JPH065077B2 - Turbo molecular pump - Google Patents

Description

TECHNICAL FIELD The present invention relates to a turbo molecular pump capable of exhibiting excellent pumping speed performance even in a low vacuum region.

[Prior Art] As is well known, a turbo molecular pump mechanically blows out gas molecules to obtain an ultra-high vacuum. For this reason, the pump body is rotated at high speed. It is provided with an impeller group in which rotor blades (moving blades) having an inclination and stator blades (static blades) having an inclination opposite thereto are normally arranged in multiple stages.

However, in this type of pump, since the compression ratio in the impeller group is low, there is a disadvantage that the exhaust performance is significantly reduced in the low vacuum region as an operating characteristic. Therefore, in order to compensate for this drawback, a structure in which rotor blades and stator blades are provided in multiple stages in the axial direction of the impeller group is also adopted, but in this case, the weight becomes large and high-speed rotation becomes difficult, It is disadvantageous in terms of cost. Specifically, in the conventional turbo molecular pump, the exhaust rate rapidly deteriorates from a vacuum degree of about 10 ⁻³ to 10 ⁻² Torr, and the exhaust rate becomes almost nothing at about 0.1 Torr. For this reason, when the turbo molecular pump is operated in a low vacuum region, an appropriate auxiliary vacuum pump such as (turbo molecular pump) + (mechanical booster pump) + (rotary pump) is connected to cover its exhaust capacity. It is common to use an exhaust system.

[Problems to be Solved by the Invention] The present invention has been made on the basis of the technical background as described above, and has a large compression ratio increasing function by itself by improving and devising the configuration of the impeller group. It is an object of the present invention to provide a turbo molecular pump in which the pumpable region of the pump is expanded to a lower vacuum side.

[Means for Solving the Problems] In order to achieve such an object, the present invention rotates the rotor blades of a turbine wheel group in which rotor blades and stator blades are alternately arranged at high speed and exhausts them. In the turbo molecular pump,
The lengths of the rotor blades and the stator blades are sequentially made shorter toward the exhaust port side in at least part of the impeller group in the axial direction, and the radial gap between the rotor and the stator is gradually narrowed. It is characterized in that a compression ratio gradually increasing portion is provided.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 show a structural example of the main part of the turbo-molecular pump according to the present invention. That is, the drive shaft 1 located at the center of the drive shaft and driven to rotate by a prime mover (not shown)
As shown in the figure, a rotor 2 (2 having a rotor blade 2II radially protruding from the outer periphery of a base portion 2I and having a predetermined inclination angle is provided.
a, 2b ... 2k) are externally fitted and press-fitted onto the drive shaft 1 so as to be sequentially fixed, and the rotors 2a, 2b ...
A stator 3 in which a base end portion 3I is sandwiched between annular spacers 4 and 4 from the outer circumference surrounding 2k and positioned and fixed.
a, 3b ... are arranged such that their stator blades 3II having an inclination angle opposite to that of the rotor blades 2II are located between the rotor blades 2II and 2II, and these rotor blades 2 are arranged alternately.
II and the stator blade 3II constitute a required impeller group. When the rotor blades 2II and the drive shaft 1 rotate at high speed, the impeller group collides with gas molecules to give momentum in the axial direction to the gas molecules, and the intake air at one end of the rotor blades 2II cooperates with the stator blades 3II. A force is generated from the port A toward the exhaust port B at the other end, and the flow is exhausted.

Now, in the conventional turbo molecular pump, the configuration of the impeller group is such that the length of the rotor blade is formed to be constant over the axial direction, or the blades of the rotor blades adjacent to each other at one point in the axial direction are provided. It is customary to change the length stepwise. On the other hand, according to the present invention, FIG.
As shown in FIG. 2, the base portion 2 of each rotor 2 is located in the lower half portion (2g to 2k in the illustrated example) located on the exhaust port B side.
The blade length 1 of the rotor blade 2II is formed to be relatively shorter toward the exhaust port B while I has a large diameter (the rotor blade 2II and the stator arranged alternately). The blade length of the blade 3II is, of course, gradually reduced), and the radial gap is gradually narrowed to a portion of the axial length L of the impeller group where the blade lengths of the rotor blade 2II and the stator blade 3II change. The compression ratio gradually increasing portion is provided. In this case, the rotors 2 located between the axial lengths L need to have their blade lengths shortened one after another.
Then, it is not always necessary to change the blade length in the axial direction.

In this manner, the blade length 1 of each rotor 2 is gradually reduced toward the exhaust port B side, and the stator blade 3II is accordingly formed.
The length of the flow path for guiding gas molecules can be increased as long as the radial gap between the rotor 2 and the stator 3 is gradually narrowed toward the exhaust port B side. Since the area is gradually narrowed at the compression ratio gradually increasing portion L, the exhaust gas sent through the rotor blades 2II and the stator blades 3II alternately has a higher molecular density at each rotor stage. Therefore, the biasing effect of the rotor blades 2II is increased, and the backflow of gas molecules is prevented. Also,
Since the stator blades 3II (corresponding to the stators 3g to 3k) are interposed where the molecular density is increased, the gas flow is made turbulent. Therefore, the number of collisions of gas molecules also increases, and in this respect also, it is effective in preventing backflow. As a result, the backflow of gas molecules to the intake port A side is effectively prevented, and the compression ratio toward the exhaust port B is increased. That is, since the compression ratio of the exhaust gas is increased, the exhaust gas can be exhausted even in the low vacuum region.

According to the turbo molecular pump of the present invention as in the above embodiment,
Since the compression ratio gradually increasing portion provided in a part of the impeller group effectively increases the compression ratio of exhaust gas, the exhaust speed curve can be extended to the low vacuum side with a high value.
That is, it is possible to exhaust to a lower vacuum region. Specifically, in the case of the illustrated example, a vacuum degree of about 10 ⁻³ to 10 ⁻² Torr can secure an exhaust speed similar to a vacuum degree of 10 ⁻³ Torr or less, and even at about 0.1 Torr, a certain degree It can sustain an effective pumping speed. Therefore, when this pump is used, it is not necessary to connect auxiliary pumps in multiple stages for vacuum assistance as in the conventional case, and a simple exhaust system such as (Tarbon molecular pump) + (rotary pump) is used. However, it can be used satisfactorily, and from this point, the exhaust system can be simplified and cost can be reduced.

In the embodiment, the case where the compression ratio gradually increasing portion L is provided at the end portion on the exhaust port B side has been described, but this gradually increasing portion L may be provided at least at a part of the impeller group in the axial direction thereof.
However, it is desirable to arrange the intake port A with a constant blade length in order to have an exhaust velocity.

[Advantages of the Invention] As described above, according to the present invention, the lengths of the rotor blades and the stator blades in the impeller group and the radial gap between the rotor and the stator are improved and devised so that gas is partially present in the axial direction. Since the compression ratio gradually increasing portion is provided to effectively prevent backflow of the pump, the compression ratio increasing effect is exerted on the pump body itself without adding a separate compression ratio increasing function.
As a result, a turbo molecular pump having an excellent pumping speed even in a low vacuum region can be provided.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a turbo molecular pump main body (impeller group) showing an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are plan views showing the form of a single rotor thereof. It is a side view. DESCRIPTION OF SYMBOLS 1 ... Drive shaft 2, 2a-2k ... Rotor 3a-3k ... Stator 2II ... Rotor blade 3II ... Stator blade 4 ... Spacer L ... Compression ratio gradually increasing part

Claims (1)

[Claims] 1. A turbo molecular pump for rotating at high speed the rotor blades of an impeller group comprising rotor blades and stator blades arranged alternately, and exhausting the rotor blades, at least in a part of the impeller group in the axial direction. A turbo molecule characterized in that the length of the blade and the stator blade are gradually reduced toward the exhaust port side, and a compression ratio gradually increasing portion is provided to gradually narrow the radial gap between the rotor and the stator. pump.