JPH05109523A - Lightweight yoke - Google Patents

Abstract

PURPOSE:To enable lightweighting of a yoke by forming an electroless Ni plating layer over the surface of a base material where holes of a porous pure iron sinter having a specified porosity are sealed by resin impregnation. CONSTITUTION:A pure iron powder is used to press-mold a compact under a predetermined pressure, and this compact is sintered in a nitrogen atmosphere to form a porous pure iron sinter having a uniform hole distribution density over the whole and a predetermined porosity within a range of 8-20%. Thereafter, holes of the porous pure iron sinter are impregnated with an acrylic resin and sealed; then, it is subjected to shot-blast treatment for removal of a surface deposition resin and to a predetermined machining work, and succesively an electroless Ni plating layer is formed over its surface. The roundness of a projection joint should be 0.2 or more and the same in rectangular crosssectional shape in the monoaxial direction. This design can make a yoke much more lightweight than the prior art molten pure iron yoke and the yoke have demanded performances.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lightweight yoke suitable for use as, for example, a VCM (voice coil motor) yoke of a magnetic disk device.

[0002]

2. Description of the Related Art Conventionally, a yoke manufactured by a plastic working and a mechanical working from a pure iron melting material has been generally used as a yoke of various electronic and electric devices. It is also known to have the shape shown in schematic perspective view in FIG.

[0003]

On the other hand, in recent years, there have been severe demands for weight reduction of various electronic and electric devices, and along with this, there has been a strong demand for weight reduction of the yokes which are these structural members. At present, a yoke made of a pure iron melting material cannot sufficiently satisfy these requirements.

[0004]

Therefore, the present inventors have
From the above-mentioned viewpoint, as a result of research to develop a lightweight yoke, using a normal powder metallurgy method, the vacancy distribution concentration is the same throughout, and a predetermined range of 8 to 20% is obtained. A porous pure iron sintered body having a porosity is formed, and the pores of this porous pure iron sintered body are sealed by resin impregnation, and an electroless Ni plating layer is preferably formed on the surface of the porous pure iron sintered body. 7-18μ
According to the research result, the yoke manufactured by forming with an average layer thickness of m has a performance (permeability) required for the yoke and can be reduced in weight.

The present invention has been made based on the above-mentioned research results, and has the same pore distribution concentration throughout, and has a predetermined porosity within the range of 8 to 20%. This is characterized by a lightweight yoke having a structure in which electroless Ni plating layers are formed on the surface of a base body in which pores of a pure iron sintered body are sealed by resin impregnation.

In the light weight yoke of the present invention, it is desirable that the shape thereof is the same as that of the VCM yoke of the magnetic disk device shown in FIG. This is because the green compact before is formed by press molding, and the dimensional and shape correction of the sintered porous pure iron sintered body is performed by pressing the die.

Further, in the lightweight yoke of the present invention, it is desirable that the root portion of the protrusion has a radius of R0.2 or more, which is the surface adhesion after the sealing treatment by the resin impregnation of the porous pure iron sintered body. This is because the resin is removed by shot blasting, and the effect of the shot that the radius is smaller than R0.2 is not exerted, resulting in insufficient resin removal.

Further, in the lightweight yoke of the present invention,
The porosity of the porous pure iron sintered body constituting this is 8 to 20%.
The reason why the porosity is less than 8% is that the desired weight reduction cannot be achieved, and on the other hand, when the porosity exceeds 20%, the strength is reduced. is there.

[0009]

EXAMPLES Next, the lightweight yoke of the present invention will be specifically described by way of examples. As the raw material powder, pure iron powder having a particle size of 100 mesh or less was used, and this was used for 4 to 7 to
The green compact is press-molded at a predetermined pressure within the range of n / cm ² , and the green compact is sintered in a nitrogen atmosphere at a temperature of 1140 ° C. for 40 minutes, and the results are shown in Table 1. A porous pure iron sintered body having the porosity shown is formed, and after barrel polishing is performed on this, dimensional and shape correction is performed by indentation of a mold, and oil adhered during correction is removed, and then Acrylic resin is impregnated into the pores of the pure pure iron sintered body under normal conditions, this is sealed, and then shot blasting treatment is applied to this to remove the surface-adhered resin, and predetermined machining is applied. , Then the surface of this under normal conditions thickness: 14 μm
By forming the electroless Ni plating layer of No. 3, each has the shape shown in FIG. 1, and the radius of the root of the protrusion is r ₁ : R0.2, r ₂ : R0.2, r ₃ : R0.6
Then, the lightweight yoke of the present invention having t ₁ : 3.7 mm, t ₂ : 26.5 mm, and a cross-sectional dimension perpendicular to the uniaxial direction of maximum width dimension: 83.4 mm × maximum height dimension: 26.5 mm. 1-4 were produced respectively.

[0010]

[Table 1]

Next, the maximum permeability of the light weight yokes 1 to 4 of the present invention obtained as a result was measured and shown in Table 1, and the weight was measured. The weight of the iron yoke was 100%, and the ratio to the weight is shown in Table 1.

[0012]

From the results shown in Table 1, all of the lightweight yokes 1 to 4 of the present invention are much lighter than the conventional fused pure iron yokes, and the performance required for the yokes (maximum magnetic permeability). It is clear that

As mentioned above, the lightweight yoke of the present invention is
In addition to fully exerting the function as a yoke, it is lightweight, and therefore, when it is used, it has industrially useful characteristics such as contributing to weight reduction of various electronic and electrical devices.

[0014]

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a yoke.

Claims (4)

[Claims] 1. The pore distribution concentration is the same throughout,
The structure has a structure in which an electroless Ni plating layer is formed on the surface of a base body in which pores of a porous pure iron sintered body having a predetermined porosity within the range of 20% are sealed by resin impregnation. A lightweight yoke characterized by this. 2. The lightweight yoke according to claim 1, wherein the lightweight yoke has the same cross-sectional shape perpendicular to the uniaxial direction. 3. The lightweight yoke according to claim 1, wherein the root of the protrusion has a radius of R0.2 or more. 4. The lightweight yoke according to claim 1, which constitutes a VCM yoke of a magnetic disk device.