JP2002147385A - Seal structure of turbo-molecular pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a seal structure capable of preventing a system gas from invading into a bearing part and a motor part in a turbo-molecular pump for performing the exhaustion of the system gas containing corrosive gas and condensing gas. SOLUTION: This seal structure comprises a bush 12 and a journal shaft part 8a rotatably inserted into the bush 12 with a slight clearance provided between the shaft part and the inner peripheral part of the bush 12. The bush 12 is swingably fitted radially into the static member 10 of the turbo-molecular pump 1 through O-rings 13a and 13b. A herringbone-shaped groove 8b and a screw groove 8c are recessed in the outer peripheral part of the journal shaft part 8a, and purge gas is led between the bush 12 and the journal bearing part 8a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seal structure of a turbo-molecular pump which is most suitable for exhausting a process gas containing a corrosive gas, a gas which easily condenses, and the like.

[0002]

2. Description of the Related Art FIG. 8 shows an example of the structure of a conventional turbo-molecular pump used in a semiconductor manufacturing apparatus or the like.

In FIG. 8, a is an intake port and b is an exhaust port. The process gas is sucked in from the intake port a by the action of the moving blades c and the stationary blades d, and is discharged from the exhaust port b.

A rotating shaft f is provided at the center of a rotor e rotating at a high speed with a large number of moving blades c mounted thereon, and rolling bearings g and h are provided.
Is supported by the housing i.

[0005] Lubrication of the rolling bearings g and h is performed by the lubricating oil stored in the lubricating oil tank j rising through the inner periphery of the oil hole k provided in the rotating shaft f by centrifugal force generated by rotation.

M is a labyrinth ring, which is stationary,
The exhaust gas is sealed with the rotating shaft f.

Incidentally, in order to avoid contact between the labyrinth ring m and the rotating shaft f, the gap p between the two has been conventionally set to about several hundred microns.

[0008]

If the gap between the labyrinth ring m and the rotating shaft f is wide as in the prior art, it is difficult to prevent a part of the exhaust gas from entering the inside beyond the labyrinth ring m. Even if a purge gas such as nitrogen gas is introduced into the gap, a small portion of the exhaust gas permeates into the bearings, corroding the bearings and the motor and causing a failure in the turbo-molecular pump. There was a problem.

Furthermore, in order to simplify the structure of the turbo-molecular pump, it is desired to employ a grease lubricated rolling bearing. However, in the case of a rolling bearing using lubricating oil, exhaustion by lubricating oil can be expected. There was a problem that the effect of diluting gas could not be expected with a grease lubrication system.

The present invention solves these problems and provides a seal structure of a turbo-molecular pump capable of safely exhausting a corrosive or condensable process gas even in the case of a grease-lubricated rolling bearing. The purpose is to provide.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a cylindrical bush which is rotatably fitted in a stationary member of a turbo molecular pump housing, and an inner peripheral portion of the bush. And a journal shaft portion rotatably inserted through the inner peripheral portion with a small gap, and a herringbone-shaped groove is formed on the outer peripheral portion of the journal shaft portion or the inner peripheral portion of the bush in the rotation direction. It is characterized in that it is recessed in a shape that is open in the shape of a letter.

[0012]

FIG. 1 shows a first embodiment of the present invention.
And FIG.

FIG. 1 is a longitudinal sectional view of a turbo-molecular pump 1 having a seal structure according to the present invention. Reference numeral 2 denotes a seal structure portion to be described later, 3 denotes an intake port, and 4 denotes an exhaust port.

Reference numeral 5 denotes a rotor, which has a number of moving blades 6 mounted radially on its outer periphery.

Reference numeral 7 denotes a stationary blade.

A rotary shaft 8 is provided at the center of the rotor 5, and the rotor 5 and the rotary shaft 8 integrally rotate at a high speed.

The rotating shaft 8 is connected to the stationary member 1 of the casing via grease-lubricated rolling bearings 9a and 9b.
0 and 11 are rotatably supported.

FIG. 2 shows the details of the seal structure portion 2.

That is, the seal structure portion 2 includes a bush 12 loosely fitted in a shaft hole 10a provided in the stationary member 10 so as to be swingable in a radial direction, and a journal shaft portion through which the bush 12 is rotatably inserted. 8a.

The journal shaft portion 8a is a part of the rotary shaft 8, and a sealing screw groove 8c and a herringbone-shaped groove 8b are formed in the outer periphery of the journal shaft portion 8a. The outer peripheral portion of the shaft portion 8a and the bush 12
Is formed so as to have a small gap of 5 to 10 microns.

The bush 12 has a cylindrical shape.
Is formed so as to have a gap of at least 100 μm or more between the outer peripheral portion and the shaft hole 10a.

Reference numerals 13a and 13b denote O-rings, which are made of an elastic material having a low modulus of elasticity. These O-rings 13a and 13b are interposed in grooves formed on the inner peripheral surface of the shaft hole 10a.
The bush 12 is connected to the shaft hole 1 of the stationary member 10.
0a so as to be swingable in the radial direction.

A circumferential annular groove 12b is formed in the outer peripheral portion of the bush 12, and a through hole 12a is provided through the bottom of the annular groove 12b. The purge gas sent from the formed ventilation hole 10b is sent into the small gap between the bush 12 and the journal shaft 8a through the through hole 12a.

The through hole 12a is formed so as to open in the middle between the thread groove 8c recessed in the journal shaft 8a and the herringbone groove 8b.

The thread groove 8c is formed obliquely parallel so as to prevent the purge gas from leaking toward the exhaust port 4 of the turbo molecular pump.

The arrow F indicates the direction of rotation of the rotating shaft 8, and the herringbone-shaped groove 8b is formed in a shape that is open in the shape of a letter toward the direction of rotation F.

Reference numeral 14 denotes a motor for driving the rotation shaft 8 to rotate.

Next, the operation and effect of the turbo-molecular pump 1 of the present embodiment will be described.

In the turbo molecular pump 1, the rotor 5 is rotated by a motor portion 14 integrally with the rotating shaft 8.

Two sets of upper and lower bearings 9a for supporting the rotating shaft 8;
Reference numeral 9b denotes a grease-filled rolling bearing, which has a simple structure that does not require a lubricating oil tank or a lubricating oil pump.

The process gas is exhausted by the high-speed rotation of the rotor 5.

The seal structure portion 2 prevents a part of the process gas from entering the bearings 9a and 9b and the motor portion 14 through the path indicated by the arrow Z.

That is, an O-ring 13 is provided between the outer peripheral portion of the bush 12 forming the seal structure portion 2 and the stationary member 10.
Since it is sealed by a and 13b, the invasion of the process gas from the space is prevented.

The gap between the inner peripheral portion of the bush 12 and the outer peripheral portion of the journal shaft portion 8a constituting the seal structure portion 2 is
The gap is set to a small value of 5 to 10 microns, and a purge gas such as nitrogen gas is supplied to the gap to prevent the process gas from entering.

It should be noted that the rotor 5 and the rotating shaft 8 that are rotating at a high speed oscillate around the center of the rotating shaft with a small amplitude due to the remaining unbalanced weight.

This amplitude is expected to be 10 microns or more. If the run-out causes the outer peripheral portion of the journal shaft portion 8a to come into contact with the inner peripheral portion of the bush 12, frictional heat may be generated and seizure may occur. There is.

However, this is because the herringbone-shaped groove 8b recessed on the outer peripheral portion of the journal shaft portion 8a and the bush 12
Acts like a gas bearing, and a force for pressing the bush 12 in the radial direction acts, and the radial deformation of the bush 12 is absorbed by the elastic deformation of the O-rings 13a and 13b. The shaft 8a and the bush 12 do not come into contact with each other.

The O-rings 13a and 13b serve to thermally insulate the bush 12 and the stationary member 10 so that they do not come into direct contact with each other.

This is because the rotating shaft 8 is
Heat and heat generated by the bearings 9a and 9b and the seal structure portion 2
The bush 12 is maintained at a high temperature substantially equal to that of the rotating shaft 8, and the bush 12 and the rotating shaft 8 (the journal shaft portion 8).
In this case, no condensation product is generated during the step (a), and the size of the gap between the journal shaft portion 8a and the bush 12 due to thermal expansion is prevented.

A seal structure of a turbo-molecular pump according to a second embodiment of the present invention will be described with reference to FIG.

The seal structure 2a of the present embodiment is different from the first embodiment in the structure of the seal portion such as a thread groove.

That is, in the present embodiment, the screw groove of the seal portion is composed of two sets of screw grooves of a first screw groove 8d and a second screw groove 8e, and these screw grooves 8d and 8e have opposite threads.
A through hole 12a is opened in the middle between these two sets of screw grooves 8d and 8e to supply a purge gas.

These screw grooves 8d and 8e are formed in a shape open in a C shape in the direction opposite to the rotation direction F of the rotating shaft 8.

In the present embodiment, the effect of preventing the system gas from entering is stronger than in the first embodiment, and the supply of the purge gas to the herringbone-shaped groove 8b is promoted, so that the gas bearing is improved. Has the advantage of increasing the action of

A seal structure of a turbo-molecular pump according to a third embodiment of the present invention will be described with reference to FIG.

The seal structure 2b of this embodiment is different from the first and second embodiments in that the screw groove is eliminated and only the herringbone-shaped groove 8b is recessed.

In this embodiment, the ventilation holes 10b for supplying the purge gas are provided in the rolling bearings 9 in the stationary member 10.
a and the bush 12 were opened.

Therefore, the purge gas is supplied to the rolling bearing 9a.
From the side to the gap between the journal shaft portion 8a and the bush 12.

This embodiment is simpler in structure than the first and second embodiments, and the herringbone-shaped groove 8b is formed larger to increase the function of the gas bearing. Has advantages.

A seal structure of a turbo-molecular pump according to a fourth embodiment of the present invention will be described with reference to FIG.

The seal structure 2c of the present embodiment has a bush 12 'having three circumferential annular grooves 15 in the inner peripheral part instead of the bush 12 in the first embodiment.
Is different from the first embodiment.

These annular grooves 15 are formed in the bush 12 'at positions opposite to the sealing screw grooves 8c so as to be at least twice as deep as the sealing screw grooves 8c.

These annular grooves 15 have an effect that the operation of the bush 12 'is easily stabilized by sealing the purge gas.

In the present embodiment, the annular groove 15 is provided on the side of the bush 12 ', but it may be provided on the side of the journal shaft 8a as shown in FIG.

That is, the sealing screw groove 8c is provided on the outer peripheral portion of the journal shaft 8a side having the sealing screw groove 8c.
The three annular grooves 16 are recessed at least twice as deep as the depth c to stabilize the operation of the bush 12.

In this embodiment, the number of the annular grooves 15 and the number of the annular grooves 16 are all three, but may be any number other than three.

A seal structure of a turbo-molecular pump according to a fifth embodiment of the present invention will be described with reference to FIG.

The seal structure 2d of the present embodiment is different from the first embodiment in that O-rings are provided on both right and left end portions of the bush 12 in the first embodiment.

That is, the bush 12 includes an O-ring 13a,
13b, O-rings 13c, 13d are coaxial with the bush 12 on both end surfaces of the bush 12 while being loosely fitted to the shaft hole 10a of the stationary member 10 so as to be swingable in the radial direction.
The bush 12 is sandwiched between the lid 10c and the flange 10d provided before and after the shaft hole 10a of the stationary member 10 via the O-rings 13c and 13d.

The distance between the lid 10c and the flange 10d is formed to be slightly larger than the length of the bush 12, so that the bush 12 does not directly contact the stationary member side.

As described above, according to the present embodiment, the stationary member is brought into contact with the stationary member via the O-rings 13a, 13b, 13c and 13d. And the ability to prevent the formation of condensed products between the bush 12 and the rotating shaft 8 (journal shaft portion 8a) and to reduce the gap between the two are improved.

In the present embodiment, the structure in which the bush 12 is engaged with the stationary member via O-rings provided on the outer peripheral portion and both end surfaces thereof is provided. The rings 13a and 13b are eliminated, and a small gap is provided between the outer peripheral portion of the bush 12 and the shaft hole 10a.
The lid 10c and the flange 10d via 3c, 13d
May be interposed between them and engaged with the stationary member 10.

[0063]

As described above, according to the present invention, the gap between the outer periphery of the journal shaft portion and the inner periphery of the bush can be made small to prevent the system gas from entering the bearing portion. This has the effect of providing a seal structure that is optimal for a turbo-molecular pump that exhausts a process gas containing a gas having condensability or a gas having condensability.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a turbo-molecular pump having a seal structure of the present invention.

FIG. 2 is a longitudinal sectional view of the seal structure according to the first embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a seal structure according to a second embodiment of the present invention.

FIG. 4 is a longitudinal sectional view of a seal structure according to a third embodiment of the present invention.

FIG. 5 is a longitudinal sectional view of a seal structure according to a fourth embodiment of the present invention.

FIG. 6 is a longitudinal sectional view of another form of the seal structure according to the fourth embodiment;

FIG. 7 is a longitudinal sectional view of a seal structure according to a fifth embodiment of the present invention.

FIG. 8 is a longitudinal sectional view of an example of a conventional turbo-molecular pump.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Turbo molecular pump 2, 2a, 2b, 2c, 2d Seal structure 8a Journal shaft part 8b Herringbone-shaped groove 8c, 8d, 8e Screw groove 10 Stationary member 12, 12 'Bush 12a Through hole 12b, 14, 15, 16 Annular grooves 13a, 13b, 13c, 13d O-ring

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) F04D 29/10 F04D 29/10 A 29/12 29/12 Z F term (reference) 3H022 AA01 BA01 BA04 BA06 BA07 CA01 CA11 CA12 CA13 CA14 CA19 CA21 CA22 CA28 CA35 CA38 CA40 CA48 CA57 CA58 CA60 DA00 DA01 DA04 DA08 DA11 3H031 DA02 EA01 EA03 EA05 EA07 EA08 EA09 FA04 FA11 FA15 FA32 FA39

Claims (11)

[Claims] 1. A turbo-molecular pump supporting a rotating shaft via a rolling bearing, a cylindrical bush fitted in a stationary member of a housing of the turbo-molecular pump so as to be capable of swinging in a radial direction, and the bush. A journal shaft portion rotatably inserted through the inner peripheral portion with a small gap in the inner peripheral portion of the journal shaft. A herringbone-shaped groove is formed in the outer peripheral portion of the journal shaft portion or the inner peripheral portion of the bush. Characterized in that it is recessed in a shape that is opened in a shape that is curved toward the rotational direction. 2. A purge gas is introduced into a gap between the bush and the journal shaft.
3. The seal structure of a turbo-molecular pump according to item 1. 3. The turbo-molecular pump according to claim 1, wherein a sealing screw groove is formed adjacent to the herringbone-shaped groove in an outer peripheral portion of the journal shaft portion inserted through the bush. Seal structure. 4. The sealing screw groove has two opposite screw threads.
4. The seal structure for a turbo-molecular pump according to claim 3, comprising a set of screw grooves, wherein a purge gas is introduced between the two sets of screw grooves. 5. The bush is loosely fitted to the stationary member with a small gap in the outer peripheral portion and is locked to the stationary member via at least two O-rings fitted to the outer peripheral portion. 2. The structure as claimed in claim 1, wherein the elasticity of the O-rings absorbs the radial swing of the bush, and the O-rings thermally insulate the bush and the stationary member of the housing. 3. The seal structure of a turbo-molecular pump according to item 1. 6. The bush according to claim 1, wherein O-rings are provided at both ends of the bush, and the bush is sandwiched between the stationary members via the O-rings. Turbo molecular pump seal structure. 7. A gap between an outer peripheral portion of the journal shaft portion and an inner peripheral portion of the bush is formed to be at most 10 μm or less, and a gap between an outer peripheral portion of the bush and the stationary member is at least. The seal structure for a turbo-molecular pump according to claim 1 or 5, wherein the seal structure is formed so as to be 100 microns or more. 8. A structure in which an annular groove in the circumferential direction is formed in the outer peripheral portion of the bush and a through hole penetrating the annular groove is provided, and the through hole is formed in a structure through which the purge gas passes. The seal structure of a turbo-molecular pump according to claim 1 or 4, wherein 9. The turbo-molecular pump according to claim 1, wherein an opening of a vent hole for supplying a purge gas is provided between the rolling bearing near the bush and the bush. Seal structure. 10. The turbo-molecule according to claim 3, wherein at least one circumferential annular groove is recessed in a portion of the inner peripheral portion of the bush opposite to the sealing screw groove. Pump seal structure. 11. The turbo-molecule according to claim 3, wherein at least one circumferential annular groove is recessed in a portion having the sealing screw groove on an outer peripheral portion of the journal shaft portion. Pump seal structure.