JPH0536671B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a magnetic fluid seal structure.

[Conventional technology]

For example, conventional magnetic fluid seal structures include:
Some are used in magnetic disk spindles. This is what is shown in Figure 4.

In the figure, H is the housing, S is the shaft,
B is a bearing interposed between the housing H and the shaft, and C is a sealing member fitted to the shaft S with a gap g, which will be described later.

The bearing B is a ball bearing in which balls 3 are interposed between an outer ring 1 and an inner ring 2, and a cover 4 is provided at an end of the outer ring 1 to cover an opening between the outer ring 1 and the inner ring 2, and a housing It is positioned at a predetermined location by a retaining ring 5 attached to H.

As shown in FIG. 4, the sealing member C is formed by sandwiching an annular magnet 7 having a magnetic pole in the axial direction of the shaft S between a pair of annular pole pieces 6, 6 and adhering them together. It is disposed adjacent to the bearing B via a non-magnetic spacer 8, and its outer peripheral surface is adhesively fixed to the inner peripheral surface of the housing H. A slight gap g is provided between the seal member C and the shaft S, and a magnetic fluid 9 is injected into this gap g.

With this configuration, a magnetic circuit 10 is formed between the pole pieces 6, 6 and the shaft S, and the magnetic fluid 9 injected therebetween is held with sufficient pressure resistance. As a result, the mist obtained by evaporating the lubricant sealed in the bearing B, such as grease, can be completely sealed so that it does not leak to the outside.

In addition, the pressure difference between the two sides of the seal member 8 can be maintained by sandwiching the seal member 8, and it is also possible to prevent dust from entering the bearing B side from the outside.

[Problem that the invention seeks to solve]

In this way, the magnetic fluid seal structure has several functions, but in general, when used for dustproofing magnetic disk spindles, etc., it is important to extend its life rather than increasing its pressure resistance.
In other words, it is necessary to inject as much magnetic fluid 9 as possible into the gap g between the pole pieces 6 and the shaft S, and to securely hold this. This is because the life of this sealing device is determined by the amount of oil in the magnetic fluid 9 that evaporates.

However, even when injecting into the gap g, since this gap g is a limited space, there is a limit to how well it can be injected. Therefore, a method was devised in which the large gap g1 between the magnet 7 and the shaft S is used to fill this part with the magnetic fluid 9.

However, this method had the following problems. That is, as shown in FIG.
When the magnetic fluid 9 is injected from the outside of the seal member C, it initially fills the gap g between the outer pole piece 6 and the shaft S, but as the injection continues, it fills the gap g1. Start along the surface of the facing pole pieces 6, 6 and magnet 7, and close the gap g.
Before being filled in one part, it reached the gap g between the inner pole piece 6 and the shaft S, which has a high magnetic flux density, and was filled in this part first. As a result, as shown in FIG. 6, a space a was created in which the gap g1 was surrounded by the magnetic fluid 9 and air was trapped therein, making it impossible to fill the gap as desired.

In this state, the magnetic fluid 9 in the gap g1 is held in (1) by the weak lines of magnetic force passing between the pole pieces 6, but separates from the gap g where the strong lines of magnetic force pass. (2), as shown by the missing note (Figure 6),
In order to move to the gap g, since the lines of magnetic force in this part run in the same direction, the attractive force due to the lines of magnetic force is not so strong, but rather the lines of force between the pole pieces 6 and 6 must be moved relative to each other. It was difficult to move to the gap g because of the strong impact. Therefore, the magnetic fluid 9 in the gap g
However, even if the amount of oil decreases due to evaporation, there is a problem in that the oil cannot move to compensate for this and cannot effectively replenish the evaporated amount. For this reason, even if a large amount of magnetic fluid is filled using the method described above, it has not been possible to extend the life of the seal structure.

Furthermore, since air is confined in the space a by the magnetic fluid 9, if this air expands due to a rise in ambient temperature, there is a risk that the seal by the magnetic fluid 9 will break. Ta.

This invention was made in order to solve such conventional problems, and the gap between the magnet and the shaft is made equal to or slightly smaller than that between the pole piece and the shaft. Therefore, an attempt is made to provide a magnetic fluid seal structure that can maintain a long service life with a small amount of magnetic fluid.

[Means for solving problems]

A magnetic fluid seal structure according to the present invention is a structure in which a magnetic fluid is injected into a gap between a shaft and an annular seal member fitted to the shaft to seal the gap. It is formed by an annular magnet having magnetic poles in the direction and an annular pole piece fixed to one or both sides of this magnet, and the gap between the magnet and the shaft is the same as that between the pole piece and the shaft. It is characterized by being slightly smaller than this.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is a sectional view of an embodiment of a magnetic fluid seal structure applied to a magnetic disk spindle, as in the conventional case, and FIG. 2 is an enlarged view of the main part of FIG. 1.

In the figure, the same reference numerals as in FIG. 4 indicate the same or corresponding parts. C1 is a sealing member, which corresponds to the conventional sealing member C. This seal member C
1 is a pair of annular pole pieces 11, 11, and an annular magnet 12 having magnetic poles in the axial direction of the shaft S.
The outer circumferential surface is adhesively fixed to the inner circumferential surface of the housing H.
In this embodiment, the gap between the seal member C1 and the shaft S is the gap between the magnet portion and the pole pieces 11, 1.
Each part is of a different size. That is, the gap g2 between the magnet 12 and the shaft S is
That between pole pieces 11, 11 and shaft S
It is slightly smaller than the .

With this configuration, as shown in FIG. When the injection is continued, it moves through the gap g2 and fills the other gap g where the magnetic flux density is high. At this time,
Since the gap g2 is a minute space, the injected magnetic fluid 9 fills the one gap g2 in such a way as to expel the air in that area, and unlike the conventional magnetic fluid 9, the injected magnetic fluid 9 does not completely expel the air. There will be no more wrapping around this. Therefore, a phenomenon in which the enclosed air expands and the magnetic fluid seal ruptures does not occur as in the prior art.

Furthermore, since the gap S2 is a minute space, the amount of magnetic fluid 9 injected therein can be far smaller than in the conventional structure. Moreover, although the amount of magnetic fluid 9 injected into the gap g is small in this way, it works rather effectively in improving the seal pressure resistance performance.

Figure 7 compares the relationship between the withstand pressure and the amount of magnetic fluid injection of the magnetic fluid seal of Figure 1 (Example) with that of the conventional magnetic fluid seal (Figure 4). This clarifies the relationship.

Considering that magnetic fluid is an expensive liquid, being able to save on magnetic fluid in this way has an extremely large economic merit.

Furthermore, the magnetic fluid 9 in the gap g2 is (1) held by the weak lines of magnetic force passing through the gap g2, and is located adjacent to the high magnetic flux density part of the gap g where the strong lines of magnetic force pass; (2), as shown by the arrow (Figure 2), when moving to the gap g,
Since it will move in the direction perpendicular to the direction of the magnetic lines of force in this part, the attractive force due to the lines of magnetic force will be
It is easy to move to the gap g part because it is more strongly affected by the lines of magnetic force in the gap g2 part. Therefore, when the magnetic fluid 9 in the gap g decreases due to evaporation of oil, the magnetic fluid 9 in the gap g2 easily flows to either side of the gap g to compensate for this. Move to. As long as the movement, or replenishment, continues, the sealing function will be maintained over a long period of time.

In the above embodiment, the size of the gap g2 is smaller than the gap g, but both g2 and g may be the same. This is because the size of the gap g2 only needs to be such that when the magnetic fluid 9 is injected into the gap g, the gap g2 does not enclose air, and the size of the gap g2 is at least the size of the gap g that does not enclose air. This is because it may be hot.

FIG. 3 shows another embodiment. This embodiment is an example in which only one pole piece 11 is used. Its operation is essentially the same as that in the embodiments described above. Tasashi, pole piece 11
Since there is only one seal, the difference is that the absolute life of the seal is correspondingly shorter.

〔Effect of the invention〕

As explained above, according to the present invention, since the gap between the magnet and the shaft is made equal to or slightly smaller than that between the pole piece and the shaft, it is possible to fill the magnet part with magnetic fluid. Then, the filled magnetic fluid can easily move to the pole piece portion, and the life of the magnetic fluid seal structure can be extended, and the amount of magnetic fluid used can be suppressed to the necessary minimum.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing an embodiment of the present invention;
The figure is an enlarged view of the main part of FIG. 1, FIG. 3 is a view corresponding to FIG. 2 showing another embodiment of the present invention, FIG. 4 is a sectional view showing a conventional magnetic fluid seal structure, and FIGS. FIG. 6 is a sectional view of a main part for explaining its operation, and FIG. 7 is a characteristic graph comparing the pressure resistance of the seal of the embodiment of the present invention with that of a conventional example. S...Shaft, C1...Seal member, 11...
... Pole piece, 12... Magnet, g... Gap between pole piece 11 and shaft S, g2... Gap between magnet 12 and shaft S.

Claims (1)

[Claims] 1 In a structure in which a magnetic fluid is injected into a gap between a shaft and an annular seal member fitted to the shaft to seal the gap, the seal member is an annular magnet having a magnetic pole in the axial direction of the shaft. and an annular pole piece fixed to one or both sides of this magnet, and the gap between the magnet and the shaft is the same as or slightly smaller than that between the pole piece and the shaft. A magnetic fluid seal structure characterized by: