JP3773132B2 - Magnetic seal device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic seal device that shields two spatial regions formed around a motion axis such as a rotation axis and a linear motion axis using a magnetic fluid.
[0002]
[Prior art]
In the industry, there are various devices in which a space in which the inside is hermetically shielded is maintained in a pressure state different from the external pressure, that is, a differential pressure state, and various processes are performed under the differential pressure state. Exists. In addition to the differential pressure state, various treatments may be performed with the inside kept in a dustproof state or a special gas atmosphere state. For example, in a semiconductor wafer depressurization apparatus, a vacuum drier, a rotating counter-cathode type X-ray generator, etc., a predetermined process is performed in a dust-proof state depressurized to a vacuum. The magnetic seal device is used to shield two space areas, that is, a space area where the predetermined processing is performed and an atmospheric pressure area.
[0003]
For example, taking a rotating anti-cathode X-ray generator as an example, as shown in FIG. 2, a magnetic seal device 2 between a region Q that is dust-free in a vacuum inside the casing 1 and an atmospheric pressure region P is used. To maintain the differential pressure state and the dustproof state. In this X-ray generator, the inside of the casing 1 is evacuated to a vacuum state by an exhaust device 4 constituted by a turbo molecular pump, a rotary pump, and the like, and a cylindrical target 5 is rotated by a rotary drive device 3 such as a motor. Let The thermoelectrons emitted from the filament 6 by energization collide with the surface of the target 5 at high speed, and X-rays are generated from the collision portion. The generated X-ray is extracted outside through an X-ray extraction window 7 formed of beryllium or the like provided at a predetermined location of the casing 1. This X-ray is used for physical analysis such as X-ray diffraction measurement.
[0004]
As the magnetic seal device 2, as disclosed in Japanese Patent Publication No. 63-24196, a plurality of magnets are arranged in the axial direction of the movement axis so that the same magnetic pole surfaces, that is, N poles or S poles face each other. There is known a magnetic seal device that is arranged side by side and further evacuates the atmospheric pressure side, that is, the high pressure side, of the magnetic fluid to reduce the pressure difference applied to the magnetic fluid. According to this magnetic seal device, since the magnetic pole surfaces of adjacent magnets are the same magnetic pole surface, the magnetic lines of force between the magnets repel each other and the magnetic lines of force formed between the individual magnets and the motion axis are made narrow. It can be focused at high density. For this reason, it is possible to form a strong magnetic fluid film having a high density in the gap between the pole piece and the motion axis, thereby ensuring the differential pressure between the two spatial regions partitioned by these magnetic fluid films. In addition, the magnetic fluid can be prevented from leaking to the low pressure side.
[0005]
[Problems to be solved by the invention]
However, according to the experience of the present inventors, it has often been found that with this conventional magnetic seal device, the high-accuracy shaft sealing ability assumed at the beginning of the design cannot be obtained as desired. In addition, although the desired shaft sealing ability was obtained at the beginning of operation, it was also found that the shaft sealing ability declined more than expected after a relatively short period of time. The present inventors conducted various experiments on why such a phenomenon occurs. As a result, when the magnets are arranged so that the magnetic pole surfaces face each other in order to form a high-density ferrofluid film between the pole piece and the motion axis, a large disturbance occurs in the magnetic flux distribution of each magnet. It has been found that this may be a cause of such an inconvenient phenomenon.
[0006]
The present invention has been made based on the above-mentioned knowledge, and after securing as much as possible the technology of forming a strong magnetic fluid film by arranging adjacent magnets so that the magnetic pole faces face each other. An object of the present invention is to provide a magnetic seal device that can prevent the magnetic flux from being disturbed as much as possible and can maintain a stable shaft sealing ability over a long period of time.
[0007]
[Means for Solving the Problems]
A magnetic seal device according to the present invention includes a plurality of pole pieces arranged around a motion axis formed of a magnetic material, a plurality of magnets that form a magnetic path between each pole piece and the motion axis, The present invention relates to a magnetic seal device having a magnetic fluid filled between a pole piece and a motion axis, and shielding two spatial regions around the motion axis with the magnetic fluid. A feature of the present invention is that the plurality of magnets are configured by arranging a plurality of magnet pairs including a pair of magnets facing the same magnetic pole surface in the axial direction of the motion axis. The at least one magnet pair adjacent to each other among the magnet pairs means that the different magnetic pole faces face each other.
[0008]
As disclosed in Japanese Patent Publication No. 63-24196, the magnetic seal device may be provided with an intermediate exhaust chamber in order to reduce a pressure difference applied to the magnetic fluid. As shown in Japanese Patent Publication No. 63-24196, the intermediate exhaust chamber may be provided at a position on the high-pressure side from all of the plurality of magnets. Sometimes it is arranged. In this case, it was found that the turbulence of the magnetic flux was particularly large with respect to the magnet provided with the intermediate exhaust chamber. Therefore, when the intermediate exhaust chamber is disposed at an intermediate position between the plurality of magnets, it is desirable that the different magnetic pole surfaces be opposed to each other with respect to the magnet pair positioned on both sides of the intermediate exhaust chamber.
[0009]
In general, if the vacuum chamber side is constantly in a vacuum, the magnetic fluid constituting the partition wall is drawn to the vacuum side by the pressure difference, and the force to pull back the magnetic fluid is covered by the magnetic flux. Therefore, if the suction force on the vacuum side becomes larger than the magnetic flux force due to some inconvenience, the magnetic fluid enters the vacuum side and contaminates the vacuum chamber. In order to avoid this phenomenon, intermediate exhaust is performed, and the details will be described as follows.
[0010]
The plurality of chambers formed by the magnetic fluid film in order to maintain the vacuum state are all atmospheric pressure at the beginning of assembly, and these chambers gradually increase the degree of vacuum when evacuating. The fact that each chamber gradually raises the degree of vacuum in this way is not only that these chambers are opened to the vacuum chamber side, but this must be kept clean. It means that the vacuum chamber must be dirty.
[0011]
In recent years, in a semiconductor manufacturing process or the like, it has been required to keep an atmosphere in a room for performing a process very clean. When the magnetic seal device is used in a semiconductor manufacturing process under such circumstances, a poor cleanliness in the process chamber may be pointed out during a long-term operation. The component iron was sometimes detected from the process chamber.
[0012]
Such mixing of iron is considered to be mainly caused by the scattering of the magnetic fluid into the vacuum chamber as described above. Furthermore, when it is insufficient to remove the water used during the magnetic fluid production process from the magnetic fluid, the components mixed in the magnetic fluid may be exhausted at the time of exhausting the process chamber or during vacuum maintenance operation. It is thought that this also causes the bursting pieces to scatter as a result of the bursting of bubbles, such as the bursting of bubbles seen during defoaming or when the soap bubbles burst.
[0013]
In order to eliminate the above inconveniences, an exhaust mechanism is provided at an intermediate position between the vacuum chamber side and the atmospheric pressure side, and most of the pressure difference between the vacuum chamber side and the atmospheric pressure side is shared by the exhaust mechanism. Thus, the pressure difference between the exhaust mechanism and the vacuum chamber is made as small as possible, and as a result, the components in the magnetic fluid located near the vacuum chamber are prevented from scattering and leaching into the vacuum chamber. .
[0014]
In the present invention, since a plurality of magnet pairs composed of a pair of magnets whose magnetic pole faces are opposed to each other are arranged in the axial direction of the motion axis, the magnetic flux can be focused by repulsion of the magnetic force lines in one magnet pair. Thereby, a strong magnetic fluid film can be obtained. In addition, since at least one magnet pair adjacent to each other among the plurality of magnet pairs is arranged so that the different magnetic pole surfaces face each other, the repulsion of the magnetic field lines does not occur at this place, and the magnet The pair behaves like a single magnet, which stabilizes the magnetic flux around multiple magnets. Due to the stability of the magnetic flux, the shaft sealing ability of the magnetic seal device can be secured in a stable state for a long period of time. In addition, since the magnetic flux is stabilized, it becomes easy to design the magnetic characteristics of the magnetic seal device.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a magnetic seal device according to the present invention. This magnetic seal device has a cylindrical housing 10 as shown in FIG. A bearing 16 is fitted in a fixed state inside the right side of the housing 10, and a motion shaft 17 formed of a magnetic material is supported by the bearing. The motion axis 17 may be a rotation axis or a linear motion axis. The magnetic material is a material having a property of being magnetized by a magnet, and is formed of, for example, a steel material. Around the movement axis 17, two space regions, an atmospheric pressure region, that is, a high pressure region P and a vacuum region, that is, a low pressure region Q, are set, and a pressure difference between these regions is maintained by the magnetic seal device. In addition, the magnetic seal device keeps the inside of the low pressure region Q clean by preventing dust, dust, gas, etc. in the high pressure region P from entering the low pressure region Q.
[0016]
Housed in the housing 10 are five ring-shaped pole pieces 8 and four ring-shaped magnets 9a, 9b, 9c, 9d sandwiched between the pole pieces. As shown in FIG. 1B, the left pair of magnets 9a and 9b constitutes a first magnet pair 9A, and the right pair of magnets 9c and 9d constitutes a second magnet pair 9B. An intermediate exhaust chamber 20 is formed between the first magnet pair 9A and the second magnet pair 9B, and a vacuum pump or other exhaust device 22 is connected to the exhaust port 21 of the intermediate exhaust chamber.
[0017]
In the pair of magnets 9a and 9b in the first magnet pair 9A, the N magnetic pole surfaces face each other, that is, the same magnetic pole surfaces face each other. Further, in the pair of magnets 9c and 9d in the second magnet pair 9B, the S magnetic pole surfaces face each other, that is, the same magnetic pole faces face each other. Further, the magnet pairs 9A and 9B facing each other with the intermediate exhaust chamber 20 in between are opposed to the different magnetic pole surfaces, that is, the N magnetic pole surface and the S magnetic pole surface. In other words, the pair of magnets 9b and 9c adjacent to each other across the intermediate exhaust chamber 20 have opposite magnetic pole faces facing each other, and the remaining magnets 9a and 9d are respectively connected to the adjacent magnets 9b and 9c. The magnetic pole faces face each other.
[0018]
A magnetic fluid 12 is injected, that is, filled into a gap formed between the inner peripheral end of each pole piece 8 and the motion shaft 17. This magnetic fluid 12 is a fluid formed by dispersing colloidal metal fine particles in a non-magnetic fluid medium. For example, a fluid such as hydrocarbon, fluorine, or fatty acid, ferrite or other magnetic fluid is used. A fluid in which body powder is dispersed can be used. The filled magnetic fluid concentrates on the magnetic field lines that exit from the N poles of the magnets 9a to 9d, pass through the pole pieces 8 and the motion shafts 17, and reach the S pole of each magnet to form a magnetic fluid film. A differential pressure state between the high pressure region P and the low pressure region Q and a clean atmosphere in the low pressure region Q are maintained by a plurality of stages of magnetic fluid films formed at appropriate positions on the inner peripheral end of each pole piece.
[0019]
A cooling water passage 13 is formed inside the pole piece 8a sandwiched between the magnet 9a and the magnet 9b and inside the pole piece 8b sandwiched between the magnet 9c and the magnet 9d, as shown in FIG. A water supply pump or other cooling water supply device 15 is connected to these cooling water passages 13. The cooling water flowing in the cooling water passage 13 cools the magnetic fluid 12 and prevents the fluorinated oil and the alkyl-based oil contained in the magnetic fluid 12 from evaporating.
[0020]
Since the magnetic seal device according to the present embodiment is configured as described above, the magnetic fluid film 12 formed between each pole piece 8 and the motion shaft 17 by the action of magnetic force causes the inside of the low pressure region Q. The low pressure state and the clean state are maintained. Further, a first magnet pair 9A composed of a pair of magnets 9a and 9b facing each other with the N poles being the same magnetic pole surface, and a second magnet consisting of a pair of magnets 9c and 9d facing the S poles being the same magnetic pole surface. Since the pair 9B is arranged in the axial direction of the motion axis 17, the magnetic flux can be converged by repulsion of the magnetic lines in each magnet pair 9A or 9B, thereby obtaining a strong magnetic fluid film 12. be able to.
[0021]
Moreover, in the relationship between the first magnet pair 9A and the second magnet pair 9B adjacent to each other, the different magnetic pole surfaces are arranged to face each other, that is, the N pole and the S pole are opposed to each other. In this place, the repulsion of the magnetic lines does not occur, and the magnet pair behaves as if it were one magnet, and the magnetic flux around the magnets 9a to 9d is stabilized. Due to the stability of the magnetic flux, the shaft sealing ability of the magnetic seal device can be kept stable over a long period of time. In addition, since the magnetic flux is stabilized, it becomes easy to design the magnetic characteristics of the magnetic seal device.
[0022]
The present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to the embodiments, and various modifications can be made within the technical scope described in the claims. For example, in the embodiment shown in FIG. 1, the case where two magnet pairs are formed by four ring-shaped magnets is shown, but three magnet pairs are formed by six magnets, or more Many magnet pairs can be formed by many magnets. However, even in such a case, the same magnetic pole faces are made to face each other for a pair of magnets in each magnet pair, and different magnetic pole faces are made to face each other between at least one pair of adjacent magnet pairs.
[0023]
In addition, the magnetic seal device according to claim 3 is not restricted by the idea of the magnet pair as described above, but at least a pair of magnets adjacent to each other across the intermediate exhaust chamber among a plurality of magnets. The gist is that the different magnetic pole surfaces face each other. Therefore, when the concept of a magnet pair is considered, the total number of magnets is necessarily an even number. However, in the magnetic seal device according to claim 3, the total number of magnets may be an even number. Sometimes it is odd. However, according to the experiments by the present inventors, it was more effective to stabilize the magnetic flux in the magnetic seal device by making the number of magnets an even number.
[0024]
【The invention's effect】
According to the magnetic seal device of claim 1, a strong magnetic fluid film is obtained by arranging adjacent magnets of a plurality of magnets arranged along the motion axis so that the magnetic pole surfaces face each other. The magnetic flux distribution in the magnetic seal device is disturbed by forming a magnet pair in which the different magnetic pole faces are opposed to each other in at least one place in the magnet array group. The generation was prevented as much as possible. As a result, a magnetic seal device capable of maintaining a stable shaft sealing ability over a long period of time was obtained.
[0025]
According to the magnetic seal device according to claim 2 and claim 3, since the magnets located on both sides of the intermediate exhaust chamber, where magnetic flux disturbance is likely to occur, are arranged so that the different magnetic surfaces face each other. The state of magnetic flux in the device could be further stabilized.
[0026]
[Brief description of the drawings]
1A and 1B are views showing an embodiment of a magnetic seal device according to the present invention, in particular, FIG. 1A is a side sectional view of the entire magnetic seal device, and FIG. 1B is an enlarged cross-sectional view of a main part.
FIG. 2 is a schematic cross-sectional view showing a rotating counter-cathode X-ray generator that is an example of a system using a magnetic seal device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Casing 2 Magnetic seal apparatus 3 Rotation drive apparatus 4 Exhaust apparatus 5 Target 6 Filament 7 X-ray extraction window 8, 8a, 8b Pole piece 9a, 9b, 9c, 9d Magnet 9A, 9B Magnet pair 10 Housing 12 Magnetic fluid 13 Cooling Water passage 15 Cooling water supply device 16 Bearing 17 Motion shaft 20 Intermediate exhaust chamber 21 Intermediate exhaust port 22 Exhaust device

Claims (3)

A plurality of pole pieces arranged around a motion axis formed by a magnetic material, a plurality of magnets forming a magnetic path between each pole piece and the motion axis, and between each pole piece and the motion axis A magnetic seal device having a magnetic fluid filled therein and shielding two spatial regions around the motion axis with the magnetic fluid;
The plurality of magnets are configured by arranging a plurality of magnet pairs, each composed of a pair of magnets facing the same magnetic pole surface, in the axial direction of the motion axis, and at least one set adjacent to each other among the plurality of magnet pairs. A magnetic seal device in which different magnetic pole faces are opposed to each other. 2. The magnetic seal device according to claim 1, wherein an intermediate exhaust chamber is disposed at an intermediate position of the plurality of magnets, and the magnet pairs located on both sides of the intermediate exhaust chamber have opposite magnetic pole faces facing each other. apparatus. A plurality of pole pieces arranged around a motion axis formed by a magnetic material, a plurality of magnets forming a magnetic path between each pole piece and the motion axis, and between each pole piece and the motion axis In a magnetic seal device having a magnetic fluid to be filled and an intermediate exhaust chamber disposed at an intermediate position of the plurality of magnets, and shielding two space regions around the motion axis with the magnetic fluid,
A magnetic seal device, wherein a pair of magnets adjacent to each other across an intermediate exhaust chamber face opposite magnetic pole faces, and the remaining magnet faces opposite magnetic pole faces.

Images