JPH04224295A - Turbo-molecular pump - Google Patents

Abstract

PURPOSE: To obtain a turbomolecular pump having a high compression ratio and not having an auxiliary pump which can exhaust into the atmosphere. CONSTITUTION: A tangential flow pump stage 10 is arranged in an exhaust side in addition to plural axial flow pump stages consisting of alternately arranged rotor 12 and stator 13 in order to raise a compression ratio. Each tangential flow pump stage is composed of a common surface ring shape stator separating and surrounding a plane disc rotor. A force-fed gas is moved in the tangential flow direction in the ring shape free passage 14. The free passage is intercepted by a baffle 15 and communicated with an intake port 17 and exhaust port 18. Thereby, the exhaust pressure is raised upto the atmospheric pressure and also exhausted directly to the atmosphere.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turbomolecular pump, and more particularly to a turbomolecular pump with an increased compression ratio so as to extend its operating range to higher pressures.

0002

BACKGROUND OF THE INVENTION Conventional turbomolecular pumps are generally 10-
They have an operating range of 7 to 10 Pa (or 1) Pa, i.e. these pumps cannot pump directly to the atmosphere. Conventional turbomolecular pumps therefore need to be coupled with an auxiliary pump that generates the necessary auxiliary vacuum and discharges the pumped gas at atmospheric pressure. however,
The lubricating oil of the auxiliary pump causes fouling of the turbomolecular pump, which impedes pumping action in the low operating range. This can be avoided by short-term maintenance, but this adds to the high initial cost of the vacuum equipment and further increases the operating costs. Moreover, coupling the turbomolecular pump to the auxiliary pump is complicated and inconvenient in most applications.

In order to reduce the need for the above-mentioned auxiliary pumps, so-called hybrid turbomolecular pumps have been developed. U.S. Patent Publications No. 4732529, No. 482639
No. 3 and No. 4797068 disclose turbomolecular pumps with a compression ratio increase section. This compression ratio increasing section is
It consists of a helically grooved rotor (or threaded rotor) that guides the gas from the high vacuum to a simple evacuation device (e.g. a thin plate pump). Although this type of composite turbomolecular pump does not require a complicated evacuation system consisting of a plurality of auxiliary vacuum pumps, it still requires an auxiliary pump because the gas cannot be evacuated at atmospheric pressure.

New types of rough pumps have been developed that can reach low ultimate pressures (3×10 −2 Pa). As described in "Vacuum Science and Technology (J. Vac. Sci. Technol.)" Vol. A turbo vacuum rough pump with a circumferential pump stage on the exhaust side, the radial pump stage consisting of an impeller rotating in a grooved passage that guides the pumped air flow radially, and the circumferential pump stage in which the pump is at atmospheric pressure. Increase the pressure so that it can be evacuated. However, this pump is just a rough pump that cannot replace a turbomolecular pump. The ultimate pressure (10-7 Pa) of the turbo molecular pump is several steps lower than the ultimate pressure (10-2 Pa) of the rough pump.

[0005]

SUMMARY OF THE INVENTION A first object of the present invention is to provide a turbomolecular pump with a high compression ratio. A second object of the present invention is to provide a turbomolecular pump capable of exhausting at atmospheric pressure without connecting an auxiliary pump. A third object of the invention is to provide a turbomolecular pump that is relatively easy to handle compared to conventional vacuum systems with similar operating ranges.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a turbo-molecular pump according to the present invention is constructed by alternately arranging rotors and stators each having a group of blades inclined in opposite directions. , a turbomolecular pump equipped with a plurality of axial pump stages on the suction side for pumping gas in the axial flow direction, the rotor and the coplanar rotor forming an annular free passage between them along a part of their periphery. a pump stage comprising a stator, the annular free passageway communicating with an inlet and an outlet, the pump stage having at least one tangential flow for pumping gas from the inlet to the outlet in a tangential flow direction relative to the rotor; It is characterized in that a pump stage is coupled to the axial pump stage on the exhaust side. According to another feature of the invention, a tangential flow pumping stage can be added, the rotor consisting of a disc with a plurality of vanes, in order to increase the pumping effect in the viscous flow range.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the turbomolecular pump according to the present invention has rotors 1 to 1a and a stator 2, respectively housed in a cylindrical pump body 3, as is conventionally known.
A predetermined number of axial flow pump stages consisting of 2a to 2a are provided. A pump stage consisting of rotor 1a and stator 2a is further illustrated in FIG. Each rotor has a rotation axis 6 (hereinafter referred to as axis 6)
It consists of a disk 5 mounted on the periphery of the disk 5, which carries on its periphery radially projecting inclined vanes 7, 7a, 7b. Each stator consists of a similar disc with a central hole for receiving the shaft 6 of the rotor. Each stator is fixed to the pump body 3 and consists of a disk 8 provided with vanes 9, 9a, 9b. These blades 9, 9a, 9b are rotor blades 7, 7.
It inclines in the opposite direction to the inclination directions of a and 7b.

The gas entering from the intake side (indicated by arrow A) is
The above-mentioned axial flow pump stage pumps the fluid in a direction parallel to the axis of the cylindrical pump body 3. That is, an axial flow of gas occurs through the alternately arranged rotors and stators, as indicated by arrow B in FIG. According to the invention, one or more pump stages according to a different concept are attached downstream of the axial pump stage. Two such pump stages are shown in FIG. 1 with the general reference numerals 10 and 30. Each pump stage 10
and 30 are the rotor and pump body 3 attached to the shaft 6.
and a stator fixed to the. The structural details of these pump stages are shown in FIGS. 2-4.

As shown in FIGS. 1-3, pump stage 10
has a rotor 12 consisting of a flat disk fixed to a shaft 6. The rotor 12 is surrounded by an annular stator 13 which is substantially coplanar and spaced from the rotor 12, thereby providing an annular free passage 14 between the rotor and the stator.
is formed. The baffle 15 blocks the passage 14 between the intake port 17 and the exhaust port 18 provided in the upper closing plate 21 and the lower closing plate 23, respectively. The closing plates 21 and 23 are interconnected by suitable means, such as by connecting the downwardly directed edges 22 of the closing plates 21, to form a closed casing housing the pump stage. In order to pass the shaft 6, the closing plate 2
A center hole is provided in both 1 and 23. Baffle 15 may be a radial projection of stator 13, as shown in FIGS. 2 and 3, or may be a separate member rigidly fixed to stator 13.

The operation of the above pump stage will now be explained. The gas pumped by the axial pump stage enters the inlet 17 (indicated by arrow D in FIGS. 1 and 2) and passes through the passage 14.
enter. Here, the gas molecules impinge on the rotating disk of rotor 12 and maintain the tangential component velocity of rotor 12 (indicated by arrow E). This process causes gas molecules to be transported in a tangential flow in the free passageway 14 from the inlet 17 to the outlet 18 and out of the passageway 14 through the outlet 18 (indicated by arrow F). The gas flow that occurs within the free passage 14 will be described as a "tangential flow" because it is parallel to the tangential velocity direction of the rotor.

The tangential flow pump stage 10 described above is effective in the pressure range of molecular or transient flows and maintains an outlet pressure of about 1 P, which is the typical outlet pressure of conventional turbomolecular pumps.
can be increased from a to 103 Pa or more. In the higher pressure range, ie in the range of viscous flow, this tangential flow pump stage with flat disk rotor is no longer effective. A different type of rotor, as detailed in FIG. 4, can then increase the outlet pressure even further to atmospheric pressure.

Referring again to FIG. 1, a second tangential flow pump stage effective in the viscous flow range is indicated at 30. Pump stage 30 is arranged downstream of pump stage 10 in series. Pump stage 30, like pump stage 10, comprises a closed casing consisting of an upper plate 31 with a downwardly directed edge 32 connected to a lower plate 33. The shaft 6 extends axially within this casing and carries a disc rotor 35 with blades 37, 37a, 37b on its periphery. Feathers 37, 37a
, 37b are located on a plane perpendicular to the plane of the rotor 35. An annular stator 36 coplanar with the rotor is spaced apart from and surrounding the rotor 35, thereby forming an annular free passage 38 between the circumference of the rotor blades and the stator. The baffle 39 is an air intake port 40 provided on the upper plate 31.
and the exhaust port 41 provided in the lower plate 33, the free passage 38
cut off.

As shown in FIG.
0 (indicated by arrow G) and enters the free passage 38 between the rotor and stator. Here, the gas molecules acquire kinetic energy by colliding with the rotor, a circulation having a tangential velocity component is generated in the free passage 38, and the gas is pumped from the intake port 40 to the exhaust port 41. In this final stage, the pressure rises to approximately 105 Pa, so that the pump can be vented directly to the atmosphere through the exhaust port 43 of the pump body 3.

[0014] The peripheral speed of the rotor in the above-mentioned turbomolecular pump having both an axial flow pump stage and a tangential flow pump stage is usually 250 m/s or more, preferably 35 m/s or more.
It is 0 to 400 m/s. For example, the diameter is 100mm (
In a small pump with a rotor of 0.1 m), the angular velocity (Va) of the rotor is 50,000 revolutions per minute, giving a circumferential velocity (Vp) of 260 m/s (Vp = 2πr
・Va). For larger diameter rotors, increase the circumferential speed by 2
The angular velocity can be reduced as long as it does not fall below 50 m/s.

It is clear from the above description that any number of axial and tangential pump stages of flat rotor type or vaned rotor type may be used according to the particular application without departing from the scope of the invention. Can be changed.

[Brief explanation of the drawing]

1 shows a partial axial section of a turbomolecular pump according to the invention, FIG.

2 is a perspective view of a part of the pump of FIG. 1, with a tangential flow pump stage according to a first embodiment shown partially cut away; FIG.

3 is a partially cutaway plan view of the pump stage of FIG. 2; FIG.

FIG. 4 is a partially cutaway perspective view of a tangential flow pump stage according to a second embodiment;

[Explanation of symbols]

1, 1a, 12, 35...rotor 2, 2a, 13, 36...Stator 6...Rotation axis 7,9,37...feather 10, 30...Tangential flow pump stage 14, 38...Free passage 15, 39...baffle 17, 40...Intake port 18, 41...Exhaust port

Claims (8)

[Claims] 1. A turbo equipped on the intake side with a plurality of axial flow pump stages for pumping gas in the axial flow direction, each of which has rotors and stators arranged alternately and each having a group of blades inclined in opposite directions. In a molecular pump, a pump stage consisting of a rotor and a coplanar stator forming an annular free passage between them along a portion of their respective peripheries, the annular free passage communicating with an inlet and an outlet. and at least one tangential flow pump stage for pumping gas in a tangential flow direction to the rotor from the intake port to the exhaust port is coupled to the axial flow pump stage on the exhaust side. pump. 2. An additional pump stage disposed downstream of the exhaust port on the exhaust side, the additional pump stage comprising a rotor with a plurality of blades and a coplanar stator, the rotor and the stator An annular free passage is formed between the periphery of the blade and the stator along a part of the periphery of the blade, and the annular free passage communicates with an intake port and an exhaust port from the intake port to the exhaust port. 2. The turbomolecular pump of claim 1, further comprising a second tangential pump stage for pumping gas tangentially to the rotor. 3. The turbomolecular pump according to claim 2, wherein the vanes are provided perpendicularly to the plane of the rotor. 4. The turbomolecular pump according to claim 1, wherein the annular free passage is defined at both ends by baffles arranged between the inlet and the outlet. 5. The rotor of the axial flow pump stage that pumps gas in an axial flow direction and the rotor of the tangential flow pump stage that pumps gas in a tangential flow direction are attached to a common rotating shaft. The turbomolecular pump according to item 1. 6. The rotor of the tangential flow type additional pump stage is further attached to the rotating shaft.
Turbomolecular pump as described. 7. The rotors of each of the axial pump stage and the tangential pump stage each have at least one rotor in operation.
The turbo molecular pump according to claim 5 or 6, which rotates at a circumferential speed of 250 m/s. 8. The turbomolecular pump according to claim 1, wherein each of said tangential flow pump stages is housed in a casing consisting of an upper plate and a lower plate having an inlet and an outlet.