JPH05288277A - Magnetic fluid shaft sealing device and method and device for driving the same - Google Patents

Abstract

PURPOSE:To provide a magnetic fluid shaft sealing device which can prevent breakage of magnetic fluid film without controlling pressure of an intermediate chamber with high precision in the magnetic fluid shaft sealing device which utilizes the intermediate chamber for differential air exhaust. CONSTITUTION:It is a magnetic fluid shaft sealing device which has a main pole piece 2 which faces a process chamber 21 and is arranged around a rotary shaft 1, a main magnet 3 which is arranged close to or in contact with the main pole piece 2, an intermediate chamber 31 which is surrounded by magnetic closed circuit which is formed by the main magnet 3, and a pump 18 which exhausts air in the intermediate chamber 31. Difference in pressure between the process chamber 21 and intermediate chamber 31 is maintained by a magnetic fluid film 4 which is formed between the main pole piece 2 and the rotary shaft 1. The main magnet 3 which forms the magnetic fluid film 4 is arranged quite close to the main pole piece 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shaft sealing device for holding a pressure difference in the axial direction around a rotary shaft arranged both inside and outside a process chamber. In particular, the present invention relates to a magnetic fluid shaft sealing device of the type in which an annular magnetic fluid film is formed on the outer peripheral surface of a rotating shaft and the pressure difference is held by the magnetic fluid film.

[0002]

2. Description of the Related Art In the industrial field, a space whose inside is hermetically shielded is kept at a pressure state different from the external pressure, that is, a differential pressure state, and various treatments are performed under the differential pressure state. There are various types of devices. For example, in a semiconductor wafer decompression processing apparatus, a vacuum dryer, a rotating anticathode type X-ray generation apparatus, and the like, predetermined processing is performed under a reduced pressure in a vacuum. The above-mentioned process chamber is a space in which such an arbitrary process is performed and is maintained at a pressure different from the outside. In an apparatus using such a process chamber, in many cases, a rotary shaft is provided inside and outside the process chamber, and various processes are performed by using the rotation of the rotary shaft as a power source. What must be noted in this type of device is that the pressure difference between the internal pressure and the external pressure of the process chamber is accurately kept constant even when the rotary shaft is arranged inside and outside the process chamber. ..

It has been widely known for a long time that there is a so-called shaft sealing device as a device for maintaining a constant pressure difference between the differential pressure region and the external region. It is already known that one of such shaft sealing devices is a so-called magnetic fluid shaft sealing device that uses a magnetic fluid. As such a magnetic fluid shaft sealing device, conventionally, there is one having a structure shown in FIG. This shaft sealing device has a plurality of, in the figure, five annular magnetic members, that is, pole pieces 52a, 52b, 52c, arranged in the axial direction around a rotary shaft 51 that rotates about an axis L, that is, pole pieces 52a, 52b, 52c, and 52d, 52
have e. Between the pole pieces 52a to 52e, annular magnets 53a, 53b, 53c, 53d are arranged so that their polarities face each other. In the figure, the atmospheric pressure region P is on the right side of the leftmost pole piece 52a,
The area on the left side thereof is a pressure state area different from the atmospheric pressure, that is, a differential pressure area Q.

Each of the pole pieces 52a to 52e and the rotary shaft 5
The magnetic fluid 54 is injected between the first and second positions. This magnetic fluid is a fluid that is already known per se, and is, for example, a liquid in which magnetic metal fine particles are dispersed in a colloidal state in a non-magnetic base solution and further stabilized to form an apparent magnetic body. As the metal fine particles, for _{example, (4 O 5 MnO · ZnO} · Fe) and the like Mangan'n zinc ferrite is used. The diameter of the metal fine particles is about 100 Å, and the surface thereof is coated with a surfactant. As the base solution, an oil having a low vapor pressure, a small evaporation amount, and stable for a long period of time is used.

In FIG. 11, magnetic lines of force emitted from the N poles of the magnets 53a to 53d travel through the adjacent pole piece, the rotary shaft 51, and the other adjacent pole piece to be focused on the S pole. As a result, a magnetic closed circuit is formed. Due to the action of this magnetic closed circuit, the pole piece 52
An annular film of magnetic fluid 54 is formed between the inner peripheral ends of a to 52e and the outer peripheral surface of the rotary shaft 51, and the magnetic fluid film 54 forms a pressure between the atmospheric pressure region P and the differential pressure region Q. The difference is retained. As shown in the figure, the multi-stage magnetic fluid film 5
By forming 4, the pressure difference obtained by adding the specific withstand pressure difference inherent to each magnetic fluid film 54 can be held as a whole.

However, in the above-described conventional magnetic fluid shaft sealing device, it is formed between the leftmost magnetic fluid film 54a and the next magnetic fluid film 54b in the process of depressurizing the differential pressure region Q. The pressure difference between the space R and the differential pressure region Q instantaneously becomes larger than the withstand pressure difference of the magnetic fluid film 54a, and therefore,
It was observed that the air in the space R broke through the magnetic fluid film 54a and was ejected to the differential pressure region Q. When this phenomenon occurs, the pressure in the differential pressure region Q instantaneously rises, or the oil forming the magnetic fluid film 54a is scattered in the differential pressure region Q and contaminates the inside thereof.

In general, the magnetic fluid shaft sealing device is used when the differential pressure region Q is to be depressurized in a clean environment, for example, high vacuum is desired. Therefore, the instantaneous increase of the pressure in the differential pressure region Q or the contamination of the inside by oil as described above significantly deteriorates the characteristics of the shaft sealing device.

A conventional magnetic fluid shaft sealing device having a structure shown in FIG. 12 is also known. In this magnetic fluid shaft sealing device, an annular magnet 53 is provided in the middle of a cylindrical pole piece 55 that surrounds the rotary shaft 51 and is provided with a plurality of comb-teeth-shaped protrusions. An intermediate chamber 56 is provided between the left pole piece projection 55a and the next projection 55b. A vacuum pump 57 is provided in the intermediate chamber 56.
Are connected.

The magnet 53 forms a magnetic path between each protrusion of the pole piece 55 and the rotating shaft 51, and a magnetic fluid film 54 is formed along the magnetic path. The magnetic fluid film 54 holds the pressure difference between the atmospheric pressure region P and the differential pressure region Q. Further, the intermediate chamber 56 is decompressed by the pump 57 so that almost no differential pressure is applied between the intermediate chamber 56 and the differential pressure region Q.

If the magnetic fluid shaft seal device of FIG. 12 operates normally, it is sure that the leftmost magnetic fluid film 54a is broken and the degree of vacuum in the differential pressure region Q is deteriorated, or the differential pressure region Q is oiled. The problem of being contaminated by can be avoided. However, in the shaft seal device of FIG. 12, since the magnet 53 is far away from the leftmost stage pole piece protrusion 55a in the direction away from the differential pressure region Q, the pole piece protrusion 55a is separated from the pole piece protrusion 55a. The magnetic force of the magnetic path formed is very weak.
Therefore, the differential pressure resistance of the magnetic fluid film 54 formed there was extremely small. Therefore, unless the pressure in the intermediate chamber 56 is controlled with extremely high precision, it is not possible to achieve the intended purpose, that is, avoiding the breakage of the magnetic fluid film 54.
In the current vacuum control technology, such high precision control is very difficult, and therefore, as a practical matter, FIG.
It was very difficult to normally operate the magnetic fluid shaft sealing device.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the conventional magnetic fluid shaft sealing device, and is a magnetic fluid shaft sealing device using an intermediate chamber. It is an object of the present invention to provide a magnetic fluid shaft sealing device capable of preventing breakage of a magnetic fluid film without requiring highly precise chamber pressure control.

[0012]

A magnetic fluid shaft sealing device according to the present invention includes a main pole piece which is in contact with a process chamber and is arranged with a gap from the rotary shaft, a main pole piece and a rotary shaft. A magnetic fluid film formed in a gap between the main pole piece, a main magnet disposed adjacent to the main pole piece, and a sub pole piece disposed opposite to the main pole piece with the main magnet interposed therebetween. It is characterized by having an intermediate chamber surrounded by a magnetic closed circuit formed via the main pole piece, the rotating shaft, and the auxiliary pole piece by the action of a magnet, and an intermediate chamber decompressing means for decompressing the intermediate chamber. ..

In the above structure, the meaning that the main magnet is provided adjacent to the main pole piece means that the main magnet is brought into direct contact with the main pole piece or near the main pole piece via an interposition such as an adhesive. This includes the case where the main magnet is arranged.

Further, in the method for driving the magnetic fluid shaft sealing device according to the present invention, in the magnetic fluid shaft sealing device described above, the pressure difference between the process chamber and the intermediate chamber is set between the main pole piece and the rotating shaft. The intermediate chamber decompression means decompresses the intermediate chamber so that the magnetic fluid film formed in the above can maintain a value equal to or lower than the differential pressure resistance that can be retained.

[0015]

The main magnet for forming the magnetic path in the gap between the main pole piece and the rotating shaft is arranged in the immediate vicinity of the main pole piece. As a result, a strong magnetic path can be formed between the pole piece and the rotating shaft, as compared with the conventional case in which the main magnet is arranged far away from the intermediate chamber in the direction away from the process chamber. Therefore, the differential pressure resistance that can be held by the magnetic fluid film formed based on the magnetic path can be increased. The increase in the differential pressure resistance of the magnetic fluid film means that it is possible to prevent the magnetic fluid film from breaking without strict pressure control of the intermediate chamber. The shaft seal device can be operated accurately with very simple control.

[0016]

【Example】

(First Embodiment) FIG. 1 shows an embodiment of a magnetic fluid shaft sealing device according to the present invention. This magnetic fluid shaft sealing device has a metal cylindrical casing 9 fixed to the wall 8 of the process chamber 21 forming the differential pressure region Q by fastening means such as bolts (not shown). The differential pressure region Q in the process chamber 21 is set to a pressure state different from the external atmospheric pressure region P, and various processes such as semiconductor wafer manufacturing process and rotation in the X-ray generator are performed under the differential pressure state. Rotation of the anticathode is performed. A bearing 10 is fixed to the right inner wall of the casing 9, and the rotating shaft 1 is supported by the bearing 10. Rotating shaft 1
Are arranged inside and outside the process chamber 21,
It is driven by a drive source (not shown) to rotate about the central axis L. The rotation of the rotary shaft 1 causes the process chamber 2 to rotate.
It is used as a driving source for various processes performed in the No. 1.

An annular main pole piece 2 made of a magnetic material is fitted inside the left end of the casing 9 via an elastic O-ring 11. The magnetic material referred to here is a material having a property of allowing a magnetic force line generated from a magnet to pass therethrough. An annular auxiliary pole piece 5 is fitted in the inner wall of the casing 9 on the right side of the main pole piece 2 so as not to move, and an annular ring is provided between the auxiliary pole piece 5 and the main pole piece 2. A main magnet 3 is provided. The main magnet 3 is
The main pole piece 2 is arranged so as to be in direct contact with the side surface of the main pole piece 2 or to be close to the side surface via an interposition such as an adhesive. In the case of the embodiment, the left side surface of the main magnet 3 is N
The right side of the pole is the S pole. Of course, there is no problem even if the polarity is reversed.

A cylindrical seal block 13 having an inner diameter slightly larger than the diameter of the rotary shaft 1 is fixedly fixed to the inner wall of the casing 9 on the right side of the auxiliary pole piece 5. Between the seal block 13 and the rotary shaft 1 and between the seal block 13 and the casing 9, respectively,
O-rings 14 and 15 are provided.

A preliminary chamber 6 which is a cylindrical space is formed between the seal block 13 and the auxiliary pole piece 5, and the preliminary chamber 6 is sealed from the atmospheric pressure region P by O-rings 14 and 15. Has been done. A small through hole 30 is provided at an appropriate position of the auxiliary pole piece 5, and the presence of the through hole 30 allows the intermediate chamber 31 and the auxiliary chamber 6 to be maintained at the same atmospheric pressure. As shown in FIG. 2, the intermediate chamber 31 is a space surrounded by a magnetic closed circuit J formed by the action of the main magnet 3 via the main pole piece 2, the rotary shaft 1, and the sub pole piece 5. The number of through holes 30 connecting the intermediate chamber 31 and the auxiliary chamber 6 is the same as the number of the intermediate chamber 31 and the auxiliary chamber 6.
It can be set freely within the range where and are maintained at the same atmospheric pressure.

In FIG. 1, an exhaust hole 16 which is a through hole is provided in a wall of a casing 9 which forms a preliminary chamber 6, and an exhaust pipe extending from a vacuum pump 18 on the shaft sealing device side is provided in the exhaust hole 16. 19 are airtightly connected. Exhaust hole 1
An intermediate chamber pressure control valve 20 is provided in the middle of 9.

FIG. 3 shows the entire drive system of the magnetic fluid shaft sealing device including the process chamber 21. In this drive system, a turbo molecular pump 23 is connected to the process chamber 21 via a valve 22. A vacuum pump 17 on the process chamber side is connected to the turbo molecular pump 23 via a valve 24. A valve 27 is provided in the middle of the exhaust pipe 26 that leads from the vacuum pump 17 to the process chamber 21. An air flow pipe 28 is provided between the process chamber 21 and the shaft sealing device side exhaust pipe 19,
A valve 29 is provided in the middle of the flow pipe 28.

The operation of the magnetic fluid shaft sealing device having the above structure and its drive system will be described below.

Due to the operation of the magnetic closed circuit J described in FIG. 2, the gap G between the main pole piece 2 and the rotary shaft 1 is formed.
The magnetic fluid film 4 which is a film formed by the magnetic fluid
Is formed. At this time, the magnetic fluid film 4a is also formed in the gap between the sub pole piece 5 and the rotating shaft 1. Of these magnetic fluid films, the main pole piece 2 and the rotating shaft 1
By the action of the magnetic fluid film 4 formed between and, the differential pressure between the intermediate chamber 31, that is, the preliminary chamber 6 and the process chamber 21 is maintained. The differential pressure between the intermediate chamber 31, that is, the preparatory chamber 6 and the atmospheric pressure region P is held by the O-rings 14 and 15 provided in the seal block 13.

In FIG. 3, a vacuum pump 18 on the shaft sealing device side is provided.
And when the process chamber side vacuum pump 17 is stopped,
The inside pressure of the intermediate chamber 31 and the process chamber 21 in the shaft sealing device is equal to the atmospheric pressure. In this state, the intermediate chamber pressure adjusting valve 20 is opened, the process chamber pressure adjusting valve 27 is opened, the valve 29 of the air flow pipe 28 is further opened, and the shaft sealing device side vacuum pump 18 and the process chamber side vacuum pump 17 are opened. Start operation. By the operation of both pumps 18 and 17, the pressure inside the intermediate chamber 31 and the process chamber 21 in the shaft sealing device is gradually reduced. At this time, since the air flow pipe 28 is provided between the process chamber 21 and the intermediate chamber 31, the atmospheric pressure difference between the two is maintained at almost zero. However,
According to the experiments by the inventor, the pressure in the intermediate chamber 31 seems to be slightly lower than the pressure in the process chamber 21. Of course, the pressure difference is smaller than the withstand pressure difference of the magnetic fluid film 4 (FIG. 2).

During the above depressurizing operation, the pressure difference between the intermediate chamber 31 and the process chamber 21 is almost equal due to the action of the air flow pipe 28, that is, the pressure difference smaller than the withstand pressure difference of the magnetic fluid film 4. Maintained at. As a result, the air in the intermediate chamber 31 is reliably prevented from breaking through the magnetic fluid film 4 and ejecting into the process chamber 21.

The pressure in the intermediate chamber 31, which is gradually reduced, has a value approximately equal to the differential pressure resistance of the magnetic fluid film 4, eg, 100 To.
When the pressure is reduced to about rr, the valve 29 of the flow pipe 28 is closed, and thereafter, the intermediate chamber 31 is depressurized by the shaft sealing device side vacuum pump 18 and the process chamber 21 is depressurized by the process chamber side vacuum pump 17, respectively. To be done. Further, when the pressure in the process chamber 21 drops to a predetermined pressure,
The valve 22 attached to the turbo molecular pump 23 is opened, and the valve 24 at the subsequent stage is opened, so that the turbo molecular pump 23 performs high-precision exhaust. Finally, the pressure in the process chamber 21 is reduced to about 10 ⁻⁸ Torr, and the pressure in the intermediate chamber 31 in the shaft sealing device is reduced to about 150 Torr.

The process chamber 2 is driven by the turbo molecular pump 23.
While decompressing the inside of the chamber 1 to a highly accurate vacuum state, the pressure difference between the intermediate chamber 31 and the process chamber 21 has already been increased.
Since the pressure resistance value is lower than the withstand pressure difference value shown in FIG. 2, the air in the intermediate chamber 31 is surely prevented from breaking the magnetic fluid film 4 and ejecting into the process chamber 21.

As described above, in FIG. 3, the pressure difference between the intermediate chamber 31 and the process chamber 21 is always equal to or lower than the withstand pressure difference value of the magnetic fluid film 4 by providing the air flow pipe 28. To be controlled. The differential pressure resistance value of the magnetic fluid film 4 referred to here is the pressure difference that can be held by the magnetic fluid film 4, and this value is the characteristics of the magnet, the characteristics of the magnetic fluid, the shape of the main pole piece 2, and It takes various values depending on factors such as the size of the gap G between the main pole piece 2 and the rotary shaft 1. According to the experiments conducted by the inventor, it has been found that the pressure resistance value has the following value when a certain specific use condition is considered.

(Experimental Example Regarding Resistance to Differential Pressure of Magnetic Fluid Film) Conditions 1. As the magnetic fluid shaft sealing device, the device having the structure shown in FIG. 2 was used.

2. Characteristics of magnetic fluid 4 Saturation magnetization: 200 Gauss Specific gravity: 2.10 Viscosity: 5,000 CPS at 20 ° C Vapor pressure: 2 × 10 ^-11 Torr at 20 ° C 5 × 10 ^-7 Torr at 100 ° C Base solution : Perfluoropolyether Metal fine particles: Manganese zinc ferrite (MnO.ZnO
・ Fe ₂ O ₃ ) 3. Characteristic type of main magnet 3: 2-17 system (Sm ₂ [Co, Cu, F
e, Zr] ₁₇ ) Residual magnetic flux density: 9.2 to 9.8 kG (kilogauss) Retention force: 7.8 to 9.4 kOe (kiloersted) Maximum energy product: 20 to 24 MGOe (megagauss oersted) or more Under the conditions, the gap G between the main pole piece 2 and the rotating shaft 1 was changed and the differential pressure resistance of the magnetic fluid film 4 at each time was measured. The results shown in Table 1 below were obtained. It was Table 1 ──────────────────────── Gap G (μm) Differential pressure resistance (Torr) ────────────── ─────────── 80 230 100 100 180 120 150 ──────────────────────── In addition, the rotation axis of the main pole piece 2 The magnetic field strength of the tip closest to 1 was 3000 G (Gauss).

When the results of Table 1 are shown in a graph, a graph as shown in FIG. 4 was obtained. What can be understood from this graph is that the area S below the obtained curve F is an area that does not exceed the differential pressure resistance value of the magnetic fluid film 4. Therefore, when using the magnetic fluid and magnet described in the above condition column,
The pressure difference between the intermediate chamber 31 (FIG. 2) and the process chamber 21 is shown in FIG.
If the pressure value is controlled to be smaller than the curve F of
This means that the pressure applied to the magnetic fluid film 4 is suppressed to a value equal to or lower than the withstanding pressure difference value peculiar to the magnetic fluid film, and the magnetic fluid film 4 can be reliably prevented from breaking.

In the drive system shown in FIG. 3, as already mentioned, since the air flow pipe 28 that connects the process chamber 21 and the intermediate chamber 31 is provided, the pressure difference between the two chambers is automatically adjusted. Is substantially equal to, that is, the differential pressure resistance value of the magnetic fluid film 4 is maintained.

(Other Embodiment of Vacuum Evacuation Drive System) FIG.
2 shows another embodiment of a vacuum exhaust system for driving the magnetic fluid shaft sealing device shown in FIG. 1. 3 is different from the vacuum exhaust system shown in FIG. 3 in that the vacuum exhaust system shown in FIG.
In (1), the air flow pipe 28 provided between the process chamber 21 and the intermediate chamber 31 is removed, and the process chamber 21 and the intermediate chamber 31 are independently exhausted.

In FIG. 5, the process chamber 21 is provided with a pressure sensor 32 for detecting the pressure inside.
Further, a pressure sensor 33 that detects the pressure in the intermediate chamber 31 is provided at an appropriate position of the exhaust pipe 19 on the shaft sealing device side. Each of the pressure sensors 32 and 33 converts the pressure information of each room into an electric signal and outputs the electric signal, and the output signal is input to an input port of a control device 34 having a built-in computer. At the output port of the control device 34, the intermediate chamber pressure control valve 20, the pressure force control valve 22 attached to the turbo molecular pump 23, and the pressure control valve 2 located at the subsequent stage of the turbo molecular pump 23.
4 and the process chamber pressure control valve 27 are turned on.
The / OFF driver is connected.

A program for controlling the operation of each device shown in the figure is stored in the program storage area in the control device 34, and the following operation is executed based on the program.

Intermediate chamber 31 and process chamber 2 in the shaft sealing device
1 is decompressed independently by vacuum pumps 18 and 17. During this depressurization operation, the control device 34 detects the pressure in the process chamber 21 by the pressure sensors 32 and 33 and calculates the difference between the two. This calculation result is compared with a predetermined threshold value corresponding to the differential pressure resistance value specific to the magnetic fluid film 4 (FIG. 2). When setting this threshold value, for example, the differential pressure resistance data regarding the magnetic fluid film shown in FIG. 4 is referred to.

The control device 34 controls the pressure control valves 20, 22, 24 and 27 based on the comparison result, and the difference between the pressure in the process chamber 21 and the pressure in the intermediate chamber 31 is determined by the magnetic fluid film 4. Always be smaller than the differential pressure resistance value of.
As a result, during the depressurizing operation of the process chamber 21 and the intermediate chamber 31 and after the inside of the process chamber 21 is set to a desired vacuum state, the air in the intermediate chamber 31 breaks the magnetic fluid film 4 and is ejected into the process chamber 21. It can be surely prevented.

(Second Embodiment) FIG. 6 shows a second embodiment of the magnetic fluid shaft sealing device. This embodiment differs from the first embodiment shown in FIG. 2 in that the left side surface of the main pole piece 2 is
That is, the auxiliary magnet 12 is fixed at a position facing the main magnet 3 with the main pole piece 2 interposed therebetween. The auxiliary magnet 12 has an N pole on the right side and an S pole on the left side. That is, the polarities of the main magnet 3 and the auxiliary magnet 12 are opposite to each other.

By providing the auxiliary magnets 12 of opposite polarities, the strength of the magnetic flux lines from the main pole piece 2 to the rotary shaft 1 due to the main magnets 3 is greater than that when the auxiliary magnets 12 are not used. Is getting stronger. Therefore, the volume of the magnetic fluid film 4 formed between the main pole piece 2 and the rotating shaft 1,
The density or strength is larger or higher than that of the magnetic fluid film 4 formed only by the main magnet 3. Therefore, the differential pressure that can be retained by the magnetic fluid film 4, that is, the differential pressure resistance is
This is larger than in the case of the first embodiment (FIG. 2). Therefore,
The differential pressure control between the intermediate chamber 31 and the process chamber 21 becomes easier.

(Third Embodiment) FIG. 7 shows a third embodiment of the magnetic fluid shaft sealing device according to the present invention. In this embodiment, the same members as those used in the embodiment shown in FIG. 1 are designated by the same reference numerals. The feature of this embodiment is that the main magnet 43 adjacent to the main pole piece 2 is provided with a through hole 40 for air flow, and the inside of the intermediate chamber 31 is exhausted by the vacuum pump 18 through the through hole 40. .. According to this structure, the auxiliary chamber 6 in the embodiment of FIG.
Is unnecessary, and the overall shape of the shaft sealing device can be made extremely small. The through hole 4 is formed in the main magnet 43.
Instead of providing 0, it is also possible to form a slit at one place of the main magnet 43 and use it as a passage for air flow.

(Fourth Embodiment) FIG. 8 shows a fourth embodiment of the magnetic fluid shaft sealing device according to the present invention. Also in this embodiment, the same members as those used in the embodiment shown in FIG. 1 are designated by the same reference numerals. The feature of this embodiment is that
The through-hole 50 for air flow is provided in a part of the auxiliary pole piece 45 arranged on the right side of the main magnet 3, and the inside of the intermediate chamber 31 is exhausted by the vacuum pump 18 through the through-hole 50. As shown in FIG. 9, the through hole 50 is provided in at least one location of the auxiliary pole piece 45 along the radial direction. Also in this embodiment, it is not necessary to provide the auxiliary chamber 6 in the embodiment of FIG. 1, and the overall shape of the shaft sealing device can be made very small. Also,
This embodiment is convenient when there is a situation in which it is difficult to form a through hole in the main magnet 3.

(Fifth Embodiment) FIG. 10 shows a fifth embodiment of the magnetic fluid shaft sealing device according to the present invention. This embodiment is a modification of the embodiment shown in FIG. Specifically, instead of the seal block 13 including the O-rings 14 and 15, a magnetic fluid shaft sealing unit 35 is used. The magnetic fluid shaft sealing unit 35 includes four pole pieces 36, four magnets 37, and a magnetic fluid 38 injected between the inner peripheral end of each pole piece 36 and the rotary shaft 1. ..

The embodiment using the O-rings 14 and 15 shown in FIG. 8 works effectively when the rotation speed of the rotary shaft 1 is relatively low. However, when the rotation speed of the rotary shaft 1 is high, it is conceivable that the airtightness is reduced and the pressure in the intermediate chamber 31 becomes unstable. On the other hand, according to the present embodiment in which the magnetic fluid shaft sealing unit 35 is used between the intermediate chamber 31 and the atmospheric pressure region P, highly accurate airtightness is secured even when the rotation speed of the rotary shaft 1 is increased. Therefore, the pressure in the intermediate chamber 31 can be stably maintained.

In the above description, as the process chamber 21, a semiconductor wafer decompression processing device, a vacuum dryer, a rotating anticathode type X-ray generator, a single crystal pulling device, an ion implanting device, and other rotary shafts are used as the process chamber. You can think of any device that needs to be installed both inside and outside.

The present invention has been described above with reference to the preferred embodiments, but the present invention is not limited to these embodiments. For example, in each of the above-described embodiments, the rotary shaft composed of a solid round bar is considered as the rotary shaft 1, but instead of this, a rotation of a so-called multi-axis structure constituted by stacking a plurality of shaft members coaxially is formed. It can also be an axis.

[0046]

According to the magnetic fluid shaft sealing device of the first aspect, since the main magnet is provided in contact with or close to the pole piece forming the intermediate chamber whose pressure is reduced, the pole piece and the rotary shaft are A strong magnetic path can be formed between the pole piece and the rotating shaft, and therefore the strength of the magnetic fluid film formed between the pole piece and the rotating shaft, that is, the magnetic fluid film that separates the process chamber and the intermediate chamber from each other, can be very high. It can be strengthened and the differential pressure resistance of the magnetic fluid film can be maintained at a high value. As a result, exhaust control for reducing the pressure in the intermediate chamber can be easily performed.

According to the magnetic fluid shaft sealing device of the second aspect, it is possible to form a magnetic fluid film having a higher withstand pressure differential, and the exhaust control of the intermediate chamber is further simplified.

According to the driving device of the magnetic fluid shaft sealing device of the fourth aspect, the difference in relative pressure between the process chamber and the intermediate chamber can be prevented by the magnetic fluid film having a very simple structure. It can be maintained below the pressure value.

According to the driving device for the magnetic fluid shaft sealing device of the fifth aspect, it is possible to automatically and highly accurately evacuate the process chamber and the intermediate chamber.

[0050]

[Brief description of drawings]

FIG. 1 is a side sectional view showing a first embodiment of a magnetic fluid shaft sealing device according to the present invention.

FIG. 2 is a cross-sectional view showing an enlarged main part of the first embodiment.

FIG. 3 is a schematic view showing an embodiment of a drive device for a magnetic fluid shaft sealing device according to the present invention.

FIG. 4 is a graph showing a relationship between a gap between a pole piece and a rotating shaft and a withstand pressure difference value.

FIG. 5 is a schematic view showing another embodiment of the drive device of the magnetic fluid shaft sealing device according to the present invention.

FIG. 6 is a sectional view showing a second embodiment of the magnetic fluid shaft sealing device according to the present invention.

FIG. 7 is a cross-sectional view showing a third embodiment of the magnetic fluid shaft sealing device according to the present invention.

FIG. 8 is a sectional view showing a fourth embodiment of the magnetic fluid shaft sealing device according to the present invention.

FIG. 9 is a perspective view showing a sub pole piece used in a fourth embodiment.

FIG. 10 is a sectional view showing a fifth embodiment of the magnetic fluid shaft sealing device according to the present invention.

FIG. 11 is a sectional view showing an example of a conventional magnetic fluid shaft sealing device.

FIG. 12 is a cross-sectional view of another example of the conventional magnetic fluid shaft sealing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 rotating shaft 2 main pole piece 3 main magnet 4 magnetic fluid film 5 sub pole piece 12 auxiliary magnet 17 process chamber side vacuum pump 18 intermediate chamber side vacuum pump 20 intermediate chamber pressure control valve 21 process chamber 31 intermediate chamber J magnetic fluid film

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tomo Numakura 3-9-12 Matsubara-cho, Akishima-shi, Tokyo Inside the Haijima factory, Rigaku Denki Co., Ltd. Incorporated company Toshiba Research Institute (72) Inventor Nobuhiro Hasegawa 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research Institute (72) Inventor Yuichiro Yamazaki 72 Horikawa-cho, Kawasaki-shi, Kanagawa Address: Toshiba Horikawacho Factory (72) Inventor Shigeya Mori 72, Horikawacho, Saiwai-ku, Kawasaki, Kanagawa Prefecture Stock: Toshiba Horikawacho Factory

Claims (5)

[Claims] 1. A magnetic fluid shaft sealing device for maintaining a pressure difference in the axial direction around a rotating shaft disposed between a process chamber and the outside of the process chamber, wherein a gap is formed between the process chamber and the rotating shaft. The main pole piece, the magnetic fluid film formed in the gap between the main pole piece and the rotating shaft, the main magnet arranged adjacent to the main pole piece, and the main magnet between them. A sub-pole piece arranged opposite to the main pole piece, an intermediate chamber surrounded by a magnetic closed circuit formed by the action of the main magnet via the main pole piece, the rotating shaft, and the sub pole piece, and the middle A magnetic fluid shaft sealing device, comprising: an intermediate chamber depressurizing means for depressurizing the chamber. 2. The magnetic fluid shaft sealing device according to claim 1, further comprising an auxiliary magnet that is arranged to face the main magnet with the main pole piece interposed therebetween, and the main magnet and the auxiliary magnet have the same pole. A magnetic fluid shaft sealing device, characterized in that they face each other. 3. A driving method for driving the magnetic fluid shaft sealing device according to claim 1, wherein a pressure difference between the process chamber and the intermediate chamber is formed between the main pole piece and the rotary shaft. A method for driving a magnetic fluid shaft sealing device, characterized in that the intermediate chamber decompressing means decompresses the intermediate chamber so as to maintain a value equal to or lower than a withstand pressure difference capable of being retained by the magnetic fluid film. 4. A drive device for driving the magnetic fluid shaft sealing device according to claim 1, wherein the drive device is provided between the process chamber pressure reducing means for reducing the pressure of the process chamber and the process chamber and the intermediate chamber. A drive device for a magnetic fluid shaft sealing device, comprising: an air flow pipe that communicates between the two chambers. 5. A drive device for driving the magnetic fluid shaft sealing device according to claim 1, further comprising: an intermediate chamber pressure control valve provided in association with the intermediate chamber pressure reducing means, and a process chamber for reducing pressure. A process chamber pressure reducing means, a process chamber pressure control valve provided in association with the process chamber pressure reducing means, a process chamber pressure sensor for detecting the pressure in the process chamber, an intermediate chamber pressure sensor for detecting the pressure in the intermediate chamber, And a control device for controlling the operation of the process chamber pressure control valve and the intermediate chamber pressure control valve by inputting the pressure signals from the chamber pressure sensor and the intermediate chamber pressure sensor. The process chamber pressure adjustment valve is set so that the pressure difference between the chamber and the chamber is maintained at a value less than the withstand pressure difference that can be retained by the magnetic fluid film formed between the main pole piece and the rotating shaft. And drive of the magnetic fluid shaft sealing apparatus characterized by controlling the intermediate chamber pressure regulating valve.