Patent Application
20230063544
This application claims the benefit of priority to Japanese Patent Application Numbers 2021-138832, and 2022-097926 filed on Aug. 27, 2021, and Jun. 17, 2022, respectively. The entire contents of the above-identified applications are hereby incorporated by reference.
The present disclosure relates to a spindle motor and a hard disk drive device, and particularly relates to a technique for forming a hub having a long axial length by cold forging.
In a hard disk drive device using a spindle motor, a hub for placing a hard disk is formed of aluminum or stainless steel (DHS1 (registered trade name), for example) (see JP 2006-254625 A). Conventionally, a hub is formed by cutting a solid metal material having a columnar shape. DHS1 is a type of free-machining steel, and is a stainless steel having cutting performance improved by inclusions such as MnS.
In recent years, an increase in the number of hard disks resulting from an increase in the capacity of hard disk drive devices has led to an increase in the axial length of the hub for placing the hard disks. A conventional method for forming a hub by cutting involves removing the interior of a cylindrical portion of the hub. Therefore, the greater the axial length of the hub, the longer the processing time and the greater the material loss. In addition, cutting a free-machining steel may generate particles due to separation of inclusions. JP 2010-035367 A discloses a technique for forming a hub of a spindle motor by cold forging DHS1 steel. Cold forging is thought to reduce material loss due to cutting.
However, in recent spindle motors including more than eight hard disks each having a diameter of 3.5 inches, the axial length of the hub is too long to form the hub by cold forging DHS1 steel. Producing a hub having a long axial length by cold forging DHS1 steel may cause the material to break in some cases.
The present disclosure has been made in view of the above circumstances, and an object is to provide a spindle motor and a hard disk drive device. The spindle motor includes a hub. The hub is formed by cold forging and has a long axial length.
The present disclosure provides a spindle motor including a fixed portion and a rotating portion including a hub. The hub is made of low-carbon steel having a carbon content of 0.23% or less, and the hub is a cold-forged product.
According to the present disclosure, since low-carbon steel having a carbon content of 0.23% or less has excellent cold forgeability, it is possible to provide a spindle motor and a hard disk drive device including a hub having a long axial length and enabling a larger number of hard disks to be mounted.
The hard disk drive device 10 also includes a swing arm 11 configured to support a plurality of magnetic heads 12 each facing a respective hard disk 13, an actuator 14 configured to drive the swing arm 11, and a control unit 15 configured to control these units. In the hard disk drive device 10, a cover portion (not illustrated) mounted at the base portion 101 so as to seal the housing 118 forms a casing (a space from the upper surface of the base portion 101 to the bottom surface of the cover portion) with the base portion 101. The height of the casing is from 1.5 to 2.0 inches, and the casing is filled with helium.
At the base portion 101, a cylindrical portion 101a extending upward in the axial direction of the shaft 102 is formed, and a stator core 103 is fixed at an outer periphery of the cylindrical portion 101a. The stator core 103 is formed by layering, in the axial direction, a plurality of thin sheet-like soft magnetic materials (for example, electromagnetic steel sheets) each having an annular shape, and includes a plurality of pole teeth protruding outward in the radial direction. The plurality of pole teeth are provided at equal intervals along a circumferential direction, and a coil 104 is wound around each pole teeth.
A rotating portion of the spindle motor 100 includes a rotor 110. The rotor 110 includes a hub 111 including a through-hole 111a at a central portion, and a sleeve 112 fixed to the through-hole 111a by an appropriate method such as press fitting or bonding. The hub 111 includes a flat plate portion 111b extending outward in the radial direction, a cylindrical portion 111c extending downward from the outer periphery of a lower end of the flat plate portion 111b, and a flange portion 114 extending outward in the radial direction from a lower end portion of the cylindrical portion 111c.
The hub 111 is composed of low-carbon steel having a carbon content of 0.23 mass % or less, for example from 0.07 to 0.23 mass %, preferably from 0.08 to 0.23 mass %. The hub 111 is preferably composed of S20C. S20C has a composition consisting of, in mass %, C: 0.18 to 0.23%, Si: 0.15 to 0.35%, Mn: 0.3 to 0.6%, P: less than 0.03%, S: less than 0.035%, and the remainder: Fe and unavoidable impurities. Low-carbon steel having such a composition has excellent cold forgeability, and can be cold-forged to form the hub 111 having a long axial length (length of the cylindrical portion 111c).
The hub 111 is preferably composed of S10C. S10C has a composition consisting of, in mass %, C: 0.08 to 0.13%, Si: 0.15 to 0.35%, Mn: 0.3 to 0.6%, P: less than 0.03%, S: less than 0.035%, and the remainder: Fe and unavoidable impurities. S10C has excellent cold forgeability compared to S20C, and by selecting S10C, the axial length of the hub 111 can be further increased to mount more hard disks 13.
Note that, as materials other than S10C, S12C (C: 0.10 to 0.15%), S15C (C: 0.13 to 0.18%), S17C (C: 0.15 to 0.20%), S09CK (C: 0.07 to 0.12%), S15CK (C: 0.13 to 0.18%), S20CK (C: 0.18 to 0.23%), or the like can be used.
The entire region of the hub 111 excluding the through-hole 111a is covered with a resin film or a plating film of metal having higher corrosion resistance than carbon steel. Here, “metal having higher corrosion resistance” means metal nobler than a base material. Electroless nickel plating, chrome plating, or the like can be used as the metal plating. Epoxy resin, acrylic resin, or the like can be used as the resin film. Such a film can be provided on both of the hub 111 and the sleeve 112 in a state where the sleeve 112 is fixed to the hub 111, or can be provided on the hub 111 only. Since carbon steel is more likely to rust than stainless steel, the above film is provided to improve rust prevention properties. Further, the film described above can prevent the generation of particles.
The hub 111 is manufactured by cold-forging the above-described low-carbon steel. The through-hole 111a is formed by thinning the low-carbon steel in a vertical direction by cold forging and punching a hole through the low-carbon steel, and is finished by lathe turning. The inner peripheral surface of the cylindrical portion 111c is also finished by lathe turning. Note that the hub 111 and the sleeve 112 can also be integrally formed of low-carbon steel.
The sleeve 112 has a substantially cylindrical shape. An inner peripheral surface of the sleeve 112 includes a tapered surface 112a in slide contact with the conical bearing members 201 and 301. With this configuration, the rotor 110 is rotatably supported by the conical bearing members 201 and 301 while being prevented from moving in the vertical direction. The sleeve 112 is made of stainless steel. By forming the sleeve 112 as a member separate from the hub 111, cold forging of the hub 111 is facilitated, and processing of the sleeve 112 is also facilitated. Further, the sleeve 112 is made of stainless steel and thus need not be plated, and high dimensional accuracy of the inner peripheral surface of the sleeve 112 can be ensured by lathe turning.
However, when a film is provided on both of the hub 111 and the sleeve 112 in a state where the sleeve 112 is fixed to the hub 111 as described above, removing the film provided on the sleeve 112 can improve dimensional accuracy. Alternatively, when the film provided on the hub 111 and the sleeve 112 is harder than the base material, it is preferable to leave the film provided on the inner peripheral surface of the sleeve 112. Accordingly, the wear resistance of the inner peripheral surface of the sleeve 112 is ensured, and the surfaces of the conical bearing members 201 and 301 need not be coated with a solid lubricant film such as a diamond-like carbon (DLC) film, reducing manufacturing costs.
In a case where the hub 111 and the sleeve 112 are integrally formed and a film is provided over the entire area of the hub 111 and the sleeve 112, the wear resistance of the inner peripheral surface of the sleeve 112 can be ensured by using a film harder than the base material.
A rotor magnet 113 having an annular shape is fixed at an inner peripheral surface side of the cylindrical portion 111c. The rotor magnet 113 is magnetized in a manner such that adjacent portions alternately have opposing magnetic poles such as S-N-S-N . . . along a circumferential direction. The inner periphery of the rotor magnet 113 faces the outer periphery of the pole teeth of the stator core 103 in a state of being spaced apart from each other. When the coil 104 is supplied with a drive current, a drive force for causing the rotor magnet 113 to rotate is generated, and the rotor 110 rotates relative to the shaft 102 and the base portion 101 with the shaft 102 serving as an axis. This mechanism is similar to that of a typical spindle motor.
As illustrated in
The hard disk 13 may be made of metal such as aluminum, but is preferably made of glass. The thermal expansion coefficient of glass is close to the thermal expansion coefficient of low-carbon steel, and combining the hard disks 13 made of glass and the hub 111 made of low-carbon steel can improve accuracy when assembling the hard disks 13.
Here, as illustrated in
In the spindle motor 100 having the configuration described above, the hub 111 is made of low-carbon steel having a carbon content of 0.23% or less, and thus has excellent cold forgeability. In addition, the hub 111 having a long axial length can be obtained by cold forging. In the hard disk drive device 10, the height of the casing can be set to from 1.5 to 2.0 inches, and thus the number of hard disks 13 to be mounted can be increased. In addition, unlike JP 2006-254625 A where a solid material is cut, the problem of material loss and the problem of particle generation or the like due to separation of inclusions such as a free-machining component after machining do not occur.
Further, since the rigidity of the hub 111 formed by cold forging is increased through work-hardening with no break in the metal flow line, it is possible to reduce the thickness of the flange portion 114 and increase the thickness of the base portion 101 at a position of the annular groove 101b opposing the flange portion 114. Accordingly, the rigidity of the base portion 101 can be increased, and the helium enclosed in the casing of the hard disk drive device 10 can be suppressed from leaking.
The present disclosure is not limited to the embodiment described above, and it is possible to make various modifications as described below.
i) As illustrated in
ii) A flange portion 115 illustrated in
In the flange portion 115 described above, when a thickness of the flange portion 115 at the center of the annular groove 115a is defined as (a) and a distance from the contact point P of the flange portion 115 to the cylindrical portion 111c is defined as (b), (a)/(b) is set to 0.37 to 0.42. Also, in the flange portion 115 described above, the thickness (a) of the flange portion 115 is defined to be thin.
iii) In the embodiment described above, the present disclosure is applied to a fixed-shaft type spindle motor including the shaft 102 fixed to the base portion 101, but the present disclosure can also be applied to a rotating-shaft type spindle motor including the shaft 102 rotatably supported by a bearing fixed to the base portion 101.
The present disclosure can be employed in a spindle motor and a hard disk drive device, and in particular, can be preferably employed in a hard disk drive device including a casing having a height of 1.5 to 2.0 inches.
While preferred embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-138832 | Aug 2021 | JP | national |
| 2022-097926 | Jun 2022 | JP | national |
