JPS61112796A - Axial seal for roughing vacuum pump - Google Patents

Abstract

PURPOSE:To need no sealing system any more by external purge gas by installing a throttle system just in front of the discharge port of a vacuum pump, and also a duct leading through a sealing section positioned between a bearing and the duct, and the upper course section of the throttle system. CONSTITUTION:An orifice 11 is set up at the upstream side of the discharge port 13 of a vacuum pump, and a purge gas duct 13 leading through a discharge duct 12 on the upstream side of the orifice 11 and a seal 10 is installed. With this constitution, gas introduced to a sealing section flows into a dust side and a bearing side, preventing lubricant oil vapor of the bearing section from entering the duct side, and thus purge gas from outside is not necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a roughing vacuum pump, and particularly to a shaft seal for a turbo-type roughing vacuum pump suitable for making the pump oil-free.

[Background of the invention]

Conventional vacuum pumps have a structure in which a bearing that supports the rotating shaft of a rotor and the gas exhausted to the rotor are in contact with each other. Therefore, if the exhausted gas comes into contact with a bearing and has the property of degrading the lubricating oil supplied to the bearing, the lubricating oil will lose its function and some parts may no longer be able to operate normally. Ta. As a device to solve this problem, as described in JP-A-58-74898, an inert gas supply mechanism is installed to supply inert gas to the bearing portion from time to time, and this inert gas is supplied. There are some types that block contact between the υ bearing and the exhausted gas.

However, providing such an inert gas supply mechanism clutters the arrangement of the vacuum pump device and impairs operability.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a roughing vacuum pump having a sealing mechanism that prevents oil vapor and the like from flowing back to the vacuum side without using an external gas purge.

[Summary of the invention]

In order to make the roughing vacuum pump of the present invention clean, it is essential to use a dry type pump mechanism that does not use oil in the part that performs the pumping action, and to prevent backflow to the oil mist flow path in the bearing part. However, for this purpose, purging with external gas is a reliable method.

However, this method has a problem in that gas must be prepared from outside. Therefore, if you use a throttle mechanism installed in the flow path inside the pump to increase the pressure of the working fluid and blow some of it into the seal instead of purge gas,
External gas supply becomes unnecessary. Further, according to this method, the length of the sealing portion can be shortened, and it is also effective in converting the vacuum tube into a vacuum tube.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, a casing 1 forming a support frame for the main body is provided with an inlet 2 for sucking in gas to be exhausted and an outlet p3 for discharging the gas. A drive motor 4 is mounted outside the casing opposite to the suction port 2, and a rotating shaft 5 of the drive motor 4 extends toward the suction port 2. A plurality of impellers 6 are attached to the rotating shaft 5, and are arranged alternately with a plurality of stators 7 fixed within the casing 1. Further, the rotating shaft 5 is supported by bearings 8 and 9, and a seal '0 is provided between the bearings 8 and the impeller 6. An orifice 11 is provided upstream of the discharge port 3, and a purge gas flow path 13 is provided that communicates a discharge flow path 12 upstream of the orifice 11 with the seal 10.

During operation, the rotating shaft 5 rotates, and the pump action of the impeller 6 and stator 7 causes gas sucked in from the suction port to be sent out toward the discharge port. The impeller 6 and stator 7 form a pair of elements, and a vortex element, a centrifugal element, a Siegbahn element, etc. are usually used in a roughing vacuum pump.

The pressure at the discharge port 3 is simply close to atmospheric pressure, and the pressure at the suction port 2 gradually decreases from a pressure close to atmospheric pressure at startup to 10" during operation. ” ~
10-'Torr is reached.

The seal 10 is provided to prevent lubricating oil vapor supplied to the bearing 8 from entering the working gas flow path, and a labyrinth seal is used. FIG. 2 shows details of the seal 10 and its surroundings. Labyrinth seals are very effective when the pressure difference before and after the seal is moderate, but for example, if a vortex stage is placed at the final stage of a roughing vacuum chamber, the pressure distribution on the back side of the impeller will be uneven in the circumferential direction. In the area with the lowest pressure, the pressure around the bearing 8 also decreases to 9.
, lubricating oil vapor will enter the flow path.

In order to prevent this, the middle part of the seal 10 and the discharge passage 1 are
A purge gas flow path 13 is provided to communicate with the gas pump 2, and a part of the discharged gas is guided as a purge gas. Furthermore, if an orifice 11 is provided slightly upstream of the discharge port 3, the pressure of the gas in the discharge channel 12 will be reduced to the pressure of the gas at the discharge port 3, that is, a pressure close to atmospheric pressure due to the throttling resistance. slightly higher than Therefore, this pressurized gas flows from the seal 10 to both the flow path section and the bearing section.

A pressure balance hole 15-bi is formed in the lower casing 14 so that the inside of the lower cage/gu 14 is always at atmospheric pressure. By providing this pressure cover 2/hole 15, the pressurized gas flows from the seal 10 toward the bearing 8.

Note that in a vacuum pump, as the evacuation progresses, the flow rate at the discharge port 3 becomes very small, so an orifice with a fixed hole diameter may not be able to provide a throttling effect. An embodiment of the present invention for that case will be explained with reference to FIG. The valve 16 is pressed against the downstream side of the orifice 11 via a spring 17. The spring force of this spring 17 is very weak, and the valve 16 opens when the pressure on the upstream side of the orifice 11 becomes slightly higher than atmospheric pressure. According to this embodiment, the pressure of the working gas can be increased in any operating state of the vacuum pump.

〔Effect of the invention〕

According to the present invention, since the gas led to the seal portion flows into the flow path side and the bearing side, there is an effect of preventing lubricating oil vapor from the bearing portion from entering the flow path side. Therefore, it is suitable for cleaning the roughing vacuum pump, and since no external purge gas is required, it is structurally and economically advantageous. Also, compared to a screw seal, the axial length is shorter, which is effective in making the vacuum pump more compact.

[Brief explanation of the drawing]

FIG. 1... Casing, 3... Discharge port, 8... Bearing, 10... Seal, 11... Orifice, 12...
・Discharge channel, 1st port

Claims (1)

[Claims] In a roughing vacuum pump whose discharge pressure is atmospheric pressure and which is operated by the rotation of a rotor supported by an oil-lubricated bearing in a casing having a suction port and a discharge port, there is a pump immediately before the discharge port. A shaft seal for a roughing vacuum pump, characterized in that a throttle mechanism is provided, and a flow path is provided that communicates a seal portion located between a bearing and a flow path with an upstream portion of the throttle mechanism.