JPH066956B2 - Turbo molecular pump - Google Patents

Description

TECHNICAL FIELD The present invention relates to a turbo molecular pump.

[Conventional technology]

A conventional turbo molecular pumpon of this type will be described with reference to FIG.

In the figure, 1 is a rotating body, and a gas turbine blade 6 is coupled to the lower end of its drive shaft 1a. 3,4
Is a radial gas bearing arranged in the casing 2, and the gas introduced from the gas inlets 3a and 4a is ejected from the porous nozzle. Reference numeral 5 is a thrust-direction gas bearing disposed in the casing 2. Reference numeral 7 is a seal member that seals between the gas bearing portion and the discharge side vacuum chamber 8.

[Problems to be solved by the invention]

However, in the above-mentioned conventional one, since the gas turbine is formed into the overhang shape by incorporating the gas bearings 3 and 4 in the radial direction, the radial reaction force of the gas bearing 4 becomes excessive and the proper bearing performance is obtained. There was a problem that I could not get. Further, the gas bearing is usually made into a split type because it has a minute gap with the drive shaft 1a. Therefore, the turbine blade 6 and the rotating body 1 are produced separately, and are joined by means such as screw connection 9 to form the rotating body 1,
There is a problem in that it is not preferable in terms of vibration reproducibility.

[Means for solving problems]

The present invention has been made in view of the above-mentioned conventional problems, in which the drive shaft is arranged in a substantially vertical direction, and the total thrust load acting on the rotating body including the drive shaft is set downward, and the downward thrust load is set. In a turbo molecular pump that supports the lower end of the same drive shaft with a downward thrust load bearing, the drive shaft is integrally provided with a gas turbine blade part having an outer diameter that is substantially the same as the outer diameter of the drive shaft, and the blade parts are sandwiched in a pair. A member having the radial gas venting of the above-mentioned mounted in the casing and having a diameter larger than the outer diameter of the drive shaft from the position corresponding to the radial gas bearing of the drive shaft to at least one of the shaft ends and the coaxial end. The present invention provides a turbo-molecular pump characterized in that

[Action]

According to the present invention configured as described above, since there is no bolt connection or connection with a separate drive shaft between the drive shaft and the gas turbine blade portion, it can be configured as an integral rotary shaft, From the aspects of backlash prevention and good alignment,
Rotational vibration stability is improved, and at the same time, since the outer diameter of the gas turbine blade is formed to be almost the same as the outer diameter of the drive shaft, a pair of radial gas bearings can be arranged so as to sandwich the same gas turbine blade. The radial gas bearing can support the load evenly,
The drive and stable rotation of the molecular pump can be ensured.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

In the figure, 1 is a rotating body, and 1 a is a drive shaft of the rotating body 1.

2 is a casing surrounding the drive shaft 1a, 3 and 4 are radial gas bearings arranged in the casing 2, which are made of porous metal having gas supply holes 3a and 4a, respectively.

Reference numeral 7 is a seal member that seals between the radial gas bearing 3 side and the discharge side vacuum chamber 8.

Further, 6 is a gas turbine arranged so as to be sandwiched between the radial gas bearings 3 and 4, and the gas turbine 6 is a blade portion formed by directly machining an end mill or the like around the drive shaft 1a. 6a, and a gas injection nozzle 6b for injecting drive gas to the blade portion 6a.

Note that the gas turbine 6 may be provided in multiple stages in relation to the output, and at this time, a plurality of radial gas bearings 3 and 4 are also provided.

Reference numeral 5 is a ball that rotatably supports the weight of the rotating body 1, that is, a load in the downward thrust direction. The ball 5 is formed by immersing it in lubricating oil or using solid lubricating oil in the contact portion. ing.

Naturally, the downward thrust load due to the weight of the rotating body 1 is larger than the upward thrust load due to the pressure difference acting on the rotating body 1, and the total thrust load acting on the rotating body 1 is always set downward. It goes without saying that it will be designed.

According to the embodiment configured as described above, since the gas turbine blade portion 6a is formed integrally with the drive shaft, it is possible to reliably suppress the occurrence of vibrations seen in the assembled rotary body, and to prevent the overhang portion of the rotary body. However, since the entire structure is simple and the blade portion 6a is arranged so as to be sandwiched between the radial gas bearings 3 and 4, the load on the gas bearings 3 and 4 is evenly divided to cause an overload phenomenon. The accompanying deterioration in bearing performance can be prevented in advance.

FIG. 3 shows another embodiment, which employs a dynamic pressure type spherical bearing 15 in place of the ball 5 which receives the thrust load in the lower portion of the above-mentioned embodiment and is located in the lubricating oil 9. Since the other configurations are the same as those of the above-described embodiment, the same portions are denoted by the same reference numerals and detailed description thereof will be omitted.

In each of the above-mentioned embodiments, when the weight of the rotating body 1 is light, the rotating body 1 does not move in the thrust direction due to the pressure difference between the turbo molecular pump suction side 8 and the side where the gas bearings 3, 4 and the like are provided. Although it may become stable, in such a case, by turning downward in the gas injection direction from the gas injection nozzle 6b in the gas turbine 6, a rotational force is applied to the rotating body 1 and at the same time the self-weight of the rotating body 1 is applied. It can be stabilized by applying a downward thrust load in the same direction as.

Further, more positively, as shown in FIG. 4, a stepped portion 10 is provided on the drive shaft 1a of the rotating body 1, and gas is directed to the stepped portion 10 in a direction indicated by an arrow 11 (downward). By injecting, it is possible to further stably support the rotating pair 1.

〔The invention's effect〕

As described above, according to the present invention, the occurrence of vibration and the overload phenomenon of the gas bearing can be eliminated, and the bearing performance can be further improved. Consequently, the stable operation of the molecular pump can be obtained and the life of the molecular pump itself can be obtained. It is possible to exert various excellent effects such as further improving.

[Brief description of drawings]

FIG. 1 is an explanatory view of essential parts showing an embodiment of the present invention, FIG. 2 is a sectional view taken along line II-II of FIG. 1, and FIG. 3 is an explanatory view of essential parts showing another embodiment of the present invention. FIG. 4 is an explanatory view of a main part showing still another embodiment of the present invention, and FIG. 5 is an explanatory view of a main part of a conventional molecular pump. 1a ... Drive shaft, 3, 4 ... Radial gas bearing, 6 ...
Gas turbine, 6a ... Gas turbine blade section, 6b ...
Gas injection nozzle

Claims (1)

[Claims] 1. A drive shaft is arranged in a substantially vertical direction, a total of thrust loads acting on a rotating body including the drive shaft is set downward, and the downward thrust load is supported by a downward thrust load bearing at the lower end of the drive shaft. In the turbo molecular pump, a gas turbine blade portion having an outer diameter that is substantially the same as the outer diameter thereof is integrally disposed on the same drive shaft, and a pair of radial gas bearings is disposed on the casing so as to sandwich the blade portion, A turbo molecular pump characterized in that a member having a diameter larger than the outer diameter of the drive shaft is not attached to a position from the position corresponding to the radial gas bearing of the drive shaft to at least one shaft end and the coaxial end. .