JP2928461B2 - Magnetic fluid sealing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic fluid sealing device.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional magnetic fluid seal is an annular magnet 1 magnetized in an axial direction.
And annular pole pieces 2B, 2B made of a magnetic material concentrically arranged at both axial ends of the magnet 1, and a housing 5 made of a non-magnetic material for fixing the magnet 1 and the pole pieces 2B, 2B. And a shaft 4 made of a magnetic material penetrating concentrically through the inner peripheral sides of the magnet 1 and the pole pieces 2B, 2B, and a magnetic circuit constituted by the magnet 1, the pole pieces 2B, 2B and the shaft 4. By pole piece 2
A magnetic fluid is magnetically held between the inner peripheral surfaces of the shafts B and 2B and the outer peripheral surface of the shaft 1 to form magnetic fluid rings 3 and 3A. The atmosphere A is sealed off.

However, if the low pressure side A has a larger low pressure ratio than the pressure resistance of the magnetic fluid ring 3 on the low pressure side,
The ferrofluid ring 3 on the low pressure side is torn, and the torn ring 3
Has scattered to the low-pressure side A, thus contaminating the low-pressure side atmosphere A with the magnetic fluid.

Therefore, a proposal for solving the above problem is made in Japanese Utility Model Publication No. 22229/1990. As shown in FIG. 4, the magnetic fluid sealing device described in Japanese Utility Model Publication No. 22229/1990 has a notched groove 8 at a part of the outer peripheral surface of the shaft 4 facing the low pressure side pole piece 2B. It is formed.

Here, since the magnetic resistance of the notch groove 8 with the pole piece 2B is sufficiently larger than that of the other shaft surface portion covered by the magnetic fluid ring 3 where the notch groove 8 does not exist. The notch groove 8 is not filled with the magnetic fluid 3, so that the low-pressure side space A and the pole pieces 2B,
The space surrounded by 2B communicates.

That is, the ferrofluid ring 3 is a stable ferrofluid ring which is not always affected by the pressure fluctuation on the low pressure side. If the ferrofluid ring 3 is broken, it is the next-stage ferrofluid ring 3A. Even if it does, the magnetic fluid ring 3 serves as a wall so that the low-pressure side atmosphere is not contaminated.

[0007]

However, the magnetic fluid sealing device described in Japanese Utility Model Publication No. 22229/1990 has the following problems. That is, as shown in FIG. 4, since the axial length of the notch groove 8 must be longer than the axial length of the pole piece 2B, there is a problem that it is disadvantageous to reduce the thickness of the bearing. .

Further, when the magnetic fluid sealing device is applied to a small-sized HDD motor, for example, since the shaft diameter of the motor is very small, if the notched groove 8 is formed in this small-diameter shaft, There is a problem that the mechanical strength of the shaft is impaired.

[0009] Here, for example, the above-mentioned actual fair 22-22529
As shown in another example of the magnetic fluid sealing device described in Japanese Patent Application Laid-Open Publication No. H11-260, a protruding flange portion 4 as shown in FIG. 5 is provided on the outer peripheral surface of the shaft 4 at a position facing the pole pieces 2B, 2B.
A and 4B may be provided, and a notch 8 may be provided in a part of the outer periphery of the low pressure side flange 4A to obtain the same effect as above while maintaining the mechanical strength of the shaft 4. In this case, since the outer diameters of the flanges 4A and 4B are larger than the outer diameter of the shaft 4, the peripheral speed at the outer periphery of the flanges 4A and 4B is larger than the peripheral speed of the outer periphery of the shaft 4, and the centrifugal force acting on the magnetic fluid increases. However, there is a problem that the pressure resistance of the seal decreases.

Further, since the peripheral speed at the outer periphery of the flange portions 4A and 4B is higher than the peripheral speed at the outer periphery of the shaft 4, there is a problem that viscous heat generation of the magnetic fluid increases and sealing performance is deteriorated.

Accordingly, the present invention is intended to reduce the thickness of the bearing, maintain the mechanical strength of the shaft, and prevent the sealing pressure resistance from decreasing and the sealing performance from deteriorating.
An object of the present invention is to provide a magnetic fluid sealing device capable of preventing scattering of a magnetic fluid.

[0012]

In order to achieve the above object, the magnetic fluid sealing device of the present invention is provided with an annular magnet magnetized in the axial direction and concentrically disposed at both ends of the magnet. An annular pole piece made of magnetic material,
A shaft made of a magnetic material penetrating concentrically through the inner peripheral side of the magnet and the pole piece, and a magnetic circuit formed by the magnet, the pole piece and the shaft causes a magnetic force between the pole piece and the shaft. In a magnetic fluid sealing device that magnetically holds a fluid, a cutout is provided at a part of the inner periphery of at least the pole piece that is on the negative pressure side during operation among the pole pieces.

[0013]

According to the magnetic fluid sealing device of the above-described means, when the internal and external pressures partitioned by the magnetic fluid seal are balanced, the magnetic fluid flows between the outer peripheral surface of the shaft and the inner peripheral surface of the pole piece. And within the notch of the pole piece. Here, when a pressure change occurs and the internal and external pressures become unbalanced, the magnetic fluid seal in the notch of the pole piece breaks because it is small compared to the magnetic flux density of other parts, but this notch causes a break with the low pressure side space. The space surrounded by the pole piece communicates with the pressure, and the pressure in the space surrounded by the pole piece and the pressure in the space surrounded by the pole piece are balanced, so that the magnetic fluid ring on the low pressure side is prevented from being broken. At this time, even if the magnetic fluid ring on the higher pressure side is broken and scattered, the magnetic fluid ring on the lower pressure side becomes a wall, so that the low pressure side atmosphere is not contaminated. When the internal and external pressures reach equilibrium, the magnetic fluid returns to the notch.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a magnetic fluid sealing device showing one embodiment of the present invention, FIG. 2 is a cross-sectional view of the magnetic fluid sealing device when the pressure inside and outside is equilibrated, and FIG. It is a cross-sectional view at the time of unbalance.

In FIGS. 1 and 2, reference numeral 11 denotes an annular magnet which is magnetized in the axial direction. Magnetic members are provided at both ends in the axial direction of the magnet 11 as shown in FIG. Annular pole pieces 12A, 12B
Are arranged concentrically.

As shown in FIG. 1, a notch 12a is formed in a part of the inner peripheral surface of the pole piece 12A on the side of the region A which is on the low pressure side during operation.
1 and the pole pieces 12A, 12B are fixed to a housing 15 made of a non-magnetic material.

The magnet 11 and the pole piece 12
The shaft 14 made of a magnetic material is provided on the inner peripheral side of the A and 12B.
Are penetrated concentrically, and the magnet 11, the pole pieces 12A and 12B, and the shaft 14
In this state, a magnetic circuit is formed.

Therefore, during non-operation (when the pressures in the regions A and B are balanced), the magnetic circuit causes the pole piece 12 to operate.
Magnetic fluids 13A, 13A are provided between the inner peripheral surfaces of the shafts A, 12B and the outer peripheral surface of the shaft 14 and in the notches 12a of the pole pieces 12A.
B is held magnetically. That is, the magnetic fluid 13A,
The region A and the region B are sealed off by 13B.

Here, a pressure change occurs during the operation, and the region A
Becomes the low-pressure side atmosphere and the area B becomes the high-pressure side atmosphere. That is, when the pressures in the areas A and B become unbalanced, the magnetic flux density in the notch 12a of the pole piece 12A is smaller than the other parts. The magnetic fluid seal in the notch 12a breaks as shown in FIG.

Then, the low pressure side space A communicates with the space surrounded by the pole pieces 12A and 12B by the notch 12a, and the pressure of the low pressure side space A and the pole piece 12
A, the pressure of the space surrounded by 12B is balanced,
Breakage of the magnetic fluid ring 13A on the low pressure side is prevented.

At this time, even if the magnetic fluid ring 13B on the higher pressure side is broken and scattered, the magnetic fluid ring 13A on the lower pressure side is a wall, so that the low pressure side atmosphere A
Is not contaminated by the scattered magnetic fluid.

When the pressures in the regions A and B reach equilibrium, the magnetic fluid returns into the notch 12a and returns to the initial state shown in FIG.

As described above, in the present embodiment, the notch 12a is provided at a part of the inner periphery of the pole piece 12A, which is on the negative pressure side at least during operation, of the pole pieces 12A and 12B. Since the magnetic fluid can be prevented from being scattered, it is possible to reduce the thickness of the bearing and to reduce the thickness of the shaft as compared with a conventional shaft having a cutout groove longer than the axial length of the pole piece. It is possible to maintain the mechanical strength of.

The magnetic fluids 13A, 13B are located between the outer peripheral surface of the shaft 14 and the inner peripheral surfaces of the pole pieces 12A, 12B.
The structure is such that a flange is provided on the shaft as in the prior art, and the magnetic fluid is held between the outer peripheral surface of the flange and the inner peripheral surface of the pole piece. The working centrifugal force and viscous heat generation can be reduced, so that it is possible to prevent a decrease in sealing pressure and a deterioration in sealing performance.

In this embodiment, the pole pieces 12A and 12B are manufactured by the press method, and the notch 12a can be formed only by providing a projection on the inner diameter press die. The apparatus can be reduced in cost as compared with the apparatus (the shaft 4 shown in FIG. 4 in which the notch groove 8 is provided, and the shaft 4 shown in FIG. 5 in which the flanges 4A, 4B and the notch groove 8 are provided). It is possible to do.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say, for example, the magnetic fluid sealing device can be any of a type in which the shaft 4 rotates and the pole pieces 12A and 12B are fixed, and a type in which the shaft 4 is fixed and the pole pieces 12A and 12B rotate. It is also applicable.

In the above embodiment, the notch 12a
Is one, but may be plural. In particular, the pole pieces 12A, 12B are formed with a plurality of notches as described above.
In the case of a type in which the notches rotate, it is desirable to dispose the notches at a position where they can be balanced.

It is also possible to provide notches in the pole piece 12B not only on the low pressure side A but also on the high pressure side B during operation. In particular, when used as a seal against dust, the magnetic fluid must be held in the notch. However, as described above, when the pressures in the regions A and B reach equilibrium, the magnetic fluid returns into the notch. Therefore, it functions as a seal against dust. However, if the size of the notch 12a and the amount of the magnetic fluid are not appropriate, a gap may be generated, or the magnetic fluid ring 13A on the low pressure side A may burst and scatter, so caution is required.

Further, in the above embodiment, the magnetic fluid seal is provided in one step (the magnet 11 and the pole piece 1).
2A, 12B), but the present invention can be similarly applied to a magnetic fluid seal having two or more stages.

The magnetic fluid sealing device of the present invention can be applied to a small motor other than a motor for HDD, for example, and can be applied to any structure using a magnetic fluid seal. is there.

[0031]

As described above, according to the magnetic fluid sealing device of the present invention, at least part of the inner periphery of the pole piece which is on the negative pressure side during operation is cut out. By providing the magnetic fluid, scattering of the magnetic fluid can be prevented, so that the bearing can be made thinner than a conventional shaft in which a notch groove longer than the axial length of the pole piece is provided in the shaft. In addition, the mechanical strength of the shaft can be maintained. In addition, since the magnetic fluid is held between the outer peripheral surface of the shaft and the inner peripheral surface of the pole piece, a flange is provided on the conventional shaft, and the outer peripheral surface of the flange portion and the inner peripheral surface of the pole piece are formed. The centrifugal force and viscous heat generated on the magnetic fluid can be reduced as compared with the configuration in which the magnetic fluid is held between them, so that it is possible to prevent a decrease in seal pressure resistance and a deterioration in seal performance. That is, it is possible to reduce the thickness of the bearing, maintain the mechanical strength of the shaft, and prevent the magnetic fluid from being scattered while reducing the sealing pressure resistance and the sealing performance.

[Brief description of the drawings]

FIG. 1 is a plan view of a magnetic fluid sealing device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the magnetic fluid sealing device at the time of internal and external pressure equilibrium.

FIG. 3 is a cross-sectional view of the ferrofluid seal device at the time of pressure imbalance between the inside and the outside.

FIG. 4 is a cross-sectional view of a magnetic fluid sealing device showing an example of the prior art.

FIG. 5 is a cross-sectional view of a magnetic fluid sealing device showing another example of the prior art.

[Explanation of symbols]

 11 Magnet 12A Pole piece which becomes negative pressure side during operation 12a Notch 12B Pole piece 13A, 13B Magnetic fluid 14 Shaft

Claims (1)

(57) [Claims] 1. An annular magnet magnetized in an axial direction, an annular pole piece made of a magnetic material concentrically disposed at both ends of the magnet, and an inner peripheral side of the magnet and the pole piece. A shaft made of a magnetic material that passes through the shaft concentrically, and a magnetic fluid is magnetically held between the pole piece and the shaft by a magnetic circuit constituted by the magnet, the pole piece, and the shaft. In the magnetic fluid sealing device, a magnetic fluid sealing device in which at least a part of the inner circumference of the pole piece that is on the negative pressure side during operation is provided in the pole piece.