STATOR BLADE UNIT FOR A TURBOMOLECULAR PUMP

Abstract

The present invention provides a stator blade unit for a turbomolecular pump comprising an array of polymer stator blades, a turbomolecular pump including such a stator blade unit, and to a method of assembling a stator blade unit for a turbomolecular pump.

Claims

1. A stator blade unit for a turbomolecular pump comprising: an array of polymer and/or moulded stator blades comprising an inner rim and an outer rim adjoined to the array of stator blades, wherein the outer rim comprises an integrally formed spacer for preventing clashing between the stator blades and an adjacent rotor, and configured to engage with an axially adjoining stator array within a stator stack and wherein the stator blade unit comprises at least two sections, in the form of single unitary structures, arranged such that stator blades of one section are alternately arranged with stator blades of the at least one other section.

2. The stator blade unit according to claim 1 wherein the stator blades axially overlap.

3. The stator blade unit according to claim 1 wherein the inner rim is configured to couple with an inner rim of another stator blade unit.

4. The stator blade unit according to claim 1 wherein the stator blade unit is injection moulded or additive manufactured, preferably an injection moulded polymer and/or metal stator blade unit.

5. The stator blade unit according to claim 1 wherein the stator blade unit comprises polymer stator blades each comprising one or more inner polymer layers and an outermost polymer layer, wherein the outermost polymer layer comprises a polymer that is less hard than the polymer forming the one or more inner layers.

6. The stator blade unit according to claim 1 wherein the stator blade unit is substantially semi-annular.

7. The stator blade unit according to claim 6 wherein the stator blade unit is configured to mate with a second substantially semi-annular stator blade array to form an annular stator blade array.

8. The stator blade unit according to claim 1 wherein each stator blade comprises an inlet-side face and an outlet-side face and wherein the inlet-side face has a different roughness to the outlet-side face.

9. A method of manufacturing a stator blade unit for a turbomolecular pump comprising the step of injection moulding a single unitary structure comprising an array of stator blades wherein an inner rim and/or outer rim are co-moulded with the stator blades, and wherein the outer rim comprises an integrally formed spacer for preventing clashing between the stator blades and an adjacent rotor.

10. The method according to claim 9 wherein injection moulding a unitary structure comprises: injection moulding a first structure comprising an array of stator blades, injection moulding a second structure comprising an array stator blades, and combining the first and second structures to form a stator blade unit.

11. The method according to claim 10 wherein, when combined, the stator blades of the first structure are alternately arranged with stator blades of the second structure.

12. The method according to claim 9 wherein the stator blades overlap.

13. A stator blade unit manufactured according to or obtainable by the method of claim 9.

14. A stator blade unit for a turbomolecular pump wherein the stator unit comprises an array of stator blades each comprising one or more inner layers and an outermost polymer layer, wherein the outermost polymer layer comprises a polymer that is less hard than a material forming one or more of the inner layers.

15. A stator blade unit for a turbomolecular pump comprising a fluid substrate moulded or additive manufactured unitary structure comprising an array of stator blades and an outer rim, wherein the outer rim comprises an integrally formed spacer for preventing clashing between the stator blades and an adjacent rotor, said blade unit comprising at least two sections each comprising an array of stator blades arranged such that stator blades of one section are alternately arranged with stator blades of the at least one other section.

16. The stator blade unit according to claim 15 wherein the sections are single unitary structures.

17. The stator blade unit according to claim 15 wherein adjacent stator blades overlap.

18. A stator blade unit for a turbomolecular pump comprising an array of stator blades wherein a stator blade has a polymer coated edge.

19. A turbomolecular pump comprising at least one stator blade unit according to claim 1.

20. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Preferred features of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0068] FIG. 1 shows a two-part semi-annular stator array according to the invention.

[0069] FIG. 2 shows an annular stator array according to the invention.

[0070] FIG. 3 shows a stator stack according to the invention.

[0071] FIG. 4 shows a stator stack according to the invention in-situ.

[0072] FIGS. 5a and 5b show snap-fit outer rim coupling.

[0073] FIG. 6 shows a snap-fit inner rim coupling.

[0074] FIGS. 7a and 7b shows an interlocking inner rim coupling

[0075] FIGS. 8a and 8b shows an outer rim coupling and identical sections

[0076] FIG. 9 shows symmetrical blades and moulding according to the invention

DETAILED DESCRIPTION

[0077] The invention provides a stator unit 1 for a molecular pump comprising an array of polymer stator blades 2. In this example, the stator blade unit 1 is formed from at least two curved sections 3, 4 of polymer material. A suitable polymer is Vectra E130i a composite comprising glass fibre reinforced liquid crystal polymer. The curved sections 3, 4 are semi-annular, so that two stator blade units 1 are required to form an annular array 5 of stator blades 2.

[0078] With reference to FIG. 1 moulded or additive manufactured polymer stator blades are provided in two curved sections 3, 4. The two curved sections 3, 4 are of substantially the same size and width. Each section 3, 4 defines a series of regularly spaced stator blades 2. The stator blades 2 of both curved sections 3, 4 are substantially the same length, preferably such that when the sections 3, 4 are nested together their inlet-side blade tips are substantially coplanar and their outlet-side blade tips are substantially coplanar. Typically, the stator blades 2 of the outlet-side curved section 4 protrude axially from their inner rim 8 and outer rim 9 in an inlet-direction, whereas the stator blades of the inlet-side curved section 3 protrude axially from their inner rim 6 and outer rim 7 in an out-let direction. Preferably the angular pitch of the stator blades is substantially the same on both curved sections 3, 4.

[0079] As shown in the example in FIG. 9, the stator blade tip and root can be moulded to flare axially along the point of adjoinment 41 to the inner and/or outer rims 6, 7, 8, 9. This enables the polymer to flow more easily into the mould and improves the strength of the unit

[0080] The first and second curved sections 3, 4 may be brought together by inserting the stator blades of the second curved 3 section through the apertures of the first curved section 4, and vice-versa, until the inner 6 and outer rims 7 of the first curved section 3 overlay the inner 8 and outer 9 rims respectively of the second curved section 4. Accordingly, as shown in FIG. 2, an array 10 of stator blades is formed, in which the stator blades of the first curved section 3 are circumferentially alternately arranged with the stator blades of the second curved section 4. As illustrated in FIG. 2, adjacent blades may overlap. Where axial overlap is desirable, such as in the compressive stages nearer the pump outlet, preferably, the stator array is axially opaque. That is to say, no spaces are visible between the stator blades when the unit is viewed directly from above or below.

[0081] As illustrated in FIG. 2, the exemplified stator unit comprises an integrally formed spacer 11. In the example, the one curved section 3 outer rim 7 provides an upper portion of the integrally formed spacer 11, whereas the other curved section 4 provides a lower portion 9 of the integrally formed spacer 11. As shown, in FIGS. 3 and 4, in use, the integrally formed spacer 11 of a first annular stator array 5 engages with the integrally formed spacer 12 of at least one adjacent stator unit 13.

[0082] When a stator array stack 14 is assembled the integrally formed spacers 11, 12 hold the stators in position relative to the impeller rotors 15, 16, 17 and prevent engagement therebetween. Typically, during use, there is a nominal clearance of about 1 mm between the stator blades of an annular array 5 and the blades of an adjacent rotor 17 within the molecular pump, preferably the maximum clearance is from about 0.5 mm to about 2 mm. The polymer is selected to ensure that stator array 5 does not contact with the rotors 17 of the molecular pump during use.

[0083] As shown in FIG. 2, the semi-annular stator units 10, 18 couple to form an annular stator array 5. In the exemplified embodiment, because the spacer 11 is integrally formed, there are axial mating surfaces 21, 22, 23, 24 which mate at the joints 19, 20 between the first 18 and second 10 stator units. To mitigate direct leaking along the mating surfaces 21, 22, 23, 24, the stator units employ a snap-fit assembly to tightly engage the adjacent spacer rings and substantially seal the joint 19, 20.

[0084] As illustrated in more detail in FIGS. 5a and 5b, a protruding male portion 25 from a first integrally formed spacer 11 mates with a corresponding female portion 26 on the integrally formed spacing ring 12 of an adjacent stator array. Additionally, or alternatively, as illustrated in FIG. 3, the joints 19, 20 of adjacent stator arrays may be circumferentially offset, in this instance by approximately 90 degrees. This too mitigates the risk of direct leakage along the axial joints 19, 20.

[0085] By varying the circumferential off-set between the joints 19, 20 of successive annular stator arrays within the stack 14, the joints 19, 20, and/or associated snap-fit assemblies 25, 26, may advantageously be used as a reference point for positioning stator arrays 5 within the stator stack 14. In the illustrated example in FIG. 5b only a first portion of a male engagement structure 25 is adjacent mating surface 22 on the unit. A second portion of the same male engagement structure is located adjacent the corresponding mating surface on the second unit forming the remainder of the annular array.

[0086] As shown in FIGS. 8a and 8b the annular stator unit can be formed from two semi-annular units, each semi-annular unit comprising two or more sections 3, 4. In the example illustrated the sections 3, 4, 4, 3 are all identical sections, formed in the same mould, such that each semi-annular unit is formed from two identical sections 3, 4 with one section orientated in the inverted position upon the transverse face of the other section such that the stator blades 2 of one section are alternately arranged with stator blades 2 of the at least one other section.

[0087] To facilitate the use of identical sections 3, 4, as shown in FIG. 9 the cross-sectional shape of the stator blades in the identical sections is mirrored, i.e. substantially symmetrical, around its centreline between the inner and outer rims such that the blade performance is substantially the same in either orientation of the sections 3, 4.

[0088] Each section 3, 4 also has a cooperating connection mechanism 30, 31, at the circumferential end of the outer rims 7, 9. In the example shown the mechanism 30, 31 is in the form of a peg 30 and hole 31 type connection, but other connection mechanism are possible, such a dove tails. Each section 3, 4 has a peg 30 at one circumferential end and a hole 31 at the other circumferential end, such that when the two semi-annular arrays, each comprising sections 3,4 are brought together to form an annular array, the cooperation of each peg 30 being received by a hole 30, provides an additional degree of strength to the annular array. In addition, the cooperating connection mechanism 30, 31 also provides an additional seal to prevent the migration of gas axially between the joints formed between semi-annular arrays.

[0089] FIG. 6 illustrates a snap-fit assembly 27a, 27b located on the inner rims 6, 8 of a stator unit. In the example, the snap-fit 27a, 27b connects two curved sections 3, 4 of the same stator unit. As explained elsewhere in the application, physically connecting the inner rims 6, 8 improves the stiffness of the array, thereby reducing deflection during use. In particular, it reduces deflection as a result of the spring (not shown) commonly used to hold the stator stack in place within the molecular pump. Improving the stiffness of the stator is advantageous as it allows closer association of the molecular pumps components, improving pump performance.

[0090] As shown in FIGS. 7a and 7b, the inner rims 6, 8 of two interesting sections 3, 4 of a part annular stator unit can be coupled together using interlocking mechanism 28, 29, 33 located at the circumferential ends of each section 3, 4. In the example shown the interlocking mechanism 28, 29, 33, of the sections 3, 4 when coupled together, form a connection mechanism 28, 34 in the form of a circumferentially extending protrusion 28 and circumferential receiving opening 34 on the sections 3 and 4 of a semi-annular unit respectively. When two semi-annular units, both comprising sections 3 and 4, joined together with the mechanism 28, 29, 33, the connection mechanism 28, 34 of one semi annular unit cooperate with the connecting mechanism 34, 28 of the other semi annular unit respectively.

[0091] It will be appreciated that various modifications may be made to the embodiments shown without departing from the spirit and scope of the invention as defined by the accompanying claims as interpreted under patent law.

[0092] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0093] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.