Base plate, spindle motor, disk drive device, and method for manufacturing a base plate

Abstract

To provide a base plate that can reduce occurrence of shrinkage cavities and a manufacturing method of the base plate.SOLUTION: A base plate 41 is a part of a housing of a disk drive apparatus and includes a base body formed of a metal die cast member and an electrodeposition coating film covering at least a part of a surface of the base body. The base body has a bottom plate 411 rectangular as viewed from an axial direction and a pivot post 413. The bottom plate extends perpendicular to a rotation axis C of a disk and a swing axis D of a head. The rotation axis extends vertically. The swing axis is arranged at a different position from the rotation axis and extends vertically. The head reads or writes information from or to the disk. The pivot post protrudes upward from an upper surface of the bottom plate along the swing axis, and a part of the die cast member is segregated.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a base plate, a spindle motor, a disk drive device, and a method for manufacturing a base plate.

Background Art

[0002] A case body (base plate) that is part of the housing of a conventional disk drive device has a rectangular bottom surface portion and an actuator mounting portion (pivot post). The actuator mounting portion protrudes upward from the upper surface of the bottom surface portion (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the case body disclosed in the above patent document, the flow of molten metal to the actuator mounting portion is poor during casting, and shrinkage cavities may occur in the actuator mounting portion. For this reason, there was a possibility that the helium gas filled inside the housing leaked to the outside through the actuator mounting portion.

[0005] An object of the present invention is to provide a base plate and a method for manufacturing a base plate that can reduce the occurrence of shrinkage cavities.

Means for Solving the Problems

[0006] An exemplary base plate of the present invention is a base plate that forms part of the housing of a disk drive device, and includes a base body made of a metal die-cast member, and an electrodeposition coating film that covers at least a part of the surface of the base body. The base body has a rectangular bottom plate portion and a pivot post when viewed in the axial direction. The bottom plate portion extends perpendicular to the rotation axis of the disk and the swing axis of the head. The rotation axis extends vertically. The swing axis is arranged at a position different from the rotation axis and extends vertically. The head reads or writes information to / from the disk. The pivot post protrudes upward from the upper surface of the bottom plate portion along the swing axis, and a part of the die-cast member is segregated.

[0007] A method for manufacturing an exemplary base plate of the present invention is a method for manufacturing a base plate that forms part of the housing of a disk drive device, and includes a casting process, a pressing process, an electrodeposition coating process, and a cutting process. In the casting process, a base body having a rectangular bottom plate portion and a pivot post when viewed in the axial direction is integrally cast using a mold. The bottom plate portion extends perpendicular to the rotation axis of the disk extending vertically and the swing axis of the head, and is rectangular when viewed in the axial direction. The swing axis is arranged at a position different from the rotation axis and extends vertically. The head reads or writes information to / from the disk. The pivot post protrudes upward from the upper surface of the bottom plate portion along the swing axis. In the pressing process, the tip of the pivot post or the lower surface of the bottom plate portion axially opposed to the pivot post is locally pressed axially within the mold. In the electrodeposition coating process, an electrodeposition coating film is formed on the surface of the base body. In the cutting process, the pivot post is cut and shaped.

Advantages of the Invention

[0008] According to an exemplary aspect of the present invention, it is possible to provide a base plate and a method for manufacturing the base plate that can reduce the occurrence of shrinkage cavities.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. In this specification, the rotation axis C of the disk 50 and the swing axis D of the head extend parallel to each other at different positions. In the present application, the direction parallel to the rotation axis C or the swing axis D is referred to as the "axial direction", the direction perpendicular to the swing axis is referred to as the "radial direction", and the direction along the arc centered on the rotation axis C or the swing axis D is referred to as the "circumferential direction". In the present application, with the axial direction as the vertical direction and the cover 42 side as the upper side with respect to the base plate 41, the shape and positional relationship of each part will be described. However, this definition of the vertical direction is not intended to limit the orientation of the base plate 41 and the disk drive device 1 according to the present invention during use.

[0011] (1. Configuration of Disk Drive Device) The disk drive device 1 according to an exemplary embodiment of the present invention will be described. FIG. 1 is a longitudinal sectional view of the disk drive device 1 according to an embodiment of the present invention.

[0012] The disk drive device 1 is a hard disk drive. The disk drive device 1 includes a spindle motor 2, a disk 50, a head 31, an arm 32, a swing mechanism 33, and a housing 40.

[0013] The housing 40 houses the spindle motor 2, the disk 50, the head 31, and the arm 32 inside.

[0014] The inside of the housing 40 is filled with a gas having a lower density than air. Specifically, helium gas is filled. Note that hydrogen gas or the like may be filled instead of helium gas.

[0015] The housing 40 is formed by casting a die-cast member made of an aluminum alloy. Note that the die-cast member may be made of a metal other than an aluminum alloy.

[0016] The housing 40 has a base plate 41 and a cover 42. Inside the housing 40, a disk 50, a spindle motor 2, and an access unit 30 are arranged on the base plate 41. The opening at the upper part of the base plate 41 is closed by the cover 42. The base plate 41 will be described in detail later.

[0017] The spindle motor 2 rotates the disk 50 about the rotation axis C while supporting the disk 50. That is, the disk 50 rotates about the rotation axis C by the spindle motor 2. The spindle motor 2 has a stationary part 10 and a rotating part 20. The stationary part 10 is relatively stationary with respect to the housing 40. The rotating part 20 is rotatably supported with respect to the stationary part 10.

[0018] The stationary part 10 has a stator 12 and a bearing unit 13. Also, a part of the base plate 41 constitutes the stationary part 10. That is, the spindle motor 2 includes the base plate 41. The base plate 41 extends perpendicular to the rotation axis C on the lower side of the rotating part 20. The base plate 41 is a part of the spindle motor 2 and also a part of the housing 40. The stator 12 and the bearing unit 13 are fixed to the base plate 41.

[0019] The stator 12 has a stator core 12a made of a magnetic material and a plurality of coils 12b. The stator core 12a has a plurality of teeth 12c protruding outward in the radial direction. The plurality of coils 12b are constituted by conductors wound around the teeth 12c.

[0020] The bearing unit 13 rotatably supports the shaft 21 on the rotating part 20 side. For example, a hydrodynamic bearing mechanism is used for the bearing unit 13.

[0021] The rotating part 20 has a shaft 21, a hub 22, and a magnet 23. The shaft 21 is a columnar member extending in the axial direction. The lower end part of the shaft 21 is accommodated inside the bearing unit 13.

[0022] The hub 22 is fixed to the upper end of the shaft 21 and extends radially outward. The upper surface of the outer peripheral portion 22a of the hub 22 supports the disk 50. The magnet 23 is fixed to the inner peripheral surface of the hub 22 and is disposed opposite to the outside in the radial direction of the stator 12 at a predetermined distance. The magnet 23 is annular, and the N pole and the S pole are alternately magnetized in the circumferential direction on the inner peripheral surface of the magnet 23.

[0023] When a drive current is supplied to the coil 12b, magnetic fluxes are generated in the plurality of teeth 12c. Then, due to the interaction of the magnetic fluxes between the teeth 12c and the magnet 23, a circumferential torque is generated. As a result, the rotating part 20 rotates about the rotation axis C with respect to the stationary part 10. The disk 50 supported by the hub 22 rotates about the rotation axis C together with the rotating part 20.

[0024] The disk 50 is a disk-shaped information recording medium having a hole in the central portion. Each disk 50 is mounted on the spindle motor 2 and is arranged axially parallel to and at equal intervals from each other via a spacer (not shown).

[0025] The head 31 magnetically reads or writes information to / from the disk 50. The arm 32 is attached to the tip of a pivot post 413 (to be described later) of the base plate 41 via a bearing 32a. The head 31 is provided at the tip of the arm 32.

[0026] The swing mechanism 33 is a mechanism for swinging the arm 32 and the head 31. When the swing mechanism 33 is driven, the arm 32 swings about the swing axis D. That is, the head 31 swings about the swing axis D by the swing mechanism 33 via the arm 32. At this time, the head 31 moves relative to the disk 50 and accesses the rotating disk 50 in proximity.

[0027] (2. Detailed Configuration of Base Plate) FIG. 2 is a perspective view schematically showing the base plate 41, and FIG. 3 is a top view schematically showing the base plate 41. FIG. 4 is a longitudinal sectional view schematically showing the base plate 41. Note that the gate mark portion 412a shown in FIG. 4 has been removed in the manufacturing process of the base plate 41 described later, but is shown in the figure for explanatory purposes.

[0028] The base plate 41 includes a base body 41a made of a metal die-cast member and an electrodeposition coating film 41b covering the surface of the base body 41a.

[0029] The base body 41a is formed in a box shape with an open upper portion, and has a bottom plate portion 411 and a peripheral wall portion 412. The bottom plate portion 411 is rectangular when viewed from the axial direction, and extends perpendicular to the rotation axis C and the swing axis D.

[0030] The peripheral wall portion 412 is formed by a plurality of walls extending upward from the outer peripheral edge of the bottom plate portion 411 and surrounding the bottom plate portion 411. The cover 42 is disposed on the upper end surface of the peripheral wall portion 412 and is, for example, screwed. Further, the peripheral wall portion 412 has a gate mark portion 412a to which the gate 214 was connected during casting, and the gate mark 412a is disposed on the outer surface of the peripheral wall portion 412 that intersects the parallel direction in which the rotation axis C and the swing axis D are aligned and faces the rotation axis C.

[0031] The pivot post 413 projects upward from the upper surface of the bottom plate portion 411 along the swing axis D and is formed in a columnar shape. The pivot post 413 has an annular pedestal portion 413a that projects radially outward from the peripheral surface of the root portion. By providing the pedestal portion 413a, the rigidity at the root portion of the pivot post 413 can be improved.

[0032] The bottom plate portion 411 has a recess 411a. The recess 411a is formed by the lower surface of the bottom plate portion 411 facing the pivot post 413 in the axial direction being recessed upward in the axial direction. By providing the recess 411a, the weight of the base plate 41 can be reduced. Further, as will be described later, by providing the recess 411a, the flow of the molten metal changes its direction upward during casting, and the flow of the molten metal toward the tip side of the pivot post 413 can be promoted.

[0033] The recess 411a is a frustum-shaped depression and is circular in a bottom view. That is, the inner diameter of the recess 411a is gradually formed smaller as it goes upward in the axial direction. Further, the top surface portion 411b disposed at the tip portion on the upper side in the axial direction of the recess 411a is formed substantially parallel to the lower surface of the bottom plate portion 411. Further, in the base plate 41 of the finished product, the diameter W1 of the top surface portion 411b is larger than the outer diameter W2 of the root portion at the upper end of the pedestal portion 413a of the pivot post 413. Note that the diameter W1 of the top surface portion 411b may be substantially the same as the outer diameter W2 of the root portion at the upper end of the pedestal portion 413a of the pivot post 413.

[0034] (3. Manufacturing method of the base plate) FIG. 5 is a flowchart showing the manufacturing process of the base plate 41. FIGS. 6 to 10 are explanatory diagrams for explaining the manufacturing process of the base plate 41.

[0035] In step S1, as shown in FIG. 6, the peripheral edge of the mold 201 and the peripheral edge of the mold 202 are brought into contact with each other in the vertical direction, and a cavity 210 is formed between the mold 201 and the mold 202. The cavity 210 has a shape corresponding to the shape of the base body 41a. Further, the cavity 210 communicates with a gate 214 extending along the opposing surfaces of the mold 201 and the mold 202. The outer end portion of the gate 214 opens to the outside of the mold 201 and the mold 202.

[0036] Further, on the opposing surfaces of the mold 201 and the mold 202, an air vent passage (not shown) for venting the air in the cavity 210 is provided separately from the gate 214. The outer end portion of the air vent passage opens to the outside of the mold 201 and the mold 202.

[0037] The cavity 210 has a plate-like portion 211, a convex portion 212, a recessed portion 213, and a through hole 215. The plate-like portion 211 is where the molten metal flows in and the bottom plate portion 411 is formed.

[0038] The convex portion 212 extends upward in the axial direction from the plate-like portion 211 and is formed in a cylindrical shape. The convex portion 212 is where the molten metal flows in and the pivot post 413 is formed. The convex portion 212 has an annular pedestal convex portion 212a that protrudes radially outward from the circumferential surface of the base portion. The pedestal convex portion 212a is where the molten metal flows in and the pedestal portion 413a is formed.

[0039] The recessed portion 213 faces the convex portion 212 in the vertical direction, and is formed by the lower surface of the plate-like portion 211 protruding upward in the axial direction. When molten metal flows into the plate-like portion 211 due to the recessed portion 213, the concave portion 411a is formed. The diameter of the recessed portion 213 is gradually formed smaller as it goes upward in the axial direction. Further, the recessed top surface portion 213a disposed at the tip portion on the upper side in the axial direction of the recessed portion 213 is formed substantially parallel to the lower surface of the plate-like portion 211.

[0040] The through hole 215 extends upward in the axial direction from the upper end of the convex portion 212 and opens to the outside of the mold 201. The inner diameter of the through hole 215 and the inner diameter of the convex portion 212 are substantially the same. A squeeze pin 100 is inserted into the through hole 215. The squeeze pin 100 is slidable in the axial direction inside the through hole 215. At this time, the lower end portion of the squeeze pin 100 can be inserted into the convex portion 212.

[0041] In step S2, molten metal is injected into the cavity 210 through the gate 214. The molten metal is, for example, a molten aluminum alloy. When the molten metal is injected into the cavity 210, the air inside the cavity 210 or the gas generated from the molten metal is pushed out from the air vent passage to the outside of the mold 201 and the mold 202. As a result, the molten metal spreads throughout the cavity 210.

[0042] At this time, due to the recessed portion 213, the flow of the molten metal changes its direction upward and it becomes easier for the molten metal to flow into the convex portion 212. Thereby, the generation of shrinkage cavities in the pivot post 413 can be reduced. The diameter of the recessed portion 213 is gradually formed smaller as it goes upward in the axial direction, and the flow of the molten metal can be smoothly redirected upward.

[0043] In step S3, after the molten metal has spread throughout the cavity 210, the molten metal is cooled and hardened. As a result, a base body 41a (see FIG. 7) is formed within the cavity 210. A chill layer (not shown) is formed on the surface of the base body 41a. The chill layer is formed at a location where hardening occurs quickly in contact with the molds 201 and 202 when the molten metal hardens. The chill layer, where the effect of the molten metal is faster than other parts, has less impurities and a high metal density.

[0044] Also, as shown in FIG. 7, the squeeze pin 100 is pushed into the convex portion 212, and while locally pressing the tip of the pivot post 413 in the axial direction within the mold 201, the pivot post 413 is cooled and hardened. As a result, for the pivot post 413, a part of the die-cast member is segregated, and the generation of shrinkage cavities can be further reduced.

[0045] In step S4, as shown in FIG. 8, the base body 41a is removed from the pair of molds 201 and 202. At this time, the peripheral wall portion 412 has a gate trace portion 41d protruding from the outer surface. The gate trace portion 41d is formed by the hardening of the molten metal accumulated in the gate 214 and the air vent passage (not shown).

[0046] In step S5, the gate trace portion 41d is cut. The gate trace portion 412a after cutting the gate trace portion 41d slightly protrudes from the outer surface of the peripheral wall portion 412 and a trace remains.

[0047] In step S6, as shown in FIG. 9, an electrodeposition coating film 41b is formed on the surface of the base body 41a. For the electrodeposition coating film 41b, for example, the base body 41a is immersed in a coating material of an epoxy resin-based, and a current is passed between the coating material and the base body 41a. As a result, the coating material adheres to the surface of the base body 41a, and the electrodeposition coating film 41b is formed on the surface of the base body 41a. At this time, the outer surface of the gate trace portion 412a is also covered with the electrodeposition coating film 41b.

[0048] In step S7, as shown in FIG. 10, among the surfaces of the base body 41a, the pivot post 413 that requires precision is precision machined and shaped by cutting.

[0049] By cutting the surface of the base body 41a, the electrodeposition coating film 41b is also cut, and a second machined surface 72 is formed on the surface of the base body 41a. That is, on at least a part of the peripheral surface of the pivot post 413, a second machined surface 72 on which the surface of the base body 41a is machined is formed. In the present embodiment, the second machined surface 72 is formed on the entire peripheral surface of the pivot post 413, and on the second machined surface 72, the surface of the base body 41a is exposed from the electrodeposition coating film 41b.

[0050] Also, in step S7, the entire outer periphery of the peripheral wall portion 412 including the gate trace portion 412a formed when the gate trace portion 41d was cut in step S5 is cut and shaped. At this time, the electrodeposition coating film 41b on the outer peripheral surface of the peripheral wall portion 412 is cut, and a first machined surface 71 is formed. That is, on at least a part of the peripheral wall portion 412, a first machined surface 71 on which the surface of the base body 41a is machined is formed so as to include at least a part of the gate trace portion 412a. In the present embodiment, on the first machined surface 71, the surface of the base body 41a is exposed from the electrodeposition coating film 41b. Further, the first machined surface 71 includes at least a part of the gate trace portion 412a and is formed on the entire outer periphery of the peripheral wall portion 412. Thereby, the gate trace portion 412a formed by accumulating in the gate 214 and the air vent passage (not shown) can be shaped by a series of operations. Therefore, the workability in the cutting process is improved.

[0051] In the present embodiment, the first machined surface 71 is formed on the entire outer periphery of the peripheral wall portion 412, but the first machined surface 71 may be formed only on one surface including the gate trace 412a of the peripheral wall portion 412. Further, the first machined surface 71 may be formed across one surface including the gate trace 412a of the peripheral wall portion 412 and at least one surface adjacent to the one surface.

[0052] Also, in step S7, the gate trace portion 412a is removed by cutting and the trace disappears, but in order to explain the trace where the gate was connected during casting, the gate trace portion 412a is shown by a broken line in the figure.

[0053] In step S8, the base body 41a is immersed in an impregnating agent. At this time, the impregnating agent infiltrates at least a part of the second machined surface 72 where the electrodeposition coating film 41b is cut and at least a part of the first machined surface 71. As the impregnating agent, for example, an epoxy resin or an acrylic resin is used. Thereby, minute cavities formed on the surface of the base body 41a are sealed with the impregnating agent at least in part of the second machined surface 72 and at least in part of the first machined surface 71. Thereby, it is possible to prevent the helium gas filled inside the housing 40 from leaking to the outside through the second machined surface 72 and the first machined surface 71.

[0054] Note that the impregnating agent has a lower viscosity than the coating material for forming the electrodeposition coating film 41. Therefore, the impregnating agent is more likely to infiltrate into minute cavities formed on the surface of the base body 41a than the coating material for forming the electrodeposition coating film 41.

[0055] As described above, the manufacturing method of the base plate 41, which is a casting product and is a part of the housing 40 of the disk drive device 1, has a casting process, an electrodeposition coating process, a cutting process, and an impregnation process in this order. In the casting process, the base body 41a having the bottom plate portion 411 and the pivot post 413 is integrally cast by the molds 201 and 202 (steps S1 to S4). In the electrodeposition coating process, an electrodeposition coating film 41b is formed on the surface of the base body 41a (step S6). In the cutting process, the pivot post 413 is cut and shaped (step S7). In the impregnation process, after the cutting process, the impregnating agent is impregnated into the machined surface where the surface of the base body 41a is exposed from the electrodeposition coating film 41b (step S8).

[0056] In the casting process, by locally pressing the tip of the pivot post 413 in the axial direction and cooling and curing the pivot post 413, part of the die-cast member of the pivot post 413 segregates, and the generation of shrinkage cavities can be further reduced.

[0057] (4. Modification example) FIG. 11 is an explanatory diagram showing a modified example of the manufacturing process of the base plate 41. The through hole 315 is provided in the mold 202. The through hole 315 communicates with the plate-like portion 211 and extends axially downward from the upper end of the recessed portion 213. The lower end of the through hole 315 opens to the outside of the mold 202. The squeeze pin 100 is inserted into the through hole 315. The squeeze pin 100 is axially slidable inside the through hole 315. At this time, the upper end portion of the squeeze pin 100 can be inserted into the plate-like portion 211.

[0058] In step S4, the squeeze pin 100 is pushed into the plate-like portion 211, and while locally pressing the lower surface of the bottom plate portion 411 axially opposed to the pivot post 413 in the mold 201, the pivot post 413 is cooled and hardened. Thereby, a part of the die-cast member of the pivot post 413 is segregated, and the generation of shrinkage cavities can be further reduced.

[0059] At this time, the recessed top surface portion 213a is formed substantially parallel to the lower surface of the plate-like portion 211. Thereby, the squeeze pin 100 can be brought into contact with the recessed top surface portion 213a and uniformly pressed axially upward. Thereby, the generation of shrinkage cavities in the pivot post 413 can be further reduced.

[0060] (5. Others) The above embodiments are merely examples of the present invention. The configurations of the embodiments may be appropriately changed without exceeding the technical idea of the present invention. Also, the embodiments may be implemented in combination within a possible range. For example, in the present embodiment, the concave portion 411a is formed on the lower surface of the bottom plate portion 411, but the bottom plate portion 411 may have a flat lower surface axially opposed to the pivot post 413. Thereby, it becomes easier to axially press the lower surface of the bottom plate portion 411 with the squeeze pin 100. Therefore, the workability in the pressing process is improved.

Industrial Applicability

[0061] According to the present invention, it can be used for a housing used in a disk drive device such as a hard disk drive.

Explanation of Reference Numerals

[0062] 1 Disk drive device 2 Spindle motor 10 Stationary part 12 Stator 12a Stator core 12b Coil 12c Teeth 13 Bearing unit 20 Rotating part 21 Shaft 22 Hub 22a Outer peripheral part 23 Magnet 30 Access part 31 Head 32 Arm 32a Bearing 33 Rocking mechanism 40 Housing 41 Base plate 41a Base body 41b Electroplated coating film 41d Gate trace part 42 Cover 50 Disk 71 First machined surface 72 Second machined surface 100 Squeeze pin 201, 202 Dies 210 Cavity 211 Plate-like part 212 Protrusion 213 Depression 213a Depression top surface 214 Gate 215, 315 Through hole 411 Bottom plate part 411a Recess 411b Top surface 412 Peripheral wall part 412a Gate trace part 413 Pivot post 413a Pedestal part C Rotation axis D Rocking axis

Claims

1. A base plate that forms part of the housing of a disk drive device, comprising a base body made of a metal die-cast member, and an electrodeposition coating film covering at least a part of the surface of the base body. The base body has a bottom plate portion that is rectangular when viewed in the axial direction, and a pivot post, wherein the bottom plate portion extends vertically with respect to the rotation axis of the disk that extends vertically, and the swing axis of the head that is arranged at a position different from the rotation axis and extends vertically and reads or writes information to / from the disk. The pivot post projects upward from the upper surface of the bottom plate portion along the swing axis, and a part of it is segregated. This is the base plate.

2. The base plate according to claim 1, wherein the bottom plate portion has a recess formed by concaving the lower surface facing the pivot post in the upper side in the axial direction.

3. The base plate according to claim 2, wherein the inner diameter of the recess becomes smaller as it goes toward the upper side in the axial direction.

4. The base plate according to claim 2 or claim 3, wherein the recess is arranged at the tip portion on the upper side in the axial direction and has a top surface portion that is substantially parallel to the lower surface of the bottom plate portion.

5. The pivot post has an annular pedestal portion that projects radially outward from the peripheral surface of the root portion, and the diameter of the top surface portion is substantially the same as the outer diameter of the root portion at the upper end of the pedestal portion of the pivot post or larger than the outer diameter of the root portion at the upper end of the pedestal portion of the pivot post. This is the base plate according to claim 4.

6. The base plate according to claim 1, wherein the lower surface of the bottom plate portion facing the pivot post in the axial direction is formed flush.

7. The base body has a peripheral wall portion that extends upward from the outer peripheral edge of the bottom plate portion and surrounds the bottom plate portion, and the peripheral wall portion has a gate mark portion where a gate was connected during casting, and the gate mark portion is arranged on the outer surface of the peripheral wall portion that intersects the parallel direction in which the rotation axis and the swing axis are aligned and faces the rotation axis, and a first machined surface obtained by machining the surface of the base body is formed on at least a part of the peripheral wall portion so as to include at least a part of the gate mark portion. This is the base plate according to any one of claims 1 to 6.

8. The peripheral wall portion The base plate according to claim 7, wherein the first machined surface is formed across one surface of the peripheral wall portion including the gate mark portion and at least one surface adjacent to the one surface.

9. The base plate according to claim 7, wherein the first machined surface is formed on the entire outer circumference of the outer surface of the peripheral wall portion.

10. The base plate according to any one of claims 7 to 9, wherein an impregnating agent is infiltrated in at least a part of the first machined surface.

11. The base plate according to any one of claims 1 to 10, wherein a second machined surface, on which the surface of the base body is machined by cutting, is formed on at least a part of the circumferential surface of the pivot post.

12. The base plate according to claim 11, wherein an impregnating agent is infiltrated in at least a part of the second machined surface.

13. The base plate according to claim 10 or claim 12, wherein the impregnating agent is an epoxy resin.

14. The base plate according to claim 10 or claim 12, wherein the impregnating agent is an acrylic resin.

15. A spindle motor including the base plate according to any one of claims 1 to 14.

16. The spindle motor according to claim 15, a disk that rotates about the rotation axis by the spindle motor, and a head that swings about the swing axis and reads or writes information to / from the disk. A disk drive device comprising:

17. The hard disk device according to claim 16, wherein a gas having a lower density than air is filled inside the housing.

18. A method for manufacturing a base plate that is part of a housing of a disk drive device, a casting step of integrally casting a base body having a bottom plate portion that extends vertically and expands perpendicular to a rotation axis of a disk that extends vertically and a swing axis of a head that is arranged at a position different from the rotation axis and extends vertically and reads or writes information to / from the disk, and that has a rectangular shape when viewed from the axial direction, a pivot post that projects upward from the upper surface of the bottom plate portion along the swing axis, using a mold; an electrodeposition coating step of forming an electrodeposition coating film on the surface of the base body; a cutting step of cutting and shaping the pivot post, in that order, In the casting step, the pivot post is cooled and hardened while locally pressing the tip of the pivot post or the lower surface of the bottom plate portion facing the pivot post in the axial direction in the mold. A method for manufacturing a base.

19. After the cutting step, The method for manufacturing a base according to claim 18, comprising an impregnation step of impregnating an impregnating agent into a processed surface where the surface of the base body is exposed from the electrodeposition coating film.

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