JPH04203386A - Screw vacuum pump - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an exhaust system for a vacuum chamber, and particularly to a screw vacuum pump suitable for minimizing damage when an abnormality occurs due to contact between rotors.

[Conventional technology]

Conventionally, the tooth profile of a screw vacuum pump capable of exhausting air from atmospheric pressure is similar to that often used in screw compressors, and the tooth profile has a multi-thread, interference-free tooth profile and Utility Model Open in Showa 63-14.
A tooth profile (hereinafter referred to as a rectangular tooth profile) using one or two square screw threads is known as disclosed in Japanese Patent No. 884. These two types of tooth profiles each have advantages and disadvantages, and are used depending on the purpose of the vacuum pump.

The principle of discharging gas from a vacuum pump will be described. The tooth grooves carved on the surface of the screw rotor are surrounded by the bore surface of the casing housing the screw rotor, forming a spiral space. This space is divided by the teeth of the other screw rotor into a plurality of spaces called working chambers. When the screw rotor is rotated, the working chamber moves in the axial direction. When the working chamber moves to the end face, there is a bore end face, so the bore end face closes one end of the working chamber, reducing the volume of the working chamber. When the volume of the working chamber is reduced to a certain value, the working chamber and the discharge port communicate with each other, and the gas in the working chamber is discharged.

The two screw rotors usually rotate synchronously without contacting each other, and a small gap is maintained between them. Additionally, a small gap is maintained between the screw rotor and the casing.

From the standpoint of reducing gas leakage and improving the performance of the vacuum pump, it is desirable that these gaps be small.

However, if the clearance is too small, the screw rotors or the screw rotors and the casing are likely to come into contact when an abnormality occurs. [Problems to be Solved by the Invention] If the casing and the casing came into contact, they would scrape each other and generate dust, which could flow back into the suction pipe and contaminate the vacuum chamber. The inside of a vacuum chamber is an environment that is extremely dust-free, and the infiltration of backflowing dust must be prevented.

The object of the present invention is to provide a screw vacuum pump that does not cause dust to flow back through the suction pipe and contaminate the vacuum chamber even if dust is generated due to contact between screw rotors or the screw rotor and the casing in the event of an abnormality. It's about making it happen.

[Means to solve the problem]

In order to achieve the above object, the present invention configures a screw vacuum pump as follows.

As a first method, the screw rotor and casing are made of a material whose main component is a ferromagnetic material such as iron or nickel. The external vacuum chamber and the suction port of the casing are connected through a suction pipe. The suction tube is part of the screw vacuum pump. A mechanism for generating a magnetic field inside the suction pipe is provided inside or around the suction pipe. As the mechanism for generating the magnetic field, a permanent magnet, an electromagnet, or a hybrid thereof may be used.

When an electromagnet is used as a mechanism for generating a magnetic field, there is no need to constantly apply current, and it is only necessary to apply current to generate magnetism when an abnormality occurs in the vacuum pump. In this case, it is necessary to equip the vacuum pump with an abnormality detection device, but the motor overload detection device may also be used.

Instead of this means, the following second means may be used. The screw rotor and casing may be made of any material. A valve is provided in the suction pipe to serve as an inlet for a purge gas consisting of an inert gas such as helium or argon or other gas. This valve is normally kept closed. This means includes the abnormality detection device and a mechanism for opening a valve in response to an abnormality detection signal.

[Operation] The first means operates as follows. That is, when the two screw rotors or the screw rotor and the bore wall of the casing come into contact for some reason, those surfaces are scraped and dispersed as dust. The cause of the contact is that the cooling water supplied to the screw vacuum pump is interrupted, or 1. The temperature suddenly changes and the thermal balance is greatly disrupted, or external vibrations or shocks are applied, or the surface of the screw rotor This may be caused by substances adhering to the rotor, causing the rotational balance to collapse. Most of the generated dust is expected to go out through the discharge port along with the gas flow, but some of it flows backwards and heads from the suction port through the suction pipe to the vacuum chamber. However, a magnetic field is applied inside the suction tube, and the ferromagnetic dust is attracted and adsorbed in a certain direction before reaching the vacuum chamber. Therefore, it is highly unlikely that any dust will reach the vacuum chamber.

The second means works as follows. That is, when the abnormality detection device detects contact between the two screw rotors or between the screw rotor and the bore wall of the casing, a valve provided in the middle of the suction pipe is opened and purge gas flows into the suction pipe.

Then, inside the suction pipe, where there was almost no flow, a strong flow is created in the direction from the vacuum pump toward the screw vacuum pump. Backflow of dust generated by this flow is prevented. This flow continues even inside the screw vacuum pump, and the dust is discharged outside from the discharge port along with the flow, so there is no problem.

〔Example] Hereinafter, the present invention will be explained based on the drawings.

FIG. 1 is a sectional view of a screw vacuum pump according to a first embodiment of the present invention. A screw rotor 1 with a rectangular tooth profile of a left-hand thread and a screw rotor with a rectangular tooth profile of a right-hand thread (in the direction of the paper, not shown) mesh with each other and are housed in a casing 2. The screw rotor 1 and the right-handed screw rotor do not come into contact with each other with a slight gap between the inner wall of the casing 2, that is, the bore 3. The tooth spaces of each screw rotor are closed by the bore surface and the teeth of the other screw rotor to form a space called a working chamber 14. A shaft 4 fixed through the two screw rotors is supported by an upper bearing 5 and a lower bearing 6, and a shaft seal 7 is provided above the upper bearing 5 to prevent lubricating oil and air from entering and exiting. . The shaft 4 is equipped with synchronous gears 8, which mesh and rotate to transmit rotational power and maintain the rotational synchronization of the two screw rotors. The synchronizing gear 8 also meshes with a driving gear 9 fastened to the output shaft of the electric motor 10. electric motor 10
The rotation generated by this is increased in speed and transmitted to the screw rotor.

A suction port 11 is provided in the upper part of the casing 2, and is connected to a vacuum chamber 2o through a suction pipe 12. The suction pipe 12 is made of a material transparent to magnetic flux, such as aluminum or plastic. A permanent magnet 15 is provided so as to sandwich the suction pipe 12 in the middle. The permanent magnet 15 is a U-shaped magnet, and its north and south poles are connected in the direction toward the back of the paper. Permanent magnet 1
Since the magnetic flux 16 directed from the north pole to the south pole of 5 passes through the suction pipe 12, a strong magnetic field is generated inside the suction pipe 12.

This screw vacuum pump works as follows.

The rotation generated by the electric motor 10 is increased in speed by gears and transmitted to the screw rotor 1. The working chamber 14 moves downward by the rotation of the two screw rotors, and the gas trapped inside is transferred from top to bottom. This action makes it possible to scrape out the air inside the vacuum chamber 20.

Usually, a minute gap is provided between the two screw rotors or between the screw rotors and the bore wall surface 3, so that they do not come into contact with each other. However, if the cooling water supplied to the screw vacuum pump is cut off or the temperature suddenly changes, causing a significant loss of thermal balance, or if external vibrations or shocks are applied, the screw rotor 1
Contact may occur if a substance adheres to the surface and the rotational balance is disrupted. Since contact itself is not a normal operation, when contact occurs continuously, the screw vacuum pump is brought to an emergency stop, and the piping with the vacuum chamber 20 is also closed to prevent the effects of the emergency stop from spreading. However, before that, the surfaces of the screw rotor l and the bore wall surface 3 are scraped by the contact, and the dust is dispersed. It is expected that most of the generated dust will go out from the discharge port along with the gas flow, but some will flow backwards and flow from the suction port 11 to the suction pipe 12.
It passes through to the vacuum chamber 20. The inside of the vacuum chamber 20 is kept clean and dust is not allowed to enter.

Here, a magnetic field is applied inside the suction pipe 12,
The ferromagnetic dust is attracted to the direction of the magnetic flux 16 and adsorbed to the inner wall of the suction pipe 12 before reaching the vacuum chamber. Therefore, it is almost impossible for dust to reach the vacuum chamber 20.
The inside of the vacuum chamber 20 can be kept clean.

In this embodiment, the permanent magnet 15 is arranged outside the suction pipe 12, but a part or the whole of the permanent magnet 15 may be arranged inside the suction pipe 12. Alternatively, the magnetic flux 16 may be strengthened using a plurality of permanent magnets. Since dust accumulates in the vicinity of the suction pipe 12 where the magnetic field is applied, it is preferable to widen the pipe only in that area or form a recess on the inner surface to store the dust and secure a flow path.

According to this embodiment, the object of the present invention can be easily achieved without significantly modifying the conventional screw vacuum pump.

Hereinafter, the present invention will be explained using FIG. 2.

FIG. 2 is a sectional view of a squew vacuum pump according to a second embodiment of the present invention. Description of parts common to the first embodiment will be omitted. The motor 10 is supplied with power from the inverter 30 and rotates. The inverter 30 has a built-in current monitoring function and automatically stops when the motor 10 becomes overloaded. Information on overload operation can also be taken out to the outside, and the wiring for that purpose is led to the relay 31. The relay 31 turns on and off current to the electromagnet 35 based on information about overload operation.

When the two screw rotors come into contact with each other or between the screw rotor and the bore wall surface 3, the rotational resistance increases rapidly and the motor 10 becomes overloaded. When the inverter 30 senses this, it automatically stops the motor 10 and at the same time activates the relay 31 to send current to the electromagnet 35. The electromagnet 35 generates a magnetic field using electric current to attract dust.

According to this embodiment, an unnecessary magnetic field is not applied during normal times, and the dust accumulated on the west face of the suction pipe 12 can be easily removed by simply turning off the current.

The present invention will be explained below based on FIG.

FIG. 3 is a sectional view of a screw vacuum pump according to a third embodiment of the present invention. Description of parts common to the first and second embodiments will be omitted. A purge gas inlet 42 is provided in the middle of the suction pipe 2, and is connected to a purge gas source 41 via a valve 4o. The purge gas source 41 is
For example, in a high-pressure container of inert gas such as helium gas,
The purge gas is self-injected into the suction pipe 12 due to the pressure difference when the valve 40 is opened. The relay 31 applies current to open and close the valve 40 based on the overload operation information generated by the inverter 30.

When the two screw rotors come into contact with each other, or between the screw rotor and the bore wall 3, the rotational resistance increases rapidly and the motor 10 becomes overloaded. When the inverter 30 senses this, the motor 10 is automatically stopped and at the same time the relay 31 is activated to open the valve 40. Then, the purge gas is self-injected into the suction pipe 12 from the purge gas source 41. motor 1o
Since the purge gas is injected faster than the gas stops, the purge gas is directed toward the suction port 11 and sweeps away the dust that is flowing back. Therefore, it is almost impossible for dust to reach the vacuum chamber 20, and the inside of the vacuum chamber 20 can be kept clean. A purge gas that does not contaminate the vacuum chamber 20 is selected.

According to this embodiment, the object of the present invention can be achieved without using magnetism. Additionally, since valves are smaller and lighter than magnetic components, devices can be made smaller.

[Effects of the Invention] According to the present invention, even if the screw rotors or the screw rotor and the casing contact each other and generate dust when an abnormality occurs, the dust will not flow back through the suction pipe and contaminate the vacuum chamber. No screw vacuum pump can be realized.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, FIG. 2 is a cross-sectional view of a second embodiment of the present invention, and FIG. 3 is a cross-sectional view of a third embodiment of the present invention. 1... Screw rotor, 2... Casing, 3...
...Bore, 4...Shaft, 5...Upper bearing, 6...
Lower bearing, 7... Shaft seal, 8... Synchronous gear, 10.
...Electric motor, ]J...Intake port, 12...Suction pipe, 1
4... Working chamber, 15... Permanent magnet, 16... Magnetic flux,
20... Vacuum chamber, 30... Inverter, 31... Relay, 35... Electromagnet, 40... Valve, 41...
- Purge gas source, 42...inlet.

Claims (1)

[Claims] 1. Teeth that mesh with each other and rotate synchronously in opposite directions around two parallel axes with a slight gap between them, maintaining non-contact, and that are twisted in opposite directions. A screw vacuum comprising two screw rotors carved with a casing and a casing having an inlet and an outlet and a set of bores having a mutually shared space and accommodating each of the two screw rotors. In the pump, at least one of the screw rotor and the casing is made of a material mainly composed of a ferromagnetic material such as iron, and a mechanism for generating a magnetic field is provided inside the suction pipe connected to the suction port, A screw vacuum pump characterized in that the magnetic field has sufficient strength to attract ferromagnetic powder floating inside the suction pipe in a predetermined direction and attract it to a predetermined position.