TECHNICAL FIELD OF THE INVENTION

[0001] The invention pertains to the field of vacuum pumps, and more specifically to a Roots, screw or claw pump used to create a rough vacuum.

TECHNOLOGICAL BACKGROUND TO THE INVENTION

[0002] Dry rough-vacuum pumps usually have a plurality of pumping stages arranged in series, through which a pumped gas flows between a suction inlet and a discharge outlet. Known vacuum pumps can be classified into rotary root, rotary claw and rotary screw pumps. When assembling the different components of the vacuum pump, an entire rotor cannot be engaged axially in the stator by simple axial movement. It is also not possible to machine a one-piece stator to make the cavities forming the compression chambers. [0003] To enable both machining and assembly, and to ensure a good seal, the stators of dry vacuum pumps are for example built by axial assembly of several stator elements assembled using the respective transverse walls thereof, which is known as edge assembly, with the interposition of respective axially compressed O-rings isolating each compression chamber from the external atmosphere.

[0004] According to another embodiment, the stators are built by assembling two half shells together in the plane passing through the rotation axes of the rotors with the end walls. In this arrangement, the gaskets can be three-dimensional gaskets, i.e. sealing both the half-shells together in a first horizontal plane and the half-shells with the end walls in two parallel second planes. Instead of three-dimensional gaskets, it is also known to use gaskets formed by a paste applied to the contact interfaces that solidifies after assembly, or to use assembled gasket portions.

[0005] Regardless of the method used to assemble the stator elements, each element of the stator has to be machined separately, before executing a long and complex assembly operation that involves adapting the two rotor shafts in a support (usually formed by two end supports that receive, via bearings, each axial end of the rotor shafts and close the stator), adjusting the position of the lobes of the last compression chamber, positioning the last stator element with a gasket, adapting the lobes of the penultimate compression chamber, positioning the penultimate stator element with a gasket, and so on until the first stator element is in position. Given that the clearance between the rotor lobes and the stator walls is very small to ensure that each compression stage of the vacuum pump is sealed, this assembly is understandably very long and complex, and several hours’ labour are estimated to be required to complete this operation for a five- or six-stage dry vacuum pump. [0006] In the surface treatment or semiconductor industry (physical or chemical deposits in vapour phase, diffusion of chemical elements or etching), the pumped process gases are increasingly aggressive to the materials of the vacuum pump, and increasingly hazardous for users, i.e. for staff who may be in the vicinity of the vacuum pumps (such as phosphine or phosphorus hydride, which are used to dope semiconductors. Therefore, to ensure the safety of installations incorporating such a vacuum pump, it is therefore very important to use gaskets that provide very good chemical resistance so that the pumped gases cannot leak out of the stator of the vacuum pump.

[0007] This means that the material and assembly of the gaskets are critical in the manufacture of vacuum pumps. It is therefore now usually essential to use gaskets made from special materials such as fluoroelastomer-based materials (notably referred to using the abbreviations FKM, FFKM and FEPM), which are very costly. Manufacturing such gaskets in three dimensions between the stator elements and each support is complex and costly, making the machining of the grooves in the stator configured to receive this type of gasket very long and difficult. The difficulty of manufacturing vacuum pumps with a guaranteed high level of safety can therefore be immediately understood.

SUMMARY OF THE INVENTION

[0008] The invention is notably intended to propose a novel, high-safety vacuum pump architecture that is simple, robust and efficient to guarantee high containment reliability for the pumped gas at reduced cost, even where said gases are chemically aggressive, as well as other advantages such as better heat management, better management of partial pressures, better management of generated noise, better compatibility between all pump types and all types of pumped gases, and better management of inflows and outflows.

[0009] For this purpose, the invention relates to a dry rough-vacuum pump comprising a stator formed by at least one end support coupled axially to at least two stator elements assembled to form at least one pumping stage mounted between a suction inlet and a discharge outlet, and two shafts provided with rotors configured to turn in a synchronized opposite rotations manner in each pumping stage to drive a pumped gas in a flow direction from the suction inlet to the discharge outlet, characterized in that the vacuum pump also includes a safety device mounted sealingly on the end support and that envelops at least the stator elements to form a containment volume for the pumped gas between the stator elements and the safety device.

[0010] Advantageously according to the invention, since the safety device is mounted sealingly on the end support, simple assemblies of grooves and O-rings made of special materials such as fluoroelastomer-based materials (notably referred to using the abbreviations FKM, FFKM and FEPM) are used. As a result, the volume of expensive material required is reduced and the geometry is very simple, robust and efficient, which guarantees high containment reliability for the pumped gas in the vacuum pump. Furthermore, the O-ring/groove assemblies can be easily doubled (two grooves, each containing a O-ring) with no particular technical difficulty. Indeed, regardless of the type of dry vacuum pump used, any type of gas can be pumped with no risk to operators in the vicinity of the pump, and at lower cost.

[0011] Furthermore, since the safety device advantageously envelops the stator elements, a volume is created between the stator elements and the safety device, thereby making the sealing between the stator elements less critical. Since the critical sealing is moved, gaskets that are less complex and have cheaper material specifications can be used between the stator elements without adversely affecting safety, and the gaskets may even be omitted for some of the pumping stages. Furthermore, better heat management is achieved, notably in terms of the uniformity of cooling of the elements of the stator. Finally, the containment volume between the stator elements and the safety device according to the invention provides other advantages, as set out below.

[0012] The invention may also include one or more of the following optional features, taken individually or in combination:

[0013] The safety device can have a protective sleeve mounted sealingly on the end support using at least one assembly comprising a groove and an O-ring. This provides a simple and robust containment envelope about the stator elements.

[0014] According to an alternative, the other end support of the stator may be enveloped by the protective sleeve, or otherwise. More specifically, the protective sleeve can envelop the stator elements and a second end support of the vacuum pump or the protective sleeve can envelop the stator elements between two end supports.

[0015] The safety device can also include at least one control element intended to change the pressure and/or the nature of the fluid in the containment volume. The control element can then be used to create depression (relative negative pressure), for example to improve pumping performance, or conversely to create overpressure (relative positive pressure), for example to prevent pumped gas from entering the containment volume. Furthermore, regardless of the pressure applied in the containment volume by a control element, the same control element or another element can then be used to bring into the containment volume a fluid other than the gas pumped by the vacuum pump to dilute the pumped gases.

[0016] The safety device can include at least one noise reduction element mounted in the containment volume to reduce the noise intensity outside the vacuum pump. The noise reduction element can for example form a resonator and/or at least one chicane to absorb some of the noise generated by the vacuum pump. [0017] The safety device can include at least one flow adjustment element intended to communicate the containment volume with an element outside the vacuum pump and/or a pumping stage of the vacuum pump to selectively modify the incoming and outgoing flows of the vacuum pump. This notably enables the architecture of the vacuum pump to be easily adapted. By way of non-limiting example, the flow adjustment element could be the suction inlet or the discharge outlet arranged in the safety device to offset the suction inlet or the discharge outlet to adapt the vacuum pump regarding the congestion around the vacuum pump.

[0018] The safety device can include at least one detection element to monitor operation of the vacuum pump. This for example makes it possible to monitor the gas or gases in this containment volume, to adapt the settings of the vacuum pump if required.

[0019] Advantageously according to the invention, the dry rough-vacuum pump can be a Roots, claw or screw pump, without losing any of the aforementioned advantages. The invention can be applied to any type of dry vacuum pump, regardless of architecture, such as the number of pumping stages or the shape of the rotors.

[0020] Finally, the sealing between the stator elements can be formed exclusively by the complementary mating surfaces of the members of the stator so that the gasket is only required for the safety device. This helps to reduce manufacturing costs by reducing the cost of the materials used and by simplifying machining and assembly.

SHORT DESCRIPTION OF THE DRAWINGS

[0021] Other details and advantages of the invention are set out clearly in the description provided below as a non-limiting example, with reference to the attached drawings, in which:

Figure 1 is a schematic view of a manufacturing facility including a vacuum pump according to the invention,

Figure 2 is a cross-section view of a first embodiment of the vacuum pump according to the invention,

Figure 3 is a schematic view of a second embodiment of the vacuum pump according to the invention,

Figure 4 is a schematic view of a variant of the second embodiment of the vacuum pump according to the invention.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION [0022] Identical or similar elements in the different figures have the same reference signs, with an additional mark where applicable. The descriptions of the structure and functions thereof are therefore not systematically reproduced. [0023] Hereinafter, the orientations refer to the orientations of the figures. In particular, the terms ‘upper’, ‘lower’, ‘left’, ‘right’, ‘above’, ‘below’, ‘forwards’ and ‘backwards’ should be understood with reference to the orientation of the figures.

[0024] ‘Vacuum pump 1’ means any device connected to a closed volume that is able to create a vacuum in said closed volume, i.e. notably to create a rough vacuum of between 100 and 0.1 Pa. According to the invention, the vacuum pump 1 preferably has at least one pumping stage including two parallel rotor drive shafts, and is preferably a Roots, screw or claw pump. More generally, all rotors compatible with two-shaft drive can be used in the invention. The invention can therefore be applied to any type of dry vacuum pump, regardless of architecture, such as the number of pumping stages or the shape of the rotors.

[0025] The rough-vacuum pumps 1 according to the invention are referred to as ‘dry’ since, when operating, the rotors turn inside a stator with no mechanical contact therebetween or with the stator, which obviates the need to use oil in the pumping stages. Where the invention is applied to a Roots vacuum pump, each shaft can then have between two and eight lobes.

[0026] Three-dimensional gasket’ means any gasket that seals multiple faces of parts of a vacuum pump 1. This is typically a one-piece gasket, i.e. a single part of unbroken material, that lies both in a vertical median plane substantially perpendicular to the central axial direction of the vacuum pump and in a horizontal median plane substantially parallel to the central axial direction of the vacuum pump.

[0027] Figure 1 shows an example manufacturing facility 2 in which a vacuum pump 1 according to the invention is used. In the example in Figure 1, at least one source 3 of process gas is linked to a process chamber 5 in which the parts are manufactured, for example semiconductor-based components. The suction inlet 4 of the vacuum pump is linked to the process chamber 5 to create a rough vacuum therein, enabling manufacture of the parts. The vacuum pump 1 is then configured to drive the waste gas from the process chamber in a flow direction from the suction inlet 4 to the discharge outlet 6, which is for example linked to a treatment device 7 intended to capture and/or destroy any harmful waste gas coming from the process chamber 5. On account of the high level of safety, the invention can naturally be used in any type of facility requiring a rough vacuum, for example creating a vacuum in a load lock.

[0028] In general, the dry rough-vacuum pump 1 comprises, in a known manner, a stator 11 formed by at least one end support 12a, 12b (two shown in Figure 2) configured to support the bearings P of the shaft 9 and miscellaneous equipment (cooling device 22, actuating elements 15, etc.). In the example in Figure 2, the end support 12a forms the first pumping stage 8a, also referred to as the low-pressure stage. Each end support 12a, 12b is coupled axially (axis A1) to at least two assembled stator elements 13 (a pair of half-shells shown in Figure 2) to form at least one pumping stage 8a, 8b, 8c, 8d (four stages 8a, 8b, 8c, 8d mounted in series shown in Figure 2) mounted between the suction inlet 4 and the discharge outlet 6. Two shafts 9 (just one is shown in Figure 2 extending axially along the rotation axis A1) provided with rotors 10a, 10b, 10c, 10d are configured to turn in a synchronized opposite rotations manner (shafts 9 rotate in opposite directions to each other) in each pumping stage 8a, 8b, 8c, 8d to drive a pumped gas in a flow direction from the suction inlet 4 towards the discharge outlet 6.

[0029] As shown for example in Figure 2, the assembled stator elements 13 can form several pumping stages 8a, 8b, 8c, 8d mounted in series between the suction inlet 4 and the discharge outlet 6. In a known manner, the pumping stages 8a, 8b, 8c, 8d are connected together such that the pumped gas flows successively through the pumping stages 8a, 8b, 8c, 8d after being sucked into the suction inlet 4 and before being blown out of the discharge outlet 6. The number of stages 8a, 8b, 8c, 8d can therefore be less than four (one to three) or more than four without thereby moving outside the scope of the invention.

[0030] In a known manner, the shafts 9 can be driven in rotation using synchronized actuating elements 15 comprising, for example, at least one electric motor 16, bearings P, and where necessary a coupling element 14 between the shafts 9 configured to turn the shafts 9 in a synchronized opposite rotations manner. Typically, each shaft 9 can be driven by a different motor 16 and an electronic management unit able to control the power supplied to each motor 16 to ensure the shafts 9 rotate in synchronization and in opposite directions. According to another preferred variant, a single motor 16 is used and the mechanical coupling element 14 ensures that the shafts 9 rotate in synchronization and in opposite directions. In a known manner, the mechanical coupling element 14 can be mounted on the end support 12a close to the motor 16 or, opposite the stator elements 13, on the end support 12b (as shown for example in Figure 2).

[0031] Advantageously according to the invention, the vacuum pump 1 also includes a safety device 17, 17’, 17” mounted sealingly on the end support 12a and that envelops at least the stator elements 13 to form a containment volume 21 for the pumped gas between the stator elements 13 and the safety device 17, 17’, 17”. As explained below, according to an alternative, the other end support 12b of the stator and at least some of the synchronized actuating elements 15 may or may not be enveloped by the safety device 17, 17’, 17”.

[0032] Advantageously according to the invention, since the safety device 17, 17’, 17” is mounted sealingly on the end support 12a and/or 12b, simple assemblies of grooves 19 and O-rings 20 made of special materials such as fluoroelastomer-based materials (notably referred to using the abbreviations FKM, FFKM and FEPM) are used to seal the vacuum pump 1. As a result, the volume of expensive material required is reduced, which significantly reduces production costs (approximately three times less material required) and the geometry is very simple, robust and efficient, which guarantees high containment reliability for the pumped gas in the vacuum pump 1, which results in a limited production cost increase. Furthermore, the assemblies of grooves 19 and O-rings 20 can be easily doubled (two grooves 19, each containing a O-ring 20) with no particular technical difficulty, since the faces to be modified have very simple geometries and are easy to access. Indeed, regardless of the type of dry vacuum pump 1 used, any type of gas can be pumped with no risk to operators in the vicinity of the pump 1, and at lower cost. [0033] Furthermore, since the safety device 17, 17’, 17” advantageously envelops the stator elements 13, a containment volume 21 is created between the stator elements 13 and the safety device 17, 17’, 17”, thereby making the seal between the stator elements 13 less critical. Since the critical seal is moved, gaskets that are less complex (typically flat instead of three-dimensional) with lower specifications in terms of materials and seal performance can be used between the stator elements 13 without adversely affecting safety, and the gaskets may even be omitted for at least some of the pumping stages 8a, 8b, 8c, 8d, which significantly reduces the production cost of the stator elements 13 (the replacement material can notably be approximately nine times cheaper). The absence of a gasket means that the seal of each pumping stage 8a, 8b, 8c, 8d involved, and incidentally the seal between the stator elements 13 involved, can be provided exclusively by the complementary mating surfaces of the members 12a, 12b, 13 of the stator 11. Consequently, even though the seal between the stator elements 13 obtained without a gasket is more reliable than with a gasket, the operation and safety of the vacuum pump 1 are not affected because the safety device 17, 17’, 17” mounted sealingly on the end support 12a and/or 12b guarantees the containment of the pumped gas inside the vacuum pump 1. Incidentally, the manufacture (simple geometry and machined grooves or gaskets and grooves not required) and the assembly (assembly with simplified gaskets or without gaskets) of the stator elements 13 are significantly simpler, thereby also reducing manufacturing costs.

[0034] Finally, despite the addition of the safety device 17, 17’, 17”, the manufacturing cost is lower than for existing vacuum pumps with three-dimensional gaskets made of special materials, while ensuring a level of safety that is at least equivalent, since the risk of leaks is significantly reduced by limiting the required sealing zones. The common containment volume 21 about the stator elements 13 also enhances heat management, notably in terms of uniformity of the cooling of the stator elements 13 in the closed volume 21, which is usually provided locally by a cooling device 22 (shown in Figure 3). Finally, the containment volume 21 between the stator elements 13 and the safety device 17, 17’, 17” according to the invention provides other advantages, as set out below.

[0035] Regardless of the embodiment or variant of the invention, the safety device 17, 17’, 17” preferably has a protective sleeve 18, 18’, 18” mounted sealingly on the end support 12a and/or 12b using at least one assembly comprising a groove 19 and a O- ring 20. This provides a simple and robust containment envelope about the stator elements 13. Indeed, the groove 19 may be formed by simple square-section machining (in a vertical median plane V1 , V2 perpendicular to the rotation axis A1 of the shaft 9), or in the thickness of a free end of the protective sleeve 18, 18’, 18”, or in the outer surface of the end support 12a, 12b. A simple static O-ring 20 made of special material, such as a fluoroelastomer-based material, is then fitted into the groove 19, thereby making assembly very easy and preventing the gasket 20 from being pinched. Naturally, an additional recess may be provided on the part facing the assembly comprising the groove 19 and the O-ring 20 to receive the gasket 20 on a non-flat concave surface in the absence of an additional recess.

[0036] As explained above, according to a first embodiment shown for example in Figure 2, the protective sleeve 18 can envelop the stator elements 13 and a second end support 12b or 12a of the vacuum pump 1 or, according to a second embodiment of the invention shown for example in Figure 3 or Figure 4, the protective sleeve 18’, 18” can envelop the stator elements between two end supports 12a, 12b. The advantages of the invention are retained in both of these embodiments. However, it is obvious that a gasket 19 that is half as voluminous is advantageously obtained in the first embodiment in relation to the second embodiment, which may not be negligible depending on the size of the vacuum pump 1 , thereby reducing the risk of a loss of seal.

[0037] Furthermore, according to other specific variants common to both embodiments and that can be combined with said embodiments, the containment volume 21 between the stator elements 13 and the safety device 17, 17’, 17” can provide other advantages not previously achievable.

[0038] By way of non-limiting example, the safety device 17, 17’, 17” can also include at least one control element intended to change the pressure and/or the nature of the fluid in the containment volume 21. Thus, according to a first variant, the control element can then be used to create negative pressure in the containment volume 21 in relation to the ambient pressure about the vacuum pump 1, for example to improve pumping efficiency and/or remove the pumped gases from the containment volume 21, or conversely to create positive pressure in the containment volume 21, for example to prevent pumped gas from entering the containment volume 21. The control element can therefore for example be a pressurized air source intended to be injected into the containment volume 21, an auxiliary vacuum pump in which the suction inlet or the discharge outlet is configured to be in fluid communication with the containment volume 21, or a valve configured to bring one of the pumping stages 8a, 8b, 8c, 8d into fluid communication with the containment volume 21.

[0039] According to a second variant, regardless of the pressure applied in the containment volume 21 by a control element, the same control element or another element can then be used to bring into the containment volume 21 a fluid other than the gas pumped by the vacuum pump 1. This notably enables the dilution of the pumped gas to be managed using an inert gas such as nitrogen, notably to limit the explosive and/or inflammable nature of the pumped gas. The control element can therefore include a source of pressurized inert gas, such as nitrogen, to be injected into the containment volume 21.

[0040] According to a third variant of the invention, the safety device 17, 17’, 17” can include at least one noise reduction element mounted in the containment volume 21 to reduce the noise intensity outside the vacuum pump 1. The noise reduction element can for example form a resonator and/or at least one chicane to absorb some of the noise generated by the vacuum pump 1. The noise reduction element can therefore be a Helmotz resonator and/or at least one rigid wall forming a deflector and/or a wall of absorbing material forming a deflector arranged in the containment volume 21.

[0041] According to a fourth variant of the invention, the safety device 17, 17’, 17” can then include at least one flow adjustment element intended to communicate the containment volume 21 with an element outside the vacuum pump 1 and/or a pumping stage 8a, 8b, 8c, 8d of the vacuum pump 1 to selectively modify the incoming and outgoing flows of the vacuum pump 1. This notably enables the architecture of the vacuum pump 1 to be adapted easily. In the example shown in Figure 2, the discharge outlet 6 communicates with the pumping stage 8d via a conduit formed respectively in the stator elements 13 and extending into the end support 12a. By way of non-limiting example, the flow adjustment element could be the suction inlet 4 or the discharge outlet 6, i.e. replacing the suction inlet 4 or the discharge outlet 6 in the example in Figure 2, arranged in the safety device 17, 17’, 17”, typically in the protective sleeve 18, 18’, 18”, to offset the suction inlet 4 or the discharge outlet 6 to lessen the congestion about the vacuum pump 1. In the example in Figure 4, two control elements comprise respectively an outlet from the stage 8d communicating with the volume 21 and a discharge outlet 6 mounted sealingly in the protective sleeve 18”. The outlet from the stage 8d therefore communicates with the volume 21 (see direction of the arrow) then the discharge outlet 6 to arrive for example at the treatment device 7. [0042] According to a fifth variant of the invention, the safety device 17, 17’, 17” can then include at least one detection element to monitor operation of the vacuum pump 1. This for example makes it possible to monitor the gas or gases in this volume 21 , to adapt the settings of the vacuum pump 1 if required. The detection element can therefore for example be a detector to detect at least one proportion of gas in the volume 21, for example to maintain a predetermined dilution rate, and/or to detect gases present in the volume 21 indicating a potential intake air leak, and/or a pressure detector to determine whether any pumped gas is flowing back upstream from the vacuum pump 1 , for example towards the process chamber 5, notably when the vacuum pump is stopped.

[0043] The invention is not limited to the embodiments and variants disclosed and other embodiments and variants will be clear to the person skilled in the art. Thus, all of the embodiments and variants can be combined with one another without thereby moving outside the scope of the invention. Without limitation, the protective sleeve 18 in Figure 2 can be modified to include the two adjustment elements from the fourth variant in Figure 4 so that the outlet from the stage 8d communicates with the volume 21 of the protective sleeve 18 in which the discharge outlet 6 is formed, without thereby moving outside the scope of the invention. It is also possible to combine the two adjustment elements in the fourth variant of the second embodiment of the safety device 17” in Figure 4 with at least one noise reduction element according to the third variant (for example at least one wall that is rigid and/or made of absorbing material forming a deflector) between the outflow from the pumping stage 8d and the outflow of the discharge outlet 6, without thereby moving outside the scope of the invention.

[0044] According to another example, as shown in Figure 2, at least some of the actuating elements 15 can also be confined similarly to the stator elements 13 in order to prevent any harmful residue coming from the process chamber 5 via a bearing P in the pumping stage 8a from being release about the vacuum pump 1. Similarly to the stator elements 13, a protective sleeve 118 can notably envelop the motor 16 with the end support 12a using an assembly comprising a groove 119 and a O-ring 120.