JPS6143588B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A shaft sealing device for a rotating shaft can be obtained using a magnetic fluid in which ferrite or other magnetic powder is dispersed in a liquid such as a hydrocarbon, a hydrofluoric acid, or a suitable fatty acid. This type of shaft seal device does not have parts that wear out due to sliding contact like Wilson seals or mechanical seals, so it has a long life and can provide perfect sealing.
It is particularly effective for sealing the shaft of high vacuum devices such as rotating anode cathode X-ray tubes. However, for this purpose, it is necessary to have a multi-stage configuration of an annular magnetic pole gap sealed with a magnetic fluid and to generate a strong magnetic field in the gap. For this purpose, for example, as shown in Figure 5 of British Patent No. 783881, annular permanent magnets magnetized in the axial direction are arranged in a straight line so that their polarities are alternately opposite, and each magnet A device is used in which an annular magnetic pole gap is formed between the inner circumferential portion of an annular magnetic pole piece inserted between the magnets and the rotating shaft of the magnetic body, and a magnetic fluid is held in this gap. However, since the pole piece cannot be made extremely thin to avoid saturation, there is a limit to the magnetic flux density between its inner surface and the rotating shaft. For this reason, it is necessary to make the magnetic pole gap extremely small, for example, 20μ or less, making it difficult to manufacture the device and requiring a large number of permanent magnets to maintain a high vacuum, which increases the size of the device. There were flaws. The present invention seeks to eliminate these drawbacks.

FIG. 1 is a longitudinal cross-sectional view of an embodiment of the present invention, in which a rotating shaft 2 made of a magnetic material is arranged at the center of a cylindrical housing 1 and held by ball bearings 3 and 4. As shown in FIG. In addition, as shown in the figure with polarities N and S, a plurality of annular permanent magnets 5, 5 magnetized in the axial direction are arranged so that magnetic poles N and N and S and S of the same polarity face each other, respectively. They are arranged coaxially on the axis of the rotating shaft 2. Further, an annular magnetic pole piece 6, 6...... is inserted between each of these permanent magnets 5, 5... coaxially with the magnet, and a similar magnetic pole piece 7 is further outside of the outermost magnet. , 7 and connect them with O-rings 8, 8
It is pressed against. Furthermore, the magnetic pole pieces 6, 6...
There is one annular groove 9, 9... on the inner surface of each.
... is formed, and the tips of the annular protrusions 10 and 11 formed on both sides of the groove are opposed to the rotating shaft 2 with a gap of several tens of microns in between, and the magnetic fluid 12, 12... is held in a ring shape.

FIG. 2 shows an enlarged view a of a part of FIG. 1 and a magnetic field intensity curve b on the surface of the rotating shaft 2. That is, magnetic flux in the same direction flows through any one magnetic pole piece 6 due to magnetic poles of the same polarity in the magnets 5, 5 on both sides thereof, for example, N and N. In addition, since one annular groove 9 is formed on the inner surface of this magnetic pole piece, the magnetic flux is transmitted to the annular protrusions 10 on both sides of the annular groove 9.
11 and enters the axis 2. Moreover, the raised portion 10,
The magnetic flux incident on shaft 2 from 11 is further divided into left and right sides and is incident on the protrusions of adjacent magnetic pole pieces, so the magnetic field strength curve on the surface of shaft 2 is as shown in Figure 2b.
It is expressed as In this way, the device of the present invention has annular magnetic pole pieces 6, 6 inserted between each magnet.
An annular groove 9 is formed on the inner surface of the magnet to separate the magnetic flux into two. Since the separated magnetic fluxes have the same polarity, they repel each other and are focused on the annular protrusions 10 and 11 on both sides. Therefore, as shown in FIG. 2b, an extremely sharp and strong magnetic field is formed on the surface of the shaft 2, and this magnetic field causes the magnetic fluids 12, 12...
is held extremely strongly. Therefore, the magnetic pole gap p
If the strength and number of the permanent magnets 5, 5, . . . are made the same, the pressure difference on both sides of the shaft sealing device can be increased.

Note that FIG. 3a is a sectional view corresponding to FIG. 2 of the device described in the British patent specification, and shows an annular magnetic pole piece 21 inserted between annular permanent magnets 20, 20... An annular protuberance 22, 22... is formed on each of the protrusions 21, 21, . . . , and magnetic fluids 24, 24, . Therefore, the magnetic flux generated from the magnets on both sides of each magnetic pole piece 21 flows, and the magnetic flux is incident on the rotating shaft 23 through the single protuberance 22. Therefore, the magnetic flux is diffused due to mutual repulsion, and only a wide and weak magnetic field is generated on the surface of the shaft 23 as shown in FIG.
is held, so in order to increase the holding force, the magnetic pole gap q must be made small. For this reason, it is difficult to manufacture, and the pressure difference K that can be maintained against changes in the number N of magnets is a low value as shown by the straight line A in FIG. On the other hand, the device of the present invention as shown in FIG. 1 and FIG. 2 has a high value as shown by straight line B.

As explained above, the present invention forms an annular groove in one magnetic pole piece inserted between two magnets,
By dividing the magnetic flux into two, a strong magnetic field is generated locally on the surface of the rotating shaft by utilizing the repulsive force between the two divided magnetic fluxes. Therefore, the holding force of the magnetic fluid is increased, making it possible to withstand high pressure differences and increasing the magnetic pole gap, making it easy to manufacture the shaft sealing device, and reducing the number of magnets to make the device more compact. can be formed.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of an embodiment of the present invention, Fig. 2 is an enlarged view of a part of Fig. 1, Fig. 3 is a sectional view corresponding to Fig. 2 of a conventional shaft sealing device, and Fig. 4. 1 is a diagram showing the characteristics of the present invention and a conventional device. In the figure, 2 is a rotating shaft, 3 and 4 are ball bearings, 5 is a permanent magnet, 6 is a magnetic pole piece, 9 is a groove, 10 and 11 are annular protrusions, and 12 is a magnetic fluid.

Claims (1)

[Claims] 1 A plurality of annular permanent magnets magnetized in the axial direction are coaxially arranged so that the magnetic poles of the same polarity face each other, and an annular groove is formed on each of the inner surfaces of each annular magnetic pole piece. A magnetic body is inserted between the permanent magnets and coaxially with the magnet, and an axis of a magnetic body that rotates relative to the annular permanent magnet and the annular magnetic pole piece is arranged on the axis of the annular permanent magnet and the annular magnetic pole piece. A magnetic fluid shaft sealing device in which magnetic fluid is attached in an annular shape between the shaft and annular ridges formed on both sides of a groove on the inner surface of the shaft.