WO2021219307A1

WO2021219307A1 - Primary vacuum pump and installation

Info

Publication number: WO2021219307A1
Application number: PCT/EP2021/058021
Authority: WO
Inventors: Stéphane Crochet; Yann Olivier
Original assignee: Pfeiffer Vacuum
Priority date: 2020-04-29
Filing date: 2021-03-26
Publication date: 2021-11-04

Abstract

A primary vacuum pump (1) comprising a suction orifice (4) and a discharge orifice (5), the vacuum pump (1) being configured to be able to discharge the pumped gases at atmospheric pressure, comprising: - a stator (2) comprising at least one pumping stage (3a-3e), - two rotor shafts (6) configured to turn synchronously in reverse directions in the at least one pumping stage (3a-3e) to drive a gas to be pumped between the suction orifice (4) and an outlet orifice (8) of the stator (2), characterized in that the vacuum pump (1) further comprises at least one cassette (11) configured to receive at least one of the elements out of a silencer (10), at least one offloading device (29), at least one purging device and a cooler (27) of the vacuum pump (1), the at least one cassette (11) being fixed removably to the stator (2) and interposed on the gas flow path.

Description

Title: Primary vacuum pump and installation

The present invention relates to a primary vacuum pump configured to be able to discharge the pumped gases at atmospheric pressure. The present invention relates also to an installation including said primary vacuum pump.

Depending on the pumping applications in which they are employed, the vacuum pumps may require the addition of specific functionalities that make it possible for example to increase their lifespan, to lower the electrical consumption, to lower the temperature of the pump body, or to lower the noise, etc.

In particular, the noise generated by the primary vacuum pumps can be significant. Such is the case notably during the depressurizing of chambers initially at atmospheric pressure. Furthermore, in the load lock pumping case used to lower the pressure around a substrate before its transfer into a process chamber maintained at a vacuum, this sound nuisance is repeated cyclically.

To reduce the noise, the vacuum pumps are provided with a silencer. The silencer is secured to the stator, at the outlet of the last pumping stage, upstream of a non-return valve preventing the pumped gases from returning into the vacuum pump.

The silencers are all the more effective when they are voluminous. They are therefore bulky. Now, one of the criteria sought for the vacuum pumps, and notably for those used for the cyclic pumping of transfer locks, is their compactness. A good trade off between the silencer effect and the dimensions thereof is therefore sought to be obtained.

Moreover, the pumped gases circulating in the silencer contribute to the heating of the vacuum pump and of its near environment. The electronics of the vacuum pump that may be arranged in this environment can therefore be heated up by the gases passing through the silencer, which can contribute to reducing its lifespan. It is therefore desirable to thermally insulate the silencer from its near environment.

Other functionalities can be incorporated in the vacuum pump to optimize its operation.

It may be necessary for example to reduce the operating temperature of the body of the vacuum pump in order to increase the efficiency of the machine. Also, it may be necessary to inject a purging gas into the pump, notably into certain critical zones, to reduce the chemical pollutants which could degrade the vacuum pump.

The functionalities of the vacuum pump are thus becoming increasingly complex, in particular for the individual access to the various pumping stages or to the discharge, which renders the fitting and maintenance operations particularly difficult. All of the vacuum pump must sometimes be entirely dismantled to allow the silencer to be cleaned or to modify or adapt a small functionality of the discharge or of a pumping stage to a specific pumping application.

One aim of the present invention is to propose an enhanced vacuum pump that at least partially resolves one of the drawbacks of the state of the art.

To this end, the subject of the invention is a primary vacuum pump comprising a suction orifice and a discharge orifice, the vacuum pump being configured to be able to discharge the pumped gases at atmospheric pressure and comprising: a stator comprising at least one pumping stage, two rotor shafts configured to turn synchronously in reverse directions in the at least one pumping stage to drive a gas to be pumped between the suction orifice and an outlet orifice of the stator, characterized in that the vacuum pump further comprises a cassette configured to receive at least one of the elements out of a silencer, at least one offloading device, at least one purging device and a cooler of the vacuum pump, the at least one cassette being fixed removably to the stator and interposed on the gas flow path.

The inlet of the cassette can communicate with the outlet orifice of the stator and/or with at least one inlet or one outlet of a pumping stage. The cassette can emerge through the discharge orifice of the vacuum pump.

The removable cassette offers the vacuum pump a high degree of modularity by allowing the functionalities of the vacuum pump to be easily adapted to the particular pumping application. For example, on a per-case basis, it makes it possible to house a silencer and/or a discharge valve and/or an additional pumping unit and/or a purging device and/or a sensor and/or a heater and/or a cooler. It is then possible to optimize these functionalities simply, by changing only the cassette, without having to dismantle all of the stator. The number of pipes is also reduced, which also contributes to lightening the vacuum pump.

Another significant advantage is that maintenance of the discharge is made easier. The operators can provide rapid maintenance work at regular intervals during which they can simply replace the cassette with a new cassette or a cleaned and operational cassette. The malfunctions or stoppages of the vacuum pumps, due to a lack of upkeep, are thus avoided, these being hitherto too spaced apart in time because they are prejudicial to production rates.

The vacuum pump can also comprise one or more of the features which are described hereinbelow, taken alone or in combination.

The cassette can be configured to be able to be slidingly mounted in a support frame of the stator. The cassette is accessed simply by pulling it out of its location like pulling on a drawer. It is then easily accessible and the fitting/dismantling thereof does not require any particular lifting handling means.

The cassette can comprise a one-piece plate in which there is formed at least one hydraulic circuit of a cooler configured to cool the stator.

The cassette can comprise a one-piece plate in which there is formed at least one duct of a purging device configured to purge at least one pumping stage.

The cassette can also receive at least one offloading device of the vacuum pump configured to offload at least one pumping stage.

The cassette can be fixed removably on the stator.

The cassette can be fixed removably under the stator. The volume available under the frame in the prior art, notably the volume between the wheels, which was not used, is thus exploited to house or arrange discharge functionalities therein.

The interior of the cassette can be arranged as silencer.

The silencer is, for example, an acoustic resonator, such as a Helmholtz resonator or a quarter-wave resonator.

The silencer is, for example, a quarter-wave resonator comprising at least one chicane, for example at least two, arranged on the trajectory of the pumped gases.

The at least one chicane can be formed by a baffle secured to a lateral wall or transverse wall of the cassette.

The cassette is, for example, of generally parallelepipedal form. The silencer can comprise at least two chicanes arranged on the trajectory of the pumped gases, formed by at least two parallel baffles, alternately secured to one of the two lateral or transverse walls of the cassette.

The cassette can comprise double walls.

The cassette can receive a phonic-absorbent material, such as mineral wool, arranged in the double wall.

The inner walls of the double wall can be pierced.

The cassette can receive a thermal insulation device surrounding the silencer, to thermally insulate the silencer.

The thermal insulation device can comprise an air-filled double wall.

The cassette can receive a cooler of the vacuum pump to cool the silencer and/or the stator.

The vacuum pump can comprise a control unit configured to be able to control the temperature of the silencer by means of the cooler independently of the stator temperature control.

The cassette can receive at least one discharge valve comprising at least one movable shutter configured to be able to shut the inlet in closed position and an elastic return member stressing the at least one movable shutter into the closed position.

The cassette can receive an additional pumping unit configured to lower the pressure, for example, upstream of the silencer, in the direction of circulation of the gas to be pumped.

Also a subject of the present invention is an installation including a load lock enclosure and a vacuum line connected to the enclosure, characterized in that the vacuum line includes a primary vacuum pump as described previously to lower the pressure in the enclosure.

Description of the drawings

Other advantages and features will become apparent on reading the following description of a particular, but nonlimiting, embodiment of the invention, and the attached drawings in which:

[Fig.1] Figure 1 represents a schematic view of an exemplary installation.

[Fig.2] Figure 2 represents a schematic view of a first example of a primary vacuum pump of the installation of figure 1. [Fig.3] Figure 3 shows a perspective view of a cassette of the primary vacuum pump of figure 2.

[Fig.4] Figure 4 shows the cassette of figure 3 with the lid removed.

[Fig.5] Figure 5 is a partial bottom view of another exemplary embodiment of the vacuum pump.

[Fig.6] Figure 6 is a diagram of a top view of another exemplary embodiment of a cassette with the lid removed.

[Fig.7] Figure 7 is a diagram of a cross-sectional view of another exemplary embodiment of a cassette.

[Fig.8] Figure 8 is a diagram of a cross-sectional view of another exemplary embodiment of a cassette.

[Fig.9] Figure 9 is a diagram of a cross-sectional view of another exemplary embodiment of a cassette.

[Fig.10] Figure 10 shows a top view of another exemplary embodiment of a cassette with the lid removed.

[Fig.11] Figure 11 is a block diagram of another exemplary embodiment of a vacuum pump.

[Fig.12] Figure 12 shows a perspective view of another exemplary primary vacuum pump.

[Fig.13] Figure 13 is a schematic representation of the primary vacuum pump of figure 12.

[Fig.14] Figure 14 shows a top view of the vacuum pump of figure 12 with the cassette open.

[Fig.15] Figure 15 shows a top view of the stator of the vacuum pump of figure 12 without cassette.

In these figures, the elements that are identical bear 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 relates to the same embodiment, or that the features apply only to a single embodiment. Simple features of different embodiments can also be combined or interchanged to provide other embodiments. A primary vacuum pump is defined as a volumetric vacuum pump which is configured to, using two rotors, suck, transfer, then discharge the pumped gases at atmospheric pressure. The rotors are borne by two shafts driven in rotation by a motor of the primary vacuum pump. The rotors can be of Roots, claw or screw type. A primary vacuum pump can be started up from atmospheric pressure.

“Upstream” is understood to refer to an element which is placed before another with respect to the direction of circulation of the gas. On the other hand, “downstream” is understood to refer to an element placed after another with respect to the direction of circulation of the gas to be pumped.

The axial direction is defined as the longitudinal direction (L) of the primary vacuum pump in which the axes of the rotor shafts extend. The transverse direction (T) is defined as the direction at right angles to the longitudinal direction (L). The plane (L, T) is the horizontal plane.

Figure 1 shows an exemplary installation 100 using a primary vacuum pump 1 configured to be able to discharge the pumped gases at atmospheric pressure.

The installation 100 comprises a load lock enclosure 101 and a vacuum line 102 connected to the enclosure 101, comprising a primary vacuum pump 1 for lowering the pressure in the enclosure 101. The vacuum line 102 can also comprise a vacuum pump of Roots or turbomolecular type interposed between the enclosure 101 and the primary vacuum pump 1 , in series and upstream of the primary vacuum pump 1.

As is known per se, a production device 107 comprises a load lock enclosure 101 having a first door 103 connecting the interior of the enclosure 101 with a zone at atmospheric pressure, such as a clean room, for loading at least one substrate 104, and a second door 105 for unloading the substrate 104 into a process chamber 106 of the device 107 after depressurization. Each loading or unloading of substrates 104 requires the pressure in the lock enclosure 101 to be alternately lowered and then raised. The load lock enclosure 101 makes it possible to maintain an acceptable rate and avoid the presence of any impurity and of any pollution in the atmosphere surrounding the substrate 104. The load locks are notably used for the production of flat display screens or of photovoltaic substrates or for the production of semiconductor substrates.

As can be seen in figure 2, the primary vacuum pump 1 comprises a suction orifice 4, a discharge orifice 5 and a stator 2 (or pump body, also called pumping block or pumping cell) comprising at least one pumping stage 3a-3e. The vacuum pump 1 is, for example, a multistage vacuum pump comprising at least two pumping stages 3a-3e mounted in series, such as between two and ten pumping stages (five in the illustrative example). The stator 2 can be produced in one or more parts, for example in several slices joined axially or in half-shells.

The vacuum pump 1 further comprises two rotor shafts 6 (just one is represented in figure 2) configured to turn synchronously in reverse directions in the at least one pumping stage 3a-3e to drive a gas to be pumped between the suction orifice 4 and an outlet orifice 8 of the stator 2.

Each pumping stage 3a-3e of the stator 2 is formed by a pumping chamber receiving two conjugate rotors, the pumping chambers comprising a respective inlet and outlet. During rotation, the gas sucked from the inlet is held captive in the volume created by the rotors and the stator 2, then is driven by the rotors to the next stage.

The successive pumping stages 3a-3e are connected in series one after the other by respective inter-stage channels connecting the outlet of the preceding pumping stage 3a-3d to the inlet of the following pumping stage 3b-3e. The inlet of the first pumping stage 3a communicates with the suction orifice 4 of the vacuum pump 1. The axial dimensions of the rotors and of the pumping chambers are, for example, equal or decreasing with the pumping stages, the pumping stage 3a situated on the side of the suction orifice 4 receiving the rotors of largest axial dimension.

The rotors have, for example, lobes of identical profiles, for example of Roots type with two lobes or more, or of claw type or of spiral type or screw type or based on another similar volumetric vacuum pump principle. The shafts bearing the rotors are driven by a motor 7 situated at one end of the vacuum pump 1, for example on the side of the outlet orifice 8 at the last pumping stage 3e of the stator 2.

These vacuum pumps are said to be “dry” because, in operation, the rotors turn inside the stator 2 with no mechanical contact between them or with the stator 2, which allows oil not to be used in the pumping stages 3a-3d.

The power supply and the speed of rotation of the vacuum pump 1 are, for example, controlled by a control unit 21 of the vacuum pump 1 , comprising a computer or controller or microprocessor or logic controller, which can be configured to monitor operating parameters of the vacuum pump 1, such as the pressure at the discharge orifice 5, the power consumed or the temperature of the stator 2. The control unit 21 can also display or report alerts to a remote unit, such as that of the device 107 when these measurements exceed predetermined thresholds.

The vacuum pump 1 can comprise a support frame 9 of the stator 2. Frame is more generally understood to mean that which supports the stator 2 and forms the link between the stator 2 and the ground. The frame 9 can comprise a rigid framework, made of a strong material, intended to support the vacuum pump 1.

The vacuum pump 1 further comprises a cassette 11 fixed removably to the stator 2 and interposed on the gas flow path.

The cassette 11 is configured to receive at least one of the elements out of a silencer 10, at least one offloading device 31, at least one purging device for injecting a dilution gas, such as nitrogen, and a cooler. The cassette 11 can also be configured to receive a sensor, such as a pressure and/or temperature and/or gas sensor and/or a heating means and/or an additional pumping unit 29.

In the first exemplary embodiment of figure 2, the inlet 12 of the cassette 11 communicates with the outlet orifice 8 of the stator 2. The cassette 11 emerges through the discharge orifice 5 of the vacuum pump 1. Furthermore in this first example, the cassette 11 is fixed removably under the stator 2. The volume available under the frame in the prior art, notably the volume between the wheels, which was not used, is thus exploited to house or arrange discharge functionalities therein.

The removable cassette offers the vacuum pump a high degree of modularity by allowing the discharge functionalities to be easily adapted to the particular pumping application. It is then possible to optimize these functionalities simply, by changing only the cassette, without having to dismantle all of the stator.

There is furthermore a greater space available for housing the discharge functionalities within the same vacuum pump 1 footprint. The number of pipes is also reduced, which also contributes to lightening the vacuum pump 1.

Another significant advantage is that maintenance of the discharge is made easier. The operators can provide rapid maintenance work at regular intervals during which they can simply replace the cassette 11 with a new cassette or a cleaned and operational cassette. The malfunctions or stoppages of the vacuum pumps which are due to a lack of upkeep are thus avoided, those being hitherto too spaced apart in time because they are potentially prejudicial to production rates. The cassette 11 can be fixed to the stator 2 for example by means of screws. The cassette 11 comprises, for example, fixing flanges 22 (figures 3 and 4), here five of them, passed through by screws, or can be directly passed through by screws. The cassette 11 is thus very easy to fix to the stator 2 and can be mounted/removed easily.

According to another example that can be seen in figure 5, the cassette 11 is configured to be able to be slidingly mounted in the frame 9. For that, the cassette 11 and the frame 9 have guides, such as, for example, complementary rails/runners or roller or castor devices. These guides can be provided with end stops and/or blocking means, such as clamps for clamping the cassette 11 to the frame 9 when the cassette 11 is fully inserted.

To access the cassette 11, it simply has to be pulled out of its location as if pulling on a drawer. It is then easily accessible and the mounting/dismantling thereof requires no particular lifting handling means.

The frame 9 is, for example, produced wholly or partly in sheet metal or cast iron.

The cassette 11 has, for example, a generally parallelepipedal form or a substantially parallelepipedal form or a form that fits within a generally substantially parallelepipedal form. It comprises, for example, two transverse walls 14 at right angles to two lateral walls 15 extending in the longitudinal direction. The cassette 11 is arranged “horizontally” under the stator 2 as in the figures. The cassette 11 has, for example, a generally elongate form, that is to say longer in the longitudinal direction than in the transverse direction.

The cassette 11 can comprise an outlet coupling 18, to form the discharge orifice 5 of the vacuum pump 1, the outlet coupling 18 being secured to the parallelepipedal part of the cassette. This outlet coupling 18 is, for example, a standard flange used in the vacuum field.

The frame 9 can also comprise at least two castors 19 and/or at least two feet 20, here four of them (figure 2). Alternatively, the castors 19 and/or the feet 20 are borne by the cassette 11. The axes of the castors are, for example, incorporated at two bottom and opposing corners of a bottom wall of the cassette 11 (not represented).

In this first exemplary embodiment, the cassette 11 is a hollow box. The cassette 11 can receive a silencer 10. The silencer 10 can thus be easily accessible to be able to be cleaned and the clogging thereof provoking a shutdown of the vacuum pump 1 is avoided.

More specifically, the cassette 11 can be arranged as silencer. The inlet 12 of the cassette 11 forming the inlet of the silencer 10 can be arranged in a top wall 13 or communicates with this top wall 13. The inlet 12 of the cassette 11 is, for example, formed to coincide vertically with the axis of the outlet orifice 8 of the last pumping stage 3e of the stator 2 when the cassette 11 is fixed to the stator 2. Their connection can be sealed by an annular seal or a flat seal.

The outlet of the silencer 10 can be formed in a transverse wall 14 of the cassette 11 , at a longitudinal end of the cassette 11 or in a lateral wall 15, and emerges in the outlet coupling 18.

According to one embodiment, the silencer 10 operates on the principle of an acoustic resonator. Acoustic resonators offer the advantage of creating little in the way of pressure drops with adequate attenuation in the low frequencies. Among acoustic resonators, there are the Helmholtz resonator or the quarter-wave resonator.

According to one exemplary embodiment of a quarter-wave resonator, the silencer 10 comprises at least one chicane 16, for example at least two, four in the illustrative example, arranged on the trajectory of the pumped gases. The chicanes 16 generate abrupt variations in the trajectory of the gases.

In the example of figures 3 and 4, the lateral 15, transverse 14, top 13 and bottom 25 walls of the cassette 11 form the walls of the silencer 10.

To form a chicane 16, the silencer 10 comprises, for example, at least one baffle 17, formed here by a transverse deflection wall, shorter than the transverse wall 14 of the cassette 11, secured to a lateral wall 15 of the cassette 11. The transverse deflection wall extends in a direction at right angles to the longitudinal direction of the silencer 10. The length of the transverse deflection wall is, for example, between half and three-quarters of the length of the transverse wall 14.

The silencer 10 comprises, for example, at least two chicanes 16 for deflecting the trajectory of the pumped gases, formed by at least two baffles 17, alternately secured to one of the two lateral walls 15 of the cassette 11. The baffles 17 are parallel to one another.

This type of silencer 10 is particularly simple to produce. Figure 6 shows a variant embodiment.

In this variant, the silencer 10 comprises at least one baffle 17 formed by a longitudinal deflection wall, shorter than the lateral wall 15 and secured to a transverse wall 14. The longitudinal deflection wall extends in the longitudinal direction of the cassette 11. The length of the longitudinal deflection wall is, for example, between half and 5/6ths of the length of the lateral wall 15.

The silencer 10 here comprises two chicanes 16 for deflecting the trajectory of the pumped gases, formed by two baffles 17, alternately secured to one of the two transverse walls 14.

More generally, the silencer 10 can be formed by any kind of passive silencer embodiment, that makes it possible to reduce the noise, notably by reflection, interference and/or absorption, notably by using a labyrinth that can deflect the trajectory of the pumped gases so as to break the acoustic waves and thus reduce the noise.

According to an exemplary embodiment schematically represented in the cross- sectional view of figure 7, the cassette 11 also receives a phonic-absorbent material 23, such as mineral wool, such as rock wool, arranged in a double wall 24 surrounding the silencer 10. The phonic-absorbent material 23 is a dissipative attenuator causing acoustic energy losses in the acoustic waves. The double wall 24 is formed by lining the lateral 15, transverse 14, top 13 and bottom 25 walls of the cassette 11, the gap between the walls 13, 14, 15, 25 receiving the phonic-absorbent material 23. The inner walls of the double wall 24 can be pierced. The principle of the silencer 10 is then similar to that of a vehicle silencer.

According to an exemplary embodiment, the cassette 11 receives a thermal insulation device 26 surrounding the silencer 10, to thermally insulate the silencer 10. For example, and as can be seen in the cross-sectional view of figure 8, the thermal insulation device 26 comprises a double wall 24 formed by lining the lateral 15, transverse 14, top 13 and bottom 25 walls. The gap between the walls 13, 14, 15, 25 is, for example, filled with air.

Alternatively or in addition, the silencer 10 can comprise one or more successive chambers, such as resonance and/or expansion chambers. These chambers are tuned and dimensioned with respect to one another to deal with the frequencies of the noise to be attenuated. The cassette 11 can receive a cooler 27 of the vacuum pump 1 for cooling the silencer 10 and/or the stator 2. The cooler 27 comprises, for example, a hydraulic circuit surrounding the silencer 10 (figure 9).

The control unit 21 of the vacuum pump 1 can be configured to be able to control the temperature of the silencer 10 by means of the cooler 27. The control unit 21 is, for example, arranged in a compartment 28 of the cassette 11, for example formed in a longitudinal extension of the silencer 10 (figures 2 to 4). In this case, the cooler 27 can also be configured to cool the control unit 21.

According to an exemplary embodiment, the control unit 21 is configured to be able to control the temperature of the silencer 10 by means of the cooler 27 independently of the control of the temperature of the stator 2. It is for example possible to heat the stator 2 while cooling the silencer 10.

It is noted that it is possible to optimize the form and the insulation of the silencer 10 because of the greater space available within the same footprint of the vacuum pump 1.

The cassette 11 can comprise other functionalities, alternatively or in addition to the silencer function.

As can be seen in figure 10, the cassette 11 can receive at least one offloading device 31 of the vacuum pump 1, here a discharge valve, comprising at least one movable shutter 33 configured to be able to shut the inlet 12 of the cassette 11 in closed position and an elastic return member, such as a spring (not visible), stressing the at least one movable shutter 33 into the closed position. The movable shutter 33 can comprise a disk or have a partly conical form.

When the vacuum pump 1 is operating normally, that is to say operating to pump an acceptable gas stream, the inlet 12 is shut by the movable shutter 33. If a gas surplus occurs, the movable shutter 33 is pushed back against the elastic member, which frees the inlet 12.

The cassette 11 can comprise an additional pumping unit 29 (figure 11). The additional pumping unit 29 is configured to lower the pressure, for example upstream of the silencer 10 when the vacuum pump 1 is provided with a silencer 10, in the direction of circulation of the gas to be pumped. The lowering of the pressure at the outlet orifice 8, upstream of the discharge valve 31 if necessary, makes it possible to reduce the electrical consumption of the vacuum pump 1. The additional pumping unit 29 is, for example, a small auxiliary volumetric vacuum pump or a venturi device.

The additional pumping unit 29 is, for example, received in a compartment 28 of the cassette 11, for example formed in a longitudinal extension of the silencer 10. The inlet 12 of the cassette 11 forms the inlet of the additional pumping unit 29, which communicates with the outlet orifice 8 of the last pumping stage 3e upstream of the discharge valve 31. The outlet of the additional pumping unit 29 in the case of an auxiliary vacuum pump can be connected downstream of the discharge valve 31, for example upstream of the silencer 10 or in the silencer 10 or after the silencer 10.

The additional pumping unit 29 is, for example, connected or started up when the control unit 21 observes an increase in the consumed power beyond a predetermined threshold, for example in the so-called ultimate vacuum pumping phases, notably in a standby phase of the device 107, when a substrate 104 is waiting at low pressure in the lock enclosure 101.

In the case of an auxiliary vacuum pump, an isolation valve can be arranged between the inlet of the additional pumping unit 29 and the outlet orifice 8 in order to connect the additional pumping unit 29 only in appropriate cases.

Figures 12 to 15 show a second exemplary embodiment of the vacuum pump 1.

In this example, the cassette 11 is fixed removably on the stator 2.

The cassette 11 can be fixed to the stator 2 for example by means of screws 34a as in this example in which the cassette 11 is passed through by screws 34a. Six fixing holes 34b in the cassette 11 and the stator 2 can be seen in figures 12, 14 and 15.

As can be seen in figures 13, 14 and 15, the cassette 11 communicates with at least one compression chamber of a pumping stage 3a-3e, such as, for example, with the compression chambers of all the pumping stages 3a-3e. The cassette 11 emerges through the discharge orifice 5 of the vacuum pump 1.

In this second exemplary embodiment, the cassette 11 comprises a one-piece plate, for example formed by a thermal conductor, such as a metal block, for example made of aluminum.

In this one-piece plate there can be formed at least one duct 35 of a purging device configured to purge at least one pumping stage 3a-3e. The cassette 11 comprises, for example, N-1 ducts 35 for N pumping stages 3a-3e, one duct 35 emerging in each compression chamber from the second pumping stage 3b (figure 15). The ducts 35 are connected to a common inlet 36 of the cassette 11 (figure 14) intended to be connected to a source of purging or dilution gas.

Also, at least one hydraulic circuit of a cooler, for example for water circulation, can be formed in the one-piece plate, to cool the stator 2. The inlet 39a and the outlet 39b of the hydraulic circuit can be distinguished in figure 14, linked to water intake pipes 41 (figure 12). The hydraulic circuit can thus extend in the cassette 11 along the pumping stages 3b-3e to cool the stator 2.

The cassette 11 also receives at least one offloading device configured to offload at least one pumping stage 3a-3e. The offloading makes it possible to evacuate the overpressures that can occur in the pumping stages 3a-3e, thus making it possible to relieve the overpressure generated by the rotors on each revolution (360°) of the at least one pumping stage 3a-3e provided with an offloading device. The offloading devices also make it possible to lower the temperature of the stator 2.

In the example, the cassette 11 receives three offloading devices: a first and a second movable shutter 33 configured to be able to shut the outlets of the first and the second pumping stages 3a, 3b in closed position and a third movable shutter 33 configured to be able to shut the outlet of the last pumping stage 3e in closed position. It is also perfectly possible to provide other locations for the offloading devices. It is also possible to provide for there to be as many offloading devices as there are pumping stages 3a-3e.

The movable shutters 33 are, for example, balls stressed into closed position by gravity on tapered seats formed in the one-piece plate of the cassette 11, possibly provided with silicone seals. The outlets of the offloading devices are, for example, connected to one another and to the discharge orifice 5 by channels 37 formed in the one-piece plate of the cassette 11 (figure 14). Also distinguishable are the offloading holes 38 linking the outlets of the compression chambers of the pumping stages 3a, 3d, 3e to the seats of the offloading devices in figure 15.

The fixing holes 34b, the hydraulic circuit, the seats and channels 37 of the offloading devices are, for example, directly machined in the one-piece plate (figure 14), the latter being closed by a cover 40, for example a flat cover, of the cassette 11 (figure 12). The cassette 11 is thus easy to produce and can incorporate several functions in a single module: cooling, offloading of overpressure in the pumping stages 3a-3e, purging of the pumping stages 3a-3e. The number of components of the vacuum pump 1 is thus reduced. It is also possible to very easily add or remove some of these functionalities depending on the pumping applications. The lowering of the temperature of the stator 2 because of the offloading and of the cooler makes it possible to improve the pumping rates. The risks of corrosion can also be controlled by the injection of purging gas.

Claims

1. A primary vacuum pump (1) comprising a suction orifice (4) and a discharge orifice (5), the vacuum pump (1) being configured to be able to discharge the pumped gases at atmospheric pressure, and comprising: - a stator (2) comprising at least one pumping stage (3a-3e),

- two rotor shafts (6) configured to turn synchronously in reverse directions in the at least one pumping stage (3a-3e) to drive a gas to be pumped between the suction orifice (4) and an outlet orifice (8) of the stator (2), characterized in that the vacuum pump (1) further comprises a cassette

(11) configured to be arranged as silencer (10) or to receive at least one of the elements out of a silencer (10), at least one offloading device (29), at least one purging device and a cooler (27) of the vacuum pump (1), the at least one cassette (11) being fixed removably to the stator (2) and interposed on the gas flow path.

2. The vacuum pump (1) as claimed in claim 1, characterized in that the inlet (12) of the cassette (11) communicates with the outlet orifice (8) of the stator (2) and/or with at least one inlet or one outlet of a pumping stage (3a-3e), the cassette (11) emerging through the discharge orifice (5) of the vacuum pump (1).

3. The vacuum pump (1) as claimed in either of the preceding claims, characterized in that the cassette (11) is configured to be able to be slidingly mounted in a support frame (9) of the stator (2).

4. The vacuum pump (1) as claimed in one of the preceding claims, characterized in that the cassette (11) comprises a one-piece plate in which there is formed at least one hydraulic circuit of a cooler configured to cool the stator (2).

5. The vacuum pump (1) as claimed in one of the preceding claims, characterized in that the cassette (11) comprises a one-piece plate in which there is formed at least one duct (35) of a purging device configured to purge at least one pumping stage (3a-3e).

6. The vacuum pump (1) as claimed in claims 4 and 5, characterized in that the cassette (11) also receives at least one offloading device configured to offload at least one pumping stage (3a-3e).

7. The vacuum pump (1) as claimed in one of claims 1 to 6, characterized in that the cassette (11) is fixed removably on the stator (2).

8. The vacuum pump (1) as claimed in one of claims 1 to 6, characterized in that the cassette is fixed removably under the stator (2).

9. The vacuum pump (1) as claimed in one of the preceding claims, characterized in that the interior of the cassette (11) is arranged as silencer (10).

10. The vacuum pump (1) as claimed in claim 9, characterized in that the silencer (10) is an acoustic resonator, such as a Helmholtz resonator or a quarter-wave resonator.

11. The vacuum pump (1) as claimed in claim 10, characterized in that the silencer (10) is a quarter-wave resonator comprising at least one chicane

(16), arranged on the trajectory of the pumped gases.

12. The vacuum pump (1) as claimed in claim 11, characterized in that the at least one chicane (16) is formed by a baffle (17) secured to a lateral wall (15) or transverse wall (14) of the cassette (11).

13. The vacuum pump (1) as claimed in claim 11, characterized in that the silencer (10) comprises at least two chicanes (16) arranged on the trajectory of the pumped gases, formed by at least two parallel baffles (17), alternately secured to one of the two lateral (15) or transverse (14) walls of the cassette (11).

14. The vacuum pump (1) as claimed in one of the preceding claims, characterized in that the cassette (11) comprises double walls (24) and receives a phonic-absorbent material (23), such as mineral wool, arranged in the double wall (24).

15. The vacuum pump (1) as claimed in the preceding claim, characterized in that the inner walls of the double wall (24) are pierced.

16. The vacuum pump (1) as claimed in one of claims 1 to 8, characterized in that the cassette (11) comprises a thermal insulation device (26) surrounding the silencer (10) to thermally insulate the silencer (10).

17. The vacuum pump (1) as claimed in the preceding claim, characterized in that the thermal insulation device (26) comprises an air-filled double wall.

18. An installation (100) including a load lock enclosure (101) and a vacuum line (102) connected to the enclosure (101), characterized in that the vacuum line (102) includes a primary vacuum pump (1) as claimed in one of the preceding claims to lower the pressure in the enclosure (101).