Turbomolecular vacuum pump and method for assembling same

Abstract

To propose a turbo molecular vacuum pump with low manufacturing costs. Each annular stator stage (9) of a vacuum pump (1) is composed of two radially opposed stator half sectors (9a, 9b), each including a finned sector (20) and a spacer sector (21) arranged around the finned sector. The spacer sector (21) abuts against a spacer sector (21) of another annular stator stage (9) or against a first annular edge (22) of a housing (8) located on the discharge port (5) side. Each spacer sector (21) is formed by a half ring from which fins extend, the fins being regularly distributed around the inner circumference of said half ring to form the finned sector (20).

Description

[Technical field]

[0001] The present invention relates to a turbomolecular vacuum pump and also to a method for assembling a turbomolecular vacuum pump. [Background technology]

[0002] To generate a high vacuum in the chamber, it is necessary to use a turbomolecular vacuum pump, in which a rotor rotates within a stator at high speeds, e.g., 30,000 revolutions per minute or more. This turbomolecular pump typically has a multi-stage peripheral stator with fins that engage between the fins of a central multi-stage rotor.

[0003] The multi-stage rotor of a turbomolecular pump is comprised of a number of axially aligned rotor stages, each of which extends substantially radially from a central ring and comprises a number of rotor fins regularly distributed about the periphery of the central ring, the assembly being mounted for rotation about a single axis of rotation and driven by a motor means. The multi-stage stator comprises an axial series of a plurality of annular stators each forming a stator stage, each stator stage being formed by an annular rim having a plurality of substantially radially inclined fins extending therefrom. The inclined fins of one stator stage are engaged between the inclined fins of two consecutive rotor stages.

[0004] According to a first prior art stator structure, a stator is manufactured by sequentially assembling multiple finned stator sectors around a monolithic rotor, the multiple finned stator sectors are radially assembled between two consecutive finned rotor stages, and an annular spacer is axially engaged between two consecutive finned stator sector stages, and the spacer is sandwiched around the upstream stator sector and the downstream stator sector.

[0005] Obviously, such a structure is difficult to assemble, requires components to be sized accurately enough that the sum of the dimensional tolerances is less than the axial dimensional tolerance of the rotor to avoid contact between the rotor fins and the stator fins during operation of the pump, and results in relatively high manufacturing costs which it is desirable to reduce.

[0006] A second prior art stator structure is formed by radially assembling two half stators, each consisting of a semi-cylindrical half-shell with a number of stator fins extending radially inwardly, arranged in a series of multiple stator stages that overlap the fins of multiple rotor stages. The two integral half stators eliminate the need to stack multiple parts one on top of the other, allowing the components of the turbomolecular pump structure to be manufactured with less strict tolerances. However, the manufacture of the half stators by machining is relatively complex and expensive, so the advantages of this pump structure are limited.

[0007] One of the aims of the present invention is to propose a turbomolecular vacuum pump which at least partially overcomes the drawbacks of the prior art and which is in particular inexpensive to manufacture.

[0008] To this end, the invention relates to a turbomolecular vacuum pump comprising a stator and a rotor arranged to rotate within said stator, said stator comprising: a casing having a housing that opens to a suction port of the vacuum pump; a high-pressure base in which a discharge port of the vacuum pump is formed; and 1. A turbomolecular vacuum pump comprising at least two annular stator stages housed within the housing of the casing and respectively arranged between two successive finned rotor stages of the rotor, each annular stator stage is formed of two radially opposed stator half-sectors each including a finned sector and a spacer sector disposed around the finned sector; The spacer sector abuts against the spacer sector of another annular stator stage or a first annular edge of the housing arranged on the discharge port side, the vacuum pump further comprises an annular resilient device, one side of which is held on a second annular edge of the housing located on the suction port side and the other side of which is held on the spacer sector of the lamination of the stator half sector; The laminations of the stator half-sectors are held in the housing by compression of the annular resilient device by axial clamping of the casing on the high pressure base of the stator.

[0009] Unlike the first prior art structure using annular spacers, the two laminations of the present invention do not have exactly the same height due to manufacturing variations caused by machining tolerances (maximum 1mm difference between the two laminations), so that when assembled, the casing cannot rest flat against the laminations to hold them in the stator. However, this difference is compensated for by an annular elastic device that allows the casing to support the two laminates even if they are misaligned in height. This structure reduces the manufacturing cost of the turbomolecular pump since the manufacturing precision of the components is not so high, and also reduces the number of parts to be assembled when assembling the turbomolecular pump compared to the first prior art structure using finned sectors and a separate annular spacer inserted between the two annular stator stages.

[0010] Moreover, with such a construction, the stator half-sectors are separate elements which are easier to manufacture as compared to the second prior art construction having a one-piece half-stator. This is because the stator half-sectors can be manufactured by stamping or casting, which can significantly reduce manufacturing costs compared to manufacturing a stator cut from a block. The location of the annular resilient device on the suction port side of the vacuum pump also provides good thermal contact between the last annular stator stage (high pressure side), the first annular edge, and the high pressure base. Specifically, if the stator of the vacuum pump is typically configured to be heated by the high pressure base, heat can be transferred to the annular stator stage by thermal conduction within the stator without the obstruction of the annular resilient device. For this purpose, the turbomolecular vacuum pump may for example be equipped with a heating device arranged to heat the stator to a temperature between 120°C and 200°C, for example 150°C.

[0011] If the vacuum pump is not configured to be heated, the heat stored in the finned sectors is more efficiently released by thermal conduction to the high pressure base, thus allowing greater passage of the pumped gas flow through the vacuum pump. Furthermore, the use of a metallic annular resilient device avoids the use of elastomeric materials, which have the disadvantage of being prone to outgassing and increasing the critical vacuum pressure.

[0012] The vacuum pump may further include one or more of the features described below, either alone or in combination. Each spacer sector is formed, for example, from a half ring from which the fins extend and are regularly distributed on the inner circumference of the half ring to form a finned sector, which includes the respective inner half ring joining the opposite ends of the fins, the spacer sector, the finned sector and the inner half ring of the respective stator half sector, and is made as a single piece. The stator half-sectors are preferably axially and angularly aligned within each lamination.

[0013] The annular resilient device is made, for example, from stainless steel. The annular resilient device is formed, for example, from a corrugated metal wire. The radial surface of the spacer sector abutting a spacer sector of another annular stator stage or the first annular edge of the housing may be flat. The radial surfaces of the spacer sectors of the first two stator half-sectors facing the annular resilient device may be flat.

[0014] The diameter of the annular resilient device may be sized about the diameter of the casing housing. According to another example, the spacer sectors of the first two stator half-sectors may have an inner annular shoulder and the diameter of the annular resilient device may be dimensioned about the annular shoulder. The first annular edge is formed, for example, by a spacer. The rotor may include a skirt downstream of the finned rotor stage configured to rotate against the spiral groove of the stator.

[0015] The present invention also relates to a method for assembling the above turbomolecular vacuum pump, comprising the steps of: Inserting an annular elastic device into the housing against a second annular edge located on the suction port side of the vacuum pump; inserting a stack of angularly aligned stator half-sectors into the housing and interposing the annular resilient device between the second annular edge and a spacer sector of the stack; Axial clamping the casing against the high pressure base of the stator; The annular resilient device is compressed to retain the laminations of the stator half-sectors within the housing. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing an axial cross section of a turbomolecular vacuum pump according to a first embodiment of the present invention. [Diagram 2] FIG. 2 shows the vacuum pump of FIG. 1 with its components disassembled. [Diagram 3] FIG. 2 is an enlarged view of a stator half-sector of the vacuum pump of FIG. 1. [Figure 4] FIG. 5 is a schematic cross-sectional view of a detailed portion of a vacuum pump according to a second embodiment of the present invention. [Diagram 5]FIG. 2 shows an axial cross-sectional view of a turbomolecular vacuum pump according to another embodiment of the invention.

[0017] Further advantages and features will become apparent from the following description and drawings of specific, but non-limiting, embodiments of the invention. In each figure, identical elements are given the same reference numbers. The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference number relates to the same embodiment or that a feature applies to only one embodiment. Individual features of different embodiments can also be combined or interchanged to produce other embodiments. "Upstream" refers to an element that is disposed before another element with respect to the direction of flow of the gas being pumped. Conversely, "downstream" refers to an element that is disposed after another element with respect to the direction of flow of the gas being pumped. The axial direction defines a direction parallel to the axis of rotation II of the vacuum pump rotor, and the radial direction defines a direction perpendicular to said axial direction.

[0018] FIG. 1 shows a turbomolecular vacuum pump according to a first embodiment of the present invention. The turbomolecular vacuum pump 1 comprises a stator 2 within which a rotor 3 rotates at high speed, for example 30,000 revolutions per minute or more. The gas to be pumped enters the turbomolecular vacuum pump 1 at an inlet port 4 and leaves at an outlet port 5. During operation, the outlet port 5 is connected to a primary pumping system.

[0019] The stator 2 includes a casing 2a in which a housing 8 is formed, and at least two annular stator stages 9 housed within the housing 8. The stator 2 also includes a high-pressure base 2b in which the discharge port 5 of the vacuum pump 1 is formed.

[0020] A housing 8 formed at least within the casing 2a has one end that opens to the suction port 4 of the vacuum pump 1. The housing 8 has a cylindrical periphery. The casing 2a is provided with an annular inlet flange 6 surrounding an intake port 4, allowing the vacuum pump 1 to be connected, for example by means of screws 7, to the chamber to be depressurised (see FIG. 2).

[0021] A number of annular stator stages 9 housed within a housing 8 of the casing 2 a are each arranged between two successive finned rotor stages 10 of the rotor 3 . A plurality of annular stator stages 9 and a plurality of finned rotor stages 10 are arranged one after the other axially along the rotation axis II of the rotor 3 in the turbomolecular vacuum pump 1. The rotor 3 includes, for example, four or more stages, for example, 4 to 12 stages of finned rotor stages 10 (12 stages in the example shown in FIG. 1). Each finned rotor stage 10 of the rotor 3 has angled blades extending generally radially from a hub 11 of the rotor 3. The rotor 3 is attached to a drive shaft 12 of the vacuum pump 1, for example by means of screws 13. The blades are regularly distributed around the circumference of the hub 11. The rotor 3 further comprises an internal bowl 15 coaxial with the axis of rotation II, which is arranged facing a bell 17 of the stator 2 and projects below the rotor 3. During operation, the rotor 3 rotates within the stator 2 without the internal bowl 15 coming into contact with the bell 17.

[0022] The rotor 3 is, for example, formed as one piece. The rotor 3 is driven to rotate within the stator 2 by an internal motor 16 of the vacuum pump 1. The motor 16 is, for example, arranged within a bell 17 of the stator 2, which is itself arranged below the internal bowl 15 of the rotor 3, the drive shaft 12 passing through the bell 17 of the stator 2. The rotor 3 is guided laterally and axially by magnetic or mechanical bearings 18 arranged in the stator 2 and supporting a drive shaft 12 for driving the rotor 3. For example, there is a first bearing 18 supporting and guiding a first end of the drive shaft 12 at the bottom of the bell 17 of the stator 2, and a second bearing 18 supporting and guiding a second end of the drive shaft 12 arranged at the top of the bell 17. The bell 17 of the stator 2 may house other electrical or electronic components, such as, for example, position sensors.

[0023] As can be seen more clearly in Figures 2 and 3, each annular stator stage 9 is formed by two stator half-sectors 9a, 9b, respectively, radially opposite each other (in the same axial row). The first annular stator stage 9 (or low pressure annular stator stage) refers to the annular stator stage 9 located on the side of the suction port 4 (in other words, the first annular stator stage 9 through which the pumped gas passes), and the last annular stator stage 9 (or high pressure annular stator stage) refers to the annular stator stage 9 located on the side of the discharge port 5 (in other words, the last annular stator stage through which the pumped gas passes).

[0024] Each stator half-sector 9a, 9b comprises a finned sector 20 and a spacer sector 21 (or outer half-rim) located around each finned sector 20 (see FIG. 3). More specifically, each spacer sector 21 is formed by forming a finned sector 20, from which the fins extend substantially radially and which are regularly distributed on the inner circumference of said half ring. The finned sector 20 may also comprise a respective inner half ring (or inner half rim) joining the opposite ends of the fins. The spacer sector 21, the finned sector 20 and the inner half ring of each stator half sector 9a, 9b are formed in one piece.

[0025] The finned sectors 20 of the annular stator stage 9 engage between the blades of two consecutive finned rotor stages 10. The blades of the rotor 3 and the fins 20 of the stator 2 are angled to direct the pumped gas molecules towards the discharge port 5. The spacer sectors 21 abut against spacer sectors 21 of another annular stator stage 9 or against a first annular edge 22 of the housing 8 located on the discharge port 5 side (see Figures 1 and 2). This first annular edge 22 is formed, for example, by a spacer (see FIG. 2), which makes it possible to adjust the axial clearance between the stator 2 and the rotor 3 in order to avoid contact between the fins of the rotor 3 and the fins of the stator 2 during operation of the vacuum pump 1. The spacer is made from a material that is a good thermal conductor, such as, for example, aluminum. The stator half-sectors 9a, 9b are stacked on top of each other to form two completely independent laminations (see FIG. 2). The stator half-sectors 9a, 9b are axially and angularly aligned within each lamination, in other words, they are not angularly offset from one stage to another, thus avoiding the risk of overhangs due to tolerance differences when assembling one stator half-sector on top of the other.

[0026] The vacuum pump 1 further comprises, on the one side, a second annular edge 24 of the housing 8 of the casing 2a located on the suction port 4 side and, on the other side, an annular elastic device 23 (or elastic load washer or elastic preload washer) made of metal, which is interposed between the housing 8 and the spacer sectors 21 of the stack of stator half-sectors 9a, 9b. The second annular edge 24 of the housing 8 of the casing 2a is formed, for example, by a shoulder (diameter reduction) between the housing 8 and the suction port 4. The laminations of the stator half-sectors 9 a , 9 b are held in the housing 8 by compression of an annular elastic device 23 by axial clamping of the casing 2 a on the high pressure base 2 b of the stator 2 .

[0027] The axial fastening of the casing 2a to the high pressure base 2b is achieved, for example, by a number of screws 25 regularly distributed around the circumference of the radial interface located between the casing 2a and the high pressure base 2b (see FIG. 1 ), which are inserted axially into the radial interface, for example through an annular flange of the high pressure base 2b. During assembly, the annular resilient device 23 is inserted into the housing 8 against a second annular rim 24 located on the side of the suction port 4 of the vacuum pump 1 . The laminations of the two angularly aligned stator half-sectors 9a, 9b are then inserted into the housing 8 so that the annular resilient device 23 is interposed between the second annular edge 24 of the laminations and the spacer sector 21. The casing 2a is then clamped axially against the high pressure base 2b of the stator 2, compressing the annular resilient device 23 and retaining the stack of stator half-sectors 9a, 9b within the housing 8. The assembly of the laminations of the stator half-sectors 9a, 9b in the casing 2a allows the laminations to be centered. Clamping the casing 2a with the high-pressure base 2b makes it possible to axially fix the laminations in the housing 8 via the annular elastic device 23.

[0028] The laminations of the two stator half sectors 9a, 9b of the annular stator stage 9 are independent of each other. Unlike the first prior art construction using an annular spacer, the two laminations of the present invention do not have exactly the same height due to manufacturing differences caused by machining tolerances (max. 1 mm difference between the two laminations), so that during assembly the casing 2a cannot rest flat on the laminations and hold them in the stator 2. However, this difference is compensated by the annular elastic device 23, which allows the casing 2a to rest on the two laminations even though they are offset in height. This structure does not require as strict a requirement for the manufacturing precision of the components, thereby reducing the manufacturing costs of the turbomolecular pump 1. Furthermore, the number of parts to be assembled when assembling the turbomolecular pump 1 is reduced compared to the first prior art structure using multiple finned sectors and separate multiple annular spacers inserted between the two annular stator stages.

[0029] Moreover, such a structure, i.e. the stator half sectors 9a, 9b being separate elements, is easier to manufacture compared to the second prior art structure having a one-piece half stator, since each stator half sector 9a, 9b can be manufactured by stamping or casting, which significantly reduces manufacturing costs compared to manufacturing several stators cut from one block.

[0030] By arranging the annular elastic device 23 on the suction port 4 side of the vacuum pump 1, good thermal contact is also achieved between the final annular stator stage 9 (high pressure side), the first annular edge 22 formed by one spacer, and the high pressure base 2b. Specifically, if the stator 2 of the vacuum pump 1 is configured to be heated, typically resulting in a high risk of condensation of the pumped gas due to the high pressure in the high pressure base 2b, the heat from the heated high pressure base 2b is transferred to the annular stator stage 9 by thermal conduction in the stator 2 without the obstruction of the annular elastic device 23 arranged on the opposite side. This makes it possible to improve the heating characteristics of the stator 2 of the vacuum pump 1 and to limit the deposition of condensable substances. For this purpose, the turbomolecular vacuum pump 1 may, for example, be equipped with a heating device configured to heat the stator 2 to a temperature between 120 ° C. and 200 ° C., for example 150 ° C. If the vacuum pump 1 is not configured to be heated, the heat stored in the finned sectors 20 is efficiently released to the high-pressure base 2b by thermal conduction, thus allowing greater passage of the gas flow to be pumped through the vacuum pump 1.

[0031] The annular elastic device 23 is made of stainless steel, for example martensitic stainless steel. The use of a metallic annular elastic device makes it possible to avoid the use of elastomeric materials, which have the disadvantage of escaping gases and increasing the critical vacuum pressure. Furthermore, the metallic annular elastic device 23 makes it possible to ensure thermal continuity between the stator half-sectors 9a, 9b, which are in contact with each other at the spacer sector 21 and, via the metallic annular elastic device 23, with the second annular edge 24 of the casing 2a. The annular elastic device 23 is for example formed by a corrugated metal wire, which for example comprises at least two corrugations, at least one for each lamination of the stator half-sectors 9a, 9b, in this case eight corrugations (see FIG. 2). The thickness of the metal wire corresponds, for example, to the thickness of the spacer sector 21. The cross section of the annular elastic device 23 is, for example, circular, elliptical, square or rectangular. By way of example, the annular elastic device 23 can exert a load force in the range of 1000N to 30000N.

[0032] The radial surfaces of the spacer sectors 21 which abut against a spacer sector 21 of another annular stator stage 9 or against a first annular edge 22 of the housing 8 are preferably flat. The radial surfaces of the spacer sectors 21 of the first two stator half-sectors 9a, 9b facing the annular resilient device 23 and the second annular edge 24 of the housing 8 may also be flat. This facilitates compression of the annular resilient device 23 and mutual contact between the stator half-sectors 9a, 9b in the stack. The diameter of the annular elastic device 23 is determined, for example, around the diameter of the housing 8 of the casing 2a, which allows costs to be kept low. Therefore, the annular part has a diameter slightly larger than the diameter of the housing 8 and is held in the radial direction by the peripheral wall of the housing 8 (see FIG. 1).

[0033] Figure 4 shows another embodiment in which the spacer sectors 21 of the first two stator half-sectors 9a, 9b have an inner annular shoulder 26. The diameter of this annular resilient device 23 is dimensioned so that it is centred on the annular shoulder 26. For this reason, the diameter of the annular part is slightly smaller than the diameter of the annular shoulder 26 so that it is radially retained by the annular shoulder 26 of the first two stator half-sectors 9a, 9b.

[0034] FIG. 5 shows another embodiment of the turbomolecular vacuum pump 1 of the present invention. In this example, the turbomolecular pump 1 is called a hybrid and, like the first example, comprises one turbomolecular stage 30 and one molecular stage 31 located downstream of the turbomolecular stage 30 in the direction of flow of the pumped gas (indicated by the arrow in FIG. 5 ). The pumped gas enters at the intake port 4, passes first through the turbomolecular stage 30, then through the molecular stage 31, and is then discharged towards the discharge port 5.

[0035] In the molecular stage 31, the rotor 3 comprises, downstream of the finned rotor stage 10, one skirt 32, called the Holweck skirt, formed for example of a smooth cylinder which rotates facing the spiral groove 33 of the stator 2 formed in the high pressure base 2b. The spiral groove 33 of the stator 2 makes it possible to compress the pumped gas and direct it towards the discharge port 5. Other features of this second embodiment are similar to the first embodiment described. [Explanation of symbols]

[0036] 1. Turbomolecular vacuum pump 2 Stator 2a Casing 2b High Pressure Base 3 Rotor 4 Intake port 5 Discharge port 8. Housing 9 Circular Status Stage 9a, 9b Stator half sectors 10 Finned rotor stage 12 Drive shaft 20 Finned Sector 21 Spacer Sector 22 First annular edge 23 Annular Elastic Device 24 Second annular edge 26 Circular shoulder

Claims

1. A rotor (3) configured to rotate within a stator (2), The stator (2) is a casing (2a) in which a housing (8) opening to a suction port (4) of the vacuum pump (1) is formed, a high-pressure base (2b) in which a discharge port (5) of the vacuum pump (1) is formed, A turbomolecular vacuum pump having at least two annular stator stages (9) housed in the housing (8) of the casing (2a) and respectively arranged between two successive finned rotor stages (10) of the rotor (3), each annular stator stage (9) is constituted by two radially opposed stator half-sectors (9a, 9b) each including a finned sector (20) and a spacer sector (21) arranged around the finned sector (20); the spacer sector (21) abuts against the spacer sector (21) of another annular stator stage (9) or against a first annular edge (22) of the housing (8) located on the discharge port (5) side; each spacer sector (21) is formed as a half ring with fins extending therefrom, said fins being regularly distributed around the inner circumference of said half ring to form said finned sector (20); The finned sector (20) includes an inner half-ring joining opposite ends of the fins; the spacer sector (21), the finned sector (20) and the inner half ring of each of the stator half sectors (9a, 9b) are integrally formed, The vacuum pump (1) further comprises an annular elastic device (23) held on one side on a second annular edge (24) of the housing (8) located on the side of the suction port (4) and on the other side on the spacer sector (21) of the stack of the stator half-sectors (9a, 9b), 1. A turbomolecular vacuum pump comprising: a lamination of stator half-sectors (9a, 9b) held in the housing (8) by compression of the annular elastic device (23) by axial clamping of the casing (2a) on the high-pressure base (2b) of the stator (2).

2. 2. A turbomolecular vacuum pump according to claim 1, characterized in that the stator half-sectors (9a, 9b) are axially and angularly aligned within each lamination.

3. 2. A turbomolecular vacuum pump according to claim 1, characterized in that the annular resilient device (23) is made of a corrugated metal wire.

4. 2. A turbomolecular vacuum pump according to claim 1, characterized in that the annular elastic device (23) is made of stainless steel.

5. 2. Turbomolecular vacuum pump according to claim 1, characterized in that the stator half-sectors (9a, 9b) are manufactured by stamping.

6. Turbomolecular vacuum pump according to claim 1, characterized in that the stator half-sectors (9a, 9b) are manufactured by casting.

7. 2. The turbomolecular vacuum pump according to claim 1, characterized in that the radial surface of the spacer sector (21) of the other annular stator stage (9) or the spacer sector (21) abutting the first annular edge (22) of the housing (8) is flat.

8. 2. A turbomolecular vacuum pump according to claim 1, characterized in that the radial surfaces of the spacer sectors (21) of the first two stator half-sectors (9a, 9b) facing the annular elastic device (23) are flat, the diameter of the annular elastic device (23) being dimensioned around the diameter of the housing (8) of the casing (2a).

9. 2. A turbomolecular vacuum pump according to claim 1, characterized in that the spacer sectors (21) of the first two stator half-sectors (9a, 9b) have an inner annular shoulder (26) and the diameter of the annular elastic device (23) is dimensioned around the annular shoulder (26).

10. 2. The turbomolecular vacuum pump of claim 1, wherein said first annular edge (22) is formed by a spacer.

11. 2. The turbomolecular vacuum pump of claim 1, wherein the rotor (3) comprises a skirt (32) downstream of the finned rotor stage (10) adapted to rotate facing the spiral groove (33) of the stator (2).

12. A method for assembling a turbomolecular vacuum pump (1) according to claim 1, comprising the steps of: inserting the annular elastic device (23) into the housing (8) opposite the second annular edge (24) on the suction port (4) side of the vacuum pump; inserting the stack of angularly aligned stator half-sectors (9a, 9b) into the housing (8) such that the annular resilient device (23) is inserted between the second annular edge (24) and the spacer sector (21); 1. A method for assembling a turbomolecular vacuum pump (1), characterized in that the casing (2a) is axially clamped to the high pressure base (2b) of the stator (2) to hold the stack of stator half-sectors (9a, 9b) in the housing (8) by compressing the annular elastic device (23).

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