JPS61132797A - Bearing unit for turbo molecular pump - Google Patents

Abstract

PURPOSE:To eliminate lubricating means by providing a gas bearing in machine room while providing a flow-out path for leading out the bearing gas to exhaust system and contactless sealing mechanism in the space between the machine room and rotor. CONSTITUTION:The drive shaft 3 is born rotatably by gas bearings 7, 8, 9 arranged in machine room A while bearing gas is fed through flow-in paths 14, 15. Contactless sealing mechanism 20 is provided at the driving shaft penetrating section at the boundary between the machine room A and rotor room B. Consequently, the bearing gas is led out sequentially through flow-out path 27 provided near the sealing mechanism 20 to the exhaust system. As a result, the service life is ensured without requiring special lubricating means.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application in LM Industry The present invention relates to a bearing device for a turbo-molecular pump using a gas bearing.

[Prior Art] A turbomolecular pump rotates rotor blades alternately with stator blades in a rotor chamber (vacuum chamber) at high speed, and uses the mechanical exhaust action of these axial flow turbine blade rows that collide with gas molecules. The device is designed to forcibly generate a gas flow, and is unique in that it can create an ultra-high vacuum.

However, looking at the support structure of the drive shaft in this type of pump, one end of the drive shaft for rotating the ER-7 blade is diverted from the machine room that provides rotational power to the rotor room. The rotor blades are attached to the extended portion, which is the free end, so that they can rotate integrally, while the rotor blades are normally rotatably supported by two radial bearings in the machine room, and the axis of rotation is not positioned. . FIG. 7 shows an example of such a conventional support structure, in which the drive shaft a is connected to the housing b at one end of the pump.
It is inserted in the axial direction through the machine chamber A formed inside the pump, and its one end extends to the rotor chamber B on the other end side of the pump, where the rotor blade C is inserted outside i! li-fixed while a machine room A
Inside, it is supported by rolling bearings (pole bearings) e and f, which are supported by housing b via dampers d, at two locations on the rotor chamber B side and the opposite side of rotor chamber B, and is free to rotate around its axis. is supported by Note that g and h are a motor stator and a motor rotor provided in the machine room A, which apply rotational power to the drive shaft a to rotate it at high speed.

However, with a support structure like this.

For example, as shown in Fig. 7, lubricating oil is supplied to the bearings e and f from an oil tank i attached to the machine room A114 of the pump through the drive shaft a, which makes the lubrication method complicated. There is also a problem that the service life of the bearings e and f is relatively short. In addition, oil-lubricated metal bearings can be used instead of rolling bearings, but the viscosity of the lubricant cannot be ignored in this type of bearing, so it is not suitable for applications such as turbo molecular pumps that require a high rotation speed on the drive shaft. This is not advantageous in terms of operation, and turbomolecular pumps generally do not like oil (steam) to enter the rotor chamber due to usage requirements, which is also undesirable. Instead of a bearing, it is possible to use a 1a floating bearing that can support the drive shaft without contact, but it is currently very expensive and not worth the cost.

[Dark Problems to be Solved by the Invention] Under these circumstances, the present invention does not suffer from the various problems caused by conventional oil lubrication, and has advantages over the case where m-air bearings are used. This was designed to provide the most durable bearing device for the drive shaft of a turbo-molecular pump. In other words, the present invention aims to ensure a long service life without requiring special lubrication means, to avoid contamination inside the pump or increase in rotational resistance when oil-lubricated bearings are used, and to have a relatively simple structure. The object of the present invention is to provide a new bearing device that can be implemented at low cost.

Means for Solving Problem L] The present invention utilizes a gas bearing as a means for achieving the above object, contrary to the conventional concept in the field regarding bearing devices for turbomolecular pumps. That is, one aspect of the present invention provides a gas bearing that supports a drive shaft through a gas film in the machine chamber of a turbo molecular pump, and an inflow passage that introduces bearing gas from a supply source into the gas bearing, and connects the machine chamber and the turbo. A non-contact type sealing mechanism is provided at the drive wheel penetration part at the boundary with the rotor chamber of the molecular pump to airtightly isolate both chambers, and an outflow passage faces the sealing mechanism to lead out the bearing gas in the machine chamber to the exhaust system. It is characterized by having the following.

[Function] With such a configuration, if the bearing gas sent from the supply source is continuously introduced and supplied from the inflow passage to each gas bearing, the drive shaft and the gas bearing will be connected to each other when the drive shaft rotates at high speed. Sufficient dynamic pressure to float and support the drive shaft is generated in the gas film layer formed between the two, and the drive shaft is stably supported without contact. Bearing gas leaking from the gas bearing portion and diffusing into the machine room is prevented from leaking into the rotor chamber (vacuum chamber) by the sealing mechanism, and the bearing gas is prevented from leaking into the rotor chamber (vacuum chamber) by the sealing mechanism. If the outflow passage is connected to the exhaust system, the bearing gas in the machine room will be sequentially led out from this outflow passage, and the bearing gas supplied to the gas bearing will absorb the heat in the machine room and carry it outside. It also acts as a refrigerant.

[Example〕 Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a partially simplified structure of a turbomolecular pump according to the present invention, in which a machine chamber A is provided in a housing l located at the lower part of the figure.

A rotor chamber (vacuum chamber) B is provided in the space enclosed by the upper casing 2, and the axis of this pump is 0.
The drive shaft 3 is threaded through the machine room A so as to coincide with the drive shaft 3, and one end of the drive shaft 3 is made a free end and extends into the rotor room B above. The drive shaft 3 has a rotor 4 fixedly attached to its extending portion within the rotor chamber B to rotate integrally with the drive shaft 3.

Rotors m5a are protruded from the outer periphery of the rotor 4 so as to be alternately arranged with stator bodies 5b protruding from the inside of the casing 2, and these blades 5a, 5b
A required axial turbine blade row is configured in the rotor chamber B by the combination of the following.

Thus, the drive shaft 3 is given rotational power by the motor 6 (stator 6a, rotor sb) installed in the machine room A, and is rotated while maintaining its axis 0. The gas bearing 7 arranged in the machine room A
．． It is rotatably supported by 8 and 9. That is, the gas bearings 7.8 are radial bearings that support the WA drive shaft in the radial direction, and are provided at intervals between the shaft ends on the rotor chamber B side and the opposite rotor chamber B side in the machine fiA. It is being The detailed structure of this radial gas bearing 7.8 is as follows. At the location where the two upper and lower radial gas bearings 7, 8 are provided, a ring-shaped bearing block 10.11 is fixed to the housing 1 and arranged in the machine room A. This bearing block 1O111 is a drive shaft 3
are inserted into a predetermined position and surround the outer periphery of the drive shaft 3, and create minute gaps 10a, lla of predetermined dimensions between the inner circumferential surface and the outer circumferential surface of the drive shaft 3, respectively. It is formed in seven places. That is, these gaps I
Qa and lla form the bearing surface of the gas bearing, which forms a gas film by introducing bearing gas into these parts, and supports the 1% moving shaft 3 in a non-contact state through this gas film during high-speed rotation. . Then, this axis ffi 11ffy 10. L
l24t, each /zi[1iRIIlOa, an inflow pocket facing lla and supplying bearing gas into the space of the gap 10a, lla) lOb, 11b, and this inflow pocket) 1
Through-holes 10c and 11 that open in 0b and llb and radially penetrate through the bearing block 10.11; through-holes 10c and llc in each bearing block io and tt and pockets IOd that radially penetrate the housing l; A bearing gas inflow passage 14.15 is provided, which is composed of a through hole 12, l3A+13B that communicates with each other via the lid and opens on the outer circumferential surface of the housing l. This inflow passage 14
．． 15 is a supply source (not shown) disposed outside the pump; and ii
! radial gas bearing 7.8 (gap 10 a,
The necessary wheel gas is introduced into L 1 a).

On the other hand, the second gas receiver 9 is an axial bearing that supports the drive shaft 3 in the test direction, and is provided at the end of the shaft opposite to the rotor chamber B in the first machine room A. The detailed structure of the axial gas bearing 9 is as follows. That is, a large-diameter seven flange portion 16 that rotates integrally with the drive shaft 3 is fitted into the lower end portion of the drive shaft 3, and the seven flange portion 16 is disposed close to the lower end surface of the bearing block 11. , a ring-shaped bearing block 17 is fixed to the housing l in the machine room A located on the r side of the seven langes M&16, and these upper and lower bearing blocks 11. l
'7, the flange portion 16 is closely held.

Bearing gas is introduced into the opposing surfaces of the upper and lower bearing blocks 11, 17 and the 7 flange portion 16 to form a gas film, thereby creating a gas bearing bearing surface that supports the drive shaft 3 in a non-contact state during high-speed rotation. Therefore, minute gaps 11e and 17a
is formed. This axial gas bearing 9 has a gap l as in the case of the radial gas bearing 7.8.
ie, inflow passage 18 for introducing bearing gas into 17a
．． 19 are provided. i.e. upper gap @ 1
1e has an inflow pocket 11f facing the gap 11e.
The inflow pocket 11f branches from the through hole 11c.
An inflow passage 18 consisting of a communication hole 11g that is open to the inside is provided. Further, in the lower gap alIl 7a, there are inflow holes facing the gap 17a, 17b and 1. An inflow passage 19 is formed with a third connecting hole 17c branching from the through hole 13A and opening into the inflow pocket 17b.

Furthermore, a non-contact type sealing mechanism 2G is provided at the drive shaft penetrating portion at the boundary between the machine chamber A and the rotor chamber B in order to airtightly isolate both chambers. This sealing mechanism 20 has four
1wA moving shaft 3 is installed at the upper end of the machine room A corresponding to the 111 penetration part.
A ring-shaped seal block 21 is arranged to surround the ring. That is, the seal mechanism 20
The outer circumferential surface of the seal block 21 and the inner circumferential surface of the seal block 21 are arranged close to each other leaving a small gap S where they do not come into direct contact, and as shown in FIG. Screws on the surface? +! 123 is engraved. This thread groove 23 is formed in a side layer in a predetermined direction corresponding to the rotational direction of the drive shaft 3, and when the drive shaft 3 is rotating at high speed, it flows from the machine room A into the gap S of this seal mechanism 20. It has the effect of forcibly pushing back the invading bearing gas downwards, prevents gas from leaking in the opposite direction from the seal mechanism 20, and makes it possible to maintain airtightness between the machine room A and the rotor room B. ing. Incidentally, the portion 22 of the drive shaft in which the thread groove 23 is provided may be formed into a tapered surface as shown in FIG. It is expected that this can be further improved.

Further, an outflow passage 27 is provided facing the sealing mechanism 20 having such a configuration to lead out the bearing gas in the machine room A to an external exhaust system. Specifically, in the case of FIG. Hole 21b
and a through hole 28 that passes through the housing l in the radial direction and communicates with the through hole 21b of the seal block 21 via the hole 21c, and is open to the outer peripheral surface of the housing l. There is. The through hole 28 opened in the outer peripheral surface of the housing 1 is connected to the exhaust port 29 of this pump as well as an exhaust system (not shown) (a back pump of a turbo molecular pump, usually a rotary pump is used), and the seal mechanism 20 The bearing gas extracted from the exhaust system is directly sucked into the exhaust system.

In the figure, numeral 30 is a presser plate that seals the upper opening of the machine chamber A, and 31 is an intake port of the turbo molecular pump provided at the upper opening of the rotor chamber B.

Next, the operation of this pump will be explained.

Inlet passages 14, 15 and 1 of gas bearings 7, 8 and 9
Connect 8.19 to a supply source to supply clean bearing gas (dry air, inert gas, etc.) to each gas bearing 7.8 and 9.
When the motor 6 in the machine room A is started and the drive shaft 3 is rotated at a high speed while supplying air, the turbine blades in the rotor room B take in air from the intake port 31 and the exhaust port 29
At this time, the drive shaft 3 is supported in the radial direction and the thrust direction in the machine room A by the gas bearings 7, 8 and 9 without contact. . That is, in each of the gaps of the gas bearing, the introduced bearing gas forms a gas film, and this gas film layer is viscous and drawn into the outer peripheral surface of the Sm shaft 3 rotating at high speed, generating high dynamic pressure. This allows the drive shaft 3 to float and be stably supported.

The bearing gas that is continuously supplied to each gas bearing is
Although the bearing gas will gradually escape from the outer edge of the gap into the machine room A, this bearing gas will not enter the rotor chamber B and impair the pump's exhaust performance.
In the drive shaft penetrating portion at the boundary between the rotor chamber B and the rotor chamber B, a non-contact type sealing mechanism 20 is provided which exhibits high sealing performance during high rotation of the wJA driving shaft 3 as described above.
Since an outflow passage 27 is provided facing the seal mechanism 20 and sucking the bearing gas into the pack pump, the bearing gas stored in the machine room A can be smoothly led out from the outflow passage 27 to the external exhaust system. It is for the sake of the monkey. In order to effectively operate a gas bearing such as a gas bearing, it is sufficient to supply a very small amount of gas at a pressure of 0.1 to 0.5 Kgf/Otori.

According to the bearing device as described above, relatively I! IQ
With a configuration that can be used easily and at low cost, a non-contact type device having almost the same good characteristics as a magnetic bearing can be realized. Therefore, this device not only eliminates the need for troublesome oil lubrication and eliminates the various disadvantages caused by conventional oil lubrication, but also has remarkable effects in the following points: becomes. That is,
Firstly, unlike oil-metal bearings, this type of non-contact type has a small influence of the viscosity of the bearing gas surrounding the drive shaft 3, so its rotational resistance is extremely small. Super high speed rotation (2QOQO~C/0O0
It is possible to provide an optimal bearing structure for a single molecular pump that rotates at 0 rpm).

In addition, since the bearing gas for man 2 is not only used for the original purpose of floating and supporting the drive shaft, but also circulates through the first machine room A before being led out to the exhaust system, the heat is removed from the machine room A. It can also be used as a refrigerant to be transferred to the outside. In other words, if this bearing device is adopted, not only an oil tank but also a cooling fan and the like are not required at all. Therefore, from this point as well, the structure I! Easy and compact design can be achieved.

When applying the bearing device using the gas bearing of the present invention to a turbo-molecular pump, maintaining airtightness between the machine room A and the pump room B is one of the important points related to its success or failure. The non-contact type seal mechanism 20 is not limited to the screw groove reverse flow type shown in FIGS. 2 and 3,
In addition, for example, a labyrinth seal system as shown in FIG.
, 24B, and engage the recesses 26a and protrusions 26b in the 16'4 force direction in a convex-concave manner so as to create a minute maze-like passage S with the facing seal blocks 25A and 25B, and also on the rotor '4B side. An outflow passage 27 (pockets 25a, 25b, etc.) is provided facing the minute gap S communicating with the end of the passage S and communicating with the exhaust system as described above.

In the illustrated embodiment, the drive shaft 3 is entirely supported by gas bearings in the machine room A. For example, only the radial bearing uses a gas bearing, and the thrust in the axial direction is prevented by using a gas bearing between the drive shaft 3 and the housing 1. This may be done by interposing an elastic member as appropriate.

In addition, in the above embodiment, the vacuum suction in one machine room A is
As shown in the figure, the pack pump (rotary pump) RP of the turbo molecular pump TMP was used as is, but if necessary, a dedicated pump RP for that purpose was additionally installed as shown in No. 654. You may also do this by doing so.

[Effects of the Invention] Since the present invention has one or more configurations, it is possible to provide a bearing device for a turbo-molecular pump that is relatively simple in structure and inexpensive, and can accurately solve the conventional problems. This is what we were able to provide. In other words, the service life is guaranteed without the need for special lubrication means, there is no contamination inside the pump or an increase in rotational resistance when oil-baited sliding bearings are used, and there is sufficient cooling function without the need for a separate cooling means. and that it is demonstrated.

[Brief explanation of drawings]

FIG. 1 is a half longitudinal sectional view of a turbomolecular pump according to an embodiment of the present invention. FIG. 2 is an enlarged view of the main part of the device shown in FIG. 1, and FIGS. 3 and 4 are views showing modifications thereof. FIG. 5 and FIG. 6 are schematic diagrams showing the exhaust system in the machine chamber of the turbo-molecular pump according to the present invention. FIG. 7 is a partial longitudinal sectional view of a turbomolecular pump showing a conventional bearing device. A: Machine room B: -Φ Rotor chamber 1: Housing zIIIa Casing 3: ll@Drive shaft
6. Motor 7. 8. Radial gas bearing 9. Axial gas bearing 14.15.18.19... Inflow passage 20... Seal mechanism z7... Outflow passage

Claims (1)

[Claims] In a turbo-molecular pump in which a drive shaft that rotationally drives rotor blades in a rotor chamber is rotatably supported via a bearing in a machine chamber that provides rotational power to the drive shaft, one driving shaft is mounted in a gas film in the machine chamber. A gas bearing supported through the rotor chamber is provided, and an inflow passage is provided for introducing bearing gas from a supply source into the gas bearing, and both chambers are hermetically isolated at a drive shaft penetration portion at the boundary between the machine chamber and the rotor chamber. 1. A bearing device for a turbo-molecular pump, comprising a non-contact type sealing mechanism and an outflow passage facing the sealing mechanism and leading out bearing gas in a machine chamber to an exhaust system.