JPH058384Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic fluid sealing device suitable for application to a sealing structure for a rotating portion of a fixed magnetic storage device.

Various improvements have been made to fixed magnetic disk drives to improve their reliability. For example, the cleanliness of the disk pack in which the disk is set is particularly important. To maintain this level of cleanliness, a magnetic fluid seal is used to prevent the intrusion of grease mist from the disk spindle bearings and dust from outside the disk pack. Therefore,
High reliability is also required for the magnetic fluid seal itself.

As shown in FIG. 1, the conventional magnetic fluid seal structure has a fixed distance between an annular permanent magnet 1 that is magnetized in the radial direction and a flat surface of the permanent magnet 1 that covers the outer diameter of the permanent magnet 1. A soft magnetic pole piece ring 2 with an L-shaped half cross section and a permanent magnet 1
A ferromagnetic shaft 4 concentrically penetrates the inner diameter of the pole piece 2 and the inner diameter of the pole piece 2, and is magnetically captured in the gap between the outer diameter of the shaft 4, the inner diameter of the pole piece 2, and the inner diameter of the permanent magnet 1. It is composed of a magnetic fluid ring film 3.

In this structure, the leakage magnetic field to the outside of the pole piece ring 2 can be reduced by the pole piece ring 2 itself, but in order to prevent the leakage magnetic field outside the side surface of the permanent magnet 1, as shown in FIG. 2' must be installed on the outer side of the permanent magnet 1.

However, incorporating pole piece 2′
The demand for miniaturization by flattening the seal structure in the axial direction cannot be met, and a drastic solution is required. That is, since the leakage magnetic field acts as noise on the magnetic disk device, it is required to be as small as possible.

In view of this, the main purpose of the present invention is to avoid the complexity of providing a separate pole piece ring and to propose a sealing device that is further improved by specially setting the shape of the permanent magnet. .

An embodiment of the present invention will be described in detail below with reference to the drawings.

Figure 3 is a diagram showing an example of the present invention, and Figure 4 is a diagram showing an example of the present invention.
FIG. 3 is a cross-sectional view showing the dimensional relationship of only the permanent magnets shown in the figure.

The seal structure of this embodiment mainly consists of annular permanent magnets 11 magnetized in the radial direction (ferrite core magnets, rare earth magnets, plastic magnets, FeCrCo magnets,
(AInico magnet, MsAIC magnet, etc.) and a soft magnetic pole piece ring 2 (martensite ferromagnetic shaft 4 (martensitic stainless steel, ferrite core stainless steel, permalloy, SS41, etc.) and a ferromagnetic shaft 4 that concentrically penetrates the inner diameter of the permanent magnet 11 and the inner diameter of the pole piece ring 2.
carbon steel, etc.) and a magnetic fluid ring film 3 that is magnetically trapped in the gap between the outer diameter of the shaft 4, the inner diameter of the pole piece 2, and the inner diameter of the permanent magnet 11 (the solvent is synthetic oil, alkylnaphthalene, In a magnetic fluid sealing device in which the magnetic powder is composed of mineral oil, silicone oil, chlorocarbon, etc. (magnetic powder is composed of magnetite, manganese zinc ferrite, Ni, FeNi, etc.), the outer diameter ro of the permanent magnet 11, the outer diameter The following relationship is satisfied between the thickness to, the inner diameter ri, and the inner diameter thickness ti: 2πro・to<2πri・ti (1).

That is, in this structure, by satisfying the relational expression of the permanent magnet 1, the cross-sectional area cut in the circumferential direction at any position in the radial direction of the permanent magnet 11 is always larger than the outer cross-sectional area. 11
The magnetic flux in the radial direction is continuous in the entire section from the outer diameter surface to the inner diameter surface of the permanent magnet 11, and no magnetic flux leaks from the side surface of the permanent magnet in the outer axial direction. If the thickness were constant from the outer circumference to the inner circumference as in the past, the magnetic flux in the radial direction would concentrate toward the center (shaft side), and some of it would leak out from the sides.This phenomenon is called magnetic flux discontinuity. It is said that According to the above configuration, since the inner circumferential cross-sectional area of the permanent magnet 11 is always larger than the outer circumferential cross-sectional area, magnetic flux is no longer concentrated. Therefore, the generation of leakage magnetic flux is eliminated.

FIG. 5 is a sectional view showing another embodiment of the present invention, in which the permanent magnet 11' in FIG. 3 is similar to FIG. 4.
Only the shape is shown. In this structure, the permanent magnet shown in FIG. 4 has a tapered part of the plane part on both sides, but only on one side.

By the way, the permanent magnet used in this invention can be further improved by imparting magnetic anisotropy in the same direction as the magnetic flux vector when used as a seal, even in the process of imparting magnetic anisotropy during permanent magnet manufacturing. It is clear that low leakage is achieved.

Furthermore, by constructing the magnetic fluid seals shown in FIGS. 6 and 7 using the permanent magnet of the present invention,
It is also easily possible to construct a magnetic fluid sealing device with low leakage magnetic flux. To explain this in detail,
The sealing device shown in FIG.
1, a ferromagnetic shaft 4 concentrically penetrating the inner diameter of the shaft 1;
The magnetic fluid ring film 3 is magnetically held in the gap between the outer diameter of the ferromagnetic shaft 4 and the inner diameter of the permanent magnet 11.

The sealing device shown in FIG. 7 includes two permanent magnets 11 closely fixed to a ferromagnetic shaft 4, and an annular soft magnetic yoke 2 that concentrically penetrates the outer diameter of the magnets 11.
The magnetic fluid ring film 3 is magnetically held in the gap between the inner diameter of the yoke 2 and the outer diameter of the permanent magnet 11.

As described above, according to the present invention, there is a half cross section between an annular permanent magnet magnetized mainly in the radial direction and a flat surface part of the permanent magnet that covers the outer diameter part of the permanent magnet. An L-shaped soft magnetic pole piece ring, a ferromagnetic shaft concentrically penetrating the inner diameter of the permanent magnet and the inner diameter of the pole piece, and a magnetic shaft in the gap between the outer diameter of the shaft and the inner diameter of the pole piece and the permanent magnet. In a magnetic fluid sealing device consisting of a magnetic fluid ring film that is captured by a permanent magnet, between the outer diameter dimension ro, the outer diameter thickness to, the inner diameter dimension ri, and the inner diameter thickness ti, ro・to・Since it satisfies the relationship <ri・ti, leakage magnetic flux generated from the side surface of a radially magnetized annular permanent magnet that is not in contact with the pole piece can be eliminated without providing a pole piece ring. This has the effect of providing a highly reliable and simple-structured magnetic fluid sealing device for use in magnetic disk devices and the like that require high reliability.

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views showing the conventional configuration;
Fig. 3 is a sectional view showing an embodiment of the present invention, Fig. 4 is a diagram for explaining the main parts of the invention, Figs.
7 and 7 are cross-sectional views showing other examples of the present invention. 2...Pole piece ring, 3...Magnetic fluid,
4...Ferromagnetic shaft, 11, 11'... Annular permanent magnet.

Claims (1)

[Claim for Utility Model Registration] An annular permanent magnet that is mainly magnetized in the radial direction, and a half section that covers the outer diameter of the permanent magnet and has a certain distance between the permanent magnet and the flat surface. An L-shaped soft magnetic pole piece ring, a ferromagnetic shaft concentrically penetrating the inner diameter of the permanent magnet and the inner diameter of the pole piece, and between the outer diameter of the shaft, the inner diameter of the pole piece, and the permanent magnet. In a magnetic fluid sealing device composed of a magnetic fluid ring film that is magnetically trapped in an air gap, the permanent magnet has an outer diameter ro, an outer diameter thickness to, and an inner diameter ri.
and an inner diameter thickness ti, the magnetic fluid sealing device is characterized in that it satisfies the relationship: ro・to<ri・ti.