JPH0363149B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sealing device using magnetic fluid suitable for application to a dust sealing device for a magnetic disk for a computer, a rotary shaft sealing device for a vacuum device, an air valve, and the like.

For example, in a magnetic disk device, at the end of a rotating shaft extending from an externally installed motor,
A disk unit may be installed, and a sealing device may be provided to block air circulation between the disk installation location and the outside in order to prevent dust or oil mist generated from the bearings from entering the disk unit.

FIG. 1 is a sectional view showing an example of a general sealing device of this type. An annular ferromagnetic body (pole piece) 2 is attached to both sides of an annular permanent magnet 1, a ferromagnetic rotating body 4 is inserted into the annular body 2, and an annular gap is formed between the pole piece 2 and the rotating shaft 4. The magnetic fluid 3 is magnetically captured. This annular film of magnetic fluid 3 functions as a sealing device.

By the way, unless a predetermined amount of magnetic fluid is injected between the pole piece 2 and the rotating shaft 4, the annular film formed by the magnetic fluid will not generate enough withstand pressure as a sealing device, and will not function as a sealing device. This is well known. However, there is a drawback that when a sufficient amount of magnetic fluid is injected and the magnetic fluid 3 is left unused or operated, the magnetic fluid 3 flows out of the sealed device due to an increase in environmental temperature and contaminates the sealed space. The reason is the first
Then, the air in the space partitioned by the two annular magnetic fluids expands thermally and presses the annular magnetic fluid film 3 to the outside of the sealing device. Second, the amount of magnetic flux that the permanent magnet 1 can supply decreases due to the increase in environmental temperature. Therefore, the seal pressure resistance decreases due to a decrease in the magnetic field that holds and fixes the magnetic fluid film 3, and the magnetic fluid film 3 becomes easy to move due to the force mentioned in the first reason, or the magnetic fluid film 3 is torn and the magnetic Fluid escapes outside the seal. Third, increased environmental temperature reduces the saturation magnetization from the ferrofluid itself, thus reducing seal pressure. As a result, due to the above-mentioned force, the magnetic fluid film 3 becomes easy to move or the magnetic fluid film 3 is torn and the magnetic fluid flows out of the sealing device. Fourthly,
As the environmental temperature increases, the surface tension and viscosity of the magnetic fluid decrease. Therefore, the magnetic fluid film 3 is easily moved by the above-mentioned force. These causes are possible.

Incidentally, the left and right spaces having a sealing mechanism using magnetic fluid are blocked from fluid. For example, in the case of an air valve, it is necessary to promote or block fluid flow in a certain temperature range. However, this type of conventional sealing mechanism has the drawbacks mentioned above.
It is extremely difficult to intentionally cause a magnetic fluid to act as a valve.

In view of this, the present invention provides a temperature-sensitive magnetic material in the magnetic path in order to suppress the deterioration of the sealing function due to an increase in the ambient temperature, and seals in a predetermined temperature range by arbitrarily setting the temperature-sensitive magnetic material. The main objective is to develop a sealing device in which the number of mechanisms can be increased or decreased in an intentional manner.

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

FIG. 2 is a sectional view showing an example of the present invention. An annular permanent magnet 1, a pole piece 2 in contact with both sides of the magnet, a magnetic rotating body 4, and the pole piece 2 and the rotating body 4.
As before, a sealing device (hereinafter referred to as MFS) is formed by the magnetic fluid 3 trapped between It is held between the left and right pole pieces 2. The temperature-sensitive magnetic material 5 is, for example, Mn-Zn.
A thermosensitive ferrite may be used.

FIG. 3 is a diagram showing the relationship between temperature change and MFS breakdown voltage. Curie point (Tc) of temperature-sensitive magnetic material 5
In the following temperature range, the magnetic flux from the permanent magnet 1 passes through the pole piece 2 and does not act on the ferromagnetic rotating body 4, but passes from the pole piece 2 through the temperature-sensitive magnetic body 5,
Since it returns to the permanent magnet 1 via the other pole piece 2, almost no withstand voltage of the MFS is generated. As the temperature rises from around the Kyrie point Tc, the saturation magnetization of the temperature-sensitive ferrite begins to decrease, so the amount of magnetic flux passing through the temperature-sensitive ferrite 5 decreases, and the magnetic flux conversely passes from the pole piece 2 to the magnetic fluid 3, It passes through the rotating shaft 4. As the amount of magnetic flux increases, the withstand voltage of the MFS increases (see curve B in Figure 3). Therefore, in a temperature range above the Curie point where the amount of magnetic flux acting on the rotating body 4 due to the action of the temperature-sensitive ferrite 5 increases as the temperature rises, the magnetic flux acting on the pole piece 2, the magnetic fluid film 3, and the rotating shaft 4 increases. and the amount of decrease in the saturation magnetization of the magnetic fluid 3 are balanced,
The withstand voltage of MFS becomes constant. In a higher temperature range, as shown in FIG. 3, the magnetic flux density that passes through and holds the magnetic fluid 3 supplied by the permanent magnet decreases, and the saturation magnetization of the magnetic fluid also decreases, so the withstand voltage of the MFS gradually decreases.

Therefore, by setting the temperature range in which the MFS's withstand pressure is constant to the variable range of the MFS operating environment, it is possible to compensate for the drop in withstand pressure due to a rise in the temperature of the MFS and prevent the magnetic fluid 3 from flowing out.

Furthermore, by considering the cross-sectional area and material of the temperature-sensitive ferrite 5 and the cross-sectional area and material of the permanent magnet 1, as shown by curve C in FIG.
The withstand voltage of MFS can be gradually increased. In addition, the outflow of the magnetic fluid 3 due to the surface tension and viscosity reduction inherent in the magnetic fluid 3 is also caused by the phenomenon of an apparent increase in the viscosity of the magnetic fluid (when the magnetic field strength applied to the magnetic fluid is increased,
This can be prevented by the phenomenon in which the viscosity of the magnetic fluid increases accordingly. In addition, in FIG. 3, curve A shows the change due to the structure of the example in FIG. 1 for reference, and it is understood that the withstand voltage characteristics deteriorate as the temperature rises. The reason is as described above.

FIG. 4 shows another embodiment in which a temperature-sensitive ferrite 5 used as a magnetic flux bypass is arranged outside the permanent magnet 1 and the pole piece 2. Since the operating principle and effects are the same as those of the embodiment shown in FIG. 2, detailed explanation will be omitted.

Next, an embodiment of the present invention in which the temperature dependence of the breakdown voltage of the MFS can be freely formed will be described below.

FIG. 5 is a sectional view showing an example of an MFS having a structure in which a temperature-sensitive ferrite 5 and a permanent magnet 1 are sandwiched between pole pieces 2 in a sandwich-like manner. At temperatures below the Kyrie point Tc of thermosensitive ferrite 5,
Since the magnetomotive force of the permanent magnet 1 is used only in the gap between the pole piece 2 and the rotating body 4, as shown in FIG. 6, the withstand pressure as an MFS is large. However, as the temperature rises, when the saturation magnetization of the temperature-sensitive ferrite 5 rapidly decreases from around Tc, the magnetomotive force loss of the temperature-sensitive ferrite 5 increases accordingly.
MFS's withstand voltage begins to decrease rapidly. Therefore, by utilizing such characteristics, it is possible to open and close the partition walls due to temperature changes caused by the magnetic fluid.

The structure shown in FIG. 7 is a combination of the MFSs of the example shown in FIG. 2 and the example shown in FIG. However, the Kyrie point of the temperature-sensitive ferrite between the pole piece 2 is Tc ₁ and the Kyrie point of the temperature-sensitive ferrite between the pole piece 2 and the permanent magnet 1 is Tc ₂ , and the relationship is set such that Tc ₁ < Tc ₂ . ing. Therefore, at temperatures below Tc ₁ , the magnetic flux mainly generated from the permanent magnet 1 passes through the temperature-sensitive ferrite 51, so no withstand pressure is generated. Further, since the amount of magnetic flux passing through the magnetic fluid 3 increases from a temperature near Tc ₁ , the withstand pressure increases. When Tc ₂ approaches, the magnetomotive force loss of the temperature-sensitive ferrite 52 increases, so the amount of magnetic flux passing through the magnetic fluid 3 decreases and the withstand voltage drops rapidly. This relationship can be expressed in a diagram as shown in FIG. Therefore, in this example, Tc ₁ ~
It is possible to block the flow path using the magnetic fluid only in the temperature range of Tc ₂ , and it has a so-called valve function.

Figure 9 is basically a combination of the example in Figure 2 and the example in Figure 5.
Although the structure is a combination of MFS, the Curie points of temperature-sensitive ferrites 61 and 62 are set to Tc ₁ and
Assuming Tc ₂ , the relationship is Tc ₁ < Tc ₂ .
Therefore, at temperatures below Tc ₁ , the magnetic flux generated from the permanent magnet 1 forms two magnetic paths.
One is permanent magnet 1 → pole piece 21 → temperature-sensitive ferrite 62 → pole piece 22 → permanent magnet 1 (hereinafter referred to as the first path). The other path is permanent magnet → temperature-sensitive ferrite 61 → pole piece 21 → rotating shaft 4 → pole piece 22 → permanent magnet 1 (hereinafter referred to as the second path). In this case, the withstand voltage is generated by the magnetic flux caused by the second path. When the temperature approaches Tc ₁ , the magnetomotive force loss of the temperature-sensitive ferrite 62 in the first path increases, magnetic flux no longer passes through the second path, and the withstand voltage begins to drop rapidly. When near Tc ₂ , the magnetic flux cannot pass through the first path, so the magnetic flux in the first path takes the path of permanent magnet → pole piece 21 → rotating shaft 4 → pole piece 22 → permanent magnet 1, and a withstand voltage is generated ( (See Figure 10).

Therefore, since the present invention allows the pressure resistance of the sealing device to be freely changed depending on the temperature, it can be applied to many applications as a device such as a fluid regulating valve.

Note that the present invention can be applied to a non-rotating shaft instead of a rotating shaft, and even when the rotating shaft is a flat plate with an infinite diameter. Further, in the above example, a temperature-sensitive magnetic material is added, but it goes without saying that the annular pole piece or the rotating shaft itself may be made of a temperature-sensitive magnetic material without the addition of such a material.

As described above, the present invention includes a shaft, a magnet device facing the shaft with a gap therebetween and forming a magnetic path between the two poles, and a magnetic fluid having fluidity that closes the gap at a predetermined location. Since the sealing device is constructed using a temperature-sensitive magnetic material and a portion in the middle of the magnetic path or adjacent to the magnetic path, the withstand pressure within the sealing device can be maintained or increased even when the environmental temperature fluctuates. can. Therefore, even if the environmental temperature fluctuates, the magnetic fluid inside the sealing device will not leak out of the sealing device, and a highly reliable sealing device (MFS) using magnetic fluid can be provided. Moreover, the present invention
MFS can be used in many ways as an opening/closing mechanism for air valves, etc., as the pressure resistance and temperature characteristics can be freely changed and set.

[Brief explanation of drawings]

Figure 1 is a sectional view of the basic structure of the magnetic fluid seal device.
FIG. 2 is a sectional view showing an example of the present invention, FIG. 3 is a breakdown voltage-temperature characteristic diagram for explaining the effects of the present invention, FIG.
The figure is a sectional view showing the third example of the present invention, and FIG.
FIG. 7 is a sectional view showing the fourth example of the present invention, FIG. 8 is a breakdown voltage-temperature characteristic diagram of the example shown in FIG. 7, and FIG. 9 is the fifth example of the present invention. A sectional view showing an example, and FIG. 10 is a breakdown voltage-temperature characteristic diagram of the example shown in FIG. 1... Permanent magnet, 2... Pole piece, 3... Magnetic fluid, 4... Rotating shaft, 5... Temperature-sensitive magnetic material.

Claims (1)

[Claims] 1. A sealing device comprising a shaft, a magnet device facing the shaft with a gap and forming a magnetic path between the two poles, and a magnetic fluid having fluidity that closes the gap at a predetermined location. A sealing device characterized in that a portion in the middle of the path or adjacent to the magnetic path is made of a temperature-sensitive magnetic material.