JPH0425673A - Double pole type magnetic seal - Google Patents

Abstract

PURPOSE:To make a magnetic fluid so as not to exert a bad influence on apparatuses in a closed box body as scattering around in this box body by making an interval between a first pole piece at the outer side of the closed box body and a spindle shaft larger than that between a second pole piece at the inner side of the box body and the spindle shaft. CONSTITUTION:In a recording medium rotational driving part of a magnetic disk unit, a diameter of a part corresponding to a first pole piece of a spindle shaft 4 is formed to be smaller than that of a part corresponding to a second pole piece 8. In consequence, since both magnetic fluids 12 at the side of the first pole piece 6 and at the side of the second pole piece 8 are of homogeneous, any possible scattering of these magnetic fluids 12 with pressure fluctuations in each space A being partitioned off in space among a permanent magnet 10, these first and second pole pieces 6, 8, the magnetic fluids 12 and the spindle shaft 4 comes to occurs preferentially on the magnetic fluid being interposed between the first pole piece 6 and the spindle shaft 4 in consequence. Accordingly, such a fear that the magnetic fluid is scattered in the inner part of a closed box body 2, where airtightness is required, is brought to nothing unless some exceptional sudden pressure fluctuations occurs in these internal space A of a magnetic seal.

Description

[Detailed Description of the Invention] Overview Regarding double-pole magnetic seals used in devices that require airtightness, such as magnetic disk drives, magnetic fluid scatters into the sealed casing and adversely affects the equipment inside the casing. In order to provide a double-pole type magnetic seal with no fear, in a double-pole type magnetic seal for a spindle shaft penetrating from the inside of a sealed casing to the outside, the first pole piece located on the outside side of the sealed casing and the above-mentioned The distance between the second pole piece and the spindle shaft is larger than the distance between the second pole piece located inside the sealed casing and the spindle shaft.

INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to an improvement in a double-pole magnetic seal used in devices requiring airtightness, such as magnetic disks.

For example, in a magnetic disk device used as a storage device for a combination coater, a magnetic head slightly floated above the surface of a rotationally driven recording medium is moved to access a desired position on the surface of the recording medium. Therefore, it is required that dust and the like are not floating in the space in which the recording medium and the magnetic head are accommodated. For this reason, in devices that require this type of airtightness, if the spindle shaft that rotates the recording medium etc. penetrates from the outside of the sealed casing to the inside, the spindle shaft of the casing may not penetrate. Magnetic seals are now being widely used in parts that are connected to devices, and optimization of their configuration is being sought.

Conventional technology The configuration of a conventional double-pole magnetic seal is shown in Figure 3 (a).
The functional principle is shown in ) in the same figure. This double pole type magnetic seal has a permanent magnet 56, which is also annular and has a larger inner diameter, sandwiched between two annular pole pieces 52 and 54 made of ferromagnetic material.
A magnetic fluid 60 is interposed in gaps formed between the spindle shaft 58 passed through the shafts 2 and 54 and the pole pieces 52 and 54, respectively. The magnetic fluid 60 is a colloid of fine particles of ferromagnetic material such as magnetite in a nonvolatile solvent. According to this configuration, as shown in FIG. 3, etc., the pole piece 52, the permanent magnet 5
6. Since a magnetic circuit is formed in the path passing through the pole piece 54, the magnetic fluid 60, the spindle shaft 58, and the magnetic fluid 60, good sealing against the spindle shaft 58 is possible.

Problems to be Solved by the Invention When the double pole magnetic seal shown in FIG. 3 is used in a recording medium rotation drive section of a magnetic disk device,
Assuming that the device was manufactured at room temperature, the air sealed in the space defined by the pole piece, permanent magnet, magnetic fluid, and spindle shaft expands as the device temperature rises during device operation. However, the magnetic fluid may scatter to the inside and/or outside of the sealed casing. If the magnetic fluid scatters inside the sealed casing, in the worst case, the magnetic fluid may scatter onto the surface of the recording medium, causing a head crash.

The present invention was created in view of the above circumstances, and its purpose is to provide a double-pole magnetic seal in which there is no risk of the magnetic fluid scattering into the sealed housing and adversely affect the equipment inside the housing. It is to be.

Means for Solving the Problems The double pole magnetic seal of the present invention has a first structure.
As shown in the figure, in a double pole magnetic seal for a spindle shaft 4 penetrating from the inside to the outside of the hermetically sealed housing 2, the first pole piece 6 located on the outside of the hermetically sealed housing 2 and the spindle shaft 4 are connected to each other. The distance is larger than the distance between the second pole piece 8 located inside the sealed casing 2 and the spindle shaft 4.

In addition, in Fig. 1(a), the inner diameter of the first pole piece is
A configuration is shown in which the inner diameter of the pole piece is larger than the inner diameter of the pole piece, and in FIG. A smaller configuration is shown.

Operation In Fig. 1, 10 indicates the first pole piece 6.
and a permanent magnet provided to be sandwiched between the second pole piece 8, and 12 indicates a gap formed between the first pole piece 6, the second pole piece 8, and the spindle shaft 4, respectively. It is a magnetic fluid provided in the magnetic fluid.

According to the configuration of the present invention, by using a ball piece or a spindle shaft having a specific shape, the distance between the first pole piece on the outside of the casing and the spindle shaft is reduced to the distance between the first pole piece on the outside of the casing and the first pole piece on the inside of the casing where airtightness is required. Since the distance between the two pole pieces and the spindle shaft is larger than that between the first pole piece and the spindle shaft, the surface area of the magnetic fluid that exists in the gap between the first pole piece and the spindle shaft is larger than the surface area of the magnetic fluid that exists in the gap between the second pole piece and the spindle shaft. This will be larger than the surface area of the magnetic fluid. As a result, if the magnetic fluid on the first pole piece side and the magnetic fluid on the second pole piece side are of the same quality, it is possible to find a structure between the permanent magnet, the first and second pole pieces, the magnetic fluid, and the spindle shaft. The scattering of the magnetic fluid due to pressure fluctuations in the space A (hereinafter referred to as the "internal space of the magnetic seal") occurs preferentially for the magnetic fluid interposed between the first pole piece and the spindle shaft. It turns out. Therefore, as long as a sudden pressure change does not occur in the internal space of the magnetic seal, there is no risk of the magnetic fluid scattering inside the sealed casing. In this way, the problems of the prior art are solved.

Example The present invention will be explained in detail below.

FIG. 2 is a sectional view of a rotational drive section of a magnetic disk device showing an embodiment of the present invention. Parts that are substantially the same as those in FIG. 1 are given the same reference numerals. The spindle shaft 4 is rotatably supported by an upper bearing 26 and a lower bearing 28 via bearings 22, 24,
The upper bearing 26 and the lower bearing 28 are sealed and fixed to the sealed casing 2 using bolts (not shown) or the like. In such a rotation mechanism, it is easy to ensure airtightness between the upper bearing 26, the lower bearing 28, and the sealed casing 2 because they are in close contact with each other. 28 and the spindle shaft 4 is not easy to ensure since the bearings 22, 24 are interposed between them. Therefore, the double pole type magnetic seal of the present invention is applied to this portion.

The double-pole magnetic seal 30 of the present invention is adhesively fixed to an upper magnetic seal stand 32 and a lower magnetic seal stand 34 from the inside of the case, and the upper magnetic seal stand 32 and the lower magnetic seal stand 34 are fixed by bolts 36, respectively. Upper bearing 2
6 and the lower bearing 28. magnetic seal 30
In this case, the distance between the first pole piece 6 and the spindle shaft 4 on the outside of the sealed casing can be reduced by using the first and second pole pieces having a specific shape as described above, or by using a spindle shaft having a specific shape. is larger than the distance between the second pole piece 8 and the spindle shaft 4 on the inside side of the sealed casing. Regarding the above-mentioned spacing, since it is required to make a difference in extremely small intervals, considering the manufacturing workability of the spindle shaft and magnetic seal, it is better to use a specific shape than to use first and second pole pieces with a specific shape. It is advantageous to use a spindle shaft of This is because it is relatively easy to partially vary the diameter of the spindle shaft using precision grinding technology.

A rotor 38 is a component of a motor (not shown) that rotationally drives the spindle shaft 4, and the rotor 38 is fixed to the lower end of the spindle shaft 4 located on the outside of the sealed casing. A hub 40 is fixed to a portion of the spindle shaft 4 located inside the sealed casing, and a plurality of recording media 42 are arranged around the hub 40.
are arranged parallel to each other and at equal intervals. Note that a magnetic head and its drive mechanism (not shown) are also housed inside the sealed casing 2, but even if the structure and operation thereof are not explained, there will be no problem in implementing the present invention. The explanation will be omitted.

In a magnetic disk drive having such a configuration, when the spindle shaft 4 is rotated, the magnetic seal 3 is damaged due to heat generated by the drive motor, heat generated by friction in the bearings, etc.
As described above, the magnetic fluid 12 may be scattered due to the thermal expansion of the air in the internal space of the magnetic seal as the temperature of the magnetic seal increases. In this embodiment, since the distance between the first ball piece 6 and the spindle shaft 4 is larger than the distance between the second pole piece 8 and the spindle shaft 4, the magnetic fluid 12 due to the thermal expansion is The scattering occurs preferentially with respect to the magnetic fluid 12 interposed between the first pole piece 6 and the spindle shaft 4 located on the outside of the sealed housing 2, and the magnetic fluid 12 disturbs the recording inside the sealed housing 2. This prevents the particles from scattering onto the medium 42 and the like.

Note that as the temperature of the device increases, the air inside the sealed casing 2 also rises, but by providing the airtight casing 2 with a breathing port equipped with a filter to prevent dust, Since the internal pressure of the magnetic seal 30 can always be kept equal to the atmospheric pressure, the magnetic fluid of the magnetic seal 30 is prevented from being subjected to undesired pressure due to thermal expansion and contraction of the air inside the sealed housing 2. I can do it.

In this embodiment, the present invention is applied to a recording medium rotation drive portion of a magnetic disk device, but the present invention may also be applied to a rotation drive mechanism of a magnetic head.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the present invention has the effect that it is possible to provide a double-pole magnetic seal in which there is no risk of the magnetic fluid scattering into the sealed housing and adversely affect the equipment inside the housing. play.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention, FIG. 2 is a cross-sectional view of a rotational drive portion of a magnetic disk device showing an embodiment of the present invention, and FIG. 3 is an explanatory diagram of the prior art. 2... Sealed casing, 4... Spindle shaft, 6... First pole piece, 8... Second pole piece, 10... Permanent magnet, 12... Magnetic fluid. L--,,,J

Claims (1)

[Claims] 1. In a double pole magnetic seal for a spindle shaft (4) penetrating from the inside to the outside of a sealed casing (2), a first pole piece located on the outside of the sealed casing (2); (6) and the spindle shaft (4) is larger than the distance between the second pole piece (8) located inside the sealed casing (2) and the spindle shaft (4). Double pole type magnetic seal. 2. The double pole type magnetic seal according to claim 1, wherein the inner diameter of the first pole piece (6) is larger than the inner diameter of the second pole piece (8). 3. A diameter of a portion of the spindle shaft (4) corresponding to the first pole piece (6) is smaller than a diameter of a portion of the spindle shaft (4) corresponding to the second pole piece (8). Double pole type magnetic seal as described.