Drag Vacuum Pump

Abstract

A friction vacuum pump (10) comprises a housing (12) defining a vaneless pump stator (30), a rotor drive and a rotor support which rotatably supports a pump rotor (16) provided with a vane (18). The housing (12) surrounds the overall axial length of the pump rotor (16), the rotor drive and the rotor support. Prior art housings are of multipart configuration and thus comprise seals between the housing portions. The seals are difficult to coat and may be or become locations where leaks occur. In contrast, the housing (12) is of one-piece configuration such that, in any case, the region of the housing (12) which is in contact with the vacuum gas is free of seals.

Description

BACKGROUND

The invention relates to a friction vacuum pump comprising a housing having a vaneless pump stator, a rotor drive and a rotor support.

The housing of such friction vacuum pumps, for example turbomolecular pumps or Holweck pumps, surrounds the overall axial length of the pump rotor, the rotor drive and the rotor support. From US 2005/220607 a screw pump is known whose housing essentially comprises three axially adjacent portions which are joined together, for example screwed together, to form a housing. The three housing portions are a stator housing portion, an outlet housing portion which supports a cartridge comprising the motor and/or the support, and a bearing housing portion. Between two adjacent housing portions respective seals are arranged for ensuring the required tightness, which seals may be difficult to coat or impossible to coat at all with a corrosion-inhibiting coating material, for example. Even the greatest care taken during the assembly work cannot completely prevent leaks from occurring in the sealing region. Further, the temperature behavior of the overall housing is inhomogeneous due to the multipart configuration of the housing.

From U.S. Pat. No. 6,514,035 a screw pump is known whose housing is composed of two portions, wherein the discharge-side housing portion is integrally formed with a bearing and motor housing. The two-part configuration of the housing leads to the aforementioned drawbacks.

It is an object of the invention to improve the physical properties of a friction vacuum pump.

SUMMARY

In the friction vacuum pump according to the invention, the housing is configured in one piece over its overall axial length such that the one-piece housing surrounds the overall axial length of the pump rotor, the rotor drive and the rotor support. The one-piece configuration of the housing ensures a homogeneous temperature behavior of the housing. Since no seals are provided, tightness of the housing can be ensured even over a long term. It is not necessary that the housing itself is composed of a plurality of parts, such that no assembly work and resultant sources of defects occur. Since no seals are provided in the housing region, the housing inside can be easily and continuously coated. The friction vacuum pump housing comprises only an end-side cover, for example, which has no load-bearing function and does thus not require any particular precision during assembly work.

The one-piece configuration of the housing improves numerous physical properties of the friction vacuum pump, in particular the temperature behavior, the tightness and the quality of coating of the housing inside.

According to a preferred aspect, the rotor support and the rotor drive are arranged in a cartridge supported by the housing and surrounded over its overall axial length by the housing. As used herein, the term cartridge refers to a device designed as a cartridge housing which is of pot-shaped or completely closed configuration and in which a shaft of the rotor support is rotatably supported, said shaft being adapted to be driven by a rotor drive disposed in the cartridge. The support and the drive are arranged in a completely preassembled condition in the closed or nearly closed cartridge. When assembling the friction vacuum pump, first the shaft extending from the cartridge can be connected with the pump rotor, and this structure can then be inserted into the housing, wherein the cartridge is mounted in the housing interior. In this manner, the friction vacuum pump can be easily and reliably assembled. The one-piece configuration of the friction vacuum pump housing and the provision of a single drive and support cartridge result in a modular design of the friction vacuum pump. Both features together facilitate the assembly and disassembly work, which, in turn, improves the assembly accuracy, reduces the assembly expenditure, and facilitates and accelerates the maintenance and repair work.

Preferably, the cartridge comprises a pot-shaped housing which is integrally formed with the friction vacuum pump. When the rotor support and the rotor drive are inserted in the pot-shaped housing, the pot opening is closed by a cartridge cover. The one-piece configuration of friction vacuum pump housing and pot-shaped cartridge housing facilitates the assembly work, reduces leaks, and in particular ensures a more precise positioning of the cartridge and/or the rotor drive and the rotor support.

According to a preferred aspect, at least 50% of the axial length of the cartridge is surrounded by the pump rotor, i.e. at least half the axial length of the cartridge axially extends into the pot-shaped pump rotor. In this manner, a friction vacuum pump configuration which is compact with regard to the overall axial length is realized.

According to a preferred aspect, a portion of the cartridge housing is defined by the friction vacuum pump housing. The cartridge housing comprises two sections, i.e. one arranged on the rotor side as seen from the mounting location of the cartridge at the housing, and one arranged remote from the rotor. The cartridge section arranged remote from the rotor may be defined by the friction vacuum-pump housing, i.e. the pot-shaped cartridge housing does not comprise a cartridge cover but is terminated by the friction vacuum pump housing. Thus, the total number of components is reduced.

According to a preferred aspect, the housing comprises a circular shoulder at its inside, against which the cartridge preferably bears on the suction side and to which the cartridge is fastened. The cartridge, together with the rotor, is inserted into the housing preferably from the suction side. The cartridge is placed upon the circular shoulder and fastened by suitable fastening means, for example threaded screws, preferably from the discharge side of the shoulder. The circular shoulder is easy to produce and allows the cartridge to be fastened in a gastight manner to the housing.

Preferably, the pump rotor is a Holweck pump rotor. The surface in the radial plane between a housing-side stator wall and a rotor-side hub may decrease towards the discharge side.

Thus the inlet cross-section of the friction vacuum pump is relatively large, which results in a relatively large gas throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described in greater detail with reference to the drawing.

The FIGURE shows a longitudinal section of the friction vacuum pump according to the invention.

DETAILED DESCRIPTION

The FIGURE shows a friction vacuum pump 10 which is a screw pump, also referred to as a Holweck pump. The friction vacuum pump 10 essentially comprises a housing 12 which narrows in a funnel-like manner towards the suction side, a cartridge 14 arranged and fastened in the housing 12, said cartridge 14 including a rotor support not shown and a rotor drive not shown, and a pump rotor 16 comprising a plurality of helically arranged vanes 18.

The housing 12 is of one-piece configuration and surrounds the overall axial length of the pump rotor 16 and the cartridge 14 including the rotor drive and the rotor support. The discharge-side end of the housing 12 is closed by a front-side housing cover 20.

In the housing 14 a circular shoulder 22 is provided at the inner circumference, on which circular shoulder 22 a corresponding circular shoulder 24 of the cartridge 14 is supported in a gastight manner. The shoulders 22,24 of the housing 12 and the cartridge 14 are screwed together.

A rotor shaft 26 extends from the suction side of the cartridge, said shaft 26 supporting the rotor 16. The rotor 16 is connected with the rotor shaft by screwing, for example.

The rotor hub 28 of the rotor 16 tapers towards the suction side. The inside of the housing 12 forms a stator wall 30 which expands towards the suction side. Due to the expansion of the inner diameter of the stator wall and the reduction of the outer diameter of the rotor hub 28 towards the suction side, the surface in the radial plane between the stator wall 30 and the rotor hub 28 increases towards the suction side and decreases towards the discharge side.

The housing 12 comprises a gas inlet 32 at its suction-side axial end. A the discharge side of the pump rotor 16 a radial gas outlet 34 is provided.

Due to its one-piece configuration the housing 12, in the portion where it encloses the vacuum, does not comprise any seal towards an adjacent housing portion. Thereby, in particular in that region of the housing 12 which is exposed to the vacuum, a homogeneous temperature behavior is achieved. Coatings of the stator wall 30 are free from discontinuities. Since no seal is provided between two housing portions, no leaks can occur.

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 friction vacuum pump comprising: a housing forming a vaneless pump stator, anda rotor drive and a rotor support which supports a pump rotor comprising a vane,wherein said housing surrounds the overall axial length of the pump rotor, the rotor drive and the rotor support, and the housing is of one-piece configuration.

2. The friction vacuum pump according to claim 1, characterized in that wherein the rotor support and the rotor drive are arranged in a cartridge which is supported by the housing and surrounded over its overall axial length by said housing.

3. The friction vacuum pump according to claim 2, wherein the cartridge comprises a pot-shaped housing which is integrally formed with the friction vacuum pump housing.

4. The friction vacuum pump according to claim 2, wherein at least 50% of the axial length of the cartridge is surrounded by the pump rotor.

5. The friction vacuum pump according to claim 2, wherein a portion of the cartridge housing is defined by the friction vacuum pump housing.

6. The friction vacuum pump according to claim 2, wherein the housing comprises a circular shoulder to which the cartridge is fastened.

7. The friction vacuum pump according to claim 1, wherein the pump rotor is a screw pump rotor.

8. The friction vacuum pump according to claim 1, the wherein a surface in a radial plane between a pump stator and a hub of the pump rotor decreases towards a discharge side.

9. A friction vacuum pump comprising: a funnel-shaped housing which tapers from an inlet end towards a discharge end, the housing being an integral one-piece construction;the one-piece housing including an integrally formed shoulder adjacent the discharge end, the shoulder being in a plane transverse to a central axis of the one-piece housing;a cartridge which houses a rotor drive and a rotor support, the cartridge being supported on the integral shoulder and extending along the central axis of the one-piece housing;a rotor having at least one vane, the rotor being supported on the rotor support and received within the housing.

10. A method of assembling the friction vacuum pump of claim 9 comprising: inserting the cartridge into the integral, one-piece housing from the inlet end;attaching the cartridge to the flange;attaching the rotor to the rotor support.