JPH0353037Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a turbomolecular pump used to obtain an ultra-high vacuum.

[Prior Art] A turbo molecular pump houses a rotor in which a rotor wheel is provided in multiple stages on its outer periphery in a casing, and a stator in which a stator wheel is interposed between each of the rotor wheels on the inner periphery of the casing. is provided, and the high-speed rotation of the rotor mechanically exhausts gas molecules from the intake port provided at one end of the casing to the exhaust port provided at the other end, thereby achieving an ultra-high vacuum.

Looking at the internal structure of turbomolecular pumps, conventional products, for example,
As shown in the publication, the radial length of the blade portions of the rotor wheel and stator wheel that have an exhaust function, that is, the blade length, is approximately constant from the intake port side to the exhaust port side. be.

In addition, as for other formats, for example,
As shown in Japanese Patent No. 57-30998, there is also a structure in which the blade lengths of the rotor wheel and stator wheel are gradually shortened from the intake port to the exhaust port.

In addition, in both the former case in which rotor-stator wheels with the same blade length are arranged in multiple stages, and the latter case in which the blade length is gradually shortened, the casing is placed on the intake port side. It has a cylindrical shape whose diameter does not change from the end to the exhaust port side.

[Problems to be solved by the invention] However, in this structure in which rotor-stator wheels with the same blade length are arranged in multiple stages, the blade length of the exhaust-side wheel is unnecessarily long. This is disadvantageous in ensuring the rigidity of the impeller.

In other words, if we focus on the exhaust characteristics inside the turbomolecular pump, the pressure gradient inside the turbomolecular pump has a difference of about 10 ⁸ between the intake port and the exhaust port, so the flow path on the exhaust port side is It may be narrower than the side channel. Therefore, as in the conventional product described above, the outer diameter of the rotor impeller on the exhaust port side is reduced, and the outer diameter of the substantial blade portion of the stator impeller that has the exhaust function is reduced, so that the molecules There are some devices in which the opening area of the annular space through which the air filter passes while being biased is smaller on the exhaust port side than on the intake port side. However, with conventional blades, the radial length of each blade portion is constant, so the rotor wheel and stator wheel on the exhaust port side, which require relatively high density molecules to be energized, have high strength. It becomes necessary to make it something like that. In other words, in this type of pump, the blade torsion angle of the impeller generally decreases gradually from the intake port side to the exhaust port side, and the thickness of the impeller is Become thin. Nevertheless, the reaction force in the thickness direction of the impeller from the molecular flow is greater for the impeller on the exhaust port side, which is located in a region with high molecular density. Therefore, the impeller on the exhaust port side tends to be weaker than the impeller on the intake port side, and there is a problem in that reinforcement measures for that portion tend to make the entire pump bulky. On the other hand, the latter has a straight casing and the blade length is gradually shortened.
Since the outer diameter of the rotor does not change, the flow path near the outer circumference of the rotor forms a cylinder along the inner circumference of the casing. Therefore, there is a problem that molecules of the gas to be exhausted tend to flow back, making it difficult to increase the compression ratio.

The present invention was developed in light of these circumstances, and the purpose is to provide a turbomolecular pump that can be reasonably reduced in weight without reducing exhaust performance or strength performance. do.

[Means for Solving the Problems] In order to achieve the above object, the present invention reduces the outer diameter of the rotor while gradually shortening the blade length of the rotor impeller from the intake port to the exhaust port. Additionally, the outer diameter of the stator is reduced while the blade length of the stator wheel is gradually shortened, and the diameter of the exhaust port side of the casing is smaller than that of the intake port side. Note that the blade length here refers to the radial length of the blade portion of the impeller that can substantially contribute to the energization of molecules, and includes the blade attachment portion held between spacers and the reinforcement portion. Therefore, it goes without saying that it does not include a plate-shaped portion or the like that connects the tips of the wings.

[Function] With this configuration, the blade length of the impeller on the exhaust port side is smaller than the blade length of the impeller on the intake port side, so the annular space formed between the rotor and the stator is The opening area can be easily reduced on the exhaust port side to match its compression characteristics. Furthermore, it is easier to increase the rigidity of a wheel with a short blade length than with a wheel with a long blade length. Therefore, for the impeller on the exhaust port side, which has traditionally had a tendency to be disadvantageous in terms of strength, it is necessary to increase the thickness of the member,
There is no need to take special reinforcement measures such as making the spacer more robust. In addition, as mentioned above, the blade length of the rotor impeller is gradually shortened and the outer diameter of the rotor is reduced, and the blade length of the stator impeller is gradually shortened and the stator outer diameter is reduced, and the casing is By making the exhaust port side smaller in diameter than the intake port side, the flow path toward the exhaust port becomes smaller in diameter in stages.
Therefore, it is possible to more effectively suppress the backflow of gas molecules than in the case where there is a straight flow path from the intake port to the exhaust port. Therefore, compression performance can be improved effectively and without difficulty. Furthermore, if the diameter of the casing is reduced on the exhaust port side as the diameter of the impeller is reduced, there will be more space around the outer periphery of the casing on the exhaust port side than when using a cylindrical casing with an unchanged diameter. It becomes possible to secure the following.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

The drawing is a half-cutaway view of the turbomolecular pump according to the present invention, in which 1 is a base plate, 2 is a motor erected on this base plate 1, and 3 is a rotor supported by a rotating shaft 2a of this motor 2. , 4
5 is a casing surrounding the rotor 3, and 5 is a stator provided on the inner periphery of the casing 4. An exhaust port 6 is provided in the base plate 1, and an intake port 7 is opened at the upper end of the casing 4, and the turbo molecular pump is installed on the outer periphery of the upper end of the casing 4, such as in an evacuated chamber (not shown). A mounting flange 8 for connection to is provided protrudingly.

In the illustrated turbomolecular pump, the outer diameters of the rotor 3 and stator 5 are gradually reduced from the intake port 7 toward the exhaust port 6.
More specifically, the rotor 3 has a large diameter portion 9a, a medium diameter portion 9b, and a small diameter portion 9c sequentially formed on the outer periphery of a cylindrical rotor body 9 fixed to the tip of the rotating shaft 2a. Large-diameter rotor wheels 11 are fitted in multiple stages to the diameter portion 9a, and intermediate-sized rotor wheels 12 are fitted to the medium-diameter portion 9b in multiple stages to form the small-diameter portion 9c.
It is constructed by fitting small diameter rotor impellers 13 in multiple stages. And rotor impellers 11, 12, 1
3, as clearly shown in the drawings, the blade length, that is, the radial dimension of the blade portion having the exhaust function, is shorter as the blade is closer to the exhaust port 6.

In addition, in the case of the illustrated example, the stator 5 has a large-diameter stator wheel 1 disposed between each rotor wheel 11 by a large-diameter spacer 14 stacked in multiple stages.
At the same time, a medium diameter stator wheel 17 disposed between each of the rotor wheels 12 is held by a medium diameter spacer 16 stacked in multiple stages, and a small diameter spacer 18 stacked in multiple stages holds The stator wheel 19 has a small diameter stator wheel 19 disposed between each rotor wheel 13. and,
Regarding these stator wheels 15, 17, and 19, the blade length, that is, the radial length of the blade portion having an exhaust function is made shorter as the stator wheels are closer to the exhaust port 6. Further, as shown in the drawings, the casing 4 also has its exhaust port 6 side facing the intake port 7 side in response to the reduction in diameter of the rotor impellers 11, 12, 13 and the stator impellers 15, 17, 19. The diameter is smaller than that.

With such a configuration, the gas molecules on the intake port 7 side are urged toward the exhaust port 6 side by operating the motor 2 and rotating the rotor 3 at high speed, as in the conventional one, and Bring the intake port 7 side to an ultra-high vacuum state. At this time, the blade length, which is the radial length of the blade portion having an exhaust function in the rotor wheels 11, 12, 13 and the stator wheels 15, 17, 19, is changed in stages from the exhaust port 6 to the intake port 7. Therefore, the opening area of the annular space formed between the rotor 3 and the stator 5 can be easily reduced on the exhaust port 6 side to match its compression characteristics. That is, when the opening area of the intake port 7 is set to a specified value, the outer diameter and blade length of the rotor 3 and stator 5 are changed in accordance with the pressure gradient, and the diameter of the rotor 3 is further reduced. As long as the rotational speed of the rotor 3 is increased to an extent that can compensate for the accompanying decrease in circumferential speed, the same pump performance as that of the conventional pump can be achieved. Moreover, the blade wheel 1 has a short radial length of the blade portion.
It is easier to increase the rigidity of the blades 3 and 19 compared to the blade wheels 11 and 15 having a long blade length. Therefore, it is necessary to take special reinforcement measures for the impellers 13 and 19 on the exhaust port 6 side, which conventionally tended to be disadvantageous in terms of strength, such as increasing the thickness of the members and making the spacer more robust. disappears.

Therefore, the entire weight of the pump can be reduced without deteriorating the pumping performance or strength performance.

Furthermore, if the length of the blade portion, which requires complicated machining, can be shortened, the number of man-hours required for the machining can be reduced accordingly. Since the blade length is changed stepwise rather than continuously, it is also possible to prevent the number of types of blade wheels from increasing. Therefore, it is possible to reduce costs by simplifying manufacturing.

In addition, the blade length of the rotor wheels 11, 12, and 13 is gradually shortened to reduce the rotor outer diameter, and the blade length of the stator wheels 15, 17, and 19 is gradually shortened to reduce the stator outer diameter. Since the diameter of the exhaust port 6 side of the casing 4 is made smaller than that of the intake port 7 side, the diameter of the flow path from the intake port 7 to the exhaust port 6 is gradually reduced. Therefore, it is possible to more effectively suppress the backflow of gas molecules than in the case where there is a straight flow path from the intake port 7 to the exhaust port 6. Therefore, it is possible to achieve the effect that a high compression ratio can be achieved without difficulty. Furthermore, the impellers 11, 12, 13, 15, 1
Along with the gradual reduction in diameter of 7 and 19, the casing 4
If the diameter is also reduced on the exhaust port 6 side, compared to using a cylindrical casing whose diameter does not change,
It becomes possible to secure a wider space around the outer periphery of the casing 4 on the exhaust port 6 side. Therefore, less installation space is required, and the arrangement of piping and peripheral equipment becomes easier.

[Effects of the invention] Since the present invention has the above-described configuration, it is possible to reasonably reduce the weight of the pump without any deterioration in the pump's pumping performance or strength performance. It is possible to provide a turbo-molecular pump that can also reduce costs by reducing the number of man-hours. Moreover, in this invention, the impeller and casing are made smaller in diameter from the intake port side to the exhaust port side, which effectively suppresses the backflow of gas molecules compared to conventional ones that have a straight flow path. This makes it possible to exhibit high compression performance. Further, by reducing the diameter of the casing on the exhaust port side, the installation space can be reduced, and the arrangement of piping and peripheral equipment can be easily achieved.

[Brief explanation of the drawing]

The drawing is a half-cutaway view showing an embodiment of the present invention. 3...Rotor, 4...Casing, 5...Stator, 6...Exhaust port, 7...Intake port, 11,1
2, 13... rotor wheel, 15, 17, 19...
stator wheel.

Claims (1)

[Scope of utility model registration request] From the intake port to the exhaust port, the blade length of the rotor impeller is gradually shortened and the outer diameter of the rotor is reduced, and the blade length of the stator impeller is gradually shortened and the outer diameter of the stator is reduced. , a turbo molecular pump characterized in that the exhaust port side of the casing has a smaller diameter than the intake port side.