JP2002223539A - Yoke-integrated rotating magnet and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To firmly fit a cylindrical magnet integrally with a cylindrical yoke and inhibit degradation in the magnetic properties of the cylindrical magnet. SOLUTION: The cylindrical yoke 12, of which the internal diameter is smaller than the external diameter of the cylindrical magnet 14 at an ordinary temperature is placed on a heating table and heated to a prescribed temperature for thermal expansion, until the cylindrical magnet 14 can be fit into the cylindrical yoke 12. The cylindrical magnet 14 is fit into the cylindrical yoke 12. When the cylindrical yoke is cooled to the ordinary temperature under this condition, the yoke 12 shrinks, so that the internal periphery may be crimped onto the outer periphery of the cylindrical magnet 14, and the yoke 12 and the magnet 14 are fitted and fixed to each other. Because the coefficient of thermal expansion of the cylindrical yoke 12 is high, the jointing strength of the yoke 12 to the magnet 14 becomes high, so that the yoke 12 can be fit integrally firmly with the magnet 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a yoke-integrated rotary magnet in which a cylindrical magnet is integrally fitted inside a cylindrical yoke, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Hard disk drives (hereinafter "HD")
D), the yoke-integrated rotary magnet for the spindle motor used for the spindle motor is made of a magnetic material on the outside of a cylindrical magnet (rare-earth bonded magnet) formed by mixing a rare-earth magnetic powder and a resin into a cylindrical shape. A cylindrical yoke is externally fitted with a predetermined clearance, and an adhesive is injected into the clearance between the two. A hardening of the adhesive forms a structure in which the cylindrical magnet and the cylindrical yoke are integrally bonded. I have.

[0003] In the HDD, higher capacity and higher storage density have been developed, and accordingly, improvement in data reading accuracy has been required. In other words, the yoke-integrated rotary magnet for the spindle motor, which is one of the components of the HDD, also requires strict accuracy in dimensions such as roundness, coaxiality, and cylindricity. Incidentally, the roundness refers to the size of the cross section perpendicular to the axis of the cylindrical magnet or the cylindrical yoke deviating from the geometric circle. The term "coaxiality" refers to a magnitude in which the axis of a cylindrical magnet or a cylindrical yoke deviates from a geometrical axis straight line. Further, the cylindricity refers to a size in which a cylindrical magnet or a cylindrical yoke deviates from a geometric cylindrical shape.

[0004] However, conventionally, between 20 and 30 μm for injecting an adhesive between the cylindrical magnet and the cylindrical yoke.
If the clearance is not maintained evenly at the time of bonding, a center deviation occurs between the cylindrical magnet and the cylindrical yoke after integration, resulting in a dynamic imbalance during high-speed rotation. May occur. As a result, there is a possibility that a data reading error or noise occurs during rotation. That is, the conventional manufacturing method cannot sufficiently meet the strict dimensional accuracy required for the yoke-integrated rotary magnet. In addition, the use of an adhesive may cause the components contained in the adhesive to evaporate and adhere to the disk or the inside of the motor, which may have an adverse effect, and there is also a problem that is inappropriate for a spindle motor requiring high cleanliness. are doing.

[0005] To cope with the above-mentioned problem, Japanese Patent Application Laid-Open No. 2000-184624 exists. The manufacturing method described in this publication is based on a method in which a cylindrical magnet having an outer diameter smaller than the inner diameter of the yoke is disposed inside the cylindrical yoke, and both are heated to cause the cylindrical magnet to oxidize and expand. The cylindrical magnet and the cylindrical yoke are integrally fitted and fixed without using an adhesive by press-fitting the inner peripheral surface of the cylindrical magnet. That is, according to this manufacturing method, since no adhesive is used, there is no need to provide the above-described clearance which causes a decrease in various dimensional accuracy, and the device can sufficiently cope with the required severe dimensional accuracy.

[0006]

SUMMARY OF THE INVENTION
When the rare-earth bonded magnet is heated in the atmosphere, it undergoes oxidative expansion, and utilizes the property of maintaining its expanded shape even when cooled. However, since the amount of oxidative expansion of the rare-earth bonded magnet is small, the joining strength between the cylindrical magnet and the cylindrical yoke integrated using only the oxidative expansion is low,
There is a case where both cannot be firmly integrated. In addition, when the rare-earth bonded magnet is heated to a high temperature, its magnetic properties deteriorate due to oxidation or the like, so that a problem of demagnetization in the obtained product (yoke-integrated rotary magnet) is pointed out.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems inherent in the prior art, and has been proposed to solve the problem suitably. It is an object of the present invention to provide a yoke-integrated rotary magnet and a method of manufacturing the yoke-integrated rotary magnet, which can achieve high integration and can suppress a decrease in magnetic characteristics of the cylindrical magnet.

[0008]

[Means for solving the problems] To overcome the above-mentioned problems,
In order to suitably achieve the intended purpose, the yoke-integrated rotary magnet according to the present invention has the cylindrical magnet fitted inside a cylindrical yoke having an inner diameter smaller than the outer diameter of the cylindrical magnet at room temperature,
The two are integrated by a contraction force that returns to the original shape by cooling after thermal expansion of the cylindrical yoke.

In order to overcome the above-mentioned problems and to appropriately achieve the intended object, a method for manufacturing a yoke-integrated rotary magnet according to another invention of the present application has an inner diameter smaller than the outer diameter of a cylindrical magnet at room temperature. In a state where the cylindrical yoke is heated and the yoke is thermally expanded, the cylindrical magnet is fitted into the inside of the cylindrical yoke, and then the cylindrical yoke is cooled to be contracted by cooling. The surface is pressed against the outer peripheral surface of the cylindrical magnet, and the cylindrical yoke and the cylindrical magnet are integrally fitted.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a yoke-integrated rotary magnet and a method of manufacturing the same according to the present invention will be described with reference to preferred embodiments.

FIG. 1 shows a yoke-integrated rotary magnet according to an embodiment.
, A cylindrical magnet 14 made of a rare-earth bonded magnet is fitted. The inner diameter of the cylindrical yoke 12 is set to be smaller than the outer diameter of the cylindrical magnet 14 at room temperature. The cylindrical yoke 12 is integrated. The cylindrical yoke 1
2 is made of free-cutting steel, stainless steel, etc., and is formed in a cylindrical shape. Various dimensions (inner / outer diameter, height, roundness, coaxiality, cylindricity, etc.) are set to high precision by machining. Is done. The cylindrical magnet 14 is made of Nd-Fe-B magnet or Sm
-A mixture obtained by mixing a rare earth magnet powder such as a Co magnet and a resin such as an epoxy resin or nylon into a cylindrical shape by press molding or injection molding. The yoke-integrated rotary magnet 10 is suitably used for a spindle motor used in the HDD.

The difference α between the outer diameter (A) of the cylindrical magnet 14 and the inner diameter (A-α) of the cylindrical yoke 12 is
Is set in accordance with the coefficient of linear expansion of the material constituting, for example, about 20 to 40 μm at room temperature.

Next, a method of manufacturing the yoke-integrated rotary magnet 10 will be described. First, the cylindrical yoke 1
2 is placed on a heating table 16 having a built-in heater and heated to a predetermined temperature, as shown in FIG. 2A, until the cylindrical magnet 14 can be fitted inside the cylindrical yoke 12. Inflate. Next, the cylindrical magnet 14 is fitted inside the cylindrical yoke 12. At this time, a small clearance (for example, 20 to 30 μm) exists between the outer peripheral surface of the cylindrical magnet 14 and the inner peripheral surface of the cylindrical yoke 12 (see FIG. 2B). When the cylindrical yoke 12 is cooled to room temperature in this state, the yoke 12 contracts and its inner peripheral surface is pressed against the outer peripheral surface of the cylindrical magnet 14.
14 is fitted and fixed integrally. In this case, since the thermal expansion of the cylindrical yoke 12 is larger than the oxidative expansion of the cylindrical magnet 14, the bonding strength between the yoke 12 and the cylindrical magnet 14 can be increased as compared with the conventional technology. , Both 1
2, 14 can be firmly and integrally fitted.

The dimensional accuracy of the cylindrical yoke 12
(Circularity, coaxiality, cylindricity, etc.) are high, and the cylindrical yoke 12 shrinks uniformly (see FIG. 2 (c)). The shape is corrected by following the inner peripheral surface of the yoke 12. That is, even when the dimensional accuracy (roundness, coaxiality, cylindricity, etc.) of the cylindrical magnet 14 is inferior to the dimensional accuracy of the cylindrical yoke 12, the cylindrical magnet 14 is corrected and the dimensional accuracy is reduced. Is improved to about the dimensional accuracy of the cylindrical yoke 12. Furthermore, since the cylindrical magnet 14 composed of a rare earth bonded magnet whose magnetic properties may be deteriorated by high-temperature heating is not heated during the manufacturing process, the magnetic properties of the magnet 14 are not reduced, and the manufactured yoke is not produced. The demagnetization of the integrated rotary magnet 10 is prevented. In addition, the yoke-integrated rotary magnet 10 of the embodiment includes the cylindrical magnet 14 and the cylindrical yoke 1.
Since no adhesive is used for fixing to the second component, no trouble occurs due to volatilization of components contained in the adhesive, and the production efficiency is improved by omitting the bonding step.

Here, as in the embodiment, the cylindrical yoke 1
2. The necessary and sufficient dimensional accuracy and joining strength can be obtained without lowering the magnetic characteristics by integrally fitting the cylindrical magnets 14 using the contraction force that returns to the original shape by cooling after the thermal expansion of 2. Although it is possible, if necessary, a step of oxidizing and expanding the cylindrical magnet 14 by heating the entire yoke-integrated rotary magnet 10 manufactured (Japanese Patent Laid-Open No. 2000-18484).
If the manufacturing method disclosed in Japanese Patent Publication No. 2 is added, the joining strength can be further increased. Moreover, in this case, since the cylindrical magnet 14 and the cylindrical yoke 12 are already integrated with a high bonding strength, the heating temperature for oxidizing and expanding the cylindrical magnet 14 can be suppressed low, and the magnetic characteristics are improved. The decrease can be suppressed. The cylindrical yoke 12
Is not limited to the heater method, and an appropriate heating method such as an induction heating method can be adopted. Further, the magnet material forming the cylindrical magnet 14 is not limited to the rare-earth bonded magnet, and other materials such as a ferrite bonded magnet can be used.

[0016]

[Test Example] A mixture of Nb-Fe-B magnet powder and 3% by weight of epoxy resin was press-molded to produce a cylindrical magnet having an inner diameter of 17 mm and an outer diameter of 19 mm. A cylindrical yoke having an inner diameter of 18.96 mm and an outer diameter of 21.2 mm was manufactured using "stainless steel (JIS SUS403)". Then, the invention example of the yoke-integrated rotary magnet in which the cylindrical magnet and the cylindrical yoke are manufactured by the manufacturing method of the above-described embodiment, and a conventional manufacturing method (Japanese Patent Application Laid-Open No.
Table 1 shows the following test results (1) to (5) for a comparative example of the yoke-integrated rotary magnet manufactured by the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 0-184622). The coaxiality and cylindricity of each inner peripheral surface of the cylindrical magnet, the cylindrical yoke, and the fitted yoke-integrated rotary magnet (inventive example, comparative example) were measured in accordance with JIS (B0621). Using a tensile tester, a yoke-integrated rotary magnet (inventive example,
The pressure when the cylindrical magnet and the cylindrical yoke of Comparative Example) are separated from each other in the axial direction, and the cylindrical magnet comes off from the cylindrical yoke.
(Joint strength) was measured. 13.7k of yoke-integrated rotating magnet (inventive example, comparative example)
The surface magnetic flux density when the inner circumference was magnetized by the magnetizing current of A was measured. The heating condition of the cylindrical yoke in the invention example was 280.
° C, and the heating condition of the cylindrical yoke and the cylindrical magnet in the comparative example was 150 ° C.

[0017]

From the above-described results, the invention example and the comparative example show that the coaxiality and the cylindricity of the inner peripheral surface of the cylindrical magnet after fitting are significantly larger than those of the cylindrical magnet alone. It was confirmed that the dimensional accuracy of the invention example was further improved than that of the comparative example. In addition, the bonding strength and the surface magnetic flux density of the invention examples were higher than those of the comparative examples. In other words, it has been confirmed that the increased joint strength provides a better correction effect of the cylindrical magnet by the cylindrical yoke with high dimensional accuracy, and prevents the magnetic properties from being lowered by heating the cylindrical magnet. Was.

[0019]

As described above, according to the yoke-integrated rotary magnet and the method of manufacturing the same according to the present invention, the cylindrical yoke having a larger thermal expansion compared to the cylindrical magnet has a cylindrical shrinkage force caused by cooling. Since the cylindrical magnet and the cylindrical yoke are integrated, the joining strength between them can be increased. Further, there is an advantage that the dimensional accuracy of the yoke-integrated rotary magnet is improved due to the increase in the bonding strength. Further, since the cylindrical magnet is not heated, when the cylindrical magnet is formed by the rare earth bonded magnet, it is possible to prevent the magnetic properties from being deteriorated due to the heating.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a yoke-integrated rotary magnet according to an embodiment.

FIG. 2 is a process chart of a method for manufacturing a yoke-integrated rotary magnet according to an example.

[Explanation of symbols]

 12 Cylindrical yoke 14 Cylindrical magnet

Claims (4)

[Claims] 1. A cylindrical magnet (14) is fitted inside a cylindrical yoke (12) having an inner diameter smaller than the outer diameter of the cylindrical magnet (14) at room temperature, and both (12, 14) are cylindrical. A yoke-integrated rotary magnet, wherein the yoke (12) is integrated by a shrinking force that returns to an original shape by cooling after thermal expansion of the yoke (12). 2. The yoke-integrated rotary magnet according to claim 1, wherein said cylindrical magnet is made of a rare-earth bonded magnet. 3. A cylindrical yoke (12) having an inner diameter smaller than the outer diameter of the cylindrical magnet (14) is heated at room temperature to thermally expand the yoke (12). The cylindrical magnet (14) is inserted into the inside of the cylindrical magnet, and then the cylindrical yoke (12) is contracted by cooling, and the inner peripheral surface of the yoke (12) is pressed against the outer peripheral surface of the cylindrical magnet (14). And a cylindrical yoke (12) and a cylindrical magnet (14) are integrally fitted together. 4. The method of manufacturing a yoke-integrated rotary magnet according to claim 3, wherein said cylindrical magnet is made of a rare earth bonded magnet.