Vacuum Side-Channel Compressor

Abstract

A vacuum side channel compressor (10) comprises a pump stator (14) and a pump rotor (12), which surround a side channel (31,32,33,34). An axial bearing (22) is provided for mounting the pump rotor (12). A sealing gap (40) is formed next to the side channel between the pump stator (14) and the pump rotor (12), part of which forms a conical ring whose imaginary cone apex (50) lies in the vicinity of the axial bearing (22).

Description

BACKGROUND

[0001] The invention relates to a vacuum side-channel compressor comprising a pump stator and a pump rotor which surround a side channel.

[0002] Side-channel compressors belong to those molecular pumps which have to rotate at high rotational speeds so as to effect a pump action in the molecular range. For keeping the backflow losses to and from a side channel as low as possible, very narrow sealing gaps are required laterally of the side channels between the pump stator and the pump rotor. However, high rotational speeds for obtaining a high compression, on the one hand and narrow gaps on the other hand are mutually conflicting goals. Apart from the high centrifugal forces generated by high rotational numbers, it is primarily the thermal expansion of the rotor, caused by heat losses of the drive engine, frictional losses of the bearings as well as by compression action, which will tend to reduce the sealing gap. A larger sealing gap, however, will impair the compression effect.

SUMMARY

[0003] It is an object of the invention to provide a vacuum side-channel compressor wherein the operational influences on the sealing gap are reduced.

[0004] In a vacuum side-channel compressor, the sealing gap at least partially forms a conical ring whose imaginary cone apex is located near the axial bearing of the rotor. The rotor of the side channel compressor is normally supported for rotation by two bearings, with one of two bearings axially fixing the rotor. In case of an overhung support of the pump rotor, this bearing is the one closest to the pump rotor. Since the sealing gap and the mutually confronting sealing-gap surfaces of the pump stator and of the pump rotor each form a conical ring having its imaginary cone apex located near the axial bearing, the pump rotor during its thermally induced expansion will in the region of the sealing gap expand substantially in parallel with the conical ring. In this manner, the distance between the sealing-gap surfaces of the pump stator and the pump rotor, i.e. the gap size of the sealing gap, will remain substantially constant at all temperatures of the pump rotor. When choosing the gap size of the sealing gap, the heat-induced influences can be largely neglected. In this manner, the size of the sealing gap does not have to include a reserve range for higher operational temperatures. The gap size can be very small, i.e. the sealing gap can be very narrow, while the gap size will remain equally narrow for all temperatures of the pump rotor so that the backflow losses will be small. Thereby, the overall pump effect of the vacuum side-channel compressor is improved.

[0005] Preferably, the cone apex is spaced by no more than half a support length from the axial bearing. The support length is the length between the two bearings holding the pump rotor. The cone apex is thus arranged around the axial bearing in a range of the length dimension of a support length.

[0006] According to a preferred embodiment, the cone apex is spaced from the axial bearing by no more than the length of an axial bearing. Thus, the cone apex is arranged around the center of an axial bearing in a range of one length of three axial bearing lengths. In the ideal case, the cone apex is located within the axial bearing itself.

[0007] Preferably, at least two side channels are provided which according to a preferred embodiment are arranged in a radial plane. In this manner, the vacuum side channel compressor can in each case be given an axially compact construction. Each of the sealing gaps between adjacent side channels respectively forms a conical ring of its own with respectively a different cone angle. The cone apexes of all conical rings are located substantially at a sole point near the axial bearing.

[0008] Preferably, the non-conical part(s) of the gaps is (are) arranged between two side channels in a radial plane and/or on a cylinder surface. Thereby, it is safeguarded that, with increasing temperature of the pump rotor, i.e. increasing thermal expansion of the pump rotor, the gaps will always be enlarged but not be reduced. Thereby, in turn, it is safeguarded that, with increasing heat-up of the pump rotor, the danger that the pump rotor happens to contact the pump stator and to get jammed thereon in the region of the gaps between the pump rotor and the pump stator is small.

[0009] Preferably, the cross section of the respective outer side channel is larger than that of the adjacent inner side channel. Thus, the side channel compressor has an inner condensation which generally results in a higher overall compression of the side channel compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] An embodiment of the invention will be explained in greater detail hereunder with reference to the drawing.

[0011] The FIGURE shows a vacuum side channel compressor according to the invention which is configured for four pumping stages.

DETAILED DESCRIPTION

[0012] Illustrated in the FIGURE is a vacuum side channel compressor 10 comprising a pump rotor 12, a pump stator 14, a housing 16, an electric drive engine 18, a shaft 20 and two bearings 22,24 supporting the shaft 20.

[0013] The pump stator 14 and the pump rotor 12 surround four side channels 31,32,33,34 which are substantially arranged in a radial plane. For this purpose, pump rotor 12 is of a disk-like shape. The cross section of the side channels 31-34 decreases from the radially outer side toward the radially inner side so that the respective radially outer side channel 31,32,33,34 is of a larger cross section than the respective adjacent radially inner side channel 32,33,34. The side channels 31-34 are serially connected to each other so that gas which has been sucked from the outside via a gas inlet 36 will pass through the four side channels 31,32,33,34 in a direction from the outside towards the inside and will finally be discharged via a gas outlet 38.

[0014] The pump rotor 12 is supported in an overhung manner. The bearing 22 arranged relatively close to pump rotor 12 is a radial-axial bearing 22 configured as a roller bearing whereas the bearing 24 relatively remote from pump rotor 12 is also a roller bearing but exclusively a radial bearing.

[0015] Between pump stator 14 and pump rotor 12, the mutually confronting surfaces 52,54 of pump stator 14 and pump rotor 12 form a respective sealing gap 40,42,44,46. The sealing gaps 40,42,44,46 each form a respective conical ring. Each of the conical rings forms a part of an imaginary cone 61,62,63,64; the common imaginary cone apex 50 of these cones is located within the axial bearing 22 on the axial line of the pump rotor. The sealing gap 40 of the outer side channel 31, forming a conical ring, is formed by a correspondingly inclined pump rotor sealing surface 52 and a correspondingly inclined opposite pump stator sealing surface 54.

[0016] Since the two sealing surfaces 52,54 and the sealing gap 40 created by these are arranged to form a conical ring whose imaginary cone apex 50 is arranged within the sole axial bearing 22, a thermally induced expansion of pump rotor 12 will cause no changes or merely slight changes of the gap size of sealing gap 40. Thus, the gap size of sealing gap 40 will be substantially constant across a wide range of temperatures and can be given a very small dimension, e.g. smaller than 0.1 mm. Thereby, in turn, the backflow losses between the four side channels 31-34 as well as between the outer side channel 31 and the gas inlet 36 are kept small.

[0017] The other non-conical gaps between pump rotor 12 and pump stator 14 are arranged in a radial plane or in a cylinder surface. These non-conical gaps will become enlarged with increasing thermal expansion of pump rotor 12.

[0018] For this purpose, the gap arranged in a cylinder plane between pump stator 14 and pump rotor 12 is formed by a pump stator gap surface which is oriented radially inwardly since, otherwise, the respective gap would become smaller with increasing heat-up of the pump rotor. Those gap surfaces of the pump rotor which are oriented radially outwardly are all arranged on a conical ring which has its imaginary cone apex located within the axial bearing, as described above.

[0019] The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

1. A vacuum side channel compressor comprising a pump stator and a pump rotor which together surround a side channel, an axial bearing for supporting the pump rotor, and a sealing gap being formed next to the side channel between the pump stator and the pump rotor, the sealing gap forming a conical ring, with an imaginary cone apex arranged on an axial line of the pump rotor in the vicinity of the axial bearing.

2. The vacuum side channel compressor according to claim 1, wherein the cone apex is spaced from the axial bearing by no more than half of its support length.

3. The vacuum side channel compressor according to claim 1, wherein the cone apex is spaced from the axial bearing by no more than half of a length of the axial bearing.

4. The vacuum side channel compressor according to claim 1, wherein at least two side channels are provided.

5. The vacuum side channel compressor according to claim 4, wherein the side channels are arranged in a common radial plane.

6. The vacuum side channel compressor according to claim 1, wherein a non-conical part of a gap is arranged between two side channels in a radial plane and/or on a cylindrical surface.

7. The vacuum side channel compressor according to 1, wherein a cross section of a respective outer side channel is larger than that of the adjacent inner side channel.

8. A vacuum side channel compressor comprising: a stator and a rotor which define a plurality of side channels disposed concentrically around an axis of rotation of the rotor; the rotor and the stator defining a plurality of sealing surfaces separated by a sealing gap, the sealing surfaces being disposed between adjacent side channels, the sealing surfaces being disposed along conical surfaces which project to a common imaginary apex disposed on the axis of rotation.

9. The vacuum side channel compressor according to claim 8, wherein the rotor is supported on a rotor shaft supported by an upper bearing and a lower bearing, the imaginary apex being disposed adjacent the upper bearing.

10. The vacuum side channel compressor according to claim 8, wherein the plurality of side channels decrease in cross section from a largest outmost side channel connected with an inlet to a smalles innermost side channel connected to an outlet.