JPS6125994A - Turbo-molecular pump and operating method thereof - Google Patents

Abstract

PURPOSE:To aim at the promotion of increment in a vane velocity ratio and a compression ratio of a pump, by cooling a part supporting a stator vane in a stator with liquid nitrogen so deeply, while lowering gas temperature in a gas molecule colliding with the stator vane. CONSTITUTION:At the time of operating a turbo-molecular pump, liquid nitrogen is housed in a vessel 27 via a liquid nitrogen port 26. With this liquid nitrogen, a spacer 24 supporting a stator vane 16 in a stator is cooled so deeply, and furthermore the stator vane 16 related to this spacer in terms of heat transmission is also cooled deeply, then a rotor 13 is rotated at high speed by rotation of a motor 19. Thus, the stator vane 16 is deeply cooled whereby gas temperature in a gas molecule colliding with the vane 16 is dropped to some extent, therefore a vane velocity ratio of the turbo-molecular pump is increased so that its compression ratio is also increased in consequence.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a turbomolecular pump and a method of operating the same.

(Prior Art) Turbomolecular pumps are explained in J.E.S.Z.A./: 1 79g/, and also in ``Vacuum Pump'' by Hiroshi Ishii (Vacuum Technology Course Volume 2, first edition dated 25th May 1999). (Published by Nikkan Kogyo Shimbun) and John F., O. I. Ron, Translated by Tamotsu Noda et al. [Vacuum Technology Manual] (first edition July 30, 1920, published by Sangyo Tosho Co., Ltd.). , seven types of momentum transport type 'Jc air pumps, which are molecular pumps consisting of a rotor and a stator with turbine-shaped blades, and are particularly effective for gas transport in the molecular flow region.

The general structure of one example will be described with reference to FIG. 7, in which a stator l/3 with a cylindrical inner surface 10 and a rotor/3 with a cylindrical outer surface 12 are arranged along the same vertical axis A as the stator. It can be accommodated more easily. In the pump space 1lIO with an annular cross section between the inner surface IO of the stator // and the outer surface 11 of the rotor 13, a number of four vanes protrude radially outward from the rotor outer surface 11, and the stator inner surface IO Many stator vanes radially inward from /
6 stands out. The p-evening blades 15 are arranged in several stages (/- stages in the illustrated example) that are successively spaced apart in the axial direction, and each stage of the rotor blades is arranged in many stages that are successively spaced apart at equal intervals in the circumferential direction. It consists of the rotor blade / j'. The stator blades 16 are arranged every other stage of the rotor blades 15 in the axial direction as several stages (72 stages in the illustrated example) that are sequentially spaced apart, and each stage of the stator blades is also arranged equally in the circumferential direction. It consists of a number of stator vanes 16 successively spaced apart.

The stator// has an intake port 17 communicating with the upper part of the pump space L, and an exhaust port 1 communicating with the lower part of the pump space L.
g is attached. The rotor 13 is connected to a motor 19 and rotates at high speed around an axis due to the drive of the motor 19.

In FIG. 1, a portion of the arrangement of the rotor blades 15 and stator blades 16 in the pump space Ida is shown in an exploded view. In FIG. 1, arrow B points from the intake port 17 to the exhaust port i.
The arrow C indicates the direction in which the rotor blades 15 travel as the rotor/3 rotates.

This figure shows one of several rotor vane stages, one of several stator vane stages, and five of the many vanes included in each vane stage. Each blade /S, /b is a flat single plate and is oriented so as to be inclined with respect to the gas transport direction B and the rotor blade traveling direction C. To be more specific, the rotor blades are
, the edge 20 in the opposite direction to the gas transport direction B, that is, the edge 20 on the side opposite the intake port, is in the rotor blade traveling direction C,
The edge in the gas transport direction B, that is, the edge on the side of the exhaust port /g is also oriented in advance, and the stator blade /6
is green in the gas transport direction B, that is, here on the side of the exhaust lower g, is in the gas transport direction B with respect to the rotor blade traveling direction C.
It is oriented so as to precede the edge 3 in the opposite direction, that is, the edge 3 on the side of the intake port 17.

A feather like this! ; , /6, when the rotor 13 is rotated, for example, by 0.000 rotations per minute, the surface of the rotor blade /S and the stator blade 16, especially in the molecular flow region. During the collision, colliding gas molecules mainly move from the intake port side to the exhaust port side.
It receives a momentum toward g, and as a result, the gas is compressed and transported in the direction indicated by B.

(Problems to be Solved by the Invention) Conventionally, the above-mentioned turbo-molecular pumps have had extremely low compression ratios (i.e., exhaust side pressure/intake side pressure), especially for light gases with small molecular weights such as hydrogen. , has the disadvantage that if the gas to be transported contains light gases, the lowest pressure that can be reached on the suction side of the turbomolecular pump is dominated by the small compression ratio of the light gases and cannot be low enough. In order to eliminate this drawback, it is conceivable to increase the rotational speed of the rotor to increase the advancing speed of the rotor blades, thereby increasing the compression ratio, but as mentioned above, the rotational speed of the rotor is already quite high. So,
It is actually technically difficult to increase this to a certain degree due to constraints such as the strength of the rotor, the strength of the bearing, the torque of the motor, and control of the motor.

(Means to Solve the Problem) In order to solve the above-mentioned conventional drawbacks, this invention provides the following method: ``When the molecular weight of a gas molecule is m1, Boltzmann's constant is 1, and the absolute temperature of the gas is T, Most probable velocity of the molecule Vg
is given by 107- of Vg-, and in a turbo-molecular pump, when the advancing speed of the rotor blade is Vg, the blade speed ratio S is defined as 8-Vb /Vg -Vb /n7, and the compression ratio There is a well-known relationship between the following: for the normally adopted rotor speed and normal gas: exp(as), a is a positive constant, and as S increases, K also increases. is used. According to this relationship, it can be seen that the compression ratio K increases even if the absolute temperature T of the gas is lowered instead of increasing the rotational speed of the rotor to increase the advancing speed vb of the rotor blades.

One possible means of lowering the absolute temperature T of the gas is to cool the stator blades or rotor blades with which the gas molecules collide.Although it is generally preferable to cool both of these blades, in practice, it is preferable to cool the rotor blades. If this is done, there is a risk that frost will adhere to the rotor and its dynamic balance will be lost. Therefore, cooling the stator blades is adopted in this invention.

In practice, cooling of the stator blades can be achieved by cooling the part of the stator that supports the stator blades, and as a cooling medium, in view of the simple structure and ease of operation of the device, In addition, from the viewpoint of cooling to a sufficiently low temperature, it is appropriate to use liquid berea or a cryogenic liquid with a boiling point lower than this.A suitable gas-cooled refrigerator can also be used.

Thus, according to the present invention, in order to eliminate the conventional drawbacks as described above, firstly, ``when operating the turbo-molecular pump, the stator vanes of the stator of the turbo-molecular pump are supported. ``A method of operating a turbomolecular pump, characterized in that the stator of a turbomolecular pump is cooled to a temperature substantially at or below the boiling point of a liquid,'' which firstly comprises: In the part that supports the stator blades,
A "turbo-molecular pump characterized in that it is equipped with a jacket of liquid nitrogen or a cryogenic liquid with a lower boiling point than liquid nitrogen" is provided.

(Function) According to the turbo-molecular pump operating method and turbo-molecular pump according to the present invention as described above, the portion of the stator that supports the stator blades is heated by liquid nitrogen or a cryogenic liquid with a lower boiling point than this. , at least the boiling point of liquid nitrogen is 77! 9 substantially cooled to a low cryogenic state;
Therefore, the stator blades supported in this area are also deeply cooled to the same extent. Therefore, the gas transported by the turbomolecular pump is cooled when its molecules impinge on the stator blades, reducing its absolute temperature, which reduces the most probable velocity Vg of the gas molecules and increases the blade speed ratio. As B increases, so does the compression ratio. Thus, the minimum pressure that can be reached on the suction side of the turbomolecular pump is lower.

Embodiments Embodiments of turbomolecular pumps according to the invention have the same general structure as that described above with respect to FIG. 1 and FIG. According to the present invention, an external thread is formed on the outer surface 2S of a portion of the stator/l that is attached to the bracket supporting the stator blade/6 in a good heat transfer relationship, such as a spacer cog. An internal thread is formed on the inner surface -g of the annular liquid wall culverter-7 having a liquid nitrogen inlet/outlet row B, and the container;! 7 is attached to the spacer 2 da in a good heat transfer relationship by the threaded engagement between the outer thread and the inner thread.

The liquid nitrogen container 27 described above constitutes a liquid nitrogen jacket.

When operating the above-mentioned turbo molecular pump, liquid nitrogen is stored in the container via the liquid nitrogen inlet/output row 6, and the liquid nitrogen deep-cools the subesakoq, and a heat transfer relationship is established between the liquid nitrogen and the liquid nitrogen. Deeply cool the stator blade/6 located in
The rotor 13 is rotated at high speed by the operation of the motor now. In this way, the gas is transported from the intake port/7 toward the exhaust lower g while being compressed. At that time, stator blade 1
6 is cooled, a high compression ratio can be obtained.

In such a turbomolecular pump, instead of liquid nitrogen,
It is clear that the same effect can be obtained even if liquid helium is used as an example of a cryogenic liquid with a low boiling point. Furthermore, if the surface of the stator is made rough, the cooling effect of the gas will be even better.

(Effects of the Invention) According to the turbomolecular pump and its operating method according to the present invention, the stator blades are deep cooled by liquid nitrogen or a cryogenic liquid with a lower freezing point via the stator portion that supports the stator blades. As a result, the gas temperature of the gas molecules that collide with the stator blades decreases. The aforementioned blade speed ratio B of the turbo-molecular pump increases due to the decrease in body temperature, and the compression ratio also increases accordingly.

Thus, according to the invention, higher compression ratios than ever before are achieved in turbomolecular pumps, and this also holds true for light gases such as hydrogen. Therefore, even for gases containing light gases, the minimum pressure that can be reached on the intake side of the turbomolecular pump can be lower than before.

According to experimental findings, the diameter θ,/rn.

- One stage stator blade, 72 stages stator blade, rotation speed 5 per minute
In a turbo-molecular pump that operates θ, 000 times, when the stator blade supporting portion is placed in a jacket (container) arranged as shown in Fig. 1 to contain liquid nitrogen and transport hydrogen gas, the compression ratio is: Compared to about lθ3 in the conventional case without cooling with liquid nitrogen, it increased by about qs to 105 times in the molecular flow region.

At this time, the pumping speed of the turbo molecular pump is approximately /4-
/, g times larger than the conventional one.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view of an embodiment of a turbomolecular pump according to the present invention, and FIG. 1 is a diagram showing the arrangement of rotor blades and stator blades in a pump space in the turbomolecular pump of FIG. In the figure, ll is the stator, /3 is the rotor, 15 is the rotor blade, 16 is the stator blade, /7 is the intake port, 7g is the exhaust port, -da is the part that supports the stator blade, and 2t is the cryogenic liquid jacket. shows.

Claims (1)

[Claims] 1. When operating the turbo-molecular pump, the portion of the stator of the turbo-molecular pump that supports the stator blades is cooled to a temperature substantially equal to or lower than the boiling point of liquid nitrogen. A method of operating a turbomolecular pump characterized by: 2. A turbo-molecular pump characterized in that a jacket of liquid nitrogen or a cryogenic liquid with a boiling point lower than this is provided in a portion of the stator of the turbo-molecular pump that supports the stator blades.