JPH04341665A - Multistage magnetic fluid sealing device for vacuum space - Google Patents

Abstract

PURPOSE:To prevent a splash of magnetic fluid from scattering in a vacuum space without fail. CONSTITUTION:The right side is a vacuum space in this case. A magnetic fluid sealing device body 3a being opposed to this vacuum space holds a permanent magnet 7 between a pair of pole pieces 8a and 9a. An inner diameter of the pole piece 8a at the vacuum space side is smaller than that of another pole piece 9a. A space 19b at the opposite side to the vacuum space in holding the magnetic fluid sealing device body 3a between is leading to a vacuum pump 2. When air in a space 19a lying between these paired pole pieces 8a and 9a is expanded, a magnetic fluid 10 at an inner circumferential edge of the pole piece 9a is bursting, thereby preventing a pressure rise in this space 19a from occurring.

Description

[Detailed description of the invention]

0001

INDUSTRIAL APPLICATION FIELD The multi-stage magnetic fluid sealing device for vacuum according to the present invention is used to maintain airtightness of a portion penetrating the wall of a container whose interior is evacuated.

0002

[Prior Art] When an object placed in a clean space inside a casing is rotated by a motor installed outside, it is necessary to prevent dust from passing through the part where the drive shaft of the motor penetrates the wall of the casing. It is necessary to provide a sealing device.

[0003] Conventionally, a sealing device installed in such a part to prevent the passage of dust, etc. has been disclosed in Japanese Patent Laid-Open No. 62-11.
No. 0080, Japanese Utility Model Application No. 58-191423, Japanese Utility Model Application Publication No. 61-13025, Japanese Utility Model Application Publication No. 61-44067,
Publication No. 61-79070, Publication No. 62-195261, Publication No. 61-204027, Publication No. 63-8419, Publication No. 63-139325, Publication No. 63-139329
Magnetic fluid seal devices described in US Pat. No. 944, US Pat. No. 4,628,384, and US Pat. No. 4,692,826 are commonly used.

The structure of the magnetic fluid seal device described in each of the above-mentioned prior art documents differs in detail, but basically the structure is as shown in FIGS. 16(A) and 16(B). have.

Of these, 1 in FIG. 16A is a housing made of a non-magnetic material such as aluminum or synthetic resin at least on its inner peripheral surface, and is fixed to, for example, the wall surface of the casing. 2 is a shaft made of a magnetic material such as iron, and the magnetic fluid sealing device main body 3 is connected to the housing 1.
A cylindrical space 6 between the inner peripheral surface 4 of the shaft 2 and the outer peripheral surface 5 of the shaft 2
is installed inside.

The magnetic fluid sealing device main body 3 includes a circular permanent magnet 7 magnetized in the axial direction (horizontal direction in FIG. 16), and a pair of circular poles made of magnetic material. By sandwiching the magnetic fluids 10, 10 between the pieces 8, 9 in a sandwich manner and holding them between the inner peripheral edge of each pole piece 8, 9 and the outer peripheral surface 5 of the shaft 2 by the magnetic force of the permanent magnet 7, It is configured. The outer diameter of the pair of pole pieces 8 and 9 is approximately the same as the inner diameter of the housing 1, and the magnetic fluid seal device main body 3 constituted by each member 7, 8, 9, and 10 is attached to the inner peripheral surface of the housing 1. 4, it is fixed by internal fitting or adhesive.

The magnetic fluid seal device main body 3 is constructed as described above, and is installed between the inner circumferential surface 4 of the housing 1 and the outer circumferential surface 5 of the shaft 2 to constitute the magnetic fluid seal device. The rotation of the shaft 2 inside the housing 1 or the rotation of the shaft 2
Regardless of the rotation of the housing 1 around The sealing property between the shaft 2 and the outer circumferential surface 5 of the shaft 2 is maintained.

Further, as shown in FIG. 16(B), the outer peripheral surface 5 of the shaft 2 is formed of a non-magnetic material, the inner peripheral surface 4 of the housing 1 is formed of a magnetic material, and a pair of permanent magnets 7 are formed. The pole pieces 8 and 9 are externally fitted and fixed on the outer peripheral surface 5 side of the shaft 2, and the magnetic fluids 10 and 10 are placed between the outer peripheral edge of each pole piece 8 and 9 and the inner peripheral surface 4 of the housing 1. Magnetic fluid sealing devices for retaining are also known in the art.

By the way, the magnetic fluid sealing device constructed as described above uses the magnetic fluids 10, 10 held by the magnetic force of the permanent magnets 7 to isolate the spaces existing on both sides of each magnetic fluid 10, 10 ( seal), so if there is a large pressure difference between the two spaces, the magnetic fluid 10
, 10 are pushed through (burst) and cannot be sealed.

[0010] For this reason, conventionally, as a magnetic fluid seal device installed in a rotating shaft penetrating portion of a high vacuum device such as a rotating anticathode X-ray tube, Japanese Patent Publications No. 51-9853 and No. 61-4
No. 3588, U.S. Patent No. 3,620,584,
As described in British Patent No. 783881, magnetic fluids 10, 10 are provided in multiple stages in the axial direction,
A vacuum multi-stage magnetic fluid sealing device is known in which the pressure difference existing on both sides of each magnetic fluid 10 is kept small.

FIG. 17 shows a first example of such a multi-stage magnetic fluid seal device for vacuum use. In this Figure 17,
Reference numeral 13 denotes a cylindrical bearing housing, which is provided on the wall surface of the casing 11 whose interior (the right side in FIG. 17) is evacuated. Rolling bearings 12, 12 are provided at two positions on the inner peripheral surface of this bearing housing 13, and both rolling bearings 12,
12 rotatably supports the shaft 2 made of magnetic material.

A vacuum multistage magnetic fluid sealing device 14 is provided between the inner peripheral surface of the bearing housing 13 and the outer peripheral surface 5 of the shaft 2. This vacuum multistage magnetic fluid sealing device 14 includes circular permanent magnets 7, 7 magnetized in the axial direction, and circular pole pieces 15, 16 made of magnetic material.
The magnetic fluids 10, 10 are placed between the inner peripheral edge of each pole piece 15, 16 and the outer peripheral surface 5 of the shaft 2,
It is constructed by being held by the magnetic force of the permanent magnets 7, 7.

In the illustrated example, each pole piece 15
, 16 are formed with grooves having a V-shaped cross section, the inner peripheral edges of each pole piece 15, 16 are bifurcated, and the magnetic fluid 10, 10 is applied to each pole piece 15, 16 in the axial direction 2. It is designed to be held over several stages. Therefore, in the case of the vacuum multi-stage magnetic fluid sealing device 14 shown in FIG. 17, the magnetic fluids 10, 10 are provided in ten stages in the axial direction (horizontal direction in FIG. 17).

As described above, the vacuum multi-stage magnetic fluid seal device 14 has the magnetic fluids 10, 10 arranged in multiple stages, so that the pressure difference existing on both sides of the magnetic fluids 10, 10 in each stage can be reduced. Multi-stage magnetic fluid seal device for vacuum while keeping it small 1
It is possible to create a large pressure difference on both sides of 4. or,
O-rings 18, 18 are attached to the grooves 17, 17 formed on the outer peripheral edges of the pole pieces 16, 16 located at both ends,
These O-rings 18, 18 are used to maintain airtightness between the outer circumferential surface of the vacuum multistage magnetic fluid sealing device 14 and the inner circumferential surface of the bearing housing 13.

[0015]

However, in the vacuum multi-stage magnetic fluid seal device constructed and used as described above, the magnetic fluid 1 is provided in multiple stages in the axial direction.
The magnetic fluid 10 may burst at any stage due to the expansion of the air sealed in the spaces 19, 19 between the 0 and 10.

That is, the vacuum multistage magnetic fluid sealing device 14
When configuring the space 19, it is inevitable that air is sealed in each of the spaces 19, 19, but if this air expands as the temperature rises, the magnetic fluid 10 that partitions the space 19 will burst, and the droplets of the magnetic fluid 10 are scattered around.

In particular, as the air sealed in the space 19a closest to the vacuum space (to the right in FIG. 17) expands,
When the magnetic fluid 10 facing the vacuum space bursts,
The droplets of the magnetic fluid 10 scatter into the vacuum space and contaminate the vacuum space.

[0018] As a technique for solving such inconveniences, Japanese Patent Laid-Open Nos. 59-126169 and 61-2369 have been proposed.
No. 71, as shown in FIG. 18, describes a technique for discharging the air in a space 19a near the vacuum space by making the space 19a communicate with a vacuum pump 25. As a result of creating a vacuum in the space 19a, the magnetic fluid 10 facing the vacuum space will not burst, but for the reasons described below, there is still a possibility that droplets of the magnetic fluid 10 will be scattered into the vacuum space. There is.

That is, by discharging the air in the space 19a near the vacuum space, the air in this space 19a is prevented from expanding, but due to the thermal expansion of the air sealed in the adjacent space 19b. , there is a risk that the magnetic fluid 10 that partitions both spaces 19a and 19b may burst. and,
Magnetic fluid 1 scattered by this burst of magnetic fluid 10
0 crosses the space 19a and is absorbed by the magnetic fluid 10 facing the vacuum space, there is a possibility that the amount of the magnetic fluid 10 facing the vacuum space becomes excessive.

If the amount of magnetic fluid 10 facing the vacuum space becomes excessive, this magnetic fluid 10 will be scattered around as the shaft 2 rotates, and droplets of magnetic fluid 10 will be scattered into the vacuum space. There is a risk that this will happen.

The vacuum multistage magnetic fluid sealing device of the present invention eliminates the above-mentioned disadvantages.

[0022]

[Means for Solving the Problems] The vacuum multi-stage magnetic fluid sealing device of the present invention has a first member made of a magnetic material having a cylindrical peripheral surface, similar to the conventional vacuum multi-stage magnetic fluid sealing device described above. a second member that is provided concentrically with the first member and rotates relative to the first member; and a cylindrical shape between the circumferential surface of the second member and the circumferential surface of the first member. a permanent magnet formed in a ring shape with a size that can be freely inserted into the cylindrical space and magnetized in the axial direction; , a pole piece fixed to the side surface of the permanent magnet, and magnetism held by the magnetic force of the permanent magnet at multiple locations in the axial direction between the circumferential edge of the pole piece and the circumferential surface of the first member. It consists of a fluid and is used with one axial side facing a vacuum space.

Furthermore, in the vacuum multistage magnetic fluid sealing device of the present invention, the holding force of the magnetic fluid in the gap between the peripheral edge of the pole piece and the peripheral surface of the first member is applied to the vacuum space. The first gap that is in contact with the first gap is made larger, and the second gap next to the first gap is made smaller, and the space that is further away from the vacuum space than the second gap and partitioned on both sides by the magnetic fluid is evacuated. It is characterized by

[0024]

[Operation] In the case of the vacuum multistage magnetic fluid sealing device of the present invention configured as described above, even if the air in the space between the first gap and the second gap expands, the holding force is weak. The magnetic fluid in the second gap is bursted to release the expansion. Therefore, the magnetic fluid in the first gap portion facing the vacuum space will not be scattered into the vacuum space.

[0025] As the air in the space further away from the vacuum space expands, the magnetic fluid that partitions this space bursts,
Even if splashes of magnetic fluid are generated as a result, these droplets are captured in the second gap portion and do not reach the first gap facing the vacuum space. Therefore, the amount of magnetic fluid facing the vacuum space does not become excessive and this magnetic fluid does not become easily scattered into the vacuum space.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 show a first embodiment of the present invention. A shaft 2 that is a first member made of a magnetic material and has a cylindrical peripheral surface.
A housing 1, which is a second member, is placed on the outside of the shaft 2.
inside this housing 1,
The shaft 2 is rotatably supported. In a cylindrical space 6 between the outer circumferential surface 5 of the shaft 2 and the inner circumferential surface 4 of the housing 1, a plurality of magnetic fluid sealing device bodies 3, 3a (
In the illustrated example, there are four spacers 20 made of non-magnetic material between each other.
, 20 are placed in series with each other. Each magnetic fluid sealing device main body 3, 3a has a circular permanent magnet 7, 7 magnetized in the axial direction (left and right direction in FIG. 1), and a pair of circular permanent magnets 7, 7 made of a magnetic material. pole piece 8
, 8a, 9, 9a in a sandwich-like manner, and a magnetic fluid 10, 10 is placed between the inner peripheral edge of each pole piece 8, 8a, 9, 9a and the outer peripheral surface 5 of the shaft 2.
It is constructed by holding it by magnetic force.

Of the pair of pole pieces 8a and 9a that constitute the magnetic fluid seal device main body 3a provided at the vacuum side end (right end in FIG. 1), the pole piece 8 facing the vacuum space
The inner diameter r of a is smaller than the inner diameter R of the pole piece 9a on the opposite side (r<R). As a result, the holding force of the magnetic fluid 10 in the first gap 21 between the inner peripheral edge of the pole piece 8a on the vacuum space side and the outer peripheral surface 5 of the shaft 2 is the same as that of the inner peripheral edge of the pole piece 9a on the opposite side. This is greater than the holding force of the magnetic fluid 10 in the second gap 22 between the outer peripheral surface 5 of the shaft 2 and the outer peripheral surface 5 of the shaft 2.

Furthermore, the space 19b between the magnetic fluid sealing device main body 3a at the vacuum side end and the adjacent magnetic fluid sealing device main body 3 is connected to the vacuum pump 25 via the intake passage 24 formed in the spacer 20. The space 19b is evacuated by communicating with the air intake port of the space 19b. In addition, the degree of vacuum in the vacuum space should be 10-4 torr or less (for example, 10-6 to 10-8
torr), the degree of vacuum in the space 19b is, for example, 10-2 to 10-4 torr.

In the case of the vacuum multistage magnetic fluid sealing device of the present invention configured as described above, even if the air in the space 19a between the first gap 21 and the second gap 22 expands,
The magnetic fluid 10 in the second gap 22 portion where the holding force is weak is bursted to release the expansion.

That is, since the magnetic fluid 10 held in the first gap 21 having a narrow width in the diametrical direction is held within this first gap 10 by a sufficiently large holding force, the magnetic fluid 10 is Even if the pressure in the space 19a increases due to the expansion of air, it is difficult to burst. On the other hand, the magnetic fluid 10 held in the wide second gap 22 is relatively easy to burst, so when the pressure in the space 19a increases, the magnetic fluid 10 in the second gap 22 bursts and bursts into the space. The air in 19a is released to the adjacent space 19b, and space 1
This prevents the pressure within 9a from increasing any further.

[0031] Therefore, the first gap 21 facing the vacuum space
Part of the magnetic fluid 10 will not be scattered into the vacuum space.

[0032] Even if the air in the space 19 further away from the vacuum space expands, the magnetic fluid 10 that partitions this space 19 bursts, and as a result, droplets of the magnetic fluid 10 are generated. It is captured in the 22 part of the gap,
It does not reach the first gap 21 facing the vacuum space. Therefore, the amount of magnetic fluid 10 facing the vacuum space does not become excessive and the magnetic fluid 10 does not easily scatter into the vacuum space.

[0033] Of the pair of pole pieces 8a and 9a constituting the magnetic fluid sealing device main body 3a at the end on the vacuum side, the inner diameter of the pole piece 9a on the side opposite to the vacuum space does not necessarily extend over the entire circumference. There is no need to make it bigger. For example, in Figure 2 (A
), the inner peripheral edge of the pole piece 9a is made into an elliptical shape, and the width of the second gap 22 is made wider in the major diameter portion, or as shown in FIG. 2(B), the inner peripheral edge It is also possible to form a cutout 26 in a part of the gap 26 and widen the width of the second gap 22 at the cutout 26 portion.

Next, FIG. 3 shows a second embodiment of the present invention. In the first embodiment described above, in order to hold the magnetic fluids 10, 10 in multiple stages, a plurality of magnetic fluid sealing device main bodies 3 are used.
, 3 were provided, whereas in the case of this embodiment, thick-walled pole pieces 27, 27 were provided on both sides of the permanent magnet 7.
A plurality of protrusions 28, 28 are formed on the inner circumferential edge of the shaft 2, and magnetic fluids 10, 10 are held between the inner circumferential edge of each protrusion 28, 28 and the outer circumferential surface 5 of the shaft 2, respectively. . The other configurations and operations are the same as in the first embodiment described above.

Next, FIG. 4 shows a third embodiment of the present invention. In the case of this embodiment, the independent magnetic fluid sealing device main body 3a as in the second embodiment is not provided, and the pole piece 27 on the vacuum side (the right side in FIG. 4) among the thick pole pieces 27, 27 The inner diameter of the protrusions 28, 28 formed on the inner peripheral edge of the tube is made smaller toward the vacuum side. A space 19 existing between the pair of pole pieces 27, 27 is communicated with a vacuum pump (not shown) via an intake passage 24 provided in the permanent magnet 7. The other configurations and operations are the same as those of the first and second embodiments described above.

Next, FIG. 5 shows a fourth embodiment of the present invention. In the case of this embodiment, of the pair of pole pieces 8a and 9a that constitute the magnetic fluid seal device main body 3a provided at the vacuum side end (right end in FIG. 5), the pole on the opposite side to the vacuum side is By forming the inner circumferential edge of the piece 9a into two, the magnetic fluids 10, 10 are held in two stages between the inner circumferential edge of the pole piece 9a and the outer circumferential surface 5 of the shaft 2. Furthermore, a pole piece 8a provided on the vacuum side of the air supply passage 24,
The inner diameter of the pole piece 9a is made smaller as the pole piece 8a on the vacuum side. Other configurations and operations are similar to those of the first to third embodiments described above.

Next, FIG. 6 shows a fifth embodiment of the present invention. In all of the first to fourth embodiments described above, by making the first gap 21 on the vacuum side smaller than the second gap 22 on the opposite side, the holding force of the magnetic fluid 10 in the first gap 21 is increased to a second level. Whereas the holding force of the magnetic fluid 10 in the gap 22 was larger than that of the magnetic fluid 10, in the case of this embodiment, a spacer 29 is provided between the pole piece 9a and the permanent magnet 7 on the side opposite to the vacuum side. By sandwiching them, the holding force of the magnetic fluid 10 in the first gap 21 is made larger than the holding force of the magnetic fluid 10 in the second gap 22.

By providing such a spacer 29, the density of the magnetic flux existing in the second gap 22 becomes lower than the density of the magnetic flux existing in the first gap 21, and the density of the magnetic flux existing in the second gap 22 becomes lower than the density of the magnetic flux existing in the first gap 21.
The holding force of the magnetic fluid 10 to the second gap 22 becomes larger than the holding force of the magnetic fluid 10 to the second gap 22. The spacer 29 may be made of a magnetic material or a non-magnetic material, but preferably a non-magnetic material.

Next, FIG. 7 shows a sixth embodiment of the present invention. In the case of this embodiment, a rolling bearing 30 is provided between the magnetic fluid sealing device main body 3a on the vacuum side end and the adjacent magnetic fluid sealing device main body 3, and the space 19b where this rolling bearing 30 exists is used as the vacuum pump. It makes me understand. In the case of this embodiment, there is an effect of preventing contamination caused by leakage, dust, or evaporation of the lubricating oil for lubricating the rolling bearing 30. The other configurations and operations are the same as in the first embodiment described above.

In each of the first to sixth embodiments described above, only the space 19b adjacent to the space 19a closest to the vacuum space is communicated with the vacuum pump, and air is left in the space 19a. However, the air in this space 19a can also be exhausted by the structure shown in FIGS. 8 to 15.

First, the structure of the first example shown in FIG. 8 is the same as the first example shown in FIG. The structure of this example is the same as the second embodiment shown in FIG. 3, except that a through hole 31 is formed in the pole piece 9a, and the structure of the third example shown in FIG. 10 is the same as that shown in FIG. In the third embodiment, through holes 31, 31 are formed in the protrusions 28, 28 of the pole piece 27. In the case of this third example, the diameter of the through hole 31 on the side of the space 19 is made larger than that of the through hole 31 on the side of the vacuum space.

Next, the structure of the fourth example shown in FIG. 11 is similar to that of the fourth example shown in FIG.
The structure of the fifth example shown in FIG. 12 in which a through hole 31 is formed in the housing 1 and the permanent magnet 7 in the first example shown in FIG. The structure of the sixth example shown in FIG. 13 is the structure of the sixth example shown in FIG. 13, which is the same as the second example shown in FIG. The structure of the seventh example shown in FIG. 14 is the same as that of the third example shown in FIG.
In the structure of the eighth example shown in FIG. 5, in the fourth example shown in FIG. 5, a passage 32 communicating with the vacuum pump is formed in the housing 1 and the permanent magnet 7.

Although not shown in the drawings, the present invention is similar to FIG.
It goes without saying that the present invention can also be applied to a vacuum multi-stage magnetic fluid sealing device having a structure in which magnetic fluid is held on the outer peripheral edge side of the pole piece as shown in (B).

[0044]

Effects of the Invention The multi-stage magnetic fluid sealing device for vacuum of the present invention is constructed and operates as described above, and therefore, it reliably prevents the magnetic fluid from scattering into the vacuum space and cleans the vacuum space. I can maintain my degree.

[Brief explanation of drawings]

FIG. 1 is a half sectional view showing a first embodiment of the present invention.

FIG. 2 is a side view showing two examples of the shape of the pole piece.

FIG. 3 is a half sectional view showing a second embodiment of the present invention.

FIG. 4 is a half sectional view showing a third embodiment of the present invention.

FIG. 5 is a half sectional view showing a fourth embodiment of the present invention.

FIG. 6 is a half sectional view showing a fifth embodiment of the present invention.

FIG. 7 is a half sectional view showing a sixth embodiment of the present invention.

FIG. 8 is a half sectional view showing a first example of a structure that evacuates a space partitioned on both sides by magnetic fluid on the vacuum space side.

FIG. 9 is a half sectional view showing a second example.

FIG. 10 is a half sectional view showing a third example.

FIG. 11 is a half sectional view showing the fourth example.

FIG. 12 is a half sectional view showing the fifth example.

FIG. 13 is a half sectional view showing the sixth example.

FIG. 14 is a half sectional view showing the seventh example.

FIG. 15 is a half sectional view showing the eighth example.

FIG. 16 is a sectional view showing two examples of the basic structure of a magnetic fluid seal device.

[Fig. 17] The first part of the conventional vacuum multistage magnetic fluid seal device
A sectional view showing an example.

FIG. 18 is a half sectional view showing the second example.

[Explanation of symbols]

1 Housing 2 Shafts 3, 3a Magnetic fluid seal device main body 4 Inner circumferential surface 5 Outer circumferential surface 6 Space 7 Permanent magnets 8, 8a Pole pieces 9, 9a Pole piece 10 Magnetic fluid 11 Casing 12 Rolling bearing 13 Bearing housing 14 Multi-stage magnetism for vacuum Fluid seal device 15
Pole piece 16 Pole piece 17 Concave groove 18 O-ring 19, 19a, 19b Space 20 Spacer 21 First gap 22 Second gap 24 Intake passage 25 Vacuum pump 26 Notch 27 Pole piece 28 Projection 29 Spacer 30 Rolling bearing 31 Through hole 32 passage

Claims (1)

[Claims] Claim 1: A first member made of a magnetic material and having a cylindrical peripheral surface; a second member that is provided concentrically with the first member and rotates relative to the first member; a permanent magnet formed in a circular ring shape and having a size that can be freely inserted into a cylindrical space between the circumferential surface of the second member and the circumferential surface of the first member, and magnetized in the axial direction; A pole piece formed in a ring shape having a size that can be freely inserted into the cylindrical space and fixed to the side surface of the permanent magnet, and a gap between the circumferential edge of the pole piece and the circumferential surface of the first member. In a vacuum multi-stage magnetic fluid seal device that is composed of magnetic fluid held at multiple locations in the axial direction by the magnetic force of the permanent magnet, and is used with one axial side facing a vacuum space, the above-mentioned The holding force of the magnetic fluid in the gap between the circumferential edge of the pole piece and the circumferential surface of the first member is increased in the first gap in contact with the vacuum space and decreased in the second gap adjacent to the first gap, and A multi-stage magnetic fluid sealing device for vacuum use, characterized in that a space portion which is further away from the vacuum space than the second gap and partitioned on both sides by the magnetic fluid is evacuated.