TURBOMOLECULAR PUMP

Abstract

A turbomolecular pump has a rotor element in a housing. The rotor element is arranged on a rotor shaft. The rotor shaft is supported by two bearing elements in the housing. The bearing element on the high-vacuum side is constructed as a roller bearing. In order to guarantee a pressure in the area of the bearing element that is acceptable for the bearing element constructed as a roller bearing, the bearing element is arranged in a chamber. The chamber is connected via a channel to the pre-vacuum area and sealed relative to the high-vacuum area by a gasket.

Description

BACKGROUND

1. Field of the Disclosure

The disclosure refers to a turbomolecular pump.

2. Discussion of the Background Art

Turbomolecular pumps comprise at least one rotor element in their housing. The rotor element has a plurality of blades and is supported on a rotor shaft. The rotor shaft is driven by an electric motor and is supported in the housing by bearing elements. Further, the turbomolecular pump comprises a stator element having a plurality of stator blades. The stator element is arranged in the housing by means of stator rings, for instance, with the stator blades protruding to between the rotor blades so that stator lades and rotor blades are arranged alternately. The turbomolecular pump can possibly comprise one or a plurality of such rotor or stator elements. It is further known that turbomolecular pumps comprise a Holweck stage arranged downstream of the rotor element in the flow direction. Two bearing elements are provided to support the fast rotating rotor shaft. In this regard, one of the bearing elements is typically arranged at the end of the rotor shaft on the pre-vacuum side. This bearing element is situated in an environment in which a comparatively low vacuum so that both magnetic bearings and roller bearings can be used in this area. Due to the relatively low vacuum, there is no risk of carbon hydrogen or other substances gassing out in large quantities from the lubricant, which typically is grease. If a bearing element is also arranged at the end of the rotor shaft on the high vacuum side, this bearing will always be a magnetic bearing. Since very low pressures or a high vacuum prevails in this area, neither roller bearings, nor encapsulated roller bearings can be used in this area, since, owing to the vacuum, components of the lubricants, in particular carbon hydrogen, will gas out from the lubricant. However, magnetic bearings are expansive bearings. Further, the structure is complicated.

In order to realize both bearing elements of a rotor element as roller bearings, it is known to support the rotor shaft in a floating manner. Thus, the bearing element on the high-vacuum side is displaced towards the pre-vacuum side so that the rotor shaft projects outward. Thereby, the bearing element is shifted into an area in which, owing to the low pressure prevailing, a gassing out of the lubricant no longer occurs or only occurs in an acceptable extent. However, rotor shafts supported in a floating manner have the disadvantage that they are heavy so as to ensure sufficient stability. Further, the cantilever length is limited.

It is an object of the disclosure to provide an economic bearing of the rotor shaft of a turbomolecular pump.

SUMMARY

In the present embodiment of the turbomolecular pump, bearing elements are arranged in each of the two end areas of the rotor shaft. Here, the bearing element on the pre-vacuum side can be a roller bearing or a magnetic bearing, with the more economic embodiment of a roller bearing being preferred. According to the disclosure, a roller bearing is also provided on the high vacuum side, despite the low pressure prevailing. This is possible, according to the disclosure, due to the arrangement of the high vacuum-side bearing element in a chamber. The chamber, which substantially fully surrounds the bearing element, is connected to a pressure area via a channel, in which area a higher pressure prevails. The channel thus connects the chamber provided in the high-vacuum area with an area in which a low vacuum prevails. As a consequence, despite the chamber being arranged in the high-vacuum area, the pressure in the chamber is not the low pressure prevailing in the high-vacuum area, but a higher pressure. This pressure substantially corresponds to the pressure prevailing in the pressure area to which the channel is connected. According to the disclosure, providing a chamber, which is connected to a corresponding pressure area via a channel, makes it possible to support the rotor shaft by means of a roller bearing also on the high-vacuum side. Thereby, the costs can be reduced significantly. In particular, it is no longer necessary to support the rotor shaft in a floating manner also when roller bearings are used, and to accept the disadvantages of a cantilever arm.

Preferably, the channel is connected with a pressure area in which a pressure of at least 1·10⁻⁵ mbar, in particular at least 1·10⁻³ mbar prevails. Preferably, the pressure in this area is between 1 mbar and 1·10⁻⁵ mbar. In the high-vacuum area, pressures can prevail that are lower than 1·10⁻³ mbar, in particular lower than 1·10⁻⁵ mbar, and particularly preferred lower than 1·10⁻mbar.

This high-vacuum side bearing element supports the rotor shaft in the pump housing. Therefore, in a preferred embodiment of the disclosure, the chamber is formed by a bearing receiving element that is directly or indirectly connected with the housing. The bearing receiving element comprises a star-shaped support element or is preferably connected with a star-shaped support element which itself is connected with the housing.

The in particular star-shaped support element thus has openings through which the medium to be conveyed is conveyed.

In another preferred embodiment of the disclosure, which in particular ensures a facilitated assembly, the chamber is closed on the high-vacuum side with a cover. The cover is preferably connected with the bearing receiving element. Thus, in a preferred embodiment, the cover spans the rotor shaft protruding into the chamber. Accordingly, the shaft end is arranged inside the chamber. This is advantageous in that no sealing has to be provided between the shaft and the cover in this area.

In a preferred embodiment of the disclosure, a gasket element is arranged between the bearing receiving element and the rotor element. In a preferred embodiment, this is a contactless gasket such as a labyrinth seal. The gasket element is preferably arranged in an annular gap formed by the bearing receiving element and the rotor element. By a relatively long sealing length, a good tightness can be achieved. In a particularly preferred embodiment, a sealing gap of the sealing element has a cross section smaller than the cross-sectional area of the channel. If a plurality of channels is provided, it is preferred that the sealing gap has a cross-sectional area smaller than the sum of the cross-sectional areas of the channels. Thereby, a preferred pumping direction is ensured, since, via the channel, a pressure prevails on one side of the gasket element that substantially corresponds to the pressure in the area of the channel opening, i.e. in particular the pressure of a pre-vacuum area, and a high vacuum prevails on the other side of the gasket element.

In a particularly preferred embodiment, the gasket element comprises an active gasket element. Thereby, medium is conveyed from the area, in which lower pressure prevails, to the area, in which higher pressure prevails. The active gasket element may e.g. be a spiral-shaped groove formed in one or both of the walls forming the annular gap. In particular, the same may be configured in a manner corresponding to a Holweck pump.

The following is a detailed description of the disclosure with reference to a preferred embodiment and to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified schematic sectional view of a turbomolecular pump with a bearing configured in accordance with the disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The turbomolecular pump, illustrated in a simplified manner, comprises a rotor shaft 10 that is rotatably supported in a housing 16 by means of a bearing element 12 on the high-vacuum side and a bearing element 14 on the pre-vacuum side. The rotor shaft 10 carries a rotor element 18 with a plurality of rotor blades 20. A stator blade 22 is provided between every two adjacent rotor blades 20. The stator blades 22 are fixed in the housing 16 by means of stator rings 24 so that in the embodiment illustrated, the stator element is formed by the stator blades 22 and the stator rings 24.

In the embodiment illustrated, the rotor shaft is driven by an electric motor 26.

The bearing element 14 on the pre-vacuum side is carried by a holder element 28. The holder element is connected with the housing 16 and comprises an outlet 30 of the turbomolecular pump.

For the evacuation of a space, not illustrated and connected with the turbomolecular pump, the medium is thus conveyed from the space through an inlet 32 of the vacuum pump towards the outlet 32.

According to the disclosure, although arranged in the high-vacuum area 34, the bearing element 12 is designed as a roller bearing. This is possible since the bearing element 12 is arranged in a chamber 36. In the embodiment illustrated, the chamber 36, into which the high-vacuum side end of the rotor shaft 10 protrudes, is formed by a bearing receiving element 38. Towards the inlet 32, the chamber 36 is closed with a covert 40. The cover 40 spans the high-vacuum side end of the rotor shaft 10 such that the same does not protrude through the cover 40. In the embodiment illustrated, the cover 40 is fixedly connected with the bearing receiving element 38.

In order to support the outer bearing ring of the high-vacuum side bearing element 12, the bearing receiving element 38 must be connected with the housing 16. In the embodiment illustrated, this is achieved with a support element 42 of a star-shaped design. Due to the star-shaped design of the support element 42, the same has openings 44 through which the medium is drawn into the turbomolecular pump by the rotor blades 22.

According to the disclosure, not only a chamber 36 is provided for arranging a roller bearing in the high-vacuum area 34. Further, the chamber 36 is connected with a pre-vacuum area 48 via a channel 46 arranged in the rotor element. Due to the connection of the chamber 36 with the pre-vacuum area 48 via the channel 46, it is ensured that substantially the same pressure that prevails in the chamber 36 prevails in the pre-vacuum area 48. In order to avoid the pressure in the chamber from decreasing and the lubricant in the roller bearing from gassing out, a gasket element 50 is further provided. For this purpose, the bearing receiving element comprises a shoulder or abutment surface 52 extending in the longitudinal direction of the pump or parallel to the rotor shaft 10, respectively. Thus, the surface 52 is a lateral surface of a cylinder. A cylinder-shaped lateral surface 54 is also formed at the rotor element 18, opposite the surface 52 and parallel to the surface 52. Accordingly, the two surfaces 52, 54 form a circular cylindrical annular gap 56. In the embodiment illustrated, a labyrinth seal is arranged as the gasket element 50 within the annular gap 56. In addition to or instead of a labyrinth seal, an active gasket such as a Holweck stage can be formed in the annular gap 56, which stage conveys medium from the high-vacuum area 34 towards the vacuum area 48.

Claims

1. A turbomolecular pump comprising

at least one rotor element with a plurality of rotor blades, said element being supported in a housing by means of a rotor element,

at least one stator element comprising a plurality of stator blades projecting between the rotor blades, and

at least two bearing elements arranged in end areas of the rotor shaft, wherein at least the bearing element on the high-vacuum side is formed as a roller bearing and is arranged in a chamber that is connected via at least one channel to a pressure area in which a higher pressure prevails than in the high-vacuum area.

2. The turbomolecular pump according to claim 1, wherein in the pressure area, in which a higher pressure prevails, the pressure prevailing is at least 1·10−5 mbar, in particular 1·10−3 mbar.

3. The turbomolecular pump as defined according to claim 1, wherein in the high-vacuum area a pressure prevails that is lower than 1·10−3 mbar, in particular lower than 1·10−5 mbar, and particularly preferred lower than 1·10−7 mbar.

4. The turbomolecular pump according to claim 1, wherein the chamber is at least partly formed by a bearing receiving element connected directly or indirectly with the housing.

5. The turbomolecular pump according to claim 1, wherein the chamber is closed on the high-vacuum side with a cover preferably connected with the bearing receiving element.

6. The turbomolecular pump according to claim 4, wherein the bearing receiving element is connected with the housing through a support element which is in particular star-shaped.

7. The turbomolecular pump according to claim 4, further comprising a gasket element arranged between the bearing receiving element and the rotor element.

8. The turbomolecular pump efaccording to claim 7, wherein the gasket element is arranged in an annular gap formed by the bearing receiving element and the rotor element.

9. The turbomolecular pump according to claim 7, wherein the gasket element comprises a labyrinth seal.

10. The turbomolecular pump according to claim 7, further comprising a sealing gap of the gasket element has a cross-sectional area smaller than the cross-sectional area of the channel or the sum of the cross-sectional areas of a plurality of channels.

11. The turbomolecular pump according to claim 7, wherein the gasket element comprises an active sealing element, the active sealing element in particular comprising the Holweck stage or being designed as a Holweck stage.

12. The turbomolecular pump according to claim 1, wherein the at least one channel is connected with the pre-vacuum area.