JP7804446B2 - Base member and method of manufacturing the same, spindle motor and hard disk drive - Google Patents

Description

The present invention relates to base members for electronic devices such as hard disk drives, and in particular to treating rough surfaces formed on base members due to melting damage from die-casting molds. The present invention also relates to spindle motors and hard disk drives that use the above-mentioned base members.

Hard disk drive base plates are generally manufactured by die-casting aluminum. Patent Document 1 discloses a technique for removing bulges formed at the corners of a product due to wear at the corners of the die-casting mold.

JP 2008-27540 (Abstract)

For disk drive devices filled with helium, which has a lower density than air, the base member is die-cast by directing the flow of molten metal along the length of the base member and reducing the cross-sectional area through which the molten metal flows, allowing the molten metal to flow at high pressure and high density. This suppresses the formation of blowholes inside the base member and improves the airtightness of the base member.

However, when molten metal is poured under high pressure, melting damage is likely to occur in the area near the gate of the mold. When melting damage occurs in the mold, the inner wall surface of the casting becomes rough with protrusions. Rough surface on the inner wall surface of the casting can lead to disruption of the air flow inside the equipment and peeling of the electro-deposition coating.

The present invention was made in consideration of the above circumstances, and aims to provide a base member that can suppress turbulence in the air flow inside the device and prevent peeling of the electrodeposition coating film by appropriately treating rough surfaces that form on the base member.

The present invention relates to a die-cast base member that forms part of the housing of a hard disk drive device. The base member has a rectangular plate-shaped bottom portion having short and long sides, and a sidewall portion extending from the entire peripheral edge of the bottom portion in a direction perpendicular to the bottom portion. The sidewall portion has a circular portion with an inner surface shape that follows the shape of the hard disk. The circular portion has a disk-facing surface that faces the hard disk and a recess that is recessed from the disk-facing surface in the radial direction of the hard disk. The entire disk-facing surface and at least a portion of the surface facing inward of the recess are machined surfaces, and the machined surfaces are covered with a coating.

The present invention also relates to a method for manufacturing a base member for a die-cast product that will become part of the housing of a hard disk drive device, which includes forming the base member with a rectangular plate-shaped bottom having short and long sides and sidewalls extending from the entire peripheral edge of the bottom in a direction perpendicular to the bottom, forming a circular portion in the sidewalls with an inner circumferential surface that conforms to the shape of the hard disk, forming in the circular portion a disk-facing surface that faces the hard disk and a recess that recesses from the disk-facing surface in the radial direction of the hard disk, machining the entire disk-facing surface and at least a portion of the surface facing inward of the recess to form a machined surface, and painting or plating the machined surface.

The present invention provides a base member that can suppress turbulence in the airflow inside the device and prevent peeling of the electrodeposition coating.

FIG. 2 is a plan view showing a base member according to the embodiment of the present invention. FIG. 2 is a perspective view showing a base member according to an embodiment of the present invention. 1 is a cross-sectional view showing a spindle motor according to an embodiment of the present invention. 1 is a plan view showing a hard disk drive device according to an embodiment of the present invention;

1. Configuration of Base Member One embodiment of the base member of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a plan view showing a base member 10. In the figure, reference numeral 11 denotes a bottom portion, which is a rectangular plate having short and long sides. A side wall portion 12 is formed around the entire periphery of the bottom portion 11, extending in a direction perpendicular to the bottom portion 11.

The side wall portion 12 comprises a circular portion 13 whose inner circumferential surface conforms to the shape of the hard disk, and a rectangular portion 14 that houses a mechanism for writing and reading data to and from the hard disk. The circular portion 13 comprises a disk-facing surface 13a that faces the hard disk. The circular portion 13 also comprises a recess 13b that is recessed in the radial direction of the hard disk.

The base member 10 is manufactured by die-casting using aluminum or an aluminum alloy. The die-casting mold has a gate for pouring molten metal near the center of the short side of the base member 10. As a result, part of the disk-facing surface 13a is molded in the part of the die-casting mold facing the gate, and melting occurs in the part of the die-casting mold near the gate of the disk-facing surface 13a and in the part that molds the recess 13b. When melting occurs in the mold, protrusions form on the cast base member 10, causing the surface to become rough.

In this embodiment, the inward-facing surfaces of the disk-facing surface 13a and the recess 13b are machined. The machining is performed by cutting the inward-facing surfaces of the disk-facing surface 13a and the recess 13b using, for example, an end mill. Therefore, the machined surfaces are provided at least in a position facing the gate of the die-casting mold. This processes the rough surfaces (protrusions) on the inward-facing surfaces of the disk-facing surface 13a and the recess 13b, which were caused by melting of the mold, into smooth, machined surfaces. Furthermore, cutting marks are formed on the inward-facing surfaces of the disk-facing surface 13a and the recess 13b in the direction of rotation of the hard disk. Incidentally, the recess 13b can also be molded in a position facing the gate of the die-casting mold.

The entire surface of the base member 10 is electrocoated. Electrocoating is a process in which the base member 10 is immersed in a solution containing a water-soluble resin, such as an epoxy resin, and an electric current is passed through it to cause the resin to adhere to the base member 10, after which it is dried and thermally cured. This electrocoating forms a smoother electrocoating film on the machined surface. The electrocoating film also prevents dust from accumulating on the surface of the base member 10. The coating method is not limited to electrocoating; powder coating, spray coating, brush coating, and plating such as electroless nickel plating may also be used.

In the base member 10 configured as described above, the roughness of the disk-facing surface 13a and the inward-facing surface of the recess 13b of the base member 10 caused by melting of the mold has been machined into a smooth, machined surface, which is further smoothed by the electrocoat coating, thereby suppressing turbulence in the airflow inside the hard disk drive and preventing peeling of the electrocoat coating.

In particular, in the above embodiment, cutting marks that run along the rotation direction of the hard disk are formed on the disk-facing surface 13a and the inward-facing surfaces of the recess 13b, so the cutting marks do not interfere with the flow of air, effectively suppressing turbulence in the airflow.

2. Spindle Motor Figure 3 is a cross-sectional view showing a spindle motor 100 according to an embodiment of the present invention, which uses the base member 10 described above. A cylindrical metal shaft 102 is fixed to the base member 10 by means of press fitting or the like. A stator core 103 is also fixed to the base member 10. The stator core 103 is made by laminating multiple thin sheets of soft magnetic material (e.g., electromagnetic steel sheets) in the axial direction, has an annular shape, and is provided with multiple pole teeth that protrude radially outward. The multiple pole teeth are arranged at equal intervals along the circumferential direction, and a coil 104 is wound around each of them via an insulator (not shown).

Conical bearing members 201 and 202 are fixed to the shaft 102, and the rotor 110 is rotatably supported by the conical bearing members 201 and 202. The rotor 110 has a cylindrical portion 111, and an annular rotor magnet 112 is fixed to the inner surface of the cylindrical portion 111. The rotor magnet 112 is magnetized so that adjacent portions along the circumferential direction, SNSN..., alternately have opposite polarities. The inner surface of the rotor magnet 112 faces the outer surface of the pole teeth of the stator core 103 with a gap between them. By passing a drive current through the coil 104, the rotor 110 rotates relative to the shaft 102 and stator core 103, which are fixed to the base member 10.

A sealing member 203 such as a pin is inserted into the hollow portion at the lower end of the shaft 102, and the sealing member 203 is fixed inside the shaft 102 with a fixing member 204 such as an adhesive. This sealing member 203 and fixing member 204 prevent the low-density gas inside the hard disk drive from leaking from the shaft 102.

In the spindle motor 100 configured as described above, the roughness of the disk-facing surface 13a and the inward-facing surface of the recess 13b of the base member 10 caused by melting of the mold has been machined into a smooth, machined surface, which is further smoothed by the electrocoat coating. This reduces airflow disturbances within the hard disk drive device in which the spindle motor 100 is incorporated, and prevents the electrocoat coating from peeling off.

4 is a diagram showing a hard disk drive 400 according to an embodiment of the present invention, which uses the spindle motor 100. A plurality of hard disks 401 are attached to the spindle motor 100 at a distance from one another. A swing arm 402 is rotatably supported on the shaft 15 of the base member 10.

A magnetic head 403 is attached to the tip of the swing arm 402. The swing arm 402 is swung by a drive mechanism 404, which is attached to the support 18. A swing arm 402 like this is provided for each hard disk 401. The swing arm 402, magnetic head 403, and drive mechanism 404 form a read/write mechanism 405 that writes and reads data to and from the hard disk 401. Reference numeral 406 denotes a circuit board that controls the read/write mechanism 405, and the circuit board 406 is attached to the support 18.

A filter or airflow adjustment member is attached to the recess 13b of the base member 10. The filter absorbs dust floating inside the hard disk drive device 400. The airflow adjustment member adjusts the airflow caused by the rotation of the hard disk 401 so that it follows the direction of rotation. In the hard disk drive device 400 described above, the maximum height of the housing in the axial direction is set to 1.5 to 2.0 inches.

The hard disk drive 400 described above is filled with a low-density gas such as helium. The spindle motor 100 rotates the hard disk 401, and the magnetic head 403 writes and reads data to and from the hard disk 401. In the hard disk drive 400 configured as described above, the roughness of the disk-facing surface 13a and the inward-facing surface of the recess 13b of the base member 10 caused by melting of the mold is machined into a smooth, machined surface, and further smoothed by the electrocoat coating. This suppresses turbulence in the airflow inside the hard disk drive 400 incorporating the spindle motor 100 and prevents peeling of the electrocoat coating.

4. Modifications The present invention is not limited to the above-described embodiment, and the following modifications are possible.
(1) The present invention is also applicable to hard disk drive devices in which low-density gas is not sealed inside the base member 10.

(2) The machining is not limited to the disk-facing surface 13a of the base member 10 and the inward-facing surface of the recess 13b, but can be performed on any location, such as the bottom surface of the bottom portion 11 or the inner surface of the rectangular portion 14.
(3) In the above embodiment, the disk-facing surface 13a of the base member 10 and the inward-facing surface of the recess 13b are machined with an end mill to form cutting marks that follow the rotation direction of the hard disk. However, it is also possible to grind them with a grinder so that cutting marks are essentially eliminated.

(4) Coating may be applied only to the disk-facing surface 13a of the base member 10 and the surface facing inward of the recess 13b.
(5) The machining may be performed on the entire disk-facing surface and only on a portion of the surface facing inward of the recess.

The present invention can be used in electronic devices such as spindle motors and hard disk drives, as well as in base members used therein.

10...base member, 11...bottom, 12...side wall portion, 13...circular portion, 13a...disk facing surface, 13b...recess, 14...rectangular portion, 15...axis, 18...support, 100...spindle motor, 102...shaft, 103...stator core, 104...stator coil, 110...rotor, 111...cylindrical portion, 112...rotor magnet, 201...bearing member, 202...bearing member, 203...sealing member, 204...fixing member, 400...hard disk drive device, 401...hard disk, 402...swing arm, 403...magnetic head, 404...drive mechanism, 405...read/write mechanism, 406...circuit board

Claims (8)

A die-cast base member that becomes part of the housing of a hard disk drive device,
The base member has a rectangular plate-shaped bottom portion having short sides and long sides;
a sidewall portion extending from the edge of the entire periphery of the bottom portion in a direction perpendicular to the bottom portion,
the side wall portion includes a circular portion having an inner circumferential surface shape that conforms to the shape of the hard disk;
the circular portion has a disk-facing surface that faces the hard disk, and a recess that is recessed from the disk-facing surface in a radial direction of the hard disk,
the entire disk-facing surface and at least a part of the surface facing inward of the recess are machined surfaces;
the machined surface is covered with a coating;
The machined surface formed in the recess is provided at least at a position facing a gate of a die-casting mold . The base member of claim 1, wherein the machined surface has cutting marks that run along the rotational direction of the hard disk. A spindle motor comprising the base member according to claim 1 or 2 . 4. A hard disk drive comprising the spindle motor according to claim 3 , wherein the recess is provided with a filter or an airflow adjusting member. 5. The hard disk drive device according to claim 4 , wherein the internal space is filled with a gas having a density lower than that of air. 6. The hard disk drive device according to claim 4 , wherein the maximum height of the housing in the axial direction is 1.5 to 2.0 inches. A method for manufacturing a base member of a die-cast product that will become part of a housing for a hard disk drive device, comprising forming a rectangular plate-shaped bottom portion having short sides and long sides in the base member, and sidewall portions extending from the edges of the bottom portion along the entire periphery in a direction perpendicular to the bottom portion;
a circular portion having an inner peripheral surface shape conforming to the shape of the hard disk is formed on the side wall portion;
a disk-facing surface facing the hard disk and a recess recessed from the disk-facing surface in a radial direction of the hard disk,
the entire disk-facing surface and at least a part of the inward-facing surface of the recess are machined to form a machined surface;
The machined surface formed in the recess is provided at a position facing at least a gate of a die-casting mold,
The method for manufacturing a base member includes painting or plating the machined surface. The method for manufacturing a base member according to claim 7 , wherein cutting marks are formed along the rotation direction of the hard disk by the machining.