CN115176068A

CN115176068A - Dry vacuum pump

Info

Publication number: CN115176068A
Application number: CN202180015940.6A
Authority: CN
Inventors: Y·奥利维尔; E·曼达拉兹; T·布尔里隆; P·菲利普
Original assignee: Pfeiffer Vacuum SAS
Current assignee: Pfeiffer Vacuum SAS
Priority date: 2020-02-20
Filing date: 2021-02-12
Publication date: 2022-10-11
Also published as: KR20220131556A; US20230033204A1; FR3107575A1; FR3107575B1; WO2021165160A1; CZ2022344A3; DE112021001178T5; JP2023514693A

Abstract

The invention relates to a dry vacuum pump (1) comprising an elastic outer seal (16) and at least one elastic inner seal (17), each of which comprises a first and a second end ring (161, 171, 162, 172) parallel to each other and interposed between the respective end piece (9, 10) and a half shell (7, 8), and two side rails (163, 173) connecting and at right angles to said end rings (161, 171, 162, 172), the side rails (163, 173) being interposed between the half shells (7, 8), the at least one inner seal (17) being arranged inside the outer seal (16) such that the at least one inner seal (17) and the outer seal (16) form at least two continuous sealing barriers to gases.

Description

Dry vacuum pump

Technical Field

The present invention relates to a dry vacuum pump.

Background

A dry vacuum pump comprises one or more pump stages in series, in which the gas to be pumped circulates. Known vacuum pumps that can be distinguished are vacuum pumps with rotating vanes, also known as "roots" type, or vacuum pumps with beak, also known as "claw" type. These vacuum pumps are said to be "dry" because, in operation, the rotors rotate inside the stator and there is no mechanical contact between the rotors or between the rotors and the stator, allowing no oil to be used in the pumping stages.

As an example, document us6,572,351b2 discloses a vacuum pump structure having a stator in the form of half-shells joined on longitudinal joining surfaces substantially parallel to the rotor axis. The vacuum pump includes an integral seal having two end ring portions and two side rails connecting the end ring portions at right angles thereto. The two end annular portions are parallel to each other and are each interposed between an end piece and a half-shell. Side rails are inserted between the half shells. The one-piece seal ensures both the seal between the half-shells and the additional end piece, in order to isolate the compression stage from the external atmosphere.

However, in certain pumping applications, such as pumping processes used in the semiconductor, "flat panel display" and photovoltaic industries, and in coating processes, the use of a metal oxide is desirableThe gases used may be corrosive, especially gases used in cleaning the process chamber. For gas NF ₃ 、ClF ₃ 、F ₂ 、Cl ₂ This is particularly the case. These corrosive gases can damage the seals located between the half shells.

In addition to the loss of performance of the pumping device, the deterioration of such seals can also lead to safety issues. On the one hand, oxygen or water vapour from the surrounding air can enter the pump chamber and react with the gas delivered, which in particular leads to a risk of ignition or explosion of the gas being pumped. Moreover, toxic gases may leak from the pump chamber of the vacuum pump to the atmosphere, especially from the high-pressure pump stage, which may pose a threat to personnel safety.

To avoid this, the vacuum pump adopts a sliced architecture in which the stator is composed by axially assembling a plurality of stator elements, including an annular seal radially compressed between the stator elements and received in the same annular seal groove

(or PTFE) seal pairs.

The seal takes the form of a strip having a parallelepiped cross-section, which is pressed between the stator elements to create a seal. Annular seal and

the pairing of the barriers makes it possible to secure the seal at a relatively economical cost.

However, this embodiment, which is well suited for pumps with a sliced architecture, cannot be simply applied to pumps with a half-shell architecture, in which the seal is produced by the integral seal described above. In fact, use

It is not easy to produce a three-dimensional seal and it is produced in a plurality of parts joined by extrusion

Barriers are also not a satisfactory solution because of the small contact surface and

the non-elastic nature of (a) does not guarantee a seal between the different components without the entry of gas.

Furthermore, in the case where the end portion comprises a nose portion axially engaged with the half-shell, fitting around the axial nose portion is neither elastic nor toroidal

Barriers are also not easy to handle. Moreover, the assembly of the half-shells in the axial direction with the nose of the extension end piece does not allow an effective compression

A barrier.

Disclosure of Invention

It is an object of the present invention to at least partly overcome one of the above disadvantages.

To this end, the subject of the invention is a dry vacuum pump comprising:

-a stator comprising at least one first and at least one second complementary half-shell and one first end piece and one second end piece, the half-shells and the end pieces being joined to each other by axial assembly to form at least one pumping chamber of a pumping stage,

-two rotor shafts configured to rotate in counter-synchronization in at least one pump stage,

characterized in that the vacuum pump further comprises:

-an elastic outer seal and at least one elastic inner seal, each comprising:

-a first and a second end annular portion, parallel to each other and interposed between the respective end piece and the half-shell, and

-two side rails connecting the end ring sections at right angles thereto, the side rails being inserted between the half shells, the at least one inner seal being arranged inside the outer seal such that the at least one inner seal and the outer seal form at least two continuous sealing barriers against gas.

The at least one inner seal is smaller than the outer seal so as to be able to be disposed inside in a "nested" arrangement. It is thus possible to double or even triple the seal. This multiplication of the sealing barrier may ensure a good seal from the outside to the inside and vice versa, and allows the use of different materials for each seal capable of providing a corrosive gas and/or a level of heat resistance that decreases with distance from the pump chamber.

The vacuum pump may also include one or more of the features described below, used alone or in combination.

The overseal may be a unitary piece.

The at least one inner seal may be unitary.

According to another exemplary embodiment, the outer seal and/or the inner seal are joined end-to-end, that is to say, are formed by placing a plurality of resilient sealing portions end-to-end.

The at least one inner seal may be formed of a material that is more corrosion, wear and/or high temperature resistant than the material of the outer seal.

The outer seal may be made of a fluorinated elastomeric material.

The at least one inner seal may be made of a perfluoroelastomer material.

According to one exemplary embodiment, the half-shells and the end-pieces are engaged with each other by axial assembly of first and second axial noses with complementary first and second axial voids, one of the axial noses and the axial voids being carried by the half-shells and the other by the end-pieces, the first and second end annular portions being interposed between the respective axial noses and the complementary axial voids.

First and at least one second circumferential annular groove may be formed in the at least one axial nose and/or the at least one axial void to receive the first and second end annular portions of the outer seal and the at least one inner seal.

According to another exemplary embodiment, the half-shells and the end pieces engage each other without the presence of complementary axial noses and voids. The end pieces and/or the half-shells have, for example, annular grooves formed in the plane of the end pieces and in the plane of the facing edges of the half-shells.

At least two longitudinal grooves may be formed in the engagement surface in one and/or the other half shell on either side of the pump chamber to receive the side rails of the outer and inner seal members.

At least one injection duct may be formed in the half shell of the stator and emerging through at least one injection orifice in the clearance space between the at least one inner and outer seals, the vacuum pump comprising a gas supply device configured to inject a neutral gas into the injection duct. This circulation of gas creates a third sealed barrier to the gas, as well as a thermal barrier. Such a sealing barrier may in particular protect the outer seal, especially in case the material of the outer seal has low corrosion, wear and/or high temperature resistance.

The injection duct may be present in the region of the gap space between the two side rails, in the joining surface of the half shells.

The gas supply may be configured to heat the neutral gas.

The gas supply may be configured to inject the neutral gas at an overpressure.

At least one suction duct may be formed in the half shell of the stator and emerging via at least one suction aperture in the clearance space between the at least one inner and outer seal, the suction duct connecting the clearance space with the pump chamber or the inter-stage channel of the vacuum pump.

The suction duct may be present in the region of the gap space between the two side rails, in the joining surface of the half-shells.

The vacuum pump may include a pressure sensor configured to measure a pressure in a clearance space between the at least one inner seal and the outer seal. A pressure change measurement above a threshold value may indicate the presence of a leak and therefore a seal defect.

The vacuum pump may include a gas sensor configured to determine whether at least one corrosive gas species, such as Cl or Cl, is present in a clearance space between the at least one inner seal and the outer seal ₂ 、O ₂ F or F ₂ H or H ₂ 、HBr、HF、HCl、ClF ₃ 、NF ₃ 、SIF ₄ . The gas sensor is, for example, of the electrochemical type, which has, for example, two or three electrodes. The presence of one of these gaseous species in the interstitial space may indicate the presence of a leak and, therefore, a seal defect in the inner seal.

The gas or pressure sensor is for example a MEMS ("micro-electro-mechanical system") sensor.

The vacuum pump for example comprises a control unit, such as a controller or microcontroller, linked to the gas sensor and configured to trigger maintenance in case a concentration threshold value of the at least one corrosive gas species is exceeded, and/or said control unit is linked to the pressure sensor and configured to trigger maintenance in case a pressure variation threshold value is exceeded.

The half-shells of the stator may form at least two pumping stages, which are mounted in series between the suction and discharge ports of the vacuum pump.

The stator may comprise at least two pairs of complementary half-shells, the resilient outer and inner seals each comprising at least one intermediate annular portion interposed between the two pairs of half-shells.

The stator may further include at least one integrated pumping stage mounted in series with at least one pumping stage formed in at least the first and second half shells.

Drawings

Other advantages and features will become apparent upon reading the following description of particular but non-limiting embodiments of the invention and the accompanying drawings, in which:

fig. 1 is an exploded schematic view of elements of a dry vacuum pump according to a first exemplary embodiment.

Fig. 2 is a perspective view of one example of a rotor shaft of the vacuum pump of fig. 1.

Figure 3 is a perspective view of half shells assembled with the outer seal, inner seal and end pieces of the vacuum pump of figure 1.

Fig. 4 is a plan view of the elements of fig. 3.

Fig. 5 is a longitudinal section of the half-shell of fig. 4, seen from the side, and an enlarged view of a detail of the half-shell.

Fig. 6 is a view in section BB of the half-shell of fig. 4, seen from the front, and an enlarged view of a detail of the half-shell.

Fig. 7 is an exploded schematic view of elements of a dry vacuum pump according to a second exemplary embodiment.

In the figures, identical or similar elements have the same reference numerals.

The drawings are simplified for clarity. Only those elements necessary for an understanding of the present invention are shown.

Detailed Description

The following examples are illustrative. Although the description refers to one or more embodiments, this does not necessarily mean that each reference is made to the same embodiment, or that the features are applicable to only a single embodiment. Simple features of different embodiments may also be combined or interchanged to provide further embodiments.

A "primary vacuum pump" defines a positive displacement vacuum pump configured to use two rotor shafts to pump, transfer, and then evacuate gases to be pumped at atmospheric pressure. The rotor shaft is rotated by a motor of the primary vacuum pump. The primary vacuum pump may be started from atmospheric pressure.

A roots-type vacuum pump or roots compressor (also referred to as a "roots blower") defines a positive displacement vacuum pump configured to draw, displace, and then expel gas to be pumped using a roots-type rotor. A roots-type vacuum pump is mounted upstream of and in series with the primary vacuum pump. The rotor is supported by two shafts which are driven to rotate by a motor of the roots-type vacuum pump. A roots vacuum pump comprises one to three pump stages.

"upstream" is understood to mean an element which is placed before another element with respect to the direction of circulation of the gas to be pumped. Conversely, "downstream" is understood to mean an element placed after another element with respect to the direction of circulation of the gas to be pumped.

The "axial direction" is defined as the longitudinal direction of the pump, along which the axis of the rotor shaft extends.

The dry vacuum pump 1 of fig. 1 comprises a stator 2, which stator 2 forms at least one pumping stage, for example at least two pumping stages 3a-3f, for example two to ten pumping stages (six in the illustrated example), which are mounted in series between a suction opening 4 and an exhaust opening 5. The vacuum pump 1 may be a primary vacuum pump (fig. 1) or a roots-type vacuum pump.

The vacuum pump 1 further comprises two rotor shafts 6 (fig. 2) configured to rotate synchronously in opposite directions in the at least one pump stage 3a-3f, such that the rotors drive the gas to be pumped between the suction opening 4 and the exhaust opening 5. The rotor shaft 6 can be one-piece or made by assembling various additional elements.

For example, the rotors have identically profiled lobes, such as a "roots" type (fig. 2) or a "claw" type or other similar positive displacement vacuum pump principle. The shaft carrying the rotor is driven by an electric motor (not shown) located, for example, at the end of the vacuum pump 1, for example, on the side of the exhaust port 5.

Each pump stage 3a-3f of the stator 2 is formed by a pump chamber receiving two conjugated rotors, which pump chambers comprise respective inlet and outlet ports. During rotation, gas drawn from the inlet is captured in the volume created by the rotor and stator 2 and then driven by the rotor to the next stage.

Successive pump stages 3a-3f are connected in series one after the other by respective interstage passages (not shown) connecting the outlet of the previous pump stage 3a-3e to the inlet of the next pump stage 3b-3 f. The inlet of the first pump stage 3a is connected to the suction opening 4 of the vacuum pump 1. The outlet of the last pump stage 3f is connected to the discharge 5. The axial dimensions of the rotor and the pump chamber are for example equal or they decrease with the pumping stage, the pumping stage 3a being located on the side of the suction opening 4 receiving the rotor 6 of the largest axial dimension.

These vacuum pumps are said to be "dry" because, in operation, the rotors rotate inside the stator 2 and there is no mechanical contact between the rotors or between the rotors and the stator 2, thus allowing no oil to be used in the pump stages 3a-3 f.

The stator 2 comprises at least one first and at least one second complementary half-

shell

7,8, and first and

second end pieces

9, 10. The half-shell architecture may reduce assembly time due to the fewer number of interfaces that need to be aligned. This architecture may also reduce the risk of alignment defect clustering. The cost of the vacuum pump 1 can be reduced and assembly simplified.

The half-

shells

7,8 are joined to each other by means of a joining surface 11 to form at least one pump chamber of the at least one pump stage 3a-3 f. The at least one compression chamber and, where appropriate, the transfer channel are formed partly in the first half-shell 7 and partly in the second half-shell 8.

The joining surface 11 is, for example, a flat joining surface, which passes through, for example, the middle plane of the dry vacuum pump 1. The flat engagement surface 11 contains, for example, the axis of the rotor shaft 6. Such a flat engagement surface 11 may be strictly flat or may, for example, have a complementary relief form, or a groove for a side rail of a seal between the half-shells, as will be seen later.

The first ends of the half-

shells

7,8 are closed by a first end-piece 9, and the second ends of the half-

shells

7,8 are closed by a second end-piece 10. Of course, apertures for the rotor shaft 6 are formed in the transverse walls 15 of the half-

shells

7,8 and in the

end pieces

9, 10, which divide the pump chambers as appropriate.

The half-

shells

7,8 and the end-

pieces

9, 10 are engaged with each other by axial assembly, for example by axial assembly of complementary first and second axial noses 12 and first and second axial voids 13, one of which is carried by the half-

shells

7,8 and the other by the end-

pieces

9, 10.

In the example shown in fig. 1 to 6, the first and second axial noses 12 are formed in the

respective end pieces

9, 10.

The axial nose 12 projects in the axial direction. For example, it has an elongated transverse form, substantially corresponding to the form of the section of the pump chamber of the pump stage 3a-3f in which the complementary axial interspace 13 is formed. The axial nose 12 has, for example, a solid form. The axial recesses 13 are formed, for example, in the pump chambers of the first pump stage 3a and the pump chambers of the last pump stage 3 f.

The vacuum pump 1 further comprises an outer seal 16 and at least one inner seal 17. The

seals

16, 17 are three-dimensional and can be one-piece, i.e. one-piece.

According to another exemplary embodiment, the outer seal 16 and/or the inner seal 17 are joined end-to-end, that is, they are formed by placing a plurality of resilient portions of the

seals

16, 17 end-to-end.

They are elastic, in particular because they comprise an elastomeric material. They are obtained, for example, by pressing or injection moulding. The outer seal 16 and the inner seal 17 have, for example, a substantially circular cross-section in the non-compressed state.

The outer seal 16 and the inner seal 17 comprise a first and a second

end ring portion

161, 162, 171, 172, respectively, which are parallel to each other, and two

side rails

163, 173 connecting the

end ring portions

161, 162, 171, 172 at right angles thereto.

The end

annular portions

161, 171, 162, 172 have a conventional annular form. They are interposed between the

end pieces

9, 10 and the respective half-

shells

7,8, for example between the respective complementary axial noses 12 and the axial interspace 13. For example, at the first axial end of the half-

shells

7,8, a first end

annular portion

161, 171 is interposed between the axial nose 12 of the first end piece 9 and the axial interspace 13 of the pumping chamber of the last pumping stage 3 f. At the second axial end of the half-

shells

7,8, a second end

annular portion

162, 172 is inserted between the axial nose 12 of the second end piece 10 and the axial interspace 13 of the pump chamber of the first pump stage 3 a.

This rounded form and the elastic properties of the end

annular portions

161, 171, 162, 172 allow them to be easily mounted on and dismounted from the respective axial noses 12.

The side rails 163, 173 of the outer seal 16 and the at least one inner seal 17 are inserted between the half-

shells

7,8 on the engagement surface 11. Thus on both sides of the pump chamber, there are two

side rails

163, 173 extending axially parallel to each other.

The at least one inner seal 17 is arranged inside the outer seal 16 such that the at least one inner seal 17 and the outer seal 16 form at least two continuous sealing barriers for the gas. The at least one inner seal 17 is smaller than the outer seal 16 and can thus be arranged inside in a "nested" arrangement.

The seal can thus be doubled. This multiplication of the sealing barrier may ensure a good seal from the outside to the inside and vice versa, and allows the use of different materials that may provide a corrosive gas and/or a level of heat resistance that decreases with distance from the pump chamber.

Indeed, it is conceivable that the at least one inner seal 17 is formed of a material that is more durable, in particular more corrosion-, wear-and/or high temperature-resistant, than the material of the outer seal 16. The material of the outer seal 16 may thus be more economical than the material of the inner seal 17, while being acceptable in terms of safety. The outer seal 16 is made of, for example, a fluorinated elastomer material (FKM) and the at least one inner seal 17 is made of, for example, a perfluoroelastomer material (FFKM).

It is also possible to triple the seals, or even more so, the vacuum pump 1 thus comprising at least two inner seals 17, at least one first inner seal being arranged inside at least one second inner seal. Also, the at least one first inner seal 17 may be formed of a more durable material than the material of the at least one second inner seal 17, in particular more corrosion, wear and/or high temperature resistant.

A first peripheral annular groove 18a and at least one second peripheral annular groove 18b may be formed in at least one axial nose 12 (fig. 5) and/or in at least one axial interspace 13 to receive the first end

annular portions

161, 171 of the outer seal 16 and of the at least one inner seal 17.

A first peripheral annular groove 18a and at least one second peripheral annular groove 18b may be formed in at least one axial nose 12 (fig. 5) and/or at least one axial void 13 to receive the second end

annular portions

162, 172 of the outer seal 16 and the at least one inner seal 17.

The axial noses 12 formed in the

end pieces

9, 10 have the following advantages: the peripheral

annular grooves

18a,18b are of a single piece, without the junction between the half-shells and therefore without additional seals. It is also easier to make the peripheral

annular grooves

18a,18b in the axial nose 12. Thus, the mounting/dismounting of the end

annular portions

161, 162, 171, 172 in the peripheral

annular grooves

18a,18b and the manufacturing thereof are simpler for the peripheral annular grooves formed in the axial noses 12 formed in the

end pieces

9, 10. Thus, for example, there are two axially offset peripheral

annular grooves

18a,18b in the axial nose 12 of each of the two

end pieces

9, 10.

On both sides of the pump chamber, at least two

longitudinal grooves

19a,19b may be formed in the engagement surface 11 in one and/or the other of the

half shells

7,8 to receive the side rails 163, 173 (fig. 6) of the outer and

inner seal members

16, 17.

For example, there are four

longitudinal grooves

19a,19b for receiving the four

side rails

163, 173 of the inner seal 17 and the outer seal 16, two

longitudinal grooves

19a,19b being formed on either side of the pump chamber.

Thus, each outer seal 16 and inner seal 17 may be received in its respective peripheral

annular groove

18a,18b and respective

longitudinal groove

19a,19 b. Further, it is preferable that a single groove is formed on one side of the stator 2 and faced with a plane, rather than forming a groove on each side. This simplifies mounting/dismounting and (machining) machining. A good seal can thus be obtained by radial compression of the end

annular portions

161, 171, 162, 172 and the side rails 163, 173.

The interstitial space 22 between the outer seal 16 and the at least one inner seal 17 defines a tightly enclosed volume.

According to an exemplary embodiment, at least one injection duct 20 is formed in the half-shell 8 of the stator 2 and enters the interstitial space 22 (fig. 6) through at least one injection orifice 21. As can be better seen in fig. 3 and 4, the guide duct 20 is present, for example, in the region of the gap space 22 between the two

side rails

163, 173 in the joining surface 11. For example, on each side of the pumping chamber of the penultimate pumping stage 3e, there are at least two injection ducts 20 formed in the half-shell 8 and present in said region.

The vacuum pump 1 further comprises a gas supply device 23 (fig. 6) configured to inject a neutral gas into the injection duct 20. Neutral gas may thus be injected into the clearance space 22 and circulate longitudinally between the side rails 163, 173 and around the axial nose 12 between the end rings 161, 171, 162, 172. This circulation of gas creates a third sealed barrier to the gas, as well as a thermal barrier. The seal barrier is particularly capable of protecting the outer seal 16, particularly where the material is less resistant to corrosion, abrasion and/or high temperatures.

The gas supply 23 can be configured to inject the neutral gas at an overpressure, that is to say a pressure greater than atmospheric pressure.

The gas supply 23 may also be configured to heat the neutral gas. For example, it comprises a coil in thermal contact with the stator 2, which is configured to heat the neutral gas circulating in the coil by heat exchange with the stator 2. The stator 2 is heated by compression of the gas and/or by its own temperature control means.

At least one suction duct (not visible) can be formed in the

half shells

7,8 of the stator 2, which emerges in the clearance space 22 via at least one suction aperture 24. The suction line connects the intermediate space 22 to a pump chamber or an interstage duct of the vacuum pump 1, for example, the first pump stage 3 a. The transfer channel is formed on the side of the pump chamber, for example in a half shell.

The pumping function of the vacuum pump 1 can thus be used alone to create a vacuum in the interstitial space 22, or together with a supplementary injection of neutral gas to circulate the neutral gas in the interstitial space 22. The interstitial space 22 may also create a third sealed barrier to gas in either the vacuum pressure mode or the gas circulation mode.

For example, the suction duct is present in the region of the gap space 22 located in the joining surface 11 and between the two

side rails

163, 173. For example, on each side of the pump chamber of the first pump stage 3a, at least two suction ducts are formed in the half-shell 8 and are present in said region.

The vacuum pump 1 may further comprise a pressure sensor 25 configured to measure the pressure in the interstitial space 22. The pressure sensor 25 is connected to the injection pipe 20 (fig. 6), for example. A pressure change measurement exceeding a threshold value may indicate the presence of a leak and thus a seal defect. This information can be used by the control unit 26 of the vacuum pump 1, which control unit 26 is linked to the pressure sensor 25 and is configured to issue a signal that a maintenance need be triggered in case a pressure variation threshold is exceeded.

The vacuum pump 1 may further comprise a gas sensor 27, the gas sensor 27 being configured to determine the presence of at least one corrosive gas species in the interstitial space 22 between the at least one inner seal 17 and the outer seal 16. The gas sensor 27 is connected to the injection pipe 20 (fig. 6), for example.

For example, the gas sensor 27 is configured to determine the presence of at least one corrosive gas species selected from Cl or Cl ₂ 、O ₂ F or F ₂ H or H ₂ 、HBr、HF、HCl、ClF ₃ 、NF ₃ 、SIF ₄ . The gas sensor 27 is, for example, of the electrochemical type, having, for example, two or three electrodes.

The presence of one of these gaseous species in the interstitial space 22 may indicate the presence of a leak and, therefore, a seal defect in the inner seal 17. This information can be used by the control unit 26, which control unit 26 is in turn linked to the gas sensor 27 and configured to signal the need to trigger maintenance in case the concentration threshold of the at least one corrosive gas species is exceeded.

The gas sensor 27 or the pressure sensor 25 is, for example, a MEMS ("micro electro mechanical system") sensor.

By detecting a pressure failure or the presence of a predetermined gaseous substance in the dead volume delimited by the two

seals

16, 17, a sealing defect can be detected without jeopardizing the safety of the personnel or of the equipment, while allowing intervention by maintenance personnel.

Fig. 7 shows a second exemplary embodiment of a vacuum pump 1.

In this example, the stator 2 comprises at least two pairs of complementary half-

shells

7,8, 70, 80, 700, 800 (three pairs in the example illustrated).

For example, two half-

shells

7,8 form two pumping

stages

3a, 3b, two half-

shells

70, 80 form the other two pumping

stages

3c, 3d, and two half-

shells

700, 800 form the other two pumping

stages

3e, 3f, the pumping stages 3a-3f being mounted in series between the suction opening 4 and the discharge opening 5 of the vacuum pump 1.

The elastic outer seal 16 and the inner seal 17 each comprise at least one intermediate

annular portion

164, 174, 165, 175 interposed between the two pairs of half-

shells

7, 8. The

intermediate ring portions

164, 174, 165, 175 are parallel to the

end ring portions

161, 171, 162, 172 and are connected to and at right angles to the two

side rails

163, 173.

Like the end

annular portions

161, 171, 162, 172, the intermediate

annular portions

164, 174, 165, 175 have a conventional annular form and are insertable between the respective complementary axial noses 12 and the axial interspace 13. For example, the first intermediate

annular portion

164, 174 is interposed between the two pairs of half-

shells

7,8, 70, 80, and the two intermediate

annular portions

165, 175 are interposed between the two pairs of half-

shells

70, 80, 700, 800. For example, an axial nose 12 is carried by the pair of half-

shells

70, 80 at a first end, and an axial void 13 is formed in the pumping chamber of the pair of half-

shells

70, 80, for example at a second end.

Furthermore, although not shown in the figures, the vacuum pump 1 may also comprise at least one integrated pumping stage, mounted in series upstream or downstream of at least one pumping stage 3a-3f formed in at least the first and second half-

shells

7, 8.

Furthermore, according to another exemplary embodiment, the half-

shells

7,8 and the

end pieces

9, 10 can engage each other without the presence of complementary axial noses and clearances. For example, the

end pieces

9, 10 and/or the half-

shells

7,8 have annular grooves formed in the plane of the end pieces and in the plane of the facing edges of the half-

shells

7, 8.

Claims

1. A dry vacuum pump (1) comprising:

-a stator (2), said stator (2) comprising at least one first and at least one second complementary half-shells (7, 8) and one first and one second end-piece (9, 10), said half-shells (7, 8) and said end-pieces (9, 10) being joined together by axial assembly to form at least one pump chamber of a pump stage (3 a-3 f),

-two rotor shafts (6), the two rotor shafts (6) being configured to counter-rotate synchronously in at least one pump stage,

characterized in that the vacuum pump (1) further comprises:

-an elastic outer seal (16) and at least one elastic inner seal (17), the outer seal (16) and the inner seal (17) each comprising:

-a first and a second end annular portion (161, 171, 162, 172) parallel to each other and interposed between the respective end piece (9, 10) and the half-shell (7, 8), and

-two side rails (163, 173) connecting and at right angles to said end annular portions (161, 171, 162, 172), said side rails (163, 173) being interposed between the half-shells (7, 8), said at least one inner seal (17) being arranged inside said outer seal (16) so that said at least one inner seal (17) and said outer seal (16) form at least two continuous sealing barriers against gases.

2. Vacuum pump (1) according to the preceding claim, characterized in that the outer seal (16) is integral.

3. Vacuum pump (1) according to any of the preceding claims, characterized in that the at least one inner seal (17) is one-piece.

4. Vacuum pump (1) according to any of the preceding claims, characterized in that the at least one inner seal (17) is formed of a material that is more corrosion-, wear-and/or high temperature resistant than the material of the outer seal (16).

5. Vacuum pump (1) according to any of the preceding claims, characterized in that the outer seal (16) is made of a fluorinated elastomeric material and the at least one inner seal (17) is made of a perfluoroelastomeric material.

6. Vacuum pump (1) according to any one of the preceding claims, characterized in that said half-shells (7, 8) and said end-pieces (9, 10) are mutually engaged by axial assembly of a first and a second axial nose (12) with a complementary first and a second axial interspace (13), one of which is carried by said half-shells (7, 8) and the other by said end-pieces (9, 10), the first and second end-ring portions (161, 171, 162, 172) being interposed between the respective complementary axial nose (12) and axial interspace (13).

7. Vacuum pump (1) according to the preceding claim, characterized in that:

-forming first and at least one second peripheral annular groove (18a, 18b) in at least one axial nose (12) and/or at least one axial void (13) to receive first and second end annular portions (161, 171, 162, 172) of the outer seal (16) and the at least one inner seal (17),

-at least two longitudinal grooves (19a, 19b) are formed in one and/or the other of the half-shells (7, 8) in the joining surface (11) and on both sides of the pump chamber to receive the side rails (163, 173) of the outer seal (16) and the inner seal (17).

8. Vacuum pump (1) according to any of the preceding claims, characterized in that at least one injection duct (20) is formed in a half-shell (7, 8) of the stator (2) and emerges through at least one injection orifice (21) in a clearance space (22) located between the at least one inner seal (17) and the outer seal (16), the vacuum pump (1) comprising a gas feed (23) configured to inject a neutral gas into the injection duct (20).

9. Vacuum pump (1) according to the preceding claim, characterized in that the injection duct (20) is present in the region of the clearance space (22) located in the joining surface (11) of the half-shells (7, 8) and between the two side rails (163, 173).

10. Vacuum pump (1) according to any of claims 8 and 9, characterized in that the gas supply means (23) are configured to heat the neutral gas.

11. Vacuum pump (1) according to any of claims 8 to 10, characterized in that the gas supply means (23) are configured to inject the neutral gas at overpressure.

12. Vacuum pump (1) according to one of claims 1 to 10, characterized in that at least one suction duct is formed in a half shell (7, 8) of the stator (2) and emerges via at least one suction aperture (24) in an interstitial space (22) located between the at least one inner seal (17) and the outer seal (16), the suction duct (24) connecting the interstitial space (22) with a pump chamber or an inter-stage channel of the vacuum pump (1).

13. Vacuum pump (1) according to the preceding claim, characterized in that the suction duct (24) is present in the region of the clearance space (22) located in the joining surface (11) of the half-shells (7, 8) and between the two side rails (163, 173).

14. Vacuum pump (1) according to any of the preceding claims, characterized in that the vacuum pump (1) comprises a pressure sensor (25), the pressure sensor (25) being configured to measure the pressure in the clearance space (22) between the at least one inner seal (17) and the outer seal (16).

15. Vacuum pump (1) according to any of the preceding claims, characterized in that the vacuum pump (1) comprises a gas sensor (27), the gas sensor (27) being configured to determine whether at least one corrosive gas species is present in the interstitial space (22) between the at least one inner seal (17) and the outer seal (16).

16. Vacuum pump (1) according to any of the preceding claims, characterized in that the half-shells (7, 8) of the stator (2) form at least two pumping stages (3 a-3 f), the pumping stages (3 a-3 f) being mounted in series between a suction opening (4) and an exhaust opening (5) of the vacuum pump (1).

17. Vacuum pump (1) according to any one of the preceding claims, characterized in that said stator (2) comprises at least two pairs of complementary half-shells (7, 8, 70, 80, 700, 800), said elastic outer seal (16) and inner seal (17) respectively comprising at least one intermediate annular portion (164, 165, 174, 175) interposed between the two pairs of half-shells (7, 8, 70, 80, 700, 800).

18. Vacuum pump (1) according to any of the preceding claims, characterized in that the stator (2) further comprises at least one integrated pumping stage mounted in series with at least one pumping stage (3 a-3 f) formed in at least a first and a second half-shell (7, 8).