JPS62168988A - Screw type vacuum pump - Google Patents

Abstract

PURPOSE:To improve an ultimate vacuum by providing a connecting part for connecting the middle part of a shaft seal means on a suction port side, to a discharge port or a part positioned in a vacuum zone in a gas flow passage on the downstream side of said discharge port, on a first stage pump body. CONSTITUTION:A connecting part 16 which is provided on a first stage pump body 1, connects the middle part of a shaft seal means 13 on a suction port 7 side or a part on a side farther than this part from a rotor 10, to a discharge port 8 or a part positioned in a vacuum zone in a gas flow passage on the lower course side of the discharge port 8, to carry out suction by vacuum from the first shaft seal means 13 part to a discharge flow passage 15 in order to keep the pressure of the first shaft seal means 13 part as low as possible. Thereby, pressure difference between the suction port 7 and the first shaft seal means 13 can be reduced, to prevent the leakage of air from the means 13 to the suction port 7 side or to reduce the expansion coefficient of air even if air has leaked. As a result, exhaust from the first stage 3 can be accelerated obtaining a high ultimate vacuum.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a screw type vacuum pump using a screw rotor.

(Prior Art) Conventionally, a screw type vacuum pump 21 shown in FIG. 3 is known.

This vacuum pump 21 has basically the same structure as a screw compressor, and has a pair of male and female screw rotors (hereinafter referred to as (referred to as rotor) 25,
The rotor 25 is rotatably supported via bearings 26 on both sides and engaged with a rotational drive section (not shown), and both bearings 26 and the rotor 25
A shaft sealing means 27 is appropriately provided between the two. Then, the suction port 22 side is connected to a part (not shown) that is evacuated, for example, a vacuum tank, and gas is sucked in from the suction port 22 as in the case of the compressor described above, and this gas is discharged from the discharge port 23. It is formed so that the mouth 22 side is a vacuum region.

By the way, in order to increase the ultimate vacuum level compared to the case where the vacuum pump 21 is used in a single stage, as shown in FIG.
For example, they are used arranged in two stages. That is, in the example shown in FIG. 4, the vacuum tank 2 is evacuated by the vacuum pumps 21 arranged in two stages.

(Problems to be Solved by the Invention) Generally, the portion of the shaft sealing means 27 of the vacuum pump 21 on the side far from the rotor 25 is at atmospheric pressure (760 Torr).
In reality, it is impossible to eliminate the gap between the shaft sealing means 27 and the shaft of the rotor 25. Gas leaks from the side to the suction port 22 side which is in the vacuum region.

Unlike in the case of a compressor, in the case of the vacuum pump 21, the pressure at the suction port 22 is very low compared to atmospheric pressure, so there is a pressure difference between the bearing 26 side of the shaft sealing means 27 and the inside of the suction port 22. becomes very large, gas leakage is likely to occur, and the expansion rate of the gas leaked into the suction port 22 also becomes very large.

For this reason, with the vacuum pump 21, it is not possible to obtain a very high degree of ultimate vacuum, and in the case of a single stage, it is approximately 1 O Torr, and as shown in Fig. 4, in the case of two stages, the limit is I Torr, which reaches the medium vacuum region. There was a problem with not being able to reach it.

The present invention was made in view of such conventional problems, and
The purpose is to provide a screw-type vacuum pump that makes it possible to improve the ultimate degree of vacuum.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a pair of male and female screw rotors that mesh with each other in a casing having a suction port on one side and a discharge port on the other side. In a screw type vacuum pump formed by arranging a pump main body rotatably housed with appropriate shaft sealing means arranged in multiple stages, the screw rotor is connected to the middle part of the shaft sealing means on the suction port side or At least the first-stage pump body is provided with a communicating portion that communicates with the discharge port, or a gas flow path downstream from the discharge port, and a portion in the vacuum region.

(Example) Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows an example in which a screw type vacuum pump I according to the present invention is connected to a vacuum tank 2 in the same manner as in FIG. 4.

This vacuum pump 1 consists of pump bodies 3 and 4 arranged in two stages, and the first stage pump body 3 is of an oil-free type as shown in FIG. is the provision. Moreover, the casing 5 is
One rotor chamber 9 has a suction lower provided in the upper part and the other has a rotor chamber 9 opened to a discharge port 8 provided in the lower part, and a pair of male and female rotors 1O that mesh with each other are rotatably housed in the rotor chamber 9. The rotor is configured so that the gas sucked in from the suction lower is confined in the rotor chamber, compressed, and then discharged from the discharge port 8.

Further, the rotor shaft 11 of the rotor IO is supported by bearings 12a and 12b that are forcibly lubricated, and the bearing 12a is
, 12b and the rotor chamber 9, first shaft sealing means 13a, 13b and second shaft sealing means 14a, 14 are installed from the rotor chamber 9 side.
b are provided in this order to prevent the lubricating oil applied to the bearings 12a and 12b from leaking into the rotor chamber 9. Here, two seal rings are arranged in parallel as the first shaft sealing means 13a, 13b, and the second shaft sealing means 14a, 14h
Labyrinth seals are used.

In addition, at the location of the first shaft sealing means 13a on the suction lower side, a part of the seal ring on the second shaft sealing means 14a side is connected to the discharge passage I5 of the pump body 3 in the vacuum region, that is, to the pump body 3. A first communication portion 16 is formed to communicate with the intermediate portion of the pump body 4, and a second communication portion, which is a through hole that communicates the end of the labyrinth on the rotor chamber 9 side with the atmosphere, is formed at the second shaft sealing means 14a. A portion 17 is formed.

Of these, the second communication portion 17 is configured to increase the pressure on the rotor chamber 9 side of the labyrinth, that is, to make it approximately equal to atmospheric pressure, so that the lubricating oil applied to the bearing 12a is transferred from the labyrinth to the first shaft sealing means 13a. This effectively prevents leakage to the sides.

On the other hand, the first communication portion 16 includes a first through hole 18 that allows the seal ring of the first shaft sealing means 13a to communicate with the outside of the casing 5, and a connection W19 that connects the first through hole 18 with the discharge flow path 15. Therefore, the first shaft sealing means 13a is evacuated from the discharge passage 15 to keep the pressure as low as possible.

As a result, the pressure difference between the suction lower and the first shaft sealing means 13a is reduced, and the first! This is to reduce the leakage of air from the shaft sealing means 13a to the suction lower side, and to reduce the expansion rate even if air leaks. Furthermore, even if lubricating oil were to leak from the labyrinth portion, the lubricating oil would be discharged by the first communication portion 16 through the discharge passage 15 which is cut off from the suction lower. Less likely to leak to the sides.

Next, the second stage pump main body 4 has substantially the same structure as the pump main body 3 except that the first communication portion 16 is not provided, and the explanation thereof will be omitted.

When we conducted a test using the vacuum pump I with the above configuration, we found that the ultimate vacuum was 0.2 Torr, and 20 Torr in the discharge flow path 15, which was achieved by simply arranging two stages of conventional vacuum pumps. It was confirmed that the ultimate vacuum degree was improved compared to the case of .

In the above embodiment, the pump body 3 is an oil-free set.
4 arranged in two stages, the present invention is not limited to this, but also includes, for example, a pump body using an oil-cooled type, and furthermore, the pump body can be arranged in two stages or more. This also includes the case where it is placed.

(Effects of the Invention) As is clear from the above description, according to the present invention, in a screw type vacuum pump formed by arranging the pump body in multiple stages, the intermediate portion of the shaft sealing means on the suction port side or this At least the first-stage pump body is provided with a communication section that connects the part of the pump that is further away from the rotor to the discharge port, or a gas flow path downstream of the discharge port, which is in a vacuum region. .

For this reason, the pressure in the pump means, especially in the intermediate part of the shaft sealing means on the suction port side of the first stage pumping means, or in the part farther away from the rotor, is lowered. The amount of gas leaking to the suction port side is reduced, and the expansion rate of the leaked gas is also reduced. As a result, the evacuation from at least the first stage is promoted, and a high ultimate degree of vacuum can be obtained.

4. Brief description of the drawings Fig. 1 is an equipment configuration diagram showing an application example of the screw type vacuum pump according to the present invention, Fig. 2 is a cross-sectional view of the first stage pump main body shown in Fig. 1, and Fig. 3 The figure is a longitudinal sectional view of a conventional screw type vacuum pump, and FIG. 4 is a device configuration diagram showing an example of application of the vacuum pump shown in FIG. 3.

DESCRIPTION OF SYMBOLS 1... Screw type vacuum pump, 3.4... Pump body, 7... Suction port, 8... Discharge port, 10... Rotor, 13a.

13b...first shaft sealing means, 14a, 14b...second
Shaft sealing means, 15...discharge flow path, 16...first communication section.

Patent Applicant: Agent of Kobe Steel, Ltd. Patent Attorney: Seihaku Ao and 2 others 1s

Claims (1)

[Claims] (1) In a casing having a suction port on one side and a discharge port on the other side, there are multiple stages of the pump body, each consisting of a pair of male and female screw rotors that engage with each other and are rotatably housed with appropriate shaft sealing means on both sides. In the screw type vacuum pump, the middle part of the shaft sealing means on the suction side, or the part on the side far from the screw rotor, is the discharge port, or the gas flow path downstream from it. A screw type vacuum pump characterized in that at least a first-stage pump body is provided with a communication portion that communicates with a portion in a vacuum region.