JP2010007721A - Dynamic pressure fluid bearing device, spindle motor with it, and manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a high-performance and long life fluid bearing without pressure leakage by shaping and flattening the excess thickness part of a bearing surface in the inner periphery of a sleeve that occurs when a dynamic pressure generation groove is form-rolled, and sealing a surface air hole in the bearing surface and the whole sleeve, and to obtain its manufacturing method. <P>SOLUTION: This invention relates to the manufacturing method of a dynamic pressure fluid bearing device provided with the sleeve with the bearing hole and the dynamic pressure generation groove in the inner periphery of the bearing hole while having the shaft inserted in the bearing hole in a relatively rotatably manner. The method performs a step for forming a molded product by forming the dynamic pressure generation groove by form rolling, a step for resintering by heat treatment of the molded product, and a ball burnishing step for shaping by passing through a ball bigger than the inner diameter of the sleeve. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device, a method of manufacturing a sleeve constituting the hydrodynamic bearing device, and a spindle motor including the same.

  In recent years, recording / reproducing apparatuses such as a hard disk apparatus, an optical disk apparatus, and a magneto-optical disk apparatus using a rotating disk have been used for an increase in information storage capacity and an increase in data transfer speed. The spindle motor bearing device is required to have high performance and reliability so that the disk load can always be rotated with high accuracy. Accordingly, a hydrodynamic bearing device suitable for high-speed rotation and a spindle motor equipped with the hydrodynamic bearing device are used in these recording / reproducing devices.

  In a hydrodynamic bearing device, a lubricating fluid (generally oil) is interposed between a shaft and a sleeve, and a pumping pressure is generated during rotation by a dynamic pressure generating groove, whereby the shaft is not in contact with the sleeve. Rotate with. Thus, the hydrodynamic bearing device is suitable for high-speed rotation because it is non-contact and has no mechanical friction.

As shown in FIG. 15, the hydrodynamic bearing device includes a shaft 101, a flange 102, a sleeve 103, a thrust plate 104, and a lubricating fluid 105, and a spindle motor 100 having the shaft 101, a rotor motor 106, a rotor It comprises a magnet 107, a stator core 108 around which a winding is wound, and a base 109. According to Patent Document 1, the inventor molded the sleeve 103, which is a component of the above-described hydrodynamic bearing device, from a sintered material, and completely sealed the surface with a resin or the like so that the lubricating fluid 105 is immersed in the sleeve 103. We proposed a configuration that would prevent leakage of lubricating fluid and reduce the generated dynamic pressure. Further, in order to manufacture the sleeve 103 in a mass-produced manner and at a low cost, first, a sintered powder material is molded and fired to produce a molded body, and then the molded body is sized and shaped to form a rolling method. A manufacturing method has been proposed in which a dynamic pressure generating groove is formed by the method described above, and the molded body is sized and shaped again, and finally the sleeve 103 is taken out from the mold by using the spring back of the molded body.
JP 2007-111372 A

The conventional method of manufacturing a hydrodynamic bearing device can improve the productivity of a sleeve that does not cause lubricating fluid leakage and the generated dynamic pressure does not decrease. It is hoped that That is, when a dynamic pressure generating groove is formed in the molded body 111 by a rolling method on a sleeve formed of sintered metal, a surplus portion 111h rising from the dynamic pressure generating surface as shown in FIG. 16 is formed at the same time. The In order to improve the bearing performance and the reliability, it is necessary to shape such an extra portion 111h incidental to the molded body 111 to eliminate the influence or to remove it. For this reason, for the purpose of pressing and shaping the dynamic pressure generating surface, sizing and the like are performed again after rolling the dynamic pressure groove, but the surplus portion is hardened due to work hardening or the like. However, simply sizing the dynamic pressure generating surface has a problem that it cannot be sufficiently shaped.
If this is left as it is, the shaft 101 will come into contact when the hydrodynamic bearing device is used at a high temperature and the viscosity of the lubricating fluid 105 decreases, or when the load such as the disk 110 is heavy. Therefore, it is possible to generate heat or rub, and it is desirable to further improve the reliability.

Accordingly, the present invention aims to further improve the reliability of the hydrodynamic bearing device.
And in order to achieve this object, the manufacturing method of the hydrodynamic bearing device of the present invention comprises:
A hydrodynamic bearing device manufacturing method comprising: a sleeve having a dynamic pressure generating groove on an inner peripheral surface of a bearing hole; and a shaft inserted in a relatively rotatable state in the bearing hole,
The sleeve is formed by forming a first molded body by molding a metal powder into a hollow cylindrical shape, and a sintering process by sintering the first molded body to form a second molded body. A first sizing step of shaping the second molded body by first sizing to form a third molded body, and dynamic pressure generation by rolling on the inner peripheral surface of the third molded body A dynamic pressure groove rolling step for forming a fourth molded body by forming a groove; a heat treatment step for heat-treating the fourth molded body to form a fifth molded body; and A ball having a diameter larger than the inner diameter of the fifth molded body is inserted into the bearing hole, and a first ball burnishing for shaping the inner diameter of the fifth molded body is performed to form a sixth molded body. 1 ball burnishing process;
Is a method for manufacturing a hydrodynamic bearing device.
The present invention further provides a hydrodynamic bearing device characterized in that the surface density is increased by subjecting at least a part of the surface of the sixth molded body to a second sizing (in-mold finishing). Is the method.
In addition, the present invention further performs second ball burnishing for shaping the inner diameter of the molded body by inserting a ball having a diameter larger than the inner diameter of the molded body into the molded body subjected to the second sizing. Is a method for manufacturing a hydrodynamic bearing device.
Further, the present invention is a method in which the surface of the sleeve is sealed by a method of forming an oxide film on the surface of the sleeve, and the surface hardness of the sleeve is internally increased by a method of forming a thin film by metal plating containing nickel. It is something that improves.

  In this way, by performing ball varnishing on the molded body in which dynamic pressure generating grooves are formed by rolling on the inner peripheral surface of the molded body to increase the surface density, and by providing a heat treatment step (re-sintering), Soften the surface of the molded product that has been work-hardened in the previous process (displace the dislocations increased by processing), and the molded product can more easily attach to the mold in the in-mold finishing (second sizing) ( This is a method for manufacturing a hydrodynamic bearing device, characterized in that the inner diameter size and shape in the finishing process are stabilized.

  As described above, the sleeve of the hydrodynamic bearing device of the present invention is formed by first forming a metal powder into a hollow cylindrical shape, and sintering it to obtain a sintered metal formed body, and then improving the density. First sizing is performed, and a dynamic pressure generating groove is formed by a rolling method. After that, heat treatment (re-sintering) is performed, and the first ball burnishing is performed to soften the work-hardened surface by groove rolling, etc., so that the dynamic pressure generating grooves are deeply and smoothly formed. it can. Also, the surface density of the inner peripheral surface of the bearing is increased in advance, and the surface density is further improved by the subsequent second sizing and second ball varnish. Since it is sealed by further surface treatment on it, the pressure generated in the dynamic pressure generating groove does not leak, and a high pressure can be generated on the hydrodynamic bearing surface of the sintered compact. it can. Accordingly, the hydrodynamic bearing device can be obtained in which the shaft can stably float and the dynamic pressure performance and reliability are good.

  Further, by performing the above heat treatment (re-sintering), the adhesion between the mold and the sintered metal in the second sizing is improved, and the surplus portion generated in the dynamic pressure generating groove portion of the inner diameter is easily crushed. Since it becomes easy to shape and the compression allowance of the second sizing can be reduced, the amount of change in deflection when the processing stress is released can be suppressed to be small, so that the inner diameter accuracy can be further stabilized.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
1 and 2 are cross-sectional views showing the configuration of the hydrodynamic bearing device of the present invention.
[Configuration of hydrodynamic bearing device and spindle motor]
In FIG. 1, the hydrodynamic bearing device includes a shaft 1, a flange 2, a sleeve 3, a thrust plate 4, and a lubricating fluid 5 (oil, high fluidity grease, ionic liquid, etc.), and the hydrodynamic bearing device Is further provided with a rotor hub 6, a rotor magnet 7, a stator 8 around which a coil is wound, and a base 9. The shaft 1 integrally has a flange 2, and the shaft 1 is rotatably inserted into the bearing hole 3 </ b> A of the sleeve 3, and the flange 2 is housed in the recess 3 </ b> J of the sleeve 3 on the lower surface portion of the sleeve 3. On the inner peripheral surface of the sleeve 3, dynamic pressure generating grooves 3B and 3C are provided. Further, dynamic pressure generating grooves 2A and 2B are provided on at least one of the facing surfaces of the flange 2 facing the sleeve 3 and the flange 2 and the thrust plate 4 facing each other. . In FIG. 1, dynamic pressure generating grooves 2 </ b> A and 2 </ b> B are provided on both surfaces of the flange 2, respectively. The thrust plate 4 is hermetically fixed to the sleeve 3 by bonding (for example, using an epoxy-based adhesive), welding (for example, welding with a laser), infiltration (for example, melting and solidifying a low melting point metal) or the like. The lubricating fluid 5 is held at least in the bearing gaps near the dynamic pressure generating grooves 3B, 3C, 2A, and 2B. The rotor hub 6 is fixed to the shaft 1 and the disk 10 is fixed to the rotor hub 6 by a clamper (not shown). 3D is a small-diameter portion of the shaft 1 and serves as a lubricating fluid reservoir. The lubricating fluid reservoir 3D can be processed on the sleeve 3 side.
In the present embodiment, the shaft 1 is made of stainless steel (for example, SUS420), high manganese chrome steel (for example, ASK8000), or carbon steel. The surface roughness of the radial bearing surface of the shaft 1 is made of a material finished in the range of 0.01 to 0.8 μm by processing.
[Operation of hydrodynamic bearing device and spindle motor]
The operation of the hydrodynamic bearing device of the present invention configured as described above, the spindle motor provided with the same, and the recording / reproducing apparatus mounted thereon will be described. In FIG. 1, when a rotating magnetic field is generated in the stator 8 by a control circuit (not shown), a rotational force is applied to the rotor magnet 7, and the rotor hub 6, the shaft 1, the flange 2, and the disk 10 start to rotate. Due to the rotation, the dynamic pressure generating grooves 3B, 3C, 2A and 2B collect the lubricating fluid 5, and the dynamic pressure between the shaft 1 and the sleeve 3, between the flange 2 and the sleeve 3, and between the flange 2 and the thrust plate 4. (Pumping pressure) is generated. As a result, the shaft 1 rotates in a non-contact manner with respect to the sleeve 3 and the thrust plate 4, and data is recorded on and reproduced from the disk 10 by a magnetic head or an optical head (not shown).
[Sleeve structure]
On the other hand, the material of the sleeve 3 is composed of an iron-based metal sintered body 3E as shown in a partial cross-sectional view in FIG. 2, and the holes 3F remaining inside the sintered body 3E are necessary on the surface of the sleeve 3. Depending on the temperature, the surface of the sleeve 3 is sealed by providing an oxide film layer 3G of triiron tetroxide or ferric trioxide to a thickness of about 1 to 10 μm by high-temperature steam treatment (steam treatment) at 400 to 700 ° C. is doing.
In this case, an oxide film layer is also formed in the holes 3F. If the sintered metal material is copper, an oxide film cannot be formed. For example, impregnated with resin, water glass or the like, or solidified by melting a low melting point metal such as tin or zinc at a high temperature. After liquefied and injected, it may be solidified at room temperature and sealed. The holes 3F may be impregnated with a thermosetting or anaerobic curable acrylic resin in a low-pressure tank. In these resin sealing holes, since the resin is sufficiently washed before the resin is cured, all of the resin remaining and adhering to the vicinity of the surface is removed, and only the resin impregnated inside remains and is cured. Thereby, the inside of the sleeve is sealed with the resin 3F.

  Further, the surface of the sleeve 3 may be formed with a metal component plating containing nickel or a DLC hard film 3H with a thickness of 1 to 10 μm in addition to the above-described sealing treatment as necessary. Thus, since the surface of the sleeve 3 is completely sealed, there is no need for a sleeve cover that covers the sleeve for preventing leakage of lubricating fluid from the sleeve formed of sintered metal as in the conventional hydrodynamic bearing device. Also, the lubricating fluid leaks into the surface holes (holes communicating with the surface such as 3F) on the inner peripheral surface of the sleeve, causing insufficient lubrication fluid inside the bearing, or leaking from the sleeve end surface or outer peripheral surface The lubricated fluid does not gasify and contaminate the surroundings of the hydrodynamic bearing device. Since the surface of the sleeve 3 is sealed, it is directly fixed to the base 9 with an adhesive (for example, an acrylic adhesive or an epoxy adhesive) without using a sleeve cover or the like. A rotor magnet 7 is attached to the rotor hub 6, and a stator 8 is fixed to the base 9 at a position facing the rotor magnet 7. In FIG. 1, the outer rotor type in which the stator 8 is disposed to face the inner peripheral side of the rotor magnet 7 is used. However, the inner rotor type in which the stator 8 is disposed to face the outer peripheral side of the rotor magnet 7 may be used. Since the sleeve 3 can be directly fixed to the base 9 without using a sleeve cover or the like, the perpendicularity and coaxiality at the time of attachment can be easily obtained, and the sleeve 3 can be assembled with high accuracy. Further, since the thrust plate 4 can be directly fixed to the sleeve 3 without using a sleeve cover or the like, the perpendicularity at the time of attachment is easily obtained, and assembly can be performed with high accuracy.

[Sleeve manufacturing method]
Below, the manufacturing method of the sleeve 3 is demonstrated using FIGS. FIG. 3 shows a process for manufacturing a sintered sleeve according to one embodiment of the present invention. The main processes up to the final process (inspection process, etc.) of the sleeve manufacturing of the present invention are the powder forming process S1, the sintering process S2, the first sizing process S3, the dynamic pressure groove rolling process S4, and the heat treatment (re-sintering) ) Step S5, first ball burnishing step S6, second sizing step S7, and second ball burnishing step S8. In the following, description will be given in order.

  First, in the powder molding step S1, iron powder or copper powder is preliminarily compression molded with a mold (not shown) to form the first molded body 11a. The molded product has a diameter of 6.5 mm and a length of about 5 mm. Next, in the sintering step S2, the compression-molded molded body 11a is sintered at about 800 to 1200 ° C. using a firing furnace (not shown) to form a second molded body 11b. In the present embodiment, the barrel process SS1 is performed after the sintering process S2. Burr remains at the edge of the sintered body. In order to remove this, a large number of compacts are placed in a container and the container is rotated to stir a large number of compacts to remove burrs. Moreover, in this Embodiment, the surface pressing process SS2 which shapes the inner peripheral edge part of the bearing hole of the molded object as it is sintered is performed. Although the shape of the second molded body 11b is slightly changed by such a process, the internal structure of the sintered molded body is not greatly changed. Therefore, for the sake of convenience, the second molded body 11b is obtained by including these processes. Called.

  When the molded body is sintered, it shrinks and distorts, so it is necessary to arrange (shape) the molded body. This is the next sizing step (first sizing step) S3, and FIG. 4 shows a first sizing die for shaping the shape and size of the second molded body 11b which has been sintered and subjected to barrel pressing. . 12 is a lower mold, 13 is an upper mold, 14 is a pin, and 15 is an outer mold. The second molded body 11b is set on the lower mold 12 of FIG. 4, and the upper mold 13 and the outer mold 15 are lowered as shown by the arrows in the drawing to compress and mold the second molded body 11b to form a third molded body. 11c is formed. After this step, the third molded body 11c may be drilled as necessary. In this case, the shape of the third molded body 11c is slightly changed by such a process, but the internal structure of the sintered molded body is not greatly changed. This is referred to as a molded body 11c.

  Next, in the dynamic pressure groove rolling step S4, the third molded body 11c is set on the mounting base 16 of the groove rolling apparatus shown in FIG. 5 so that the sintered metal body does not shift during processing. The clamp 17 is lowered in the direction of the arrow in the figure to fix it, and a rolling tool 18 in which a plurality of balls 18b are integrally arranged on the outer peripheral surface of the shank 18a is press-fitted into the inner diameter of the third molded body 11c. While applying forward and backward feed (axial direction) to 18a, forward direction rotation and reverse direction rotation are given, and the dynamic pressure generating groove 11g is processed by the ball 18b on the third molded body 11c, and the fourth molded body 11d is moved. Form. Here, the ball 18b is fixed to the shank 18a. And the outer diameter line which passes the outermost diameter of the some ball | bowl 18b centering on the center axis | shaft of the shank 18a is made larger about 10 micrometers in radius than the internal diameter of the 3rd molded object 11c. At this time, the dynamic pressure generating groove 11g processed into the third molded body 11c has a groove depth (hg) of about 10 μm as shown in FIG. A lot of the remaining portion 11h made of etc. remains. Further, since the dynamic pressure generating groove is formed by ball rolling as described above, the cross-sectional shape thereof is a substantially arc shape. Further, the groove bottom surface and the groove side surface are smooth with a small surface roughness due to the surface squeezing effect that the rolled ball gives to the groove.

  Conventionally, the process has shifted to the next second sizing process (in-mold finishing process), but in the embodiment of the present invention, a heat treatment (re-sintering) process S5 is performed again using a firing furnace (not shown). To form a fifth molded body. The heat treatment temperature is about 800 to 1200 ° C. When a metal is processed, lattice defects called dislocations increase, and they are entangled with each other, so that the dislocations are difficult to move and the hardness is increased. This is work hardening, and the fourth molded body 11d is in this state. Therefore, even if the second sizing is performed as it is, since the work is hardened, the shaping effect is small. Therefore, in the present invention, heat treatment (re-sintering) is performed at this point to eliminate dislocations increased by work hardening and return to the original hardness.

Thereafter, a first ball burnishing step S6 for shaping the inner diameter through a ball (usually a steel ball) having a diameter 2 to 5 μm larger than the inner diameter of the molded body is performed to form a sixth molded body. By performing this ball burnishing step, it is possible to shape the surplus portion or correct the inner diameter cylindricity by the inner diameter swelling in the sizing step. Further, surface vacancies having a size corresponding to the groove depth and groove width as disclosed in JP-A-2006-46540 can be reduced. These steps will be described in detail later.
Next, as shown in FIG. 7, the second sizing step S7 is performed so that the surface vacancies can be surely sealed at locations other than the dynamic pressure groove forming portion (particularly the end surface portion) of the sintered compact. This is a step of shaping a sintered compact in a mold. FIG. 7 is a cross-sectional view in the manufacturing process of the sleeve 3 of the present invention. In the present embodiment, the sixth cross section of the molded body that performs the second sizing step S7 and the subsequent cross section of the shape are shown. A1, B1, and C1 in the figure indicate axial dimensions of respective portions of the sixth molded body. A2, B2, and C2 indicate the axial dimensions of the respective portions after the second sizing step S7. Thus, by compressing and molding the end face of the sixth molded body in the mold, the surface vacancies on the end face can be made small and small.

FIG. 8 is data showing the relationship between various shapes of the dynamic pressure generating grooves 3B and 3C of the sleeve 3 and the bearing life of the hydrodynamic bearing device shown in FIG. According to the inventor's experiment, the hydrodynamic bearing device bearing has a shallow groove depth (hg) as shown by symbol (A) in the figure and no protrusions such as the surplus portion 11h. The life and the groove depth (hg) as shown in the symbol (B) are sufficient to be 5 μm, but the shape of the dynamic pressure generating grooves 3B and 3C is broken as shown in FIG. The bearing life of the hydrodynamic bearing device with no surface formed could only satisfy about half of the required life. On the other hand, as shown in FIG. 1C, the hydrodynamic bearing device shown in FIG. 1 is necessary and sufficient under the condition of a bearing having a groove depth (hg) of 5 μm and sufficient depth and no groove in the groove shape. I was able to get a long life. The relationship between the groove depth of 5 μm here and the groove depth of 10 μm at the time of the above-described groove rolling is that the groove depth changes through the dynamic pressure groove rolling and the ball burnishing process after the heat treatment. .
Because of this influence, it is important to eliminate as much as possible the extra portion made of burrs or the like generated on the inner peripheral surface of the hydrodynamic bearing. However, in the conventional manufacturing method, the hardness of the surplus portion is increased by work hardening at the time of groove rolling, and the inner peripheral surface of the hydrodynamic bearing is flattened only by performing the second sizing (in-mold finishing). I found it difficult.

Therefore, in the present invention, as described above, between the dynamic pressure groove rolling step S4 after the first sizing step S3 and the first ball burnishing step S6 before the second sizing step (in-mold finishing step) S7. By performing heat treatment (re-sintering) at a temperature of 800 to 1200 ° C., softening the work-hardened surface in the first sizing step or dynamic pressure groove rolling step, the dynamic pressure generating groove portion of the inner diameter of the bearing hole It was found that the generated surplus portion 11h exhibits an effect of being easily crushed. Therefore, the adhesion between the molded body and the mold is improved during the second sizing step S7, and the mold accuracy is easily transferred to the molded body with a smaller compression allowance (compression stress), so that the elastic deformation strain at the time of releasing the compression The inner diameter accuracy of the main dimensions can be easily stabilized.
Further, the dimensional accuracy can be improved by performing the first ball burnishing step S6 after the heat treatment (re-sintering) step S5.

The effect of this heat treatment (re-sintering) will be further described with reference to FIGS.
First, FIG. 9A shows a measurement method for comparing the hardness of the inner diameter portion of the sleeve 3. A ball having a size of about 1 to 4 μm larger than the inner diameter of the sleeve 3, and two balls 30 and 31 having a ball size difference of 1 μm are connected to a rod 32 connected to a load sensor 33 relative to the mounting table 35 of the sleeve 3. A measuring device 34 and its system are schematically shown in which the inner diameter of the sleeve 3 is passed by moving and the dynamic load for each coordinate at that time can be plotted continuously. In the following description, an example is shown in which a ball having a diameter of 1 μm and 2 μm larger than the inner diameter D1 of the sleeve 3 is passed. FIG. 9B shows a comparison of the hardness of the sintered compact before and after the heat treatment based on the data measured in FIG. 9A. The horizontal axis represents the coordinate in the axial direction of the sleeve 3, and the vertical axis represents the load difference when the two balls having a diameter difference of 1 μm are passed. (BT coefficient is a numerical value indicating a load difference per 1 μm, and the larger the value, the higher the hardness of the sleeve inner diameter portion)
FIG. 9B shows a case where a ball having a diameter of 1 μm and 2 μm larger than the inner diameter is passed through a sleeve having an axial length of 2 mm. Before the heat treatment, there is a peak of the BT coefficient in the vicinity of 1.2 mm from the entrance, and the maximum value is about 1450 g / μm. On the other hand, after the heat treatment, the change in the BT coefficient is almost flat, and the maximum value is about 1.7 mm from the entrance and is about 950 g / μm. As can be seen, the BT coefficient is reduced by heat treatment (re-sintering). This is because the dislocations increased by work hardening disappeared by heat treatment (re-sintering) on the inner diameter surface, and softened, and in the second sizing, it becomes easy to adhere to the mold, and the mold shape is easily transferred to the molded body. It is thought.
Since the above measurement is performed within the elastic deformation region of the sleeve, no practically harmful deformation remains in the sleeve after the measurement.
Next, FIG. 10 is a graph showing how many μm larger a ball with respect to the inner diameter of the sleeve 3 is expanded and deformed by using the measurement system of FIG. 9A. (This is a range exceeding the elastic deformation region unlike the above.) The horizontal axis indicates the difference in diameter from the sleeve inner diameter of the ball passed through the sleeve (passing ball diameter minus sleeve inner diameter before passing). The vertical axis shows the sleeve inner diameter change before and after the ball is passed.
First, before the heat treatment, the inner diameter did not change in the balls having a diameter difference of 3.5 μm before the heat treatment. That is, in this case, it is a change in the elastic region, indicating that the inner diameter of the sleeve returns to the original state after passing the ball. Therefore, it can be seen that shaping such as sizing has no effect unless a change greater than this value is given. Before the heat treatment, an inner diameter change of about 1 μm occurred through a ball having a diameter difference of about 5.2 μm.
On the other hand, after the heat treatment, the inner diameter did not change with a ball having a diameter difference of about 2 μm, but when the ball having a diameter difference of about 5.2 μm was passed, the inner diameter change of about 2.5 μm occurred. From the above, since the inner diameter of the sleeve is easily adhered to the mold by performing heat treatment (re-sintering), the inner diameter of the sleeve is easily transferred to an accurate mold shape with a smaller compression amount (compression force). Is shown.
Moreover, the effect of this invention is demonstrated in FIG. FIG. 11A shows an axial dynamic pressure groove shape in which a dynamic pressure groove is formed on the inner diameter of the sleeve using the rolling tool 18 after the first sizing step S3 and before the heat treatment step S5. The U-shaped trough in the figure indicates the dynamic pressure groove 11g. Square projections on both sides of the peak portion in the figure indicate the surplus portion 11h. It turns out that the surplus part 11h (height ha) has generate | occur | produced by the rolling process. FIG. 11B shows the shape of the dynamic pressure groove after the ball burnishing process in which a ball 2.5 μm larger than the diameter is passed through the sleeve inner diameter of FIG. 11A (without heat treatment). It turns out that the surplus part 11h1 (height hb) still remains only. Here, ha> hb.
On the other hand, FIG. 11 (c) shows a first example in which a heat treatment (re-sintering) step S5 is performed in FIG. 11 (a) after the groove rolling step S4, and then a ball 2.5 μm larger than the diameter is passed through the sleeve inner diameter. The axial dynamic pressure groove shape after the ball burnishing step S6 is shown. It turns out that the surplus part is not seen. After heat treatment (re-sintering), as described with reference to FIG. 10, it is considered that work hardening due to groove rolling is relaxed, and it is easier to follow along with an accurate mold. In the above embodiment, the ball diameter is 2.5 μm larger than the inner diameter of the sleeve, but it has been found that the same effect is obtained if it is in the range of 2 to 5 μm. The effect of performing the first ball burnishing step S6 after the heat treatment step S5 is specifically shown in FIGS. Assuming that the line connecting the apexes of the dynamic pressure groove crests (also referred to as ridges) in FIG. 11 (c) is the approximate apex line L, the product subjected to the first ball burnishing step S6 after the heat treatment step S5 is As shown by, the edges on both sides thereof are smoothly formed so as not to exceed the approximate vertex line L. This is because when the ball in the ball burnishing process is in the vicinity of the boundary where the ball moves from the dynamic pressure groove trough (also referred to as the groove) to the dynamic pressure groove crest, the area receiving the pressure received from the ball is small, so the edge is deformed more greatly. Because it receives. Further, the shape of the edge portion includes a line N parallel to the approximate vertex line L connecting the points where the actual groove shape is smoothly separated from the approximate groove line M extending from the dynamic pressure groove valley portion, and an approximate vertex. The distance from the line L is 0.1 μm or more.

It has also been found that the heat treatment (re-sintering) step may be performed either before or after the step of forming the dynamic pressure generating groove using the rolling tool 18. This will be described with reference to FIGS. 12 and 11 (e) and 11 (f). The difference between FIG. 3 and FIG. 12 is that the dynamic pressure groove rolling step S4 and the heat treatment (re-sintering) step S5 are interchanged. FIG. 11 (f) shows a dynamic pressure groove rolling step S4 in which a heat treatment (re-sintering) step S5 is performed after the first sizing step S3, and then a dynamic pressure groove is formed on the inner diameter of the sleeve using the rolling tool 18. The axial direction shape of the dynamic pressure groove which performed was shown. The surplus portion 11h2 (height hc) is generated by the dynamic pressure groove rolling process. However, it was found that when the first ball burnishing is performed thereafter, the surplus portion 11h2 is shaped smoothly. FIG. 11 (f) shows the shape of the dynamic pressure groove after the first ball burnishing step S6 through which a ball 2.5 μm larger than the sleeve inner diameter is passed. As in FIG. 11 (c), no surplus portion is seen, so by adding heat treatment, it becomes possible to finish with a smaller compressive force, so there is less deformation at the time of release of pressure, and the dimensional accuracy of the sleeve It was confirmed that became easy to stabilize. The latter (FIG. 12 and FIGS. 11 (e) and 11 (f)) is re-sintered continuously after the sintering process, so there is a merit that man-hours and freight required for the process movement of the product are reduced, and mass productivity is achieved. I think it is excellent.
As described above, in order to finish the molded body obtained through the powder molding, sintering, and first sizing into a molded body having a small excess portion in the dynamic pressure groove forming portion of the sleeve inner diameter so that there is no practical problem. Is obtained through 1) dynamic pressure groove rolling → heat treatment (re-sintering) → ball burnishing process, or 2) heat treatment (re-sintering) → dynamic pressure groove rolling → ball burnishing process. I found out that
In the above description, only the basic process for forming the molded body has been described. However, as shown in FIGS. 3 and 12, a barrel process or the like for removing small burrs as necessary, and communication are performed. A processing step for forming the hole may be inserted.

  Further, the molded body having a small surplus portion obtained in this way is practically free from problems, and the surface vacancies are further reduced by the second sizing (in-mold finishing) step S7, or the surface vacancies in other portions are removed. Make the hole small. Thereafter, by the second ball burnishing process in which a ball having a diameter larger by 1 to 2 μm than the inner diameter of the sleeve is passed, a dynamic pressure groove forming portion and a sleeve having a small inner diameter of the sleeve can be obtained.

  As shown in FIG. 3 and FIG. 12, the sleeve molded body of the present embodiment thus obtained has an oxide film layer of triiron tetroxide or ferric trioxide by high-temperature steam (steam) treatment SS3. Forming and almost completely sealing the surface vacancies of the sleeve.

  In addition, you may perform a surface hardening process after this. The surface hardened layer 3H in FIG. 2 mainly employs electroless plating mainly composed of nickel and phosphorus, and the surface has a Vickers hardness of 600 or more. Thereby, sufficient abrasion resistance can be given with respect to the axis | shaft 1 of stainless steel, high manganese chromium steel, or carbon steel mentioned above. Or you may give DLC coating by a three-dimensional DLC processing apparatus (example: Kurita Seisakusho). In this case, the surface has a Vickers hardness of 800 or more. By providing any one of these hardened layers 3H, the wear resistance and reliability of the hydrodynamic bearing device are improved.

In addition, regarding the components of the sleeve 3 in FIG. 1, the metal powder used for powder molding (compact molding) may be a copper-based one such as brass, but in order to reduce the difference in the coefficient of thermal expansion from the rotating shaft of the motor. Is preferably an iron-based powder or pure iron comprising an iron component accounting for 80% by weight or more of the total. After iron powder is powder-molded, it is sintered and used as a sintered body material for bearings. Generally, the clearance between the sleeve 3 and the shaft 1 in the hydrodynamic bearing device is set to about 2 to 5 μm, and the problem of the temperature difference in the operating environment in the surface treatment accuracy after the sealing treatment and the difference in the thermal expansion coefficient at the time of use is a problem. Important for bearing devices. Further, by adopting an iron-based material as a component of the sleeve 3, triiron tetroxide (Fe ₃ O ₄ ) or dioxide trioxide is formed on the porous surface of the molded body obtained by powder molding and the above-described various steps. An iron oxide film of iron (Fe ₂ O ₃ ) can be easily formed.

In addition, although the small diameter part provided in the axis | shaft 1 is a lubricating fluid reservoir part, it is not restricted to this, You may provide a large diameter part in the internal peripheral part of a sintered compact. However, providing a concave portion such as a large-diameter portion increases man-hours for manufacturing the sleeve and equipment costs. (Refer to the above-mentioned Patent Document 1 for the method of forming the large diameter portion.)
A hydrodynamic bearing device and a spindle motor including the same according to the present embodiment are disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-197309 (a motor including a hydrodynamic bearing and a recording disk driving device including the motor). As shown in FIG. 2, a rotor hub is fixed to the upper side of the shaft, and a ring-shaped member is attached to the lower side of the shaft. A periphery of the ring-shaped member has a lubricating fluid reservoir adjacent to the radial bearing surface. The present invention can also be applied to a hydrodynamic bearing device in which the upper surface of the sleeve and the upper surface of the sleeve are opposed to form a thrust bearing surface.

  The hydrodynamic bearing device of the present embodiment has been described with a shaft-rotating bearing structure in which the shaft rotates. However, a shaft-fixed bearing (not shown) in which both ends of the shaft are fixed and the sleeve rotates around the shaft is shown. The present invention can also be applied to a fluid bearing having a structure.

(Embodiment 2)
FIG. 13 is a modification example relating to the process arrangement of the heat treatment (re-sintering) process in the first embodiment. The second embodiment is a method in which the effect of mitigating work hardening by heat treatment (re-sintering) is utilized in the second sizing step. After performing the first sizing step S3, the dynamic pressure groove rolling step S4 is performed, and the surplus portion generated there is shaped in the first ball burnishing step S5. In the second embodiment, the second sizing (in-mold finishing) step S7 is not performed thereafter, and the heat treatment (re-sintering) step S5 is performed here. Also by this method, the work hardening of the surplus portion that could not be completely shaped in the first ball burnishing step S6 can be mitigated, so that an excessive compressive stress is applied to the mold in the second sizing (in-mold finishing) step S7. And the surplus portion can be shaped to a level where there is no practical problem. In addition, the life of the mold is extended, which is economical.

(Embodiment 3)
FIG. 14 is a cross-sectional view showing a hydrodynamic bearing device according to a third embodiment which is a third embodiment. 21 is a shaft, 22 is a flange, 23 is a sleeve, 23A is a bearing hole, 23B and 23C are dynamic pressure generating grooves, 22A and 22B are dynamic pressure generating grooves provided in the flange 22, 23D is a large diameter portion, and 23J is a continuous portion. A passage, 24 is a thrust plate, 25 is a lubricating fluid, 26 is a cap, and 27 is a sleeve holder. The large diameter portion 23 </ b> D provided on the sleeve 23 may be provided on the shaft 21 as a small diameter portion. Here, the sleeve holder 27 is made of stainless steel (for example, DHS1) or a sealed sintered compact that will be described later. The thrust plate is made of stainless steel (for example, SUS420) or a super steel alloy. The cap 26 is made of resin (for example, Ultem resin which is a translucent polyetherimide resin) or stainless steel.

The operation of the hydrodynamic bearing device of the third embodiment is substantially the same as that of the first embodiment shown in FIG. The difference is that 1) a lubricating fluid reservoir 28 is provided between the cap 26 and the sleeve 23, and 2) a circulation path is formed by the communication passage 23J, and the bubbles 29 are transferred from the hydrodynamic bearing to the lubricating fluid reservoir. 3) The sleeve 23 is covered with a sleeve holder 27 and a communication path 23J is formed between them. A communication hole opened in at least one place in the sleeve 23 may be used.
Bubbles (air) 29 contained in the lubricating fluid 25 in the bearing are generated by the circulating force from the top to the bottom as shown by the arrows in the figure generated by the dynamic pressure generating groove 23B having an axially asymmetric length (thrust). The circulating fluid may be generated from the bearing 22A), the lubricating fluid 25 in the bearing gap is moved from the upper side to the lower side in the drawing, and the inside of the communication hole 23J is further moved from the lower side to the upper side in the drawing to generate the dynamic pressure generating groove 23B. , 23C, 22A, and 22B, or bubbles that have been entangled from the opening are circulated and discharged to the lubricating fluid reservoir 28. Thus, an oil film (lubricating fluid film) of the lubricating fluid 25 can be reliably formed in the bearing gap, and the reliability of the hydrodynamic bearing device can be improved. For example, as shown in FIG. 14, the lubricating fluid reservoir 28 has a configuration in which the gap becomes smaller toward the inner periphery. As a result, the lubricating fluid 25 is drawn in the narrow gap direction by capillary action, so that the lubricating fluid 25 and the bubbles 29 can be separated. In FIG. 14, the circulation path is a radial bearing gap in which 23B and 23C are formed → a thrust bearing gap in which 22A is formed → an outer periphery of the flange 22 → a communication path 23J → a lubricating fluid reservoir 28 → 23B and 23C. It becomes the radial bearing gap formed. Further, the cap 26 may be provided with a ventilation hole communicating with the outside air that discharges the separated bubbles 29.

  The communication path 23 </ b> J is configured by providing at least one groove or notch on the outer peripheral surface of the sleeve 23 and forming a space between the sleeve holder 27. Alternatively, the sleeve 23 made of a sintered compact may be processed by a method of making a communication hole of about φ0.4 mm that connects the upper end surface and the lower end surface of the sleeve 3 with a drill (not shown). In addition, the sleeve 23 and the sleeve holder 27 having the groove-shaped communication path 23J on the outer peripheral surface are both formed of a sintered molded body, and after sintering at a high temperature, the sleeve 23 is press-fitted into the sleeve holder 27 to be integrated at the same time. 23J may be configured. If the sleeve 23 and the sleeve holder 27 are combined in this way, the communication path 23J can be configured most inexpensively. The existence of the communication passage 23J is very effective for ensuring the performance and reliability at high speed rotation of the hydrodynamic bearing device, and the communication passage 23J is configured by combining two sintered metal bodies in this way. The economic effect of doing this is great. Also with this hydrodynamic bearing device, the same effect as the hydrodynamic bearing device of the first embodiment can be obtained.

  The present invention relates to a hydrodynamic bearing device used in a device using a recording medium such as a hard disk device, an optical disk device, a magneto-optical disk device, etc., and a spindle motor equipped with the hydrodynamic bearing device, and the dynamic pressure generating groove is processed with high accuracy. A high-performance and long-life hydrodynamic bearing device free from pressure leakage and a manufacturing method thereof are obtained. It can also be used for a CPU cooling fan used in a personal computer.

Sectional drawing of the hydrodynamic bearing device and spindle motor which concern on the 1st Embodiment of this invention Partial sectional view of sleeve in the hydrodynamic bearing device Process drawing in the first embodiment of the hydrodynamic bearing device Sectional view of first sizing mold in manufacturing method of hydrodynamic bearing device Cross section of dynamic pressure generating groove rolling device in manufacturing method of same hydrodynamic bearing device Bearing inner peripheral surface sectional view of the sintered compact of the hydrodynamic bearing device The graph which shows the relationship between the surplus part (protrusion part) of the sintered compact of the same hydrodynamic bearing device, and a bearing life Sectional drawing of the second sizing mold in the manufacturing method of the hydrodynamic bearing device A measurement system for measuring the effect of heat treatment (re-sintering) and a graph showing the effect of heat treatment (re-sintering) in the manufacturing method of the hydrodynamic bearing device Graph showing the effect of heat treatment (re-sintering) in the manufacturing method of the hydrodynamic bearing device The graph which shows the surface shape measurement result of the bearing inner peripheral surface of the sleeve in the same hydrodynamic bearing device Process drawing in which the heat treatment (re-sintering) process in the first embodiment of the hydrodynamic bearing device is replaced. Process drawing in the second embodiment of the hydrodynamic bearing device Sectional drawing of the hydrodynamic bearing apparatus which concerns on 3rd Embodiment of the hydrodynamic bearing apparatus Sectional view of conventional hydrodynamic bearing device and spindle motor Partial sectional view of a conventional sleeve

Explanation of symbols

1 shaft 2 flange 3 sleeve 3A bearing hole 3B, 3C, 2A, 2B dynamic pressure generating groove 3D large diameter portion 3J recess 4 thrust plate 5 lubricating fluid 6 rotor hub 7 rotor magnet 8 stator 9 base 10 disk 11 sintered compact 12 lower mold 13 Upper mold 14 Pin 15 External mold 16 Mounting base 17 Clamp 18 Rolling tool 18A Shank 18B Rolling ball

Claims (21)

A sleeve having a dynamic pressure generating groove on the inner peripheral surface of the bearing hole;
A hydrodynamic bearing device comprising: a shaft inserted in a relatively rotatable state in the bearing hole;
The sleeve is
A powder molding step of forming metal powder into a hollow cylinder to form a first molded body;
A sintering step of sintering the first molded body to form a second molded body;
A first sizing step of shaping the second molded body by performing a first sizing to form a third molded body;
A dynamic pressure groove rolling step in which a dynamic pressure generating groove is formed by rolling on the inner peripheral surface of the third molded body to form a fourth molded body;
A heat treatment step of heat-treating the fourth molded body to form a fifth molded body;
A ball having a diameter larger than the inner diameter of the fifth molded body is inserted into the bearing hole of the fifth molded body, and a first ball burnishing for shaping the inner diameter of the fifth molded body is performed. A first ball burnishing step for forming a molded body of
A method of manufacturing a hydrodynamic bearing device, comprising: A sleeve having a dynamic pressure generating groove on the inner peripheral surface of the bearing hole;
A hydrodynamic bearing device comprising: a shaft inserted in a relatively rotatable state in the bearing hole;
The sleeve is
A powder molding step of forming metal powder into a hollow cylinder to form a first molded body;
A sintering step of sintering the first molded body to form a second molded body;
A first sizing step of shaping the second molded body by performing a first sizing to form a third molded body;
A heat treatment step of heat-treating the third molded body to form a fourth molded body;
A dynamic pressure groove rolling step of forming a dynamic pressure generating groove by rolling on the inner peripheral surface of the fourth molded body to form a fifth molded body;
A ball having a diameter larger than the inner diameter of the fifth molded body is inserted into the bearing hole of the fifth molded body, and a first ball burnishing for shaping the inner diameter of the fifth molded body is performed. A first ball burnishing step for forming a molded body of
A method of manufacturing a hydrodynamic bearing device, comprising: A sleeve having a dynamic pressure generating groove on the inner peripheral surface of the bearing hole;
A hydrodynamic bearing device comprising: a shaft inserted in a relatively rotatable state in the bearing hole;
The sleeve is formed by molding a metal powder into a hollow cylindrical shape to form a first molded body,
A sintering step of sintering the first molded body to form a second molded body;
A first sizing step of shaping the second molded body by performing a first sizing to form a third molded body;
A dynamic pressure groove rolling step in which a dynamic pressure generating groove is formed by rolling on the inner peripheral surface of the third molded body to form a fourth molded body;
A ball having a diameter larger than the inner diameter of the fourth molded body is inserted into the bearing hole of the fourth molded body, and the first ball burnishing for shaping the inner diameter of the fourth molded body is performed. A first ball burnishing step for forming a molded body of
A heat treatment step of heat-treating the fifth molded body to form a sixth molded body;
A method of manufacturing a hydrodynamic bearing device, comprising:   The method for manufacturing a hydrodynamic bearing device according to claim 1, wherein a heat treatment temperature in the heat treatment step according to claim 1 is 700 ° C. to 1200 ° C. 5.   The diameter of the ball used for the ball burnishing in the first ball burnishing process according to any one of claims 1, 2, and 3 is 2 to 5 µm larger than the inner diameter of the molded body before the process. A method for manufacturing a hydrodynamic bearing device.   The method for manufacturing a hydrodynamic bearing device according to any one of claims 1 to 5, further comprising a second sizing step of performing second sizing on at least a part of the surface of the molded body. A method for manufacturing a hydrodynamic bearing device.   The method for manufacturing a hydrodynamic bearing device according to claim 6 further includes: a second ball varnish that inserts a ball having a diameter larger than the inner diameter of the molded body into the molded body to shape the inner diameter of the molded body. A method of manufacturing a hydrodynamic bearing device, comprising a second ball burnishing step.   8. The hydrodynamic bearing device according to claim 7, wherein a diameter of a ball used for the ball burnishing in the second ball burnishing step according to claim 7 is 1-2 μm larger than an inner diameter of the molded body before the step. Method.   9. A hydrodynamic bearing device according to claim 1, wherein an oxide film containing triiron tetroxide or ferric trioxide is further formed on the surface of the sleeve after the process according to any one of claims 1 to 8. Method.   9. A method for manufacturing a hydrodynamic bearing device, wherein the surface of the sleeve is further impregnated with resin or water glass after the step according to claim 1.   9. A method of manufacturing a hydrodynamic bearing device according to claim 1, further comprising impregnating the surface of the sleeve with a heat-dissolved metal after the step according to any one of claims 1 to 8.   A method for manufacturing a hydrodynamic bearing device, wherein a thin film is further formed on the sleeve surface by metal plating containing nickel after the process according to any one of claims 9 to 11.   A method of manufacturing a hydrodynamic bearing device, wherein a thin film is further formed on the sleeve surface by DLC coating after the step according to any one of claims 9 to 11. The axis,
A sleeve having a bearing hole into which the shaft is inserted in a relatively rotatable state;
A dynamic pressure surface formed on the inner peripheral surface of the bearing hole;
A dynamic pressure generating groove formed on the inner peripheral surface;
A lubricating fluid held in a gap formed by the shaft and the sleeve;
With
The hydrodynamic bearing device is characterized in that both ends of the hill portion formed between the dynamic pressure generation grooves on the dynamic pressure surface do not protrude in the inner diameter direction than the central portion.   The hydrodynamic bearing device according to claim 14, wherein both end portions of the hill portion are formed to be lower than the central portion by 0.1 μm or more.   The hydrodynamic bearing device according to claim 14, wherein an oxide film containing triiron tetroxide or ferric trioxide is formed on the surface of the sleeve to seal the surface.   The hydrodynamic bearing device according to claim 14, wherein a surface of the sleeve is impregnated with resin or water glass.   The hydrodynamic bearing device according to claim 14, wherein a surface of the sleeve is impregnated with heat-dissolved metal.   A hydrodynamic bearing device in which a thin film made of a metal containing nickel is formed on the surface of the sleeve according to any one of claims 16 to 18.   A hydrodynamic bearing device in which a thin film made of DLC is formed on the surface of the sleeve according to any one of claims 16 to 18. The hydrodynamic bearing device according to any one of claims 14 to 20,
A rotor hub that is rotatably fixed to the hydrodynamic bearing device;
A rotor magnet fixed to the hub;
A base plate for fixing the hydrodynamic bearing device;
A stator fixed to the base so as to face the rotor magnet;
A spindle motor equipped with.

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