Clamshell stator for a vacuum pump, vacuum pump and method of manufacture

Abstract

There is provided a method (400) of manufacturing a clamshell stator for a vacuum pump comprising providing (410) a first half-shell stator component and a second half-shell stator component, wherein the first half-shell stator component and the second half-shell stator component comprise respective first and second internal walls for defining a plurality of pump chambers having gas transfer passages arranged therebetween; boring (420) a first bore extending through one or more of the first internal walls and defining first portholes; boring (430) a second bore extending through one or more of the second internal walls and defining second portholes; arranging (440) a first sealing means and a second sealing means respectively to seal one or more of the first portholes and second portholes such that a fluid connection is provided between the outlet and inlet of adjacent pump chambers.

Description

[0001] CLAMSHELL STATOR FOR A VACUUM PUMP, VACUUM PUMP AND METHOD OF MANUFACTURE

[0002] FIELD OF THE INVENTION

[0003] The field of the invention relates to vacuum pumps, and more specifically to vacuum pumps comprising clamshell stators.

[0004] BACKGROUND

[0005] Vacuum pumps are typically employed as a component of a vacuum system to evacuate working gases from the system. These pumps can be used to evacuate fabrication equipment used in, for example, the production of semiconductors. Whilst compression from a vacuum to atmosphere may be performed in a single stage using a single pump, it is common in such applications to provide multi-stage vacuum pumps wherein each stage performs a portion of the compression range required to transition from a vacuum to atmospheric pressure.

[0006] In a clamshell vacuum pump, the stator comprises two stator halves (respectively referred to as half-shell stator components). The two half-shell stator components, when clamped together, define an internal volume therebetween that is used to house a rotor. In a multi-stage clamshell vacuum pump, the internal volume is divided into a plurality of pump chambers between the inlet port to the vacuum pump and the outlet port (or ‘exhaust’). The division of the internal volume into pump chambers is typically achieved using internal walls extending from the respective stator halves. To allow for a process gas received at the inlet port of a multi-stage vacuum pump to be be exhausted to the outlet port, the plurality of pump chambers must be in fluid connection. This is achieved through the use of gas transfer passages connecting an outlet of one pump chamber with the inlet of an adjacent pump chamber.

[0007] Corrosion resistant vacuum pumps tend to be required in applications where corrosive gases are being exhausted. Corrosive gases may arise in applications such as semiconductor manufacturing, for instance. The corrosion resistance of vacuum pump components, such as the stators, is generally achieved through the use of coatings. For instance, low alloy steel stators may need to be Nickel plated to provide the required corrosion protection. For pumps operating at high temperatures (i.e., above 150°C) all surfaces that will come into contact with corrosive process gases will need to be machined before plating. This ensures good adhesion of the coating (i.e., the Nickel plating) to the stator.

[0008] To machine the gas transfer ports themselves, the current manufacturing process involves drilling the stator halves from both their top and bottom sides. As a result of this machining process, access holes are made in the stator components that extend all the way through the stator component, for each gas transfer port. Resultantly, the pump chambers end up in fluid connection with the exterior environment through each access hole, a feature that would render the vacuum pump inoperable. Resultantly, post-machining, corrosion resistant cover plates are fitted to the exterior of the clamshell stator components using o-rings to seal the plurality of access holes. The o-rings themselves are typically seated in grooves and purged with a gas such as Nitrogen for protection from the corrosive process gases.

[0009] The introduction of multiple access holes through current machining processes and hence the need for cover plates and purged o-rings, tends to introduce additional cost and complexity to vacuum pump designs.

[0010] It is desirable to provide a clamshell stator for a vacuum pump and a method of manufacture that mitigates these issues.

[0011] SUMMARY OF THE INVENTION

[0012] In a first aspect, there is provided a clamshell stator for a vacuum pump, comprising: a first half-shell stator component and a second half-shell stator component for attaching together to define an interior volume for housing a rotor, wherein the first half-shell stator component comprises a first port at a first end of the clamshell stator and through which a process gas can be received into the interior volume, wherein the second half-shell stator component comprises a second port at a second end of the clamshell stator and through which the process gas can be exhausted from the interior volume; wherein the first half-shell stator component and the second half-shell stator component comprise respective first and second internal walls for dividing the internal volume into a plurality of pump chambers having gas transfer passages arranged therebetween, each of the pump chambers having an inlet and an outlet, wherein the plurality of pump chambers comprise at least a first chamber in fluid connection with the first port and a second chamber in fluid connection with the second port; wherein the first half-shell stator component comprises a first bore extending from the second end of the clamshell stator through one or more of the first internal walls, the first bore defining respective first portholes in an exterior wall of the first half-shell stator and in the one or more of the first internal walls, wherein the second half-shell stator component comprises a second bore extending from the first end of the clamshell stator through one or more of the second internal walls, the second bore defining respective second portholes in an exterior wall of the second half-shell stator component and in the one or more of the second internal walls, such that each of the gas transfer passages provides a fluid connection between adjacent pump chambers of the plurality of pump chambers; wherein the clamshell stator further comprises a first sealing means and a second sealing means arranged respectively to seal one or more of the first portholes and one or more of the second portholes such that the fluid connection provided by each of the gas transfer passages is a fluid connection between the outlet and inlet of adjacent pump chambers.

[0013] The inventor has found that by providing the first bore and the second bore, a fluid connection can be achieved between adjacent pump chambers via a gas transfer passage. This tends to be achievable by boring into the half-shell stator components longitudinally. This tends to result in only one access hole in the exterior wall of each of the half-shell stator components, in contrast to the relatively large number of access holes created when boring transversely using current manufacturing methods.

[0014] The clamshell stator design of the first aspect tends to allow for improved heat transfer across a stator between the first end and second end. This tends to be because, in the longitudinal direction, the top and bottom parts of the stator components are uninterrupted i.e., they form a solid continuous mass of material uninterrupted by access holes extending transversely to the longitudinal axis.

[0015] The clamshell stator design of the first aspect tends to allow for heater elements to be embedded into the half-shell stator components more conveniently without their location being restricted by the prevalence of access holes.

[0016] The clamshell stator design of the first aspect tends to mitigate the need for relatively large and expensive corrosion resistant cover plates, supplementary o-rings, and the additional purging required for the o-rings.

[0017] The clamshell stator design of the first aspect tends to reduce the overall cost and complexity of a clamshell vacuum pump.

[0018] The first bore may extend entirely through the first half-shell stator; and / or the second bore may extend entirely through the second half-shell stator. In this regard, all of the pump chambers may be in fluid connection with each other via their gas transfer passages. Having the first and / or second bores extend entirely through their respective half-shell stators (i.e., from the exterior at the first end to the exterior at the second end) provides for easier manufacture because two access holes are provided in each half-shell stator component i.e., a first porthole is provided in each end exterior wall of the first half-shell stator component, with similar for the second portholes in the second half-shell stator component.

[0019] The first bore may extend partially through the first half-shell stator component and / or the second bore may extend partially through the second half-shell stator component. This tends to reduce the portholes in the exterior walls of the half-shell stator components to one i.e., one first porthole in the exterior wall of the first half-shell stator component and one second porthole in the exterior wall of the second half-shell stator component. This tends to reduce the requirement (material, cost) of the first sealing means and second sealing means for sealing the exterior walls. The first bore may extend through the first half-shell stator component to the first internal wall adjacent the first chamber; and / or the second bore may extend through the second half-shell stator component to the second internal wall adjacent the second chamber. The first bore thus does not extend through the first internal wall and is a ‘blind’ hole. The second bore thus does not extend through the second internal wall and is a ‘blind’ hole. This further tends to reduce the demand on the first sealing means and the second sealing means by reducing the number of respective portholes requiring sealing in order to provide the desired gas flow path through the pump chambers.

[0020] The first portholes may have a diameter of less than or equal to 40mm; and / orthe second portholes may have a diameter of less than or equal to 40mm.

[0021] The first sealing means may comprise one or more first plugs and / or the second sealing means comprise one or more second plugs. The first and second plugs tend to provide a low-cost sealing means for the clamshell stator. The first and second plugs may be fitted into the first and second portholes using a suitable drift and press, optionally starting at one end of the clamshell stator and progressing along the clamshell stator longitudinally. The first and second plugs may be located manually at each position prior to pressing.

[0022] The first plugs and / or the second plugs may comprise stainless steel. For instance, 304 stainless steel may be used. A seven-stage pump (i.e., a pump with seven pump chambers) may require twelve stainless steel plugs which may be core plugs that are readily available at relatively low cost. The stainless steel plugs tend to be able to be manufactured to be sufficiently thin so as to not distort the internal walls of the half-shell stator components or damage any coating or plating of the stator (such as Nickel plating) when pressed into the portholes.

[0023] The first plugs and / or second plugs may be configured to provide an interference fit to their respective first portholes and / or second portholes. By providing an interference fit, the first plugs and second plugs tend to be retained without movement during operation of a vacuum pump comprising the clamshell stator. The first plugs may seal first portholes in the exterior wall of the first halfshell stator component. The second plugs may seal second portholes in the exterior wall of the second half-shell stator component. The first plugs and / or second plugs may not only seal portholes in the internal walls but may also / alternatively seal portholes in the exterior walls.

[0024] The first sealing means may comprise a first baffle. The second sealing means may comprise a second baffle. A baffle tends to restrain a fluid from flowing, in this instance through one or more of the first portholes and / or one or more of the second portholes. A baffle tends to be a more appropriate sealing means if distortion of the internal / exterior walls of the stator is of concern when pressing plugs into the portholes.

[0025] The first baffle may comprise an elongate member having a slide-fit with the first portholes. The second baffle may comprise an elongate member having a slide-fit with the second portholes. The baffles may thus be slid into the respective first or second portholes as a one-piece element (i.e., a cylindrical element conformal to the circular cross-section portholes. The baffles may be slid into their respective half-shell stator components before assembly (i.e., before a rotor is fitted into the stator).

[0026] The first baffle and the second baffle may comprise one or more cut-outs for providing the fluid connection between the outlet and the inlet of adjacent pump chambers via the gas transfer passages. The elongate baffles when slid into the respective portholes of the first half-shell stator component and second half-shell stator component, may close off all of the portholes. The cut-outs tend to allow for the fluid connection provided by the gas transfer passages through the appropriate portholes of the first and second portholes.

[0027] The first baffle may be secured to the first exterior wall of the first halfshell stator component using a first fastening means. The second baffle may be secured to the second exterior wall of the second half-shell stator component using a second fastening means. The first fastening means and second fastening means tend to mitigate axial translation and rotation of the first baffle and second baffle. The first fastening means and second fastening means may comprise an engraving or channel in the exterior of the baffles that is substantially coplanar and aligned with a similar engraving / channel in the exterior wall of the half-shell stator components. An elongate member may be screwed into the engraving or channel to extend across the baffle and exterior wall to mitigate rotation and axial movement.

[0028] One or more heater elements may be embedded in the first half-shell stator component or second half-shell stator component. The heater elements may be aligned with the gas transfer passages. This tends to be achievable owing to the lack of transverse access holes in the stator components.

[0029] The clamshell stator may comprise a stainless-steel stator. The clamshell stator may comprise a low-alloy steel stator. The clamshell stator may be Nickel plated. The clamshell stator disclosed herein tends to be suitable for use at temperatures greater than or equal to 150°C.

[0030] According to a second aspect, there is provided a vacuum pump comprising: the clamshell stator of the first aspect; and a rotor housed within the interior volume.

[0031] According to a third aspect, there is provided a method of manufacturing a clamshell stator for a vacuum pump, comprising: providing a first half-shell stator component and a second half-shell stator component for attaching together to define an interior volume for housing a rotor, wherein the first halfshell stator component comprises a first port at a first end of the clamshell stator through which a process gas can be received into the internal volume, wherein the second half-shell stator component comprises a second port at a second end of the clamshell stator through which the process gas can be exhausted from the internal volume, wherein the first half-shell stator component and the second half-shell stator component comprise respective first and second internal walls for dividing the internal volume into a plurality of pump chambers having gas transfer passages arranged therebetween, each of the pump chambers having an inlet and an outlet, wherein the plurality of pump chambers comprise at least a first chamber in fluid connection with the first port and a second chamber in fluid connection with the second port; boring a first bore extending from the second end of the clamshell stator through one or more of the first internal walls of the first half-shell stator component, the first bore defining respective first portholes in an exterior wall of the first half-shell stator and in the one or more of the first internal walls; boring a second bore extending from the first end of the clamshell stator through one or more of the second internal walls of the second half-shell stator component, the second bore defining respective second portholes in an exterior wall of the second half-shell stator component and in the one or more of the second internal walls, such that each of the gas transfer passages provides a fluid connection between adjacent pump chambers of the plurality of pump chambers; arranging a first sealing means and a second sealing means respectively to seal one or more of the first portholes and one or more of the second portholes such that the fluid connection provided by each of the gas transfer passages is a fluid connection between the outlet and inlet of adjacent pump chambers.

[0032] The term ‘boring’ includes, for instance, drilling or other similar machining techniques.

[0033] It will be appreciated that particular features of different aspects of the invention tend to share the technical effects and benefits of corresponding features of other aspects of the invention. More specifically, the methods described herein share the same technical benefits as the clamshell stator and vacuum pump described herein.

[0034] It will also be appreciated that the use of the terms “first” and “second”, and the like, are merely intended to help distinguish between similar features and are not intended to indicate a relative importance of one feature over another, unless otherwise specified.

[0035] The term half-shell stator component and half-shell stator may be used interchangeably.

[0036] BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0038] Figure 1A shows an example, in perspective view, of a prior art clamshell stator of a vacuum pump. Figure 1 B shows an example, in a further perspective view, of the prior art clamshell stator of the vacuum pump of Figure 1 A.

[0039] Figure 1 C shows an example, in cross-sectional view, of the clamshell stator of the prior art vacuum pump of Figure 1 A.

[0040] Figure 2A shows an example, in cross-sectional view, of a clamshell stator in accordance with aspects of the present disclosure.

[0041] Figure 2B shows an example, in cross-sectional view, of the clamshell stator of Figure 2A further comprising first and second plugs.

[0042] Figure 2C shows an example, in cross-sectional view, of the clamshell stator of Figure 2A further comprising first and second baffles.

[0043] Figure 3A shows an example, in perspective view, of a vacuum pump in accordance with aspects of the present disclosure.

[0044] Figure 3B shows an example, in cutaway perspective view, of the vacuum pump of Figure 3A.

[0045] Figure 4 show an example of a method in accordance with aspects of the present disclosure.

[0046] DETAILED DESCRIPTION

[0047] Figure 1A shows an example, in perspective view, of a prior art clamshell stator 100 of a vacuum pump. The clamshell stator 100 has a first half-shell stator component 110 (or ‘upper’ half-shell stator component) and a second half-shell stator component 120 (or ‘lower half-shell stator component) attached together to define an interior volume for housing a rotor (not visible). The first half-shell stator component 110 comprises a first port 112 at a first end 102 of the clamshell stator 100 and through which a process gas can be received into the interior volume of the clamshell stator 100. The second half-shell stator component 120 comprises a second port (not visible) at a second end 104 of the clamshell stator 100 and through which the process gas can be exhausted from the interior volume. The first half-shell stator component 110 and the second half-shell stator component 120 comprise respective first and second internal walls for dividing the internal volume of the shell stator 100 into a plurality of pump chambers (not visible) having gas transfer passages (not visible) arranged therebetween, each of the pump chambers having an inlet and an outlet, wherein the plurality of pump chambers comprise at least a first chamber in fluid connection with the first / inlet port 112 and a second chamber in fluid connection with the second / exhaust port.

[0048] During manufacture of the half-shell stator components 110, 120, the plurality of pump chambers and gas transfer passages are machined to interconnect with each other, thus achieving a fluid connection between the first port and second port when the shell stator 100 is in use. Currently, the half-shell stator components 110, 120 are machined transversely to the longitudinal axis ‘A’ of the shell stator 100. A consequence of the current manufacturing process is that a plurality of access holes 130 are created through the exterior wall of the half-shell stator components 110, 120. The plurality of access holes 130 extend entirely through the half-shell stator components 110, 120, with each access hole 130 providing access to the interconnection between an internal pump chamber and a gas transfer passage. For the first half-shell stator component 110 there are six access holes 130.

[0049] Each access hole 130 creates a fluid connection between the internal volume of the shell stator 100 and the external ambient environment. Such a fluid connection renders the shell stator 100 and associated vacuum pump inoperable. To seal the access holes 130 an external cover plate 140 is fastened over the access holes 130. O-rings 150 are provided between the external cover plate 140 and access holes 130. The o-rings 150 are Viton o- rings which may be susceptible to degradation during the operating conditions of the shell stator 100 and associated vacuum pump (i.e., owing to exposures to temperatures of operation and the corrosive process gases). The o-rings 150 are consequently seated in grooves in the first half-shell stator component 110, the grooves being provided with a purge gas such as Nitrogen. Furthermore the cover plate 140 may also be required to be manufactured from a corrosion resistant material for similar reasons.

[0050] The plurality of access holes 130, external cover plate 140, o-rings 150 and purge gas, all tend to add complexity to the design of a shell stator 100. Furthermore, the additional components all tend to increase manufacturing costs. In addition, the additional components all tend to require maintenance and replacement over time, further tending to increase through-life servicing requirements.

[0051] Figure 1 B shows an example, in a further perspective view, of the prior art clamshell stator 100 of Figure 1A. The second half-shell stator component 120 is shown with a similar plurality of access holes 130 machined therethrough. A further external cover plate 140 seals the access holes 130, having o-rings 150 arranged therebetween. The second port 122 for exhausting process gases is also shown.

[0052] Figure 1 C shows an example, in cross-sectional view, of the prior art clamshell stator 100 of Figure 1A. The first half-shell stator component 110 and second half-shell stator component 120 are shown separated by longitudinal axis ‘A. The first half-shell stator component 110 comprises the first port 112 at first end 102 of clamshell stator 100 for receiving process gases. The second half-shell stator component 120 comprises the second port 122 at the second end 104 of clamshell stator 100 through which process gases are exhausted.

[0053] The clamshell stator 100 comprises a plurality of pump chambers 161 , 162, 163, 164, 165. The plurality of pump chambers 161 , 162, 163, 164, 165 comprise a first / inlet chamber 161 and a second / outlet chamber 165. The first chamber 161 is in fluid connection with the first port 112. The second chamber 165 is in fluid connection with the second port 122.

[0054] Arranged between the pump chambers 161 , 162, 163, 164, 165 are gas transfer passages 171 , 172, 173, 174. The gas transfer passages 171 , 172, 173, 174 provide a fluid connection between respective outlets and inlets of adjacent pump chambers. By way of example, gas transfer passage 171 connects the outlet 161 b of first pump chamber 161 with the inlet 162a of the adjacent pump chamber 162. During manufacture of the clamshell stator 100, each half-shell stator component 110, 120 is machined transversely to longitudinal axis A. It is possible to machine / drill the pump chambers 161 , 162, 163, 164, 165 from one side of each of half-shell stator component 110, 120. For the first half-shell stator component 110, this involves machining / drilling linearly from the plane comprising axis A, transversely through first half-shell stator component 110. For the second half-shell stator component 120, this involves machining / drilling linearly from the plane comprising axis A, transversely through the half-shell stator component 120. The gas transfer passages 171 , 172, 173, 174, can be similarly machined.

[0055] However, the above-mentioned linear machining / drilling from just one side of the half-shell stator components 110, 120 is not sufficient to connect the gas transfer passages 171 , 172, 173, 174 with their adjacent pump chambers 161 , 162, 163, 164, 165. By way of example, the region 181 between pump chamber 161 and gas transfer passage 171 cannot be accessed. Furthermore, the region 182 between gas transfer passage 171 and pump chamber 162 cannot be accessed. To overcome this issue, the prior art machining / drilling methods require machining / drilling from the other side of half-shell stator components 110, 120, creating access holes 130. By machining the access holes 130 the gas transfer passages 171 , 172, 173, 174 can be fluidly connected with the pump chambers 161 , 162, 163, 164, 164. However, the access holes 130 also fluidly connect the interior of the clamshell stator 100 to the ambient environment. To mitigate this latter outcome, the external cover plates 140 are attached to the half-shell stator components 110, 120 to seal the access holes 130. O-rings 150 are used between the cover plates 140 and halfshell stator components 110, 120 to provide an effective seal.

[0056] Figure 2A shows an example, in cross-sectional view, of a clamshell stator 200 in accordance with aspects of the present disclosure.

[0057] The clamshell stator 200 comprises a first half-shell stator component 210 and a second half-shell stator component 220 for attaching together to define an interior volume for housing a rotor (not visible). The clamshell stator 200 is split into the first half-shell stator component 210 and the second half- shell stator component 220 at the plane comprising axis A. The half-shell stator components 210, 220 are made from a low alloy steel. The half-shell stator components 210, 220 are Nickel plated for corrosion resistance.

[0058] The first half-shell stator component 210 comprises a first port 212 at a first end 202 of the clamshell stator 200 and through which a process gas can be received into the interior volume of the clamshell stator 200. The second half-shell stator component 220 comprises a second port 222 at a second end 204 of the clamshell stator 200 and through which the process gas can be exhausted from the interior volume of the clamshell stator 200. The first port 212 is substantially tubular having a diameter of 40mm. The second port 222 is substantially tubular having a diameter of 40mm.

[0059] The first half-shell stator component 210 and the second half-shell stator component 220 comprise respective first 214 and second internal walls 224 for dividing the internal volume into a plurality of pump chambers 261 , 262, 263, 264, 265 having gas transfer passages 271 , 272, 273, 274 arranged therebetween. Each of the pump chambers 261 , 262, 263, 264, 265 has an inlet 261a, 262a, 263a, 264a, 265a and an outlet 261 b, 262b, 263b, 264b, 265b. The plurality of pump chambers 261 , 262, 263, 264, 265 comprise at least a first chamber 261 in fluid connection with the first port 212 and a second chamber 265 in fluid connection with the second port 222. The plurality of pump chambers 261 , 262, 263, 264, 265 gradually decrease in volume from the first end 202 to second end 204. Each pump chamber 261 , 262, 263, 264, 265, in- use, contains a rotor blade of a rotor (not shown).

[0060] The first half-shell stator component 210 comprises a first bore 282 extending from the second end 204 of the clamshell stator 200 through one or more of the first internal walls 214. The first bore 282 and second bore 284 are substantially tubular with a circular cross-section. The bores 282, 284 have diameters of approximately 40mm. The first bore 282 defines respective first portholes 282a in an exterior wall 216 of the first half-shell stator 210 and in the one or more of the first internal walls 214. The second half-shell stator component 220 comprises a second bore 284 extending from the first end 202 of the clamshell stator 200 through one or more of the second internal walls 224. The second bore 284 defines respective second portholes 284a in an exterior wall 226 of the second half-shell stator component 220 and in the one or more of the second internal walls 224. The gas transfer passages 271 , 272, 273, 274 resultantly provide a fluid connection between adjacent pump chambers of the plurality of pump chambers 261 , 262, 263, 264, 265.

[0061] The first bore 282 extends through the first half-shell stator component 210 to a first internal wall 214a adjacent the first chamber 261 . The second bore 284 extends through the second half-shell stator component 220 to a second internal wall 224a adjacent the second chamber 265. The first bore 282 and second bore 284 are thus ‘blind’ holes. The first bore 282 and second bore 284 have been machined / drilled longitudinally i.e. , parallel to axis ‘A’.

[0062] In the clamshell stator 200 a first sealing means and second sealing means are required to seal the first portholes 282a and second portholes 284a to achieve the correct flow of process gases between the inlets 261a, 262a, 263a, 264a, 265a and the outlets 261 b, 262b, 263b, 264b, 265b of the pump chambers 261 , 262, 263, 264, 265. Two exemplary embodiments of sealing means will now be described.

[0063] Figure 2B shows an example, in cross-sectional view, of the clamshell stator 200 of Figure 2A. The clamshell stator 200 further comprises first and second sealing means comprising respective first plugs 292 and second plugs 294. The first plugs 292 and second plugs 294 are arranged respectively to seal one or more of the first portholes 282a and one or more of the second portholes 284a such that the fluid connection provided by each of the gas transfer passages 271 , 272, 273, 274 is a fluid connection between the outlet 261 b, 262b, 263b, 264b of an adjacent pump chamber and the inlet 262a, 263a, 264a, 265a of another adjacent pump chamber.

[0064] The first plugs 292 and second plugs 294 comprise stainless steel. The first plugs 292 and second plugs 294 are configured to provide an interference fit to their respective first portholes 282a and second portholes 284a. The plugs 292, 294 may comprise a substantially circular cross-section conformal to the portholes 282a, 284a. The plugs 292, 294 may comprise a peripheral rim that gradually increases their diameter such that when fitted into the portholes 282a, 284a, an interference fit can be achieved. The plugs 292, 294 may be fitted with a drift and press starting at one end 202, 204 and gradually working along the stator 200. The plugs 292, 294 may be ‘core plugs’ and may be positioned manually before pressing into place. The plugs 292, 294 may have a material thickness of less than or equal to 1 mm. This tends to allow the plugs 292, 294 to be pressed into the portholes 282a, 284a whilst not damaging coatings or plating on the stator components 210, 220.

[0065] The first plugs 292 seal first portholes 282a in the exterior wall 216 of the first half-shell stator component 210. The second plugs 294 seal second portholes 284a in the exterior wall 226 of the second half-shell stator component 220. In total, four first plugs 292 and four second plugs 294 are used in the stator 200 (i.e. , in a stator comprising five pump chambers 261 , 262, 263, 264, 265. The number of pump chambers is not intended to be limiting and is provided purely for example purposes.

[0066] When the clamshell stator 200 is in-use, a process gas (such as gases from a semiconductor manufacturing apparatus) is received into the first chamber 261 through the inlet 261a. The process gas is pumped (by a rotor, not visible) through outlet 261b into gas transfer passage 271. The process gas enters the adjacent chamber 262 via inlet 262a. The process gas is pumped through outlet 262b into gas transfer passage 272. The process gas enters the adjacent chamber 263 via inlet 263a. The process gas is pumped through outlet 263b into gas transfer passage 273. The process gas enters the adjacent chamber 264 via inlet 264a. The process gas is pumped through outlet 264b into gas transfer passage 274. The process gas enters the adjacent chamber 265 via inlet 265a. The process gas is pumped through outlet 265b and exhausted from the stator 200.

[0067] Comparing the clamshell stator 200 of Figure 2B to the prior art clamshell stator 100 of Figure 1 C, it is evident that no external cover plate 140 with o- rings 150 and purge gassing is required. This is because the plurality of access holes 130 drilled transversely to axis ‘A’ are not required for each half-shell stator 210, 220 in the stator 200 of Figure 2B. Instead, one porthole 282a in exterior wall 216 and one porthole 284a in exterior wall 226 are plugged with a respective first plug 292 and second plug 294. This tends to provide more uniform external longitudinal walls of half-shell stator components 210, 220, improving heat transfer. This further tends to free-up the external longitudinal walls of half-shell stator components 210, 220 for positioning / embedding of heater elements. This further tends to provide a simpler to manufacture and maintain clamshell stator, reducing overall cost.

[0068] Figure 2C shows an example, in cross-sectional view, of the clamshell stator 200 of Figure 2A. The clamshell stator 200 further comprises an alternative first and second sealing means comprising a first baffle 292’ and a second baffle 294’. The first baffle 292’ and second baffle 294’ are arranged respectively to seal one or more of the first portholes 282a and one or more of the second portholes 284a such that the fluid connection provided by each of the gas transfer passages 271 , 272, 273, 274 is a fluid connection between the outlet 261 b, 262b, 263b, 264b of an adjacent pump chamber and the inlet 262a, 263a, 264a, 265a of another adjacent pump chamber.

[0069] The first baffle 292’ comprises an elongate member having a slide-fit with the first portholes 282a. The second baffle 294’ comprises an elongate member having a slide-fit with the second portholes 284a.

[0070] The first baffle 292’ and the second baffle 294’ comprise one or more cut-outs 292a’, 294a’ for providing the fluid connection between the outlet 261 b, 262b, 263b, 264b and the inlet 262a, 263a, 264a, 265a of adjacent pump chambers via the gas transfer passages 271 , 272, 273, 274. The baffles 292’, 294’ may be cylindrical bars of elongate material, such as stainless steel, that has been machined to provide the cut-outs 292a’, 294a’.

[0071] The first baffle 292’ may be secured to the first exterior wall 216 of the first half-shell stator component 210 using a first fastening means 292b’. The second baffle 294’ is secured to the second exterior wall 226 of the second halfshell stator component 220 using a second fastening means 294b’. The first and second fastening means 292b’, 294b’ comprise a groove extending a across an exterior face of the baffles 292’, 294’. Said groove also extending into the exterior walls 216, 226. A first rod is arranged into the groove, extending from the first exterior wall 216 across the exterior face of the baffle 292’ and into the first exterior wall 216 on an opposing side of the face of the baffle 292. This tends to prevent axial rotation of the first baffle 292’. The first rod is bolted, screwed, or otherwise fastened to both the first baffle 292’ and first exterior wall 216. This tends to prevent axial displacement of the first baffle 292’. A similar arrangement is provided for the second fastening means 294b for the second baffle 294’.

[0072] When the clamshell stator 200 is in-use, a process gas (such as gases from a semiconductor manufacturing apparatus) is received into the first chamber 261 through the inlet 261a. The process gas is pumped (by a rotor, not visible) through outlet 261b into gas transfer passage 271. The process gas enters the adjacent chamber 262 via inlet 262a. The process gas is pumped through outlet 262b into gas transfer passage 272. The process gas enters the adjacent chamber 263 via inlet 263a. The process gas is pumped through outlet 263b into gas transfer passage 273. The process gas enters the adjacent chamber 264 via inlet 264a. The process gas is pumped through outlet 264b into gas transfer passage 274. The process gas enters the adjacent chamber 265 via inlet 265a. The process gas is pumped through outlet 265b and exhausted from the stator 200.

[0073] Comparing the clamshell stator 200 of Figure 2C to the prior art clamshell stator 100 of Figure 1 C, it is evident that no external cover plate 140 with o-rings 150 and purge gassing is required. This is because the plurality of access holes 130 drilled transversely to axis ‘A’ are not required for each halfshell stator 210, 220 in the stator 200 of Figure 2C. Instead, one porthole 282a in exterior wall 216 and one porthole 284a in exterior wall 226 are sealed with a respective first baffle 292’ and second baffle 294’. This tends to provide more uniform external longitudinal walls of half-shell stator components 210, 220, improving heat transfer. This further tends to free-up the external longitudinal walls of half-shell stator components 210, 220 for positioning / embedding of heater elements. This further tends to provide a simpler to manufacture and maintain clamshell stator, reducing overall cost.

[0074] Figure 3A shows an example, in perspective view, of a vacuum pump

[0075] 300 in accordance with aspects of the present disclosure. The vacuum pump 300 comprises a clamshell stator 301 which may be the clamshell stator 200 of Figure 2A. The first sealing means and second sealing means are removed. A first half-shell stator component 310 and second half-shell stator component 320 are visible. Within the stator 301 are rotors 303. The vacuum pump 300 is shown from the perspective of a first end 304 and viewed longitudinally (i.e., looking along axis ‘A’ of Figure 2A, for instance). A first bore 382 and second bore 384 are shown as being circular and having a diameter of approximately 40mm.

[0076] Figure 3B shows an example, in cutaway perspective view, of the vacuum pump 300 of Figure 3A. The first half-clam shell component 310 is shown attached to the second half-clam shell component 320 defining a plurality of pump chambers 360 therebetween. In the clamshell stator 301 there are seven pump stages and hence seven pump chambers. Each of the pump chambers 360 contains part of rotors 303. Arranged between the pump chambers 360 are gas transfer passages 370 in fluid connection with the adjacent pump chambers 360. A first baffle 392 has been slid into the first bore 382, with a second baffle 394 slid into the second bore 384.

[0077] Figure 4 show an example method 400 of manufacturing a clamshell stator for a vacuum pump. The clamshell stator may be the clamshell stator 200 of Figure 2 or the clamshell stator 301 of Figure 3. The vacuum pump may be the vacuum pump 300 of Figure 3, for instance.

[0078] A first step 410 comprises providing a first half-shell stator component and a second half-shell stator component for attaching together to define an interior volume for housing a rotor, wherein the first half-shell stator component comprises a first port at a first end of the clamshell stator through which a process gas can be received into the internal volume, wherein the second halfshell stator component comprises a second port at a second end of the clamshell stator through which the process gas can be exhausted from the internal volume, wherein the first half-shell stator component and the second half-shell stator component comprise respective first and second internal walls for dividing the internal volume into a plurality of pump chambers having gas transfer passages arranged therebetween, each of the pump chambers having an inlet and an outlet, wherein the plurality of pump chambers comprise at least a first chamber in fluid connection with the first port and a second chamber in fluid connection with the second port.

[0079] A further step 420 comprises boring a first bore extending from the second end of the clamshell stator through one or more of the first internal walls of the first half-shell stator component, the first bore defining respective first portholes in an exterior wall of the first half-shell stator and in the one or more of the first internal walls.

[0080] A further step 430 comprises boring a second bore extending from the first end of the clamshell stator through one or more of the second internal walls of the second half-shell stator component, the second bore defining respective second portholes in an exterior wall of the second half-shell stator component and in the one or more of the second internal walls, such that each of the gas transfer passages provides a fluid connection between adjacent pump chambers of the plurality of pump chambers.

[0081] A further step 440 comprises arranging a first sealing means and a second sealing means respectively to seal one or more of the first portholes and one or more of the second portholes such that the fluid connection provided by each of the gas transfer passages is a fluid connection between the outlet and inlet of adjacent pump chambers.

[0082] In addition to the specific advantages already described herein, the above-described clamshell stator and vacuum pump tends to allow for operation at temperatures equal to or in excess of 150°C, for instance at 160°C, 170°C, 180°C, 190°C, 200°C and 250°C.

[0083] Although illustrative examples of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise examples and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents. Whilst the examples described herein may refer to specific dimensions, it will be appreciated that the dimensions may vary dependent upon the specific application of the clamshell stator and vacuum pump.

[0084] Whilst the examples described herein may refer to particular cross- sectional shapes of portholes, plugs or baffles, any particular cross-sectional shape may be used provided that the cross-sectional shape of the plugs or baffles cooperates with the portholes. A circular cross-section may be preferred for manufacturing purposes.

[0085] Whilst the examples described herein may refer to the use of baffles, alternatively plugs can be used to seal the portholes. A combination of baffles and plugs may also be used.

[0086] Generally, the disclosure herein tends to provide a clamshell stator and method that simplifies the design of a machined all over corrosion resistant clamshell stator for a multi-staged roots pump. The clamshell stator comprises portholes that tend to eliminate the large access ports in the top and bottom of half-shell stator components that are currently required when manufacturing clam shell stators. This tends to eliminate the need for corrosion resistant external cover plates, o-rings and additional gas purging.

[0087] Reference numeral list

[0088] 100 clamshell stator

[0089] 102 first end

[0090] 104 second end

[0091] 110 first half-shell stator

[0092] 112 first port

[0093] 120 second half-shell stator

[0094] 122 second port

[0095] 130 access holes

[0096] 140 external cover plate

[0097] 150 o-rings

[0098] A longitudinal axis

[0099] 161 , 162, 163, 164, 165 pump chambers

[0100] 161a, 162a, 163a, 164a, 165a inlets

[0101] 161 b, 162b, 163b, 164b, 165b outlets

[0102] 171 , 172, 173, 174 gas transfer passages

[0103] 181 , 182 regions

[0104] 200 clamshell stator

[0105] 202 first end

[0106] 204 second end

[0107] 210 first half-shell stator component

[0108] 212 first port

[0109] 214 first walls

[0110] 214a first wall adjacent first pump chamber

[0111] 216 exterior wall

[0112] 220 second half-shell stator component 222 second port

[0113] 224 second walls

[0114] 224a second wall adjacent second chamber

[0115] 226 exterior wall

[0116] 261 , 262, 263, 264, 265 pump chambers

[0117] 261a, 262a, 263a, 264a, 265a inlets

[0118] 261 b, 262b, 263b, 264b, 265b outlets

[0119] 271 , 272, 273, 274 gas transfer passages

[0120] 282 first bore

[0121] 282a first portholes

[0122] 284 second bore

[0123] 284a second portholes

[0124] 292 first plugs

[0125] 294 second plugs

[0126] 292' first baffle

[0127] 292a' cut out

[0128] 292b' first fastening means

[0129] 294' second baffle

[0130] 294a' cut out

[0131] 294b' second fastening means

[0132] 300 vacuum pump

[0133] 301 clamshell stator

[0134] 303 rotor

[0135] 304 first end

[0136] 310 first half-shell stator component

[0137] 320 second half-shell stator component 360 plurality of pump chambers

[0138] 370 plurality of gas transfer passages

[0139] 382 first bore

[0140] 384 second bore

[0141] 392 first baffle

[0142] 394 second baffle

[0143] 400 method

[0144] 410 providing step

[0145] 420 boring step

[0146] 430 boring step

[0147] 440 arranging step

Claims

CLAIMS1. A clamshell stator for a vacuum pump, comprising: a first half-shell stator component and a second half-shell stator component for attaching together to define an interior volume for housing a rotor, wherein the first half-shell stator component comprises a first port at a first end of the clamshell stator and through which a process gas can be received into the interior volume and the second half-shell stator component comprises a second port at a second end of the clamshell stator and through which the process gas can be exhausted from the interior volume; wherein the first half-shell stator component and the second half-shell stator component comprise respective first and second internal walls for dividing the internal volume into a plurality of pump chambers having gas transfer passages arranged therebetween, each of the pump chambers having an inlet and an outlet, wherein the plurality of pump chambers comprise at least a first chamber in fluid connection with the first port and a second chamber in fluid connection with the second port; wherein the first half-shell stator component comprises a first bore extending from the second end of the clamshell stator through one or more of the first internal walls, the first bore defining respective first portholes in an exterior wall of the first half-shell stator and in the one or more of the first internal walls, wherein the second half-shell stator component comprises a second bore extending from the first end of the clamshell stator through one or more of the second internal walls, the second bore defining respective second portholes in an exterior wall of the second half-shell stator component and in the one or more of the second internal walls, such that each of the gas transfer passages provides a fluid connection between adjacent pump chambers of the plurality of pump chambers; wherein the clamshell stator further comprises a first sealing means and a second sealing means arranged respectively to seal one or more of the first portholes and one or more of the second portholes such that the fluidconnection provided by each of the gas transfer passages is a fluid connection between the outlet and inlet of adjacent pump chambers.

2. The clamshell stator of claim 1 , wherein: the first bore extends entirely through the first half-shell stator component; and / or the second bore extends entirely through the second half-shell stator component.

3. The clamshell stator of claim 1 , wherein: the first bore extends partially through the first half-shell stator component; and / or the second bore extends partially through the second half-shell stator component.

4. The clamshell stator of claim 3, wherein: the first bore extends through the first half-shell stator component to the first internal wall adjacent the first chamber; and / or the second bore extends through the second half-shell stator component to the second internal wall adjacent the second chamber.

5. The clamshell stator of any preceding claim, wherein: the first portholes have a diameter of less than or equal to 40mm; and / or the second portholes have a diameter of less than or equal to 40mm.

6. The clamshell stator of any preceding claim, wherein: the first sealing means comprise one or more first plugs; and / orthe second sealing means comprise one or more second plugs.

7. The clamshell stator of claim 6, wherein: the first plugs and / or second plugs comprise stainless steel.

8. The clamshell stator of any one of claims 6-7, wherein: the first plugs and / or second plugs are configured to provide an interference fit to their respective first portholes and / or second portholes.

9. The clamshell stator of any one of claims 6-8, wherein: the first plugs seal first portholes in the exterior wall of the first half-shell stator component; and the second plugs seal second portholes in the exterior wall of the second half-shell stator component.

10. The clamshell stator of any preceding claim, wherein: the first sealing means comprises a first baffle; and / or the second sealing means comprises a second baffle.11 . The clamshell stator of claim 10, wherein: the first baffle comprises an elongate member having a slide-fit with the first portholes; and / or the second baffle comprises an elongate member having a slide-fit with the second portholes.

12. The clamshell stator of claim 11 , wherein:the first baffle and the second baffle comprise one or more cut-outs for providing the fluid connection between the outlet and the inlet of adjacent pump chambers via the gas transfer passages.

13. The clamshell stator of any one of claims 10-12, wherein: the first baffle is secured to the exterior wall of the first half-shell stator component using a first fastening means; and / or the second baffle is secured to the exterior wall of the second half-shell stator component using a second fastening means.

14. A vacuum pump comprising: the clamshell stator of any preceding claim; and a rotor housed within the interior volume.

15. A method of manufacturing a clamshell stator for a vacuum pump, comprising: providing a first half-shell stator component and a second half-shell stator component for attaching together to define an interior volume for housing a rotor, wherein the first half-shell stator component comprises a first port at a first end of the clamshell stator through which a process gas can be received into the internal volume, wherein the second half-shell stator component comprises a second port at a second end of the clamshell stator through which the process gas can be exhausted from the internal volume, wherein the first half-shell stator component and the second half-shell stator component comprise respective first and second internal walls for dividing the internal volume into a plurality of pump chambers having gas transfer passages arranged therebetween, each of the pump chambers having an inlet and an outlet, wherein the plurality of pump chambers comprise at least a first chamber in fluid connection with the first port and a second chamber in fluid connection with the second port;boring a first bore extending from the second end of the clamshell stator through one or more of the first internal walls of the first half-shell stator component, the first bore defining respective first portholes in an exterior wall of the first half-shell stator and in the one or more of the first internal walls; boring a second bore extending from the first end of the clamshell stator through one or more of the second internal walls of the second half-shell stator component, the second bore defining respective second portholes in an exterior wall of the second half-shell stator component and in the one or more of the second internal walls, such that each of the gas transfer passages provides a fluid connection between adjacent pump chambers of the plurality of pump chambers; arranging a first sealing means and a second sealing means respectively to seal one or more of the first portholes and one or more of the second portholes such that the fluid connection provided by each of the gas transfer passages is a fluid connection between the outlet and inlet of adjacent pump chambers.

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