TURBOMOLECULAR PUMP

Abstract

A turbomolecular pump (10) includes a rotor (12) connected to a drive shaft (10). The rotor (12) has multiple rotor vanes (16). The rotor (12) is surrounded by stator rings (26) with one stator ring (26) is provided for each rotor vane (16). In order to enable radial expansion of the rotor vanes during operation, the stator rings (26) have annular grooves (32).

Description

The invention relates to a turbomolecular pump.

Turbomolecular pumps comprise a rotor connected to a drive shaft and carrying a plurality of rotor vanes. Between the individual rotor vanes, stationary stator disks are arranged. In many cases, the stator disks are not directly connected to the pump housing but are supported by stator rings. In such arrangements, one stator ring is provided per rotor vane, wherein, for mounting the stator rings, the stator rings will be shifted over the rotor. Between the rotor vanes or rotor vane tips and the stationary housing or the stator rings, a gap has to be provided. This gap is required so that, in all operative conditions, the rotor vanes are prevented from contacting the stationary components, i.e. the housing or the stator rings. For this purpose, the width of the gap must be sufficiently large to allow for the occurrence of thermal expansion of the rotor vanes in all operating conditions without causing a contact to the stationary components. Further, regarding the width of the provided gap, there has to be considered a possible occurrence of oblique orientations of the rotor due to the rotor dynamics. Further still, particularly in magnetically supported drive shafts, consideration has to be given to excursion movements caused by tolerances relative to the safety bearings. Also, centrifugal forces will generate an expansion of the rotor, particularly in radial directions. Further to be considered are possible accumulations of tolerances. In turbomolecular pumps with a rotor diameter of about 200 mm, the gap between the rotor vanes and the housing or the stator rings has a size of 2 mm. Due to the existing gap, a part of the pumped gas will flow back. This backflow causes a noticeable deterioration of the efficiency of the turbomolecular pump.

It is an object of the invention to provide a turbomolecular pump wherein the volume of the gas backflow can be reduced and the efficiency can thus be improved.

According to the invention, the above object is achieved by the features indicated in claim 1.

The turbomolecular pump according to the invention comprises a rotor with a plurality of rotor vanes. The rotor is connected to a drive shaft and surrounded by a stator element. The stator element, preferably having a cylindrical shape, can be formed by the housing of the turbomolecular pump itself or by one or preferably a plurality of stator rings. According to the invention, the stator element comprises at least one annular groove. This surrounding annular groove is assigned to a rotor vane and is arranged in the corresponding vane plane of this rotor. Thus, in the operational condition, the annular groove is arranged at the height of the assigned rotor vane. Thereby, it is rendered possible that an expansion of the rotor vane during operation will radially extend into the annular groove. Since, during operation, there will occur primarily a radial expansion of the rotor vane, caused by thermal stresses and by the occurring centrifugal forces, the tip of the rotor vane pointing towards the annular groove will enter the annular groove. Generated thereby is a kind of contactless labyrinth sealing which, in the operating condition wherein the rotor vanes are expanding in radial directions, will bring about a kind of self-sealing effect.

The dimensions of the annular groove are herein selected in such a manner that, in all operating conditions, the rotor vane is prevented from contacting either the bottom or the side walls of the annular groove. Since, during operation of the turbomolecular pump, the tip of the annular groove extends into the annular groove, the gap at the tip of the rotor vane is provided with a U-shaped cross section. Thereby, the volume of the gas flowing back will be considerably reduced, resulting in an improved efficiency of the turbomolecular pump.

Since the expected expansion of the rotor vanes, caused particularly by thermal influences, is less in the axial direction than in radial directions, a smaller gap width can be provided in the axial direction than in the radial directions. Thereby, the sealing effect can be further improved.

Preferably, the rotor vanes are formed with a radial projection. This projection, pointing in the direction of the annular groove, is particularly of an annular shape. Thus, the annular projection surrounds the individual blades of the rotor vanes so that, during operation, it is preferably exclusively the annular projection and not the blades that is inserted into the annular groove during operation.

Preferably, each rotor vane has an annular groove assigned thereto, while preferably each rotor vane is formed with an annular projection. By the provision of a plurality of annular grooves for a plurality of rotor vanes, particularly for at least two rotor blades, a further improvement of the sealing effect can be accomplished. Since, according to an especially preferred embodiment, respectively one annular groove is provided for each rotor vane, a meander-shaped gap is formed during operation, serving as a contactless labyrinth sealing, with a resultant considerable improvement of the efficiency of the turbomolecular pump.

The at least one annular groove can be provided on an inner side of a housing formed as a stator element. Preferably, however, a plurality of stator rings are provided within a pump housing. Usually, respectively one stator ring is provided per rotor vane, with the stator rings being arranged behind each other in the axial direction. Thus, the stator rings are located behind each other in the direction of the drive shaft or the main conveying direction of the gas. Depending on the configuration of the turbomolecular pump of the invention, the inventive annular groove is arranged in one or a plurality of the stator rings. Preferably, all of the stator rings are provided with an annular groove which, specifically, is configured to be entered, during operation, by the annular projection connected to the corresponding rotor vanes. The height of the annular grooves depends on the vane heights which decrease from the inlet side to the outlet side (corresponding to the condensation). Accordingly, the groove depth will vary from about 0.5 mm in small rotors to about 4 mm in large rotors. The groove width will vary from 2 mm in flat vanes of small rotors to 15 mm in steep vanes of large rotors.

A preferred embodiment of the invention will be explained in greater detail hereunder with reference to the accompanying drawings.

In the drawings, the following is shown:

FIG. 1 is an enlarged schematic sectional view of a portion of a turbomolecular pump according to the state of the art;

FIG. 2 is a schematic sectional view of a turbomolecular pump according to the invention; and

FIG. 3 is an enlarged schematic sectional view of the portion III in FIG. 2.

According to the embodiment of a turbomolecular pump of the state of the art as illustrated in FIG. 1, a drive shaft 10 (FIG. 2) has a rotor 12 arranged thereon. Rotor 12 is provided with rotor vanes 16 extending radially with respect to a longitudinal axis 14 and respectively the axis of rotation of shaft 10. Each rotor vane comprises rotor blades 18 which are suitably inclined to impart to the transported gas a main flow direction parallel to said longitudinal axis, i.e. in FIG. 1 in the downward direction marked by arrow 20. Rotor 12 is arranged in a housing 22 which, for accommodating the rotor, is formed with a cylindrical, optionally stepped chamber 24.

A part of the rotor vanes 16 is surrounded by stator rings 26. When viewed in the longitudinal direction 14, the stator rings 26 are arranged behind each other and thus cover an inner side of said cylindrical chamber 24 of housing 22. Provided between adjacent stator rings 26 are stator disks 28 facing inward in the direction of the rotor. Thus, each stator disk 28 is arranged between two adjacent rotor vanes 16.

In order to prevent, during operation of the turbomolecular pump, that the radially outer ends of the rotor vanes 16, i.e. the tips of rotor vanes 16, happen to contact the stator rings 26, a gap a is formed between the radial ends of rotor vanes 16 and the inner sides, i.e. the sides 30 facing towards the rotor vanes 16. Gas which is to be conveyed during operation will flow, against the conveying direction 20, through this gap a back into a suction chamber from which the gas is to be sucked.

In the description of a preferred embodiment of the invention rendered hereunder with reference to FIGS. 2 and 3, components similar or identical to those described above will be identified by the same reference numerals as above.

In correspondence to the state of the art, also the turbomolecular pump of the invention comprises a drive shaft 10 carrying the rotor 12. Also here, rotor 12 comprises rotor vanes 16 carrying rotor blades 18. Also in the illustrated embodiment, stator rings 26 are arranged within housing 22. Further, in the embodiment shown, stator disks 28 are arranged between adjacent rotor vanes 16.

According to the invention, all stator rings 26 in the illustrated embodiment are provided, on their inner sides facing towards rotor 12, with an annular groove 32. The annular groove 32 is closed in itself and extends along the whole inner side of each individual stator ring 26.

In the illustrated embodiment, the rotor vanes 16 are respectively formed with an annular projection 34 on their outer ends facing towards the stator rings 26. During operation, said annular projection 34 will be displaced into the respective annular groove 32 under the effect of the thermal expansion, the centrifugal forces etc.

Thus, in each rotor vane, the annular grooves 32 and the annular projections 34 are located on a common vane plane 36 extending respectively horizontally in FIG. 3, only one such vane plane 36 being shown in FIG. 3 for reasons of clarity.

The upper rotor vane 16 in FIG. 3 is not surrounded by a stator ring. To obtain an improved sealing effect also in regard to this rotor vane 16, an annular groove 38 is provided in housing 22. In operation, a projection 34 of upper rotor vane 16 will extend also into this annular groove 38.

In a condition where the turbomolecular pump is not in operation and there will thus occur no expansion or displacement of the rotor vanes 16, it is provided that a mounting gap b exists between the radial ends of the rotor vanes 16 and an inner side of the stator rings 26. Said gap is necessitated to allow the stator rings 26 to be shifted over rotor 12 for mounting them.

Claims

1. A turbomolecular pump, comprising:

a rotor arranged on a drive shaft and having a plurality of rotor vanes, and

a stator element surrounding the rotor,

wherein

said stator element comprises at least one surrounding annular groove assigned to a respective one of the rotor vanes, said annular groove being arranged in a vane plane of the assigned rotor vane to allow for radial expansion of the rotor vane during operation.

2. The turbomolecular pump according to claim 1, wherein said at least one rotor vane comprises an annular projection extending radially in the direction towards the annular groove.

3. The turbomolecular pump according to claim 1, wherein a plurality of rotor vanes, particularly at least two rotor vanes, have at least one annular groove assigned to them.

4. The turbomolecular pump according to claim 1, wherein the stator element is formed by a housing in such a manner that said at least one annular groove is provided on the inner side of the housing facing towards the rotor.

5. The turbomolecular pump according to claim 1, wherein the stator element comprises a plurality of stator rings arranged behind each other in the axial direction, said at least one annular groove being provided in one of the stator rings.

6. The turbomolecular pump according to claim 5, wherein each stator ring is connected to a stator disk arranged between two adjacent rotor vanes.

7. The turbomolecular pump according to claim 5, wherein one stator ring is provided per rotor vane, each stator ring defining an annular groove.

8. The turbomolecular pump according to claim 5, wherein in a mounting condition, an inner diameter of the stator rings is larger than an outer diameter of the rotor vanes by a width of a mounting gap.

9. A turbomolecular pump comprising:

a stator housing;

a rotor shaft rotatably disposed in the stator housing;

a plurality of rotor vanes mounted to the rotor shaft and extending radially outward therefrom along a rotor plane to a rotor tip;

a plurality of stator rings disposed between the rotor planes, each stator ring carrying an array of stator vanes extending radially inward and defining a circumferential groove in the rotor plane configured to receive a corresponding rotor tip.