EP2902637A2 - Vacuum pump - Google Patents

Abstract

The invention relates to a vacuum pump (1) having at least one Holweckpumpstufe (70) with at least one Holweckstator (74) and at least one Holweckrotor (72), wherein in the Holweckstator (74) of at least one Holweckpumpstufe (70) at least one gas inlet (80 , 82) is provided.

Description

The invention relates to a vacuum pump with at least one Holweckpumpstufe with at least one Holweckstator and at least one Holweckrotor.

The prior art ( EP 1 668 255 B1 ) includes a vacuum pump, which has two turbomolecular pumping stages and a Holweckpumpstufe and is used for the evacuation of chambers of a mass spectrometer.

In this prior art vacuum pump, an inlet is provided in front of the Holweckstator from a chamber to be evacuated and the incoming gas is passed completely through the Holweckpumpstufe.

This belonging to the prior art vacuum pump has the disadvantage that the high gas load generates a high pressure, which leads due to gas friction to a very high power consumption and high temperatures.

The technical problem underlying the invention is to pump the gas load, but with reduced power consumption.

This technical problem is solved by a vacuum pump having the features according to claim 1.

The vacuum pump according to the invention with at least one Holweckpumpstufe with at least one Holweckstator and at least one Holweckrotor is characterized in that at least one gas inlet is provided in the Holweckstator the at least one Holweckpumpstufe.

This embodiment of a vacuum pump according to the invention has the advantage that the Holweck stage, which has an axial length, makes it possible to distribute one or more taps (Interstage ports) in axial length. This has the advantage that the high gas load of the corresponding chamber, which is associated with the inlet, does not flow completely through a tapping of the Holweck stage, but divides itself, so that a part of the gas stream takes a shorter path through the Holweck stage. This reduces the gas friction and especially the power consumption and the temperature.

It is advantageous to provide at least one gas inlet in the Holweckstator. This already ensures that the high gas load does not flow completely through the entire Holweckstufe.

It is advantageous to provide at least two inlets in the axial direction of the Holweckstators, as a result, a better division can be achieved.

According to a further advantageous embodiment of the invention, at least two inlets are provided in the tangential direction of the Holweckstators.

This means that at least one gas inlet is provided in the axial direction of the Holweckstators. The gas inlets in the axial direction, which are arranged at one and the same pressure level, but can be distributed over several inlets, which are advantageously arranged tangentially symmetrical in Holweckstator. However, they can also be arranged asymmetrically with respect to the radial circumference.

The at least one inlet may be formed as a bore and / or slot and / or slot. These embodiments can be adapted to customer-specific requirements. This makes any geometry possible.

A further embodiment of the invention provides that the inlets have the same or different cross sections.

Advantageously, the inlets have different cross sections, as a result, an optimized pumping action can be adjusted.

In the high vacuum range, the openings of the inlets are advantageously larger than the openings in the fore-vacuum area.

According to a further advantageous embodiment of the invention, each inlet is connected to only one chamber to be evacuated.

However, there is also the possibility that several inlets are connected to only one chamber to be evacuated. It is also advantageous that with a plurality of taps a lower pressure in the chamber is achieved. By different inlet geometries, therefore, a user-desired pressure profile in the chamber can be achieved.

The arrangement of at least one inlet in the region of the Holweckstators has the advantage that in addition to the inlets further compression stages are present, which, as already stated, has a positive effect on the gas friction and the power consumption and temperature.

By a second inlet so the gas friction is reduced in the Holweckstufe. This reduction can also be used to pump a higher gas load again to achieve the same gas friction as in the prior art.

In the vacuum pump, at least one additional turbomolecular pump stage is advantageously provided.

According to a further advantageous embodiment of the invention, at least two inlets are arranged in the Holweckstator and the inlet, which is arranged in the axial direction of the vacuum pump closer to the turbomolecular pumping stage, is designed as an inlet arranged in the region of molecular flow.

According to a further advantageous embodiment of the invention, at least two inlets are arranged in the Holweckstator and the inlet, which is arranged in the axial direction of the vacuum pump further away from the turbomolecular pumping stage, is advantageously designed as an arranged in the region of the Knudsen flow inlet.

The transition from the viscous flow to the molecular flow is called Knudsen flow. The Knudsen flow prevails in the fine vacuum range from 0.1 Pascal to 100 Pascal.

If the Knudsen number between 0.01 and 0.5 one speaks of Knudsen flow. Since many process pressures are in the fine vacuum range, this type of flow is correspondingly frequently represented in technical vacuum applications.

With Knudsen numbers greater than 0.5, an interaction of the particles with each other practically no longer takes place. There is molecular flow. The mean free path is significantly larger than the width of the flow channel. In this case, the width of the flow channel typically corresponds to the cross section of the inlet.

The molecular flow prevails in contrast to the viscous flow, when the mean free path of the gas particles is significantly larger than the diameter of the flow, that is, when the Knudsen number is significantly greater than 1. The molecular flow is predominant in the high vacuum range ( 10 ^-3 to 10 ^-7 hPa) and ultrahigh vacuum range (smaller 10 ^-7 hPa).

The Knudsen number K _n is the ratio of mean free path ( I ) and the diameter (d) of a flow channel: $$K_n=\frac{\tilde{I}}{d}\mathrm{,}$$

According to an advantageous embodiment of the invention, the inlets are tapered in the direction of the Holweckrotors. By means of this tapering of the inlets existing in the radial direction, an optimization of the inlet flow is obtained, as a result of which the power of the pumping stage is significantly improved.

According to a further advantageous embodiment of the invention, the Holweckstator on channels and the at least one inlet is arranged in the region of a channel bottom. As a result, the pump-active structure of the Holweckstators is maintained, although an inlet is provided in the region of Holweckstators.

According to a further advantageous embodiment of the invention, the at least one inlet is arranged exclusively in a channel bottom. This ensures that the channels of the Holweckstators are not changed and thereby an optimal pumping action is achieved.

A further advantageous embodiment of the invention provides that all inlets are arranged in the region of a channel bottom.

Fig. 1

einen Längsschnitt durch eine Vakuumpumpe mit Holweckpumpstufe;

Fig. 2

eine Prinzipdarstellung einer Vakuumpumpe im Längsschnitt;

Fig. 3

ein geändertes Ausführungsbeispiel;

Fig. 4

einen Längsschnitt durch einen Holweckstator;

Fig. 5

einen Querschnitt durch einen Holweckstator,

Fig. 6

ein Berechnungsbeispiel einer zum Stand der Technik gehörenden Holweckpumpstufe;

Fig. 7

ein Berechnungsbeispiel für eine Holweckpumpstufe gemäß der Erfindung.

Further features and advantages of the invention will become apparent from the accompanying drawings, in which several embodiments a vacuum pump according to the invention are shown only by way of example. In the drawing show:

Fig. 1

a longitudinal section through a vacuum pump with Holweckpumpstufe;

Fig. 2

a schematic diagram of a vacuum pump in longitudinal section;

Fig. 3

a modified embodiment;

Fig. 4

a longitudinal section through a Holweckstator;

Fig. 5

a cross section through a Holweckstator,

Fig. 6

a calculation example of a Holweckpumpstufe belonging to the prior art;

Fig. 7

a calculation example for Holweckpumpstufe according to the invention.

In Fig. 1 a vacuum pump 1 and a chamber system 2 is shown. In a chamber housing 2, a fore-vacuum chamber 4 and a high-vacuum chamber 12 are provided, which are connected to one another via a high-vacuum diaphragm 22. For example, a particle beam can enter the pre-vacuum chamber 4 through a pre-vacuum diaphragm 14.

With the chamber housing 2, a pump housing 40 of the vacuum pump 1 is vacuum-tight and releasably connected. In a pump housing 40, a shaft 42 is arranged, which of a high-vacuum-side bearing 44 and a fore-vacuum side bearing 48 is rotatably supported.

Any storage is conceivable. The storage can be realized, for example, by two bearings, furthermore, the vorvakuumseitige bearing can be designed as a rolling bearing and the high-vacuum side bearing as a permanent magnet bearing. Even a fully magnetic storage is possible.

On the shaft 42, a permanent magnet 52 is provided which cooperates with the magnetic field of a drive coil 50 and thus the shaft 42 is set in rapid rotation. Within the scope of such a vacuum pump 1, fast means that the pump-active components develop a pumping effect due to molecular mechanisms and the rotational speed is at some 10,000 revolutions per minute.

The vacuum pump 1 has a first inlet 80 and a second inlet 82. The first inlet 80 is connected to the fore-vacuum chamber 4, while the second inlet 82 is connected to the high-vacuum chamber 12. The gas entering the vacuum pump 1 through the first inlet 80 passes into a pumping stage 70, as does the second inlet 82. This pumping stage 70 is formed as a Holweckpumpstufe with a Holweckstator 74 and a Holweckzylinder 72. The Holweckstator 74 essentially has a thick-walled hollow cylinder with thread-like, running on its inside channels 76 with a square cross section. Within this cylinder, a ring nut 72 connected to the shaft 42 runs. The ring nut cylinder 72 may be made of a compound material such as carbon fiber reinforced plastic (CFRP), but may also be made of a metal, ideally an aluminum alloy. This at least partially surrounds the high-vacuum side bearing 44 and a bearing support 46 which fixes this bearing 44 on the pump housing 10.

In the vacuum pump 1, a further pumping stage 60 is provided. The pumping stage 60 is designed as a turbomolecular pumping stage and therefore has respective rotor disks 62 and stator disks 64 provided with a blade ring. These are axially spaced by spacers 66. The pumping stage 60 may comprise a plurality of rotor and stator disks, depending on the required pressure ratio between the suction region and the discharge region of the pumping stage. The gas is transferred from the pumping stage 60 to an outlet 54 of the vacuum pump 1 and leaves through this the vacuum pump 1.

For example, the turbo disks 62 may be individually fitted to the shaft 42, but one-piece turbo disks (bell rotors) are also possible.

Through the inlet 80, the fore-vacuum chamber 4 is evacuated. Through the inlet 82, the high vacuum chamber 12 is evacuated. The inlets 80 and 82 are at different pressure levels of the Holweckpumpstufe 70. The pressure level of the high vacuum chamber 12 is below the pressure level of the Vorvakuumkammer. 4

The gas ejected from the pumping stage 70 is conveyed further by the pumping stage 60 in the direction of the outlet 54.

The arrangement of the inlets 80 and 82 in the region of Holweckstators 74 ensures that the high gas load of the chamber 4 does not flow completely through the Holweckpumpstufe 70, but only through a part, so that the gas flow flowing through the inlet 80, a takes a shorter path through the Holweckstufe. This reduces the gas friction and especially the power consumption and the temperature.

Fig. 2 shows the vacuum pump 1 with a chamber housing 2. Parts with Fig. 1 match, are provided with the same reference numbers. In the chamber housing 2, three chambers 5, 6, 7 are arranged. Between the chambers 5, 6, a diaphragm 3 and between the chambers 6, 7, a diaphragm 8 is arranged. In the aperture 3 and in the aperture 8 openings are provided, so that in the direction of arrows A, B, the gas can enter the adjacent chambers.

The Holweckpumpstufe 70 with the Holweckstator 74 has two inlets 11, 13, through which the gas from the chamber 6 in the direction of arrows C, D can get into the Holweckpumpstufe 70. These multiple inlets 11, 13 have the advantage that they are distributed in the axial length of the vacuum pumping stage 70. This has the advantage that the high gas load of the corresponding chamber 6 does not flow completely through an inlet 11 of the Holweckstufe 70, but divides, so that a portion of the gas stream takes a shorter path through the Holweckstufe 70. This reduces the gas friction and especially the power consumption and the temperature.

In the chamber 7, a further outlet 9 is provided, so that the chamber 7 is evacuated by the turbomolecular pumping stage 60.

Through the pre-vacuum diaphragm 14, a particle beam can enter the vacuum chamber 5.

The gas exiting the chamber 6 into the Holweckpumpstufe 70 is provided by the Holweckpumpstufe 70, consisting from Holweckstator 74 and Holweckrotor 72, promoted toward the turbomolecular pumping stage 60 and discharged via an outlet 54.

Fig. 3 shows the vacuum pump 1 with a chamber system 2. The same parts are provided with the same reference numbers.

In the chamber 6, an additional aperture 15 is arranged, so that about 80% of the gas from the chamber 6 are evacuated through the inlet 11 in the region of the Holweckstators 74 and about the inlet 13 about 20%.

Advantageously, the inlet 11 has a larger cross-section than the inlet 13. This means that the inlet, which is arranged closer to the turbomolecular pumping stage 60 in the axial direction, has a smaller cross-section than the inlet, which is arranged farther away from the turbomolecular pumping stage 60 ,

As in Fig. 4 shown, the Holweckstator 74 channels 76. According to an advantageous embodiment of the invention, the inlet 11 is arranged in the region of a channel 76 in order not to substantially change the structure of the Holweckstators 74 and thereby achieve an optimized pumping action.

Fig. 5 shows the Holweckstator 74 with the channels 76. Radially symmetrically distributed inlets 11, 16, 17 in the Holweckstator 74 are arranged. These inlets 11, 16, 17 are seen in the axial direction of Holweckstators 74 at a pressure level, that is arranged lying at the same height. The inlet 16 is designed to taper in the direction of the hollow rotor 72, for example, but the inlets may also be cylindrical in cross-section, like the inlet 11.

The vacuum pump can become very hot due to high gas friction. Therefore, in certain applications, the heat must be dissipated by means of cooling. Conceivable cooling is here a convection cooling, a forced air cooling by means of a fan or a water cooling.

Fig. 6 shows a chamber 12 in which a gas load Q of 5 mbar l / s (liters per second) flows. The chamber 12 has a tap 82 to a Holweckstufe 72, 74. The single tap 82 has an inverse flow resistance, or conductance L of 4 l / s. In the pumping Holweck stage 72, 74 there is a nominal pumping speed S ₀ of 10 l / s at the axial height of the tap.

Together with the conductance of the tap 82, there is an effective pumping rate S _eff of 2.86 1 / s in the chamber 12. This results in a chamber pressure p _chamber of 1.75 mbar.

In the Holweck stage 72, 74 itself, a pressure (Holweckdruck) p _HW of 0.5 mbar sets. At the outlet of the Holweck stage, the suction capacity at the outlet S _{0 outlet} = 5 l / s. Thus, the pressure in the Holweck stage (outlet pressure Holweck stage) p _outlet = 1 mbar.

The pumping direction runs in the direction of arrow E.

According to Fig. 7 an embodiment of the invention with two outlets 80, 82 is shown. In the chamber 12 flows a gas load Q of 5 mbar l / s. The chamber 12 has the two taps 80, 82 to the Holweckstufe 72, 74. The upper tap 82 has an inverse flow resistance or conductance L ₁ of 4 l / s. In the pumping Holweckstufe 72, 74 there is a nominal pumping speed S _0-1 of 10 l / s at the axial height of the upper tap. Along with the conductance of the upper tap 82, there is an effective pumping rate S _{eff- 1} of 2.86 1 / s at the upper tap 82 of the chamber 12.

The lower tap 80 has an inverse flow resistance or conductance L ₂ of 4 l / s. In the pumping Holweck stage 72, 74 there is a nominal pumping speed S _0-1 of 5 1 / s at the axial height of the lower tap.

Along with the conductance of the lower tap 80, there is an effective pumping rate S _{eff- 2} of 2.22 l / s at the lower tap 80 of the chamber 12.

This results in a total absorbency S _{eff Ges} in the chamber of 5.08 l / s. This results in a chamber pressure p _chamber of 0.98 mbar. The gas load is through the upper tap Q ₁ = 2.81 mbar l / s. The gas load through the lower tap is Q ₂ = 2.19 mbar l / s. Thus, the pressure at the upper tap in the Holweckstufe p _HW1 = 0.281 mbar. The pressure at the lower tap in the Holweck stage is p _HW2 = 1 mbar.

This results in a lower chamber pressure, a smaller gas load in the upper part of the Holweck stage, a lower pressure along the Holweck stage and a lower gas friction throughout the Holweck stage.

reference numerals

1

vacuum pump

2

chamber housing

3

cover

4

preliminary vacuum

5

chamber

6

chamber

7

chamber

8th

cover

9

outlet

10

pump housing

11

inlet

12

High vacuum chamber

13

inlet

14

Vorvakuumblende

15

cover

16

inlet

17

inlet

22

High vacuum aperture

40

pump housing

42

wave

44

camp

46

bearing bracket

48

camp

50

drive coil

52

permanent magnet

54

outlet

60

Turbo molecular pump stage

62

rotor disc

64

stator

66

spacer

70

Holweckpumpstufe

72

Holweckzylinder

74

Holweckstator

76

channels

80

inlet

82

inlet

A

arrow

B

arrow

C

arrow

D

arrow

e

arrow

Claims (15)

Vacuum pump with at least one Holweckpumpstufe with at least one Holweckstator and at least one Holweckrotor,
characterized in that in the Holweckstator (74) of at least one Holweckpumpstufe (70) at least one gas inlet (11, 13, 16, 17) is provided. Vacuum pump according to claim 1, characterized in that in the axial direction of the Holweckstators (74) at least two inlets (11, 13) are provided. Vacuum pump according to claim 1 or 2, characterized in that in the tangential direction of the Holweckstators (74) at least two inlets (11, 13, 16, 17) are provided. Vacuum pump according to claim 3, characterized in that the at least two inlets (11, 13, 16, 17) are arranged tangentially symmetrical or asymmetrical in the Holweckstator (74). Vacuum pump according to one of the preceding claims, characterized in that the at least one inlet (11, 13, 16, 17) is formed as a bore and / or slot and / or slot. Vacuum pump according to one of the preceding claims, characterized in that the inlets (11, 13, 16, 17) have the same or different cross sections. Vacuum pump according to one of the preceding claims, characterized in that each inlet (11, 13) is connected to only one chamber to be evacuated. Vacuum pump according to one of the preceding claims, characterized in that a plurality of inlets (11, 13, 16, 17) are connected to only one chamber (6) to be evacuated. Vacuum pump according to one of the preceding claims, characterized in that the vacuum pump (1) has at least one additional turbomolecular pumping stage (60). Vacuum pump according to claim 9, characterized in that in the Holweckstator (74) at least two inlets (11, 13, 80, 82) are arranged, and that the inlet (13, 80) in the axial direction of the vacuum pump (1) closer is arranged on the turbomolecular pumping stage (60), is designed as an inlet (11, 80) arranged in the region of molecular flow. Vacuum pump according to claim 9, characterized in that in the Holweckstator (74) at least two inlets (11, 13, 80, 82) are arranged, and that the inlet (11, 82), in the axial direction of the vacuum pump (1) on away from the turbomolecular pumping stage (60) is formed as an arranged in the region of a Knudsen flow inlet (11, 82). Vacuum pump according to one of the preceding claims, characterized in that the at least one inlet (11, 82) in the high vacuum region has a larger cross section than the at least one inlet (13, 80) in the pre-vacuum region. Vacuum pump according to one of the preceding claims, characterized in that at the at least one inlet (11, 13, 80, 82) a pressure of 1 to 100 Pascal is applied. Vacuum pump according to one of the preceding claims, characterized in that the inlets (16) in the direction of the Holweckrotors (72) are tapered. Vacuum pump according to one of the preceding claims, characterized in that the Holweckstator (74) channels (76), and that the at least one inlet (11, 13, 16, 17, 80, 82) is arranged in the region of a channel bottom or that at least one inlet (11, 13, 16, 17, 80, 82) is arranged exclusively in a channel bottom or that all inlets (11, 13, 16, 17, 80, 82) are arranged in the region of a channel bottom.

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