member, a step of forming a smooth base treatment layer in a wood bath, which is an aqueous solution mainly containing a chloride containing nickel chloride,
Forming a plating layer by applying electroless nickel plating to the member on which the undertreatment layer is formed;
A method for producing a hydrodynamic bearing, comprising: A method of manufacturing a hydrodynamic bearing according to claim 1,
Prior to the step of forming the lower treatment layer, the material of the second member is pickled with an acid containing a fluoride such as hydrofluoric acid, sodium fluoride, potassium fluoride, or calcium fluoride. The manufacturing method of a dynamic pressure bearing characterized by including the process to perform. A method of manufacturing a hydrodynamic bearing according to any one of claims 1 to 2,
A method for manufacturing a hydrodynamic bearing, wherein a solution containing nickel chloride and hydrochloric acid as main components is used for the wood bath. A method of manufacturing a hydrodynamic bearing according to any one of claims 1 to 3,
The second member is made of a copper alloy such as phosphor bronze and brass, and a material mainly composed of copper, excluding the pretreatment layer and the plating layer.
A method of manufacturing a hydrodynamic bearing, wherein A method of manufacturing a hydrodynamic bearing according to any one of claims 1 to 4,
The first member is made of stainless steel;
A method of manufacturing a hydrodynamic bearing, wherein A method of manufacturing a hydrodynamic bearing according to any one of claims 1 to 5,
The first member is a shaft, and the second member is a sleeve having a bearing hole in which the shaft is accommodated;
The outer peripheral surface of the shaft and the inner peripheral surface of the sleeve are opposed to each other through a minute gap to constitute a radial dynamic pressure bearing portion.
A method of manufacturing a hydrodynamic bearing, wherein An electric motor,
A hydrodynamic bearing manufactured by the hydrodynamic bearing manufacturing method according to any one of claims 1 to 6;
A drive device for rotating the first member relative to the second member;
A motor comprising: