JP2006329262A - Dynamic pressure bearing device and motor equipped with the device, and disk device using the motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dynamic pressure bearing device which hardly generates chipping of a nitrided layer formed by nitriding treatment and prevents the occurrence of burning and the deterioration over a long term, a motor equipped with the device, and a disk device using the motor. <P>SOLUTION: In a dynamic pressure bearing device equipped with a shaft member and sleeve member relatively rotating, the shaft member is made of austenitic stainless steel. The outer peripheral surface has a nitrided layer. The nitride in the nitrided layer consists predominantly of chromium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device, a motor using the same, and a disk device including the motor, and more particularly to a shaft member of the hydrodynamic bearing device formed of stainless steel.

Generally, a dynamic pressure bearing device includes a shaft member and a sleeve member that rotate relative to each other, and a dynamic pressure generating groove is formed on at least one of the outer peripheral surface of the shaft member and the inner peripheral surface of the sleeve member. In the hydrodynamic bearing device, once the shaft member and the sleeve member start to relatively rotate at a high speed, dynamic pressure is generated by the dynamic pressure generating groove, and the rotating side member rotates with high rigidity and high core runout accuracy. For example, when used as a bearing device for a hard disk drive motor, a high recording density can be obtained.
As the sleeve member in the hydrodynamic bearing device, a copper alloy is usually used from the viewpoint of ease of processing. On the other hand, as the shaft member, a stainless material, particularly an austenitic stainless material, may be used for the purpose of matching the thermal expansion with the copper alloy constituting the bearing member described above and improving the wear resistance. is there.
As such a hydrodynamic bearing device, as described in Patent Document 1, the sleeve is made of a copper alloy, the shaft is made of austenitic stainless steel, and the surface layer of the shaft is nitrided to increase the surface hardness. Hydrodynamic bearings are known.
Japanese Patent Laid-Open No. 10-89345

  However, since the nitriding treatment replaces the non-moving body film of stainless steel with a nitride such as iron nitride or chromium nitride, the nitriding treatment improves the hardness of the surface of the stainless steel, but the surface is brittle. There are many important layers. Since iron nitride and chromium nitride in which stainless steel and chromium nitride are nitrided coexist, increase in rotational torque and insufficient dynamic pressure are inevitably generated at low speeds such as when the motor is started or stopped. Therefore, the shaft member and the sleeve member are in contact with each other, and a part of the nitriding layer made of iron nitride and chromium nitride is likely to be lost. The missing nitride layer enters the bearing component, becomes a foreign substance, increases the wear of the hydrodynamic surface, and causes seizure of the shaft member and the sleeve member.

  The present invention has been made in view of such a conventional problem, and a nitriding layer formed by a nitriding process is less likely to be lost, is not seized, and does not deteriorate over a long period of time. It is an object of the present invention to provide a motor provided with this device and a disk device using this motor.

  The invention according to claim 1 includes a shaft member and a sleeve member that rotate relative to each other, a dynamic pressure bearing portion is formed between the outer peripheral surface of the shaft member and the inner peripheral surface of the sleeve member, and the dynamic pressure In the hydrodynamic bearing device in which the shaft member and the sleeve member are rotated relative to each other by the dynamic pressure action by the bearing portion, at least the shaft member is formed of austenitic stainless steel, and has a nitriding treatment layer on an outer peripheral surface thereof. The nitride in the treatment layer is formed mainly of chromium.

  The invention according to claim 2 includes a shaft member and a sleeve member that rotate relative to each other, a dynamic pressure bearing portion is formed between the outer peripheral surface of the shaft member and the inner peripheral surface of the sleeve member, and the dynamic pressure In the hydrodynamic bearing device in which the shaft member and the sleeve member are relatively rotated by a dynamic pressure action by the bearing portion, at least the shaft member is formed of austenitic stainless steel, and has a nitriding treatment layer on an outer peripheral surface, and the shaft The surface obtained by cutting the cross section of the member and performing mirror polishing and edging treatment is a dark layer in which the surface nitriding layer is darker than the light color of the substrate.

  According to a third aspect of the present invention, a shaft member and a sleeve member that rotate relative to each other are provided, a dynamic pressure bearing portion is formed between the outer peripheral surface of the shaft member and the inner peripheral surface of the sleeve member, and the dynamic pressure In the hydrodynamic bearing device in which the shaft member and the sleeve member are relatively rotated by a dynamic pressure action by the bearing portion, at least the shaft member is formed of austenitic stainless steel, and has a nitriding treatment layer on an outer peripheral surface, and the shaft The surface layer of the member has an N / Cr weight concentration ratio of 0.6 or less by component analysis.

  According to a fourth aspect of the present invention, the nitriding layer has a depth of 10 μm or more from the outer surface.

  According to a fifth aspect of the present invention, the hydrodynamic bearing device according to any one of the first to fourth aspects, a stator having a coil fixed to one of the shaft member and the sleeve member, the shaft member, and And a rotating member having a magnet fixed to the other of the sleeve members and facing the coil.

  According to a sixth aspect of the present invention, there is provided a disk device having a disc-shaped recording medium on which information can be recorded, a housing, a motor that is fixed inside the housing and rotates the recording medium, and a required recording medium. An information access means for writing information to or reading information from a position, wherein the motor is the motor according to claim 5.

  According to the present invention, nitriding treatment is performed using austenitic stainless steel for the shaft member. The nitride in the nitriding layer of the shaft member is formed mainly of chromium and contains almost no iron nitride. Therefore, the nitrided layer is not mixed with nitride, and the grain boundary is difficult to be clarified. For this reason, the nitriding layer is not easily lost.

  Therefore, even when the shaft member and the sleeve member are in contact with each other in the low-speed rotation state such as when the motor is started or stopped, the shaft member having a nitrided layer formed mainly of chromium with nitride is not missing nitride. Do not wake up.

  In addition, since the nitrided layer does not cause the lack of nitride, it is possible to provide a hydrodynamic bearing device that is stable for a long time.

  According to the invention of claim 4, the nitriding layer of the present invention has a depth of 10 μm or more from the outer surface. Therefore, it can have a hardness that can sufficiently withstand the rotation and impact of the hydrodynamic bearing device.

  According to a fifth aspect of the present invention, a motor of the present invention includes the hydrodynamic bearing device having the above-described nitriding layer of the present invention. Therefore, it is possible to provide a motor that can rotate stably over a long period of time.

  According to a sixth aspect of the present invention, a disk device of the present invention includes the motor of the present invention described above. For this reason, a super-long-life disk device can be realized by using the motor described above.

<Structure of spindle motor>
FIG. 1 is a longitudinal sectional view schematically showing a schematic configuration of a spindle motor 100 as one embodiment of the present invention.
The spindle motor 100 is a spindle motor for driving a recording disk, and constitutes a part of a recording disk device such as a hard disk. A schematic diagram of the hard disk drive 11 using the spindle motor 100 is shown in FIG.
Note that OO shown in FIG. 1 is the rotation axis of the spindle motor 100. In the description of the present embodiment, the vertical direction in FIG. 1 is referred to as the “axis vertical direction” for convenience, but the direction in the actual mounting state of the spindle motor 100 is not limited.

  A spindle motor 100 shown in FIG. 1 rotates relative to the bracket 101, a shaft 102 whose one end is fitted and fixed in a central opening provided in the bracket 101, and the shaft 102. And a flexible rotor 103. The rotor 103 is positioned on the inner peripheral side of the rotor hub 103a on which a recording disk (shown as a disk plate 13 in FIG. 2) is placed on the outer periphery, and the shaft 102 through a minute gap in which oil is held. And a sleeve 103b supported by the shaft. A rotor magnet 104 is fixed to the inner peripheral portion of the rotor hub 103a by means such as adhesion, and a stator 105 is mounted on the bracket 101 so as to face the rotor magnet 104 in the radial direction.

  A through hole 103c that penetrates the sleeve 103b in the axial direction is formed in the substantially central portion of the sleeve 103b so as to form a minute gap in which the inner peripheral surface is held between the outer peripheral surface of the shaft 102 and oil. An annular upper thrust plate 106 and a lower thrust plate 107 projecting outward in the radial direction are respectively attached to the upper portion and the lower portion.

  At both ends in the axial direction of the sleeve 103b, corresponding to the upper thrust plate 106 and the lower thrust plate 107, an upper thrust surface 103d and a lower thrust surface 103e that are larger in diameter than the outer diameters of the upper and lower thrust plates 106, 107. Is formed. An annular and hollow cylindrical upper bushing member 108 and lower bushing member 109 are mounted and closed on the outer peripheral portions of the upper thrust surface 103d and the lower thrust surface 103e.

  An annular protrusion 103f is formed on the outer periphery of the sleeve 103b. The annular protrusion 103f protrudes radially outward. The outer peripheral surface of the annular protrusion 103f and the inner peripheral surface of the rotor hub 103a are, for example, press-fitted. Fastened by means.

  A fine gap for holding oil is formed between the upper thrust surface 103d and the lower surface (the inner surface in the axial direction) of the upper thrust plate 106, and the upper thrust bearing portion 1S1 is configured.

  Further, a minute gap for holding oil is formed between the lower thrust surface 103e and the upper surface (axial inner surface) of the lower thrust plate 107, and the lower thrust bearing portion 1S2 is configured. An upper radial bearing portion 1R1 and a lower radial bearing portion 1R2 are configured between the inner peripheral surface of the through hole 103c and the outer peripheral surface of the shaft 102.

<Configuration, operation and characteristics of hard disk device>
FIG. 2 shows a schematic diagram of a hard disk device 11 having a general spindle motor 100.
Each part of the hard disk device 11 is contained in a housing 12, and mainly includes a spindle motor 100, a recording disk 13, and a head moving mechanism 14. The interior of the housing 12 forms a good environment with extremely little dust. The bracket 101 of the spindle motor 100 is fixed in contact with the inner surface of the housing 12 so that the spindle motor 100 and the housing 12 are electrically connected.
The recording disk 13 is a disk-shaped member that records information by magnetism. The recording disk 13 is fitted on the outer peripheral surface of the rotor 103 of the spindle motor 100.
The head moving mechanism 14 reads and writes information from and to the recording disk 13. The head moving mechanism 14 includes a head 15, an arm 16, and an actuator unit 17. Further, since the head moving mechanism 14 is fixed to the inner surface of the housing 12, conduction with the housing 12 is ensured. For this reason, each part of the head moving mechanism 14 and the housing 12 are electrically connected.
The head 15 is provided in the vicinity of the recording disk 13 by being provided at one end of the arm 16, and reads / writes the recording disk 13. The arm 16 is a member that supports the head 15. The actuator unit 17 supports the other end of the arm 16 and moves the arm 16. The arm 16 swings and moves the head 15 to a required position on the recording disk 13 by the actuator unit 17.

<Another spindle motor structure>
FIG. 3 is a longitudinal sectional view schematically showing a schematic configuration of a spindle motor 200 as another embodiment of the present invention.

  The spindle motor 200 shown in FIG. 2 includes a substantially disc-shaped upper wall portion 201a (top plate) and a cylindrical peripheral wall portion 201b that hangs downward from the outer peripheral edge portion of the upper wall portion 201a. A rotor 203 composed of a rotor hub 201, a shaft 202 having one end fitted and fixed to the central portion of the upper wall portion 201a of the rotor hub 201, and a hollow cylindrical shape that rotatably supports the shaft 202 A sleeve 204, a cover member 205 for closing the lower portion of the sleeve 204, and a bracket 206 integrally formed with a cylindrical portion 207 for holding the sleeve 204 are provided.

  A stator 208 is disposed on the outer peripheral side of the cylindrical portion 207 of the bracket 206, and the inner peripheral surface of the cylindrical peripheral wall portion 201 b of the rotor hub 201 is opposed to the stator 208 via a gap in the radial direction so that the rotor The magnet 209 is fixed.

  Further, on the outer peripheral surface of the cylindrical peripheral wall portion 201b of the rotor hub 201, a flange-like disk mounting portion 201c on which a recording disk such as a hard disk (shown as the recording disk 13 in FIG. 2) is mounted is provided. The shaft 202 is secured to the cover member 205 side of the sleeve 204 by a pin member 210 to prevent the rotor 203 from coming off.

  A thrust bearing portion 2S for generating a levitation force of the rotor 203 is formed between the bottom surface of the rotor hub 201 and the upper end surface of the sleeve 204, and the outer peripheral surface of the shaft 202 and the sleeve 204 provided integrally with the rotor hub 201 are formed. The upper radial bearing portion 2R1 and the lower radial bearing portion 2R2 are configured to act on the alignment of the rotor 203 and to prevent the rotor 203 from falling through the air intervening portion 211 communicating with the outside air. .

  A ring-shaped member 212 made of a ferromagnetic material such as stainless steel is disposed at a position facing the rotor magnet 209 of the bracket 206 in the axial direction, and a magnetic force acting between the rotor magnet 209 and the ring-shaped member 212. A support force in a direction to suppress the floating of the rotor 203 is obtained by a suction force. The floating force applied to the rotor 203 by the dynamic pressure generated in the thrust bearing portion 2S and the upper radial bearing portion 2R1 and the magnetic attractive force acting between the rotor magnet 209 and the ring-shaped member 212 are balanced and applied to the rotor 203. Supports axial loads.

  In the hydrodynamic bearing used for the various motors as described above, it is necessary to eliminate the difference in thermal expansion between the sleeve and the shaft and reduce the change in the gap due to the temperature change. As a material satisfying such conditions, a copper-based material such as phosphor bronze is used as the material of the sleeve, and an austenitic stainless steel material such as SUS303 or SUS304 is used as the material of the shaft. Here, since the austenitic stainless steel material used for the shaft cannot be hardened even after quenching and tempering, it is necessary to prevent scratches and abrasive wear in the machining process and to prevent the shaft from being removed. In order to harden the surface, it is necessary to perform nitriding treatment. Any method may be applied to the nitriding treatment, and examples thereof include gas nitriding, salt bath nitriding, ion nitriding, and plasma nitriding.

In this embodiment, as an example of the nitriding treatment, an NV nitriding process (manufactured by Air Water Co., Ltd.) that can be treated at a relatively high temperature is applied. In this NV nitriding process, first, the shaft is fluorinated using a fluorine-based gas such as NF ₃ , and then heated in a mixed gas atmosphere of N ₂ and NH ₃ . Nitriding was performed so that a nitrided layer was formed.

  The surface of the shaft subjected to nitriding treatment thus obtained may be subjected to cutting and polishing to prevent adhesion.

  Next, the cross-sectional structure of the shaft and the evaluation of the rotational impact test in this embodiment will be described.

  FIG. 4 shows a cross-sectional observation photograph of the surface portion of the shaft of Example 1 using a metallographic microscope. In Example 1, austenitic stainless steel SUS304Se having a crystal grain size of 7 was used. After performing nitriding treatment under the above nitriding conditions, cutting is performed, and the cut surface is subjected to mirror polishing and edging. In FIG. 4, a phase different from the base material, that is, a fine layer mainly composed of chromium is confirmed on the surface side (the black layer on the upper side in the drawing) on the shaft base material (the white layer on the lower side in the drawing). It was done. Further, the depth of the layer mainly composed of nitride of chromium was about 10 μm. The surface hardness is approximately 1000 to 1200 in terms of Vickers hardness. In addition, since the nitriding layer of Example 1 has a crystal grain size of 7 or more, a finer nitriding layer can be formed.

  Next, the cross-sectional observation photograph by the metallographic microscope of the surface part of the shaft of the comparative example 1 is shown in FIG. Similar to Example 1, a nitrided layer having a phase different from that of the base material is confirmed on the base material (white layer in the lower part of the figure) on the surface side of the shaft. However, when Example 1 (FIG. 4) is compared with Comparative Example 1 (FIG. 5), the nitride layer formed in Comparative Example 1 is a mixture of chromium nitride (black) and iron nitride (white). That is confirmed. Moreover, the grain boundary of chromium nitride (black) and iron nitride (white) can be confirmed clearly.

  The X-ray diffraction measurement results of Example 1 and Comparative Example 1 are shown in FIG. In this measurement, the X-ray incident angle was measured at 5 °, and copper characteristic X-rays were used. From the results of X-ray diffraction of Example 1 and Comparative Example 1, it is confirmed that the nitride of Example 1 is a nitride layer mainly composed of chromium, and Comparative Example 1 has a nitride layer mainly composed of iron nitride. Is done.

  FIG. 7 shows the results of a rotational impact test for measuring the degree of chipping of the shafts subjected to nitriding treatment in the examples and comparative examples.

  Example 1, Example 2, and Comparative Example 1 are shafts 102 obtained by nitriding SUS304Se. The surface portion of the shaft 102 of Example 1 and Example 2 is formed of a nitride layer whose nitride is mainly composed of chromium, and the surface portion of the shaft 102 of Comparative Example 1 is formed of iron nitride and chromium nitride. Formed of a nitride layer. Each of these 50 shafts was put into a rotating machine, and the rotational speed (1.8, 5, 10, 20, 30, 40 rpm) was changed to apply rotational shock vibration to the shafts. The number of occurrences of chipping at the number of revolutions was counted.

  From the results shown in FIG. 7, it was confirmed that Example 1 is a shaft that is substantially free of chipping, that is, a shaft that can withstand rotational impact, and that Example 2 is also less likely to be applied than Comparative Example 1. In Comparative Example 1, the number of occurrences of chipping is greatly increased in proportion to the increase in the rotational speed. Since Comparative Example 1 is a mixed nitriding treatment layer of iron nitride and chromium nitride, it is presumed that the nitride is easily missing from the grain boundary and becomes brittle. From this, it was confirmed that the ratio of the chromium nitride formed by nitriding treatment on the shaft surface and the ratio of iron nitride existing on the shaft surface affect the probability of chipping.

  Moreover, when EDS (energy dispersive X-ray analyzer) analysis was performed on the nitrided layers of Example 1, Example 2 and Comparative Example 1, as shown in Table 1, the ratio of nitrogen to chromium and iron The proportion of nitrogen present is different. Surface analysis was performed under analysis conditions of an acceleration voltage of 15 kV and a magnification of 1000 times. Therefore, it was confirmed that the nitride layer had a low N / Cr weight concentration ratio and contained almost no iron nitride, which is a shaft that can withstand rotational impact and is not easily chipped. In particular, Example 2 and Comparative Example 1 are compared, and the N / Cr weight concentration ratio needs to be 0.6 or less. Moreover, when the N / Cr weight concentration ratio is 0.4 or less, the chipping probability can be further maintained low for a long period of time.

  As a result, by using an austenitic stainless steel material having a nitride layer that is less prone to chipping, the shaft can be rotated with high rigidity and high core runout accuracy. It will not mix and cause rocking or burning. Therefore, it is possible to provide a spindle motor that can rotate stably over a long period of time. In addition, a long-life disk device can be realized by using the spindle motor described above.

  Here, in the present embodiment, the fluid dynamic pressure bearing has been described as an example of the spindle motor. However, the present invention is not limited to this, and a generally used sliding member can be applied. Also in this embodiment, austenitic stainless steel material is used for the shaft and nitriding is performed, but other rotor hubs, sleeves, and brackets may be formed of austenitic stainless steel material and subjected to nitriding treatment.

1 is a longitudinal sectional view schematically showing a schematic configuration of a spindle motor 100 as one embodiment of the present invention. 1 is a schematic diagram of a hard disk device 11 including a spindle motor 100. FIG. It is a longitudinal cross-sectional view which shows typically schematic structure of the spindle motor 200 as other embodiment of this invention. 2 is a cross-sectional observation photograph of a surface portion of a shaft of Example 1 using a metal microscope. 6 is a cross-sectional observation photograph of a surface portion of a shaft of Comparative Example 1 using a metal microscope. The X-ray-diffraction result of the nitriding process layer of Example 1 and Comparative Example 1 is shown. It is a figure which shows the result of having done the rotational impact test which measures the difficulty of the notch | chip of the shaft which performed the nitriding process of the Example and the comparative example.

Explanation of symbols

100, 200 Spindle motor 101, 206 Bracket 102, 202 Shaft 103, 203 Rotor 103b, 204 Sleeve

Claims (6)

A shaft member and a sleeve member that rotate relative to each other, and a dynamic pressure bearing portion is formed between an outer peripheral surface of the shaft member and an inner peripheral surface of the sleeve member, and the shaft is driven by a dynamic pressure action by the dynamic pressure bearing portion. In the hydrodynamic bearing device that relatively rotates the member and the sleeve member,
At least the shaft member is made of austenitic stainless steel, has a nitriding layer on the outer peripheral surface, and the nitride in the nitriding layer is formed mainly of chromium, and is a hydrodynamic bearing device . A shaft member and a sleeve member that rotate relative to each other, and a dynamic pressure bearing portion is formed between an outer peripheral surface of the shaft member and an inner peripheral surface of the sleeve member, and the shaft is driven by a dynamic pressure action by the dynamic pressure bearing portion. In the hydrodynamic bearing device that relatively rotates the member and the sleeve member,
At least the shaft member is made of austenitic stainless steel, has a nitriding layer on the outer peripheral surface, and the surface of the shaft member that has been subjected to mirror polishing and edging treatment is made of a surface nitriding layer. A hydrodynamic bearing device, characterized in that it is a darker layer with a darker color than the bright color. A shaft member and a sleeve member that rotate relative to each other, and a dynamic pressure bearing portion is formed between an outer peripheral surface of the shaft member and an inner peripheral surface of the sleeve member, and the shaft is driven by a dynamic pressure action by the dynamic pressure bearing portion. In the hydrodynamic bearing device that relatively rotates the member and the sleeve member,
At least the shaft member is made of austenitic stainless steel, has a nitriding layer on the outer peripheral surface, and has an N / Cr weight concentration ratio of 0.6 or less by component analysis in the surface layer of the shaft member. The hydrodynamic bearing device.   The hydrodynamic bearing device according to claim 1, wherein the nitriding layer has a depth of 10 μm or more from an outer surface. The hydrodynamic bearing device according to any one of claims 1 to 4,
A stator having a coil fixed to one of the shaft member and the sleeve member;
And a rotating member having a magnet fixed to the other of the shaft member and the sleeve member and facing the coil. In a disk device to which a disk-shaped recording medium capable of recording information is mounted,
A housing;
A motor that is fixed inside the housing and rotates the recording medium;
A disk device having information access means for writing or reading information at a required position of the recording medium,
The disk apparatus according to claim 5, wherein the motor is the motor according to claim 5.