Holweck Vacuum Pump

Abstract

A Holweck vacuum pump includes a pump rotor (16) having a rotating tube (24), a respective pump stator (12,14) comprising a helical thread groove (21,23) on the radial inside and outside of said rotor tube (24), and an inlet-side rotor blade disk (28) provided with a supporting ring (30) which supports said rotor tube (24). The blades (18) of said blade disk include rotor-side shoulders (40) which support the supporting ring (30).

Description

[0001] The invention relates to a Holweck vacuum pump comprising a pump rotor and a rotating tube.

[0002] From WO 2004/055375 A1 a two-pass Holweck vacuum pump is known which comprises a pump stator radially inside and outside the rotor tube, said pump stator being respectively defined by a helical thread groove. For improving the pumping properties, a rotor blade disk is provided on the inlet side, said rotor blade disk comprising a supporting ring which supports the rotor tube. The axial length of the supporting ring is larger than that of the blades of the blade disk such that the supporting ring penetrates the blades, i.e. radially separates the blades into two sections. A portion of the supporting ring axially extends from the plane of the rotor blade. At the cantilevered portion of the supporting ring the rotor tube is fastened by being fitted to the outside of the supporting ring, for example. All forces acting between the supporting ring and the rotor tube are directly transmitted to the blades of the blade disk. Tests have revealed that in particular the radial and tangential forces produced by the centrifugal forces exert a considerable mechanical stress on the blades and in particular the supporting ring, and reduce their service life.

[0003] It is an object of the invention to provide a two-pass Holweck vacuum pump with an improved service life of the blade disk.

[0004] According to the invention, this object is achieved through the features of claim 1.

[0005] In the Holweck vacuum pump according to the invention, the blades of the blade disk comprise rotor-side proximal shoulders which support the supporting ring. The supporting ring no longer axially projects beyond the blades but is radially inwardly supported by a corresponding stepped shoulder defined in the blades. The blades thus have a larger axial length radially inside the supporting ring than radially outside the supporting ring. The shoulders of the blades are configured such that the supporting ring bears on the radial outside of the stepped shoulder. Thus the supporting ring is supported essentially over its overall axial length by the blades of the blade disk. The blade structure supporting the supporting ring is considerably strengthened such that the forces acting between the blades and the supporting ring result in lower local peak stresses acting on the blades. The rotor tube is pushed from radially outside onto the portion of the supporting ring supported by the blades. The rotor tube, which is preferably made from a lightweight material highly resistant to tensile strength, embraces the supporting ring such that the rotor tube is supported to withstand the high centrifugal forces occurring at the high rotational speed of several 10,000 rpm. This allows the tangential forces generated in the supporting ring to be kept at such a low level that the supporting ring is capable of withstanding correspondingly high rotational speeds.

[0006] Preferably, the supporting ring does not axially extend into the non-stepped region of the blades. The axial length of the supporting ring approximately corresponds to the axial length of the axial steps of the blades. The major portion of the blades is not penetrated by the supporting ring over their overall radial length. Thus it is ensured that forces acting between the rotor tube and the supporting ring are directly applied to the blades only in the region of the blade shoulders, but not to the overall axial length of the blades. The limitation of the axial extension of the supporting ring to the axial length of the shoulder ensures that the overall axial length of the supporting ring is supported on the outside by the rotor tube to withstand high centrifugal forces.

[0007] According to a preferred embodiment, the blades of the blade disk comprise intake-side (distal) stepped shoulders which support a backing ring. The stepped shoulders supporting the backing ring are thus axially arranged opposite the stepped shoulders of the blades supporting the supporting ring, while the axially intermediate region does not comprise any step and supporting ring. When the rotor tube is clamped to the outside of the supporting ring, a corresponding backing ring can compensate for a non-uniform stress exerted on the blades by the clamped rotor tube. In this manner, the backing ring improves the symmetry of the forces applied to the blades.

[0008] Preferably, the axial length of the blades radially decreases from the shoulder towards the inside. The contour of the adjacent inner pump stator is correspondingly adapted to this. The axial length of the blades radially decreasing towards the inside allows the inner geometry to be kept at as optimum a level as possible in terms of flow when the blades are sufficiently rigid. This allows higher intakes capacities to be realized.

[0009] According to a preferred embodiment, the rotor tube is made from a fiber-reinforced material. In particular non-metallic materials are suitable, for example a carbon fiber-reinforced plastic material. Fiber-reinforced non-metallic materials are relatively lightweight while offering a high mechanical rigidity, in particular a high tensile strength. The rotor tube made from a fiber-reinforced material can thus be rotated at high rotational speeds without its diameter increasing to a considerable extent. This fact is of great importance to the realization of small gaps between rotor and stator. Further, the high tensile strength ensures that the rotor tube is also capable of supporting the backing ring against destructive tangential forces.

[0010] Preferably, the threads of the thread grooves, that is their thread bottoms, radially taper from the inlet towards the outlet. Thus the depth and the cross section of the thread groove decrease from the inlet towards the outlet. Therefore the inlet cross section of the two Holweck stages or passes is relatively large such that the intake capacity of the Holweck stage is enhanced.

[0011] Two embodiments of the invention will now be described in greater detail with reference to the drawings in which:

[0012] FIG. 1 shows a longitudinal section of a Holweck vacuum pump comprising a blade disk provided with a supporting ring, and

[0013] FIG. 2 shows a longitudinal section of a Holweck vacuum pump comprising a blade disk provided with a supporting ring and a backing ring.

[0014] FIGS. 1 and 2 show a Holweck vacuum pump 10,50 comprising two parallel Holweck pump stages 12,14. On the inlet side the two Holweck vacuum pumps 10,50 comprise a respective rotor blade disk 28,28' having a respective plurality of blades 18,58.

[0015] The two Holweck pump stages 12,14 are essentially defined by a radially outer pump stator 20, a radially inner pump stator 22 and a rotating rotor tube 24 arranged between the two stators 20,22. Both the inner and the outer pump stator 20,22 comprise a helical thread groove 21,23 whose respective groove bottom radially tapers from the outlet.

[0016] The pump rotor 16 essentially comprises a shaft 26 supported by roller bearings and/or magnetic bearings, a hub 27, the blades 18, a supporting ring 30 and the rotor tube 24. The pump rotor 56 of the vacuum pump 50 shown in FIG. 2 further comprises a second backing ring 60. The hub 27, the blades 18 and the supporting ring 30 and possibly the supporting ring 60 are formed in one piece and are made from aluminum, but may also be manufactured as individual components and then be assembled. In particular the supporting ring 60 may be manufactured as a separate component and then be attached to the blades 58. The rotor tube 24 is made from a fiber-reinforced material, for example a carbon fiber-reinforced plastic material.

[0017] On the rotor side the blades 18,58 comprise a stepped shoulder 40 which supports the supporting ring 30. The axial shoulder length approximately equals the axial length of the supporting ring 30. In the direction of the pump inlet the supporting ring 30 does not axially extend into the blade 18 such that the radial spaces between the blades 18 outside the shoulders 40 are radially continuous. The supporting ring 30 is circular cylindrical and supports the rotor tube 24 which is clamped or pressed to the supporting ring 30.

[0018] The axial length of the blades 18 radially decreases from the shoulder 40 towards the inside. However, the axial length of the blades 18 near the hub exceeds the axial length of the blades 18 radially outside the shoulders 40 and/or the supporting ring 30.

[0019] In the Holweck vacuum pump 50 of FIG. 2 the blades 58 comprise a second shoulder 62 on the inlet side, which supports the backing ring 60. In the inlet-side region, too, the axial length of the blades 58 continuously decreases towards the hub 27.

[0020] By providing a shoulder 40 at the blades 18, the supporting ring 30 is supported in the best manner possible in the region in which it supports the rotor tube 24. Since this allows the supporting ring 30 not to penetrate the blades 18 in the inlet-side region, the application of forces transmitted between the rotor tube 24, the supporting ring 30 and the shoulders 40 is considerably reduced. Further, the generation of tangential forces in the supporting ring 30 is considerably reduced since the rotor tube 24 radially supports the supporting ring 30 over its overall axial length against the centrifugal forces.

Claims

1. A Holweck vacuum pump comprising a pump rotor having a rotating tube and an inlet-side rotor blade disk provided with a supporting ring which supports said rotor tube, a respective pump stator arranged radially inside and outside said rotor tube and provided with a helical thread groove, and blades of said blade disk defining rotor-side shoulders which support said supporting ring.

2. The Holweck vacuum pump according to claim 1, wherein the supporting ring does not axially extend into a non-stepped region of the blades.

3. The Holweck vacuum pump according to claim 2, wherein the rotor tube covers an overall axial length of the supporting ring.

4. The Holweck vacuum pump according to claim 1, wherein the blades of the blade disk also define inlet-side shoulders which support a backing ring.

5. The Holweck vacuum pump according to claim 1, wherein an axial length of the blades respectively radially decreases from the shoulder towards the inside.

6. The Holweck vacuum pump according to claim 1, wherein the rotor tube is made from a fiber-reinforced material.

7. The Holweck vacuum pump according to claim 1, wherein the stator includes thread grooves which radially taper from the inlet towards the outlet.

8. The Holweck vacuum pump according to claim 1, wherein the rotor tube is made of carbon fiber-reinforced plastic material.

9. A Holweck vacuum pump comprising: a stator including an inner helical thread and an outer helical thread; a rotor including a blade disc having a plurality of blades, the blades defining shoulders; a supporting ring mounted to the blade shoulders; and a rotor tube supported by the supporting ring and extending between the inner helical threads and the outer helical threads of the stator.

10. The Holweck pump according to claim 9 wherein the blades further define inlet-side shoulders and further including: a backing ring supported by the inlet-side shoulders.