Vacuum pump

Abstract

The invention relates to a dry vacuum pump (1) comprising at least one cleaning duct (16) comprising two channels (17, 18) arranged within the thickness of an interstage transverse half-wall (9a) of a half-shell (4), each channel (17, 18) opening from a front face (19) of said interstage transverse half-wall (9a) via a respective orifice (20, 21) into a space inside a pump stage (T1-T6), the cleaning duct further comprises a transverse groove (22) provided in the interstage transverse half-wall (9a) at the joining surface (13) of the half-shells (3, 4), the channel (17, 18) being formed by a tubular duct formed between an inclined plane (23) of the transverse groove (22) and the front face (19).

Description

Technical Field

[0001] The present invention relates to a vacuum pump, and more particularly to a cleaning pipeline of the vacuum pump. Background Art

[0002] A dry vacuum pump has one or more pumping stages in series, in which the gas being pumped circulates between a suction port and a delivery port. Among the known vacuum pumps, there are vacuum pumps with rotating vanes (also called "Roots" pumps) and vacuum pumps with claws (also called "claw" pumps). These vacuum pumps are called "dry" vacuum pumps because, in operation, the rotor rotates within the stator without any mechanical contact between the rotors or between the rotor and the stator, eliminating the need for oil in the pumping stages.

[0003] Certain vacuum pumps are used in manufacturing processes for semiconductors, flat screens, photovoltaic panels or coatings, in particular processes for depositing thin films under vacuum, i.e. high aspect ratio processes (HARP), in particular CVD, PECVD, SACVD, ALD etc. These processes usually alternate deposition steps, in which process gases such as resin vapor or precursors are introduced into the reactor for thin film deposition, with cleaning steps, in which reactive gases such as corrosive gaseous substances are introduced into the reactor for cleaning the walls of the reactor.

[0004] The gases used for the deposition steps generate a large number of byproducts in solid form (powders, pastes, chips). Large amounts of powder build up on the moving parts of the vacuum pump and can quickly cause the pump to stop operating due to mechanical seizure. Therefore, it is crucial to reduce the failure rate of these powder generation processes.

[0005] In order to prevent the polymerization by-products from contaminating the pumping device, it is known to use traps in the vacuum line. These traps separate the solid by-products from the gas, for example by gravity or centrifugal force or by condensation or pyrolysis, and retain the solid by-products by accumulation. One problem is that the accumulation of powder in the trap increases the probability of encountering substances of different chemical nature. This can cause and promote undesirable chemical reactions, such as the above-mentioned polymerization reactions. Moreover, the high temperature of these traps (generally between 140° C. and 170° C.) provides activation energy that promotes these chemical reactions. Therefore, these traps must be cleaned frequently.

[0006] Another solution is to adjust the geometry of the vacuum pump by design to facilitate evacuation of the powder, for example by providing wider transfer channels between the pumping stages or by vertical vacuum pumping.

[0007] It is also known to inject a purge fluid such as nitrogen into the vacuum pump to dilute the pumped gas and facilitate evacuation of the powder. This injection is generally carried out at several points along the pump stage through injection nozzles into the transmission channel or at the delivery port of the pump stage.

[0008] However, if the manufacturing process (such as the one described above) is highly polluting and the by-products formed are particularly prone to adhesion, these injections may prove to be insufficient. In the meshing areas between the rotors, where the clearance is very small, the by-products may continue to accumulate. In fact, it has been noted that powders are sucked and accumulated in these narrow clearance areas, and compression in these areas further compacts the powders, making them even harder and more prone to adhesion.

[0009] Document EP1990543A1 proposes a device for spraying a cleaning fluid that allows for more efficient cleaning of the rotor. To this end, a cleaning duct is provided in the thickness of the stator sheet, which is discharged into the pump stage. Thus, the cleaning fluid provided in the stator body can reach the temperature of the pump body before being injected into the stage. Guide grooves for the cleaning fluid can be provided in the front face of the stator sheet to clean precisely and effectively between the rotors. The localized spraying of the cleaning fluid allows targeted spraying in these areas, which ensures both dilution of the contaminants and dispersion of solid and gaseous byproducts that may be deposited on the rotor by mechanical action.

[0010] However, although this solution is very suitable for vacuum pumps with a laminar structure (i.e., the stator is formed by axially bonding together a plurality of stator laminae), it is difficult to implement it in the interstage walls of vacuum pump stators with a half-shell structure. In fact, the interstage walls of a half-shell stator can be very thin, thinner than those of a laminar structure stator, making it difficult to machine cleaning ducts. Summary of the invention

[0011] An object of the present invention is to propose a vacuum pump which solves at least one of the above-mentioned disadvantages.

[0012] To this end, the present invention relates to a dry vacuum pump, comprising:

[0013] a stator comprising at least a first half-shell and a second half-shell, said first and second half-shells being complementary and joined together to form at least two pump stages, said pump stages being arranged in series and axially spaced from one another by respective interstage transverse walls of said half-shells,

[0014] - the shafts of the two rotors, which extend in the axial direction and are designed to rotate in the pump stage,

[0015] Characterized in that the vacuum pump comprises at least one cleaning pipeline, and the cleaning pipeline comprises:

[0016] - two channels provided in the thickness of the interstage transverse half-walls of the half-shells, each channel opening via a respective orifice from the front face of the interstage transverse half-wall into the space inside the pump stage, and

[0017] - a transverse groove provided in said interstage transverse half-wall at the joint surface of the half-shells, said passage being formed by a tubular duct formed between the inclined plane of the transverse groove and said front face.

[0018] Therefore, the cleaning line leading into the pump stage from the front side facing the rotor cleans the rotor profile, especially the critical area between the rotors, by means of a jet sequenced by the rotor rotation. In fact, the jet may be locally located in the meshing area between the rotor profiles, where the volume is reduced.

[0019] The transverse grooves provided in the interstage transverse half-walls provide access for tools used to form the passages by drilling. Oblique drilling of the interstage transverse half-walls is possible because the transverse grooves have inclined planes which allow the orifices to be formed below the joint plane to (into) the front face, regardless of the thickness of the interstage transverse wall.

[0020] The vacuum pump may also have one or more of the features described below, which may be applied individually or in combination.

[0021] The transverse groove has, for example, a V-shaped longitudinal cross section.

[0022] The surface of the interstage transverse half wall of the other half shell at the joint surface may be flat.

[0023] The cleaning duct comprises, for example, a common duct arranged in the interstage transverse half-wall and opening into the center of the transverse slot.

[0024] The apertures may be arranged on a circle defined by the radial end sweep of each rotor.

[0025] The orifice may be arranged at a distance of between 5 mm (millimetres) and 15 mm from the joining surface in a direction perpendicular to the longitudinal direction and the transverse direction.

[0026] The length of the channel is for example between 6 mm and 14 mm, for example 10 mm.

[0027] The diameter of the tubular channel is for example between 1 mm and 3 mm, for example 2 mm.

[0028] For example, the channel opens out from the front side of the interstage transverse half-wall of the half-shell with the pump stage outlet.

[0029] The vacuum pump may have more than two pump stages. In this case, the half shell may have a plurality of interstage transverse half walls, in each of which a cleaning duct may be provided.

[0030] The joining surface is penetrated, for example, by the axis of rotation of the shaft of the rotor. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further advantages and features will become apparent upon reading the following description of specific but non-limiting embodiments in conjunction with the accompanying drawings, in which:

[0032] [ Figure 1 ] Figure 1 is a highly schematic representation of an exemplary vacuum pump.

[0033] [ Figure 2 ] Figure 2 A perspective view of a vacuum pump half-shell is shown.

[0034] [ Figure 3 ] Figure 3 Shows Figure 2 Another perspective view of the half shell in FIG.

[0035] [ Figure 4 ] Figure 4 Shows Figure 2 Enlarged elevation view of a detail of the interstage transverse half wall of the half shell.

[0036] [ Figure 5 ] Figure 5 An enlarged top view of the transverse grooves of the interstage transverse half-wall is shown.

[0037] [ Figure 6 ] Figure 6 An enlarged view of a longitudinal section of the channels and transverse grooves along the transverse half-wall of the interstage is shown.

[0038] [ Figure 7 ] Figure 7 Shows Figure 2 A partial cross-sectional view of the half shell along the longitudinal section through the channel of the cleaning pipe.

[0039] [ Figure 8 ] Figure 8 Shows Figure 2 Cross-section of the half shell.

[0040] [ Fig. 9 ] Fig. 9 Shows Figure 2 A partial cross-sectional view of the half shells along the longitudinal section of the common pipe passing through the cleaning pipe.

[0041] [ Fig.10 ] Fig.10 A schematic perspective view of a rotor arranged in front of the front face of an interstage transverse half-wall provided with openings is shown.

[0042] [ Fig.11a ] Fig.11a shows the initial angular position Fig.10 The rotor in the.

[0043] [ Fig.11b ] Fig.11b Shows that Fig.11a The angular position after the angular position in Fig.10 The rotor in the.

[0044] [ Fig.11c ] Fig.11c Shows that Fig.11b The angular position after the angular position in Fig.10 The rotor in the.

[0045] [ Fig.11d ] Fig.11d Shows that Fig.11c The angular position after the angular position in Fig.10 The rotor in the.

[0046] In these figures, the same elements are denoted by the same reference numerals. DETAILED DESCRIPTION

[0047] 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 a feature applies only to a single embodiment. Individual features of different embodiments may also be combined or interchanged to provide other embodiments.

[0048] A rough vacuum pump is a positive displacement vacuum pump designed to draw, transfer, and then deliver the gas being pumped at or above atmospheric pressure. The rotor of the rough vacuum pump can be a Roots rotor or a claw rotor. The rotor is carried on two shafts that are driven to rotate by the motor of the rough vacuum pump. The rough vacuum pump is also designed so that it can be started at atmospheric pressure.

[0049] A Roots vacuum pump (also called a blower, Roots compressor or booster) is a positive displacement vacuum pump designed to use two Roots rotors to suck, transfer and then deliver the pumped gas. The Roots vacuum pump is arranged upstream of the rough vacuum pump and in series with the rough vacuum pump. The rotors are carried by two shafts, which are driven to rotate by the motor of the Roots vacuum pump.

[0050] An "upstream" element is an element that is located before another element relative to the flow direction of the pumped gas. Conversely, a "downstream" element is an element that is located after another element relative to the flow direction of the pumped gas. Figure 1 The arrows F in FIG. 1 show the flow direction of the pumped gas.

[0051] The axial direction L is the longitudinal direction of the vacuum pump, along which the rotor shaft extends. The transverse direction T is a direction perpendicular to the axial direction L. The transverse plane (T, V) is a plane perpendicular to the longitudinal plane (L, T).

[0052] The invention is applicable to any type of dry vacuum pump, i.e. a dry vacuum pump comprising two or more pumping stages, for example a dry vacuum pump comprising two to ten pumping stages. The vacuum pump may be a rough vacuum pump comprising a plurality of pumping stages and designed to deliver pumped gas at atmospheric pressure, or may be a Roots vacuum pump or compressor having two or three pumping stages, which, in use, is connected in series with the rough vacuum pump and is located upstream of the rough vacuum pump, and whose delivery pressure is the delivery pressure obtained by the rough vacuum pump.

[0053] Figure 1 A schematic diagram of such a vacuum pump 1 is shown.

[0054] The vacuum pump 1 comprises a stator 2, which comprises at least a complementary and joined first half-shell 3 and a second half-shell 4. The stator 2 may further comprise a first end piece 5 and a second end piece 6 joined to the axial ends of the half-shells 3,4.

[0055] The half shells 3, 4 of the stator 2 form at least two pumping stages T1-T6, which are arranged in series between the suction port 7 and the delivery port 8 of the vacuum pump 1, for example two to ten pumping stages (six in the illustrative example). The pumping stages T1-T6 are axially separated from each other by corresponding interstage transverse walls 9 of the half shells 3, 4.

[0056] The vacuum pump 1 also comprises shafts of two rotors 10 which are designed to rotate in the pumping stages T1-T6 so that the rotors 10 are located between the suction port 7 and the delivery port 8 ( Figure 1 ) drives the pumped gas between.

[0057] The rotor has blades of the same profile, for example a "Roots" rotor with two or more blades ( Fig.10 The shaft carrying the rotor is driven by a motor M, for example, located next to the delivery stage T6 at the axial end of the vacuum pump 1.

[0058] Each pump stage houses two paired rotors 10, which include respective inlets and respective outlets. When the shafts of the rotors 10 rotate in opposite directions about their respective rotation axes, the gas sucked in from the inlets is trapped in the volume formed by the rotors 10 and the stator 2, and then driven by the rotors 10 toward the next stage.

[0059] The consecutive pumping stages T1-T6 are connected in series via respective transfer channels 12, which connect the outlet of the previous pumping stage to the inlet of the next pumping stage. For example, there are two transfer channels 12 for connecting the outlet of one pumping stage to the inlet of the next pumping stage, and the transfer channels 12 are arranged on both sides of the pumping stage. The opening of the transfer half channel 12 is at Figure 2This half-shell is the half-shell 4 in which the outlets of the pump stages T1-T6 are provided, here called the second half-shell.

[0060] The inlet of the first pumping stage T1 communicates with the suction port 7. The outlet of the last pumping stage T6 communicates with the delivery port 8. The duct 11 connecting the outlet of the last pumping stage T6 and the delivery port 8 of the vacuum pump 1 is for example formed in the body of the half-shell 4 below the pumping stages T1-T6.

[0061] The axial dimensions of the rotor and the pumping chamber (and therefore the displacement) are for example the same or decrease from stage to stage, the pumping stage T1 on the suction port 7 side housing the rotor with the largest axial dimension and the largest displacement.

[0062] These vacuum pumps are called “dry” vacuum pumps because, in operation, the rotors rotate inside the stator 2 without any mechanical contact between the rotors or between the rotors and the stator 2, thereby eliminating the need for oil at the pump stage.

[0063] The half shells 3, 4 are joined together at a joint surface 13. The pump stages T1-T6, the interstage transverse wall 9 and the transfer channel 12 are formed partly in the first half shell 3 and partly in the second half shell 4. In other words, more specifically, the interstage transverse wall 9 is formed by joining two interstage transverse half walls 9a, 9b together.

[0064] The joint surface 13 passes, for example, through a longitudinal midplane of the dry vacuum pump 1, which midplane contains, for example, the axis of rotation II of the shaft of the rotor 10. At the joint surface 13, a sealing groove 14 can be provided in the half shells 3, 4 to accommodate a sealing gasket (not shown).

[0065] The first ends of the half-shells 3, 4 are closed by a first end piece 5, and the second ends of the half-shells 3, 4 are closed by a second end piece 6. Of course, holes 15 for the passage of the shaft of the rotor 10 are provided in the interstage transverse walls 9 of the half-shells 3, 4 separating the pump stages T1-T6 and in the end pieces 5, 6.

[0066] The vacuum pump 1 further comprises at least one purge line 16 designed to be injected with a purge gas such as nitrogen.

[0067] The cleaning duct 16 comprises two channels 17, 18 which are arranged in the thickness of the interstage transverse half wall 9a of the half shell 4 ( Figure 2 ).

[0068] Each channel 17, 18 discharges from the front face 19 of the interstage transverse half-wall 9a via a corresponding orifice 20, 21 into the space inside the pumping stage T1-T6 ( Figure 3 and 4 ), which space is partially defined by the interstage transverse half wall 9a.

[0069] The front face 9 of the interstage transverse half-wall 9a arranged between pumping stages N and N+1 is the face delimiting pumping stage N. In other words, the channel is oriented to open to the rear, which is opposite to the flow direction of the pumped gas.

[0070] These orifices 20, 21 are advantageously arranged on a circle C defined by the radial end sweep of the respective rotor 10 ( Figure 4 ), the center of which is the rotation axis II of the rotor 10. The openings 20, 21 are arranged, for example, at a distance d between 5 mm and 15 mm from the joint surface 13 in a direction (V) perpendicular to the longitudinal direction (L) and the transverse direction (T). This distance d is related to the shape of the rotor 10 and is adjusted so that the jet of cleaning gas is discharged at the delivery port of the meshing area of ​​the rotor 10.

[0071] like Figure 5 and 6 As is more clearly shown, the cleaning duct 16 comprises a transverse groove 22 provided in the interstage transverse half-wall 9 a at the junction surface 13 of the half-shells 3 , 4 .

[0072] The surface of the interstage transverse half wall 9b of the other half shell 3 at the joint surface 13 may be flat.

[0073] The channels 17, 18 are formed by (straight) tubular ducts formed between the inclined plane 23 of the transverse groove 22 and the front face 19 ( Figure 6 and 7 The plane 23 is inclined, for example, over the entire groove 22 relative to the longitudinal plane (L, T) of the joint surface 13 separating the half shells 3, 4, for example at an angle of between 30° and 60°, for example 45°.

[0074] The transverse groove 22 has a longitudinal cross section which is, for example, V-shaped, one branch of the "V" forming an inclined plane 23 ( 23 ) into which the channels 17, 18 discharge on the side of the pump stage. Figure 6 and Figure 7 ). This V-shape is easy to process.

[0075] The transverse groove 22 provided in the interstage transverse half-wall 9a provides access for the tool for forming said channels 17, 18 by drilling. Regardless of the thickness of the interstage transverse half-wall 9, it is possible to perform an oblique drilling operation on the interstage transverse half-wall 9a, since the transverse groove 22 has an inclined plane 23 below the joint face 13 and allowing the formation of the holes 20, 21 that discharge into the front face 19.

[0076] The length of the channels 17, 18 between the inclined plane 23 and the front face 19 is, for example, between 6 mm and 14 mm, for example, 10 mm. The diameter of the tubular channels 17, 18 is, for example, between 1 mm and 3 mm, for example, 2 mm.

[0077] The channels 17, 18 lead, for example, from the front face 19 of the interstage transverse half wall 9a of the half shell 4 with the outlets of the pumping stages T1-T6, here called the second half shell. Thus, the cleaning gas is injected to the side where the gas pressure is highest and therefore the risk of deposit formation is highest.

[0078] like Figure 8 As shown more clearly in the cross-sectional view in FIG. 1 , the cleaning duct 16 comprises, for example, a common duct 24 arranged in the interstage transverse half wall 9a, which communicates with the transverse groove 22. The common duct 24 opens at the center of the transverse groove 22, for example.

[0079] In this illustrative example, the common conduit 24 is formed by first and second straight conduits 24a, 24b that communicate with each other. The first conduit 24a extends perpendicularly to the joint surface 13, which makes it easy to form by machining from the joint surface 13. The second conduit 24b extends perpendicularly to the outer surface (in this case flat) of the half shell 4, making it also easy to form by machining from the outer surface of the stator 2. This provides, for example, an elbow-shaped common conduit 24 extending between the transverse groove 22 provided at the joint surface 13 and the outer surface of the stator 2 (for example, on one side of the vacuum pump 1).

[0080] For example, in the thickness of the last interstage transverse half wall 9a of the vacuum pump 1, a cleaning duct 16 is provided in the flow direction F of the pumped gas, and channels 17, 18 open into the space in the last pump stage T6. The last pump stage T6 is the pump stage with the highest gas pressure.

[0081] According to an exemplary embodiment, the half-shells 3, 4 have a plurality of interstage transverse half-walls 9a (five in the illustrated example), and a cleaning duct 16 is provided in each interstage transverse half-wall 9a. Thus, all common ducts 24 extend, for example, in a vertical plane in the corresponding interstage transverse half-wall 9a ( Fig. 9 ) and are discharged laterally from the stator 2 via the corresponding outlet openings 25 ( Figure 3 ). These outlet openings 25 are connected to a cleaning gas source via an external distributor (not shown).

[0082] In operation, the purge gas is distributed to the purge ducts 16 of each pumping stage T1-T6, first into the common duct 24, then into the transverse grooves 22, then into the channels 16 and 17 and from the front wall 9 into the space inside the pumping stages T1-T6.

[0083] Figures 11a to 11d The rotation of the rotor 10 in the pump stages is schematically shown in succession, with a total rotation angle of approximately 120°. Fig.10The rotors 10 are shown in a perspective view in front of the front face 19 of the interstage transverse half-walls 9a in which the openings 20 , 21 are provided.

[0084] exist Fig.11a and Fig.11b It can be seen that the cleaning gas injected through the first orifice 20 flows around the periphery of the first rotor 10, while the second orifice 21 is closed by the second rotor 10. Therefore, all the gas injected into the cleaning pipe 16 is mainly discharged to the edge of the first rotor 10 through the open first orifice 20. Then, as the rotor 10 continues to rotate ( Fig.11c , followed by Fig.11d ), the first orifice 20 is closed by the first rotor 10, and the second orifice 21 allows the cleaning gas injected into the cleaning pipe 16 to flow through the periphery of the second rotor 10. Then, the rotor 10 continues to rotate back to the Fig.11a The initial angular position in matches the angular position in Figures 11a to 11d Between the angular positions shown, there is a position in which the rotor 10 simultaneously closes both holes 20, 21. The cleaning gas is then forced to flow out from behind the rotor 10, between the rotor 10 and the front face 19, thereby cleaning the rotor 10.

[0085] Thus, the cleaning duct 16 leading from the front face 9 facing the rotor 10 into the pump stage T1-16 cleans the profile of the rotor 10, in particular in the critical areas between the rotors 10, by means of a spray sequenced by the rotation of the rotor 10. In fact, the spray may be localized in the meshing areas between the profiles of the rotor 10, where the volume is reduced.

Claims

1. A dry vacuum pump (1), comprising: A stator (2) comprising at least a first half-shell (3) and a second half-shell (4) which are complementary and joined together to form at least two pump stages (T1-T6), said pump stages being arranged in series and axially separated from one another by respective interstage transverse walls (9) of these half-shells (3, 4), the shafts of two rotors (10) extending in an axial direction and designed to rotate in said pump stages (T1-T6), Characterized in that the dry vacuum pump comprises at least one cleaning pipeline (16), the cleaning pipeline comprising: two channels (17, 18) arranged in the thickness of an interstage transverse half-wall (9a) of one half-shell (4), each channel (17, 18) leading from a front face (19) of said interstage transverse half-wall (9a) via a respective orifice (20, 21) into the space inside the pump stage (T1-T6), and A transverse groove (22) is provided in the interstage transverse half-wall (9a) at the joint surface (13) of the half-shells (3, 4), the channels (17, 18) being formed by tubular ducts formed between an inclined plane (23) of the transverse groove (22) and the front face (19).

2. The vacuum pump (1) according to claim 1, characterized in that The transverse groove (22) has a V-shaped longitudinal cross section.

3. The vacuum pump (1) according to one of the preceding claims, characterized in that The surface of the interstage transverse half wall (9b) of the other half shell (3) is flat at the joint surface (13).

4. The vacuum pump (1) according to one of the preceding claims, characterized in that The cleaning duct (16) comprises a common duct (24) arranged in the interstage transverse half-wall (9a) and opening into the center of the transverse groove (22).

5. The vacuum pump (1) according to one of the preceding claims, characterized in that The apertures (20, 21) are arranged on a circle (C) defined by the sweep of the radial ends of the respective rotor (10).

6. The vacuum pump (1) according to one of the preceding claims, characterized in that The orifices (20, 21) are arranged at a distance (d) between 5 mm and 15 mm from the engagement surface (13) in a direction (V) perpendicular to the longitudinal direction (L) and the transverse direction (T).

7. The vacuum pump (1) according to one of the preceding claims, characterized in that The length of the channels (17, 18) is between 6 mm and 14 mm, for example 10 mm.

8. The vacuum pump (1) according to one of the preceding claims, characterized in that The diameter of the tubular passages (17, 18) is between 1 mm and 3 mm, for example 2 mm.

9. The vacuum pump (1) according to one of the preceding claims, characterized in that The channels (17, 18) open into the front face (19) of the interstage transverse half-wall (9a) of the half-shell (4) carrying the outlets of the pump stages (T1-T6).

10. The vacuum pump (1) according to one of the preceding claims, characterized in that The half shells (3, 4) have a plurality of inter-stage transverse half walls (9a), and a cleaning pipe (16) is provided in each inter-stage transverse half wall (9a).

11. The vacuum pump (1) according to one of the preceding claims, characterized in that The joint surface (13) is penetrated by the rotation axis (II) of the shafts of the rotors (10).

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