JPH0526038B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to screw vacuum pumps.

[Prior art] Semiconductor manufacturing is performed by storing wafers in a vacuum container. To create a vacuum inside the container, an inert gas such as nitrogen gas is supplied into the container. At the same time, a vacuum pump is used to remove impurities (mainly O ₂ ) inside the container, creating a high vacuum state.

These high vacuum pumps used in the semiconductor manufacturing process are highly efficient.
Most pumps are lubricated type, in which a large amount of lubricating oil is injected into the casing to provide lubrication between the rotors and seal the various parts.

[Problem to be solved by the invention]

However, in this type of lubricating pump, a large amount of lubricating oil is stored in the casing, so it comes into contact with various gases (e.g., arsenic, gallium, etc.) used in the semiconductor manufacturing process, and its life as a lubricating oil is extremely shortened. There was a problem. Further, there was a problem in that oil molecules back-diffused into the semiconductor manufacturing container, which was unfavorable in the semiconductor manufacturing process.

Furthermore, a structure in which the working chamber is not lubricated and the shaft sealing device and the bearing are lubricated with oil is also considered. However, in this case, the lubricating oil in the shaft sealing device is exposed to the atmosphere at the end of the rotor shaft, so it is equal to atmospheric pressure, but at the shaft portion on the suction side, the pressure is considerably lower than atmospheric pressure, and between both sides of the shaft sealing device. A differential pressure is generated, and the shaft sealing device alone cannot reliably prevent lubricating oil from entering the working chamber within the casing. As a result, the problems of conventional technology, such as oil molecules back-diffusing and entering the vacuum vessel, or air entering from the shaft seal, reducing efficiency, have yet to be fully resolved. do not have.

Furthermore, it is also possible to connect the chamber containing the outer bearing of the shaft sealing device to the suction side, but in this case,
Since gas mixed with oil flows to the area closest to the vacuum container, it is difficult to prevent back diffusion of oil.

Utility Model Application No. 50-66209 discloses, in a screw compressor equipped with a thrust force adjustment mechanism, the low pressure side (bearing chamber) of the thrust force adjustment mechanism is connected to a position close to the suction pressure in the compression process of the screw rotor. This discloses an example in which the forces applied to the thrust force adjustment mechanism are balanced. However, in this example, the bearing chamber and the suction port are communicated with each other, and no consideration is given to the diffusion of lubricating oil to the suction side.

Further, Japanese Patent Publication No. 41-13226 discloses a vacuum pump in which an oil reservoir chamber and a discharge side are communicated through a ventilation pipe, and an oil separation cover is attached to the ventilation pipe. However, in this example, no consideration is given to the diffusion of oil to the vacuum side due to the generation of a differential pressure between the oil reservoir chamber and the pump suction side.

The present invention has been made in view of the above-mentioned problems, and its object is to provide a screw vacuum pump that can prevent back diffusion of oil.

[Means to solve the problem]

The above problem is caused by a pump casing in which a suction port and a discharge port are formed, a shaft part supported by a bearing, and a pump in which the groove part and the land part mesh with each other to rotate and form a plurality of working chambers. A screw vacuum pump comprising a pair of male and female screw rotors disposed in a casing, and a bearing chamber provided at a shaft end on the discharge port side of the pair of screw rotors and housing the bearing and a synchronous gear. , a shaft sealing device installed between the bearing and the working chamber, and an air bleed passage communicating between the bearing chamber and the working chamber that is blocked from the suction port and does not communicate with the discharge port among the plurality of working chambers. This is achieved by a screw vacuum pump characterized in that the air extraction passage is provided with an oil mist separator.

[Effect]

Since the working chamber, which is isolated from the suction port and the discharge port, and the bearing chamber containing the synchronous gear are communicated through the air bleed passage, the pressure in the bearing chamber is maintained between the pressure on the suction side and the pressure on the discharge side. , from the discharge side end face of the screw rotor, the shaft sealing device, the bearing chamber,
A gas flow is formed through the bleed passage to the working chamber, and oil for lubricating the synchronous gear in the bearing chamber is prevented from diffusing into the working chamber through the shaft sealing device.

In addition, since an oil mist separator is provided in the bleed passage, the oil in the bearing chamber flows into the working chamber as the gas in the bleed passage flows from the discharge side end face of the screw rotor to the working chamber via the bearing chamber. This prevents it from spreading to.

〔Example〕

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

In FIG. 1, FIG. 2a, and FIG. 2b, reference numerals 2 and 4 indicate a pair of male and female screw rotors disposed to mesh with each other in the casing 1, each having a plurality of land portions 36, 38 and groove portions. 36A,
38A, and the shaft of each rotor 2, 4 is equipped with a radial bearing 5 or a thrust bearing 6 (6A, 6B).
It is supported by Synchronous gears 9 and 10 are provided on the shafts of both rotors 2 and 4 so that both rotors 2 and 4 rotate synchronously. Gas is sucked into both rotors 2 and 4, compressed, and discharged to a discharge port 12 formed at the lower end of the casing 1, so that the inside of a vacuum container (not shown) communicating with the suction port 11 is brought into a vacuum state. It's getting old. Lubricating oil is supplied to the radial bearing 5, thrust bearing 6, and synchronous gears 9 and 10, and in order to prevent these lubricating oil from entering the casing in which both rotors 2 and 4 are housed, the rotor shaft supports are supplied with lubricating oil. Shaft seal devices 16 and 17 consisting of a carbon ring seal 14 and a screw seal 15 are provided.

The chamber 51 in which the bearings 5, 6A, 6B and the synchronous gears 9, 10 are housed communicates with the working chamber 18A, which does not communicate with either the suction port 11 or the discharge port 12 in the working chamber 18, through a bleed passage 19. has been done. An oil mist separator 20 is installed in the middle of this bleed passage 19. Bleeding passage 1
9 to the working chamber 18, that is, the air bleed position is determined by the sealing ability of the shaft sealing device 16. If the sealing ability is low, the bearing chamber 51
so that the pressure is close to the suction pressure,
Working chamber 18A immediately after being shut off from suction port 11
If the sealing ability is high, the pressure in the bearing chamber 51 is selected to be connected to the working chamber 18A immediately before communicating with the discharge port 12 so that the pressure in the bearing chamber 51 approaches the discharge pressure.

Thereby, it is possible to select an air bleed position suitable for the sealing capacity of the shaft sealing device 16, and it is possible to install the air bleed position closer to the discharge port 12 of the screw rotors 2, 4.

FIGS. 3 and 4 are diagrams showing other embodiments of the non-lubricated screw vacuum pump according to the present invention.

In these figures, a first rotor 30 and a second rotor 40 are disposed in parallel in a cylindrical chamber 22 of a pump casing 21 and rotate while meshing with each other. Rotor 30, 40
The rotor shaft portions of are equipped with radial bearings 31 and 41, respectively.
and the thrust bearings 32, 42, the axis 30
It is rotatably supported around A and 40A.
At one end of the rotor shaft are synchronous gears 3 that mesh with each other.
3 and 43, and the other end of the rotor shaft protrudes through the pump casing 21 and is connected to a prime mover (not shown) via a speed increasing pinion 50 and a coupling ring (not shown). rotor 30,
Carbon ring seal 3 is installed on the rotor shaft of 40.
A shaft sealing device consisting of bearings 31, 32, 41, 4 and screw seals 35, 45 is installed.
2. The lubricating oil supplied in the bearing chamber 51 is prevented from entering the working chamber 18 in the cylindrical chamber 22.

The first rotor 30 has male screw blades 36 and female screw blades 3 with opposite torsional directions.
8 are formed on the same axis, and on the other hand, the second rotor 40 is also formed with a male screw blade 46 and a female screw blade 48 whose twist directions are opposite to each other, and are formed in the exact same shape. One of the two rotors is arranged in the opposite direction. The male and female screw blades 36 and 48, 38 and 46 formed on the pair of rotors 30 and 40 mesh with each other, but are prevented from coming into contact by the synchronizing gears 33 and 43 so that they rotate in opposite directions. It's summery.

A suction port 52 communicating with the suction port 52A is formed in the upper part of the cylindrical chamber 22 facing the center in the rotor axial direction between the two rotors 30 and 40, while the cylindrical chamber 2
A discharge port 54 communicating with the discharge port 54A is formed below both longitudinal ends of the discharge port 2 . Suction port 5
2A is connected to a suction pipe 56 extending from a vacuum container (not shown) whose interior is to be evacuated, and when both rotors 30 and 40 rotate while meshing, the gas in the vacuum container is It is sucked in through the suction port 52A and the suction port 52 by male and female screw blades 36 and 48, 38 and 46, compressed, and then discharged to the outside (atmosphere) through the discharge port 54 and the discharge port 54A.

In addition, the operation chamber 18A in the bearing chamber 51 and the cylindrical chamber 22, and the operation in the shaft support casing 60 and the cylindrical chamber 22 installed in the casing on the opposite side to the side where the bearing chamber 51 is installed. The chamber 18B has oil mist separators 62, 6 in the middle of the pipe.
3 are connected through bleed pipes 64 and 65, respectively. As shown in FIG. 5, the pressure in the working chambers 18A and 18B within the cylindrical chamber 22 increases from the center of the cylindrical chamber toward both ends, and becomes equal to atmospheric pressure at both ends. Working chamber 18A in the cylindrical chamber 22 of the exhaust pipes 64, 65,
The connection to 18B is a space separated from the suction port 52, defined by the land portions of the male and female rotors meshing with each other, the groove portions, and the inner circumferential wall surface of the cylindrical chamber 22, and the cylindrical The pressure P ₁ is slightly lower than atmospheric pressure near both ends of the chamber 22 in the longitudinal direction.
(See Figure 5).

By providing air bleed pipes 64 and 65 equipped with oil mist separators 62 and 63, the bearing chamber 51
The pressure inside is slightly lower than the pressure P ₀ (which is equal to atmospheric pressure) at the position of the working chamber 18A in the cylindrical chamber 22 and the side wall 22A on the side of the bearing chamber 51, and the pressure inside the shaft support casing 60 is the side wall 2 on the shaft supporting casing 60 side of the working chamber 18B in the cylindrical chamber 22.
Since the pressure at position 2B is slightly lower than P ₀ (which is equal to atmospheric pressure), bearings 31, 32, 41,
42 and the bearing chamber 51, the lubricating oil is supplied to the carbon ring seals 34, 44 and the screw seal 3.
The cylindrical chamber 22 is passed through the shaft sealing device consisting of 5 and 45.
Intrusion into the interior is reliably prevented. Furthermore, even if the oil mist separators 62 and 63 fail, the bleed pipes 64 and 65 are connected to the suction port 52 at a position separated by a plurality of land portions and grooves, so that the upstream side of oil molecules The risk of diffusion to the suction side is extremely low.

Note that both the first and second rotors 30 and 40 are supported at both ends and are not supported at all in the center, but since the load on the vacuum pump is very small, it is not necessary to support the center of the rotor. There are no structural problems.

According to this embodiment, there are the following effects.

Since the opening position of the working chamber of the bleed passage can be placed closer to the discharge port, lubricating oil does not enter into the cylindrical chamber 22, and back diffusion of oil molecules is prevented.

In addition, by installing the air bleed pipes 64 and 65, the pressure of the shaft seal device is lower than the discharge pressure in the cylindrical chamber 22, and the differential pressure on both sides can be reduced. It can also prevent oil molecules from entering the skin.

In the embodiments shown in Figures 3 and 4, there is no shaft support or shaft seal device on the suction side, so gas (atmosphere) does not enter into the cylindrical chamber 22 from the suction side, resulting in excellent compression efficiency and a high vacuum state. is obtained. Therefore, it can be used in a wide pressure range that is not possible with conventional non-lubricated systems.

In the embodiment shown in Figs. 3 and 4, the thrust acting in the axial direction of the rotor is balanced, so the thrust bearing 3
2 and 42 can be reduced in capacity, the amount of lubricating oil supplied to this bearing can be reduced, and shaft sealing can be facilitated.

In the embodiment shown in Figs. 3 and 4, the first and second rotors 30 and 40 are formed in exactly the same shape, so the rotors can be machined using only a pair of male and female rotor machining hobs, resulting in extremely high workability. good.

〔Effect of the invention〕

As is clear from the above description, the present invention has the effect of preventing oil from diffusing from the bearing chamber provided with the synchronous gear into the working chamber via the shaft sealing device in the non-lubricated screw vacuum pump.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional plan view of one embodiment of the present invention, and FIG.
Figure a is a vertical sectional front view of Figure 1, Figure 2 b is Figure 2 a
FIG. 3 is a longitudinal sectional plan view of another embodiment of the present invention, FIG. 4 is a longitudinal sectional front view of FIG. 3, and FIG.
The figure shows the pressure distribution in the longitudinal direction of the cylindrical chamber. 1, 21...Pump casing, 2...Male rotor,
4...Female rotor, 5...Radial bearing, 6A, 6B...
Thrust bearing, 9, 10, 33, 43... Synchronous gear, 11, 52... Suction port, 12, 54A... Discharge port, 14, 34, 44... Carbon ring seal, 15, 35, 45... Screw seal, 16, 1
7...Shaft sealing device, 18A, 18B...Working chamber, 19,
64, 65... Air bleed pipe, 20, 62, 63... Oil mist separator, 36, 46, 76, 86... Land part or groove part of male rotor, 38, 48, 78, 8
8... Groove or land portion of female rotor, 51... Bearing chamber.

Claims (1)

[Claims] 1. A pump casing in which a suction port and a discharge port are formed, a shaft portion supported by a bearing, and a groove portion and a land portion meshing with each other to rotate and form a plurality of working chambers in the pump casing. a pair of male and female screw rotors disposed; a bearing chamber provided at a shaft end on the discharge port side of the pair of screw rotors and housing the bearing and a synchronous gear;
A screw vacuum pump comprising: a shaft sealing device installed between the bearing and the working chamber; and a working chamber that is shut off from the suction port and does not communicate with the discharge port among the plurality of working chambers, and the bearing chamber. A screw vacuum pump comprising: a bleed passage communicating with the bleed passage; and an oil mist separator provided in the bleed passage.