JPH065076B2 - 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 mitigate 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 blade and the stator blade are gradually reduced toward the exhaust port side in at least a portion of the impeller group in the axial direction, and the radial gap between the rotor and the stator is gradually narrowed. At the same time, it is characterized in that a gradually increasing compression ratio portion is provided in which the thickness of the rotor blade is gradually increased toward the exhaust port side.

[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) formed by protruding rotor blades 2II radially having a predetermined inclination angle from the outer periphery of the base portion 2I.
a, 2b ... 2i) are externally fitted and press-fitted onto the drive shaft 1 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 2i and positioned and fixed, respectively.
a, 3b ... 3h are connected to the rotor blades 2II and 2II having stator blades 3II having an inclination angle opposite to that of the rotor blades 2II.
The rotor blades 2II and the stator blades 3II, which are arranged alternately between the two IIs, are arranged alternately to form a required impeller group.
When the rotor blades 2II and the drive shaft 1 rotate at high speed, such a group of impellers collides with gas molecules and gives an operation amount in the axial direction to the gas molecules. A flow is forcibly generated from the intake 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 this impeller group is such that the length of the rotor blades is formed to be constant over the axial direction, or the rotor blades are arranged between adjacent rotor blades at one location in the axial direction. It is customary to change the blade length stepwise. In addition, the thickness of the rotor blade is usually formed to be uniform in the axial direction. On the other hand, according to the present invention, as shown in FIGS. 1 and 2, each of the rotors 2 has a substantially lower half portion (2g to 2i in the illustrated example) located on the exhaust port B side. While the base portion 2I has a large diameter, the blade length 1 of the rotor blade 2II thereof is relatively short toward the exhaust port B (the rotor blade 2II is accordingly formed).
Of course, the blade length of the stator blades 3II arranged alternately is also gradually reduced, and the radial clearance between the rotor 2 and the stator 3 is also gradually narrowed). At the same time, as is clear from Fig. 1, this lower half (2g ~ 2g)
In i), the thickness t of the rotor blade 2II is gradually increased toward the exhaust port B side. Thus, the blade length 1 and the blade thickness t of the rotor blade 2II are sequentially changed toward the exhaust port B side, and the radial clearance between the rotor 2 and the stator 3 is gradually reduced. In addition, the turbo molecular pump is configured to be provided with a gradually increasing compression ratio portion. (Note that the rotors 2 positioned between the axial lengths L need to have their blade lengths shortened in sequence as described above, but for each single rotor 2, the blade lengths need to be changed in the axial direction. In this way, 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 in 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 in each portion of the exhaust gas. 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 and 3h) are interposed where the molecular density increases, 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.
Further, since the blade thickness t of each rotor 2 is successively increased toward the exhaust port B, the gas molecules passing through this impeller group increase the blade thickness t of the rotor 2. As a result, the returning distance becomes longer for each step of that portion, and it becomes more difficult for gas molecules to flow backward. Therefore, by the joint action of these, the backflow is effectively prevented in the compression ratio gradually increasing portion L, and the compression ratio of the exhaust gas is effectively 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.

As described above, the present invention has the forming means for gradually changing the rotor blade length 1 and the blade thickness t and gradually reducing the radial clearance between the rotor 2 and the stator 3 to gradually increase the compression ratio of the impeller group. Part L is provided, and the rotors (2a to 2f in the illustrated example) on the intake port A side are arranged with the same blade length and blade thickness, while on the exhaust port B side. A few
The rotor of the stage (2g to 2i in the illustrated example) is made to change abruptly from the one on the intake port A side, and its blade length 1 and blade thickness t are set to the exhaust port as shown in FIG. It is formed to have a gradually smaller size and a larger size toward the B side, and a compression ratio gradually increasing portion is provided at a portion having an axial length L thereof.

As described above, in the turbo molecular pump of the present invention listed in the examples,
Since the compression ratio gradually increasing portion provided inside 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 the cost can be reduced.

In the above 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 portion in the axial direction thereof. However, it is desirable to arrange the intake port A having a constant blade length and the like in order to have an exhaust velocity. Further, in the illustrated example, the thickness of the stator is shown to be constant, but the blade thickness of the stator may be increased according to the blade thickness of the rotor.

[Advantages of the Invention] As described above, according to the present invention, the blade length and blade thickness of the rotor and the radial clearance between the rotor and the stator in the impeller group are improved and compressed so as to partially compress them in the axial direction. Since the ratio increasing portion is provided, the compression ratio increasing effect is exerted on the pump body itself without adding a function for increasing the compression ratio, which makes it possible to obtain a turbo molecule having an excellent pumping speed even in a low vacuum region. The pump was able to provide.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a turbo molecular pump body (impeller group) showing an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are plan views showing the form of one rotor thereof. It is a side view. 1 ... Drive shaft 2, 2a-2k ... Rotor 3a-3k ... Stator 2II ... Rotor blade, 3II ... Stator blade A ... Intake port, B ... Exhaust port L. ..Compression ratio increasing section

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. The length of the blade and the stator blade is gradually reduced toward the exhaust port side to gradually narrow the radial gap between the rotor and the stator, and the thickness of the rotor blade is directed toward the exhaust port side. The turbo molecular pump is characterized in that a gradually increasing compression ratio increasing portion is provided.