JPS5946394A - Turbo molecular pump - Google Patents

Abstract

PURPOSE:To improve the degree of attained vacuum and obtain clean vacuum at all times including the time when the pump is stopped by a method wherein a bearing at a high-vacuum side is constituted by an attracting type magnetic bearing of a permanent magnet having no change of magnetic characteristics after a high-temperature treatment. CONSTITUTION:The high-vacuum side of a rotor 6 is supported by the attracting force of the permanent magnet 9 while the low-vacuum side thereof is supported by the magnetic bearings 12, 13 so as to be capable of rotating stably. When the rotor 6 is rotated by a motor 16, the molecules of gas in an apparatus to be evacuated are moved from a suction port 1A to a delivery port 3A by the effects of rotor blades 5 and stator blades 4, arranged alternately, transferred with a high compression ratio and discharged out of the delivery port 3A. Titanium alloys or stainless steels are employed for the materials of the knietic blades 5 or the rotor 6 and rare earth elements series magnetic materials, capable of receiving the high-temperature treatment, are employed for the material of permanent magnet 9 thereby enabling to increase the degree of attained vacuum since the baking temperatures thereof may be increased to a high temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a turbo-molecular pump, and particularly to a turbo-molecular pump used in equipment requiring ultra-high vacuum.

[Background of the invention]

Turbomolecular pumps are generally used in equipment that requires vacuum, such as nuclear fusion devices and electron microscopes. The degree of vacuum obtained with current turbo molecular pumps is 10"l'o
It is said that it is possible to achieve up to about rr. Furthermore, recently there has been a strong demand not only for increasing the degree of vacuum, but also for a so-called clean vacuum free of residual gases such as hydrocarbons such as oil vapor.

Based on the principle of operation of a turbomolecular pump, the higher the molecular weight of the gas, the higher the compression ratio can be set, so it is said that it has extremely good exhaust performance against oil vapor and can provide a clean vacuum. However, in turbomolecular pumps that use oil-lubricated ball bearings as rotor support bearings, there is no oil vapor contamination of the vacuum vessel during operation;
Once the bomb is stopped, the lubricating oil vapor back diffuses and
In some cases, there was a drawback that even the vacuum container could be contaminated. In order to eliminate these drawbacks, various improvement proposals have been made, for example, the Japanese Patent Application Laid-Open No. 5
As disclosed in Japanese Patent No. 0-77913, there is a turbo molecular pump whose bearing is a controlled electromagnetic bearing.

On the other hand, the demand for ultra-high vacuum has increased in recent years.
In order to meet this requirement, it is necessary to minimize gas emissions from the surfaces of the vacuum vessel and the pump's own components1. Gas is released by heating the member to a high temperature. In other words, by increasing the temperature of the surface of the component exposed to ultra-high vacuum, the gas stored in the component is released as much as possible, and then the entire body is returned to room temperature to increase the degree of vacuum. It is.

This baking effect becomes more pronounced as the heating temperature increases. Therefore, in order to increase the degree of vacuum, it can be said that increasing the allowable baking temperature as much as possible is an extremely effective means.

However, current turbomolecular pumps have a built-in bearing to support the rotor on the high vacuum side, that is, the suction side. type magnetic bearings are used.In such bearing mechanisms, the permissible temperature for ball type bearings is due to the allowable temperature limit of the lubricating oil, and for magnetic bearings, the permissible temperature limit is 1.
It is about 00'0 to 120'0. Therefore, all of the current turbomolecular pumps have a baking temperature of 120°F or less at the suction port according to the above-mentioned allowable baking temperature. As a result, it is currently difficult to further increase the degree of vacuum in an ultra-high vacuum.

[Purpose of the invention]

The present invention has been made based on the above-mentioned matters, and provides a turbo-molecular pump that can improve the achieved wall thickness compared to conventional pumps and can obtain a clean vacuum even when the pump is stopped. The purpose is to

[Summary of the invention]

In order to achieve the above object, the present invention includes stator vanes provided in multiple stages in the axial direction within a casing, and movable vanes provided on the outer periphery of a rotor located between the stator vanes and located at the center of the casing. In a turbo molecular pump comprising blades, the high vacuum side and the low vacuum side of the rotor are each supported by bearing means, and the bearing means on the high vacuum side is replaced by a first fixed side bearing means that does not have a change in magnetic properties after high temperature heat treatment. It is constructed of an attraction type magnetic bearing made up of a permanent magnet and a second permanent magnet on the rotor side facing the permanent magnet.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the turbomolecular pump of the present invention. In the figure, the casing is composed of a suction side casing 1 having a suction port IA, an intermediate casing 2 and a discharge side casing 3 having a discharge port 3A. It is configured. The suction side casing 1 and the discharge side casing 3 are each fastened to the intermediate casing 2 with bolts. Stator blades 4 are installed inside the suction side casing 1 and the intermediate casing 2.
are arranged in multiple stages in the casing axis direction.

A rotor blade 5 is arranged between the stationary blades 4. This moving blade 5
is provided on the rotor 6. The stator vanes 4 are inserted between annular spacers 7 arranged alternately. The rotor blades 5 are alternately stacked in weight similar to the static R4, inserted between spacers 8 constituting the rotor 6, and fixed to the rotor 6 by, for example, diffusion bonding means. Moving blade5. In consideration of strength, it is preferable to use titanium alloy or stainless steel for the spacer 7.80.

An annular space S in which permanent magnets 9 are housed is formed on the upper side of the rotor 6 including the rotor blades 5 . The rotor 6 is supported by a permanent magnet 9 consisting of an annular permanent magnet 9A provided on the rotor 6 side in the annular space S, and two annular permanent magnets 9B placed in the annular space S to face it. has been done. The permanent magnet 9 on the rotor side of this permanent magnet 9
Point A faces the two permanent magnets 9B on the fixed side and is arranged between these two permanent magnets 9B on the radial surface. This arrangement of magnets provides the necessary attraction to the Girotaro.

The permanent magnet 9B is fixed to a support arm 10 which extends in the radial direction. The support arm 10 is fixed to the joint of the casings 1 and 2. Furthermore, these permanent magnets 9A and 9B are made of rare earth magnets with a single curri point. The magnetic properties of this magnetic material do not deteriorate even if it is heated at 300'O in relation to the baking effect.

At least one stage of rotor blades 5 is provided on the bearing means on the high vacuum side mentioned above, that is, on the rotor above the permanent magnets 9, and is arranged so as to face between the static vibrations 4 on the casing side. The rotor blade 5 forms a pressure corresponding to the unreached pressure on the vacuum side above the permanent magnet 9, and acts so that the gas discharge from the permanent magnet 9 does not affect the suction side.

The lower part of the rotor 6 is supported by a controlled radial magnetic bearing 12 and a controlled thrust magnetic bearing 13. These magnetic bearings 12 and 13 are controlled by a radial sensor 14 and a thrust sensor 15. A motor 16, which serves as a drive source for the rotor 6, is arranged at the lower part of the rotor on the low vacuum side. In this example, the motor 16 includes an end plate 16A fixed to the rotor 6 and a discharge side casing 3.
It is also possible to use a high-frequency motor, which is configured with an end plate motor 75 consisting of a stator coil 16B provided in the motor.

The thrust magnetic bearing 120 provided at the bottom of the rotor 6 is equipped with an auxiliary bearing 17 that helps the rotor 6 continue to rotate in the event of a power outage, etc. 1. This auxiliary bearing 17 maintains a clean atmosphere. Lubricant? '14] Dry rollers that do not use 9 bearings are used.

As this auxiliary bearing, instead of a rolling bearing, a dry bibo-kari type bearing may also be used.

In the embodiment shown in FIG. 1 described above, the high vacuum side of the rotor 6 is supported by the attractive force of the permanent magnet 9, and the low vacuum side of the rotor 6 is supported by magnetic bearings 12 and 13 for stable rotation. There is. When the rotor 6 is rotated by the motor 15, gas molecules in the equipment to be evacuated are moved to the suction port I by the action of the rotor blades 5 and stator blades 4 arranged alternately.
A toward the discharge port 3A, moving with a high compression ratio,
It is discharged from the discharge port 3A. As a result, a vacuum state of 10"'I'orr or more can be achieved in the equipment connected to this turbomolecular pump and the suction side casing 1 of the turbomolecular pump. Such an ultra-high vacuum can be achieved. This is because the following conditions can be met: In the embodiment of the present invention described above, the members of the suction side casing of the turbomolecular pump, which are exposed to ultra-high vacuum, are heated at a temperature of about 300 O. This is because the rotor blade 5 is made of a material that can be subjected to baking treatment.
This is due to the fact that the rotor 6 is made of titanium alloy or stainless steel, and the permanent magnet 9 is made of a rare earth magnet material that can be treated at high temperatures. The ability to raise the baking temperature to such a high temperature is very effective in increasing the degree of vacuum achieved and shortening the time required to obtain ultra-high vacuum. On the other hand, since the magnetic bearings 12 and 13 disposed on the low vacuum side of the turbo molecular pump are exposed to low vacuum, the conventional baking treatment temperature (about 120° C.) is sufficient.

Furthermore, the embodiments of the present invention described above have the following advantages. In other words, since the upper bearing of the radial bearing uses a bearing with a permanent magnet 9, the number of bearings is smaller than that using a controlled magnetic bearing, making it possible to significantly reduce the cost. Become. Furthermore, auxiliary bearing 1
Since the rotor 7 is configured to be supported at the lower end of the rotor, its diameter can be reduced. As a result, the circumferential speed during operation can be kept low. Also, this auxiliary bearing 1
Even if a dry type bearing is used for bearing 7, damage to the bearing during an emergency stop is significantly reduced, and maintenance can be greatly improved compared to conventional bearings.

Although the above-described embodiment uses magnetic bearings 12 and 13 as bearings for supporting the lower part of the rotor, it is also possible to use a pivot-type Pesci bearing 18 as shown in FIG. 2. This pivot type Pesci bearing 18 has a pivot shaft 18A,
It is equipped with a bearing body 18B and is used by being immersed in lubricating oil 19.

By using this pivot type flat bearing 18, since the pivot type flat bearing 18 has a small shaft diameter,
Its circumferential speed is low, and the amount of heat generated due to its loss is small. Therefore, compared to a roller bearing under the same load and rotational speed conditions, a lubricating oil with lower vapor pressure and higher viscosity can be used. As an example of the lubricating oil, a 7-horn type oil having a vapor pressure of 10''l'orr or less at room temperature can be used.

With this configuration, the suction side of the turbomolecular pump, which is exposed to ultra-high vacuum, can obtain clean ultra-high vacuum during pump operation and stop, similar to the embodiment shown in FIG. On the other hand, since the lower part of the rotor 6 uses a pivot type bearing 18 that uses oil, this is the only place where oil vapor is generated, but as mentioned above, lubricating oil has a low vapor pressure. There is very little contamination caused by this lubricating oil vapor when the pump is stopped.

This is a significant advantage when compared to conventional turbomolecular pumps using ball bearings.

That is, in conventional pumps, oil with a vapor pressure of about 10-4 Torr, such as spindle oil, must be used as the lubricating oil for the ball bearing. Therefore, as mentioned above, when the pump is stopped, this oil vapor back-diffuses to the high vacuum side and contaminates the vacuum container. The partial pressure of steam is 10-
Since it can be suppressed to 10 Torr or less, in fact,
There is no need to worry about such contamination. Furthermore, since this embodiment uses oil that is extremely difficult to evaporate, replenishment of oil is not necessary at all, and this is extremely effective in terms of maintenance. Furthermore, compared to those using controlled magnetic bearings, there is no need for a bearing control section or an electromagnet, so it is significantly advantageous in terms of cost.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to bake the parts exposed to ultra-high vacuum at high temperatures, so it is possible to achieve ultra-high vacuum to a greater extent than with conventional turbomolecular pumps. I can do it. 1. As a result, it is possible to provide a reliable turbomolecular pump that can meet the demands of equipment requiring ultra-high vacuum.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing one embodiment of the turbo-molecular pump of the present invention, and FIG. 2 is a longitudinal cross-sectional view showing another embodiment of the turbo-molecular pump of the present invention. l... Suction side casing, 2... Intermediate casing,
3... Discharge casing, 4... Stationary blade, 5... Moving blade, 6... Rotor, 7, 8... Spacer, 9... Permanent magnet, 12° 13... Magnetic bearing , 18... Pivot type bevel bearing.

Claims (1)

[Claims] 1. A rotor blade provided within a casing in multiple stages in the axial direction thereof, and a rotor blade located between the stator blades and provided on the outer periphery of the rotor located at the center of the casing. In the turbo-molecular pump, the high vacuum side and the low vacuum side of the rotor are supported by bearing means, and the high vacuum side bearing means is replaced by the first bearing means on the fixed side that does not change magnetic properties after high temperature heat treatment.
1. A turbo-molecular pump characterized in that it is constituted by an attraction type magnetic bearing made up of a permanent magnet and a second permanent magnet on the rotor side facing the permanent magnet. 2. The turbo-molecular pump according to claim 1, wherein the permanent magnet is made of a rare earth magnetic material. 3. The first permanent magnet is fixedly arranged within the annular space formed on the outer periphery of the rotor between the rotor blades, and the second permanent magnet
Claim 2, characterized in that permanent magnets are provided on the rotor in the annular space so as to face each other.
Turbomolecular pump as described in section. 4. The first permanent magnet includes several annular permanent magnets with different diameters arranged concentrically, and the second permanent magnet facing the first permanent magnet has the same number as that of the first permanent magnet. 4. The turbo-molecular pump according to claim 3, further comprising annular permanent magnets arranged to face each other between two annular permanent magnets. 5. Claim 3, characterized in that the rotor is provided with at least one stage of rotor blades arranged on the high vacuum side above the bearing means on the high vacuum side and facing between the stationary blades on the casing side. or the tar described in paragraph 4. Bomolecular pump. 6. The turbo-molecular pump according to claim 5, wherein the bearing means on the low vacuum side of the rotor is a controlled magnetic bearing. 7. The turbo-molecular pump according to claim 5, wherein the bearing means on the low vacuum side of the rotor is a pivot type bearing.