JP4691242B2 - Turbo molecular pump seal structure - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a seal structure for a turbo molecular pump that is optimal for exhausting process gas containing corrosive gas, gas that easily condenses, and the like.
[0002]
[Prior art]
An example of the structure of a conventional turbo molecular pump used in a semiconductor manufacturing apparatus or the like is shown in FIG.
[0003]
In FIG. 8, a is an intake port and b is an exhaust port. The process gas is sucked from the intake port a by the action of the moving blade c and the stationary blade d, and is discharged from the exhaust port b.
[0004]
A rotation shaft f is provided at the center of a rotor e that rotates at a high speed with a large number of blades c attached thereto, and is supported on the housing i via rolling bearings g and h.
[0005]
The rolling bearings g and h are lubricated by the lubricating oil accumulated in the lubricating oil tank j rising by the centrifugal force generated by the rotation of the inner periphery of the oil hole k provided in the rotating shaft f.
[0006]
m is a labyrinth ring that is stationary and seals exhaust gas with the rotating shaft f.
[0007]
In order to avoid contact between the labyrinth ring m and the rotating shaft f, the gap p between them has been conventionally set to about several hundred microns.
[0008]
[Problems to be solved by the invention]
If the gap between the labyrinth ring m and the rotary 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, and a purge gas such as nitrogen gas is introduced into the gap. However, there is a problem that a part of the exhaust gas penetrates into the bearing portion and corrodes the bearing, the motor, etc., and induces a failure in the turbo molecular pump.
[0009]
Furthermore, in order to simplify the structure of the turbo molecular pump, it is desired to use a grease lubricated rolling bearing, but in the case of a rolling bearing using lubricating oil, the dilution of exhaust gas with lubricating oil can be expected. There was a problem that the effect could not be expected with the grease lubrication type.
[0010]
The present invention eliminates these problems and provides a turbo molecular pump seal structure capable of safely exhausting corrosive and condensable process gas even in the case of grease lubricated rolling bearings. With the goal.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has a cylindrical bush fitted into a stationary member of a turbomolecular pump housing so as to be capable of rocking in the radial direction, and a small gap in the inner periphery of the bush. It consists of a journal shaft part that is movably inserted through the inner peripheral part, and a herringbone-shaped groove is formed in the outer peripheral part of the journal shaft part so as to be recessed in a shape that is open in the direction of rotation, Purge gas is introduced into the gap between the bush and the journal shaft, and the bush is loosely fitted to the stationary member with a small gap at the outer circumference and at least two O fitted to the outer circumference. A structure in which the bushing is locked to the stationary member is absorbed by the elasticity of the O-ring to absorb the swinging of the bush in the radial direction, and the bushing and the stationary member of the housing are heated by the intervention of the O-ring. Characterized by being insulated.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS.
[0013]
FIG. 1 is a longitudinal sectional view of a turbo molecular pump 1 having a seal structure according to the present invention, in which 2 is a seal structure part to be described later, 3 is an intake port, and 4 is an exhaust port.
[0014]
Reference numeral 5 denotes a rotor having a large number of blades 6 radially attached to the outer periphery.
[0015]
7 is a stationary blade.
[0016]
There is a rotating shaft 8 at the center of the rotor 5, and the rotor 5 and the rotating shaft 8 rotate at a high speed.
[0017]
The rotary shaft 8 is rotatably supported by stationary members 10 and 11 of the casing via grease lubricated rolling bearings 9a and 9b.
[0018]
Details of the seal structure portion 2 are shown in FIG.
[0019]
That is, the seal structure portion 2 includes a bush 12 that is 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 8a that is rotatably inserted into the bush 12. Become.
[0020]
The journal shaft portion 8a is a part of the rotating shaft 8, and a seal screw groove 8c and a herringbone-shaped groove 8b are recessed in the outer peripheral portion of the journal shaft portion 8a. The outer periphery of the bush 12 and the inner periphery of the bush 12 are formed so as to have a slight gap of 5 to 10 microns.
[0021]
The bush 12 is cylindrical, and is formed to have a gap of at least 100 microns between the outer periphery of the bush 12 and the shaft hole 10a.
[0022]
Reference numerals 13a and 13b denote O-rings which are made of an elastic material having a low elastic modulus, and the bushing 12 is fixed to the stationary member by the O-rings 13a and 13b interposed in grooves formed on the inner peripheral surface of the shaft hole 10a. Ten shaft holes 10a are engaged so as to be swingable in the radial direction.
[0023]
An annular groove 12b in the circumferential direction is recessed in the outer peripheral portion of the bush 12, and a through hole 12a is provided through the bottom of the annular groove 12b, and is formed in the stationary member 10. The purge gas sent from the vent hole 10b passes through the through hole 12a and is sent into a small gap between the bush 12 and the journal shaft portion 8a.
[0024]
The through hole 12a is formed so as to open in the middle between the thread groove 8c recessed in the journal shaft portion 8a and the herringbone groove 8b.
[0025]
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.
[0026]
An arrow F indicates the direction of rotation of the rotary shaft 8, and the herringbone-shaped groove 8 b is formed in a shape that opens in a letter shape toward the rotation direction F.
[0027]
Reference numeral 14 denotes a motor portion that rotationally drives the rotary shaft 8.
[0028]
Next, the operation and effect of the turbo molecular pump 1 of the present embodiment will be described.
[0029]
In the turbo molecular pump 1, the rotor 5 is integrated with the rotary shaft 8 and is driven to rotate by a motor portion 14.
[0030]
The two upper and lower bearings 9a and 9b that support the rotary shaft 8 are both grease-filled rolling bearings, and have a simple structure that does not require a lubricating oil tank or lubricating oil pump.
[0031]
The process gas is exhausted by the high-speed rotation of the rotor 5.
[0032]
It is the seal structure portion 2 that prevents 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.
[0033]
That is, since the space between the outer peripheral portion of the bush 12 constituting the seal structure portion 2 and the stationary member 10 is sealed by the O-rings 13a and 13b, the intrusion of the process gas from this space is prevented.
[0034]
The gap between the inner peripheral part of the bush 12 constituting the seal structure part 2 and the outer peripheral part of the journal shaft part 8a is set to a slight value of 5 to 10 microns, and a purge gas such as nitrogen gas is introduced into the gap. Supply and prevent ingress of process gas.
[0035]
Note that the rotor 5 and the rotating shaft 8 rotating at high speed swing around with a small amplitude around the center of the rotating shaft due to the remaining unbalanced weight.
[0036]
This amplitude is expected to be 10 microns or more. If the outer peripheral portion of the journal shaft portion 8a and the inner peripheral portion of the bush 12 come into contact with each other due to this vibration, there is a fear of generating frictional heat and seizing.
[0037]
However, this acts as a gas bearing between the herringbone-shaped groove 8b provided in the outer periphery of the journal shaft portion 8a and the bush 12, and the force pressing the bush 12 in the radial direction works. Since the radial deformation of the bush 12 is absorbed by the elastic deformation of the rings 13a and 13b, the journal shaft portion 8a and the bush 12 do not contact each other.
[0038]
The O-rings 13a and 13b function to thermally insulate the bush 12 from the stationary member 10 so that they are not in direct contact.
[0039]
This is because the temperature of the rotating shaft 8 is increased by heat generated by the motor portion 14, heat generated by the bearings 9 a and 9 b and heat generated by gas agitation in the seal structure portion 2. Maintaining the same high temperature to prevent condensation products from being generated between the bush 12 and the rotary shaft 8 (journal shaft portion 8a), and the size of the gap between the journal shaft portion 8a and the bush 12 due to thermal expansion. This prevents a decrease in the length.
[0040]
A seal structure of a turbo molecular pump according to a second embodiment of the present invention will be described with reference to FIG.
[0041]
The seal structure 2a of the present embodiment is different from the first embodiment in the structure of the thread groove and the like of the seal portion.
[0042]
That is, in the present embodiment, the screw groove of the seal portion is composed of two sets of screw grooves, that is, the first screw groove 8d and the second screw groove 8e. A through-hole 12a is opened in the middle of the thread grooves 8d and 8e to supply a purge gas.
[0043]
These thread grooves 8 d and 8 e are formed in a shape opened in a C shape in the direction opposite to the rotation direction F of the rotation shaft 8.
[0044]
The present embodiment is more effective in preventing the invasion of system gas than in the first embodiment, and the supply of purge gas to the herringbone-shaped groove 8b is facilitated, so that the operation of the gas bearing is enhanced. Has the advantage of increasing.
[0045]
A seal structure of a turbo molecular pump according to a third embodiment of the present invention will be described with reference to FIG.
[0046]
The seal structure 2b of the present 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.
[0047]
In the present embodiment, the vent hole 10 b for supplying the purge gas is opened to the intermediate portion between the rolling bearing 9 a and the bush 12 in the stationary member 10.
[0048]
Accordingly, the purge gas is diffused into the gap between the journal shaft portion 8a and the bush 12 from the side of the rolling bearing 9a.
[0049]
The present embodiment is simpler than the first and second embodiments, and has the advantage that the herringbone-shaped groove 8b can be formed larger to increase the action of the gas bearing. .
[0050]
A seal structure of a turbo molecular pump according to a fourth embodiment of the present invention will be described with reference to FIG.
[0051]
The seal structure 2c of this embodiment is different from the bush 12 of the first embodiment in that the bush 12 'having three circumferential annular grooves 15 on the inner peripheral portion is used. Different from the first embodiment.
[0052]
These annular grooves 15 are recessed at a depth of at least twice the depth of the sealing screw groove 8c at a portion of the bush 12 'facing the sealing screw groove 8c.
[0053]
These annular grooves 15 have an effect that the operation of the bush 12 ′ is easily stabilized by filling the purge gas.
[0054]
In the present embodiment, the annular groove 15 is provided on the bush 12 'side, but it may be provided on the journal shaft 8a side as shown in FIG.
[0055]
That is, three annular grooves 16 are recessed in the portion having the sealing screw groove 8c on the outer peripheral portion on the journal shaft portion 8a side at a depth at least twice the depth of the sealing screw groove 8c. The operation of 12 is stabilized.
[0056]
In the present embodiment, the number of the annular grooves 15 or the annular grooves 16 is three, but the number may be other than three.
[0057]
A turbo molecular pump seal structure according to a fifth embodiment of the present invention will be described with reference to FIG.
[0058]
The seal structure 2d of the present embodiment is different from the first embodiment in that O-rings are provided on both left and right end surface portions of the bush 12 in the first embodiment.
[0059]
That is, the bush 12 is loosely fitted to the shaft hole 10a of the stationary member 10 through the O-rings 13a and 13b so as to be swingable in the radial direction, and is concentric with the bush 12 at both end surface portions of the bush 12. O-rings 13c and 13d are provided, and the bush 12 is sandwiched from both sides by 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. ing.
[0060]
The gap between the lid 10c and the flange 10d is formed to be slightly larger than the length of the bush 12, and the bush 12 does not directly contact the stationary member side.
[0061]
Thus, in this embodiment, since the stationary member side is contacted via the O-rings 13a, 13b, 13c, and 13d, the thermal insulation between the bush 12 and the stationary member side is improved. Further, the ability to prevent condensation products from being generated between the bush 12 and the rotating shaft 8 (journal shaft portion 8a) or the gap between the two from being reduced is improved.
[0062]
In the present embodiment, the structure is such that it is locked to the stationary member side via O-rings provided on the outer peripheral portion and both end surface portions of the bush 12, but this is the O-ring 13a on the outer peripheral portion of the bush 12. 13b is eliminated, and a small clearance is provided between the outer periphery of the bush 12 and the shaft hole 10a. The bush 12 is connected to the lid 10c and the flange 10d via the O-rings 13c and 13d. It may be held between the stationary members 10 by being sandwiched between them.
[0063]
【The invention's effect】
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 an optimum seal structure for a turbo molecular pump that exhausts a process gas containing a gas having a property.
[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 a seal structure portion according to the first embodiment of the present invention.
FIG. 3 is a longitudinal sectional view of a seal structure portion according to a second embodiment of the present invention.
FIG. 4 is a longitudinal sectional view of a seal structure portion according to a third embodiment of the present invention.
FIG. 5 is a longitudinal sectional view of a seal structure portion 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 portion 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]
1 Turbo molecular pump 2, 2a, 2b, 2c, 2d Seal structure 8a Journal shaft portion 8b Herringbone-shaped grooves 8c, 8d, 8e Screw groove 10 Stationary member 12, 12 'Bush 12a Through holes 12b, 14, 15, 16 Annular grooves 13a, 13b, 13c, 13d O-ring

Claims (8)

In a turbo molecular pump that supports a rotating shaft via a rolling bearing, a cylindrical bush fitted into a stationary member of a housing of the turbo molecular pump so as to be swingable in a radial direction, and an inner peripheral portion of the bush It consists of a journal shaft that is inserted through the inner periphery of the journal shaft with a slight gap, and a herringbone-shaped groove is opened on the outer periphery of the journal shaft. In addition , the purge gas is introduced into the gap between the bush and the journal shaft, and the bush is loosely fitted to the stationary member with a small clearance at the outer circumference and is also fitted to the outer circumference. The structure is such that the stationary member is locked via at least two fitted O-rings, and the bushing is absorbed by the elasticity of the O-rings by the elasticity of the O-rings, and the Seal structure of a turbo molecular pump to a stationary member Gerhard and the housing, characterized in that the thermally insulating. 2. The turbo molecular pump seal structure according to claim 1 , wherein a seal screw groove is provided adjacent to the herringbone-shaped groove on an outer peripheral portion of a journal shaft portion inserted through the bush. The turbo molecular pump seal structure according to claim 2 , wherein the sealing thread groove is composed of two sets of thread grooves that are reversely threaded, and purge gas is introduced between the two sets of thread grooves. . Installed each O-ring at both ends face of the bush, the turbomolecular pump according to claim 1 or claim 2, characterized in that the sandwiched by Ru structure the stationary member through these O-ring Seal structure. The gap between the outer periphery of the journal shaft and the inner periphery of the bush is formed to be 10 microns or less at the most, and the gap between the outer periphery of the bush and the stationary member is at least 100 microns or more. 5. The turbo-molecular pump seal structure according to claim 1 , wherein the seal structure is formed as described above. Claims, characterized in that the the outer periphery of the bush provided with a through hole passing through the annular grooves as well as recessed circumferential annular groove, formed in the structure you pass through the through hole is the purge gas 1 to the seal structure of a turbo molecular pump according to any one of claims 5. 2. The turbo molecular pump seal structure according to claim 1, wherein an opening of a vent hole for supplying purge gas is provided in the middle of the rolling bearing near the bush and the bush . The turbo molecular pump seal structure according to claim 2 , wherein at least one circumferential annular groove is recessed in a portion of the outer peripheral portion of the journal shaft portion having the seal screw groove .

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