JP7333234B2 - Base member, spindle motor and hard disk drive - Google Patents

Description

The present invention relates to a base member of electronic equipment, such as a hard disk drive, in which a low-density gas such as helium gas is sealed, and more particularly to a technology for preventing leakage of the low-density gas from the base member to the outside. The present invention also relates to a spindle motor and a hard disk drive using the base member.

A hard disk drive accommodates a plurality of hard disks to increase the capacity. In order to suppress the increase in size accompanying the increase in capacity, the distance between the hard disks is minimized. As a result, the resistance between the air existing between the hard disks and the rotating hard disk is increased, which adversely affects the performance of the hard disk drive, such as an increase in the power consumption of the hard disk drive. In order to avoid such a problem, conventionally, a gas having a lower density than air, such as helium gas, has been sealed inside the hard disk drive.

By the way, inside the base member of a hard disk drive manufactured by die casting, cavities (cast cavities) may be formed during casting. It has been reported that the low-density gas enclosed inside may leak through the cavities (for example, Patent Document 1). As a means for preventing leakage of low-density gas, in Patent Document 1, by forming an impregnated resin layer that fills the pores on the surface of the base member made of aluminum die-cast, leakage of low-density gas through the pores of the base member. prevent

JP 2017-75340 A

However, forming an impregnated resin layer on the base member as described in Patent Document 1 results in a relatively high manufacturing cost. On the other hand, if the formation of cavities during casting of the base member can be suppressed, leakage of the low-density gas can be prevented.

The present invention has been made in view of the above circumstances, and is capable of suppressing the formation of cavities during casting of the base member and preventing leakage of the low-density gas when the low-density gas is sealed inside. It is an object of the present invention to provide a base member, a spindle motor and a hard disk drive.

In the die casting of the base member, the mold is provided with a first gate and a second gate, and molten metal is injected into the cavity through the first gate. Since the area of the second gate is set smaller than the area of the first gate, excess molten metal is discharged from the second gate after the molten metal fills the cavity. After the molten metal is cooled and solidified in the cavity, the mold is opened, the base member is taken out, and the solidified portion remaining on the runner leading to the first and second gates is removed by machining. The parts corresponding to the first gate and the second gate of the base member remain marks due to the machining, so in the following description, these parts are referred to as "first gate part" and "second gate part".

As a result of investigations by the inventors, it has been found that cavities tend to form on the second gate portion side of the base member. From such events, the inventors of the present invention came to the conclusion that, in the vicinity of the second gate on the downstream side of the flow of the molten metal, the molten metal stagnates and entrains air to form cavities. Based on this, the present inventor has arrived at the inference that if the flow speed of the molten metal is increased on the downstream side of the flow of the molten metal, the formation of cavities can be suppressed. Therefore, the present inventor investigated the air content in the base member using casting process simulation software. found that the air content in the base member can be reduced.

The present invention has been made based on the above findings, and includes a die-cast base member, the base member having a rectangular plate-shaped bottom portion having short sides and long sides and edge portions around the entire circumference of the bottom portion. a side wall portion extending in a direction orthogonal to the bottom portion from the bottom portion; and a rib portion projecting from the entire circumference of the end surface of the side wall portion in a direction orthogonal to the bottom portion, wherein the thickness of the rib portion is smaller than the thickness of the side wall portion, The side wall portion has a first end portion on the short side provided with the first gate portion corresponding to the inlet of the molten metal, and the side wall portion of the molten metal located on the opposite side of the first end portion and having a smaller area than the first gate portion. The base member has a second end provided with a second gate corresponding to the outlet, and the rib portion is a base member whose thickness gradually decreases in a tapered manner from the first end toward the second end. be.

In the present invention, since the thickness of the rib portion gradually decreases from the first end side to the second end side, the cross-sectional area of the flow path of the molten metal decreases in the direction in which the molten metal flows. Increases flow speed. Therefore, entrainment of air caused by stagnation of the molten metal can be suppressed, thereby suppressing the formation of cavities.

Further, the present invention is a die-cast base member, the base member having a rectangular plate-shaped bottom portion having short sides and long sides and extending in a direction orthogonal to the bottom portion from the edge of the entire circumference of the bottom portion. A side wall portion and a rib portion protruding in a direction orthogonal to the bottom portion from the entire circumference of the end surface of the side wall portion, the thickness of the rib portion being smaller than the thickness of the side wall portion, and the side wall portion having a circular inner peripheral surface. A base member comprising a circular portion having a shape and a rectangular portion having a rectangular inner peripheral surface shape, wherein the rib portion is a base member whose thickness gradually decreases in a tapered manner from the circular portion side toward the rectangular portion side. .

When the base member of the present invention is used in, for example, a hard disk drive, the hard disk is accommodated in the circular portion and the data read/write mechanism is accommodated in the rectangular portion. Since the circular part has a simple structure with fewer members to be fixed than the rectangular part, by providing the first gate part, which is the inlet side for pouring the molten metal, on the outer wall part on the short side of the circular part side, the molten metal can be injected more smoothly.

Here, according to the study of the present inventor, it has been found that the formation of cavities can be more effectively suppressed when the angle formed by the inner wall portion and the outer wall portion of the rib portion is 0.3 to 1.5°. . Therefore, it is desirable that the angle formed by the inner wall portion and the outer wall portion of the rib portion is 0.3 to 1.5°. More preferably, it is 0.5 to 0.8°.

The present invention is a spindle motor comprising the above base member, a stator fixed to the base member, and a rotor rotatably supported with respect to the stator. The present invention also provides a hard disk drive comprising such a spindle motor having a plurality of hard disks and a base member having a read/write mechanism for writing data to and reading data from the hard disks. Furthermore, this hard disk drive can be filled with gas such as helium gas, which has a lower density than air.

According to the present invention, there are provided a base member, a spindle motor, and a hard disk drive that can suppress the formation of cavities during casting and prevent leakage of the low-density gas when the low-density gas is sealed inside. can provide.

(A) is a plan view showing a base member according to an embodiment of the present invention, and (B) is a cross-sectional view showing a modified example of rib portions. It is a perspective view which shows the base member of embodiment of this invention. FIG. 4 is a partially enlarged perspective view showing the base member of the embodiment of the present invention; It is a sectional view showing a spindle motor of an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the hard disk drive of embodiment of this invention, (A) is a top view of the state which removed the cover, (B) is sectional drawing.

1. Base Member One embodiment of the base member of the present invention will now be described with reference to FIGS. In the figure, reference numeral 10 denotes a base member of the embodiment, and the base member 10 is manufactured by die-casting an aluminum alloy. Reference numeral 11 denotes a bottom portion, and the bottom portion 11 has a rectangular plate shape having short sides and long sides. A side wall portion 12 extending in a direction orthogonal to the bottom portion 11 is formed around the entire circumference of the bottom portion 11 .

The side wall portion 12 includes a circular portion 12a having an inner peripheral surface shape that conforms to the shape of the hard disk, and a rectangular portion 12b having a rectangular shape that accommodates a mechanism for writing data to and reading data from the hard disk. In addition, the outer wall portion on the short side of the side wall portion 12 has a first gate portion 12c as a machining trace of the first gate of the die casting mold, and the outer wall portion on the short side opposite to the first gate portion 12c. has a second gate portion 12d as a machining trace of the second gate of the die casting mold. Since the area of the second gate is smaller than the area of the first gate, the area of the second gate portion 12d is smaller than the area of the first gate portion 12c.

A rib portion 13 is formed on an upper surface (end surface) 12 e of the side wall portion 12 so as to be flatly continuous with the outer wall portion of the side wall portion 12 . The thickness of rib portion 13 is set smaller than the thickness of side wall portion 12 . In addition, the thickness of the long side portion of the rib portion 13 gradually decreases in a tapered manner from the first gate portion 12c side toward the second gate portion 12d side. Specifically, the angle θ between the inner wall portion 13a and the outer wall portion 13b of the rib portion 13 is set to 0.3 to 1.5°. In the drawing, reference numeral 15 denotes a shaft used when the base member 10 is used in a hard disk drive, and reference numeral 18 denotes a support for fixing the data read/write mechanism of the hard disk drive. These shaft 15 and strut 18 are integrally die-cast with the base member 10 .

In the base member 10 configured as described above, the end portion on the side of the first gate portion 12c is the first end portion 10c of the present invention, and the end portion on the side of the second gate portion 12d is the second end portion 10d. In the base member 10 configured as described above, the thickness of the rib portion 13 gradually decreases in a tapered manner from the first end portion 10c toward the second end portion 10d. , the cross-sectional area of the flow path of the molten metal becomes smaller in the direction in which the molten metal flows, and the flow speed of the molten metal increases. Therefore, entrainment of air caused by stagnation of the molten metal can be suppressed, thereby suppressing the formation of cavities.

In the above embodiment, the inner wall portion 13a and the outer wall portion 13b forming the rib portion 13 are flat surfaces, but the configuration is not limited to such. In short, it is sufficient that the thickness of the rib portion 13 gradually decreases from the first gate portion 12c side to the second gate portion 12d side, and the inner wall portion 13a and the outer wall portion 13b may be stepped. It may be wavy. Alternatively, the height of the rib portion 13 may decrease from the first gate portion 12c side toward the second gate portion 12d side.

Moreover, although the outer wall portion 13b of the rib portion 13 is flatly continuous with the outer wall portion of the side wall portion 12, it is not limited to such a configuration. For example, as shown in FIG. 1B, the rib portion 13 may be configured to rise from the middle portion in the thickness direction of the upper surface of the side wall portion 12 .

The configuration of the outer wall portion provided with the first gate portion 12c and the second gate portion 12d is not particularly limited, but as in the above embodiment, the first gate portion 12c is located on the short side of the circular portion 12a, It is preferable that the second gate portion 12d is provided on the outer wall portion on the short side of the rectangular portion 12b. Unlike the rectangular portion 12b that accommodates the data read/write mechanism, the circular portion 12a that accommodates the hard disk has a simple structure without fixing members such as the shaft 15 and the support 18. By providing the first gate portion 12c on the outer wall portion on the short side of the circular portion 12a, the molten metal can be poured more smoothly.

2. Spindle Motor FIG. 4 is a sectional view showing a spindle motor 100 according to an embodiment of the present invention using the base member 10 described above. A cylindrical metal (for example, brass) shaft 102 is fixed to the base member 10 by press-fitting or other means. A stator core 103 is fixed to the base member 10 . The stator core 103 is made by laminating a plurality of thin sheets of soft magnetic material (for example, electromagnetic steel sheets) in the axial direction, has an annular shape, and includes a plurality of pole teeth protruding radially outward. A plurality of pole teeth are provided at regular intervals along the circumferential direction, and a coil 104 is wound around each of the pole teeth.

Conical bearing members 201 and 202 are fixed to the shaft 102 , and a rotor 110 is rotatably supported by the bearing members 201 and 202 . The rotor 110 has an outer cylindrical portion 111 , and an annular rotor magnet 112 is fixed to the inner peripheral surface of the outer cylindrical portion 111 . The rotor magnet 112 is magnetized such that portions adjacent to SNSN . . . along the circumferential direction alternately have different polarities. The inner periphery of rotor magnet 112 faces the outer periphery of the pole teeth of stator core 103 with a gap therebetween. By applying a drive current to the coil 104 , the rotor 110 rotates with respect to the shaft 102 fixed to the base member 10 and the stator core 103 .

A sealing member 203 such as a pin is inserted into the hollow portion of 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. The sealing member 203 and the fixing member 204 prevent internal gas from leaking from the shaft 102 .

In the spindle motor 100 configured as described above, the formation of cavities in the base member 10 is suppressed. Gas leakage can be prevented.

3. Hard Disk Drive FIG. 5 is a diagram showing a hard disk drive 400 according to an embodiment of the present invention using the spindle motor 100 described above. A plurality of hard disks 401 are attached to the spindle motor 100 while being spaced apart from each other. 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 . Also, the swing arm 402 is swung by a drive mechanism 404 . A drive mechanism 404 is attached to the column 18 . Such a swing arm 402 is provided for each hard disk 401 . The swing arm 402 , the magnetic head 403 , and the drive mechanism 404 constitute a read/write mechanism 405 for writing and reading data to/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 column 18. FIG.

As shown in FIG. 5B, an inner cover 16 is attached to the base member 10 with screws or the like in a helium gas environment. A sealing material (not shown) such as a gasket is provided between the inner cover 16 and the upper surface 12 e of the side wall portion 12 of the base member 10 . An outer cover 17 is fixed to the upper surface of the rib portion 13 of the base member 10 . The outer cover 17 is welded to the entire periphery of the rib portion 13 by means such as laser welding, as indicated by weld beads 17a. Therefore, the hard disk drive 400 has a double-sealed structure with the inner cover 16 and the outer cover 17 to prevent leakage of the helium gas sealed inside.

In the hard disk drive device 400 configured as described above, the hard disk 401 is rotated by the spindle motor 100 and data is written to and read from the hard disk 401 by the magnetic head 403 . In the hard disk drive device 400 configured as described above, since the formation of cavities in the base member 10 is suppressed, leakage of helium gas through the cavities can be prevented.

In the above embodiment, helium gas is sealed inside the hard disk drive device 400, but other gas with a lower density than air can also be sealed. Alternatively, by attaching the inner cover 16 to the base member 10 under reduced pressure, the internal gas can be made to have a lower specific gravity than air at normal pressure.

The effects of the present invention will be described below with reference to specific examples.
1. EXAMPLE As an example of the present invention, the thickness t1 at the end of the rib portion 13 on the first gate portion 12c side in FIG. The thickness t2 is set to 1.67 mm, and the thickness is set so as to gradually decrease in a tapered manner from the end on the first gate portion 12c side to the end on the second gate portion 12d side, and the casting temperature is set to 650 to A simulation of casting the base member 10 was performed using a casting process simulation software (MAGMASOFT: manufactured by MAGMA) by setting the temperature within the range of 750°C.

The angle θ between the inner wall portion 13a and the outer wall portion 13b of the rib portion 13 in this example was 0.67°. In this simulation, the air content rate was estimated at various locations of the base member 10, and the maximum value of the air content rate and the location where the maximum air content rate was obtained. As a result, the maximum air content was 2.7% by volume at point A shown in FIG. In addition, the air content rate here is volume% which the air per 1 mesh calculated by software occupies.

2. Conventional example Next, as a conventional example, the same conditions as above except that the thickness of the rib portion 13 was uniformly set to 1.67 mm from the end portion on the side of the first gate portion 12c to the end portion on the side of the second gate portion 12d. Then, a simulation of casting the base member 10 was performed. As a result, the maximum air content at point B of the base member 10 shown in FIG. 1 was 3.11% by volume.

3. Comparative Example Further, as a comparative example, a simulation of casting the base member 10 having the rib portion 13 having the tapered structure in the direction opposite to that of the embodiment of the present invention was performed. In this simulation, the thickness t1 at the end of the rib portion 13 on the first gate portion 12c side was set to 1.67 mm, and the thickness t2 at the end of the rib portion 13 on the second gate portion 12d side was set to 3.00 mm. The conditions were the same as above except that the thickness was set so that the thickness gradually increased in a tapered manner from the end on the side of the first gate portion 12c to the end on the side of the second gate portion 12d. As a result, the maximum air content at point C of the base member 10 shown in FIG. 1 was 3.98% by volume.

Table 1 shows the above simulation results. As shown in Table 1, the maximum air content in the example of the present invention is lower than that in the conventional example by 13%. 28% more than that. These results show that the present invention suppresses the occurrence of cavities during casting of the base member 10. From this, the rib portion 13 is moved from the first gate portion 12c side to the second gate portion 12d side. The effect of the present invention in which the thickness gradually decreases was confirmed.

INDUSTRIAL APPLICABILITY The present invention is applicable to electronic devices such as spindle motors and hard disk drives, and base members used therein.

Reference Signs List 10 Base member 10c First end 10d Second end 11 Bottom 12 Side wall 12a Circular part 12b Rectangular part 12c First gate part 12d Second gate Part 12e Upper surface (end surface) 13 Rib portion 13a Inner wall portion 13b Outer wall portion 15 Shaft 16 Inner cover 17 Outer cover 17a Weld bead 18 Post 100 Spindle DESCRIPTION OF SYMBOLS Motor 102... Shaft 103... Stator core 104... Stator coil 110... Rotor 111... Outer cylindrical portion 112... Rotor magnet 201... Bearing member 202... Bearing member 203... Sealing member 204... Fixed member , 400... Hard disk drive, 401... Hard disk, 402... Swing arm, 403... Magnetic head, 404... Drive mechanism, 405... Read/write mechanism, 406... Circuit board, t1... Thickness, t2... Thickness.

Claims (6)

A die-cast base member,
The base member includes a rectangular plate-shaped bottom portion having short sides and long sides, side wall portions extending in a direction orthogonal to the bottom portion from the edges of the entire periphery of the bottom portion, A rib portion protruding in a direction orthogonal to the bottom portion,
the thickness of the rib portion is smaller than the thickness of the sidewall portion;
The side wall has a first end on the short side provided with a first gate corresponding to the entrance of the molten metal;
a second end provided with a second gate portion corresponding to a molten metal outlet having a smaller area than the first gate portion, the second end portion being located on the opposite side of the first end portion;
The rib portion is a base member whose thickness gradually decreases in a tapered manner from the first end side toward the second end side. A die-cast base member,
The base member includes a rectangular plate-shaped bottom portion having short sides and long sides, side wall portions extending in a direction orthogonal to the bottom portion from the edges of the entire periphery of the bottom portion, A rib portion protruding in a direction orthogonal to the bottom portion,
the thickness of the rib portion is smaller than the thickness of the sidewall portion;
The side wall portion includes a circular portion having a circular inner peripheral surface shape and a rectangular portion having a rectangular inner peripheral surface shape,
The rib portion is a base member whose thickness gradually decreases in a tapered manner from the circular portion side toward the rectangular portion side. 3. The base member according to claim 1, wherein the rib portion has an inner wall portion and an outer wall portion, and the angle between the inner wall portion and the outer wall portion is 0.3 to 1.5 degrees. a base member according to any one of claims 1 to 3;
a stator fixed to the base member;
and a rotor rotatably supported with respect to the stator. 5. A hard disk drive comprising a plurality of hard disks in the spindle motor according to claim 4, and a read/write mechanism for writing and reading data to and from said hard disks in said base member. 6. A hard disk drive according to claim 5, wherein a gas having a density lower than that of air is sealed inside.

Images